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man: document automatic dependencies 

For all units ensure there's an "Automatic Dependencies" section in the
man page, and explain which dependencies are automatically added in all
cases, and which ones are added on top if DefaultDependencies=yes is
set.

This is also done for systemd.exec(5), systemd.resource-control(5) and
systemd.unit(5) as these pages describe common behaviour of various unit
types.
This commit is contained in:
Lennart Poettering 2015-11-11 20:47:07 +01:00
parent ea0ec5cea7
commit c129bd5df3
14 changed files with 312 additions and 67 deletions
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20
man/systemd.automount.xml
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@ -85,10 +85,24 @@
<para>Automount units may be used to implement on-demand mounting
as well as parallelized mounting of file systems.</para>
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<para>If an automount unit is beneath another mount unit in the
file system hierarchy, both a requirement and an ordering
dependency between both units are created automatically.</para>
<para>An implicit <varname>Before=</varname> dependency is created
between an automount unit and the mount unit it activates.</para>
<para>Automount units acquire automatic <varname>Before=</varname>
and <varname>Conflicts=</varname> on
<filename>umount.target</filename> in order to be stopped during
shutdown, unless <varname>DefaultDependencies=no</varname> is
set.</para>
<para>If an automount point is beneath another mount point in the
file system hierarchy, a dependency between both units is created
automatically.</para>
</refsect1>
<refsect1>

11
man/systemd.device.xml
View File

@ -83,7 +83,18 @@
the escaping logic used to convert a file system path to a unit
name see
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<para>Many unit types automatically acquire dependencies on device
units of devices they require. For example,
<filename>.socket</filename> unit acquire dependencies on the
device units of the network interface specified in
<varname>BindToDevice=</varname>. Similar, swap and mount units
acquire dependencies on the units encapsulating their backing
block devices.</para>
</refsect1>
<refsect1>

44
man/systemd.exec.xml
View File

@ -76,6 +76,31 @@
unit type.</para>
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<para>A few execution parameters result in additional, automatic
dependencies to be added.</para>
<para>Units with <varname>WorkingDirectory=</varname> or
<varname>RootDirectory=</varname> set automatically gain
dependencies of type <varname>Requires=</varname> and
<varname>After=</varname> on all mount units required to access
the specified paths. This is equivalent to having them listed
explicitly in <varname>RequiresMountsFor=</varname>.</para>
<para>Similar, units with <varname>PrivateTmp=</varname> enabled
automatically get mount unit dependencies for all mounts
required to access <filename>/tmp</filename> and
<filename>/var/tmp</filename>.</para>
<para>Units whose output standard output or error output is
connected to any other sink but <option>null</option>,
<option>tty</option> and <option>socket</option> automatically
acquire dependencies of type <varname>After=</varname> on
<filename>journald.socket</filename>.</para>
</refsect1>
<refsect1>
<title>Options</title>
@ -93,7 +118,9 @@
and the respective user's home directory if run as user. If
the setting is prefixed with the <literal>-</literal>
character, a missing working directory is not considered
fatal.</para></listitem>
fatal. Note that setting this parameter might result in
additional dependencies to be added to the unit (see
above).</para></listitem>
</varlistentry>
<varlistentry>
@ -104,7 +131,9 @@
project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>2</manvolnum></citerefentry>
system call. If this is used, it must be ensured that the
process binary and all its auxiliary files are available in
the <function>chroot()</function> jail.</para></listitem>
the <function>chroot()</function> jail. Note that setting this
parameter might result in additional dependencies to be added
to the unit (see above).</para></listitem>
</varlistentry>
<varlistentry>
@ -351,6 +380,7 @@
<para>This setting defaults to
<option>null</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>StandardOutput=</varname></term>
<listitem><para>Controls where file descriptor 1 (STDOUT) of
@ -416,8 +446,11 @@
<para>This setting defaults to the value set with
<option>DefaultStandardOutput=</option> in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which defaults to <option>journal</option>.</para></listitem>
which defaults to <option>journal</option>. Note that setting
this parameter might result in additional dependencies to be
added to the unit (see above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>StandardError=</varname></term>
<listitem><para>Controls where file descriptor 2 (STDERR) of
@ -428,8 +461,11 @@
standard error. This setting defaults to the value set with
<option>DefaultStandardError=</option> in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which defaults to <option>inherit</option>.</para></listitem>
which defaults to <option>inherit</option>. Note that setting
this parameter might result in additional dependencies to be
added to the unit (see above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TTYPath=</varname></term>
<listitem><para>Sets the terminal device node to use if

