man/systemd.special.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7 -->
   8
   9 <refentry id="systemd.special">
  10
  11   <refentryinfo>
  12     <title>systemd.special</title>
  13     <productname>systemd</productname>
  14   </refentryinfo>
  15
  16   <refmeta>
  17     <refentrytitle>systemd.special</refentrytitle>
  18     <manvolnum>7</manvolnum>
  19   </refmeta>
  20
  21   <refnamediv>
  22     <refname>systemd.special</refname>
  23     <refpurpose>Special systemd units</refpurpose>
  24   </refnamediv>
  25
  26   <refsynopsisdiv><para>
  27     <!-- sort alphabetically, targets first --><filename>basic.target</filename>,
  28     <filename>bluetooth.target</filename>,
  29     <filename>cryptsetup-pre.target</filename>,
  30     <filename>cryptsetup.target</filename>,
  31     <filename>ctrl-alt-del.target</filename>,
  32     <filename>boot-complete.target</filename>,
  33     <filename>default.target</filename>,
  34     <filename>emergency.target</filename>,
  35     <filename>exit.target</filename>,
  36     <filename>final.target</filename>,
  37     <filename>getty.target</filename>,
  38     <filename>getty-pre.target</filename>,
  39     <filename>graphical.target</filename>,
  40     <filename>halt.target</filename>,
  41     <filename>hibernate.target</filename>,
  42     <filename>hybrid-sleep.target</filename>,
  43     <filename>suspend-then-hibernate.target</filename>,
  44     <filename>initrd-fs.target</filename>,
  45     <filename>initrd-root-device.target</filename>,
  46     <filename>initrd-root-fs.target</filename>,
  47     <filename>kbrequest.target</filename>,
  48     <filename>kexec.target</filename>,
  49     <filename>local-fs-pre.target</filename>,
  50     <filename>local-fs.target</filename>,
  51     <filename>machines.target</filename>
  52     <filename>multi-user.target</filename>,
  53     <filename>network-online.target</filename>,
  54     <filename>network-pre.target</filename>,
  55     <filename>network.target</filename>,
  56     <filename>nss-lookup.target</filename>,
  57     <filename>nss-user-lookup.target</filename>,
  58     <filename>paths.target</filename>,
  59     <filename>poweroff.target</filename>,
  60     <filename>printer.target</filename>,
  61     <filename>reboot.target</filename>,
  62     <filename>remote-cryptsetup.target</filename>,
  63     <filename>remote-fs-pre.target</filename>,
  64     <filename>remote-fs.target</filename>,
  65     <filename>rescue.target</filename>,
  66     <filename>rpcbind.target</filename>,
  67     <filename>runlevel2.target</filename>,
  68     <filename>runlevel3.target</filename>,
  69     <filename>runlevel4.target</filename>,
  70     <filename>runlevel5.target</filename>,
  71     <filename>shutdown.target</filename>,
  72     <filename>sigpwr.target</filename>,
  73     <filename>sleep.target</filename>,
  74     <filename>slices.target</filename>,
  75     <filename>smartcard.target</filename>,
  76     <filename>sockets.target</filename>,
  77     <filename>sound.target</filename>,
  78     <filename>suspend.target</filename>,
  79     <filename>swap.target</filename>,
  80     <filename>sysinit.target</filename>,
  81     <filename>system-update.target</filename>,
  82     <filename>system-update-pre.target</filename>,
  83     <filename>time-sync.target</filename>,
  84     <filename>timers.target</filename>,
  85     <filename>umount.target</filename>,
  86     <!-- slices --><filename>-.slice</filename>,
  87     <filename>system.slice</filename>,
  88     <filename>user.slice</filename>,
  89     <filename>machine.slice</filename>,
  90     <!-- the rest --><filename>-.mount</filename>,
  91     <filename>dbus.service</filename>,
  92     <filename>dbus.socket</filename>,
  93     <filename>display-manager.service</filename>,
  94     <filename>init.scope</filename>,
  95     <filename>syslog.socket</filename>,
  96     <filename>system-update-cleanup.service</filename>
  97   </para></refsynopsisdiv>
  98
  99   <refsect1>
 100     <title>Description</title>
 101
 102     <para>A few units are treated specially by systemd. Many of them have
 103     special internal semantics and cannot be renamed, while others simply
 104     have a standard meaning and should be present on all systems.</para>
 105   </refsect1>
 106
 107   <refsect1>
 108     <title>Units managed by the system's service manager</title>
 109
 110     <refsect2>
 111       <title>Special System Units</title>
 112
 113       <variablelist>
 114         <varlistentry>
 115           <term><filename>-.mount</filename></term>
 116           <listitem>
 117             <para>The root mount point, i.e. the mount unit for the <filename>/</filename>
 118             path. This unit is unconditionally active, during the entire time the system is up, as
 119             this mount point is where the basic userspace is running from.</para>
 120           </listitem>
 121         </varlistentry>
 122
 123         <varlistentry>
 124           <term><filename>basic.target</filename></term>
 125           <listitem>
 126             <para>A special target unit covering basic boot-up.</para>
 127
 128             <para>systemd automatically adds dependency of the type
 129             <varname>After=</varname> for this target unit to all
 130             services (except for those with
 131             <varname>DefaultDependencies=no</varname>).</para>
 132
 133             <para>Usually, this should pull-in all local mount points plus
 134             <filename>/var</filename>, <filename>/tmp</filename> and
 135             <filename>/var/tmp</filename>, swap devices, sockets, timers,
 136             path units and other basic initialization necessary for general
 137             purpose daemons. The mentioned mount points are special cased
 138             to allow them to be remote.
