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docs: add a "front matter" snippet to our markdown pages It turns out Jekyll (the engine behind GitHub Pages) requires that pages include a "Front Matter" snippet of YAML at the top for proper rendering. Omitting it will still render the pages, but including it opens up new possibilities, such as using a {% for %} loop to generate index.md instead of requiring a separate script. I'm hoping this will also fix the issue with some of the pages (notably CODE_OF_CONDUCT.html) not being available under systemd.io Tested locally by rendering the website with Jekyll. Before this change, the *.md files were kept unchanged (so not sure how that even works?!), after this commit, proper *.html files were generated from it.
2019-01-02 22:16:34 +00:00
---
docs: drop "The" in categorization titles of Markdown documentation I think it makes sense to keep the "The" in place for the actual page's title, but let's drop it from the categorization header, to make it easier to find stuff, as the "The" isn't helpful to that. In particular as we sometimes do it this and sometimes the other way so far, hence let's stick to one common rule.
2020-01-14 09:11:19 +00:00
title: Boot Loader Specification
docs: place all our markdown docs in rough categories
2019-12-11 09:49:28 +00:00
category: Booting
docs: make it pretty Add custom Jekyll theme, logo, webfont and .gitignore FIXME: the markdown files have some H1 headers which need to be replaced with H2
2019-12-11 16:01:46 +00:00
layout: default
docs: add spdx tags to all .md files I have no idea if this is going to cause rendering problems, and it is fairly hard to check. So let's just merge this, and if it github markdown processor doesn't like it, revert.
2021-09-14 14:05:21 +00:00
SPDX-License-Identifier: LGPL-2.1-or-later
docs: add a "front matter" snippet to our markdown pages It turns out Jekyll (the engine behind GitHub Pages) requires that pages include a "Front Matter" snippet of YAML at the top for proper rendering. Omitting it will still render the pages, but including it opens up new possibilities, such as using a {% for %} loop to generate index.md instead of requiring a separate script. I'm hoping this will also fix the issue with some of the pages (notably CODE_OF_CONDUCT.html) not being available under systemd.io Tested locally by rendering the website with Jekyll. Before this change, the *.md files were kept unchanged (so not sure how that even works?!), after this commit, proper *.html files were generated from it.
2019-01-02 22:16:34 +00:00
---
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
# The Boot Loader Specification
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
This document defines a set of file formats and naming conventions that allow
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
the boot loader menu entries to be shared between multiple operating systems
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
and boot loaders installed on one device.
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
Operating systems cooperatively manage boot loader menu entry directories that
contain drop-in files, making multi-boot scenarios easy to support. Boot menu
entries are defined via two simple formats that can be understood by different
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
boot loader implementations, operating systems, and userspace programs. The
same scheme can be used to prepare OS media for cases where the firmware
includes a boot loader.
docs: use Title Case for section titles as per: https://titlecase.com/
2022-08-26 13:59:07 +00:00
## Target Audience
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
The target audience for this specification is:
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
* Boot loader developers, to write a boot loader that directly reads its
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
menu entries from these files
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
* Firmware developers, to add generic boot loading support directly to the
firmware itself
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
* OS installer developers, to create appropriate partitions and set up the
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
initial boot loader menu entries
* Distribution developers, to create appropriate menu entry snippets when
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
installing or updating kernel packages
* UI developers, to implement user interfaces that list and select among the
available boot options
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
## The Partitions
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
docs/BLS: clear up the confusion about what $BOOT means The text used was originally written for everything being on the ESP. It was later generalized for support XBOOTLDR, and "$BOOT" was introduced to mean something like "XBOOTLDR if present, the ESP otherwise", and most of the text was changed to talk about $BOOT. Sadly, this doesn't work, because the two partitions are not interchangeable. sd-boot loads entries from both partitions, and its configuration, random-seed, etc. only from the ESP. The terms are redefined: $BOOT now means either the ESP or the "boot partition" playing the same role on MBR systems, and $XBOOTLDR is XBOOTLDR. Like various previous commits, this makes the specification describe our current implementation. Also, the let's just accept the common practice of using /boot and /boot/efi. Since both partitions need to be read to gather configuration, it isn't a problem that one is mounted underneath the other one. I think having /boot and /efi is OK, but not better in any measureable way, so let's stop trying to push people towards this setup. A note that XBOOTLDR must be on the same disk as ESP is added.
2022-05-25 11:41:29 +00:00
Everything described below is located on one or two partitions. The boot loader
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
or user-space programs reading the boot loader menu entries should locate them
docs/BLS: clear up the confusion about what $BOOT means The text used was originally written for everything being on the ESP. It was later generalized for support XBOOTLDR, and "$BOOT" was introduced to mean something like "XBOOTLDR if present, the ESP otherwise", and most of the text was changed to talk about $BOOT. Sadly, this doesn't work, because the two partitions are not interchangeable. sd-boot loads entries from both partitions, and its configuration, random-seed, etc. only from the ESP. The terms are redefined: $BOOT now means either the ESP or the "boot partition" playing the same role on MBR systems, and $XBOOTLDR is XBOOTLDR. Like various previous commits, this makes the specification describe our current implementation. Also, the let's just accept the common practice of using /boot and /boot/efi. Since both partitions need to be read to gather configuration, it isn't a problem that one is mounted underneath the other one. I think having /boot and /efi is OK, but not better in any measureable way, so let's stop trying to push people towards this setup. A note that XBOOTLDR must be on the same disk as ESP is added.
2022-05-25 11:41:29 +00:00
in the following manner:
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
* On disks with an MBR partition table:
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
* The boot partition — a partition with the type ID of `0xEA` — shall be used
as the single location for boot loader menu entries.
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
docs: say XBOOTLDR instead of just giving the GPT identifier Fixes #14832. Also, say "MBR partition table" and not "MBR disk label". "disk label" doesn't seem to mean anything.
2020-02-28 10:45:30 +00:00
* On disks with GPT (GUID Partition Table)
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
* The EFI System Partition (ESP for short) — a partition with a GPT type GUID
of `c12a7328-f81f-11d2-ba4b-00a0c93ec93b` — may be used as one of two locations for
boot loader menu entries.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
docs/BLS: clear up the confusion about what $BOOT means The text used was originally written for everything being on the ESP. It was later generalized for support XBOOTLDR, and "$BOOT" was introduced to mean something like "XBOOTLDR if present, the ESP otherwise", and most of the text was changed to talk about $BOOT. Sadly, this doesn't work, because the two partitions are not interchangeable. sd-boot loads entries from both partitions, and its configuration, random-seed, etc. only from the ESP. The terms are redefined: $BOOT now means either the ESP or the "boot partition" playing the same role on MBR systems, and $XBOOTLDR is XBOOTLDR. Like various previous commits, this makes the specification describe our current implementation. Also, the let's just accept the common practice of using /boot and /boot/efi. Since both partitions need to be read to gather configuration, it isn't a problem that one is mounted underneath the other one. I think having /boot and /efi is OK, but not better in any measureable way, so let's stop trying to push people towards this setup. A note that XBOOTLDR must be on the same disk as ESP is added.
2022-05-25 11:41:29 +00:00
* Optionally, an Extended Boot Loader Partition (XBOOTLDR partition for
short) — a partition with GPT type GUID of
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
`bc13c2ff-59e6-4262-a352-b275fd6f7172` — may be used as the second of two
locations for boot loader menu entries. This partition must be located on
the same disk as the ESP.
docs/BLS: clear up the confusion about what $BOOT means The text used was originally written for everything being on the ESP. It was later generalized for support XBOOTLDR, and "$BOOT" was introduced to mean something like "XBOOTLDR if present, the ESP otherwise", and most of the text was changed to talk about $BOOT. Sadly, this doesn't work, because the two partitions are not interchangeable. sd-boot loads entries from both partitions, and its configuration, random-seed, etc. only from the ESP. The terms are redefined: $BOOT now means either the ESP or the "boot partition" playing the same role on MBR systems, and $XBOOTLDR is XBOOTLDR. Like various previous commits, this makes the specification describe our current implementation. Also, the let's just accept the common practice of using /boot and /boot/efi. Since both partitions need to be read to gather configuration, it isn't a problem that one is mounted underneath the other one. I think having /boot and /efi is OK, but not better in any measureable way, so let's stop trying to push people towards this setup. A note that XBOOTLDR must be on the same disk as ESP is added.
2022-05-25 11:41:29 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
There may be at most one partition of each of the types listed above on the
same disk.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
**Note:** _These partitions are **shared** among all OS installations on the
same disk. Instead of maintaining one boot partition per installed OS (as
`/boot/` was traditionally handled), all installed OSes use the same place for
boot loader menu entries._
For systems where the firmware is able to read file systems directly, the ESP
must — and the MBR boot and GPT XBOOTLDR partition should — be a file system
readable by the firmware. For most systems this means VFAT (16 or 32
bit). Applications accessing both partitions should hence not assume that
fancier file system features such as symlinks, hardlinks, access control or
case sensitivity are supported.
