systemd.unit(5) - Unit configuration

[amurleopard]

SYSTEMD.UNIT(5) 		 systemd.unit		       SYSTEMD.UNIT(5)

NAME
       systemd.unit - Unit configuration

SYNOPSIS
       service.service, socket.socket, device.device, mount.mount,
       automount.automount, swap.swap, target.target, path.path, timer.timer,
       slice.slice, scope.scope

       /etc/systemd/system/*
       /run/systemd/system/*
       /lib/systemd/system/*
       ...

       $XDG_CONFIG_HOME/systemd/user/*
       $HOME/.config/systemd/user/*
       /etc/systemd/user/*
       $XDG_RUNTIME_DIR/systemd/user/*
       /run/systemd/user/*
       $XDG_DATA_HOME/systemd/user/*
       $HOME/.local/share/systemd/user/*
       /usr/lib/systemd/user/*
       ...

DESCRIPTION
       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 watched file system path, a timer
       controlled and supervised by systemd(1), a resource management slice or
       a group of externally created processes. The syntax is inspired by XDG
       Desktop Entry Specification[1] .desktop files, which are in turn
       inspired by Microsoft Windows .ini files.

       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.

       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:
       systemd.service(5), systemd.socket(5), systemd.device(5),
       systemd.mount(5), systemd.automount(5), systemd.swap(5),
       systemd.target(5), systemd.path(5), systemd.timer(5), systemd.slice(5),
       systemd.scope(5).

       Various settings are allowed to be specified more than once, in which
       case the interpretation depends on the setting. Often, multiple
       settings form a list, and setting to an empty value "resets", which
       means that previous assignments are ignored. When this is allowed, it
       is mentioned in the description of the setting. Note that using
       multiple assignments to the same value makes the unit file incompatible
       with parsers for the XDG .desktop file format.

       Unit files are loaded from a set of paths determined during
       compilation, described in the next section.

       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 or section name is
       prefixed with X-, it is ignored completely by systemd. Options within
       an ignored section do not need the prefix. Applications may use this to
       include additional information in the unit files.

       Boolean arguments used in unit files can be written in various formats.
       For positive settings the strings 1, yes, true and on are equivalent.
       For negative settings, the strings 0, no, false and off are equivalent.

       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 systemd.time(7).

       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.

       Along with a unit file foo.service, the directory foo.service.wants/
       may exist. All unit files symlinked from such a directory are
       implicitly added as dependencies of type Wants= 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 Wants=,
       see below. The preferred way to create symlinks in the .wants/
       directory of a unit file is with the enable command of the systemctl(1)
       tool which reads information from the [Install] section of unit files
       (see below). A similar functionality exists for Requires= type
       dependencies as well, the directory suffix is .requires/ in this case.

       Along with a unit file foo.service, a "drop-in" directory
       foo.service.d/ may exist. All files with the suffix ".conf" from this
       directory will be parsed after the file itself is parsed. This is
       useful to alter or add configuration settings for a unit, without
       having to modify unit files. Each drop-in file must have appropriate
       section headers. Note that for instantiated units, this logic will
       first look for the instance ".d/" subdirectory and read its ".conf"
       files, followed by the template ".d/" subdirectory and the ".conf"
       files there. Also note that settings from the "[Install]" section are
       not honoured in drop-in unit files, and have no effect.

       In addition to /etc/systemd/system, the drop-in ".conf" files for
       system services can be placed in /lib/systemd/system or
       /run/systemd/system directories. Drop-in files in /etc take precedence
       over those in /run which in turn take precedence over those in /lib.
       Drop-in files under any of these directories take precedence over unit
       files wherever located. (Of course, since /run is temporary and
       /usr/lib is for vendors, it is unlikely drop-ins should be used in
       either of those places.)

       Some unit names reflect paths existing in the file system namespace.
       Example: a device unit dev-sda.device refers to a device with the
       device node /dev/sda 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 filename. Basically, given a path, "/" is replaced
       by "-", and all other characters which are not ASCII alphanumerics are
       replaced by C-style "\x2d" escapes (except that "_" is never replaced
       and "." is only replaced when it would be the first character in the
       escaped path). The root directory "/" is encoded as single dash, while
       otherwise the initial and ending "/" are removed from all paths during
       transformation. This escaping is reversible. Properly escaped paths can
       be generated using the systemd-escape(1) command.

       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 file system. 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 [email protected] is requested and no
       file by that name is found, systemd will look for [email protected] and
       instantiate a service from that configuration file if it is found.

