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 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", "fstab", and "tmpfs".
49 Use "gpt-auto" to explicitly request automatic root file system
51 discovery via systemd-gpt-auto-generator(8).
52 Use "fstab" to explicitly request automatic root file system
54 discovery via the initrd /etc/fstab rather than via kernel command
55 line.
56 Use "tmpfs" in order to mount a tmpfs(5) file system as root file
58 system of the OS. This is useful in combination with mount.usr=
59 (see below) in order to combine a volatile root file system with a
60 separate, immutable /usr/ file system. Also see systemd.volatile=
61 below.
62 rootfstype=
64 Takes the root filesystem type that will be passed to the mount
65 command. rootfstype= is honored by the initrd.
66 rootflags=
68 Takes the root filesystem mount options to use. rootflags= is
69 honored by the initrd.
70 Note that unlike most kernel command line options this setting does
72 not override settings made in configuration files (specifically:
73 the mount option string in /etc/fstab). See systemd-remount-
74 fs.service(8).
75 mount.usr=
77 Takes the /usr/ filesystem to be mounted by the initrd. If
78 mount.usrfstype= or mount.usrflags= is set, then mount.usr= will
79 default to the value set in root=.
80 Otherwise, this parameter defaults to the /usr/ entry found in
82 /etc/fstab on the root filesystem.
83 mount.usr= is honored by the initrd.
85 mount.usrfstype=
87 Takes the /usr/ filesystem type that will be passed to the mount
88 command. If mount.usr= or mount.usrflags= is set, then
89 mount.usrfstype= will default to the value set in rootfstype=.
90 Otherwise, this value will be read from the /usr/ entry in
92 /etc/fstab on the root filesystem.
93 mount.usrfstype= is honored by the initrd.
95 mount.usrflags=
97 Takes the /usr/ filesystem mount options to use. If mount.usr= or
98 mount.usrfstype= is set, then mount.usrflags= will default to the
99 value set in rootflags=.
100 Otherwise, this value will be read from the /usr/ entry in
102 /etc/fstab on the root filesystem.
103 mount.usrflags= is honored by the initrd.
105 roothash=, usrhash=
107 These options are primarily read by systemd-veritysetup-
108 generator(8). When set this indicates that the root file system (or
109 /usr/) shall be mounted from Verity volumes with the specified
110 hashes. If these kernel command line options are set the root (or
111 /usr/) file system is thus mounted from a device mapper volume
112 /dev/mapper/root (or /dev/mapper/usr).
113 systemd.volatile=
115 Controls whether the system shall boot up in volatile mode. Takes a
116 boolean argument or the special value state.
117 If false (the default), this generator makes no changes to the
119 mount tree and the system is booted up in normal mode.
120 If true the generator ensures systemd-volatile-root.service(8) is
122 run in the initrd. This service changes the mount table before
123 transitioning to the host system, so that a volatile memory file
124 system ("tmpfs") is used as root directory, with only /usr/ mounted
125 into it from the configured root file system, in read-only mode.
126 This way the system operates in fully stateless mode, with all
127 configuration and state reset at boot and lost at shutdown, as
128 /etc/ and /var/ will be served from the (initially unpopulated)
129 volatile memory file system.
130 If set to state the generator will leave the root directory mount
132 point unaltered, however will mount a "tmpfs" file system to /var/.
133 In this mode the normal system configuration (i.e. the contents of
134 "/etc/") is in effect (and may be modified during system runtime),
135 however the system state (i.e. the contents of "/var/") is reset at
136 boot and lost at shutdown.
137 If this setting is set to "overlay" the root file system is set up
139 as "overlayfs" mount combining the read-only root directory with a
140 writable "tmpfs", so that no modifications are made to disk, but
141 the file system may be modified nonetheless with all changes being
142 lost at reboot.
143 Note that in none of these modes the root directory, /etc/, /var/
145 or any other resources stored in the root file system are
146 physically removed. It's thus safe to boot a system that is
147 normally operated in non-volatile mode temporarily into volatile
148 mode, without losing data.
149 Note that with the exception of "overlay" mode, enabling this
151 setting will only work correctly on operating systems that can boot
152 up with only /usr/ mounted, and are able to automatically populate
153 /etc/, and also /var/ in case of "systemd.volatile=yes".
154 Also see root=tmpfs above, for a method to combine a "tmpfs" file
156 system with a regular /usr/ file system (as configured via
157 mount.usr=). The main distinction between systemd.volatile=yes, and
158 root=tmpfs in combination mount.usr= is that the former operates on
159 top of a regular root file system and temporarily obstructs the
160 files and directories above its /usr/ subdirectory, while the
161 latter does not hide any files, but simply mounts a unpopulated
162 tmpfs as root file system and combines it with a user picked /usr/
163 file system.
164 systemd.swap=
166 Takes a boolean argument or enables the option if specified without
167 an argument. If disabled, causes the generator to ignore any swap
168 devices configured in /etc/fstab. Defaults to enabled.
169 systemd.mount-extra=WHAT:WHERE[:FSTYPE[:OPTIONS]],
171 rd.systemd.mount-extra=WHAT:WHERE[:FSTYPE[:OPTIONS]]
172 Specifies the mount unit. Takes at least two and at most four
173 fields separated with a colon (":"). Each field is handled as the
174 corresponding fstab field. This option can be specified multiple
175 times. rd.systemd.mount-extra= is honored only in the initrd,
176 while systemd.mount-extra= is honored by both the main system and
177 the initrd. In the initrd, the mount point (and also source path if
178 the mount is bind mount) specified in systemd.mount-extra= is
179 prefixed with /sysroot/.
180 Example:
182 systemd.mount-extra=/dev/sda1:/mount-point:ext4:rw,noatime
184 systemd.swap-extra=WHAT[:OPTIONS], rd.systemd.swap-extra=WHAT[:OPTIONS]
187 Specifies the swap unit. Takes the block device to be used as a
188 swap device, and optionally takes mount options followed by a colon
189 (":"). This option can be specified multiple times.
190 rd.systemd.swap-extra= is honored only in the initrd, while
191 systemd.swap-extra= is honored by both the main system and the
192 initrd.
193 Example:
195 systemd.swap-extra=/dev/sda2:x-systemd.makefs
197
200 fstab.extra
201 This credential may contain addition mounts to establish, in the
202 same format as fstab(5), with one mount per line. It is read in
203 addition to /etc/fstab.
204
206 systemd(1), fstab(5), systemd.mount(5), systemd.swap(5), systemd-
207 cryptsetup-generator(8), systemd-gpt-auto-generator(8), kernel-command-
208 line(7), Known Environment Variables[1]
209
211 1. Known Environment Variables
212 https://systemd.io/ENVIRONMENT/
213systemd 254 SYSTEMD-FSTAB-GENERATOR(8)