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
  16   WITHOUT ANY WARRANTY; without even the implied warranty of
  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/>.
  22 -->
  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>nss-lookup.target</filename>,
  76                 <filename>nss-user-lookup.target</filename>,
  77                 <filename>paths.target</filename>,
  78                 <filename>poweroff.target</filename>,
  79                 <filename>printer.target</filename>,
  80                 <filename>reboot.target</filename>,
  81                 <filename>remote-fs.target</filename>,
  82                 <filename>remote-fs-pre.target</filename>,
  83                 <filename>rescue.target</filename>,
  84                 <filename>initrd-root-fs.target</filename>,
  85                 <filename>rpcbind.target</filename>,
  86                 <filename>runlevel2.target</filename>,
  87                 <filename>runlevel3.target</filename>,
  88                 <filename>runlevel4.target</filename>,
  89                 <filename>runlevel5.target</filename>,
  90                 <filename>shutdown.target</filename>,
  91                 <filename>sigpwr.target</filename>,
  92                 <filename>sleep.target</filename>,
  93                 <filename>smartcard.target</filename>,
  94                 <filename>sockets.target</filename>,
  95                 <filename>sound.target</filename>,
  96                 <filename>suspend.target</filename>,
  97                 <filename>swap.target</filename>,
  98                 <filename>sysinit.target</filename>,
  99                 <filename>syslog.socket</filename>,
 100                 <filename>system-update.target</filename>,
 101                 <filename>time-sync.target</filename>,
 102                 <filename>timers.target</filename>,
 103                 <filename>umount.target</filename>,
 104                 <filename>-.slice</filename>,
 105                 <filename>system.slice</filename>,
 106                 <filename>user.slice</filename>,
 107                 <filename>machine.slice</filename></para>
 108         </refsynopsisdiv>
 109
 110         <refsect1>
 111                 <title>Description</title>
 112
 113                 <para>A few units are treated specially by
 114                 systemd. They have special internal semantics and
 115                 cannot be renamed.</para>
 116         </refsect1>
 117
 118         <refsect1>
 119                 <title>Special System Units</title>
 120
 121                 <variablelist>
 122                         <varlistentry>
 123                                 <term><filename>basic.target</filename></term>
 124                                 <listitem>
 125                                         <para>A special target unit
 126                                         covering basic boot-up.</para>
 127                                         <para>systemd automatically
 128                                         adds dependencies of the types
 129                                         <varname>Requires=</varname>
 130                                         and <varname>After=</varname>
 131                                         for this target unit to all
 132                                         services (except for those
 133                                         with
 134                                         <varname>DefaultDependencies=no</varname>).</para>
 135
 136                                         <para>Usually this should
 137                                         pull-in all mount points, swap
 138                                         devices, sockets, timers, and
 139                                         path units and other basic
 140                                         initialization necessary for
 141                                         general purpose
 142                                         daemons.</para>
 143                                 </listitem>
 144                         </varlistentry>
 145                         <varlistentry>
 146                                 <term><filename>ctrl-alt-del.target</filename></term>
 147                                 <listitem>
 148                                         <para>systemd starts this
 149                                         target whenever
 150                                         Control+Alt+Del is pressed on
 151                                         the console. Usually this
 152                                         should be aliased (symlinked)
 153                                         to
 154                                         <filename>reboot.target</filename>.</para>
 155                                 </listitem>
 156                         </varlistentry>
 157                         <varlistentry>
 158                                 <term><filename>cryptsetup.target</filename></term>
 159                                 <listitem>
 160                                         <para>A target that pulls in
 161                                         setup services for all
 162                                         encrypted block
 163                                         devices.</para>
 164                                 </listitem>
 165                         </varlistentry>
 166                         <varlistentry>
 167                                 <term><filename>dbus.service</filename></term>
 168                                 <listitem>
 169                                         <para>A special unit for the
 170                                         D-Bus bus daemon. As soon as
 171                                         this service is fully started
 172                                         up systemd will connect to it
 173                                         and register its
 174                                         service.</para>
 175                                 </listitem>
 176                         </varlistentry>
 177                         <varlistentry>
 178                                 <term><filename>dbus.socket</filename></term>
 179                                 <listitem>
 180                                         <para>A special unit for the
 181                                         D-Bus system bus socket. All
 182                                         units with
 183                                         <varname>Type=dbus</varname>
 184                                         automatically gain a
 185                                         dependency on this
 186                                         unit.</para>
 187                                 </listitem>
 188                         </varlistentry>
 189                         <varlistentry>
 190                                 <term><filename>default.target</filename></term>
 191                                 <listitem>
 192                                         <para>The default unit systemd
 193                                         starts at bootup. Usually this
 194                                         should be aliased (symlinked)
 195                                         to
 196                                         <filename>multi-user.target</filename>
 197                                         or
 198                                         <filename>graphical.target</filename>.</para>
 199
 200                                         <para>The default unit systemd
 201                                         starts at bootup can be
 202                                         overridden with the
 203                                         <varname>systemd.unit=</varname>
 204                                         kernel command line option.</para>
