SYSTEMD.UNIT(5) systemd.unit SYSTEMD.UNIT(5)
NAME
systemd.unit - Unit configuration
SYNOPSIS
service.service, socket.socket, device.device, mount.mount,
automount.automount, swap.swap, target.target, path.path, timer.timer,
slice.slice, scope.scope
System Unit Search Path
/etc/systemd/system.control/*
/run/systemd/system.control/*
/run/systemd/transient/*
/run/systemd/generator.early/*
/etc/systemd/system/*
/etc/systemd/system.attached/*
/run/systemd/system/*
/run/systemd/system.attached/*
/run/systemd/generator/*
...
/usr/local/lib/systemd/system/*
/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/*
$XDG_CONFIG_DIRS/systemd/user/*
/etc/systemd/user/*
$XDG_RUNTIME_DIR/systemd/user/*
/run/systemd/user/*
$XDG_RUNTIME_DIR/systemd/generator/*
$XDG_DATA_HOME/systemd/user/*
$XDG_DATA_DIRS/systemd/user/*
...
/usr/local/lib/systemd/user/*
/usr/lib/systemd/user/*
$XDG_RUNTIME_DIR/systemd/generator.late/*
DESCRIPTION
A unit file is a plain text ini-style file that encodes information
about a service, a socket, a device, a mount point, an automount point,
a swap file or partition, a start-up target, a watched file system path,
a timer controlled and supervised by systemd(1), a resource management
slice or a group of externally created processes. See systemd.syntax(7)
for a general description of the syntax.
This man page lists the common configuration options of all the unit
types. These options need to be configured in the [Unit] or [Install]
sections of the unit files.
In addition to the generic [Unit] and [Install] sections described here,
each unit may have a type-specific section, e.g. [Service] for a service
unit. See the respective man pages for more information:
systemd.service(5), systemd.socket(5), systemd.device(5),
systemd.mount(5), systemd.automount(5), systemd.swap(5),
systemd.target(5), systemd.path(5), systemd.timer(5), systemd.slice(5),
systemd.scope(5).
Unit files are loaded from a set of paths determined during compilation,
described in the next section.
Valid unit names consist of a "unit name prefix", and a suffix
specifying the unit type which begins with a dot. The "unit name prefix"
must consist of one or more valid characters (ASCII letters, digits,
":", "-", "_", ".", and "\"). The total length of the unit name
including the suffix must not exceed 255 characters. The unit type
suffix must be one of ".service", ".socket", ".device", ".mount",
".automount", ".swap", ".target", ".path", ".timer", ".slice", or
".scope".
Unit names can be parameterized by a single argument called the
"instance name". The unit is then constructed based on a "template file"
which serves as the definition of multiple services or other units. A
template unit must have a single "@" at the end of the unit name prefix
(right before the type suffix). The name of the full unit is formed by
inserting the instance name between "@" and the unit type suffix. In the
unit file itself, the instance parameter may be referred to using "%i"
and other specifiers, see below.
Unit files may contain additional options on top of those listed here.
If systemd encounters an unknown option, it will write a warning log
message but continue loading the unit. If an option or section name is
prefixed with X-, it is ignored completely by systemd. Options within an
ignored section do not need the prefix. Applications may use this to
include additional information in the unit files. To access those
options, applications need to parse the unit files on their own.
Units can be aliased (have an alternative name), by creating a symlink
from the new name to the existing name in one of the unit search paths.
For example, systemd-networkd.service has the alias
dbus-org.freedesktop.network1.service, created during installation as a
symlink, so when systemd is asked through D-Bus to load
dbus-org.freedesktop.network1.service, it'll load
systemd-networkd.service. As another example, default.target — the
default system target started at boot — is commonly aliased to either
multi-user.target or graphical.target to select what is started by
default. Alias names may be used in commands like disable, start, stop,
status, and similar, and in all unit dependency directives, including
Wants=, Requires=, Before=, After=. Aliases cannot be used with the
preset command.
Aliases obey the following restrictions: a unit of a certain type
(".service", ".socket", ...) can only be aliased by a name with the same
type suffix. A plain unit (not a template or an instance), may only be
aliased by a plain name. A template instance may only be aliased by
another template instance, and the instance part must be identical. A
template may be aliased by another template (in which case the alias
applies to all instances of the template). As a special case, a template
instance (e.g. "alias@inst.service") may be a symlink to different
template (e.g. "template@inst.service"). In that case, just this
specific instance is aliased, while other instances of the template
(e.g. "alias@foo.service", "alias@bar.service") are not aliased. Those
rules preserve the requirement that the instance (if any) is always
uniquely defined for a given unit and all its aliases. The target of
alias symlink must point to a valid unit file location, i.e. the symlink
target name must match the symlink source name as described, and the
destination path must be in one of the unit search paths, see UNIT FILE
LOAD PATH section below for more details. Note that the target file
might not exist, i.e. the symlink may be dangling.
Unit files may specify aliases through the Alias= directive in the
[Install] section. When the unit is enabled, symlinks will be created
for those names, and removed when the unit is disabled. For example,
reboot.target specifies Alias=ctrl-alt-del.target, so when enabled, the
symlink /etc/systemd/system/ctrl-alt-del.target pointing to the
reboot.target file will be created, and when Ctrl+Alt+Del is invoked,
systemd will look for ctrl-alt-del.target, follow the symlink to
reboot.target, and execute reboot.service as part of that target.
systemd does not look at the [Install] section at all during normal
operation, so any directives in that section only have an effect through
the symlinks created during enablement.
Along with a unit file foo.service, the directory foo.service.wants/ may
exist. All unit files symlinked from such a directory are implicitly
added as dependencies of type Wants= to the unit. Similar functionality
exists for Requires= type dependencies as well, the directory suffix is
.requires/ in this case. This functionality is useful to hook units into
the start-up of other units, without having to modify their unit files.
For details about the semantics of Wants= and Requires=, see below. The
preferred way to create symlinks in the .wants/ or .requires/
directories is by specifying the dependency in [Install] section of the
target unit, and creating the symlink in the file system with the enable
or preset commands of systemctl(1). The target can be a normal unit
(either plain or a specific instance of a template unit). In case when
the source unit is a template, the target can also be a template, in
which case the instance will be "propagated" to the target unit to form
a valid unit instance. The target of symlinks in .wants/ or .requires/
must thus point to a valid unit file location, i.e. the symlink target
name must satisfy the described requirements, and the destination path
must be in one of the unit search paths, see UNIT FILE LOAD PATH section
below for more details. Note that the target file might not exist, i.e.
the symlink may be dangling.
Along with a unit file foo.service, a "drop-in" directory foo.service.d/
may exist. All files with the suffix ".conf" from this directory will be
merged in the alphanumeric order and parsed after the main unit file
itself has been parsed. This is useful to alter or add configuration
settings for a unit, without having to modify unit files. Each drop-in
file must contain appropriate section headers. For instantiated units,
this logic will first look for the instance ".d/" subdirectory (e.g.
"foo@bar.service.d/") and read its ".conf" files, followed by the
template ".d/" subdirectory (e.g. "foo@.service.d/") and the ".conf"
files there. Moreover, for unit names containing dashes ("-"), the set
of directories generated by repeatedly truncating the unit name after
all dashes is searched too. Specifically, for a unit name
foo-bar-baz.service not only the regular drop-in directory
foo-bar-baz.service.d/ is searched but also both foo-bar-.service.d/ and
foo-.service.d/. This is useful for defining common drop-ins for a set
of related units, whose names begin with a common prefix. This scheme is
particularly useful for mount, automount and slice units, whose
systematic naming structure is built around dashes as component
separators. Note that equally named drop-in files further down the
prefix hierarchy override those further up, i.e.
foo-bar-.service.d/10-override.conf overrides
foo-.service.d/10-override.conf.
In cases of unit aliases (described above), dropins for the aliased name
and all aliases are loaded. In the example of default.target aliasing
graphical.target, default.target.d/, default.target.wants/,
default.target.requires/, graphical.target.d/, graphical.target.wants/,
graphical.target.requires/ would all be read. For templates, dropins for
the template, any template aliases, the template instance, and all alias
instances are read. When just a specific template instance is aliased,
then the dropins for the target template, the target template instance,
and the alias template instance are read.
