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>
  51     <para><filename>basic.target</filename>,
  52     <filename>bluetooth.target</filename>,
  53     <filename>ctrl-alt-del.target</filename>,
  54     <filename>cryptsetup.target</filename>,
  55     <filename>cryptsetup-pre.target</filename>,
  56     <filename>dbus.service</filename>,
  57     <filename>dbus.socket</filename>,
  58     <filename>default.target</filename>,
  59     <filename>display-manager.service</filename>,
  60     <filename>emergency.target</filename>,
  61     <filename>exit.target</filename>,
  62     <filename>final.target</filename>,
  63     <filename>getty.target</filename>,
  64     <filename>graphical.target</filename>,
  65     <filename>halt.target</filename>,
  66     <filename>hibernate.target</filename>,
  67     <filename>hybrid-sleep.target</filename>,
  68     <filename>initrd-fs.target</filename>,
  69     <filename>kbrequest.target</filename>,
  70     <filename>kexec.target</filename>,
  71     <filename>local-fs.target</filename>,
  72     <filename>local-fs-pre.target</filename>,
  73     <filename>multi-user.target</filename>,
  74     <filename>network.target</filename>,
  75     <filename>network-online.target</filename>,
  76     <filename>network-pre.target</filename>,
  77     <filename>nss-lookup.target</filename>,
  78     <filename>nss-user-lookup.target</filename>,
  79     <filename>paths.target</filename>,
  80     <filename>poweroff.target</filename>,
  81     <filename>printer.target</filename>,
  82     <filename>reboot.target</filename>,
  83     <filename>remote-fs.target</filename>,
  84     <filename>remote-fs-pre.target</filename>,
  85     <filename>rescue.target</filename>,
  86     <filename>initrd-root-fs.target</filename>,
  87     <filename>rpcbind.target</filename>,
  88     <filename>runlevel2.target</filename>,
  89     <filename>runlevel3.target</filename>,
  90     <filename>runlevel4.target</filename>,
  91     <filename>runlevel5.target</filename>,
  92     <filename>shutdown.target</filename>,
  93     <filename>sigpwr.target</filename>,
  94     <filename>sleep.target</filename>,
  95     <filename>smartcard.target</filename>,
  96     <filename>sockets.target</filename>,
  97     <filename>sound.target</filename>,
  98     <filename>suspend.target</filename>,
  99     <filename>swap.target</filename>,
 100     <filename>sysinit.target</filename>,
 101     <filename>syslog.socket</filename>,
 102     <filename>system-update.target</filename>,
 103     <filename>time-sync.target</filename>,
 104     <filename>timers.target</filename>,
 105     <filename>umount.target</filename>,
 106     <filename>-.slice</filename>,
 107     <filename>system.slice</filename>,
 108     <filename>user.slice</filename>,
 109     <filename>machine.slice</filename></para>
 110   </refsynopsisdiv>
 111
 112   <refsect1>
 113     <title>Description</title>
 114
 115     <para>A few units are treated specially by systemd. They have
 116     special internal semantics and cannot be renamed.</para>
 117   </refsect1>
 118
 119   <refsect1>
 120     <title>Special System Units</title>
 121
 122     <variablelist>
 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 dependencies of the types
 129           <varname>Requires=</varname> and <varname>After=</varname>
 130           for this target unit to all 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
 149         </listitem>
 150       </varlistentry>
 151       <varlistentry>
 152         <term><filename>ctrl-alt-del.target</filename></term>
 153         <listitem>
 154           <para>systemd starts this target whenever Control+Alt+Del is
 155           pressed on the console. Usually this should be aliased
 156           (symlinked) to <filename>reboot.target</filename>.</para>
 157         </listitem>
 158       </varlistentry>
 159       <varlistentry>
 160         <term><filename>cryptsetup.target</filename></term>
 161         <listitem>
