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
 116                 systemd. They have special internal semantics and
 117                 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
 128                                         covering basic boot-up.</para>
 129                                         <para>systemd automatically
 130                                         adds dependencies of the types
 131                                         <varname>Requires=</varname>
 132                                         and <varname>After=</varname>
 133                                         for this target unit to all
 134                                         services (except for those
 135                                         with
 136                                         <varname>DefaultDependencies=no</varname>).</para>
 137
 138                                         <para>Usually this should
 139                                         pull-in all mount points, swap
 140                                         devices, sockets, timers, and
 141                                         path units and other basic
 142                                         initialization necessary for
 143                                         general purpose
 144                                         daemons.</para>
 145                                 </listitem>
 146                         </varlistentry>
 147                         <varlistentry>
 148                                 <term><filename>ctrl-alt-del.target</filename></term>
 149                                 <listitem>
 150                                         <para>systemd starts this
 151                                         target whenever
 152                                         Control+Alt+Del is pressed on
 153                                         the console. Usually this
 154                                         should be aliased (symlinked)
 155                                         to
 156                                         <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
 163                                         setup services for all
 164                                         encrypted block
 165                                         devices.</para>
 166                                 </listitem>
 167                         </varlistentry>
 168                         <varlistentry>
 169                                 <term><filename>dbus.service</filename></term>
 170                                 <listitem>
 171                                         <para>A special unit for the
 172                                         D-Bus bus daemon. As soon as
 173                                         this service is fully started
 174                                         up systemd will connect to it
 175                                         and register its
 176                                         service.</para>
 177                                 </listitem>
 178                         </varlistentry>
 179                         <varlistentry>
 180                                 <term><filename>dbus.socket</filename></term>
 181                                 <listitem>
 182                                         <para>A special unit for the
 183                                         D-Bus system bus socket. All
 184                                         units with
 185                                         <varname>Type=dbus</varname>
 186                                         automatically gain a
 187                                         dependency on this
 188                                         unit.</para>
 189                                 </listitem>
 190                         </varlistentry>
 191                         <varlistentry>
 192                                 <term><filename>default.target</filename></term>
 193                                 <listitem>
 194                                         <para>The default unit systemd
 195                                         starts at bootup. Usually this
 196                                         should be aliased (symlinked)
 197                                         to
 198                                         <filename>multi-user.target</filename>
 199                                         or
 200                                         <filename>graphical.target</filename>.</para>
 201
 202                                         <para>The default unit systemd
 203                                         starts at bootup can be
 204                                         overridden with the
 205                                         <varname>systemd.unit=</varname>
 206                                         kernel command line option.</para>
 207                                 </listitem>
 208                         </varlistentry>
 209                         <varlistentry>
 210                                 <term><filename>display-manager.service</filename></term>
 211                                 <listitem>
 212                                         <para>The display manager
 213                                         service. Usually this should
 214                                         be aliased (symlinked) to
 215                                         <filename>gdm.service</filename>
 216                                         or a similar display manager
 217                                         service.</para>
 218                                 </listitem>
 219                         </varlistentry>
 220                         <varlistentry>
 221                                 <term><filename>emergency.target</filename></term>
 222                                 <listitem>
 223                                         <para>A special target unit
 224                                         that starts an emergency
 225                                         shell on the main
 226                                         console. This unit is supposed
 227                                         to be used with the kernel
 228                                         command line option
 229                                         <varname>systemd.unit=</varname>
 230                                         and has otherwise little use.
 231                                         </para>
 232                                 </listitem>
 233                         </varlistentry>
 234                         <varlistentry>
 235                                 <term><filename>final.target</filename></term>
 236                                 <listitem>
 237                                         <para>A special target unit
 238                                         that is used during the
 239                                         shutdown logic and may be used
 240                                         to pull in late services after
 241                                         all normal services are
 242                                         already terminated and all
 243                                         mounts unmounted.
 244                                         </para>
 245                                 </listitem>
 246                         </varlistentry>
 247                         <varlistentry>
 248                                 <term><filename>getty.target</filename></term>
 249                                 <listitem>
 250                                         <para>A special target unit
 251                                         that pulls in statically
 252                                         configured local TTY
 253                                         <filename>getty</filename>
 254                                         instances.
 255                                         </para>
 256                                 </listitem>
 257                         </varlistentry>
 258                         <varlistentry>
 259                                 <term><filename>graphical.target</filename></term>
 260                                 <listitem>
 261                                         <para>A special target unit
 262                                         for setting up a graphical
 263                                         login screen. This pulls in
 264                                         <filename>multi-user.target</filename>.</para>
 265
 266                                         <para>Units that are needed
 267                                         for graphical logins shall add
 268                                         <varname>Wants=</varname>
 269                                         dependencies for their unit to
 270                                         this unit (or
 271                                         <filename>multi-user.target</filename>)
 272                                         during installation. This is
 273                                         best configured via
 274                                         <varname>WantedBy=graphical.target</varname>
 275                                         in the unit's
 276                                         <literal>[Install]</literal>
 277                                         section.</para>
 278                                 </listitem>
 279                         </varlistentry>
 280                         <varlistentry>
 281                                 <term><filename>hibernate.target</filename></term>
 282                                 <listitem>
 283                                         <para>A special target unit
 284                                         for hibernating the
 285                                         system. This pulls in
 286                                         <filename>sleep.target</filename>.</para>
 287                                 </listitem>
 288                         </varlistentry>
 289                         <varlistentry>
 290                                 <term><filename>hybrid-sleep.target</filename></term>
 291                                 <listitem>
 292                                         <para>A special target unit
 293                                         for hibernating and suspending the
 294                                         system at the same time. This pulls in
 295                                         <filename>sleep.target</filename>.</para>
 296                                 </listitem>
 297                         </varlistentry>
 298                         <varlistentry>
 299                                 <term><filename>halt.target</filename></term>
 300                                 <listitem>
 301                                         <para>A special target unit
 302                                         for shutting down and halting
 303                                         the system. Note that this
 304                                         target is distinct from
 305                                         <filename>poweroff.target</filename>
 306                                         in that it generally really
 307                                         just halts the system rather
 308                                         than powering it down.</para>
 309
 310                                         <para>Applications wanting to
 311                                         halt the system should start
 312                                         this unit.</para>
 313                                 </listitem>
 314                         </varlistentry>
 315                         <varlistentry>
 316                                 <term><filename>initrd-fs.target</filename></term>
 317                                 <listitem>
 318                                         <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 319                                         automatically adds
 320                                         dependencies of type
 321                                         <varname>Before=</varname> to
 322                                         <filename>sysroot-usr.mount</filename>
 323                                         and all mount points found in
 324                                         <filename>/etc/fstab</filename>
 325                                         that have
 326                                         <option>x-initrd.mount</option>
 327                                         and not have <option>noauto</option>
 328                                         mount options set.</para>
 329                                 </listitem>
 330                         </varlistentry>
 331                         <varlistentry>
 332                                 <term><filename>kbrequest.target</filename></term>
 333                                 <listitem>
 334                                         <para>systemd starts this
 335                                         target whenever Alt+ArrowUp is
 336                                         pressed on the console. This
 337                                         is a good candidate to be
 338                                         aliased (symlinked) to
 339                                         <filename>rescue.target</filename>.</para>
 340                                 </listitem>
 341                         </varlistentry>
 342                         <varlistentry>
 343                                 <term><filename>kexec.target</filename></term>
 344                                 <listitem>
 345                                         <para>A special target unit
 346                                         for shutting down and rebooting the system via kexec.</para>
 347
 348                                         <para>Applications wanting to
 349                                         reboot the system with kexec should start
 350                                         this unit.</para>
 351                                 </listitem>
 352                         </varlistentry>
 353                         <varlistentry>
 354                                 <term><filename>local-fs.target</filename></term>
 355                                 <listitem>
 356                                         <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 357                                         automatically adds
 358                                         dependencies of type
 359                                         <varname>Before=</varname> to
 360                                         all mount units that refer to
 361                                         local mount points for this
 362                                         target unit. In addition, it
 363                                         adds dependencies of type
 364                                         <varname>Wants=</varname> to
 365                                         this target unit for those
 366                                         mounts listed in
 367                                         <filename>/etc/fstab</filename>
 368                                         that have the
 369                                         <option>auto</option> mount
 370                                         option set.</para>
 371                                 </listitem>
 372                         </varlistentry>
 373                         <varlistentry>
 374                                 <term><filename>multi-user.target</filename></term>
 375                                 <listitem>
 376                                         <para>A special target unit
 377                                         for setting up a multi-user
 378                                         system (non-graphical). This
 379                                         is pulled in by
 380                                         <filename>graphical.target</filename>.</para>
 381
 382                                         <para>Units that are needed
 383                                         for a multi-user system shall
 384                                         add <varname>Wants=</varname>
 385                                         dependencies for their unit to
 386                                         this unit during
 387                                         installation. This is best
 388                                         configured via
 389                                         <varname>WantedBy=multi-user.target</varname>
 390                                         in the unit's
 391                                         <literal>[Install]</literal>
 392                                         section.</para>
 393                                 </listitem>
 394                         </varlistentry>
 395                         <varlistentry>
 396                                 <term><filename>network-online.target</filename></term>
 397                                 <listitem>
 398                                         <para>Units that strictly
 399                                         require a configured network
 400                                         connection should pull in
 401                                         <filename>network-online.target</filename>
 402                                         (via a
 403                                         <varname>Wants=</varname> type
 404                                         dependency) and order
 405                                         themselves after it. This
 406                                         target unit is intended to
 407                                         pull in a service that delays
 408                                         further execution until the
 409                                         network is sufficiently set
 410                                         up. What precisely this
 411                                         requires is left to the
 412                                         implementation of the network
 413                                         managing service.</para>
 414
 415                                         <para>Note the distinction
 416                                         between this unit and
 417                                         <filename>network.target</filename>. This
 418                                         unit is an active unit
 419                                         (i.e. pulled in by the
 420                                         consumer rather than the
 421                                         provider of this
 422                                         functionality) and pulls in a
 423                                         service which possibly adds
 424                                         substantial delays to further
 425                                         execution. In contrast,
 426                                         <filename>network.target</filename>
 427                                         is a passive unit (i.e. pulled
 428                                         in by the provider of the
 429                                         functionality, rather than the
 430                                         consumer) that usually does
 431                                         not delay execution
 432                                         much. Usually,
 433                                         <filename>network.target</filename>
 434                                         is part of the boot of most
 435                                         systems, while
 436                                         <filename>network-online.target</filename>
 437                                         is not, except when at least
 438                                         one unit requires it. Also see
 439                                         <ulink
 440                                         url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 441                                         Services After the Network is
 442                                         up</ulink> for more
 443                                         information.</para>
 444
 445                                         <para>All mount units for
 446                                         remote network file systems
 447                                         automatically pull in this
 448                                         unit, and order themselves
 449                                         after it. Note that networking
 450                                         daemons that simply provide
 451                                         functionality to other hosts
 452                                         generally do not need to pull
 453                                         this in.</para>
 454                                         </listitem>
 455                         </varlistentry>
 456                         <varlistentry>
 457                                 <term><filename>paths.target</filename></term>
 458                                 <listitem>
 459                                         <para>A special target unit
 460                                         that sets up all path units
 461                                         (see
 462                                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 463                                         for details) that shall be
 464                                         active after boot.</para>
 465
 466                                         <para>It is recommended that
 467                                         path units installed by
 468                                         applications get pulled in via
 469                                         <varname>Wants=</varname>
 470                                         dependencies from this
 471                                         unit. This is best configured
 472                                         via a
 473                                         <varname>WantedBy=paths.target</varname>
 474                                         in the path unit's
 475                                         <literal>[Install]</literal>
 476                                         section.</para>
 477                                 </listitem>
 478                         </varlistentry>
 479                         <varlistentry>
 480                                 <term><filename>poweroff.target</filename></term>
 481                                 <listitem>
 482                                         <para>A special target unit
 483                                         for shutting down and powering off the system.</para>
 484
 485                                         <para>Applications wanting to
 486                                         power off the system should start
 487                                         this unit.</para>
 488
 489                                         <para><filename>runlevel0.target</filename>
 490                                         is an alias for this target
 491                                         unit, for compatibility with SysV.</para>
 492                                 </listitem>
 493                         </varlistentry>
 494                         <varlistentry>
 495                                 <term><filename>reboot.target</filename></term>
 496                                 <listitem>
 497                                         <para>A special target unit
 498                                         for shutting down and rebooting the system.</para>
 499
 500                                         <para>Applications wanting to
 501                                         reboot the system should start
 502                                         this unit.</para>
 503
 504                                         <para><filename>runlevel6.target</filename>
 505                                         is an alias for this target
 506                                         unit, for compatibility with SysV.</para>
 507                                 </listitem>
 508                         </varlistentry>
 509                         <varlistentry>
 510                                 <term><filename>remote-fs.target</filename></term>
 511                                 <listitem>
 512                                         <para>Similar to
 513                                         <filename>local-fs.target</filename>,
 514                                         but for remote mount
 515                                         points.</para>
 516
 517                                         <para>systemd automatically
 518                                         adds dependencies of type
 519                                         <varname>After=</varname> for
 520                                         this target unit to all SysV
 521                                         init script service units with
 522                                         an LSB header referring to the
 523                                         <literal>$remote_fs</literal>
 524                                         facility.</para>
 525                                 </listitem>
 526                         </varlistentry>
 527                         <varlistentry>
 528                                 <term><filename>rescue.target</filename></term>
 529                                 <listitem>
 530                                         <para>A special target unit
 531                                         for setting up the base system
 532                                         and a rescue shell.</para>
 533
 534                                         <para><filename>runlevel1.target</filename>
 535                                         is an alias for this target
 536                                         unit, for compatibility with SysV.</para>
 537                                 </listitem>
 538                         </varlistentry>
 539                         <varlistentry>
 540                                 <term><filename>initrd-root-fs.target</filename></term>
 541                                 <listitem>
 542                                         <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 543                                         automatically adds
 544                                         dependencies of type
 545                                         <varname>Before=</varname> to
 546                                         the
 547                                         <filename>sysroot.mount</filename>
 548                                         unit, which is generated from
 549                                         the kernel command line.
 550                                         </para>
 551                                 </listitem>
 552                         </varlistentry>
 553                         <varlistentry>
 554                                 <term><filename>runlevel2.target</filename></term>
 555                                 <term><filename>runlevel3.target</filename></term>
 556                                 <term><filename>runlevel4.target</filename></term>
 557                                 <term><filename>runlevel5.target</filename></term>
 558                                 <listitem>
 559                                         <para>These are targets that
 560                                         are called whenever the SysV
 561                                         compatibility code asks for
 562                                         runlevel 2, 3, 4, 5,
 563                                         respectively. It is a good
 564                                         idea to make this an alias for
 565                                         (i.e. symlink to)
 566                                         <filename>multi-user.target</filename>
 567                                         (for runlevel 2) or
 568                                         <filename>graphical.target</filename>
 569                                         (the others).</para>
 570                                 </listitem>
 571                         </varlistentry>
 572                         <varlistentry>
 573                                 <term><filename>shutdown.target</filename></term>
 574                                 <listitem>
 575                                         <para>A special target unit
 576                                         that terminates the services
 577                                         on system shutdown.</para>
 578
 579                                         <para>Services that shall be
 580                                         terminated on system shutdown
 581                                         shall add <varname>Conflicts=</varname>
 582                                         dependencies to this unit for
 583                                         their service unit, which is
 584                                         implicitly done when
 585                                         <varname>DefaultDependencies=yes</varname>
 586                                         is set (the default).</para>
 587                                 </listitem>
 588                         </varlistentry>
 589                         <varlistentry>
 590                                 <term><filename>sigpwr.target</filename></term>
 591                                 <listitem>
 592                                         <para>A special target that is
 593                                         started when systemd receives
 594                                         the SIGPWR process signal,
 595                                         which is normally sent by the
 596                                         kernel or UPS daemons when
 597                                         power fails.</para>
 598                                 </listitem>
 599                         </varlistentry>
 600                         <varlistentry>
 601                                 <term><filename>sleep.target</filename></term>
 602                                 <listitem>
 603                                         <para>A special target unit
 604                                         that is pulled in by
 605                                         <filename>suspend.target</filename>,
 606                                         <filename>hibernate.target</filename>
 607                                         and
 608                                         <filename>hybrid-sleep.target</filename>
 609                                         and may be used to hook units
 610                                         into the sleep state
 611                                         logic.</para>
 612                                 </listitem>
 613                         </varlistentry>
 614                         <varlistentry>
 615                                 <term><filename>sockets.target</filename></term>
 616                                 <listitem>
 617                                         <para>A special target unit
 618                                         that sets up all socket
 619                                         units.(see
 620                                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 621                                         for details) that shall be
 622                                         active after boot.</para>
 623
 624                                         <para>Services that can be
 625                                         socket-activated shall add
 626                                         <varname>Wants=</varname>
 627                                         dependencies to this unit for
 628                                         their socket unit during
 629                                         installation. This is best
 630                                         configured via a
 631                                         <varname>WantedBy=sockets.target</varname>
 632                                         in the socket unit's
 633                                         <literal>[Install]</literal>
 634                                         section.</para>
 635                                 </listitem>
 636                         </varlistentry>
 637                         <varlistentry>
 638                                 <term><filename>suspend.target</filename></term>
 639                                 <listitem>
 640                                         <para>A special target unit
 641                                         for suspending the
 642                                         system. This pulls in
 643                                         <filename>sleep.target</filename>.</para>
 644                                 </listitem>
 645                         </varlistentry>
 646                         <varlistentry>
 647                                 <term><filename>swap.target</filename></term>
 648                                 <listitem>
 649                                         <para>Similar to
 650                                         <filename>local-fs.target</filename>, but for swap
 651                                         partitions and swap
 652                                         files.</para>
 653                                 </listitem>
 654                         </varlistentry>
 655                         <varlistentry>
 656                                 <term><filename>sysinit.target</filename></term>
 657                                 <listitem>
 658                                         <para>A special target unit
 659                                         covering early boot-up scripts.</para>
 660                                 </listitem>
 661                         </varlistentry>
 662                         <varlistentry>
 663                                 <term><filename>syslog.socket</filename></term>
 664                                 <listitem>
 665                                         <para>The socket unit
 666                                         syslog implementations should
 667                                         listen on. All userspace log
 668                                         messages will be made
 669                                         available on this socket. For
 670                                         more information about syslog
 671                                         integration, please consult
 672                                         the <ulink
 673                                         url="http://www.freedesktop.org/wiki/Software/systemd/syslog">Syslog
 674                                         Interface</ulink>
 675                                         document.</para>
 676                                 </listitem>
 677                         </varlistentry>
 678                         <varlistentry>
 679                                 <term><filename>system-update.target</filename></term>
 680                                 <listitem>
 681                                         <para>A special target unit
 682                                         that is used for off-line
 683                                         system updates.
 684                                         <citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 685                                         will redirect the boot process
 686                                         to this target if
 687                                         <filename>/system-update</filename>
 688                                         exists. For more information
 689                                         see the <ulink
 690                                         url="http://freedesktop.org/wiki/Software/systemd/SystemUpdates">System
 691                                         Updates
 692                                         Specification</ulink>.</para>
 693                                 </listitem>
 694                         </varlistentry>
 695                         <varlistentry>
 696                                 <term><filename>timers.target</filename></term>
 697                                 <listitem>
 698                                         <para>A special target unit
 699                                         that sets up all timer
 700                                         units (see
 701                                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 702                                         for details) that shall be
 703                                         active after boot.</para>
 704
 705                                         <para>It is recommended that
 706                                         timer units installed by
 707                                         applications get pulled in via
 708                                         <varname>Wants=</varname>
 709                                         dependencies from this
 710                                         unit. This is best configured
 711                                         via
 712                                         <varname>WantedBy=timers.target</varname>
 713                                         in the timer unit's
 714                                         <literal>[Install]</literal>
 715                                         section.</para>
 716                                 </listitem>
 717                         </varlistentry>
 718                         <varlistentry>
 719                                 <term><filename>umount.target</filename></term>
 720                                 <listitem>
 721                                         <para>A special target unit
 722                                         that umounts all mount and
 723                                         automount points on system
 724                                         shutdown.</para>
 725
 726                                         <para>Mounts that shall be
 727                                         unmounted on system shutdown
 728                                         shall add Conflicts
 729                                         dependencies to this unit for
 730                                         their mount unit, which is
 731                                         implicitly done when
 732                                         <varname>DefaultDependencies=yes</varname>
 733                                         is set (the default).</para>
 734                                 </listitem>
 735                         </varlistentry>
 736
 737                 </variablelist>
 738         </refsect1>
 739
 740         <refsect1>
 741                 <title>Special System Units for Devices</title>
 742
 743                 <para>Some target units are automatically pulled in as
 744                 devices of certain kinds show up in the system. These
 745                 may be used to automatically activate various services
 746                 based on the specific type of the available
 747                 hardware.</para>
 748
 749                 <variablelist>
 750                         <varlistentry>
 751                                 <term><filename>bluetooth.target</filename></term>
 752                                 <listitem>
 753                                         <para>This target is started
 754                                         automatically as soon as a
 755                                         Bluetooth controller is
 756                                         plugged in or becomes
 757                                         available at boot.</para>
 758
 759                                         <para>This may be used to pull
 760                                         in Bluetooth management
 761                                         daemons dynamically when
 762                                         Bluetooth hardware is
 763                                         found.</para>
 764                                 </listitem>
 765                         </varlistentry>
 766                         <varlistentry>
 767                                 <term><filename>printer.target</filename></term>
 768                                 <listitem>
 769                                         <para>This target is started
 770                                         automatically as soon as a
 771                                         printer is plugged in or
 772                                         becomes available at
 773                                         boot.</para>
 774
 775                                         <para>This may be used to pull
 776                                         in printer management
 777                                         daemons dynamically when
 778                                         printer hardware is
 779                                         found.</para>
 780                                 </listitem>
 781                         </varlistentry>
 782                         <varlistentry>
 783                                 <term><filename>smartcard.target</filename></term>
 784                                 <listitem>
 785                                         <para>This target is started
 786                                         automatically as soon as a
 787                                         smartcard controller is
 788                                         plugged in or becomes
 789                                         available at boot.</para>
 790
 791                                         <para>This may be used to pull
 792                                         in smartcard management
 793                                         daemons dynamically when
 794                                         smartcard hardware is
 795                                         found.</para>
 796                                 </listitem>
 797                         </varlistentry>
 798                         <varlistentry>
 799                                 <term><filename>sound.target</filename></term>
 800                                 <listitem>
 801                                         <para>This target is started
 802                                         automatically as soon as a
 803                                         sound card is plugged in or
 804                                         becomes available at
 805                                         boot.</para>
 806
 807                                         <para>This may be used to pull
 808                                         in audio management daemons
 809                                         dynamically when audio
 810                                         hardware is found.</para>
 811                                 </listitem>
 812                         </varlistentry>
 813                 </variablelist>
 814         </refsect1>
 815
 816         <refsect1>
 817                 <title>Special Passive System Units </title>
 818
 819                 <para>A number of special system targets are defined
 820                 that can be used to properly order boot-up of optional
 821                 services. These targets are generally not part of the
 822                 initial boot transaction, unless they are explicitly
 823                 pulled in by one of the implementing services. Note
 824                 specifically that these <emphasis>passive</emphasis>
 825                 target units are generally not pulled in by the
 826                 consumer of a service, but by the provider of the
 827                 service. This means: a consuming service should order
 828                 itself after these targets (as appropriate), but not
 829                 pull it in. A providing service should order itself
 830                 before these targets (as appropriate) and pull it in
 831                 (via a <varname>Wants=</varname> type
 832                 dependency).</para>
 833
 834                 <para>Note that these passive units cannot be started
 835                 manually, i.e. <literal>systemctl start
 836                 time-sync.target</literal> will fail with an
 837                 error. They can only be pulled in by dependency. This
 838                 is enforced since they exist for ordering purposes
 839                 only and thus are not useful as only unit within a
 840                 transaction.</para>
 841
 842                 <variablelist>
 843                         <varlistentry>
 844                                 <term><filename>cryptsetup-pre.target</filename></term>
 845                                 <listitem>
 846                                         <para>This passive target unit
 847                                         may be pulled in by services
 848                                         that want to run before any
 849                                         encrypted block device is set
 850                                         up. All encrypted block
 851                                         devices are set up after this
 852                                         target has been reached. Since
 853                                         the shutdown order is
 854                                         implicitly the reverse
 855                                         start-up order between units,
 856                                         this target is particularly
 857                                         useful to ensure that a
 858                                         service is shut down only
 859                                         after all encrypted block
 860                                         devices are fully
 861                                         stopped.</para>
 862                                 </listitem>
 863                         </varlistentry>
 864                         <varlistentry>
 865                                 <term><filename>local-fs-pre.target</filename></term>
 866                                 <listitem>
 867                                         <para>This target unit is
 868                                         automatically ordered before
 869                                         all local mount points marked
 870                                         with <option>auto</option>
 871                                         (see above). It can be used to
 872                                         execute certain units before
 873                                         all local mounts.</para>
 874                                 </listitem>
 875                         </varlistentry>
 876                         <varlistentry>
 877                                 <term><filename>network.target</filename></term>
 878                                 <listitem>
 879                                         <para>This unit is supposed to
 880                                         indicate when network
 881                                         functionality is available,
 882                                         but it is only very weakly
 883                                         defined what that is supposed
 884                                         to mean, with one exception:
 885                                         at shutdown, a unit that is
 886                                         ordered after
 887                                         <filename>network.target</filename>
 888                                         will be stopped before the
 889                                         network -- to whatever level
 890                                         it might be set up then -- is
 891                                         shut down. It is hence useful
 892                                         when writing service files
 893                                         that require network access on
 894                                         shutdown, which should order
 895                                         themselves after this target,
 896                                         but not pull it in. Also see
 897                                         <ulink
 898                                         url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 899                                         Services After the Network is
 900                                         up</ulink> for more
 901                                         information. Also see
 902                                         <filename>network-online.target</filename>
 903                                         described above.</para>
 904
 905                                         <para>systemd automatically
 906                                         adds dependencies of type
 907                                         <varname>After=</varname> for
 908                                         this target unit to all SysV
 909                                         init script service units with
 910                                         an LSB header referring to the
 911                                         <literal>$network</literal>
 912                                         facility.</para>
 913                                 </listitem>
 914                         </varlistentry>
 915                         <varlistentry>
 916                                 <term><filename>network-pre.target</filename></term>
 917                                 <listitem>
 918                                         <para>This passive target unit
 919                                         may be pulled in by services
 920                                         that want to run before any
 921                                         network is set up, for example
 922                                         for the purpose of setting up a
 923                                         firewall. All network
 924                                         management software orders
 925                                         itself after this target, but
 926                                         does not pull it in.</para>
 927                                 </listitem>
 928                         </varlistentry>
 929                         <varlistentry>
 930                                 <term><filename>nss-lookup.target</filename></term>
 931                                 <listitem>
 932                                         <para>A target that should be
 933                                         used as synchronization point
 934                                         for all host/network name
 935                                         service lookups. Note that
 936                                         this is independent of
 937                                         user/group name lookups for
 938                                         which
 939                                         <filename>nss-user-lookup.target</filename>
 940                                         should be used. All services
 941                                         for which the availability of
 942                                         full host/network name
 943                                         resolution is essential should
 944                                         be ordered after this target,
 945                                         but not pull it in. systemd
 946                                         automatically adds
 947                                         dependencies of type
 948                                         <varname>After=</varname> for
 949                                         this target unit to all SysV
 950                                         init script service units with
 951                                         an LSB header referring to the
 952                                         <literal>$named</literal>
 953                                         facility.</para>
 954                                 </listitem>
 955                         </varlistentry>
 956                         <varlistentry>
 957                                 <term><filename>nss-user-lookup.target</filename></term>
 958                                 <listitem>
 959                                         <para>A target that should be
 960                                         used as synchronization point
 961                                         for all user/group name
 962                                         service lookups. Note that
 963                                         this is independent of
 964                                         host/network name lookups for
 965                                         which
 966                                         <filename>nss-lookup.target</filename>
 967                                         should be used. All services
 968                                         for which the availability of
 969                                         the full user/group database is
 970                                         essential should be ordered
 971                                         after this target, but not
 972                                         pull it in. Note that system
 973                                         users are always resolvable,
 974                                         and hence do not require any
 975                                         special ordering against this
 976                                         target.</para>
 977                                 </listitem>
 978                         </varlistentry>
 979                         <varlistentry>
 980                                 <term><filename>remote-fs-pre.target</filename></term>
 981                                 <listitem>
 982                                         <para>This target unit is
 983                                         automatically ordered before
 984                                         all remote mount point units
 985                                         (see above). It can be used to
 986                                         run certain units before the
 987                                         remote mounts are
 988                                         established. Note that this
 989                                         unit is generally not part of
 990                                         the initial transaction,
 991                                         unless the unit that wants to
 992                                         be ordered before all remote
 993                                         mounts pulls it in via a
 994                                         <varname>Wants=</varname> type
 995                                         dependency. If the unit wants
 996                                         to be pulled in by the first
 997                                         remote mount showing up, it
 998                                         should use
 999                                         <filename>network-online.target</filename>
1000                                         (see above).</para>
1001                                 </listitem>
1002                         </varlistentry>
1003                         <varlistentry>
1004                                 <term><filename>rpcbind.target</filename></term>
1005                                 <listitem>
1006                                         <para>The portmapper/rpcbind
1007                                         pulls in this target and
1008                                         orders itself before it, to
1009                                         indicate its
1010                                         availability. systemd
1011                                         automatically adds
1012                                         dependencies of type
1013                                         <varname>After=</varname> for
1014                                         this target unit to all SysV
1015                                         init script service units with
1016                                         an LSB header referring to the
1017                                         <literal>$portmap</literal>
1018                                         facility.</para>
1019                                 </listitem>
1020                         </varlistentry>
1021                         <varlistentry>
1022                                 <term><filename>time-sync.target</filename></term>
1023                                 <listitem>
1024                                         <para>Services responsible for
1025                                         synchronizing the system clock
1026                                         from a remote source (such as
1027                                         NTP client implementations)
1028                                         should pull in this target and
1029                                         order themselves before
1030                                         it. All services where correct
1031                                         time is essential should be
1032                                         ordered after this unit, but
1033                                         not pull it in. systemd
1034                                         automatically adds
1035                                         dependencies of type
1036                                         <varname>After=</varname> for
1037                                         this target unit to all SysV
1038                                         init script service units with
1039                                         an LSB header referring to the
1040                                         <literal>$time</literal>
1041                                         facility. </para>
1042                                 </listitem>
1043                         </varlistentry>
1044                 </variablelist>
1045         </refsect1>
1046
1047         <refsect1>
1048                 <title>Special User Units</title>
1049
1050                 <para>When systemd runs as a user instance, the
1051                 following special units are available, which have
1052                 similar definitions as their system counterparts:
1053                 <filename>default.target</filename>,
1054                 <filename>shutdown.target</filename>,
1055                 <filename>sockets.target</filename>,
1056                 <filename>timers.target</filename>,
1057                 <filename>paths.target</filename>,
1058                 <filename>bluetooth.target</filename>,
1059                 <filename>printer.target</filename>,
1060                 <filename>smartcard.target</filename>,
1061                 <filename>sound.target</filename>.</para>
1062
1063                 <para>In addition, the following special unit is
1064                 understood only when systemd runs as service instance:</para>
1065
1066                 <variablelist>
1067                         <varlistentry>
1068                                 <term><filename>exit.target</filename></term>
1069                                 <listitem>
1070                                         <para>A special service unit
1071                                         for shutting down the
1072                                         user service manager.</para>
1073
1074                                         <para>Applications wanting to
1075                                         terminate the user service
1076                                         manager should start this
1077                                         unit. If systemd receives
1078                                         <constant>SIGTERM</constant> or <constant>SIGINT</constant> when running
1079                                         as user service daemon, it will
1080                                         start this unit.</para>
1081
1082                                         <para>Normally, this pulls in
1083                                         <filename>shutdown.target</filename>
1084                                         which in turn should be
1085                                         conflicted by all units that
1086                                         want to be shut down on
1087                                         user service manager exit.</para>
1088                                 </listitem>
1089                         </varlistentry>
1090                 </variablelist>
1091         </refsect1>
1092
1093         <refsect1>
1094                 <title>Special Slice Units</title>
1095
1096                 <para>There are four <literal>.slice</literal> units
1097                 which form the basis of the hierarchy for assignment
1098                 of resources for services, users, and virtual machines
1099                 or containers.</para>
1100
1101                 <variablelist>
1102                         <varlistentry>
1103                                 <term><filename>-.slice</filename></term>
1104                                 <listitem>
1105                                         <para>The root slice is the
1106                                         root of the hierarchy. It
1107                                         usually does not contain units
1108                                         directly, but may be used to
1109                                         set defaults for the whole
1110                                         tree.</para>
1111                                 </listitem>
1112                         </varlistentry>
1113
1114                         <varlistentry>
1115                                 <term><filename>system.slice</filename></term>
1116                                 <listitem>
1117                                         <para>By default, all services
1118                                         services started by
1119                                         <command>systemd</command> are
1120                                         found in this slice.</para>
1121                                 </listitem>
1122                         </varlistentry>
1123
1124                         <varlistentry>
1125                                 <term><filename>user.slice</filename></term>
1126                                 <listitem>
1127                                         <para>By default, all user
1128                                         processes and services started
1129                                         on behalf of the user,
1130                                         including the per-user systemd
1131                                         instance are found in this
1132                                         slice.</para>
1133                                 </listitem>
1134                         </varlistentry>
1135
1136                         <varlistentry>
1137                                 <term><filename>machine.slice</filename></term>
1138                                 <listitem>
1139                                         <para>By default, all virtual
1140                                         machines and containers
1141                                         registered with
1142                                         <command>systemd-machined</command>
1143                                         are found in this slice.
1144                                         </para>
1145                                 </listitem>
1146                         </varlistentry>
1147                 </variablelist>
1148         </refsect1>
1149
1150         <refsect1>
1151                   <title>See Also</title>
1152                   <para>
1153                           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1154                           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1155                           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1156                           <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1157                           <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1158                           <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1159                           <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1160                           <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1161                   </para>
1162         </refsect1>
1163
1164 </refentry>