SYSTEMD.UNIT(5) systemd.unit SYSTEMD.UNIT(5)
NAME
systemd.unit - Unit configuration
SYNOPSIS
service.service, socket.socket, device.device, mount.mount,
automount.automount, swap.swap, target.target, path.path, timer.timer,
slice.slice, scope.scope
/etc/systemd/system.control/*
/run/systemd/system.control/*
/run/systemd/transient/*
/run/systemd/generator.early/*
/etc/systemd/system/*
/run/systemd/system/*
/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/*
/etc/systemd/user/*
$XDG_RUNTIME_DIR/systemd/user/*
/run/systemd/user/*
$XDG_RUNTIME_DIR/systemd/generator/*
~/.local/share/systemd/user/*
...
/usr/lib/systemd/user/*
$XDG_RUNTIME_DIR/systemd/generator.late/*
DESCRIPTION
A unit file is a plain text ini-style file that encodes information
about a service, a socket, a device, a mount point, an automount point,
a swap file or partition, a start-up target, a watched file system
path, a timer controlled and supervised by systemd(1), a resource
management slice or a group of externally created processes. See
systemd.syntax(5) 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.
Unit files 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.
Boolean arguments used in unit files can be written in various formats.
For positive settings the strings 1, yes, true and on are equivalent.
For negative settings, the strings 0, no, false and off are equivalent.
Time span values encoded in unit files can be written in various
formats. A stand-alone number specifies a time in seconds. If suffixed
with a time unit, the unit is honored. A concatenation of multiple
values with units is supported, in which case the values are added up.
Example: "50" refers to 50 seconds; "2min 200ms" refers to 2 minutes
and 200 milliseconds, i.e. 120200 ms. The following time units are
understood: "s", "min", "h", "d", "w", "ms", "us". For details see
systemd.time(7).
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
the symlink
/usr/lib/systemd/system/dbus-org.freedesktop.network1.service. In
addition, unit files may specify aliases through the Alias= directive
in the [Install] section; those aliases are only effective when the
unit is enabled. 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 it
will be invoked whenever CTRL+ALT+DEL is pressed. Alias names may be
used in commands like enable, disable, start, stop, status, ..., and in
unit dependency directives Wants=, Requires=, Before=, After=, ...,
with the limitation that aliases specified through Alias= are only
effective when the unit is enabled. Aliases cannot be used with the
preset command.
Along with a unit file foo.service, the directory foo.service.wants/
may exist. All unit files symlinked from such a directory are
implicitly added as dependencies of type Wants= to the unit. This is
useful to hook units into the start-up of other units, without having
to modify their unit files. For details about the semantics of Wants=,
see below. The preferred way to create symlinks in the .wants/
directory of a unit file is with the enable command of the systemctl(1)
tool which reads information from the [Install] section of unit files
(see below). A similar functionality exists for Requires= type
dependencies as well, the directory suffix is .requires/ in this case.
Along with a unit file foo.service, a "drop-in" directory
foo.service.d/ may exist. All files with the suffix ".conf" from this
directory will be parsed after the 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 AT bar.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 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 AT tty3.service is requested and no
file by that name is found, systemd will look for getty@.service and
instantiate a service from that configuration file if it is found.
To refer to the instance string from within the configuration file you
may use the special "%i" specifier in many of the configuration
options. See below for details.
If a unit file is empty (i.e. has the file size 0) or is symlinked to
/dev/null, its configuration will not be loaded and it appears with a
load state of "masked", and cannot be activated. Use this as an
effective way to fully disable a unit, making it impossible to start it
even manually.
The unit file format is covered by the Interface Stability Promise[1].
STRING ESCAPING FOR INCLUSION IN UNIT NAMES
Sometimes it is useful to convert arbitrary strings into unit names. To
facilitate this, a method of string escaping is used, in order to map
strings containing arbitrary byte values (except NUL) into valid unit
names and their restricted character set. A common special case are
unit names that reflect paths to objects in the file system hierarchy.
