systemd-fstab-generator(8) — Linux manual page



NAME         top

       systemd-fstab-generator - Unit generator for /etc/fstab

SYNOPSIS         top


DESCRIPTION         top

       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

       See systemd.mount(5) and systemd.swap(5) for more information
       about special /etc/fstab mount options this generator

       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

           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", "fstab", and

           Use "gpt-auto" to explicitly request automatic root file
           system discovery via 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.

           Takes the root filesystem type that will be passed to the
           mount command.  rootfstype= is honored by the initrd.

           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).

           Takes the /usr/ filesystem to be mounted by the initrd. If
           mount.usrfstype= or mount.usrflags= is set, then mount.usr=
           will default to the value set in root=.

           Otherwise, this parameter defaults to the /usr/ entry found
           in /etc/fstab on the root filesystem.

           mount.usr= is honored by the initrd.

           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

           Otherwise, this value will be read from the /usr/ entry in
           /etc/fstab on the root filesystem.

           mount.usrfstype= is honored by the initrd.

           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.

       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).

           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

           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

           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.

           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

           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.



           Specifies the swap unit. Takes the block device to be used as
           a swap device, and optionally takes mount options followed by
           a colon (":").



SEE ALSO         top

       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]

NOTES         top

        1. Known Environment Variables

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-06-23.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-06-23.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
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       (which is not part of the original manual page), send a mail to

systemd 253                                   SYSTEMD-FSTAB-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-gpt-auto-generator(8)systemd-makefs@.service(8)systemd-remount-fs.service(8)systemd-volatile-root.service(8)