systemd.preset(5) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | PRESET FILE FORMAT | EXAMPLES | MOTIVATION FOR THE PRESET LOGIC | SEE ALSO | NOTES | COLOPHON

SYSTEMD.PRESET(5)            systemd.preset            SYSTEMD.PRESET(5)

NAME         top

       systemd.preset - Service enablement presets

SYNOPSIS         top

       /etc/systemd/system-preset/*.preset

       /run/systemd/system-preset/*.preset

       /usr/lib/systemd/system-preset/*.preset

       /etc/systemd/user-preset/*.preset

       /run/systemd/user-preset/*.preset

       /usr/lib/systemd/user-preset/*.preset

DESCRIPTION         top

       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         top

       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 /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.

EXAMPLES         top

       Example 1. Default to off

           # /usr/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

           # /usr/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

           # /usr/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         top

       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         top

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

       daemon(8) has a discussion of packaging scriptlets.

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

NOTES         top

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

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2021-04-01.  (At that
       time, the date of the most recent commit that was found in the
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       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
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       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 248                                            SYSTEMD.PRESET(5)

Pages that refer to this page: systemctl(1)systemd.directives(7)systemd.index(7)