mirror of
https://github.com/systemd/systemd
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330 lines
20 KiB
XML
330 lines
20 KiB
XML
<?xml version="1.0"?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd-gpt-auto-generator" conditional='HAVE_BLKID'
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>systemd-gpt-auto-generator</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-gpt-auto-generator</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-gpt-auto-generator</refname>
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<refpurpose>Generator for automatically discovering and mounting root, <filename>/home/</filename>,
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<filename>/srv/</filename>, <filename>/var/</filename> and <filename>/var/tmp/</filename> partitions, as
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well as discovering and enabling swap partitions, based on GPT partition type GUIDs</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>/usr/lib/systemd/system-generators/systemd-gpt-auto-generator</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>systemd-gpt-auto-generator</filename> is a unit generator that automatically discovers
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the root partition, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>,
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<filename>/var/tmp/</filename>, the EFI System Partition, the Extended Boot Loader Partition, and swap
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partitions and creates mount and swap units for them, based on the partition type GUIDs of GUID partition
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tables (GPT). See <ulink url="https://uefi.org/specifications">UEFI Specification</ulink>, chapter 5 for
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more details. It implements the <ulink
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url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable
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Partitions Specification</ulink>.</para>
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<para>Note that this generator has no effect on non-GPT systems. It will also not create mount point
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configuration for directories which already contain files or if the mount point is explicitly configured
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in <citerefentry
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project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>. If
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the units this generator creates are overridden, for example by units in directories with higher
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precedence, drop-ins and additional dependencies created by this generator might still be used.</para>
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<para>This generator will only look for the root partition on the same physical disk where the EFI System
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Partition (ESP) is located. Note that support from the boot loader is required: the EFI variable
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<varname>LoaderDevicePartUUID</varname> of the <constant>4a67b082-0a4c-41cf-b6c7-440b29bb8c4f</constant>
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vendor UUID is used to determine from which partition, and hence the disk, from which the system was
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booted. If the boot loader does not set this variable, this generator will not be able to detect the root
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partition. See the <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>
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for details.</para>
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<para>Similarly, this generator will only look for the other partitions on the same physical disk as the
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root partition. In this case, boot loader support is not required. These partitions will not be searched
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for on systems where the root file system is distributed on multiple disks, for example via btrfs RAID.
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</para>
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<para><filename>systemd-gpt-auto-generator</filename> is useful for centralizing file system
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configuration in the partition table and making configuration in <filename>/etc/fstab</filename> or on
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the kernel command line unnecessary.</para>
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<para>This generator looks for the partitions based on their
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partition type GUID. The following partition type GUIDs are
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identified:</para>
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<table>
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<title>Partition Type GUIDs</title>
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<tgroup cols='3' align='left' colsep='1' rowsep='1'>
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<colspec colname="guid" />
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<colspec colname="name" />
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<colspec colname="where" />
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<colspec colname="explanation" />
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<thead>
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<row>
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<entry>Partition Type GUID</entry>
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<entry>Name</entry>
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<entry>Mount Point</entry>
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<entry>Explanation</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><constant>SD_GPT_ROOT_X86_64</constant> <constant>4f68bce3-e8cd-4db1-96e7-fbcaf984b709</constant></entry>
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<entry><filename>Root Partition (x86-64)</filename></entry>
