Man page
systemd.unit
SYSTEMD.UNIT(5) systemd.unit SYSTEMD.UNIT(5)
NAME
systemd.unit - Unit configuration
SYNOPSIS
service.service, socket.socket, device.device, mount.mount,
automount.automount, swap.swap, target.target, path.path, timer.timer,
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.
Table 1. Load path when running in system mode (--system).
+------------------------------+--------------------------+
|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) |
+------------------------------+--------------------------+
Table 2. Load path when running in session mode (--user).
+------------------------------------+--------------------------+
|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) |
+------------------------------------+--------------------------+
Additional units might be loaded into systemd ("linked") from
directories not on the unit load path. See the link command for
systemctl(1).
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:
Table 3. Specifiers available in unit files
+----------+---------------------+---------------------+
|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 | For system |
| | path where units | instances this |
| | are placed. | usually resolves to |
| | | /system, except in |
| | | containers, where |
| | | the path might be |
| | | prefixed with the |
| | | container's root |
| | | control group. |
+----------+---------------------+---------------------+
|%R | Parent directory of | For system |
| | the control group | instances this |
| | path where units | usually resolves to |
| | are placed. | /, 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
systemd(1), systemctl(8), 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.snapshot(5),
systemd.time(7), capabilities(7), systemd.directives(7)
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
(http://www.dsm.fordham.edu/cgi-bin/man-cgi.pl?topic=systemd.unit&sect=5)