systemd.unit — Unit configuration
service.servicesocket.socketdevice.devicemount.mountautomount.automountswap.swaptarget.targetpath.pathtimer.timerslice.slicescope.scope
/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/*
…
/usr/lib/systemd/system/*
/run/systemd/generator.late/*
~/.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/*
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 "unit name prefix", and a suffix specifying the unit type which
begins with a dot. The "unit name 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 255
characters. The unit type suffix must be one of ".service", ".socket",
".device", ".mount", ".automount",
".swap", ".target", ".path",
".timer", ".slice", or ".scope".
Unit 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 unit name prefix (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 /usr/lib/systemd/system or
/run/systemd/system directories. Drop-in files in /etc/
take precedence over those in /run/ which in turn take precedence over those
in /usr/lib/. Drop-in files under any of these directories take precedence
over unit files wherever located. Multiple drop-in files with different names are applied in
lexicographic order, regardless of which of the directories they reside in.
Units also support a top-level drop-in with type.d/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/type.d/
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.
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.
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 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 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 dbus API |
/run/systemd/system.control | |
/run/systemd/transient | Dynamic configuration for transient units |
/run/systemd/generator.early | Generated units with high priority (see early-dir in systemd.generator(7)) |
/etc/systemd/system | System units created by the administrator |
/run/systemd/system | Runtime units |
/run/systemd/generator | Generated units with medium priority (see normal-dir in systemd.generator(7)) |
/usr/local/lib/systemd/system | System units installed by the administrator |
/usr/lib/systemd/system | System units installed by the distribution package manager |
/run/systemd/generator.late | Generated units with low priority (see late-dir in systemd.generator(7)) |
Table 2.
Load path when running in user mode (--user).
| Path | Description |
|---|---|
$XDG_CONFIG_HOME/systemd/user.control or ~/.config/systemd/user.control | Persistent and transient configuration created using the dbus API ($XDG_CONFIG_HOME is used if set, ~/.config otherwise) |
$XDG_RUNTIME_DIR/systemd/user.control | |
$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 $HOME/.config/systemd/user | User configuration ($XDG_CONFIG_HOME is used if set, ~/.config otherwise) |
$XDG_CONFIG_DIRS/systemd/user or /etc/xdg/systemd/user | Additional configuration directories as specified by the XDG base directory specification ($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 $HOME/.local/share/systemd/user | Units of packages that have been installed in the home directory ($XDG_DATA_HOME is used if set, ~/.local/share otherwise) |
$XDG_DATA_DIRS/systemd/user or /usr/local/share/systemd/user and /usr/share/systemd/user | Additional data directories as specified by the XDG base directory specification ($XDG_DATA_DIRS is used if set, /usr/local/share and /usr/share otherwise) |
$dir/systemd/user for each $dir in $XDG_DATA_DIRS | Additional locations for 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.
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:
Another loaded unit references it with a dependency such as After=,
Wants=, …
The unit is currently starting, running, reloading or stopping.
The unit is currently in the failed state. (But see below.)
A job for the unit is pending.
The unit is pinned by an active IPC client program.
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.
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.
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
"), so it should be capitalized, and should not be a
full sentence, or a phrase with a continuous verb. Bad examples include "description.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. The restart happens without delay, and usual per-unit rate-limit applies.
When Upholds=b.service is used on a.service, this
dependency will show as UpheldBy=a.service in the property listing of
b.service.
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.
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. If this is specified on a unit (say,
a.service has JoinsNamespaceOf=b.service), then the inverse
dependency (JoinsNamespaceOf=a.service for b.service) is implied. 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 and these do not share
their namespace, then 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.
OnSuccessJobMode=, 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
OnSuccess=/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
OnSuccess=/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.
SurviveFinalKillSignal=¶Takes a boolean argument. Defaults to no. If yes,
processes belonging to this unit will not be sent the final "SIGTERM" and
"SIGKILL" signals during the final phase of the system shutdown process.
