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/system.attached/*
       /run/systemd/system/*
       /run/systemd/system.attached/*
       /run/systemd/generator/*
       ...
       /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/*
       $XDG_CONFIG_DIRS/systemd/user/*
       /etc/systemd/user/*
       $XDG_RUNTIME_DIR/systemd/user/*
       /run/systemd/user/*
       $XDG_RUNTIME_DIR/systemd/generator/*
       $XDG_DATA_HOME/systemd/user/*
       $XDG_DATA_DIRS/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. To access those options,
       applications need to parse the unit files on their own.

       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 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 rules preserve the
       requirement that the instance (if any) is always uniquely defined for a given unit and all
       its aliases. The target of alias symlink must point to a valid unit file location, i.e.
       the symlink target name must match the symlink source name as described, and the
       destination path must be in one of the unit search paths, see UNIT FILE LOAD PATH section
       below for more details. Note that the target file may not exist, i.e. the symlink may be
       dangling.

       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/system/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= and Requires=, see below. The preferred way to create
       symlinks in the .wants/ or .requires/ directories is by specifying 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). The target can be a normal unit (either plain
       or a specific instance of a template unit). In case when the source unit is a template,
       the target can also be a template, in which case the instance will be "propagated" to the
       target unit to form a valid unit instance. The target of symlinks in .wants/ or .requires/
       must thus point to a valid unit file location, i.e. the symlink target name must satisfy
       the described requirements, and the destination path must be in one of the unit search
       paths, see UNIT FILE LOAD PATH section below for more details. Note that the target file
       may not exist, i.e. the symlink may be dangling.

       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 merged in the alphanumeric order
       and parsed after the main unit file itself has been parsed. This is useful to alter or add
       configuration settings for a unit, without having to modify unit files. Each drop-in file
       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 unit names containing dashes ("-"), the set of
       directories generated by repeatedly 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 /lib/systemd/system or /run/systemd/system directories. Drop-in files in
       /etc/ take precedence over those in /run/ which in turn take precedence over those in
       /lib/. Drop-in files under any of these directories take precedence over unit files
       wherever located. 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. Files in type.d/ have lower precedence compared to files in
       name-specific override directories. The usual rules apply: multiple drop-in files with
       different names are applied in lexicographic order, regardless of which of the directories
       they reside in, so a file in type.d/ applies to a unit only if there are no drop-ins or
       masks with that name in directories with higher precedence. See Examples.

       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 Portability and 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=. See systemd.target(5) for details. Note that
       this behavior can be opted out by setting DefaultDependencies=no in the specified units,
       or it can be selectively overridden via an explicit Before= dependency.

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 the │
       │/run/systemd/system.control   │ 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                   │
       ├──────────────────────────────┼─────────────────────────────────┤
       │/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                      │
       ├─────────────────────────────────────────┼──────────────────────────────────┤
       │$XDG_CONFIG_HOME/systemd/user.control    │ Persistent and transient         │
       │or                                       │ configuration created using the  │
       │~/.config/systemd/user.control           │ dbus API ($XDG_CONFIG_HOME is    │
       ├─────────────────────────────────────────┤ used if set, ~/.config           │
       │$XDG_RUNTIME_DIR/systemd/user.control    │ otherwise)                       │
       ├─────────────────────────────────────────┼──────────────────────────────────┤
       │$XDG_RUNTIME_DIR/systemd/transient       │ Dynamic configuration for        │
       │                                         │ transient units                  │
       ├─────────────────────────────────────────┼──────────────────────────────────┤
       │$XDG_RUNTIME_DIR/systemd/generator.early │ Generated units with high        │
       │                                         │ priority (see early-dir in       │
       │                                         │ systemd.generator(7))            │
       ├─────────────────────────────────────────┼──────────────────────────────────┤
       │$XDG_CONFIG_HOME/systemd/user or         │ User configuration               │
       │$HOME/.config/systemd/user               │ ($XDG_CONFIG_HOME is used if     │
       │                                         │ set, ~/.config otherwise)        │
       ├─────────────────────────────────────────┼──────────────────────────────────┤
       │$XDG_CONFIG_DIRS/systemd/user or         │ Additional configuration         │
       │/etc/xdg/systemd/user                    │ directories as specified by the  │
       │                                         │ XDG base directory specification │
       │                                         │ ($XDG_CONFIG_DIRS is used if     │
       │                                         │ set, /etc/xdg 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))            │
       ├─────────────────────────────────────────┼──────────────────────────────────┤
       │$XDG_DATA_HOME/systemd/user or           │ Units of packages that have been │
       │$HOME/.local/share/systemd/user          │ installed in the home directory  │
       │                                         │ ($XDG_DATA_HOME is used if set,  │
       │                                         │ ~/.local/share otherwise)        │
       ├─────────────────────────────────────────┼──────────────────────────────────┤
       │$XDG_DATA_DIRS/systemd/user or           │ Additional data directories as   │
       │/usr/local/share/systemd/user and        │ specified by the XDG base        │
       │/usr/share/systemd/user                  │ directory specification          │
       │                                         │ ($XDG_DATA_DIRS is used if set,  │
       │                                         │ /usr/local/share and /usr/share  │
       │                                         │ otherwise)                       │
       ├─────────────────────────────────────────┼──────────────────────────────────┤
       │$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; see systemctl(1). The file system where the linked unit files are
       located must be accessible when systemd is started (e.g. anything underneath /home/ or
       /var/ is not allowed, unless those directories are located on the root file system).