In addition to /etc/systemd/system, the drop-in ".d/" directories for
system services can be placed in /usr/lib/systemd/system or
/run/systemd/system directories. Drop-in files in /etc/ take precedence
over those in /run/ which in turn take precedence over those in
/usr/lib/. Drop-in files under any of these directories take precedence
over unit files wherever located. Multiple drop-in files with different
names are applied in lexicographic order, regardless of which of the
directories they reside in.
Units also support a top-level drop-in with type.d/, where type may be
e.g. "service" or "socket", that allows altering or adding to the
settings of all corresponding unit files on the system. The formatting
and precedence of applying drop-in configurations follow what is defined
above. Files in type.d/ have lower precedence compared to files in
name-specific override directories. The usual rules apply: multiple
drop-in files with different names are applied in lexicographic order,
regardless of which of the directories they reside in, so a file in
type.d/ applies to a unit only if there are no drop-ins or masks with
that name in directories with higher precedence. See Examples.
Note that while systemd offers a flexible dependency system between
units it is recommended to use this functionality only sparingly and
instead rely on techniques such as bus-based or socket-based activation
which make dependencies implicit, resulting in a both simpler and more
flexible system.
As mentioned above, a unit may be instantiated from a template file.
This allows creation of multiple units from a single configuration file.
If systemd looks for a unit configuration file, it will first search for
the literal unit name in the file system. If that yields no success and
the unit name contains an "@" character, systemd will look for a unit
template that shares the same name but with the instance string (i.e.
the part between the "@" character and the suffix) removed. Example: if
a service getty@tty3.service is requested and no file by that name is
found, systemd will look for getty@.service and instantiate a service
from that configuration file if it is found.
To refer to the instance string from within the configuration file you
may use the special "%i" specifier in many of the configuration options.
See below for details.
If a unit file is empty (i.e. has the file size 0) or is symlinked to
/dev/null, its configuration will not be loaded and it appears with a
load state of "masked", and cannot be activated. Use this as an
effective way to fully disable a unit, making it impossible to start it
even manually.
The unit file format is covered by the Interface Portability and
Stability Promise[1].
STRING ESCAPING FOR INCLUSION IN UNIT NAMES
Sometimes it is useful to convert arbitrary strings into unit names. To
facilitate this, a method of string escaping is used, in order to map
strings containing arbitrary byte values (except NUL) into valid unit
names and their restricted character set. A common special case are unit
names that reflect paths to objects in the file system hierarchy.
Example: a device unit dev-sda.device refers to a device with the device
node /dev/sda in the file system.
The escaping algorithm operates as follows: given a string, any "/"
character is replaced by "-", and all other characters which are not
ASCII alphanumerics, ":", "_" or "." are replaced by C-style "\x2d"
escapes. In addition, "." is replaced with such a C-style escape when
it would appear as the first character in the escaped string.
When the input qualifies as absolute file system path, this algorithm is
extended slightly: the path to the root directory "/" is encoded as
single dash "-". In addition, any leading, trailing or duplicate "/"
characters are removed from the string before transformation. Example:
/foo//bar/baz/ becomes "foo-bar-baz".
This escaping is fully reversible, as long as it is known whether the
escaped string was a path (the unescaping results are different for
paths and non-path strings). The systemd-escape(1) command may be used
to apply and reverse escaping on arbitrary strings. Use systemd-escape
--path to escape path strings, and systemd-escape without --path
otherwise.
AUTOMATIC DEPENDENCIES
Implicit Dependencies
A number of unit dependencies are implicitly established, depending on
unit type and unit configuration. These implicit dependencies can make
unit configuration file cleaner. For the implicit dependencies in each
unit type, please refer to section "Implicit Dependencies" in respective
man pages.
For example, service units with Type=dbus automatically acquire
dependencies of type Requires= and After= on dbus.socket. See
systemd.service(5) for details.
Default Dependencies
Default dependencies are similar to implicit dependencies, but can be
turned on and off by setting DefaultDependencies= to yes (the default)
and no, while implicit dependencies are always in effect. See section
"Default Dependencies" in respective man pages for the effect of
enabling DefaultDependencies= in each unit types.
For example, target units will complement all configured dependencies of
type Wants= or Requires= with dependencies of type After=. See
systemd.target(5) for details. Note that this behavior can be opted out
by setting DefaultDependencies=no in the specified units, or it can be
selectively overridden via an explicit Before= dependency.
UNIT FILE LOAD PATH
Unit files are loaded from a set of paths determined during compilation,
described in the two tables below. Unit files found in directories
listed earlier override files with the same name in directories lower in
the list [2].
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) │
├──────────────────────────────────────────┼────────────────────────────┤
│ $XDG_RUNTIME_DIR/systemd/transient │ Dynamic configuration for │
│ │ transient units │
├──────────────────────────────────────────┼────────────────────────────┤
│ $XDG_RUNTIME_DIR/systemd/generator.early │ Generated units with high │
│ │ priority (see early-dir in │
│ │ systemd.generator(7)) │
├──────────────────────────────────────────┼────────────────────────────┤
│ $XDG_CONFIG_HOME/systemd/user or │ User configuration │
│ $HOME/.config/systemd/user │ ($XDG_CONFIG_HOME is used │
│ │ if set, ~/.config │
│ │ otherwise) │
├──────────────────────────────────────────┼────────────────────────────┤
│ $XDG_CONFIG_DIRS/systemd/user or │ Additional configuration │
│ /etc/xdg/systemd/user │ directories as specified │
│ │ by the XDG base directory │
│ │ specification │
│ │ ($XDG_CONFIG_DIRS is used │
│ │ if set, /etc/xdg │
│ │ otherwise) │
├──────────────────────────────────────────┼────────────────────────────┤
│ /etc/systemd/user │ User units created by the │
│ │ administrator │
├──────────────────────────────────────────┼────────────────────────────┤
│ $XDG_RUNTIME_DIR/systemd/user │ Runtime units (only used │
│ │ when $XDG_RUNTIME_DIR is │
│ │ set) │
├──────────────────────────────────────────┼────────────────────────────┤
│ /run/systemd/user │ Runtime units │
├──────────────────────────────────────────┼────────────────────────────┤
│ $XDG_RUNTIME_DIR/systemd/generator │ Generated units with │
│ │ medium priority (see │
│ │ normal-dir in │
│ │ systemd.generator(7)) │
├──────────────────────────────────────────┼────────────────────────────┤
│ $XDG_DATA_HOME/systemd/user or │ Units of packages that │
│ $HOME/.local/share/systemd/user │ have been installed in the │
│ │ home directory │
│ │ ($XDG_DATA_HOME is used if │
│ │ set, ~/.local/share │
│ │ otherwise) │
├──────────────────────────────────────────┼────────────────────────────┤
│ $XDG_DATA_DIRS/systemd/user or │ Additional data │
│ /usr/local/share/systemd/user and │ directories as specified │
│ /usr/share/systemd/user │ by the XDG base directory │
│ │ specification │
│ │ ($XDG_DATA_DIRS is used if │
│ │ set, /usr/local/share and │
│ │ /usr/share otherwise) │
├──────────────────────────────────────────┼────────────────────────────┤
│ $dir/systemd/user for each $dir in │ Additional locations for │
│ $XDG_DATA_DIRS │ installed user units, one │
│ │ for each entry in │
│ │ $XDG_DATA_DIRS │
├──────────────────────────────────────────┼────────────────────────────┤
│ /usr/local/lib/systemd/user │ User units installed by │
│ │ the administrator │
├──────────────────────────────────────────┼────────────────────────────┤
│ /usr/lib/systemd/user │ User units installed by │
│ │ the distribution package │
│ │ manager │
├──────────────────────────────────────────┼────────────────────────────┤
│ $XDG_RUNTIME_DIR/systemd/generator.late │ Generated units with low │
│ │ priority (see late-dir in │
│ │ systemd.generator(7)) │
└──────────────────────────────────────────┴────────────────────────────┘
The set of load paths for the user manager instance may be augmented or
changed using various environment variables. And environment variables
may in turn be set using environment generators, see
systemd.environment-generator(7). In particular, $XDG_DATA_HOME and
$XDG_DATA_DIRS may be easily set using systemd-environment-d-
generator(8). Thus, directories listed here are just the defaults. To
see the actual list that would be used based on compilation options and
current environment use
systemd-analyze --user unit-paths
Moreover, additional units might be loaded into systemd from directories
not on the unit load path by creating a symlink pointing to a unit file
in the directories. You can use systemctl link for this; see
systemctl(1). The file system where the linked unit files are located
must be accessible when systemd is started (e.g. anything underneath
/home/ or /var/ is not allowed, unless those directories are located on
the root file system).