 139             </para>
 140
 141             <para>This target usually does not pull in any non-target units
 142             directly, but rather does so indirectly via other early boot targets.
 143             It is instead meant as a synchronization point for late boot
 144             services. Refer to
 145             <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 146             for details on the targets involved.
 147             </para>
 148           </listitem>
 149         </varlistentry>
 150         <varlistentry>
 151           <term><filename>boot-complete.target</filename></term>
 152           <listitem>
 153             <para>This target is intended as generic synchronization point for services that shall determine or act on
 154             whether the boot process completed successfully. Order units that are required to succeed for a boot process
 155             to be considered successful before this unit, and add a <varname>Requires=</varname> dependency from the
 156             target unit to them. Order units that shall only run when the boot process is considered successful after the
 157             target unit and pull in the target from it, also with <varname>Requires=</varname>. Note that by default this
 158             target unit is not part of the initial boot transaction, but is supposed to be pulled in only if required by
 159             units that want to run only on successful boots.</para>
 160
 161             <para>See
 162             <citerefentry><refentrytitle>systemd-boot-check-no-failures.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 163             for a service that implements a generic system health check and orders itself before
 164             <filename>boot-complete.target</filename>.</para>
 165
 166             <para>See
 167             <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 168             for a service that propagates boot success information to the boot loader, and orders itself after
 169             <filename>boot-complete.target</filename>.</para>
 170           </listitem>
 171         </varlistentry>
 172         <varlistentry>
 173           <term><filename>ctrl-alt-del.target</filename></term>
 174           <listitem>
 175             <para>systemd starts this target whenever Control+Alt+Del is
 176             pressed on the console. Usually, this should be aliased
 177             (symlinked) to <filename>reboot.target</filename>.</para>
 178           </listitem>
 179         </varlistentry>
 180         <varlistentry>
 181           <term><filename>cryptsetup.target</filename></term>
 182           <listitem>
 183             <para>A target that pulls in setup services for all
 184             encrypted block devices.</para>
 185           </listitem>
 186         </varlistentry>
 187         <varlistentry>
 188           <term><filename>dbus.service</filename></term>
 189           <listitem>
 190             <para>A special unit for the D-Bus bus daemon. As soon as
 191             this service is fully started up systemd will connect to it
 192             and register its service.</para>
 193           </listitem>
 194         </varlistentry>
 195         <varlistentry>
 196           <term><filename>dbus.socket</filename></term>
 197           <listitem>
 198             <para>A special unit for the D-Bus system bus socket. All
 199             units with <varname>Type=dbus</varname> automatically gain a
 200             dependency on this unit.</para>
 201           </listitem>
 202         </varlistentry>
 203         <varlistentry>
 204           <term><filename>default.target</filename></term>
 205           <listitem>
 206             <para>The default unit systemd starts at bootup. Usually,
 207             this should be aliased (symlinked) to
 208             <filename>multi-user.target</filename> or
 209             <filename>graphical.target</filename>.</para>
 210
 211             <para>The default unit systemd starts at bootup can be
 212             overridden with the <varname>systemd.unit=</varname> kernel
 213             command line option.</para>
 214           </listitem>
 215         </varlistentry>
 216         <varlistentry>
 217           <term><filename>display-manager.service</filename></term>
 218           <listitem>
 219             <para>The display manager service. Usually, this should be
 220             aliased (symlinked) to <filename>gdm.service</filename> or a
 221             similar display manager service.</para>
 222           </listitem>
 223         </varlistentry>
 224         <varlistentry>
 225           <term><filename>emergency.target</filename></term>
 226           <listitem>
 227             <para>A special target unit that starts an emergency shell on the main console. This
 228             target does not pull in any services or mounts. It is the most minimal version of
 229             starting the system in order to acquire an interactive shell; the only processes running
 230             are usually just the system manager (PID 1) and the shell process. This unit is supposed
 231             to be used with the kernel command line option <varname>systemd.unit=</varname>; it is
 232             also used when a file system check on a required file system fails, and boot-up cannot
 233             continue. Compare with <filename>rescue.target</filename>, which serves a similar
 234             purpose, but also starts the most basic services and mounts all file systems.</para>
 235
 236             <para>Use the <literal>systemd.unit=emergency.target</literal> kernel command line
 237             option to boot into this mode. A short alias for this kernel command line option is
 238             <literal>emergency</literal>, for compatibility with SysV.</para>
 239
 240             <para>In many ways booting into <filename>emergency.target</filename> is similar to the
 241             effect of booting with <literal>init=/bin/sh</literal> on the kernel command line,
 242             except that emergency mode provides you with the full system and service manager, and
 243             allows starting individual units in order to continue the boot process in steps.</para>
 244           </listitem>
 245         </varlistentry>
 246         <varlistentry>
 247           <term><filename>exit.target</filename></term>
 248           <listitem>
 249             <para>A special service unit for shutting down the system or
 250             user service manager. It is equivalent to
 251             <filename>poweroff.target</filename> on non-container
 252             systems, and also works in containers.</para>
 253
 254             <para>systemd will start this unit when it receives the
 255             <constant>SIGTERM</constant> or <constant>SIGINT</constant>
 256             signal when running as user service daemon.</para>
 257
 258             <para>Normally, this (indirectly) pulls in
 259             <filename>shutdown.target</filename>, which in turn should be
 260             conflicted by all units that want to be scheduled for
 261             shutdown when the service manager starts to exit.</para>
 262           </listitem>
 263         </varlistentry>
 264         <varlistentry>
 265           <term><filename>final.target</filename></term>
 266           <listitem>
 267             <para>A special target unit that is used during the shutdown
 268             logic and may be used to pull in late services after all
 269             normal services are already terminated and all mounts
 270             unmounted.