Example: a device unit dev-sda.device refers to a device with the
device node /dev/sda in the file system.
The escaping algorithm operates as follows: given a string, any "/"
character is replaced by "-", and all other characters which are not
ASCII alphanumerics or "_" are replaced by C-style "\x2d" escapes. In
addition, "." is replaced with such a C-style escape when it would
appear as the first character in the escaped string.
When the input qualifies as absolute file system path, this algorithm
is extended slightly: the path to the root directory "/" is encoded as
single dash "-". In addition, any leading, trailing or duplicate "/"
characters are removed from the string before transformation. Example:
/foo//bar/baz/ becomes "foo-bar-baz".
This escaping is fully reversible, as long as it is known whether the
escaped string was a path (the unescaping results are different for
paths and non-path strings). The systemd-escape(1) command may be used
to apply and reverse escaping on arbitrary strings. Use systemd-escape
--path to escape path strings, and systemd-escape without --path
otherwise.
AUTOMATIC DEPENDENCIES
Implicit Dependencies
A number of unit dependencies are implicitly established, depending on
unit type and unit configuration. These implicit dependencies can make
unit configuration file cleaner. For the implicit dependencies in each
unit type, please refer to section "Implicit Dependencies" in
respective man pages.
For example, service units with Type=dbus automatically acquire
dependencies of type Requires= and After= on dbus.socket. See
systemd.service(5) for details.
Default Dependencies
Default dependencies are similar to implicit dependencies, but can be
turned on and off by setting DefaultDependencies= to yes (the default)
and no, while implicit dependencies are always in effect. See section
"Default Dependencies" in respective man pages for the effect of
enabling DefaultDependencies= in each unit types.
For example, target units will complement all configured dependencies
of type Wants= or Requires= with dependencies of type After= unless
DefaultDependencies=no is set in the specified units. See
systemd.target(5) for details. Note that this behavior can be turned
off by setting DefaultDependencies=no.
UNIT FILE LOAD PATH
Unit files are loaded from a set of paths determined during
compilation, described in the two tables below. Unit files found in
directories listed earlier override files with the same name in
directories lower in the list.
When the variable $SYSTEMD_UNIT_PATH is set, the contents of this
variable overrides the unit load path. If $SYSTEMD_UNIT_PATH ends with
an empty component (":"), the usual unit load path will be appended to
the contents of the variable.
Table 1. Load path when running in system mode (--system).
+------------------------------+----------------------------+
|Path | Description |
+------------------------------+----------------------------+
|/etc/systemd/system.control | Persistent and transient |
+------------------------------+ configuration created |
|/run/systemd/system.control | using the dbus API |
+------------------------------+----------------------------+
|/run/systemd/transient | Dynamic configuration for |
| | transient units |
+------------------------------+----------------------------+
|/run/systemd/generator.early | Generated units with high |
| | priority (see early-dir in |
| | system.generator(7)) |
+------------------------------+----------------------------+
|/etc/systemd/system | Local configuration |
+------------------------------+----------------------------+
|/run/systemd/system | Runtime units |
+------------------------------+----------------------------+
|/run/systemd/generator | Generated units with |
| | medium priority (see |
| | normal-dir in |
| | system.generator(7)) |
+------------------------------+----------------------------+
|/usr/local/lib/systemd/system | Units of installed |
+------------------------------+ packages |
|/usr/lib/systemd/system | |
+------------------------------+----------------------------+
|/run/systemd/generator.late | Generated units with low |
| | priority (see late-dir in |
| | system.generator(7)) |
+------------------------------+----------------------------+
Table 2. Load path when running in user mode (--user).