### The `$BOOT` Partition Placeholder
In the text below, the placeholder `$BOOT` will be used to refer to the
partition determined as follows:
1. On disks with an MBR partition table: → the boot partition, as described above
2. On disks with a GPT partition table: → the XBOOTLDR partition if it exists
3. Otherwise, on disks with a GPT partition table: → the ESP
`$BOOT` is the *primary* place to put boot menu entry resources into, but
typically not the only one. Most importantly, boot loaders should also pick up
menu entries from the ESP, even if XBOOTLDR exists (for details see below).
### Creating These Partitions
An installer for an operating system should use this logic when selecting or
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
creating partitions:
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
* If a boot partition (in case of MBR) or an XBOOTLDR partition (in case of
GPT) already exists it should be used as `$BOOT` and used as primary
location to place boot loader menu resources in.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
* Otherwise, if on GPT and an ESP is found and it is large enough (let's say
at least 1G) it should be used as `$BOOT` and used as primary location to
place boot loader menu resources in.
docs/BLS: clear up the confusion about what $BOOT means The text used was originally written for everything being on the ESP. It was later generalized for support XBOOTLDR, and "$BOOT" was introduced to mean something like "XBOOTLDR if present, the ESP otherwise", and most of the text was changed to talk about $BOOT. Sadly, this doesn't work, because the two partitions are not interchangeable. sd-boot loads entries from both partitions, and its configuration, random-seed, etc. only from the ESP. The terms are redefined: $BOOT now means either the ESP or the "boot partition" playing the same role on MBR systems, and $XBOOTLDR is XBOOTLDR. Like various previous commits, this makes the specification describe our current implementation. Also, the let's just accept the common practice of using /boot and /boot/efi. Since both partitions need to be read to gather configuration, it isn't a problem that one is mounted underneath the other one. I think having /boot and /efi is OK, but not better in any measureable way, so let's stop trying to push people towards this setup. A note that XBOOTLDR must be on the same disk as ESP is added.
2022-05-25 11:41:29 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
* Otherwise, if on GPT and neither XBOOTLDR nor ESP exist, an ESP should be
created of the appropriate size and be used as `$BOOT`, and used as primary
location to place boot loader menu resources in.
docs/BLS: clear up the confusion about what $BOOT means The text used was originally written for everything being on the ESP. It was later generalized for support XBOOTLDR, and "$BOOT" was introduced to mean something like "XBOOTLDR if present, the ESP otherwise", and most of the text was changed to talk about $BOOT. Sadly, this doesn't work, because the two partitions are not interchangeable. sd-boot loads entries from both partitions, and its configuration, random-seed, etc. only from the ESP. The terms are redefined: $BOOT now means either the ESP or the "boot partition" playing the same role on MBR systems, and $XBOOTLDR is XBOOTLDR. Like various previous commits, this makes the specification describe our current implementation. Also, the let's just accept the common practice of using /boot and /boot/efi. Since both partitions need to be read to gather configuration, it isn't a problem that one is mounted underneath the other one. I think having /boot and /efi is OK, but not better in any measureable way, so let's stop trying to push people towards this setup. A note that XBOOTLDR must be on the same disk as ESP is added.
2022-05-25 11:41:29 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
* Otherwise, a boot partition (in case of MBR) or XBOOTLDR partition (in case
of GPT) should be created of an appropriate size, and be used as `$BOOT`,
and used as primary location to place boot loader menu resources in.
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
These partitions shall be determined during _installation time_, and
`/etc/fstab` entries may be created.
### Mount Points
It is recommended to mount `$BOOT` to `/boot/`, and the ESP to `/efi/`. If
`$BOOT` and the ESP are the same, then either a bind mount or a symlink should
be established making the partition available under both paths.
(Mounting the ESP to `/boot/efi/`, as was traditionally done, is not
recommended. Such a nested setup complicates an implementation via direct
`autofs` mounts — as implemented by `systemd` for example —, as establishing
the inner `autofs` will trigger the outer one. Mounting the two partitions via
`autofs` is recommended because the simple VFAT file system has weak data
integrity properties and should remain unmounted whenever possible.)
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
docs: use Title Case for section titles as per: https://titlecase.com/
2022-08-26 13:59:07 +00:00
## Boot Loader Entries
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
docs: tweaks to the boot loader spec A couple of changes: 1. Clearly name the drop-in entry files "Type #1", and the unified kernel images "Type #2", and be clearer that the latter is specific to UEFI. 2. Suffix all directory paths with a trailing "/" to clarify that these are directories. Also, enclose them all in ``. 3. Add introductory paragraph that explains that there is Type #1 and Type #2 and what they are about. 4. Explain that Type #2 is about signed UEFI SecureBoot. 5. Don't claim that $BOOT/loader/ contains really all files defined by the spec, because that's not true, Type #2 images are not located there after all. Fixes: #10399
2018-10-16 10:01:18 +00:00
This specification defines two types of boot loader entries. The first type is
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
text based, very simple, and suitable for a variety of firmware, architecture
docs: tweaks to the boot loader spec A couple of changes: 1. Clearly name the drop-in entry files "Type #1", and the unified kernel images "Type #2", and be clearer that the latter is specific to UEFI. 2. Suffix all directory paths with a trailing "/" to clarify that these are directories. Also, enclose them all in ``. 3. Add introductory paragraph that explains that there is Type #1 and Type #2 and what they are about. 4. Explain that Type #2 is about signed UEFI SecureBoot. 5. Don't claim that $BOOT/loader/ contains really all files defined by the spec, because that's not true, Type #2 images are not located there after all. Fixes: #10399
2018-10-16 10:01:18 +00:00
and image types ("Type #1"). The second type is specific to EFI, but allows
Fix a few docs typos (#10907) Found with [codespell](https://github.com/codespell-project/codespell)
2018-11-23 19:28:39 +00:00
single-file images that embed all metadata in the kernel binary itself, which
docs: tweaks to the boot loader spec A couple of changes: 1. Clearly name the drop-in entry files "Type #1", and the unified kernel images "Type #2", and be clearer that the latter is specific to UEFI. 2. Suffix all directory paths with a trailing "/" to clarify that these are directories. Also, enclose them all in ``. 3. Add introductory paragraph that explains that there is Type #1 and Type #2 and what they are about. 4. Explain that Type #2 is about signed UEFI SecureBoot. 5. Don't claim that $BOOT/loader/ contains really all files defined by the spec, because that's not true, Type #2 images are not located there after all. Fixes: #10399
2018-10-16 10:01:18 +00:00
is useful to cryptographically sign them as one file for the purpose of
SecureBoot ("Type #2").
Not all boot loader entries will apply to all systems. For example, Type #1
entries that use the `efi` key and all Type #2 entries only apply to EFI
systems. Entries using the `architecture` key might specify an architecture that
doesn't match the local one. Boot loaders should ignore all entries that don't
match the local platform and what the boot loader can support, and hide them
from the user. Only entries matching the feature set of boot loader and system
shall be considered and displayed. This allows image builders to put together
images that transparently support multiple different architectures.
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
Note that the three partitions described above are not supposed to be the
exclusive territory of this specification. This specification only defines
semantics of the `/loader/entries/` directory (along with the companion file
`/loader/entries.srel`) and the `/EFI/Linux/` directory inside the file system,
but it doesn't intend to define contents of the rest of the file system. Boot
loaders, firmware, and other software implementing this specification may
choose to place other files and directories in the same file system. For
example, boot loaders that implement this specification might install their own
boot code on the same partition; this is particularly common in the case of the
ESP. Implementations of this specification must be able to operate correctly if
files or directories other than `/loader/entries/` and `/EFI/Linux/` are found
in the top level directory. Implementations that add their own files or
directories to the file systems should use well-named directories, to make name
collisions between multiple users of the file system unlikely.
docs: clarify that we don't want to own $BOOT exclusively Let's be clearer here. Prompted by a quick discussion I had with @gicmo.
2020-01-16 11:09:29 +00:00
docs: tweaks to the boot loader spec A couple of changes: 1. Clearly name the drop-in entry files "Type #1", and the unified kernel images "Type #2", and be clearer that the latter is specific to UEFI. 2. Suffix all directory paths with a trailing "/" to clarify that these are directories. Also, enclose them all in ``. 3. Add introductory paragraph that explains that there is Type #1 and Type #2 and what they are about. 4. Explain that Type #2 is about signed UEFI SecureBoot. 5. Don't claim that $BOOT/loader/ contains really all files defined by the spec, because that's not true, Type #2 images are not located there after all. Fixes: #10399
2018-10-16 10:01:18 +00:00
### Type #1 Boot Loader Specification Entries
Add a description of unified kernel images
2018-06-19 10:56:26 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
`/loader/entries/` in `$BOOT` is the primary directory containing Type #1
drop-in snippets defining boot entries, one `.conf` file for each boot menu
item. Each OS may provide one or more such entries.
If the ESP is separate from `$BOOT` it may also contain a `/loader/entries/`
directory, where the boot loader should look for boot entry snippets, as an
additional source. The boot loader should enumerate both directories and
present a merged list to the user. Note that this is done for compatibility
only: while boot loaders should look in both places, OSes should only add their
files to `$BOOT`.