 271             </para>
 272           </listitem>
 273         </varlistentry>
 274         <varlistentry>
 275           <term><filename>getty.target</filename></term>
 276           <listitem>
 277             <para>A special target unit that pulls in statically
 278             configured local TTY <filename>getty</filename> instances.
 279             </para>
 280           </listitem>
 281         </varlistentry>
 282         <varlistentry>
 283           <term><filename>graphical.target</filename></term>
 284           <listitem>
 285             <para>A special target unit for setting up a graphical login
 286             screen. This pulls in
 287             <filename>multi-user.target</filename>.</para>
 288
 289             <para>Units that are needed for graphical logins shall add
 290             <varname>Wants=</varname> dependencies for their unit to
 291             this unit (or <filename>multi-user.target</filename>) during
 292             installation. This is best configured via
 293             <varname>WantedBy=graphical.target</varname> in the unit's
 294             <literal>[Install]</literal> section.</para>
 295           </listitem>
 296         </varlistentry>
 297         <varlistentry>
 298           <term><filename>hibernate.target</filename></term>
 299           <listitem>
 300             <para>A special target unit for hibernating the system. This
 301             pulls in <filename>sleep.target</filename>.</para>
 302           </listitem>
 303         </varlistentry>
 304         <varlistentry>
 305           <term><filename>hybrid-sleep.target</filename></term>
 306           <listitem>
 307             <para>A special target unit for hibernating and suspending
 308             the system at the same time. This pulls in
 309             <filename>sleep.target</filename>.</para>
 310           </listitem>
 311         </varlistentry>
 312         <varlistentry>
 313           <term><filename>suspend-then-hibernate.target</filename></term>
 314           <listitem>
 315             <para>A special target unit for suspending the system for a period
 316             of time, waking it and putting it into hibernate. This pulls in
 317             <filename>sleep.target</filename>.</para>
 318           </listitem>
 319         </varlistentry>
 320
 321         <varlistentry>
 322           <term><filename>halt.target</filename></term>
 323           <listitem>
 324             <para>A special target unit for shutting down and halting
 325             the system. Note that this target is distinct from
 326             <filename>poweroff.target</filename> in that it generally
 327             really just halts the system rather than powering it
 328             down.</para>
 329
 330             <para>Applications wanting to halt the system should not start this unit
 331             directly, but should instead execute <command>systemctl halt</command>
 332             (possibly with the <option>--no-block</option> option) or call
 333             <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 334             <command>org.freedesktop.systemd1.Manager.Halt</command> D-Bus method
 335             directly.</para>
 336           </listitem>
 337         </varlistentry>
 338         <varlistentry>
 339           <term><filename>init.scope</filename></term>
 340           <listitem>
 341             <para>This scope unit is where the system and service manager (PID 1) itself resides. It
 342             is active as long as the system is running.</para>
 343           </listitem>
 344         </varlistentry>
 345         <varlistentry>
 346           <term><filename>initrd-fs.target</filename></term>
 347           <listitem>
 348             <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 349             automatically adds dependencies of type
 350             <varname>Before=</varname> to
 351             <filename>sysroot-usr.mount</filename> and all mount points
 352             found in <filename>/etc/fstab</filename> that have
 353             <option>x-initrd.mount</option> and not have
 354             <option>noauto</option> mount options set.</para>
 355           </listitem>
 356         </varlistentry>
 357         <varlistentry>
 358           <term><filename>initrd-root-device.target</filename></term>
 359           <listitem>
 360             <para>A special initrd target unit that is reached when the root filesystem device is available, but before
 361             it has been mounted.
 362             <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 363             and
 364             <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 365             automatically setup the appropriate dependencies to make this happen.
 366             </para>
 367           </listitem>
 368         </varlistentry>
 369         <varlistentry>
 370           <term><filename>initrd-root-fs.target</filename></term>
 371           <listitem>
 372             <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 373             automatically adds dependencies of type
 374             <varname>Before=</varname> to the
 375             <filename>sysroot.mount</filename> unit, which is generated
 376             from the kernel command line.