 162           <para>A target that pulls in setup services for all
 163           encrypted block devices.</para>
 164         </listitem>
 165       </varlistentry>
 166       <varlistentry>
 167         <term><filename>dbus.service</filename></term>
 168         <listitem>
 169           <para>A special unit for the D-Bus bus daemon. As soon as
 170           this service is fully started up systemd will connect to it
 171           and register its service.</para>
 172         </listitem>
 173       </varlistentry>
 174       <varlistentry>
 175         <term><filename>dbus.socket</filename></term>
 176         <listitem>
 177           <para>A special unit for the D-Bus system bus socket. All
 178           units with <varname>Type=dbus</varname> automatically gain a
 179           dependency on this unit.</para>
 180         </listitem>
 181       </varlistentry>
 182       <varlistentry>
 183         <term><filename>default.target</filename></term>
 184         <listitem>
 185           <para>The default unit systemd starts at bootup. Usually
 186           this should be aliased (symlinked) to
 187           <filename>multi-user.target</filename> or
 188           <filename>graphical.target</filename>.</para>
 189
 190           <para>The default unit systemd starts at bootup can be
 191           overridden with the <varname>systemd.unit=</varname> kernel
 192           command line option.</para>
 193         </listitem>
 194       </varlistentry>
 195       <varlistentry>
 196         <term><filename>display-manager.service</filename></term>
 197         <listitem>
 198           <para>The display manager service. Usually this should be
 199           aliased (symlinked) to <filename>gdm.service</filename> or a
 200           similar display manager service.</para>
 201         </listitem>
 202       </varlistentry>
 203       <varlistentry>
 204         <term><filename>emergency.target</filename></term>
 205         <listitem>
 206           <para>A special target unit that starts an emergency shell
 207           on the main console. This unit is supposed to be used with
 208           the kernel command line option
 209           <varname>systemd.unit=</varname> and has otherwise little
 210           use.
 211           </para>
 212         </listitem>
 213       </varlistentry>
 214       <varlistentry>
 215         <term><filename>exit.target</filename></term>
 216         <listitem>
 217           <para>A special service unit for shutting down the system or
 218           user service manager. It also works in containers and is
 219           equivalent to <filename>poweroff.target</filename> on
 220           non-container systems.</para>
 221
 222           <para>Applications wanting to terminate the user service
 223           manager should start this unit. If systemd receives
 224           <constant>SIGTERM</constant> or <constant>SIGINT</constant>
 225           when running as user service daemon, it will start this
 226           unit.</para>
 227
 228           <para>Normally, this pulls in
 229           <filename>shutdown.target</filename> which in turn should be
 230           conflicted by all units that want to be shut down on user
 231           service manager exit.</para>
 232         </listitem>
 233       </varlistentry>
 234       <varlistentry>
 235         <term><filename>final.target</filename></term>
 236         <listitem>
 237           <para>A special target unit that is used during the shutdown
 238           logic and may be used to pull in late services after all
 239           normal services are already terminated and all mounts
 240           unmounted.
 241           </para>
 242         </listitem>
 243       </varlistentry>
 244       <varlistentry>
 245         <term><filename>getty.target</filename></term>
 246         <listitem>
 247           <para>A special target unit that pulls in statically
 248           configured local TTY <filename>getty</filename> instances.