**Note:** _In all cases the `/loader/entries/` directory should be located
directly in the root of the file system. Specifically, the `/loader/entries/`
directory should **not** be located under the `/EFI/` subdirectory on the ESP._
The file name of the boot entry snippets is used for identification of the boot
item but shall never be presented to the user in the UI. The file name may be
chosen freely but should be unique enough to avoid clashes between OS
installations. More specifically, it is suggested to include the `entry-token`
(see
docs/BLS: rework the description of directory layout We said "`$BOOT/loader/` is the directory containing all files needed for Type #1 entries" which is blatantly wrong. And also saying that we define two directories, /loader and /loader/entries, but only ever defining the second one was not very consistent. Instead, let's say that /loader/ is for "boot loader configuration", and /loader/entries has the snippets. A new section about /<entry-token>/<version>/ is added. This is described as the "recommended layout for additional files". Also, we said that ID= should be used in the file name, but in fact it wasn't in the example that was given, and afaik, nobody ever did that. So this part is reduced to say "kernel version (as returned by `uname -r`, including the OS identifier)". AFAIK, all distros include some form of OS identifier in the version, so this should be good enough. Since we now don't depend on autodetection (e.g. with entry-token and layout configured), the installed doesn't need to always create /loader/entries and things will still work. So don't say that the installer needs to create it. Part of the discussion is moved to the Discussion section. Overall, this brings the specification more in line with actual practice.
2022-05-23 18:49:54 +00:00
[kernel-install](https://www.freedesktop.org/software/systemd/man/kernel-install.html))
or machine ID (see
[/etc/machine-id](https://www.freedesktop.org/software/systemd/man/machine-id.html)),
and the kernel version (as returned by `uname -r`, including the OS
identifier), so that the whole filename is
`$BOOT/loader/entries/<entry-token-or-machine-id>-<version>.conf`.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
Example: `$BOOT/loader/entries/6a9857a393724b7a981ebb5b8495b9ea-3.8.0-2.fc19.x86_64.conf`.
doc: document charset to use for bootspec entry names Prompted-by: https://github.com/systemd/systemd/issues/12572#issuecomment-711074702
2020-10-19 12:19:52 +00:00
In order to maximize compatibility with file system implementations and
restricted boot loader environments, and to minimize conflicting character use
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
with other programs, file names shall be chosen from a restricted character
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
set: ASCII upper and lower case characters, digits, "+", "-", "_" and ".".
Also, the file names should have a length of at least one and at most 255
characters (including the file name suffix).
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
These boot loader menu snippets shall be UNIX-style text files (i.e. lines
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
separated by a single newline character), in the UTF-8 encoding. The
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
boot loader menu snippets are loosely inspired by Grub1's configuration syntax.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
Lines beginning with "#" are used for comments and shall be ignored. The first
word of a line is used as key and is separated by one or more spaces from the
value.
#### Type #1 Boot Loader Entry Keys
The following keys are recognized:
* `title` is a human-readable title for this menu item to be displayed in the
boot menu. It is a good idea to initialize this from the `PRETTY_NAME=` of
docs: /etc/os-release → os-release(3) It's /usr/lib/os-release now mostly. But let's link to the man page.
2022-05-23 12:27:44 +00:00
[os-release](https://www.freedesktop.org/software/systemd/man/os-release.html).
This name should be descriptive and does not have to be unique. If a boot
loader discovers two entries with the same title it should show more than
just the raw title in the UI, for example by appending the `version`
field. This field is optional.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
Example: `title Fedora 18 (Spherical Cow)`
* `version` is a human-readable version for this menu item. This is usually the
kernel version and is intended for use by OSes to install multiple kernel
docs/BLS: describe version comparisons Fixes #23346.
2022-05-24 14:25:58 +00:00
versions with the same `title` field. This field is used for sorting entries,
so that the boot loader can order entries by age or select the newest one
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
automatically. This field is optional.
docs/BLS: describe version comparisons Fixes #23346.
2022-05-24 14:25:58 +00:00
See [Sorting](#sorting) below.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
Example: `version 3.7.2-201.fc18.x86_64`
* `machine-id` is the machine ID of the OS. This can be used by boot loaders
and applications to filter out boot entries, for example to show only a
single newest kernel per OS, to group items by OS, or to filter out the
currently booted OS when showing only other installed operating systems.
This ID shall be formatted as 32 lower case hexadecimal characters
(i.e. without any UUID formatting). This key is optional.
Example: `machine-id 4098b3f648d74c13b1f04ccfba7798e8`
* `sort-key` is a short string used for sorting entries on display. This should
typically be initialized from the `IMAGE_ID=` or `ID=` fields of
docs: /etc/os-release → os-release(3) It's /usr/lib/os-release now mostly. But let's link to the man page.
2022-05-23 12:27:44 +00:00
[os-release](https://www.freedesktop.org/software/systemd/man/os-release.html),
docs/BLS: describe version comparisons Fixes #23346.
2022-05-24 14:25:58 +00:00
possibly with an additional suffix. This field is optional.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
Example: `sort-key fedora`
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
* `linux` is the Linux kernel image to execute and takes a path relative to the
root of the file system containing the boot entry snippet itself. It is
recommended that every distribution creates an entry-token/machine-id and
version specific subdirectory and places its kernels and initrd images there
(see below).
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
Example: `linux /6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/linux`
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
* `initrd` is the initrd `cpio` image to use when executing the kernel. This key
may appear more than once in which case all specified images are used, in the
order they are listed.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
Example: `initrd 6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/initrd`
docs/BLS: clear up the confusion about what $BOOT means The text used was originally written for everything being on the ESP. It was later generalized for support XBOOTLDR, and "$BOOT" was introduced to mean something like "XBOOTLDR if present, the ESP otherwise", and most of the text was changed to talk about $BOOT. Sadly, this doesn't work, because the two partitions are not interchangeable. sd-boot loads entries from both partitions, and its configuration, random-seed, etc. only from the ESP. The terms are redefined: $BOOT now means either the ESP or the "boot partition" playing the same role on MBR systems, and $XBOOTLDR is XBOOTLDR. Like various previous commits, this makes the specification describe our current implementation. Also, the let's just accept the common practice of using /boot and /boot/efi. Since both partitions need to be read to gather configuration, it isn't a problem that one is mounted underneath the other one. I think having /boot and /efi is OK, but not better in any measureable way, so let's stop trying to push people towards this setup. A note that XBOOTLDR must be on the same disk as ESP is added.
2022-05-25 11:41:29 +00:00
* `efi` refers to an arbitrary EFI program. If this key is set, and the system
is not an EFI system, this entry should be hidden.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
* `options` shall contain kernel parameters to pass to the Linux kernel to
spawn. This key is optional and may appear more than once in which case all
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
specified parameters are combined in the order they are listed.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
Example: `options root=UUID=6d3376e4-fc93-4509-95ec-a21d68011da2 quiet`
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
* `devicetree` refers to the binary device tree to use when executing the
docs/BLS: clear up the confusion about what $BOOT means The text used was originally written for everything being on the ESP. It was later generalized for support XBOOTLDR, and "$BOOT" was introduced to mean something like "XBOOTLDR if present, the ESP otherwise", and most of the text was changed to talk about $BOOT. Sadly, this doesn't work, because the two partitions are not interchangeable. sd-boot loads entries from both partitions, and its configuration, random-seed, etc. only from the ESP. The terms are redefined: $BOOT now means either the ESP or the "boot partition" playing the same role on MBR systems, and $XBOOTLDR is XBOOTLDR. Like various previous commits, this makes the specification describe our current implementation. Also, the let's just accept the common practice of using /boot and /boot/efi. Since both partitions need to be read to gather configuration, it isn't a problem that one is mounted underneath the other one. I think having /boot and /efi is OK, but not better in any measureable way, so let's stop trying to push people towards this setup. A note that XBOOTLDR must be on the same disk as ESP is added.
2022-05-25 11:41:29 +00:00
kernel. This key is optional.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
Example: `devicetree 6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.armv7hl/tegra20-paz00.dtb`
boot-loader-spec: add devicetree-overlay key Device tree overlays are a convenient way to patch device trees, e.g., add new devices to a device tree or enable/disable devices. This is useful for non-discoverable but configurable hardware. Device tree overlays are commonly used for displays on the Raspberry Pi or for describing the content of FPGA bitstreams. Add the devicetree-overlay key to boot loader specification entries to allow boot loaders to apply overlays. See #13537
2019-10-18 13:14:35 +00:00
* `devicetree-overlay` refers to a list of device tree overlays that should be
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
applied by the boot loader. Multiple overlays are separated by spaces and
applied in the same order as they are listed. This key is optional but
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
depends on the `devicetree` key.
Example: `devicetree-overlay /6a9857a393724b7a981ebb5b8495b9ea/overlays/overlay_A.dtbo /6a9857a393724b7a981ebb5b8495b9ea/overlays/overlay_B.dtbo`
* `architecture` refers to the architecture this entry is for. The argument
should be an architecture identifier, using the architecture vocabulary
defined by the EFI specification (i.e. `IA32`, `x64`, `IA64`, `ARM`, `AA64`,
…). If specified and it does not match the local system architecture this
entry should be hidden. The comparison should be done case-insensitively.
