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<refentry id="systemd.service">
<refentryinfo>
<title>systemd.service</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.service</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd.service</refname>
<refpurpose>Service unit configuration</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename><replaceable>service</replaceable>.service</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>A unit configuration file whose name ends in
<filename>.service</filename> encodes information about a process
controlled and supervised by systemd.</para>
<para>This man page lists the configuration options specific to
this unit type. See
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for the common options of all unit configuration files. The common
configuration items are configured in the generic
<literal>[Unit]</literal> and <literal>[Install]</literal>
sections. The service specific configuration options are
configured in the <literal>[Service]</literal> section.</para>
<para>Additional options are listed in
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which define the execution environment the commands are executed
in, and in
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which define the way the processes of the service are terminated,
and in
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which configure resource control settings for the processes of the
service.</para>
<para>If a service is requested under a certain name but no unit
configuration file is found, systemd looks for a SysV init script
by the same name (with the <filename>.service</filename> suffix
removed) and dynamically creates a service unit from that script.
This is useful for compatibility with SysV. Note that this
compatibility is quite comprehensive but not 100%. For details
about the incompatibilities, see the <ulink
url="https://www.freedesktop.org/wiki/Software/systemd/Incompatibilities">Incompatibilities
with SysV</ulink> document.</para>
</refsect1>
<refsect1>
<title>Implicit Dependencies</title>
<para>The following dependencies are implicitly added:</para>
<itemizedlist>
<listitem><para>Services with <varname>Type=dbus</varname> set automatically
acquire dependencies of type <varname>Requires=</varname> and
<varname>After=</varname> on
<filename>dbus.socket</filename>.</para></listitem>
<listitem><para>Socket activated services are automatically ordered after
their activating <filename>.socket</filename> units via an
automatic <varname>After=</varname> dependency.
Services also pull in all <filename>.socket</filename> units
listed in <varname>Sockets=</varname> via automatic
<varname>Wants=</varname> and <varname>After=</varname> dependencies.</para></listitem>
</itemizedlist>
<para>Additional implicit dependencies may be added as result of
execution and resource control parameters as documented in
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
</refsect1>
<refsect1>
<title>Default Dependencies</title>
<para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para>
<itemizedlist>
<listitem><para>Service units will have dependencies of type <varname>Requires=</varname> and
<varname>After=</varname> on <filename>sysinit.target</filename>, a dependency of type <varname>After=</varname> on
<filename>basic.target</filename> as well as dependencies of type <varname>Conflicts=</varname> and
<varname>Before=</varname> on <filename>shutdown.target</filename>. These ensure that normal service units pull in
basic system initialization, and are terminated cleanly prior to system shutdown. Only services involved with early
boot or late system shutdown should disable this option.</para></listitem>
<listitem><para>Instanced service units (i.e. service units with an <literal>@</literal> in their name) are assigned by
default a per-template slice unit (see
<citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>), named after the
template unit, containing all instances of the specific template. This slice is normally stopped at shutdown,
together with all template instances. If that is not desired, set <varname>DefaultDependencies=no</varname> in the
template unit, and either define your own per-template slice unit file that also sets
<varname>DefaultDependencies=no</varname>, or set <varname>Slice=system.slice</varname> (or another suitable slice)
in the template unit. Also see
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</itemizedlist>
</refsect1>
<refsect1>
<title>Options</title>
<para>Service files must include a <literal>[Service]</literal>
section, which carries information about the service and the
process it supervises. A number of options that may be used in
this section are shared with other unit types. These options are
documented in
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
The options specific to the <literal>[Service]</literal> section
of service units are the following:</para>
<variablelist class='unit-directives'>
<varlistentry>
<term><varname>Type=</varname></term>
<listitem><para>Configures the process start-up type for this
service unit. One of
<option>simple</option>,
<option>forking</option>,
<option>oneshot</option>,
<option>dbus</option>,
<option>notify</option> or
<option>idle</option>.</para>
<para>If set to <option>simple</option> (the default if
neither <varname>Type=</varname> nor
<varname>BusName=</varname>, but <varname>ExecStart=</varname>
are specified), it is expected that the process configured
with <varname>ExecStart=</varname> is the main process of the
service. In this mode, if the process offers functionality to
other processes on the system, its communication channels
should be installed before the daemon is started up (e.g.
sockets set up by systemd, via socket activation), as systemd
will immediately proceed starting follow-up units.</para>
<para>If set to <option>forking</option>, it is expected that
the process configured with <varname>ExecStart=</varname> will
call <function>fork()</function> as part of its start-up. The
parent process is expected to exit when start-up is complete
and all communication channels are set up. The child continues
to run as the main daemon process. This is the behavior of
traditional UNIX daemons. If this setting is used, it is
recommended to also use the <varname>PIDFile=</varname>
option, so that systemd can identify the main process of the
daemon. systemd will proceed with starting follow-up units as
soon as the parent process exits.</para>
<para>Behavior of <option>oneshot</option> is similar to
<option>simple</option>; however, it is expected that the
process has to exit before systemd starts follow-up units.
<varname>RemainAfterExit=</varname> is particularly useful for
this type of service. This is the implied default if neither
<varname>Type=</varname> nor <varname>ExecStart=</varname> are
specified.</para>
<para>Behavior of <option>dbus</option> is similar to
<option>simple</option>; however, it is expected that the
daemon acquires a name on the D-Bus bus, as configured by
<varname>BusName=</varname>. systemd will proceed with
starting follow-up units after the D-Bus bus name has been
acquired. Service units with this option configured implicitly
gain dependencies on the <filename>dbus.socket</filename>
unit. This type is the default if <varname>BusName=</varname>
is specified.</para>
<para>Behavior of <option>notify</option> is similar to
<option>simple</option>; however, it is expected that the
daemon sends a notification message via
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
or an equivalent call when it has finished starting up.