This functionality replaces the older mechanism that allowed a program to set
"argv[0][0] = '@'" as described at
systemd and Storage Daemons for the Root File
System, which however continues to be supported.
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,
exit-force, soft-reboot, soft-reboot-force,
kexec, kexec-force, halt,
halt-force and halt-immediate. In system mode, all options are
allowed. In user mode, only none, exit,
exit-force, soft-reboot and soft-reboot-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, kexec, kexec-force,
halt, halt-force and halt-immediate have the
effect of powering down the system, executing kexec, and halting the system respectively 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.
soft-reboot will trigger a userspace reboot operation.
soft-reboot-force does that too, but does not go through the shutdown transaction
beforehand.
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 DefaultDeviceTimeoutSec=.
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).
The special value "infinity" can be used to limit the total number of start
attempts, even if they happen at large time intervals.
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.
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("
matches systems with a device tree that are compatible with "value)value".
"smbios-field(" matches systems
with a SMBIOS field containing a certain value. field
operator 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 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=valueEnvironment= 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 following values are recognized:
Table 3. Recognized security technologies
| Value | Description |
|---|---|
| selinux | SELinux MAC |
| apparmor | AppArmor MAC |
| tomoyo | Tomoyo MAC |
| smack | SMACK MAC |
| ima | Integrity Measurement Architecture (IMA) |
| audit | Linux Audit Framework |
| uefi-secureboot | UEFI SecureBoot |
| tpm2 | Trusted Platform Module 2.0 (TPM2) |
| cvm | Confidential virtual machine (SEV/TDX) |
| measured-uki | Unified Kernel Image with PCR 11 Measurements, as per systemd-stub(7). |
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 or whether the legacy v1 cgroup or the modern v2 cgroup hierarchy is used.
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", "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.
Alternatively, two special strings "v1" and "v2" may be
specified (without any controller names). "v2" will pass if the unified v2 cgroup
hierarchy is used, and "v1" will pass if the legacy v1 hierarchy or the hybrid
hierarchy are used. Note that legacy or hybrid hierarchies have been deprecated. See
systemd(1) for
more information.
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)
.
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.
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 4. "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 |
Upholds= | UpheldBy= | [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 |
Conflicts= | ConflictedBy= | [Unit] section | an automatic property |
Triggers= | TriggeredBy= | Automatic properties, see notes below | |
PropagatesReloadTo= | ReloadPropagatedFrom= | [Unit] section | |
ReloadPropagatedFrom= | PropagatesReloadTo= | ||
PropagatesStopTo= | StopPropagatedFrom= | [Unit] section | |
StopPropagatedFrom= | PropagatesStopTo= | ||
Following= | n/a | An automatic property | |
Note: WantedBy=, RequiredBy=, and UpheldBy=
are used in the [Install] section to create symlinks in .wants/,
.requires/, and .upholds/ 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.
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=, UpheldBy=¶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/, .requires/,
or .upholds/ 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=, Requires=, or Upholds= being added
from the listed unit to the current unit. See the description of the mentioned dependency types
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/, .requires/, or .upholds/
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.
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 5. 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 version | The operating system 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 ID | The operating system 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 root | This is either /etc/ (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 prefix | This is the string between the last "-" and the end of the prefix name. If there is no "-", this is the same as "%p". |
"%J" | Unescaped final component of the prefix | Same as "%j", but with 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_STATE_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 identifier | The operating system 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 $XDG_STATE_HOME resolves to (for user managers). |
"%t" | Runtime directory root | This is either /run/ (for the system manager) or the path "$XDG_RUNTIME_DIR" resolves to (for user managers). |
"%T" | Directory for temporary files | This is either /tmp or the path "$TMPDIR", "$TEMP" or "$TMP" are set to. (Note that the directory may be specified without a trailing slash.) |
"%u" | User name | This is the name of the user running the service manager instance. In case of the system manager this resolves to "root".
Note that this setting is not influenced by the User= setting configurable in the [Service] section of the service unit. |
"%U" | User UID | This is the numeric UID of the user running the service manager instance. In case of the system manager this resolves to "0".