It is important to distinguish "linked unit files" from "unit file
aliases": any symlink where the symlink target is within the unit load
path becomes an alias: the source name and the target file name must
satisfy specific constraints listed above in the discussion of aliases,
but the symlink target does not have to exist, and in fact the symlink
target path is not used, except to check whether the target is within
the unit load path. In contrast, a symlink which goes outside of the
unit load path signifies a linked unit file. The symlink is followed
when loading the file, but the destination name is otherwise unused (and
may even not be a valid unit file name). For example, symlinks
/etc/systemd/system/alias1.service → service1.service,
/etc/systemd/system/alias2.service → /usr/lib/systemd/service1.service,
/etc/systemd/system/alias3.service →
/etc/systemd/system/service1.service are all valid aliases and
service1.service will have four names, even if the unit file is located
at /run/systemd/system/service1.service. In contrast, a symlink
/etc/systemd/system/link1.service → ../link1_service_file means that
link1.service is a "linked unit" and the contents of
/etc/systemd/link1_service_file provide its configuration.
UNIT GARBAGE COLLECTION
The system and service manager loads a unit's configuration
automatically when a unit is referenced for the first time. It will
automatically unload the unit configuration and state again when the
unit is not needed anymore ("garbage collection"). A unit may be
referenced through a number of different mechanisms:
1. Another loaded unit references it with a dependency such as After=,
Wants=, ...
2. The unit is currently starting, running, reloading or stopping.
3. The unit is currently in the failed state. (But see below.)
4. A job for the unit is pending.
5. The unit is pinned by an active IPC client program.
6. The unit is a special "perpetual" unit that is always active and
loaded. Examples for perpetual units are the root mount unit -.mount
or the scope unit init.scope that the service manager itself lives
in.
7. The unit has running processes associated with it.
The garbage collection logic may be altered with the CollectMode=
option, which allows configuration whether automatic unloading of units
that are in failed state is permissible, see below.
Note that when a unit's configuration and state is unloaded, all
execution results, such as exit codes, exit signals, resource
consumption and other statistics are lost, except for what is stored in
the log subsystem.
Use systemctl daemon-reload or an equivalent command to reload unit
configuration while the unit is already loaded. In this case, all
configuration settings are flushed out and replaced with the new
configuration (which however might not be in effect immediately),
however all runtime state is saved/restored.
[UNIT] SECTION OPTIONS
The unit file may include a [Unit] section, which carries generic
information about the unit that is not dependent on the type of unit:
Description=
A short human readable title of the unit. This may be used by
systemd (and other UIs) as a user-visible label for the unit, so
this string should identify the unit rather than describe it,
despite the name. This string also should not just repeat the unit
name. "Apache2 Web Server" is a good example. Bad examples are
"high-performance lightweight HTTP server" (too generic) or
"Apache2" (meaningless for people who do not know Apache, duplicates
the unit name). systemd may use this string as a noun in status
messages ("Starting description...", "Started description.",
"Reached target description.", "Failed to start description."), so
it should be capitalized, and should not be a full sentence, or a
phrase with a continuous verb. Bad examples include "exiting the
container" or "updating the database once per day.".
Added in version 201.
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.
Added in version 201.
Wants=
Configures (weak) requirement dependencies on other units. This
option may be specified more than once or multiple space-separated
units may be specified in one option in which case dependencies for
all listed names will be created. Dependencies of this type may also
be configured outside of the unit configuration file by adding a
symlink to a .wants/ directory accompanying the unit file. For
details, see above.
Units listed in this option will be started if the configuring unit
is. However, if the listed units fail to start or cannot be added to
the transaction, this has no impact on the validity of the
transaction as a whole, and this unit will still be started. This is
the recommended way to hook the start-up of one unit to the start-up
of another unit.
Note that requirement dependencies do not influence the order in
which services are started or stopped. This has to be configured
independently with the After= or Before= options. If unit
foo.service pulls in unit bar.service as configured with Wants= and
no ordering is configured with After= or Before=, then both units
will be started simultaneously and without any delay between them if
foo.service is activated.
Added in version 201.
Requires=
Similar to Wants=, but declares a stronger requirement dependency.
Dependencies of this type may also be configured by adding a symlink
to a .requires/ directory accompanying the unit file.
If this unit gets activated, the units listed will be activated as
well. If one of the other units fails to activate, and an ordering
dependency After= on the failing unit is set, this unit will not be
started. Besides, with or without specifying After=, this unit will
be stopped (or restarted) if one of the other units is explicitly
stopped (or restarted).
Often, it is a better choice to use Wants= instead of Requires= in
order to achieve a system that is more robust when dealing with
failing services.
Note that this dependency type does not imply that the other unit
always has to be in active state when this unit is running.
Specifically: failing condition checks (such as
ConditionPathExists=, ConditionPathIsSymbolicLink=, ... — see below)
do not cause the start job of a unit with a Requires= dependency on
it to fail. Also, some unit types may deactivate on their own (for
example, a service process may decide to exit cleanly, or a device
may be unplugged by the user), which is not propagated to units
having a Requires= dependency. Use the BindsTo= dependency type
together with After= to ensure that a unit may never be in active
state without a specific other unit also in active state (see
below).
Added in version 201.
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.
Added in version 201.
BindsTo=
Configures requirement dependencies, very similar in style to
Requires=. However, this dependency type is stronger: in addition to
the effect of Requires= it declares that if the unit bound to is
stopped, this unit will be stopped too. This means a unit bound to
another unit that suddenly enters inactive state will be stopped
too. Units can suddenly, unexpectedly enter inactive state for
different reasons: the main process of a service unit might
terminate on its own choice, the backing device of a device unit
might be unplugged or the mount point of a mount unit might be
unmounted without involvement of the system and service manager.
When used in conjunction with After= on the same unit the behaviour
of BindsTo= is even stronger. In this case, the unit bound to
strictly has to be in active state for this unit to also be in
active state. This not only means a unit bound to another unit that
suddenly enters inactive state, but also one that is bound to
another unit that gets skipped due to an unmet condition check (such
as ConditionPathExists=, ConditionPathIsSymbolicLink=, ... — see
below) will be stopped, should it be running. Hence, in many cases
it is best to combine BindsTo= with After=.
When BindsTo=b.service is used on a.service, this dependency will
show as BoundBy=a.service in property listing of b.service.
BoundBy= dependency cannot be specified directly.
Added in version 201.
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.
Added in version 201.
Upholds=
Configures dependencies similar to Wants=, but as long as this unit
is up, all units listed in Upholds= are started whenever found to be
inactive or failed, and no job is queued for them. While a Wants=
dependency on another unit has a one-time effect when this units
started, a Upholds= dependency on it has a continuous effect,
constantly restarting the unit if necessary. This is an alternative
to the Restart= setting of service units, to ensure they are kept
running whatever happens. The restart happens without delay, and
usual per-unit rate-limit applies.
When Upholds=b.service is used on a.service, this dependency will
show as UpheldBy=a.service in the property listing of b.service.
Added in version 249.
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 does not 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.
Added in version 201.
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
does not matter if the ordering dependency is After= or Before=, in
this case. It also does not 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 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.
Added in version 201.
OnFailure=
A space-separated list of one or more units that are activated when
this unit enters the "failed" state.
Added in version 201.
OnSuccess=
A space-separated list of one or more units that are activated when
this unit enters the "inactive" state.
Added in version 249.
PropagatesReloadTo=, ReloadPropagatedFrom=
A space-separated list of one or more units to which reload requests
from this unit shall be propagated to, or units from which reload
requests shall be propagated to this unit, respectively. Issuing a
reload request on a unit will automatically also enqueue reload
requests on all units that are linked to it using these two
settings.
Added in version 201.
