|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
SYSTEMD.UNIT(5) systemd.unit SYSTEMD.UNIT(5)
systemd.unit - Unit configuration
service.service, socket.socket, device.device, mount.mount,
automount.automount, swap.swap, target.target, path.path,
timer.timer, slice.slice, scope.scope
System Unit Search Path
/etc/systemd/system.control/*
/run/systemd/system.control/*
/run/systemd/transient/*
/run/systemd/generator.early/*
/etc/systemd/system/*
/etc/systemd/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/*
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. "[email protected]") may be a symlink to
different template (e.g. "[email protected]"). In that case,
just this specific instance is aliased, while other instances of
the template (e.g. "[email protected]", "[email protected]") 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.service pointing to the
reboot.target file will be created, and when Ctrl+Alt+Del is
invoked, systemd will look for the ctrl-alt-del.service and
execute reboot.service. systemd does not look at the [Install]
section at all during normal operation, so any directives in that
section only have an effect through the symlinks created during
enablement.
Along with a unit file foo.service, the directory
foo.service.wants/ may exist. All unit files symlinked from such
a directory are implicitly added as dependencies of type Wants=
to the unit. Similar functionality exists for Requires= type
dependencies as well, the directory suffix is .requires/ in this
case. This functionality is useful to hook units into the
start-up of other units, without having to modify their unit
files. For details about the semantics of Wants= and Requires=,
see below. The preferred way to create symlinks in the .wants/ or
.requires/ directories is by specifying the dependency in
[Install] section of the target unit, and creating the symlink in
the file system with the enable or preset commands of
systemctl(1). The target can be a normal unit (either plain or a
specific instance of a template unit). In case when the source
unit is a template, the target can also be a template, in which
case the instance will be "propagated" to the target unit to form
a valid unit instance. The target of symlinks in .wants/ or
.requires/ must thus point to a valid unit file location, i.e.
the symlink target name must satisfy the described requirements,
and the destination path must be in one of the unit search paths,
see UNIT FILE LOAD PATH section below for more details. Note that
the target file 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.
"[email protected]/") and read its ".conf" files, followed by the
template ".d/" subdirectory (e.g. "[email protected]/") 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
[email protected] is requested and no file by that name is
found, systemd will look for [email protected] 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].
Sometimes it is useful to convert arbitrary strings into unit
names. To facilitate this, a method of string escaping is used,
in order to map strings containing arbitrary byte values (except
NUL) into valid unit names and their restricted character set. A
common special case are unit names that reflect paths to objects
in the file system hierarchy. Example: a device unit
dev-sda.device refers to a device with the device node /dev/sda
in the file system.
The escaping algorithm operates as follows: given a string, any
"/" character is replaced by "-", and all other characters which
are not ASCII alphanumerics, ":", "_" or "." are replaced by
C-style "\x2d" escapes. In addition, "." is replaced with such a
C-style escape when it would appear as the first character in the
escaped string.
When the input qualifies as absolute file system path, this
algorithm is extended slightly: the path to the root directory
"/" is encoded as single dash "-". In addition, any leading,
trailing or duplicate "/" characters are removed from the string
before transformation. Example: /foo//bar/baz/ becomes
"foo-bar-baz".
This escaping is fully reversible, as long as it is known whether
the escaped string was a path (the unescaping results are
different for paths and non-path strings). The systemd-escape(1)
command may be used to apply and reverse escaping on arbitrary
strings. Use systemd-escape --path to escape path strings, and
systemd-escape without --path otherwise.
Implicit Dependencies
A number of unit dependencies are implicitly established,
depending on unit type and unit configuration. These implicit
dependencies can make unit configuration file cleaner. For the
implicit dependencies in each unit type, please refer to section
"Implicit Dependencies" in respective man pages.
For example, service units with Type=dbus automatically acquire
dependencies of type Requires= and After= on dbus.socket. See
systemd.service(5) for details.
Default Dependencies
Default dependencies are similar to implicit dependencies, but
can be turned on and off by setting DefaultDependencies= to yes
(the default) and no, while implicit dependencies are always in
effect. See section "Default Dependencies" in respective man
pages for the effect of enabling DefaultDependencies= in each
unit types.
For example, target units will complement all configured
dependencies of type Wants= or Requires= with dependencies of
type After=. See systemd.target(5) for details. Note that this
behavior can be opted out by setting DefaultDependencies=no in
the specified units, or it can be selectively overridden via an
explicit Before= dependency.
