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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="systemd.special">
+
+ <refentryinfo>
+ <title>systemd.special</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>systemd.special</refentrytitle>
+ <manvolnum>7</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>systemd.special</refname>
+ <refpurpose>Special systemd units</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv><para>
+ <!-- sort alphabetically, targets first --><filename>basic.target</filename>,
+ <filename>bluetooth.target</filename>,
+ <filename>cryptsetup-pre.target</filename>,
+ <filename>cryptsetup.target</filename>,
+ <filename>veritysetup-pre.target</filename>,
+ <filename>veritysetup.target</filename>,
+ <filename>ctrl-alt-del.target</filename>,
+ <filename>blockdev@.target</filename>,
+ <filename>boot-complete.target</filename>,
+ <filename>default.target</filename>,
+ <filename>emergency.target</filename>,
+ <filename>exit.target</filename>,
+ <filename>factory-reset.target</filename>,
+ <filename>final.target</filename>,
+ <filename>first-boot-complete.target</filename>,
+ <filename>getty.target</filename>,
+ <filename>getty-pre.target</filename>,
+ <filename>graphical.target</filename>,
+ <filename>halt.target</filename>,
+ <filename>hibernate.target</filename>,
+ <filename>hybrid-sleep.target</filename>,
+ <filename>suspend-then-hibernate.target</filename>,
+ <filename>initrd.target</filename>,
+ <filename>initrd-fs.target</filename>,
+ <filename>initrd-root-device.target</filename>,
+ <filename>initrd-root-fs.target</filename>,
+ <filename>initrd-usr-fs.target</filename>,
+ <filename>integritysetup-pre.target</filename>,
+ <filename>integritysetup.target</filename>,
+ <filename>kbrequest.target</filename>,
+ <filename>kexec.target</filename>,
+ <filename>local-fs-pre.target</filename>,
+ <filename>local-fs.target</filename>,
+ <filename>machines.target</filename>
+ <filename>multi-user.target</filename>,
+ <filename>network-online.target</filename>,
+ <filename>network-pre.target</filename>,
+ <filename>network.target</filename>,
+ <filename>nss-lookup.target</filename>,
+ <filename>nss-user-lookup.target</filename>,
+ <filename>paths.target</filename>,
+ <filename>poweroff.target</filename>,
+ <filename>printer.target</filename>,
+ <filename>reboot.target</filename>,
+ <filename>remote-cryptsetup.target</filename>,
+ <filename>remote-veritysetup.target</filename>,
+ <filename>remote-fs-pre.target</filename>,
+ <filename>remote-fs.target</filename>,
+ <filename>rescue.target</filename>,
+ <filename>rpcbind.target</filename>,
+ <filename>runlevel2.target</filename>,
+ <filename>runlevel3.target</filename>,
+ <filename>runlevel4.target</filename>,
+ <filename>runlevel5.target</filename>,
+ <filename>shutdown.target</filename>,
+ <filename>sigpwr.target</filename>,
+ <filename>sleep.target</filename>,
+ <filename>slices.target</filename>,
+ <filename>smartcard.target</filename>,
+ <filename>sockets.target</filename>,
+ <filename>sound.target</filename>,
+ <filename>suspend.target</filename>,
+ <filename>swap.target</filename>,
+ <filename>sysinit.target</filename>,
+ <filename>system-update.target</filename>,
+ <filename>system-update-pre.target</filename>,
+ <filename>time-set.target</filename>,
+ <filename>time-sync.target</filename>,
+ <filename>timers.target</filename>,
+ <filename>umount.target</filename>,
+ <filename>usb-gadget.target</filename>,
+ <!-- slices --><filename>-.slice</filename>,
+ <filename>system.slice</filename>,
+ <filename>user.slice</filename>,
+ <filename>machine.slice</filename>,
+ <!-- the rest --><filename>-.mount</filename>,
+ <filename>dbus.service</filename>,
+ <filename>dbus.socket</filename>,
+ <filename>display-manager.service</filename>,
+ <filename>init.scope</filename>,
+ <filename>syslog.socket</filename>,
+ <filename>system-update-cleanup.service</filename>
+ </para></refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>A few units are treated specially by systemd. Many of them have
+ special internal semantics and cannot be renamed, while others simply
+ have a standard meaning and should be present on all systems.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Units managed by the system service manager</title>
+
+ <refsect2>
+ <title>Special System Units</title>
+
+ <variablelist>
+ <varlistentry>
+ <term><filename>-.mount</filename></term>
+ <listitem>
+ <para>The root mount point, i.e. the mount unit for the <filename>/</filename>
+ path. This unit is unconditionally active, during the entire time the system is up, as
+ this mount point is where the basic userspace is running from.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>basic.target</filename></term>
+ <listitem>
+ <para>A special target unit covering basic boot-up.</para>
+
+ <para>systemd automatically adds dependency of the type
+ <varname>After=</varname> for this target unit to all
+ services (except for those with
+ <varname>DefaultDependencies=no</varname>).</para>
+
+ <para>Usually, this should pull-in all local mount points plus
+ <filename>/var/</filename>, <filename>/tmp/</filename> and
+ <filename>/var/tmp/</filename>, swap devices, sockets, timers,
+ path units and other basic initialization necessary for general
+ purpose daemons. The mentioned mount points are special cased
+ to allow them to be remote.
+ </para>
+
+ <para>This target usually does not pull in any non-target units
+ directly, but rather does so indirectly via other early boot targets.
