Provided by: systemd_229-4ubuntu21.31_amd64 
NAME
systemd.unit - Unit configuration
SYNOPSIS
service.service, socket.socket, device.device, mount.mount, automount.automount, swap.swap,
target.target, path.path, timer.timer, slice.slice, scope.scope
/etc/systemd/system/*
/run/systemd/system/*
/lib/systemd/system/*
...
$XDG_CONFIG_HOME/systemd/user/*
$HOME/.config/systemd/user/*
/etc/systemd/user/*
$XDG_RUNTIME_DIR/systemd/user/*
/run/systemd/user/*
$XDG_DATA_HOME/systemd/user/*
$HOME/.local/share/systemd/user/*
/usr/lib/systemd/user/*
...
DESCRIPTION
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 systemd(1), a resource management slice or a group of externally created
processes. The syntax is inspired by XDG Desktop Entry Specification[1] .desktop files, which are in turn
inspired by Microsoft Windows .ini files.
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
1, yes, true and on are equivalent. For negative settings, the strings 0, no, false and off are
equivalent.
Time span values encoded in unit files can be written in various formats. A stand-alone number specifies
a time in seconds. If suffixed with a time unit, the unit is honored. A concatenation of multiple values
with units is supported, in which case the values are added up. Example: "50" refers to 50 seconds; "2min
200ms" refers to 2 minutes 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, the directory foo.service.wants/ may exist. All unit files symlinked
from such a directory are implicitly added as dependencies of type Wants= to the unit. This is useful to
hook units into the start-up of other units, without having to modify their unit files. For details about
the semantics of Wants=, see below. The preferred way to create symlinks in the .wants/ directory of a
unit file is with the enable command of the systemctl(1) tool which reads information from the [Install]
section of unit files (see below). A similar functionality exists for Requires= type dependencies as
well, the directory suffix is .requires/ in this case.
Along with a unit file foo.service, a "drop-in" directory foo.service.d/ may exist. All files with the
suffix ".conf" from this directory will be parsed after the 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 /etc/systemd/system, the drop-in ".conf" files for system services can be placed in
/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 /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 device node /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 systemd-escape(1) command.
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 "@" character and the suffix) removed. Example: if a service
getty@tty3.service is requested and no file by that name is found, systemd will look for getty@.service
and instantiate a service from that configuration file if it is found.
To refer to the instance string from within the configuration file you may use the special "%i" specifier
in many of the configuration options. See below for details.
If a unit file is empty (i.e. has the file size 0) or is symlinked to /dev/null, its configuration will
not be loaded and it appears with a load state of "masked", and cannot be activated. Use this as an
effective way to fully disable a unit, making it impossible to start it even manually.
The unit file format is covered by the Interface Stability Promise[2].
AUTOMATIC DEPENDENCIES
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).
If DefaultDependencies=yes is set, units that are referenced by other units of type .target via a Wants=
or Requires= dependency might automatically gain an Before= dependency too. See systemd.target(5) for
details.
UNIT FILE LOAD PATH
Unit files are loaded from a set of paths determined during compilation, described in the two tables
below. Unit files found in directories listed earlier override files with the same name in directories
lower in the list.
When the variable $SYSTEMD_UNIT_PATH is set, the contents of this variable overrides the unit load path.
If $SYSTEMD_UNIT_PATH ends with an empty component (":"), the usual unit load path will be appended to
the contents of the variable.
Table 1. Load path when running in system mode (--system).
┌────────────────────┬─────────────────────────────┐
│Path │ Description │
├────────────────────┼─────────────────────────────┤
│/etc/systemd/system │ Local configuration │
├────────────────────┼─────────────────────────────┤
│/run/systemd/system │ Runtime units │
├────────────────────┼─────────────────────────────┤
│/lib/systemd/system │ Units of installed packages │
└────────────────────┴─────────────────────────────┘
Table 2. Load path when running in user mode (--user).
