man/systemd.special.xml

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