 249           </para>
 250         </listitem>
 251       </varlistentry>
 252       <varlistentry>
 253         <term><filename>graphical.target</filename></term>
 254         <listitem>
 255           <para>A special target unit for setting up a graphical login
 256           screen. This pulls in
 257           <filename>multi-user.target</filename>.</para>
 258
 259           <para>Units that are needed for graphical logins shall add
 260           <varname>Wants=</varname> dependencies for their unit to
 261           this unit (or <filename>multi-user.target</filename>) during
 262           installation. This is best configured via
 263           <varname>WantedBy=graphical.target</varname> in the unit's
 264           <literal>[Install]</literal> section.</para>
 265         </listitem>
 266       </varlistentry>
 267       <varlistentry>
 268         <term><filename>hibernate.target</filename></term>
 269         <listitem>
 270           <para>A special target unit for hibernating the system. This
 271           pulls in <filename>sleep.target</filename>.</para>
 272         </listitem>
 273       </varlistentry>
 274       <varlistentry>
 275         <term><filename>hybrid-sleep.target</filename></term>
 276         <listitem>
 277           <para>A special target unit for hibernating and suspending
 278           the system at the same time. This pulls in
 279           <filename>sleep.target</filename>.</para>
 280         </listitem>
 281       </varlistentry>
 282       <varlistentry>
 283         <term><filename>halt.target</filename></term>
 284         <listitem>
 285           <para>A special target unit for shutting down and halting
 286           the system. Note that this target is distinct from
 287           <filename>poweroff.target</filename> in that it generally
 288           really just halts the system rather than powering it
 289           down.</para>
 290
 291           <para>Applications wanting to halt the system should start
 292           this unit.</para>
 293         </listitem>
 294       </varlistentry>
 295       <varlistentry>
 296         <term><filename>initrd-fs.target</filename></term>
 297         <listitem>
 298           <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 299           automatically adds dependencies of type
 300           <varname>Before=</varname> to
 301           <filename>sysroot-usr.mount</filename> and all mount points
 302           found in <filename>/etc/fstab</filename> that have
 303           <option>x-initrd.mount</option> and not have
 304           <option>noauto</option> mount options set.</para>
 305         </listitem>
 306       </varlistentry>
 307       <varlistentry>
 308         <term><filename>kbrequest.target</filename></term>
 309         <listitem>
 310           <para>systemd starts this target whenever Alt+ArrowUp is
 311           pressed on the console. This is a good candidate to be
 312           aliased (symlinked) to
 313           <filename>rescue.target</filename>.</para>
 314         </listitem>
 315       </varlistentry>
 316       <varlistentry>
 317         <term><filename>kexec.target</filename></term>
 318         <listitem>
 319           <para>A special target unit for shutting down and rebooting
 320           the system via kexec.</para>
 321
 322           <para>Applications wanting to reboot the system with kexec
 323           should start this unit.</para>
 324         </listitem>
 325       </varlistentry>
 326       <varlistentry>
 327         <term><filename>local-fs.target</filename></term>
 328         <listitem>
 329           <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 330           automatically adds dependencies of type
 331           <varname>Before=</varname> to all mount units that refer to
 332           local mount points for this target unit. In addition, it
 333           adds dependencies of type <varname>Wants=</varname> to this
 334           target unit for those mounts listed in
 335           <filename>/etc/fstab</filename> that have the
 336           <option>auto</option> mount option set.</para>
 337         </listitem>
 338       </varlistentry>
 339       <varlistentry>
 340         <term><filename>multi-user.target</filename></term>
 341         <listitem>
 342           <para>A special target unit for setting up a multi-user
 343           system (non-graphical). This is pulled in by
 344           <filename>graphical.target</filename>.</para>
 345
 346           <para>Units that are needed for a multi-user system shall
 347           add <varname>Wants=</varname> dependencies for their unit to
 348           this unit during installation. This is best configured via
 349           <varname>WantedBy=multi-user.target</varname> in the unit's
 350           <literal>[Install]</literal> section.</para>
 351         </listitem>
 352       </varlistentry>
 353       <varlistentry>
 354         <term><filename>network-online.target</filename></term>
 355         <listitem>
 356           <para>Units that strictly require a configured network
