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 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
https://systemd.io/ENVIRONMENT/
systemd 252 SYSTEMD-FSTAB-GENERATOR(8)
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