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diff --git a/man/systemd.special.xml b/man/systemd.special.xml new file mode 100644 index 0000000..85eb8ad --- /dev/null +++ b/man/systemd.special.xml @@ -0,0 +1,1391 @@ +<?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> |