systemd.unit

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

   System Unit Search Path
       /etc/systemd/system.control/*
       /run/systemd/system.control/*
       /run/systemd/transient/*
       /run/systemd/generator.early/*
       /etc/systemd/system/*
       /etc/systemd/systemd.attached/*
       /run/systemd/system/*
       /run/systemd/systemd.attached/*
       /run/systemd/generator/*
       ...
       /usr/lib/systemd/system/*
       /run/systemd/generator.late/*

   User Unit Search Path
       ~/.config/systemd/user.control/*
       $XDG_RUNTIME_DIR/systemd/user.control/*
       $XDG_RUNTIME_DIR/systemd/transient/*
       $XDG_RUNTIME_DIR/systemd/generator.early/*
       ~/.config/systemd/user/*
       /etc/systemd/user/*
       $XDG_RUNTIME_DIR/systemd/user/*
       /run/systemd/user/*
       $XDG_RUNTIME_DIR/systemd/generator/*
       ~/.local/share/systemd/user/*
       ...
       /usr/lib/systemd/user/*
       $XDG_RUNTIME_DIR/systemd/generator.late/*

DESCRIPTION
       A unit file is a plain text ini-style file that 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. See systemd.syntax(7) for a
       general description of the syntax.

       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).

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

       Valid unit names consist of a "name prefix" and a dot and a suffix
       specifying the unit type. The "unit prefix" must consist of one or more
       valid characters (ASCII letters, digits, ":", "-", "_", ".", and "\").
       The total length of the unit name including the suffix must not exceed
       256 characters. The type suffix must be one of ".service", ".socket",
       ".device", ".mount", ".automount", ".swap", ".target", ".path", ".timer",
       ".slice", or ".scope".

       Units names can be parameterized by a single argument called the
       "instance name". The unit is then constructed based on a "template file"
       which serves as the definition of multiple services or other units. A
       template unit must have a single "@" at the end of the name (right before
       the type suffix). The name of the full unit is formed by inserting the
       instance name between "@" and the unit type suffix. In the unit file
       itself, the instance parameter may be referred to using "%i" and other
       specifiers, see below.

       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.

       Units can be aliased (have an alternative name), by creating a symlink
       from the new name to the existing name in one of the unit search paths.
       For example, systemd-networkd.service has the alias
       dbus-org.freedesktop.network1.service, created during installation as a
       symlink, so when systemd is asked through D-Bus to load
       dbus-org.freedesktop.network1.service, it'll load
       systemd-networkd.service. As another example, default.target — the
       default system target started at boot — is commonly symlinked (aliased)
       to either multi-user.target or graphical.target to select what is started
       by default. Alias names may be used in commands like disable, start,
       stop, status, and similar, and in all unit dependency directives,
       including Wants=, Requires=, Before=, After=. Aliases cannot be used with
       the preset command.

       Aliases obey the following restrictions: a unit of a certain type
       (".service", ".socket", ...) can only be aliased by a name with the same
       type suffix. A plain unit (not a template or an instance), may only be
       aliased by a plain name. A template instance may only be aliased by
       another template instance, and the instance part must be identical. A
       template may be aliased by another template (in which case the alias
       applies to all instances of the template). As a special case, a template
       instance (e.g.  "alias@inst.service") may be a symlink to different
       template (e.g.  "template@inst.service"). In that case, just this
       specific instance is aliased, while other instances of the template (e.g.
       "alias@foo.service", "alias@bar.service") are not aliased. Those rule
       preserve the requirement that the instance (if any) is always uniquely
       defined for a given unit and all its aliases.

       Unit files may specify aliases through the Alias= directive in the
       [Install] section. When the unit is enabled, symlinks will be created for
       those names, and removed when the unit is disabled. For example,
       reboot.target specifies Alias=ctrl-alt-del.target, so when enabled, the
       symlink /etc/systemd/systemd/ctrl-alt-del.service pointing to the
       reboot.target file will be created, and when Ctrl+Alt+Del is invoked,
       systemd will look for the ctrl-alt-del.service and execute
       reboot.service.  systemd does not look at the [Install] section at all
       during normal operation, so any directives in that section only have an
       effect through the symlinks created during enablement.

       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. Similar functionality
       exists for Requires= type dependencies as well, the directory suffix is
       .requires/ in this case. This functionality 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/ or .requires/ directory of a unit file
       is by embedding the dependency in [Install] section of the target unit,
       and creating the symlink in the file system with the enable or preset
       commands of systemctl(1).

       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 unit file itself is parsed. This is useful to alter or
       add configuration settings for a unit, without having to modify unit
       files. Drop-in files must contain appropriate section headers. For
       instantiated units, this logic will first look for the instance ".d/"
       subdirectory (e.g.  "foo@bar.service.d/") and read its ".conf" files,
       followed by the template ".d/" subdirectory (e.g.  "foo@.service.d/") and
       the ".conf" files there. Moreover for units names containing dashes
       ("-"), the set of directories generated by truncating the unit name after
       all dashes is searched too. Specifically, for a unit name
       foo-bar-baz.service not only the regular drop-in directory
       foo-bar-baz.service.d/ is searched but also both foo-bar-.service.d/ and
       foo-.service.d/. This is useful for defining common drop-ins for a set of
       related units, whose names begin with a common prefix. This scheme is
       particularly useful for mount, automount and slice units, whose
       systematic naming structure is built around dashes as component
       separators. Note that equally named drop-in files further down the prefix
       hierarchy override those further up, i.e.
       foo-bar-.service.d/10-override.conf overrides
       foo-.service.d/10-override.conf.

       In cases of unit aliases (described above), dropins for the aliased name
       and all aliases are loaded. In the example of default.target aliasing
       graphical.target, default.target.d/, default.target.wants/,
       default.target.requires/, graphical.target.d/, graphical.target.wants/,
       graphical.target.requires/ would all be read. For templates, dropins for
       the template, any template aliases, the template instance, and all alias
       instances are read. When just a specific template instance is aliased,
       then the dropins for the target template, the target template instance,
       and the alias template instance are read.

