SYSTEMD.UNIT(5) systemd.unit SYSTEMD.UNIT(5)
systemd.unit - Unit configuration
service.service, socket.socket, device.device, mount.mount,
automount.automount, swap.swap, target.target, path.path,
timer.timer, slice.slice, scope.scope
System Unit Search Path
/etc/systemd/system.control/*
/run/systemd/system.control/*
/run/systemd/transient/*
/run/systemd/generator.early/*
/etc/systemd/system/*
/etc/systemd/systemd.attached/*
/run/systemd/system/*
/run/systemd/systemd.attached/*
/run/systemd/generator/*
...
/usr/lib/systemd/system/*
/run/systemd/generator.late/*
User Unit Search Path
~/.config/systemd/user.control/*
$XDG_RUNTIME_DIR/systemd/user.control/*
$XDG_RUNTIME_DIR/systemd/transient/*
$XDG_RUNTIME_DIR/systemd/generator.early/*
~/.config/systemd/user/*
/etc/systemd/user/*
$XDG_RUNTIME_DIR/systemd/user/*
/run/systemd/user/*
$XDG_RUNTIME_DIR/systemd/generator/*
~/.local/share/systemd/user/*
...
/usr/lib/systemd/user/*
$XDG_RUNTIME_DIR/systemd/generator.late/*
A unit file is a plain text ini-style file that encodes information
about a service, a socket, a device, a mount point, an automount
point, a swap file or partition, a start-up target, a watched file
system path, a timer controlled and supervised by systemd(1), a
resource management slice or a group of externally created processes.
See systemd.syntax(7) for a general description of the syntax.
This man page lists the common configuration options of all the unit
types. These options need to be configured in the [Unit] or [Install]
sections of the unit files.
In addition to the generic [Unit] and [Install] sections described
here, each unit may have a type-specific section, e.g. [Service] for
a service unit. See the respective man pages for more information:
systemd.service(5), systemd.socket(5), systemd.device(5),
systemd.mount(5), systemd.automount(5), systemd.swap(5),
systemd.target(5), systemd.path(5), systemd.timer(5),
systemd.slice(5), systemd.scope(5).
Unit files are loaded from a set of paths determined during
compilation, described in the next section.
Valid unit names consist of a "name prefix" and a dot and a suffix
specifying the unit type. The "unit prefix" must consist of one or
more valid characters (ASCII letters, digits, ":", "-", "_", ".", and
"\"). The total length of the unit name including the suffix must not
exceed 256 characters. The type suffix must be one of ".service",
".socket", ".device", ".mount", ".automount", ".swap", ".target",
".path", ".timer", ".slice", or ".scope".
Units names can be parameterized by a single argument called the
"instance name". The unit is then constructed based on a "template
file" which serves as the definition of multiple services or other
units. A template unit must have a single "@" at the end of the name
(right before the type suffix). The name of the full unit is formed
by inserting the instance name between "@" and the unit type suffix.
In the unit file itself, the instance parameter may be referred to
using "%i" and other specifiers, see below.
Unit files may contain additional options on top of those listed
here. If systemd encounters an unknown option, it will write a
warning log message but continue loading the unit. If an option or
section name is prefixed with X-, it is ignored completely by
systemd. Options within an ignored section do not need the prefix.
Applications may use this to include additional information in the
unit files.
Units can be aliased (have an alternative name), by creating a
symlink from the new name to the existing name in one of the unit
search paths. For example, systemd-networkd.service has the alias
dbus-org.freedesktop.network1.service, created during installation as
a symlink, so when systemd is asked through D-Bus to load
dbus-org.freedesktop.network1.service, it'll load
systemd-networkd.service. As another example, default.target — the
default system target started at boot — is commonly symlinked
(aliased) to either multi-user.target or graphical.target to select
what is started by default. Alias names may be used in commands like
disable, start, stop, status, and similar, and in all unit dependency
directives, including Wants=, Requires=, Before=, After=. Aliases
cannot be used with the preset command.
Aliases obey the following restrictions: a unit of a certain type
(".service", ".socket", ...) can only be aliased by a name with the
same type suffix. A plain unit (not a template or an instance), may
only be aliased by a plain name. A template instance may only be
aliased by another template instance, and the instance part must be
identical. A template may be aliased by another template (in which
case the alias applies to all instances of the template). As a
special case, a template instance (e.g. "alias@inst.service") may be
a symlink to different template (e.g. "template@inst.service"). In
that case, just this specific instance is aliased, while other
instances of the template (e.g. "alias@foo.service",
"alias@bar.service") are not aliased. Those rule preserve the
requirement that the instance (if any) is always uniquely defined for
a given unit and all its aliases.
Unit files may specify aliases through the Alias= directive in the
[Install] section. When the unit is enabled, symlinks will be created
for those names, and removed when the unit is disabled. For example,
reboot.target specifies Alias=ctrl-alt-del.target, so when enabled,
the symlink /etc/systemd/systemd/ctrl-alt-del.service pointing to the
reboot.target file will be created, and when Ctrl+Alt+Del is invoked,
systemd will look for the ctrl-alt-del.service and execute
reboot.service. systemd does not look at the [Install] section at
all during normal operation, so any directives in that section only
have an effect through the symlinks created during enablement.
Along with a unit file foo.service, the directory foo.service.wants/
may exist. All unit files symlinked from such a directory are
implicitly added as dependencies of type Wants= to the unit. Similar
functionality exists for Requires= type dependencies as well, the
directory suffix is .requires/ in this case. This functionality is
useful to hook units into the start-up of other units, without having
to modify their unit files. For details about the semantics of
Wants=, see below. The preferred way to create symlinks in the
.wants/ or .requires/ directory of a unit file is by embedding the
dependency in [Install] section of the target unit, and creating the
symlink in the file system with the enable or preset commands of
systemctl(1).
Along with a unit file foo.service, a "drop-in" directory
foo.service.d/ may exist. All files with the suffix ".conf" from this
directory will be parsed after the unit file itself is parsed. This
is useful to alter or add configuration settings for a unit, without
having to modify unit files. Drop-in files must contain appropriate
section headers. For instantiated units, this logic will first look
for the instance ".d/" subdirectory (e.g. "foo@bar.service.d/") and
read its ".conf" files, followed by the template ".d/" subdirectory
(e.g. "foo@.service.d/") and the ".conf" files there. Moreover for
units names containing dashes ("-"), the set of directories generated
by truncating the unit name after all dashes is searched too.
Specifically, for a unit name foo-bar-baz.service not only the
regular drop-in directory foo-bar-baz.service.d/ is searched but also
both foo-bar-.service.d/ and foo-.service.d/. This is useful for
defining common drop-ins for a set of related units, whose names
begin with a common prefix. This scheme is particularly useful for
mount, automount and slice units, whose systematic naming structure
is built around dashes as component separators. Note that equally
named drop-in files further down the prefix hierarchy override those
further up, i.e. foo-bar-.service.d/10-override.conf overrides
foo-.service.d/10-override.conf.
In cases of unit aliases (described above), dropins for the aliased
name and all aliases are loaded. In the example of default.target
aliasing graphical.target, default.target.d/, default.target.wants/,
default.target.requires/, graphical.target.d/,
graphical.target.wants/, graphical.target.requires/ would all be
read. For templates, dropins for the template, any template aliases,
the template instance, and all alias instances are read. When just a
specific template instance is aliased, then the dropins for the
target template, the target template instance, and the alias template
instance are read.
In addition to /etc/systemd/system, the drop-in ".d/" directories for
system services can be placed in /usr/lib/systemd/system or
/run/systemd/system directories. Drop-in files in /etc take
precedence over those in /run which in turn take precedence over
those in /usr/lib. Drop-in files under any of these directories take
precedence over unit files wherever located. Multiple drop-in files
with different names are applied in lexicographic order, regardless
of which of the directories they reside in.
Units also support a top-level drop-in with type.d/, where type may
be e.g. "service" or "socket", that allows altering or adding to the
settings of all corresponding unit files on the system. The
formatting and precedence of applying drop-in configurations follow
what is defined above. Configurations in type.d/ have the lowest
precedence compared to settings in the name specific override
directories. So the contents of foo-.service.d/10-override.conf would
override service.d/10-override.conf.
Note that while systemd offers a flexible dependency system between
units it is recommended to use this functionality only sparingly and
instead rely on techniques such as bus-based or socket-based
activation which make dependencies implicit, resulting in a both
simpler and more flexible system.
As mentioned above, a unit may be instantiated from a template file.