+----------------------------------------+----------------------------+
|Path | Description |
+----------------------------------------+----------------------------+
|$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 |
| | system.generator(7)) |
+----------------------------------------+----------------------------+
|$XDG_CONFIG_HOME/systemd/user or | User configuration |
|$HOME/.config/systemd/user | ($XDG_CONFIG_HOME is used |
| | if set, ~/.config |
| | otherwise) |
+----------------------------------------+----------------------------+
|/etc/systemd/user | Local configuration |
+----------------------------------------+----------------------------+
|$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 |
| | system.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 |
| | $XDG_DATA_DIRS |
+----------------------------------------+----------------------------+
|/usr/local/lib/systemd/user | Units of packages that |
+----------------------------------------+ have been installed |
|/usr/lib/systemd/user | system-wide |
+----------------------------------------+----------------------------+
|$XDG_RUNTIME_DIR/systemd/generator.late | Generated units with low |
| | priority (see late-dir in |
| | system.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 ("linked") from
directories not on the unit load path. See the link command for
systemctl(1).
UNIT GARBAGE COLLECTION
The system and service manager loads a unit's configuration
automatically when a unit is referenced for the first time. It will
automatically unload the unit configuration and state again when the
unit is not needed anymore ("garbage collection"). A unit may be
referenced through a number of different mechanisms:
1. Another loaded unit references it with a dependency such as After=,
Wants=, ...
2. The unit is currently starting, running, reloading or stopping.
3. The unit is currently in the failed state. (But see below.)
4. A job for the unit is pending.
5. The unit is pinned by an active IPC client program.
6. The unit is a special "perpetual" unit that is always active and
loaded. Examples for perpetual units are the root mount unit
-.mount or the scope unit init.scope that the service manager
itself lives in.
7. The unit has running processes associated with it.
The garbage collection logic may be altered with the CollectMode=
option, which allows configuration whether automatic unloading of units
that are in failed state is permissible, see below.
Note that when a unit's configuration and state is unloaded, all
execution results, such as exit codes, exit signals, resource
consumption and other statistics are lost, except for what is stored in
the log subsystem.
Use systemctl daemon-reload or an equivalent command to reload unit
configuration while the unit is already loaded. In this case all
configuration settings are flushed out and replaced with the new
configuration (which however might not be in effect immediately),
however all runtime state is saved/restored.
[UNIT] SECTION OPTIONS
The unit file may include a [Unit] section, which carries generic
information about the unit that is not dependent on the type of unit:
Description=
A free-form string describing the unit. This is intended for use in
UIs to show descriptive information along with the unit name. The
description should contain a name that means something to the end
user. "Apache2 Web Server" is a good example. Bad examples are
"high-performance light-weight HTTP server" (too generic) or
"Apache2" (too specific and meaningless for people who do not know
Apache).
Documentation=
A space-separated list of URIs referencing documentation for this
unit or its configuration. Accepted are only URIs of the types
"http://", "https://", "file:", "info:", "man:". For more
information about the syntax of these URIs, see uri(7). The URIs
should be listed in order of relevance, starting with the most
relevant. It is a good idea to first reference documentation that
explains what the unit's purpose is, followed by how it is
configured, followed by any other related documentation. This
option may be specified more than once, in which case the specified
list of URIs is merged. If the empty string is assigned to this
option, the list is reset and all prior assignments will have no
effect.
Requires=
Configures requirement dependencies on other units. If this unit
gets activated, the units listed here will be activated as well. If
one of the other units 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. This
option may be specified more than once or multiple space-separated
units may be specified in one option in which case requirement
dependencies for all listed names will be created. Note that
requirement dependencies do not influence the order in which
services are started or stopped. This has to be configured
independently with the After= or Before= options. If a unit
foo.service requires a unit bar.service as configured with
Requires= and no ordering is configured with After= or Before=,
then both units will be started simultaneously and without any
delay between them if foo.service is activated. Often, it is a
better choice to use Wants= instead of Requires= in order to
achieve a system that is more robust when dealing with failing
services.
Note that 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).
Note that dependencies of this type may also be configured outside
of the unit configuration file by adding a symlink to a .requires/
directory accompanying the unit file. For details, see above.