+ It is instead meant as a synchronization point for late boot
+ services. Refer to
+ <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ for details on the targets involved.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>boot-complete.target</filename></term>
+ <listitem>
+ <para>This target is intended as generic synchronization point for services that shall determine or act on
+ whether the boot process completed successfully. Order units that are required to succeed for a boot process
+ to be considered successful before this unit, and add a <varname>Requires=</varname> dependency from the
+ target unit to them. Order units that shall only run when the boot process is considered successful after the
+ target unit and pull in the target from it, also with <varname>Requires=</varname>. Note that by default this
+ target unit is not part of the initial boot transaction, but is supposed to be pulled in only if required by
+ units that want to run only on successful boots.</para>
+
+ <para>See
+ <citerefentry><refentrytitle>systemd-boot-check-no-failures.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for a service that implements a generic system health check and orders itself before
+ <filename>boot-complete.target</filename>.</para>
+
+ <para>See
+ <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for a service that propagates boot success information to the boot loader, and orders itself after
+ <filename>boot-complete.target</filename>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>ctrl-alt-del.target</filename></term>
+ <listitem>
+ <para>systemd starts this target whenever Control+Alt+Del is
+ pressed on the console. Usually, this should be aliased
+ (symlinked) to <filename>reboot.target</filename>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>cryptsetup.target</filename></term>
+ <listitem>
+ <para>A target that pulls in setup services for all
+ encrypted block devices.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>veritysetup.target</filename></term>
+ <listitem>
+ <para>A target that pulls in setup services for all
+ verity integrity protected block devices.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>dbus.service</filename></term>
+ <listitem>
+ <para>A special unit for the D-Bus bus daemon. As soon as
+ this service is fully started up systemd will connect to it
+ and register its service.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>dbus.socket</filename></term>
+ <listitem>
+ <para>A special unit for the D-Bus system bus socket. All
+ units with <varname>Type=dbus</varname> automatically gain a
+ dependency on this unit.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>default.target</filename></term>
+ <listitem>
+ <para>The default unit systemd starts at bootup. Usually, this should be aliased (symlinked) to
+ <filename>multi-user.target</filename> or <filename>graphical.target</filename>. See
+ <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
+ more discussion.</para>
+
+ <para>The default unit systemd starts at bootup can be overridden with the
+ <varname>systemd.unit=</varname> kernel command line option, or more conveniently, with the short
+ names like <varname>single</varname>, <varname>rescue</varname>, <varname>1</varname>,
+ <varname>3</varname>, <varname>5</varname>, …; see
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>display-manager.service</filename></term>
+ <listitem>
+ <para>The display manager service. Usually, this should be
+ aliased (symlinked) to <filename>gdm.service</filename> or a
+ similar display manager service.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>emergency.target</filename></term>
+ <listitem>
+ <para>A special target unit that starts an emergency shell on the main console. This
+ target does not pull in other services or mounts. It is the most minimal version of
+ starting the system in order to acquire an interactive shell; the only processes running
+ are usually just the system manager (PID 1) and the shell process. This unit may be used
+ by specifying <varname>emergency</varname> on the kernel command line; it is
+ also used when a file system check on a required file system fails and boot-up cannot
+ continue. Compare with <filename>rescue.target</filename>, which serves a similar
+ purpose, but also starts the most basic services and mounts all file systems.</para>
+
+ <para>In many ways booting into <filename>emergency.target</filename> is similar to the
+ effect of booting with <literal>init=/bin/sh</literal> on the kernel command line,
+ except that emergency mode provides you with the full system and service manager, and
+ allows starting individual units in order to continue the boot process in steps.</para>
+
+ <para>Note that depending on how <filename>emergency.target</filename> is reached, the root file
+ system might be mounted read-only or read-write (no remounting is done specially for this
+ target). For example, the system may boot with root mounted read-only when <varname>ro</varname>
+ is used on the kernel command line and remain this way for <filename>emergency.target</filename>,
+ or the system may transition to <filename>emergency.target</filename> after the system has been
+ partially booted and disks have already been remounted read-write.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>exit.target</filename></term>
+ <listitem>
+ <para>A special service unit for shutting down the system or
+ user service manager. It is equivalent to
+ <filename>poweroff.target</filename> on non-container
+ systems, and also works in containers.</para>
+
+ <para>systemd will start this unit when it receives the
+ <constant>SIGTERM</constant> or <constant>SIGINT</constant>
+ signal when running as user service daemon.</para>
+
+ <para>Normally, this (indirectly) pulls in
+ <filename>shutdown.target</filename>, which in turn should be
+ conflicted by all units that want to be scheduled for
+ shutdown when the service manager starts to exit.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>factory-reset.target</filename></term>
+ <listitem>
+ <para>A special target to trigger a factory reset.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>final.target</filename></term>
+ <listitem>
+ <para>A special target unit that is used during the shutdown
+ logic and may be used to pull in late services after all
+ normal services are already terminated and all mounts
+ unmounted.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>getty.target</filename></term>
+ <listitem>
+ <para>A special target unit that pulls in statically
+ configured local TTY <filename>getty</filename> instances.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>graphical.target</filename></term>
+ <listitem>
+ <para>A special target unit for setting up a graphical login
+ screen. This pulls in
+ <filename>multi-user.target</filename>.</para>
+
+ <para>Units that are needed for graphical logins shall add
+ <varname>Wants=</varname> dependencies for their unit to
+ this unit (or <filename>multi-user.target</filename>) during
+ installation. This is best configured via
+ <varname>WantedBy=graphical.target</varname> in the unit's
+ [Install] section.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>hibernate.target</filename></term>
+ <listitem>
+ <para>A special target unit for hibernating the system. This
+ pulls in <filename>sleep.target</filename>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>hybrid-sleep.target</filename></term>
+ <listitem>
+ <para>A special target unit for hibernating and suspending
+ the system at the same time. This pulls in
+ <filename>sleep.target</filename>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>suspend-then-hibernate.target</filename></term>
+ <listitem>
+ <para>A special target unit for suspending the system for a period
+ of time, waking it and putting it into hibernate. This pulls in
+ <filename>sleep.target</filename>.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>halt.target</filename></term>
+ <listitem>
+ <para>A special target unit for shutting down and halting
+ the system. Note that this target is distinct from
+ <filename>poweroff.target</filename> in that it generally
+ really just halts the system rather than powering it
+ down.</para>
+
+ <para>Applications wanting to halt the system should not start this unit
+ directly, but should instead execute <command>systemctl halt</command>
+ (possibly with the <option>--no-block</option> option) or call
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
+ <command>org.freedesktop.systemd1.Manager.Halt</command> D-Bus method
+ directly.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>init.scope</filename></term>
+ <listitem>
+ <para>This scope unit is where the system and service manager (PID 1) itself resides. It
+ is active as long as the system is running.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>initrd.target</filename></term>
+ <listitem>
+ <para>This is the default target in the initrd, similar to <filename>default.target</filename> in
+ the main system. It is used to mount the real root and transition to it. See
+ <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
+ more discussion.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>initrd-fs.target</filename></term>
+ <listitem>
+ <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ automatically adds dependencies of type <varname>Before=</varname> to
+ <filename>sysroot-usr.mount</filename> and all mount points found in
+ <filename>/etc/fstab</filename> that have the <option>x-initrd.mount</option> mount option set
+ and do not have the <option>noauto</option> mount option set. It is also indirectly ordered after
+ <filename>sysroot.mount</filename>. Thus, once this target is reached the
+ <filename>/sysroot/</filename> hierarchy is fully set up, in preparation for the transition to
+ the host OS.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>initrd-root-device.target</filename></term>
+ <listitem>
+ <para>A special initrd target unit that is reached when the root filesystem device is available, but before
+ it has been mounted.
