man/systemd.special.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   This file is part of systemd.
   7
   8   Copyright 2010 Lennart Poettering
   9
  10   systemd is free software; you can redistribute it and/or modify it
  11   under the terms of the GNU Lesser General Public License as published by
  12   the Free Software Foundation; either version 2.1 of the License, or
  13   (at your option) any later version.
  14
  15   systemd is distributed in the hope that it will be useful, but
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  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18   Lesser General Public License for more details.
  19
  20   You should have received a copy of the GNU Lesser General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
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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>dbus.service</filename>,
  56                 <filename>dbus.socket</filename>,
  57                 <filename>default.target</filename>,
  58                 <filename>display-manager.service</filename>,
  59                 <filename>emergency.target</filename>,
  60                 <filename>exit.target</filename>,
  61                 <filename>final.target</filename>,
  62                 <filename>getty.target</filename>,
  63                 <filename>graphical.target</filename>,
  64                 <filename>halt.target</filename>,
  65                 <filename>hibernate.target</filename>,
  66                 <filename>hybrid-sleep.target</filename>,
  67                 <filename>initrd-fs.target</filename>,
  68                 <filename>kbrequest.target</filename>,
  69                 <filename>kexec.target</filename>,
  70                 <filename>local-fs.target</filename>,
  71                 <filename>local-fs-pre.target</filename>,
  72                 <filename>multi-user.target</filename>,
  73                 <filename>network.target</filename>,
  74                 <filename>network-online.target</filename>,
  75                 <filename>network-pre.target</filename>,
  76                 <filename>nss-lookup.target</filename>,
  77                 <filename>nss-user-lookup.target</filename>,
  78                 <filename>paths.target</filename>,
  79                 <filename>poweroff.target</filename>,
  80                 <filename>printer.target</filename>,
  81                 <filename>reboot.target</filename>,
  82                 <filename>remote-fs.target</filename>,
  83                 <filename>remote-fs-pre.target</filename>,
  84                 <filename>rescue.target</filename>,
  85                 <filename>initrd-root-fs.target</filename>,
  86                 <filename>rpcbind.target</filename>,
  87                 <filename>runlevel2.target</filename>,
  88                 <filename>runlevel3.target</filename>,
  89                 <filename>runlevel4.target</filename>,
  90                 <filename>runlevel5.target</filename>,
  91                 <filename>shutdown.target</filename>,
  92                 <filename>sigpwr.target</filename>,
  93                 <filename>sleep.target</filename>,
  94                 <filename>smartcard.target</filename>,
  95                 <filename>sockets.target</filename>,
  96                 <filename>sound.target</filename>,
  97                 <filename>suspend.target</filename>,
  98                 <filename>swap.target</filename>,
  99                 <filename>sysinit.target</filename>,
 100                 <filename>syslog.socket</filename>,
 101                 <filename>system-update.target</filename>,
 102                 <filename>time-sync.target</filename>,
 103                 <filename>timers.target</filename>,
 104                 <filename>umount.target</filename>,
 105                 <filename>-.slice</filename>,
 106                 <filename>system.slice</filename>,
 107                 <filename>user.slice</filename>,
 108                 <filename>machine.slice</filename></para>
 109         </refsynopsisdiv>
 110
 111         <refsect1>
 112                 <title>Description</title>
 113
 114                 <para>A few units are treated specially by
 115                 systemd. They have special internal semantics and
 116                 cannot be renamed.</para>
 117         </refsect1>
 118
 119         <refsect1>
 120                 <title>Special System Units</title>
 121
 122                 <variablelist>
 123                         <varlistentry>
 124                                 <term><filename>basic.target</filename></term>
 125                                 <listitem>
 126                                         <para>A special target unit
 127                                         covering basic boot-up.</para>
 128                                         <para>systemd automatically
 129                                         adds dependencies of the types
 130                                         <varname>Requires=</varname>
 131                                         and <varname>After=</varname>
 132                                         for this target unit to all
 133                                         services (except for those
 134                                         with
 135                                         <varname>DefaultDependencies=no</varname>).</para>
 136
 137                                         <para>Usually this should
 138                                         pull-in all mount points, swap
 139                                         devices, sockets, timers, and
 140                                         path units and other basic
 141                                         initialization necessary for
 142                                         general purpose
 143                                         daemons.</para>
 144                                 </listitem>
 145                         </varlistentry>
 146                         <varlistentry>
 147                                 <term><filename>ctrl-alt-del.target</filename></term>
 148                                 <listitem>
 149                                         <para>systemd starts this
 150                                         target whenever
 151                                         Control+Alt+Del is pressed on
