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 by the initial RAM disk (initrd) while
fstab= is honored by both the main system
and the initrd.
root=¶Takes the root filesystem to mount in the
initrd. root= is honored by the
initrd.
rootfstype=¶Takes the root filesystem type that will be
passed to the mount command. rootfstype= is
honored by the initrd.
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).
mount.usr=¶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.
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.
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.
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 as part of the initial RAM disk ("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".
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.