+ <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ and
+ <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ automatically setup the appropriate dependencies to make this happen.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>initrd-root-fs.target</filename></term>
+ <listitem>
+ <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ automatically adds dependencies of type <varname>Before=</varname> to the
+ <filename>sysroot.mount</filename> unit, which is generated from the kernel command line's
+ <varname>root=</varname> setting (or equivalent).</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>initrd-usr-fs.target</filename></term>
+ <listitem>
+ <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ automatically adds dependencies of type <varname>Before=</varname> to the
+ <filename>sysusr-usr.mount</filename> unit, which is generated from the kernel command line's
+ <varname>usr=</varname> switch. Services may order themselves after this target unit in order to
+ run once the <filename>/sysusr/</filename> hierarchy becomes available, on systems that come up
+ initially without a root file system, but with an initialized <filename>/usr/</filename> and need
+ to access that before setting up the root file system to ultimately switch to. On systems where
+ <varname>usr=</varname> is not used this target is ordered after
+ <filename>sysroot.mount</filename> and thus mostly equivalent to
+ <filename>initrd-root-fs.target</filename>. In effect on any system once this target is reached
+ the file system backing <filename>/usr/</filename> is mounted, though possibly at two different
+ locations, either below the <filename>/sysusr/</filename> or the <filename>/sysroot/</filename>
+ hierarchies.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>kbrequest.target</filename></term>
+ <listitem>
+ <para>systemd starts this target whenever Alt+ArrowUp is
+ pressed on the console. Note that any user with physical access
+ to the machine will be able to do this, without authentication,
+ so this should be used carefully.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>kexec.target</filename></term>
+ <listitem>
+ <para>A special target unit for shutting down and rebooting
+ the system via kexec.</para>
+
+ <para>Applications wanting to reboot the system should not start this unit
+ directly, but should instead execute <command>systemctl kexec</command>
+ (possibly with the <option>--no-block</option> option) or call
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
+ <command>org.freedesktop.systemd1.Manager.KExec</command> D-Bus method
+ directly.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>local-fs.target</filename></term>
+ <listitem>
+ <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ automatically adds dependencies of type
+ <varname>Before=</varname> to all mount units that refer to
+ local mount points for this target unit. In addition, it
+ adds dependencies of type <varname>Wants=</varname> to this
+ target unit for those mounts listed in
+ <filename>/etc/fstab</filename> that have the
+ <option>auto</option> mount option set.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>machines.target</filename></term>
+ <listitem>
+ <para>A standard target unit for starting all the containers
+ and other virtual machines. See <filename>systemd-nspawn@.service</filename>
+ for an example.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>multi-user.target</filename></term>
+ <listitem>
+ <para>A special target unit for setting up a multi-user
+ system (non-graphical). This is pulled in by
+ <filename>graphical.target</filename>.</para>
+
+ <para>Units that are needed for a multi-user system shall
+ add <varname>Wants=</varname> dependencies for their unit to
+ this unit during installation. This is best configured via
+ <varname>WantedBy=multi-user.target</varname> in the unit's
+ [Install] section.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>network-online.target</filename></term>
+ <listitem>
+ <para>Units that strictly require a configured network
+ connection should pull in
+ <filename>network-online.target</filename> (via a
+ <varname>Wants=</varname> type dependency) and order
+ themselves after it. This target unit is intended to pull in
+ a service that delays further execution until the network is
+ sufficiently set up. What precisely this requires is left to
+ the implementation of the network managing service.</para>
+
+ <para>Note the distinction between this unit and <filename>network.target</filename>. This unit
+ is an active unit (i.e. pulled in by the consumer rather than the provider of this functionality)
+ and pulls in a service which possibly adds substantial delays to further execution. In contrast,
+ <filename>network.target</filename> is a passive unit (i.e. pulled in by the provider of the
+ functionality, rather than the consumer) that usually does not delay execution much. Usually,
+ <filename>network.target</filename> is part of the boot of most systems, while
+ <filename>network-online.target</filename> is not, except when at least one unit requires
+ it. Also see <ulink url="https://systemd.io/NETWORK_ONLINE">Running Services After the Network Is
+ Up</ulink> for more information.</para>
+
+ <para>All mount units for remote network file systems automatically pull in this unit, and order
+ themselves after it. Note that networking daemons that simply <emphasis>provide</emphasis>
+ functionality to other hosts (as opposed to <emphasis>consume</emphasis> functionality of other
+ hosts) generally do not need to pull this in.</para>
+
+ <para>systemd automatically adds dependencies of type <varname>Wants=</varname> and
+ <varname>After=</varname> for this target unit to all SysV init script service units
+ with an LSB header referring to the <literal>$network</literal> facility.</para>
+
+ <para>Note that this unit is only useful during the original system start-up
+ logic. After the system has completed booting up, it will not track the online state of
+ the system anymore. Due to this it cannot be used as a network connection monitor
+ concept, it is purely a one-time system start-up concept.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>paths.target</filename></term>
+ <listitem>
+ <para>A special target unit that sets up all path units (see
+ <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details) that shall be active after boot.</para>
+
+ <para>It is recommended that path units installed by
+ applications get pulled in via <varname>Wants=</varname>
