systemd.unit — Unit configuration
A unit configuration file 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
a resource management slice or
a group of externally created processes. The syntax is inspired by
Desktop Entry Specification
files, which are in turn inspired by Microsoft Windows
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).
Various settings are allowed to be specified more than once,
in which case the interpretation depends on the setting. Often,
multiple settings form a list, and setting to an empty value
"resets", which means that previous assignments are ignored. When
this is allowed, it is mentioned in the description of the
setting. Note that using multiple assignments to the same value
makes the unit file incompatible with parsers for the XDG
.desktop file format.
Unit files are loaded from a set of paths determined during compilation, described in the next section.
Unit files may contain additional options on top of those
listed here. If systemd encounters an unknown option, it will
write a warning log message but continue loading the unit. If an
option or section name is prefixed with
X-, it is
ignored completely by systemd. Options within an ignored section
do not need the prefix. Applications may use this to include
additional information in the unit files.
Boolean arguments used in unit files can be written in
various formats. For positive settings the strings
on are equivalent. For negative settings, the
Time span values encoded in unit files can be written in various formats. A stand-alone number specifies a time in seconds. If suffixed with a time unit, the unit is honored. A concatenation of multiple values with units is supported, in which case the values are added up. Example: "50" refers to 50 seconds; "2min 200ms" refers to 2 minutes plus 200 milliseconds, i.e. 120200ms. The following time units are understood: s, min, h, d, w, ms, us. For details see systemd.time(7).
Empty lines and lines starting with # or ; are ignored. This may be used for commenting. Lines ending in a backslash are concatenated with the following line while reading and the backslash is replaced by a space character. This may be used to wrap long lines.
Along with a unit file
foo.service.wants/ may exist. All
unit files symlinked from such a directory are implicitly added as
dependencies of type
Wants= to the unit. This
is useful to hook units into the start-up of other units, without
having to modify their unit files. For details about the semantics
Wants=, see below. The preferred way to
create symlinks in the
.wants/ directory of a
unit file is with the enable command of the
tool which reads information from the [Install] section of unit
files (see below). A similar functionality exists for
Requires= type dependencies as well, the
directory suffix is
.requires/ in this
Along with a unit file
foo.service, a "drop-in" directory
foo.service.d/ may exist. All files with the suffix "
.conf" from this
directory will be parsed after the file itself is parsed. This is useful to alter or add configuration settings for
a unit, without having to modify unit files. Each drop-in file must have appropriate section headers. Note that for
instantiated units, this logic will first look for the instance "
.d/" subdirectory and read its
.conf" files, followed by the template "
.d/" subdirectory and the
.conf" files there. Also note that settings from the "
[Install]" section are not
honoured in drop-in unit files, and have no effect.
In addition to
the drop-in "
.conf" files for system services
can be placed in
/run/systemd/system directories. Drop-in
/etc take precedence over those in
/run which in turn take precedence over
/usr/lib. Drop-in files under any of
these directories take precedence over unit files wherever located.
(Of course, since
/run is temporary and
/usr/lib is for vendors, it is unlikely
drop-ins should be used in either of those places.)
Some unit names reflect paths existing in the file system
namespace. Example: a device unit
dev-sda.device refers to a device with the
/dev/sda in the
file system namespace. If this applies, a special way to escape
the path name is used, so that the result is usable as part of a
filename. Basically, given a path, "/" is replaced by "-", and all
other characters which are not ASCII alphanumerics are replaced by
C-style "\x2d" escapes (except that "_" is never replaced and "."
is only replaced when it would be the first character in the
escaped path). The root directory "/" is encoded as single dash,
while otherwise the initial and ending "/" are removed from all
paths during transformation. This escaping is reversible. Properly
escaped paths can be generated using the
Optionally, units may be instantiated from a
template file at runtime. 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 "
and the suffix) removed. Example: if a service
email@example.com is requested
and no file by that name is found, systemd will look
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 "
specifier in many of the configuration options. See below for
If a unit file is empty (i.e. has the file size 0) or is
/dev/null, its configuration
will not be loaded and it appears with a load state of
masked", and cannot be activated. Use this as an
effective way to fully disable a unit, making it impossible to
start it even manually.