       To refer to the instance string from within the configuration file you
       may use the special "%i" specifier in many of the configuration
       options. See below for details.

       If a unit file is empty (i.e. has the file size 0) or is symlinked to
       /dev/null, its configuration will not be loaded and it appears with a
       load state of "masked", and cannot be activated. Use this as an
       effective way to fully disable a unit, making it impossible to start it
       even manually.

       The unit file format is covered by the Interface Stability Promise[2].

AUTOMATIC DEPENDENCIES
       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.

       A number of unit dependencies are automatically established, depending
       on unit configuration. On top of that, for units with
       DefaultDependencies=yes (the default) a couple of additional
       dependencies are added. The precise effect of DefaultDependencies=yes
       depends on the unit type (see below).

       If DefaultDependencies=yes is set, units that are referenced by other
       units of type .target via a Wants= or Requires= dependency might
       automatically gain an Before= dependency too. See systemd.target(5) for
       details.

UNIT FILE LOAD PATH
       Unit files are loaded from a set of paths determined during
       compilation, described in the two tables below. Unit files found in
       directories listed earlier override files with the same name in
       directories lower in the list.

       When the variable $SYSTEMD_UNIT_PATH is set, the contents of this
       variable overrides the unit load path. If $SYSTEMD_UNIT_PATH ends with
       an empty component (":"), the usual unit load path will be appended to
       the contents of the variable.

       Table 1.  Load path when running in system mode (--system).
       ┌────────────────────┬─────────────────────┐
       │Path		    │ Description	  │
       ├────────────────────┼─────────────────────┤
       │/etc/systemd/system │ Local configuration │
       ├────────────────────┼─────────────────────┤
       │/run/systemd/system │ Runtime units	  │
       ├────────────────────┼─────────────────────┤
       │/lib/systemd/system │ Units of installed  │
       │		    │ packages		  │
       └────────────────────┴─────────────────────┘

       Table 2.  Load path when running in user mode (--user).
       ┌────────────────────────────────┬────────────────────────────┐
       │Path				│ Description		     │
       ├────────────────────────────────┼────────────────────────────┤
<standard input>:1011: warning [p 9, 5.3i, div `3tbd8,2', 0.3i]: can't break line
<standard input>:1284: warning [p 10, 22.5i]: can't break line
       │$XDG_CONFIG_HOME/systemd/user	│ User configuration (only   │
       │				│ used when $XDG_CONFIG_HOME │
       │				│ is set)		     │
       ├────────────────────────────────┼────────────────────────────┤
       │$HOME/.config/systemd/user	│ User configuration (only   │
       │				│ used when $XDG_CONFIG_HOME │
       │				│ is not set)		     │
       ├────────────────────────────────┼────────────────────────────┤
       │/etc/systemd/user		│ Local configuration	     │
       ├────────────────────────────────┼────────────────────────────┤
       │$XDG_RUNTIME_DIR/systemd/user	│ Runtime units (only used   │
       │				│ when $XDG_RUNTIME_DIR is   │
       │				│ set)			     │
       ├────────────────────────────────┼────────────────────────────┤
       │/run/systemd/user		│ Runtime units 	     │
       ├────────────────────────────────┼────────────────────────────┤
       │$XDG_DATA_HOME/systemd/user	│ Units of packages that     │
       │				│ have been installed in the │
       │				│ home directory (only used  │
       │				│ when $XDG_DATA_HOME is     │
       │				│ set)			     │
       ├────────────────────────────────┼────────────────────────────┤
       │$HOME/.local/share/systemd/user │ Units of packages that     │
       │				│ have been installed in the │
       │				│ home directory (only used  │
       │				│ when $XDG_DATA_HOME is not │
       │				│ set)			     │
       ├────────────────────────────────┼────────────────────────────┤
       │/usr/lib/systemd/user		│ Units of packages that     │
       │				│ have been installed	     │
       │				│ system-wide		     │
       └────────────────────────────────┴────────────────────────────┘

       Additional units might be loaded into systemd ("linked") from
       directories not on the unit load path. See the link command for
       systemctl(1). Also, some units are dynamically created via a
       systemd.generator(7).

[UNIT] SECTION OPTIONS
       The unit file may include a [Unit] section, which carries generic
       information about the unit that is not dependent on the type of unit:

       Description=
	   A free-form string describing the unit. This is intended for use in
	   UIs to show descriptive information along with the unit name. The
	   description should contain a name that means something to the end
	   user.  "Apache2 Web Server" is a good example. Bad examples are
	   "high-performance light-weight HTTP server" (too generic) or
	   "Apache2" (too specific and meaningless for people who do not know
	   Apache).