PropagatesStopTo=, StopPropagatedFrom=
A space-separated list of one or more units to which stop requests
from this unit shall be propagated to, or units from which stop
requests shall be propagated to this unit, respectively. Issuing a
stop request on a unit will automatically also enqueue stop requests
on all units that are linked to it using these two settings.
Added in version 249.
JoinsNamespaceOf=
For units that start processes (such as service units), lists one or
more other units whose network and/or temporary file namespace to
join. If this is specified on a unit (say, a.service has
JoinsNamespaceOf=b.service), then the inverse dependency
(JoinsNamespaceOf=a.service for b.service) is implied. This only
applies to unit types which support the PrivateNetwork=,
NetworkNamespacePath=, PrivateIPC=, IPCNamespacePath=, and
PrivateTmp= directives (see systemd.exec(5) for details). If a unit
that has this setting set is started, its processes will see the
same /tmp/, /var/tmp/, IPC namespace and network namespace as one
listed unit that is started. If multiple listed units are already
started and these do not share their namespace, then it is not
defined which namespace is joined. Note that this setting only has
an effect if PrivateNetwork=/NetworkNamespacePath=,
PrivateIPC=/IPCNamespacePath= and/or PrivateTmp= is enabled for both
the unit that joins the namespace and the unit whose namespace is
joined.
Added in version 209.
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.
Added in version 201.
WantsMountsFor=
Same as RequiresMountsFor=, but adds dependencies of type Wants=
instead of Requires=.
Added in version 256.
OnSuccessJobMode=, OnFailureJobMode=
Takes a value of "fail", "replace", "replace-irreversibly",
"isolate", "flush", "ignore-dependencies" or "ignore-requirements".
Defaults to "replace". Specifies how the units listed in
OnSuccess=/OnFailure= will be enqueued. See systemctl(1)'s
--job-mode= option for details on the possible values. If this is
set to "isolate", only a single unit may be listed in
OnSuccess=/OnFailure=.
Added in version 209.
IgnoreOnIsolate=
Takes a boolean argument. If true, this unit will not be stopped
when isolating another unit. Defaults to false for service, target,
socket, timer, and path units, and true for slice, scope, device,
swap, mount, and automount units.
Added in version 201.
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.
Added in version 201.
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.
Added in version 201.
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.
Added in version 201.
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.
Added in version 201.
SurviveFinalKillSignal=
Takes a boolean argument. Defaults to no. If yes, processes
belonging to this unit will not be sent the final "SIGTERM" and
"SIGKILL" signals during the final phase of the system shutdown
process. This functionality replaces the older mechanism that
allowed a program to set "argv[0][0] = '@'" as described at systemd
and Storage Daemons for the Root File System[3], which however
continues to be supported.
Added in version 255.
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.
Added in version 236.
FailureAction=, SuccessAction=
Configure the action to take when the unit stops and enters a failed
state or inactive state. Takes one of none, reboot, reboot-force,
reboot-immediate, poweroff, poweroff-force, poweroff-immediate,
exit, exit-force, soft-reboot, soft-reboot-force, kexec,
kexec-force, halt, halt-force and halt-immediate. In system mode,
all options are allowed. In user mode, only none, exit, 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, kexec, kexec-force, halt, halt-force and
halt-immediate have the effect of powering down the system,
executing kexec, and halting the system respectively with similar
semantics. exit causes the manager to exit following the normal
shutdown procedure, and exit-force causes it terminate without
shutting down services. When exit or exit-force is used by default
the exit status of the main process of the unit (if this applies) is
returned from the service manager. However, this may be overridden
with FailureActionExitStatus=/SuccessActionExitStatus=, see below.
soft-reboot will trigger a userspace reboot operation.
soft-reboot-force does that too, but does not go through the
shutdown transaction beforehand.
Added in version 236.
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.
Added in version 240.
JobTimeoutSec=, JobRunningTimeoutSec=
JobTimeoutSec= specifies a timeout for the whole job that starts
running when the job is queued. JobRunningTimeoutSec= specifies a
timeout that starts running when the queued job is actually started.
If either limit is reached, the job will be cancelled, the unit
however will not change state or even enter the "failed" mode.
Both settings take a time span with the default unit of seconds, but
other units may be specified, see systemd.time(7). The default is
"infinity" (job timeouts disabled), except for device units where
JobRunningTimeoutSec= defaults to DefaultDeviceTimeoutSec=.
Note: these timeouts are independent from any unit-specific timeouts
(for example, the timeout set with TimeoutStartSec= in service
units). The job timeout has no effect on the unit itself. Or in
other words: unit-specific timeouts are useful to abort unit state
changes, and revert them. The job timeout set with this option
however is useful to abort only the job waiting for the unit state
to change.
Added in version 201.
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
FailureAction=/SuccessAction=. Defaults to none.
JobTimeoutRebootArgument= configures an optional reboot string to
pass to the reboot(2) system call.
Added in version 240.
StartLimitIntervalSec=interval, StartLimitBurst=burst
Configure unit start rate limiting. Units which are started more
than burst times within an interval time span are not permitted to
start any more. Use StartLimitIntervalSec= to configure the checking
interval and StartLimitBurst= to configure how many starts per
interval are allowed.
interval is a time span with the default unit of seconds, but other
units may be specified, see systemd.time(7). The special value
"infinity" can be used to limit the total number of start attempts,
even if they happen at large time intervals. Defaults to
DefaultStartLimitIntervalSec= in manager configuration file, and may
be set to 0 to disable any kind of rate limiting. burst is a number
and defaults to DefaultStartLimitBurst= in manager configuration
file.
These configuration options are particularly useful in conjunction
with the service setting Restart= (see systemd.service(5)); however,
they apply to all kinds of starts (including manual), not just those
triggered by the Restart= logic.
Note that units which are configured for Restart=, and which reach
the start limit are not attempted to be restarted anymore; however,
they may still be restarted manually or from a timer or socket at a
later point, after the interval has passed. From that point on, the
restart logic is activated again. systemctl reset-failed will cause
the restart rate counter for a service to be flushed, which is
useful if the administrator wants to manually start a unit and the
start limit interferes with that. Rate-limiting is enforced after
any unit condition checks are executed, and hence unit activations
with failing conditions do not count towards the rate limit.
When a unit is unloaded due to the garbage collection logic (see
above) its rate limit counters are flushed out too. This means that
configuring start rate limiting for a unit that is not referenced
continuously has no effect.
This setting does not apply to slice, target, device, and scope
units, since they are unit types whose activation may either never
fail, or may succeed only a single time.
Added in version 229.
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.
Added in version 229.
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.
Added in version 229.
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.
Added in version 201.
Conditions and Asserts
Unit files may also include a number of Condition...= and Assert...=
settings. Before the unit is started, systemd will verify that the
specified conditions and asserts are true. If not, the starting of the
unit will be (mostly silently) skipped (in case of conditions), or
aborted with an error message (in case of asserts). Failing conditions
or asserts will not result in the unit being moved into the "failed"
state. The conditions and asserts are checked at the time the queued
start job is to be executed. The ordering dependencies are still
respected, so other units are still pulled in and ordered as if this
unit was successfully activated, and the conditions and asserts are
executed the precise moment the unit would normally start and thus can
validate system state after the units ordered before completed
initialization. Use condition expressions for skipping units that do not
apply to the local system, for example because the kernel or runtime
environment does not require their functionality.
If multiple conditions are specified, the unit will be executed if all
of them apply (i.e. a logical AND is applied). Condition checks can use
a pipe symbol ("|") after the equals sign ("Condition...=|..."), which
causes the condition to become a triggering condition. If at least one
triggering condition is defined for a unit, then the unit will be
started if at least one of the triggering conditions of the unit applies
and all of the regular (i.e. non-triggering) conditions apply. If you
prefix an argument with the pipe symbol and an exclamation mark, the
pipe symbol must be passed first, the exclamation second. If any of
these options is assigned the empty string, the list of conditions is
reset completely, all previous condition settings (of any kind) will
have no effect.
The AssertArchitecture=, AssertVirtualization=, ... options are similar
to conditions but cause the start job to fail (instead of being
skipped). The failed check is logged. Units with unmet conditions are
considered to be in a clean state and will be garbage collected if they
are not referenced. This means that when queried, the condition failure
may or may not show up in the state of the unit.