The unit file format is covered by the Interface Stability Promise.
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.
A number of unit dependencies are automatically established,
depending on unit configuration. On top of that, for units with
DefaultDependencies=yes (the default) a couple
of additional dependencies are added. The precise effect of
DefaultDependencies=yes depends on the unit
type (see below).
DefaultDependencies=yes is set, units
that are referenced by other units of type
.target via a
Requires= dependency might automatically gain
Before= dependency too. See
Unit files are loaded from a set of paths determined during compilation, described in the two tables below. Unit files found in directories listed earlier override files with the same name in directories lower in the list.
When the variable
$SYSTEMD_UNIT_PATH is set,
the contents of this variable overrides the unit load path. If
$SYSTEMD_UNIT_PATH ends with an empty component
:"), the usual unit load path will be appended
to the contents of the variable.
Load path when running in system mode (
|Units of installed packages|
Load path when running in user mode (
|User configuration (only used when $XDG_CONFIG_HOME is set)|
|User configuration (only used when $XDG_CONFIG_HOME is not set)|
|Runtime units (only used when $XDG_RUNTIME_DIR is set)|
|Units of packages that have been installed in the home directory (only used when $XDG_DATA_HOME is set)|
|Units of packages that have been installed in the home directory (only used when $XDG_DATA_HOME is not set)|
|Units of packages that have been installed system-wide|
Additional units might be loaded into systemd ("linked") from directories not on the unit load path. See the link command for systemctl(1). Also, some units are dynamically created via a systemd.generator(7).
The unit file may include a [Unit] section, which carries generic information about the unit that is not dependent on the type of unit:
A free-form string describing the unit. This
is intended for use in UIs to show descriptive information
along with the unit name. The description should contain a
name that means something to the end user. "
Web Server" is a good example. Bad examples are
high-performance light-weight HTTP server"
(too generic) or "
Apache2" (too specific and
meaningless for people who do not know
A space-separated list of URIs referencing
documentation for this unit or its configuration. Accepted are
only URIs of the types "
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
Configures requirement dependencies on other
units. If this unit gets activated, the units listed here will
be activated as well. If one of the other units gets
deactivated or its activation fails, this unit will be
deactivated. This option may be specified more than once or
multiple space-separated units may be specified in one option
in which case requirement dependencies for all listed names
will be created. Note that requirement dependencies do not
influence the order in which services are started or stopped.
This has to be configured independently with the
options. If a unit
foo.service requires a
bar.service as configured with
Requires= and no ordering is configured
then both units will be started simultaneously and without any
delay between them if
activated. Often, it is a better choice to use
Wants= instead of
Requires= in order to achieve a system that
is more robust when dealing with failing services.
Note that dependencies of this type may also be
configured outside of the unit configuration file by adding a
symlink to a
accompanying the unit file. For details, see
However, if the units listed here are not started already,
they will not be started and the transaction will fail
A weaker version of
Requires=. Units listed in this option will
be started if the configuring unit is. However, if the listed
units fail to start or cannot be added to the transaction,
this has no impact on the validity of the transaction as a
whole. This is the recommended way to hook start-up of one
unit to the start-up of another unit.
Note that dependencies of this type may also be
configured outside of the unit configuration file by adding
symlinks to a
accompanying the unit file. For details, see
Configures requirement dependencies, very
similar in style to
Requires=, however in
addition to this behavior, it also declares that this unit is
stopped when any of the units listed suddenly disappears.
Units can suddenly, unexpectedly disappear if a service
terminates on its own choice, a device is unplugged or a mount
point unmounted without involvement of
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.
A space-separated list of unit names.