       It is important to distinguish "linked unit files" from "unit file aliases": any symlink
       where the symlink target is within the unit load path becomes an alias: the source name
       and the target file name must satisfy specific constraints listed above in the discussion
       of aliases, but the symlink target doesn't have to exist, and in fact the symlink target
       path is not used, except to check whether the target is within the unit load path. In
       contrast, a symlink which goes outside of the unit load path signifies a linked unit file.
       The symlink is followed when loading the file, but the destination name is otherwise
       unused (and may even not be a valid unit file name). For example, symlinks
       /etc/systemd/system/alias1.service → service1.service, /etc/systemd/system/alias2.service
       → /usr/lib/systemd/service1.service, /etc/systemd/system/alias3.service →
       /etc/systemd/system/service1.service are all valid aliases and service1.service will have
       four names, even if the unit file is located at /run/systemd/system/service1.service. In
       contrast, a symlink /etc/systemd/system/link1.service → ../link1_service_file means that
       link1.service is a "linked unit" and the contents of /etc/systemd/link1_service_file
       provide its configuration.

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 short human readable title of the unit. This may be used by systemd (and other UIs)
           as a user-visible label for the unit, so this string should identify the unit rather
           than describe it, despite the name. This string also shouldn't just repeat the unit
           name.  "Apache2 Web Server" is a good example. Bad examples are "high-performance
           light-weight HTTP server" (too generic) or "Apache2" (meaningless for people who do
           not know Apache, duplicates the unit name).  systemd may 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 (weak) 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 requirement 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 (or restarted) if one of the other units is explicitly
           stopped (or restarted).

           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 an unmet 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.

       Upholds=
           Configures dependencies similar to Wants=, but as long as this unit is up, all units
           listed in Upholds= are started whenever found to be inactive or failed, and no job is
           queued for them. While a Wants= dependency on another unit has a one-time effect when
           this units started, a Upholds= dependency on it has a continuous effect, constantly
           restarting the unit if necessary. This is an alternative to the Restart= setting of
           service units, to ensure they are kept running whatever happens.

           When Upholds=b.service is used on a.service, this dependency will show as
           UpheldBy=a.service in the property listing of b.service. The UpheldBy= 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.

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

       PropagatesReloadTo=, ReloadPropagatedFrom=
           A space-separated list of one or more units to which reload requests from this unit
           shall be propagated to, or units from which reload requests shall be propagated to
           this unit, respectively. Issuing a reload request on a unit will automatically also
           enqueue reload requests on all units that are linked to it using these two settings.

       PropagatesStopTo=, StopPropagatedFrom=
           A space-separated list of one or more units to which stop requests from this unit
           shall be propagated to, or units from which stop requests shall be propagated to this
           unit, respectively. Issuing a stop request on a unit will automatically also enqueue
           stop requests on all units that are linked to it using 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=, PrivateIPC=,
           IPCNamespacePath=, 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/, IPC namespace 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=, PrivateIPC=/IPCNamespacePath= 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=
           JobTimeoutSec= specifies a timeout for the whole job that starts running when the job
           is queued.  JobRunningTimeoutSec= specifies a timeout that starts running when the
           queued job is actually started. If either limit is reached, the job will be cancelled,
           the unit however will not change state or even enter the "failed" mode.