 357           connection should pull in
 358           <filename>network-online.target</filename> (via a
 359           <varname>Wants=</varname> type dependency) and order
 360           themselves after it. This target unit is intended to pull in
 361           a service that delays further execution until the network is
 362           sufficiently set up. What precisely this requires is left to
 363           the implementation of the network managing service.</para>
 364
 365           <para>Note the distinction between this unit and
 366           <filename>network.target</filename>. This unit is an active
 367           unit (i.e. pulled in by the consumer rather than the
 368           provider of this functionality) and pulls in a service which
 369           possibly adds substantial delays to further execution. In
 370           contrast, <filename>network.target</filename> is a passive
 371           unit (i.e. pulled in by the provider of the functionality,
 372           rather than the consumer) that usually does not delay
 373           execution much. Usually, <filename>network.target</filename>
 374           is part of the boot of most systems, while
 375           <filename>network-online.target</filename> is not, except
 376           when at least one unit requires it. Also see <ulink
 377           url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 378           Services After the Network is up</ulink> for more
 379           information.</para>
 380
 381           <para>All mount units for remote network file systems
 382           automatically pull in this unit, and order themselves after
 383           it. Note that networking daemons that simply provide
 384           functionality to other hosts generally do not need to pull
 385           this in.</para>
 386           </listitem>
 387       </varlistentry>
 388       <varlistentry>
 389         <term><filename>paths.target</filename></term>
 390         <listitem>
 391           <para>A special target unit that sets up all path units (see
 392           <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 393           for details) that shall be active after boot.</para>
 394
 395           <para>It is recommended that path units installed by
 396           applications get pulled in via <varname>Wants=</varname>
 397           dependencies from this unit. This is best configured via a
 398           <varname>WantedBy=paths.target</varname> in the path unit's
 399           <literal>[Install]</literal> section.</para>
 400         </listitem>
 401       </varlistentry>
 402       <varlistentry>
 403         <term><filename>poweroff.target</filename></term>
 404         <listitem>
 405           <para>A special target unit for shutting down and powering
 406           off the system.</para>
 407
 408           <para>Applications wanting to power off the system should
 409           start this unit.</para>
 410
 411           <para><filename>runlevel0.target</filename> is an alias for
 412           this target unit, for compatibility with SysV.</para>
 413         </listitem>
 414       </varlistentry>
 415       <varlistentry>
 416         <term><filename>reboot.target</filename></term>
 417         <listitem>
 418           <para>A special target unit for shutting down and rebooting
 419           the system.</para>
 420
 421           <para>Applications wanting to reboot the system should start
 422           this unit.</para>
 423
 424           <para><filename>runlevel6.target</filename> is an alias for
 425           this target unit, for compatibility with SysV.</para>
 426         </listitem>
 427       </varlistentry>
 428       <varlistentry>
 429         <term><filename>remote-fs.target</filename></term>
 430         <listitem>
 431           <para>Similar to <filename>local-fs.target</filename>, but
 432           for remote mount points.</para>
 433
 434           <para>systemd automatically adds dependencies of type
 435           <varname>After=</varname> for this target unit to all SysV
 436           init script service units with an LSB header referring to
 437           the <literal>$remote_fs</literal> facility.</para>
 438         </listitem>
 439       </varlistentry>
 440       <varlistentry>
 441         <term><filename>rescue.target</filename></term>
 442         <listitem>
 443           <para>A special target unit for setting up the base system
 444           and a rescue shell.</para>
 445
 446           <para><filename>runlevel1.target</filename> is an alias for
 447           this target unit, for compatibility with SysV.</para>
 448         </listitem>
 449       </varlistentry>
 450       <varlistentry>
 451         <term><filename>initrd-root-fs.target</filename></term>
 452         <listitem>
 453           <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 454           automatically adds dependencies of type
 455           <varname>Before=</varname> to the
 456           <filename>sysroot.mount</filename> unit, which is generated
 457           from the kernel command line.