┌────────────────────────────────┬───────────────────────────────────────┐
│Path │ Description │
├────────────────────────────────┼───────────────────────────────────────┤
│$XDG_CONFIG_HOME/systemd/user │ User configuration (only used when │
│ │ $XDG_CONFIG_HOME is set) │
├────────────────────────────────┼───────────────────────────────────────┤
│$HOME/.config/systemd/user │ User configuration (only used when │
│ │ $XDG_CONFIG_HOME is not set) │
├────────────────────────────────┼───────────────────────────────────────┤
│/etc/systemd/user │ Local configuration │
├────────────────────────────────┼───────────────────────────────────────┤
│$XDG_RUNTIME_DIR/systemd/user │ Runtime units (only used when │
│ │ $XDG_RUNTIME_DIR is set) │
├────────────────────────────────┼───────────────────────────────────────┤
│/run/systemd/user │ Runtime units │
├────────────────────────────────┼───────────────────────────────────────┤
│$XDG_DATA_HOME/systemd/user │ Units of packages that have been │
│ │ installed in the home directory (only │
│ │ used when $XDG_DATA_HOME is set) │
├────────────────────────────────┼───────────────────────────────────────┤
│$HOME/.local/share/systemd/user │ Units of packages that have been │
│ │ installed in the home directory (only │
│ │ used when $XDG_DATA_HOME is not set) │
├────────────────────────────────┼───────────────────────────────────────┤
│/usr/lib/systemd/user │ 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).
[UNIT] SECTION OPTIONS
The unit file may include a [Unit] section, which carries generic information about the unit that is not
dependent on the type of unit:
Description=
A free-form string describing the unit. This is intended for use in UIs to show descriptive
information along with the unit name. The description should contain a name that means something to
the end user. "Apache2 Web Server" is a good example. Bad examples are "high-performance
light-weight HTTP server" (too generic) or "Apache2" (too specific and meaningless for people who do
not know Apache).
Documentation=
A space-separated list of URIs referencing documentation for this unit or its configuration. Accepted
are only URIs of the types "http://", "https://", "file:", "info:", "man:". For more information
about the syntax of these URIs, see uri(7). The URIs should be listed in order of relevance, starting
with the most relevant. It is a good idea to first reference documentation that explains what the
unit's purpose is, followed by how it is configured, followed by any other related documentation.
This option may be specified more than once, in which case the specified list of URIs is merged. If
the empty string is assigned to this option, the list is reset and all prior assignments will have no
effect.
Requires=
Configures requirement dependencies on other units. If this unit gets activated, the units listed
here will be activated as well. If one of the other units 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 After= or Before=
options. If a unit foo.service requires a unit bar.service as configured with Requires= and no
ordering is configured with After= or Before=, then both units will be started simultaneously and
without any delay between them if foo.service is activated. Often, it is a better choice to use
Wants= instead of Requires= in order to achieve a system that is more robust when dealing with
failing services.
Note that dependencies of this type may also be configured outside of the unit configuration file by
adding a symlink to a .requires/ directory accompanying the unit file. For details, see above.
Requisite=
Similar to Requires=. However, if the units listed here are not started already, they will not be
started and the transaction will fail immediately.
Wants=
A weaker version of Requires=. Units listed in this option will be started if the configuring unit
is. However, if the listed units fail to start or cannot be added to the transaction, this has no
impact on the validity of the transaction as a whole. This is the recommended way to hook start-up of
one unit to the start-up of another unit.
Note that dependencies of this type may also be configured outside of the unit configuration file by
adding symlinks to a .wants/ directory accompanying the unit file. For details, see above.
BindsTo=
Configures requirement dependencies, very similar in style to Requires=, however 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 systemd.
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.
Conflicts=
A space-separated list of unit names. Configures negative requirement dependencies. If a unit has a
Conflicts= setting on another unit, starting the former will stop the latter and vice versa. Note
that this setting is independent of and orthogonal to the After= and Before= ordering dependencies.