       Documentation=
	   A space-separated list of URIs referencing documentation for this
	   unit or its configuration. Accepted are only URIs of the types
	   "http://", "https://", "file:", "info:", "man:". For more
	   information about the syntax of these URIs, see uri(7). 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.

       Requires=
	   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 or multiple space-separated units may be specified in one
	   option in which case requirement dependencies for all listed names
	   will be 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 After= or Before=
	   options. If a unit foo.service requires a unit bar.service as
	   configured with Requires= and no ordering is configured with After=
	   or Before=, then both units will be started simultaneously and
	   without any delay between them if foo.service is activated. Often,
	   it is a better choice to use Wants= instead of Requires= in order
	   to achieve a system that is more robust when dealing with failing
	   services.

	   Note that dependencies of this type may also be configured outside
	   of the unit configuration file by adding a symlink to a .requires/
	   directory accompanying the unit file. For details, see above.

       Requisite=
	   Similar to Requires=. However, if the units listed here are not
	   started already, they will not be started and the transaction will
	   fail immediately.

       Wants=
	   A weaker version of Requires=. Units listed in this option will be
	   started if the configuring unit is. However, if the listed units
	   fail to start or cannot be added to the transaction, this has no
	   impact on the validity of the transaction as a whole. This is the
	   recommended way to hook start-up of one unit to the start-up of
	   another unit.

	   Note that dependencies of this type may also be configured outside
	   of the unit configuration file by adding symlinks to a .wants/
	   directory accompanying the unit file. For details, see above.

       BindsTo=
	   Configures requirement dependencies, very similar in style to
	   Requires=, 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.

       PartOf=
	   Configures dependencies similar to Requires=, 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.

       Conflicts=
	   A space-separated list of unit names. Configures negative
	   requirement dependencies. If a unit has a Conflicts= 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 After= and Before= ordering dependencies.

	   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.

       Before=, After=
	   A space-separated list of unit names. Configures ordering
	   dependencies between units. If a unit foo.service contains a
	   setting Before=bar.service and both units are being started,
	   bar.service's start-up is delayed until foo.service is started up.
	   Note that this setting is independent of and orthogonal to the
	   requirement dependencies as configured by Requires=. It is a common
	   pattern to include a unit name in both the After= and Requires=
	   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.  After= is the inverse of Before=,
	   i.e. while After= ensures that the configured unit is started after
	   the listed unit finished starting up, Before= 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 After= 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 of whether the ordering
	   dependency is actually of type After= or Before=. If two units have
	   no ordering dependencies between them, they are shut down or
	   started up simultaneously, and no ordering takes place.

       OnFailure=
	   A space-separated list of one or more units that are activated when
	   this unit enters the "failed" state.

       PropagatesReloadTo=, ReloadPropagatedFrom=
	   A space-separated list of one or more units where reload requests
	   on this unit will be propagated to, or reload requests on the other
	   unit will be propagated to this unit, respectively. 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.

       JoinsNamespaceOf=
	   For units that start processes (such as service units), lists one
	   or more other units whose network and/or temporary file namespace
	   to join. This only applies to unit types which support the
	   PrivateNetwork= and PrivateTmp= directives (see systemd.exec(5) for
	   details). If a unit that has this setting set is started, its
	   processes will see the same /tmp, /tmp/var and network namespace as
	   one listed unit that is started. If multiple listed units are
	   already started, it is not defined which namespace is joined. Note
	   that this setting only has an effect if PrivateNetwork= and/or
	   PrivateTmp= is enabled for both the unit that joins the namespace
	   and the unit whose namespace is joined.

       RequiresMountsFor=
	   Takes a space-separated list of absolute paths. Automatically adds
	   dependencies of type Requires= and After= for all mount units
	   required to access the specified path.

	   Mount points marked with noauto are not mounted automatically and
	   will be ignored for the purposes of this option. If such a mount
	   should be a requirement for this unit, direct dependencies on the
	   mount units may be added (Requires= and After= or some other
	   combination).

       OnFailureJobMode=
	   Takes a value of "fail", "replace", "replace-irreversibly",
	   "isolate", "flush", "ignore-dependencies" or "ignore-requirements".
	   Defaults to "replace". Specifies how the units listed in OnFailure=
	   will be enqueued. See systemctl(1)'s --job-mode= option for details
	   on the possible values. If this is set to "isolate", only a single
	   unit may be listed in OnFailure=..