 458           </para>
 459         </listitem>
 460       </varlistentry>
 461       <varlistentry>
 462         <term><filename>runlevel2.target</filename></term>
 463         <term><filename>runlevel3.target</filename></term>
 464         <term><filename>runlevel4.target</filename></term>
 465         <term><filename>runlevel5.target</filename></term>
 466         <listitem>
 467           <para>These are targets that are called whenever the SysV
 468           compatibility code asks for runlevel 2, 3, 4, 5,
 469           respectively. It is a good idea to make this an alias for
 470           (i.e. symlink to) <filename>multi-user.target</filename>
 471           (for runlevel 2) or <filename>graphical.target</filename>
 472           (the others).</para>
 473         </listitem>
 474       </varlistentry>
 475       <varlistentry>
 476         <term><filename>shutdown.target</filename></term>
 477         <listitem>
 478           <para>A special target unit that terminates the services on
 479           system shutdown.</para>
 480
 481           <para>Services that shall be terminated on system shutdown
 482           shall add <varname>Conflicts=</varname> dependencies to this
 483           unit for their service unit, which is implicitly done when
 484           <varname>DefaultDependencies=yes</varname> is set (the
 485           default).</para>
 486         </listitem>
 487       </varlistentry>
 488       <varlistentry>
 489         <term><filename>sigpwr.target</filename></term>
 490         <listitem>
 491           <para>A special target that is started when systemd receives
 492           the SIGPWR process signal, which is normally sent by the
 493           kernel or UPS daemons when power fails.</para>
 494         </listitem>
 495       </varlistentry>
 496       <varlistentry>
 497         <term><filename>sleep.target</filename></term>
 498         <listitem>
 499           <para>A special target unit that is pulled in by
 500           <filename>suspend.target</filename>,
 501           <filename>hibernate.target</filename> and
 502           <filename>hybrid-sleep.target</filename> and may be used to
 503           hook units into the sleep state logic.</para>
 504         </listitem>
 505       </varlistentry>
 506       <varlistentry>
 507         <term><filename>sockets.target</filename></term>
 508         <listitem>
 509           <para>A special target unit that sets up all socket
 510           units.(see
 511           <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 512           for details) that shall be active after boot.</para>
 513
 514           <para>Services that can be socket-activated shall add
 515           <varname>Wants=</varname> dependencies to this unit for
 516           their socket unit during installation. This is best
 517           configured via a <varname>WantedBy=sockets.target</varname>
 518           in the socket unit's <literal>[Install]</literal>
 519           section.</para>
 520         </listitem>
 521       </varlistentry>
 522       <varlistentry>
 523         <term><filename>suspend.target</filename></term>
 524         <listitem>
 525           <para>A special target unit for suspending the system. This
 526           pulls in <filename>sleep.target</filename>.</para>
 527         </listitem>
 528       </varlistentry>
 529       <varlistentry>
 530         <term><filename>swap.target</filename></term>
 531         <listitem>
 532           <para>Similar to <filename>local-fs.target</filename>, but
 533           for swap partitions and swap files.</para>
 534         </listitem>
 535       </varlistentry>
 536       <varlistentry>
 537         <term><filename>sysinit.target</filename></term>
 538         <listitem>
 539           <para>This target pulls in the services required for system
 540           initialization. System services pulled in by this target should
 541           declare <varname>DefaultDependencies=no</varname> and specify
 542           all their dependencies manually, including access to anything
 543           more than a read only root filesystem. For details on the
 544           dependencies of this target, refer to
 545           <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 546           </para>
 547         </listitem>
 548       </varlistentry>
 549       <varlistentry>
 550         <term><filename>syslog.socket</filename></term>
 551         <listitem>
 552           <para>The socket unit syslog implementations should listen
 553           on. All userspace log messages will be made available on
 554           this socket. For more information about syslog integration,
 555           please consult the <ulink
 556           url="http://www.freedesktop.org/wiki/Software/systemd/syslog">Syslog
 557           Interface</ulink> document.</para>
 558         </listitem>
 559       </varlistentry>
 560       <varlistentry>
 561         <term><filename>system-update.target</filename></term>
 562         <listitem>
 563           <para>A special target unit that is used for off-line system
 564           updates.