Unit files are loaded from a set of paths determined during
compilation, described in the two tables below. Unit files found
in directories listed earlier override files with the same name
in directories lower in the list [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 │
│ $XDG_RUNTIME_DIR/systemd/user.control │ used 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 doesn't have to
exist, and in fact the symlink target path is not used, except to
check whether the target is within the unit load path. In
contrast, a symlink which goes outside of the unit load path
signifies a linked unit file. The symlink is followed when
loading the file, but the destination name is otherwise unused
(and may even not be a valid unit file name). For example,
symlinks /etc/systemd/system/alias1.service → service1.service,
/etc/systemd/system/alias2.service →
/usr/lib/systemd/service1.service,
/etc/systemd/system/alias3.service →
/etc/systemd/system/service1.service are all valid aliases and
service1.service will have four names, even if the unit file is
located at /run/systemd/system/service1.service. In contrast, a
symlink /etc/systemd/system/link1.service → ../link1_service_file
means that link1.service is a "linked unit" and the contents of
/etc/systemd/link1_service_file provide its configuration.
The system and service manager loads a unit's configuration
automatically when a unit is referenced for the first time. It
will automatically unload the unit configuration and state again
when the unit is not needed anymore ("garbage collection"). A
unit may be referenced through a number of different mechanisms:
1. Another loaded unit references it with a dependency such as
After=, Wants=, ...
2. The unit is currently starting, running, reloading or
stopping.
3. The unit is currently in the failed state. (But see below.)
4. A job for the unit is pending.
5. The unit is pinned by an active IPC client program.
6. The unit is a special "perpetual" unit that is always active
and loaded. Examples for perpetual units are the root mount
unit -.mount or the scope unit init.scope that the service
manager itself lives in.
7. The unit has running processes associated with it.
The garbage collection logic may be altered with the CollectMode=
option, which allows configuration whether automatic unloading of
units that are in failed state is permissible, see below.
Note that when a unit's configuration and state is unloaded, all
execution results, such as exit codes, exit signals, resource
consumption and other statistics are lost, except for what is
stored in the log subsystem.
Use systemctl daemon-reload or an equivalent command to reload
unit configuration while the unit is already loaded. In this case
all configuration settings are flushed out and replaced with the
new configuration (which however might not be in effect
immediately), however all runtime state is saved/restored.
The unit file may include a [Unit] section, which carries generic
information about the unit that is not dependent on the type of
unit:
Description=
A short human readable title of the unit. This may be used by
systemd (and other UIs) as a user-visible label for the unit,
so this string should identify the unit rather than describe
it, despite the name. This string also shouldn't just repeat
the unit name. "Apache2 Web Server" is a good example. Bad
examples are "high-performance light-weight HTTP server" (too
generic) or "Apache2" (meaningless for people who do not know
Apache, duplicates the unit name). systemd may use this
string as a noun in status messages ("Starting
description...", "Started description.", "Reached target
description.", "Failed to start description."), so it should
be capitalized, and should not be a full sentence, or a
phrase with a continuous verb. Bad examples include "exiting
the container" or "updating the database once per day.".
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 doesn't matter which
of the two ordering dependencies is used, because stop jobs
are always ordered before start jobs, see the discussion in
Before=/After= below.
If unit A that conflicts with unit B is scheduled to be
started at the same time as B, the transaction will either
fail (in case both are required parts of the transaction) or
be modified to be fixed (in case one or both jobs are not a
required part of the transaction). In the latter case, the
job that is not required will be removed, or in case both are
not required, the unit that conflicts will be started and the
unit that is conflicted is stopped.
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 doesn't matter if
the ordering dependency is After= or Before=, in this case.
It also doesn't matter which of the two is shut down, as long
as one is shut down and the other is started up; the shutdown
is ordered before the start-up in all cases. If two units
have no ordering dependencies between them, they are shut
down or started up simultaneously, and no ordering takes
place. It depends on the unit type when precisely a unit has
finished starting up. Most importantly, for service units
start-up is considered completed for the purpose of
Before=/After= when all its configured start-up commands have
been invoked and they either failed or reported start-up
success. Note that this does includes ExecStartPost= (or
ExecStopPost= for the shutdown case).