If a unit A that conflicts with a unit B is scheduled to be started at the same time as B, the
transaction will either fail (in case both are required part of the transaction) or be modified to be
fixed (in case one or both jobs are not a required part of the transaction). In the latter case, the
job that is not the required will be removed, or in case both are not required, the unit that
conflicts will be started and the unit that is conflicted is stopped.
Before=, After=
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 started, bar.service's
start-up is delayed until 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 After= and 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 created. After= is the inverse of
Before=, i.e. while After= ensures that the configured unit is started after the listed unit finished
starting up, Before= ensures the opposite, 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. If one unit with an
ordering dependency on another unit is shut down while the latter is started up, the shut down is
ordered before the start-up regardless of whether the ordering dependency is actually of type After=
or Before=. If two units have no ordering dependencies between them, they are shut down or started up
simultaneously, and no ordering takes place.
OnFailure=
A space-separated list of one or more units that are activated when this unit enters the "failed"
state.
PropagatesReloadTo=, ReloadPropagatedFrom=
A space-separated list of one or more units where reload requests on this unit will be propagated to,
or reload requests on the other unit will be propagated to this unit, respectively. Issuing a reload
request on a unit will automatically also enqueue a reload request on all units that the reload
request shall be propagated to via these two settings.
JoinsNamespaceOf=
For units that start processes (such as service units), lists one or more other units whose network
and/or temporary file namespace to join. This only applies to unit types which support the
PrivateNetwork= and PrivateTmp= directives (see systemd.exec(5) for details). If a unit that has this
setting set is started, its processes will see the same /tmp, /tmp/var and network namespace as one
listed unit that is started. If multiple listed units are already started, it is not defined which
namespace is joined. Note that this setting only has an effect if PrivateNetwork= and/or PrivateTmp=
is enabled for both the unit that joins the namespace and the unit whose namespace is joined.
RequiresMountsFor=
Takes a space-separated list of absolute paths. Automatically adds dependencies of type Requires= and
After= for all mount units required to access the specified path.
Mount points marked with noauto are not mounted automatically 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 (Requires= and After= or some other combination).
OnFailureJobMode=
Takes a value of "fail", "replace", "replace-irreversibly", "isolate", "flush", "ignore-dependencies"
or "ignore-requirements". Defaults to "replace". Specifies how the units listed in OnFailure= will be
enqueued. See systemctl(1)'s --job-mode= option for details on the possible values. If this is set to
"isolate", only a single unit may be listed in OnFailure=..
IgnoreOnIsolate=
Takes a boolean argument. If true, this unit will not be stopped when isolating another unit.
Defaults to false.
StopWhenUnneeded=
Takes a boolean argument. If true, this unit will be stopped when it is no longer used. Note that, in
order to minimize the work to be executed, systemd will not stop units by default unless they are
conflicting with other units, or the user explicitly requested their shut down. If this option is
set, a unit will be automatically cleaned up if no other active unit requires it. Defaults to false.
RefuseManualStart=, RefuseManualStop=
Takes a boolean argument. If true, this unit can only be activated or deactivated indirectly. In this
case, explicit start-up or termination requested by the user is denied, however if it is started or
stopped as a dependency of another unit, start-up or termination will succeed. This is mostly a
safety feature to ensure that the user does not accidentally activate units that are not intended to
be activated explicitly, and not accidentally deactivate units that are not intended to be
deactivated. These options default to false.
AllowIsolate=
Takes a boolean argument. If true, this unit may be used with the systemctl isolate command.
Otherwise, this will be refused. It probably is a good idea to leave this disabled except for target
units that shall be used similar to runlevels in SysV init systems, just as a precaution to avoid
unusable system states. This option defaults to false.
DefaultDependencies=
Takes a boolean argument. If true, (the default), a few default dependencies will implicitly be
created for the unit. The actual dependencies created depend on the unit type. For example, for
service units, these dependencies ensure that the service is started only after basic system
initialization is completed and is properly terminated on system shutdown. See the respective man
pages for details. Generally, only services involved with early boot or late shutdown should set this
option to false. It is highly recommended to leave this option enabled for the majority of common
units. If set to false, this option does not disable all implicit dependencies, just non-essential
ones.