systemd will proceed with starting follow-up units after this
notification message has been sent. If this option is used,
<varname>NotifyAccess=</varname> (see below) should be set to
open access to the notification socket provided by systemd. If
<varname>NotifyAccess=</varname> is missing or set to
<option>none</option>, it will be forcibly set to
<option>main</option>. Note that currently
<varname>Type=</varname><option>notify</option> will not work
if used in combination with
<varname>PrivateNetwork=</varname><option>yes</option>.</para>
<para>Behavior of <option>idle</option> is very similar to <option>simple</option>; however, actual execution
of the service binary is delayed until all active jobs are dispatched. This may be used to avoid interleaving
of output of shell services with the status output on the console. Note that this type is useful only to
improve console output, it is not useful as a general unit ordering tool, and the effect of this service type
is subject to a 5s time-out, after which the service binary is invoked anyway.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>RemainAfterExit=</varname></term>
<listitem><para>Takes a boolean value that specifies whether
the service shall be considered active even when all its
processes exited. Defaults to <option>no</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>GuessMainPID=</varname></term>
<listitem><para>Takes a boolean value that specifies whether
systemd should try to guess the main PID of a service if it
cannot be determined reliably. This option is ignored unless
<option>Type=forking</option> is set and
<option>PIDFile=</option> is unset because for the other types
or with an explicitly configured PID file, the main PID is
always known. The guessing algorithm might come to incorrect
conclusions if a daemon consists of more than one process. If
the main PID cannot be determined, failure detection and
automatic restarting of a service will not work reliably.
Defaults to <option>yes</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>PIDFile=</varname></term>
<listitem><para>Takes an absolute filename pointing to the
PID file of this daemon. Use of this option is recommended for
services where <varname>Type=</varname> is set to
<option>forking</option>. systemd will read the PID of the
main process of the daemon after start-up of the service.
systemd will not write to the file configured here, although
it will remove the file after the service has shut down if it
still exists.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>BusName=</varname></term>
<listitem><para>Takes a D-Bus bus name that this service is
reachable as. This option is mandatory for services where
<varname>Type=</varname> is set to
<option>dbus</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>ExecStart=</varname></term>
<listitem><para>Commands with their arguments that are
executed when this service is started. The value is split into
zero or more command lines according to the rules described
below (see section "Command Lines" below).
</para>
<para>Unless <varname>Type=</varname> is <option>oneshot</option>, exactly one command must be given. When
<varname>Type=oneshot</varname> is used, zero or more commands may be specified. Commands may be specified by
providing multiple command lines in the same directive, or alternatively, this directive may be specified more
than once with the same effect. If the empty string is assigned to this option, the list of commands to start
is reset, prior assignments of this option will have no effect. If no <varname>ExecStart=</varname> is
specified, then the service must have <varname>RemainAfterExit=yes</varname> and at least one
<varname>ExecStop=</varname> line set. (Services lacking both <varname>ExecStart=</varname> and
<varname>ExecStop=</varname> are not valid.)</para>
<para>For each of the specified commands, the first argument must be an absolute path to an
executable. Optionally, this filename may be prefixed with a number of special characters:</para>
<table>
<title>Special executable prefixes</title>
<tgroup cols='2'>
<colspec colname='prefix'/>
<colspec colname='meaning'/>
<thead>
<row>
<entry>Prefix</entry>
<entry>Effect</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>@</literal></entry>
<entry>If the executable path is prefixed with <literal>@</literal>, the second specified token will be passed as <literal>argv[0]</literal> to the executed process (instead of the actual filename), followed by the further arguments specified.</entry>
</row>
<row>
<entry><literal>-</literal></entry>
<entry>If the executable path is prefixed with <literal>-</literal>, an exit code of the command normally considered a failure (i.e. non-zero exit status or abnormal exit due to signal) is ignored and considered success.</entry>
</row>
<row>
<entry><literal>+</literal></entry>
<entry>If the executable path is prefixed with <literal>+</literal> then the process is executed with full privileges. In this mode privilege restrictions configured with <varname>User=</varname>, <varname>Group=</varname>, <varname>CapabilityBoundingSet=</varname> or the various file system namespacing options (such as <varname>PrivateDevices=</varname>, <varname>PrivateTmp=</varname>) are not applied to the invoked command line (but still affect any other <varname>ExecStart=</varname>, <varname>ExecStop=</varname>, … lines).</entry>
</row>
<row>
<entry><literal>!</literal></entry>
<entry>Similar to the <literal>+</literal> character discussed above this permits invoking command lines with elevated privileges. However, unlike <literal>+</literal> the <literal>!</literal> character exclusively alters the effect of <varname>User=</varname>, <varname>Group=</varname> and <varname>SupplementaryGroups=</varname>, i.e. only the stanzas the affect user and group credentials. Note that this setting may be combined with <varname>DynamicUser=</varname>, in which case a dynamic user/group pair is allocated before the command is invoked, but credential changing is left to the executed process itself.</entry>
</row>
<row>
<entry><literal>!!</literal></entry>
<entry>This prefix is very similar to <literal>!</literal>, however it only has an effect on systems lacking support for ambient process capabilities, i.e. without support for <varname>AmbientCapabilities=</varname>. It's intended to be used for unit files that take benefit of ambient capabilities to run processes with minimal privileges wherever possible while remaining compatible with systems that lack ambient capabilities support. Note that when <literal>!!</literal> is used, and a system lacking ambient capability support is detected any configured <varname>SystemCallFilter=</varname> and <varname>CapabilityBoundingSet=</varname> stanzas are implicitly modified, in order to permit spawned processes to drop credentials and capabilities themselves, even if this is configured to not be allowed. Moreover, if this prefix is used and a system lacking ambient capability support is detected <varname>AmbientCapabilities=</varname> will be skipped and not be applied. On systems supporting ambient capabilities, <literal>!!</literal> has no effect and is redundant.</entry>
</row>
</tbody>
</tgroup>
</table>
<para><literal>@</literal>, <literal>-</literal>, and one of
<literal>+</literal>/<literal>!</literal>/<literal>!!</literal> may be used together and they can appear in any
order. However, only one of <literal>+</literal>, <literal>!</literal>, <literal>!!</literal> may be used at a
time. Note that these prefixes are also supported for the other command line settings,
i.e. <varname>ExecStartPre=</varname>, <varname>ExecStartPost=</varname>, <varname>ExecReload=</varname>,
<varname>ExecStop=</varname> and <varname>ExecStopPost=</varname>.</para>
<para>If more than one command is specified, the commands are
invoked sequentially in the order they appear in the unit
