systemd-gpt-auto-generator

SYSTEMD-GPT-AUTO-GENERATOR(systemd-gpt-auto-generatSYSTEMD-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
       /usr/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                       Name             Mount Point     Explanation      │
       │GUID                                 │                  │                 │                  │
       ├─────────────────────────────────────┼──────────────────┼─────────────────┼──────────────────┤
       │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       │
       │                                     │ (Itanium/IA-64)  │                 │ systems, 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        │
       │                                     │ Partition        │                 │ variable 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        │
       │                                     │ Partition        │                 │ temporary 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        │
       │                                     │ Loader Partition │                 │ Extended Boot    │
       │                                     │                  │                 │ Loader Partition │
       │                                     │                  │                 │ is mounted to    │
       │                                     │                  │                 │ /boot/, see      │
       │                                     │                  │                 │ below.           │
       └─────────────────────────────────────┴──────────────────┴─────────────────┴──────────────────┘

       This generator understands the following attribute flags for partitions:

       Table 2. Partition Attributes
       ┌──────────────────────────────┬────────────────────┬──────────────────┬──────────────────┐
       │Name                          Value              Applicable to    Explanation      │
       ├──────────────────────────────┼────────────────────┼──────────────────┼──────────────────┤
       │GPT_FLAG_READ_ONLY            │ 0x1000000000000000 │ /, /home/,       │ Partition is     │
       │                              │                    │ /srv/, /var/,    │ mounted          │
       │                              │                    │ /var/tmp/,       │ read-only        │
       │                              │                    │ Extended Boot    │                  │
       │                              │                    │ Loader Partition │                  │
       ├──────────────────────────────┼────────────────────┼──────────────────┼──────────────────┤
       │GPT_FLAG_NO_AUTO              │ 0x8000000000000000 │ /, /home/,       │ Partition is not │
       │                              │                    │ /srv/, /var/,    │ mounted          │
       │                              │                    │ /var/tmp/,       │ automatically    │
       │                              │                    │ Extended Boot    │                  │
       │                              │                    │ 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



systemd 246                                        SYSTEMD-GPT-AUTO-GENERATOR(8)