Note that neither assertion nor condition expressions result in unit
state changes. Also note that both are checked at the time the job is to
be executed, i.e. long after depending jobs and it itself were queued.
Thus, neither condition nor assertion expressions are suitable for
conditionalizing unit dependencies.
The condition verb of systemd-analyze(1) can be used to test condition
and assert expressions.
Except for ConditionPathIsSymbolicLink=, all path checks follow
symlinks.
ConditionArchitecture=
Check whether the system is running on a specific architecture.
Takes one of "x86", "x86-64", "ppc", "ppc-le", "ppc64", "ppc64-le",
"ia64", "parisc", "parisc64", "s390", "s390x", "sparc", "sparc64",
"mips", "mips-le", "mips64", "mips64-le", "alpha", "arm", "arm-be",
"arm64", "arm64-be", "sh", "sh64", "m68k", "tilegx", "cris", "arc",
"arc-be", or "native".
Use systemd-analyze(1) for the complete list of known architectures.
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.
Added in version 201.
ConditionFirmware=
Check whether the system's firmware is of a certain type. The
following values are possible:
• "uefi" matches systems with EFI.
• "device-tree" matches systems with a device tree.
• "device-tree-compatible(value)" matches systems with a device
tree that are compatible with "value".
• "smbios-field(field operator value)" matches systems with a
SMBIOS field containing a certain value. field is the name of
the SMBIOS field exposed as "sysfs" attribute file below
/sys/class/dmi/id/. operator is one of "<", "<=", ">=", ">",
"==", "<>" for version comparisons, "=" and "!=" for literal
string comparisons, or "$=", "!$=" for shell-style glob
comparisons. value is the expected value of the SMBIOS field
value (possibly containing shell style globs in case "$="/"!$="
is used).
Added in version 249.
ConditionVirtualization=
Check whether the system is executed in a virtualized environment
and optionally test whether it is a specific implementation. Takes
either boolean value to check if being executed in any virtualized
environment, or one of "vm" and "container" to test against a
generic type of virtualization solution, or one of "qemu", "kvm",
"amazon", "zvm", "vmware", "microsoft", "oracle", "powervm", "xen",
"bochs", "uml", "bhyve", "qnx", "apple", "sre", "openvz", "lxc",
"lxc-libvirt", "systemd-nspawn", "docker", "podman", "rkt", "wsl",
"proot", "pouch", "acrn" to test against a specific implementation,
or "private-users" to check whether we are running in a user
namespace. See systemd-detect-virt(1) for a full list of known
virtualization technologies and their identifiers. If multiple
virtualization technologies are nested, only the innermost is
considered. The test may be negated by prepending an exclamation
mark.
Added in version 244.
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.
Added in version 244.
ConditionKernelCommandLine=
ConditionKernelCommandLine= may be used to check whether a specific
kernel command line option is set (or if prefixed with the
exclamation mark — unset). The argument must either be a single
word, or an assignment (i.e. two words, separated by "="). In the
former case the kernel command line is searched for the word
appearing as is, or as left hand side of an assignment. In the
latter case, the exact assignment is looked for with right and left
hand side matching. This operates on the kernel command line
communicated to userspace via /proc/cmdline, except when the service
manager is invoked as payload of a container manager, in which case
the command line of PID 1 is used instead (i.e. /proc/1/cmdline).
Added in version 244.
ConditionKernelVersion=
ConditionKernelVersion= may be used to check whether the kernel
version (as reported by uname -r) matches a certain expression, or
if prefixed with the exclamation mark, does not match. The argument
must be a list of (potentially quoted) expressions. Each expression
starts with one of "=" or "!=" for string comparisons, "<", "<=",
"==", "<>", ">=", ">" for version comparisons, or "$=", "!$=" for a
shell-style glob match. If no operator is specified, "$=" is
implied.
Note that using the kernel version string is an unreliable way to
determine which features are supported by a kernel, because of the
widespread practice of backporting drivers, features, and fixes from
newer upstream kernels into older versions provided by
distributions. Hence, this check is inherently unportable and should
not be used for units which may be used on different distributions.
Added in version 244.
ConditionCredential=
ConditionCredential= may be used to check whether a credential by
the specified name was passed into the service manager. See System
and Service Credentials[4] for details about credentials. If used in
services for the system service manager this may be used to
conditionalize services based on system credentials passed in. If
used in services for the per-user service manager this may be used
to conditionalize services based on credentials passed into the
unit@.service service instance belonging to the user. The argument
must be a valid credential name.
Added in version 252.
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.
Added in version 246.
ConditionSecurity=
ConditionSecurity= may be used to check whether the given security
technology is enabled on the system. Currently, the following values
are recognized:
Table 3. Recognized security technologies
┌─────────────────┬────────────────────────────┐
│ Value │ Description │
├─────────────────┼────────────────────────────┤
│ selinux │ SELinux MAC │
├─────────────────┼────────────────────────────┤
│ apparmor │ AppArmor MAC │
├─────────────────┼────────────────────────────┤
│ tomoyo │ Tomoyo MAC │
├─────────────────┼────────────────────────────┤
│ smack │ SMACK MAC │
├─────────────────┼────────────────────────────┤
│ ima │ Integrity Measurement │
│ │ Architecture (IMA) │
├─────────────────┼────────────────────────────┤
│ audit │ Linux Audit Framework │
├─────────────────┼────────────────────────────┤
│ uefi-secureboot │ UEFI SecureBoot │
├─────────────────┼────────────────────────────┤
│ tpm2 │ Trusted Platform Module │
│ │ 2.0 (TPM2) │
├─────────────────┼────────────────────────────┤
│ cvm │ Confidential virtual │
│ │ machine (SEV/TDX) │
├─────────────────┼────────────────────────────┤
│ measured-uki │ Unified Kernel Image with │
│ │ PCR 11 Measurements, as │
│ │ per systemd-stub(7). Added │
│ │ in version 255. │
└─────────────────┴────────────────────────────┘
The test may be negated by prepending an exclamation mark.
Added in version 244.
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.
Added in version 244.
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.
Added in version 244.
ConditionNeedsUpdate=
Takes one of /var/ or /etc/ as argument, possibly prefixed with a
"!" (to invert the condition). This condition may be used to
conditionalize units on whether the specified directory requires an
update because /usr/'s modification time is newer than the stamp
file .updated in the specified directory. This is useful to
implement offline updates of the vendor operating system resources
in /usr/ that require updating of /etc/ or /var/ on the next
following boot. Units making use of this condition should order
themselves before systemd-update-done.service(8), to make sure they
run before the stamp file's modification time gets reset indicating
a completed update.
If the systemd.condition_needs_update= option is specified on the
kernel command line (taking a boolean), it will override the result
of this condition check, taking precedence over any file
modification time checks. If the kernel command line option is used,
systemd-update-done.service will not have immediate effect on any
following ConditionNeedsUpdate= checks, until the system is rebooted
where the kernel command line option is not specified anymore.
Note that to make this scheme effective, the timestamp of /usr/
should be explicitly updated after its contents are modified. The
kernel will automatically update modification timestamp on a
directory only when immediate children of a directory are modified;
an modification of nested files will not automatically result in
mtime of /usr/ being updated.
Also note that if the update method includes a call to execute
appropriate post-update steps itself, it should not touch the
timestamp of /usr/. In a typical distribution packaging scheme,
packages will do any required update steps as part of the
installation or upgrade, to make package contents immediately
usable. ConditionNeedsUpdate= should be used with other update
mechanisms where such an immediate update does not happen.
Added in version 244.
ConditionFirstBoot=
Takes a boolean argument. This condition may be used to
conditionalize units on whether the system is booting up for the
first time. This roughly means that /etc/ was unpopulated when the
system started booting (for details, see "First Boot Semantics" in
machine-id(5)). First Boot is considered finished (this condition
will evaluate as false) after the manager has finished the startup
phase.
This condition may be used to populate /etc/ on the first boot after
factory reset, or when a new system instance boots up for the first
time.
Note that the service manager itself will perform setup steps during
First Boot: it will initialize machine-id(5) and preset all units,
enabling or disabling them according to the systemd.preset(5)
settings. Additional setup may be performed via units with
ConditionFirstBoot=yes.