Note that this setting is not influenced by the User= setting configurable in the [Service] section of the service unit. |
"%v" | Kernel release | Identical to uname -r output. |
"%V" | Directory for larger and persistent temporary files | This is either /var/tmp or the path "$TMPDIR", "$TEMP" or "$TMP" are set to. (Note that the directory may be specified without a trailing slash.) |
"%w" | Operating system version ID | The operating system 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 ID | The operating system 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 fragment | This is the directory part of "%y". |
"%%" | Single percent sign | Use "%%" in place of "%" to specify a single percent sign. |
Example 1. Allowing units to be enabled
The following snippet (highlighted) allows a unit (e.g.
foo.service) to be enabled via
systemctl enable:
[Unit] Description=Foo [Service] ExecStart=/usr/sbin/foo-daemon [Install] WantedBy=multi-user.target
After running systemctl enable, a
symlink
/etc/systemd/system/multi-user.target.wants/foo.service
linking to the actual unit will be created. It tells systemd to
pull in the unit when starting
multi-user.target. The inverse
systemctl disable will remove that symlink
again.
Example 2. Overriding vendor settings
There are two methods of overriding vendor settings in
unit files: copying the unit file from
/usr/lib/systemd/system to
/etc/systemd/system and modifying the
chosen settings. Alternatively, one can create a directory named
unit.d//etc/systemd/system and place a drop-in
file name.conf
The advantage of the first method is that one easily overrides the complete unit, the vendor unit is not parsed at all anymore. It has the disadvantage that improvements to the unit file by the vendor are not automatically incorporated on updates.
The advantage of the second method is that one only overrides the settings one specifically wants, where updates to the unit by the vendor automatically apply. This has the disadvantage that some future updates by the vendor might be incompatible with the local changes.
This also applies for user instances of systemd, but with different locations for the unit files. See the section on unit load paths for further details.
Suppose there is a vendor-supplied unit
/usr/lib/systemd/system/httpd.service with
the following contents:
[Unit] Description=Some HTTP server After=remote-fs.target sqldb.service Requires=sqldb.service AssertPathExists=/srv/webserver [Service] Type=notify ExecStart=/usr/sbin/some-fancy-httpd-server Nice=5 [Install] WantedBy=multi-user.target
Now one wants to change some settings as an administrator:
firstly, in the local setup, /srv/webserver
might not exist, because the HTTP server is configured to use
/srv/www instead. Secondly, the local
configuration makes the HTTP server also depend on a memory
cache service, memcached.service, that
should be pulled in (Requires=) and also be
ordered appropriately (After=). Thirdly, in
order to harden the service a bit more, the administrator would
like to set the PrivateTmp= setting (see
systemd.exec(5)
for details). And lastly, the administrator would like to reset
the niceness of the service to its default value of 0.
The first possibility is to copy the unit file to
/etc/systemd/system/httpd.service and
change the chosen settings:
[Unit] Description=Some HTTP server After=remote-fs.target sqldb.service memcached.service Requires=sqldb.service memcached.service AssertPathExists=/srv/www [Service] Type=notify ExecStart=/usr/sbin/some-fancy-httpd-server Nice=0 PrivateTmp=yes [Install] WantedBy=multi-user.target
Alternatively, the administrator could create a drop-in
file
/etc/systemd/system/httpd.service.d/local.conf
with the following contents:
[Unit] After=memcached.service Requires=memcached.service # Reset all assertions and then re-add the condition we want AssertPathExists= AssertPathExists=/srv/www [Service] Nice=0 PrivateTmp=yes
Note that for drop-in files, if one wants to remove
entries from a setting that is parsed as a list (and is not a
dependency), such as AssertPathExists= (or
e.g. ExecStart= in service units), one needs
to first clear the list before re-adding all entries except the
one that is to be removed. Dependencies (After=, etc.)
cannot be reset to an empty list, so dependencies can only be
added in drop-ins. If you want to remove dependencies, you have
to override the entire unit.
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.
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)