+ dependencies from this unit. This is best configured via a
+ <varname>WantedBy=paths.target</varname> in the path unit's
+ [Install] section.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>poweroff.target</filename></term>
+ <listitem>
+ <para>A special target unit for shutting down and powering
+ off the system.</para>
+
+ <para>Applications wanting to power off the system should not start this unit
+ directly, but should instead execute <command>systemctl poweroff</command>
+ (possibly with the <option>--no-block</option> option) or call
+ <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
+ <command>org.freedesktop.login1.Manager.PowerOff</command> D-Bus method
+ directly.</para>
+
+ <para><filename>runlevel0.target</filename> is an alias for
+ this target unit, for compatibility with SysV.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>reboot.target</filename></term>
+ <listitem>
+ <para>A special target unit for shutting down and rebooting
+ the system.</para>
+
+ <para>Applications wanting to reboot the system should not start this unit
+ directly, but should instead execute <command>systemctl reboot</command>
+ (possibly with the <option>--no-block</option> option) or call
+ <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
+ <command>org.freedesktop.login1.Manager.Reboot</command> D-Bus method
+ directly.</para>
+
+ <para><filename>runlevel6.target</filename> is an alias for
+ this target unit, for compatibility with SysV.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>remote-cryptsetup.target</filename></term>
+ <listitem>
+ <para>Similar to <filename>cryptsetup.target</filename>, but for encrypted
+ devices which are accessed over the network. It is used for
+ <citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ entries marked with <option>_netdev</option>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>remote-veritysetup.target</filename></term>
+ <listitem>
+ <para>Similar to <filename>veritysetup.target</filename>, but for verity
+ integrity protected devices which are accessed over the network. It is used for
+ <citerefentry><refentrytitle>veritytab</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ entries marked with <option>_netdev</option>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>remote-fs.target</filename></term>
+ <listitem>
+ <para>Similar to <filename>local-fs.target</filename>, but
+ for remote mount points.</para>
+
+ <para>systemd automatically adds dependencies of type
+ <varname>After=</varname> for this target unit to all SysV
+ init script service units with an LSB header referring to
+ the <literal>$remote_fs</literal> facility.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>rescue.target</filename></term>
+ <listitem>
+ <para>A special target unit that pulls in the base system (including system mounts) and
+ spawns a rescue shell. Isolate to this target in order to administer the system in
+ single-user mode with all file systems mounted but with no services running, except for
+ the most basic. Compare with <filename>emergency.target</filename>, which is much more
+ reduced and does not provide the file systems or most basic services. Compare with
+ <filename>multi-user.target</filename>, this target could be seen as
+ <filename>single-user.target</filename>.</para>
+
+ <para><filename>runlevel1.target</filename> is an alias for this target unit, for
+ compatibility with SysV.</para>
+
+ <para>Use the <literal>systemd.unit=rescue.target</literal> kernel command line option
+ to boot into this mode. A short alias for this kernel command line option is
+ <literal>1</literal>, for compatibility with SysV.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>runlevel2.target</filename></term>
+ <term><filename>runlevel3.target</filename></term>
+ <term><filename>runlevel4.target</filename></term>
+ <term><filename>runlevel5.target</filename></term>
+ <listitem>
+ <para>These are targets that are called whenever the SysV
+ compatibility code asks for runlevel 2, 3, 4, 5,
+ respectively. It is a good idea to make this an alias for
+ (i.e. symlink to) <filename>graphical.target</filename>
+ (for runlevel 5) or <filename>multi-user.target</filename>
+ (the others).</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>shutdown.target</filename></term>
+ <listitem>
+ <para>A special target unit that terminates the services on
+ system shutdown.</para>
+
+ <para>Services that shall be terminated on system shutdown
+ shall add <varname>Conflicts=</varname> and
+ <varname>Before=</varname> dependencies to this unit for
+ their service unit, which is implicitly done when
+ <varname>DefaultDependencies=yes</varname> is set (the
+ default).</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>sigpwr.target</filename></term>
+ <listitem>
+ <para>A special target that is started when systemd receives
+ the SIGPWR process signal, which is normally sent by the
+ kernel or UPS daemons when power fails.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>sleep.target</filename></term>
+ <listitem>
+ <para>A special target unit that is pulled in by
+ <filename>suspend.target</filename>,
+ <filename>hibernate.target</filename> and
+ <filename>hybrid-sleep.target</filename> and may be used to
+ hook units into the sleep state logic.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>slices.target</filename></term>
+ <listitem>
+ <para>A special target unit that sets up all slice units (see
+ <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details) that shall always be active after boot. By default the generic
+ <filename>system.slice</filename> slice unit as well as the root slice unit
+ <filename>-.slice</filename> are pulled in and ordered before this unit (see
+ below).</para>
+
+ <para>Adding slice units to <filename>slices.target</filename> is generally not
+ necessary. Instead, when some unit that uses <varname>Slice=</varname> is started, the
+ specified slice will be started automatically. Adding
+ <varname>WantedBy=slices.target</varname> lines to the [Install]
+ section should only be done for units that need to be always active. In that case care
+ needs to be taken to avoid creating a loop through the automatic dependencies on
+ "parent" slices.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>sockets.target</filename></term>
+ <listitem>
+ <para>A special target unit that sets up all socket
+ units (see
+ <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details) that shall be active after boot.</para>