 205                                 </listitem>
 206                         </varlistentry>
 207                         <varlistentry>
 208                                 <term><filename>display-manager.service</filename></term>
 209                                 <listitem>
 210                                         <para>The display manager
 211                                         service. Usually this should
 212                                         be aliased (symlinked) to
 213                                         <filename>gdm.service</filename>
 214                                         or a similar display manager
 215                                         service.</para>
 216                                 </listitem>
 217                         </varlistentry>
 218                         <varlistentry>
 219                                 <term><filename>emergency.target</filename></term>
 220                                 <listitem>
 221                                         <para>A special target unit
 222                                         that starts an emergency
 223                                         shell on the main
 224                                         console. This unit is supposed
 225                                         to be used with the kernel
 226                                         command line option
 227                                         <varname>systemd.unit=</varname>
 228                                         and has otherwise little use.
 229                                         </para>
 230                                 </listitem>
 231                         </varlistentry>
 232                         <varlistentry>
 233                                 <term><filename>final.target</filename></term>
 234                                 <listitem>
 235                                         <para>A special target unit
 236                                         that is used during the
 237                                         shutdown logic and may be used
 238                                         to pull in late services after
 239                                         all normal services are
 240                                         already terminated and all
 241                                         mounts unmounted.
 242                                         </para>
 243                                 </listitem>
 244                         </varlistentry>
 245                         <varlistentry>
 246                                 <term><filename>getty.target</filename></term>
 247                                 <listitem>
 248                                         <para>A special target unit
 249                                         that pulls in statically
 250                                         configured local TTY
 251                                         <filename>getty</filename>
 252                                         instances.
 253                                         </para>
 254                                 </listitem>
 255                         </varlistentry>
 256                         <varlistentry>
 257                                 <term><filename>graphical.target</filename></term>
 258                                 <listitem>
 259                                         <para>A special target unit
 260                                         for setting up a graphical
 261                                         login screen. This pulls in
 262                                         <filename>multi-user.target</filename>.</para>
 263
 264                                         <para>Units that are needed
 265                                         for graphical logins shall add
 266                                         <varname>Wants=</varname>
 267                                         dependencies for their unit to
 268                                         this unit (or
 269                                         <filename>multi-user.target</filename>)
 270                                         during installation. This is
 271                                         best configured via
 272                                         <varname>WantedBy=graphical.target</varname>
 273                                         in the unit's
 274                                         <literal>[Install]</literal>
 275                                         section.</para>
 276                                 </listitem>
 277                         </varlistentry>
 278                         <varlistentry>
 279                                 <term><filename>hibernate.target</filename></term>
 280                                 <listitem>
 281                                         <para>A special target unit
 282                                         for hibernating the
 283                                         system. This pulls in
 284                                         <filename>sleep.target</filename>.</para>
 285                                 </listitem>
 286                         </varlistentry>
 287                         <varlistentry>
 288                                 <term><filename>hybrid-sleep.target</filename></term>
 289                                 <listitem>
 290                                         <para>A special target unit
 291                                         for hibernating and suspending the
 292                                         system at the same time. This pulls in
 293                                         <filename>sleep.target</filename>.</para>
 294                                 </listitem>
 295                         </varlistentry>
 296                         <varlistentry>
 297                                 <term><filename>halt.target</filename></term>
 298                                 <listitem>
 299                                         <para>A special target unit
 300                                         for shutting down and halting
 301                                         the system. Note that this
 302                                         target is distinct from
 303                                         <filename>poweroff.target</filename>
 304                                         in that it generally really
 305                                         just halts the system rather
 306                                         than powering it down.</para>
 307
 308                                         <para>Applications wanting to
 309                                         halt the system should start
 310                                         this unit.</para>
 311                                 </listitem>
 312                         </varlistentry>
 313                         <varlistentry>
 314                                 <term><filename>initrd-fs.target</filename></term>
 315                                 <listitem>
 316                                         <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 317                                         automatically adds
 318                                         dependencies of type
 319                                         <varname>Before=</varname> to
 320                                         <filename>sysroot-usr.mount</filename>
 321                                         and all mount points found in
 322                                         <filename>/etc/fstab</filename>
 323                                         that have the
 324                                         <option>auto</option> and
 325                                         <option>x-initrd.mount</option>
 326                                         mount options set.