       In addition to /etc/systemd/system, the drop-in ".d/" directories for
       system services can be placed in /usr/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 /usr/lib.
       Drop-in files under any of these directories take precedence over unit
       files wherever located. Multiple drop-in files with different names are
       applied in lexicographic order, regardless of which of the directories
       they reside in.

       Units also support a top-level drop-in with type.d/, where type may be
       e.g.  "service" or "socket", that allows altering or adding to the
       settings of all corresponding unit files on the system. The formatting
       and precedence of applying drop-in configurations follow what is defined
       above. Configurations in type.d/ have the lowest precedence compared to
       settings in the name specific override directories. So the contents of
       foo-.service.d/10-override.conf would override
       service.d/10-override.conf.

       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.

       As mentioned above, a unit may be instantiated from a template file. 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 getty@tty3.service is requested and no file by that name is
       found, systemd will look for getty@.service 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[1].

STRING ESCAPING FOR INCLUSION IN UNIT NAMES
       Sometimes it is useful to convert arbitrary strings into unit names. To
       facilitate this, a method of string escaping is used, in order to map
       strings containing arbitrary byte values (except NUL) into valid unit
       names and their restricted character set. A common special case are unit
       names that reflect paths to objects in the file system hierarchy.
       Example: a device unit dev-sda.device refers to a device with the device
       node /dev/sda in the file system.

       The escaping algorithm operates as follows: given a string, any "/"
       character is replaced by "-", and all other characters which are not
       ASCII alphanumerics or "_" are replaced by C-style "\x2d" escapes. In
       addition, "."  is replaced with such a C-style escape when it would
       appear as the first character in the escaped string.

       When the input qualifies as absolute file system path, this algorithm is
       extended slightly: the path to the root directory "/" is encoded as
       single dash "-". In addition, any leading, trailing or duplicate "/"
       characters are removed from the string before transformation. Example:
       /foo//bar/baz/ becomes "foo-bar-baz".

       This escaping is fully reversible, as long as it is known whether the
       escaped string was a path (the unescaping results are different for paths
       and non-path strings). The systemd-escape(1) command may be used to apply
       and reverse escaping on arbitrary strings. Use systemd-escape --path to
       escape path strings, and systemd-escape without --path otherwise.

AUTOMATIC DEPENDENCIES
   Implicit Dependencies
       A number of unit dependencies are implicitly established, depending on
       unit type and unit configuration. These implicit dependencies can make
       unit configuration file cleaner. For the implicit dependencies in each
       unit type, please refer to section "Implicit Dependencies" in respective
       man pages.

       For example, service units with Type=dbus automatically acquire
       dependencies of type Requires= and After= on dbus.socket. See
       systemd.service(5) for details.

   Default Dependencies
       Default dependencies are similar to implicit dependencies, but can be
       turned on and off by setting DefaultDependencies= to yes (the default)
       and no, while implicit dependencies are always in effect. See section
       "Default Dependencies" in respective man pages for the effect of enabling
       DefaultDependencies= in each unit types.

       For example, target units will complement all configured dependencies of
       type Wants= or Requires= with dependencies of type After= unless
       DefaultDependencies=no is set in the specified units. See
       systemd.target(5) for details. Note that this behavior can be turned off
       by setting DefaultDependencies=no.

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.control   │ Persistent and transient    │
       ├──────────────────────────────┤ configuration created using │
       │/run/systemd/system.control   │ the dbus API                │
       ├──────────────────────────────┼─────────────────────────────┤
       │/run/systemd/transient        │ Dynamic configuration for   │
       │                              │ transient units             │
       ├──────────────────────────────┼─────────────────────────────┤
       │/run/systemd/generator.early  │ Generated units with high   │
       │                              │ priority (see early-dir in  │
       │                              │ systemd.generator(7))       │
       ├──────────────────────────────┼─────────────────────────────┤
       │/etc/systemd/system           │ System units created by the │
       │                              │ administrator               │
       ├──────────────────────────────┼─────────────────────────────┤
       │/run/systemd/system           │ Runtime units               │
       ├──────────────────────────────┼─────────────────────────────┤
       │/run/systemd/generator        │ Generated units with medium │
       │                              │ priority (see normal-dir in │
       │                              │ systemd.generator(7))       │
       ├──────────────────────────────┼─────────────────────────────┤
       │/usr/local/lib/systemd/system │ System units installed by   │
       │                              │ the administrator           │
       ├──────────────────────────────┼─────────────────────────────┤
       │/usr/lib/systemd/system       │ System units installed by   │
       │                              │ the distribution package    │
       │                              │ manager                     │
       ├──────────────────────────────┼─────────────────────────────┤
       │/run/systemd/generator.late   │ Generated units with low    │
       │                              │ priority (see late-dir in   │
       │                              │ systemd.generator(7))       │
       └──────────────────────────────┴─────────────────────────────┘