+
+ <para>Services that can be socket-activated shall add
+ <varname>Wants=</varname> dependencies to this unit for
+ their socket unit during installation. This is best
+ configured via a <varname>WantedBy=sockets.target</varname>
+ in the socket unit's [Install]
+ section.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>suspend.target</filename></term>
+ <listitem>
+ <para>A special target unit for suspending the system. This
+ pulls in <filename>sleep.target</filename>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>swap.target</filename></term>
+ <listitem>
+ <para>Similar to <filename>local-fs.target</filename>, but
+ for swap partitions and swap files.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>sysinit.target</filename></term>
+ <listitem>
+ <para>systemd automatically adds dependencies of the types
+ <varname>Requires=</varname> and <varname>After=</varname>
+ for this target unit to all services (except for those with
+ <varname>DefaultDependencies=no</varname>).</para>
+
+ <para>This target pulls in the services required for system
+ initialization. System services pulled in by this target should
+ declare <varname>DefaultDependencies=no</varname> and specify
+ all their dependencies manually, including access to anything
+ more than a read only root filesystem. For details on the
+ dependencies of this target, refer to
+ <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>syslog.socket</filename></term>
+ <listitem>
+ <para>The socket unit syslog implementations should listen
+ on. All userspace log messages will be made available on
+ this socket. For more information about syslog integration,
+ please consult the <ulink
+ url="https://www.freedesktop.org/wiki/Software/systemd/syslog">Syslog
+ Interface</ulink> document.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>system-update.target</filename></term>
+ <term><filename>system-update-pre.target</filename></term>
+ <term><filename>system-update-cleanup.service</filename></term>
+ <listitem>
+ <para>A special target unit that is used for offline system updates.
+ <citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ will redirect the boot process to this target if <filename>/system-update</filename>
+ exists. For more information see
+ <citerefentry><refentrytitle>systemd.offline-updates</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
+ </para>
+
+ <para>Updates should happen before the <filename>system-update.target</filename> is
+ reached, and the services which implement them should cause the machine to reboot. The
+ main units executing the update should order themselves after
+ <filename>system-update-pre.target</filename> but not pull it in. Services which want to
+ run during system updates only, but before the actual system update is executed should
+ order themselves before this unit and pull it in. As a safety measure, if this does not
+ happen, and <filename>/system-update</filename> still exists after
+ <filename>system-update.target</filename> is reached,
+ <filename>system-update-cleanup.service</filename> will remove this symlink and reboot
+ the machine.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>timers.target</filename></term>
+ <listitem>
+ <para>A special target unit that sets up all timer units
+ (see
+ <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details) that shall be active after boot.</para>
+
+ <para>It is recommended that timer units installed by
+ applications get pulled in via <varname>Wants=</varname>
+ dependencies from this unit. This is best configured via
+ <varname>WantedBy=timers.target</varname> in the timer
+ unit's [Install] section.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>umount.target</filename></term>
+ <listitem>
+ <para>A special target unit that unmounts all mount and
+ automount points on system shutdown.</para>
+
+ <para>Mounts that shall be unmounted on system shutdown
+ shall add Conflicts dependencies to this unit for their
+ mount unit, which is implicitly done when
+ <varname>DefaultDependencies=yes</varname> is set (the
+ default).</para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+ </refsect2>
+
+ <refsect2>
+ <title>Special System Units for Devices</title>
+
+ <para>Some target units are automatically pulled in as devices of
+ certain kinds show up in the system. These may be used to
+ automatically activate various services based on the specific type
+ of the available hardware.</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><filename>bluetooth.target</filename></term>
+ <listitem>
+ <para>This target is started automatically as soon as a
+ Bluetooth controller is plugged in or becomes available at
+ boot.</para>
+
+ <para>This may be used to pull in Bluetooth management
+ daemons dynamically when Bluetooth hardware is found.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>printer.target</filename></term>
+ <listitem>
+ <para>This target is started automatically as soon as a
+ printer is plugged in or becomes available at boot.</para>
+
+ <para>This may be used to pull in printer management daemons
+ dynamically when printer hardware is found.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>smartcard.target</filename></term>
+ <listitem>
+ <para>This target is started automatically as soon as a
+ smartcard controller is plugged in or becomes available at
+ boot.</para>
+
+ <para>This may be used to pull in smartcard management
+ daemons dynamically when smartcard hardware is found.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>sound.target</filename></term>
+ <listitem>
+ <para>This target is started automatically as soon as a
+ sound card is plugged in or becomes available at
+ boot.</para>
+
+ <para>This may be used to pull in audio management daemons
+ dynamically when audio hardware is found.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>usb-gadget.target</filename></term>
+ <listitem>
+ <para>This target is started automatically as soon as a
+ USB Device Controller becomes available at boot.</para>
+
+ <para>This may be used to pull in usb gadget
+ dynamically when UDC hardware is found.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect2>
+
+ <refsect2>
+ <title>Special Passive System Units </title>
+
+ <para>A number of special system targets are defined that can be
+ used to properly order boot-up of optional services. These targets
+ are generally not part of the initial boot transaction, unless
+ they are explicitly pulled in by one of the implementing services.