 565           <citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 566           will redirect the boot process to this target if
 567           <filename>/system-update</filename> exists. For more
 568           information see the <ulink
 569           url="http://freedesktop.org/wiki/Software/systemd/SystemUpdates">System
 570           Updates Specification</ulink>.</para>
 571         </listitem>
 572       </varlistentry>
 573       <varlistentry>
 574         <term><filename>timers.target</filename></term>
 575         <listitem>
 576           <para>A special target unit that sets up all timer units
 577           (see
 578           <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 579           for details) that shall be active after boot.</para>
 580
 581           <para>It is recommended that timer units installed by
 582           applications get pulled in via <varname>Wants=</varname>
 583           dependencies from this unit. This is best configured via
 584           <varname>WantedBy=timers.target</varname> in the timer
 585           unit's <literal>[Install]</literal> section.</para>
 586         </listitem>
 587       </varlistentry>
 588       <varlistentry>
 589         <term><filename>umount.target</filename></term>
 590         <listitem>
 591           <para>A special target unit that umounts all mount and
 592           automount points on system shutdown.</para>
 593
 594           <para>Mounts that shall be unmounted on system shutdown
 595           shall add Conflicts dependencies to this unit for their
 596           mount unit, which is implicitly done when
 597           <varname>DefaultDependencies=yes</varname> is set (the
 598           default).</para>
 599         </listitem>
 600       </varlistentry>
 601
 602     </variablelist>
 603   </refsect1>
 604
 605   <refsect1>
 606     <title>Special System Units for Devices</title>
 607
 608     <para>Some target units are automatically pulled in as devices of
 609     certain kinds show up in the system. These may be used to
 610     automatically activate various services based on the specific type
 611     of the available hardware.</para>
 612
 613     <variablelist>
 614       <varlistentry>
 615         <term><filename>bluetooth.target</filename></term>
 616         <listitem>
 617           <para>This target is started automatically as soon as a
 618           Bluetooth controller is plugged in or becomes available at
 619           boot.</para>
 620
 621           <para>This may be used to pull in Bluetooth management
 622           daemons dynamically when Bluetooth hardware is found.</para>
 623         </listitem>
 624       </varlistentry>
 625       <varlistentry>
 626         <term><filename>printer.target</filename></term>
 627         <listitem>
 628           <para>This target is started automatically as soon as a
 629           printer is plugged in or becomes available at boot.</para>
 630
 631           <para>This may be used to pull in printer management daemons
 632           dynamically when printer hardware is found.</para>
 633         </listitem>
 634       </varlistentry>
 635       <varlistentry>
 636         <term><filename>smartcard.target</filename></term>
 637         <listitem>
 638           <para>This target is started automatically as soon as a
 639           smartcard controller is plugged in or becomes available at
 640           boot.</para>
 641
 642           <para>This may be used to pull in smartcard management
 643           daemons dynamically when smartcard hardware is found.</para>
 644         </listitem>
 645       </varlistentry>
 646       <varlistentry>
 647         <term><filename>sound.target</filename></term>
 648         <listitem>
 649           <para>This target is started automatically as soon as a
 650           sound card is plugged in or becomes available at
 651           boot.</para>
 652
 653           <para>This may be used to pull in audio management daemons
 654           dynamically when audio hardware is found.</para>
 655         </listitem>
 656       </varlistentry>
 657     </variablelist>
 658   </refsect1>
 659
 660   <refsect1>
 661     <title>Special Passive System Units </title>
 662
 663     <para>A number of special system targets are defined that can be
 664     used to properly order boot-up of optional services. These targets
 665     are generally not part of the initial boot transaction, unless
 666     they are explicitly pulled in by one of the implementing services.