file. If one of the commands fails (and is not prefixed with
<literal>-</literal>), other lines are not executed, and the
unit is considered failed.</para>
<para>Unless <varname>Type=forking</varname> is set, the
process started via this command line will be considered the
main process of the daemon.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>ExecStartPre=</varname></term>
<term><varname>ExecStartPost=</varname></term>
<listitem><para>Additional commands that are executed before
or after the command in <varname>ExecStart=</varname>,
respectively. Syntax is the same as for
<varname>ExecStart=</varname>, except that multiple command
lines are allowed and the commands are executed one after the
other, serially.</para>
<para>If any of those commands (not prefixed with
<literal>-</literal>) fail, the rest are not executed and the
unit is considered failed.</para>
<para><varname>ExecStart=</varname> commands are only run after
all <varname>ExecStartPre=</varname> commands that were not prefixed
with a <literal>-</literal> exit successfully.</para>
<para><varname>ExecStartPost=</varname> commands are only run after the commands specified in
<varname>ExecStart=</varname> have been invoked successfully, as determined by <varname>Type=</varname>
(i.e. the process has been started for <varname>Type=simple</varname> or <varname>Type=idle</varname>, the last
<varname>ExecStart=</varname> process exited successfully for <varname>Type=oneshot</varname>, the initial
process exited successfully for <varname>Type=forking</varname>, <literal>READY=1</literal> is sent for
<varname>Type=notify</varname>, or the <varname>BusName=</varname> has been taken for
<varname>Type=dbus</varname>).</para>
<para>Note that <varname>ExecStartPre=</varname> may not be
used to start long-running processes. All processes forked
off by processes invoked via <varname>ExecStartPre=</varname> will
be killed before the next service process is run.</para>
<para>Note that if any of the commands specified in <varname>ExecStartPre=</varname>,
<varname>ExecStart=</varname>, or <varname>ExecStartPost=</varname> fail (and are not prefixed with
<literal>-</literal>, see above) or time out before the service is fully up, execution continues with commands
specified in <varname>ExecStopPost=</varname>, the commands in <varname>ExecStop=</varname> are skipped.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>ExecReload=</varname></term>
<listitem><para>Commands to execute to trigger a configuration
reload in the service. This argument takes multiple command
lines, following the same scheme as described for
<varname>ExecStart=</varname> above. Use of this setting is
optional. Specifier and environment variable substitution is
supported here following the same scheme as for
<varname>ExecStart=</varname>.</para>
<para>One additional, special environment variable is set: if
known, <varname>$MAINPID</varname> is set to the main process
of the daemon, and may be used for command lines like the
following:</para>
<programlisting>/bin/kill -HUP $MAINPID</programlisting>
<para>Note however that reloading a daemon by sending a signal
(as with the example line above) is usually not a good choice,
because this is an asynchronous operation and hence not
suitable to order reloads of multiple services against each
other. It is strongly recommended to set
<varname>ExecReload=</varname> to a command that not only
triggers a configuration reload of the daemon, but also
synchronously waits for it to complete.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>ExecStop=</varname></term>
<listitem><para>Commands to execute to stop the service
started via <varname>ExecStart=</varname>. This argument takes
multiple command lines, following the same scheme as described
for <varname>ExecStart=</varname> above. Use of this setting
is optional. After the commands configured in this option are
run, it is implied that the service is stopped, and any processes
remaining for it are terminated
according to the <varname>KillMode=</varname> setting (see
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
If this option is not specified, the process is terminated by
sending the signal specified in <varname>KillSignal=</varname>
when service stop is requested. Specifier and environment
variable substitution is supported (including
<varname>$MAINPID</varname>, see above).</para>
<para>Note that it is usually not sufficient to specify a command for this setting that only asks the service
to terminate (for example, by queuing some form of termination signal for it), but does not wait for it to do
so. Since the remaining processes of the services are killed according to <varname>KillMode=</varname> and
<varname>KillSignal=</varname> as described above immediately after the command exited, this may not result in
a clean stop. The specified command should hence be a synchronous operation, not an asynchronous one.</para>
<para>Note that the commands specified in <varname>ExecStop=</varname> are only executed when the service
started successfully first. They are not invoked if the service was never started at all, or in case its
start-up failed, for example because any of the commands specified in <varname>ExecStart=</varname>,
<varname>ExecStartPre=</varname> or <varname>ExecStartPost=</varname> failed (and weren't prefixed with
<literal>-</literal>, see above) or timed out. Use <varname>ExecStopPost=</varname> to invoke commands when a
service failed to start up correctly and is shut down again. Also note that, service restart requests are
implemented as stop operations followed by start operations. This means that <varname>ExecStop=</varname> and
<varname>ExecStopPost=</varname> are executed during a service restart operation.</para>
<para>It is recommended to use this setting for commands that communicate with the service requesting clean
termination. When the commands specified with this option are executed it should be assumed that the service is
still fully up and is able to react correctly to all commands. For post-mortem clean-up steps use
<varname>ExecStopPost=</varname> instead.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ExecStopPost=</varname></term>
<listitem><para>Additional commands that are executed after the service is stopped. This includes cases where
the commands configured in <varname>ExecStop=</varname> were used, where the service does not have any
<varname>ExecStop=</varname> defined, or where the service exited unexpectedly. This argument takes multiple
command lines, following the same scheme as described for <varname>ExecStart=</varname>. Use of these settings
is optional. Specifier and environment variable substitution is supported. Note that – unlike
<varname>ExecStop=</varname> – commands specified with this setting are invoked when a service failed to start
up correctly and is shut down again.</para>
<para>It is recommended to use this setting for clean-up operations that shall be executed even when the
service failed to start up correctly. Commands configured with this setting need to be able to operate even if
the service failed starting up half-way and left incompletely initialized data around. As the service's
processes have been terminated already when the commands specified with this setting are executed they should
not attempt to communicate with them.</para>
<para>Note that all commands that are configured with this setting are invoked with the result code of the
service, as well as the main process' exit code and status, set in the <varname>$SERVICE_RESULT</varname>,
<varname>$EXIT_CODE</varname> and <varname>$EXIT_STATUS</varname> environment variables, see
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RestartSec=</varname></term>
<listitem><para>Configures the time to sleep before restarting
a service (as configured with <varname>Restart=</varname>).