+ Note specifically that these <emphasis>passive</emphasis> target
+ units are generally not pulled in by the consumer of a service,
+ but by the provider of the service. This means: a consuming
+ service should order itself after these targets (as appropriate),
+ but not pull it in. A providing service should order itself before
+ these targets (as appropriate) and pull it in (via a
+ <varname>Wants=</varname> type dependency).</para>
+
+ <para>Note that these passive units cannot be started manually,
+ i.e. <literal>systemctl start time-sync.target</literal> will fail
+ with an error. They can only be pulled in by dependency. This is
+ enforced since they exist for ordering purposes only and thus are
+ not useful as only unit within a transaction.</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><filename>blockdev@.target</filename></term>
+ <listitem><para>This template unit is used to order mount units and other consumers of block
+ devices after services that synthesize these block devices. In particular, this is intended to be
+ used with storage services (such as
+ <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>/
+ <citerefentry><refentrytitle>systemd-veritysetup@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>)
+ that allocate and manage a virtual block device. Storage services are ordered before an instance of
+ <filename>blockdev@.target</filename>, and the consumer units after it. The ordering is
+ particularly relevant during shutdown, as it ensures that the mount is deactivated first and the
+ service backing the mount later. The <filename>blockdev@.target</filename> instance should be
+ pulled in via a <option>Wants=</option> dependency of the storage daemon and thus generally not be
+ part of any transaction unless a storage daemon is used. The instance name for instances of this
+ template unit must be a properly escaped block device node path, e.g.
+ <filename index="false">blockdev@dev-mapper-foobar.target</filename> for the storage device
+ <filename index="false">/dev/mapper/foobar</filename>.</para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>cryptsetup-pre.target</filename></term>
+ <listitem>
+ <para>This passive target unit may be pulled in by services
+ that want to run before any encrypted block device is set
+ up. All encrypted block devices are set up after this target
+ has been reached. Since the shutdown order is implicitly the
+ reverse start-up order between units, this target is
+ particularly useful to ensure that a service is shut down
+ only after all encrypted block devices are fully
+ stopped.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>veritysetup-pre.target</filename></term>
+ <listitem>
+ <para>This passive target unit may be pulled in by services
+ that want to run before any verity integrity protected block
+ device is set up. All verity integrity protected block
+ devices are set up after this target has been reached. Since
+ the shutdown order is implicitly the reverse start-up order
+ between units, this target is particularly useful to ensure
+ that a service is shut down only after all verity integrity
+ protected block devices are fully stopped.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>first-boot-complete.target</filename></term>
+ <listitem>
+ <para>This passive target is intended as a synchronization point for units that need to run once
+ during the first boot. Only after all units ordered before this target have finished, will the
+ <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ be committed to disk, marking the first boot as completed. If the boot is aborted at any time
+ before that, the next boot will re-run any units with <varname>ConditionFirstBoot=yes</varname>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>getty-pre.target</filename></term>
+ <listitem>
+ <para>A special passive target unit. Users of this target
+ are expected to pull it in the boot transaction via
+ a dependency (e.g. <varname>Wants=</varname>). Order your
+ unit before this unit if you want to make use of the console
+ just before <filename>getty</filename> is started.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>local-fs-pre.target</filename></term>
+ <listitem>
+ <para>This target unit is
+ automatically ordered before
+ all local mount points marked
+ with <option>auto</option>
+ (see above). It can be used to
+ execute certain units before
+ all local mounts.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>network.target</filename></term>
+ <listitem>
+ <para>This unit is supposed to indicate when network functionality is available, but it is only
+ very weakly defined what that is supposed to mean. However, the following should apply at
+ minimum:</para>
+
+ <itemizedlist>
+ <listitem><para>At start-up, any configured synthetic network devices (i.e. not physical ones
+ that require hardware to show up and be probed, but virtual ones like bridge devices and
+ similar which are created programmatically) that do not depend on any underlying hardware
+ should be allocated by the time this target is reached. It is not necessary for these
+ interfaces to also have completed IP level configuration by the time
+ <filename>network.target</filename> is reached.</para></listitem>
+
+ <listitem><para>At shutdown, a unit that is ordered after <filename>network.target</filename>
+ will be stopped before the network — to whatever level it might be set up by then — is shut
+ down. It is hence useful when writing service files that require network access on shutdown,
+ which should order themselves after this target, but not pull it in. Also see <ulink
+ url="https://systemd.io/NETWORK_ONLINE">Running Services After the Network Is Up</ulink> for
+ more information.</para></listitem>
+ </itemizedlist>
+
+ <para>It must emphasized that at start-up there's no guarantee that hardware-based devices have
+ shown up by the time this target is reached, or even acquired complete IP configuration. For that
+ purpose use <filename>network-online.target</filename> as described above.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>network-pre.target</filename></term>
+ <listitem>
+ <para>This passive target unit may be pulled in by services that want to run before any network
+ is set up, for example for the purpose of setting up a firewall. All network management software
+ orders itself after this target, but does not pull it in. Also see <ulink
+ url="https://systemd.io/NETWORK_ONLINE">Running Services After the Network Is Up</ulink> for more
+ information.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>nss-lookup.target</filename></term>
+ <listitem>
+ <para>A target that should be used as synchronization point for all host/network name
+ service lookups. Note that this is independent of UNIX user/group name lookups for which
+ <filename>nss-user-lookup.target</filename> should be used. All services for which the
+ availability of full host/network name resolution is essential should be ordered after
+ this target, but not pull it in. systemd automatically adds dependencies of type
+ <varname>After=</varname> for this target unit to all SysV init script service units
+ with an LSB header referring to the <literal>$named</literal> facility.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>nss-user-lookup.target</filename></term>
+ <listitem>
+ <para>A target that should be used as synchronization point for all regular UNIX
+ user/group name service lookups. Note that this is independent of host/network name
+ lookups for which <filename>nss-lookup.target</filename> should be used. All services
+ for which the availability of the full user/group database is essential should be
+ ordered after this target, but not pull it in. All services which provide parts of the
+ user/group database should be ordered before this target, and pull it in. Note that this
+ unit is only relevant for regular users and groups — system users and groups are
+ required to be resolvable during earliest boot already, and hence do not need any
+ special ordering against this target.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>remote-fs-pre.target</filename></term>
+ <listitem>
+ <para>This target unit is automatically ordered before all
+ mount point units (see above) and cryptsetup/veritysetup devices
+ marked with the <option>_netdev</option>. It can be used to run
+ certain units before remote encrypted devices and mounts are established.
