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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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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> ,
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<filename > systemd.timer</filename> ,
<filename > systemd.snapshot</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 all the 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]
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sections described here, each unit should have a
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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
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written in various formats. For positive settings the
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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
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unit, the unit is honored. A concatenation of
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multiple values with units is supported, in which case
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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
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ignored. This may be used for commenting. Lines ending
in a backslash are concatenated with the following
line while reading and the backslash is replaced by a
space character. This may be used to wrap long lines.</para>
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<para > If a line starts with <option > .include</option>
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followed by a file name, the specified file will be
read as if its contents were listed in place of the
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<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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<para > Some unit names reflect paths existing in the
file system name space. Example: a device unit
<filename > dev-sda.device</filename> refers to a device
with the device node <filename > /dev/sda</filename> in
the file system namespace. If this applies a special
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way to escape the path name is used, so that the
result is usable as part of a file name. Basically,
given a path, "/" is replaced by "-", and all
unprintable characters and the "-" are replaced by
C-style "\x20" escapes. The root directory "/" is
encoded as single dash, while otherwise the initial
and ending "/" is removed from all paths during
transformation. This escaping is reversible.</para>
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<para > Optionally, units may be instantiated from a
template file at runtime. This allows creation of
multiple units from a single configuration file. If
systemd looks for a unit configuration file it will
first search for the literal unit name in the
filesystem. If that yields no success and the unit
name contains an @ character, systemd will look for a
unit template that shares the same name but with the
instance string (i.e. the part between the @ character
and the suffix) removed. Example: if a service
<filename > getty@tty3.service</filename> is requested
and no file by that name is found, systemd will look
for <filename > getty@.service</filename> and
instantiate a service from that configuration file if
it is found. To refer to the instance string from
within the configuration file you may use the special
<literal > %i</literal> specifier in many of the
configuration options. Other specifiers that may be
used are <literal > %n</literal> , <literal > %N</literal> ,
<literal > %p</literal> , <literal > %P</literal> and
<literal > %I</literal> , for the full unit name, the
unescaped unit name, the prefix name, the unescaped
prefix name and the unescaped instance name,
respectively. The prefix name here refers to the
string before the @, i.e. "getty" in the example
above, where "tty3" is the instance name.</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
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describing the unit. This is intended
for use in UIs to show descriptive
information along with the unit
name.</para> </listitem>
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</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
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unit gets activated, the units listed
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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
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start are ignored if the startup was
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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,
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if the listed unit fails to start up
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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
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has a
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<varname > Conflicts=</varname> setting
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on another unit, starting the former
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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>
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and both units are being started,
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<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
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inverse of the start-up order is
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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
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the unit stops without being requested
by the user, all units
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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
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if a unit stops without a user request,
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units depending on it will not be
terminated. Only if the user requested
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shutdown of a unit, all units depending
on that unit will be shut down as well
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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
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minimize the work to be executed,
systemd will not stop units by default
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unless they are conflicting with other
units, or the user explicitly
requested their shut down. If this
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option is set, a unit will be
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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>
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this unit can only be activated
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indirectly. In this case explicit
start-up requested by the user is
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denied, however if it is started as a
dependency of another unit, start-up
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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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<varlistentry >
<term > <varname > DefaultDependencies=</varname> </term>
<listitem > <para > Takes a boolean
argument. If <option > true</option>
(the default), a few default
dependencies will implicitly be
created for the unit. The actual
dependencies created depend on the
unit type. For example, for service
units, these dependencies ensure that
the service is started only after
basic system initialization is
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completed and is properly terminated on
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system shutdown. See the respective
man pages for details. Generally, only
services involved with early boot or
late shutdown should set this option
to <option > false</option> . It is
highly recommended to leave this
option enabled for the majority of
common units. If set to
<option > false</option> this option
does not disable all implicit
dependencies, just non-essential
ones.</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
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too. <command > WantedBy=foo.service</command>
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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
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option configured,
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<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> ,
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<citerefentry > <refentrytitle > systemd.timer</refentrytitle> <manvolnum > 5</manvolnum> </citerefentry> ,
<citerefentry > <refentrytitle > systemd.snapshot</refentrytitle> <manvolnum > 5</manvolnum> </citerefentry>
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</para>
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</refsect1>
</refentry>
