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 │ This path does not │
│ │ the unit │ include the │
│ │ │ /sys/fs/cgroup/systemd/ │
│ │ │ prefix. │
├──────────┼──────────────────────────┼──────────────────────────┤
│"%r" │ Control group path of │ This usually maps to the │
│ │ the slice the unit is │ parent cgroup path of │
│ │ placed in │ "%c". │
├──────────┼──────────────────────────┼──────────────────────────┤
│"%R" │ Root control group path │ For system instances, │
│ │ below which slices and │ this resolves to /, │
│ │ units are placed │ except in 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