       Table 2.  Load path when running in user mode (--user).
       ┌────────────────────────────────────────┬─────────────────────────────┐
       │Path                                    Description                 │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │$XDG_CONFIG_HOME/systemd/user.control   │ Persistent and transient    │
       │or                                      │ configuration created using │
       │~/.config/systemd/user.control          │ the dbus API                │
       ├────────────────────────────────────────┤ ($XDG_CONFIG_HOME is used   │
       │$XDG_RUNTIME_DIR/systemd/user.control   │ if set, ~/.config           │
       │                                        │ otherwise)                  │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │/run/systemd/transient                  │ Dynamic configuration for   │
       │                                        │ transient units             │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │/run/systemd/generator.early            │ Generated units with high   │
       │                                        │ priority (see early-dir in  │
       │                                        │ systemd.generator(7))       │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │$XDG_CONFIG_HOME/systemd/user or        │ User configuration          │
       │$HOME/.config/systemd/user              │ ($XDG_CONFIG_HOME is used   │
       │                                        │ if set, ~/.config           │
       │                                        │ otherwise)                  │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │/etc/systemd/user                       │ User units created by the   │
       │                                        │ administrator               │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │$XDG_RUNTIME_DIR/systemd/user           │ Runtime units (only used    │
       │                                        │ when $XDG_RUNTIME_DIR is    │
       │                                        │ set)                        │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │/run/systemd/user                       │ Runtime units               │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │$XDG_RUNTIME_DIR/systemd/generator      │ Generated units with medium │
       │                                        │ priority (see normal-dir in │
       │                                        │ systemd.generator(7))       │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │$XDG_DATA_HOME/systemd/user or          │ Units of packages that have │
       │$HOME/.local/share/systemd/user         │ been installed in the home  │
       │                                        │ directory ($XDG_DATA_HOME   │
       │                                        │ is used if set,             │
       │                                        │ ~/.local/share otherwise)   │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │$dir/systemd/user for each $dir in      │ Additional locations for    │
       │$XDG_DATA_DIRS                          │ installed user units, one   │
       │                                        │ for each entry in           │
       │                                        │ $XDG_DATA_DIRS              │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │/usr/local/lib/systemd/user             │ User units installed by the │
       │                                        │ administrator               │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │/usr/lib/systemd/user                   │ User units installed by the │
       │                                        │ distribution package        │
       │                                        │ manager                     │
       ├────────────────────────────────────────┼─────────────────────────────┤
       │$XDG_RUNTIME_DIR/systemd/generator.late │ Generated units with low    │
       │                                        │ priority (see late-dir in   │
       │                                        │ systemd.generator(7))       │
       └────────────────────────────────────────┴─────────────────────────────┘

       The set of load paths for the user manager instance may be augmented or
       changed using various environment variables. And environment variables
       may in turn be set using environment generators, see systemd.environment-
       generator(7). In particular, $XDG_DATA_HOME and $XDG_DATA_DIRS may be
       easily set using systemd-environment-d-generator(8). Thus, directories
       listed here are just the defaults. To see the actual list that would be
       used based on compilation options and current environment use

           systemd-analyze --user unit-paths

       Moreover, additional units might be loaded into systemd from directories
       not on the unit load path by creating a symlink pointing to a unit file
       in the directories. You can use systemctl link for this operation. See
       systemctl(1) for its usage and precaution.

UNIT GARBAGE COLLECTION
       The system and service manager loads a unit's configuration automatically
       when a unit is referenced for the first time. It will automatically
       unload the unit configuration and state again when the unit is not needed
       anymore ("garbage collection"). A unit may be referenced through a number
       of different mechanisms:

        1. Another loaded unit references it with a dependency such as After=,
           Wants=, ...

        2. The unit is currently starting, running, reloading or stopping.

        3. The unit is currently in the failed state. (But see below.)

        4. A job for the unit is pending.

        5. The unit is pinned by an active IPC client program.

        6. The unit is a special "perpetual" unit that is always active and
           loaded. Examples for perpetual units are the root mount unit -.mount
           or the scope unit init.scope that the service manager itself lives
           in.

        7. The unit has running processes associated with it.

       The garbage collection logic may be altered with the CollectMode= option,
       which allows configuration whether automatic unloading of units that are
       in failed state is permissible, see below.

       Note that when a unit's configuration and state is unloaded, all
       execution results, such as exit codes, exit signals, resource consumption
       and other statistics are lost, except for what is stored in the log
       subsystem.

       Use systemctl daemon-reload or an equivalent command to reload unit
       configuration while the unit is already loaded. In this case all
       configuration settings are flushed out and replaced with the new
       configuration (which however might not be in effect immediately), however
       all runtime state is saved/restored.

[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 human readable name for the unit. This is used by systemd (and
           other UIs) as the label for the unit, so this string should identify
           the unit rather than describe it, despite the name.  "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).  systemd will use
           this string as a noun in status messages ("Starting description...",
           "Started description.", "Reached target description.", "Failed to
           start description."), so it should be capitalized, and should not be
           a full sentence or a phrase with a continuous verb. Bad examples
           include "exiting the container" or "updating the database once per
           day.".

       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.

       Wants=
           Configures requirement dependencies on other units. This option may
           be specified more than once or multiple space-separated units may be
           specified in one option in which case dependencies for all listed
           names will be created. Dependencies of this type may also be
           configured outside of the unit configuration file by adding a symlink
           to a .wants/ directory accompanying the unit file. For details, see
           above.

           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, and this unit will still be started. This is
           the recommended way to hook the start-up of one unit to the start-up
           of another unit.

           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 unit foo.service
           pulls in unit bar.service as configured with Wants= 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.

       Requires=
           Similar to Wants=, but declares a stronger dependency. Dependencies
           of this type may also be configured by adding a symlink to a
           .requires/ directory accompanying the unit file.

           If this unit gets activated, the units listed will be activated as
           well. If one of the other units fails to activate, and an ordering
           dependency After= on the failing unit is set, this unit will not be
           started. Besides, with or without specifying After=, this unit will
           be stopped if one of the other units is explicitly stopped.

           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 this dependency type does not imply that the other unit
           always has to be in active state when this unit is running.
           Specifically: failing condition checks (such as ConditionPathExists=,
           ConditionPathIsSymbolicLink=, ... — see below) do not cause the start
           job of a unit with a Requires= dependency on it to fail. Also, some
           unit types may deactivate on their own (for example, a service
           process may decide to exit cleanly, or a device may be unplugged by
           the user), which is not propagated to units having a Requires=
           dependency. Use the BindsTo= dependency type together with After= to
           ensure that a unit may never be in active state without a specific
           other unit also in active state (see below).

