| <?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> |
