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diff --git a/man/systemd.special.xml b/man/systemd.special.xml new file mode 100644 index 0000000..fd5639b --- /dev/null +++ b/man/systemd.special.xml @@ -0,0 +1,1109 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<!-- + SPDX-License-Identifier: LGPL-2.1+ +--> + +<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>ctrl-alt-del.target</filename>, + <filename>boot-complete.target</filename>, + <filename>default.target</filename>, + <filename>emergency.target</filename>, + <filename>exit.target</filename>, + <filename>final.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-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>system-update.target</filename>, + <filename>system-update-pre.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>-.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's 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>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 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>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>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-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>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>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 + <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> + + <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 + <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 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-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 <literal>[Install]</literal> + 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 <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-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 <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> + </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> + </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>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>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, 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> + </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 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 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> + </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's service manager</title> + + <refsect2> + <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> + </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 <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> + </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> |