Takes a unit-less value in seconds, or a time span value such
as "5min 20s". Defaults to 100ms.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TimeoutStartSec=</varname></term>
<listitem><para>Configures the time to wait for start-up. If a
daemon service does not signal start-up completion within the
configured time, the service will be considered failed and
will be shut down again. Takes a unit-less value in seconds,
or a time span value such as "5min 20s". Pass
<literal>infinity</literal> to disable the timeout logic. Defaults to
<varname>DefaultTimeoutStartSec=</varname> from the manager
configuration file, except when
<varname>Type=oneshot</varname> is used, in which case the
timeout is disabled by default (see
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
</para>
<para>If a service of <varname>Type=notify</varname> sends <literal>EXTEND_TIMEOUT_USEC=…</literal>, this may cause
the start time to be extended beyond <varname>TimeoutStartSec=</varname>. The first receipt of this message
must occur before <varname>TimeoutStartSec=</varname> is exceeded, and once the start time has exended beyond
<varname>TimeoutStartSec=</varname>, the service manager will allow the service to continue to start, provided
the service repeats <literal>EXTEND_TIMEOUT_USEC=…</literal> within the interval specified until the service
startup status is finished by <literal>READY=1</literal>. (see
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TimeoutStopSec=</varname></term>
<listitem><para>Configures the time to wait for stop. If a
service is asked to stop, but does not terminate in the
specified time, it will be terminated forcibly via
<constant>SIGTERM</constant>, and after another timeout of
equal duration with <constant>SIGKILL</constant> (see
<varname>KillMode=</varname> in
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
Takes a unit-less value in seconds, or a time span value such
as "5min 20s". Pass <literal>infinity</literal> to disable the
timeout logic. Defaults to
<varname>DefaultTimeoutStopSec=</varname> from the manager
configuration file (see
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
</para>
<para>If a service of <varname>Type=notify</varname> sends <literal>EXTEND_TIMEOUT_USEC=…</literal>, this may cause
the stop time to be extended beyond <varname>TimeoutStopSec=</varname>. The first receipt of this message
must occur before <varname>TimeoutStopSec=</varname> is exceeded, and once the stop time has exended beyond
<varname>TimeoutStopSec=</varname>, the service manager will allow the service to continue to stop, provided
the service repeats <literal>EXTEND_TIMEOUT_USEC=…</literal> within the interval specified, or terminates itself
(see <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TimeoutSec=</varname></term>
<listitem><para>A shorthand for configuring both
<varname>TimeoutStartSec=</varname> and
<varname>TimeoutStopSec=</varname> to the specified value.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RuntimeMaxSec=</varname></term>
<listitem><para>Configures a maximum time for the service to run. If this is used and the service has been
active for longer than the specified time it is terminated and put into a failure state. Note that this setting
does not have any effect on <varname>Type=oneshot</varname> services, as they terminate immediately after
activation completed. Pass <literal>infinity</literal> (the default) to configure no runtime
limit.</para>
<para>If a service of <varname>Type=notify</varname> sends <literal>EXTEND_TIMEOUT_USEC=…</literal>, this may cause
the runtime to be extended beyond <varname>RuntimeMaxSec=</varname>. The first receipt of this message
must occur before <varname>RuntimeMaxSec=</varname> is exceeded, and once the runtime has exended beyond
<varname>RuntimeMaxSec=</varname>, the service manager will allow the service to continue to run, provided
the service repeats <literal>EXTEND_TIMEOUT_USEC=…</literal> within the interval specified until the service
shutdown is acheived by <literal>STOPPING=1</literal> (or termination). (see
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>WatchdogSec=</varname></term>
<listitem><para>Configures the watchdog timeout for a service.
The watchdog is activated when the start-up is completed. The
service must call
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
regularly with <literal>WATCHDOG=1</literal> (i.e. the
"keep-alive ping"). If the time between two such calls is
larger than the configured time, then the service is placed in
a failed state and it will be terminated with
<constant>SIGABRT</constant>. By setting
<varname>Restart=</varname> to <option>on-failure</option>,
<option>on-watchdog</option>, <option>on-abnormal</option> or
<option>always</option>, the service will be automatically
restarted. The time configured here will be passed to the
executed service process in the
<varname>WATCHDOG_USEC=</varname> environment variable. This
allows daemons to automatically enable the keep-alive pinging
logic if watchdog support is enabled for the service. If this
option is used, <varname>NotifyAccess=</varname> (see below)
should be set to open access to the notification socket
provided by systemd. If <varname>NotifyAccess=</varname> is
not set, it will be implicitly set to <option>main</option>.
Defaults to 0, which disables this feature. The service can
check whether the service manager expects watchdog keep-alive
notifications. See
<citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for details.
<citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
may be used to enable automatic watchdog notification support.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Restart=</varname></term>
<listitem><para>Configures whether the service shall be
restarted when the service process exits, is killed, or a
timeout is reached. The service process may be the main
service process, but it may also be one of the processes
specified with <varname>ExecStartPre=</varname>,
<varname>ExecStartPost=</varname>,
<varname>ExecStop=</varname>,
<varname>ExecStopPost=</varname>, or
<varname>ExecReload=</varname>. When the death of the process
is a result of systemd operation (e.g. service stop or
restart), the service will not be restarted. Timeouts include
missing the watchdog "keep-alive ping" deadline and a service
start, reload, and stop operation timeouts.</para>
<para>Takes one of
<option>no</option>,
<option>on-success</option>,
<option>on-failure</option>,
<option>on-abnormal</option>,
<option>on-watchdog</option>,
<option>on-abort</option>, or
<option>always</option>.
If set to <option>no</option> (the default), the service will
not be restarted. If set to <option>on-success</option>, it
will be restarted only when the service process exits cleanly.
