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SYSTEMD.UNIT(5) | systemd.unit | SYSTEMD.UNIT(5) |
NAME¶
systemd.unit - Unit configurationSYNOPSIS¶
service.service, socket.socket, device.device, mount.mount, automount.automount, swap.swap, target.target, path.path, timer.timer, snapshot.snapshot/etc/systemd/system/* /run/systemd/system/* /usr/lib/systemd/system/* ...
/etc/systemd/user/* /run/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 file system path, or a timer controlled and supervised by systemd(1). 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.snapshot(5). 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 is prefixed with X- it is ignored completely by systemd. 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 Wanted= 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 Wanted= 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 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 to a unit, without having to modify their unit files. Make sure that the file that is included has the appropriate section headers before any directive. If a line starts with .include followed by a file name, the specified file will be parsed at this point. Make sure that the file that is included has the appropriate section headers before any directives. 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. Some unit names reflect paths existing in the file system name space. 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 file name. Basically, given a path, "/" is replaced by "-", and all unprintable characters and the "-" are replaced by C-style "\x20" escapes. The root directory "/" is encoded as single dash, while otherwise the initial and ending "/" is removed from all paths during transformation. This escaping is reversible. 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 filesystem. 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].UNIT 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 higher in the hierarchy override files with the same name lower in the hierarchy, thus allowing overrides. When systemd is running in user mode ( --user) and the variable $SYSTEMD_UNIT_PATH is set, this contents of this variable overrides the unit load path.Path | Description |
/run/systemd/generator.early | Generated units (early) |
/etc/systemd/system | Local configuration |
/run/systemd/systemd | Volatile units |
/run/systemd/generator | Generated units (middle) |
/usr/local/lib/systemd/system | Units for local packages |
/usr/lib/systemd/system | Units for installed packages |
/run/systemd/generator.late | Generated units (late) |
Path | Description |
/tmp/systemd-generator.early.XXXXXX | Generated units (early) |
/etc/systemd/user | Local configuration |
/run/systemd/user | Volatile units |
/tmp/systemd-generator.XXXXXX | Generated units (middle) |
/usr/local/lib/systemd/user | Units for local packages |
/usr/lib/systemd/user | Units for installed packages |
/tmp/systemd-generator.late.XXXXXX | Generated units (late) |
OPTIONS¶
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.
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, in
which case requirement dependencies for all listed names are 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.
RequiresOverridable=
Similar to Requires=. Dependencies
listed in RequiresOverridable= which cannot be fulfilled or fail to
start are ignored if the startup was explicitly requested by the user. If the
start-up was pulled in indirectly by some dependency or automatic start-up of
units that is not requested by the user this dependency must be fulfilled and
otherwise the transaction fails. Hence, this option may be used to configure
dependencies that are normally honored unless the user explicitly starts up
the unit, in which case whether they failed or not is irrelevant.
Requisite=, RequisiteOverridable=
Similar to Requires= and
RequiresOverridable=, respectively. However, if a unit listed here is
not started already it will not be started and the transaction fails
immediately.
Wants=
A weaker version of Requires=. A unit
listed in this option will be started if the configuring unit is. However, if
the listed unit fails to start up 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 a symlink 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=
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=
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 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=
Lists one or more units that are activated
when this unit enters the 'failed' state.
PropagatesReloadTo=, ReloadPropagatedFrom=
Lists one or more units where reload requests
on the unit will be propagated to/on the other unit will be propagated from.
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.
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.
OnFailureIsolate=
Takes a boolean argument. If true the
unit listed in OnFailure= will be enqueued in isolation mode, i.e. all
units that are not its dependency will be stopped. If this is set only a
single unit may be listed in OnFailure=. Defaults to
false.
IgnoreOnIsolate=
Takes a boolean argument. If true this
unit will not be stopped when isolating another unit. Defaults to
false.
IgnoreOnSnapshot=
Takes a boolean argument. If true this
unit will not be included in snapshots. Defaults to true for device and
snapshot units, false for the others.