Example: `architecture aa64`
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
Each boot loader menu entry drop-in snippet must include at least a `linux` or an `efi`
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
key. Here is an example for a complete drop-in file:
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
Wording and formatting updates UTF-8 is not a character set. Unicode is the character set. UTF-* are encodings.
2018-06-19 07:33:16 +00:00
# /boot/loader/entries/6a9857a393724b7a981ebb5b8495b9ea-3.8.0-2.fc19.x86_64.conf
boot-loader-spec: elaborate on 'architecture' stanza a bit and use it in the example
2018-10-17 09:38:45 +00:00
title Fedora 19 (Rawhide)
docs: add new "sort-key" field to boot loader spec This allows snippet generators to explicitly order entries: any string can be set as an entry's "sort key". If set, sd-boot will use it to sort entries on display. New logic is hence (ignore the boot counting logic) sort-key is set → primary sort key: sort-key (lexicographically increasing order) → secondary sort key: machine-id (also increasing order) → tertiary sort key: version (lexicographically decreasing order!) sort-key is not set → primary sort key: entry filename (aka id), lexicographically increasing order) With this scheme we can order OSes by their names from A-Z but then put within the same OS still the newest version first. This should clean up the order to match expectations more. Based on discussions here: https://github.com/systemd/systemd/pull/22391#issuecomment-1040092633
2022-02-15 13:19:40 +00:00
sort-key fedora
boot-loader-spec: elaborate on 'architecture' stanza a bit and use it in the example
2018-10-17 09:38:45 +00:00
machine-id 6a9857a393724b7a981ebb5b8495b9ea
docs: add new "sort-key" field to boot loader spec This allows snippet generators to explicitly order entries: any string can be set as an entry's "sort key". If set, sd-boot will use it to sort entries on display. New logic is hence (ignore the boot counting logic) sort-key is set → primary sort key: sort-key (lexicographically increasing order) → secondary sort key: machine-id (also increasing order) → tertiary sort key: version (lexicographically decreasing order!) sort-key is not set → primary sort key: entry filename (aka id), lexicographically increasing order) With this scheme we can order OSes by their names from A-Z but then put within the same OS still the newest version first. This should clean up the order to match expectations more. Based on discussions here: https://github.com/systemd/systemd/pull/22391#issuecomment-1040092633
2022-02-15 13:19:40 +00:00
version 3.8.0-2.fc19.x86_64
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
options root=UUID=6d3376e4-fc93-4509-95ec-a21d68011da2 quiet
boot-loader-spec: elaborate on 'architecture' stanza a bit and use it in the example
2018-10-17 09:38:45 +00:00
architecture x64
linux /6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/linux
initrd /6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/initrd
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
docs: adjust the spec a bit with firmware authros in mind This borrows heavily from Nico Huber's https://github.com/systemd/systemd/pull/10398, but makes a number of changes. Replaces: #10398
2019-03-13 15:44:53 +00:00
On EFI systems all Linux kernel images should be EFI images. In order to
increase compatibility with EFI systems it is highly recommended only to
install EFI kernel images, even on non-EFI systems, if that's applicable and
supported on the specific architecture.
Conversely, in order to increase compatibility it is recommended to install
generic kernel images that make few assumptions about the firmware they run on,
i.e. it is a good idea that both images shipped as UEFI PE images and those
which are not don't make unnecessary assumption on the underlying firmware,
i.e. don't hard depend on legacy BIOS calls or UEFI boot services.
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
When Type #1 boot loader menu entry snippets refer to other files (for `linux`,
docs/BLS: rework the description of directory layout We said "`$BOOT/loader/` is the directory containing all files needed for Type #1 entries" which is blatantly wrong. And also saying that we define two directories, /loader and /loader/entries, but only ever defining the second one was not very consistent. Instead, let's say that /loader/ is for "boot loader configuration", and /loader/entries has the snippets. A new section about /<entry-token>/<version>/ is added. This is described as the "recommended layout for additional files". Also, we said that ID= should be used in the file name, but in fact it wasn't in the example that was given, and afaik, nobody ever did that. So this part is reduced to say "kernel version (as returned by `uname -r`, including the OS identifier)". AFAIK, all distros include some form of OS identifier in the version, so this should be good enough. Since we now don't depend on autodetection (e.g. with entry-token and layout configured), the installed doesn't need to always create /loader/entries and things will still work. So don't say that the installer needs to create it. Part of the discussion is moved to the Discussion section. Overall, this brings the specification more in line with actual practice.
2022-05-23 18:49:54 +00:00
`initrd`, `efi`, `devicetree`, and `devicetree-overlay`), those files must be
docs/BLS: clear up the confusion about what $BOOT means The text used was originally written for everything being on the ESP. It was later generalized for support XBOOTLDR, and "$BOOT" was introduced to mean something like "XBOOTLDR if present, the ESP otherwise", and most of the text was changed to talk about $BOOT. Sadly, this doesn't work, because the two partitions are not interchangeable. sd-boot loads entries from both partitions, and its configuration, random-seed, etc. only from the ESP. The terms are redefined: $BOOT now means either the ESP or the "boot partition" playing the same role on MBR systems, and $XBOOTLDR is XBOOTLDR. Like various previous commits, this makes the specification describe our current implementation. Also, the let's just accept the common practice of using /boot and /boot/efi. Since both partitions need to be read to gather configuration, it isn't a problem that one is mounted underneath the other one. I think having /boot and /efi is OK, but not better in any measureable way, so let's stop trying to push people towards this setup. A note that XBOOTLDR must be on the same disk as ESP is added.
2022-05-25 11:41:29 +00:00
located on the same partition, and the paths must be absolute paths relative to
the root of that file system. The naming of those files can be chosen by the
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
installer. A recommended scheme is described in the next section. Paths should
be normalized, i.e. not include `..`, `.` or a sequence of more than one
`/`. Paths may be prefixed with a `/`, but this is optional and has the same
effect as paths without it: all paths are always relative to the root directory
of the partition they are referenced from.
docs/BLS: rework the description of directory layout We said "`$BOOT/loader/` is the directory containing all files needed for Type #1 entries" which is blatantly wrong. And also saying that we define two directories, /loader and /loader/entries, but only ever defining the second one was not very consistent. Instead, let's say that /loader/ is for "boot loader configuration", and /loader/entries has the snippets. A new section about /<entry-token>/<version>/ is added. This is described as the "recommended layout for additional files". Also, we said that ID= should be used in the file name, but in fact it wasn't in the example that was given, and afaik, nobody ever did that. So this part is reduced to say "kernel version (as returned by `uname -r`, including the OS identifier)". AFAIK, all distros include some form of OS identifier in the version, so this should be good enough. Since we now don't depend on autodetection (e.g. with entry-token and layout configured), the installed doesn't need to always create /loader/entries and things will still work. So don't say that the installer needs to create it. Part of the discussion is moved to the Discussion section. Overall, this brings the specification more in line with actual practice.
2022-05-23 18:49:54 +00:00
boot-loader-spec: add comment about case sensitivity of file names
2022-08-31 16:30:33 +00:00
Even though the backing file system is typically case-insensitive (i.e. VFAT)
it is strongly recommended to reference files in the casing actually used for
the directories/files, so that placing these files on other file systems is
still safe and robust.
docs/BLS: rework the description of directory layout We said "`$BOOT/loader/` is the directory containing all files needed for Type #1 entries" which is blatantly wrong. And also saying that we define two directories, /loader and /loader/entries, but only ever defining the second one was not very consistent. Instead, let's say that /loader/ is for "boot loader configuration", and /loader/entries has the snippets. A new section about /<entry-token>/<version>/ is added. This is described as the "recommended layout for additional files". Also, we said that ID= should be used in the file name, but in fact it wasn't in the example that was given, and afaik, nobody ever did that. So this part is reduced to say "kernel version (as returned by `uname -r`, including the OS identifier)". AFAIK, all distros include some form of OS identifier in the version, so this should be good enough. Since we now don't depend on autodetection (e.g. with entry-token and layout configured), the installed doesn't need to always create /loader/entries and things will still work. So don't say that the installer needs to create it. Part of the discussion is moved to the Discussion section. Overall, this brings the specification more in line with actual practice.
2022-05-23 18:49:54 +00:00
### Recommended Directory Layout for Additional Files
doc: fix typo Follow-ups for #23504.
2022-05-30 16:16:01 +00:00
It is recommended to place the kernel and other other files comprising a single
docs/BLS: rework the description of directory layout We said "`$BOOT/loader/` is the directory containing all files needed for Type #1 entries" which is blatantly wrong. And also saying that we define two directories, /loader and /loader/entries, but only ever defining the second one was not very consistent. Instead, let's say that /loader/ is for "boot loader configuration", and /loader/entries has the snippets. A new section about /<entry-token>/<version>/ is added. This is described as the "recommended layout for additional files". Also, we said that ID= should be used in the file name, but in fact it wasn't in the example that was given, and afaik, nobody ever did that. So this part is reduced to say "kernel version (as returned by `uname -r`, including the OS identifier)". AFAIK, all distros include some form of OS identifier in the version, so this should be good enough. Since we now don't depend on autodetection (e.g. with entry-token and layout configured), the installed doesn't need to always create /loader/entries and things will still work. So don't say that the installer needs to create it. Part of the discussion is moved to the Discussion section. Overall, this brings the specification more in line with actual practice.