Requisite=
Similar to Requires=. However, if the units listed here are not
started already, they will not be started and the 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.
Wants=
A weaker version of Requires=. Units listed in this option will be
started if the configuring unit is. However, if the listed units
fail to start or cannot be added to the transaction, this has no
impact on the validity of the transaction as a whole. This is the
recommended way to hook start-up of one unit to the start-up of
another unit.
Note that dependencies of this type may also be configured outside
of the unit configuration file by adding symlinks to a .wants/
directory accompanying the unit file. For details, see above.
BindsTo=
Configures requirement dependencies, very similar in style to
Requires=. However, 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 is independent of and orthogonal to
the After= and Before= ordering dependencies.
If a unit A that conflicts with a unit B is scheduled to be started
at the same time as B, the transaction will either fail (in case
both are required part of the transaction) or be modified to be
fixed (in case one or both jobs are not a required part of the
transaction). In the latter case, the job that is not the required
will be removed, or in case both are not required, the unit that
conflicts will be started and the unit that is conflicted is
stopped.
Before=, After=
These two settings expect a space-separated list of unit names.
They configure ordering dependencies between units. If a unit
foo.service contains a setting Before=bar.service and both units
are being started, bar.service's start-up is delayed until
foo.service has finished starting up. Note that this setting is
independent of and orthogonal to the requirement dependencies as
configured by Requires=, Wants= or BindsTo=. It is a common pattern
to include a unit name in both the After= and Requires= options, in
which case the unit listed will be started before the unit that is
configured with these options. This option may be specified more
than once, in which case ordering dependencies for all listed names
are created. After= is the inverse of Before=, i.e. while After=
ensures that the configured unit is started after the listed unit
finished starting up, Before= ensures the opposite, that the
configured unit is fully started up before the listed unit is
started. Note that when two units with an ordering dependency
between them are shut down, the inverse of the start-up order is
applied. i.e. if a unit is configured with After= on another unit,
the former is stopped before the latter if both are shut down.
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.
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= 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= 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 true, (the default), a few default
dependencies will implicitly be created for the unit. The actual
dependencies created depend on the unit type. For example, for
service units, these dependencies ensure that the service is
started only after basic system initialization is completed and is
properly terminated on system shutdown. See the respective man
pages for details. Generally, only services involved with early
boot or late shutdown should set this option to false. It is highly
recommended to leave this option enabled for the majority of common
units. If set to false, this option does not disable all implicit
dependencies, just non-essential ones.
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. 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.
JobTimeoutSec=, JobRunningTimeoutSec=, JobTimeoutAction=,
JobTimeoutRebootArgument=
When a job for this unit is queued, a time-out 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= optionally configures an additional action to
take when the time-out is hit. 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 setting FailureAction=/SuccessAction= settings
and executes the same actions. If none is set, hitting the rate
limit will trigger no action besides 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.
ConditionArchitecture=, ConditionVirtualization=, ConditionHost=,
ConditionKernelCommandLine=, ConditionKernelVersion=,
ConditionSecurity=, ConditionCapability=, ConditionACPower=,
ConditionNeedsUpdate=, ConditionFirstBoot=, ConditionPathExists=,
ConditionPathExistsGlob=, ConditionPathIsDirectory=,
ConditionPathIsSymbolicLink=, ConditionPathIsMountPoint=,
ConditionPathIsReadWrite=, ConditionDirectoryNotEmpty=,
ConditionFileNotEmpty=, ConditionFileIsExecutable=, ConditionUser=,
ConditionGroup=, ConditionControlGroupController=
Before starting a unit, verify that the specified condition is
true. If it is not true, the starting of the unit will be (mostly
silently) skipped, however all ordering dependencies of it are
still respected. A failing condition will not result in the unit
being moved into a failure state. The condition is checked at the
time the queued start job is to be executed. Use condition
expressions in order to silently skip units that do not apply to
the local running system, for example because the kernel or runtime
environment doesn't require its functionality. Use the various
AssertArchitecture=, AssertVirtualization=, ... options for a
similar mechanism that puts the unit in a failure state and logs
about the failed check (see below).
