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 the
 326                                         <option>auto</option> and
 327                                         <option>x-initrd.mount</option>
 328                                         mount options set.
 329                                         </para>
 330                                 </listitem>
 331                         </varlistentry>
 332                         <varlistentry>
 333                                 <term><filename>kbrequest.target</filename></term>
 334                                 <listitem>
 335                                         <para>systemd starts this
 336                                         target whenever Alt+ArrowUp is
 337                                         pressed on the console. This
 338                                         is a good candidate to be
 339                                         aliased (symlinked) to
 340                                         <filename>rescue.target</filename>.</para>
 341                                 </listitem>
 342                         </varlistentry>
 343                         <varlistentry>
 344                                 <term><filename>kexec.target</filename></term>
 345                                 <listitem>
 346                                         <para>A special target unit
 347                                         for shutting down and rebooting the system via kexec.</para>
 348
 349                                         <para>Applications wanting to
 350                                         reboot the system with kexec should start
 351                                         this unit.</para>
 352                                 </listitem>
 353                         </varlistentry>
 354                         <varlistentry>
 355                                 <term><filename>local-fs.target</filename></term>
 356                                 <listitem>
 357                                         <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 358                                         automatically adds
 359                                         dependencies of type
 360                                         <varname>Before=</varname> to
 361                                         all mount units that refer to
 362                                         local mount points for this
 363                                         target unit. In addition, it
 364                                         adds dependencies of type
 365                                         <varname>Wants=</varname> to
 366                                         this target unit for those
 367                                         mounts listed in
 368                                         <filename>/etc/fstab</filename>
 369                                         that have the
 370                                         <option>auto</option> mount
 371                                         option set.</para>
 372                                 </listitem>
 373                         </varlistentry>
 374                         <varlistentry>
 375                                 <term><filename>multi-user.target</filename></term>
 376                                 <listitem>
 377                                         <para>A special target unit
 378                                         for setting up a multi-user
 379                                         system (non-graphical). This
 380                                         is pulled in by
 381                                         <filename>graphical.target</filename>.</para>
 382
 383                                         <para>Units that are needed
 384                                         for a multi-user system shall
 385                                         add <varname>Wants=</varname>
 386                                         dependencies for their unit to
 387                                         this unit during
 388                                         installation. This is best
 389                                         configured via
 390                                         <varname>WantedBy=multi-user.target</varname>
 391                                         in the unit's
 392                                         <literal>[Install]</literal>
 393                                         section.</para>
 394                                 </listitem>
 395                         </varlistentry>
 396                         <varlistentry>
 397                                 <term><filename>network-online.target</filename></term>
 398                                 <listitem>
 399                                         <para>Units that strictly
 400                                         require a configured network
 401                                         connection should pull in
 402                                         <filename>network-online.target</filename>
 403                                         (via a
 404                                         <varname>Wants=</varname> type
 405                                         dependency) and order
 406                                         themselves after it. This
 407                                         target unit is intended to
 408                                         pull in a service that delays
 409                                         further execution until the
 410                                         network is sufficiently set
 411                                         up. What precisely this
 412                                         requires is left to the
 413                                         implementation of the network
 414                                         managing service.</para>
 415
 416                                         <para>Note the distinction
 417                                         between this unit and
 418                                         <filename>network.target</filename>. This
 419                                         unit is an active unit
 420                                         (i.e. pulled in by the
 421                                         consumer rather than the
 422                                         provider of this
 423                                         functionality) and pulls in a
 424                                         service which possibly adds
 425                                         substantial delays to further
 426                                         execution. In contrast,
 427                                         <filename>network.target</filename>
 428                                         is a passive unit (i.e. pulled
 429                                         in by the provider of the
 430                                         functionality, rather than the
 431                                         consumer) that usually does
 432                                         not delay execution
 433                                         much. Usually,
 434                                         <filename>network.target</filename>
 435                                         is part of the boot of most