2022-05-23 18:49:54 +00:00
boot loader entry in a separate directory:
`/<entry-token-or-machine-id>/<version>/`. This naming scheme uses the same
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
elements as the boot loader menu entry snippet, providing the same level of
docs/BLS: rework the description of directory layout We said "`$BOOT/loader/` is the directory containing all files needed for Type #1 entries" which is blatantly wrong. And also saying that we define two directories, /loader and /loader/entries, but only ever defining the second one was not very consistent. Instead, let's say that /loader/ is for "boot loader configuration", and /loader/entries has the snippets. A new section about /<entry-token>/<version>/ is added. This is described as the "recommended layout for additional files". Also, we said that ID= should be used in the file name, but in fact it wasn't in the example that was given, and afaik, nobody ever did that. So this part is reduced to say "kernel version (as returned by `uname -r`, including the OS identifier)". AFAIK, all distros include some form of OS identifier in the version, so this should be good enough. Since we now don't depend on autodetection (e.g. with entry-token and layout configured), the installed doesn't need to always create /loader/entries and things will still work. So don't say that the installer needs to create it. Part of the discussion is moved to the Discussion section. Overall, this brings the specification more in line with actual practice.
2022-05-23 18:49:54 +00:00
uniqueness.
Example: `$BOOT/6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/linux`
`$BOOT/6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/initrd`
Other naming schemes are possible. In particular, traditionally a flat naming
scheme with files in the root directory was used. This is not recommended
because it is hard to avoid conflicts in a multi-boot installation.
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
### Standard-conformance Marker File
docs: add /loader/entries.srel to the boot loader spec This new file is supposed to address conflicts with Fedora/Grub's frankenbootloaderspec implementation, that squatted the /loader/entries/ dir, but place incompatible files in them (that do variable expansion?). A simple text file /loader/entries.srel shall indicate which spec is implemented. If it contains the string "type1\n" then the /loader/entries/ directory implements our standard spec, otherwise something else.
2022-03-17 17:35:53 +00:00
Unfortunately, there are implementations of boot loading infrastructure that
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
are also using the `/loader/entries/` directory, but install files that do not
follow this specification. In order to minimize confusion, a boot loader
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
implementation may place the file `/loader/entries.srel` next to the
`/loader/entries/` directory containing the ASCII string `type1` (followed by a
UNIX newline). Tools that need to determine whether an existing directory
implements the semantics described here may check for this file and contents:
if it exists and contains the mentioned string, it shall assume a
standards-compliant implementation is in place. If it exists but contains a
different string it shall assume other semantics are implemented. If the file
does not exist, no assumptions should be made.
docs: add /loader/entries.srel to the boot loader spec This new file is supposed to address conflicts with Fedora/Grub's frankenbootloaderspec implementation, that squatted the /loader/entries/ dir, but place incompatible files in them (that do variable expansion?). A simple text file /loader/entries.srel shall indicate which spec is implemented. If it contains the string "type1\n" then the /loader/entries/ directory implements our standard spec, otherwise something else.
2022-03-17 17:35:53 +00:00
docs: tweaks to the boot loader spec A couple of changes: 1. Clearly name the drop-in entry files "Type #1", and the unified kernel images "Type #2", and be clearer that the latter is specific to UEFI. 2. Suffix all directory paths with a trailing "/" to clarify that these are directories. Also, enclose them all in ``. 3. Add introductory paragraph that explains that there is Type #1 and Type #2 and what they are about. 4. Explain that Type #2 is about signed UEFI SecureBoot. 5. Don't claim that $BOOT/loader/ contains really all files defined by the spec, because that's not true, Type #2 images are not located there after all. Fixes: #10399
2018-10-16 10:01:18 +00:00
### Type #2 EFI Unified Kernel Images
A unified kernel image is a single EFI PE executable combining an EFI stub
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
loader, a kernel image, an initrd image, and the kernel command line. See
[systemd-stub(7)](https://www.freedesktop.org/software/systemd/man/systemd-stub.html)
for details. The primary place for such unified images is the `/EFI/Linux/`
directory in `$BOOT`. Operating systems should place unified EFI kernels only
in the `$BOOT` partition. Boot loaders should also look in the `/EFI/Linux/` of
the ESP — if it is different from `$BOOT` — and present a merged list of menu
entries from both partitions. Regardless if placed in the primary or secondary
location: the files must have the extension `.efi`. Support for images of this
type is of course specific to systems with EFI firmware. Ignore this section if
you work on systems not supporting EFI.
Add a description of unified kernel images
2018-06-19 10:56:26 +00:00
doc: document charset to use for bootspec entry names Prompted-by: https://github.com/systemd/systemd/issues/12572#issuecomment-711074702
2020-10-19 12:19:52 +00:00
Type #2 file names should be chosen from the same restricted character set as
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
Type #1 described above (but with the file name suffix of `.efi` instead of
`.conf`).
doc: document charset to use for bootspec entry names Prompted-by: https://github.com/systemd/systemd/issues/12572#issuecomment-711074702
2020-10-19 12:19:52 +00:00
docs: tweaks to the boot loader spec A couple of changes: 1. Clearly name the drop-in entry files "Type #1", and the unified kernel images "Type #2", and be clearer that the latter is specific to UEFI. 2. Suffix all directory paths with a trailing "/" to clarify that these are directories. Also, enclose them all in ``. 3. Add introductory paragraph that explains that there is Type #1 and Type #2 and what they are about. 4. Explain that Type #2 is about signed UEFI SecureBoot. 5. Don't claim that $BOOT/loader/ contains really all files defined by the spec, because that's not true, Type #2 images are not located there after all. Fixes: #10399
2018-10-16 10:01:18 +00:00
Images of this type have the advantage that all metadata and payload that makes
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
up the boot entry is contained in a single PE file that can be signed
docs: tweaks to the boot loader spec A couple of changes: 1. Clearly name the drop-in entry files "Type #1", and the unified kernel images "Type #2", and be clearer that the latter is specific to UEFI. 2. Suffix all directory paths with a trailing "/" to clarify that these are directories. Also, enclose them all in ``. 3. Add introductory paragraph that explains that there is Type #1 and Type #2 and what they are about. 4. Explain that Type #2 is about signed UEFI SecureBoot. 5. Don't claim that $BOOT/loader/ contains really all files defined by the spec, because that's not true, Type #2 images are not located there after all. Fixes: #10399
2018-10-16 10:01:18 +00:00
cryptographically as one for the purpose of EFI SecureBoot.
Add a description of unified kernel images
2018-06-19 10:56:26 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
A valid unified kernel image in the `/EFI/Linux/` directory must contain two PE sections:
Add a description of unified kernel images
2018-06-19 10:56:26 +00:00
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
* `.cmdline` section with the kernel command line,
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
* `.osrel` section with an embedded copy of the
[os-release](https://www.freedesktop.org/software/systemd/man/os-release.html)
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
file describing the image.
Add description of field correspondence
2018-06-19 11:52:04 +00:00
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
The `PRETTY_NAME=` and `VERSION_ID=` fields in the embedded `os-release` file
are used the same as `title` and `version` in the Type #1 entries. The
`.cmdline` section is used instead of the `options` field. `linux` and `initrd`
fields are not necessary, and there is no counterpart for the `machine-id`
field.
Add a description of unified kernel images
2018-06-19 10:56:26 +00:00
docs: tweaks to the boot loader spec A couple of changes: 1. Clearly name the drop-in entry files "Type #1", and the unified kernel images "Type #2", and be clearer that the latter is specific to UEFI. 2. Suffix all directory paths with a trailing "/" to clarify that these are directories. Also, enclose them all in ``. 3. Add introductory paragraph that explains that there is Type #1 and Type #2 and what they are about. 4. Explain that Type #2 is about signed UEFI SecureBoot. 5. Don't claim that $BOOT/loader/ contains really all files defined by the spec, because that's not true, Type #2 images are not located there after all. Fixes: #10399
2018-10-16 10:01:18 +00:00
On EFI, any such images shall be added to the list of valid boot entries.
Add a description of unified kernel images
2018-06-19 10:56:26 +00:00
docs: use Title Case for section titles as per: https://titlecase.com/
2022-08-26 13:59:07 +00:00
### Additional Notes
Add a description of unified kernel images
2018-06-19 10:56:26 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
Note that these boot entry snippets and unified kernels do not need to be the
only menu entry sources for a boot loader. It may extend this list of
entries with additional items from other configuration files (for example its
own native configuration files) or automatically detected other entries without
explicit configuration.
Add a description of unified kernel images
2018-06-19 10:56:26 +00:00
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
To make this explicitly clear: this specification is designed with "free"
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
operating systems in mind, starting Windows or MacOS is out of focus with these
boot loader menu entry snippets, use boot-loader specific solutions for
that. In the text above, if we say "OS" we hence imply "free", i.e. primarily
Linux (though this could be easily be extended to the BSDs and whatnot).
