1SYSTEMD-GPT-AUTO-GENERATOR(s8y)stemd-gpt-auto-generatSoYrSTEMD-GPT-AUTO-GENERATOR(8)
2
6 systemd-gpt-auto-generator - Generator for automatically discovering
7 and mounting root, /home/, /srv/, /var/ and /var/tmp/ partitions, as
8 well as discovering and enabling swap partitions, based on GPT
9 partition type GUIDs
10
12 /usr/lib/systemd/system-generators/systemd-gpt-auto-generator
13
15 systemd-gpt-auto-generator is a unit generator that automatically
16 discovers root, /home/, /srv/, /var/, /var/tmp/, the EFI System
17 Partition, the Extended Boot Loader Partition and swap partitions and
18 creates mount and swap units for them, based on the partition type
19 GUIDs of GUID partition tables (GPT), see UEFI Specification[1],
20 chapter 5. It implements the Discoverable Partitions Specification[2].
21 Note that this generator has no effect on non-GPT systems, and on
22 specific mount points that are directories already containing files.
23 Also, on systems where the units are explicitly configured (for
24 example, listed in fstab(5)), the units this generator creates are
25 overridden, but additional implicit dependencies might be created.
26 This generator will only look for the root partition on the same
28 physical disk where the EFI System Partition (ESP) is located. Note
29 that support from the boot loader is required: the EFI variable
30 LoaderDevicePartUUID of the 4a67b082-0a4c-41cf-b6c7-440b29bb8c4f vendor
31 UUID is used to determine from which partition, and hence the disk from
32 which the system was booted. If the boot loader does not set this
33 variable, this generator will not be able to autodetect the root
34 partition. See the Boot Loader Interface[3] for details.
35 Similarly, this generator will only look for the other partitions on
37 the same physical disk as the root partition. In this case, boot loader
38 support is not required. These partitions will not be searched for on
39 systems where the root file system is distributed on multiple disks,
40 for example via btrfs RAID.
41 systemd-gpt-auto-generator is useful for centralizing file system
43 configuration in the partition table and making configuration in
44 /etc/fstab or on the kernel command line unnecessary.
45 This generator looks for the partitions based on their partition type
47 GUID. The following partition type GUIDs are identified:
48 Table 1. Partition Type GUIDs
50 ┌─────────────────────────────────────┬──────────────────┬─────────────────┬───────────────────┐
51 │Partition Type │ Name │ Mount Point │ Explanation │
52 │GUID │ │ │ │
53 ├─────────────────────────────────────┼──────────────────┼─────────────────┼───────────────────┤
54 │SD_GPT_ROOT_X86_64 │ Root Partition │ / │ The first │
55 │4f68bce3-e8cd-4db1-96e7-fbcaf984b709 │ (x86-64) │ │ partition with │
56 │ │ │ │ this type UUID, │
57 │ │ │ │ located on the │
58 │ │ │ │ same disk as the │
59 │ │ │ │ ESP, is used as │
60 │ │ │ │ the root file │
61 │ │ │ │ system / on │
62 │ │ │ │ AMD64 / 64-bit │
63 │ │ │ │ x86 systems. │
64 ├─────────────────────────────────────┼──────────────────┼─────────────────┼───────────────────┤