52
man/systemd.mount.xml
View File

@ -94,10 +94,6 @@
unit, to allow on-demand or parallelized mounting. See
<citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
<para>If a mount point is beneath another mount point in the file
system hierarchy, a dependency between both units is created
automatically.</para>
<para>Mount points created at runtime (independently of unit files
or <filename>/etc/fstab</filename>) will be monitored by systemd
and appear like any other mount unit in systemd. See
@ -113,6 +109,52 @@
File Systems</ulink>.</para>
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<para>If a mount unit is beneath another mount unit in the file
system hierarchy, both a requirement dependency and an ordering
dependency between both units are created automatically.</para>
<para>Block device backed file systems automatically gain
<varname>BindsTo=</varname> and <varname>After=</varname> type
dependencies on the device unit encapsulating the block
device (see below).</para>
<para>If traditional file system quota is enabled for a mount
unit, automatic <varname>Wants=</varname> and
<varname>Before=</varname> dependencies on
<filename>systemd-quotacheck.service</filename> and
<filename>quotaon.service</filename> are added.</para>
<para>For mount units with
<varname>DefaultDependencies=yes</varname> (the default) a couple
additional dependencies are added. Mount units referring to local
file systems automatically gain an <varname>After=</varname>
dependency on <filename>local-fs-pre.target</filename>. Network
mount units automatically acquire <varname>After=</varname>
dependencies on <filename>remote-fs-pre.target</filename>,
<filename>network.target</filename> and
<filename>network-online.target</filename>. Towards the latter a
<varname>Wants=</varname> unit is added as well. Mount units
referring to local and network file systems are distinguished by
their file system type specification. In some cases this is not
sufficient (for example network block device based mounts, such as
iSCSI), in which case <option>_netdev</option> may be added to the
mount option string of the unit, which forces systemd to consider the
mount unit a network mount. Mount units (regardless if local or
network) also acquire automatic <varname>Before=</varname> and
<varname>Conflicts=</varname> on
<filename>umount.target</filename> in order to be stopped
during shutdown.</para>
<para>Additional implicit dependencies may be added as result of
execution and resource control parameters as documented in
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
</refsect1>
<refsect1>
<title><filename>fstab</filename></title>
@ -130,7 +172,7 @@
<para>When reading <filename>/etc/fstab</filename> a few special
mount options are understood by systemd which influence how
dependencies are created for mount points. systemd will create a
dependency of type <option>Wants</option> or
dependency of type <varname>Wants=</varname> or
<option>Requires</option> (see option <option>nofail</option>
below), from either <filename>local-fs.target</filename> or
<filename>remote-fs.target</filename>, depending whether the file

17
man/systemd.path.xml
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@ -79,13 +79,24 @@
limitations as inotify, and for example cannot be used to monitor
files or directories changed by other machines on remote NFS file
systems.</para>
</refsect1>
<para>If a path unit is beneath another mount point in the file
system hierarchy, a dependency between both units is created
automatically.</para>
<refsect1>
<title>Automatic Dependencies</title>
<para>If a path unit is beneath another mount unit in the file
system hierarchy, both a requirement and an ordering dependency
between both units are created automatically.</para>
<para>An implicit <varname>Before=</varname> dependency is added
between a path unit and the unit it is supposed to activate.</para>
<para>Unless <varname>DefaultDependencies=false</varname> is used,
path units will implicitly have dependencies of type
<varname>Before=</varname> on <filename>paths.target</filename>,
dependencies of type <varname>After=</varname> and
<varname>Requires=</varname> on
<filename>sysinit.target</filename>, and have dependencies of type
<varname>Conflicts=</varname> and <varname>Before=</varname> on
<filename>shutdown.target</filename>. These ensure that path units
are terminated cleanly prior to system shutdown. Only path units

