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>final.target</filename></term>
 216         <listitem>
 217           <para>A special target unit that is used during the shutdown
 218           logic and may be used to pull in late services after all
 219           normal services are already terminated and all mounts
 220           unmounted.
 221           </para>
 222         </listitem>
 223       </varlistentry>
 224       <varlistentry>
 225         <term><filename>getty.target</filename></term>
 226         <listitem>
 227           <para>A special target unit that pulls in statically
 228           configured local TTY <filename>getty</filename> instances.
 229           </para>
 230         </listitem>
 231       </varlistentry>
 232       <varlistentry>
 233         <term><filename>graphical.target</filename></term>
 234         <listitem>
 235           <para>A special target unit for setting up a graphical login
 236           screen. This pulls in
 237           <filename>multi-user.target</filename>.</para>
 238
 239           <para>Units that are needed for graphical logins shall add
 240           <varname>Wants=</varname> dependencies for their unit to
 241           this unit (or <filename>multi-user.target</filename>) during
 242           installation. This is best configured via
 243           <varname>WantedBy=graphical.target</varname> in the unit's
 244           <literal>[Install]</literal> section.</para>
 245         </listitem>
 246       </varlistentry>
 247       <varlistentry>
 248         <term><filename>hibernate.target</filename></term>
 249         <listitem>
 250           <para>A special target unit for hibernating the system. This
 251           pulls in <filename>sleep.target</filename>.</para>
 252         </listitem>
 253       </varlistentry>
 254       <varlistentry>
 255         <term><filename>hybrid-sleep.target</filename></term>
 256         <listitem>
 257           <para>A special target unit for hibernating and suspending
 258           the system at the same time. This pulls in
 259           <filename>sleep.target</filename>.</para>
 260         </listitem>
 261       </varlistentry>
 262       <varlistentry>
 263         <term><filename>halt.target</filename></term>
 264         <listitem>
 265           <para>A special target unit for shutting down and halting
 266           the system. Note that this target is distinct from
 267           <filename>poweroff.target</filename> in that it generally
 268           really just halts the system rather than powering it
 269           down.</para>
 270
 271           <para>Applications wanting to halt the system should start
 272           this unit.</para>
 273         </listitem>
 274       </varlistentry>
 275       <varlistentry>
 276         <term><filename>initrd-fs.target</filename></term>
 277         <listitem>
 278           <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 279           automatically adds dependencies of type
 280           <varname>Before=</varname> to
 281           <filename>sysroot-usr.mount</filename> and all mount points
 282           found in <filename>/etc/fstab</filename> that have
 283           <option>x-initrd.mount</option> and not have
 284           <option>noauto</option> mount options set.</para>
 285         </listitem>
 286       </varlistentry>
 287       <varlistentry>
 288         <term><filename>kbrequest.target</filename></term>
 289         <listitem>
 290           <para>systemd starts this target whenever Alt+ArrowUp is
 291           pressed on the console. This is a good candidate to be
 292           aliased (symlinked) to
 293           <filename>rescue.target</filename>.</para>
 294         </listitem>
 295       </varlistentry>
 296       <varlistentry>
 297         <term><filename>kexec.target</filename></term>
 298         <listitem>
 299           <para>A special target unit for shutting down and rebooting
 300           the system via kexec.</para>
 301
 302           <para>Applications wanting to reboot the system with kexec
 303           should start this unit.</para>
 304         </listitem>
 305       </varlistentry>
 306       <varlistentry>
 307         <term><filename>local-fs.target</filename></term>
 308         <listitem>
 309           <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 310           automatically adds dependencies of type
 311           <varname>Before=</varname> to all mount units that refer to
 312           local mount points for this target unit. In addition, it
 313           adds dependencies of type <varname>Wants=</varname> to this
 314           target unit for those mounts listed in
 315           <filename>/etc/fstab</filename> that have the
 316           <option>auto</option> mount option set.</para>
 317         </listitem>
 318       </varlistentry>
 319       <varlistentry>
 320         <term><filename>multi-user.target</filename></term>
 321         <listitem>
 322           <para>A special target unit for setting up a multi-user
 323           system (non-graphical). This is pulled in by
 324           <filename>graphical.target</filename>.</para>
 325
 326           <para>Units that are needed for a multi-user system shall
 327           add <varname>Wants=</varname> dependencies for their unit to
 328           this unit during installation. This is best configured via
 329           <varname>WantedBy=multi-user.target</varname> in the unit's