ConditionArchitecture= may be used to check whether the system is
running on a specific architecture. Takes one of x86, x86-64, ppc,
ppc-le, ppc64, ppc64-le, ia64, parisc, parisc64, s390, s390x,
sparc, sparc64, mips, mips-le, mips64, mips64-le, alpha, arm,
arm-be, arm64, arm64-be, sh, sh64, m68k, tilegx, cris, arc, arc-be
to test against a specific architecture. The architecture is
determined from the information returned by uname(2) and is thus
subject to personality(2). Note that a Personality= setting in the
same unit file has no effect on this condition. A special
architecture name native is mapped to the architecture the system
manager itself is compiled for. The test may be negated by
prepending an exclamation mark.
ConditionVirtualization= may be used to check whether the system is
executed in a virtualized environment and optionally test whether
it is a specific implementation. Takes either boolean value to
check if being executed in any virtualized environment, or one of
vm and container to test against a generic type of virtualization
solution, or one of qemu, kvm, "amazon", zvm, vmware, microsoft,
oracle, xen, bochs, uml, bhyve, qnx, openvz, lxc, lxc-libvirt,
systemd-nspawn, docker, rkt 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= may be used to match against the hostname or machine
ID of the host. This either takes a hostname string (optionally
with shell style globs) which is tested against the locally set
hostname as returned by gethostname(2), or a machine ID formatted
as string (see machine-id(5)). The test may be negated by
prepending an exclamation mark.
ConditionKernelCommandLine= may be used to check whether a specific
kernel command line option is set (or if prefixed with the
exclamation mark unset). The argument must either be a single word,
or an assignment (i.e. two words, separated "="). In the former
case the kernel command line is searched for the word appearing as
is, or as left hand side of an assignment. In the latter case, the
exact assignment is looked for with right and left hand side
matching.
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 single string. If the string 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.
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= may be used to check whether the given
capability exists in the capability bounding set of the service
manager (i.e. this does not check whether capability is actually
available in the permitted or effective sets, see capabilities(7)
for details). Pass a capability name such as "CAP_MKNOD", possibly
prefixed with an exclamation mark to negate the check.
ConditionACPower= may be used to check whether the system has AC
power, or is exclusively battery powered at the time of activation
of the unit. This takes a boolean argument. If set to true, the
condition will hold only if at least one AC connector of the system
is connected to a power source, or if no AC connectors are known.
Conversely, if set to false, the condition will hold only if there
is at least one AC connector known and all AC connectors are
disconnected from a power source.
ConditionNeedsUpdate= takes one of /var or /etc as argument,
possibly prefixed with a "!" (for inverting the condition). This
condition may be used to conditionalize units on whether the
specified directory requires an update because /usr's modification
time is newer than the stamp file .updated in the specified
directory. This is useful to implement offline updates of the
vendor operating system resources in /usr that require updating of
/etc or /var on the next following boot. Units making use of this
condition should order themselves before systemd-update-
done.service(8), to make sure they run before the stamp file's
modification time gets reset indicating a completed update.
ConditionFirstBoot= takes a boolean argument. This condition may be
used to conditionalize units on whether the system is booting up
with an unpopulated /etc directory (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.
With ConditionPathExists= a file existence condition is checked
before a unit is started. If the specified absolute path name does
not exist, the condition will fail. If the absolute path name
passed to ConditionPathExists= is prefixed with an exclamation mark
("!"), the test is negated, and the unit is only started if the
path does not exist.
ConditionPathExistsGlob= is similar to ConditionPathExists=, but
checks for the existence of at least one file or directory matching
the specified globbing pattern.
ConditionPathIsDirectory= is similar to ConditionPathExists= but
verifies whether a certain path exists and is a directory.
