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NAME | SYNOPSIS | DESCRIPTION | PRESET FILE FORMAT | EXAMPLES | MOTIVATION FOR THE PRESET LOGIC | SEE ALSO | NOTES | COLOPHON |
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SYSTEMD.PRESET(5) systemd.preset SYSTEMD.PRESET(5)
systemd.preset - Service enablement presets
/etc/systemd/system-preset/*.preset
/run/systemd/system-preset/*.preset
/usr/local/lib/systemd/system-preset/*.preset
/usr/lib/systemd/system-preset/*.preset
/etc/systemd/user-preset/*.preset
/run/systemd/user-preset/*.preset
/usr/local/lib/systemd/user-preset/*.preset
/usr/lib/systemd/user-preset/*.preset
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, preset operations 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.)
When the machine is booted for the first time, systemd(1) will
enable/disable all units according to preset policy, similarly to
systemctl preset-all. Also see ConditionFirstBoot= in
systemd.unit(5) and "First Boot Semantics" in machine-id(5).
The preset files contain a list of directives, one per line.
Empty lines and lines whose first non-whitespace character is "#"
or ";" are ignored. Each directive consists of one of the words
"enable", "disable", or "ignore", followed by whitespace and a
unit name. The unit name may contain shell-style wildcards.
For the enable directive for template units, one or more instance
names may be specified as a space-separated list after the unit
name. In this case, those instances will be enabled instead of
the instance specified via DefaultInstance= in the unit.
Presets must refer to the "real" unit file, and not to any
aliases. See systemd.unit(5) for a description of unit aliasing.
Three different directives are understood: "enable" may be used
to enable units by default, "disable" to disable units by
default, and "ignore" to ignore units and leave existing
configuration intact.
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.
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 [email protected] foo bar baz
This enables all three of [email protected], [email protected]
and [email protected].
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.
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.
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].
1. Features/PackagePresets
https://fedoraproject.org/wiki/Features/PackagePresets
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 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) If you discover any rendering
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
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 257~devel SYSTEMD.PRESET(5)
Pages that refer to this page: systemctl(1), systemd(1), systemd-firstboot(1), systemd.unit(5), systemd.directives(7), systemd.index(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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