       Requisite=
           Similar to Requires=. However, if the units listed here are not
           started already, they will not be started and the starting of this
           unit will fail immediately.  Requisite= does not imply an ordering
           dependency, even if both units are started in the same transaction.
           Hence this setting should usually be combined with After=, to ensure
           this unit is not started before the other unit.

           When Requisite=b.service is used on a.service, this dependency will
           show as RequisiteOf=a.service in property listing of b.service.
           RequisiteOf= dependency cannot be specified directly.

       BindsTo=
           Configures requirement dependencies, very similar in style to
           Requires=. However, this dependency type is stronger: in addition to
           the effect of Requires= it declares that if the unit bound to is
           stopped, this unit will be stopped too. This means a unit bound to
           another unit that suddenly enters inactive state will be stopped too.
           Units can suddenly, unexpectedly enter inactive state for different
           reasons: the main process of a service unit might terminate on its
           own choice, the backing device of a device unit might be unplugged or
           the mount point of a mount unit might be unmounted without
           involvement of the system and service manager.

           When used in conjunction with After= on the same unit the behaviour
           of BindsTo= is even stronger. In this case, the unit bound to
           strictly has to be in active state for this unit to also be in active
           state. This not only means a unit bound to another unit that suddenly
           enters inactive state, but also one that is bound to another unit
           that gets skipped due to a failed condition check (such as
           ConditionPathExists=, ConditionPathIsSymbolicLink=, ... — see below)
           will be stopped, should it be running. Hence, in many cases it is
           best to combine BindsTo= with After=.

           When BindsTo=b.service is used on a.service, this dependency will
           show as BoundBy=a.service in property listing of b.service.  BoundBy=
           dependency cannot be specified directly.

       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.

           When PartOf=b.service is used on a.service, this dependency will show
           as ConsistsOf=a.service in property listing of b.service.
           ConsistsOf= dependency cannot be specified directly.

       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 does not imply an ordering dependency,
           similarly to the Wants= and Requires= dependencies described above.
           This means that to ensure that the conflicting unit is stopped before
           the other unit is started, an After= or Before= dependency must be
           declared. It doesn't matter which of the two ordering dependencies is
           used, because stop jobs are always ordered before start jobs, see the
           discussion in Before=/After= below.

           If unit A that conflicts with unit B is scheduled to be started at
           the same time as B, the transaction will either fail (in case both
           are required parts 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 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=
           These two settings expect a space-separated list of unit names. They
           may be specified more than once, in which case dependencies for all
           listed names are created.

           Those two settings configure ordering dependencies between units. If
           unit foo.service contains the setting Before=bar.service and both
           units are being started, bar.service's start-up is delayed until
           foo.service has finished starting up.  After= is the inverse of
           Before=, i.e. while Before= ensures that the configured unit is
           started before the listed unit begins starting up, After= ensures the
           opposite, that the listed unit is fully started up before the
           configured unit is started.

           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. Given two units with any ordering
           dependency between them, if one unit is shut down and the other is
           started up, the shutdown is ordered before the start-up. It doesn't
           matter if the ordering dependency is After= or Before=, in this case.
           It also doesn't matter which of the two is shut down, as long as one
           is shut down and the other is started up; the shutdown is ordered
           before the start-up in all cases. If two units have no ordering
           dependencies between them, they are shut down or started up
           simultaneously, and no ordering takes place. It depends on the unit
           type when precisely a unit has finished starting up. Most
           importantly, for service units start-up is considered completed for
           the purpose of Before=/After= when all its configured start-up
           commands have been invoked and they either failed or reported
           start-up success. Note that this does includes ExecStartPost= (or
           ExecStopPost= for the shutdown case).

           Note that those settings are independent of and orthogonal to the
           requirement dependencies as configured by Requires=, Wants=,
           Requisite=, or BindsTo=. It is a common pattern to include a unit
           name in both the After= and Wants= options, in which case the unit
           listed will be started before the unit that is configured with these
           options.

           Note that Before= dependencies on device units have no effect and are
           not supported. Devices generally become available as a result of an
           external hotplug event, and systemd creates the corresponding device
           unit without delay.

       OnFailure=
           A space-separated list of one or more units that are activated when
           this unit enters the "failed" state. A service unit using Restart=
           enters the failed state only after the start limits are reached.

       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=, NetworkNamespacePath= 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, /var/tmp 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=/NetworkNamespacePath= 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 through
           local-fs.target, but are still honored for the purposes of this
           option, i.e. they will be pulled in by this unit.

       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 for service, target,
           socket, timer, and path units, and true for slice, scope, device,
           swap, mount, and automount units.

       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 yes, (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 no. It is highly recommended to
           leave this option enabled for the majority of common units. If set to
           no, this option does not disable all implicit dependencies, just
           non-essential ones.

       CollectMode=
           Tweaks the "garbage collection" algorithm for this unit. Takes one of
           inactive or inactive-or-failed. If set to inactive the unit will be
           unloaded if it is in the inactive state and is not referenced by
           clients, jobs or other units — however it is not unloaded if it is in
           the failed state. In failed mode, failed units are not unloaded until
           the user invoked systemctl reset-failed on them to reset the failed
           state, or an equivalent command. This behaviour is altered if this
           option is set to inactive-or-failed: in this case the unit is
           unloaded even if the unit is in a failed state, and thus an
           explicitly resetting of the failed state is not necessary. Note that
           if this mode is used unit results (such as exit codes, exit signals,
           consumed resources, ...) are flushed out immediately after the unit
           completed, except for what is stored in the logging subsystem.
           Defaults to inactive.

       FailureAction=, SuccessAction=
           Configure the action to take when the unit stops and enters a failed
           state or inactive state. Takes one of none, reboot, reboot-force,
           reboot-immediate, poweroff, poweroff-force, poweroff-immediate, exit,
           and exit-force. In system mode, all options are allowed. In user
           mode, only none, exit, and exit-force are allowed. Both options
           default to none.