This allows creation of multiple units from a single configuration
file. If systemd looks for a unit configuration file, it will first
search for the literal unit name in the file system. If that yields
no success and the unit name contains an "@" character, systemd will
look for a unit template that shares the same name but with the
instance string (i.e. the part between the "@" character and the
suffix) removed. Example: if a service getty@tty3.service is
requested and no file by that name is found, systemd will look for
getty@.service and instantiate a service from that configuration file
if it is found.
To refer to the instance string from within the configuration file
you may use the special "%i" specifier in many of the configuration
options. See below for details.
If a unit file is empty (i.e. has the file size 0) or is symlinked to
/dev/null, its configuration will not be loaded and it appears with a
load state of "masked", and cannot be activated. Use this as an
effective way to fully disable a unit, making it impossible to start
it even manually.
The unit file format is covered by the Interface Stability
Promise[1].
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.
Implicit Dependencies
A number of unit dependencies are implicitly established, depending
on unit type and unit configuration. These implicit dependencies can
make unit configuration file cleaner. For the implicit dependencies
in each unit type, please refer to section "Implicit Dependencies" in
respective man pages.
For example, service units with Type=dbus automatically acquire
dependencies of type Requires= and After= on dbus.socket. See
systemd.service(5) for details.
Default Dependencies
Default dependencies are similar to implicit dependencies, but can be
turned on and off by setting DefaultDependencies= to yes (the
default) and no, while implicit dependencies are always in effect.
See section "Default Dependencies" in respective man pages for the
effect of enabling DefaultDependencies= in each unit types.
For example, target units will complement all configured dependencies
of type Wants= or Requires= with dependencies of type After= unless
DefaultDependencies=no is set in the specified units. See
systemd.target(5) for details. Note that this behavior can be turned
off by setting DefaultDependencies=no.
Unit 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 │
│/run/systemd/system.control │ using the dbus API │
├──────────────────────────────┼───────────────────────────┤
│/run/systemd/transient │ Dynamic configuration for │
│ │ transient units │
├──────────────────────────────┼───────────────────────────┤
│/run/systemd/generator.early │ Generated units with high │
│ │ priority (see early-dir │
│ │ in systemd.generator(7)) │
├──────────────────────────────┼───────────────────────────┤
│/etc/systemd/system │ System units created by │
│ │ the administrator │
├──────────────────────────────┼───────────────────────────┤
│/run/systemd/system │ Runtime units │
├──────────────────────────────┼───────────────────────────┤
│/run/systemd/generator │ Generated units with │
│ │ medium priority (see │
│ │ normal-dir in │
│ │ systemd.generator(7)) │
├──────────────────────────────┼───────────────────────────┤
│/usr/local/lib/systemd/system │ System units installed by │
│ │ the administrator │
├──────────────────────────────┼───────────────────────────┤
│/usr/lib/systemd/system │ System units installed by │
│ │ the distribution package │
│ │ manager │
├──────────────────────────────┼───────────────────────────┤
│/run/systemd/generator.late │ Generated units with low │
│ │ priority (see late-dir in │
│ │ systemd.generator(7)) │
└──────────────────────────────┴───────────────────────────┘
Table 2. Load path when running in user mode (--user).
┌────────────────────────────────────────┬───────────────────────────┐
│Path │ Description │
├────────────────────────────────────────┼───────────────────────────┤
│$XDG_CONFIG_HOME/systemd/user.control │ Persistent and transient │
│or │ configuration created │
│~/.config/systemd/user.control │ using the dbus API │
├────────────────────────────────────────┤ ($XDG_CONFIG_HOME is used │
│$XDG_RUNTIME_DIR/systemd/user.control │ if set, ~/.config │
│ │ otherwise) │
├────────────────────────────────────────┼───────────────────────────┤
│/run/systemd/transient │ Dynamic configuration for │
│ │ transient units │
├────────────────────────────────────────┼───────────────────────────┤
│/run/systemd/generator.early │ Generated units with high │
│ │ priority (see early-dir │
│ │ in systemd.generator(7)) │
├────────────────────────────────────────┼───────────────────────────┤
│$XDG_CONFIG_HOME/systemd/user or │ User configuration │
│$HOME/.config/systemd/user │ ($XDG_CONFIG_HOME is used │
│ │ if set, ~/.config │
│ │ otherwise) │
├────────────────────────────────────────┼───────────────────────────┤
│/etc/systemd/user │ User units created by the │
│ │ administrator │
├────────────────────────────────────────┼───────────────────────────┤
│$XDG_RUNTIME_DIR/systemd/user │ Runtime units (only used │
│ │ when $XDG_RUNTIME_DIR is │
│ │ set) │
├────────────────────────────────────────┼───────────────────────────┤
│/run/systemd/user │ Runtime units │
├────────────────────────────────────────┼───────────────────────────┤
│$XDG_RUNTIME_DIR/systemd/generator │ Generated units with │
│ │ medium priority (see │
│ │ normal-dir in │
│ │ systemd.generator(7)) │
├────────────────────────────────────────┼───────────────────────────┤
│$XDG_DATA_HOME/systemd/user or │ Units of packages that │
│$HOME/.local/share/systemd/user │ have been installed in │
│ │ the home directory │
│ │ ($XDG_DATA_HOME is used │
│ │ if set, ~/.local/share │
│ │ otherwise) │
├────────────────────────────────────────┼───────────────────────────┤
│$dir/systemd/user for each $dir in │ Additional locations for │
│$XDG_DATA_DIRS │ installed user units, one │
│ │ for each entry in │
│ │ $XDG_DATA_DIRS │
├────────────────────────────────────────┼───────────────────────────┤
│/usr/local/lib/systemd/user │ User units installed by │
│ │ the administrator │
├────────────────────────────────────────┼───────────────────────────┤
│/usr/lib/systemd/user │ User units installed by │
│ │ the distribution package │
│ │ manager │
├────────────────────────────────────────┼───────────────────────────┤
│$XDG_RUNTIME_DIR/systemd/generator.late │ Generated units with low │
│ │ priority (see late-dir in │
│ │ systemd.generator(7)) │
└────────────────────────────────────────┴───────────────────────────┘
The set of load paths for the user manager instance may be augmented
or changed using various environment variables. And environment
variables may in turn be set using environment generators, see
systemd.environment-generator(7). In particular, $XDG_DATA_HOME and
$XDG_DATA_DIRS may be easily set using
systemd-environment-d-generator(8). Thus, directories listed here are
just the defaults. To see the actual list that would be used based on
compilation options and current environment use
systemd-analyze --user unit-paths
Moreover, additional units might be loaded into systemd from
directories not on the unit load path by creating a symlink pointing
to a unit file in the directories. You can use systemctl link for
this operation. See systemctl(1) for its usage and precaution.
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.
The unit file may include a [Unit] section, which carries generic
information about the unit that is not dependent on the type of unit:
Description=
A human readable name for the unit. This is used by systemd (and
other UIs) as the label for the unit, so this string should
identify the unit rather than describe it, despite the name.
"Apache2 Web Server" is a good example. Bad examples are
"high-performance light-weight HTTP server" (too generic) or
"Apache2" (too specific and meaningless for people who do not
know Apache). systemd will use this string as a noun in status
messages ("Starting description...", "Started description.",
"Reached target description.", "Failed to start description."),
so it should be capitalized, and should not be a full sentence or
a phrase with a continuous verb. Bad examples include "exiting
the container" or "updating the database once per day.".
Documentation=
A space-separated list of URIs referencing documentation for this
unit or its configuration. Accepted are only URIs of the types
"http://", "https://", "file:", "info:", "man:". For more
information about the syntax of these URIs, see uri(7). The URIs
should be listed in order of relevance, starting with the most
relevant. It is a good idea to first reference documentation that
explains what the unit's purpose is, followed by how it is
configured, followed by any other related documentation. This
option may be specified more than once, in which case the
specified list of URIs is merged. If the empty string is assigned
to this option, the list is reset and all prior assignments will
have no effect.
Wants=
Configures requirement dependencies on other units. This option
may be specified more than once or multiple space-separated units
may be specified in one option in which case dependencies for all
listed names will be created. Dependencies of this type may also
be configured outside of the unit configuration file by adding a
symlink to a .wants/ directory accompanying the unit file. For
details, see above.
Units listed in this option will be started if the configuring
unit is. However, if the listed units fail to start or cannot be
added to the transaction, this has no impact on the validity of
the transaction as a whole, and this unit will still be started.
