SYSTEMD-GPT-AUTO-GENERATORsystemd-gpt-auto-generaSYSTEMD-GPT-AUTO-GENERATOR(8)
NAME
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
SYNOPSIS
/lib/systemd/system-generators/systemd-gpt-auto-generator
DESCRIPTION
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 partitions │ / │ The first │
│SD_GPT_ROOT_ARM SD_GPT_ROOT_ARM64 │ for other │ │ partition with │
│SD_GPT_ROOT_IA64 │ architectures │ │ the type UUID │
│SD_GPT_ROOT_LOONGARCH64 │ │ │ matching the │
│SD_GPT_ROOT_MIPS SD_GPT_ROOT_MIPS64 │ │ │ architecture, │
│SD_GPT_ROOT_MIPS_LE │ │ │ located on the │
│SD_GPT_ROOT_MIPS64_LE │ │ │ same disk as the │
│SD_GPT_ROOT_PARISC SD_GPT_ROOT_PPC │ │ │ ESP, is used as │
│SD_GPT_ROOT_PPC64 │ │ │ the root file │
│SD_GPT_ROOT_PPC64_LE │ │ │ system /. For │
│SD_GPT_ROOT_RISCV32 │ │ │ the full list │
│SD_GPT_ROOT_RISCV64 SD_GPT_ROOT_S390 │ │ │ and constant │
│SD_GPT_ROOT_S390X SD_GPT_ROOT_TILEGX │ │ │ values, see │
│SD_GPT_ROOT_X86 SD_GPT_ROOT_X86_64 │ │ │ Discoverable │
│SD_GPT_USR_ALPHA SD_GPT_USR_ARC │ │ │ Partitions │
│SD_GPT_USR_ARM SD_GPT_USR_IA64 │ │ │ Specification[2]. │
│SD_GPT_USR_LOONGARCH64 │ │ │ │
│SD_GPT_USR_MIPS_LE │ │ │ │
│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 /boot/ │ The first │
│c12a7328-f81f-11d2-ba4b-00a0c93ec93b │ Partition (ESP) │ │ partition with │
│ │ │ │ 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 │ │ partition with │
│ │ │ │ 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).
KERNEL COMMAND LINE
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 false value may be
used to disable it (e.g. "systemd.gpt_auto=0").
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).
SEE ALSO
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)
NOTES
1. UEFI Specification
https://uefi.org/specifications
2. Discoverable Partitions Specification
https://systemd.io/DISCOVERABLE_PARTITIONS
3. Boot Loader Interface
https://systemd.io/BOOT_LOADER_INTERFACE
4. Boot Loader Specification
https://systemd.io/BOOT_LOADER_SPECIFICATION
systemd 252 SYSTEMD-GPT-AUTO-GENERATOR(8)
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