Configures negative requirement dependencies. If a unit has a
Conflicts= setting on another unit,
starting the former will stop the latter and vice versa. Note
that this setting is independent of and orthogonal to the
If a unit A that conflicts with a unit B is scheduled to be started at the same time as B, the transaction will either fail (in case both are required part of the transaction) or be modified to be fixed (in case one or both jobs are not a required part of the transaction). In the latter case, the job that is not the required will be removed, or in case both are not required, the unit that conflicts will be started and the unit that is conflicted is stopped.
A space-separated list of unit names.
Configures ordering dependencies between units. If a unit
foo.service contains a setting
Before=bar.service and both units are being
bar.service's start-up is
foo.service is started up.
Note that this setting is independent of and orthogonal to the
requirement dependencies as configured by
Requires=. It is a common pattern to
include a unit name in both the
Requires= option, in which case the unit
listed will be started before the unit that is configured with
these options. This option may be specified more than once, in
which case ordering dependencies for all listed names are
After= is the inverse of
Before=, i.e. while
After= ensures that the configured unit is
started after the listed unit finished starting up,
Before= ensures the opposite, i.e. that the
configured unit is fully started up before the listed unit is
started. Note that when two units with an ordering dependency
between them are shut down, the inverse of the start-up order
is applied. i.e. if a unit is configured with
After= on another unit, the former is
stopped before the latter if both are shut down. Given two units
with any ordering dependency between them, if one unit is shut
down and the other is started up, the shutdown is ordered
before the start-up. It doesn't matter if the ordering
Before=. 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
A space-separated list of one or more units
that are activated when this unit enters the
A space-separated list of one or more units where reload requests on this unit will be propagated to, or reload requests on the other unit will be propagated to this unit, respectively. Issuing a reload request on a unit will automatically also enqueue a reload request on all units that the reload request shall be propagated to via these two settings.
For units that start processes (such as
service units), lists one or more other units whose network
and/or temporary file namespace to join. This only applies to
unit types which support the
PrivateTmp= directives (see
for details). If a unit that has this setting set is started,
its processes will see the same
/var/tmp and network namespace as one
listed unit that is started. If multiple listed units are
already started, it is not defined which namespace is joined.
Note that this setting only has an effect if
PrivateTmp= is enabled for both the unit
that joins the namespace and the unit whose namespace is
Takes a space-separated list of absolute
paths. Automatically adds dependencies of type
all mount units required to access the specified path.
Mount points marked with
noauto are not
mounted automatically and will be ignored for the purposes of
this option. If such a mount should be a requirement for this
unit, direct dependencies on the mount units may be added
some other combination).
Takes a value of
ignore-requirements". Defaults to
replace". Specifies how the units listed in
OnFailure= will be enqueued. See
--job-mode= option for details on the
possible values. If this is set to "
only a single unit may be listed in
Takes a boolean argument. If
true, this unit will not be stopped when
isolating another unit. Defaults to
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
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
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
Takes a boolean argument. If
true, (the default), a few default
dependencies will implicitly be created for the unit. The
actual dependencies created depend on the unit type. For
example, for service units, these dependencies ensure that the
service is started only after basic system initialization is
completed and is properly terminated on system shutdown. See
the respective man pages for details. Generally, only services
involved with early boot or late shutdown should set this
false. It is highly recommended to
leave this option enabled for the majority of common units. If
false, this option does not disable
all implicit dependencies, just non-essential
When a job for this unit is queued, a time-out may be configured. If this time limit is
reached, the job will be cancelled, the unit however will not change state or even enter the
failed" mode. This value defaults to "
infinity" (job timeouts disabled),
except for device units. NB: this timeout is independent from any unit-specific timeout (for example, the
timeout set with
TimeoutStartSec= in service units) as the job timeout has no effect on the
unit itself, only on the job that might be pending for it. Or in other words: unit-specific timeouts are useful
to abort unit state changes, and revert them. The job timeout set with this option however is useful to abort
only the job waiting for the unit state to change.