           If none is set, no action will be triggered.  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 (i.e. equivalent to systemctl reboot -ff).
           Similarly, poweroff, poweroff-force, poweroff-immediate have the
           effect of powering down the system with similar semantics.  exit
           causes the manager to exit following the normal shutdown procedure,
           and exit-force causes it terminate without shutting down services.
           When exit or exit-force is used by default the exit status of the
           main process of the unit (if this applies) is returned from the
           service manager. However, this may be overridden with
           FailureActionExitStatus=/SuccessActionExitStatus=, see below.

       FailureActionExitStatus=, SuccessActionExitStatus=
           Controls the exit status to propagate back to an invoking container
           manager (in case of a system service) or service manager (in case of
           a user manager) when the FailureAction=/SuccessAction= are set to
           exit or exit-force and the action is triggered. By default the exit
           status of the main process of the triggering unit (if this applies)
           is propagated. Takes a value in the range 0...255 or the empty string
           to request default behaviour.

       JobTimeoutSec=, JobRunningTimeoutSec=
           When a job for this unit is queued, a timeout JobTimeoutSec= may be
           configured. Similarly, JobRunningTimeoutSec= starts counting when the
           queued job is actually started. If either 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 (JobRunningTimeoutSec=
           defaults to DefaultTimeoutStartSec=). 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=, JobTimeoutRebootArgument=
           JobTimeoutAction= optionally configures an additional action to take
           when the timeout is hit, see description of JobTimeoutSec= and
           JobRunningTimeoutSec= above. It takes the same values as
           StartLimitAction=. Defaults to none.  JobTimeoutRebootArgument=
           configures an optional reboot string to pass to the reboot(2) system
           call.

       StartLimitIntervalSec=interval, StartLimitBurst=burst
           Configure unit start rate limiting. Units which are started more than
           burst times within an interval time interval are not permitted to
           start any more. Use StartLimitIntervalSec= to configure the checking
           interval (defaults to DefaultStartLimitIntervalSec= in manager
           configuration file, set it 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, after the interval
           has passed. From this point on, the restart logic is activated again.
           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 do not count towards this rate limit. This setting
           does not apply to slice, target, device, and scope units, since they
           are unit types whose activation may either never fail, or may succeed
           only a single time.

           When a unit is unloaded due to the garbage collection logic (see
           above) its rate limit counters are flushed out too. This means that
           configuring start rate limiting for a unit that is not referenced
           continuously has no effect.

       StartLimitAction=
           Configure an additional action to take if the rate limit configured
           with StartLimitIntervalSec= and StartLimitBurst= is hit. Takes the
           same values as the FailureAction=/SuccessAction= settings. If none is
           set, hitting the rate limit will trigger no action except that the
           start will not be permitted. Defaults to none.

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

       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.

   Conditions and Asserts
       Unit files may also include a number of Condition...= and Assert...=
       settings. Before the unit is started, systemd will verify that the
       specified conditions are true. If not, the starting of the unit will be
       (mostly silently) skipped. Failing conditions will not result in the unit
       being moved into the "failed" state. The conditions are checked at the
       time the queued start job is to be executed. The ordering dependencies
       are still respected, so other units are still pulled in and ordered as if
       this unit was successfully activated. Use condition expressions in order
       to skip units that do not apply to the local system, for example because
       the kernel or runtime environment doesn't require their functionality.

       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 use a
       pipe symbol ("|") after the equals sign ("Condition...=|..."), which
       causes the 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. 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.

       The AssertArchitecture=, AssertVirtualization=, ... options provide a
       similar mechanism that causes the job to fail (instead of being skipped).
       The failed check is logged. Units with failed conditions are considered
       to be in a clean state and will be garbage collected if they are not
       referenced. This means that when queried, the condition failure may or
       may not show up in the state of the unit.

       Note that neither assertion nor condition expressions result in unit
       state changes. Also note that both are checked at the time the job is to
       be executed, i.e. long after depending jobs and it itself were queued.
       Thus, neither condition nor assertion expressions are suitable for
       conditionalizing unit dependencies.

       The condition verb of systemd-analyze(1) can be used to test condition
       and assert expressions.

       Except for ConditionPathIsSymbolicLink=, all path checks follow symlinks.

       ConditionArchitecture=
           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", "m68k", "tilegx", "cris", "arc", "arc-be",
           or "native".

           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=
           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", "bhyve",
           "qnx", "openvz", "lxc", "lxc-libvirt", "systemd-nspawn", "docker",
           "podman", "rkt", "wsl", "proot", "acrn" to test against a specific
           implementation, or "private-users" to check whether we are running in
           a user namespace. 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=
           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=
           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 by "="). 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.

       ConditionKernelVersion=
           ConditionKernelVersion= may be used to check whether the kernel
           version (as reported by uname -r) matches a certain expression (or if
           prefixed with the exclamation mark does not match it). The argument
           must be a list of (potentially quoted) expressions. For each of the
           expressions, if it starts with one of "<", "<=", "=", "!=", ">=", ">"
           a relative version comparison is done, otherwise the specified string
           is matched with shell-style globs.

           Note that using the kernel version string is an unreliable way to
           determine which features are supported by a kernel, because of the
           widespread practice of backporting drivers, features, and fixes from
           newer upstream kernels into older versions provided by distributions.
           Hence, this check is inherently unportable and should not be used for
           units which may be used on different distributions.

       ConditionEnvironment=
           ConditionEnvironment= may be used to check whether a specific
           environment variable is set (or if prefixed with the exclamation mark
           — unset) in the service manager's environment block. The argument may
           be a single word, to check if the variable with this name is defined
           in the environment block, or an assignment ("name=value"), to check
           if the variable with this exact value is defined. Note that the
           environment block of the service manager itself is checked, i.e. not
           any variables defined with Environment= or EnvironmentFile=, as
           described above. This is particularly useful when the service manager
           runs inside a containerized environment or as per-user service
           manager, in order to check for variables passed in by the enclosing
           container manager or PAM.