       IgnoreOnIsolate=
	   Takes a boolean argument. If true, this unit will not be stopped
	   when isolating another unit. Defaults to false.

       StopWhenUnneeded=
	   Takes a boolean argument. If true, 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 false.

       RefuseManualStart=, RefuseManualStop=
	   Takes a boolean argument. If true, 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 false.

       AllowIsolate=
	   Takes a boolean argument. If true, this unit may be used with the
	   systemctl isolate 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 false.

       DefaultDependencies=
	   Takes a boolean argument. If true, (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 false. It is highly
	   recommended to leave this option enabled for the majority of common
	   units. If set to false, this option does not disable all implicit
	   dependencies, just non-essential ones.

       JobTimeoutSec=, JobTimeoutAction=, JobTimeoutRebootArgument=
	   When a job for this unit is queued, a time-out may be configured.
	   If this time limit is reached, the job will be cancelled, the unit
	   however will not change state or even enter the "failed" mode. This
	   value defaults to "infinity" (job timeouts disabled), except for
	   device units. NB: this timeout is independent from any
	   unit-specific timeout (for example, the timeout set with
	   TimeoutStartSec= 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.

	   JobTimeoutAction= optionally configures an additional action to
	   take when the time-out is hit. It takes the same values as the
	   per-service StartLimitAction= setting, see systemd.service(5) for
	   details. Defaults to none.  JobTimeoutRebootArgument= configures an
	   optional reboot string to pass to the reboot(2) system call.

       StartLimitInterval=, StartLimitBurst=
	   Configure unit start rate limiting. By default, units which are
	   started more than 5 times within 10 seconds are not permitted to
	   start any more times until the 10 second interval ends. With these
	   two options, this rate limiting may be modified. Use
	   StartLimitInterval= to configure the checking interval (defaults to
	   DefaultStartLimitInterval= in manager configuration file, set to 0
	   to disable any kind of rate limiting). Use StartLimitBurst= to
	   configure how many starts per interval are allowed (defaults to
	   DefaultStartLimitBurst= in manager configuration file). These
	   configuration options are particularly useful in conjunction with
	   the service setting Restart= (see systemd.service(5)); however,
	   they apply to all kinds of starts (including manual), not just
	   those triggered by the Restart= logic. Note that units which are
	   configured for Restart= and which reach the start limit are not
	   attempted to be restarted anymore; however, they may still be
	   restarted manually at a later point, from which point on, the
	   restart logic is again activated. Note that systemctl reset-failed
	   will cause the restart rate counter for a service to be flushed,
	   which is useful if the administrator wants to manually start a unit
	   and the start limit interferes with that. Note that this
	   rate-limiting is enforced after any unit condition checks are
	   executed, and hence unit activations with failing conditions are
	   not counted by this rate limiting.

       StartLimitAction=
	   Configure the action to take if the rate limit configured with
	   StartLimitInterval= and StartLimitBurst= is hit. Takes one of none,
	   reboot, reboot-force, reboot-immediate, poweroff, poweroff-force or
	   poweroff-immediate. If none is set, hitting the rate limit will
	   trigger no action besides that the start will not be permitted.
	   reboot causes a reboot following the normal shutdown procedure
	   (i.e. equivalent to systemctl reboot).  reboot-force causes a
	   forced reboot which will terminate all processes forcibly but
	   should cause no dirty file systems on reboot (i.e. equivalent to
	   systemctl reboot -f) and reboot-immediate causes immediate
	   execution of the reboot(2) system call, which might result in data
	   loss. Similarly, poweroff, poweroff-force, poweroff-immediate have
	   the effect of powering down the system with similar semantics.
	   Defaults to none.

       RebootArgument=
	   Configure the optional argument for the reboot(2) system call if
	   StartLimitAction= or a service's FailureAction= is a reboot action.
	   This works just like the optional argument to systemctl reboot
	   command.

       ConditionArchitecture=, ConditionVirtualization=, ConditionHost=,
       ConditionKernelCommandLine=, ConditionSecurity=, ConditionCapability=,
       ConditionACPower=, ConditionNeedsUpdate=, ConditionFirstBoot=,
       ConditionPathExists=, ConditionPathExistsGlob=,
       ConditionPathIsDirectory=, ConditionPathIsSymbolicLink=,
       ConditionPathIsMountPoint=, ConditionPathIsReadWrite=,
       ConditionDirectoryNotEmpty=, ConditionFileNotEmpty=,
       ConditionFileIsExecutable=
	   Before starting a unit, verify that the specified condition is
	   true. If it is not true, the starting of the unit will be (mostly
	   silently) 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. Use condition
	   expressions in order to silently skip units that do not apply to
	   the local running system, for example because the kernel or runtime
	   environment doesn't require its functionality. Use the various
	   AssertArchitecture=, AssertVirtualization=, ... options for a
	   similar mechanism that puts the unit in a failure state and logs
	   about the failed check (see below).

