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 which uses this information to enable or disable a unit.
       Depending on that policy, systemctl preset is identical to systemctl enable or systemctl disable.
       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, see systemctl(1).

       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, see below.

       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. Multiple instance names
       for unit templates may be specified as a space separated list at the end of the line instead of the
       customary position between "@" and the unit suffix.

       Presets must refer to the "real" unit file, and not to any aliases. See systemd.unit(5) for a description
       of unit aliasing.

       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>-<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.

EXAMPLES

       Example 1. Default to off

           # /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.

       Example 2. Enable multiple template instances

           # /lib/systemd/system-preset/80-dirsrv.preset

           enable dirsrv@.service foo bar baz

       This enables all three of dirsrv@foo.service, dirsrv@bar.service and dirsrv@baz.service.

       Example 3. A GNOME spin

           # /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 4. 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 override all other preset policy files.

MOTIVATION FOR THE PRESET LOGIC

       Different distributions have different policies on which services shall be enabled by default when the
       package they are shipped in is installed. On Fedora all services stay off by default, so that installing
       a package will not cause a service to be enabled (with some exceptions). On Debian all services are
       immediately enabled by default, so that installing a package will cause its services to be enabled
       right-away.

       Even within a single distribution, different spins (flavours, remixes, whatever you might want to call
       them) of a distribution also have different policies on what services to enable, and what services to
       leave off. For example, Fedora Workstation will enable gdm as display manager by default, while the
       Fedora KDE spin will enable sddm instead.

       Different sites might also have different policies what to turn on by default and what to turn off. For
       example, one administrator would prefer to enforce the policy of "sshd should be always on, but
       everything else off", while another one might say "snmpd always on, and for everything else use the
       distribution policy defaults".

       Traditionally, policy about which services shall be enabled were implemented in each package
       individually. This made it cumbersome to implement different policies per spin or per site, or to create
       software packages that do the right thing on more than one distribution. The enablement mechanism was
       also encoding the enablement policy.

       The preset mechanism allows clean separation of the enablement mechanism (inside the package scriptlets,
       by invoking systemctl preset) and enablement policy (centralized in the preset files), and lifts the
       configuration out of individual packages. Preset files may be written for specific distributions, for
       specific spins or for specific sites, in order to enforce different policies as needed. It is recommended
       to apply the policy encoded in preset files in package installation scriptlets.

SEE ALSO

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

       daemon(7) has a discussion of packaging scriptlets.

       Fedora page introducing the use of presets: Features/PackagePresets[1].

NOTES

        1. Features/PackagePresets
           https://fedoraproject.org/wiki/Features/PackagePresets

systemd 249                                                                                    SYSTEMD.PRESET(5)