 152                                         the console. Usually this
 153                                         should be aliased (symlinked)
 154                                         to
 155                                         <filename>reboot.target</filename>.</para>
 156                                 </listitem>
 157                         </varlistentry>
 158                         <varlistentry>
 159                                 <term><filename>cryptsetup.target</filename></term>
 160                                 <listitem>
 161                                         <para>A target that pulls in
 162                                         setup services for all
 163                                         encrypted block
 164                                         devices.</para>
 165                                 </listitem>
 166                         </varlistentry>
 167                         <varlistentry>
 168                                 <term><filename>dbus.service</filename></term>
 169                                 <listitem>
 170                                         <para>A special unit for the
 171                                         D-Bus bus daemon. As soon as
 172                                         this service is fully started
 173                                         up systemd will connect to it
 174                                         and register its
 175                                         service.</para>
 176                                 </listitem>
 177                         </varlistentry>
 178                         <varlistentry>
 179                                 <term><filename>dbus.socket</filename></term>
 180                                 <listitem>
 181                                         <para>A special unit for the
 182                                         D-Bus system bus socket. All
 183                                         units with
 184                                         <varname>Type=dbus</varname>
 185                                         automatically gain a
 186                                         dependency on this
 187                                         unit.</para>
 188                                 </listitem>
 189                         </varlistentry>
 190                         <varlistentry>
 191                                 <term><filename>default.target</filename></term>
 192                                 <listitem>
 193                                         <para>The default unit systemd
 194                                         starts at bootup. Usually this
 195                                         should be aliased (symlinked)
 196                                         to
 197                                         <filename>multi-user.target</filename>
 198                                         or
 199                                         <filename>graphical.target</filename>.</para>
 200
 201                                         <para>The default unit systemd
 202                                         starts at bootup can be
 203                                         overridden with the
 204                                         <varname>systemd.unit=</varname>
 205                                         kernel command line option.</para>
 206                                 </listitem>
 207                         </varlistentry>
 208                         <varlistentry>
 209                                 <term><filename>display-manager.service</filename></term>
 210                                 <listitem>
 211                                         <para>The display manager
 212                                         service. Usually this should
 213                                         be aliased (symlinked) to
 214                                         <filename>gdm.service</filename>
 215                                         or a similar display manager
 216                                         service.</para>
 217                                 </listitem>
 218                         </varlistentry>
 219                         <varlistentry>
 220                                 <term><filename>emergency.target</filename></term>
 221                                 <listitem>
 222                                         <para>A special target unit
 223                                         that starts an emergency
 224                                         shell on the main
 225                                         console. This unit is supposed
 226                                         to be used with the kernel
 227                                         command line option
 228                                         <varname>systemd.unit=</varname>
 229                                         and has otherwise little use.
 230                                         </para>
 231                                 </listitem>
 232                         </varlistentry>
 233                         <varlistentry>
 234                                 <term><filename>final.target</filename></term>
 235                                 <listitem>
 236                                         <para>A special target unit
 237                                         that is used during the
 238                                         shutdown logic and may be used
 239                                         to pull in late services after
 240                                         all normal services are
 241                                         already terminated and all
 242                                         mounts unmounted.
 243                                         </para>
 244                                 </listitem>
 245                         </varlistentry>
 246                         <varlistentry>
 247                                 <term><filename>getty.target</filename></term>
 248                                 <listitem>
 249                                         <para>A special target unit
 250                                         that pulls in statically
 251                                         configured local TTY
 252                                         <filename>getty</filename>
 253                                         instances.
