1SYSTEMD-FSTAB-GENERATOR(8) systemd-fstab-generator SYSTEMD-FSTAB-GENERATOR(8)
2
6 systemd-fstab-generator - Unit generator for /etc/fstab
7
9 /usr/lib/systemd/system-generators/systemd-fstab-generator
10
12 systemd-fstab-generator is a generator that translates /etc/fstab (see
13 fstab(5) for details) into native systemd units early at boot and when
14 configuration of the system manager is reloaded. This will instantiate
15 mount and swap units as necessary.
16 The passno field is treated like a simple boolean, and the ordering
18 information is discarded. However, if the root file system is checked,
19 it is checked before all the other file systems.
20 See systemd.mount(5) and systemd.swap(5) for more information about
22 special /etc/fstab mount options this generator understands.
23 One special topic is handling of symbolic links. Historical init
25 implementations supported symlinks in /etc/fstab. Because mount units
26 will refuse mounts where the target is a symbolic link, this generator
27 will resolve any symlinks as far as possible when processing /etc/fstab
28 in order to enhance backwards compatibility. If a symlink target does
29 not exist at the time that this generator runs, it is assumed that the
30 symlink target is the final target of the mount.
31 systemd-fstab-generator implements systemd.generator(7).
33
35 systemd-fstab-generator understands the following kernel command line
36 parameters:
37 fstab=, rd.fstab=
39 Takes a boolean argument. Defaults to "yes". If "no", causes the
40 generator to ignore any mounts or swap devices configured in
41 /etc/fstab. rd.fstab= is honored only in the initrd, while fstab=
42 is honored by both the main system and the initrd.
43 root=
45 Configures the operating system's root filesystem to mount when
46 running in the initrd. This accepts a device node path (usually
47 /dev/disk/by-uuid/... or /dev/disk/by-label/... or similar), or
48 the special values "gpt-auto" and "tmpfs".
49 Use "gpt-auto" to explicitly request automatic root file system
51 discovery via systemd-gpt-auto-generator(8).
52 Use "tmpfs" in order to mount a tmpfs(5) file system as root file
54 system of the OS. This is useful in combination with mount.usr=
55 (see below) in order to combine a volatile root file system with a
56 separate, immutable /usr/ file system. Also see systemd.volatile=
57 below.
58 rootfstype=
60 Takes the root filesystem type that will be passed to the mount
61 command. rootfstype= is honored by the initrd.
62 rootflags=
64 Takes the root filesystem mount options to use. rootflags= is
65 honored by the initrd.
66 Note that unlike most kernel command line options this setting does
68 not override settings made in configuration files (specifically:
69 the mount option string in /etc/fstab). See systemd-remount-
70 fs.service(8).
71 mount.usr=
73 Takes the /usr/ filesystem to be mounted by the initrd. If
74 mount.usrfstype= or mount.usrflags= is set, then mount.usr= will
75 default to the value set in root=.
76 Otherwise, this parameter defaults to the /usr/ entry found in
78 /etc/fstab on the root filesystem.
79 mount.usr= is honored by the initrd.
81 mount.usrfstype=
83 Takes the /usr/ filesystem type that will be passed to the mount
84 command. If mount.usr= or mount.usrflags= is set, then
85 mount.usrfstype= will default to the value set in rootfstype=.
86 Otherwise, this value will be read from the /usr/ entry in
88 /etc/fstab on the root filesystem.
89 mount.usrfstype= is honored by the initrd.
91 mount.usrflags=
93 Takes the /usr/ filesystem mount options to use. If mount.usr= or
94 mount.usrfstype= is set, then mount.usrflags= will default to the
95 value set in rootflags=.
96 Otherwise, this value will be read from the /usr/ entry in
98 /etc/fstab on the root filesystem.
99 mount.usrflags= is honored by the initrd.
101 roothash=, usrhash=
103 These options are primarily read by systemd-veritysetup-
104 generator(8). When set this indicates that the root file system (or
105 /usr/) shall be mounted from Verity volumes with the specified
106 hashes. If these kernel command line options are set the root (or
107 /usr/) file system is thus mounted from a device mapper volume
108 /dev/mapper/root (or /dev/mapper/usr).
109 systemd.volatile=
111 Controls whether the system shall boot up in volatile mode. Takes a
112 boolean argument or the special value state.
113 If false (the default), this generator makes no changes to the
115 mount tree and the system is booted up in normal mode.
116 If true the generator ensures systemd-volatile-root.service(8) is
118 run in the initrd. This service changes the mount table before
119 transitioning to the host system, so that a volatile memory file
120 system ("tmpfs") is used as root directory, with only /usr/ mounted
121 into it from the configured root file system, in read-only mode.
122 This way the system operates in fully stateless mode, with all
123 configuration and state reset at boot and lost at shutdown, as
124 /etc/ and /var/ will be served from the (initially unpopulated)
125 volatile memory file system.
126 If set to state the generator will leave the root directory mount
128 point unaltered, however will mount a "tmpfs" file system to /var/.
129 In this mode the normal system configuration (i.e. the contents of
130 "/etc/") is in effect (and may be modified during system runtime),
131 however the system state (i.e. the contents of "/var/") is reset at
132 boot and lost at shutdown.
133 If this setting is set to "overlay" the root file system is set up
135 as "overlayfs" mount combining the read-only root directory with a
136 writable "tmpfs", so that no modifications are made to disk, but
137 the file system may be modified nonetheless with all changes being
138 lost at reboot.
139 Note that in none of these modes the root directory, /etc/, /var/
141 or any other resources stored in the root file system are
142 physically removed. It's thus safe to boot a system that is
143 normally operated in non-volatile mode temporarily into volatile
144 mode, without losing data.
145 Note that with the exception of "overlay" mode, enabling this
147 setting will only work correctly on operating systems that can boot
148 up with only /usr/ mounted, and are able to automatically populate
149 /etc/, and also /var/ in case of "systemd.volatile=yes".
150 Also see root=tmpfs above, for a method to combine a "tmpfs" file
152 system with a regular /usr/ file system (as configured via
153 mount.usr=). The main distinction between systemd.volatile=yes, and
154 root=tmpfs in combination mount.usr= is that the former operates on
155 top of a regular root file system and temporarily obstructs the
156 files and directories above its /usr/ subdirectory, while the
157 latter does not hide any files, but simply mounts a unpopulated
158 tmpfs as root file system and combines it with a user picked /usr/
159 file system.
160 systemd.swap=
162 Takes a boolean argument or enables the option if specified without
163 an argument. If disabled, causes the generator to ignore any swap
164 devices configured in /etc/fstab. Defaults to enabled.
165
167 systemd(1), fstab(5), systemd.mount(5), systemd.swap(5), systemd-
168 cryptsetup-generator(8), systemd-gpt-auto-generator(8), kernel-command-
169 line(7), Known Environment Variables[1]
170
172 1. Known Environment Variables
173 https://systemd.io/ENVIRONMENT/
174systemd 253 SYSTEMD-FSTAB-GENERATOR(8)