           Both settings take a time span with the default unit of seconds, but other units may
           be specified, see systemd.time(5). The default is "infinity" (job timeouts disabled),
           except for device units where JobRunningTimeoutSec= defaults to
           DefaultTimeoutStartSec=.

           Note: these timeouts are independent from any unit-specific timeouts (for example, the
           timeout set with TimeoutStartSec= in service units). The job timeout has no effect on
           the unit itself. 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 span are not permitted to start any more. Use
           StartLimitIntervalSec= to configure the checking interval and StartLimitBurst= to
           configure how many starts per interval are allowed.

           interval is a time span with the default unit of seconds, but other units may be
           specified, see systemd.time(5). Defaults to DefaultStartLimitIntervalSec= in manager
           configuration file, and may be set to 0 to disable any kind of rate limiting.  burst
           is a number and 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
           or from a timer or socket at a later point, after the interval has passed. From that
           point on, the restart logic is activated again.  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. Rate-limiting
           is enforced after any unit condition checks are executed, and hence unit activations
           with failing conditions do not count towards the rate limit.

           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.

           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.

       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 and asserts are true.
       If not, the starting of the unit will be (mostly silently) skipped (in case of
       conditions), or aborted with an error message (in case of asserts). Failing conditions or
       asserts will not result in the unit being moved into the "failed" state. The conditions
       and asserts 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, and the conditions and asserts are executed the
       precise moment the unit would normally start and thus can validate system state after the
       units ordered before completed initialization. Use condition expressions for skipping
       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 to become a triggering condition.
       If at least one triggering condition is defined for a unit, then the unit will be started
       if at least one of the triggering conditions of the unit applies and all of the regular
       (i.e. non-triggering) conditions apply. 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 are similar to conditions but
       cause the start job to fail (instead of being skipped). The failed check is logged. Units
       with unmet 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.

       ConditionFirmware=
           Check whether the system's firmware is of a certain type. The following values are
           possible:

           •   "uefi" matches systems with EFI.

           •   "device-tree" matches systems with a device tree.

           •   "device-tree-compatible(value)" matches systems with a device tree that is
               compatible with "value".

           •   "smbios-field(field operator value)" matches systems with a SMBIOS field
               containing a certain value.  field is the name of the SMBIOS field exposed as
               "sysfs" attribute file below /sys/class/dmi/id/.  operator is one of "<", "<=",
               ">=", ">", "==", "<>" for version comparisons, "=" and "!=" for literal string
               comparisons, or "$=", "!$=" for shell-style glob comparisons.  value is the
               expected value of the SMBIOS field value (possibly containing shell style globs in
               case "$="/"!$=" is used).

       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", "amazon",
           "zvm", "vmware", "microsoft", "oracle", "powervm", "xen", "bochs", "uml", "bhyve",
           "qnx", "apple", "sre", "openvz", "lxc", "lxc-libvirt", "systemd-nspawn", "docker",
           "podman", "rkt", "wsl", "proot", "pouch", "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. This operates on the kernel command line
           communicated to userspace via /proc/cmdline, except when the service manager is
           invoked as payload of a container manager, in which case the command line of PID 1 is
           used instead (i.e.  /proc/1/cmdline).

       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. The argument must be a list of (potentially quoted) expressions. Each
           expression starts with one of "=" or "!=" for string comparisons, "<", "<=", "==",
           "<>", ">=", ">" for version comparisons, or "$=", "!$=" for a shell-style glob match.
           If no operator is specified, "$=" is implied.

           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.

       ConditionCredential=
           ConditionCredential= may be used to check whether a credential by the specified name
           was passed into the service manager. See System and Service Credentials[2] for details
           about credentials. If used in services for the system service manager this may be used
           to conditionalize services based on system credentials passed in. If used in services
           for the per-user service manager this may be used to conditionalize services based on
           credentials passed into the unit@.service service instance belonging to the user. The
           argument must be a valid credential name.

       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", "uefi-secureboot" and "tpm2". 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 the kernel command line option
           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.