 330           <literal>[Install]</literal> section.</para>
 331         </listitem>
 332       </varlistentry>
 333       <varlistentry>
 334         <term><filename>network-online.target</filename></term>
 335         <listitem>
 336           <para>Units that strictly require a configured network
 337           connection should pull in
 338           <filename>network-online.target</filename> (via a
 339           <varname>Wants=</varname> type dependency) and order
 340           themselves after it. This target unit is intended to pull in
 341           a service that delays further execution until the network is
 342           sufficiently set up. What precisely this requires is left to
 343           the implementation of the network managing service.</para>
 344
 345           <para>Note the distinction between this unit and
 346           <filename>network.target</filename>. This unit is an active
 347           unit (i.e. pulled in by the consumer rather than the
 348           provider of this functionality) and pulls in a service which
 349           possibly adds substantial delays to further execution. In
 350           contrast, <filename>network.target</filename> is a passive
 351           unit (i.e. pulled in by the provider of the functionality,
 352           rather than the consumer) that usually does not delay
 353           execution much. Usually, <filename>network.target</filename>
 354           is part of the boot of most systems, while
 355           <filename>network-online.target</filename> is not, except
 356           when at least one unit requires it. Also see <ulink
 357           url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 358           Services After the Network is up</ulink> for more
 359           information.</para>
 360
 361           <para>All mount units for remote network file systems
 362           automatically pull in this unit, and order themselves after
 363           it. Note that networking daemons that simply provide
 364           functionality to other hosts generally do not need to pull
 365           this in.</para>
 366           </listitem>
 367       </varlistentry>
 368       <varlistentry>
 369         <term><filename>paths.target</filename></term>
 370         <listitem>
 371           <para>A special target unit that sets up all path units (see
 372           <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 373           for details) that shall be active after boot.</para>
 374
 375           <para>It is recommended that path units installed by
 376           applications get pulled in via <varname>Wants=</varname>
 377           dependencies from this unit. This is best configured via a
 378           <varname>WantedBy=paths.target</varname> in the path unit's
 379           <literal>[Install]</literal> section.</para>
 380         </listitem>
 381       </varlistentry>
 382       <varlistentry>
 383         <term><filename>poweroff.target</filename></term>
 384         <listitem>
 385           <para>A special target unit for shutting down and powering
 386           off the system.</para>
 387
 388           <para>Applications wanting to power off the system should
 389           start this unit.</para>
 390
 391           <para><filename>runlevel0.target</filename> is an alias for
 392           this target unit, for compatibility with SysV.</para>
 393         </listitem>
 394       </varlistentry>
 395       <varlistentry>
 396         <term><filename>reboot.target</filename></term>
 397         <listitem>
 398           <para>A special target unit for shutting down and rebooting
 399           the system.</para>
 400
 401           <para>Applications wanting to reboot the system should start
 402           this unit.</para>
 403
 404           <para><filename>runlevel6.target</filename> is an alias for
 405           this target unit, for compatibility with SysV.</para>
 406         </listitem>
 407       </varlistentry>
 408       <varlistentry>
 409         <term><filename>remote-fs.target</filename></term>
 410         <listitem>
 411           <para>Similar to <filename>local-fs.target</filename>, but
 412           for remote mount points.</para>
 413
 414           <para>systemd automatically adds dependencies of type
 415           <varname>After=</varname> for this target unit to all SysV
 416           init script service units with an LSB header referring to
 417           the <literal>$remote_fs</literal> facility.</para>
 418         </listitem>
 419       </varlistentry>
 420       <varlistentry>
 421         <term><filename>rescue.target</filename></term>
 422         <listitem>
 423           <para>A special target unit for setting up the base system
 424           and a rescue shell.</para>
 425
 426           <para><filename>runlevel1.target</filename> is an alias for
 427           this target unit, for compatibility with SysV.</para>
 428         </listitem>
 429       </varlistentry>
 430       <varlistentry>
 431         <term><filename>initrd-root-fs.target</filename></term>
 432         <listitem>
 433           <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 434           automatically adds dependencies of type
 435           <varname>Before=</varname> to the
 436           <filename>sysroot.mount</filename> unit, which is generated
 437           from the kernel command line.
