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|
<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2010 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<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>Unit configuration</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 page lists the common configuration
options of all the unit types. These options need to
be configured in the [Unit] or [Install]
sections of the unit files.</para>
<para>In addition to the generic [Unit] and [Install]
sections described here, each unit may 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. For details
see
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</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>Along with a unit file
<filename>foo.service</filename> the directory
<filename>foo.service.wants/</filename> may exist. All
unit files 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 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 unit file
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). A similar
functionality exists for <varname>Requires=</varname>
type dependencies as well, the directory suffix is
<filename>.requires/</filename> in this case.</para>
<para>Along with a unit file
<filename>foo.service</filename> a directory
<filename>foo.service.d/</filename> may exist. All
files with the suffix <filename>.conf</filename> from
this directory will be parsed after the file itself is
parsed. This is useful to alter or add configuration
settings to a unit, without having to modify their
unit files. Make sure that the file that is included
has the appropriate section headers before any
directive.</para>
<para>If a line starts with <option>.include</option>
followed by a file name, the specified file will be
parsed at this point. Make sure that the file that is
included has the appropriate section headers before
any directives.</para>
<para>Note that while systemd offers a flexible
dependency system between units it is recommended to
use this functionality only sparingly and instead rely
on techniques such as bus-based or socket-based
activation which make dependencies implicit, resulting
in a both 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.</para>
<para>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. See below for details.</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 class='unit-directives'>
<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>Documentation=</varname></term>
<listitem><para>A space separated list
of URIs referencing documentation for
this unit or its
configuration. Accepted are only URIs
of the types
<literal>http://</literal>,
<literal>https://</literal>,
<literal>file:</literal>,
<literal>info:</literal>,
<literal>man:</literal>. For more
information about the syntax of these
URIs see
<citerefentry><refentrytitle>uri</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The
URIs should be listed in order of
relevance, starting with the most
relevant. It is a good idea to first
reference documentation that explains
what the unit's purpose is, followed
by how it is configured, followed by
any other related documentation. This
option may be specified more than once
in which case the specified list of
URIs is merged. If the empty string is
assigned to this option the list is
reset and all prior assignments will
have no effect.</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>
<para>Note that dependencies of this
type may also be configured outside of
the unit configuration file by
adding a symlink to a
<filename>.requires/</filename> directory
accompanying the unit file. For
details see above.</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>
and <varname>RequiresOverridable=</varname>, respectively. 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.</para>
<para>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>BindsTo=</varname></term>
<listitem><para>Configures requirement
dependencies, very similar in style to
<varname>Requires=</varname>, however
in addition to this behavior 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>PartOf=</varname></term>
<listitem><para>Configures dependencies
similar to <varname>Requires=</varname>,
but limited to stopping and restarting
of units. When systemd stops or restarts
the units listed here, the action is
propagated to this unit.
Note that this is a one way dependency -
changes to this unit do not affect the
listed units.
</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
or 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>PropagatesReloadTo=</varname></term>
<term><varname>ReloadPropagatedFrom=</varname></term>
<listitem><para>Lists one or more
units where reload requests on the
unit will be propagated to/on the
other unit will be propagated
from. Issuing a reload request on a
unit will automatically also enqueue a
reload request on all units that the
reload request shall be propagated to
via these two
settings.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RequiresMountsFor=</varname></term>
<listitem><para>Takes a space
separated list of absolute paths. Automatically
adds dependencies of type
<varname>Requires=</varname> and
<varname>After=</varname> for all
mount units required to access the
specified path.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>OnFailureIsolate=</varname></term>
<listitem><para>Takes a boolean
argument. If <option>true</option> the
unit listed in
<varname>OnFailure=</varname> will be