optionally configures an additional
action to take when the time-out is
hit. It takes the same values as the
for details. Defaults to
configures an optional reboot string
to pass to the
Configure unit start rate limiting. By default, units which are started more than 5 times
within 10 seconds are not permitted to start any more times until the 10 second interval ends. With these two
options, this rate limiting may be modified. Use
StartLimitIntervalSec= to configure the
checking interval (defaults to
DefaultStartLimitIntervalSec= in manager configuration file,
set to 0 to disable any kind of rate limiting). Use
StartLimitBurst= to configure how many
starts per interval are allowed (defaults to
DefaultStartLimitBurst= in manager
configuration file). These configuration options are particularly useful in conjunction with the service
they apply to all kinds of starts (including manual), not just those triggered by the
Restart= logic. Note that units which are configured for
which reach the start limit are not attempted to be restarted anymore; however, they may still be restarted
manually at a later point, from which point on, the restart logic is again activated. Note that
systemctl reset-failed will cause the restart rate counter for a service to be flushed,
which is useful if the administrator wants to manually start a unit and the start limit interferes with
that. Note that this rate-limiting is enforced after any unit condition checks are executed, and hence unit
activations with failing conditions are not counted by this rate limiting. Slice, target, device and scope
units do not enforce this setting, as they are unit types whose activation may either never fail, or may
succeed only a single time.
Configure the action to take if the rate limit configured with
StartLimitBurst= is hit. Takes one of
none is set, hitting the rate limit will trigger no
action besides that the start will not be permitted.
reboot causes a reboot following the
normal shutdown procedure (i.e. equivalent to systemctl reboot).
reboot-force causes a forced reboot which will terminate all processes forcibly but should
cause no dirty file systems on reboot (i.e. equivalent to systemctl reboot -f) and
reboot-immediate causes immediate execution of the
reboot(2) system call, which
might result in data loss. Similarly,
poweroff-immediate have the effect of powering down the system with similar
semantics. Defaults to
Configure the optional argument for the
reboot(2) system call if
StartLimitAction= or a service's
FailureAction= is a reboot action. This
works just like the optional argument to systemctl reboot command.
Before starting a unit, verify that the specified condition is true. If it is not true, the
starting of the unit will be (mostly silently) skipped, however all ordering dependencies of it are still
respected. A failing condition will not result in the unit being moved into a failure state. The condition is
checked at the time the queued start job is to be executed. Use condition expressions in order to silently skip
units that do not apply to the local running system, for example because the kernel or runtime environment
doesn't require its functionality. Use the various
AssertVirtualization=, … options for a similar mechanism that puts the unit in a failure
state and logs about the failed check (see below).
ConditionArchitecture= may be used to
check whether the system is running on a specific
architecture. Takes one of
cris to test
against a specific architecture. The architecture is
determined from the information returned by
and is thus subject to
Note that a
Personality= setting in the
same unit file has no effect on this condition. A special
native is mapped to the
architecture the system manager itself is compiled for. The
test may be negated by prepending an exclamation mark.
ConditionVirtualization= may be used
to check whether the system is executed in a virtualized
environment and optionally test whether it is a specific
implementation. Takes either boolean value to check if being
executed in any virtualized environment, or one of
container to test against a generic type of
virtualization solution, or one of
rkt to test
against a specific implementation. See
for a full list of known virtualization technologies and their
identifiers. If multiple virtualization technologies are
nested, only the innermost is considered. The test may be
negated by prepending an exclamation mark.