 438           </para>
 439         </listitem>
 440       </varlistentry>
 441       <varlistentry>
 442         <term><filename>runlevel2.target</filename></term>
 443         <term><filename>runlevel3.target</filename></term>
 444         <term><filename>runlevel4.target</filename></term>
 445         <term><filename>runlevel5.target</filename></term>
 446         <listitem>
 447           <para>These are targets that are called whenever the SysV
 448           compatibility code asks for runlevel 2, 3, 4, 5,
 449           respectively. It is a good idea to make this an alias for
 450           (i.e. symlink to) <filename>multi-user.target</filename>
 451           (for runlevel 2) or <filename>graphical.target</filename>
 452           (the others).</para>
 453         </listitem>
 454       </varlistentry>
 455       <varlistentry>
 456         <term><filename>shutdown.target</filename></term>
 457         <listitem>
 458           <para>A special target unit that terminates the services on
 459           system shutdown.</para>
 460
 461           <para>Services that shall be terminated on system shutdown
 462           shall add <varname>Conflicts=</varname> dependencies to this
 463           unit for their service unit, which is implicitly done when
 464           <varname>DefaultDependencies=yes</varname> is set (the
 465           default).</para>
 466         </listitem>
 467       </varlistentry>
 468       <varlistentry>
 469         <term><filename>sigpwr.target</filename></term>
 470         <listitem>
 471           <para>A special target that is started when systemd receives
 472           the SIGPWR process signal, which is normally sent by the
 473           kernel or UPS daemons when power fails.</para>
 474         </listitem>
 475       </varlistentry>
 476       <varlistentry>
 477         <term><filename>sleep.target</filename></term>
 478         <listitem>
 479           <para>A special target unit that is pulled in by
 480           <filename>suspend.target</filename>,
 481           <filename>hibernate.target</filename> and
 482           <filename>hybrid-sleep.target</filename> and may be used to
 483           hook units into the sleep state logic.</para>
 484         </listitem>
 485       </varlistentry>
 486       <varlistentry>
 487         <term><filename>sockets.target</filename></term>
 488         <listitem>
 489           <para>A special target unit that sets up all socket
 490           units.(see
 491           <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 492           for details) that shall be active after boot.</para>
 493
 494           <para>Services that can be socket-activated shall add
 495           <varname>Wants=</varname> dependencies to this unit for
 496           their socket unit during installation. This is best
 497           configured via a <varname>WantedBy=sockets.target</varname>
 498           in the socket unit's <literal>[Install]</literal>
 499           section.</para>
 500         </listitem>
 501       </varlistentry>
 502       <varlistentry>
 503         <term><filename>suspend.target</filename></term>
 504         <listitem>
 505           <para>A special target unit for suspending the system. This
 506           pulls in <filename>sleep.target</filename>.</para>
 507         </listitem>
 508       </varlistentry>
 509       <varlistentry>
 510         <term><filename>swap.target</filename></term>
 511         <listitem>
 512           <para>Similar to <filename>local-fs.target</filename>, but
 513           for swap partitions and swap files.</para>
 514         </listitem>
 515       </varlistentry>
 516       <varlistentry>
 517         <term><filename>sysinit.target</filename></term>
 518         <listitem>
 519           <para>This target pulls in the services required for system
 520           initialization. System services pulled in by this target should
 521           declare <varname>DefaultDependencies=no</varname> and specify
 522           all their dependencies manually, including access to anything
 523           more than a read only root filesystem. For details on the
 524           dependencies of this target, refer to
 525           <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 526           </para>
 527         </listitem>
 528       </varlistentry>
 529       <varlistentry>
 530         <term><filename>syslog.socket</filename></term>
 531         <listitem>
 532           <para>The socket unit syslog implementations should listen
 533           on. All userspace log messages will be made available on
 534           this socket. For more information about syslog integration,
 535           please consult the <ulink
 536           url="http://www.freedesktop.org/wiki/Software/systemd/syslog">Syslog
 537           Interface</ulink> document.</para>
 538         </listitem>
 539       </varlistentry>
 540       <varlistentry>
 541         <term><filename>system-update.target</filename></term>
 542         <listitem>
 543           <para>A special target unit that is used for off-line system
 544           updates.