JobTimeoutSec=, JobTimeoutAction=, JobTimeoutRebootArgument=
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.
JobTimeoutAction= optionally configures an additional action to take when the time-out is hit. It
takes the same values as the per-service StartLimitAction= setting, see systemd.service(5) for
details. Defaults to none. JobTimeoutRebootArgument= configures an optional reboot string to pass to
the reboot(2) system call.
StartLimitInterval=, StartLimitBurst=
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 StartLimitInterval= to configure the checking
interval (defaults to DefaultStartLimitInterval= 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 setting Restart= (see
systemd.service(5)); however, they apply to all kinds of starts (including manual), not just those
triggered by the Restart= logic. Note that units which are configured for Restart= and which reach
the start limit are not attempted to be restarted anymore; however, they may still be restarted
manually at a later point, 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.
StartLimitAction=
Configure the action to take if the rate limit configured with StartLimitInterval= and
StartLimitBurst= is hit. Takes one of none, reboot, reboot-force, reboot-immediate, poweroff,
poweroff-force or poweroff-immediate. If 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, poweroff-force, poweroff-immediate have the
effect of powering down the system with similar semantics. Defaults to none.
RebootArgument=
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.
ConditionArchitecture=, ConditionVirtualization=, ConditionHost=, ConditionKernelCommandLine=,
ConditionSecurity=, ConditionCapability=, ConditionACPower=, ConditionNeedsUpdate=, ConditionFirstBoot=,
ConditionPathExists=, ConditionPathExistsGlob=, ConditionPathIsDirectory=, ConditionPathIsSymbolicLink=,
ConditionPathIsMountPoint=, ConditionPathIsReadWrite=, ConditionDirectoryNotEmpty=,
ConditionFileNotEmpty=, ConditionFileIsExecutable=
Before starting a unit, verify that the specified condition is true. If it is not true, the starting
of the unit will be (mostly silently) skipped, however all ordering dependencies of it are still
respected. A failing condition will not result in the unit being moved into a failure state. The
condition is checked at the time the queued start job is to be executed. Use condition expressions in
order to silently skip units that do not apply to the local running system, for example because the
kernel or runtime environment doesn't require its functionality. Use the various AssertArchitecture=,
AssertVirtualization=, ... options for a similar mechanism that puts the unit in a failure state and
logs about the failed check (see below).
ConditionArchitecture= may be used to check whether the system is running on a specific architecture.
Takes one of x86, x86-64, ppc, ppc-le, ppc64, ppc64-le, ia64, parisc, parisc64, s390, s390x, sparc,
sparc64, mips, mips-le, mips64, mips64-le, alpha, arm, arm-be, arm64, arm64-be, sh, sh64, m86k,
tilegx, cris to test against a specific architecture. The architecture is determined from the
information returned by uname(2) and is thus subject to personality(2). Note that a Personality=
setting in the same unit file has no effect on this condition. A special architecture name native is
mapped to the architecture the system manager itself is compiled for. The test may be negated by
prepending an exclamation mark.
ConditionVirtualization= may be used to check whether the system is executed in a virtualized
environment and optionally test whether it is a specific implementation. Takes either boolean value
to check if being executed in any virtualized environment, or one of vm and container to test against
a generic type of virtualization solution, or one of qemu, kvm, zvm, vmware, microsoft, oracle, xen,
bochs, uml, openvz, lxc, lxc-libvirt, systemd-nspawn, docker, rkt, wsl to test against a specific
implementation. See systemd-detect-virt(1) for a full list of known virtualization technologies and
their identifiers. If multiple virtualization technologies are nested, only the innermost is
considered. The test may be negated by prepending an exclamation mark.
ConditionHost= may be used to match against the hostname or machine ID of the host. This either takes
a hostname string (optionally with shell style globs) which is tested against the locally set
hostname as returned by gethostname(2), or a machine ID formatted as string (see machine-id(5)). The
test may be negated by prepending an exclamation mark.