 377             </para>
 378           </listitem>
 379         </varlistentry>
 380         <varlistentry>
 381           <term><filename>kbrequest.target</filename></term>
 382           <listitem>
 383             <para>systemd starts this target whenever Alt+ArrowUp is
 384             pressed on the console. Note that any user with physical access
 385             to the machine will be able to do this, without authentication,
 386             so this should be used carefully.</para>
 387           </listitem>
 388         </varlistentry>
 389         <varlistentry>
 390           <term><filename>kexec.target</filename></term>
 391           <listitem>
 392             <para>A special target unit for shutting down and rebooting
 393             the system via kexec.</para>
 394
 395             <para>Applications wanting to reboot the system should not start this unit
 396             directly, but should instead execute <command>systemctl kexec</command>
 397             (possibly with the <option>--no-block</option> option) or call
 398             <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 399             <command>org.freedesktop.systemd1.Manager.KExec</command> D-Bus method
 400             directly.</para>
 401           </listitem>
 402         </varlistentry>
 403         <varlistentry>
 404           <term><filename>local-fs.target</filename></term>
 405           <listitem>
 406             <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 407             automatically adds dependencies of type
 408             <varname>Before=</varname> to all mount units that refer to
 409             local mount points for this target unit. In addition, it
 410             adds dependencies of type <varname>Wants=</varname> to this
 411             target unit for those mounts listed in
 412             <filename>/etc/fstab</filename> that have the
 413             <option>auto</option> mount option set.</para>
 414           </listitem>
 415         </varlistentry>
 416         <varlistentry>
 417           <term><filename>machines.target</filename></term>
 418           <listitem>
 419             <para>A standard target unit for starting all the containers
 420             and other virtual machines. See <filename>systemd-nspawn@.service</filename>
 421             for an example.</para>
 422           </listitem>
 423         </varlistentry>
 424         <varlistentry>
 425           <term><filename>multi-user.target</filename></term>
 426           <listitem>
 427             <para>A special target unit for setting up a multi-user
 428             system (non-graphical). This is pulled in by
 429             <filename>graphical.target</filename>.</para>
 430
 431             <para>Units that are needed for a multi-user system shall
 432             add <varname>Wants=</varname> dependencies for their unit to
 433             this unit during installation. This is best configured via
 434             <varname>WantedBy=multi-user.target</varname> in the unit's
 435             <literal>[Install]</literal> section.</para>
 436           </listitem>
 437         </varlistentry>
 438         <varlistentry>
 439           <term><filename>network-online.target</filename></term>
 440           <listitem>
 441             <para>Units that strictly require a configured network
 442             connection should pull in
 443             <filename>network-online.target</filename> (via a
 444             <varname>Wants=</varname> type dependency) and order
 445             themselves after it. This target unit is intended to pull in
 446             a service that delays further execution until the network is
 447             sufficiently set up. What precisely this requires is left to
 448             the implementation of the network managing service.</para>
 449
 450             <para>Note the distinction between this unit and
 451             <filename>network.target</filename>. This unit is an active
 452             unit (i.e. pulled in by the consumer rather than the
 453             provider of this functionality) and pulls in a service which
 454             possibly adds substantial delays to further execution. In
 455             contrast, <filename>network.target</filename> is a passive
 456             unit (i.e. pulled in by the provider of the functionality,
 457             rather than the consumer) that usually does not delay
 458             execution much. Usually, <filename>network.target</filename>
 459             is part of the boot of most systems, while
 460             <filename>network-online.target</filename> is not, except
 461             when at least one unit requires it. Also see <ulink
 462             url="https://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 463             Services After the Network is up</ulink> for more
 464             information.</para>
 465
 466             <para>All mount units for remote network file systems
 467             automatically pull in this unit, and order themselves after
 468             it. Note that networking daemons that simply provide
 469             functionality to other hosts generally do not need to pull
 470             this in.</para>
 471
 472             <para>systemd automatically adds dependencies of type <varname>Wants=</varname> and
 473             <varname>After=</varname> for this target unit to all SysV init script service units
 474             with an LSB header referring to the <literal>$network</literal> facility.</para>
 475
 476             <para>Note that this unit is only useful during the original system start-up
 477             logic. After the system has completed booting up, it will not track the online state of
 478             the system anymore. Due to this it cannot be used as a network connection monitor
 479             concept, it is purely a one-time system start-up concept.</para>
 480             </listitem>
 481         </varlistentry>
 482         <varlistentry>
 483           <term><filename>paths.target</filename></term>
 484           <listitem>
 485             <para>A special target unit that sets up all path units (see
 486             <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 487             for details) that shall be active after boot.</para>
 488
 489             <para>It is recommended that path units installed by
 490             applications get pulled in via <varname>Wants=</varname>
 491             dependencies from this unit. This is best configured via a
 492             <varname>WantedBy=paths.target</varname> in the path unit's
 493             <literal>[Install]</literal> section.</para>
 494           </listitem>
 495         </varlistentry>
 496         <varlistentry>
 497           <term><filename>poweroff.target</filename></term>
 498           <listitem>
 499             <para>A special target unit for shutting down and powering
 500             off the system.</para>
 501
 502             <para>Applications wanting to power off the system should not start this unit
 503             directly, but should instead execute <command>systemctl poweroff</command>
 504             (possibly with the <option>--no-block</option> option) or call
 505             <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
 506             <command>org.freedesktop.login1.Manager.PowerOff</command> D-Bus method
 507             directly.</para>
 508
 509             <para><filename>runlevel0.target</filename> is an alias for
 510             this target unit, for compatibility with SysV.</para>
 511           </listitem>
 512         </varlistentry>
 513         <varlistentry>
 514           <term><filename>reboot.target</filename></term>
 515           <listitem>
 516             <para>A special target unit for shutting down and rebooting
 517             the system.</para>
 518
 519             <para>Applications wanting to reboot the system should not start this unit
 520             directly, but should instead execute <command>systemctl reboot</command>
 521             (possibly with the <option>--no-block</option> option) or call
 522             <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
 523             <command>org.freedesktop.login1.Manager.Reboot</command> D-Bus method
 524             directly.</para>
 525
 526             <para><filename>runlevel6.target</filename> is an alias for
 527             this target unit, for compatibility with SysV.</para>
 528           </listitem>
 529         </varlistentry>
 530         <varlistentry>
 531           <term><filename>remote-cryptsetup.target</filename></term>
 532           <listitem>
 533             <para>Similar to <filename>cryptsetup.target</filename>, but for encrypted
 534             devices which are accessed over the network. It is used for
 535             <citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 536             entries marked with <option>_netdev</option>.</para>
