eudev/man/systemd.unit.xml

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<refentry id="systemd.unit">
<refentryinfo>
<title>systemd.unit</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>systemd.unit</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd.unit</refname>
<refpurpose>systemd unit configuration files</refpurpose>
</refnamediv>
<refsynopsisdiv>
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<para><filename>systemd.service</filename>,
<filename>systemd.socket</filename>,
<filename>systemd.device</filename>,
<filename>systemd.mount</filename>,
<filename>systemd.automount</filename>,
<filename>systemd.swap</filename>,
<filename>systemd.target</filename>,
<filename>systemd.path</filename>,
<filename>systemd.timer</filename></para>
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</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>A unit configuration file encodes information
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about a service, a socket, a device, a mount point, an
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automount point, a swap file or partition, a start-up
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target, a file system path or a timer controlled and
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supervised by
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>. The
syntax is inspired by <ulink
url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG
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Desktop Entry Specification</ulink> <filename>.desktop</filename> files, which are in turn
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inspired by Microsoft Windows
<filename>.ini</filename> files.</para>
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<para>This man pages lists the common configuration
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options of the all unit types. These options need to
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be configured in the [Unit] resp. [Install]
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section of the unit files.</para>
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<para>In addition to the generic [Unit] and [Install]
sections described here each unit should have a
type-specific section, e.g. [Service] for a service
unit. See the respective man pages for more
information.</para>
<para>Unit files may contain additional options on top
of those listed here. If systemd encounters an unknown
option it will write a warning log message but
continue loading the unit. If an option is prefixed
with <option>X-</option> it is ignored completely by
systemd. Applications may use this to include
additional information in the unit files.</para>
<para>Boolean arguments used in unit files can be
written in various forms. For positive settings the
strings <option>1</option>, <option>yes</option>,
<option>true</option> and <option>on</option> are
equivalent. For negative settings the strings
<option>0</option>, <option>no</option>,
<option>false</option> and <option>off</option> are
equivalent.</para>
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<para>Time span values encoded in unit files can be
written in various formats. A stand-alone number
specifies a time in seconds. If suffixed with a time
unit, the unit is honored. A concatentation of
multiple value with units is supported, in which case
the values are added up. Example: "50" refers to 50
seconds; "2min 200ms" refers to 2 minutes plus 200
milliseconds, i.e. 120200ms. The following time units
are understood: s, min, h, d, w, ms, us.</para>
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<para>Empty lines and lines starting with # or ; are
ignored. This may be used for commenting.</para>
<para>If a line starts with <option>.include</option>
followed by a file name the specified file will be
read as if its contents where listed in place of the
<option>.include</option> directive.</para>
<para>Along with a unit file
<filename>foo.service</filename> a directory
<filename>foo.service.wants/</filename> may exist. All
units symlinked from such a directory are implicitly
added as dependencies of type
<varname>Wanted=</varname> to the unit. This is useful
to hook units into the start-up of other units,
without having to modify their unit configuration
files. For details about the semantics of
<varname>Wanted=</varname> see below. The preferred
way to create symlinks in the
<filename>.wants/</filename> directory of a service is
with the
<citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
tool which reads information from the [Install]
section of unit files. (See below.)</para>
<para>Note that while systemd offers a flexible
dependency system between units it is recommended to
use this functionality only sparsely and instead rely
on techniques such as bus-based or socket-based
activation which makes dependencies implicit, which
both results in a simpler and more flexible
system.</para>
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</refsect1>
<refsect1>
<title>Options</title>
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<para>Unit file may include a [Unit] section, which
carries generic information about the unit that is not
dependent on the type of unit:</para>
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<variablelist>
<varlistentry>
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<term><varname>Names=</varname></term>
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<listitem><para>Additional names for
this unit. The names listed here must
have the same suffix (i.e. type) as
the unit file name. This option may be
specified more than once, in which