 545           <citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 546           will redirect the boot process to this target if
 547           <filename>/system-update</filename> exists. For more
 548           information see the <ulink
 549           url="http://freedesktop.org/wiki/Software/systemd/SystemUpdates">System
 550           Updates Specification</ulink>.</para>
 551         </listitem>
 552       </varlistentry>
 553       <varlistentry>
 554         <term><filename>timers.target</filename></term>
 555         <listitem>
 556           <para>A special target unit that sets up all timer units
 557           (see
 558           <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 559           for details) that shall be active after boot.</para>
 560
 561           <para>It is recommended that timer units installed by
 562           applications get pulled in via <varname>Wants=</varname>
 563           dependencies from this unit. This is best configured via
 564           <varname>WantedBy=timers.target</varname> in the timer
 565           unit's <literal>[Install]</literal> section.</para>
 566         </listitem>
 567       </varlistentry>
 568       <varlistentry>
 569         <term><filename>umount.target</filename></term>
 570         <listitem>
 571           <para>A special target unit that umounts all mount and
 572           automount points on system shutdown.</para>
 573
 574           <para>Mounts that shall be unmounted on system shutdown
 575           shall add Conflicts dependencies to this unit for their
 576           mount unit, which is implicitly done when
 577           <varname>DefaultDependencies=yes</varname> is set (the
 578           default).</para>
 579         </listitem>
 580       </varlistentry>
 581
 582     </variablelist>
 583   </refsect1>
 584
 585   <refsect1>
 586     <title>Special System Units for Devices</title>
 587
 588     <para>Some target units are automatically pulled in as devices of
 589     certain kinds show up in the system. These may be used to
 590     automatically activate various services based on the specific type
 591     of the available hardware.</para>
 592
 593     <variablelist>
 594       <varlistentry>
 595         <term><filename>bluetooth.target</filename></term>
 596         <listitem>
 597           <para>This target is started automatically as soon as a
 598           Bluetooth controller is plugged in or becomes available at
 599           boot.</para>
 600
 601           <para>This may be used to pull in Bluetooth management
 602           daemons dynamically when Bluetooth hardware is found.</para>
 603         </listitem>
 604       </varlistentry>
 605       <varlistentry>
 606         <term><filename>printer.target</filename></term>
 607         <listitem>
 608           <para>This target is started automatically as soon as a
 609           printer is plugged in or becomes available at boot.</para>
 610
 611           <para>This may be used to pull in printer management daemons
 612           dynamically when printer hardware is found.</para>
 613         </listitem>
 614       </varlistentry>
 615       <varlistentry>
 616         <term><filename>smartcard.target</filename></term>
 617         <listitem>
 618           <para>This target is started automatically as soon as a
 619           smartcard controller is plugged in or becomes available at
 620           boot.</para>
 621
 622           <para>This may be used to pull in smartcard management
 623           daemons dynamically when smartcard hardware is found.</para>
 624         </listitem>
 625       </varlistentry>
 626       <varlistentry>
 627         <term><filename>sound.target</filename></term>
 628         <listitem>
 629           <para>This target is started automatically as soon as a
 630           sound card is plugged in or becomes available at
 631           boot.</para>
 632
 633           <para>This may be used to pull in audio management daemons
 634           dynamically when audio hardware is found.</para>
 635         </listitem>
 636       </varlistentry>
 637     </variablelist>
 638   </refsect1>
 639
 640   <refsect1>
 641     <title>Special Passive System Units </title>
 642
 643     <para>A number of special system targets are defined that can be
 644     used to properly order boot-up of optional services. These targets
 645     are generally not part of the initial boot transaction, unless
 646     they are explicitly pulled in by one of the implementing services.