 254                                         </para>
 255                                 </listitem>
 256                         </varlistentry>
 257                         <varlistentry>
 258                                 <term><filename>graphical.target</filename></term>
 259                                 <listitem>
 260                                         <para>A special target unit
 261                                         for setting up a graphical
 262                                         login screen. This pulls in
 263                                         <filename>multi-user.target</filename>.</para>
 264
 265                                         <para>Units that are needed
 266                                         for graphical logins shall add
 267                                         <varname>Wants=</varname>
 268                                         dependencies for their unit to
 269                                         this unit (or
 270                                         <filename>multi-user.target</filename>)
 271                                         during installation. This is
 272                                         best configured via
 273                                         <varname>WantedBy=graphical.target</varname>
 274                                         in the unit's
 275                                         <literal>[Install]</literal>
 276                                         section.</para>
 277                                 </listitem>
 278                         </varlistentry>
 279                         <varlistentry>
 280                                 <term><filename>hibernate.target</filename></term>
 281                                 <listitem>
 282                                         <para>A special target unit
 283                                         for hibernating the
 284                                         system. This pulls in
 285                                         <filename>sleep.target</filename>.</para>
 286                                 </listitem>
 287                         </varlistentry>
 288                         <varlistentry>
 289                                 <term><filename>hybrid-sleep.target</filename></term>
 290                                 <listitem>
 291                                         <para>A special target unit
 292                                         for hibernating and suspending the
 293                                         system at the same time. This pulls in
 294                                         <filename>sleep.target</filename>.</para>
 295                                 </listitem>
 296                         </varlistentry>
 297                         <varlistentry>
 298                                 <term><filename>halt.target</filename></term>
 299                                 <listitem>
 300                                         <para>A special target unit
 301                                         for shutting down and halting
 302                                         the system. Note that this
 303                                         target is distinct from
 304                                         <filename>poweroff.target</filename>
 305                                         in that it generally really
 306                                         just halts the system rather
 307                                         than powering it down.</para>
 308
 309                                         <para>Applications wanting to
 310                                         halt the system should start
 311                                         this unit.</para>
 312                                 </listitem>
 313                         </varlistentry>
 314                         <varlistentry>
 315                                 <term><filename>initrd-fs.target</filename></term>
 316                                 <listitem>
 317                                         <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 318                                         automatically adds
 319                                         dependencies of type
 320                                         <varname>Before=</varname> to
 321                                         <filename>sysroot-usr.mount</filename>
 322                                         and all mount points found in
 323                                         <filename>/etc/fstab</filename>
 324                                         that have the
 325                                         <option>auto</option> and
 326                                         <option>x-initrd.mount</option>
 327                                         mount options set.
 328                                         </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>local-fs-pre.target</filename></term>
 845                                 <listitem>
 846                                         <para>This target unit is
 847                                         automatically ordered before
 848                                         all local mount points marked
 849                                         with <option>auto</option>
 850                                         (see above). It can be used to
 851                                         execute certain units before
 852                                         all local mounts.</para>
 853                                 </listitem>
 854                         </varlistentry>
 855                         <varlistentry>
 856                                 <term><filename>network.target</filename></term>
 857                                 <listitem>
 858                                         <para>This unit is supposed to
 859                                         indicate when network
 860                                         functionality is available,
 861                                         but it is only very weakly
 862                                         defined what that is supposed
 863                                         to mean, with one exception:
 864                                         at shutdown, a unit that is
 865                                         ordered after
 866                                         <filename>network.target</filename>
 867                                         will be stopped before the
 868                                         network -- to whatever level
 869                                         it might be set up then -- is
 870                                         shut down. It is hence useful
 871                                         when writing service files
 872                                         that require network access on
 873                                         shutdown, which should order
 874                                         themselves after this target,
 875                                         but not pull it in. Also see
 876                                         <ulink
 877                                         url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 878                                         Services After the Network is
 879                                         up</ulink> for more
 880                                         information. Also see
 881                                         <filename>network-online.target</filename>
 882                                         described above.</para>
 883
 884                                         <para>systemd automatically
 885                                         adds dependencies of type
 886                                         <varname>After=</varname> for