	   ConditionArchitecture= may be used to check whether the system is
	   running on a specific architecture. Takes one of x86, x86-64, ppc,
	   ppc-le, ppc64, ppc64-le, ia64, parisc, parisc64, s390, s390x,
	   sparc, sparc64, mips, mips-le, mips64, mips64-le, alpha, arm,
	   arm-be, arm64, arm64-be, sh, sh64, m86k, tilegx, cris to test
	   against a specific architecture. The architecture is determined
	   from the information returned by uname(2) and is thus subject to
	   personality(2). Note that a Personality= setting in the same unit
	   file has no effect on this condition. A special architecture name
	   native is mapped to the architecture the system manager itself is
	   compiled for. The test may be negated by prepending an exclamation
	   mark.

	   ConditionVirtualization= 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
	   vm and container to test against a generic type of virtualization
	   solution, or one of qemu, kvm, zvm, vmware, microsoft, oracle, xen,
	   bochs, uml, openvz, lxc, lxc-libvirt, systemd-nspawn, docker, rkt
	   to test against a specific implementation. See systemd-detect-
	   virt(1) for a full list of known virtualization technologies and
	   their identifiers. If multiple virtualization technologies are
	   nested, only the innermost is considered. The test may be negated
	   by prepending an exclamation mark.

	   ConditionHost= may be used to match against the hostname or machine
	   ID of the host. This either takes a hostname string (optionally
	   with shell style globs) which is tested against the locally set
	   hostname as returned by gethostname(2), or a machine ID formatted
	   as string (see machine-id(5)). The test may be negated by
	   prepending an exclamation mark.

	   ConditionKernelCommandLine= 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.

	   ConditionSecurity= may be used to check whether the given security
	   module is enabled on the system. Currently, the recognized values
	   are selinux, apparmor, ima, smack and audit. The test may be
	   negated by prepending an exclamation mark.

	   ConditionCapability= 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 capabilities(7)
	   for details). Pass a capability name such as "CAP_MKNOD", possibly
	   prefixed with an exclamation mark to negate the check.

	   ConditionACPower= 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 true, 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 false, the condition will hold only if there
	   is at least one AC connector known and all AC connectors are
	   disconnected from a power source.

	   ConditionNeedsUpdate= takes one of /var or /etc as argument,
	   possibly prefixed with a "!"  (for inverting the condition). This
	   condition may be used to conditionalize units on whether the
	   specified directory requires an update because /usr's modification
	   time is newer than the stamp file .updated in the specified
	   directory. This is useful to implement offline updates of the
	   vendor operating system resources in /usr that require updating of
	   /etc or /var on the next following boot. Units making use of this
	   condition should order themselves before systemd-update-
	   done.service(8), to make sure they run before the stamp file's
	   modification time gets reset indicating a completed update.

	   ConditionFirstBoot= takes a boolean argument. This condition may be
	   used to conditionalize units on whether the system is booting up
	   with an unpopulated /etc directory. This may be used to populate
	   /etc on the first boot after factory reset, or when a new system
	   instances boots up for the first time.

	   With ConditionPathExists= 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 ConditionPathExists= is prefixed with an exclamation mark
	   ("!"), the test is negated, and the unit is only started if the
	   path does not exist.

	   ConditionPathExistsGlob= is similar to ConditionPathExists=, but
	   checks for the existence of at least one file or directory matching
	   the specified globbing pattern.

	   ConditionPathIsDirectory= is similar to ConditionPathExists= but
	   verifies whether a certain path exists and is a directory.

	   ConditionPathIsSymbolicLink= is similar to ConditionPathExists= but
	   verifies whether a certain path exists and is a symbolic link.

	   ConditionPathIsMountPoint= is similar to ConditionPathExists= but
	   verifies whether a certain path exists and is a mount point.

	   ConditionPathIsReadWrite= is similar to ConditionPathExists= but
	   verifies whether the underlying file system is readable and
	   writable (i.e. not mounted read-only).