 647     Note specifically that these <emphasis>passive</emphasis> target
 648     units are generally not pulled in by the consumer of a service,
 649     but by the provider of the service. This means: a consuming
 650     service should order itself after these targets (as appropriate),
 651     but not pull it in. A providing service should order itself before
 652     these targets (as appropriate) and pull it in (via a
 653     <varname>Wants=</varname> type dependency).</para>
 654
 655     <para>Note that these passive units cannot be started manually,
 656     i.e. <literal>systemctl start time-sync.target</literal> will fail
 657     with an error. They can only be pulled in by dependency. This is
 658     enforced since they exist for ordering purposes only and thus are
 659     not useful as only unit within a transaction.</para>
 660
 661     <variablelist>
 662       <varlistentry>
 663         <term><filename>cryptsetup-pre.target</filename></term>
 664         <listitem>
 665           <para>This passive target unit may be pulled in by services
 666           that want to run before any encrypted block device is set
 667           up. All encrypted block devices are set up after this target
 668           has been reached. Since the shutdown order is implicitly the
 669           reverse start-up order between units, this target is
 670           particularly useful to ensure that a service is shut down
 671           only after all encrypted block devices are fully
 672           stopped.</para>
 673         </listitem>
 674       </varlistentry>
 675       <varlistentry>
 676         <term><filename>local-fs-pre.target</filename></term>
 677         <listitem>
 678           <para>This target unit is
 679           automatically ordered before
 680           all local mount points marked
 681           with <option>auto</option>
 682           (see above). It can be used to
 683           execute certain units before
 684           all local mounts.</para>
 685         </listitem>
 686       </varlistentry>
 687       <varlistentry>
 688         <term><filename>network.target</filename></term>
 689         <listitem>
 690           <para>This unit is supposed to indicate when network
 691           functionality is available, but it is only very weakly
 692           defined what that is supposed to mean, with one exception:
 693           at shutdown, a unit that is ordered after
 694           <filename>network.target</filename> will be stopped before
 695           the network -- to whatever level it might be set up then --
 696           is shut down. It is hence useful when writing service files
 697           that require network access on shutdown, which should order
 698           themselves after this target, but not pull it in. Also see
 699           <ulink url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 700           Services After the Network is up</ulink> for more
 701           information. Also see
 702           <filename>network-online.target</filename> described
 703           above.</para>
 704
 705           <para>systemd automatically adds dependencies of type
 706           <varname>After=</varname> for this target unit to all SysV
 707           init script service units with an LSB header referring to
 708           the <literal>$network</literal> facility.</para>
 709         </listitem>
 710       </varlistentry>
 711       <varlistentry>
 712         <term><filename>network-pre.target</filename></term>
 713         <listitem>
 714           <para>This passive target unit may be pulled in by services
 715           that want to run before any network is set up, for example
 716           for the purpose of setting up a firewall. All network
 717           management software orders itself after this target, but
 718           does not pull it in.</para>
 719         </listitem>
 720       </varlistentry>
 721       <varlistentry>
 722         <term><filename>nss-lookup.target</filename></term>
 723         <listitem>
 724           <para>A target that should be used as synchronization point
 725           for all host/network name service lookups. Note that this is
 726           independent of user/group name lookups for which
 727           <filename>nss-user-lookup.target</filename> should be used.
 728           All services for which the availability of full host/network
 729           name resolution is essential should be ordered after this
 730           target, but not pull it in. systemd automatically adds
 731           dependencies of type <varname>After=</varname> for this
 732           target unit to all SysV init script service units with an
 733           LSB header referring to the <literal>$named</literal>
 734           facility.</para>
 735         </listitem>
 736       </varlistentry>
 737       <varlistentry>
 738         <term><filename>nss-user-lookup.target</filename></term>
 739         <listitem>
 740           <para>A target that should be used as synchronization point
 741           for all user/group name service lookups. Note that this is
 742           independent of host/network name lookups for which
 743           <filename>nss-lookup.target</filename> should be used. All
 744           services for which the availability of the full user/group
 745           database is essential should be ordered after this target,
 746           but not pull it in. Note that system users are always
 747           resolvable, and hence do not require any special ordering
 748           against this target.</para>
 749         </listitem>
 750       </varlistentry>
 751       <varlistentry>
 752         <term><filename>remote-fs-pre.target</filename></term>
 753         <listitem>
 754           <para>This target unit is automatically ordered before all
 755           remote mount point units (see above). It can be used to run
 756           certain units before the remote mounts are established. Note
