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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>
<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>,
<filename>systemd.snapshot</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>A unit configuration file encodes information
about a service, a socket, a device, a mount point, an
automount point, a swap file or partition, a start-up
target, a file system path or a timer controlled and
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
Desktop Entry Specification</ulink> <filename>.desktop</filename> files, which are in turn
inspired by Microsoft Windows
<filename>.ini</filename> files.</para>
<para>This man pages lists the common configuration
options of all the unit types. These options need to
be configured in the [Unit] resp. [Install]
section of the unit files.</para>
<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 formats. 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>
<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 concatenation of
multiple values 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>
<para>Empty lines and lines starting with # or ; are
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>
<para>If a line starts with <option>.include</option>
followed by a file name, the specified file will be
read as if its contents were 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 <command>enable</command> command of the
<citerefentry><refentrytitle>systemctl</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>
<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
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>
<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>,
<literal>%I</literal> and <literal>%f</literal>, for
the full unit name, the unescaped unit name, the
prefix name, the unescaped prefix name, the unescaped
instance name and the unescaped filename,
respectively. The unescaped filename is either the
unescaped instance name (if set) with / prepended (if
necessary), or the prefix name similarly prepended
with /. The prefix name here refers to the string
before the @, i.e. "getty" in the example above, where
"tty3" is the instance name.</para>
<para>If a unit file is empty (i.e. has the file size
0) or is symlinked to <filename>/dev/null</filename>
its configuration will not be loaded and it appears
with a load state of <literal>masked</literal>, and
cannot be activated. Use this as an effective way to
fully disable a unit, making it impossible to start it
even manually.</para>
<para>The unit file format is covered by the
<ulink
url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
Stability Promise</ulink>.</para>
</refsect1>
<refsect1>
<title>Options</title>
<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>
<variablelist>
<varlistentry>
<term><varname>Names=</varname></term>
<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
below. See below for details.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>Description=</varname></term>
<listitem><para>A free-form string
describing the unit. This is intended
for use in UIs to show descriptive
information along with the unit
name.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Requires=</varname></term>
<listitem><para>Configures requirement
dependencies on other units. If this
unit gets 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
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>
</varlistentry>
<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 if 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
that are normally honored unless the
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,
if 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>BindTo=</varname></term>
<listitem><para>Configures requirement
dependencies, very similar in style to
<varname>Requires=</varname>, however
in addition to this behaviour it also
declares that this unit is stopped
when any of the units listed suddenly
disappears. Units can suddenly,
unexpectedly disappear if a service
terminates on its own choice, a device
is unplugged or a mount point
unmounted without involvement of
systemd.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Conflicts=</varname></term>
<listitem><para>Configures negative
requirement dependencies. If a unit
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>
<para>If a unit A that conflicts with
a unit B is scheduled to be started at
the same time as B, the transaction
will either fail (in case both are
required part of the transaction) or
be modified to be fixed (in case one
or both jobs are not a required part
of the transaction). In the latter
case the job that is not the required
will be removed, or in case both are
not required the unit that conflicts
will be started and the unit that is
conflicted is
stopped.</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 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>OnFailure=</varname></term>
<listitem><para>Lists one or more
units that are activated when this
unit enters the
'<literal>failed</literal>'
state.</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 not stop units by default
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>RefuseManualStart=</varname></term>
<term><varname>RefuseManualStop=</varname></term>
<listitem><para>Takes a boolean
argument. If <option>true</option>
this unit can only be activated
(resp. deactivated) indirectly. In
this case explicit start-up
(resp. termination) requested by the
user is denied, however if it is
started (resp. stopped) as a
dependency of another unit, start-up
(resp. termination) will succeed. This
is mostly a safety feature to ensure
that the user does not accidentally
activate units that are not intended
to be activated explicitly, and not
accidentally deactivate units that are
not intended to be deactivated.
These options default to
<option>false</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>AllowIsolate=</varname></term>
<listitem><para>Takes a boolean
argument. If <option>true</option>
this unit may be used with the
<command>systemctl isolate</command>
command. Otherwise this will be
refused. It probably is a good idea to
leave this disabled except for target
units that shall be used similar to
runlevels in SysV init systems, just
as a precaution to avoid unusable
system states. This option defaults to
<option>false</option>.</para></listitem>
</varlistentry>
<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
completed and is properly terminated on
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>
<varlistentry>
<term><varname>JobTimeoutSec=</varname></term>
<listitem><para>When clients are
waiting for a job of this unit to
complete, time out after the specified
time. If this time limit is reached
the job will be cancelled, the unit
however will not change state or even
enter the '<literal>failed</literal>'
mode. This value defaults to 0 (job
timeouts disabled), except for device
units. NB: this timeout is independent
from any unit-specific timeout (for
example, the timeout set with
<varname>Timeout=</varname> in service
units) as the job timeout has no
effect on the unit itself, only on the
job that might be pending for it. Or
in other words: unit-specific timeouts
are useful to abort unit state
changes, and revert them. The job
timeout set with this option however
is useful to abort only the job
waiting for the unit state to
change.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ConditionPathExists=</varname></term>
<term><varname>ConditionDirectoryNotEmpty=</varname></term>
<term><varname>ConditionKernelCommandLine=</varname></term>
<term><varname>ConditionNull=</varname></term>
<listitem><para>Before starting a unit
verify that the specified condition is
true. With
<varname>ConditionPathExists=</varname>
a file existance condition can be
checked before a unit is started. If
the specified absolute path name does
not exist startup of a unit will not
actually happen, however the unit is
still useful for ordering purposes in
this case. The condition is checked at
the time the queued start job is to be
executed. If the absolute path name
passed to
<varname>ConditionPathExists=</varname>
is prefixed with an exclamation mark
(!), the test is negated, and the unit
only started if the path does not
exist. <varname>ConditionDirectoryNotEmpty=</varname>
is similar to
<varname>ConditionPathExists=</varname>
but verifies whether a cetrain path is
exists and is a non-empty
directory. Similarly
<varname>ConditionKernelCommandLine=</varname>
may be used to check whether a
specific kernel command line option is
set (or if prefixed with the
exclamation mark unset). The argument
must either be a single word, or an
assignment (i.e. two words, seperated
by the equality sign). In the former
case the kernel command line is
searched for the word appearing as is,
or as left hand side of an
assignment. In the latter case the
exact assignment is looked for with
right and left hand side
matching. Finally,
<varname>ConditionNull=</varname> may
be used to add a constant condition
check value to the unit. It takes a
boolean argument. If set to
<varname>false</varname> the condition
will always fail, otherwise
succeed. If multiple conditions are
specified the unit will be executed
iff at least one of them applies
(i.e. a logical OR is
applied).</para></listitem>
</varlistentry>
</variablelist>
<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
<command>enable</command> and
<command>disable</command> commands of the
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
tool during installation of a unit:</para>
<variablelist>
<varlistentry>
<term><varname>Alias=</varname></term>
<listitem><para>Additional names this
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
time,
<command>systemctl enable</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
if the unit has actually been
installed with the
<command>systemctl enable</command>
command. Also, if systemd searches for a
unit, it will discover symlinked alias
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
too. <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>systemctl enable</command>
will automatically install units
listed in this option as
well.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</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>,
<citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>