SYSTEMD-GPT-AUTO-GENERATOR(8) systemd-gpt-auto-generator
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 (ESP), the Extended Boot Loader Partition (XBOOTLDR),
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). Additionally no unit will be created for the ESP or the
XBOOTLDR partition if mount entries are found in the /boot/ or /efi/
hierarchies 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.
When run in the initial RAM disk (initrd) this generator can
automatically search for the root file system. Specifically:
• It will 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 for this to work: the EFI variable
LoaderDevicePartUUID of the 4a67b082-0a4c-41cf-b6c7-440b29bb8c4f
vendor UUID is used to determine from which partition (and hence
disk) 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.
• Alternatively, it will look for the root file system on a loopback
block device whose ".lo_name" field is set to one of the literal
strings "rootdisk" or "rootdisk.raw". This field can be set via
losetup's --loop-ref= string. For images downloaded via systemd-
import-generator(8) make sure to set the "blockdev" option and set
the local name string to "rootdisk" to achieve this effect. Note
that discovery of the root file system on loopback block devices
like this is only done if "root=gpt-auto" or "root=dissect" is
specified explicitly on the kernel command line, unlike the
discovery based on the boot loader reported ESP which is also
enabled if no "root=" parameter is specified at all. (The latter
relies on systemd-udevd.service's /dev/gpt-auto-root block device
symlink generation).
When run on the host system (i.e. after successfully transitioning out
of the initrd into the root filesystem) this generator will look for
all other partitions on the same physical disk as the root partition.
For this discovery, boot loader support is not required. Moreover, it
is not required that the root partition was automatically discovered by
the initrd (as described above) for the discovery of the non-root file
partitions to take place. Or in other words: automatic discovery of the
root file system and of the non-root file systems are independent
operations, that do not rely on each other, and are done during two
distinct phases of the boot process (one in the initrd, the other
after). These partitions will not be searched for on systems where the
root file system is distributed on multiple disks, for example via
btrfs RAID.
The root partition can be configured explicitly 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).
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 │ 4f68bce3-e8cd-4db1-96e7-fbcaf984b709 │ Root │ / │ The first │
│ │ │ Partition │ │ partition with │
│ │ │ (x86-64) │ │ this type UUID, │
│ │ │ │ │ located on the │
│ │ │ │ │ same disk as the │
│ │ │ │ │ ESP used for │
│ │ │ │ │ booting, is used │
│ │ │ │ │ as the root file │
│ │ │ │ │ system / on AMD64 │
│ │ │ │ │ / 64-bit x86 │
│ │ │ │ │ systems. │
├────────────────────────┼──────────────────────────────────────┼───────────────┼─────────────┼───────────────────┤
│SD_GPT_ROOT_ARM64 │ b921b045-1df0-41c3-af44-4c6f280d3fae │ Root │ / │ The first │
│ │ │ Partition │ │ partition with │
│ │ │ (64-bit ARM) │ │ this type UUID, │
│ │ │ │ │ located on the │
│ │ │ │ │ same disk as the │
│ │ │ │ │ ESP used for │
│ │ │ │ │ booting, is used │
│ │ │ │ │ as the root file │
│ │ │ │ │ system / on │
│ │ │ │ │ AArch64 / 64-bit │
│ │ │ │ │ ARM systems. │
├────────────────────────┼──────────────────────────────────────┼───────────────┼─────────────┼───────────────────┤
│SD_GPT_ROOT_ALPHA │ ... │ Root │ / │ The first │
│SD_GPT_ROOT_ARC │ │ partitions │ │ partition with │
│SD_GPT_ROOT_ARM │ │ for other │ │ the type UUID │
│SD_GPT_ROOT_ARM64 │ │ architectures │ │ matching the │