9
man/systemd.resource-control.xml
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@ -89,6 +89,15 @@
use of resource control APIs from programs.</para>
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<para>Units with the <varname>Slice=</varname> setting set get
automatic <varname>Requires=</varname> and
<varname>After=</varname> dependencies on the specified slice
unit.</para>
</refsect1>
<refsect1>
<title>Options</title>

9
man/systemd.scope.xml
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@ -72,6 +72,10 @@
url="http://www.freedesktop.org/wiki/Software/systemd/ControlGroupInterface/">New
Control Group Interfaces</ulink> for an introduction on how to make
use of scope units from programs.</para>
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<para>Unless <varname>DefaultDependencies=false</varname>
is used, scope units will implicitly have dependencies of
@ -82,6 +86,11 @@
shutdown. Only scope units involved with early boot or
late system shutdown should disable this option.
</para>
<para>Additional implicit dependencies may be added as result of
resource control parameters as documented in
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
</refsect1>
<refsect1>

49
man/systemd.service.xml
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@ -1,4 +1,4 @@
<?xml version='1.0'?> <!--*-nxml-*-->
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
@ -77,18 +77,6 @@
which configure resource control settings for the processes of the
service.</para>
<para>Unless <varname>DefaultDependencies=</varname> is set to
<option>false</option>, service units will implicitly have
dependencies of type <varname>Requires=</varname> and
<varname>After=</varname> on <filename>basic.target</filename> as
well as dependencies of type <varname>Conflicts=</varname> and
<varname>Before=</varname> on
<filename>shutdown.target</filename>. These ensure that normal
service units pull in basic system initialization, and are
terminated cleanly prior to system shutdown. Only services
involved with early boot or late system shutdown should disable
this option.</para>
<para>If a service is requested under a certain name but no unit
configuration file is found, systemd looks for a SysV init script
by the same name (with the <filename>.service</filename> suffix
@ -97,8 +85,39 @@
compatibility is quite comprehensive but not 100%. For details
about the incompatibilities, see the <ulink
url="http://www.freedesktop.org/wiki/Software/systemd/Incompatibilities">Incompatibilities
with SysV</ulink> document.
</para>
with SysV</ulink> document.</para>
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<para>Services with <varname>Type=dbus</varname> set automatically
acquire dependencies of type <varname>Requires=</varname> and
<varname>After=</varname> on
<filename>dbus.socket</filename>.</para>
<para>Socket activated service are automatically ordered after
their activated <filename>.socket</filename> units via an
automatic <varname>After=</varname> dependency.</para>
<para>Unless <varname>DefaultDependencies=</varname> is set to
<option>false</option>, service units will implicitly have
dependencies of type <varname>Requires=</varname> and
<varname>After=</varname> on <filename>sysinit.target</filename>,
a dependency of type <varname>After=</varname> on
<filename>basic.target</filename> as well as dependencies of
type <varname>Conflicts=</varname> and <varname>Before=</varname>
on <filename>shutdown.target</filename>. These ensure that normal
service units pull in basic system initialization, and are
terminated cleanly prior to system shutdown. Only services
involved with early boot or late system shutdown should disable
this option.</para>
<para>Additional implicit dependencies may be added as result of
execution and resource control parameters as documented in
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
</refsect1>
<refsect1>