ConditionHost= may be used to match
against the hostname or machine ID of the host. This either
takes a hostname string (optionally with shell style globs)
which is tested against the locally set hostname as returned
or a machine ID formatted as string (see
The test may be negated by prepending an exclamation
ConditionKernelCommandLine= may be
used to check whether a specific kernel command line option is
set (or if prefixed with the exclamation mark unset). The
argument must either be a single word, or an assignment (i.e.
two words, separated "
="). In the former case
the kernel command line is searched for the word appearing as
is, or as left hand side of an assignment. In the latter case,
the exact assignment is looked for with right and left hand
ConditionSecurity= may be used to
check whether the given security module is enabled on the
system. Currently, the recognized values are
audit. The test may be negated by
prepending an exclamation mark.
ConditionCapability= may be used to
check whether the given capability exists in the capability
bounding set of the service manager (i.e. this does not check
whether capability is actually available in the permitted or
effective sets, see
for details). Pass a capability name such as
CAP_MKNOD", possibly prefixed with an
exclamation mark to negate the check.
ConditionACPower= may be used to
check whether the system has AC power, or is exclusively
battery powered at the time of activation of the unit. This
takes a boolean argument. If set to
the condition will hold only if at least one AC connector of
the system is connected to a power source, or if no AC
connectors are known. Conversely, if set to
false, the condition will hold only if
there is at least one AC connector known and all AC connectors
are disconnected from a power source.
ConditionNeedsUpdate= takes one of
argument, possibly prefixed with a "
inverting the condition). This condition may be used to
conditionalize units on whether the specified directory
requires an update because
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
/var on the next following boot. Units
making use of this condition should order themselves before
to make sure they run before the stamp file's modification
time gets reset indicating a completed update.
ConditionFirstBoot= takes a boolean
argument. This condition may be used to conditionalize units
on whether the system is booting up with an unpopulated
/etc directory. This may be used to
/etc on the first boot after
factory reset, or when a new system instances boots up for the
ConditionPathExists= a file
existence condition is checked before a unit is started. If
the specified absolute path name does not exist, the condition
will fail. If the absolute path name passed to
ConditionPathExists= is prefixed with an
exclamation mark ("
!"), the test is negated,
and the unit is only started if the path does not
ConditionPathExistsGlob= is similar
ConditionPathExists=, but checks for the
existence of at least one file or directory matching the
specified globbing pattern.
ConditionPathIsDirectory= is similar
ConditionPathExists= but verifies
whether a certain path exists and is a directory.
verifies whether a certain path exists and is a symbolic
ConditionPathIsMountPoint= is similar
ConditionPathExists= but verifies
whether a certain path exists and is a mount point.
ConditionPathIsReadWrite= is similar
ConditionPathExists= but verifies
whether the underlying file system is readable and writable
(i.e. not mounted read-only).
verifies whether a certain path exists and is a non-empty
ConditionFileNotEmpty= is similar to
ConditionPathExists= but verifies whether a
certain path exists and refers to a regular file with a
ConditionFileIsExecutable= is similar
ConditionPathExists= but verifies
whether a certain path exists, is a regular file and marked
If multiple conditions are specified, the unit will be
executed if all of them apply (i.e. a logical AND is applied).
Condition checks can be prefixed with a pipe symbol (|) in
which case a condition becomes a triggering condition. If at
least one triggering condition is defined for a unit, then the
unit will be executed if at least one of the triggering
conditions apply and all of the non-triggering conditions. If
you prefix an argument with the pipe symbol and an exclamation
mark, the pipe symbol must be passed first, the exclamation
second. Except for
ConditionPathIsSymbolicLink=, all path
checks follow symlinks. If any of these options is assigned
the empty string, the list of conditions is reset completely,
all previous condition settings (of any kind) will have no
Similar to the
ConditionVirtualization=, …, condition settings described above, these settings add
assertion checks to the start-up of the unit. However, unlike the conditions settings, any assertion setting
that is not met results in failure of the start job (which means this is logged loudly). Use assertion
expressions for units that cannot operate when specific requirements are not met, and when this is something
the administrator or user should look into.
A path to a configuration file this unit has been generated from. This is primarily useful for implementation of generator tools that convert configuration from an external configuration file format into native unit files. This functionality should not be used in normal units.