 537           </listitem>
 538         </varlistentry>
 539         <varlistentry>
 540           <term><filename>remote-fs.target</filename></term>
 541           <listitem>
 542             <para>Similar to <filename>local-fs.target</filename>, but
 543             for remote mount points.</para>
 544
 545             <para>systemd automatically adds dependencies of type
 546             <varname>After=</varname> for this target unit to all SysV
 547             init script service units with an LSB header referring to
 548             the <literal>$remote_fs</literal> facility.</para>
 549           </listitem>
 550         </varlistentry>
 551         <varlistentry>
 552           <term><filename>rescue.target</filename></term>
 553           <listitem>
 554             <para>A special target unit that pulls in the base system (including system mounts) and
 555             spawns a rescue shell. Isolate to this target in order to administer the system in
 556             single-user mode with all file systems mounted but with no services running, except for
 557             the most basic. Compare with <filename>emergency.target</filename>, which is much more
 558             reduced and does not provide the file systems or most basic services. Compare with
 559             <filename>multi-user.target</filename>, this target could be seen as
 560             <filename>single-user.target</filename>.</para>
 561
 562             <para><filename>runlevel1.target</filename> is an alias for this target unit, for
 563             compatibility with SysV.</para>
 564
 565             <para>Use the <literal>systemd.unit=rescue.target</literal> kernel command line option
 566             to boot into this mode. A short alias for this kernel command line option is
 567             <literal>1</literal>, for compatibility with SysV.</para>
 568           </listitem>
 569         </varlistentry>
 570         <varlistentry>
 571           <term><filename>runlevel2.target</filename></term>
 572           <term><filename>runlevel3.target</filename></term>
 573           <term><filename>runlevel4.target</filename></term>
 574           <term><filename>runlevel5.target</filename></term>
 575           <listitem>
 576             <para>These are targets that are called whenever the SysV
 577             compatibility code asks for runlevel 2, 3, 4, 5,
 578             respectively. It is a good idea to make this an alias for
 579             (i.e. symlink to) <filename>graphical.target</filename>
 580             (for runlevel 5) or <filename>multi-user.target</filename>
 581             (the others).</para>
 582           </listitem>
 583         </varlistentry>
 584         <varlistentry>
 585           <term><filename>shutdown.target</filename></term>
 586           <listitem>
 587             <para>A special target unit that terminates the services on
 588             system shutdown.</para>
 589
 590             <para>Services that shall be terminated on system shutdown
 591             shall add <varname>Conflicts=</varname> and
 592             <varname>Before=</varname> dependencies to this unit for
 593             their service unit, which is implicitly done when
 594             <varname>DefaultDependencies=yes</varname> is set (the
 595             default).</para>
 596           </listitem>
 597         </varlistentry>
 598         <varlistentry>
 599           <term><filename>sigpwr.target</filename></term>
 600           <listitem>
 601             <para>A special target that is started when systemd receives
 602             the SIGPWR process signal, which is normally sent by the
 603             kernel or UPS daemons when power fails.</para>
 604           </listitem>
 605         </varlistentry>
 606         <varlistentry>
 607           <term><filename>sleep.target</filename></term>
 608           <listitem>
 609             <para>A special target unit that is pulled in by
 610             <filename>suspend.target</filename>,
 611             <filename>hibernate.target</filename> and
 612             <filename>hybrid-sleep.target</filename> and may be used to
 613             hook units into the sleep state logic.</para>
 614           </listitem>
 615         </varlistentry>
 616         <varlistentry>
 617           <term><filename>slices.target</filename></term>
 618           <listitem>
 619             <para>A special target unit that sets up all slice units (see
 620             <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 621             for details) that shall always be active after boot. By default the generic
 622             <filename>system.slice</filename> slice unit as well as the root slice unit
 623             <filename>-.slice</filename> are pulled in and ordered before this unit (see
 624             below).</para>
 625
 626             <para>Adding slice units to <filename>slices.target</filename> is generally not
 627             necessary. Instead, when some unit that uses <varname>Slice=</varname> is started, the
 628             specified slice will be started automatically. Adding
 629             <varname>WantedBy=slices.target</varname> lines to the <literal>[Install]</literal>
 630             section should only be done for units that need to be always active. In that case care
 631             needs to be taken to avoid creating a loop through the automatic dependencies on
 632             "parent" slices.</para>
 633           </listitem>
 634         </varlistentry>
 635         <varlistentry>
 636           <term><filename>sockets.target</filename></term>
 637           <listitem>
 638             <para>A special target unit that sets up all socket
 639             units (see
 640             <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 641             for details) that shall be active after boot.</para>
 642
 643             <para>Services that can be socket-activated shall add
 644             <varname>Wants=</varname> dependencies to this unit for
 645             their socket unit during installation. This is best
 646             configured via a <varname>WantedBy=sockets.target</varname>
 647             in the socket unit's <literal>[Install]</literal>
 648             section.</para>
 649           </listitem>
 650         </varlistentry>
 651         <varlistentry>
 652           <term><filename>suspend.target</filename></term>
 653           <listitem>
 654             <para>A special target unit for suspending the system. This
 655             pulls in <filename>sleep.target</filename>.</para>
 656           </listitem>
 657         </varlistentry>
 658         <varlistentry>
 659           <term><filename>swap.target</filename></term>
 660           <listitem>
 661             <para>Similar to <filename>local-fs.target</filename>, but
 662             for swap partitions and swap files.</para>
 663           </listitem>
 664         </varlistentry>
 665         <varlistentry>
 666           <term><filename>sysinit.target</filename></term>
 667           <listitem>
 668             <para>systemd automatically adds dependencies of the types
 669             <varname>Requires=</varname> and <varname>After=</varname>
 670             for this target unit to all services (except for those with
 671             <varname>DefaultDependencies=no</varname>).</para>
 672
 673             <para>This target pulls in the services required for system
 674             initialization. System services pulled in by this target should
 675             declare <varname>DefaultDependencies=no</varname> and specify
 676             all their dependencies manually, including access to anything
 677             more than a read only root filesystem. For details on the
 678             dependencies of this target, refer to
 679             <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 680             </para>
 681           </listitem>
 682         </varlistentry>
 683         <varlistentry>
 684           <term><filename>syslog.socket</filename></term>
 685           <listitem>
 686             <para>The socket unit syslog implementations should listen
 687             on. All userspace log messages will be made available on
 688             this socket. For more information about syslog integration,
 689             please consult the <ulink
 690             url="https://www.freedesktop.org/wiki/Software/systemd/syslog">Syslog
 691             Interface</ulink> document.</para>
 692           </listitem>
 693         </varlistentry>
 694         <varlistentry>
 695           <term><filename>system-update.target</filename></term>
 696           <term><filename>system-update-pre.target</filename></term>
 697           <term><filename>system-update-cleanup.service</filename></term>
 698           <listitem>
 699             <para>A special target unit that is used for offline system updates.
