man/systemd.special.xml

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