systemd-gpt-auto-generator
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 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 245 SYSTEMD-GPT-AUTO-GENERATOR(8)
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