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

       ConditionCapability=
           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=
           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 "!"
           (to invert 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.

           If the systemd.condition-needs-update= option is specified on the
           kernel command line (taking a boolean), it will override the result
           of this condition check, taking precedence over any file modification
           time checks. If it is used systemd-update-done.service will not have
           immediate effect on any following ConditionNeedsUpdate= checks, until
           the system is rebooted where the kernel command line option is not
           specified anymore.

       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 (specifically: an /etc with no
           /etc/machine-id). This may be used to populate /etc on the first boot
           after factory reset, or when a new system instance boots up for the
           first time.

           If the systemd.condition-first-boot= option is specified on the
           kernel command line (taking a boolean), it will override the result
           of this condition check, taking precedence over /etc/machine-id
           existence checks.

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

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

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

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

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

       ConditionPathIsEncrypted=
           ConditionPathIsEncrypted= is similar to ConditionPathExists= but
           verifies that the underlying file system's backing block device is
           encrypted using dm-crypt/LUKS. Note that this check does not cover
           ext4 per-directory encryption, and only detects block level
           encryption. Moreover, if the specified path resides on a file system
           on top of a loopback block device, only encryption above the loopback
           device is detected. It is not detected whether the file system
           backing the loopback block device is encrypted.

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

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

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

       ConditionUser=
           ConditionUser= takes a numeric "UID", a UNIX user name, or the
           special value "@system". This condition may be used to check whether
           the service manager is running as the given user. The special value
           "@system" can be used to check if the user id is within the system
           user range. This option is not useful for system services, as the
           system manager exclusively runs as the root user, and thus the test
           result is constant.

       ConditionGroup=
           ConditionGroup= is similar to ConditionUser= but verifies that the
           service manager's real or effective group, or any of its auxiliary
           groups, match the specified group or GID. This setting does not
           support the special value "@system".

       ConditionControlGroupController=
           Verify that the given cgroup controller (eg.  "cpu") is available for
           use on the system. For example, a particular controller may not be
           available if it was disabled on the kernel command line with
           cgroup_disable=controller. Multiple controllers may be passed with a
           space separating them; in this case the condition will only pass if
           all listed controllers are available for use. Controllers unknown to
           systemd are ignored. Valid controllers are "cpu", "cpuacct", "io",
           "blkio", "memory", "devices", and "pids".

       ConditionMemory=
           Verify that the specified amount of system memory is available to the
           current system. Takes a memory size in bytes as argument, optionally
           prefixed with a comparison operator "<", "<=", "=", "!=", ">=", ">".
           On bare-metal systems compares the amount of physical memory in the
           system with the specified size, adhering to the specified comparison
           operator. In containers compares the amount of memory assigned to the
           container instead.

       ConditionCPUs=
           Verify that the specified number of CPUs is available to the current
           system. Takes a number of CPUs as argument, optionally prefixed with
           a comparison operator "<", "<=", "=", "!=", ">=", ">". Compares the
           number of CPUs in the CPU affinity mask configured of the service
           manager itself with the specified number, adhering to the specified
           comparison operator. On physical systems the number of CPUs in the
           affinity mask of the service manager usually matches the number of
           physical CPUs, but in special and virtual environments might differ.
           In particular, in containers the affinity mask usually matches the
           number of CPUs assigned to the container and not the physically
           available ones.

       AssertArchitecture=, AssertVirtualization=, AssertHost=,
       AssertKernelCommandLine=, AssertKernelVersion=, AssertSecurity=,
       AssertCapability=, AssertACPower=, AssertNeedsUpdate=, AssertFirstBoot=,
       AssertPathExists=, AssertPathExistsGlob=, AssertPathIsDirectory=,
       AssertPathIsSymbolicLink=, AssertPathIsMountPoint=,
       AssertPathIsReadWrite=, AssertDirectoryNotEmpty=, AssertFileNotEmpty=,
       AssertFileIsExecutable=, AssertUser=, AssertGroup=,
       AssertControlGroupController=
           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). Note that hitting
           a configured assertion does not cause the unit to enter the "failed"
           state (or in fact result in any state change of the unit), it affects
           only the job queued for it. 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.

MAPPING OF UNIT PROPERTIES TO THEIR INVERSES
       Unit settings that create a relationship with a second unit usually show
       up in properties of both units, for example in systemctl show output. In
       some cases the name of the property is the same as the name of the
       configuration setting, but not always. This table lists the properties
       that are shown on two units which are connected through some dependency,
       and shows which property on "source" unit corresponds to which property
       on the "target" unit.

       Table 3.  Forward and reverse unit properties
       ┌──────────────────────┬───────────────────────┬─────────────────────────────────┐
       │"Forward"             "Reverse"             Where used                      │
       │property              property              │                                 │
       ├──────────────────────┼───────────────────────┼─────────────────────────────────┤
       │Before=               After=                │                                 │
       ├──────────────────────┼───────────────────────┤ [Unit] section                  │
       │After=                Before=               │                                 │
       ├──────────────────────┼───────────────────────┼─────────────────┬───────────────┤
       │Requires=             RequiredBy=           │ [Unit] section  │ [Install]     │
       │                      │                       │                 │ section       │
       ├──────────────────────┼───────────────────────┼─────────────────┼───────────────┤
       │Wants=                WantedBy=             │ [Unit] section  │ [Install]     │
       │                      │                       │                 │ section       │
       ├──────────────────────┼───────────────────────┼─────────────────┼───────────────┤
       │PartOf=               ConsistsOf=           │ [Unit] section  │ an automatic  │
       │                      │                       │                 │ property      │
       ├──────────────────────┼───────────────────────┼─────────────────┼───────────────┤
       │BindsTo=              BoundBy=              │ [Unit] section  │ an automatic  │
       │                      │                       │                 │ property      │
       ├──────────────────────┼───────────────────────┼─────────────────┼───────────────┤
       │Requisite=            RequisiteOf=          │ [Unit] section  │ an automatic  │
       │                      │                       │                 │ property      │
       ├──────────────────────┼───────────────────────┼─────────────────┴───────────────┤
       │Triggers=             TriggeredBy=          │ Automatic properties, see notes │
       │                      │                       │ below                           │
       ├──────────────────────┼───────────────────────┼─────────────────┬───────────────┤
       │Conflicts=            ConflictedBy=         │ [Unit] section  │ an automatic  │
       │                      │                       │                 │ property      │
       ├──────────────────────┼───────────────────────┼─────────────────┴───────────────┤
       │PropagatesReloadTo=   ReloadPropagatedFrom= │                                 │
       ├──────────────────────┼───────────────────────┤ [Unit] section                  │
       │ReloadPropagatedFrom= PropagatesReloadTo=   │                                 │
       ├──────────────────────┼───────────────────────┼─────────────────┬───────────────┤
       │Following=            │ n/a                   │ An automatic    │               │
       │                      │                       │ property        │               │
       └──────────────────────┴───────────────────────┴─────────────────┴───────────────┘

