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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | SYNOPSIS | DESCRIPTION | KERNEL COMMAND LINE | SYSTEM CREDENTIALS | SEE ALSO | NOTES | COLOPHON |
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SYSTEMD-...GENERATOR(8) systemd-fstab-generator SYSTEMD-...GENERATOR(8)
systemd-fstab-generator - Unit generator for /etc/fstab
/usr/lib/systemd/system-generators/systemd-fstab-generator
systemd-fstab-generator is a generator that translates /etc/fstab
(see fstab(5) for details) into native systemd units early at boot
and when configuration of the system manager is reloaded. This
will instantiate mount and swap units as necessary.
The passno field is treated like a simple boolean, and the
ordering information is discarded. However, if the root file
system is checked, it is checked before all the other file
systems.
See systemd.mount(5) and systemd.swap(5) for more information
about special /etc/fstab mount options this generator understands.
One special topic is handling of symbolic links. Historical init
implementations supported symlinks in /etc/fstab. Because mount
units will refuse mounts where the target is a symbolic link, this
generator will resolve any symlinks as far as possible when
processing /etc/fstab in order to enhance backwards compatibility.
If a symlink target does not exist at the time that this generator
runs, it is assumed that the symlink target is the final target of
the mount.
systemd-fstab-generator implements systemd.generator(7).
systemd-fstab-generator understands the following kernel command
line parameters:
fstab=, rd.fstab=
Takes a boolean argument. Defaults to "yes". If "no", causes
the generator to ignore any mounts or swap devices configured
in /etc/fstab. rd.fstab= is honored only in the initrd, while
fstab= is honored by both the main system and the initrd.
Added in version 186.
root=
Configures the operating system's root filesystem to mount
when running in the initrd. This accepts a device node path
(usually /dev/disk/by-uuid/... or /dev/disk/by-label/... or
similar), or the special values "gpt-auto", "gpt-auto-force",
"dissect", "dissect-force", "fstab", "fstab", and "off".
Set to "gpt-auto", "gpt-auto-force", "dissect",
"dissect-force" to explicitly request automatic root file
system discovery, implemented in
systemd-gpt-auto-generator(8).
Use "fstab" to explicitly request automatic root file system
discovery via the initrd /etc/fstab rather than via kernel
command line.
Use "tmpfs" in order to mount a tmpfs(5) file system as root
file system of the OS. This is useful in combination with
mount.usr= (see below) in order to combine a volatile root
file system with a separate, immutable /usr/ file system. Also
see systemd.volatile= below.
Use "bind:..." to bind mount another directory as operating
system root filesystems (added in v258). Expects an absolute
path name referencing an existing directory within the
initrd's file hierarchy to boot into.
Set to "off" to turn off mounting of a root file system.
Note that further root= values may be supported, implemented
in additional packages.
Added in version 217.
rootfstype=
Takes the root filesystem type that will be passed to the
mount command. rootfstype= is honored by the initrd.
Added in version 217.
rootflags=
Takes the root filesystem mount options to use. rootflags= is
honored by the initrd.
Note that unlike most kernel command line options this setting
does not override settings made in configuration files
(specifically: the mount option string in /etc/fstab). See
systemd-remount-fs.service(8).
Added in version 217.
mount.usr=
Takes the /usr/ filesystem to be mounted by the initrd. If
mount.usrfstype= or mount.usrflags= is set, then the mount
configured via mount.usr= will default to the the same value
set in root=.
Set to "dissect" to explicitly request automatic /usr/ file
system discovery, implemented in
systemd-gpt-auto-generator(8).
Set to "off" to turn off mounting of a separate /usr/ file
system.
mount.usr= is honored by the initrd.
Added in version 217.
mount.usrfstype=
Takes the /usr/ filesystem type that will be passed to the
mount command. If mount.usr= or mount.usrflags= is set, then
mount.usrfstype= will default to the value set in rootfstype=.
Otherwise, this value will be read from the /usr/ entry in
/etc/fstab on the root filesystem.
mount.usrfstype= is honored by the initrd.
Added in version 217.
mount.usrflags=
Takes the /usr/ filesystem mount options to use. If mount.usr=
or mount.usrfstype= is set, then mount.usrflags= will default
to the value set in rootflags=.
Otherwise, this value will be read from the /usr/ entry in
/etc/fstab on the root filesystem.
mount.usrflags= is honored by the initrd.
Added in version 217.
roothash=, usrhash=
These options are primarily read by
systemd-veritysetup-generator(8). When set this indicates that
the root file system (or /usr/) shall be mounted from Verity
volumes with the specified hashes. If these kernel command
line options are set the root (or /usr/) file system is thus
mounted from a device mapper volume /dev/mapper/root (or
/dev/mapper/usr).