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
Note that all paths used in the boot loader menu entry snippets use a
Unix-style "/" as path separator. This needs to be converted to an EFI-style
"\\" separator in EFI boot loaders.
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
docs: use Title Case for section titles as per: https://titlecase.com/
2022-08-26 13:59:07 +00:00
## Locating Boot Entries
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
A _boot loader_ locates the XBOOTLDR partition and the ESP, then simply reads
all the files `/loader/entries/*.conf` in them, and populates its boot menu
(and handle gracefully if one of the two partitions is missing). On EFI, it
then extends this with any unified kernel images found in `/EFI/Linux/*.efi` in
the two partitions. It may also add additional entries, for example a "Reboot
into firmware" option. Optionally it may sort the menu based on the
`sort-key`, `machine-id` and `version` fields, and possibly others. It uses the
file name to identify specific items, for example in case it supports storing
away default entry information somewhere. A boot loader should generally not
modify these files.
docs: tweaks to the boot loader spec A couple of changes: 1. Clearly name the drop-in entry files "Type #1", and the unified kernel images "Type #2", and be clearer that the latter is specific to UEFI. 2. Suffix all directory paths with a trailing "/" to clarify that these are directories. Also, enclose them all in ``. 3. Add introductory paragraph that explains that there is Type #1 and Type #2 and what they are about. 4. Explain that Type #2 is about signed UEFI SecureBoot. 5. Don't claim that $BOOT/loader/ contains really all files defined by the spec, because that's not true, Type #2 images are not located there after all. Fixes: #10399
2018-10-16 10:01:18 +00:00
For "Boot Loader Specification Entries" (Type #1), the _kernel package
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
installer_ installs the kernel and initrd images to `$BOOT`. It is recommended
to place these files in a vendor and OS and installation specific directory. It
then generates a boot loader menu entry snippet, placing it in
`$BOOT/loader/entries/xyz.conf`, with "xyz" as concatenation of
entry-token/machine-id and version information (see above). The files created
by a kernel package are tied to the kernel package and should be removed along
with it.
docs: tweaks to the boot loader spec A couple of changes: 1. Clearly name the drop-in entry files "Type #1", and the unified kernel images "Type #2", and be clearer that the latter is specific to UEFI. 2. Suffix all directory paths with a trailing "/" to clarify that these are directories. Also, enclose them all in ``. 3. Add introductory paragraph that explains that there is Type #1 and Type #2 and what they are about. 4. Explain that Type #2 is about signed UEFI SecureBoot. 5. Don't claim that $BOOT/loader/ contains really all files defined by the spec, because that's not true, Type #2 images are not located there after all. Fixes: #10399
2018-10-16 10:01:18 +00:00
For "EFI Unified Kernel Images" (Type #2), the vendor or kernel package
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
installer should create the combined image and drop it into
`$BOOT/EFI/Linux/`. This file is also tied to the kernel package and should be
removed along with it.
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
A _UI application_ intended to show available boot options shall operate
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
similarly to a boot loader (and thus search both `$BOOT` and the ESP if
distinct), but might apply additional filters, for example by filtering the
booted OS via the machine ID, or by suppressing all but the newest kernel
versions.
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
An _OS installer_ picks the right place for `$BOOT` as defined above (possibly
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
creating a partition and file system for it) and creates the `/loader/entries/`
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
directory and the `/loader/entries.srel` file in it (the latter only if the
directory didn't exist yet). It then installs an appropriate boot loader that
can read these snippets. Finally, it installs one or more kernel packages.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
docs/BLS: move "boot counting" into the main spec The boot-counting file-renaming entry-sorting part that the boot loader implements is moved to the main document. The second document describes a specific implementation that is provided through systemd units. The sorting algorithm is extended to say that bad entries should be sorted later. I also added a note that bad entries should be available for booting. For some reason, the second document said that it applies only to EFI systems. AFAIK there are no implementations for non-EFI, but the specification should work just fine, if somebody were to implement it. So that part is dropped. Fixes #23345. Sadly, bootctl doesn't implement sorting of boot entries with counting :(((( But I'm leaving that for another PR.
2022-06-09 10:15:46 +00:00
## Boot counting
The main idea is that when boot entries are initially installed, they are
marked as "indeterminate" and assigned a number of boot attempts. Each time the
boot loader tries to boot an entry, it decreases this count by one. If the
operating system considers the boot as successful, it removes the counter
altogether and the entry becomes "good". Otherwise, once the assigned number of
boots is exhausted, the entry is marked as "bad".
Which boots are "successful" is determined by the operating system. systemd
provides a generic mechanism that can be extended with arbitrary checks and
tree-wide: fix typo
2022-06-09 23:26:08 +00:00
actions, see [Automatic Boot Assessment](AUTOMATIC_BOOT_ASSESSMENT.md), but the
boot-loader-spec: fix typo
2022-08-31 16:31:02 +00:00
boot counting mechanism described in this specification can also be used with
docs/BLS: move "boot counting" into the main spec The boot-counting file-renaming entry-sorting part that the boot loader implements is moved to the main document. The second document describes a specific implementation that is provided through systemd units. The sorting algorithm is extended to say that bad entries should be sorted later. I also added a note that bad entries should be available for booting. For some reason, the second document said that it applies only to EFI systems. AFAIK there are no implementations for non-EFI, but the specification should work just fine, if somebody were to implement it. So that part is dropped. Fixes #23345. Sadly, bootctl doesn't implement sorting of boot entries with counting :(((( But I'm leaving that for another PR.
2022-06-09 10:15:46 +00:00
other implementations.
The boot counting data is stored in the name of the boot loader entry. A boot
loader entry file name may contain a plus (`+`) followed by a number. This may
optionally be followed by a minus (`-`) followed by a second number. The dot
(`.`) and file name suffix (`conf` of `efi`) must immediately follow. Boot
counting is enabled for entries which match this pattern.
The first number is the "tries left" counter signifying how many attempts to boot
this entry shall still be made. The second number is the "tries done" counter,
showing how many failed attempts to boot it have already been made. Each time
a boot loader entry marked this way is booted, the first counter is decremented,
and the second one incremented. (If the second counter is missing,
then it is assumed to be equivalent to zero.) If the "tries left" counter is
above zero the entry is still considered "indeterminate". A boot entry with the
"tries left" counter at zero is considered "bad".
If the boot attempt completed successfully the entry's counters are removed
from the name (entry state becomes "good"), thus turning off boot counting for
this entry.
docs/BLS: describe version comparisons Fixes #23346.
2022-05-24 14:25:58 +00:00
## Sorting
The boot loader menu should generally show entries in some order meaningful to
the user. The `title` key is free-form and not suitable to be used as the
primary sorting key. Instead, the boot loader should use the following rules:
docs/BLS: move "boot counting" into the main spec The boot-counting file-renaming entry-sorting part that the boot loader implements is moved to the main document. The second document describes a specific implementation that is provided through systemd units. The sorting algorithm is extended to say that bad entries should be sorted later. I also added a note that bad entries should be available for booting. For some reason, the second document said that it applies only to EFI systems. AFAIK there are no implementations for non-EFI, but the specification should work just fine, if somebody were to implement it. So that part is dropped. Fixes #23345. Sadly, bootctl doesn't implement sorting of boot entries with counting :(((( But I'm leaving that for another PR.
2022-06-09 10:15:46 +00:00
1. Entries which are subject to boot counting and are marked as "bad", should
be sorted later than all other entries. Entries which are marked as
"indeterminate" or "good" (or were not subject to boot counting at all),
are thus sorted earlier.
2. If `sort-key` is set on both entries, use in order of priority,
the `sort-key` (A-Z, increasing [alphanumerical order](#alphanumerical-order)),
`machine-id` (A-Z, increasing alphanumerical order),
and `version` keys (decreasing [version order](#version-order)).
3. If `sort-key` is set on one entry, it sorts earlier.
4. At the end, if necessary, when `sort-key` is not set or those fields are not
set or are all equal, the boot loader should sort using the file name of the
entry (decreasing version sort), with the suffix removed.
docs/BLS: describe version comparisons Fixes #23346.
2022-05-24 14:25:58 +00:00
**Note:** _This description assumes that the boot loader shows entries in a
traditional menu, with newest and "best" entries at the top, thus entries with
a higher version number are sorter *earlier*. The boot loader is free to
use a different direction (or none at all) during display._
docs/BLS: move "boot counting" into the main spec The boot-counting file-renaming entry-sorting part that the boot loader implements is moved to the main document. The second document describes a specific implementation that is provided through systemd units. The sorting algorithm is extended to say that bad entries should be sorted later. I also added a note that bad entries should be available for booting. For some reason, the second document said that it applies only to EFI systems. AFAIK there are no implementations for non-EFI, but the specification should work just fine, if somebody were to implement it. So that part is dropped. Fixes #23345. Sadly, bootctl doesn't implement sorting of boot entries with counting :(((( But I'm leaving that for another PR.