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=
When clients are waiting for a job of this
unit to complete, time out after the specified time. 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 0 (job timeouts
disabled), except for device units. NB: this timeout is independent from any
unit-specific timeout (for example, the timeout set with Timeout= 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.
ConditionPathExists=, ConditionPathExistsGlob=,
ConditionPathIsDirectory=, ConditionPathIsSymbolicLink=,
ConditionPathIsMountPoint=, ConditionPathIsReadWrite=,
ConditionDirectoryNotEmpty=, ConditionFileNotEmpty=,
ConditionFileIsExecutable=, ConditionKernelCommandLine=,
ConditionVirtualization=, ConditionSecurity=,
ConditionCapability=, ConditionHost=, ConditionACPower=,
ConditionNull=
Before starting a unit verify that the
specified condition is true. If it is not true the starting of the unit will
be 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.
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.
Similar, 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.
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, vmware, microsoft, oracle, xen,
bochs, chroot, openvz, lxc, lxc-libvirt,
systemd-nspawn to test against a specific implementation. If multiple
virtualization technologies are nested only the innermost is considered. The
test may be negated by prepending an exclamation mark.
ConditionSecurity= may be used to check whether the given security module
is enabled on the system. Currently the only recognized values are
selinux, apparmor, and smack. 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.
ConditionHost= may be used to match against the host name or machine ID
of the host. This either takes a host name string (optionally with shell style
globs) which is tested against the locally set host name 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.
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.
Finally, ConditionNull= may be used to add a constant condition check
value to the unit. It takes a boolean argument. If set to false the
condition will always fail, otherwise succeed.
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.
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. Thus functionality should not be used in normal
units.
Unit file may include a [Install] section, which carries installation
information for the unit. This section is not interpreted by systemd(1)
during runtime. It is used exclusively by the enable and disable
commands of the systemctl(1) tool during installation of a unit:
Alias=
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 file name.
WantedBy=, RequiredBy=
Installs a symlink in the .wants/ or
.requires/ subdirectory for a unit, respectively. This has the effect that
when the listed unit name is activated the unit listing it is activated too.
WantedBy=foo.service in a service bar.service is mostly equivalent to
Alias=foo.service.wants/bar.service in the same file.
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.
The following specifiers are interpreted in the Install section: %n, %N, %p, %i,
%U, %u, %m, %H, %b. 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:Specifier | Meaning | Details |
%n | Full unit name | |
%N | Unescaped full unit name | |
%p | Prefix name | For instantiated units this refers to the string before the @. For non-instantiated units this refers to to the name of the unit with the type suffix removed. |
%P | Unescaped prefix name | |
%i | Instance name | For instantiated units: this is the string between the @ character and the suffix. |
%I | Unescaped instance name | |
%f | Unescaped file name | This is either the unescaped instance name (if applicable) with / prepended (if applicable), or the prefix name similarly prepended with /. |
%c | Control group path of the unit | |
%r | Root control group path where units are placed. | For system instances this usually resolves to /system, except in containers, where the path might be prefixed with the container's root control group. |
%R | Parent directory of the control group path where units are placed. | For system instances this usually resolves to /, except in containers, where this resolves to the container's root directory. This specifier is particularly useful in the ControlGroup= setting (see systemd.exec(5)). |
%t | Runtime socket dir | This is either /run (for the system manager) or $XDG_RUNTIME_DIR (for user managers). |
%u | User name | This is the name of the configured user of the unit, or (if none is set) the user running the systemd instance. |
%U | User UID | This is the UID of the configured user of the unit, or (if none is set) the user running the systemd instance. |
%h | User home directory | This is the home directory of the configured user of the unit, or (if none is set) the user running the systemd instance. |
%s | User shell | This is the shell of the configured user of the unit, or (if none is set) the user running the systemd instance. If the user is root (UID equal to 0), the shell configured in account database is ignored and /bin/sh is always used. |
%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 host name of the running system. |
%% | Escaped % | Single percent sign. |
SEE ALSO¶
NOTES¶
- 1.
- XDG Desktop Entry Specification
- 2.
- Interface Stability Promise
systemd 204 |