case all listed names are used. Note
that this option is different from the
<varname>Alias=</varname> option from
the [Install] section mentioned
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below. See below for details.</para>
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</listitem>
</varlistentry>
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<varlistentry>
<term><varname>Description=</varname></term>
<listitem><para>A free-form string
describing the unit. This is intended for use
in UIs wanting to show
descriptive information along with the
unit name.</para></listitem>
</varlistentry>
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<varlistentry>
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<term><varname>Requires=</varname></term>
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<listitem><para>Configures requirement
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dependencies on other units. If this
units get activated the units listed
here will be activated as well. If one
of the other units gets deactivated or
its activation fails, this unit will
be deactivated. This option may be
specified more than once, in which
case requirement dependencies for all
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listed names are created. Note that
requirement dependencies do not
influence the order in which services
are started or stopped. This has to be
configured independently with the
<varname>After=</varname> or
<varname>Before=</varname> options. If
a unit
<filename>foo.service</filename>
requires a unit
<filename>bar.service</filename> as
configured with
<varname>Requires=</varname> and no
ordering is configured with
<varname>After=</varname> or
<varname>Before=</varname>, then both
units will be started simultaneously
and without any delay between them if
<filename>foo.service</filename> is
activated. Often it is a better choice
to use <varname>Wants=</varname>
instead of
<varname>Requires=</varname> in order
to achieve a system that is more
robust when dealing with failing
services.</para></listitem>
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</varlistentry>
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<varlistentry>
<term><varname>RequiresOverridable=</varname></term>
<listitem><para>Similar to
<varname>Requires=</varname>.
Dependencies listed in
<varname>RequiresOverridable=</varname>
which cannot be fulfilled or fail to
start are ignored iff the startup was
explicitly requested by the user. If
the start-up was pulled in indirectly
by some dependency or automatic
start-up of units that is not
requested by the user this dependency
must be fulfilled and otherwise the
transaction fails. Hence, this option
may be used to configure dependencies
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that are normally honored unless the
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user explicitly starts up the unit, in
which case whether they failed or not
is irrelevant.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Requisite=</varname></term>
<term><varname>RequisiteOverridable=</varname></term>
<listitem><para>Similar to
<varname>Requires=</varname>
resp. <varname>RequiresOverridable=</varname>. However,
if a unit listed here is not started
already it will not be started and the
transaction fails
immediately.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Wants=</varname></term>
<listitem><para>A weaker version of
<varname>Requires=</varname>. A unit
listed in this option will be started
if the configuring unit is. However,
it the listed unit fails to start up
or cannot be added to the transaction
this has no impact on the validity of
the transaction as a whole. This is
the recommended way to hook start-up
of one unit to the start-up of another
unit. Note that dependencies of this
type may also be configured outside of
the unit configuration file by
adding a symlink to a
<filename>.wants/</filename> directory
accompanying the unit file. For
details see above.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Conflicts=</varname></term>
<listitem><para>Configures negative
requirement dependencies. If a unit
that has a
<varname>Conflicts=</varname> setting
on another unit starting the former
will stop the latter and vice
versa. Note that this setting is
independent of and orthogonal to the
<varname>After=</varname> and
<varname>Before=</varname> ordering
dependencies.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Before=</varname></term>
<term><varname>After=</varname></term>
<listitem><para>Configures ordering
dependencies between units. If a unit
<filename>foo.service</filename>
contains a setting
<option>Before=bar.service</option>
and both units are being started
<filename>bar.service</filename>'s
start-up is delayed until
<filename>foo.service</filename> is
started up. Note that this setting is
independent of and orthogonal to the
requirement dependencies as configured
by <varname>Requires=</varname>. It is
a common pattern to include a unit
name in both the
<varname>After=</varname> and
<varname>Requires=</varname> option in
which case the unit listed will be
started before the unit that is
configured with these options. This
option may be specified more than
once, in which case ordering
dependencies for all listed names are
created. <varname>After=</varname> is
the inverse of
<varname>Before=</varname>, i.e. while
<varname>After=</varname> ensures that
the configured unit is started after
the listed unit finished starting up,
<varname>Before=</varname> ensures the
opposite, i.e. that the configured
unit is fully started up before the
listed unit is started. Note that when
two units with an ordering dependency