Added in version 251.
systemd.volatile=
Controls whether the system shall boot up in volatile mode.
Takes a boolean argument or the special value state.
If false (the default), this generator makes no changes to the
mount tree and the system is booted up in normal mode.
If true the generator ensures systemd-volatile-root.service(8)
is run in the initrd. This service changes the mount table
before transitioning to the host system, so that a volatile
memory file system ("tmpfs") is used as root directory, with
only /usr/ mounted into it from the configured root file
system, in read-only mode. This way the system operates in
fully stateless mode, with all configuration and state reset
at boot and lost at shutdown, as /etc/ and /var/ will be
served from the (initially unpopulated) volatile memory file
system.
If set to state the generator will leave the root directory
mount point unaltered, however will mount a "tmpfs" file
system to /var/. In this mode the normal system configuration
(i.e. the contents of "/etc/") is in effect (and may be
modified during system runtime), however the system state
(i.e. the contents of "/var/") is reset at boot and lost at
shutdown.
If this setting is set to "overlay" the root file system is
set up as "overlayfs" mount combining the read-only root
directory with a writable "tmpfs", so that no modifications
are made to disk, but the file system may be modified
nonetheless with all changes being lost at reboot.
Note that in none of these modes the root directory, /etc/,
/var/ or any other resources stored in the root file system
are physically removed. It's thus safe to boot a system that
is normally operated in non-volatile mode temporarily into
volatile mode, without losing data.
Note that with the exception of "overlay" mode, enabling this
setting will only work correctly on operating systems that can
boot up with only /usr/ mounted, and are able to automatically
populate /etc/, and also /var/ in case of
"systemd.volatile=yes".
Also see root=tmpfs above, for a method to combine a "tmpfs"
file system with a regular /usr/ file system (as configured
via mount.usr=). The main distinction between
systemd.volatile=yes, and root=tmpfs in combination mount.usr=
is that the former operates on top of a regular root file
system and temporarily obstructs the files and directories
above its /usr/ subdirectory, while the latter does not hide
any files, but simply mounts a unpopulated tmpfs as root file
system and combines it with a user picked /usr/ file system.
Added in version 233.
systemd.swap=
Takes a boolean argument or enables the option if specified
without an argument. If disabled, causes the generator to
ignore any swap devices configured in /etc/fstab. Defaults to
enabled.
Added in version 246.
systemd.mount-extra=WHAT:WHERE[:FSTYPE[:OPTIONS]],
rd.systemd.mount-extra=WHAT:WHERE[:FSTYPE[:OPTIONS]]
Specifies the mount unit. Takes at least two and at most four
fields separated with a colon (":"). Each field is handled as
the corresponding fstab field. This option can be specified
multiple times. rd.systemd.mount-extra= is honored only in
the initrd, while systemd.mount-extra= is honored by both the
main system and the initrd. In the initrd, the mount point
(and also source path if the mount is bind mount) specified in
systemd.mount-extra= is prefixed with /sysroot/.
Example:
systemd.mount-extra=/dev/sda1:/mount-point:ext4:rw,noatime
Added in version 254.
systemd.swap-extra=WHAT[:OPTIONS],
rd.systemd.swap-extra=WHAT[:OPTIONS]
Specifies the swap unit. Takes the block device to be used as
a swap device, and optionally takes mount options followed by
a colon (":"). This option can be specified multiple times.
rd.systemd.swap-extra= is honored only in the initrd, while
systemd.swap-extra= is honored by both the main system and the
initrd.
Example:
systemd.swap-extra=/dev/sda2:x-systemd.makefs
Added in version 254.
fstab.extra
This credential may contain addition mounts to establish, in
the same format as fstab(5), with one mount per line. It is
read in addition to /etc/fstab.
Added in version 254.
systemd(1), fstab(5), systemd.mount(5), systemd.swap(5),
systemd-cryptsetup-generator(8), systemd-gpt-auto-generator(8),
kernel-command-line(7), Known Environment Variables[1]
1. Known Environment Variables
https://systemd.io/ENVIRONMENT/
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 258~rc2 SYSTEMD-...GENERATOR(8)
Pages that refer to this page: systemd.mount(5), systemd.swap(5), kernel-command-line(7), systemd.directives(7), systemd.generator(7), systemd.index(7), systemd.special(7), systemd.system-credentials(7), systemd-cryptsetup-generator(8), systemd-gpt-auto-generator(8), [email protected](8), systemd-pcrphase.service(8), systemd-remount-fs.service(8), [email protected](8), systemd-veritysetup-generator(8), systemd-volatile-root.service(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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