65 │SD_GPT_ROOT_ARM64 │ Root Partition │ / │ The first │
66 │b921b045-1df0-41c3-af44-4c6f280d3fae │ (64-bit ARM) │ │ partition with │
67 │ │ │ │ this type UUID, │
68 │ │ │ │ located on the │
69 │ │ │ │ same disk as the │
70 │ │ │ │ ESP, is used as │
71 │ │ │ │ the root file │
72 │ │ │ │ system / on │
73 │ │ │ │ AArch64 / 64-bit │
74 │ │ │ │ ARM systems. │
75 ├─────────────────────────────────────┼──────────────────┼─────────────────┼───────────────────┤
76 │SD_GPT_ROOT_ALPHA SD_GPT_ROOT_ARC │ root partitions │ / │ The first │
77 │SD_GPT_ROOT_ARM SD_GPT_ROOT_ARM64 │ for other │ │ partition with │
78 │SD_GPT_ROOT_IA64 │ architectures │ │ the type UUID │
79 │SD_GPT_ROOT_LOONGARCH64 │ │ │ matching the │
80 │SD_GPT_ROOT_MIPS SD_GPT_ROOT_MIPS64 │ │ │ architecture, │
81 │SD_GPT_ROOT_MIPS_LE │ │ │ located on the │
82 │SD_GPT_ROOT_MIPS64_LE │ │ │ same disk as the │
83 │SD_GPT_ROOT_PARISC SD_GPT_ROOT_PPC │ │ │ ESP, is used as │
84 │SD_GPT_ROOT_PPC64 │ │ │ the root file │
85 │SD_GPT_ROOT_PPC64_LE │ │ │ system /. For │
86 │SD_GPT_ROOT_RISCV32 │ │ │ the full list │
87 │SD_GPT_ROOT_RISCV64 SD_GPT_ROOT_S390 │ │ │ and constant │
88 │SD_GPT_ROOT_S390X SD_GPT_ROOT_TILEGX │ │ │ values, see │
89 │SD_GPT_ROOT_X86 SD_GPT_ROOT_X86_64 │ │ │ Discoverable │
90 │SD_GPT_USR_ALPHA SD_GPT_USR_ARC │ │ │ Partitions │
91 │SD_GPT_USR_ARM SD_GPT_USR_IA64 │ │ │ Specification[2]. │
92 │SD_GPT_USR_LOONGARCH64 │ │ │ │
93 │SD_GPT_USR_MIPS_LE │ │ │ │
94 │SD_GPT_USR_MIPS64_LE │ │ │ │
95 │SD_GPT_USR_PARISC SD_GPT_USR_PPC │ │ │ │
96 │SD_GPT_USR_PPC64 SD_GPT_USR_PPC64_LE │ │ │ │
97 │SD_GPT_USR_RISCV32 │ │ │ │
98 │SD_GPT_USR_RISCV64 SD_GPT_USR_S390 │ │ │ │
99 │SD_GPT_USR_S390X SD_GPT_USR_TILEGX │ │ │ │
100 │SD_GPT_USR_X86 │ │ │ │
101 ├─────────────────────────────────────┼──────────────────┼─────────────────┼───────────────────┤
102 │SD_GPT_HOME │ Home Partition │ /home/ │ The first │
103 │933ac7e1-2eb4-4f13-b844-0e14e2aef915 │ │ │ partition with │
104 │ │ │ │ this type UUID on │
105 │ │ │ │ the same disk as │
106 │ │ │ │ the ESP is │
107 │ │ │ │ mounted to │
108 │ │ │ │ /home/. │
109 ├─────────────────────────────────────┼──────────────────┼─────────────────┼───────────────────┤
110 │SD_GPT_SRV │ Server Data │ /srv/ │ The first │
111 │3b8f8425-20e0-4f3b-907f-1a25a76f98e8 │ Partition │ │ partition with │
112 │ │ │ │ this type UUID on │
113 │ │ │ │ the same disk as │
114 │ │ │ │ the ESP is │
115 │ │ │ │ mounted to /srv/. │
116 ├─────────────────────────────────────┼──────────────────┼─────────────────┼───────────────────┤
117 │SD_GPT_VAR │ Variable Data │ /var/ │ The first │
118 │4d21b016-b534-45c2-a9fb-5c16e091fd2d │ Partition │ │ partition with │
119 │ │ │ │ this type UUID on │
120 │ │ │ │ the same disk as │
121 │ │ │ │ the ESP is │
122 │ │ │ │ mounted to /var/ │
123 │ │ │ │ — under the │
124 │ │ │ │ condition its │
125 │ │ │ │ partition UUID │
126 │ │ │ │ matches the first │
127 │ │ │ │ 128 bit of the │
128 │ │ │ │ HMAC-SHA256 of │
129 │ │ │ │ the GPT type uuid │
130 │ │ │ │ of this partition │
131 │ │ │ │ keyed by the │
132 │ │ │ │ machine ID of the │
133 │ │ │ │ installation │
134 │ │ │ │ stored in │
135 │ │ │ │ machine-id(5). │