Note that those settings are independent of and orthogonal to
the requirement dependencies as configured by Requires=,
Wants=, Requisite=, or BindsTo=. It is a common pattern to
include a unit name in both the After= and Wants= options, in
which case the unit listed will be started before the unit
that is configured with these options.
Note that Before= dependencies on device units have no effect
and are not supported. Devices generally become available as
a result of an external hotplug event, and systemd creates
the corresponding device unit without delay.
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(5). The default is "infinity" (job timeouts
disabled), except for device units where
JobRunningTimeoutSec= defaults to DefaultDeviceTimeoutSec=.
Note: these timeouts are independent from any unit-specific
timeouts (for example, the timeout set with TimeoutStartSec=
in service units). The job timeout has no effect on the unit
itself. Or in other words: unit-specific timeouts are useful
to abort unit state changes, and revert them. The job timeout
set with this option however is useful to abort only the job
waiting for the unit state to change.
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(5). The
special value "infinity" can be used to limit the total
number of start attempts, even if they happen at large time
intervals. Defaults to DefaultStartLimitIntervalSec= in
manager configuration file, and may be set to 0 to disable
any kind of rate limiting. burst is a number and defaults to
DefaultStartLimitBurst= in manager configuration file.
These configuration options are particularly useful in
conjunction with the service setting Restart= (see
systemd.service(5)); however, they apply to all kinds of
starts (including manual), not just those triggered by the
Restart= logic.
Note that units which are configured for Restart=, and which
reach the start limit are not attempted to be restarted
anymore; however, they may still be restarted manually or
from a timer or socket at a later point, after the interval
has passed. From that point on, the restart logic is
activated again. systemctl reset-failed will cause the
restart rate counter for a service to be flushed, which is
useful if the administrator wants to manually start a unit
and the start limit interferes with that. Rate-limiting is
enforced after any unit condition checks are executed, and
hence unit activations with failing conditions do not count
towards the rate limit.
When a unit is unloaded due to the garbage collection logic
(see above) its rate limit counters are flushed out too. This
means that configuring start rate limiting for a unit that is
not referenced continuously has no effect.
This setting does not apply to slice, target, device, and
scope units, since they are unit types whose activation may
either never fail, or may succeed only a single time.
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 doesn't require their
functionality.
If multiple conditions are specified, the unit will be executed
if all of them apply (i.e. a logical AND is applied). Condition
checks can use a pipe symbol ("|") after the equals sign
("Condition...=|..."), which causes the condition to become a
triggering condition. If at least one triggering condition is
defined for a unit, then the unit will be started if at least one
of the triggering conditions of the unit applies and all of the
regular (i.e. non-triggering) conditions apply. If you prefix an
argument with the pipe symbol and an exclamation mark, the pipe
symbol must be passed first, the exclamation second. If any of
these options is assigned the empty string, the list of
conditions is reset completely, all previous condition settings
(of any kind) will have no effect.
The AssertArchitecture=, AssertVirtualization=, ... options are
similar to conditions but cause the start job to fail (instead of
being skipped). The failed check is logged. Units with unmet
conditions are considered to be in a clean state and will be
garbage collected if they are not referenced. This means that
when queried, the condition failure may or may not show up in the
state of the unit.
Note that neither assertion nor condition expressions result in
unit state changes. Also note that both are checked at the time
the job is to be executed, i.e. long after depending jobs and it
itself were queued. Thus, neither condition nor assertion
expressions are suitable for conditionalizing unit dependencies.
The condition verb of systemd-analyze(1) can be used to test
condition and assert expressions.
Except for ConditionPathIsSymbolicLink=, all path checks follow
symlinks.
ConditionArchitecture=
Check whether the system is running on a specific
architecture. Takes one of "x86", "x86-64", "ppc", "ppc-le",
"ppc64", "ppc64-le", "ia64", "parisc", "parisc64", "s390",
"s390x", "sparc", "sparc64", "mips", "mips-le", "mips64",
"mips64-le", "alpha", "arm", "arm-be", "arm64", "arm64-be",
"sh", "sh64", "m68k", "tilegx", "cris", "arc", "arc-be", or
"native".
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 [email protected]
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).
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.
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.
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 [email protected]
will result in systemctl enable [email protected] creating a
getty.target.wants/[email protected] link to [email protected].
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,
[email protected] in a service [email protected] will
result in systemctl enable [email protected] creating a
[email protected]/[email protected] link to
[email protected], which applies to all instances of
[email protected].
