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| Copyright 2010 Lennart Poettering |
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| |
| <refentry id="systemd.special"> |
| |
| <refentryinfo> |
| <title>systemd.special</title> |
| <productname>systemd</productname> |
| |
| <authorgroup> |
| <author> |
| <contrib>Developer</contrib> |
| <firstname>Lennart</firstname> |
| <surname>Poettering</surname> |
| <email>lennart@poettering.net</email> |
| </author> |
| </authorgroup> |
| </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>ctrl-alt-del.target</filename>, |
| <filename>default.target</filename>, |
| <filename>emergency.target</filename>, |
| <filename>exit.target</filename>, |
| <filename>final.target</filename>, |
| <filename>getty.target</filename>, |
| <filename>graphical.target</filename>, |
| <filename>halt.target</filename>, |
| <filename>hibernate.target</filename>, |
| <filename>hybrid-sleep.target</filename>, |
| <filename>initrd-fs.target</filename>, |
| <filename>initrd-root-device.target</filename>, |
| <filename>initrd-root-fs.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-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>syslog.socket</filename>, |
| <filename>system-update.target</filename>, |
| <filename>time-sync.target</filename>, |
| <filename>timers.target</filename>, |
| <filename>umount.target</filename>, |
| <!-- slices --> |
| <filename>-.slice</filename>, |
| <filename>system.slice</filename>, |
| <filename>user.slice</filename>, |
| <filename>machine.slice</filename>, |
| <!-- the rest --> |
| <filename>dbus.service</filename>, |
| <filename>dbus.socket</filename>, |
| <filename>display-manager.service</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>Special System Units</title> |
| |
| <variablelist> |
| <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>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>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>.</para> |
| |
| <para>The default unit systemd starts at bootup can be |
| overridden with the <varname>systemd.unit=</varname> kernel |
| command line option.</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 |
| any 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 is supposed to be used with the kernel command line option |
| <varname>systemd.unit=</varname>; 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>Use the <literal>systemd.unit=emergency.target</literal> kernel command line option to boot into this |
| mode. A short alias for this kernel command line option is <literal>emergency</literal>, for compatibility |
| with SysV.</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> |
| </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 a |
| request to shut down over D-Bus or a |
| <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>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 |
| <literal>[Install]</literal> 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>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 start |
| this unit.</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 |
| <option>x-initrd.mount</option> and not have |
| <option>noauto</option> mount options set.</para> |
| </listitem> |
| </varlistentry> |
| <varlistentry> |
| <term><filename>kbrequest.target</filename></term> |
| <listitem> |
| <para>systemd starts this target whenever Alt+ArrowUp is |
| pressed on the console. This is a good candidate to be |
| aliased (symlinked) to |
| <filename>rescue.target</filename>.</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 with kexec |
| should start this unit.</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> |
| <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>$local_fs</literal> |
| facility.</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 |
| <literal>[Install]</literal> 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://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">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 provide |
| functionality to other hosts generally do not need to pull |
| this in.</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 |
| <literal>[Install]</literal> 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 |
| start this unit.</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 start |
| this unit.</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-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.</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>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. |
| </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 be active after boot. By default the generic <filename>user.slice</filename>, |
| <filename>system.slice</filename>, <filename>machines.slice</filename> slice units, as well as the root |
| slice unit <filename>-.slice</filename> are pulled in and ordered before this unit (see below).</para> |
| |
| <para>It's a good idea to add <varname>WantedBy=slices.target</varname> lines to the <literal>[Install]</literal> |
| section of all slices units that may be installed dynamically.</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 <literal>[Install]</literal> |
| 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-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. 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 <literal>[Install]</literal> 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> |
| </refsect1> |
| |
| <refsect1> |
| <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> |
| </variablelist> |
| </refsect1> |
| |
| <refsect1> |
| <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>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>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, with one exception: |
| 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 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://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running |
| Services After the Network is up</ulink> for more |
| information. Also see |
| <filename>network-online.target</filename> described |
| above.</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>$network</literal> facility.</para> |
| </listitem> |
| </varlistentry> |
| <varlistentry> |
| <term><filename>network-pre.target</filename></term> |
| <listitem> |
| <para>This passive target unit may be pulled in by services |
| that want to run before any network is set up, for example |
| for the purpose of setting up a firewall. All network |
| management software orders itself after this target, but |
| does not pull it in.</para> |
| </listitem> |
| </varlistentry> |
| <varlistentry> |
| <term><filename>nss-lookup.target</filename></term> |
| <listitem> |
| <para>A target that should be used as synchronization point |
| for all host/network name service lookups. Note that this is |
| independent of user/group name lookups for which |
| <filename>nss-user-lookup.target</filename> should be used. |
| All services for which the availability of full host/network |
| name resolution is essential should be ordered after this |
| target, but not pull it in. systemd automatically adds |
| dependencies of type <varname>After=</varname> for this |
| target unit to all SysV init script service units with an |
| LSB header referring to the <literal>$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 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. Note that system users are always |
| resolvable, and hence do not require 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 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>$portmap</literal> facility.</para> |
| </listitem> |
| </varlistentry> |
| <varlistentry> |
| <term><filename>time-sync.target</filename></term> |
| <listitem> |
| <para>Services responsible for synchronizing the system |
| clock from a remote source (such as NTP client |
| implementations) should pull in this target and order |
| themselves before it. All services where correct time is |
| essential should be ordered after this unit, but not pull it |
| in. systemd automatically adds dependencies of type |
| <varname>After=</varname> for this target unit to all SysV |
| init script service units with an LSB header referring to |
| the <literal>$time</literal> facility. </para> |
| </listitem> |
| </varlistentry> |
| </variablelist> |
| </refsect1> |
| |
| <refsect1> |
| <title>Special User Units</title> |
| |
| <para>When systemd runs as a user instance, the following special |
| units are available, which have similar definitions as their |
| system counterparts: |
| <filename>exit.target</filename>, |
| <filename>default.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> |
| </refsect1> |
| |
| <refsect1> |
| <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 <literal>[Unit]</literal> 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> |
| </variablelist> |
| |
| </refsect1> |
| |
| <refsect1> |
| <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.</para> |
| |
| <variablelist> |
| <varlistentry> |
| <term><filename>-.slice</filename></term> |
| <listitem> |
| <para>The root slice is the root of the 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.</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. |
| </para> |
| </listitem> |
| </varlistentry> |
| </variablelist> |
| </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 project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| </para> |
| </refsect1> |
| |
| </refentry> |