In this context, a clean exit means an exit code of 0, or one
of the signals
<constant>SIGHUP</constant>,
<constant>SIGINT</constant>,
<constant>SIGTERM</constant> or
<constant>SIGPIPE</constant>, and
additionally, exit statuses and signals specified in
<varname>SuccessExitStatus=</varname>. If set to
<option>on-failure</option>, the service will be restarted
when the process exits with a non-zero exit code, is
terminated by a signal (including on core dump, but excluding
the aforementioned four signals), when an operation (such as
service reload) times out, and when the configured watchdog
timeout is triggered. If set to <option>on-abnormal</option>,
the service will be restarted when the process is terminated
by a signal (including on core dump, excluding the
aforementioned four signals), when an operation times out, or
when the watchdog timeout is triggered. If set to
<option>on-abort</option>, the service will be restarted only
if the service process exits due to an uncaught signal not
specified as a clean exit status. If set to
<option>on-watchdog</option>, the service will be restarted
only if the watchdog timeout for the service expires. If set
to <option>always</option>, the service will be restarted
regardless of whether it exited cleanly or not, got terminated
abnormally by a signal, or hit a timeout.</para>
<table>
<title>Exit causes and the effect of the <varname>Restart=</varname> settings on them</title>
<tgroup cols='2'>
<colspec colname='path' />
<colspec colname='expl' />
<thead>
<row>
<entry>Restart settings/Exit causes</entry>
<entry><option>no</option></entry>
<entry><option>always</option></entry>
<entry><option>on-success</option></entry>
<entry><option>on-failure</option></entry>
<entry><option>on-abnormal</option></entry>
<entry><option>on-abort</option></entry>
<entry><option>on-watchdog</option></entry>
</row>
</thead>
<tbody>
<row>
<entry>Clean exit code or signal</entry>
<entry/>
<entry>X</entry>
<entry>X</entry>
<entry/>
<entry/>
<entry/>
<entry/>
</row>
<row>
<entry>Unclean exit code</entry>
<entry/>
<entry>X</entry>
<entry/>
<entry>X</entry>
<entry/>
<entry/>
<entry/>
</row>
<row>
<entry>Unclean signal</entry>
<entry/>
<entry>X</entry>
<entry/>
<entry>X</entry>
<entry>X</entry>
<entry>X</entry>
<entry/>
</row>
<row>
<entry>Timeout</entry>
<entry/>
<entry>X</entry>
<entry/>
<entry>X</entry>
<entry>X</entry>
<entry/>
<entry/>
</row>
<row>
<entry>Watchdog</entry>
<entry/>
<entry>X</entry>
<entry/>
<entry>X</entry>
<entry>X</entry>
<entry/>
<entry>X</entry>
</row>
</tbody>
</tgroup>
</table>
<para>As exceptions to the setting above, the service will not
be restarted if the exit code or signal is specified in
<varname>RestartPreventExitStatus=</varname> (see below) or
the service is stopped with <command>systemctl stop</command>
or an equivalent operation. Also, the services will always be
restarted if the exit code or signal is specified in
<varname>RestartForceExitStatus=</varname> (see below).</para>
<para>Note that service restart is subject to unit start rate
limiting configured with <varname>StartLimitIntervalSec=</varname>
and <varname>StartLimitBurst=</varname>, see
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details.</para>
<para>Setting this to <option>on-failure</option> is the
recommended choice for long-running services, in order to
increase reliability by attempting automatic recovery from
errors. For services that shall be able to terminate on their
own choice (and avoid immediate restarting),
<option>on-abnormal</option> is an alternative choice.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>SuccessExitStatus=</varname></term>
<listitem><para>Takes a list of exit status definitions that,
when returned by the main service process, will be considered
successful termination, in addition to the normal successful
exit code 0 and the signals <constant>SIGHUP</constant>,
<constant>SIGINT</constant>, <constant>SIGTERM</constant>, and
<constant>SIGPIPE</constant>. Exit status definitions can
either be numeric exit codes or termination signal names,
separated by spaces. For example:
<programlisting>SuccessExitStatus=1 2 8 SIGKILL</programlisting>
ensures that exit codes 1, 2, 8 and
the termination signal <constant>SIGKILL</constant> are
considered clean service terminations.
</para>
<para>This option may appear more than once, in which case the
list of successful exit statuses is merged. If the empty
string is assigned to this option, the list is reset, all
prior assignments of this option will have no
effect.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RestartPreventExitStatus=</varname></term>
<listitem><para>Takes a list of exit status definitions that,
when returned by the main service process, will prevent
automatic service restarts, regardless of the restart setting
configured with <varname>Restart=</varname>. Exit status
definitions can either be numeric exit codes or termination
signal names, and are separated by spaces. Defaults to the
empty list, so that, by default, no exit status is excluded
from the configured restart logic. For example:
<programlisting>RestartPreventExitStatus=1 6 SIGABRT</programlisting>
ensures that exit codes 1 and 6 and the termination signal
<constant>SIGABRT</constant> will not result in automatic
service restarting. This option may appear more than once, in
which case the list of restart-preventing statuses is
merged. If the empty string is assigned to this option, the
list is reset and all prior assignments of this option will
have no effect.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RestartForceExitStatus=</varname></term>
<listitem><para>Takes a list of exit status definitions that,
when returned by the main service process, will force automatic
service restarts, regardless of the restart setting configured
with <varname>Restart=</varname>. The argument format is
similar to
<varname>RestartPreventExitStatus=</varname>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PermissionsStartOnly=</varname></term>
<listitem><para>Takes a boolean argument. If true, the
permission-related execution options, as configured with
<varname>User=</varname> and similar options (see
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for more information), are only applied to the process started
with
<varname>ExecStart=</varname>, and not to the various other
<varname>ExecStartPre=</varname>,
<varname>ExecStartPost=</varname>,
<varname>ExecReload=</varname>,
<varname>ExecStop=</varname>, and
<varname>ExecStopPost=</varname>
commands. If false, the setting is applied to all configured
commands the same way. Defaults to false.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RootDirectoryStartOnly=</varname></term>
<listitem><para>Takes a boolean argument. If true, the root
directory, as configured with the
<varname>RootDirectory=</varname> option (see
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for more information), is only applied to the process started
with <varname>ExecStart=</varname>, and not to the various
other <varname>ExecStartPre=</varname>,
<varname>ExecStartPost=</varname>,
<varname>ExecReload=</varname>, <varname>ExecStop=</varname>,
and <varname>ExecStopPost=</varname> commands. If false, the
setting is applied to all configured commands the same way.