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.
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 │ This is either │
│ │ root │ /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 │ This is the home │
│ │ directory │ 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 │ The operating system │
│ │ ID │ 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 │ This is either /var/lib │
│ │ root │ (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 "$TMP" are │
│ │ │ set to. (Note that the │
│ │ │ directory may be │
│ │ │ specified without a │
│ │ │ trailing slash.) │
├───────────┼────────────────────┼──────────────────────────┤
│ "%u" │ User name │ This is the name of the │
│ │ │ user running the service │
│ │ │ manager instance. In │
│ │ │ case of the system │
│ │ │ manager this resolves to │
│ │ │ "root". │
│ │ │ │
│ │ │ Note that this setting │
│ │ │ is not influenced by the │
│ │ │ User= setting │
│ │ │ configurable in the │
│ │ │ [Service] section of the │
│ │ │ service unit. │
├───────────┼────────────────────┼──────────────────────────┤
│ "%U" │ User UID │ This is the numeric UID │
│ │ │ of the user running the │
│ │ │ service manager │
│ │ │ instance. In case of the │
│ │ │ system manager this │
│ │ │ resolves to "0". │
│ │ │ │
│ │ │ Note that this setting │
│ │ │ is not influenced by the │
│ │ │ User= setting │
│ │ │ configurable in the │
│ │ │ [Service] section of the │
│ │ │ service unit. │
├───────────┼────────────────────┼──────────────────────────┤
│ "%v" │ Kernel release │ Identical to uname -r │
│ │ │ output. │
├───────────┼────────────────────┼──────────────────────────┤
│ "%V" │ Directory for │ This is either /var/tmp │
│ │ larger and │ or the path "$TMPDIR", │
│ │ persistent │ "$TEMP" or "$TMP" are │
│ │ temporary files │ 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 don't have a │
│ │ │ fragment file, this │
│ │ │ specifier will raise an │
│ │ │ error. │
├───────────┼────────────────────┼──────────────────────────┤
│ "%Y" │ The directory of │ This is the directory │
│ │ the fragment │ part of "%y". │
├───────────┼────────────────────┼──────────────────────────┤
│ "%%" │ Single percent │ Use "%%" in place of "%" │
│ │ sign │ to specify a single │
│ │ │ percent sign. │
└───────────┴────────────────────┴──────────────────────────┘
Example 1. Allowing units to be enabled
The following snippet (highlighted) allows a unit (e.g.
foo.service) to be enabled via systemctl enable:
[Unit]
Description=Foo
[Service]
ExecStart=/usr/sbin/foo-daemon
[Install]
WantedBy=multi-user.target
After running systemctl enable, a symlink
/etc/systemd/system/multi-user.target.wants/foo.service linking
to the actual unit will be created. It tells systemd to pull in
the unit when starting multi-user.target. The inverse systemctl
disable will remove that symlink again.
Example 2. Overriding vendor settings
There are two methods of overriding vendor settings in unit
files: copying the unit file from /usr/lib/systemd/system to
/etc/systemd/system and modifying the chosen settings.
Alternatively, one can create a directory named unit.d/ within
/etc/systemd/system and place a drop-in file name.conf there that
only changes the specific settings one is interested in. Note
that multiple such drop-in files are read if present, processed
in lexicographic order of their filename.
The advantage of the first method is that one easily overrides
the complete unit, the vendor unit is not parsed at all anymore.
It has the disadvantage that improvements to the unit file by the
vendor are not automatically incorporated on updates.
The advantage of the second method is that one only overrides the
settings one specifically wants, where updates to the unit by the
vendor automatically apply. This has the disadvantage that some
future updates by the vendor might be incompatible with the local
changes.
This also applies for user instances of systemd, but with
different locations for the unit files. See the section on unit
load paths for further details.
Suppose there is a vendor-supplied unit
/usr/lib/systemd/system/httpd.service with the following
contents:
[Unit]
Description=Some HTTP server
After=remote-fs.target sqldb.service
Requires=sqldb.service
AssertPathExists=/srv/webserver
[Service]
Type=notify
ExecStart=/usr/sbin/some-fancy-httpd-server
Nice=5
[Install]
WantedBy=multi-user.target
Now one wants to change some settings as an administrator:
firstly, in the local setup, /srv/webserver might not exist,
because the HTTP server is configured to use /srv/www instead.