│SD_GPT_ROOT_IA64 │ │ │ │ architecture, │
│SD_GPT_ROOT_LOONGARCH64 │ │ │ │ located on the │
│SD_GPT_ROOT_MIPS │ │ │ │ same disk as the │
│SD_GPT_ROOT_MIPS64 │ │ │ │ ESP used for │
│SD_GPT_ROOT_MIPS_LE │ │ │ │ booting, is used │
│SD_GPT_ROOT_MIPS64_LE │ │ │ │ as the root file │
│SD_GPT_ROOT_PARISC │ │ │ │ system /. For the │
│SD_GPT_ROOT_PPC │ │ │ │ full list and │
│SD_GPT_ROOT_PPC64 │ │ │ │ constant values, │
│SD_GPT_ROOT_PPC64_LE │ │ │ │ see Discoverable │
│SD_GPT_ROOT_RISCV32 │ │ │ │ Partitions │
│SD_GPT_ROOT_RISCV64 │ │ │ │ Specification[2]. │
│SD_GPT_ROOT_S390 │ │ │ │ │
│SD_GPT_ROOT_S390X │ │ │ │ │
│SD_GPT_ROOT_TILEGX │ │ │ │ │
│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 │ 933ac7e1-2eb4-4f13-b844-0e14e2aef915 │ Home │ /home/ │ The first │
│ │ │ Partition │ │ partition with │
│ │ │ │ │ this type UUID on │
│ │ │ │ │ the same disk as │
│ │ │ │ │ the root │
│ │ │ │ │ partition is │
│ │ │ │ │ mounted to │
│ │ │ │ │ /home/. │
├────────────────────────┼──────────────────────────────────────┼───────────────┼─────────────┼───────────────────┤
│SD_GPT_SRV │ 3b8f8425-20e0-4f3b-907f-1a25a76f98e8 │ Server Data │ /srv/ │ The first │
│ │ │ Partition │ │ partition with │
│ │ │ │ │ this type UUID on │
│ │ │ │ │ the same disk as │
│ │ │ │ │ the root │
│ │ │ │ │ partition is │
│ │ │ │ │ mounted to /srv/. │
├────────────────────────┼──────────────────────────────────────┼───────────────┼─────────────┼───────────────────┤
│SD_GPT_VAR │ 4d21b016-b534-45c2-a9fb-5c16e091fd2d │ Variable Data │ /var/ │ The first │
│ │ │ Partition │ │ partition with │
│ │ │ │ │ this type UUID on │
│ │ │ │ │ the same disk as │
│ │ │ │ │ the root │
│ │ │ │ │ partition 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). │
│ │ │ │ │ This can be │
│ │ │ │ │ generated using │
│ │ │ │ │ systemd-id128(1). │
├────────────────────────┼──────────────────────────────────────┼───────────────┼─────────────┼───────────────────┤
│SD_GPT_TMP │ 7ec6f557-3bc5-4aca-b293-16ef5df639d1 │ Temporary │ /var/tmp/ │ The first │
│ │ │ Data │ │ partition with │
│ │ │ Partition │ │ this type UUID on │
│ │ │ │ │ the same disk as │
│ │ │ │ │ the root │
│ │ │ │ │ partition is │
│ │ │ │ │ mounted to │
│ │ │ │ │ /var/tmp/. │
├────────────────────────┼──────────────────────────────────────┼───────────────┼─────────────┼───────────────────┤
│SD_GPT_SWAP │ 0657fd6d-a4ab-43c4-84e5-0933c84b4f4f │ Swap │ n/a │ All partitions │
│ │ │ │ │ with this type │
│ │ │ │ │ UUID on the same │
│ │ │ │ │ disk as the root │
│ │ │ │ │ partition are │
│ │ │ │ │ used as swap. │
├────────────────────────┼──────────────────────────────────────┼───────────────┼─────────────┼───────────────────┤
│SD_GPT_ESP │ c12a7328-f81f-11d2-ba4b-00a0c93ec93b │ EFI System │ /efi/ or │ The first │
│ │ │ 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 │ bc13c2ff-59e6-4262-a352-b275fd6f7172 │ Extended Boot │ /boot/ │ The first │
│ │ │ 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 │ Value │ Applicable to │ Explanation │
├─────────────────────────────────┼────────────────────┼──────────────────┼──────────────────┤
│SD_GPT_FLAG_READ_ONLY │ 0x1000000000000000 │ /, /home/, │ Partition is │
│ │ │ /srv/, /var/, │ mounted │
│ │ │ /var/tmp/, │ read-only │
│ │ │ Extended Boot │ │
│ │ │ Loader Partition │ │
├─────────────────────────────────┼────────────────────┼──────────────────┼──────────────────┤
│SD_GPT_FLAG_NO_AUTO │ 0x8000000000000000 │ /, /home/, │ Partition is not │
│ │ │ /srv/, /var/, │ mounted │
│ │ │ /var/tmp/, │ automatically │
│ │ │ Extended Boot │ │
│ │ │ Loader Partition │ │
├─────────────────────────────────┼────────────────────┼──────────────────┼──────────────────┤
│SD_GPT_FLAG_NO_BLOCK_IO_PROTOCOL │ 0x0000000000000002 │ EFI System │ Partition is not │
│ │ │ Partition (ESP) │ mounted │
│ │ │ │ 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).
