systemd.preset — Service enablement presets
Preset files may be used to encode policy which units shall be enabled by default and which ones shall be disabled. They are read by systemctl preset (for more information see systemctl(1)) which uses this information to enable or disable a unit according to preset policy. systemctl preset is used by the post install scriptlets of RPM packages (or other OS package formats), to enable/disable specific units by default on package installation, enforcing distribution, spin or administrator preset policy. This allows choosing a certain set of units to be enabled/disabled even before installing the actual package.
For more information on the preset logic please have a look at the Presets document.
It is not recommended to ship preset files within the respective software packages implementing the units, but rather centralize them in a distribution or spin default policy, which can be amended by administrator policy.
If no preset files exist, systemctl
preset will enable all units that are
installed by default. If this is not desired and all
units shall rather be disabled, it is necessary to ship
a preset file with a single, catchall
disable *" line. (See example 1,
The preset files contain a list of
directives consisting of either the word
disable" followed by a space and a
unit name (possibly with shell style wildcards),
separated by newlines. Empty lines and lines whose
first non-whitespace character is # or ; are
Two different directives are understood:
enable" may be used to enable units
by default, "
disable" to disable
units by default.
If multiple lines apply to a unit name, the first matching one takes precedence over all others.
Each preset file shall be named in the style of
/etc/ override files
with the same name in
/run/. Files in
/run/ override files with the
same name in
should install their preset files in
/usr/lib/. Files in
/etc/ are reserved for the local
administrator, who may use this logic to override the
preset files installed by vendor packages. All preset
files are sorted by their filename in lexicographic
order, regardless in which of the directories they
reside. If multiple files specify the same unit name,
the entry in the file with the lexicographically earliest
name will be applied. It is recommended to prefix all
filenames with a two-digit number and a dash, to simplify
the ordering of the files.
If the administrator wants to disable a preset
file supplied by the vendor, the recommended way is to
place a symlink to
bearing the same filename.
This disables all units. Due to the filename
99-", it will be read last and
hence can easily be overridden by spin or
administrator preset policy or suchlike.
Example 2. A GNOME spin example
enable gdm.service enable colord.service enable accounts-daemon.service enable avahi-daemon.*
This enables the three mentioned units, plus all
avahi-daemon regardless of which
unit type. A file like this could be useful for
inclusion in a GNOME spin of a distribution. It will
ensure that the units necessary for GNOME are properly
enabled as they are installed. It leaves all other
units untouched, and subject to other (later) preset
files, for example like the one from the first example
Example 3. Administrator policy
enable httpd.service enable sshd.service enable postfix.service disable *
This enables three specific services and
disables all others. This is useful for administrators
to specifically select the units to enable, and
disable all others. Due to the filename prefix
00-" it will be read early and hence
overrides all other preset policy files.