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SYSTEMD-FSTAB-GENERATOR(8) systemd-fstab-generator SYSTEMD-FSTAB-GENERATOR(8)
NAME
systemd-fstab-generator - Unit generator for /etc/fstab
SYNOPSIS
/lib/systemd/system-generators/systemd-fstab-generator
DESCRIPTION
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 by the
initial RAM disk (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.
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".
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)
systemd 249 SYSTEMD-FSTAB-GENERATOR(8)
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