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).
Mount constraint metadata contained in the file systems is validated by
pulling in systemd-validatefs@.service(8) for generated mounts.
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=
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.
Note that the specified image policy is not taken into account for
automatic root or /usr/ file system discovery unless
root=dissect/mount.usr=dissect (or root=dissect-force) are
specified. (The policy will always be applied to the other
auto-discoverable partition types.)
Added in version 254.
systemd.image_filter=
Takes an image dissection filter string as argument (as per
systemd.image-filter(7)), and allows enforcing a set of globbing
patterns on the partition matching of the automatically discovered
GPT partition table entries.
Note that the specified image filter is not taken into account for
automatic root or /usr/ file system discovery unless
root=dissect/mount.usr=dissect (or root=dissect-force) are
specified. (The filter will always be applied to the other
auto-discoverable partition types.)
Added in version 258.
root=, rootfstype=, rootflags=
When root= is used with the special value "gpt-auto", basic
automatic discovery of the root partition based on the GPT
partition type is enabled. Use of the root partition is delayed
until factory reset mode is left, in case it is enabled during the
current boot. See Factory Reset[5] for more information on that. If
"gpt-auto-force" is specified automatic discovery of the root
partition is enabled, ignoring any factory reset mode.
If root= is set to the special value "dissect" full automatic
discovery of the root partition based on GPT partition information
is enabled. This is a superset of root=gpt-auto, as it
automatically configures Verity partitions (including
signature-based setup) following the logic defined for that in the
Discoverable Partitions Specification[6]. Moreover it takes the
configured image policy and image filter into account for all
partition types, including the root file system. "root=dissect"
will wait for the factory reset phase to be completed if it is in
effect before activating the root file system. Use
"root=dissect-force" to ignore the factory reset phase and activate
the root file system immediately.
Any other value (i.e. besides "gpt-auto", "gpt-auto-force",
"dissect", "dissect-force") disables automatic root file system
discovery.
If root= is not specified at all on the kernel command line
automatic discovery of the root partition via the ESP reported by
the boot loader is also enabled (taking factory reset state into
account, i.e. equivalent to "root=gpt-auto"), however in this case
discovery based on the loopback block device ".lo_name" field is
not enabled.
The rootfstype= and rootflags= options are used to select the file
system type and options when the root file system is automatically
discovered.
Added in version 242.
mount.usr=, mount.usrfstype=, mount.usrflags=
Similar to root=, rootfstype=, rootflags= (see above), but applies
to the /usr/ partition instead. Note that the "gpt-auto",
"gpt-auto-force", "dissect-force" settings that root= understands
are not supported by mount.usr= (however "dissect" is).
Also note that automatic partition discovery for /usr/ must be
enabled explicitly, unlike the discovery for the root file system,
which is enabled if no root= parameter is passed at all.
Added in version 258.
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), systemd-validatefs@.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
5. Factory Reset
https://systemd.io/FACTORY_RESET
6. Discoverable Partitions Specification
https://uapi-
group.org/specifications/specs/discoverable_partitions_specification/
systemd 258 SYSTEMD-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