 700             <citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 701             will redirect the boot process to this target if <filename>/system-update</filename>
 702             exists. For more information see
 703             <citerefentry><refentrytitle>systemd.offline-updates</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 704             </para>
 705
 706             <para>Updates should happen before the <filename>system-update.target</filename> is
 707             reached, and the services which implement them should cause the machine to reboot. The
 708             main units executing the update should order themselves after
 709             <filename>system-update-pre.target</filename> but not pull it in. Services which want to
 710             run during system updates only, but before the actual system update is executed should
 711             order themselves before this unit and pull it in. As a safety measure, if this does not
 712             happen, and <filename>/system-update</filename> still exists after
 713             <filename>system-update.target</filename> is reached,
 714             <filename>system-update-cleanup.service</filename> will remove this symlink and reboot
 715             the machine.</para>
 716           </listitem>
 717         </varlistentry>
 718         <varlistentry>
 719           <term><filename>timers.target</filename></term>
 720           <listitem>
 721             <para>A special target unit that sets up all timer units
 722             (see
 723             <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 724             for details) that shall be active after boot.</para>
 725
 726             <para>It is recommended that timer units installed by
 727             applications get pulled in via <varname>Wants=</varname>
 728             dependencies from this unit. This is best configured via
 729             <varname>WantedBy=timers.target</varname> in the timer
 730             unit's <literal>[Install]</literal> section.</para>
 731           </listitem>
 732         </varlistentry>
 733         <varlistentry>
 734           <term><filename>umount.target</filename></term>
 735           <listitem>
 736             <para>A special target unit that unmounts all mount and
 737             automount points on system shutdown.</para>
 738
 739             <para>Mounts that shall be unmounted on system shutdown
 740             shall add Conflicts dependencies to this unit for their
 741             mount unit, which is implicitly done when
 742             <varname>DefaultDependencies=yes</varname> is set (the
 743             default).</para>
 744           </listitem>
 745         </varlistentry>
 746
 747       </variablelist>
 748     </refsect2>
 749
 750     <refsect2>
 751       <title>Special System Units for Devices</title>
 752
 753       <para>Some target units are automatically pulled in as devices of
 754       certain kinds show up in the system. These may be used to
 755       automatically activate various services based on the specific type
 756       of the available hardware.</para>
 757
 758       <variablelist>
 759         <varlistentry>
 760           <term><filename>bluetooth.target</filename></term>
 761           <listitem>
 762             <para>This target is started automatically as soon as a
 763             Bluetooth controller is plugged in or becomes available at
 764             boot.</para>
 765
 766             <para>This may be used to pull in Bluetooth management
 767             daemons dynamically when Bluetooth hardware is found.</para>
 768           </listitem>
 769         </varlistentry>
 770         <varlistentry>
 771           <term><filename>printer.target</filename></term>
 772           <listitem>
 773             <para>This target is started automatically as soon as a
 774             printer is plugged in or becomes available at boot.</para>
 775
 776             <para>This may be used to pull in printer management daemons
 777             dynamically when printer hardware is found.</para>
 778           </listitem>
 779         </varlistentry>
 780         <varlistentry>
 781           <term><filename>smartcard.target</filename></term>
 782           <listitem>
 783             <para>This target is started automatically as soon as a
 784             smartcard controller is plugged in or becomes available at
 785             boot.</para>
 786
 787             <para>This may be used to pull in smartcard management
 788             daemons dynamically when smartcard hardware is found.</para>
 789           </listitem>
 790         </varlistentry>
 791         <varlistentry>
 792           <term><filename>sound.target</filename></term>
 793           <listitem>
 794             <para>This target is started automatically as soon as a
 795             sound card is plugged in or becomes available at
 796             boot.</para>
 797
 798             <para>This may be used to pull in audio management daemons
 799             dynamically when audio hardware is found.</para>
 800           </listitem>
 801         </varlistentry>
 802       </variablelist>
 803     </refsect2>
 804
 805     <refsect2>
 806       <title>Special Passive System Units </title>
 807
 808       <para>A number of special system targets are defined that can be
 809       used to properly order boot-up of optional services. These targets
 810       are generally not part of the initial boot transaction, unless
 811       they are explicitly pulled in by one of the implementing services.