 327                                         </para>
 328                                 </listitem>
 329                         </varlistentry>
 330                         <varlistentry>
 331                                 <term><filename>kbrequest.target</filename></term>
 332                                 <listitem>
 333                                         <para>systemd starts this
 334                                         target whenever Alt+ArrowUp is
 335                                         pressed on the console. This
 336                                         is a good candidate to be
 337                                         aliased (symlinked) to
 338                                         <filename>rescue.target</filename>.</para>
 339                                 </listitem>
 340                         </varlistentry>
 341                         <varlistentry>
 342                                 <term><filename>kexec.target</filename></term>
 343                                 <listitem>
 344                                         <para>A special target unit
 345                                         for shutting down and rebooting the system via kexec.</para>
 346
 347                                         <para>Applications wanting to
 348                                         reboot the system with kexec should start
 349                                         this unit.</para>
 350                                 </listitem>
 351                         </varlistentry>
 352                         <varlistentry>
 353                                 <term><filename>local-fs.target</filename></term>
 354                                 <listitem>
 355                                         <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 356                                         automatically adds
 357                                         dependencies of type
 358                                         <varname>Before=</varname> to
 359                                         all mount units that refer to
 360                                         local mount points for this
 361                                         target unit. In addition, it
 362                                         adds dependencies of type
 363                                         <varname>Wants=</varname> to
 364                                         this target unit for those
 365                                         mounts listed in
 366                                         <filename>/etc/fstab</filename>
 367                                         that have the
 368                                         <option>auto</option> mount
 369                                         option set.</para>
 370                                 </listitem>
 371                         </varlistentry>
 372                         <varlistentry>
 373                                 <term><filename>multi-user.target</filename></term>
 374                                 <listitem>
 375                                         <para>A special target unit
 376                                         for setting up a multi-user
 377                                         system (non-graphical). This
 378                                         is pulled in by
 379                                         <filename>graphical.target</filename>.</para>
 380
 381                                         <para>Units that are needed
 382                                         for a multi-user system shall
 383                                         add <varname>Wants=</varname>
 384                                         dependencies for their unit to
 385                                         this unit during
 386                                         installation. This is best
 387                                         configured via
 388                                         <varname>WantedBy=multi-user.target</varname>
 389                                         in the unit's
 390                                         <literal>[Install]</literal>
 391                                         section.</para>
 392                                 </listitem>
 393                         </varlistentry>
 394                         <varlistentry>
 395                                 <term><filename>network-online.target</filename></term>
 396                                 <listitem>
 397                                         <para>Units that strictly
 398                                         require a configured network
 399                                         connection should pull in
 400                                         <filename>network-online.target</filename>
 401                                         (via a
 402                                         <varname>Wants=</varname> type
 403                                         dependency) and order
 404                                         themselves after it. This
 405                                         target unit is intended to
 406                                         pull in a service that delays
 407                                         further execution until the
 408                                         network is sufficiently set
 409                                         up. What precisely this
 410                                         requires is left to the
 411                                         implementation of the network
 412                                         managing service.</para>
 413
 414                                         <para>Note the distinction
 415                                         between this unit and
 416                                         <filename>network.target</filename>. This
 417                                         unit is an active unit
 418                                         (i.e. pulled in by the
 419                                         consumer rather than the
 420                                         provider of this
 421                                         functionality) and pulls in a
 422                                         service which possibly adds
 423                                         substantial delays to further
 424                                         execution. In contrast,
 425                                         <filename>network.target</filename>
 426                                         is a passive unit (i.e. pulled
 427                                         in by the provider of the
 428                                         functionality, rather than the
 429                                         consumer) that usually does
 430                                         not delay execution
 431                                         much. Usually,
 432                                         <filename>network.target</filename>
 433                                         is part of the boot of most
 434                                         systems, while
 435                                         <filename>network-online.target</filename>