+ Note that this unit is generally not part of the initial
+ transaction, unless the unit that wants to be ordered before
+ all remote mounts pulls it in via a
+ <varname>Wants=</varname> type dependency. If the unit wants
+ to be pulled in by the first remote mount showing up, it
+ should use <filename>network-online.target</filename> (see
+ above).</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>rpcbind.target</filename></term>
+ <listitem>
+ <para>The portmapper/rpcbind pulls in this target and orders
+ itself before it, to indicate its availability. systemd
+ automatically adds dependencies of type
+ <varname>After=</varname> for this target unit to all SysV
+ init script service units with an LSB header referring to
+ the <literal>$portmap</literal> facility.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>time-set.target</filename></term>
+ <listitem>
+ <para>Services responsible for setting the system clock (<constant>CLOCK_REALTIME</constant>)
+ from a local source (such as a maintained timestamp file or imprecise real-time clock) should
+ pull in this target and order themselves before it. Services where approximate, roughly monotonic
+ time is desired should be ordered after this unit, but not pull it in.</para>
+
+ <para>This target does not provide the accuracy guarantees of
+ <filename>time-sync.target</filename> (see below), however does not depend on remote clock
+ sources to be reachable, i.e. the target is typically not delayed by network problems and
+ similar. Use of this target is recommended for services where approximate clock accuracy and
+ rough monotonicity is desired but activation shall not be delayed for possibly unreliable network
+ communication.</para>
+
+ <para>The service manager automatically adds dependencies of type <varname>After=</varname> for
+ this target unit to all timer units with at least one <varname>OnCalendar=</varname>
+ directive.</para>
+
+ <para>The
+ <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ service is a simple daemon that pulls in this target and orders itself before it. Besides
+ implementing the SNTP network protocol it maintains a timestamp file on disk whose modification
+ time is regularlary updated. At service start-up the local system clock is set from that modification time,
+ ensuring it increases roughly monotonically.</para>
+
+ <para>Note that ordering a unit after <filename>time-set.target</filename> only has effect if
+ there's actually a service ordered before it that delays it until the clock is adjusted for rough
+ monotonicity. Otherwise, this target might get reached before the clock is adjusted to be roughly
+ monotonic. Enable
+ <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ or an alternative NTP implementation to delay the target.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><filename>time-sync.target</filename></term>
+ <listitem>
+ <para>Services indicating completed synchronization of the system clock
+ (<constant>CLOCK_REALTIME</constant>) to a remote source should pull in this target and order
+ themselves before it. Services where accurate time is essential should be ordered after this
+ unit, but not pull it in.</para>
+
+ <para>The service manager automatically adds dependencies of type <varname>After=</varname> for
+ this target unit to all SysV init script service units with an LSB header referring to the
+ <literal>$time</literal> facility, as well to all timer units with at least one
+ <varname>OnCalendar=</varname> directive.</para>
+
+ <para>This target provides stricter clock accuracy guarantees than
+ <filename>time-set.target</filename> (see above), but likely requires
+ network communication and thus introduces unpredictable delays.
+ Services that require clock accuracy and where network
+ communication delays are acceptable should use this target. Services that require a less accurate
+ clock, and only approximate and roughly monotonic clock behaviour should use
+ <filename>time-set.target</filename> instead.</para>
+
+ <para>Note that ordering a unit after <filename>time-sync.target</filename> only has effect if
+ there's actually a service ordered before it that delays it until clock synchronization is
+ reached. Otherwise, this target might get reached before the clock is synchronized to any remote
+ accurate reference clock. When using
+ <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ enable
+ <citerefentry><refentrytitle>systemd-time-wait-sync.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ to delay the target; or use an equivalent service for other NTP implementations.</para>
+
+ <table>
+ <title>Comparison</title>
+ <tgroup cols='2' align='left' colsep='1' rowsep='1'>
+ <colspec colname="time-set" />
+ <colspec colname="time-sync" />
+ <thead>
+ <row>
+ <entry><filename>time-set.target</filename></entry>
+ <entry><filename>time-sync.target</filename></entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>"quick" to reach</entry>
+ <entry>"slow" to reach</entry>
+ </row>
+ <row>
+ <entry>typically uses local clock sources, boot process not affected by availability of external resources</entry>
+ <entry>typically uses remote clock sources, inserts dependencies on remote resources into boot process</entry>
+ </row>
+ <row>
+ <entry>reliable, because local</entry>
+ <entry>unreliable, because typically network involved</entry>
+ </row>
+ <row>
+ <entry>typically guarantees an approximate and roughly monotonic clock only</entry>
+ <entry>typically guarantees an accurate clock</entry>
+ </row>
+ <row>
+ <entry>implemented by <filename>systemd-timesyncd.service</filename></entry>
+ <entry>implemented by <filename>systemd-time-wait-sync.service</filename></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect2>
+
+ <refsect2>
+ <title>Special Slice Units</title>
+
+ <para>There are four <literal>.slice</literal> units which form the basis of the hierarchy for
+ assignment of resources for services, users, and virtual machines or containers. See
+ <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ for details about slice units.</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><filename>-.slice</filename></term>
+ <listitem>
+ <para>The root slice is the root of the slice hierarchy. It usually does not contain
+ units directly, but may be used to set defaults for the whole tree.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>system.slice</filename></term>
+ <listitem>
+ <para>By default, all system services started by
+ <command>systemd</command> are found in this slice.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>user.slice</filename></term>
+ <listitem>
+ <para>By default, all user processes and services started on
+ behalf of the user, including the per-user systemd instance
+ are found in this slice. This is pulled in by