For robustness, units with ConditionFirstBoot=yes should order
themselves before first-boot-complete.target and pull in this
passive target with Wants=. This ensures that in a case of an
aborted first boot, these units will be re-run during the next
system startup.
If the systemd.condition_first_boot= option is specified on the
kernel command line (taking a boolean), it will override the result
of this condition check, taking precedence over /etc/machine-id
existence checks.
Added in version 244.
ConditionPathExists=
Check for the existence of a file. If the specified absolute path
name does not exist, the condition will fail. If the absolute path
name passed to ConditionPathExists= is prefixed with an exclamation
mark ("!"), the test is negated, and the unit is only started if the
path does not exist.
Added in version 244.
ConditionPathExistsGlob=
ConditionPathExistsGlob= is similar to ConditionPathExists=, but
checks for the existence of at least one file or directory matching
the specified globbing pattern.
Added in version 244.
ConditionPathIsDirectory=
ConditionPathIsDirectory= is similar to ConditionPathExists= but
verifies that a certain path exists and is a directory.
Added in version 244.
ConditionPathIsSymbolicLink=
ConditionPathIsSymbolicLink= is similar to ConditionPathExists= but
verifies that a certain path exists and is a symbolic link.
Added in version 244.
ConditionPathIsMountPoint=
ConditionPathIsMountPoint= is similar to ConditionPathExists= but
verifies that a certain path exists and is a mount point.
Added in version 244.
ConditionPathIsReadWrite=
ConditionPathIsReadWrite= is similar to ConditionPathExists= but
verifies that the underlying file system is readable and writable
(i.e. not mounted read-only).
Added in version 244.
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.
Added in version 246.
ConditionDirectoryNotEmpty=
ConditionDirectoryNotEmpty= is similar to ConditionPathExists= but
verifies that a certain path exists and is a non-empty directory.
Added in version 244.
ConditionFileNotEmpty=
ConditionFileNotEmpty= is similar to ConditionPathExists= but
verifies that a certain path exists and refers to a regular file
with a non-zero size.
Added in version 244.
ConditionFileIsExecutable=
ConditionFileIsExecutable= is similar to ConditionPathExists= but
verifies that a certain path exists, is a regular file, and marked
executable.
Added in version 244.
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.
Added in version 244.
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".
Added in version 244.
ConditionControlGroupController=
Check whether given cgroup controllers (e.g. "cpu") are available
for use on the system or whether the legacy v1 cgroup or the modern
v2 cgroup hierarchy is used.
Multiple controllers may be passed with a space separating them; in
this case, the condition will only pass if all listed controllers
are available for use. Controllers unknown to systemd are ignored.
Valid controllers are "cpu", "io", "memory", and "pids". Even if
available in the kernel, a particular controller may not be
available if it was disabled on the kernel command line with
cgroup_disable=controller.
Alternatively, two special strings "v1" and "v2" may be specified
(without any controller names). "v2" will pass if the unified v2
cgroup hierarchy is used, and "v1" will pass if the legacy v1
hierarchy or the hybrid hierarchy are used. Note that legacy or
hybrid hierarchies have been deprecated. See systemd(1) for more
information.
Added in version 244.
ConditionMemory=
Verify that the specified amount of system memory is available to
the current system. Takes a memory size in bytes as argument,
optionally prefixed with a comparison operator "<", "<=", "=" (or
"=="), "!=" (or "<>"), ">=", ">". On bare-metal systems compares the
amount of physical memory in the system with the specified size,
adhering to the specified comparison operator. In containers
compares the amount of memory assigned to the container instead.
Added in version 244.
ConditionCPUs=
Verify that the specified number of CPUs is available to the current
system. Takes a number of CPUs as argument, optionally prefixed with
a comparison operator "<", "<=", "=" (or "=="), "!=" (or "<>"),
">=", ">". Compares the number of CPUs in the CPU affinity mask
configured of the service manager itself with the specified number,
adhering to the specified comparison operator. On physical systems
the number of CPUs in the affinity mask of the service manager
usually matches the number of physical CPUs, but in special and
virtual environments might differ. In particular, in containers the
affinity mask usually matches the number of CPUs assigned to the
container and not the physically available ones.
Added in version 244.
ConditionCPUFeature=
Verify that a given CPU feature is available via the "CPUID"
instruction. This condition only does something on i386 and x86-64
processors. On other processors it is assumed that the CPU does not
support the given feature. It checks the leaves "1", "7",
"0x80000001", and "0x80000007". Valid values are: "fpu", "vme",
"de", "pse", "tsc", "msr", "pae", "mce", "cx8", "apic", "sep",
"mtrr", "pge", "mca", "cmov", "pat", "pse36", "clflush", "mmx",
"fxsr", "sse", "sse2", "ht", "pni", "pclmul", "monitor", "ssse3",
"fma3", "cx16", "sse4_1", "sse4_2", "movbe", "popcnt", "aes",
"xsave", "osxsave", "avx", "f16c", "rdrand", "bmi1", "avx2", "bmi2",
"rdseed", "adx", "sha_ni", "syscall", "rdtscp", "lm", "lahf_lm",
"abm", "constant_tsc".
Added in version 248.
ConditionOSRelease=
Verify that a specific "key=value" pair is set in the host's os-
release(5).
Other than exact string matching (with "=" and "!="), relative
comparisons are supported for versioned parameters (e.g.
"VERSION_ID"; with "<", "<=", "==", "<>", ">=", ">"), and
shell-style wildcard comparisons ("*", "?", "[]") are supported with
the "$=" (match) and "!$=" (non-match).
If the given key is not found in the file, the match is done against
an empty value.
Added in version 249.
ConditionMemoryPressure=, ConditionCPUPressure=, ConditionIOPressure=
Verify that the overall system (memory, CPU or IO) pressure is below
or equal to a threshold. This setting takes a threshold value as
argument. It can be specified as a simple percentage value, suffixed
with "%", in which case the pressure will be measured as an average
over the last five minutes before the attempt to start the unit is
performed. Alternatively, the average timespan can also be specified
using "/" as a separator, for example: "10%/1min". The supported
timespans match what the kernel provides, and are limited to
"10sec", "1min" and "5min". The "full" PSI will be checked first,
and if not found "some" will be checked. For more details, see the
documentation on PSI (Pressure Stall Information)[5].
Optionally, the threshold value can be prefixed with the slice unit
under which the pressure will be checked, followed by a ":". If the
slice unit is not specified, the overall system pressure will be
measured, instead of a particular cgroup's.
Added in version 250.
AssertArchitecture=, AssertVirtualization=, AssertHost=,
AssertKernelCommandLine=, AssertKernelVersion=, AssertCredential=,
AssertEnvironment=, AssertSecurity=, AssertCapability=, AssertACPower=,
AssertNeedsUpdate=, AssertFirstBoot=, AssertPathExists=,
AssertPathExistsGlob=, AssertPathIsDirectory=,
AssertPathIsSymbolicLink=, AssertPathIsMountPoint=,
AssertPathIsReadWrite=, AssertPathIsEncrypted=,
AssertDirectoryNotEmpty=, AssertFileNotEmpty=, AssertFileIsExecutable=,
AssertUser=, AssertGroup=, AssertControlGroupController=, AssertMemory=,
AssertCPUs=, AssertCPUFeature=, AssertOSRelease=, AssertMemoryPressure=,
AssertCPUPressure=, AssertIOPressure=
Similar to the ConditionArchitecture=, ConditionVirtualization=,
..., condition settings described above, these settings add
assertion checks to the start-up of the unit. However, unlike the
conditions settings, any assertion setting that is not met results
in failure of the start job (which means this is logged loudly).
Note that hitting a configured assertion does not cause the unit to
enter the "failed" state (or in fact result in any state change of
the unit), it affects only the job queued for it. Use assertion
expressions for units that cannot operate when specific requirements
are not met, and when this is something the administrator or user
should look into.
Added in version 218.
