NAME¶
systemd.preset - Service enablement presets
SYNOPSIS¶
/etc/systemd/system-preset/*.preset
/run/systemd/system-preset/*.preset
/lib/systemd/system-preset/*.preset
/etc/systemd/user-preset/*.preset
/run/systemd/user-preset/*.preset
/usr/lib/systemd/user-preset/*.preset
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[1] 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.)
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 lexicographic order, regardless of which
of the directories they reside in. 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 /dev/null in
/etc/systemd/system-preset/ bearing the same filename.
EXAMPLE¶
Example 1. Default off example
/lib/systemd/system-preset/99-default.preset:
This disables all units. Due to the filename prefix "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
/lib/systemd/system-preset/50-gnome.preset:
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.
Example 3. Administrator policy
/etc/systemd/system-preset/00-lennart.preset:
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.
SEE ALSO¶
systemd(1),
systemctl(1),
systemd-delta(1)
NOTES¶
- 1.
- Presets