 812       Note specifically that these <emphasis>passive</emphasis> target
 813       units are generally not pulled in by the consumer of a service,
 814       but by the provider of the service. This means: a consuming
 815       service should order itself after these targets (as appropriate),
 816       but not pull it in. A providing service should order itself before
 817       these targets (as appropriate) and pull it in (via a
 818       <varname>Wants=</varname> type dependency).</para>
 819
 820       <para>Note that these passive units cannot be started manually,
 821       i.e. <literal>systemctl start time-sync.target</literal> will fail
 822       with an error. They can only be pulled in by dependency. This is
 823       enforced since they exist for ordering purposes only and thus are
 824       not useful as only unit within a transaction.</para>
 825
 826       <variablelist>
 827         <varlistentry>
 828           <term><filename>cryptsetup-pre.target</filename></term>
 829           <listitem>
 830             <para>This passive target unit may be pulled in by services
 831             that want to run before any encrypted block device is set
 832             up. All encrypted block devices are set up after this target
 833             has been reached. Since the shutdown order is implicitly the
 834             reverse start-up order between units, this target is
 835             particularly useful to ensure that a service is shut down
 836             only after all encrypted block devices are fully
 837             stopped.</para>
 838           </listitem>
 839         </varlistentry>
 840         <varlistentry>
 841           <term><filename>getty-pre.target</filename></term>
 842           <listitem>
 843             <para>A special passive target unit. Users of this target
 844             are expected to pull it in the boot transaction via
 845             a dependency (e.g. <varname>Wants=</varname>). Order your
 846             unit before this unit if you want to make use of the console
 847             just before <filename>getty</filename> is started.
 848             </para>
 849           </listitem>
 850         </varlistentry>
 851         <varlistentry>
 852           <term><filename>local-fs-pre.target</filename></term>
 853           <listitem>
 854             <para>This target unit is
 855             automatically ordered before
 856             all local mount points marked
 857             with <option>auto</option>
 858             (see above). It can be used to
 859             execute certain units before
 860             all local mounts.</para>
 861           </listitem>
 862         </varlistentry>
 863         <varlistentry>
 864           <term><filename>network.target</filename></term>
 865           <listitem>
 866             <para>This unit is supposed to indicate when network
 867             functionality is available, but it is only very weakly
 868             defined what that is supposed to mean, with one exception:
 869             at shutdown, a unit that is ordered after
 870             <filename>network.target</filename> will be stopped before
 871             the network — to whatever level it might be set up then —
 872             is shut down. It is hence useful when writing service files
 873             that require network access on shutdown, which should order
 874             themselves after this target, but not pull it in. Also see
 875             <ulink url="https://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 876             Services After the Network is up</ulink> for more
 877             information. Also see
 878             <filename>network-online.target</filename> described
 879             above.</para>
 880           </listitem>
 881         </varlistentry>
 882         <varlistentry>
 883           <term><filename>network-pre.target</filename></term>
 884           <listitem>
 885             <para>This passive target unit may be pulled in by services
 886             that want to run before any network is set up, for example
 887             for the purpose of setting up a firewall. All network
 888             management software orders itself after this target, but
 889             does not pull it in.</para>
 890           </listitem>
 891         </varlistentry>
 892         <varlistentry>
 893           <term><filename>nss-lookup.target</filename></term>
 894           <listitem>
 895             <para>A target that should be used as synchronization point for all host/network name
 896             service lookups. Note that this is independent of UNIX user/group name lookups for which
 897             <filename>nss-user-lookup.target</filename> should be used.  All services for which the
 898             availability of full host/network name resolution is essential should be ordered after
 899             this target, but not pull it in. systemd automatically adds dependencies of type
 900             <varname>After=</varname> for this target unit to all SysV init script service units
 901             with an LSB header referring to the <literal>$named</literal> facility.</para>
 902           </listitem>
 903         </varlistentry>
 904         <varlistentry>
 905           <term><filename>nss-user-lookup.target</filename></term>
 906           <listitem>
 907             <para>A target that should be used as synchronization point for all regular UNIX
 908             user/group name service lookups. Note that this is independent of host/network name
 909             lookups for which <filename>nss-lookup.target</filename> should be used. All services
 910             for which the availability of the full user/group database is essential should be
 911             ordered after this target, but not pull it in. All services which provide parts of the
 912             user/group database should be ordered before this target, and pull it in. Note that this
 913             unit is only relevant for regular users and groups — system users and groups are
 914             required to be resolvable during earliest boot already, and hence do not need any
 915             special ordering against this target.</para>
 916           </listitem>
 917         </varlistentry>
 918         <varlistentry>
 919           <term><filename>remote-fs-pre.target</filename></term>
 920           <listitem>
 921             <para>This target unit is automatically ordered before all
 922             mount point units (see above) and cryptsetup devices
 923             marked with the <option>_netdev</option>. It can be used to run
 924             certain units before remote encrypted devices and mounts are established.