 436                                         systems, while
 437                                         <filename>network-online.target</filename>
 438                                         is not, except when at least
 439                                         one unit requires it. Also see
 440                                         <ulink
 441                                         url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 442                                         Services After the Network is
 443                                         up</ulink> for more
 444                                         information.</para>
 445
 446                                         <para>All mount units for
 447                                         remote network file systems
 448                                         automatically pull in this
 449                                         unit, and order themselves
 450                                         after it. Note that networking
 451                                         daemons that simply provide
 452                                         functionality to other hosts
 453                                         generally do not need to pull
 454                                         this in.</para>
 455                                         </listitem>
 456                         </varlistentry>
 457                         <varlistentry>
 458                                 <term><filename>paths.target</filename></term>
 459                                 <listitem>
 460                                         <para>A special target unit
 461                                         that sets up all path units
 462                                         (see
 463                                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 464                                         for details) that shall be
 465                                         active after boot.</para>
 466
 467                                         <para>It is recommended that
 468                                         path units installed by
 469                                         applications get pulled in via
 470                                         <varname>Wants=</varname>
 471                                         dependencies from this
 472                                         unit. This is best configured
 473                                         via a
 474                                         <varname>WantedBy=paths.target</varname>
 475                                         in the path unit's
 476                                         <literal>[Install]</literal>
 477                                         section.</para>
 478                                 </listitem>
 479                         </varlistentry>
 480                         <varlistentry>
 481                                 <term><filename>poweroff.target</filename></term>
 482                                 <listitem>
 483                                         <para>A special target unit
 484                                         for shutting down and powering off the system.</para>
 485
 486                                         <para>Applications wanting to
 487                                         power off the system should start
 488                                         this unit.</para>
 489
 490                                         <para><filename>runlevel0.target</filename>
 491                                         is an alias for this target
 492                                         unit, for compatibility with SysV.</para>
 493                                 </listitem>
 494                         </varlistentry>
 495                         <varlistentry>
 496                                 <term><filename>reboot.target</filename></term>
 497                                 <listitem>
 498                                         <para>A special target unit
 499                                         for shutting down and rebooting the system.</para>
 500
 501                                         <para>Applications wanting to
 502                                         reboot the system should start
 503                                         this unit.</para>
 504
 505                                         <para><filename>runlevel6.target</filename>
 506                                         is an alias for this target
 507                                         unit, for compatibility with SysV.</para>
 508                                 </listitem>
 509                         </varlistentry>
 510                         <varlistentry>
 511                                 <term><filename>remote-fs.target</filename></term>
 512                                 <listitem>
 513                                         <para>Similar to
 514                                         <filename>local-fs.target</filename>,
 515                                         but for remote mount
 516                                         points.</para>
 517
 518                                         <para>systemd automatically
 519                                         adds dependencies of type
 520                                         <varname>After=</varname> for
 521                                         this target unit to all SysV
 522                                         init script service units with
 523                                         an LSB header referring to the
 524                                         <literal>$remote_fs</literal>
 525                                         facility.</para>
 526                                 </listitem>
 527                         </varlistentry>
 528                         <varlistentry>
 529                                 <term><filename>rescue.target</filename></term>
 530                                 <listitem>
 531                                         <para>A special target unit
 532                                         for setting up the base system
 533                                         and a rescue shell.</para>
 534
 535                                         <para><filename>runlevel1.target</filename>
 536                                         is an alias for this target
 537                                         unit, for compatibility with SysV.</para>
 538                                 </listitem>
 539                         </varlistentry>
 540                         <varlistentry>
 541                                 <term><filename>initrd-root-fs.target</filename></term>
 542                                 <listitem>
 543                                         <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 544                                         automatically adds
 545                                         dependencies of type
 546                                         <varname>Before=</varname> to
 547                                         the
 548                                         <filename>sysroot.mount</filename>
 549                                         unit, which is generated from
 550                                         the kernel command line.