8
man/systemd.slice.xml
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@ -97,6 +97,14 @@
url="http://www.freedesktop.org/wiki/Software/systemd/ControlGroupInterface/">New
Control Group Interfaces</ulink> for an introduction on how to make
use of slice units from programs.</para>
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<para>Slice units automatically gain dependencies of type
<varname>After=</varname> and <varname>Requires=</varname> on
their immediate parent slice unit.</para>
<para>Unless <varname>DefaultDependencies=false</varname>
is used, slice units will implicitly have dependencies of

46
man/systemd.socket.xml
View File

@ -133,6 +133,40 @@
service file).</para>
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<para>Socket units automatically gain a <varname>Before=</varname>
dependency on the service units they activate.</para>
<para>Socket units referring to file system paths (such as AF_UNIX
sockets or FIFOs) implicitly gain <varname>Requires=</varname> and
<varname>After=</varname> dependencies on all mount units
necessary to access those paths.</para>
<para>Socket units using the <varname>BindToDevice=</varname>
setting automatically gain a <varname>BindsTo=</varname> and
<varname>After=</varname> dependency on the device unit
encapsulating the specified network interface.</para>
<para>If <varname>DefaultDependencies=yes</varname> is set (the
default), socket units automatically gain a
<varname>Before=</varname> dependency on
<filename>sockets.target</filename>. They also gain a pair of
<varname>After=</varname> and <varname>Requires=</varname>
dependency on <filename>sysinit.target</filename>, and a pair of
<varname>Before=</varname> and <varname>Conflicts=</varname>
dependencies on <filename>shutdown.target</filename>. These
dependencies ensure that the socket unit is started before normal
services at boot, and is stopped on shutdown.</para>
<para>Additional implicit dependencies may be added as result of
execution and resource control parameters as documented in
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
</refsect1>
<refsect1>
<title>Options</title>
@ -309,12 +343,14 @@
<listitem><para>Specifies a network interface name to bind
this socket to. If set, traffic will only be accepted from the
specified network interfaces. This controls the
SO_BINDTODEVICE socket option (see
<citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
SO_BINDTODEVICE socket option (see <citerefentry
project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details). If this option is used, an automatic dependency
from this socket unit on the network interface device unit
(<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
is created.</para></listitem>
is created. Note that setting this parameter might result in
additional dependencies to be added to the unit (see
above).</para></listitem>
</varlistentry>
<varlistentry>
@ -719,7 +755,9 @@
with <varname>Accept=no</varname>. It defaults to the service
that bears the same name as the socket (with the suffix
replaced). In most cases, it should not be necessary to use
this option.</para></listitem>
this option. Note that setting this parameter might result in
additional dependencies to be added to the unit (see
above).</para></listitem>
</varlistentry>
<varlistentry>

34
man/systemd.swap.xml
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@ -68,14 +68,15 @@
<para>Additional options are listed in
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which define the execution environment the
<citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
binary is executed in, and in
which define the execution environment the <citerefentry
project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
binary is executed in, in
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which define the way the processes are terminated, and in
which define the way the these processes are
terminated, and in
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which configure resource control settings for the processes of the
service.</para>
which configure resource control settings for these processes of the
unit.</para>
<para>Swap units must be named after the devices
or files they control. Example: the swap device
@ -84,15 +85,28 @@
the escaping logic used to convert a file system path to a unit
name, see
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
</refsect1>
<para>All swap units automatically get the appropriate
dependencies on the devices or on the mount points of the files
<refsect1>
<title>Automatic Dependencies</title>
<para>All swap units automatically get the
<varname>BindsTo=</varname> and <varname>After=</varname>
dependencies on the device units or the mount units of the files
they are activated from.</para>
<para>Swap units with <varname>DefaultDependencies=</varname>
enabled implicitly acquire a conflicting dependency to
enabled implicitly acquire a <varname>Conflicts=</varname> and an
<varname>After=</varname> dependency on
<filename>umount.target</filename> so that they are deactivated at
shutdown.</para>
shutdown, unless <varname>DefaultDependencies=no</varname> is
specified.</para>
<para>Additional implicit dependencies may be added as result of
execution and resource control parameters as documented in
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
</refsect1>
<refsect1>

