Section: systemd.unit (5)
service.service, socket.socket, device.device, mount.mount, automount.automount, swap.swap, target.target, path.path, timer.timer, snapshot.snapshot, 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/* /run/systemd/user/* $XDG_DATA_HOME/systemd/user/* $HOME/.local/share/systemd/user/* /usr/lib/systemd/user/* ...
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 temporary system state snapshot, a resource management slice or a group of externally created processes. The syntax is inspired by m[blue]XDG Desktop Entry Specificationm.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: (5), (5), (5), (5), (5), (5), (5), (5), (5), (5). (5). (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 (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.
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 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 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 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 firstname.lastname@example.org 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.
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 systemd is running in user mode (--user) and the variable $SYSTEMD_UNIT_PATH is set, this contents of this variable overrides the unit load path.
Table 1. Load path when running in system mode (--system).
<TABLE BORDER> <TR VALIGN="top| <TD CLASS="c1|Path</TD> <TD>Description
</TD> </TR> <TR VALIGN="top| <TD>/etc/systemd/system</TD> <TD>Local configuration
</TD> </TR> <TR VALIGN="top| <TD>/run/systemd/system</TD> <TD>Runtime units
</TD> </TR> <TR VALIGN="top| <TD>/lib/systemd/system</TD> <TD>Units of installed packages
</TD> </TR> </TABLE>
Table 2. Load path when running in user mode (--user).
<TABLE BORDER> <TR VALIGN="top| <TD CLASS="c1|Path</TD> <TD>Description
</TD> </TR> <TR VALIGN="top| <TD>$XDG_CONFIG_HOME/systemd/user</TD> <TD>User configuration (only used when $XDG_CONFIG_HOME is set)
</TD> </TR> <TR VALIGN="top| <TD>$HOME/.config/systemd/user</TD> <TD>User configuration (only used when $XDG_CONFIG_HOME is not set)
</TD> </TR> <TR VALIGN="top| <TD>/etc/systemd/user</TD> <TD>Local configuration
</TD> </TR> <TR VALIGN="top| <TD>/run/systemd/user</TD> <TD>Runtime units
</TD> </TR> <TR VALIGN="top| <TD>$XDG_DATA_HOME/systemd/user</TD> <TD>Units of packages that have been installed in the home directory (only used when $XDG_DATA_HOME is set)
</TD> </TR> <TR VALIGN="top| <TD>$HOME/.local/share/systemd/user</TD> <TD>Units of packages that have been installed in the home directory (only used when $XDG_DATA_HOME is not set)
</TD> </TR> <TR VALIGN="top| <TD>/usr/lib/systemd/user</TD> <TD>Units of packages that have been installed system-wide
</TD> </TR> </TABLE>
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 generators m[blue]Generatorsm.
Unit file may include a [Unit] section, which carries generic information about the unit that is not dependent on the type of unit:
: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.
: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.
: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.
: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).
ConditionArchitecture=, ConditionVirtualization=, ConditionHost=, ConditionKernelCommandLine=, ConditionSecurity=, ConditionCapability=, ConditionACPower=, ConditionNeedsUpdate=, ConditionPathExists=, ConditionPathExistsGlob=, ConditionPathIsDirectory=, ConditionPathIsSymbolicLink=, ConditionPathIsMountPoint=, ConditionPathIsReadWrite=, ConditionDirectoryNotEmpty=, ConditionFileNotEmpty=, ConditionFileIsExecutable=, 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.
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 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.
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 values are selinux, apparmor, ima 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.
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 (8), to make sure they run before the stamp files's modification time gets reset indicating a completed update.
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.
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.
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:
: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 email@example.com creating a firstname.lastname@example.org link to getty@.service.
: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.
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
<TABLE BORDER> <TR VALIGN="top| <TD CLASS="c1|Specifier</TD> <TD CLASS="c1|Meaning</TD> <TD>Details
</TD> </TR> <TR VALIGN="top| <TD>"%n"</TD> <TD>Full unit name</TD> <TD>
</TD> </TR> <TR VALIGN="top| <TD>"%N"</TD> <TD>Unescaped full unit name</TD> <TD>Same as "%n", but with escaping undone
</TD> </TR> <TR VALIGN="top| <TD>"%p"</TD> <TD>Prefix name</TD> <TD>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.
</TD> </TR> <TR VALIGN="top| <TD>"%P"</TD> <TD>Unescaped prefix name</TD> <TD>Same as "%p", but with escaping undone
</TD> </TR> <TR VALIGN="top| <TD>"%i"</TD> <TD>Instance name</TD> <TD>For instantiated units: this is the string between the "@" character and the suffix of the unit name.
</TD> </TR> <TR VALIGN="top| <TD>"%I"</TD> <TD>Unescaped instance name</TD> <TD>Same as "%i", but with escaping undone
</TD> </TR> <TR VALIGN="top| <TD>"%f"</TD> <TD>Unescaped filename</TD> <TD>This is either the unescaped instance name (if applicable) with / prepended (if applicable), or the prefix name prepended with /.
</TD> </TR> <TR VALIGN="top| <TD>"%c"</TD> <TD>Control group path of the unit</TD> <TD>This path does not include the /sys/fs/cgroup/systemd/ prefix.
</TD> </TR> <TR VALIGN="top| <TD>"%r"</TD> <TD>Control group path of the slice the unit is placed in</TD> <TD>This usually maps to the parent cgroup path of "%c".
</TD> </TR> <TR VALIGN="top| <TD>"%R"</TD> <TD>Root control group path below which slices and units are placed</TD> <TD>For system instances, this resolves to /, except in containers, where this maps to the container's root control group path.
</TD> </TR> <TR VALIGN="top| <TD>"%t"</TD> <TD>Runtime directory</TD> <TD>This is either /run (for the system manager) or the path "$XDG_RUNTIME_DIR" resolves to (for user managers).
</TD> </TR> <TR VALIGN="top| <TD>"%u"</TD> <TD>User name</TD> <TD>This is the name of the configured user of the unit, or (if none is set) the user running the systemd instance.
</TD> </TR> <TR VALIGN="top| <TD>"%U"</TD> <TD>User UID</TD> <TD>This is the numeric UID of the configured user of the unit, or (if none is set) the user running the systemd user instance. Note that this specifier is not available for units run by the systemd system instance (as opposed to those run by a systemd user instance), unless the user has been configured as a numeric UID in the first place or the configured user is the root user.
</TD> </TR> <TR VALIGN="top| <TD>"%h"</TD> <TD>User home directory</TD> <TD>This is the home directory of the configured user of the unit, or (if none is set) the user running the systemd user instance. Similar to "%U", this specifier is not available for units run by the systemd system instance, unless the configured user is the root user.
</TD> </TR> <TR VALIGN="top| <TD>"%s"</TD> <TD>User shell</TD> <TD>This is the shell of the configured user of the unit, or (if none is set) the user running the systemd user instance. Similar to "%U", this specifier is not available for units run by the systemd system instance, unless the configured user is the root user.
</TD> </TR> <TR VALIGN="top| <TD>"%H"</TD> <TD>Host name</TD> <TD>The hostname of the running system at the point in time the unit configuation is loaded.
</TD> </TR> <TR VALIGN="top| <TD>"%v"</TD> <TD>Kernel release</TD> <TD>Identical to uname -r output
</TD> </TR> <TR VALIGN="top| <TD>""</TD> <TD>Single percent sign</TD> <TD>Use "" in place of "%" to specify a single percent sign.
</TD> </TR> </TABLE>
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