       Note: WantedBy= and RequiredBy= are used in the [Install] section to
       create symlinks in .wants/ and .requires/ directories. They cannot be
       used directly as a unit configuration setting.

       Note: ConsistsOf=, BoundBy=, RequisiteOf=, ConflictedBy= are created
       implicitly along with their reverses and cannot be specified directly.

       Note: Triggers= is created implicitly between a socket, path unit, or an
       automount unit, and the unit they activate. By default a unit with the
       same name is triggered, but this can be overridden using Sockets=,
       Service=, and Unit= settings. See systemd.service(5), systemd.socket(5),
       systemd.path(5), and systemd.automount(5) for details.  TriggeredBy= is
       created implicitly on the triggered unit.

       Note: Following= is used to group device aliases and points to the
       "primary" device unit that systemd is using to track device state,
       usually corresponding to a sysfs path. It does not show up in the
       "target" unit.

[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.

       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 filename. 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. Note that not all unit types support such alias names,
           and this setting is not supported for them. Specifically, mount,
           slice, swap, and automount units do not support aliasing.

       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
           getty@.service will result in systemctl enable getty@tty2.service
           creating a getty.target.wants/getty@tty2.service link to
           getty@.service.

       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, %j, %g, %G, %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. Specifiers must be known and resolvable for the
       setting to be valid. The following specifiers are understood:

       Table 4. Specifiers available in unit files
       ┌──────────┬──────────────────────┬────────────────────────┐
       │Specifier Meaning              Details                │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%a"      │ Architecture         │ A short string         │
       │          │                      │ identifying the        │
       │          │                      │ architecture of the    │
       │          │                      │ local system. A        │
       │          │                      │ string such as x86,    │
       │          │                      │ x86-64 or arm64. See   │
       │          │                      │ the architectures      │
       │          │                      │ defined for            │
       │          │                      │ ConditionArchitecture= │
       │          │                      │ above for a full       │
       │          │                      │ list.                  │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%b"      │ Boot ID              │ The boot ID of the     │
       │          │                      │ running system,        │
       │          │                      │ formatted as string.   │
       │          │                      │ See random(4) for more │
       │          │                      │ information.           │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%B"      │ Operating system     │ The operating system   │
       │          │ build ID             │ build identifier of    │
       │          │                      │ the running system, as │
       │          │                      │ read from the          │
       │          │                      │ BUILD_ID= field of     │
       │          │                      │ /etc/os-release. If    │
       │          │                      │ not set, resolves to   │
       │          │                      │ an empty string. See   │
       │          │                      │ os-release(5) for more │
       │          │                      │ information.           │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%C"      │ Cache directory root │ This is either         │
       │          │                      │ /var/cache (for the    │
       │          │                      │ system manager) or the │
       │          │                      │ path "$XDG_CACHE_HOME" │
       │          │                      │ resolves to (for user  │
       │          │                      │ managers).             │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%E"      │ Configuration        │ This is either /etc    │
       │          │ directory root       │ (for the system        │
       │          │                      │ manager) or the path   │
       │          │                      │ "$XDG_CONFIG_HOME"     │
       │          │                      │ resolves to (for user  │
       │          │                      │ managers).             │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%f"      │ Unescaped filename   │ This is either the     │
       │          │                      │ unescaped instance     │
       │          │                      │ name (if applicable)   │
       │          │                      │ with / prepended (if   │
       │          │                      │ applicable), or the    │
       │          │                      │ unescaped prefix name  │
       │          │                      │ prepended with /. This │
       │          │                      │ implements unescaping  │
       │          │                      │ according to the rules │
       │          │                      │ for escaping absolute  │
       │          │                      │ file system paths      │
       │          │                      │ discussed above.       │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%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".            │
       │          │                      │                        │
       │          │                      │ Note that this setting │
       │          │                      │ is not influenced by   │
       │          │                      │ the User= setting      │
       │          │                      │ configurable in the    │
       │          │                      │ [Service] section of   │
       │          │                      │ the service unit.      │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%H"      │ Host name            │ The hostname of the    │
       │          │                      │ running system at the  │
       │          │                      │ point in time the unit │
       │          │                      │ configuration is       │
       │          │                      │ loaded.                │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%l"      │ Short host name      │ The hostname of the    │
       │          │                      │ running system at the  │
       │          │                      │ point in time the unit │
       │          │                      │ configuration is       │
       │          │                      │ loaded, truncated at   │
       │          │                      │ the first dot to       │
       │          │                      │ remove any domain      │
       │          │                      │ component.             │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%i"      │ Instance name        │ For instantiated units │
       │          │                      │ this is the string     │
       │          │                      │ between the first "@"  │
       │          │                      │ character and the type │
       │          │                      │ suffix. Empty for      │
       │          │                      │ non-instantiated       │
       │          │                      │ units.                 │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%I"      │ Unescaped instance   │ Same as "%i", but with │
       │          │ name                 │ escaping undone.       │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%j"      │ Final component of   │ This is the string     │
       │          │ the prefix           │ between the last "-"   │
       │          │                      │ and the end of the     │
       │          │                      │ prefix name. If there  │
       │          │                      │ is no "-", this is the │
       │          │                      │ same as "%p".          │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%J"      │ Unescaped final      │ Same as "%j", but with │
       │          │ component of the     │ escaping undone.       │
       │          │ prefix               │                        │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%L"      │ Log directory root   │ This is either         │
       │          │                      │ /var/log (for the      │
       │          │                      │ system manager) or the │
       │          │                      │ path                   │
       │          │                      │ "$XDG_CONFIG_HOME"     │
       │          │                      │ resolves to with /log  │
       │          │                      │ appended (for user     │
       │          │                      │ managers).             │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%m"      │ Machine ID           │ The machine ID of the  │
       │          │                      │ running system,        │
       │          │                      │ formatted as string.   │
       │          │                      │ See machine-id(5) for  │
       │          │                      │ more information.      │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%o"      │ Operating system ID  │ The operating system   │
       │          │                      │ identifier of the      │
       │          │                      │ running system, as     │
       │          │                      │ read from the ID=      │
       │          │                      │ field of               │
       │          │                      │ /etc/os-release. See   │
       │          │                      │ os-release(5) for more │
       │          │                      │ information.           │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%n"      │ Full unit name       │                        │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%N"      │ Full unit name       │ Same as "%n", but with │
       │          │                      │ the type suffix        │
       │          │                      │ removed.               │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%p"      │ Prefix name          │ For instantiated       │
       │          │                      │ units, this refers to  │
       │          │                      │ the string before the  │
       │          │                      │ first "@" character of │
       │          │                      │ the unit name. For     │
       │          │                      │ non-instantiated       │
       │          │                      │ units, same as "%N".   │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%P"      │ Unescaped prefix     │ Same as "%p", but with │
       │          │ name                 │ escaping undone.       │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%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".             │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%S"      │ State directory root │ This is either         │
       │          │                      │ /var/lib (for the      │
       │          │                      │ system manager) or the │
       │          │                      │ path                   │
       │          │                      │ "$XDG_CONFIG_HOME"     │
       │          │                      │ resolves to (for user  │
       │          │                      │ managers).             │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%t"      │ Runtime directory    │ This is either /run    │
       │          │ root                 │ (for the system        │
       │          │                      │ manager) or the path   │
       │          │                      │ "$XDG_RUNTIME_DIR"     │
       │          │                      │ resolves to (for user  │
       │          │                      │ managers).             │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%T"      │ Directory for        │ This is either /tmp or │
       │          │ temporary files      │ the path "$TMPDIR",    │
       │          │                      │ "$TEMP" or "$TMP" are  │
       │          │                      │ set to.                │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%g"      │ User group           │ This is the name of    │
       │          │                      │ the group running the  │
       │          │                      │ service manager        │
       │          │                      │ instance. In case of   │
       │          │                      │ the system manager     │
       │          │                      │ this resolves to       │
       │          │                      │ "root".                │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%G"      │ User GID             │ This is the numeric    │
       │          │                      │ GID of the user        │
       │          │                      │ running the service    │
       │          │                      │ manager instance. In   │
       │          │                      │ case of the system     │
       │          │                      │ manager this resolves  │
       │          │                      │ to "0".                │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%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".                │
       │          │                      │                        │
       │          │                      │ Note that this setting │
       │          │                      │ is not influenced by   │
       │          │                      │ the User= setting      │
       │          │                      │ configurable in the    │
       │          │                      │ [Service] section of   │
       │          │                      │ the service unit.      │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%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".                │
       │          │                      │                        │
       │          │                      │ Note that this setting │
       │          │                      │ is not influenced by   │
       │          │                      │ the User= setting      │
       │          │                      │ configurable in the    │
       │          │                      │ [Service] section of   │
       │          │                      │ the service unit.      │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%v"      │ Kernel release       │ Identical to uname -r  │
       │          │                      │ output.                │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%V"      │ Directory for larger │ This is either         │
       │          │ and persistent       │ /var/tmp or the path   │
       │          │ temporary files      │ "$TMPDIR", "$TEMP" or  │
       │          │                      │ "$TMP" are set to.     │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%w"      │ Operating system     │ The operating system   │
       │          │ version ID           │ version identifier of  │
       │          │                      │ the running system, as │
       │          │                      │ read from the          │
       │          │                      │ VERSION_ID= field of   │
       │          │                      │ /etc/os-release. If    │
       │          │                      │ not set, resolves to   │
       │          │                      │ an empty string. See   │
       │          │                      │ os-release(5) for more │
       │          │                      │ information.           │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%W"      │ Operating system     │ The operating system   │
       │          │ variant ID           │ variant identifier of  │
       │          │                      │ the running system, as │
       │          │                      │ read from the          │
       │          │                      │ VARIANT_ID= field of   │
       │          │                      │ /etc/os-release. If    │
       │          │                      │ not set, resolves to   │
       │          │                      │ an empty string. See   │
       │          │                      │ os-release(5) for more │
       │          │                      │ information.           │
       ├──────────┼──────────────────────┼────────────────────────┤
       │"%%"      │ Single percent sign  │ Use "%%" in place of   │
       │          │                      │ "%" to specify a       │
       │          │                      │ single percent sign.   │
       └──────────┴──────────────────────┴────────────────────────┘

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 /usr/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,
       processed in lexicographic order of their filename.

       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.

       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
       /usr/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.exec(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 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
       AssertPathExists= (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. 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-system.conf(5), 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. Interface Stability Promise
           https://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise



systemd 246                                                      SYSTEMD.UNIT(5)