2022-06-09 10:15:46 +00:00
**Note:** _The boot loader should allow booting "bad" entries, e.g. in case no
other entries are left or they are unusable for other reasons. It may
deemphasize or hide such entries by default._
**Note:** _"Bad" boot entries have a suffix of "+0-`n`", where `n` is the
number of failed boot attempts. Removal of the suffix is not necessary for
comparisons described by the last point above. In the unlikely scenario that we
have multiple such boot entries that differ only by the boot counting data, we
would sort them by `n`._
docs: use Title Case for section titles as per: https://titlecase.com/
2022-08-26 13:59:07 +00:00
### Alphanumerical Order
docs/BLS: describe version comparisons Fixes #23346.
2022-05-24 14:25:58 +00:00
Free-form strings and machine IDs should be compared using a method equivalent
to [strcmp(3)](https://man7.org/linux/man-pages/man3/strcmp.3.html) on their
doc: fix typo Follow-ups for #23504.
2022-05-30 16:16:01 +00:00
UTF-8 representations. If just one of the strings is unspecified or empty, it
docs/BLS: describe version comparisons Fixes #23346.
2022-05-24 14:25:58 +00:00
compares lower. If both strings are unspecified or empty, they compare equal.
docs: use Title Case for section titles as per: https://titlecase.com/
2022-08-26 13:59:07 +00:00
### Version Order
docs/BLS: describe version comparisons Fixes #23346.
2022-05-24 14:25:58 +00:00
The following method should be used to compare version strings. The algorithm
is based on rpm's `rpmvercmp()`, but not identical.
ASCII letters (`a-z`, `A-Z`) and digits (`0-9`) form alphanumerical components of the version.
Minus (`-`) separates the version and release parts.
Dot (`.`) separates parts of version or release.
Tilde (`~`) is a prefix that always compares lower.
Caret (`^`) is a prefix that always compares higher.
Both strings are compared from the beginning until the end, or until the
strings are found to compare as different. In a loop:
1. Any characters which are outside of the set of listed above (`a-z`, `A-Z`, `0-9`, `-`, `.`, `~`, `^`)
are skipped in both strings. In particular, this means that non-ASCII characters
that are Unicode digits or letters are skipped too.
2. If one of the strings has ended: if the other string hasn't, the string that
has remaining characters compares higher. Otherwise, the strings compare
equal.
3. If the remaining part of one of strings starts with `~`:
if other remaining part does not start with `~`,
the string with `~` compares lower. Otherwise, both tilde characters are skipped.
4. The check from point 2. is repeated here.
5. If the remaining part of one of strings starts with `-`:
if the other remaining part does not start with `-`,
the string with `-` compares lower. Otherwise, both minus characters are skipped.
6. If the remaining part of one of strings starts with `^`:
if the other remaining part does not start with `^`,
the string with `^` compares higher. Otherwise, both caret characters are skipped.
6. If the remaining part of one of strings starts with `.`:
if the other remaining part does not start with `.`,
the string with `.` compares lower. Otherwise, both dot characters are skipped.
7. If either of the remaining parts starts with a digit, numerical prefixes are
compared numerically. Any leading zeroes are skipped.
The numerical prefixes (until the first non-digit character) are evaluated as numbers.
If one of the prefixes is empty, it evaluates as 0.
If the numbers are different, the string with the bigger number compares higher.
Otherwise, the comparison continues at the following characters at point 1.
8. Leading alphabetical prefixes are compared alphabetically.
The substrings are compared letter-by-letter.
If both letters are the same, the comparison continues with the next letter.
Capital letters compare lower than lower-case letters (`A < a`).
When the end of one substring has been reached (a non-letter character or the end
of the whole string), if the other substring has remaining letters, it compares higher.
Otherwise, the comparison continues at the following characters at point 1.
Examples (with '' meaning the empty string):
* `11 == 11`
* `systemd-123 == systemd-123`
* `bar-123 < foo-123`
* `123a > 123`
* `123.a > 123`
* `123.a < 123.b`
* `123a > 123.a`
* `11α == 11β`
* `A < a`
* '' < `0`
* `0.` > `0`
* `0.0` > `0`
* `0` < `~`
* '' < `~`
Note: [systemd-analyze](https://www.freedesktop.org/software/systemd/man/systemd-analyze.html)
implements this version comparison algorithm as
```
systemd-analyze compare-versions <version-a> <version-b>
```
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
## Additional discussion
### Why is there a need for this specification?
This specification brings the following advantages:
* Installation of new boot entries is more robust, as no explicit rewriting of
configuration files is required.
* It allows an out-of-the-box boot experience on any platform without the need
of traditional firmware mechanisms (e.g. BIOS calls, UEFI Boot Services).
* It improves dual-boot scenarios. Without cooperation, multiple Linux
installations tend to fight over which boot loader becomes the primary one in
possession of the MBR or the boot partition, and only that one installation
can then update the boot loader configuration. Other Linux installs have to
be manually configured to never touch the MBR and instead install a
chain-loaded boot loader in their own partition headers. In this new scheme
all installations share a loader directory and no manual configuration has to
take place. All participants implicitly cooperate due to removal of name
collisions and can install/remove their own boot menu entries without
interfering with the entries of other installed operating systems.
* Drop-in directories are now pretty ubiquitous on Linux as an easy way to
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
extend boot loader menus without having to edit, regenerate or manipulate
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
configuration files. For the sake of uniformity, we should do the same for
the boot menu.
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
* Userspace code can sanely parse boot loader menu entries which is essential
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
with modern firmware which does not necessarily initialize USB keyboards
during boot, which makes boot menus hard to reach for the user. If userspace
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
code can parse the boot loader menu entries too, UI can be written that
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
select a boot menu item to boot into before rebooting the machine, thus not
requiring interactivity during early boot.
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
* To unify and thus simplify menu entries of the various boot loaders, which
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
makes configuration of the boot loading process easier for users,
administrators, and developers alike.
* For boot loaders with configuration _scripts_ such as grub2, adopting this
spec allows for mostly static scripts that are generated only once at first
installation, but then do not need to be updated anymore as that is done via
drop-in files exclusively.
### Why not simply rely on the EFI boot menu logic?
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
EFI is not ubiquitous, especially not in embedded systems. But even on systems
with EFI, which provides a boot options logic that can offer similar
doc: fix typo Follow-ups for #23504.
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functionality, this specification is still needed for the following reasons:
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
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* The various EFI implementations implement the boot order/boot item logic to
different levels. Some firmware implementations do not offer a boot menu at
all and instead unconditionally follow the EFI boot order, booting the first
item that is working.
* If the firmware setup is used to reset data, usually all EFI boot entries
are lost, making the system entirely unbootable, as the firmware setups
generally do not offer a UI to define additional boot items. By placing the
menu item information on disk, it is always available, even if the firmware
configuration is lost.
* Harddisk images should be movable between machines and be bootable without
doc: fix typo Follow-ups for #23504.
2022-05-30 16:16:01 +00:00
requiring firmware configuration. This also requires that the list
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
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of boot options is defined on disk, and not in EFI variables alone.
* EFI is not universal yet (especially on non-x86 platforms), this
specification is useful both for EFI and non-EFI boot loaders.
* Many EFI systems disable USB support during early boot to optimize boot
times, thus making keyboard input unavailable in the EFI menu. It is thus
useful if the OS UI has a standardized way to discover available boot options
which can be booted to.
doc: fix typo Follow-ups for #23504.
2022-05-30 16:16:01 +00:00
### Why is the version comparison logic so complicated?
docs/BLS: describe version comparisons Fixes #23346.
2022-05-24 14:25:58 +00:00
The `sort-key` allows us to group entries by "operating system", e.g. all
versions of Fedora together, no matter if they identify themselves as "Fedora
Workstation" or "Fedora Rawhide (prerelease)". The `sort-key` was introduced
only recently, so we need to provide a meaningful order for entries both with
and without it. Since it is a new concept, it is assumed that entries with
`sort-key` are newer.
In a traditional menu with entries displayed vertically, we want names to be
sorter alpabetically (CentOS, Debian, Fedora, OpenSUSE, …), it would be strange
to have them in reverse order. But when multiple kernels are available for the
same installation, we want to display the latest kernel with highest priority,
i.e. earlier in the list.
docs/BLS: move "boot counting" into the main spec The boot-counting file-renaming entry-sorting part that the boot loader implements is moved to the main document. The second document describes a specific implementation that is provided through systemd units. The sorting algorithm is extended to say that bad entries should be sorted later. I also added a note that bad entries should be available for booting. For some reason, the second document said that it applies only to EFI systems. AFAIK there are no implementations for non-EFI, but the specification should work just fine, if somebody were to implement it. So that part is dropped. Fixes #23345. Sadly, bootctl doesn't implement sorting of boot entries with counting :(((( But I'm leaving that for another PR.
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### Why do you use file renames to store the counter? Why not a regular file?
Mainly two reasons: it's relatively likely that renames can be implemented
atomically even in simpler file systems, as renaming generally avoids
allocating or releasing data blocks. Writing to file contents has a much bigger
chance to be result in incomplete or corrupt data. Moreover renaming has the
benefit that the boot count metadata is directly attached to the boot loader
entry file, and thus the lifecycle of the metadata and the entry itself are
bound together. This means no additional clean-up needs to take place to drop
the boot loader counting information for an entry when it is removed.