136 ├─────────────────────────────────────┼──────────────────┼─────────────────┼───────────────────┤
137 │SD_GPT_TMP │ Temporary Data │ /var/tmp/ │ The first │
138 │7ec6f557-3bc5-4aca-b293-16ef5df639d1 │ Partition │ │ partition with │
139 │ │ │ │ this type UUID on │
140 │ │ │ │ the same disk as │
141 │ │ │ │ the ESP is │
142 │ │ │ │ mounted to │
143 │ │ │ │ /var/tmp/. │
144 ├─────────────────────────────────────┼──────────────────┼─────────────────┼───────────────────┤
145 │SD_GPT_SWAP │ Swap │ n/a │ All partitions │
146 │0657fd6d-a4ab-43c4-84e5-0933c84b4f4f │ │ │ with this type │
147 │ │ │ │ UUID on the same │
148 │ │ │ │ disk as the ESP │
149 │ │ │ │ are used as swap. │
150 ├─────────────────────────────────────┼──────────────────┼─────────────────┼───────────────────┤
151 │SD_GPT_ESP │ EFI System │ /efi/ or /boot/ │ The first │
152 │c12a7328-f81f-11d2-ba4b-00a0c93ec93b │ Partition (ESP) │ │ partition with │
153 │ │ │ │ this type UUID │
154 │ │ │ │ located on the │
155 │ │ │ │ same disk as the │
156 │ │ │ │ root partition is │
157 │ │ │ │ mounted to /boot/ │
158 │ │ │ │ or /efi/, see │
159 │ │ │ │ below. │
160 ├─────────────────────────────────────┼──────────────────┼─────────────────┼───────────────────┤
161 │SD_GPT_XBOOTLDR │ Extended Boot │ /boot/ │ The first │
162 │bc13c2ff-59e6-4262-a352-b275fd6f7172 │ Loader Partition │ │ partition with │
163 │ │ │ │ this type UUID │
164 │ │ │ │ located on the │
165 │ │ │ │ same disk as the │
166 │ │ │ │ root partition is │
167 │ │ │ │ mounted to │
168 │ │ │ │ /boot/, see │
169 │ │ │ │ below. │
170 └─────────────────────────────────────┴──────────────────┴─────────────────┴───────────────────┘
171 This generator understands the following attribute flags for
173 partitions:
174 Table 2. Partition Attribute Flags
176 ┌─────────────────────────────────┬───────────────────┬───────────────────┐
177 │Flag │ Applicable to │ Explanation │
178 ├─────────────────────────────────┼───────────────────┼───────────────────┤
179 │SD_GPT_FLAG_READ_ONLY │ /, /home/, /srv/, │ Partition is │
180 │0x1000000000000000 │ /var/, /var/tmp/, │ mounted read-only │
181 │ │ Extended Boot │ │
182 │ │ Loader Partition │ │
183 ├─────────────────────────────────┼───────────────────┼───────────────────┤
184 │SD_GPT_FLAG_NO_AUTO │ /, /home/, /srv/, │ Partition is not │
185 │0x8000000000000000 │ /var/, /var/tmp/, │ mounted │
186 │ │ Extended Boot │ automatically │
187 │ │ Loader Partition │ │
188 ├─────────────────────────────────┼───────────────────┼───────────────────┤
189 │SD_GPT_FLAG_NO_BLOCK_IO_PROTOCOL │ EFI System │ Partition is not │
190 │0x0000000000000002 │ Partition (ESP) │ mounted │
191 │ │ │ automatically │
192 └─────────────────────────────────┴───────────────────┴───────────────────┘
193 The /home/, /srv/, /var/ and /var/tmp/ partitions may be encrypted in
195 LUKS format. In this case, a device mapper device is set up under the
196 names /dev/mapper/home, /dev/mapper/srv, /dev/mapper/var and
197 /dev/mapper/tmp. Note that this might create conflicts if the same
198 partition is listed in /etc/crypttab with a different device mapper
199 device name.