Defaults to false.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>NonBlocking=</varname></term>
<listitem><para>Set the <constant>O_NONBLOCK</constant> flag for all file descriptors passed via socket-based
activation. If true, all file descriptors >= 3 (i.e. all except stdin, stdout, stderr), excluding those passed
in via the file descriptor storage logic (see <varname>FileDescriptorStoreMax=</varname> for details), will
have the <constant>O_NONBLOCK</constant> flag set and hence are in non-blocking mode. This option is only
useful in conjunction with a socket unit, as described in
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> and has no
effect on file descriptors which were previously saved in the file-descriptor store for example. Defaults to
false.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>NotifyAccess=</varname></term>
<listitem><para>Controls access to the service status notification socket, as accessible via the
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry> call. Takes one
of <option>none</option> (the default), <option>main</option>, <option>exec</option> or
<option>all</option>. If <option>none</option>, no daemon status updates are accepted from the service
processes, all status update messages are ignored. If <option>main</option>, only service updates sent from the
main process of the service are accepted. If <option>exec</option>, only service updates sent from any of the
main or control processes originating from one of the <varname>Exec*=</varname> commands are accepted. If
<option>all</option>, all services updates from all members of the service's control group are accepted. This
option should be set to open access to the notification socket when using <varname>Type=notify</varname> or
<varname>WatchdogSec=</varname> (see above). If those options are used but <varname>NotifyAccess=</varname> is
not configured, it will be implicitly set to <option>main</option>.</para>
<para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if
either the sending process is still around at the time PID 1 processes the message, or if the sending process
is explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally
forked off the process, i.e. on all processes that match <option>main</option> or
<option>exec</option>. Conversely, if an auxiliary process of the unit sends an
<function>sd_notify()</function> message and immediately exits, the service manager might not be able to
properly attribute the message to the unit, and thus will ignore it, even if
<varname>NotifyAccess=</varname><option>all</option> is set for it.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Sockets=</varname></term>
<listitem><para>Specifies the name of the socket units this
service shall inherit socket file descriptors from when the
service is started. Normally, it should not be necessary to use
this setting, as all socket file descriptors whose unit shares
the same name as the service (subject to the different unit
name suffix of course) are passed to the spawned
process.</para>
<para>Note that the same socket file descriptors may be passed
to multiple processes simultaneously. Also note that a
different service may be activated on incoming socket traffic
than the one which is ultimately configured to inherit the
socket file descriptors. Or, in other words: the
<varname>Service=</varname> setting of
<filename>.socket</filename> units does not have to match the
inverse of the <varname>Sockets=</varname> setting of the
<filename>.service</filename> it refers to.</para>
<para>This option may appear more than once, in which case the
list of socket units is merged. If the empty string is
assigned to this option, the list of sockets is reset, and all
prior uses of this setting will have no
effect.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>FileDescriptorStoreMax=</varname></term>
<listitem><para>Configure how many file descriptors may be stored in the service manager for the service using
<citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s
<literal>FDSTORE=1</literal> messages. This is useful for implementing services that can restart after an
explicit request or a crash without losing state. Any open sockets and other file descriptors which should not
be closed during the restart may be stored this way. Application state can either be serialized to a file in
<filename>/run</filename>, or better, stored in a
<citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> memory file
descriptor. Defaults to 0, i.e. no file descriptors may be stored in the service manager. All file descriptors
passed to the service manager from a specific service are passed back to the service's main process on the next
service restart. Any file descriptors passed to the service manager are automatically closed when
<constant>POLLHUP</constant> or <constant>POLLERR</constant> is seen on them, or when the service is fully
stopped and no job is queued or being executed for it.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>USBFunctionDescriptors=</varname></term>
<listitem><para>Configure the location of a file containing
<ulink
url="https://www.kernel.org/doc/Documentation/usb/functionfs.txt">USB
FunctionFS</ulink> descriptors, for implementation of USB
gadget functions. This is used only in conjunction with a
socket unit with <varname>ListenUSBFunction=</varname>
configured. The contents of this file are written to the
<filename>ep0</filename> file after it is
opened.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>USBFunctionStrings=</varname></term>
<listitem><para>Configure the location of a file containing
USB FunctionFS strings. Behavior is similar to
<varname>USBFunctionDescriptors=</varname>
above.</para></listitem>
</varlistentry>
</variablelist>
<para>Check
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for more settings.</para>
</refsect1>
<refsect1>
<title>Command lines</title>
<para>This section describes command line parsing and
variable and specifier substitutions for
<varname>ExecStart=</varname>,
<varname>ExecStartPre=</varname>,
<varname>ExecStartPost=</varname>,
<varname>ExecReload=</varname>,
<varname>ExecStop=</varname>, and
<varname>ExecStopPost=</varname> options.</para>
<para>Multiple command lines may be concatenated in a single
directive by separating them with semicolons (these semicolons
must be passed as separate words). Lone semicolons may be escaped
as <literal>\;</literal>.</para>
<para>Each command line is split on whitespace, with the first item being the command to
execute, and the subsequent items being the arguments. Double quotes ("…") and single quotes
('…') may be used to wrap a whole item (the opening quote may appear only at the beginning or
after whitespace that is not quoted, and the closing quote must be followed by whitespace or the
end of line), in which case everything until the next matching quote becomes part of the same
argument. Quotes themselves are removed. C-style escapes are also supported. The table below
contains the list of known escape patterns. Only escape patterns which match the syntax in the
table are allowed; other patterns may be added in the future and unknown patterns will result in
a warning. In particular, any backslashes should be doubled. Finally, a trailing backslash
(<literal>\</literal>) may be used to merge lines.</para>
<para>This syntax is inspired by shell syntax, but only the meta-characters and expansions
described in the following paragraphs are understood, and the expansion of variables is
different. Specifically, redirection using
<literal>&lt;</literal>,
<literal>&lt;&lt;</literal>,
<literal>&gt;</literal>, and
<literal>&gt;&gt;</literal>, pipes using
<literal>|</literal>, running programs in the background using
<literal>&amp;</literal>, and <emphasis>other elements of shell
syntax are not supported</emphasis>.</para>
<para>The command to execute must be an absolute path name. It may
contain spaces, but control characters are not allowed.</para>
<para>The command line accepts <literal>%</literal> specifiers as
described in
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
Note that the first argument of the command line (i.e. the program
to execute) may not include specifiers.</para>
<para>Basic environment variable substitution is supported. Use
<literal>${FOO}</literal> as part of a word, or as a word of its
own, on the command line, in which case it will be replaced by the
value of the environment variable including all whitespace it
contains, resulting in a single argument. Use
<literal>$FOO</literal> as a separate word on the command line, in
which case it will be replaced by the value of the environment
variable split at whitespace, resulting in zero or more arguments.
