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