Provided by: systemd_245.4-4ubuntu3_amd64 bug

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 the EFI
       System Partition (ESP) is located on. 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 GUIDNameMount PointExplanation         │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼─────────────────────┤
       │44479540-f297-41b2-9af7-d131d5f0458a │ Root Partition   │ /               │ On 32-bit x86       │
       │                                     │ (x86)            │                 │ systems, the first  │
       │                                     │                  │                 │ x86 root partition  │
       │                                     │                  │                 │ on the disk the EFI │
       │                                     │                  │                 │ ESP is located on   │
       │                                     │                  │                 │ is mounted to the   │
       │                                     │                  │                 │ root directory /.   │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼─────────────────────┤
       │4f68bce3-e8cd-4db1-96e7-fbcaf984b709 │ Root Partition   │ /               │ On 64-bit x86       │
       │                                     │ (x86-64)         │                 │ systems, the first  │
       │                                     │                  │                 │ x86-64 root         │
       │                                     │                  │                 │ partition on the    │
       │                                     │                  │                 │ disk the EFI ESP is │
       │                                     │                  │                 │ located on is       │
       │                                     │                  │                 │ mounted to the root │
       │                                     │                  │                 │ directory /.        │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼─────────────────────┤
       │69dad710-2ce4-4e3c-b16c-21a1d49abed3 │ Root Partition   │ /               │ On 32-bit ARM       │
       │                                     │ (32-bit ARM)     │                 │ systems, the first  │
       │                                     │                  │                 │ ARM root partition  │
       │                                     │                  │                 │ on the disk the EFI │
       │                                     │                  │                 │ ESP is located on   │
       │                                     │                  │                 │ is mounted to the   │
       │                                     │                  │                 │ root directory /.   │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼─────────────────────┤
       │b921b045-1df0-41c3-af44-4c6f280d3fae │ Root Partition   │ /               │ On 64-bit ARM       │
       │                                     │ (64-bit ARM)     │                 │ systems, the first  │
       │                                     │                  │                 │ ARM root partition  │
       │                                     │                  │                 │ on the disk the EFI │
       │                                     │                  │                 │ ESP is located on   │
       │                                     │                  │                 │ is mounted to the   │
       │                                     │                  │                 │ root directory /.   │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼─────────────────────┤
       │993d8d3d-f80e-4225-855a-9daf8ed7ea97 │ Root Partition   │ /               │ On Itanium systems, │
       │                                     │ (Itanium/IA-64)  │                 │ the first Itanium   │
       │                                     │                  │                 │ root partition on   │
       │                                     │                  │                 │ the disk the EFI    │
       │                                     │                  │                 │ ESP is located on   │
       │                                     │                  │                 │ is mounted to the   │
       │                                     │                  │                 │ root directory /.   │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼─────────────────────┤
       │933ac7e1-2eb4-4f13-b844-0e14e2aef915 │ Home Partition   │ /home/          │ The first home      │
       │                                     │                  │                 │ partition on the    │
       │                                     │                  │                 │ disk the root       │
       │                                     │                  │                 │ partition is        │
       │                                     │                  │                 │ located on is       │
       │                                     │                  │                 │ mounted to /home/.  │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼─────────────────────┤
       │3b8f8425-20e0-4f3b-907f-1a25a76f98e8 │ Server Data      │ /srv/           │ The first server    │
       │                                     │ Partition        │                 │ data partition on   │
       │                                     │                  │                 │ the disk the root   │
       │                                     │                  │                 │ partition is        │
       │                                     │                  │                 │ located on is       │
       │                                     │                  │                 │ mounted to /srv/.   │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼─────────────────────┤
       │4d21b016-b534-45c2-a9fb-5c16e091fd2d │ Variable Data    │ /var/           │ The first variable  │
       │                                     │ Partition        │                 │ data partition on   │
       │                                     │                  │                 │ the disk the root   │
       │                                     │                  │                 │ partition is        │
       │                                     │                  │                 │ located on 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).   │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼─────────────────────┤
       │7ec6f557-3bc5-4aca-b293-16ef5df639d1 │ Temporary Data   │ /var/tmp/       │ The first temporary │
       │                                     │ Partition        │                 │ data partition on   │
       │                                     │                  │                 │ the disk the root   │
       │                                     │                  │                 │ partition is        │
       │                                     │                  │                 │ located on is       │
       │                                     │                  │                 │ mounted to          │
       │                                     │                  │                 │ /var/tmp/.          │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼─────────────────────┤
       │0657fd6d-a4ab-43c4-84e5-0933c84b4f4f │ Swap             │ n/a             │ All swap partitions │
       │                                     │                  │                 │ located on the disk │
       │                                     │                  │                 │ the root partition  │
       │                                     │                  │                 │ is located on are   │
       │                                     │                  │                 │ enabled.            │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼─────────────────────┤
       │c12a7328-f81f-11d2-ba4b-00a0c93ec93b │ EFI System       │ /efi/ or /boot/ │ The first ESP       │
       │                                     │ Partition (ESP)  │                 │ located on the disk │
       │                                     │                  │                 │ the root partition  │
       │                                     │                  │                 │ is located on is    │
       │                                     │                  │                 │ mounted to /boot/   │
       │                                     │                  │                 │ or /efi/, see       │
       │                                     │                  │                 │ below.              │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼─────────────────────┤
       │bc13c2ff-59e6-4262-a352-b275fd6f7172 │ Extended Boot    │ /boot/          │ The first Extended  │
       │                                     │ Loader Partition │                 │ Boot Loader         │
       │                                     │                  │                 │ Partition is        │
       │                                     │                  │                 │ mounted to /boot/,  │
       │                                     │                  │                 │ see below.          │
       └─────────────────────────────────────┴──────────────────┴─────────────────┴─────────────────────┘

       This generator understands the following attribute flags for partitions:

       Table 2. Partition Attributes
       ┌──────────────────────────────┬────────────────────┬───────────────────┬───────────────────┐
       │NameValueApplicable toExplanation       │
       ├──────────────────────────────┼────────────────────┼───────────────────┼───────────────────┤
       │GPT_FLAG_READ_ONLY            │ 0x1000000000000000 │ /, /home/, /srv/, │ Partition is      │
       │                              │                    │ /var/, /var/tmp/, │ mounted read-only │
       │                              │                    │ Extended Boot     │                   │
       │                              │                    │ Loader Partition  │                   │
       ├──────────────────────────────┼────────────────────┼───────────────────┼───────────────────┤
       │GPT_FLAG_NO_AUTO              │ 0x8000000000000000 │ /, /home/, /srv/, │ Partition is not  │
       │                              │                    │ /var/, /var/tmp/, │ mounted           │
       │                              │                    │ Extended Boot     │ automatically     │
       │                              │                    │ Loader Partition  │                   │
       ├──────────────────────────────┼────────────────────┼───────────────────┼───────────────────┤
       │GPT_FLAG_NO_BLOCK_IO_PROTOCOL │ 0x0000000000000002 │ EFI System        │ Partition is not  │
       │                              │                    │ 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).

       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 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).

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