           Note that to make this scheme effective, the timestamp of /usr/ should be explicitly
           updated after its contents are modified. The kernel will automatically update
           modification timestamp on a directory only when immediate children of a directory are
           modified; an modification of nested files will not automatically result in mtime of
           /usr/ being updated.

           Also note that if the update method includes a call to execute appropriate post-update
           steps itself, it should not touch the timestamp of /usr/. In a typical distribution
           packaging scheme, packages will do any required update steps as part of the
           installation or upgrade, to make package contents immediately usable.
           ConditionNeedsUpdate= should be used with other update mechanisms where such an
           immediate update does not happen.

       ConditionFirstBoot=
           Takes a boolean argument. This condition may be used to conditionalize units on
           whether the system is booting up for the first time. This roughly means that /etc/ was
           unpopulated when the system started booting (for details, see "First Boot Semantics"
           in machine-id(5)). First boot is considered finished (this condition will evaluate as
           false) after the manager has finished the startup phase.

           This condition 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.

           For robustness, units with ConditionFirstBoot=yes should order themselves before
           first-boot-complete.target and pull in this passive target with Wants=. This ensures
           that in a case of an aborted first boot, these units will be re-run during the next
           system startup.

           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 existence 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=
           Check whether given cgroup controllers (e.g.  "cpu") are available for use on the
           system.

           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", "cpuset", "io", "memory",
           and "pids". Even if available in the kernel, a particular controller may not be
           available if it was disabled on the kernel command line with
           cgroup_disable=controller.

       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 "<", "<=", "=" (or "=="), "!=" (or "<>"), ">=", ">". 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 "<", "<=",
           "=" (or "=="), "!=" (or "<>"), ">=", ">". 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.

       ConditionCPUFeature=
           Verify that a given CPU feature is available via the "CPUID" instruction. This
           condition only does something on i386 and x86-64 processors. On other processors it is
           assumed that the CPU does not support the given feature. It checks the leaves "1",
           "7", "0x80000001", and "0x80000007". Valid values are: "fpu", "vme", "de", "pse",
           "tsc", "msr", "pae", "mce", "cx8", "apic", "sep", "mtrr", "pge", "mca", "cmov", "pat",
           "pse36", "clflush", "mmx", "fxsr", "sse", "sse2", "ht", "pni", "pclmul", "monitor",
           "ssse3", "fma3", "cx16", "sse4_1", "sse4_2", "movbe", "popcnt", "aes", "xsave",
           "osxsave", "avx", "f16c", "rdrand", "bmi1", "avx2", "bmi2", "rdseed", "adx", "sha_ni",
           "syscall", "rdtscp", "lm", "lahf_lm", "abm", "constant_tsc".

       ConditionOSRelease=
           Verify that a specific "key=value" pair is set in the host's os-release(5).

           Other than exact string matching (with "=" and "!="), relative comparisons are
           supported for versioned parameters (e.g.  "VERSION_ID"; with "<", "<=", "==", "<>",
           ">=", ">"), and shell-style wildcard comparisons ("*", "?", "[]") are supported with
           the "$=" (match) and "!$=" (non-match).

       ConditionMemoryPressure=, ConditionCPUPressure=, ConditionIOPressure=
           Verify that the overall system (memory, CPU or IO) pressure is below or equal to a
           threshold. This setting takes a threshold value as argument. It can be specified as a
           simple percentage value, suffixed with "%", in which case the pressure will be
           measured as an average over the last five minutes before the attempt to start the unit
           is performed. Alternatively, the average timespan can also be specified using "/" as a
           separator, for example: "10%/1min". The supported timespans match what the kernel
           provides, and are limited to "10sec", "1min" and "5min". The "full" PSI will be
           checked first, and if not found "some" will be checked. For more details, see the
           documentation on PSI (Pressure Stall Information)[3].

           Optionally, the threshold value can be prefixed with the slice unit under which the
           pressure will be checked, followed by a ":". If the slice unit is not specified, the
           overall system pressure will be measured, instead of a particular cgroup's.