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<entry><filename>/</filename></entry>
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<entry>The first partition with this type UUID, located on the same disk as the ESP, is used as the root file system <filename>/</filename> on AMD64 / 64-bit x86 systems.</entry>
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</row>
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<row>
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<entry><constant>SD_GPT_ROOT_ARM64</constant> <constant>b921b045-1df0-41c3-af44-4c6f280d3fae</constant></entry>
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<entry><filename>Root Partition (64-bit ARM)</filename></entry>
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<entry><filename>/</filename></entry>
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<entry>The first partition with this type UUID, located on the same disk as the ESP, is used as the root file system <filename>/</filename> on AArch64 / 64-bit ARM systems.</entry>
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</row>
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<row>
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<entry>
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<constant>SD_GPT_ROOT_ALPHA</constant> <constant>SD_GPT_ROOT_ARC</constant> <constant>SD_GPT_ROOT_ARM</constant> <constant>SD_GPT_ROOT_ARM64</constant> <constant>SD_GPT_ROOT_IA64</constant> <constant>SD_GPT_ROOT_LOONGARCH64</constant> <constant>SD_GPT_ROOT_MIPS</constant> <constant>SD_GPT_ROOT_MIPS64</constant> <constant>SD_GPT_ROOT_MIPS_LE</constant> <constant>SD_GPT_ROOT_MIPS64_LE</constant> <constant>SD_GPT_ROOT_PARISC</constant> <constant>SD_GPT_ROOT_PPC</constant> <constant>SD_GPT_ROOT_PPC64</constant> <constant>SD_GPT_ROOT_PPC64_LE</constant> <constant>SD_GPT_ROOT_RISCV32</constant> <constant>SD_GPT_ROOT_RISCV64</constant> <constant>SD_GPT_ROOT_S390</constant> <constant>SD_GPT_ROOT_S390X</constant> <constant>SD_GPT_ROOT_TILEGX</constant> <constant>SD_GPT_ROOT_X86</constant> <constant>SD_GPT_ROOT_X86_64</constant> <constant>SD_GPT_USR_ALPHA</constant> <constant>SD_GPT_USR_ARC</constant> <constant>SD_GPT_USR_ARM</constant> <constant>SD_GPT_USR_IA64</constant> <constant>SD_GPT_USR_LOONGARCH64</constant> <constant>SD_GPT_USR_MIPS_LE</constant> <constant>SD_GPT_USR_MIPS64_LE</constant> <constant>SD_GPT_USR_PARISC</constant> <constant>SD_GPT_USR_PPC</constant> <constant>SD_GPT_USR_PPC64</constant> <constant>SD_GPT_USR_PPC64_LE</constant> <constant>SD_GPT_USR_RISCV32</constant> <constant>SD_GPT_USR_RISCV64</constant> <constant>SD_GPT_USR_S390</constant> <constant>SD_GPT_USR_S390X</constant> <constant>SD_GPT_USR_TILEGX</constant> <constant>SD_GPT_USR_X86</constant>
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</entry>
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<entry>root partitions for other architectures</entry>
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<entry><filename>/</filename></entry>
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<entry>The first partition with the type UUID matching the architecture, located on the same disk as the ESP, is used as the root file system <filename>/</filename>. For the full list and constant values, see <ulink url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions Specification</ulink>.</entry>
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</row>
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<row>
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<entry><constant>SD_GPT_HOME</constant> <constant>933ac7e1-2eb4-4f13-b844-0e14e2aef915</constant></entry>
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<entry>Home Partition</entry>
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<entry><filename>/home/</filename></entry>
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<entry>The first partition with this type UUID on the same disk as the ESP is mounted to <filename>/home/</filename>.</entry>
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</row>
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<row>
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<entry><constant>SD_GPT_SRV</constant> <constant>3b8f8425-20e0-4f3b-907f-1a25a76f98e8</constant></entry>
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<entry>Server Data Partition</entry>
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<entry><filename>/srv/</filename></entry>
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<entry>The first partition with this type UUID on the same disk as the ESP is mounted to <filename>/srv/</filename>.</entry>
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</row>
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<row>
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<entry><constant>SD_GPT_VAR</constant> <constant>4d21b016-b534-45c2-a9fb-5c16e091fd2d</constant></entry>
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<entry>Variable Data Partition</entry>
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<entry><filename>/var/</filename></entry>
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<entry>The first partition with this type UUID on the same disk as the ESP is mounted to <filename>/var/</filename> — under the condition its partition UUID matches the first 128 bit of the HMAC-SHA256 of the GPT type uuid of this partition keyed by the machine ID of the installation stored in <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</entry>
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</row>
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<row>
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<entry><constant>SD_GPT_TMP</constant> <constant>7ec6f557-3bc5-4aca-b293-16ef5df639d1</constant></entry>
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<entry>Temporary Data Partition</entry>
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<entry><filename>/var/tmp/</filename></entry>
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<entry>The first partition with this type UUID on the same disk as the ESP is mounted to <filename>/var/tmp/</filename>.</entry>
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</row>
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<row>