 667     Note specifically that these <emphasis>passive</emphasis> target
 668     units are generally not pulled in by the consumer of a service,
 669     but by the provider of the service. This means: a consuming
 670     service should order itself after these targets (as appropriate),
 671     but not pull it in. A providing service should order itself before
 672     these targets (as appropriate) and pull it in (via a
 673     <varname>Wants=</varname> type dependency).</para>
 674
 675     <para>Note that these passive units cannot be started manually,
 676     i.e. <literal>systemctl start time-sync.target</literal> will fail
 677     with an error. They can only be pulled in by dependency. This is
 678     enforced since they exist for ordering purposes only and thus are
 679     not useful as only unit within a transaction.</para>
 680
 681     <variablelist>
 682       <varlistentry>
 683         <term><filename>cryptsetup-pre.target</filename></term>
 684         <listitem>
 685           <para>This passive target unit may be pulled in by services
 686           that want to run before any encrypted block device is set
 687           up. All encrypted block devices are set up after this target
 688           has been reached. Since the shutdown order is implicitly the
 689           reverse start-up order between units, this target is
 690           particularly useful to ensure that a service is shut down
 691           only after all encrypted block devices are fully
 692           stopped.</para>
 693         </listitem>
 694       </varlistentry>
 695       <varlistentry>
 696         <term><filename>local-fs-pre.target</filename></term>
 697         <listitem>
 698           <para>This target unit is
 699           automatically ordered before
 700           all local mount points marked
 701           with <option>auto</option>
 702           (see above). It can be used to
 703           execute certain units before
 704           all local mounts.</para>
 705         </listitem>
 706       </varlistentry>
 707       <varlistentry>
 708         <term><filename>network.target</filename></term>
 709         <listitem>
 710           <para>This unit is supposed to indicate when network
 711           functionality is available, but it is only very weakly
 712           defined what that is supposed to mean, with one exception:
 713           at shutdown, a unit that is ordered after
 714           <filename>network.target</filename> will be stopped before
 715           the network -- to whatever level it might be set up then --
 716           is shut down. It is hence useful when writing service files
 717           that require network access on shutdown, which should order
 718           themselves after this target, but not pull it in. Also see
 719           <ulink url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 720           Services After the Network is up</ulink> for more
 721           information. Also see
 722           <filename>network-online.target</filename> described
 723           above.</para>
 724
 725           <para>systemd automatically adds dependencies of type
 726           <varname>After=</varname> for this target unit to all SysV
 727           init script service units with an LSB header referring to
 728           the <literal>$network</literal> facility.</para>
 729         </listitem>
 730       </varlistentry>
 731       <varlistentry>
 732         <term><filename>network-pre.target</filename></term>
 733         <listitem>
 734           <para>This passive target unit may be pulled in by services
 735           that want to run before any network is set up, for example
 736           for the purpose of setting up a firewall. All network
 737           management software orders itself after this target, but
 738           does not pull it in.</para>
 739         </listitem>
 740       </varlistentry>
 741       <varlistentry>
 742         <term><filename>nss-lookup.target</filename></term>
 743         <listitem>
 744           <para>A target that should be used as synchronization point
 745           for all host/network name service lookups. Note that this is
 746           independent of user/group name lookups for which
 747           <filename>nss-user-lookup.target</filename> should be used.