Secondly, the local configuration makes the HTTP server also
depend on a memory cache service, memcached.service, that should
be pulled in (Requires=) and also be ordered appropriately
(After=). Thirdly, in order to harden the service a bit more, the
administrator would like to set the PrivateTmp= setting (see
systemd.exec(5) for details). And lastly, the administrator would
like to reset the niceness of the service to its default value of
0.
The first possibility is to copy the unit file to
/etc/systemd/system/httpd.service and change the chosen settings:
[Unit]
Description=Some HTTP server
After=remote-fs.target sqldb.service memcached.service
Requires=sqldb.service memcached.service
AssertPathExists=/srv/www
[Service]
Type=notify
ExecStart=/usr/sbin/some-fancy-httpd-server
Nice=0
PrivateTmp=yes
[Install]
WantedBy=multi-user.target
Alternatively, the administrator could create a drop-in file
/etc/systemd/system/httpd.service.d/local.conf with the following
contents:
[Unit]
After=memcached.service
Requires=memcached.service
# Reset all assertions and then re-add the condition we want
AssertPathExists=
AssertPathExists=/srv/www
[Service]
Nice=0
PrivateTmp=yes
Note that for drop-in files, if one wants to remove entries from
a setting that is parsed as a list (and is not a dependency),
such as AssertPathExists= (or e.g. ExecStart= in service units),
one needs to first clear the list before re-adding all entries
except the one that is to be removed. Dependencies (After=, etc.)
cannot be reset to an empty list, so dependencies can only be
added in drop-ins. If you want to remove dependencies, you have
to override the entire unit.
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/[email protected]:
[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 [email protected] as an
OnFailure= dependency for all service units.
/etc/systemd/system/service.d/10-all.conf:
[Unit]
OnFailure=failure-handler@%N.service
Now, after running systemctl daemon-reload all services will have
acquired an OnFailure= dependency on failure-handler@%N.service.
The template instance units will also have gained the dependency
which results in the creation of a recursive dependency chain.
systemd will try to detect these recursive dependency chains
where a template unit directly and recursively depends on itself
and will remove such dependencies automatically if it finds them.
If systemd doesn't detect the recursive dependency chain, we can
break the chain ourselves by disabling the drop-in for the
template instance units via a symlink to /dev/null:
mkdir /etc/systemd/system/[email protected]/
ln -s /dev/null /etc/systemd/system/[email protected]/10-all.conf
systemctl daemon-reload
This ensures that if a [email protected] instance fails it
will not trigger an instance named
[email protected].
systemd(1), systemctl(1), systemd-system.conf(5),
systemd.special(7), systemd.service(5), systemd.socket(5),
systemd.device(5), systemd.mount(5), systemd.automount(5),
systemd.swap(5), systemd.target(5), systemd.path(5),
systemd.timer(5), systemd.scope(5), systemd.slice(5),
systemd.time(7), systemd-analyze(1), capabilities(7),
systemd.directives(7), uname(1)
1. Interface 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
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have
a bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 257~devel SYSTEMD.UNIT(5)
Pages that refer to this page: portablectl(1), run0(1), systemctl(1), systemd(1), systemd-ac-power(1), systemd-analyze(1), systemd-delta(1), systemd-escape(1), systemd-firstboot(1), systemd-mount(1), systemd-notify(1), systemd-run(1), sd_bus_creds_get_pid(3), os-release(5), repart.d(5), systemd.automount(5), systemd.device(5), systemd.dnssd(5), systemd.exec(5), systemd.kill(5), systemd.link(5), systemd.mount(5), systemd.netdev(5), systemd.network(5), systemd.path(5), systemd.preset(5), systemd.resource-control(5), systemd.scope(5), systemd.service(5), systemd.slice(5), systemd.socket(5), systemd.swap(5), systemd-system.conf(5), systemd.target(5), systemd.timer(5), sysupdate.d(5), sysusers.d(5), tmpfiles.d(5), [email protected](5), daemon(7), file-hierarchy(7), kernel-command-line(7), nfs.systemd(7), systemd.directives(7), systemd.generator(7), systemd.index(7), systemd.special(7), systemd.syntax(7), systemd.time(7), systemd.v(7), udev(7), kernel-install(8), systemd-run-generator(8), systemd-sysext(8), systemd-update-done.service(8)
|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|