enqueued in isolation mode, i.e. all
units that are not its dependency will
be stopped. If this is set only a
single unit may be listed in
<varname>OnFailure=</varname>. Defaults
to
<option>false</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IgnoreOnIsolate=</varname></term>
<listitem><para>Takes a boolean
argument. If <option>true</option>
this unit will not be stopped when
isolating another unit. Defaults to
<option>false</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IgnoreOnSnapshot=</varname></term>
<listitem><para>Takes a boolean
argument. If <option>true</option>
this unit will not be included in
snapshots. Defaults to
<option>true</option> for device and
snapshot units, <option>false</option>
for the others.</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
or deactivated indirectly. In
this case explicit start-up
or termination requested by the
user is denied, however if it is
started or stopped as a
dependency of another unit, start-up
or 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>ConditionPathExistsGlob=</varname></term>
<term><varname>ConditionPathIsDirectory=</varname></term>
<term><varname>ConditionPathIsSymbolicLink=</varname></term>
<term><varname>ConditionPathIsMountPoint=</varname></term>
<term><varname>ConditionPathIsReadWrite=</varname></term>
<term><varname>ConditionDirectoryNotEmpty=</varname></term>
<term><varname>ConditionFileNotEmpty=</varname></term>
<term><varname>ConditionFileIsExecutable=</varname></term>
<term><varname>ConditionKernelCommandLine=</varname></term>
<term><varname>ConditionVirtualization=</varname></term>
<term><varname>ConditionSecurity=</varname></term>
<term><varname>ConditionCapability=</varname></term>
<term><varname>ConditionHost=</varname></term>
<term><varname>ConditionACPower=</varname></term>
<term><varname>ConditionNull=</varname></term>
<listitem><para>Before starting a unit
verify that the specified condition is
true. If it is not true the starting
of the unit will be skipped, however
all ordering dependencies of it are
still respected. A failing condition
will not result in the unit being
moved into a failure state. The
condition is checked at the time the
queued start job is to be
executed.</para>
<para>With
<varname>ConditionPathExists=</varname>
a file existence condition is
checked before a unit is started. If
the specified absolute path name does
not exist the condition will
fail. If the absolute path name passed
to
<varname>ConditionPathExists=</varname>
is prefixed with an exclamation mark
('!'), the test is negated, and the unit
is only started if the path does not
exist.</para>
<para><varname>ConditionPathExistsGlob=</varname>
is similar to
<varname>ConditionPathExists=</varname>,
but checks for the existence of at
least one file or directory matching
the specified globbing pattern.</para>
<para><varname>ConditionPathIsDirectory=</varname>
is similar to
<varname>ConditionPathExists=</varname>
but verifies whether a certain path
exists and is a
directory.</para>
<para><varname>ConditionPathIsSymbolicLink=</varname>
is similar to
<varname>ConditionPathExists=</varname>
but verifies whether a certain path
exists and is a symbolic
link.</para>
<para><varname>ConditionPathIsMountPoint=</varname>
is similar to
<varname>ConditionPathExists=</varname>
but verifies whether a certain path
exists and is a mount
point.</para>
<para><varname>ConditionPathIsReadWrite=</varname>
is similar to
<varname>ConditionPathExists=</varname>
but verifies whether the underlying
file system is readable and writable
(i.e. not mounted
read-only).</para>
<para><varname>ConditionDirectoryNotEmpty=</varname>
is similar to
<varname>ConditionPathExists=</varname>
but verifies whether a certain path
exists and is a non-empty
directory.</para>
<para><varname>ConditionFileNotEmpty=</varname>
is similar to
<varname>ConditionPathExists=</varname>
but verifies whether a certain path
exists and refers to a regular file
with a non-zero size.</para>
<para><varname>ConditionFileIsExecutable=</varname>
is similar to
<varname>ConditionPathExists=</varname>
but verifies whether a certain path
exists, is a regular file and marked
executable.</para>
<para>Similar,
<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, separated
'='). 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.</para>
<para><varname>ConditionVirtualization=</varname>
may be used to check whether the
system is executed in a virtualized
environment and optionally test
whether it is a specific
implementation. Takes either boolean
value to check if being executed in
any virtualized environment, or one of
<varname>vm</varname> and
<varname>container</varname> to test
against a generic type of
virtualization solution, or one of
<varname>qemu</varname>,
<varname>kvm</varname>,
<varname>vmware</varname>,
<varname>microsoft</varname>,
<varname>oracle</varname>,
<varname>xen</varname>,
<varname>bochs</varname>,
<varname>chroot</varname>,
<varname>openvz</varname>,
<varname>lxc</varname>,
<varname>lxc-libvirt</varname>,
<varname>systemd-nspawn</varname> to
test against a specific
implementation. If multiple
virtualization technologies are nested
only the innermost is considered. The
test may be negated by prepending an
exclamation mark.</para>
<para><varname>ConditionSecurity=</varname>
may be used to check whether the given
security module is enabled on the
system. Currently the only recognized
value is <varname>selinux</varname>.