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 4. 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 │
├───────────────────────┼───────────────────────┼─────────────────┼───────────────┤
│ Upholds= │ UpheldBy= │ [Unit] section │ [Install] │
│ │ │ │ section │
├───────────────────────┼───────────────────────┼─────────────────┼───────────────┤
│ PartOf= │ ConsistsOf= │ [Unit] section │ an automatic │
│ │ │ │ property │
├───────────────────────┼───────────────────────┼─────────────────┼───────────────┤
│ BindsTo= │ BoundBy= │ [Unit] section │ an automatic │
│ │ │ │ property │
├───────────────────────┼───────────────────────┼─────────────────┼───────────────┤
│ Requisite= │ RequisiteOf= │ [Unit] section │ an automatic │
│ │ │ │ property │
├───────────────────────┼───────────────────────┼─────────────────┼───────────────┤
│ Conflicts= │ ConflictedBy= │ [Unit] section │ an automatic │
│ │ │ │ property │
├───────────────────────┼───────────────────────┼─────────────────┴───────────────┤
│ Triggers= │ TriggeredBy= │ Automatic properties, see notes │
│ │ │ below │
├───────────────────────┼───────────────────────┼─────────────────────────────────┤
│ PropagatesReloadTo= │ ReloadPropagatedFrom= │ │
├───────────────────────┼───────────────────────┤ [Unit] section │
│ ReloadPropagatedFrom= │ PropagatesReloadTo= │ │
├───────────────────────┼───────────────────────┼─────────────────────────────────┤
│ PropagatesStopTo= │ StopPropagatedFrom= │ │
├───────────────────────┼───────────────────────┤ [Unit] section │
│ StopPropagatedFrom= │ PropagatesStopTo= │ │
├───────────────────────┼───────────────────────┼─────────────────┬───────────────┤
│ Following= │ n/a │ An automatic │ │
│ │ │ property │ │
└───────────────────────┴───────────────────────┴─────────────────┴───────────────┘
Note: WantedBy=, RequiredBy=, and UpheldBy= are used in the [Install]
section to create symlinks in .wants/, .requires/, and .upholds/
directories. They cannot be used directly as a unit configuration
setting.
Note: ConsistsOf=, BoundBy=, RequisiteOf=, ConflictedBy= are created
implicitly along with their reverses and cannot be specified directly.
Note: Triggers= is created implicitly between a socket, path unit, or an
automount unit, and the unit they activate. By default, a unit with the
same name is triggered, but this can be overridden using Sockets=,
Service=, and Unit= settings. See systemd.service(5), systemd.socket(5),
systemd.path(5), and systemd.automount(5) for details. TriggeredBy= is
created implicitly on the triggered unit.
Note: Following= is used to group device aliases and points to the
"primary" device unit that systemd is using to track device state,
usually corresponding to a sysfs path. It does not show up in the
"target" unit.
[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.
Added in version 201.
WantedBy=, RequiredBy=, UpheldBy=
This option may be used more than once, or a space-separated list of
unit names may be given. A symbolic link is created in the .wants/,
.requires/, or .upholds/ directory of each of the listed units when
this unit is installed by systemctl enable. This has the effect of a
dependency of type Wants=, Requires=, or Upholds= being added from
the listed unit to the current unit. See the description of the
mentioned dependency types in the [Unit] section for details.
In case of template units listing non template units, the listing
unit must have DefaultInstance= set, or systemctl enable must be
called with an instance name. The instance (default or specified)
will be added to the .wants/, .requires/, or .upholds/ list of the
listed unit. For example, WantedBy=getty.target in a service
getty@.service will result in systemctl enable getty@tty2.service
creating a getty.target.wants/getty@tty2.service link to
getty@.service. This also applies to listing specific instances of
templated units: this specific instance will gain the dependency. A
template unit may also list a template unit, in which case a generic
dependency will be added where each instance of the listing unit
will have a dependency on an instance of the listed template with
the same instance value. For example, WantedBy=container@.target in
a service monitor@.service will result in systemctl enable
monitor@.service creating a container@.target.wants/monitor@.service
link to monitor@.service, which applies to all instances of
container@.target.
Added in version 201.
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.
Added in version 201.
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.
Added in version 215.
The following specifiers are interpreted in the Install section: %a, %b,
%B, %g, %G, %H, %i, %j, %l, %m, %n, %N, %o, %p, %u, %U, %v, %w, %W, %%.
For their meaning see the next section.
SPECIFIERS
Many settings resolve specifiers which may be used to write generic unit
files referring to runtime or unit parameters that are replaced when the
unit files are loaded. Specifiers must be known and resolvable for the
setting to be valid. The following specifiers are understood:
Table 5. Specifiers available in unit files
┌───────────┬──────────────────────┬──────────────────────────┐
│ Specifier │ Meaning │ Details │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%a" │ Architecture │ A short string │
│ │ │ identifying the │
│ │ │ architecture of the │
│ │ │ local system. A │
│ │ │ string such as x86, │
│ │ │ x86-64 or arm64. See │
│ │ │ the architectures │
│ │ │ defined for │
│ │ │ ConditionArchitecture= │
│ │ │ above for a full │
│ │ │ list. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%A" │ Operating system │ The operating system │
│ │ image version │ image version │
│ │ │ identifier of the │
│ │ │ running system, as │
│ │ │ read from the │
│ │ │ IMAGE_VERSION= field │
│ │ │ of /etc/os-release. If │
│ │ │ not set, resolves to │
│ │ │ an empty string. See │
│ │ │ os-release(5) for more │
│ │ │ information. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%b" │ Boot ID │ The boot ID of the │
│ │ │ running system, │
│ │ │ formatted as string. │
│ │ │ See random(4) for more │
│ │ │ information. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%B" │ Operating system │ The operating system │
│ │ build ID │ build identifier of │
│ │ │ the running system, as │
│ │ │ read from the │
│ │ │ BUILD_ID= field of │
│ │ │ /etc/os-release. If │
│ │ │ not set, resolves to │
│ │ │ an empty string. See │
│ │ │ os-release(5) for more │
│ │ │ information. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%C" │ Cache directory root │ This is either │
│ │ │ /var/cache (for the │
│ │ │ system manager) or the │
│ │ │ path "$XDG_CACHE_HOME" │
│ │ │ resolves to (for user │
│ │ │ managers). │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%d" │ Credentials │ This is the value of │
│ │ directory │ the │
│ │ │ "$CREDENTIALS_DIRECTORY" │
│ │ │ environment variable │
│ │ │ if available. See │
│ │ │ section "Credentials" │
│ │ │ in systemd.exec(5) for │
│ │ │ more information. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%D" │ Shared data │ This is either │
│ │ directory │ /usr/share/ (for the │
│ │ │ system manager) or the │
│ │ │ path "$XDG_DATA_HOME" │
│ │ │ resolves to (for user │
│ │ │ managers). │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%E" │ Configuration │ This is either /etc/ │
│ │ directory root │ (for the system manager) │
│ │ │ or the path │
│ │ │ "$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. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%g" │ User group │ This is the name of the │
│ │ │ group running the │
│ │ │ service manager │
│ │ │ instance. In case of the │
│ │ │ system manager this │
│ │ │ resolves to "root". │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%G" │ User GID │ This is the numeric GID │
│ │ │ of the user running the │
│ │ │ service manager │
│ │ │ instance. In case of the │
│ │ │ system manager this │
│ │ │ resolves to "0". │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%h" │ User home directory │ This is the home │
│ │ │ directory of the user │
│ │ │ running the service │
│ │ │ manager instance. In │
│ │ │ case of the system │
│ │ │ manager this resolves to │
│ │ │ "/root". │
│ │ │ │
│ │ │ Note that this setting │
│ │ │ is not influenced by the │
│ │ │ User= setting │
│ │ │ configurable in the │
│ │ │ [Service] section of the │
│ │ │ service unit. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%H" │ Host name │ The hostname of the │
│ │ │ running system at the │
│ │ │ point in time the unit │
│ │ │ configuration is loaded. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%i" │ Instance name │ For instantiated units │
│ │ │ this is the string │
│ │ │ between the first "@" │
│ │ │ character and the type │
│ │ │ suffix. Empty for │
│ │ │ non-instantiated units. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%I" │ Unescaped instance │ 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" │ Short host name │ The hostname of the │
