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, slice.slice, scope.scope
/etc/systemd/system/*
/run/systemd/system/*
/usr/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 temporary system state
snapshot, 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.snapshot(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 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 for instanced units
this logic will first look for the instance ".d/" subdirectory and read
its ".conf" files, followed by the template ".d/" subdirectory and
reads its ".conf" files.
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 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 AT 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 listed earlier override files with the same name in
directories lower in the list.
Table 1. Load path when running in system mode (--system).
+------------------------+---------------------+
|Path | Description |
+------------------------+---------------------+
|/etc/systemd/system | Local configuration |
+------------------------+---------------------+
|/run/systemd/system | Runtime units |
+------------------------+---------------------+
|/usr/lib/systemd/system | Units of installed |
| | packages |
+------------------------+---------------------+
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 GARBAGE COLLECTION
The system and service manager loads a unit's configuration
automatically when a unit is referenced for the first time. It will
automatically unload the unit configuration and state again when the
unit is not needed anymore ("garbage collection"). A unit may be
referenced through a number of different mechanisms:
1. Another loaded unit references it with a dependency such as After=,
Wants=, ...
2. The unit is currently starting, running, reloading or stopping.
3. The unit is currently in the failed state. (But see below.)
4. A job for the unit is pending.
5. The unit is pinned by an active IPC client program.
6. The unit is a special "perpetual" unit that is always active and
loaded. Examples for perpetual units are the root mount unit
-.mount or the scope unit init.scope that the service manager
itself lives in.
7. The unit has running processes associated with it.
The garbage collection logic may be altered with the CollectMode=
option, which allows configuration whether automatic unloading of units
that are in failed state is permissible, see below.
Note that when a unit's configuration and state is unloaded, all
execution results, such as exit codes, exit signals, resource
consumption and other statistics are lost, except for what is stored in
the log subsystem.
Use systemctl daemon-reload or an equivalent command to reload unit
configuration while the unit is already loaded. In this case all
configuration settings are flushed out and replaced with the new
configuration (which however might not be in effect immediately),
however all runtime state is saved/restored.
[UNIT] SECTION 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. 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.
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 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.
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.
CollectMode=
Tweaks the "garbage collection" algorithm for this unit. Takes one
of inactive or inactive-or-failed. If set to inactive the unit will
be unloaded if it is in the inactive state and is not referenced by
clients, jobs or other units -- however it is not unloaded if it is
in the failed state. In failed mode, failed units are not unloaded
until the user invoked systemctl reset-failed on them to reset the
failed state, or an equivalent command. This behaviour is altered
if this option is set to inactive-or-failed: in this case the unit
is unloaded even if the unit is in a failed state, and thus an
explicitly resetting of the failed state is not necessary. Note
that if this mode is used unit results (such as exit codes, exit
signals, consumed resources, ...) are flushed out immediately after
the unit completed, except for what is stored in the logging
subsystem. Defaults to inactive.
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 0 (job timeouts disabled), except for device
units. NB: this timeout is independent from any unit-specific
timeout (for example, the timeout set with StartTimeoutSec= 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.
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 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, docker 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
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 files'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 it was triggered by.
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 file 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 exclusively by the enable and
disable commands of the systemctl(1) tool during installation of a
unit:
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 AT tty2.service
creating a getty.target.wants/getty AT 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 2. Specifiers available in unit files
+----------+---------------------+-------------------------+
|Specifier | Meaning | Details |
+----------+---------------------+-------------------------+
|"%n" | Full unit name | |
+----------+---------------------+-------------------------+
|"%N" | Unescaped full unit | Same as "%n", but |
| | name | with escaping |
| | | undone |
+----------+---------------------+-------------------------+
|"%p" | Prefix name | For instantiated |
| | | units, this refers |
| | | to the string |
| | | before the "@" |
| | | character of the |
| | | unit name. For |
| | | non-instantiated |
| | | units, this refers |
| | | to the name of the |
| | | unit with the type |
| | | suffix removed. |
+----------+---------------------+-------------------------+
|"%P" | Unescaped prefix | Same as "%p", but |
| | name | with escaping |
| | | undone |
+----------+---------------------+-------------------------+
|"%i" | Instance name | For instantiated |
| | | units: this is the |
| | | string between the |
| | | "@" character and |
| | | the suffix of the |
| | | unit name. |
+----------+---------------------+-------------------------+
|"%I" | Unescaped instance | Same as "%i", but |
| | name | with escaping |
| | | undone |
+----------+---------------------+-------------------------+
|"%f" | Unescaped filename | This is either the |
| | | unescaped instance |
| | | name (if |
| | | applicable) with / |
| | | prepended (if |
| | | applicable), or the |
| | | prefix name |
| | | prepended with /. |
+----------+---------------------+-------------------------+
|"%c" | Control group path | This path does not |
| | of the unit | include the |
| | | /sys/fs/cgroup/systemd/ |
| | | prefix. |
+----------+---------------------+-------------------------+
|"%r" | Control group path | This usually maps to |
| | of the slice the | the parent cgroup path |
| | unit is placed in | of "%c". |
+----------+---------------------+-------------------------+
|"%R" | Root control group | For system instances, |
| | path below which | this resolves to /, |
| | slices and units | except in containers, |
| | are placed | where this maps to the |
| | | container's root |
| | | control group path. |
+----------+---------------------+-------------------------+
|"%t" | Runtime directory | This is either /run |
| | | (for the system |
| | | manager) or the path |
| | | "$XDG_RUNTIME_DIR" |
| | | resolves to (for user |
| | | managers). |
+----------+---------------------+-------------------------+
|"%u" | User name | This is the name of the |
| | | configured user of the |
| | | unit, or (if none is |
| | | set) the user running |
| | | the systemd instance. |
+----------+---------------------+-------------------------+
|"%U" | User UID | 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. |
+----------+---------------------+-------------------------+
|"%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 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. |
+----------+---------------------+-------------------------+
|"%s" | User shell | 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. |
+----------+---------------------+-------------------------+
|"%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 |
| | | configuation 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.
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 /usr/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.
Suppose there is a vendor-supplied unit
/usr/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.snapshot(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
systemd 219 SYSTEMD.UNIT(5)
Linux-Distributionen
Huschi als Linux-Admin