### Why not use EFI variables for storing the boot counter?
The memory chips used to back the persistent EFI variables are generally not of
the highest quality, hence shouldn't be written to more than necessary. This
means we can't really use it for changes made regularly during boot, but should
use it only for seldom-made configuration changes.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
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### Out of Focus
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
Minor grammar changes mostly inserting / removing commas / periods as appropriate. occasionally fixing duplicated words, proper brand case, and singular/plurals.
2018-07-20 19:40:15 +00:00
There are a couple of items that are out of focus for this specification:
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
* If userspace can figure out the available boot options, then this is only
useful so much: we'd still need to come up with a way how userspace could
communicate to the boot loader the default boot loader entry temporarily or
persistently. Defining a common scheme for this is certainly a good idea, but
out of focus for this specification.
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
* This specification is just about "Free" Operating systems. Hooking in other
operating systems (like Windows and macOS) into the boot menu is a different
story and should probably happen outside of this specification. For example,
boot loaders might choose to detect other available OSes dynamically at
runtime without explicit configuration (like `systemd-boot` does it), or via
native configuration (for example via explicit Grub2 configuration generated
once at installation).
docs: reworder/rewrite BLS to read more like a specification I tried not to introduce any semantic changes, but to reorder the whole text to be more usable as a reference specification: more sections are created and the discussion and justifications are moved to the end. Also, "BIOS" is changed to "firmware" in various places, and other parts of the text that made sense when this was originally written are now dated are adjusted. I separated and extended the examples a bit. The abstract at the top ("TL;DR: Currently there’s no common boot scheme…") is dropped. It didn't seem to fit anywhere.
2022-05-23 12:22:40 +00:00
doc: rebreak boot loader spec
2021-11-19 14:39:32 +00:00
* This specification leaves undefined what to do about systems which are
upgraded from an OS that does not implement this specification. As the
previous boot loader logic was largely handled by in distribution-specific
ways we probably should leave the upgrade path (and whether there actually is
one) to the distributions. The simplest solution might be to simply continue
with the old scheme for old installations and use this new scheme only for
new installations.
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
docs/BLS: rework the description of directory layout We said "`$BOOT/loader/` is the directory containing all files needed for Type #1 entries" which is blatantly wrong. And also saying that we define two directories, /loader and /loader/entries, but only ever defining the second one was not very consistent. Instead, let's say that /loader/ is for "boot loader configuration", and /loader/entries has the snippets. A new section about /<entry-token>/<version>/ is added. This is described as the "recommended layout for additional files". Also, we said that ID= should be used in the file name, but in fact it wasn't in the example that was given, and afaik, nobody ever did that. So this part is reduced to say "kernel version (as returned by `uname -r`, including the OS identifier)". AFAIK, all distros include some form of OS identifier in the version, so this should be good enough. Since we now don't depend on autodetection (e.g. with entry-token and layout configured), the installed doesn't need to always create /loader/entries and things will still work. So don't say that the installer needs to create it. Part of the discussion is moved to the Discussion section. Overall, this brings the specification more in line with actual practice.
2022-05-23 18:49:54 +00:00
* Referencing kernels or initrds on other partitions other than the partition
containing the Type #1 boot loader entry. This is by design, as specifying
other partitions or devices would require a non-trivial language for denoting
boot-loader-spec: undo redefinition of $BOOT In 53c26db4dac0f5b79ca2a57364ee7df78a14bbfd the meaning of $BOOT was redefined. I think that's quite problematic, since the concept is implemented in code and interface of bootctl. Thus, I think we should stick to the original definition, which is: "where to *place* boot menu entries" (as opposed to "where to *read* boot menu entries from"). The aforementioned change was done to address two things afaiu: 1. it focussed on a $BOOT as the single place to put boot entries in, instead of mentioning that both ESP and $BOOT are expected to be the source 2. it mentioned the /loader/ dir (as location for boot loader resources) itself as part of the spec, which however only really makes sense in the ESP. /loader/entries/ otoh makes sense in either the ESP or $BOOT. With this rework I try to address these two issues differently: 1. I intend to make clear the $BOOT is the "primary" place to put stuff in, and is what should be mounted to /boot/. 2. The ESP (if different from $BOOT) is listed as "secondary" source to read from, and is what should be mounted to /efi/. NB we now make the distinction between "where to put" (which is single partition) and "where to read from". 3. This drops any reference of the /loader/ dir witout the /entries/ suffix. Only the full /loader/entries/ dir (and its companion file /loader/entries.srel) are now mentioned. Thus isolated /loader/ directory hence becomes irrelevant in the spec, and the fact that sd-boot maintains some files there (and only in the ESP) is kept out of the spec, because it is irrelevant to other boot loaders. 4. It puts back the suggestion to mount $BOOT to /boot/ and the ESP to /efi/ (and suggests adding a symlink or bind mount if both are the same partition). Why? Because the dirs are semantically unrelated: it's OK and common to have and ESP but no $BOOT, hence putting ESP inside of a useless, non-existing "ghost" dir /boot/ makes little sense. More importantly though, because these partitions are typically backed by VFAT we want to maintain them as an autofs, with a short idle delay, so that the file systems are unmounted (and thus fully clean) at almost all times. This doesn't work if they are nested within each other, as the establishment of the inner autofs would pin the outer one, making the excercise useless. Now I don't think the spec should mention autofs (since that is an implementation detail), but it should arrange things so that this specific, very efficient, safe and robust implementation can be implemented. The net result should be easy from an OS perspective: 1. *Put* boot loader entries in /boot/, always. 2. *Read* boot loader entries from both /boot/ and /efi/ -- if these are distinct. 3. The only things we define in the spec are /loader/entries/*.conf and /EFI/Linux/*.efi in these two partitions (well, and the companion file /loader/entries.srel 4. /efi/ and /boot/ because not nested can be autofs. 5. bootctl code and interface (in particular --esp-path= and --boot-path=) match the spec again. `bootctl -x` and `bootctl -p` will now print the path to $BOOT and ESP again, matching the concepts in the spec again. From the sd-boot perspective things are equally easy: 1. Read boot enrties from ESP and XBOOTLDR. 2. Maintain boot loader config/other resources in ESP only. And that's it. Fixes: #24247
2022-08-31 16:43:24 +00:00
device paths. In particular this means that on non-EFI systems boot loader
menu entry snippets following this specification cannot be used to spawn
other operating systems (such as Windows).
docs/BLS: rework the description of directory layout We said "`$BOOT/loader/` is the directory containing all files needed for Type #1 entries" which is blatantly wrong. And also saying that we define two directories, /loader and /loader/entries, but only ever defining the second one was not very consistent. Instead, let's say that /loader/ is for "boot loader configuration", and /loader/entries has the snippets. A new section about /<entry-token>/<version>/ is added. This is described as the "recommended layout for additional files". Also, we said that ID= should be used in the file name, but in fact it wasn't in the example that was given, and afaik, nobody ever did that. So this part is reduced to say "kernel version (as returned by `uname -r`, including the OS identifier)". AFAIK, all distros include some form of OS identifier in the version, so this should be good enough. Since we now don't depend on autodetection (e.g. with entry-token and layout configured), the installed doesn't need to always create /loader/entries and things will still work. So don't say that the installer needs to create it. Part of the discussion is moved to the Discussion section. Overall, this brings the specification more in line with actual practice.
2022-05-23 18:49:54 +00:00
Rename back to "The Boot Loader Specification"
2014-03-07 03:58:09 +00:00
## Links
docs: interlink the docs to make it easier to navigate
2020-02-28 10:47:03 +00:00
[GUID Partition Table](https://en.wikipedia.org/wiki/GUID_Partition_Table)<br>
docs: use relative links Allows for links to work both on systemd.io (or forks) and when viewed on https://github.com/systemd/systemd/tree/main/docs Note that the markdown links are converted by jekyll-relative-links[1] to html. This plugin is enabled by default on github pages[2][3]. Due to a bug in jekyll-relative-links – see https://github.com/benbalter/jekyll-relative-links/issues/61 – we need to avoid line-wrapped links when using relative markdown links. [1] https://github.com/benbalter/jekyll-relative-links [2] https://github.blog/2016-12-05-relative-links-for-github-pages/ [3] https://docs.github.com/en/pages/setting-up-a-github-pages-site-with-jekyll/about-github-pages-and-jekyll#plugins
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[Boot Loader Interface](BOOT_LOADER_INTERFACE.md)<br>
[Discoverable Partitions Specification](DISCOVERABLE_PARTITIONS.md)<br>
docs: make man page links in markdown Links section use teletype font, as we usually do
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[`systemd-boot(7)`](https://www.freedesktop.org/software/systemd/man/systemd-boot.html)<br>
[`bootctl(1)`](https://www.freedesktop.org/software/systemd/man/bootctl.html)<br>
[`systemd-gpt-auto-generator(8)`](https://www.freedesktop.org/software/systemd/man/systemd-gpt-auto-generator.html)
Reference in a new issue Copy permalink