	   ConditionDirectoryNotEmpty= is similar to ConditionPathExists= but
	   verifies whether a certain path exists and is a non-empty
	   directory.

	   ConditionFileNotEmpty= is similar to ConditionPathExists= but
	   verifies whether a certain path exists and refers to a regular file
	   with a non-zero size.

	   ConditionFileIsExecutable= is similar to ConditionPathExists= but
	   verifies whether a certain path exists, is a regular file and
	   marked executable.

	   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
	   ConditionPathIsSymbolicLink=, 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.

       AssertArchitecture=, AssertVirtualization=, AssertHost=,
       AssertKernelCommandLine=, AssertSecurity=, AssertCapability=,
       AssertACPower=, AssertNeedsUpdate=, AssertFirstBoot=,
       AssertPathExists=, AssertPathExistsGlob=, AssertPathIsDirectory=,
       AssertPathIsSymbolicLink=, AssertPathIsMountPoint=,
       AssertPathIsReadWrite=, AssertDirectoryNotEmpty=, AssertFileNotEmpty=,
       AssertFileIsExecutable=
	   Similar to the ConditionArchitecture=, ConditionVirtualization=,
	   ..., condition settings described above, these settings add
	   assertion checks to the start-up of the unit. However, unlike the
	   conditions settings, any assertion setting that is not met results
	   in failure of the start job (which means this is logged loudly).
	   Use assertion expressions for units that cannot operate when
	   specific requirements are not met, and when this is something the
	   administrator or user should look into.

       SourcePath=
	   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. This functionality should not be used in
	   normal units.

[INSTALL] SECTION OPTIONS
       Unit files may include an "[Install]" section, which carries
       installation information for the unit. This section is not interpreted
       by systemd(1) during runtime; it is used by the enable and disable
       commands of the systemctl(1) tool during installation of a unit. Note
       that settings in the "[Install]" section may not appear in .d/*.conf
       unit file drop-ins (see above).

       Alias=
	   A space-separated list of 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, systemctl enable will create symlinks from these
	   names to the unit filename.

       WantedBy=, RequiredBy=
	   This option may be used more than once, or a space-separated list
	   of unit names may be given. A symbolic link is created in the
	   .wants/ or .requires/ directory of each of the listed units when
	   this unit is installed by systemctl enable. This has the effect
	   that a dependency of type Wants= or Requires= is added from the
	   listed unit to the current unit. The primary result is that the
	   current unit will be started when the listed unit is started. See
	   the description of Wants= and Requires= in the [Unit] section for
	   details.

	   WantedBy=foo.service in a service bar.service is mostly equivalent
	   to Alias=foo.service.wants/bar.service in the same file. In case of
	   template units, systemctl enable must be called with an instance
	   name, and this instance will be added to the .wants/ or .requires/
	   list of the listed unit. E.g.  WantedBy=getty.target in a service
	   [email protected] will result in systemctl enable [email protected]
	   creating a getty.target.wants/[email protected] link to
	   [email protected].

       Also=
	   Additional units to install/deinstall when this unit is
	   installed/deinstalled. If the user requests
	   installation/deinstallation of a unit with this option configured,
	   systemctl enable and systemctl disable will automatically
	   install/uninstall units listed in this option as well.

	   This option may be used more than once, or a space-separated list
	   of unit names may be given.

       DefaultInstance=
	   In template unit files, this specifies for which instance the unit
	   shall be enabled if the template is enabled without any explicitly
	   set instance. This option has no effect in non-template unit files.
	   The specified string must be usable as instance identifier.

       The following specifiers are interpreted in the Install section: %n,
       %N, %p, %i, %U, %u, %m, %H, %b, %v. For their meaning see the next
       section.

SPECIFIERS
       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:

