NAME
systemd-fstab-generator - Unit generator for /etc/fstabSYNOPSIS
/lib/systemd/system-generators/systemd-fstab-generatorDESCRIPTION
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).KERNEL COMMAND LINE
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" and "tmpfs".
Use "gpt-auto" to explicitly request automatic root file system
discovery via systemd-gpt-auto-generator(8).
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.
SEE ALSO
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
- 1.
- Known Environment Variables
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