Description¶

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, below.)

Preset File Format¶

The preset files contain a list of directives consisting of either the word enable or 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 ignored.

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 <priority>-<program>.conf. Files in /etc/ override files with the same name in /usr/lib/ and /run/. Files in /run/ override files with the same name in /usr/lib/. Packages 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 alphabetical order, regardless in which of the directories they reside, to guarantee that a specific preset file takes precedence over another file with an alphabetically earlier name, if both files contain lines that apply to the same unit names. It is recommended to prefix all file names with two-digit number, to simplify ordering.

If the administrator wants to disable a preset file supplied by the vendor the recommended way is to place a symlink to /dev/null in /etc/systemd/system-preset/ bearing the same file name.

Example¶

disable *

This disables all units. Due to the file name prefix 99- it will be read last and hence can easily be overridden by spin or administrator preset policy or suchlike.

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 above.

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 file name prefix 00- it will be read early and hence overrides all other preset policy files.

See Also¶

systemd(1), systemctl(1), systemd-delta(1)