       Table 3. Specifiers available in unit files
       ┌──────────┬─────────────────────┬─────────────────────────┐
       │Specifier │ Meaning		│ Details		  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%n"	  │ Full unit name	│			  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%N"	  │ Unescaped full unit │ Same as "%n", but	  │
       │	  │ name		│ with escaping 	  │
       │	  │			│ undone		  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%p"	  │ Prefix name 	│ For instantiated	  │
       │	  │			│ units, this refers	  │
       │	  │			│ to the string 	  │
       │	  │			│ before the "@"	  │
       │	  │			│ character of the	  │
       │	  │			│ unit name. For	  │
       │	  │			│ non-instantiated	  │
       │	  │			│ units, this refers	  │
       │	  │			│ to the name of the	  │
       │	  │			│ unit with the type	  │
       │	  │			│ suffix removed.	  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%P"	  │ Unescaped prefix	│ Same as "%p", but	  │
       │	  │ name		│ with escaping 	  │
       │	  │			│ undone		  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%i"	  │ Instance name	│ For instantiated	  │
       │	  │			│ units: this is the	  │
       │	  │			│ string between the	  │
       │	  │			│ "@" character and	  │
       │	  │			│ the suffix of the	  │
       │	  │			│ unit name.		  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%I"	  │ Unescaped instance	│ Same as "%i", but	  │
       │	  │ name		│ with escaping 	  │
       │	  │			│ undone		  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%f"	  │ Unescaped filename	│ This is either the	  │
       │	  │			│ unescaped instance	  │
       │	  │			│ name (if		  │
       │	  │			│ applicable) with /	  │
       │	  │			│ prepended (if 	  │
       │	  │			│ applicable), or the	  │
       │	  │			│ prefix name		  │
       │	  │			│ prepended with /.	  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%c"	  │ Control group path	│ This path does not	  │
       │	  │ of the unit 	│ include the		  │
       │	  │			│ /sys/fs/cgroup/systemd/ │
       │	  │			│ prefix.		  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%r"	  │ Control group path	│ This usually maps to	  │
       │	  │ of the slice the	│ the parent cgroup path  │
       │	  │ unit is placed in	│ of "%c".		  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%R"	  │ Root control group	│ For system instances,   │
       │	  │ path below which	│ this resolves to /,	  │
       │	  │ slices and units	│ except in containers,   │
       │	  │ are placed		│ where this maps to the  │
       │	  │			│ container's root	  │
       │	  │			│ control group path.	  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%t"	  │ Runtime directory	│ This is either /run	  │
       │	  │			│ (for the system	  │
       │	  │			│ manager) or the path	  │
       │	  │			│ "$XDG_RUNTIME_DIR"	  │
       │	  │			│ resolves to (for user   │
       │	  │			│ managers).		  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%u"	  │ User name		│ This is the name of the │
       │	  │			│ user running the	  │
       │	  │			│ service manager	  │
       │	  │			│ instance. In case of	  │
       │	  │			│ the system manager this │
       │	  │			│ resolves to "root".	  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%U"	  │ User UID		│ This is the numeric UID │
       │	  │			│ of the user running the │
       │	  │			│ service manager	  │
       │	  │			│ instance. In case of	  │
       │	  │			│ the system manager this │
       │	  │			│ resolves to "0".	  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%h"	  │ User home directory │ This is the home	  │
       │	  │			│ directory of the user   │
       │	  │			│ running the service	  │
       │	  │			│ manager instance. In	  │
       │	  │			│ case of the system	  │
       │	  │			│ manager this resolves   │
       │	  │			│ to "/root".		  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%s"	  │ User shell		│ This is the shell of	  │
       │	  │			│ the user running the	  │
       │	  │			│ service manager	  │
       │	  │			│ instance. In case of	  │
       │	  │			│ the system manager this │
       │	  │			│ resolves to "/bin/sh".  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%m"	  │ Machine ID		│ The machine ID of the   │
       │	  │			│ running system,	  │
       │	  │			│ formatted as string.	  │
       │	  │			│ See machine-id(5) for   │
       │	  │			│ more information.	  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%b"	  │ Boot ID		│ The boot ID of the	  │
       │	  │			│ running system,	  │
       │	  │			│ formatted as string.	  │
       │	  │			│ See random(4) for more  │
       │	  │			│ information.		  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%H"	  │ Host name		│ The hostname of the	  │
       │	  │			│ running system at the   │
       │	  │			│ point in time the unit  │
       │	  │			│ configuration is	  │
       │	  │			│ loaded.		  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%v"	  │ Kernel release	│ Identical to uname -r   │
       │	  │			│ output		  │
       ├──────────┼─────────────────────┼─────────────────────────┤
       │"%%"	  │ Single percent sign │ Use "%%" in place of	  │
       │	  │			│ "%" to specify a single │
       │	  │			│ percent sign. 	  │
       └──────────┴─────────────────────┴─────────────────────────┘

       Please note that specifiers "%U", "%h", "%s" are mostly useless when
       systemd is running in system mode. PID 1 cannot query the user account
       database for information, so the specifiers only work as shortcuts for
       things which are already specified in a different way in the unit file.
       They are fully functional when systemd is running in --user mode.