 748           All services for which the availability of full host/network
 749           name resolution is essential should be ordered after this
 750           target, but not pull it in. systemd automatically adds
 751           dependencies of type <varname>After=</varname> for this
 752           target unit to all SysV init script service units with an
 753           LSB header referring to the <literal>$named</literal>
 754           facility.</para>
 755         </listitem>
 756       </varlistentry>
 757       <varlistentry>
 758         <term><filename>nss-user-lookup.target</filename></term>
 759         <listitem>
 760           <para>A target that should be used as synchronization point
 761           for all user/group name service lookups. Note that this is
 762           independent of host/network name lookups for which
 763           <filename>nss-lookup.target</filename> should be used. All
 764           services for which the availability of the full user/group
 765           database is essential should be ordered after this target,
 766           but not pull it in. Note that system users are always
 767           resolvable, and hence do not require any special ordering
 768           against this target.</para>
 769         </listitem>
 770       </varlistentry>
 771       <varlistentry>
 772         <term><filename>remote-fs-pre.target</filename></term>
 773         <listitem>
 774           <para>This target unit is automatically ordered before all
 775           remote mount point units (see above). It can be used to run
 776           certain units before the remote mounts are established. Note
 777           that this unit is generally not part of the initial
 778           transaction, unless the unit that wants to be ordered before
 779           all remote mounts pulls it in via a
 780           <varname>Wants=</varname> type dependency. If the unit wants
 781           to be pulled in by the first remote mount showing up, it
 782           should use <filename>network-online.target</filename> (see
 783           above).</para>
 784         </listitem>
 785       </varlistentry>
 786       <varlistentry>
 787         <term><filename>rpcbind.target</filename></term>
 788         <listitem>
 789           <para>The portmapper/rpcbind pulls in this target and orders
 790           itself before it, to indicate its availability. systemd
 791           automatically adds dependencies of type
 792           <varname>After=</varname> for this target unit to all SysV
 793           init script service units with an LSB header referring to
 794           the <literal>$portmap</literal> facility.</para>
 795         </listitem>
 796       </varlistentry>
 797       <varlistentry>
 798         <term><filename>time-sync.target</filename></term>
 799         <listitem>
 800           <para>Services responsible for synchronizing the system
 801           clock from a remote source (such as NTP client
 802           implementations) should pull in this target and order
 803           themselves before it. All services where correct time is
 804           essential should be ordered after this unit, but not pull it
 805           in. systemd automatically adds dependencies of type
 806           <varname>After=</varname> for this target unit to all SysV
 807           init script service units with an LSB header referring to
 808           the <literal>$time</literal> facility. </para>
 809         </listitem>
 810       </varlistentry>
 811     </variablelist>
 812   </refsect1>
 813
 814   <refsect1>
 815     <title>Special User Units</title>
 816
 817     <para>When systemd runs as a user instance, the following special
 818     units are available, which have similar definitions as their
 819     system counterparts:
 820     <filename>exit.target</filename>,
 821     <filename>default.target</filename>,
 822     <filename>shutdown.target</filename>,
 823     <filename>sockets.target</filename>,
 824     <filename>timers.target</filename>,
 825     <filename>paths.target</filename>,
 826     <filename>bluetooth.target</filename>,
 827     <filename>printer.target</filename>,
 828     <filename>smartcard.target</filename>,
 829     <filename>sound.target</filename>.</para>
 830   </refsect1>
 831
 832   <refsect1>
 833     <title>Special Slice Units</title>
 834
 835     <para>There are four <literal>.slice</literal> units which form
 836     the basis of the hierarchy for assignment of resources for
 837     services, users, and virtual machines or containers.</para>
 838
 839     <variablelist>
 840       <varlistentry>
 841         <term><filename>-.slice</filename></term>
 842         <listitem>
 843           <para>The root slice is the root of the hierarchy. It
 844           usually does not contain units directly, but may be used to
 845           set defaults for the whole tree.</para>
 846         </listitem>
 847       </varlistentry>
 848
 849       <varlistentry>
 850         <term><filename>system.slice</filename></term>
 851         <listitem>
 852           <para>By default, all system services started by
 853           <command>systemd</command> are found in this slice.</para>
 854         </listitem>
 855       </varlistentry>
 856
 857       <varlistentry>
 858         <term><filename>user.slice</filename></term>
 859         <listitem>
 860           <para>By default, all user processes and services started on
 861           behalf of the user, including the per-user systemd instance
 862           are found in this slice.</para>
 863         </listitem>
 864       </varlistentry>
 865
 866       <varlistentry>
 867         <term><filename>machine.slice</filename></term>
 868         <listitem>
 869           <para>By default, all virtual machines and containers
 870           registered with <command>systemd-machined</command> are
 871           found in this slice.
 872           </para>
 873         </listitem>
 874       </varlistentry>
 875     </variablelist>
 876   </refsect1>
 877
 878   <refsect1>
 879       <title>See Also</title>
 880       <para>
 881         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 882         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 883         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 884         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 885         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 886         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 887         <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 888         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 889       </para>
 890   </refsect1>
 891
 892 </refentry>