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NAME | SYNOPSIS | DESCRIPTION | KERNEL COMMAND LINE | SEE ALSO | NOTES | COLOPHON |
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SYSTEMD-GPT-AUTO-GENERATOR(8)d-gpt-auto-generatorD-GPT-AUTO-GENERATOR(8)
systemd-gpt-auto-generator - Generator for automatically
discovering and mounting root, /home/, /srv/, /var/ and /var/tmp/
partitions, as well as discovering and enabling swap partitions,
based on GPT partition type GUIDs
/usr/lib/systemd/system-generators/systemd-gpt-auto-generator
systemd-gpt-auto-generator is a unit generator that automatically
discovers root, /home/, /srv/, /var/, /var/tmp/, the EFI System
Partition, the Extended Boot Loader Partition and swap partitions
and creates mount and swap units for them, based on the partition
type GUIDs of GUID partition tables (GPT), see UEFI
Specification[1], chapter 5. It implements the Discoverable
Partitions Specification[2]. Note that this generator has no
effect on non-GPT systems, and on specific mount points that are
directories already containing files. Also, on systems where the
units are explicitly configured (for example, listed in
fstab(5)), the units this generator creates are overridden, but
additional implicit dependencies might be created.
This generator will only look for the root partition on the same
physical disk where the EFI System Partition (ESP) is located.
Note that support from the boot loader is required: the EFI
variable LoaderDevicePartUUID of the
4a67b082-0a4c-41cf-b6c7-440b29bb8c4f vendor UUID is used to
determine from which partition, and hence the disk from which the
system was booted. If the boot loader does not set this variable,
this generator will not be able to autodetect the root partition.
See the Boot Loader Interface[3] for details.
Similarly, this generator will only look for the other partitions
on the same physical disk as the root partition. In this case,
boot loader support is not required. These partitions will not be
searched for on systems where the root file system is distributed
on multiple disks, for example via btrfs RAID.
systemd-gpt-auto-generator is useful for centralizing file system
configuration in the partition table and making configuration in
/etc/fstab or on the kernel command line unnecessary.
This generator looks for the partitions based on their partition
type GUID. The following partition type GUIDs are identified:
Table 1. Partition Type GUIDs
┌─────────────────────────────────────┬────────────────┬─────────────┬───────────────────┐
│Partition Type │ Name │ Mount Point │ Explanation │
│GUID │ │ │ │
├─────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
│SD_GPT_ROOT_X86_64 │ Root Partition │ / │ The first │
│4f68bce3-e8cd-4db1-96e7-fbcaf984b709 │ (x86-64) │ │ partition with │
│ │ │ │ this type │
│ │ │ │ UUID, located │
│ │ │ │ on the same │
│ │ │ │ disk as the │
│ │ │ │ ESP, is used │
│ │ │ │ as the root │
│ │ │ │ file system / │
│ │ │ │ on AMD64 / │
│ │ │ │ 64-bit x86 │
│ │ │ │ systems. │
├─────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
│SD_GPT_ROOT_ARM64 │ Root Partition │ / │ The first │
│b921b045-1df0-41c3-af44-4c6f280d3fae │ (64-bit ARM) │ │ partition with │
│ │ │ │ this type │
│ │ │ │ UUID, located │
│ │ │ │ on the same │
│ │ │ │ disk as the │
│ │ │ │ ESP, is used │
│ │ │ │ as the root │
│ │ │ │ file system / │
│ │ │ │ on AArch64 / │
│ │ │ │ 64-bit ARM │
│ │ │ │ systems. │
├─────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
│SD_GPT_ROOT_ALPHA SD_GPT_ROOT_ARC │ root │ / │ The first │
│SD_GPT_ROOT_ARM SD_GPT_ROOT_ARM64 │ partitions for │ │ partition with │
│SD_GPT_ROOT_IA64 │ other │ │ the type UUID │
│SD_GPT_ROOT_LOONGARCH64 │ architectures │ │ matching the │
│SD_GPT_ROOT_MIPS_LE │ │ │ architecture, │
│SD_GPT_ROOT_MIPS64_LE │ │ │ located on the │
│SD_GPT_ROOT_PARISC SD_GPT_ROOT_PPC │ │ │ same disk as │
│SD_GPT_ROOT_PPC64 │ │ │ the ESP, is │
│SD_GPT_ROOT_PPC64_LE │ │ │ used as the │