ConditionKernelCommandLine= may be used to check whether a specific kernel command line option is set
(or if prefixed with the exclamation mark unset). The argument must either be a single word, or an
assignment (i.e. two words, separated "="). In the former case the kernel command line is searched
for the word appearing as is, or as left hand side of an assignment. In the latter case, the exact
assignment is looked for with right and left hand side matching.
ConditionSecurity= may be used to check whether the given security module is enabled on the system.
Currently, the recognized values are selinux, apparmor, ima, smack and 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 capabilities(7) for details). Pass a capability
name such as "CAP_MKNOD", possibly prefixed with an exclamation mark to negate the check.
ConditionACPower= may be used to check whether the system has AC power, or is exclusively battery
powered at the time of activation of the unit. This takes a boolean argument. If set to true, the
condition will hold only if at least one AC connector of the system is connected to a power source,
or if no AC connectors are known. Conversely, if set to false, the condition will hold only if there
is at least one AC connector known and all AC connectors are disconnected from a power source.
ConditionNeedsUpdate= takes one of /var or /etc as argument, possibly prefixed with a "!" (for
inverting the condition). This condition may be used to conditionalize units on whether the specified
directory requires an update because /usr's modification time is newer than the stamp file .updated
in the specified directory. This is useful to implement offline updates of the vendor operating
system resources in /usr that require updating of /etc or /var on the next following boot. Units
making use of this condition should order themselves before systemd-update-done.service(8), to make
sure they run before the stamp file's modification time gets reset indicating a completed update.
ConditionFirstBoot= takes a boolean argument. This condition may be used to conditionalize units on
whether the system is booting up with an unpopulated /etc directory. This may be used to populate
/etc on the first boot after factory reset, or when a new system instances boots up for the first
time.
With ConditionPathExists= a file existence condition is checked before a unit is started. If the
specified absolute path name does not exist, the condition will fail. If the absolute path name
passed to ConditionPathExists= is prefixed with an exclamation mark ("!"), the test is negated, and
the unit is only started if the path does not exist.
ConditionPathExistsGlob= is similar to ConditionPathExists=, but checks for the existence of at least
one file or directory matching the specified globbing pattern.
ConditionPathIsDirectory= is similar to ConditionPathExists= but verifies whether a certain path
exists and is a directory.
ConditionPathIsSymbolicLink= is similar to ConditionPathExists= but verifies whether a certain path
exists and is a symbolic link.
ConditionPathIsMountPoint= is similar to ConditionPathExists= but verifies whether a certain path
exists and is a mount point.
ConditionPathIsReadWrite= is similar to ConditionPathExists= but verifies whether the underlying file
system is readable and writable (i.e. not mounted read-only).
ConditionDirectoryNotEmpty= is similar to ConditionPathExists= but verifies whether a certain path
exists and is a non-empty directory.
ConditionFileNotEmpty= is similar to ConditionPathExists= but verifies whether a certain path exists
and refers to a regular file with a non-zero size.
ConditionFileIsExecutable= is similar to ConditionPathExists= but verifies whether a certain path
exists, is a regular file and marked executable.
If multiple conditions are specified, the unit will be executed if all of them apply (i.e. a logical
AND is applied). Condition checks can be prefixed with a pipe symbol (|) in which case a condition
becomes a triggering condition. If at least one triggering condition is defined for a unit, then the
unit will be executed if at least one of the triggering conditions apply and all of the
non-triggering conditions. If you prefix an argument with the pipe symbol and an exclamation mark,
the pipe symbol must be passed first, the exclamation second. Except for
ConditionPathIsSymbolicLink=, all path checks follow symlinks. If any of these options is assigned
the empty string, the list of conditions is reset completely, all previous condition settings (of any
kind) will have no effect.
