systemd.unit(5)
NAME
systemd.unit - Unit configuration
SYNOPSIS
service.service, socket.socket, device.device, mount.mount, automount.automount, swap.swap, target.target, path.path, timer.timer, slice.slice, scope.scope /etc/systemd/system/* /run/systemd/system/* /lib/systemd/system/* ... ~/.config/systemd/user/* /etc/systemd/user/* $XDG_RUNTIME_DIR/systemd/user/* /run/systemd/user/* ~/.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 and 200 milliseconds, i.e. 120200 ms. The following time units are understood: "s", "min", "h", "d", "w", "ms", "us". For details see systemd.time(7). 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. Units can be aliased (have an alternative name), by creating a symlink from the new name to the existing name in one of the unit search paths. For example, systemd-networkd.service has the alias dbus-org.freedesktop.network1.service, created during installation as the symlink /lib/systemd/system/dbus-org.freedesktop.network1.service. In addition, unit files may specify aliases through the Alias= directive in the [Install] section; those aliases are only effective when the unit is enabled. When the unit is enabled, symlinks will be created for those names, and removed when the unit is disabled. For example, reboot.target specifies Alias=ctrl-alt-del.target, so when enabled it will be invoked whenever CTRL+ALT+DEL is pressed. Alias names may be used in commands like enable, disable, start, stop, status, ..., and in unit dependency directives Wants=, Requires=, Before=, After=, ..., with the limitation that aliases specified through Alias= are only effective when the unit is enabled. Aliases cannot be used with the preset command. Along with a unit file foo.service, the directory foo.service.wants/ may exist. All unit files symlinked from such a directory are implicitly added as dependencies of type Wants= to the unit. This is useful to hook units into the start-up of other units, without having to modify their unit files. For details about the semantics of Wants=, see below. The preferred way to create symlinks in the .wants/ directory of a unit file is with the enable command of the systemctl(1) tool which reads information from the [Install] section of unit files (see below). A similar functionality exists for Requires= type dependencies as well, the directory suffix is .requires/ in this case. Along with a unit file foo.service, a "drop-in" directory foo.service.d/ may exist. All files with the suffix ".conf" from this directory will be parsed after the 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 honored in drop-in unit files, and have no effect. In addition to /etc/systemd/system, the drop-in ".d" directories 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. 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. 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=. 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.
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, /var/tmp and network namespace as
one listed unit that is started. If multiple listed units are
already started, it is not defined which namespace is joined. Note
that this setting only has an effect if PrivateNetwork= and/or
PrivateTmp= is enabled for both the unit that joins the namespace
and the unit whose namespace is joined.
RequiresMountsFor=
Takes a space-separated list of absolute paths. Automatically adds
dependencies of type Requires= and After= for all mount units
required to access the specified path.
Mount points marked with noauto are not mounted automatically 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.
StartLimitIntervalSec=, 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
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 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
StartLimitIntervalSec= 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
to test against a specific implementation, or private-users to
check whether we are running in a user namespace. See systemd-
detect-virt(1) for a full list of known virtualization technologies
and their identifiers. If multiple virtualization technologies are
nested, only the innermost is considered. The test may be negated
by prepending an exclamation mark.
ConditionHost= may be used to match against the hostname or machine
ID of the host. This either takes a hostname string (optionally
with shell style globs) which is tested against the locally set
hostname as returned by gethostname(2), or a machine ID formatted
as string (see machine-id(5)). The test may be negated by
prepending an exclamation mark.
ConditionKernelCommandLine= may be used to check whether a specific
kernel command line option is set (or if prefixed with the
exclamation mark unset). The argument must either be a single word,
or an assignment (i.e. two words, separated "="). In the former
case the kernel command line is searched for the word appearing as
is, or as left hand side of an assignment. In the latter case, the
exact assignment is looked for with right and left hand side
matching.
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. Note that not all unit types support such alias names, and this setting is not supported for them. Specifically, mount, slice, swap, and automount units do not support aliasing. WantedBy=, RequiredBy= This option may be used more than once, or a space-separated list of unit names may be given. A symbolic link is created in the .wants/ or .requires/ directory of each of the listed units when this unit is installed by systemctl enable. This has the effect that a dependency of type Wants= or Requires= is added from the listed unit to the current unit. The primary result is that the current unit will be started when the listed unit is started. See the description of Wants= and Requires= in the [Unit] section for details. WantedBy=foo.service in a service bar.service is mostly equivalent to Alias=foo.service.wants/bar.service in the same file. In case of template units, systemctl enable must be called with an instance name, and this instance will be added to the .wants/ or .requires/ list of the listed unit. E.g. WantedBy=getty.target in a service getty@.service will result in systemctl enable getty@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 Same as "%n", but
name 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 Same as "%p", but
name 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 Same as "%i", but
name with escaping
undone
"%f" Unescaped filename This is either the
unescaped instance
name (if
applicable) with /
prepended (if
applicable), or the
unescaped prefix
name prepended with
/.
"%c" Control group path This path does not
of the unit include the
/sys/fs/cgroup/systemd/
prefix.
"%r" Control group path This usually maps to
of the slice the the parent control
unit is placed in group path of "%c".
"%R" Root control group For system instances,
path below which this resolves to /,
slices and units except in containers,
are placed 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
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