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.
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",
"fstab", and "tmpfs".
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.
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.
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).
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.
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.
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
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