│ │ │ running system at the │
│ │ │ point in time the unit │
│ │ │ configuration is loaded, │
│ │ │ truncated at the first │
│ │ │ dot to remove any domain │
│ │ │ component. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%L" │ Log directory root │ This is either /var/log │
│ │ │ (for the system manager) │
│ │ │ or the path │
│ │ │ $XDG_STATE_HOME resolves │
│ │ │ to with /log appended │
│ │ │ (for user managers). │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%m" │ Machine ID │ The machine ID of the │
│ │ │ running system, │
│ │ │ formatted as string. See │
│ │ │ machine-id(5) for more │
│ │ │ information. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%M" │ Operating system │ The operating system │
│ │ image identifier │ image identifier of the │
│ │ │ running system, as read │
│ │ │ from the IMAGE_ID= field │
│ │ │ of /etc/os-release. If │
│ │ │ not set, resolves to an │
│ │ │ empty string. See os- │
│ │ │ release(5) for more │
│ │ │ information. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%n" │ Full unit name │ │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%N" │ Full unit name │ Same as "%n", but with │
│ │ │ the type suffix removed. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%o" │ Operating system ID │ The operating system │
│ │ │ identifier of the │
│ │ │ running system, as read │
│ │ │ from the ID= field of │
│ │ │ /etc/os-release. See os- │
│ │ │ release(5) for more │
│ │ │ information. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%p" │ Prefix name │ For instantiated units, │
│ │ │ this refers to the │
│ │ │ string before the first │
│ │ │ "@" character of the │
│ │ │ unit name. For │
│ │ │ non-instantiated units, │
│ │ │ same as "%N". │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%P" │ Unescaped prefix │ Same as "%p", but with │
│ │ name │ escaping undone. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%q" │ Pretty host name │ The pretty hostname of │
│ │ │ the running system at │
│ │ │ the point in time the │
│ │ │ unit configuration is │
│ │ │ loaded, as read from the │
│ │ │ PRETTY_HOSTNAME= field │
│ │ │ of /etc/machine-info. If │
│ │ │ not set, resolves to the │
│ │ │ short hostname. See │
│ │ │ machine-info(5) for more │
│ │ │ information. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%s" │ User shell │ This is the shell of the │
│ │ │ user running the service │
│ │ │ manager instance. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%S" │ State directory root │ This is either /var/lib │
│ │ │ (for the system manager) │
│ │ │ or the path │
│ │ │ $XDG_STATE_HOME resolves │
│ │ │ to (for user managers). │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%t" │ Runtime directory │ This is either /run/ │
│ │ root │ (for the system manager) │
│ │ │ or the path │
│ │ │ "$XDG_RUNTIME_DIR" │
│ │ │ resolves to (for user │
│ │ │ managers). │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%T" │ Directory for │ This is either /tmp or │
│ │ temporary files │ the path "$TMPDIR", │
│ │ │ "$TEMP" or "$TMP" are │
│ │ │ set to. (Note that the │
│ │ │ directory may be │
│ │ │ specified without a │
│ │ │ trailing slash.) │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%u" │ User name │ This is the name of the │
│ │ │ user running the service │
│ │ │ manager instance. In │
│ │ │ case of the system │
│ │ │ manager this resolves to │
│ │ │ "root". │
│ │ │ │
│ │ │ Note that this setting │
│ │ │ is not influenced by the │
│ │ │ User= setting │
│ │ │ configurable in the │
│ │ │ [Service] section of the │
│ │ │ service unit. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%U" │ User UID │ This is the numeric UID │
│ │ │ of the user running the │
│ │ │ service manager │
│ │ │ instance. In case of the │
│ │ │ system manager this │
│ │ │ resolves to "0". │
│ │ │ │
│ │ │ Note that this setting │
│ │ │ is not influenced by the │
│ │ │ User= setting │
│ │ │ configurable in the │
│ │ │ [Service] section of the │
│ │ │ service unit. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%v" │ Kernel release │ Identical to uname -r │
│ │ │ output. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%V" │ Directory for larger │ This is either /var/tmp │
│ │ and persistent │ or the path "$TMPDIR", │
│ │ temporary files │ "$TEMP" or "$TMP" are │
│ │ │ set to. (Note that the │
│ │ │ directory may be │
│ │ │ specified without a │
│ │ │ trailing slash.) │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%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. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%y" │ The path to the │ This is the path where │
│ │ fragment │ the main part of the │
│ │ │ unit file is located. │
│ │ │ For linked unit files, │
│ │ │ the real path outside of │
│ │ │ the unit search │
│ │ │ directories is used. For │
│ │ │ units that do not have a │
│ │ │ fragment file, this │
│ │ │ specifier will raise an │
│ │ │ error. │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%Y" │ The directory of the │ This is the directory │
│ │ fragment │ part of "%y". │
├───────────┼──────────────────────┼──────────────────────────┤
│ "%%" │ Single percent sign │ Use "%%" in place of "%" │
│ │ │ to specify a single │
│ │ │ percent sign. │
└───────────┴──────────────────────┴──────────────────────────┘
EXAMPLES
Example 1. Allowing units to be enabled
The following snippet (highlighted) allows a unit (e.g. foo.service) to
be enabled via systemctl enable:
[Unit]
Description=Foo
[Service]
ExecStart=/usr/sbin/foo-daemon
[Install]
WantedBy=multi-user.target
After running systemctl enable, a symlink
/etc/systemd/system/multi-user.target.wants/foo.service linking to the
actual unit will be created. It tells systemd to pull in the unit when
starting multi-user.target. The inverse systemctl disable will remove
that symlink again.
Example 2. Overriding vendor settings
There are two methods of overriding vendor settings in unit files:
copying the unit file from /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.
Example 3. Top level drop-ins with template units
Top level per-type drop-ins can be used to change some aspect of all
units of a particular type. For example, by creating the
/etc/systemd/system/service.d/ directory with a drop-in file, the
contents of the drop-in file can be applied to all service units. We can
take this further by having the top-level drop-in instantiate a
secondary helper unit. Consider for example the following set of units
and drop-in files where we install an OnFailure= dependency for all
service units.
/etc/systemd/system/failure-handler@.service:
[Unit]
Description=My failure handler for %i
[Service]
Type=oneshot
# Perform some special action for when %i exits unexpectedly.
ExecStart=/usr/sbin/myfailurehandler %i
We can then add an instance of failure-handler@.service as an OnFailure=
dependency for all service units.
/etc/systemd/system/service.d/10-all.conf:
[Unit]
OnFailure=failure-handler@%N.service
Now, after running systemctl daemon-reload all services will have
acquired an OnFailure= dependency on failure-handler@%N.service. The
template instance units will also have gained the dependency which
results in the creation of a recursive dependency chain. systemd will
try to detect these recursive dependency chains where a template unit
directly and recursively depends on itself and will remove such
dependencies automatically if it finds them. If systemd does not detect
the recursive dependency chain, we can break the chain ourselves by
disabling the drop-in for the template instance units via a symlink to
/dev/null:
mkdir /etc/systemd/system/failure-handler@.service.d/
ln -s /dev/null /etc/systemd/system/failure-handler@.service.d/10-all.conf
systemctl daemon-reload
This ensures that if a failure-handler@.service instance fails it will
not trigger an instance named failure-handler@failure-handler.service.
SEE ALSO
systemd(1), systemctl(1), systemd-system.conf(5), systemd.special(7),
systemd.service(5), systemd.socket(5), systemd.device(5),
systemd.mount(5), systemd.automount(5), systemd.swap(5),
systemd.target(5), systemd.path(5), systemd.timer(5), systemd.scope(5),
systemd.slice(5), systemd.time(7), systemd-analyze(1), capabilities(7),
systemd.directives(7), uname(1)
NOTES
1. Interface Portability and Stability Promise
https://systemd.io/PORTABILITY_AND_STABILITY/
2. 💣💥🧨💥💥💣 Please note that those configuration files must be available
at all times. If /usr/local/ is a separate partition, it may not be
available during early boot, and must not be used for configuration.
3. systemd and Storage Daemons for the Root File System
https://systemd.io/ROOT_STORAGE_DAEMONS
4. System and Service Credentials
https://systemd.io/CREDENTIALS
5. PSI (Pressure Stall Information)
https://docs.kernel.org/accounting/psi.html
systemd 257.9 SYSTEMD.UNIT(5)
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