This is the recommended way to hook the start-up of one unit to
the start-up of another unit.
Note that requirement dependencies do not influence the order in
which services are started or stopped. This has to be configured
independently with the After= or Before= options. If unit
foo.service pulls in unit bar.service as configured with Wants=
and no ordering is configured with After= or Before=, then both
units will be started simultaneously and without any delay
between them if foo.service is activated.
Requires=
Similar to Wants=, but declares a stronger dependency.
Dependencies of this type may also be configured by adding a
symlink to a .requires/ directory accompanying the unit file.
If this unit gets activated, the units listed will be activated
as well. If one of the other units fails to activate, and an
ordering dependency After= on the failing unit is set, this unit
will not be started. Besides, with or without specifying After=,
this unit will be stopped if one of the other units is explicitly
stopped.
Often, it is a better choice to use Wants= instead of Requires=
in order to achieve a system that is more robust when dealing
with failing services.
Note that this dependency type does not imply that the other unit
always has to be in active state when this unit is running.
Specifically: failing condition checks (such as
ConditionPathExists=, ConditionPathIsSymbolicLink=, ... — see
below) do not cause the start job of a unit with a Requires=
dependency on it to fail. Also, some unit types may deactivate on
their own (for example, a service process may decide to exit
cleanly, or a device may be unplugged by the user), which is not
propagated to units having a Requires= dependency. Use the
BindsTo= dependency type together with After= to ensure that a
unit may never be in active state without a specific other unit
also in active state (see below).
Requisite=
Similar to Requires=. However, if the units listed here are not
started already, they will not be started and the starting of
this unit will fail immediately. Requisite= does not imply an
ordering dependency, even if both units are started in the same
transaction. Hence this setting should usually be combined with
After=, to ensure this unit is not started before the other unit.
When Requisite=b.service is used on a.service, this dependency
will show as RequisiteOf=a.service in property listing of
b.service. RequisiteOf= dependency cannot be specified directly.
BindsTo=
Configures requirement dependencies, very similar in style to
Requires=. However, this dependency type is stronger: in addition
to the effect of Requires= it declares that if the unit bound to
is stopped, this unit will be stopped too. This means a unit
bound to another unit that suddenly enters inactive state will be
stopped too. Units can suddenly, unexpectedly enter inactive
state for different reasons: the main process of a service unit
might terminate on its own choice, the backing device of a device
unit might be unplugged or the mount point of a mount unit might
be unmounted without involvement of the system and service
manager.
When used in conjunction with After= on the same unit the
behaviour of BindsTo= is even stronger. In this case, the unit
bound to strictly has to be in active state for this unit to also
be in active state. This not only means a unit bound to another
unit that suddenly enters inactive state, but also one that is
bound to another unit that gets skipped due to a failed condition
check (such as ConditionPathExists=,
ConditionPathIsSymbolicLink=, ... — see below) will be stopped,
should it be running. Hence, in many cases it is best to combine
BindsTo= with After=.
When BindsTo=b.service is used on a.service, this dependency will
show as BoundBy=a.service in property listing of b.service.
BoundBy= dependency cannot be specified directly.
PartOf=
Configures dependencies similar to Requires=, but limited to
stopping and restarting of units. When systemd stops or restarts
the units listed here, the action is propagated to this unit.
Note that this is a one-way dependency — changes to this unit do
not affect the listed units.
When PartOf=b.service is used on a.service, this dependency will
show as ConsistsOf=a.service in property listing of b.service.
ConsistsOf= dependency cannot be specified directly.
Conflicts=
A space-separated list of unit names. Configures negative
requirement dependencies. If a unit has a Conflicts= setting on
another unit, starting the former will stop the latter and vice
versa.
Note that this setting does not imply an ordering dependency,
similarly to the Wants= and Requires= dependencies described
above. This means that to ensure that the conflicting unit is
stopped before the other unit is started, an After= or Before=
dependency must be declared. It doesn't matter which of the two
ordering dependencies is used, because stop jobs are always
ordered before start jobs, see the discussion in Before=/After=
below.
If unit A that conflicts with unit B is scheduled to be started
at the same time as B, the transaction will either fail (in case
both are required parts of the transaction) or be modified to be
fixed (in case one or both jobs are not a required part of the
transaction). In the latter case, the job that is not required
will be removed, or in case both are not required, the unit that
conflicts will be started and the unit that is conflicted is
stopped.
Before=, After=
These two settings expect a space-separated list of unit names.
They may be specified more than once, in which case dependencies
for all listed names are created.
Those two settings configure ordering dependencies between units.
If unit foo.service contains the setting Before=bar.service and
both units are being started, bar.service's start-up is delayed
until foo.service has finished starting up. After= is the
inverse of Before=, i.e. while Before= ensures that the
configured unit is started before the listed unit begins starting
up, After= ensures the opposite, that the listed unit is fully
started up before the configured unit is started.
When two units with an ordering dependency between them are shut
down, the inverse of the start-up order is applied. I.e. if a
unit is configured with After= on another unit, the former is
stopped before the latter if both are shut down. Given two units
with any ordering dependency between them, if one unit is shut
down and the other is started up, the shutdown is ordered before
the start-up. It doesn't matter if the ordering dependency is
After= or Before=, in this case. It also doesn't matter which of
the two is shut down, as long as one is shut down and the other
is started up; the shutdown is ordered before the start-up in all
cases. If two units have no ordering dependencies between them,
they are shut down or started up simultaneously, and no ordering
takes place. It depends on the unit type when precisely a unit
has finished starting up. Most importantly, for service units
start-up is considered completed for the purpose of
Before=/After= when all its configured start-up commands have
been invoked and they either failed or reported start-up success.
Note that this does includes ExecStartPost= (or ExecStopPost= for
the shutdown case).
Note that those settings are independent of and orthogonal to the
requirement dependencies as configured by Requires=, Wants=,
Requisite=, or BindsTo=. It is a common pattern to include a unit
name in both the After= and Wants= options, in which case the
unit listed will be started before the unit that is configured
with these options.
Note that Before= dependencies on device units have no effect and
are not supported. Devices generally become available as a result
of an external hotplug event, and systemd creates the
corresponding device unit without delay.
OnFailure=
A space-separated list of one or more units that are activated
when this unit enters the "failed" state. A service unit using
Restart= enters the failed state only after the start limits are
reached.
PropagatesReloadTo=, ReloadPropagatedFrom=
A space-separated list of one or more units where reload requests
on this unit will be propagated to, or reload requests on the
other unit will be propagated to this unit, respectively. Issuing
a reload request on a unit will automatically also enqueue a
reload request on all units that the reload request shall be
propagated to via these two settings.
JoinsNamespaceOf=
For units that start processes (such as service units), lists one
or more other units whose network and/or temporary file namespace
to join. This only applies to unit types which support the
PrivateNetwork=, NetworkNamespacePath= and PrivateTmp= directives
(see systemd.exec(5) for details). If a unit that has this
setting set is started, its processes will see the same /tmp,
/var/tmp and network namespace as one listed unit that is
started. If multiple listed units are already started, it is not
defined which namespace is joined. Note that this setting only
has an effect if PrivateNetwork=/NetworkNamespacePath= and/or
PrivateTmp= is enabled for both the unit that joins the namespace
and the unit whose namespace is joined.
RequiresMountsFor=
Takes a space-separated list of absolute paths. Automatically
adds dependencies of type Requires= and After= for all mount
units required to access the specified path.
Mount points marked with noauto are not mounted automatically
through local-fs.target, but are still honored for the purposes
of this option, i.e. they will be pulled in by this unit.
OnFailureJobMode=
Takes a value of "fail", "replace", "replace-irreversibly",
"isolate", "flush", "ignore-dependencies" or
"ignore-requirements". Defaults to "replace". Specifies how the
units listed in OnFailure= will be enqueued. See systemctl(1)'s
--job-mode= option for details on the possible values. If this is
set to "isolate", only a single unit may be listed in OnFailure=.
IgnoreOnIsolate=
Takes a boolean argument. If true, this unit will not be stopped
when isolating another unit. Defaults to false for service,
target, socket, busname, timer, and path units, and true for
slice, scope, device, swap, mount, and automount units.
StopWhenUnneeded=
Takes a boolean argument. If true, this unit will be stopped when
it is no longer used. Note that, in order to minimize the work to
be executed, systemd will not stop units by default unless they
are conflicting with other units, or the user explicitly
requested their shut down. If this option is set, a unit will be
automatically cleaned up if no other active unit requires it.
Defaults to false.
RefuseManualStart=, RefuseManualStop=
Takes a boolean argument. If true, this unit can only be
activated or deactivated indirectly. In this case, explicit
start-up or termination requested by the user is denied, however
if it is started or stopped as a dependency of another unit,
start-up or termination will succeed. This is mostly a safety
feature to ensure that the user does not accidentally activate
units that are not intended to be activated explicitly, and not
accidentally deactivate units that are not intended to be
deactivated. These options default to false.
AllowIsolate=
Takes a boolean argument. If true, this unit may be used with the
systemctl isolate command. Otherwise, this will be refused. It
probably is a good idea to leave this disabled except for target
units that shall be used similar to runlevels in SysV init
systems, just as a precaution to avoid unusable system states.
This option defaults to false.
DefaultDependencies=
Takes a boolean argument. If yes, (the default), a few default
dependencies will implicitly be created for the unit. The actual
dependencies created depend on the unit type. For example, for
service units, these dependencies ensure that the service is
started only after basic system initialization is completed and
is properly terminated on system shutdown. See the respective man
pages for details. Generally, only services involved with early
boot or late shutdown should set this option to no. It is highly
recommended to leave this option enabled for the majority of
common units. If set to no, this option does not disable all
implicit dependencies, just non-essential ones.
CollectMode=
Tweaks the "garbage collection" algorithm for this unit. Takes
one of inactive or inactive-or-failed. If set to inactive the
unit will be unloaded if it is in the inactive state and is not
referenced by clients, jobs or other units — however it is not
unloaded if it is in the failed state. In failed mode, failed
units are not unloaded until the user invoked systemctl
reset-failed on them to reset the failed state, or an equivalent
command. This behaviour is altered if this option is set to
inactive-or-failed: in this case the unit is unloaded even if the
unit is in a failed state, and thus an explicitly resetting of
the failed state is not necessary. Note that if this mode is used
unit results (such as exit codes, exit signals, consumed
resources, ...) are flushed out immediately after the unit
completed, except for what is stored in the logging subsystem.
Defaults to inactive.
FailureAction=, SuccessAction=
Configure the action to take when the unit stops and enters a
failed state or inactive state. Takes one of none, reboot,
reboot-force, reboot-immediate, poweroff, poweroff-force,
poweroff-immediate, exit, and exit-force. In system mode, all
options are allowed. In user mode, only none, exit, and
exit-force are allowed. Both options default to none.
If none is set, no action will be triggered. reboot causes a
reboot following the normal shutdown procedure (i.e. equivalent
to systemctl reboot). reboot-force causes a forced reboot which
will terminate all processes forcibly but should cause no dirty
file systems on reboot (i.e. equivalent to systemctl reboot -f)
and reboot-immediate causes immediate execution of the reboot(2)
system call, which might result in data loss (i.e. equivalent to
systemctl reboot -ff). Similarly, poweroff, poweroff-force,
poweroff-immediate have the effect of powering down the system
with similar semantics. exit causes the manager to exit
following the normal shutdown procedure, and exit-force causes it
terminate without shutting down services. When exit or exit-force
is used by default the exit status of the main process of the
unit (if this applies) is returned from the service manager.
However, this may be overridden with
FailureActionExitStatus=/SuccessActionExitStatus=, see below.
FailureActionExitStatus=, SuccessActionExitStatus=
Controls the exit status to propagate back to an invoking
container manager (in case of a system service) or service
manager (in case of a user manager) when the
FailureAction=/SuccessAction= are set to exit or exit-force and
the action is triggered. By default the exit status of the main
process of the triggering unit (if this applies) is propagated.
Takes a value in the range 0...255 or the empty string to request
default behaviour.
JobTimeoutSec=, JobRunningTimeoutSec=
When a job for this unit is queued, a timeout JobTimeoutSec= may
be configured. Similarly, JobRunningTimeoutSec= starts counting
when the queued job is actually started. If either time limit is
reached, the job will be cancelled, the unit however will not
change state or even enter the "failed" mode. This value defaults
to "infinity" (job timeouts disabled), except for device units
(JobRunningTimeoutSec= defaults to DefaultTimeoutStartSec=). NB:
this timeout is independent from any unit-specific timeout (for
example, the timeout set with TimeoutStartSec= in service units)
as the job timeout has no effect on the unit itself, only on the
job that might be pending for it. Or in other words:
unit-specific timeouts are useful to abort unit state changes,
and revert them. The job timeout set with this option however is
useful to abort only the job waiting for the unit state to
change.
JobTimeoutAction=, JobTimeoutRebootArgument=
JobTimeoutAction= optionally configures an additional action to
take when the timeout is hit, see description of JobTimeoutSec=
and JobRunningTimeoutSec= above. It takes the same values as
StartLimitAction=. Defaults to none. JobTimeoutRebootArgument=
configures an optional reboot string to pass to the reboot(2)
system call.
StartLimitIntervalSec=interval, StartLimitBurst=burst
Configure unit start rate limiting. Units which are started more
than burst times within an interval time interval are not
permitted to start any more. Use StartLimitIntervalSec= to
configure the checking interval (defaults to
DefaultStartLimitIntervalSec= in manager configuration file, set
it to 0 to disable any kind of rate limiting). Use
StartLimitBurst= to configure how many starts per interval are
allowed (defaults to DefaultStartLimitBurst= in manager
configuration file). These configuration options are particularly
useful in conjunction with the service setting Restart= (see
systemd.service(5)); however, they apply to all kinds of starts
(including manual), not just those triggered by the Restart=
logic. Note that units which are configured for Restart= and
which reach the start limit are not attempted to be restarted
anymore; however, they may still be restarted manually at a later
point, after the interval has passed. From this point on, the
restart logic is activated again. Note that systemctl
reset-failed will cause the restart rate counter for a service to
be flushed, which is useful if the administrator wants to
manually start a unit and the start limit interferes with that.
Note that this rate-limiting is enforced after any unit condition
checks are executed, and hence unit activations with failing
conditions do not count towards this rate limit. This setting
does not apply to slice, target, device, and scope units, since
they are unit types whose activation may either never fail, or
may succeed only a single time.
When a unit is unloaded due to the garbage collection logic (see
above) its rate limit counters are flushed out too. This means
that configuring start rate limiting for a unit that is not
referenced continuously has no effect.
StartLimitAction=
Configure an additional action to take if the rate limit
configured with StartLimitIntervalSec= and StartLimitBurst= is
hit. Takes the same values as the FailureAction=/SuccessAction=
settings. If none is set, hitting the rate limit will trigger no
action except that the start will not be permitted. Defaults to
none.
RebootArgument=
Configure the optional argument for the reboot(2) system call if
StartLimitAction= or FailureAction= is a reboot action. This
works just like the optional argument to systemctl reboot
command.
SourcePath=
A path to a configuration file this unit has been generated from.
This is primarily useful for implementation of generator tools
that convert configuration from an external configuration file
format into native unit files. This functionality should not be
used in normal units.
Conditions and Asserts
Unit files may also include a number of Condition...= and Assert...=
settings. Before the unit is started, systemd will verify that the
specified conditions are true. If not, the starting of the unit will
be (mostly silently) skipped. Failing conditions will not result in
the unit being moved into the "failed" state. The conditions are
checked at the time the queued start job is to be executed. The
ordering dependencies are still respected, so other units are still
pulled in and ordered as if this unit was successfully activated. Use
condition expressions in order to skip units that do not apply to the
local system, for example because the kernel or runtime environment
doesn't require their functionality.
If multiple conditions are specified, the unit will be executed if
all of them apply (i.e. a logical AND is applied). Condition checks
can use a pipe symbol ("|") after the equals sign
("Condition...=|..."), which causes the condition becomes a
triggering condition. If at least one triggering condition is defined
for a unit, then the unit will be executed if at least one of the
triggering conditions apply and all of the non-triggering conditions.
If you prefix an argument with the pipe symbol and an exclamation
mark, the pipe symbol must be passed first, the exclamation second.
If any of these options is assigned the empty string, the list of
conditions is reset completely, all previous condition settings (of
any kind) will have no effect.
The AssertArchitecture=, AssertVirtualization=, ... options provide a
similar mechanism that causes the job to fail (instead of being
skipped). The failed check is logged. Units with failed conditions
are considered to be in a clean state and will be garbage collected
if they are not referenced. This means that when queried, the
condition failure may or may not show up in the state of the unit.
Note that neither assertion nor condition expressions result in unit
state changes. Also note that both are checked at the time the job is
to be executed, i.e. long after depending jobs and it itself were
queued. Thus, neither condition nor assertion expressions are
suitable for conditionalizing unit dependencies.
The condition verb of systemd-analyze(1) can be used to test
condition and assert expressions.
Except for ConditionPathIsSymbolicLink=, all path checks follow
symlinks.
ConditionArchitecture=
Check whether the system is running on a specific architecture.
Takes one of "x86", "x86-64", "ppc", "ppc-le", "ppc64",
"ppc64-le", "ia64", "parisc", "parisc64", "s390", "s390x",
"sparc", "sparc64", "mips", "mips-le", "mips64", "mips64-le",
"alpha", "arm", "arm-be", "arm64", "arm64-be", "sh", "sh64",
"m68k", "tilegx", "cris", "arc", "arc-be", or "native".
The architecture is determined from the information returned by
uname(2) and is thus subject to personality(2). Note that a
Personality= setting in the same unit file has no effect on this
condition. A special architecture name "native" is mapped to the
architecture the system manager itself is compiled for. The test
may be negated by prepending an exclamation mark.
ConditionVirtualization=
Check whether the system is executed in a virtualized environment
and optionally test whether it is a specific implementation.
Takes either boolean value to check if being executed in any
virtualized environment, or one of "vm" and "container" to test
against a generic type of virtualization solution, or one of
"qemu", "kvm", "zvm", "vmware", "microsoft", "oracle", "xen",
"bochs", "uml", "bhyve", "qnx", "openvz", "lxc", "lxc-libvirt",
"systemd-nspawn", "docker", "podman", "rkt", "wsl", "proot",
"acrn" to test against a specific implementation, or
"private-users" to check whether we are running in a user
namespace. See systemd-detect-virt(1) for a full list of known
virtualization technologies and their identifiers. If multiple
virtualization technologies are nested, only the innermost is
considered. The test may be negated by prepending an exclamation
mark.
ConditionHost=
ConditionHost= may be used to match against the hostname or
machine ID of the host. This either takes a hostname string
(optionally with shell style globs) which is tested against the
locally set hostname as returned by gethostname(2), or a machine
ID formatted as string (see machine-id(5)). The test may be
negated by prepending an exclamation mark.
ConditionKernelCommandLine=
ConditionKernelCommandLine= may be used to check whether a
specific kernel command line option is set (or if prefixed with
the exclamation mark — unset). The argument must either be a
single word, or an assignment (i.e. two words, separated by "=").
In the former case the kernel command line is searched for the
word appearing as is, or as left hand side of an assignment. In
the latter case, the exact assignment is looked for with right
and left hand side matching.
ConditionKernelVersion=
ConditionKernelVersion= may be used to check whether the kernel
version (as reported by uname -r) matches a certain expression
(or if prefixed with the exclamation mark does not match it). The
argument must be a list of (potentially quoted) expressions. For
each of the expressions, if it starts with one of "<", "<=", "=",
"!=", ">=", ">" a relative version comparison is done, otherwise
the specified string is matched with shell-style globs.
Note that using the kernel version string is an unreliable way to
determine which features are supported by a kernel, because of
the widespread practice of backporting drivers, features, and
fixes from newer upstream kernels into older versions provided by
distributions. Hence, this check is inherently unportable and
should not be used for units which may be used on different
distributions.
ConditionEnvironment=
ConditionEnvironment= may be used to check whether a specific
environment variable is set (or if prefixed with the exclamation
mark — unset) in the service manager's environment block. The
argument may be a single word, to check if the variable with this
name is defined in the environment block, or an assignment
("name=value"), to check if the variable with this exact value is
defined. Note that the environment block of the service manager
itself is checked, i.e. not any variables defined with
Environment= or EnvironmentFile=, as described above. This is
particularly useful when the service manager runs inside a
containerized environment or as per-user service manager, in
order to check for variables passed in by the enclosing container
manager or PAM.
ConditionSecurity=
ConditionSecurity= may be used to check whether the given
security technology is enabled on the system. Currently, the
recognized values are "selinux", "apparmor", "tomoyo", "ima",
"smack", "audit" and "uefi-secureboot". The test may be negated
by prepending an exclamation mark.
ConditionCapability=
Check whether the given capability exists in the capability
bounding set of the service manager (i.e. this does not check
whether capability is actually available in the permitted or
effective sets, see capabilities(7) for details). Pass a
capability name such as "CAP_MKNOD", possibly prefixed with an
exclamation mark to negate the check.
ConditionACPower=
Check whether the system has AC power, or is exclusively battery
powered at the time of activation of the unit. This takes a
boolean argument. If set to "true", the condition will hold only
if at least one AC connector of the system is connected to a
power source, or if no AC connectors are known. Conversely, if
set to "false", the condition will hold only if there is at least
one AC connector known and all AC connectors are disconnected
from a power source.
ConditionNeedsUpdate=
Takes one of /var or /etc as argument, possibly prefixed with a
"!" (to invert the condition). This condition may be used to
conditionalize units on whether the specified directory requires
an update because /usr's modification time is newer than the
stamp file .updated in the specified directory. This is useful to
implement offline updates of the vendor operating system
resources in /usr that require updating of /etc or /var on the
next following boot. Units making use of this condition should
order themselves before systemd-update-done.service(8), to make
sure they run before the stamp file's modification time gets
reset indicating a completed update.
If the systemd.condition-needs-update= option is specified on the
kernel command line (taking a boolean), it will override the
result of this condition check, taking precedence over any file
modification time checks. If it is used
systemd-update-done.service will not have immediate effect on any
following ConditionNeedsUpdate= checks, until the system is
rebooted where the kernel command line option is not specified
anymore.
ConditionFirstBoot=
Takes a boolean argument. This condition may be used to
conditionalize units on whether the system is booting up with an
unpopulated /etc directory (specifically: an /etc with no
/etc/machine-id). This may be used to populate /etc on the first
boot after factory reset, or when a new system instance boots up
for the first time.
If the systemd.condition-first-boot= option is specified on the
kernel command line (taking a boolean), it will override the
result of this condition check, taking precedence over
/etc/machine-id existence checks.
ConditionPathExists=
Check for the exists of a file. If the specified absolute path
name does not exist, the condition will fail. If the absolute
path name passed to ConditionPathExists= is prefixed with an
exclamation mark ("!"), the test is negated, and the unit is only
started if the path does not exist.
ConditionPathExistsGlob=
ConditionPathExistsGlob= is similar to ConditionPathExists=, but
checks for the existence of at least one file or directory
matching the specified globbing pattern.
ConditionPathIsDirectory=
ConditionPathIsDirectory= is similar to ConditionPathExists= but
verifies that a certain path exists and is a directory.
ConditionPathIsSymbolicLink=
ConditionPathIsSymbolicLink= is similar to ConditionPathExists=
but verifies that a certain path exists and is a symbolic link.
ConditionPathIsMountPoint=
ConditionPathIsMountPoint= is similar to ConditionPathExists= but
verifies that a certain path exists and is a mount point.
ConditionPathIsReadWrite=
ConditionPathIsReadWrite= is similar to ConditionPathExists= but
verifies that the underlying file system is readable and writable
(i.e. not mounted read-only).
ConditionPathIsEncrypted=
ConditionPathIsEncrypted= is similar to ConditionPathExists= but
verifies that the underlying file system's backing block device
is encrypted using dm-crypt/LUKS. Note that this check does not
cover ext4 per-directory encryption, and only detects block level
encryption. Moreover, if the specified path resides on a file
system on top of a loopback block device, only encryption above
the loopback device is detected. It is not detected whether the
file system backing the loopback block device is encrypted.
ConditionDirectoryNotEmpty=
ConditionDirectoryNotEmpty= is similar to ConditionPathExists=
but verifies that a certain path exists and is a non-empty
directory.
ConditionFileNotEmpty=
ConditionFileNotEmpty= is similar to ConditionPathExists= but
verifies that a certain path exists and refers to a regular file
with a non-zero size.
ConditionFileIsExecutable=
ConditionFileIsExecutable= is similar to ConditionPathExists= but
verifies that a certain path exists, is a regular file, and
marked executable.
ConditionUser=
ConditionUser= takes a numeric "UID", a UNIX user name, or the
special value "@system". This condition may be used to check
whether the service manager is running as the given user. The
special value "@system" can be used to check if the user id is
within the system user range. This option is not useful for
system services, as the system manager exclusively runs as the
root user, and thus the test result is constant.
ConditionGroup=
ConditionGroup= is similar to ConditionUser= but verifies that
the service manager's real or effective group, or any of its
auxiliary groups, match the specified group or GID. This setting
does not support the special value "@system".
ConditionControlGroupController=
Verify that the given cgroup controller (eg. "cpu") is available
for use on the system. For example, a particular controller may
not be available if it was disabled on the kernel command line
with cgroup_disable=controller. Multiple controllers may be
passed with a space separating them; in this case the condition
will only pass if all listed controllers are available for use.
Controllers unknown to systemd are ignored. Valid controllers are
"cpu", "cpuacct", "io", "blkio", "memory", "devices", and "pids".
ConditionMemory=
Verify that the specified amount of system memory is available to
the current system. Takes a memory size in bytes as argument,
optionally prefixed with a comparison operator "<", "<=", "=",
"!=", ">=", ">". On bare-metal systems compares the amount of
physical memory in the system with the specified size, adhering
to the specified comparison operator. In containers compares the
amount of memory assigned to the container instead.
ConditionCPUs=
Verify that the specified number of CPUs is available to the
current system. Takes a number of CPUs as argument, optionally
prefixed with a comparison operator "<", "<=", "=", "!=", ">=",
">". Compares the number of CPUs in the CPU affinity mask
configured of the service manager itself with the specified
number, adhering to the specified comparison operator. On
physical systems the number of CPUs in the affinity mask of the
service manager usually matches the number of physical CPUs, but
in special and virtual environments might differ. In particular,
in containers the affinity mask usually matches the number of
CPUs assigned to the container and not the physically available
ones.
AssertArchitecture=, AssertVirtualization=, AssertHost=,
AssertKernelCommandLine=, AssertKernelVersion=, AssertSecurity=,
AssertCapability=, AssertACPower=, AssertNeedsUpdate=,
AssertFirstBoot=, AssertPathExists=, AssertPathExistsGlob=,
AssertPathIsDirectory=, AssertPathIsSymbolicLink=,
AssertPathIsMountPoint=, AssertPathIsReadWrite=,
AssertDirectoryNotEmpty=, AssertFileNotEmpty=,
AssertFileIsExecutable=, AssertUser=, AssertGroup=,
AssertControlGroupController=
Similar to the ConditionArchitecture=, ConditionVirtualization=,
..., condition settings described above, these settings add
assertion checks to the start-up of the unit. However, unlike the
conditions settings, any assertion setting that is not met
results in failure of the start job (which means this is logged
loudly). Note that hitting a configured assertion does not cause
the unit to enter the "failed" state (or in fact result in any
state change of the unit), it affects only the job queued for it.
Use assertion expressions for units that cannot operate when
specific requirements are not met, and when this is something the
administrator or user should look into.
Unit settings that create a relationship with a second unit usually
show up in properties of both units, for example in systemctl show
output. In some cases the name of the property is the same as the
name of the configuration setting, but not always. This table lists
the properties that are shown on two units which are connected
through some dependency, and shows which property on "source" unit
corresponds to which property on the "target" unit.
Table 3. Forward and reverse unit properties
┌──────────────────────┬───────────────────────┬───────────────────────────────┐
│"Forward" │ "Reverse" │ Where used │
│property │ property │ │
├──────────────────────┼───────────────────────┼───────────────────────────────┤
│Before= │ After= │ │
├──────────────────────┼───────────────────────┤ [Unit] section │
│After= │ Before= │ │
├──────────────────────┼───────────────────────┼────────────────┬──────────────┤
│Requires= │ RequiredBy= │ [Unit] section │ [Install] │
│ │ │ │ section │
├──────────────────────┼───────────────────────┼────────────────┼──────────────┤
│Wants= │ WantedBy= │ [Unit] section │ [Install] │
│ │ │ │ section │
├──────────────────────┼───────────────────────┼────────────────┼──────────────┤
│PartOf= │ ConsistsOf= │ [Unit] section │ an automatic │
│ │ │ │ property │
├──────────────────────┼───────────────────────┼────────────────┼──────────────┤
│BindsTo= │ BoundBy= │ [Unit] section │ an automatic │
│ │ │ │ property │
├──────────────────────┼───────────────────────┼────────────────┼──────────────┤
│Requisite= │ RequisiteOf= │ [Unit] section │ an automatic │
│ │ │ │ property │
├──────────────────────┼───────────────────────┼────────────────┴──────────────┤
│Triggers= │ TriggeredBy= │ Automatic properties, see │
│ │ │ notes below │
├──────────────────────┼───────────────────────┼────────────────┬──────────────┤
│Conflicts= │ ConflictedBy= │ [Unit] section │ an automatic │
│ │ │ │ property │
├──────────────────────┼───────────────────────┼────────────────┴──────────────┤
│PropagatesReloadTo= │ ReloadPropagatedFrom= │ │
├──────────────────────┼───────────────────────┤ [Unit] section │
│ReloadPropagatedFrom= │ PropagatesReloadTo= │ │
├──────────────────────┼───────────────────────┼────────────────┬──────────────┤
│Following= │ n/a │ An automatic │ │
│ │ │ property │ │
└──────────────────────┴───────────────────────┴────────────────┴──────────────┘
Note: WantedBy= and RequiredBy= are used in the [Install] section to
create symlinks in .wants/ and .requires/ directories. They cannot be
used directly as a unit configuration setting.
Note: ConsistsOf=, BoundBy=, RequisiteOf=, ConflictedBy= are created
implicitly along with their reverses and cannot be specified
directly.
Note: Triggers= is created implicitly between a socket, path unit, or
an automount unit, and the unit they activate. By default a unit with
the same name is triggered, but this can be overridden using
Sockets=, Service=, and Unit= settings. See systemd.service(5),
systemd.socket(5), systemd.path(5), and systemd.automount(5) for
details. TriggeredBy= is created implicitly on the triggered unit.
Note: Following= is used to group device aliases and points to the
"primary" device unit that systemd is using to track device state,
usually corresponding to a sysfs path. It does not show up in the
"target" unit.
Unit files may include an [Install] section, which carries
installation information for the unit. This section is not
interpreted by systemd(1) during runtime; it is used by the enable
and disable commands of the systemctl(1) tool during installation of
a unit.
Alias=
A space-separated list of additional names this unit shall be
installed under. The names listed here must have the same suffix
(i.e. type) as the unit filename. This option may be specified
more than once, in which case all listed names are used. At
installation time, systemctl enable will create symlinks from
these names to the unit filename. Note that not all unit types
support such alias names, and this setting is not supported for
them. Specifically, mount, slice, swap, and automount units do
not support aliasing.
WantedBy=, RequiredBy=
This option may be used more than once, or a space-separated list
of unit names may be given. A symbolic link is created in the
.wants/ or .requires/ directory of each of the listed units when
this unit is installed by systemctl enable. This has the effect
that a dependency of type Wants= or Requires= is added from the
listed unit to the current unit. The primary result is that the
current unit will be started when the listed unit is started. See
the description of Wants= and Requires= in the [Unit] section for
details.
WantedBy=foo.service in a service bar.service is mostly
equivalent to Alias=foo.service.wants/bar.service in the same
file. In case of template units, systemctl enable must be called
with an instance name, and this instance will be added to the
.wants/ or .requires/ list of the listed unit. E.g.
WantedBy=getty.target in a service getty@.service will result in
systemctl enable getty@tty2.service creating a
getty.target.wants/getty@tty2.service link to getty@.service.
Also=
Additional units to install/deinstall when this unit is
installed/deinstalled. If the user requests
installation/deinstallation of a unit with this option
configured, systemctl enable and systemctl disable will
automatically install/uninstall units listed in this option as
well.
This option may be used more than once, or a space-separated list
of unit names may be given.
DefaultInstance=
In template unit files, this specifies for which instance the
unit shall be enabled if the template is enabled without any
explicitly set instance. This option has no effect in
non-template unit files. The specified string must be usable as
instance identifier.
The following specifiers are interpreted in the Install section: %n,
%N, %p, %i, %j, %g, %G, %U, %u, %m, %H, %b, %v. For their meaning see
the next section.