 551                                         </para>
 552                                 </listitem>
 553                         </varlistentry>
 554                         <varlistentry>
 555                                 <term><filename>runlevel2.target</filename></term>
 556                                 <term><filename>runlevel3.target</filename></term>
 557                                 <term><filename>runlevel4.target</filename></term>
 558                                 <term><filename>runlevel5.target</filename></term>
 559                                 <listitem>
 560                                         <para>These are targets that
 561                                         are called whenever the SysV
 562                                         compatibility code asks for
 563                                         runlevel 2, 3, 4, 5,
 564                                         respectively. It is a good
 565                                         idea to make this an alias for
 566                                         (i.e. symlink to)
 567                                         <filename>multi-user.target</filename>
 568                                         (for runlevel 2) or
 569                                         <filename>graphical.target</filename>
 570                                         (the others).</para>
 571                                 </listitem>
 572                         </varlistentry>
 573                         <varlistentry>
 574                                 <term><filename>shutdown.target</filename></term>
 575                                 <listitem>
 576                                         <para>A special target unit
 577                                         that terminates the services
 578                                         on system shutdown.</para>
 579
 580                                         <para>Services that shall be
 581                                         terminated on system shutdown
 582                                         shall add <varname>Conflicts=</varname>
 583                                         dependencies to this unit for
 584                                         their service unit, which is
 585                                         implicitly done when
 586                                         <varname>DefaultDependencies=yes</varname>
 587                                         is set (the default).</para>
 588                                 </listitem>
 589                         </varlistentry>
 590                         <varlistentry>
 591                                 <term><filename>sigpwr.target</filename></term>
 592                                 <listitem>
 593                                         <para>A special target that is
 594                                         started when systemd receives
 595                                         the SIGPWR process signal,
 596                                         which is normally sent by the
 597                                         kernel or UPS daemons when
 598                                         power fails.</para>
 599                                 </listitem>
 600                         </varlistentry>
 601                         <varlistentry>
 602                                 <term><filename>sleep.target</filename></term>
 603                                 <listitem>
 604                                         <para>A special target unit
 605                                         that is pulled in by
 606                                         <filename>suspend.target</filename>,
 607                                         <filename>hibernate.target</filename>
 608                                         and
 609                                         <filename>hybrid-sleep.target</filename>
 610                                         and may be used to hook units
 611                                         into the sleep state
 612                                         logic.</para>
 613                                 </listitem>
 614                         </varlistentry>
 615                         <varlistentry>
 616                                 <term><filename>sockets.target</filename></term>
 617                                 <listitem>
 618                                         <para>A special target unit
 619                                         that sets up all socket
 620                                         units.(see
 621                                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 622                                         for details) that shall be
 623                                         active after boot.</para>
 624
 625                                         <para>Services that can be
 626                                         socket-activated shall add
 627                                         <varname>Wants=</varname>
 628                                         dependencies to this unit for
 629                                         their socket unit during
 630                                         installation. This is best
 631                                         configured via a
 632                                         <varname>WantedBy=sockets.target</varname>
 633                                         in the socket unit's
 634                                         <literal>[Install]</literal>
 635                                         section.</para>
 636                                 </listitem>
 637                         </varlistentry>
 638                         <varlistentry>
 639                                 <term><filename>suspend.target</filename></term>
 640                                 <listitem>
 641                                         <para>A special target unit
 642                                         for suspending the
 643                                         system. This pulls in
 644                                         <filename>sleep.target</filename>.</para>
 645                                 </listitem>
 646                         </varlistentry>
 647                         <varlistentry>
 648                                 <term><filename>swap.target</filename></term>
 649                                 <listitem>
 650                                         <para>Similar to
 651                                         <filename>local-fs.target</filename>, but for swap
 652                                         partitions and swap
 653                                         files.</para>
 654                                 </listitem>
 655                         </varlistentry>
 656                         <varlistentry>
 657                                 <term><filename>sysinit.target</filename></term>
 658                                 <listitem>
 659                                         <para>A special target unit
 660                                         covering early boot-up scripts.</para>
 661                                 </listitem>
 662                         </varlistentry>
 663                         <varlistentry>
 664                                 <term><filename>syslog.socket</filename></term>
 665                                 <listitem>
 666                                         <para>The socket unit
 667                                         syslog implementations should
 668                                         listen on. All userspace log
 669                                         messages will be made
 670                                         available on this socket. For
 671                                         more information about syslog
 672                                         integration, please consult
 673                                         the <ulink
 674                                         url="http://www.freedesktop.org/wiki/Software/systemd/syslog">Syslog
 675                                         Interface</ulink>
 676                                         document.</para>
 677                                 </listitem>
 678                         </varlistentry>
 679                         <varlistentry>
 680                                 <term><filename>system-update.target</filename></term>
 681                                 <listitem>
 682                                         <para>A special target unit
 683                                         that is used for off-line
 684                                         system updates.
 685                                         <citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 686                                         will redirect the boot process
 687                                         to this target if
 688                                         <filename>/system-update</filename>
 689                                         exists. For more information
 690                                         see the <ulink
 691                                         url="http://freedesktop.org/wiki/Software/systemd/SystemUpdates">System
 692                                         Updates
 693                                         Specification</ulink>.</para>
 694                                 </listitem>
 695                         </varlistentry>
 696                         <varlistentry>
 697                                 <term><filename>timers.target</filename></term>
 698                                 <listitem>
 699                                         <para>A special target unit
 700                                         that sets up all timer
 701                                         units (see
 702                                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 703                                         for details) that shall be
 704                                         active after boot.</para>
 705
 706                                         <para>It is recommended that
 707                                         timer units installed by
 708                                         applications get pulled in via
 709                                         <varname>Wants=</varname>
 710                                         dependencies from this
 711                                         unit. This is best configured
 712                                         via
 713                                         <varname>WantedBy=timers.target</varname>
 714                                         in the timer unit's
 715                                         <literal>[Install]</literal>
 716                                         section.</para>
 717                                 </listitem>
 718                         </varlistentry>
 719                         <varlistentry>
 720                                 <term><filename>umount.target</filename></term>
 721                                 <listitem>
 722                                         <para>A special target unit
 723                                         that umounts all mount and
 724                                         automount points on system
 725                                         shutdown.</para>
 726
 727                                         <para>Mounts that shall be
 728                                         unmounted on system shutdown
 729                                         shall add Conflicts
 730                                         dependencies to this unit for
 731                                         their mount unit, which is
 732                                         implicitly done when
 733                                         <varname>DefaultDependencies=yes</varname>
 734                                         is set (the default).</para>
 735                                 </listitem>
 736                         </varlistentry>
 737
 738                 </variablelist>
 739         </refsect1>
 740
 741         <refsect1>
 742                 <title>Special System Units for Devices</title>
 743
 744                 <para>Some target units are automatically pulled in as
 745                 devices of certain kinds show up in the system. These
 746                 may be used to automatically activate various services
 747                 based on the specific type of the available
 748                 hardware.</para>
 749
 750                 <variablelist>
 751                         <varlistentry>
 752                                 <term><filename>bluetooth.target</filename></term>
 753                                 <listitem>
 754                                         <para>This target is started
 755                                         automatically as soon as a
 756                                         Bluetooth controller is
 757                                         plugged in or becomes
 758                                         available at boot.</para>
 759
 760                                         <para>This may be used to pull
 761                                         in Bluetooth management
 762                                         daemons dynamically when
 763                                         Bluetooth hardware is
 764                                         found.</para>
 765                                 </listitem>
 766                         </varlistentry>
 767                         <varlistentry>
 768                                 <term><filename>printer.target</filename></term>
 769                                 <listitem>
 770                                         <para>This target is started
 771                                         automatically as soon as a
 772                                         printer is plugged in or
 773                                         becomes available at
 774                                         boot.</para>
 775
 776                                         <para>This may be used to pull
 777                                         in printer management
 778                                         daemons dynamically when
 779                                         printer hardware is
 780                                         found.</para>
 781                                 </listitem>
 782                         </varlistentry>
 783                         <varlistentry>
 784                                 <term><filename>smartcard.target</filename></term>
 785                                 <listitem>
 786                                         <para>This target is started
 787                                         automatically as soon as a
 788                                         smartcard controller is
 789                                         plugged in or becomes
 790                                         available at boot.</para>
 791
 792                                         <para>This may be used to pull
 793                                         in smartcard management
 794                                         daemons dynamically when
 795                                         smartcard hardware is
 796                                         found.</para>
 797                                 </listitem>
 798                         </varlistentry>
 799                         <varlistentry>
 800                                 <term><filename>sound.target</filename></term>
 801                                 <listitem>
 802                                         <para>This target is started
 803                                         automatically as soon as a
 804                                         sound card is plugged in or
 805                                         becomes available at
 806                                         boot.</para>
 807
 808                                         <para>This may be used to pull
 809                                         in audio management daemons
 810                                         dynamically when audio
 811                                         hardware is found.</para>
 812                                 </listitem>
 813                         </varlistentry>
 814                 </variablelist>
 815         </refsect1>
 816
 817         <refsect1>
 818                 <title>Special Passive System Units </title>
 819
 820                 <para>A number of special system targets are defined
 821                 that can be used to properly order boot-up of optional
 822                 services. These targets are generally not part of the
 823                 initial boot transaction, unless they are explicitly
 824                 pulled in by one of the implementing services. Note
 825                 specifically that these <emphasis>passive</emphasis>
 826                 target units are generally not pulled in by the
 827                 consumer of a service, but by the provider of the
 828                 service. This means: a consuming service should order
 829                 itself after these targets (as appropriate), but not
 830                 pull it in. A providing service should order itself
 831                 before these targets (as appropriate) and pull it in
 832                 (via a <varname>Wants=</varname> type
 833                 dependency).</para>
 834
 835                 <para>Note that these passive units cannot be started
 836                 manually, i.e. <literal>systemctl start
 837                 time-sync.target</literal> will fail with an
 838                 error. They can only be pulled in by dependency. This
 839                 is enforced since they exist for ordering purposes
 840                 only and thus are not useful as only unit within a
 841                 transaction.</para>
 842
 843                 <variablelist>
 844                         <varlistentry>
 845                                 <term><filename>cryptsetup-pre.target</filename></term>
 846                                 <listitem>
 847                                         <para>This passive target unit
 848                                         may be pulled in by services
 849                                         that want to run before any
 850                                         encrypted block device is set
 851                                         up. All encrypted block
 852                                         devices are set up after this
 853                                         target has been reached. Since
 854                                         the shutdown order is
 855                                         implicitly the reverse
 856                                         start-up order between units,
 857                                         this target is particularly
 858                                         useful to ensure that a
 859                                         service is shut down only
 860                                         after all encrypted block
 861                                         devices are fully
 862                                         stopped.</para>
 863                                 </listitem>
 864                         </varlistentry>
 865                         <varlistentry>
 866                                 <term><filename>local-fs-pre.target</filename></term>
 867                                 <listitem>
 868                                         <para>This target unit is
 869                                         automatically ordered before
 870                                         all local mount points marked
 871                                         with <option>auto</option>
 872                                         (see above). It can be used to
 873                                         execute certain units before
 874                                         all local mounts.</para>
 875                                 </listitem>
 876                         </varlistentry>
 877                         <varlistentry>
 878                                 <term><filename>network.target</filename></term>
 879                                 <listitem>
 880                                         <para>This unit is supposed to
 881                                         indicate when network
 882                                         functionality is available,
 883                                         but it is only very weakly
 884                                         defined what that is supposed
 885                                         to mean, with one exception:
 886                                         at shutdown, a unit that is
 887                                         ordered after
 888                                         <filename>network.target</filename>
 889                                         will be stopped before the
 890                                         network -- to whatever level
 891                                         it might be set up then -- is
 892                                         shut down. It is hence useful
 893                                         when writing service files
 894                                         that require network access on
 895                                         shutdown, which should order
 896                                         themselves after this target,
 897                                         but not pull it in. Also see
 898                                         <ulink
 899                                         url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 900                                         Services After the Network is
 901                                         up</ulink> for more
 902                                         information. Also see
 903                                         <filename>network-online.target</filename>
 904                                         described above.</para>
 905
 906                                         <para>systemd automatically
 907                                         adds dependencies of type
 908                                         <varname>After=</varname> for
 909                                         this target unit to all SysV
 910                                         init script service units with
 911                                         an LSB header referring to the
 912                                         <literal>$network</literal>
 913                                         facility.</para>
 914                                 </listitem>
 915                         </varlistentry>
 916                         <varlistentry>
 917                                 <term><filename>network-pre.target</filename></term>
 918                                 <listitem>
 919                                         <para>This passive target unit
 920                                         may be pulled in by services
 921                                         that want to run before any
 922                                         network is set up, for example
 923                                         for the purpose of setting up a
 924                                         firewall. All network
 925                                         management software orders
 926                                         itself after this target, but
 927                                         does not pull it in.</para>
 928                                 </listitem>
 929                         </varlistentry>
 930                         <varlistentry>
 931                                 <term><filename>nss-lookup.target</filename></term>
 932                                 <listitem>
 933                                         <para>A target that should be
 934                                         used as synchronization point
 935                                         for all host/network name
 936                                         service lookups. Note that
 937                                         this is independent of
 938                                         user/group name lookups for
 939                                         which
 940                                         <filename>nss-user-lookup.target</filename>
 941                                         should be used. All services
 942                                         for which the availability of
 943                                         full host/network name
 944                                         resolution is essential should
 945                                         be ordered after this target,
 946                                         but not pull it in. systemd
 947                                         automatically adds
 948                                         dependencies of type
 949                                         <varname>After=</varname> for
 950                                         this target unit to all SysV
 951                                         init script service units with
 952                                         an LSB header referring to the
 953                                         <literal>$named</literal>
 954                                         facility.</para>
 955                                 </listitem>
 956                         </varlistentry>
 957                         <varlistentry>
 958                                 <term><filename>nss-user-lookup.target</filename></term>
 959                                 <listitem>
 960                                         <para>A target that should be
 961                                         used as synchronization point
 962                                         for all user/group name
 963                                         service lookups. Note that
 964                                         this is independent of
 965                                         host/network name lookups for
 966                                         which
 967                                         <filename>nss-lookup.target</filename>
 968                                         should be used. All services
 969                                         for which the availability of
 970                                         the full user/group database is
 971                                         essential should be ordered
 972                                         after this target, but not
 973                                         pull it in. Note that system
 974                                         users are always resolvable,
 975                                         and hence do not require any
 976                                         special ordering against this
 977                                         target.</para>
 978                                 </listitem>
 979                         </varlistentry>
 980                         <varlistentry>
 981                                 <term><filename>remote-fs-pre.target</filename></term>
 982                                 <listitem>
 983                                         <para>This target unit is
 984                                         automatically ordered before
 985                                         all remote mount point units
 986                                         (see above). It can be used to
 987                                         run certain units before the
 988                                         remote mounts are
 989                                         established. Note that this
 990                                         unit is generally not part of
 991                                         the initial transaction,
 992                                         unless the unit that wants to
 993                                         be ordered before all remote
 994                                         mounts pulls it in via a
 995                                         <varname>Wants=</varname> type
 996                                         dependency. If the unit wants
 997                                         to be pulled in by the first
 998                                         remote mount showing up, it
 999                                         should use
1000                                         <filename>network-online.target</filename>
1001                                         (see above).</para>
1002                                 </listitem>
1003                         </varlistentry>
1004                         <varlistentry>
1005                                 <term><filename>rpcbind.target</filename></term>
1006                                 <listitem>
1007                                         <para>The portmapper/rpcbind
1008                                         pulls in this target and
1009                                         orders itself before it, to
1010                                         indicate its
1011                                         availability. systemd
1012                                         automatically adds
1013                                         dependencies of type
1014                                         <varname>After=</varname> for
1015                                         this target unit to all SysV
1016                                         init script service units with
1017                                         an LSB header referring to the
1018                                         <literal>$portmap</literal>
1019                                         facility.</para>
1020                                 </listitem>
1021                         </varlistentry>
1022                         <varlistentry>
1023                                 <term><filename>time-sync.target</filename></term>
1024                                 <listitem>
1025                                         <para>Services responsible for
1026                                         synchronizing the system clock
1027                                         from a remote source (such as
1028                                         NTP client implementations)
1029                                         should pull in this target and
1030                                         order themselves before
1031                                         it. All services where correct
1032                                         time is essential should be
1033                                         ordered after this unit, but
1034                                         not pull it in. systemd
1035                                         automatically adds
1036                                         dependencies of type
1037                                         <varname>After=</varname> for
1038                                         this target unit to all SysV
1039                                         init script service units with
1040                                         an LSB header referring to the
1041                                         <literal>$time</literal>
1042                                         facility. </para>
1043                                 </listitem>
1044                         </varlistentry>
1045                 </variablelist>
1046         </refsect1>
1047
1048         <refsect1>
1049                 <title>Special User Units</title>
1050
1051                 <para>When systemd runs as a user instance, the
1052                 following special units are available, which have
1053                 similar definitions as their system counterparts:
1054                 <filename>default.target</filename>,
1055                 <filename>shutdown.target</filename>,
1056                 <filename>sockets.target</filename>,
1057                 <filename>timers.target</filename>,
1058                 <filename>paths.target</filename>,
1059                 <filename>bluetooth.target</filename>,
1060                 <filename>printer.target</filename>,
1061                 <filename>smartcard.target</filename>,
1062                 <filename>sound.target</filename>.</para>
1063
1064                 <para>In addition, the following special unit is
1065                 understood only when systemd runs as service instance:</para>
1066
1067                 <variablelist>
1068                         <varlistentry>
1069                                 <term><filename>exit.target</filename></term>
1070                                 <listitem>
1071                                         <para>A special service unit
1072                                         for shutting down the
1073                                         user service manager.</para>
1074
1075                                         <para>Applications wanting to
1076                                         terminate the user service
1077                                         manager should start this
1078                                         unit. If systemd receives
1079                                         <constant>SIGTERM</constant> or <constant>SIGINT</constant> when running
1080                                         as user service daemon, it will
1081                                         start this unit.</para>
1082
1083                                         <para>Normally, this pulls in
1084                                         <filename>shutdown.target</filename>
1085                                         which in turn should be
1086                                         conflicted by all units that
1087                                         want to be shut down on
1088                                         user service manager exit.</para>
1089                                 </listitem>
1090                         </varlistentry>
1091                 </variablelist>
1092         </refsect1>
1093
1094         <refsect1>
1095                 <title>Special Slice Units</title>
1096
1097                 <para>There are four <literal>.slice</literal> units
1098                 which form the basis of the hierarchy for assignment
1099                 of resources for services, users, and virtual machines
1100                 or containers.</para>
1101
1102                 <variablelist>
1103                         <varlistentry>
1104                                 <term><filename>-.slice</filename></term>
1105                                 <listitem>
1106                                         <para>The root slice is the
1107                                         root of the hierarchy. It
1108                                         usually does not contain units
1109                                         directly, but may be used to
1110                                         set defaults for the whole
1111                                         tree.</para>
1112                                 </listitem>
1113                         </varlistentry>
1114
1115                         <varlistentry>
1116                                 <term><filename>system.slice</filename></term>
1117                                 <listitem>
1118                                         <para>By default, all services
1119                                         services started by
1120                                         <command>systemd</command> are
1121                                         found in this slice.</para>
1122                                 </listitem>
1123                         </varlistentry>
1124
1125                         <varlistentry>
1126                                 <term><filename>user.slice</filename></term>
1127                                 <listitem>
1128                                         <para>By default, all user
1129                                         processes and services started
1130                                         on behalf of the user,
1131                                         including the per-user systemd
1132                                         instance are found in this
1133                                         slice.</para>
1134                                 </listitem>
1135                         </varlistentry>
1136
1137                         <varlistentry>
1138                                 <term><filename>machine.slice</filename></term>
1139                                 <listitem>
1140                                         <para>By default, all virtual
1141                                         machines and containers
1142                                         registered with
1143                                         <command>systemd-machined</command>
1144                                         are found in this slice.
1145                                         </para>
1146                                 </listitem>
1147                         </varlistentry>
1148                 </variablelist>
1149         </refsect1>
1150
1151         <refsect1>
1152                   <title>See Also</title>
1153                   <para>
1154                           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1155                           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1156                           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1157                           <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1158                           <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1159                           <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1160                           <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1161                           <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1162                   </para>
1163         </refsect1>
1164
1165 </refentry>