15
man/systemd.target.xml
View File

@ -77,15 +77,20 @@
See
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details).</para>
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<para>Unless <varname>DefaultDependencies=</varname> is set to
<option>false</option>, target units will implicitly complement
all configured dependencies of type <varname>Wants=</varname>,
<option>no</option>, target units will implicitly complement all
configured dependencies of type <varname>Wants=</varname>,
<varname>Requires=</varname>,
<varname>RequiresOverridable=</varname> with dependencies of type
<varname>After=</varname> if the units in question also have
<varname>DefaultDependencies=true</varname>.
</para>
<varname>After=</varname>, unless an ordering dependency of any
kind between the target and the respective other unit is already
in place. Note that this behaviour is disabled if either unit has
<varname>DefaultDependencies=no</varname>.</para>
</refsect1>
<refsect1>

32
man/systemd.timer.xml
View File

@ -1,4 +1,4 @@
<?xml version='1.0'?> <!--*-nxml-*-->
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
@ -73,19 +73,29 @@
<filename>foo.timer</filename> activates a matching service
<filename>foo.service</filename>. The unit to activate may be
controlled by <varname>Unit=</varname> (see below).</para>
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<para>Timer units automatically gain a <varname>Before=</varname>
dependency on the service they are supposed to activate.</para>
<para>Unless <varname>DefaultDependencies=</varname> is set to
<option>false</option>, all timer units will implicitly have
dependencies of type <varname>Conflicts=</varname> and
<varname>Before=</varname> on <filename>shutdown.target</filename>
to ensure that they are stopped cleanly prior to system shutdown.
Timer units with at least one <varname>OnCalendar=</varname>
directive will have an additional <varname>After=</varname>
dependency on <filename>timer-sync.target</filename> to avoid
being started before the system clock has been correctly set. Only
timer units involved with early boot or late system shutdown
should disable the <varname>DefaultDependencies=</varname>
option.</para>
dependencies of type <varname>Requires=</varname> and
<varname>After=</varname> on <filename>sysinit.target</filename>,
a dependency of type <varname>Before=</varname> on
<filename>timers.target</filename>, as well as
<varname>Conflicts=</varname> and <varname>Before=</varname> on
<filename>shutdown.target</filename> to ensure that they are
stopped cleanly prior to system shutdown. Timer units with at
least one <varname>OnCalendar=</varname> directive will have an
additional <varname>After=</varname> dependency on
<filename>timer-sync.target</filename> to avoid being started
before the system clock has been correctly set. Only timer units
involved with early boot or late system shutdown should disable
the <varname>DefaultDependencies=</varname> option.</para>
</refsect1>
<refsect1>

33
man/systemd.unit.xml
View File

@ -1,4 +1,4 @@
<?xml version='1.0'?> <!--*-nxml-*-->
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
<!ENTITY % entities SYSTEM "custom-entities.ent" >
@ -195,12 +195,6 @@
consider it mostly obsolete, and want people to
use .d/ drop-ins instead. -->
<para>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.</para>
<para>Some unit names reflect paths existing in the file system
namespace. Example: a device unit
<filename>dev-sda.device</filename> refers to a device with the
@ -253,6 +247,31 @@
</refsect1>
<refsect1>
<title>Automatic Dependencies</title>
<para>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.</para>
<para>A number of unit dependencies are automatically established,
depending on unit configuration. On top of that, for units with
<varname>DefaultDependencies=yes</varname> (the default) a couple
of additional dependencies are added. The precise effect of
<varname>DefaultDependencies=yes</varname> depends on the unit
type (see below).</para>
<para>If <varname>DefaultDependencies=yes</varname> is set, units
that are referenced by other units of type
<filename>.target</filename> via a <varname>Wants=</varname> or
<varname>Requires=</varname> dependency might automatically gain
an <varname>Before=</varname> dependency too. See
<citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details.</para>
</refsect1>
<refsect1>
<title>Unit File Load Path</title>