AssertArchitecture=, AssertVirtualization=, AssertHost=, AssertKernelCommandLine=, AssertSecurity=,
AssertCapability=, AssertACPower=, AssertNeedsUpdate=, AssertFirstBoot=, AssertPathExists=,
AssertPathExistsGlob=, AssertPathIsDirectory=, AssertPathIsSymbolicLink=, AssertPathIsMountPoint=,
AssertPathIsReadWrite=, AssertDirectoryNotEmpty=, AssertFileNotEmpty=, AssertFileIsExecutable=
Similar to the ConditionArchitecture=, ConditionVirtualization=, ..., condition settings described
above, these settings add assertion checks to the start-up of the unit. However, unlike the
conditions settings, any assertion setting that is not met results in failure of the start job (which
means this is logged loudly). Use assertion expressions for units that cannot operate when specific
requirements are not met, and when this is something the administrator or user should look into.
SourcePath=
A path to a configuration file this unit has been generated from. This is primarily useful for
implementation of generator tools that convert configuration from an external configuration file
format into native unit files. This functionality should not be used in normal units.
[INSTALL] SECTION OPTIONS
Unit files may include an "[Install]" section, which carries installation information for the unit. This
section is not interpreted by systemd(1) during runtime; it is used by the enable and disable commands of
the systemctl(1) tool during installation of a unit. Note that settings in the "[Install]" section may
not appear in .d/*.conf unit file drop-ins (see above).
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 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.
WantedBy=, RequiredBy=
This option may be used more than once, or a space-separated list of unit names may be given. A
symbolic link is created in the .wants/ or .requires/ directory of each of the listed units when this
unit is installed by systemctl enable. This has the effect that a dependency of type Wants= or
Requires= is added from the listed unit to the current unit. The primary result is that the current
unit will be started when the listed unit is started. See the description of Wants= and Requires= in
the [Unit] section for details.
WantedBy=foo.service in a service bar.service is mostly equivalent to
Alias=foo.service.wants/bar.service in the same file. In case of template units, systemctl enable
must be called with an instance name, and this instance will be added to the .wants/ or .requires/
list of the listed unit. E.g. WantedBy=getty.target in a service getty@.service will result in
systemctl enable getty@tty2.service creating a getty.target.wants/getty@tty2.service link to
getty@.service.
Also=
Additional units to install/deinstall when this unit is installed/deinstalled. If the user requests
installation/deinstallation of a unit with this option configured, systemctl enable and systemctl
disable will automatically install/uninstall units listed in this option as well.
This option may be used more than once, or a space-separated list of unit names may be given.
DefaultInstance=
In template unit files, this specifies for which instance the unit shall be enabled if the template
is enabled without any explicitly set instance. This option has no effect in non-template unit files.
The specified string must be usable as instance identifier.
The following specifiers are interpreted in the Install section: %n, %N, %p, %i, %U, %u, %m, %H, %b, %v.
For their meaning see the next section.
SPECIFIERS
Many settings resolve specifiers which may be used to write generic unit files referring to runtime or
unit parameters that are replaced when the unit files are loaded. The following specifiers are
understood:
Table 3. Specifiers available in unit files
┌──────────┬──────────────────────────────┬──────────────────────────────┐
│Specifier │ Meaning │ Details │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%n" │ Full unit name │ │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%N" │ Unescaped full unit name │ Same as "%n", but with │
│ │ │ escaping undone │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%p" │ Prefix name │ For instantiated units, this │
│ │ │ refers to the string before │
│ │ │ the "@" character of the │
│ │ │ unit name. For │
│ │ │ non-instantiated units, this │
│ │ │ refers to the name of the │
│ │ │ unit with the type suffix │
│ │ │ removed. │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%P" │ Unescaped prefix name │ Same as "%p", but with │
│ │ │ escaping undone │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%i" │ Instance name │ For instantiated units: this │
│ │ │ is the string between the │
│ │ │ "@" character and the suffix │
│ │ │ of the unit name. │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%I" │ Unescaped instance name │ Same as "%i", but with │