between them are shut down, the
inverse of of the start-up order is
applied. i.e. if a unit is configured
with <varname>After=</varname> on
another unit, the former is stopped
before the latter if both are shut
down. If one unit with an ordering
dependency on another unit is shut
down while the latter is started up,
the shut down is ordered before the
start-up regardless whether the
ordering dependency is actually of
type <varname>After=</varname> or
<varname>Before=</varname>. If two
units have no ordering dependencies
between them they are shut down
resp. started up simultaneously, and
no ordering takes
place. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RecursiveStop=</varname></term>
<listitem><para>Takes a boolean
argument. If <option>true</option> and
the unit stops without this being
requested by the user all units
depending on it will be stopped as
well. (e.g. if a service exits or
crashes on its own behalf, units using
it will be stopped) Note that normally
if a unit stops without user request
units depending on it will not be
terminated. Only if the user requested
shutdown of a unit all units depending
on the unit will be shut down as well
and at the same time. Defaults to
<option>false</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>StopWhenUnneeded=</varname></term>
<listitem><para>Takes a boolean
argument. If <option>true</option>
this unit will be stopped when it is
no longer used. Note that in order to
minimize the work to be executed
systemd will by default not stop units
unless they are conflicting with other
units, or the user explicitly
requested their shut down. If this
option is set a unit will be
automatically cleaned up if no other
active unit requires it. Defaults to
<option>false</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>OnlyByDependency=</varname></term>
<listitem><para>Takes a boolean
argument. If <option>true</option>
this unit may only be activated
indirectly. In this case explicit
start-up requested by the user is
denied, however if it is started as
dependency of another unit start-up
will succeed. This is mostly a safety
feature to ensure that the user does
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not accidentally activate units that are
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not intended to be activated
explicitly. This option defaults to
<option>false</option>.</para></listitem>
</varlistentry>
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</variablelist>
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<para>Unit file may include a [Install] section, which
carries installation information for the unit. This
section is not interpreted by
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
during runtime. It is used exclusively by the
<citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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tool during installation of a unit:</para>
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<variablelist>
<varlistentry>
<term><varname>Alias=</varname></term>
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<listitem><para>Additional names, this
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unit shall be installed under. The
names listed here must have the same
suffix (i.e. type) as the unit file
name. This option may be specified
more than once, in which case all
listed names are used. At installation
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time,
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<command>systemd-install</command>
will create symlinks from these names
to the unit file name. Note that this
is different from the
<varname>Names=</varname> option from
the [Unit] section mentioned above:
The names from
<varname>Names=</varname> apply
unconditionally if the unit is
loaded. The names from
<varname>Alias=</varname> apply only
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if the unit has actually been
installed with the
<command>systemd-install</command>
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tool. Also, if systemd searches for a
unit, it will discover symlinked alias
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names as configured with
<varname>Alias=</varname>, but not
names configured with
<varname>Names=</varname> only. It is
a common pattern to list a name in
both options. In this case, a unit
will be active under all names if
installed, but also if not installed
but requested explicitly under its
main name.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>WantedBy=</varname></term>
<listitem><para>Installs a symlink in
the <filename>.wants/</filename>
subdirectory for a unit. This has the
effect that when the listed unit name
is activated the unit listing it is
activated
to. <command>WantedBy=foo.service</command>
in a service
<filename>bar.service</filename> is
mostly equivalent to
<command>Alias=foo.service.wants/bar.service</command>
in the same file.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Also=</varname></term>
<listitem><para>Additional units to
install when this unit is
installed. If the user requests
installation of a unit with this
option configured
<command>systemd-install</command>
will automatically install units
listed in this option as
well.</para></listitem>
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</varlistentry>
</variablelist>
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</refsect1>
<refsect1>
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<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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</para>
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</refsect1>
</refentry>