1SYSTEMD-FSTAB-GENERATOR(8) systemd-fstab-generator SYSTEMD-FSTAB-GENERATOR(8)
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6 systemd-fstab-generator - Unit generator for /etc/fstab
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9 /usr/lib/systemd/system-generators/systemd-fstab-generator
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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).
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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 by the initial RAM disk
42 (initrd) while fstab= is honored by both the main system and the
43 initrd.
44 root=
46 Configures the operating system's root filesystem to mount when
47 running in the initrd. This accepts a device node path (usually
48 /dev/disk/by-uuid/... or /dev/disk/by-label/... or similar), or
49 the special values "gpt-auto" and "tmpfs".
50 Use "gpt-auto" to explicitly request automatic root file system
52 discovery via systemd-gpt-auto-generator(8).
53 Use "tmpfs" in order to mount a tmpfs(5) file system as root file
55 system of the OS. This is useful in combination with mount.usr=
56 (see below) in order to combine a volatile root file system with a
57 separate, immutable /usr/ file system. Also see systemd.volatile=
58 below.
59 rootfstype=
61 Takes the root filesystem type that will be passed to the mount
62 command. rootfstype= is honored by the initrd.
63 rootflags=
65 Takes the root filesystem mount options to use. rootflags= is
66 honored by the initrd.
67 Note that unlike most kernel command line options this setting does
69 not override settings made in configuration files (specifically:
70 the mount option string in /etc/fstab). See systemd-remount-
71 fs.service(8).
72 mount.usr=
74 Takes the /usr/ filesystem to be mounted by the initrd. If
75 mount.usrfstype= or mount.usrflags= is set, then mount.usr= will
76 default to the value set in root=.
77 Otherwise, this parameter defaults to the /usr/ entry found in
79 /etc/fstab on the root filesystem.
80 mount.usr= is honored by the initrd.
82 mount.usrfstype=
84 Takes the /usr/ filesystem type that will be passed to the mount
85 command. If mount.usr= or mount.usrflags= is set, then
86 mount.usrfstype= will default to the value set in rootfstype=.
87 Otherwise, this value will be read from the /usr/ entry in
89 /etc/fstab on the root filesystem.
90 mount.usrfstype= is honored by the initrd.
92 mount.usrflags=
94 Takes the /usr/ filesystem mount options to use. If mount.usr= or
95 mount.usrfstype= is set, then mount.usrflags= will default to the
96 value set in rootflags=.
97 Otherwise, this value will be read from the /usr/ entry in
99 /etc/fstab on the root filesystem.
100 mount.usrflags= is honored by the initrd.
102 roothash=, usrhash=
104 These options are primarily read by systemd-veritysetup-
105 generator(8). When set this indicates that the root file system (or
106 /usr/) shall be mounted from Verity volumes with the specified
107 hashes. If these kernel command line options are set the root (or
108 /usr/) file system is thus mounted from a device mapper volume
109 /dev/mapper/root (or /dev/mapper/usr).
110 systemd.volatile=
112 Controls whether the system shall boot up in volatile mode. Takes a
113 boolean argument or the special value state.
114 If false (the default), this generator makes no changes to the
116 mount tree and the system is booted up in normal mode.
117 If true the generator ensures systemd-volatile-root.service(8) is
119 run as part of the initial RAM disk ("initrd"). This service
120 changes the mount table before transitioning to the host system, so
121 that a volatile memory file system ("tmpfs") is used as root
122 directory, with only /usr/ mounted into it from the configured root
123 file system, in read-only mode. This way the system operates in
124 fully stateless mode, with all configuration and state reset at
125 boot and lost at shutdown, as /etc/ and /var/ will be served from
126 the (initially unpopulated) volatile memory file system.
127 If set to state the generator will leave the root directory mount
129 point unaltered, however will mount a "tmpfs" file system to /var/.
130 In this mode the normal system configuration (i.e. the contents of
131 "/etc/") is in effect (and may be modified during system runtime),
132 however the system state (i.e. the contents of "/var/") is reset at
133 boot and lost at shutdown.
134 If this setting is set to "overlay" the root file system is set up
136 as "overlayfs" mount combining the read-only root directory with a
137 writable "tmpfs", so that no modifications are made to disk, but
138 the file system may be modified nonetheless with all changes being
139 lost at reboot.
140 Note that in none of these modes the root directory, /etc/, /var/
142 or any other resources stored in the root file system are
143 physically removed. It's thus safe to boot a system that is
144 normally operated in non-volatile mode temporarily into volatile
145 mode, without losing data.
146 Note that with the exception of "overlay" mode, enabling this
148 setting will only work correctly on operating systems that can boot
149 up with only /usr/ mounted, and are able to automatically populate
150 /etc/, and also /var/ in case of "systemd.volatile=yes".
151 Also see root=tmpfs above, for a method to combine a "tmpfs" file
153 system with a regular /usr/ file system (as configured via
154 mount.usr=). The main distinction between systemd.volatile=yes, and
155 root=tmpfs in combination mount.usr= is that the former operates on
156 top of a regular root file system and temporarily obstructs the
157 files and directories above its /usr/ subdirectory, while the
158 latter does not hide any files, but simply mounts a unpopulated
159 tmpfs as root file system and combines it with a user picked /usr/
160 file system.
161 systemd.swap
163 Takes a boolean argument or enables the option if specified without
164 an argument. If disabled, causes the generator to ignore any swap
165 devices configured in /etc/fstab. Defaults to enabled.
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168 systemd(1), fstab(5), systemd.mount(5), systemd.swap(5), systemd-
169 cryptsetup-generator(8), systemd-gpt-auto-generator(8), kernel-command-
170 line(7)
171systemd 250 SYSTEMD-FSTAB-GENERATOR(8)