 887                                         this target unit to all SysV
 888                                         init script service units with
 889                                         an LSB header referring to the
 890                                         <literal>$network</literal>
 891                                         facility.</para>
 892                                 </listitem>
 893                         </varlistentry>
 894                         <varlistentry>
 895                                 <term><filename>network-pre.target</filename></term>
 896                                 <listitem>
 897                                         <para>This passive target unit
 898                                         may be pulled in by services
 899                                         that want to run before any
 900                                         network is set up, for example
 901                                         for the purpose of setting up a
 902                                         firewall. All network
 903                                         management software orders
 904                                         itself after this target, but
 905                                         does not pull it in.</para>
 906                                 </listitem>
 907                         </varlistentry>
 908                         <varlistentry>
 909                                 <term><filename>nss-lookup.target</filename></term>
 910                                 <listitem>
 911                                         <para>A target that should be
 912                                         used as synchronization point
 913                                         for all host/network name
 914                                         service lookups. Note that
 915                                         this is independent of
 916                                         user/group name lookups for
 917                                         which
 918                                         <filename>nss-user-lookup.target</filename>
 919                                         should be used. All services
 920                                         for which the availability of
 921                                         full host/network name
 922                                         resolution is essential should
 923                                         be ordered after this target,
 924                                         but not pull it in. systemd
 925                                         automatically adds
 926                                         dependencies of type
 927                                         <varname>After=</varname> for
 928                                         this target unit to all SysV
 929                                         init script service units with
 930                                         an LSB header referring to the
 931                                         <literal>$named</literal>
 932                                         facility.</para>
 933                                 </listitem>
 934                         </varlistentry>
 935                         <varlistentry>
 936                                 <term><filename>nss-user-lookup.target</filename></term>
 937                                 <listitem>
 938                                         <para>A target that should be
 939                                         used as synchronization point
 940                                         for all user/group name
 941                                         service lookups. Note that
 942                                         this is independent of
 943                                         host/network name lookups for
 944                                         which
 945                                         <filename>nss-lookup.target</filename>
 946                                         should be used. All services
 947                                         for which the availability of
 948                                         the full user/group database is
 949                                         essential should be ordered
 950                                         after this target, but not
 951                                         pull it in. Note that system
 952                                         users are always resolvable,
 953                                         and hence do not require any
 954                                         special ordering against this
 955                                         target.</para>
 956                                 </listitem>
 957                         </varlistentry>
 958                         <varlistentry>
 959                                 <term><filename>remote-fs-pre.target</filename></term>
 960                                 <listitem>
 961                                         <para>This target unit is
 962                                         automatically ordered before
 963                                         all remote mount point units
 964                                         (see above). It can be used to
 965                                         run certain units before the
 966                                         remote mounts are
 967                                         established. Note that this
 968                                         unit is generally not part of
 969                                         the initial transaction,
 970                                         unless the unit that wants to
 971                                         be ordered before all remote
 972                                         mounts pulls it in via a
 973                                         <varname>Wants=</varname> type
 974                                         dependency. If the unit wants
 975                                         to be pulled in by the first
 976                                         remote mount showing up, it
 977                                         should use
 978                                         <filename>network-online.target</filename>
 979                                         (see above).</para>
 980                                 </listitem>
 981                         </varlistentry>
 982                         <varlistentry>
 983                                 <term><filename>rpcbind.target</filename></term>
 984                                 <listitem>
 985                                         <para>The portmapper/rpcbind
 986                                         pulls in this target and
 987                                         orders itself before it, to
 988                                         indicate its
 989                                         availability. systemd
 990                                         automatically adds
 991                                         dependencies of type
 992                                         <varname>After=</varname> for
 993                                         this target unit to all SysV
 994                                         init script service units with
 995                                         an LSB header referring to the
 996                                         <literal>$portmap</literal>
 997                                         facility.</para>
 998                                 </listitem>
 999                         </varlistentry>
1000                         <varlistentry>
1001                                 <term><filename>time-sync.target</filename></term>
1002                                 <listitem>
1003                                         <para>Services responsible for