       AssertArchitecture=, AssertVirtualization=, AssertHost=, AssertKernelCommandLine=,
       AssertKernelVersion=, AssertCredential=, AssertEnvironment=, AssertSecurity=,
       AssertCapability=, AssertACPower=, AssertNeedsUpdate=, AssertFirstBoot=,
       AssertPathExists=, AssertPathExistsGlob=, AssertPathIsDirectory=,
       AssertPathIsSymbolicLink=, AssertPathIsMountPoint=, AssertPathIsReadWrite=,
       AssertPathIsEncrypted=, AssertDirectoryNotEmpty=, AssertFileNotEmpty=,
       AssertFileIsExecutable=, AssertUser=, AssertGroup=, AssertControlGroupController=,
       AssertMemory=, AssertCPUs=, AssertCPUFeature=, AssertOSRelease=, AssertMemoryPressure=,
       AssertCPUPressure=, AssertIOPressure=
           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" property    │ "Reverse" property    │ Where used                            │
       ├──────────────────────┼───────────────────────┼───────────────────────────────────────┤
       │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
           of a dependency of type Wants= or Requires= being 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.

           In case of template units listing non template units, the listing unit must have
           DefaultInstance= set, or systemctl enable must be called with an instance name. The
           instance (default or specified) will be added to the .wants/ or .requires/ list of the
           listed unit. For example, 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. This also applies to
           listing specific instances of templated units: this specific instance will gain the
           dependency. A template unit may also list a template unit, in which case a generic
           dependency will be added where each instance of the listing unit will have a
           dependency on an instance of the listed template with the same instance value. For
           example, WantedBy=container@.target in a service monitor@.service will result in
           systemctl enable monitor@.service creating a container@.target.wants/monitor@.service
           link to monitor@.service, which applies to all instances of container@.target.

       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: %a, %b, %B, %g, %G, %H,
       %i, %j, %l, %m, %n, %N, %o, %p, %u, %U, %v, %w, %W, %%. 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.   │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%A"      │ Operating system image   │ The operating system     │
       │          │ version                  │ image version identifier │
       │          │                          │ of the running system,   │
       │          │                          │ as read from the         │
       │          │                          │ IMAGE_VERSION= field of  │
       │          │                          │ /etc/os-release. If not  │
       │          │                          │ set, resolves to an      │
       │          │                          │ empty string. See os-    │
       │          │                          │ release(5) for more      │
       │          │                          │ information.             │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%b"      │ Boot ID                  │ The boot ID of the       │
       │          │                          │ running system,          │
       │          │                          │ formatted as string. See │
       │          │                          │ random(4) for more       │
       │          │                          │ information.             │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%B"      │ Operating system build   │ The operating system     │
       │          │ 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 "$XDG_CACHE_HOME"   │
       │          │                          │ resolves to (for user    │
       │          │                          │ managers).               │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%d"      │ Credentials directory    │ This is the value of the │
       │          │                          │ "$CREDENTIALS_DIRECTORY" │
       │          │                          │ environment variable if  │
       │          │                          │ available. See section   │
       │          │                          │ "Credentials" in         │
       │          │                          │ systemd.exec(5) for more │
       │          │                          │ information.             │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%E"      │ Configuration directory  │ This is either /etc/     │
       │          │ 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.         │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%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".         │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%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. │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%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 name  │ Same as "%i", but with   │
       │          │                          │ escaping undone.         │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%j"      │ Final component of the   │ This is the string       │
       │          │ 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 prefix  │ escaping undone.         │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%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.               │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%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.             │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%M"      │ Operating system image   │ The operating system     │
       │          │ identifier               │ image identifier of the  │
       │          │                          │ running system, as read  │
       │          │                          │ from the IMAGE_ID= field │
       │          │                          │ of /etc/os-release. If   │
       │          │                          │ not set, resolves to an  │
       │          │                          │ empty string. See os-    │
       │          │                          │ release(5) for more      │
       │          │                          │ information.             │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%n"      │ Full unit name           │                          │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%N"      │ Full unit name           │ Same as "%n", but with   │
       │          │                          │ the type suffix removed. │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%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.             │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%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 name    │ Same as "%p", but with   │
       │          │                          │ escaping undone.         │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%q"      │ Pretty host name         │ The pretty hostname of   │
       │          │                          │ the running system at    │
       │          │                          │ the point in time the    │
       │          │                          │ unit configuration is    │
       │          │                          │ loaded, as read from the │
       │          │                          │ PRETTY_HOSTNAME= field   │
       │          │                          │ of /etc/machine-info. If │
       │          │                          │ not set, resolves to the │
       │          │                          │ short hostname. See      │
       │          │                          │ machine-info(5) for more │
       │          │                          │ information.             │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%s"      │ User shell               │ This is the shell of the │
       │          │                          │ user running the service │
       │          │                          │ manager instance.        │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%S"      │ State directory root     │ This is either /var/lib  │
       │          │                          │ (for the system manager) │
       │          │                          │ or the path              │
       │          │                          │ "$XDG_CONFIG_HOME"       │
       │          │                          │ resolves to (for user    │
       │          │                          │ managers).               │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%t"      │ Runtime directory root   │ This is either /run/     │
       │          │                          │ (for the system manager) │
       │          │                          │ or the path              │
       │          │                          │ "$XDG_RUNTIME_DIR"       │
       │          │                          │ resolves to (for user    │
       │          │                          │ managers).               │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%T"      │ Directory for temporary  │ This is either /tmp or   │
       │          │ files                    │ the path "$TMPDIR",      │
       │          │                          │ "$TEMP" or "$TMP" are    │
       │          │                          │ set to. (Note that the   │
       │          │                          │ directory may be         │
       │          │                          │ specified without a      │
       │          │                          │ trailing slash.)         │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%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 and │ This is either /var/tmp  │
       │          │ persistent temporary     │ or the path "$TMPDIR",   │
       │          │ files                    │ "$TEMP" or "$TMP" are    │
       │          │                          │ set to. (Note that the   │
       │          │                          │ directory may be         │
       │          │                          │ specified without a      │
       │          │                          │ trailing slash.)         │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%w"      │ Operating system version │ The operating system     │
       │          │ 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 variant │ The operating system     │
       │          │ 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.             │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%y"      │ The path to the fragment │ This is the path where   │
       │          │                          │ the main part of the     │
       │          │                          │ unit file is located.    │
       │          │                          │ For linked unit files,   │
       │          │                          │ the real path outside of │
       │          │                          │ the unit search          │
       │          │                          │ directories is used. For │
       │          │                          │ units that don't have a  │
       │          │                          │ fragment file, this      │
       │          │                          │ specifier will raise an  │
       │          │                          │ error.                   │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%Y"      │ The directory of the     │ This is the directory    │
       │          │ fragment                 │ part of "%y".            │
       ├──────────┼──────────────────────────┼──────────────────────────┤
       │"%%"      │ 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 /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 /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.