ConditionPathIsSymbolicLink= is similar to ConditionPathExists= but
verifies whether a certain path exists and is a symbolic link.
ConditionPathIsMountPoint= is similar to ConditionPathExists= but
verifies whether a certain path exists and is a mount point.
ConditionPathIsReadWrite= is similar to ConditionPathExists= but
verifies whether the underlying file system is readable and
writable (i.e. not mounted read-only).
ConditionDirectoryNotEmpty= is similar to ConditionPathExists= but
verifies whether a certain path exists and is a non-empty
directory.
ConditionFileNotEmpty= is similar to ConditionPathExists= but
verifies whether a certain path exists and refers to a regular file
with a non-zero size.
ConditionFileIsExecutable= is similar to ConditionPathExists= but
verifies whether a certain path exists, is a regular file and
marked executable.
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= 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 have
a special value "@system".
ConditionControlGroupController= takes a cgroup controller name
(eg. cpu), verifying that it 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.
If multiple conditions are specified, the unit will be executed if
all of them apply (i.e. a logical AND is applied). Condition checks
can be prefixed with a pipe symbol (|) in which case a condition
becomes a triggering condition. If at least one triggering
condition is defined for a unit, then the unit will be executed if
at least one of the triggering conditions apply and all of the
non-triggering conditions. If you prefix an argument with the pipe
symbol and an exclamation mark, the pipe symbol must be passed
first, the exclamation second. Except for
ConditionPathIsSymbolicLink=, all path checks follow symlinks. If
any of these options is assigned the empty string, the list of
conditions is reset completely, all previous condition settings (of
any kind) will have no effect.
AssertArchitecture=, AssertVirtualization=, AssertHost=,
AssertKernelCommandLine=, 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).
Use assertion expressions for units that cannot operate when
specific requirements are not met, and when this is something the
administrator or user should look into.
SourcePath=
A path to a configuration file this unit has been generated from.
This is primarily useful for implementation of generator tools that
convert configuration from an external configuration file format
into native unit files. This functionality should not be used in
normal units.
MAPPING OF UNIT PROPERTIES TO THEIR INVERSES
Unit settings that create a relationship with a second unit usually
show up in properties of both units, for example in systemctl show
output. In some cases the name of the property is the same as the name
of the configuration setting, but not always. This table lists the
properties that are shown on two units which are connected through some
dependency, and shows which property on "source" unit corresponds to
which property on the "target" unit.
Table 3. Forward and reverse unit properties
+----------------------+-----------------------+---------------------+
|"Forward" property | "Reverse" property | Where used |
+----------------------+-----------------------+---------------------+
|Before= | After= | Both are unit file |
+----------------------+-----------------------+ options |
|After= | Before= | |
+----------------------+-----------------------+---------------------+
|Requires= | RequiredBy= | A unit file option; |
| | | an option in the |
| | | [Install] section |
+----------------------+-----------------------+---------------------+
|Wants= | WantedBy= | A unit file option; |
| | | an option in the |
| | | [Install] section |
+----------------------+-----------------------+---------------------+
|PartOf= | ConsistsOf= | A unit file option; |
| | | an automatic |
| | | property |
+----------------------+-----------------------+---------------------+
|BindsTo= | BoundBy= | A unit file option; |
| | | an automatic |
| | | property |
+----------------------+-----------------------+---------------------+
|Requisite= | RequisiteOf= | A unit file option; |
| | | an automatic |
| | | property |
+----------------------+-----------------------+---------------------+
|Triggers= | TriggeredBy= | Automatic |
| | | properties, see |
| | | notes below |
+----------------------+-----------------------+---------------------+
|Conflicts= | ConflictedBy= | A unit file option; |
| | | an automatic |
| | | property |
+----------------------+-----------------------+---------------------+
|PropagatesReloadTo= | ReloadPropagatedFrom= | Both are unit file |
+----------------------+-----------------------+ options |
|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 reverse 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. TriggersBy= is created implicitly on the triggered unit.