 436                                         is not, except when at least
 437                                         one unit requires it. Also see
 438                                         <ulink
 439                                         url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 440                                         Services After the Network is
 441                                         up</ulink> for more
 442                                         information.</para>
 443
 444                                         <para>All mount units for
 445                                         remote network file systems
 446                                         automatically pull in this
 447                                         unit, and order themselves
 448                                         after it. Note that networking
 449                                         daemons that simply provide
 450                                         functionality to other hosts
 451                                         generally do not need to pull
 452                                         this in.</para>
 453                                         </listitem>
 454                         </varlistentry>
 455                         <varlistentry>
 456                                 <term><filename>paths.target</filename></term>
 457                                 <listitem>
 458                                         <para>A special target unit
 459                                         that sets up all path units
 460                                         (see
 461                                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 462                                         for details) that shall be
 463                                         active after boot.</para>
 464
 465                                         <para>It is recommended that
 466                                         path units installed by
 467                                         applications get pulled in via
 468                                         <varname>Wants=</varname>
 469                                         dependencies from this
 470                                         unit. This is best configured
 471                                         via a
 472                                         <varname>WantedBy=paths.target</varname>
 473                                         in the path unit's
 474                                         <literal>[Install]</literal>
 475                                         section.</para>
 476                                 </listitem>
 477                         </varlistentry>
 478                         <varlistentry>
 479                                 <term><filename>poweroff.target</filename></term>
 480                                 <listitem>
 481                                         <para>A special target unit
 482                                         for shutting down and powering off the system.</para>
 483
 484                                         <para>Applications wanting to
 485                                         power off the system should start
 486                                         this unit.</para>
 487
 488                                         <para><filename>runlevel0.target</filename>
 489                                         is an alias for this target
 490                                         unit, for compatibility with SysV.</para>
 491                                 </listitem>
 492                         </varlistentry>
 493                         <varlistentry>
 494                                 <term><filename>reboot.target</filename></term>
 495                                 <listitem>
 496                                         <para>A special target unit
 497                                         for shutting down and rebooting the system.</para>
 498
 499                                         <para>Applications wanting to
 500                                         reboot the system should start
 501                                         this unit.</para>
 502
 503                                         <para><filename>runlevel6.target</filename>
 504                                         is an alias for this target
 505                                         unit, for compatibility with SysV.</para>
 506                                 </listitem>
 507                         </varlistentry>
 508                         <varlistentry>
 509                                 <term><filename>remote-fs.target</filename></term>
 510                                 <listitem>
 511                                         <para>Similar to
 512                                         <filename>local-fs.target</filename>,
 513                                         but for remote mount
 514                                         points.</para>
 515
 516                                         <para>systemd automatically
 517                                         adds dependencies of type
 518                                         <varname>After=</varname> for
 519                                         this target unit to all SysV
 520                                         init script service units with
 521                                         an LSB header referring to the
 522                                         <literal>$remote_fs</literal>
 523                                         facility.</para>
 524                                 </listitem>
 525                         </varlistentry>
 526                         <varlistentry>
 527                                 <term><filename>rescue.target</filename></term>
 528                                 <listitem>
 529                                         <para>A special target unit
 530                                         for setting up the base system
 531                                         and a rescue shell.</para>
 532
 533                                         <para><filename>runlevel1.target</filename>
 534                                         is an alias for this target
 535                                         unit, for compatibility with SysV.</para>
 536                                 </listitem>
 537                         </varlistentry>
 538                         <varlistentry>
 539                                 <term><filename>initrd-root-fs.target</filename></term>
 540                                 <listitem>
 541                                         <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 542                                         automatically adds
 543                                         dependencies of type
 544                                         <varname>Before=</varname> to
 545                                         the
 546                                         <filename>sysroot.mount</filename>
 547                                         unit, which is generated from
 548                                         the kernel command line.