200 When systemd is running in the initrd the / partition may be encrypted
202 in LUKS format as well. In this case, a device mapper device is set up
203 under the name /dev/mapper/root, and a sysroot.mount is set up that
204 mounts the device under /sysroot. For more information, see bootup(7).
205 The root partition can be specified by symlinking
207 /run/systemd/volatile-root to /dev/block/$major:$minor. This is
208 especially useful if the root mount has been replaced by some form of
209 volatile file system (overlayfs).
210 Mount and automount units for the EFI System Partition (ESP) are
212 generated on EFI systems. The ESP is mounted to /boot/ (except if an
213 Extended Boot Loader partition exists, see below), unless a mount point
214 directory /efi/ exists, in which case it is mounted there. Since this
215 generator creates an automount unit, the mount will only be activated
216 on-demand, when accessed. On systems where /boot/ (or /efi/ if it
217 exists) is an explicitly configured mount (for example, listed in
218 fstab(5)) or where the /boot/ (or /efi/) mount point is non-empty, no
219 mount units are generated.
220 If the disk contains an Extended Boot Loader partition, as defined in
222 the Boot Loader Specification[4], it is made available at /boot/ (by
223 means of an automount point, similar to the ESP, see above). If both an
224 EFI System Partition and an Extended Boot Loader partition exist the
225 latter is preferably mounted to /boot/. Make sure to create both /efi/
226 and /boot/ to ensure both partitions are mounted.
227 When using this generator in conjunction with btrfs file systems, make
229 sure to set the correct default subvolumes on them, using btrfs
230 subvolume set-default.
231 If the system was booted via systemd-stub(7) and the stub reported to
233 userspace that the kernel image was measured to a TPM2 PCR, then any
234 discovered root and /var/ volume identifiers (and volume encryption key
235 in case it is encrypted) will be automatically measured into PCR 15 on
236 activation, via systemd-pcrfs@.service(8).
237 systemd-gpt-auto-generator implements systemd.generator(7).
239
241 systemd-gpt-auto-generator understands the following kernel command
242 line parameters:
243 systemd.gpt_auto, rd.systemd.gpt_auto
245 Those options take an optional boolean argument, and default to
246 yes. The generator is enabled by default, and a false value may be
247 used to disable it (e.g. "systemd.gpt_auto=0").
248 root=, rootfstype=, rootflags=
250 When root= is used with the special value "gpt-auto" (or if the
251 parameter is not used at all), automatic discovery of the root
252 partition based on the GPT partition type is enabled. Any other
253 value disables this logic.
254 The rootfstype= and rootflags= are used to select the file system
256 type and options when the root file system is automatically
257 discovered.
258 rw, ro
260 Mount the root partition read-write or read-only initially.
261 Note that unlike most kernel command line options these settings do
263 not override configuration in the file system, and the file system
264 may be remounted later. See systemd-remount-fs.service(8).
265
267 systemd(1), systemd.mount(5), systemd.swap(5), systemd-fstab-
268 generator(8), systemd-cryptsetup@.service(8), systemd-
269 pcrfs@.service(8), machine-id(5), cryptsetup(8), fstab(5), btrfs(8)
270
272 1. UEFI Specification
273 https://uefi.org/specifications
274 2. Discoverable Partitions Specification
276 https://uapi-group.org/specifications/specs/discoverable_partitions_specification
277 3. Boot Loader Interface
279 https://systemd.io/BOOT_LOADER_INTERFACE
280 4. Boot Loader Specification
282 https://uapi-group.org/specifications/specs/boot_loader_specification
283systemd 253 SYSTEMD-GPT-AUTO-GENERATOR(8)