Many settings resolve specifiers which may be used to write generic
unit files referring to runtime or unit parameters that are replaced
when the unit files are loaded. Specifiers must be known and
resolvable for the setting to be valid. The following specifiers are
understood:
Table 4. Specifiers available in unit files
┌──────────┬─────────────────────┬────────────────────────┐
│Specifier │ Meaning │ Details │
├──────────┼─────────────────────┼────────────────────────┤
│"%a" │ Architecture │ A short string │
│ │ │ identifying the │
│ │ │ architecture of the │
│ │ │ local system. A │
│ │ │ string such as x86, │
│ │ │ x86-64 or arm64. │
│ │ │ See the │
│ │ │ architectures │
│ │ │ defined for │
│ │ │ ConditionArchitecture= │
│ │ │ above for a full │
│ │ │ list. │
├──────────┼─────────────────────┼────────────────────────┤
│"%b" │ Boot ID │ The boot ID of the │
│ │ │ running system, │
│ │ │ formatted as string. │
│ │ │ See random(4) for more │
│ │ │ information. │
├──────────┼─────────────────────┼────────────────────────┤
│"%B" │ Operating system │ The operating system │
│ │ build ID │ build identifier of │
│ │ │ the running system, as │
│ │ │ read from the │
│ │ │ BUILD_ID= field of │
│ │ │ /etc/os-release. If │
│ │ │ not set, resolves to │
│ │ │ an empty string. See │
│ │ │ os-release(5) for more │
│ │ │ information. │
├──────────┼─────────────────────┼────────────────────────┤
│"%C" │ Cache directory │ This is either │
│ │ root │ /var/cache (for the │
│ │ │ system manager) or the │
│ │ │ path "$XDG_CACHE_HOME" │
│ │ │ resolves to (for user │
│ │ │ managers). │
├──────────┼─────────────────────┼────────────────────────┤
│"%E" │ Configuration │ This is either /etc │
│ │ directory root │ (for the system │
│ │ │ manager) or the path │
│ │ │ "$XDG_CONFIG_HOME" │
│ │ │ resolves to (for user │
│ │ │ managers). │
├──────────┼─────────────────────┼────────────────────────┤
│"%f" │ Unescaped filename │ This is either the │
│ │ │ unescaped instance │
│ │ │ name (if applicable) │
│ │ │ with / prepended (if │
│ │ │ applicable), or the │
│ │ │ unescaped prefix name │
│ │ │ prepended with /. This │
│ │ │ implements unescaping │
│ │ │ according to the rules │
│ │ │ for escaping absolute │
│ │ │ file system paths │
│ │ │ discussed above. │
├──────────┼─────────────────────┼────────────────────────┤
│"%h" │ User home directory │ This is the home │
│ │ │ directory of the user │
│ │ │ running the service │
│ │ │ manager instance. In │
│ │ │ case of the system │
│ │ │ manager this resolves │
│ │ │ to "/root". │
│ │ │ │
│ │ │ Note that this setting │
│ │ │ is not influenced by │
│ │ │ the User= setting │
│ │ │ configurable in the │
│ │ │ [Service] section of │
│ │ │ the service unit. │
├──────────┼─────────────────────┼────────────────────────┤
│"%H" │ Host name │ The hostname of the │
│ │ │ running system at the │
│ │ │ point in time the unit │
│ │ │ configuration is │
│ │ │ loaded. │
├──────────┼─────────────────────┼────────────────────────┤
│"%l" │ Short host name │ The hostname of the │
│ │ │ running system at the │
│ │ │ point in time the unit │
│ │ │ configuration is │
│ │ │ loaded, truncated at │
│ │ │ the first dot to │
│ │ │ remove any domain │
│ │ │ component. │
├──────────┼─────────────────────┼────────────────────────┤
│"%i" │ Instance name │ For instantiated units │
│ │ │ this is the string │
│ │ │ between the first "@" │
│ │ │ character and the type │
│ │ │ suffix. Empty for │
│ │ │ non-instantiated │
│ │ │ units. │
├──────────┼─────────────────────┼────────────────────────┤
│"%I" │ Unescaped instance │ Same as "%i", but with │
│ │ name │ escaping undone. │
├──────────┼─────────────────────┼────────────────────────┤
│"%j" │ Final component of │ This is the string │
│ │ the prefix │ between the last "-" │
│ │ │ and the end of the │
│ │ │ prefix name. If there │
│ │ │ is no "-", this is the │
│ │ │ same as "%p". │
├──────────┼─────────────────────┼────────────────────────┤
│"%J" │ Unescaped final │ Same as "%j", but with │
│ │ component of the │ escaping undone. │
│ │ prefix │ │
├──────────┼─────────────────────┼────────────────────────┤
│"%L" │ Log directory root │ This is either │
│ │ │ /var/log (for the │
│ │ │ system manager) or the │
│ │ │ path │
│ │ │ "$XDG_CONFIG_HOME" │
│ │ │ resolves to with /log │
│ │ │ appended (for user │
│ │ │ managers). │
├──────────┼─────────────────────┼────────────────────────┤
│"%m" │ Machine ID │ The machine ID of the │
│ │ │ running system, │
│ │ │ formatted as string. │
│ │ │ See machine-id(5) for │
│ │ │ more information. │
├──────────┼─────────────────────┼────────────────────────┤
│"%o" │ Operating system ID │ The operating system │
│ │ │ identifier of the │
│ │ │ running system, as │
│ │ │ read from the ID= │
│ │ │ field of │
│ │ │ /etc/os-release. See │
│ │ │ os-release(5) for more │
│ │ │ information. │
├──────────┼─────────────────────┼────────────────────────┤
│"%n" │ Full unit name │ │
├──────────┼─────────────────────┼────────────────────────┤
│"%N" │ Full unit name │ Same as "%n", but with │
│ │ │ the type suffix │
│ │ │ removed. │
├──────────┼─────────────────────┼────────────────────────┤
│"%p" │ Prefix name │ For instantiated │
│ │ │ units, this refers to │
│ │ │ the string before the │
│ │ │ first "@" character of │
│ │ │ the unit name. For │
│ │ │ non-instantiated │
│ │ │ units, same as "%N". │
├──────────┼─────────────────────┼────────────────────────┤
│"%P" │ Unescaped prefix │ Same as "%p", but with │
│ │ name │ escaping undone. │
├──────────┼─────────────────────┼────────────────────────┤
│"%s" │ User shell │ This is the shell of │
│ │ │ the user running the │
│ │ │ service manager │
│ │ │ instance. In case of │
│ │ │ the system manager │
│ │ │ this resolves to │
│ │ │ "/bin/sh". │
├──────────┼─────────────────────┼────────────────────────┤
│"%S" │ State directory │ This is either │
│ │ root │ /var/lib (for the │
│ │ │ system manager) or the │
│ │ │ path │
│ │ │ "$XDG_CONFIG_HOME" │
│ │ │ resolves to (for user │
│ │ │ managers). │
├──────────┼─────────────────────┼────────────────────────┤
│"%t" │ Runtime directory │ This is either /run │
│ │ root │ (for the system │
│ │ │ manager) or the path │
│ │ │ "$XDG_RUNTIME_DIR" │
│ │ │ resolves to (for user │
│ │ │ managers). │
├──────────┼─────────────────────┼────────────────────────┤
│"%T" │ Directory for │ This is either /tmp or │
│ │ temporary files │ the path "$TMPDIR", │
│ │ │ "$TEMP" or "$TMP" are │
│ │ │ set to. │
├──────────┼─────────────────────┼────────────────────────┤
│"%g" │ User group │ This is the name of │
│ │ │ the group running the │
│ │ │ service manager │
│ │ │ instance. In case of │
│ │ │ the system manager │
│ │ │ this resolves to │
│ │ │ "root". │
├──────────┼─────────────────────┼────────────────────────┤
│"%G" │ User GID │ This is the numeric │
│ │ │ GID of the user │
│ │ │ running the service │
│ │ │ manager instance. In │
│ │ │ case of the system │
│ │ │ manager this resolves │
│ │ │ to "0". │
├──────────┼─────────────────────┼────────────────────────┤
│"%u" │ User name │ This is the name of │
│ │ │ the user running the │
│ │ │ service manager │
│ │ │ instance. In case of │
│ │ │ the system manager │
│ │ │ this resolves to │
│ │ │ "root". │
│ │ │ │
│ │ │ Note that this setting │
│ │ │ is not influenced by │
│ │ │ the User= setting │
│ │ │ configurable in the │
│ │ │ [Service] section of │
│ │ │ the service unit. │
├──────────┼─────────────────────┼────────────────────────┤
│"%U" │ User UID │ This is the numeric │
│ │ │ UID of the user │
│ │ │ running the service │
│ │ │ manager instance. In │
│ │ │ case of the system │
│ │ │ manager this resolves │
│ │ │ to "0". │
│ │ │ │
│ │ │ Note that this setting │
│ │ │ is not influenced by │
│ │ │ the User= setting │
│ │ │ configurable in the │
│ │ │ [Service] section of │
│ │ │ the service unit. │
├──────────┼─────────────────────┼────────────────────────┤
│"%v" │ Kernel release │ Identical to uname -r │
│ │ │ output. │
├──────────┼─────────────────────┼────────────────────────┤
│"%V" │ Directory for │ This is either │
│ │ larger and │ /var/tmp or the path │
│ │ persistent │ "$TMPDIR", "$TEMP" or │
│ │ temporary files │ "$TMP" are set to. │
├──────────┼─────────────────────┼────────────────────────┤
│"%w" │ Operating system │ The operating system │
│ │ version ID │ version identifier of │
│ │ │ the running system, as │
│ │ │ read from the │
│ │ │ VERSION_ID= field of │
│ │ │ /etc/os-release. If │
│ │ │ not set, resolves to │
│ │ │ an empty string. See │
│ │ │ os-release(5) for more │
│ │ │ information. │
├──────────┼─────────────────────┼────────────────────────┤
│"%W" │ Operating system │ The operating system │
│ │ variant ID │ variant identifier of │
│ │ │ the running system, as │
│ │ │ read from the │
│ │ │ VARIANT_ID= field of │
│ │ │ /etc/os-release. If │
│ │ │ not set, resolves to │
│ │ │ an empty string. See │
│ │ │ os-release(5) for more │
│ │ │ information. │
├──────────┼─────────────────────┼────────────────────────┤
│"%%" │ Single percent sign │ Use "%%" in place of │
│ │ │ "%" to specify a │
│ │ │ single percent sign. │
└──────────┴─────────────────────┴────────────────────────┘
Example 1. Allowing units to be enabled
The following snippet (highlighted) allows a unit (e.g. foo.service)
to be enabled via systemctl enable:
[Unit]
Description=Foo
[Service]
ExecStart=/usr/sbin/foo-daemon
[Install]
WantedBy=multi-user.target
After running systemctl enable, a symlink
/etc/systemd/system/multi-user.target.wants/foo.service linking to
the actual unit will be created. It tells systemd to pull in the unit
when starting multi-user.target. The inverse systemctl disable will
remove that symlink again.