 757           that this unit is generally not part of the initial
 758           transaction, unless the unit that wants to be ordered before
 759           all remote mounts pulls it in via a
 760           <varname>Wants=</varname> type dependency. If the unit wants
 761           to be pulled in by the first remote mount showing up, it
 762           should use <filename>network-online.target</filename> (see
 763           above).</para>
 764         </listitem>
 765       </varlistentry>
 766       <varlistentry>
 767         <term><filename>rpcbind.target</filename></term>
 768         <listitem>
 769           <para>The portmapper/rpcbind pulls in this target and orders
 770           itself before it, to indicate its availability. systemd
 771           automatically adds dependencies of type
 772           <varname>After=</varname> for this target unit to all SysV
 773           init script service units with an LSB header referring to
 774           the <literal>$portmap</literal> facility.</para>
 775         </listitem>
 776       </varlistentry>
 777       <varlistentry>
 778         <term><filename>time-sync.target</filename></term>
 779         <listitem>
 780           <para>Services responsible for synchronizing the system
 781           clock from a remote source (such as NTP client
 782           implementations) should pull in this target and order
 783           themselves before it. All services where correct time is
 784           essential should be ordered after this unit, but not pull it
 785           in. systemd automatically adds dependencies of type
 786           <varname>After=</varname> for this target unit to all SysV
 787           init script service units with an LSB header referring to
 788           the <literal>$time</literal> facility. </para>
 789         </listitem>
 790       </varlistentry>
 791     </variablelist>
 792   </refsect1>
 793
 794   <refsect1>
 795     <title>Special User Units</title>
 796
 797     <para>When systemd runs as a user instance, the following special
 798     units are available, which have similar definitions as their
 799     system counterparts:
 800     <filename>default.target</filename>,
 801     <filename>shutdown.target</filename>,
 802     <filename>sockets.target</filename>,
 803     <filename>timers.target</filename>,
 804     <filename>paths.target</filename>,
 805     <filename>bluetooth.target</filename>,
 806     <filename>printer.target</filename>,
 807     <filename>smartcard.target</filename>,
 808     <filename>sound.target</filename>.</para>
 809
 810     <para>In addition, the following special unit is understood only
 811     when systemd runs as service instance:</para>
 812
 813     <variablelist>
 814       <varlistentry>
 815         <term><filename>exit.target</filename></term>
 816         <listitem>
 817           <para>A special service unit for shutting down the user
 818           service manager.</para>
 819
 820           <para>Applications wanting to terminate the user service
 821           manager should start this unit. If systemd receives
 822           <constant>SIGTERM</constant> or <constant>SIGINT</constant>
 823           when running as user service daemon, it will start this
 824           unit.</para>
 825
 826           <para>Normally, this pulls in
 827           <filename>shutdown.target</filename> which in turn should be
 828           conflicted by all units that want to be shut down on user
 829           service manager exit.</para>
 830         </listitem>
 831       </varlistentry>
 832     </variablelist>
 833   </refsect1>
 834
 835   <refsect1>
 836     <title>Special Slice Units</title>
 837
 838     <para>There are four <literal>.slice</literal> units which form
 839     the basis of the hierarchy for assignment of resources for
 840     services, users, and virtual machines or containers.</para>
 841
 842     <variablelist>
 843       <varlistentry>
 844         <term><filename>-.slice</filename></term>
 845         <listitem>
 846           <para>The root slice is the root of the hierarchy. It
 847           usually does not contain units directly, but may be used to
 848           set defaults for the whole tree.</para>
 849         </listitem>
 850       </varlistentry>
 851
 852       <varlistentry>
 853         <term><filename>system.slice</filename></term>
 854         <listitem>
 855           <para>By default, all system services started by
 856           <command>systemd</command> are found in this slice.</para>
 857         </listitem>
 858       </varlistentry>
 859
 860       <varlistentry>
 861         <term><filename>user.slice</filename></term>
 862         <listitem>
 863           <para>By default, all user processes and services started on
 864           behalf of the user, including the per-user systemd instance
 865           are found in this slice.</para>
 866         </listitem>
 867       </varlistentry>
 868
 869       <varlistentry>
 870         <term><filename>machine.slice</filename></term>
 871         <listitem>
 872           <para>By default, all virtual machines and containers
 873           registered with <command>systemd-machined</command> are
 874           found in this slice.
 875           </para>
 876         </listitem>
 877       </varlistentry>
 878     </variablelist>
 879   </refsect1>
 880
 881   <refsect1>
 882       <title>See Also</title>
 883       <para>
 884         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 885         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 886         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 887         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 888         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 889         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 890         <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 891         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 892       </para>
 893   </refsect1>
 894
 895 </refentry>