│SD_GPT_ROOT_RISCV32 │ │ │ root file │
│SD_GPT_ROOT_RISCV64 SD_GPT_ROOT_S390 │ │ │ system /. For │
│SD_GPT_ROOT_S390X SD_GPT_ROOT_TILEGX │ │ │ the full list │
│SD_GPT_ROOT_X86 SD_GPT_ROOT_X86_64 │ │ │ and constant │
│SD_GPT_USR_ALPHA SD_GPT_USR_ARC │ │ │ values, see │
│SD_GPT_USR_ARM SD_GPT_USR_IA64 │ │ │ Discoverable │
│SD_GPT_USR_LOONGARCH64 │ │ │ Partitions │
│SD_GPT_USR_MIPS_LE │ │ │ Specification[2]. │
│SD_GPT_USR_MIPS64_LE │ │ │ │
│SD_GPT_USR_PARISC SD_GPT_USR_PPC │ │ │ │
│SD_GPT_USR_PPC64 SD_GPT_USR_PPC64_LE │ │ │ │
│SD_GPT_USR_RISCV32 │ │ │ │
│SD_GPT_USR_RISCV64 SD_GPT_USR_S390 │ │ │ │
│SD_GPT_USR_S390X SD_GPT_USR_TILEGX │ │ │ │
│SD_GPT_USR_X86 │ │ │ │
├─────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
│SD_GPT_HOME │ Home Partition │ /home/ │ The first │
│933ac7e1-2eb4-4f13-b844-0e14e2aef915 │ │ │ partition with │
│ │ │ │ this type UUID on │
│ │ │ │ the same disk as │
│ │ │ │ the ESP is │
│ │ │ │ mounted to │
│ │ │ │ /home/. │
├─────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
│SD_GPT_SRV │ Server Data │ /srv/ │ The first │
│3b8f8425-20e0-4f3b-907f-1a25a76f98e8 │ Partition │ │ partition with │
│ │ │ │ this type UUID on │
│ │ │ │ the same disk as │
│ │ │ │ the ESP is │
│ │ │ │ mounted to /srv/. │
├─────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
│SD_GPT_VAR │ Variable Data │ /var/ │ The first │
│4d21b016-b534-45c2-a9fb-5c16e091fd2d │ Partition │ │ partition with │
│ │ │ │ this type UUID on │
│ │ │ │ the same disk as │
│ │ │ │ the ESP is │
│ │ │ │ mounted to /var/ │
│ │ │ │ — 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 │
│ │ │ │ machine-id(5). │
├─────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
│SD_GPT_TMP │ Temporary Data │ /var/tmp/ │ The first │
│7ec6f557-3bc5-4aca-b293-16ef5df639d1 │ Partition │ │ partition with │
│ │ │ │ this type UUID on │
│ │ │ │ the same disk as │
│ │ │ │ the ESP is │
│ │ │ │ mounted to │
│ │ │ │ /var/tmp/. │
├─────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
│SD_GPT_SWAP │ Swap │ n/a │ All partitions │
│0657fd6d-a4ab-43c4-84e5-0933c84b4f4f │ │ │ with this type │
│ │ │ │ UUID on the same │
│ │ │ │ disk as the ESP │
│ │ │ │ are used as swap. │
├─────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
│SD_GPT_ESP │ EFI System │ /efi/ or │ The first │
│c12a7328-f81f-11d2-ba4b-00a0c93ec93b │ Partition │ /boot/ │ partition with │
│ │ (ESP) │ │ this type UUID │
│ │ │ │ located on the │
│ │ │ │ same disk as the │
│ │ │ │ root partition is │
│ │ │ │ mounted to /boot/ │
│ │ │ │ or /efi/, see │
│ │ │ │ below. │
├─────────────────────────────────────┼────────────────┼─────────────┼───────────────────┤
│SD_GPT_XBOOTLDR │ Extended Boot │ /boot/ │ The first │
│bc13c2ff-59e6-4262-a352-b275fd6f7172 │ Loader │ │ partition with │
│ │ Partition │ │ this type UUID │
│ │ │ │ located on the │
│ │ │ │ same disk as the │
│ │ │ │ root partition is │
│ │ │ │ mounted to │
│ │ │ │ /boot/, see │
│ │ │ │ below. │
└─────────────────────────────────────┴────────────────┴─────────────┴───────────────────┘
This generator understands the following attribute flags for
partitions:
Table 2. Partition Attribute Flags
┌─────────────────────────────────┬───────────────────┬───────────────────┐
│Flag │ Applicable to │ Explanation │
├─────────────────────────────────┼───────────────────┼───────────────────┤
│SD_GPT_FLAG_READ_ONLY │ /, /home/, /srv/, │ Partition is │
│0x1000000000000000 │ /var/, /var/tmp/, │ mounted read-only │
│ │ Extended Boot │ │
│ │ Loader Partition │ │
├─────────────────────────────────┼───────────────────┼───────────────────┤
│SD_GPT_FLAG_NO_AUTO │ /, /home/, /srv/, │ Partition is not │
│0x8000000000000000 │ /var/, /var/tmp/, │ mounted │
│ │ Extended Boot │ automatically │
│ │ Loader Partition │ │
├─────────────────────────────────┼───────────────────┼───────────────────┤
│SD_GPT_FLAG_NO_BLOCK_IO_PROTOCOL │ EFI System │ Partition is not │
│0x0000000000000002 │ Partition (ESP) │ mounted │