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<entry><constant>SD_GPT_SWAP</constant> <constant>0657fd6d-a4ab-43c4-84e5-0933c84b4f4f</constant></entry>
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<entry>Swap</entry>
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<entry>n/a</entry>
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<entry>All partitions with this type UUID on the same disk as the ESP are used as swap.</entry>
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</row>
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<row>
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<entry><constant>SD_GPT_ESP</constant> <constant>c12a7328-f81f-11d2-ba4b-00a0c93ec93b</constant></entry>
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<entry>EFI System Partition (ESP)</entry>
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<entry><filename>/efi/</filename> or <filename>/boot/</filename></entry>
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<entry>The first partition with this type UUID located on the same disk as the root partition is mounted to <filename>/boot/</filename> or <filename>/efi/</filename>, see below.</entry>
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</row>
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<row>
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<entry><constant>SD_GPT_XBOOTLDR</constant> <constant>bc13c2ff-59e6-4262-a352-b275fd6f7172</constant></entry>
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<entry>Extended Boot Loader Partition</entry>
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<entry><filename>/boot/</filename></entry>
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<entry>The first partition with this type UUID located on the same disk as the root partition is mounted to <filename>/boot/</filename>, see below.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>This generator understands the following attribute flags for partitions:</para>
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<table>
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<title>Partition Attribute Flags</title>
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<tgroup cols='3' align='left' colsep='1' rowsep='1'>
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<colspec colname="flag" />
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<colspec colname="where" />
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<colspec colname="explanation" />
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<thead>
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<row>
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<entry>Flag</entry>
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<entry>Applicable to</entry>
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<entry>Explanation</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><constant>SD_GPT_FLAG_READ_ONLY</constant> <constant>0x1000000000000000</constant></entry>
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<entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>, <filename>/var/tmp/</filename>, Extended Boot Loader Partition</entry>
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<entry>Partition is mounted read-only</entry>
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</row>
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<row>
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<entry><constant>SD_GPT_FLAG_NO_AUTO</constant> <constant>0x8000000000000000</constant></entry>
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<entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>, <filename>/var/tmp/</filename>, Extended Boot Loader Partition</entry>
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<entry>Partition is not mounted automatically</entry>
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</row>
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<row>
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<entry><constant>SD_GPT_FLAG_NO_BLOCK_IO_PROTOCOL</constant> <constant>0x0000000000000002</constant></entry>
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<entry>EFI System Partition (ESP)</entry>
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<entry>Partition is not mounted automatically</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>The <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>,
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<filename>/var/tmp/</filename> and swap partitions may be encrypted in LUKS format. In this case, a
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device mapper device is set up under the names <filename>/dev/mapper/home</filename>,
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<filename>/dev/mapper/srv</filename>, <filename>/dev/mapper/var</filename>,
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<filename>/dev/mapper/tmp</filename> or <filename>/dev/mapper/swap</filename>. Note that this might
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create conflicts if the same partition is listed in <filename>/etc/crypttab</filename> with a different
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device mapper device name.</para>
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<para>When systemd is running in the initrd the <filename>/</filename> partition may be encrypted with
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LUKS as well. In this case, a device mapper device is set up under the name
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<filename>/dev/mapper/root</filename>, and a <filename>sysroot.mount</filename> is set up that mounts the
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device under <filename>/sysroot</filename>. For more information, see
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<citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
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</para>
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<para>The root partition can be specified by symlinking <filename>/run/systemd/volatile-root</filename>
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to <filename>/dev/block/$major:$minor</filename>. This is especially useful if the root mount has been
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replaced by some form of volatile file system (overlayfs).