 925             Note that this unit is generally not part of the initial
 926             transaction, unless the unit that wants to be ordered before
 927             all remote mounts pulls it in via a
 928             <varname>Wants=</varname> type dependency. If the unit wants
 929             to be pulled in by the first remote mount showing up, it
 930             should use <filename>network-online.target</filename> (see
 931             above).</para>
 932           </listitem>
 933         </varlistentry>
 934         <varlistentry>
 935           <term><filename>rpcbind.target</filename></term>
 936           <listitem>
 937             <para>The portmapper/rpcbind pulls in this target and orders
 938             itself before it, to indicate its availability. systemd
 939             automatically adds dependencies of type
 940             <varname>After=</varname> for this target unit to all SysV
 941             init script service units with an LSB header referring to
 942             the <literal>$portmap</literal> facility.</para>
 943           </listitem>
 944         </varlistentry>
 945         <varlistentry>
 946           <term><filename>time-sync.target</filename></term>
 947           <listitem>
 948             <para>Services responsible for synchronizing the system
 949             clock from a remote source (such as NTP client
 950             implementations) should pull in this target and order
 951             themselves before it. All services where correct time is
 952             essential should be ordered after this unit, but not pull it
 953             in. systemd automatically adds dependencies of type
 954             <varname>After=</varname> for this target unit to all SysV
 955             init script service units with an LSB header referring to
 956             the <literal>$time</literal> facility. </para>
 957           </listitem>
 958         </varlistentry>
 959       </variablelist>
 960     </refsect2>
 961
 962     <refsect2>
 963       <title>Special Slice Units</title>
 964
 965       <para>There are four <literal>.slice</literal> units which form the basis of the hierarchy for
 966       assignment of resources for services, users, and virtual machines or containers. See
 967       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 968       for details about slice units.</para>
 969
 970       <variablelist>
 971         <varlistentry>
 972           <term><filename>-.slice</filename></term>
 973           <listitem>
 974             <para>The root slice is the root of the slice hierarchy. It usually does not contain
 975             units directly, but may be used to set defaults for the whole tree.</para>
 976           </listitem>
 977         </varlistentry>
 978
 979         <varlistentry>
 980           <term><filename>system.slice</filename></term>
 981           <listitem>
 982             <para>By default, all system services started by
 983             <command>systemd</command> are found in this slice.</para>
 984           </listitem>
 985         </varlistentry>
 986
 987         <varlistentry>
 988           <term><filename>user.slice</filename></term>
 989           <listitem>
 990             <para>By default, all user processes and services started on
 991             behalf of the user, including the per-user systemd instance
 992             are found in this slice.  This is pulled in by
 993             <filename>systemd-logind.service</filename></para>
 994           </listitem>
 995         </varlistentry>
 996
 997         <varlistentry>
 998           <term><filename>machine.slice</filename></term>
 999           <listitem>
1000             <para>By default, all virtual machines and containers
1001             registered with <command>systemd-machined</command> are
1002             found in this slice.  This is pulled in by
1003             <filename>systemd-machined.service</filename></para>
1004           </listitem>
1005         </varlistentry>
1006       </variablelist>
1007     </refsect2>
1008   </refsect1>
1009
1010   <refsect1>
1011     <title>Units managed by the user's service manager</title>
1012
1013     <refsect2>
1014       <title>Special User Units</title>
1015
1016       <para>When systemd runs as a user instance, the following special
1017       units are available, which have similar definitions as their
1018       system counterparts:
1019       <filename>exit.target</filename>,
1020       <filename>default.target</filename>,
1021       <filename>shutdown.target</filename>,
1022       <filename>sockets.target</filename>,
1023       <filename>timers.target</filename>,
1024       <filename>paths.target</filename>,
1025       <filename>bluetooth.target</filename>,
1026       <filename>printer.target</filename>,
1027       <filename>smartcard.target</filename>,
1028       <filename>sound.target</filename>.</para>
1029     </refsect2>
1030
1031     <refsect2>
1032       <title>Special Passive User Units</title>
1033
1034       <variablelist>
1035         <varlistentry>
1036           <term><filename>graphical-session.target</filename></term>
1037           <listitem>
1038             <para>This target is active whenever any graphical session is running. It is used to
1039             stop user services which only apply to a graphical (X, Wayland, etc.) session when the
1040             session is terminated. Such services should have
1041             <literal>PartOf=graphical-session.target</literal> in their <literal>[Unit]</literal>
1042             section. A target for a particular session (e. g.
1043             <filename>gnome-session.target</filename>) starts and stops
1044             <literal>graphical-session.target</literal> with
1045             <literal>BindsTo=graphical-session.target</literal>.</para>
1046
1047             <para>Which services are started by a session target is determined by the
1048             <literal>Wants=</literal> and <literal>Requires=</literal> dependencies.  For services
1049             that can be enabled independently, symlinks in <literal>.wants/</literal> and
1050             <literal>.requires/</literal> should be used, see
1051             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
1052             Those symlinks should either be shipped in packages, or should be added dynamically
1053             after installation, for example using <literal>systemctl add-wants</literal>, see
1054             <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
1055             </para>
1056
1057             <example>
1058               <title>Nautilus as part of a GNOME session</title>
1059
1060               <para><literal>gnome-session.target</literal> pulls in Nautilus as top-level service:</para>
1061
1062               <programlisting>[Unit]
1063   Description=User systemd services for GNOME graphical session
1064   Wants=nautilus.service
1065   BindsTo=graphical-session.target</programlisting>
1066
1067               <para><literal>nautilus.service</literal> gets stopped when the session stops:</para>
1068
1069               <programlisting>[Unit]
1070   Description=Render the desktop icons with Nautilus
1071   PartOf=graphical-session.target
1072
1073   [Service]
1074   …</programlisting>
1075             </example>
1076           </listitem>
1077         </varlistentry>
1078
1079         <varlistentry>
1080           <term><filename>graphical-session-pre.target</filename></term>
1081           <listitem>
1082             <para>This target contains services which set up the environment or global configuration
1083             of a graphical session, such as SSH/GPG agents (which need to export an environment
1084             variable into all desktop processes) or migration of obsolete d-conf keys after an OS
1085             upgrade (which needs to happen before starting any process that might use them). This
1086             target must be started before starting a graphical session like
1087             <filename>gnome-session.target</filename>.</para>
1088           </listitem>
1089         </varlistentry>
1090       </variablelist>
1091     </refsect2>
1092   </refsect1>
1093
1094   <refsect1>
1095       <title>See Also</title>
1096       <para>
1097         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1098         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1099         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1100         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1101         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1102         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1103         <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1104         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1105         <citerefentry><refentrytitle>user@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1106       </para>
1107   </refsect1>
1108
1109 </refentry>