Note: Following= is used to group device aliases and points to the
"primary" device unit that systemd is using to track device state,
usually corresponding to a sysfs path. It does not show up in the
"target" unit.
[INSTALL] SECTION OPTIONS
Unit files may include an "[Install]" section, which carries
installation information for the unit. This section is not interpreted
by systemd(1) during runtime; it is used by the enable and disable
commands of the systemctl(1) tool during installation of a unit.
Alias=
A space-separated list of additional names this unit shall be
installed under. The names listed here must have the same suffix
(i.e. type) as the unit filename. This option may be specified more
than once, in which case all listed names are used. At installation
time, systemctl enable will create symlinks from these names to the
unit filename. Note that not all unit types support such alias
names, and this setting is not supported for them. Specifically,
mount, slice, swap, and automount units do not support aliasing.
WantedBy=, RequiredBy=
This option may be used more than once, or a space-separated list
of unit names may be given. A symbolic link is created in the
.wants/ or .requires/ directory of each of the listed units when
this unit is installed by systemctl enable. This has the effect
that a dependency of type Wants= or Requires= is added from the
listed unit to the current unit. The primary result is that the
current unit will be started when the listed unit is started. See
the description of Wants= and Requires= in the [Unit] section for
details.
WantedBy=foo.service in a service bar.service is mostly equivalent
to Alias=foo.service.wants/bar.service in the same file. In case of
template units, systemctl enable must be called with an instance
name, and this instance will be added to the .wants/ or .requires/
list of the listed unit. E.g. WantedBy=getty.target in a service
getty@.service will result in systemctl enable getty AT tty2.service
creating a getty.target.wants/getty AT 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, %U, %u, %m, %H, %b, %v. For their meaning see the next
section.
SPECIFIERS
Many settings resolve specifiers which may be used to write generic
unit files referring to runtime or unit parameters that are replaced
when the unit files are loaded. Specifiers must be known and resolvable
for the setting to be valid. The following specifiers are understood:
Table 4. Specifiers available in unit files
+----------+---------------------+---------------------+
|Specifier | Meaning | Details |
+----------+---------------------+---------------------+
|"%b" | Boot ID | The boot ID of the |
| | | running system, |
| | | formatted as |
| | | string. See |
| | | random(4) 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". |
+----------+---------------------+---------------------+
|"%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 | Same as "%i", but |
| | name | with 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 |
| | component of the | with escaping |
| | prefix | undone. |
+----------+---------------------+---------------------+
|"%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. |
+----------+---------------------+---------------------+
|"%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 |
| | name | with 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 |
| | temporary files | or the path |
| | | "$TMPDIR", "$TEMP" |
| | | or "$TMP" are set |
| | | to. |
+----------+---------------------+---------------------+
|"%u" | User name | This is the name of |
| | | the user running |
| | | the service manager |
| | | instance. In case |
| | | of the system |
| | | manager this |
| | | resolves to "root". |
+----------+---------------------+---------------------+
|"%U" | User UID | This is the numeric |
| | | UID of the user |
| | | running the service |
| | | manager instance. |
| | | In case of the |
| | | system manager this |
| | | resolves to "0". |
+----------+---------------------+---------------------+
|"%v" | Kernel release | Identical to uname |
| | | -r output |
+----------+---------------------+---------------------+
|"%V" | Directory for | This is either |
| | larger and | /var/tmp or the |
| | persistent | path "$TMPDIR", |
| | temporary files | "$TEMP" or "$TMP" |
| | | are set to. |
+----------+---------------------+---------------------+
|"%%" | Single percent sign | Use "%%" in place |
| | | of "%" to specify a |
| | | single percent |
| | | sign. |
+----------+---------------------+---------------------+
EXAMPLES
Example 1. Allowing units to be enabled
The following snippet (highlighted) allows a unit (e.g. foo.service)
to be enabled via systemctl enable:
[Unit]
Description=Foo
[Service]
ExecStart=/usr/sbin/foo-daemon
[Install]
WantedBy=multi-user.target
After running systemctl enable, a symlink
/etc/systemd/system/multi-user.target.wants/foo.service linking to the
actual unit will be created. It tells systemd to pull in the unit when
starting multi-user.target. The inverse systemctl disable will remove
that symlink again.