Unit files may 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. Note that settings in the "
[Install]" section may not appear in
.d/*.conf unit file drop-ins (see above).
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 file name. 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.
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
.requires/ directory of each of the
listed units when this unit is installed by systemctl
enable. This has the effect that a dependency of
is added from the listed unit to the current unit. The primary
result is that the current unit will be started when the
listed unit is started. See the description of
the [Unit] section for details.
WantedBy=foo.service in a service
bar.service is mostly equivalent to
Alias=foo.service.wants/bar.service in the
same file. In case of template units, systemctl
enable must be called with an instance name, and
this instance will be added to the
.requires/ list of the listed unit. E.g.
WantedBy=getty.target in a service
getty@.service will result in
systemctl enable firstname.lastname@example.org
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.
In template unit files, this specifies for which instance the unit shall be enabled if the template is enabled without any explicitly set instance. This option has no effect in non-template unit files. The specified string must be usable as instance identifier.
The following specifiers are interpreted in the Install section: %n, %N, %p, %i, %U, %u, %m, %H, %b, %v. For their meaning see the next section.
Many settings resolve specifiers which may be used to write generic unit files referring to runtime or unit parameters that are replaced when the unit files are loaded. The following specifiers are understood:
Table 3. Specifiers available in unit files
|"||Full unit name|
|"||Unescaped full unit name||Same as "|
|"||Prefix name||For instantiated units, this refers to the string before the "|
|"||Unescaped prefix name||Same as "|
|"||Instance name||For instantiated units: this is the string between the "|
|"||Unescaped instance name||Same as "|
|"||Unescaped filename||This is either the unescaped instance name (if applicable) with |
|"||Control group path of the unit||This path does not include the |
|"||Control group path of the slice the unit is placed in||This usually maps to the parent cgroup path of "|
|"||Root control group path below which slices and units are placed||For system instances, this resolves to |
|"||Runtime directory||This is either |
|"||User name||This is the name of the user running the service manager instance. In case of the system manager this resolves to "|
|"||User UID||This is the numeric UID of the user running the service manager instance. In case of the system manager this resolves to "|
|"||User home directory||This is the home directory of the user running the service manager instance. In case of the system manager this resolves to "|
|"||User shell||This is the shell of the user running the service manager instance. In case of the system manager this resolves to "|
|"||Machine ID||The machine ID of the running system, formatted as string. See machine-id(5) for more information.|
|"||Boot ID||The boot ID of the running system, formatted as string. See random(4) for more information.|
|"||Host name||The hostname of the running system at the point in time the unit configuration is loaded.|
|"||Kernel release||Identical to uname -r output|
|"||Single percent sign||Use "|
Please note that specifiers "
%s" are mostly useless
when systemd is running in system mode. PID 1 cannot query the
user account database for information, so the specifiers only work
as shortcuts for things which are already specified in a different
way in the unit file. They are fully functional when systemd is
Example 1. Allowing units to be enabled
The following snippet (highlighted) allows a unit (e.g.
foo.service) to be enabled via
[Unit] Description=Foo [Service] ExecStart=/usr/sbin/foo-daemon [Install] WantedBy=multi-user.target
After running systemctl enable, a
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
Example 2. Overriding vendor settings
There are two methods of overriding vendor settings in
unit files: copying the unit file from
/etc/systemd/system and modifying the
chosen settings. Alternatively, one can create a directory named
/etc/systemd/system and place a drop-in
there that only changes the specific settings one is interested
in. Note that multiple such drop-in files are read if
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.
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
ExecStart= in service units), one needs
to first clear the list before re-adding all entries except the
one that is to be removed. See below for an example.
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
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,
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
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
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
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
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 dependencies (
cannot be reset to an empty list, so dependencies can only be
added in drop-ins. If you want to remove dependencies, you have
to override the entire unit.
systemd(1), systemctl(1), systemd.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)