EXAMPLES
       Example 1. Allowing units to be enabled

       The following snippet (highlighted) allows a unit (e.g.	foo.service)
       to be enabled via systemctl enable:

	   [Unit]
	   Description=Foo

	   [Service]
	   ExecStart=/usr/sbin/foo-daemon

	   [Install]
	   WantedBy=multi-user.target

       After running systemctl enable, a symlink
       /etc/systemd/system/multi-user.target.wants/foo.service linking to the
       actual unit will be created. It tells systemd to pull in the unit when
       starting multi-user.target. The inverse systemctl disable will remove
       that symlink again.

       Example 2. Overriding vendor settings

       There are two methods of overriding vendor settings in unit files:
       copying the unit file from /lib/systemd/system to /etc/systemd/system
       and modifying the chosen settings. Alternatively, one can create a
       directory named unit.d/ within /etc/systemd/system and place a drop-in
       file name.conf there that only changes the specific settings one is
       interested in. Note that multiple such drop-in files are read if
       present.

       The advantage of the first method is that one easily overrides the
       complete unit, the vendor unit is not parsed at all anymore. It has the
       disadvantage that improvements to the unit file by the vendor are not
       automatically incorporated on updates.

       The advantage of the second method is that one only overrides the
       settings one specifically wants, where updates to the unit by the
       vendor automatically apply. This has the disadvantage that some future
       updates by the vendor might be incompatible with the local changes.

       Note that for drop-in files, if one wants to remove entries from a
       setting that is parsed as a list (and is not a dependency), such as
       ConditionPathExists= (or e.g.  ExecStart= in service units), one needs
       to first clear the list before re-adding all entries except the one
       that is to be removed. See below for an example.

       This also applies for user instances of systemd, but with different
       locations for the unit files. See the section on unit load paths for
       further details.

       Suppose there is a vendor-supplied unit
       /lib/systemd/system/httpd.service with the following contents:

	   [Unit]
	   Description=Some HTTP server
	   After=remote-fs.target sqldb.service
	   Requires=sqldb.service
	   AssertPathExists=/srv/webserver

	   [Service]
	   Type=notify
	   ExecStart=/usr/sbin/some-fancy-httpd-server
	   Nice=5

	   [Install]
	   WantedBy=multi-user.target

       Now one wants to change some settings as an administrator: firstly, in
       the local setup, /srv/webserver might not exist, because the HTTP
       server is configured to use /srv/www instead. Secondly, the local
       configuration makes the HTTP server also depend on a memory cache
       service, memcached.service, that should be pulled in (Requires=) and
       also be ordered appropriately (After=). Thirdly, in order to harden the
       service a bit more, the administrator would like to set the PrivateTmp=
       setting (see systemd.service(5) for details). And lastly, the
       administrator would like to reset the niceness of the service to its
       default value of 0.

       The first possibility is to copy the unit file to
       /etc/systemd/system/httpd.service and change the chosen settings:

	   [Unit]
	   Description=Some HTTP server
	   After=remote-fs.target sqldb.service memcached.service
	   Requires=sqldb.service memcached.service
	   AssertPathExists=/srv/www

	   [Service]
	   Type=notify
	   ExecStart=/usr/sbin/some-fancy-httpd-server
	   Nice=0
	   PrivateTmp=yes

	   [Install]
	   WantedBy=multi-user.target

       Alternatively, the administrator could create a drop-in file
       /etc/systemd/system/httpd.service.d/local.conf with the following
       contents:

	   [Unit]
	   After=memcached.service
	   Requires=memcached.service
	   # Reset all assertions and then re-add the condition we want
	   AssertPathExists=
	   AssertPathExists=/srv/www

	   [Service]
	   Nice=0
	   PrivateTmp=yes

       Note that dependencies (After=, etc.) cannot be reset to an empty list,
       so dependencies can only be added in drop-ins. If you want to remove
       dependencies, you have to override the entire unit.

SEE ALSO
       systemd(1), systemctl(1), systemd.special(7), systemd.service(5),
       systemd.socket(5), systemd.device(5), systemd.mount(5),
       systemd.automount(5), systemd.swap(5), systemd.target(5),
       systemd.path(5), systemd.timer(5), systemd.scope(5), systemd.slice(5),
       systemd.time(7), systemd-analyze(1), capabilities(7),
       systemd.directives(7), uname(1)

NOTES
	1. XDG Desktop Entry Specification
	   http://standards.freedesktop.org/desktop-entry-spec/latest/

	2. Interface Stability Promise
	   http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise

systemd						       SYSTEMD.UNIT(5)