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</para>
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<para>Mount and automount units for the EFI System Partition (ESP) and Extended Boot Loader Partition
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(XBOOTLDR) are generated on EFI systems. If the disk contains an XBOOTLDR partition, as defined in the
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<ulink url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader
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Specification</ulink>, it is made available at <filename>/boot/</filename>. This generator creates an
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automount unit; the mount will only be activated on-demand when accessed. The mount point will be created
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if necessary.</para>
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<para>The ESP is mounted to <filename>/boot/</filename> if that directory exists and is not used for
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XBOOTLDR, and otherwise to <filename>/efi/</filename>. Same as for <filename>/boot/</filename>, an
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automount unit is used. The mount point will be created if necessary.</para>
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<para>No configuration is created for mount points that are configured in <citerefentry
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project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry> or when
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the target directory contains files.</para>
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<para>When using this generator in conjunction with btrfs file
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systems, make sure to set the correct default subvolumes on them,
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using <command>btrfs subvolume set-default</command>.</para>
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<para>If the system was booted via
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<citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> and the
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stub reported to userspace that the kernel image was measured to a TPM2 PCR, then any discovered root and
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<filename>/var/</filename> volume identifiers (and volume encryption key in case it is encrypted) will be
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automatically measured into PCR 15 on activation, via
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<citerefentry><refentrytitle>systemd-pcrfs@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
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<para><filename>systemd-gpt-auto-generator</filename> implements
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<citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
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</refsect1>
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<refsect1>
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<title>Kernel Command Line</title>
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<para><filename>systemd-gpt-auto-generator</filename> understands the following kernel command line
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parameters:</para>
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<variablelist class='kernel-commandline-options'>
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<varlistentry>
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<term><varname>systemd.gpt_auto</varname></term>
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<term><varname>rd.systemd.gpt_auto</varname></term>
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<listitem><para>Those options take an optional boolean argument, and default to yes.
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The generator is enabled by default, and a false value may be used to disable it
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(e.g. <literal>systemd.gpt_auto=0</literal>).
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</para>
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<xi:include href="version-info.xml" xpointer="v242"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.image_policy=</varname></term>
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<term><varname>rd.systemd.image_policy=</varname></term>
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<listitem><para>Takes an image dissection policy string as argument (as per
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<citerefentry><refentrytitle>systemd.image-policy</refentrytitle><manvolnum>7</manvolnum></citerefentry>),
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and allows enforcing a policy on dissection and use of the automatically discovered GPT partition
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table entries.</para>
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<xi:include href="version-info.xml" xpointer="v254"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>root=</varname></term>
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<term><varname>rootfstype=</varname></term>
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<term><varname>rootflags=</varname></term>
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<listitem><para>When <varname>root=</varname> is used with the special value
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<literal>gpt-auto</literal> (or if the parameter is not used at all), automatic discovery of the root
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partition based on the GPT partition type is enabled. Any other value disables this
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logic.</para>
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<para>The <varname>rootfstype=</varname> and <varname>rootflags=</varname> are used to select the
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file system type and options when the root file system is automatically discovered.</para>
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<xi:include href="version-info.xml" xpointer="v242"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>rw</varname></term>
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<term><varname>ro</varname></term>
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<listitem><para>Mount the root partition read-write or read-only <emphasis>initially</emphasis>.</para>
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<para>Note that unlike most kernel command line options these settings do not override configuration
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in the file system, and the file system may be remounted later. See
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<citerefentry><refentrytitle>systemd-remount-fs.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
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</para>
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<xi:include href="version-info.xml" xpointer="v242"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.swap=</varname></term>
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<listitem><para>Takes a boolean argument or enables the option if specified without an argument.
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If disabled, automatic discovery of swap partition(s) based on GPT partition type is disabled.
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Defaults to enabled.</para>
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<xi:include href="version-info.xml" xpointer="v254"/></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para><simplelist type="inline">
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<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-pcrfs@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
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<member><citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
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<member><citerefentry project='url'><refentrytitle url='https://btrfs.readthedocs.io/en/latest/btrfs.html'>btrfs</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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