│ │ │ escaping undone │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%f" │ Unescaped filename │ This is either the unescaped │
│ │ │ instance name (if │
│ │ │ applicable) with / prepended │
│ │ │ (if applicable), or the │
│ │ │ prefix name prepended with │
│ │ │ /. │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%c" │ Control group path of the │ This path does not include │
│ │ unit │ the /sys/fs/cgroup/systemd/ │
│ │ │ prefix. │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%r" │ Control group path of the │ This usually maps to the │
│ │ slice the unit is placed in │ parent cgroup path of "%c". │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%R" │ Root control group path │ For system instances, this │
│ │ below which slices and units │ resolves to /, except in │
│ │ are placed │ containers, where this maps │
│ │ │ to the container's root │
│ │ │ control group path. │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%t" │ Runtime directory │ This is either /run (for the │
│ │ │ system manager) or the path │
│ │ │ "$XDG_RUNTIME_DIR" resolves │
│ │ │ to (for user managers). │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%u" │ User name │ This is the name of the user │
│ │ │ running the service manager │
│ │ │ instance. In case of the │
│ │ │ system manager this resolves │
│ │ │ to "root". │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%U" │ User UID │ This is the numeric UID of │
│ │ │ the user running the service │
│ │ │ manager instance. In case of │
│ │ │ the system manager this │
│ │ │ resolves to "0". │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%h" │ User home directory │ This is the home directory │
│ │ │ of the user running the │
│ │ │ service manager instance. In │
│ │ │ case of the system manager │
│ │ │ this resolves to "/root". │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%s" │ User shell │ This is the shell of the │
│ │ │ user running the service │
│ │ │ manager instance. In case of │
│ │ │ the system manager this │
│ │ │ resolves to "/bin/sh". │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%m" │ Machine ID │ The machine ID of the │
│ │ │ running system, formatted as │
│ │ │ string. See machine-id(5) │
│ │ │ for more information. │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%b" │ Boot ID │ The boot ID of the running │
│ │ │ system, formatted as string. │
│ │ │ See random(4) for more │
│ │ │ information. │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%H" │ Host name │ The hostname of the running │
│ │ │ system at the point in time │
│ │ │ the unit configuration is │
│ │ │ loaded. │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%v" │ Kernel release │ Identical to uname -r output │
├──────────┼──────────────────────────────┼──────────────────────────────┤
│"%%" │ Single percent sign │ Use "%%" in place of "%" to │
│ │ │ specify a single percent │
│ │ │ sign. │
└──────────┴──────────────────────────────┴──────────────────────────────┘
Please note that specifiers "%U", "%h", "%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 running in --user mode.
EXAMPLES
Example 1. Allowing units to be enabled
The following snippet (highlighted) allows a unit (e.g. foo.service) to be enabled via systemctl enable:
[Unit]
Description=Foo
[Service]
ExecStart=/usr/sbin/foo-daemon
[Install]
WantedBy=multi-user.target
After running systemctl enable, a symlink /etc/systemd/system/multi-user.target.wants/foo.service linking
to the actual unit will be created. It tells systemd to pull in the unit when starting multi-user.target.
The inverse systemctl disable will remove that symlink again.
Example 2. Overriding vendor settings
There are two methods of overriding vendor settings in unit files: copying the unit file from
/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.
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 ConditionPathExists= (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. 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 /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.service(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 dependencies (After=, etc.) cannot be reset to an empty list, so dependencies can only be added
in drop-ins. If you want to remove dependencies, you have to override the entire unit.
SEE ALSO
systemd(1), systemctl(1), systemd.special(7), systemd.service(5), systemd.socket(5), systemd.device(5), systemd.mount(5), systemd.automount(5), systemd.swap(5), systemd.target(5), systemd.path(5), systemd.timer(5), systemd.scope(5), systemd.slice(5), systemd.time(7), systemd-analyze(1), capabilities(7), systemd.directives(7), uname(1)
NOTES
1. XDG Desktop Entry Specification
http://standards.freedesktop.org/desktop-entry-spec/latest/
2. Interface Stability Promise
http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise