Provided by: systemd_229-4ubuntu21.31_amd64 bug


       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[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

       Each preset file shall be named in the style of <priority>-<policy-name>.preset. Files in
       /etc/ override files with the same name in /usr/lib/ and /run/. Files in /run/ override
       files with the same name in /lib/. Packages should install their preset files in /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 1. Default off example /lib/systemd/system-preset/99-default.preset:

           disable *

       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.


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


        1. Presets