Provided by: systemd_255.4-1ubuntu8.4_amd64 
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
/usr/lib/systemd/system-generators/systemd-gpt-auto-generator
DESCRIPTION
systemd-gpt-auto-generator is a unit generator that automatically discovers the root
partition, /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 for more details. It implements the Discoverable Partitions Specification[2].
Note that this generator has no effect on non-GPT systems. It will also not create mount
point configuration for directories which already contain files or if the mount point is
explicitly configured in fstab(5). If the units this generator creates are overridden, for
example by units in directories with higher precedence, drop-ins and additional
dependencies created by this generator might still be used.
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 detect 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 GUID │ Name │ Mount Point │ Explanation │
├─────────────────────────────────────┼─────────────────────┼─────────────────┼─────────────────────┤
│SD_GPT_ROOT_X86_64 │ Root Partition │ / │ The first partition │
│4f68bce3-e8cd-4db1-96e7-fbcaf984b709 │ (x86-64) │ │ 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 partition │
│b921b045-1df0-41c3-af44-4c6f280d3fae │ (64-bit ARM) │ │ 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 for │ / │ The first partition │
│SD_GPT_ROOT_ARM SD_GPT_ROOT_ARM64 │ other architectures │ │ with the type UUID │
│SD_GPT_ROOT_IA64 │ │ │ matching the │
│SD_GPT_ROOT_LOONGARCH64 │ │ │ architecture, │
│SD_GPT_ROOT_MIPS SD_GPT_ROOT_MIPS64 │ │ │ located on the same │
│SD_GPT_ROOT_MIPS_LE │ │ │ disk as the ESP, is │
│SD_GPT_ROOT_MIPS64_LE │ │ │ used as the root │
│SD_GPT_ROOT_PARISC SD_GPT_ROOT_PPC │ │ │ file system /. For │
│SD_GPT_ROOT_PPC64 │ │ │ the full list and │
│SD_GPT_ROOT_PPC64_LE │ │ │ constant values, │
│SD_GPT_ROOT_RISCV32 │ │ │ see Discoverable │
│SD_GPT_ROOT_RISCV64 SD_GPT_ROOT_S390 │ │ │ Partitions │
│SD_GPT_ROOT_S390X SD_GPT_ROOT_TILEGX │ │ │ Specification[2]. │
│SD_GPT_ROOT_X86 SD_GPT_ROOT_X86_64 │ │ │ │
│SD_GPT_USR_ALPHA SD_GPT_USR_ARC │ │ │ │
│SD_GPT_USR_ARM SD_GPT_USR_IA64 │ │ │ │
│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 partition │
│933ac7e1-2eb4-4f13-b844-0e14e2aef915 │ │ │ with this type UUID │
│ │ │ │ on the same disk as │
│ │ │ │ the ESP is mounted │
│ │ │ │ to /home/. │
├─────────────────────────────────────┼─────────────────────┼─────────────────┼─────────────────────┤
│SD_GPT_SRV │ Server Data │ /srv/ │ The first partition │
│3b8f8425-20e0-4f3b-907f-1a25a76f98e8 │ Partition │ │ with this type UUID │
│ │ │ │ on the same disk as │
│ │ │ │ the ESP is mounted │
│ │ │ │ to /srv/. │
├─────────────────────────────────────┼─────────────────────┼─────────────────┼─────────────────────┤
│SD_GPT_VAR │ Variable Data │ /var/ │ The first partition │
│4d21b016-b534-45c2-a9fb-5c16e091fd2d │ 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 partition │
│7ec6f557-3bc5-4aca-b293-16ef5df639d1 │ 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 with │
│0657fd6d-a4ab-43c4-84e5-0933c84b4f4f │ │ │ this type UUID on │
│ │ │ │ the same disk as │
│ │ │ │ the ESP are used as │
│ │ │ │ swap. │
├─────────────────────────────────────┼─────────────────────┼─────────────────┼─────────────────────┤
│SD_GPT_ESP │ EFI System │ /efi/ or /boot/ │ The first partition │
│c12a7328-f81f-11d2-ba4b-00a0c93ec93b │ Partition (ESP) │ │ 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 partition │
│bc13c2ff-59e6-4262-a352-b275fd6f7172 │ Loader 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/, /var/, │ Partition is mounted │
│0x1000000000000000 │ /var/tmp/, Extended Boot │ read-only │
│ │ Loader Partition │ │
├─────────────────────────────────┼──────────────────────────┼──────────────────────────┤
│SD_GPT_FLAG_NO_AUTO │ /, /home/, /srv/, /var/, │ Partition is not mounted │
│0x8000000000000000 │ /var/tmp/, Extended Boot │ automatically │
│ │ Loader Partition │ │
├─────────────────────────────────┼──────────────────────────┼──────────────────────────┤
│SD_GPT_FLAG_NO_BLOCK_IO_PROTOCOL │ EFI System Partition │ Partition is not mounted │
│0x0000000000000002 │ (ESP) │ automatically │
└─────────────────────────────────┴──────────────────────────┴──────────────────────────┘
The /home/, /srv/, /var/, /var/tmp/ and swap 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, /dev/mapper/tmp or /dev/mapper/swap. 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 with LUKS 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) and Extended Boot Loader
Partition (XBOOTLDR) are generated on EFI systems. If the disk contains an XBOOTLDR
partition, as defined in the Boot Loader Specification[4], it is made available at /boot/.
This generator creates an automount unit; the mount will only be activated on-demand when
accessed. The mount point will be created if necessary.
The ESP is mounted to /boot/ if that directory exists and is not used for XBOOTLDR, and
otherwise to /efi/. Same as for /boot/, an automount unit is used. The mount point will be
created if necessary.
No configuration is created for mount points that are configured in fstab(5) or when the
target directory contains files.
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.
If the system was booted via systemd-stub(7) and the stub reported to userspace that the
kernel image was measured to a TPM2 PCR, then any discovered root and /var/ volume
identifiers (and volume encryption key in case it is encrypted) will be automatically
measured into PCR 15 on activation, via systemd-pcrfs@.service(8).
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").
Added in version 242.
systemd.image_policy=, rd.systemd.image_policy=
Takes an image dissection policy string as argument (as per systemd.image-policy(7)),
and allows enforcing a policy on dissection and use of the automatically discovered
GPT partition table entries.
Added in version 254.
root=, rootfstype=, rootflags=
When root= is used with the special value "gpt-auto" (or if the parameter is not used
at all), automatic discovery of the root partition based on the GPT partition type is
enabled. Any other value disables this logic.
The rootfstype= and rootflags= are used to select the file system type and options
when the root file system is automatically discovered.
Added in version 242.
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).
Added in version 242.
systemd.swap=
Takes a boolean argument or enables the option if specified without an argument. If
disabled, automatic discovery of swap partition(s) based on GPT partition type is
disabled. Defaults to enabled.
Added in version 254.
SEE ALSO
systemd(1), systemd.mount(5), systemd.swap(5), systemd-fstab-generator(8), systemd-
cryptsetup@.service(8), systemd-pcrfs@.service(8), machine-id(5), cryptsetup(8), fstab(5),
btrfs(8)
NOTES
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