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man: document the new grow-file-system flag

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Lennart Poettering 2021-04-21 18:03:07 +02:00
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docs/DISCOVERABLE_PARTITIONS.md
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@ -94,24 +94,48 @@ localized.
## Partition Flags ## Partition Flags
For the root, `/usr/`, server data, home, variable data, temporary data and swap This specification defines three GPT partition flags that may be set for the
partitions, the partition flag bit 63 ("*no-auto*") may be used to turn off partition types defined above:
auto-discovery for the specific partition. If set, the partition will not be
automatically mounted or enabled.
For the root, `/usr/`, server data, home, variable data and temporary data 1. For the root, `/usr/`, Verity, home, server data, variable data, temporary data,
partitions, the partition flag bit 60 ("*read-only*") may be used to mark a swap and extended boot loader partitions, the partition flag bit 63
partition for read-only mounts only. If set, the partition will be mounted ("*no-auto*") may be used to turn off auto-discovery for the specific
read-only instead of read-write. Note that the variable data partition and the partition. If set, the partition will not be automatically mounted or
temporary data partition will generally not be able to serve their purpose if enabled.
marked read-only, since by their very definition they are supposed to be
mutable. (The home and server data partitions are generally assumed to be
mutable as well, but the requirement for them is not equally strong.) Because
of that, while the read-only flag is defined and supported, it's almost never a
good idea to actually use it for these partitions.
Note that these two flag definitions happen to map nicely to the ones used by 2. For the root, `/usr/`, Verity, home, server data, variable data, temporary
Microsoft Basic Data Partitions. data and extended boot loader partitions, the partition flag bit 60
("*read-only*") may be used to mark a partition for read-only mounts only.
If set, the partition will be mounted read-only instead of read-write. Note
that the variable data partition and the temporary data partition will
generally not be able to serve their purpose if marked read-only, since by
their very definition they are supposed to be mutable. (The home and server
data partitions are generally assumed to be mutable as well, but the
requirement for them is not equally strong.) Because of that, while the
read-only flag is defined and supported, it's almost never a good idea to
actually use it for these partitions. Also note that Verity partitions are
by their semantics always read-only. The flag is hence of little effect for
them, and it is recommended to set it unconditionally for the Verity
partition types.
3. For the root, `/usr/`, home, server data, variable data, temporary data and
extended boot loader partitions, the partition flag bit 59
("*grow-file-system*") may be used to mark a partition for automatic growing
of the contained file system to the size of the partition when
mounted. Tools that automatically mount disk image with a GPT partition
table are suggested to implicitly grow the contained file system to the
partition size they are contained in. This flag is without effect on
partitions marked read-only.
Note that the first two flag definitions happen to map nicely to the ones used
by Microsoft Basic Data Partitions.
All three of these flags generally affect only auto-discovery and automatic
mounting of disk images. If partitions marked with these flags are mounted
using low-level commands like
[mount(8)](https://man7.org/linux/man-pages/man2/mount.8.html) or directly with
[mount(2)](https://man7.org/linux/man-pages/man2/mount.2.html), they typically
have no effect.
## Suggested Mode of Operation ## Suggested Mode of Operation