       Example 3. Top level drop-ins with template units

       Top level per-type drop-ins can be used to change some aspect of all units of a particular
       type. For example by creating the /etc/systemd/system/service.d/ directory with a drop-in
       file, the contents of the drop-in file can be applied to all service units. We can take
       this further by having the top-level drop-in instantiate a secondary helper unit. Consider
       for example the following set of units and drop-in files where we install an OnFailure=
       dependency for all service units.

       /etc/systemd/system/failure-handler@.service:

           [Unit]
           Description=My failure handler for %i

           [Service]
           Type=oneshot
           # Perform some special action for when %i exits unexpectedly.
           ExecStart=/usr/sbin/myfailurehandler %i

       We can then add an instance of failure-handler@.service as an OnFailure= dependency for
       all service units.

       /etc/systemd/system/service.d/10-all.conf:

           [Unit]
           OnFailure=failure-handler@%N.service

       Now, after running systemctl daemon-reload all services will have acquired an OnFailure=
       dependency on failure-handler@%N.service. The template instance units will also have
       gained the dependency which results in the creation of a recursive dependency chain.
       systemd will try to detect these recursive dependency chains where a template unit
       directly and recursively depends on itself and will remove such dependencies automatically
       if it finds them. If systemd doesn't detect the recursive dependency chain, we can break
       the chain ourselves by disabling the drop-in for the template instance units via a symlink
       to /dev/null:

           mkdir /etc/systemd/system/failure-handler@.service.d/
           ln -s /dev/null /etc/systemd/system/failure-handler@.service.d/10-all.conf
           systemctl daemon-reload

       This ensures that if a failure-handler@.service instance fails it will not trigger an
       instance named failure-handler@failure-handler.service.

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 Portability and Stability Promise
           https://systemd.io/PORTABILITY_AND_STABILITY/

        2. System and Service Credentials
           https://systemd.io/CREDENTIALS

        3. PSI (Pressure Stall Information)
           https://docs.kernel.org/accounting/psi.html