+ <filename>systemd-logind.service</filename>.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>machine.slice</filename></term>
+ <listitem>
+ <para>By default, all virtual machines and containers
+ registered with <command>systemd-machined</command> are
+ found in this slice. This is pulled in by
+ <filename>systemd-machined.service</filename>.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect2>
+ </refsect1>
+
+ <refsect1>
+ <title>Units managed by the user service manager</title>
+
+ <refsect2>
+ <title>Special User Units</title>
+
+ <para>When systemd runs as a user instance, the following special
+ units are available:</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><filename>default.target</filename></term>
+ <listitem>
+ <para>This is the main target of the user session, started by default. Various services that
+ compose the normal user session should be pulled into this target. In this regard,
+ <filename>default.target</filename> is similar to <filename>multi-user.target</filename> in the
+ system instance, but it is a real unit, not an alias.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+ <para>In addition, the following units are available which have definitions similar to their
+ system counterparts:
+ <filename>exit.target</filename>,
+ <filename>shutdown.target</filename>,
+ <filename>sockets.target</filename>,
+ <filename>timers.target</filename>,
+ <filename>paths.target</filename>,
+ <filename>bluetooth.target</filename>,
+ <filename>printer.target</filename>,
+ <filename>smartcard.target</filename>,
+ <filename>sound.target</filename>.</para>
+ </refsect2>
+
+ <refsect2>
+ <title>Special Passive User Units</title>
+
+ <variablelist>
+ <varlistentry>
+ <term><filename>graphical-session.target</filename></term>
+ <listitem>
+ <para>This target is active whenever any graphical session is running. It is used to
+ stop user services which only apply to a graphical (X, Wayland, etc.) session when the
+ session is terminated. Such services should have
+ <literal>PartOf=graphical-session.target</literal> in their [Unit]
+ section. A target for a particular session (e. g.
+ <filename>gnome-session.target</filename>) starts and stops
+ <literal>graphical-session.target</literal> with
+ <literal>BindsTo=graphical-session.target</literal>.</para>
+
+ <para>Which services are started by a session target is determined by the
+ <literal>Wants=</literal> and <literal>Requires=</literal> dependencies. For services
+ that can be enabled independently, symlinks in <literal>.wants/</literal> and
+ <literal>.requires/</literal> should be used, see
+ <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+ Those symlinks should either be shipped in packages, or should be added dynamically
+ after installation, for example using <literal>systemctl add-wants</literal>, see
+ <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
+ </para>
+
+ <example>
+ <title>Nautilus as part of a GNOME session</title>
+
+ <para><literal>gnome-session.target</literal> pulls in Nautilus as top-level service:</para>
+
+ <programlisting>[Unit]
+Description=User systemd services for GNOME graphical session
+Wants=nautilus.service
+BindsTo=graphical-session.target</programlisting>
+
+ <para><literal>nautilus.service</literal> gets stopped when the session stops:</para>
+
+ <programlisting>[Unit]
+Description=Render the desktop icons with Nautilus
+PartOf=graphical-session.target
+
+[Service]
+…</programlisting>
+ </example>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>graphical-session-pre.target</filename></term>
+ <listitem>
+ <para>This target contains services which set up the environment or global configuration
+ of a graphical session, such as SSH/GPG agents (which need to export an environment
+ variable into all desktop processes) or migration of obsolete d-conf keys after an OS
+ upgrade (which needs to happen before starting any process that might use them). This
+ target must be started before starting a graphical session like
+ <filename>gnome-session.target</filename>.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>xdg-desktop-autostart.target</filename></term>
+ <listitem>
+ <para>The XDG specification defines a way to autostart applications using XDG desktop files.
+ systemd ships
+ <citerefentry><refentrytitle>systemd-xdg-autostart-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for the XDG desktop files in autostart directories. Desktop Environments can opt-in to use this
+ service by adding a <varname>Wants=</varname> dependency on
+ <filename>xdg-desktop-autostart.target</filename>.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect2>
+
+ <refsect2>
+ <title>Special User Slice Units</title>
+
+ <para>There are four <literal>.slice</literal> units which form the basis of the user hierarchy for
+ assignment of resources for user applications and services. See
+ <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ for details about slice units and the documentation about
+ <ulink url="https://systemd.io/DESKTOP_ENVIRONMENTS">Desktop Environments</ulink>
+ for further information.</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><filename>-.slice</filename></term>
+ <listitem>
+ <para>The root slice is the root of the user's slice hierarchy.
+ It usually does not contain units directly, but may be used to set defaults for the whole tree.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>app.slice</filename></term>
+ <listitem>
+ <para>By default, all user services and applications managed by
+ <command>systemd</command> are found in this slice.
+ All interactively launched applications like web browsers and text editors
+ as well as non-critical services should be placed into this slice.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>session.slice</filename></term>
+ <listitem>
+ <para>All essential services and applications required for the
+ session should use this slice.
+ These are services that either cannot be restarted easily
+ or where latency issues may affect the interactivity of the system and applications.
+ This includes the display server, screen readers and other services such as DBus or XDG portals.
+ Such services should be configured to be part of this slice by
+ adding <varname>Slice=session.slice</varname> to their unit files.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>background.slice</filename></term>
+ <listitem>
+ <para>All services running low-priority background tasks should use this slice.
+ This permits resources to be preferentially assigned to the other slices.
+ Examples include non-interactive tasks like file indexing or backup operations
+ where latency is not important.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect2>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>user@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>