│ │ │ automatically │
└─────────────────────────────────┴───────────────────┴───────────────────┘
The /home/, /srv/, /var/ and /var/tmp/ partitions may be
encrypted in LUKS format. In this case, a device mapper device is
set up under the names /dev/mapper/home, /dev/mapper/srv,
/dev/mapper/var and /dev/mapper/tmp. Note that this might create
conflicts if the same partition is listed in /etc/crypttab with a
different device mapper device name.
When systemd is running in the initrd the / partition may be
encrypted in LUKS format as well. In this case, a device mapper
device is set up under the name /dev/mapper/root, and a
sysroot.mount is set up that mounts the device under /sysroot.
For more information, see bootup(7).
The root partition can be specified by symlinking
/run/systemd/volatile-root to /dev/block/$major:$minor. This is
especially useful if the root mount has been replaced by some
form of volatile file system (overlayfs).
Mount and automount units for the EFI System Partition (ESP) are
generated on EFI systems. The ESP is mounted to /boot/ (except if
an Extended Boot Loader partition exists, see below), unless a
mount point directory /efi/ exists, in which case it is mounted
there. Since this generator creates an automount unit, the mount
will only be activated on-demand, when accessed. On systems where
/boot/ (or /efi/ if it exists) is an explicitly configured mount
(for example, listed in fstab(5)) or where the /boot/ (or /efi/)
mount point is non-empty, no mount units are generated.
If the disk contains an Extended Boot Loader partition, as
defined in the Boot Loader Specification[4], it is made available
at /boot/ (by means of an automount point, similar to the ESP,
see above). If both an EFI System Partition and an Extended Boot
Loader partition exist the latter is preferably mounted to
/boot/. Make sure to create both /efi/ and /boot/ to ensure both
partitions are mounted.
When using this generator in conjunction with btrfs file systems,
make sure to set the correct default subvolumes on them, using
btrfs subvolume set-default.
systemd-gpt-auto-generator implements systemd.generator(7).
systemd-gpt-auto-generator understands the following kernel
command line parameters:
systemd.gpt_auto, rd.systemd.gpt_auto
Those options take an optional boolean argument, and default
to yes. The generator is enabled by default, and a negative
value may be used to disable it.
root=
When used with the special value "gpt-auto", automatic
discovery of the root partition based on the GPT partition
type is enabled. Any other value disables this generator.
rw, ro
Mount the root partition read-write or read-only initially.
Note that unlike most kernel command line options these
settings do not override configuration in the file system,
and the file system may be remounted later. See
systemd-remount-fs.service(8).
systemd(1), systemd.mount(5), systemd.swap(5),
systemd-fstab-generator(8), systemd-cryptsetup@.service(8),
machine-id(5), cryptsetup(8), fstab(5), btrfs(8)
1. UEFI Specification
https://uefi.org/specifications
2. Discoverable Partitions Specification
https://uapi-group.org/specifications/specs/discoverable_partitions_specification
3. Boot Loader Interface
https://systemd.io/BOOT_LOADER_INTERFACE
4. Boot Loader Specification
https://uapi-group.org/specifications/specs/boot_loader_specification
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have
a bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2022-12-17. (At that
time, the date of the most recent commit that was found in the
repository was 2022-12-16.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 252 SYSTEMD-GPT-AUTO-GENERATOR(8)
Pages that refer to this page: repart.d(5), sysupdate.d(5), file-hierarchy(7), kernel-command-line(7), systemd.directives(7), systemd.generator(7), systemd.index(7), systemd-fstab-generator(8), systemd-remount-fs.service(8)
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