For this type of expansion, quotes are respected when splitting
into words, and afterwards removed.</para>
<para>Example:</para>
<programlisting>Environment="ONE=one" 'TWO=two two'
ExecStart=/bin/echo $ONE $TWO ${TWO}</programlisting>
<para>This will execute <command>/bin/echo</command> with four
arguments: <literal>one</literal>, <literal>two</literal>,
<literal>two</literal>, and <literal>two two</literal>.</para>
<para>Example:</para>
<programlisting>Environment=ONE='one' "TWO='two two' too" THREE=
ExecStart=/bin/echo ${ONE} ${TWO} ${THREE}
ExecStart=/bin/echo $ONE $TWO $THREE</programlisting>
<para>This results in <filename>echo</filename> being
called twice, the first time with arguments
<literal>'one'</literal>,
<literal>'two two' too</literal>, <literal></literal>,
and the second time with arguments
<literal>one</literal>, <literal>two two</literal>,
<literal>too</literal>.
</para>
<para>To pass a literal dollar sign, use <literal>$$</literal>.
Variables whose value is not known at expansion time are treated
as empty strings. Note that the first argument (i.e. the program
to execute) may not be a variable.</para>
<para>Variables to be used in this fashion may be defined through
<varname>Environment=</varname> and
<varname>EnvironmentFile=</varname>. In addition, variables listed
in the section "Environment variables in spawned processes" in
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which are considered "static configuration", may be used (this
includes e.g. <varname>$USER</varname>, but not
<varname>$TERM</varname>).</para>
<para>Note that shell command lines are not directly supported. If
shell command lines are to be used, they need to be passed
explicitly to a shell implementation of some kind. Example:</para>
<programlisting>ExecStart=/bin/sh -c 'dmesg | tac'</programlisting>
<para>Example:</para>
<programlisting>ExecStart=/bin/echo one ; /bin/echo "two two"</programlisting>
<para>This will execute <command>/bin/echo</command> two times,
each time with one argument: <literal>one</literal> and
<literal>two two</literal>, respectively. Because two commands are
specified, <varname>Type=oneshot</varname> must be used.</para>
<para>Example:</para>
<programlisting>ExecStart=/bin/echo / &gt;/dev/null &amp; \; \
/bin/ls</programlisting>
<para>This will execute <command>/bin/echo</command>
with five arguments: <literal>/</literal>,
<literal>&gt;/dev/null</literal>,
<literal>&amp;</literal>, <literal>;</literal>, and
<literal>/bin/ls</literal>.</para>
<table>
<title>C escapes supported in command lines and environment variables</title>
<tgroup cols='2'>
<colspec colname='escape' />
<colspec colname='meaning' />
<thead>
<row>
<entry>Literal</entry>
<entry>Actual value</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>\a</literal></entry>
<entry>bell</entry>
</row>
<row>
<entry><literal>\b</literal></entry>
<entry>backspace</entry>
</row>
<row>
<entry><literal>\f</literal></entry>
<entry>form feed</entry>
</row>
<row>
<entry><literal>\n</literal></entry>
<entry>newline</entry>
</row>
<row>
<entry><literal>\r</literal></entry>
<entry>carriage return</entry>
</row>
<row>
<entry><literal>\t</literal></entry>
<entry>tab</entry>
</row>
<row>
<entry><literal>\v</literal></entry>
<entry>vertical tab</entry>
</row>
<row>
<entry><literal>\\</literal></entry>
<entry>backslash</entry>
</row>
<row>
<entry><literal>\"</literal></entry>
<entry>double quotation mark</entry>
</row>
<row>
<entry><literal>\'</literal></entry>
<entry>single quotation mark</entry>
</row>
<row>
<entry><literal>\s</literal></entry>
<entry>space</entry>
</row>
<row>
<entry><literal>\x<replaceable>xx</replaceable></literal></entry>
<entry>character number <replaceable>xx</replaceable> in hexadecimal encoding</entry>
</row>
<row>
<entry><literal>\<replaceable>nnn</replaceable></literal></entry>
<entry>character number <replaceable>nnn</replaceable> in octal encoding</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1>
<title>Examples</title>
<example>
<title>Simple service</title>
<para>The following unit file creates a service that will
execute <filename>/usr/sbin/foo-daemon</filename>. Since no
<varname>Type=</varname> is specified, the default
<varname>Type=</varname><option>simple</option> will be assumed.