Example 2. Overriding vendor settings
There are two methods of overriding vendor settings in unit files:
copying the unit file from /usr/lib/systemd/system to
/etc/systemd/system and modifying the chosen settings. Alternatively,
one can create a directory named unit.d/ within /etc/systemd/system
and place a drop-in file name.conf there that only changes the
specific settings one is interested in. Note that multiple such
drop-in files are read if present, processed in lexicographic order
of their filename.
The advantage of the first method is that one easily overrides the
complete unit, the vendor unit is not parsed at all anymore. It has
the disadvantage that improvements to the unit file by the vendor are
not automatically incorporated on updates.
The advantage of the second method is that one only overrides the
settings one specifically wants, where updates to the unit by the
vendor automatically apply. This has the disadvantage that some
future updates by the vendor might be incompatible with the local
changes.
This also applies for user instances of systemd, but with different
locations for the unit files. See the section on unit load paths for
further details.
Suppose there is a vendor-supplied unit
/usr/lib/systemd/system/httpd.service with the following contents:
[Unit]
Description=Some HTTP server
After=remote-fs.target sqldb.service
Requires=sqldb.service
AssertPathExists=/srv/webserver
[Service]
Type=notify
ExecStart=/usr/sbin/some-fancy-httpd-server
Nice=5
[Install]
WantedBy=multi-user.target
Now one wants to change some settings as an administrator: firstly,
in the local setup, /srv/webserver might not exist, because the HTTP
server is configured to use /srv/www instead. Secondly, the local
configuration makes the HTTP server also depend on a memory cache
service, memcached.service, that should be pulled in (Requires=) and
also be ordered appropriately (After=). Thirdly, in order to harden
the service a bit more, the administrator would like to set the
PrivateTmp= setting (see systemd.exec(5) for details). And lastly,
the administrator would like to reset the niceness of the service to
its default value of 0.
The first possibility is to copy the unit file to
/etc/systemd/system/httpd.service and change the chosen settings:
[Unit]
Description=Some HTTP server
After=remote-fs.target sqldb.service memcached.service
Requires=sqldb.service memcached.service
AssertPathExists=/srv/www
[Service]
Type=notify
ExecStart=/usr/sbin/some-fancy-httpd-server
Nice=0
PrivateTmp=yes
[Install]
WantedBy=multi-user.target
Alternatively, the administrator could create a drop-in file
/etc/systemd/system/httpd.service.d/local.conf with the following
contents:
[Unit]
After=memcached.service
Requires=memcached.service
# Reset all assertions and then re-add the condition we want
AssertPathExists=
AssertPathExists=/srv/www
[Service]
Nice=0
PrivateTmp=yes
Note that for drop-in files, if one wants to remove entries from a
setting that is parsed as a list (and is not a dependency), such as
AssertPathExists= (or e.g. ExecStart= in service units), one needs
to first clear the list before re-adding all entries except the one
that is to be removed. Dependencies (After=, etc.) cannot be reset to
an empty list, so dependencies can only be added in drop-ins. If you
want to remove dependencies, you have to override the entire unit.
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)
1. Interface Stability Promise
https://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2020-08-13. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-08-11.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to man-pages@man7.org
systemd 246 SYSTEMD.UNIT(5)
Pages that refer to this page: init(1) , portablectl(1) , systemctl(1) , systemd(1) , systemd-analyze(1) , systemd-delta(1) , systemd-escape(1) , systemd-firstboot(1) , systemd-firstboot.service(1) , systemd-mount(1) , systemd-notify(1) , systemd-run(1) , systemd-umount(1) , sd_bus_creds_get_audit_login_uid(3) , sd_bus_creds_get_audit_session_id(3) , sd_bus_creds_get_cgroup(3) , sd_bus_creds_get_cmdline(3) , sd_bus_creds_get_comm(3) , sd_bus_creds_get_description(3) , sd_bus_creds_get_egid(3) , sd_bus_creds_get_euid(3) , sd_bus_creds_get_exe(3) , sd_bus_creds_get_fsgid(3) , sd_bus_creds_get_fsuid(3) , sd_bus_creds_get_gid(3) , sd_bus_creds_get_owner_uid(3) , sd_bus_creds_get_pid(3) , sd_bus_creds_get_ppid(3) , sd_bus_creds_get_selinux_context(3) , sd_bus_creds_get_session(3) , sd_bus_creds_get_sgid(3) , sd_bus_creds_get_slice(3) , sd_bus_creds_get_suid(3) , sd_bus_creds_get_supplementary_gids(3) , sd_bus_creds_get_tid(3) , sd_bus_creds_get_tid_comm(3) , sd_bus_creds_get_tty(3) , sd_bus_creds_get_uid(3) , sd_bus_creds_get_unique_name(3) , sd_bus_creds_get_unit(3) , sd_bus_creds_get_user_slice(3) , sd_bus_creds_get_user_unit(3) , sd_bus_creds_get_well_known_names(3) , sd_bus_creds_has_bounding_cap(3) , sd_bus_creds_has_effective_cap(3) , sd_bus_creds_has_inheritable_cap(3) , sd_bus_creds_has_permitted_cap(3) , repart.d(5) , system.conf.d(5) , systemd.automount(5) , systemd.device(5) , systemd.dnssd(5) , systemd.exec(5) , systemd.kill(5) , systemd.link(5) , systemd.mount(5) , systemd.netdev(5) , systemd.network(5) , systemd.path(5) , systemd.preset(5) , systemd.resource-control(5) , systemd.scope(5) , systemd.service(5) , systemd.slice(5) , systemd.socket(5) , systemd.swap(5) , systemd-system.conf(5) , systemd.target(5) , systemd.timer(5) , systemd-user.conf(5) , systemd-user-runtime-dir(5) , sysusers.d(5) , tmpfiles.d(5) , user.conf.d(5) , user-runtime-dir.service(5) , user-runtime-dir@.service(5) , user.service(5) , user@.service(5) , 30-systemd-environment-d-generator(7) , daemon(7) , file-hierarchy(7) , kernel-command-line(7) , nfs.systemd(7) , systemd.directives(7) , systemd.generator(7) , systemd.index(7) , systemd.special(7) , systemd.syntax(7) , systemd.time(7) , udev(7) , systemd-run-generator(8) , systemd-update-done(8) , systemd-update-done.service(8)