1004                                         synchronizing the system clock
1005                                         from a remote source (such as
1006                                         NTP client implementations)
1007                                         should pull in this target and
1008                                         order themselves before
1009                                         it. All services where correct
1010                                         time is essential should be
1011                                         ordered after this unit, but
1012                                         not pull it in. systemd
1013                                         automatically adds
1014                                         dependencies of type
1015                                         <varname>After=</varname> for
1016                                         this target unit to all SysV
1017                                         init script service units with
1018                                         an LSB header referring to the
1019                                         <literal>$time</literal>
1020                                         facility. </para>
1021                                 </listitem>
1022                         </varlistentry>
1023                 </variablelist>
1024         </refsect1>
1025
1026         <refsect1>
1027                 <title>Special User Units</title>
1028
1029                 <para>When systemd runs as a user instance, the
1030                 following special units are available, which have
1031                 similar definitions as their system counterparts:
1032                 <filename>default.target</filename>,
1033                 <filename>shutdown.target</filename>,
1034                 <filename>sockets.target</filename>,
1035                 <filename>timers.target</filename>,
1036                 <filename>paths.target</filename>,
1037                 <filename>bluetooth.target</filename>,
1038                 <filename>printer.target</filename>,
1039                 <filename>smartcard.target</filename>,
1040                 <filename>sound.target</filename>.</para>
1041
1042                 <para>In addition, the following special unit is
1043                 understood only when systemd runs as service instance:</para>
1044
1045                 <variablelist>
1046                         <varlistentry>
1047                                 <term><filename>exit.target</filename></term>
1048                                 <listitem>
1049                                         <para>A special service unit
1050                                         for shutting down the
1051                                         user service manager.</para>
1052
1053                                         <para>Applications wanting to
1054                                         terminate the user service
1055                                         manager should start this
1056                                         unit. If systemd receives
1057                                         <constant>SIGTERM</constant> or <constant>SIGINT</constant> when running
1058                                         as user service daemon, it will
1059                                         start this unit.</para>
1060
1061                                         <para>Normally, this pulls in
1062                                         <filename>shutdown.target</filename>
1063                                         which in turn should be
1064                                         conflicted by all units that
1065                                         want to be shut down on
1066                                         user service manager exit.</para>
1067                                 </listitem>
1068                         </varlistentry>
1069                 </variablelist>
1070         </refsect1>
1071
1072         <refsect1>
1073                 <title>Special Slice Units</title>
1074
1075                 <para>There are four <literal>.slice</literal> units
1076                 which form the basis of the hierarchy for assignment
1077                 of resources for services, users, and virtual machines
1078                 or containers.</para>
1079
1080                 <variablelist>
1081                         <varlistentry>
1082                                 <term><filename>-.slice</filename></term>
1083                                 <listitem>
1084                                         <para>The root slice is the
1085                                         root of the hierarchy. It
1086                                         usually does not contain units
1087                                         directly, but may be used to
1088                                         set defaults for the whole
1089                                         tree.</para>
1090                                 </listitem>
1091                         </varlistentry>
1092
1093                         <varlistentry>
1094                                 <term><filename>system.slice</filename></term>
1095                                 <listitem>
1096                                         <para>By default, all services
1097                                         services started by
1098                                         <command>systemd</command> are
1099                                         found in this slice.</para>
1100                                 </listitem>
1101                         </varlistentry>
1102
1103                         <varlistentry>
1104                                 <term><filename>user.slice</filename></term>
1105                                 <listitem>
1106                                         <para>By default, all user
1107                                         processes and services started
1108                                         on behalf of the user,
1109                                         including the per-user systemd
1110                                         instance are found in this
1111                                         slice.</para>
1112                                 </listitem>
1113                         </varlistentry>
1114
1115                         <varlistentry>
1116                                 <term><filename>machine.slice</filename></term>
1117                                 <listitem>
1118                                         <para>By defalt, all virtual
1119                                         machines and containers
1120                                         registered with
1121                                         <command>systemd-machined</command>
1122                                         are found in this slice.
1123                                         </para>
1124                                 </listitem>
1125                         </varlistentry>
1126                 </variablelist>
1127         </refsect1>
1128
1129         <refsect1>
1130                   <title>See Also</title>
1131                   <para>
1132                           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1133                           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1134                           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1135                           <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1136                           <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1137                           <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1138                           <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1139                           <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1140                   </para>
1141         </refsect1>
1142
1143 </refentry>