systemd will assume the unit to be started immediately after the
program has begun executing.</para>
<programlisting>[Unit]
Description=Foo
[Service]
ExecStart=/usr/sbin/foo-daemon
[Install]
WantedBy=multi-user.target</programlisting>
<para>Note that systemd assumes here that the process started by
systemd will continue running until the service terminates. If
the program daemonizes itself (i.e. forks), please use
<varname>Type=</varname><option>forking</option> instead.</para>
<para>Since no <varname>ExecStop=</varname> was specified,
systemd will send SIGTERM to all processes started from this
service, and after a timeout also SIGKILL. This behavior can be
modified, see
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details.</para>
<para>Note that this unit type does not include any type of
notification when a service has completed initialization. For
this, you should use other unit types, such as
<varname>Type=</varname><option>notify</option> if the service
understands systemd's notification protocol,
<varname>Type=</varname><option>forking</option> if the service
can background itself or
<varname>Type=</varname><option>dbus</option> if the unit
acquires a DBus name once initialization is complete. See
below.</para>
</example>
<example>
<title>Oneshot service</title>
<para>Sometimes, units should just execute an action without
keeping active processes, such as a filesystem check or a
cleanup action on boot. For this,
<varname>Type=</varname><option>oneshot</option> exists. Units
of this type will wait until the process specified terminates
and then fall back to being inactive. The following unit will
perform a cleanup action:</para>
<programlisting>[Unit]
Description=Cleanup old Foo data
[Service]
Type=oneshot
ExecStart=/usr/sbin/foo-cleanup
[Install]
WantedBy=multi-user.target</programlisting>
<para>Note that systemd will consider the unit to be in the
state "starting" until the program has terminated, so ordered
dependencies will wait for the program to finish before starting
themselves. The unit will revert to the "inactive" state after
the execution is done, never reaching the "active" state. That
means another request to start the unit will perform the action
again.</para>
<para><varname>Type=</varname><option>oneshot</option> are the
only service units that may have more than one
<varname>ExecStart=</varname> specified. They will be executed
in order until either they are all successful or one of them
fails.</para>
</example>
<example>
<title>Stoppable oneshot service</title>
<para>Similarly to the oneshot services, there are sometimes
units that need to execute a program to set up something and
then execute another to shut it down, but no process remains
active while they are considered "started". Network
configuration can sometimes fall into this category. Another use
case is if a oneshot service shall not be executed each time
when they are pulled in as a dependency, but only the first
time.</para>
<para>For this, systemd knows the setting
<varname>RemainAfterExit=</varname><option>yes</option>, which
causes systemd to consider the unit to be active if the start
action exited successfully. This directive can be used with all
types, but is most useful with
<varname>Type=</varname><option>oneshot</option> and
<varname>Type=</varname><option>simple</option>. With
<varname>Type=</varname><option>oneshot</option>, systemd waits
until the start action has completed before it considers the
unit to be active, so dependencies start only after the start
action has succeeded. With
<varname>Type=</varname><option>simple</option>, dependencies
will start immediately after the start action has been
dispatched. The following unit provides an example for a simple
static firewall.</para>
<programlisting>[Unit]
Description=Simple firewall
[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/local/sbin/simple-firewall-start
ExecStop=/usr/local/sbin/simple-firewall-stop
[Install]
WantedBy=multi-user.target</programlisting>
<para>Since the unit is considered to be running after the start
action has exited, invoking <command>systemctl start</command>
on that unit again will cause no action to be taken.</para>
</example>
<example>
<title>Traditional forking services</title>
<para>Many traditional daemons/services background (i.e. fork,
daemonize) themselves when starting. Set
<varname>Type=</varname><option>forking</option> in the
service's unit file to support this mode of operation. systemd
will consider the service to be in the process of initialization
while the original program is still running. Once it exits
successfully and at least a process remains (and
<varname>RemainAfterExit=</varname><option>no</option>), the
service is considered started.</para>
<para>Often, a traditional daemon only consists of one process.
Therefore, if only one process is left after the original
process terminates, systemd will consider that process the main
process of the service. In that case, the
<varname>$MAINPID</varname> variable will be available in
<varname>ExecReload=</varname>, <varname>ExecStop=</varname>,
etc.</para>
<para>In case more than one process remains, systemd will be
unable to determine the main process, so it will not assume
there is one. In that case, <varname>$MAINPID</varname> will not
expand to anything. However, if the process decides to write a
traditional PID file, systemd will be able to read the main PID
from there. Please set <varname>PIDFile=</varname> accordingly.
Note that the daemon should write that file before finishing
with its initialization. Otherwise, systemd might try to read the
file before it exists.</para>
<para>The following example shows a simple daemon that forks and
just starts one process in the background:</para>
<programlisting>[Unit]
Description=Some simple daemon
[Service]
Type=forking
ExecStart=/usr/sbin/my-simple-daemon -d
[Install]
WantedBy=multi-user.target</programlisting>
<para>Please see
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details on how you can influence the way systemd terminates
the service.</para>
</example>
<example>
<title>DBus services</title>
<para>For services that acquire a name on the DBus system bus,
use <varname>Type=</varname><option>dbus</option> and set
<varname>BusName=</varname> accordingly. The service should not
fork (daemonize). systemd will consider the service to be
initialized once the name has been acquired on the system bus.
The following example shows a typical DBus service:</para>
<programlisting>[Unit]
Description=Simple DBus service
[Service]
Type=dbus
BusName=org.example.simple-dbus-service
ExecStart=/usr/sbin/simple-dbus-service
[Install]
WantedBy=multi-user.target</programlisting>
<para>For <emphasis>bus-activatable</emphasis> services, do not
include a <literal>[Install]</literal> section in the systemd
service file, but use the <varname>SystemdService=</varname>
option in the corresponding DBus service file, for example
(<filename>/usr/share/dbus-1/system-services/org.example.simple-dbus-service.service</filename>):</para>
<programlisting>[D-BUS Service]
Name=org.example.simple-dbus-service
Exec=/usr/sbin/simple-dbus-service
User=root
SystemdService=simple-dbus-service.service</programlisting>
<para>Please see
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details on how you can influence the way systemd terminates
the service.</para>
</example>
<example>
<title>Services that notify systemd about their initialization</title>
<para><varname>Type=</varname><option>simple</option> services
are really easy to write, but have the major disadvantage of
systemd not being able to tell when initialization of the given
service is complete. For this reason, systemd supports a simple
notification protocol that allows daemons to make systemd aware
that they are done initializing. Use
<varname>Type=</varname><option>notify</option> for this. A
typical service file for such a daemon would look like
this:</para>
<programlisting>[Unit]
Description=Simple notifying service
[Service]
Type=notify
ExecStart=/usr/sbin/simple-notifying-service
[Install]
WantedBy=multi-user.target</programlisting>
<para>Note that the daemon has to support systemd's notification
protocol, else systemd will think the service has not started yet
and kill it after a timeout. For an example of how to update
daemons to support this protocol transparently, take a look at
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
systemd will consider the unit to be in the 'starting' state
until a readiness notification has arrived.</para>
<para>Please see
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details on how you can influence the way systemd terminates
the service.</para>
</example>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>