Example 2. Overriding vendor settings
There are two methods of overriding vendor settings in unit files:
copying the unit file from /usr/lib/systemd/system to
/etc/systemd/system and modifying the chosen settings. Alternatively,
one can create a directory named unit.d/ within /etc/systemd/system and
place a drop-in file name.conf there that only changes the specific
settings one is interested in. Note that multiple such drop-in files
are read if present, processed in lexicographic order of their
filename.
The advantage of the first method is that one easily overrides the
complete unit, the vendor unit is not parsed at all anymore. It has the
disadvantage that improvements to the unit file by the vendor are not
automatically incorporated on updates.
The advantage of the second method is that one only overrides the
settings one specifically wants, where updates to the unit by the
vendor automatically apply. This has the disadvantage that some future
updates by the vendor might be incompatible with the local changes.
This also applies for user instances of systemd, but with different
locations for the unit files. See the section on unit load paths for
further details.
Suppose there is a vendor-supplied unit
/usr/lib/systemd/system/httpd.service with the following contents:
[Unit]
Description=Some HTTP server
After=remote-fs.target sqldb.service
Requires=sqldb.service
AssertPathExists=/srv/webserver
[Service]
Type=notify
ExecStart=/usr/sbin/some-fancy-httpd-server
Nice=5
[Install]
WantedBy=multi-user.target
Now one wants to change some settings as an administrator: firstly, in
the local setup, /srv/webserver might not exist, because the HTTP
server is configured to use /srv/www instead. Secondly, the local
configuration makes the HTTP server also depend on a memory cache
service, memcached.service, that should be pulled in (Requires=) and
also be ordered appropriately (After=). Thirdly, in order to harden the
service a bit more, the administrator would like to set the PrivateTmp=
setting (see systemd.exec(5) for details). And lastly, the
administrator would like to reset the niceness of the service to its
default value of 0.
The first possibility is to copy the unit file to
/etc/systemd/system/httpd.service and change the chosen settings:
[Unit]
Description=Some HTTP server
After=remote-fs.target sqldb.service memcached.service
Requires=sqldb.service memcached.service
AssertPathExists=/srv/www
[Service]
Type=notify
ExecStart=/usr/sbin/some-fancy-httpd-server
Nice=0
PrivateTmp=yes
[Install]
WantedBy=multi-user.target
Alternatively, the administrator could create a drop-in file
/etc/systemd/system/httpd.service.d/local.conf with the following
contents:
[Unit]
After=memcached.service
Requires=memcached.service
# Reset all assertions and then re-add the condition we want
AssertPathExists=
AssertPathExists=/srv/www
[Service]
Nice=0
PrivateTmp=yes
Note that for drop-in files, if one wants to remove entries from a
setting that is parsed as a list (and is not a dependency), such as
AssertPathExists= (or e.g. ExecStart= in service units), one needs to
first clear the list before re-adding all entries except the one that
is to be removed. Dependencies (After=, etc.) cannot be reset to an
empty list, so dependencies can only be added in drop-ins. If you want
to remove dependencies, you have to override the entire unit.
SEE ALSO
systemd(1), systemctl(1), systemd.special(7), systemd.service(5),
systemd.socket(5), systemd.device(5), systemd.mount(5),
systemd.automount(5), systemd.swap(5), systemd.target(5),
systemd.path(5), systemd.timer(5), systemd.scope(5), systemd.slice(5),
systemd.time(7), systemd-analyze(1), capabilities(7),
systemd.directives(7), uname(1)
NOTES
1. Interface Stability Promise
https://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise
systemd 239 SYSTEMD.UNIT(5)
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