The test may be negated by prepending
an exclamation
mark.</para>
<para><varname>ConditionCapability=</varname>
may be used to check whether the given
capability exists in the capability
bounding set of the service manager
(i.e. this does not check whether
capability is actually available in
the permitted or effective sets, see
<citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details). Pass a capability name
such as <literal>CAP_MKNOD</literal>,
possibly prefixed with an exclamation
mark to negate the check.</para>
<para><varname>ConditionHost=</varname>
may be used to match against the
host name or machine ID of the
host. This either takes a host name
string (optionally with shell style
globs) which is tested against the
locally set host name as returned by
<citerefentry><refentrytitle>gethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
or a machine ID formatted as string
(see
<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
The test may be negated by prepending
an exclamation mark.</para>
<para><varname>ConditionACPower=</varname>
may be used to check whether the
system has AC power, or is exclusively
battery powered at the time of
activation of the unit. This takes a
boolean argument. If set to
<varname>true</varname> the condition
will hold only if at least one AC
connector of the system is connected
to a power source, or if no AC
connectors are known. Conversely, if
set to <varname>false</varname> the
condition will hold only if there is
at least one AC connector known and
all AC connectors are disconnected
from a power source.</para>
<para>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.</para>
<para>If multiple conditions are
specified the unit will be executed if
all of them apply (i.e. a logical AND
is applied). Condition checks can be
prefixed with a pipe symbol (|) in
which case a condition becomes a
triggering condition. If at least one
triggering condition is defined for a
unit then the unit will be executed if
at least one of the triggering
conditions apply and all of the
non-triggering conditions. If you
prefix an argument with the pipe
symbol and an exclamation mark the
pipe symbol must be passed first, the
exclamation second. Except for
<varname>ConditionPathIsSymbolicLink=</varname>,
all path checks follow symlinks. If
any of these options is assigned the
empty string the list of conditions is
reset completely, all previous
condition settings (of any kind) will
have no effect.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SourcePath=</varname></term>
<listitem><para>A path to a
configuration file this unit has been
generated from. This is primarily
useful for implementation of generator
tools that convert configuration from
an external configuration file format
into native unit files. Thus
functionality should not be used in
normal units.</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 class='unit-directives'>
<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.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>WantedBy=</varname></term>
<term><varname>RequiredBy=</varname></term>
<listitem><para>Installs a symlink in
the <filename>.wants/</filename>
or <filename>.requires/</filename>
subdirectory for a unit, respectively. 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>Specifiers</title>
<para>Many settings resolve specifiers which may be
used to write generic unit files referring to runtime
or unit parameters that are replaced when the unit
files are loaded. The following specifiers are
understood:</para>
<table>
<title>Specifiers available in unit files</title>
<tgroup cols='3' align='left' colsep='1' rowsep='1'>
<colspec colname="spec" />
<colspec colname="mean" />
<colspec colname="detail" />
<thead>
<row>
<entry>Specifier</entry>
<entry>Meaning</entry>
<entry>Details</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>%n</literal></entry>
<entry>Full unit name</entry>
<entry></entry>
</row>
<row>
<entry><literal>%N</literal></entry>
<entry>Unescaped full unit name</entry>
<entry></entry>
</row>
<row>
<entry><literal>%p</literal></entry>
<entry>Prefix name</entry>
<entry>For instantiated units this refers to the string before the @. For non-instantiated units this refers to to the name of the unit with the type suffix removed.</entry>
</row>
<row>
<entry><literal>%P</literal></entry>
<entry>Unescaped prefix name</entry>
<entry></entry>
</row>
<row>
<entry><literal>%i</literal></entry>
<entry>Instance name</entry>
<entry>For instantiated units: this is the string between the @ character and the suffix.</entry>
</row>
<row>
<entry><literal>%I</literal></entry>
<entry>Unescaped instance name</entry>
<entry></entry>
</row>
<row>
<entry><literal>%f</literal></entry>
<entry>Unescaped file name</entry>
<entry>This is either the unescaped instance name (if applicable) with / prepended (if applicable), or the prefix name similarly prepended with /.</entry>
</row>
<row>
<entry><literal>%c</literal></entry>
<entry>Control group path of the unit</entry>
<entry></entry>
</row>
<row>
<entry><literal>%r</literal></entry>
<entry>Root control group path of systemd</entry>
<entry></entry>
</row>
<row>
<entry><literal>%R</literal></entry>
<entry>Parent directory of the root control group path of systemd</entry>
<entry></entry>
</row>
<row>
<entry><literal>%t</literal></entry>
<entry>Runtime socket dir</entry>
<entry>This is either <filename>/run</filename> (for the system manager) or <literal>$XDG_RUNTIME_DIR</literal> (for user managers).</entry>
</row>
<row>
<entry><literal>%u</literal></entry>
<entry>User name</entry>
<entry>This is the name of the configured user of the unit, or (if none is set) the user running the systemd instance.</entry>
</row>
<row>
<entry><literal>%U</literal></entry>
<entry>User UID</entry>
<entry>This is the UID of the configured user of the unit, or (if none is set) the user running the systemd instance.</entry>
</row>
<row>
<entry><literal>%h</literal></entry>
<entry>User home directory</entry>
<entry>This is the home directory of the configured user of the unit, or (if none is set) the user running the systemd instance.</entry>
</row>
<row>
<entry><literal>%s</literal></entry>
<entry>User shell</entry>
<entry>This is the shell of the configured user of the unit, or (if none is set) the user running the systemd instance.</entry>
</row>
<row>
<entry><literal>%m</literal></entry>
<entry>Machine ID</entry>
<entry>The machine ID of the running system, formatted as string. See <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more information.</entry>
</row>
<row>
<entry><literal>%b</literal></entry>
<entry>Boot ID</entry>
<entry>The boot ID of the running system, formatted as string. See <citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> for more information.</entry>
</row>
<row>
<entry><literal>%H</literal></entry>
<entry>Host name</entry>
<entry>The host name of the running system.</entry>
</row>
</tbody>
</tgroup>
</table>
</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>,
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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