 549                                         </para>
 550                                 </listitem>
 551                         </varlistentry>
 552                         <varlistentry>
 553                                 <term><filename>runlevel2.target</filename></term>
 554                                 <term><filename>runlevel3.target</filename></term>
 555                                 <term><filename>runlevel4.target</filename></term>
 556                                 <term><filename>runlevel5.target</filename></term>
 557                                 <listitem>
 558                                         <para>These are targets that
 559                                         are called whenever the SysV
 560                                         compatibility code asks for
 561                                         runlevel 2, 3, 4, 5,
 562                                         respectively. It is a good
 563                                         idea to make this an alias for
 564                                         (i.e. symlink to)
 565                                         <filename>multi-user.target</filename>
 566                                         (for runlevel 2) or
 567                                         <filename>graphical.target</filename>
 568                                         (the others).</para>
 569                                 </listitem>
 570                         </varlistentry>
 571                         <varlistentry>
 572                                 <term><filename>shutdown.target</filename></term>
 573                                 <listitem>
 574                                         <para>A special target unit
 575                                         that terminates the services
 576                                         on system shutdown.</para>
 577
 578                                         <para>Services that shall be
 579                                         terminated on system shutdown
 580                                         shall add <varname>Conflicts=</varname>
 581                                         dependencies to this unit for
 582                                         their service unit, which is
 583                                         implicitly done when
 584                                         <varname>DefaultDependencies=yes</varname>
 585                                         is set (the default).</para>
 586                                 </listitem>
 587                         </varlistentry>
 588                         <varlistentry>
 589                                 <term><filename>sigpwr.target</filename></term>
 590                                 <listitem>
 591                                         <para>A special target that is
 592                                         started when systemd receives
 593                                         the SIGPWR process signal,
 594                                         which is normally sent by the
 595                                         kernel or UPS daemons when
 596                                         power fails.</para>
 597                                 </listitem>
 598                         </varlistentry>
 599                         <varlistentry>
 600                                 <term><filename>sleep.target</filename></term>
 601                                 <listitem>
 602                                         <para>A special target unit
 603                                         that is pulled in by
 604                                         <filename>suspend.target</filename>,
 605                                         <filename>hibernate.target</filename>
 606                                         and
 607                                         <filename>hybrid-sleep.target</filename>
 608                                         and may be used to hook units
 609                                         into the sleep state
 610                                         logic.</para>
 611                                 </listitem>
 612                         </varlistentry>
 613                         <varlistentry>
 614                                 <term><filename>sockets.target</filename></term>
 615                                 <listitem>
 616                                         <para>A special target unit
 617                                         that sets up all socket
 618                                         units.(see
 619                                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 620                                         for details) that shall be
 621                                         active after boot.</para>
 622
 623                                         <para>Services that can be
 624                                         socket-activated shall add
 625                                         <varname>Wants=</varname>
 626                                         dependencies to this unit for
 627                                         their socket unit during
 628                                         installation. This is best
 629                                         configured via a
 630                                         <varname>WantedBy=sockets.target</varname>
 631                                         in the socket unit's
 632                                         <literal>[Install]</literal>
 633                                         section.</para>
 634                                 </listitem>
 635                         </varlistentry>
 636                         <varlistentry>
 637                                 <term><filename>suspend.target</filename></term>
 638                                 <listitem>
 639                                         <para>A special target unit
 640                                         for suspending the
 641                                         system. This pulls in
 642                                         <filename>sleep.target</filename>.</para>
 643                                 </listitem>
 644                         </varlistentry>
 645                         <varlistentry>
 646                                 <term><filename>swap.target</filename></term>
 647                                 <listitem>
 648                                         <para>Similar to
 649                                         <filename>local-fs.target</filename>, but for swap
 650                                         partitions and swap
 651                                         files.</para>
 652                                 </listitem>
 653                         </varlistentry>
 654                         <varlistentry>
 655                                 <term><filename>sysinit.target</filename></term>
 656                                 <listitem>
 657                                         <para>A special target unit
 658                                         covering early boot-up scripts.</para>
 659                                 </listitem>
 660                         </varlistentry>
 661                         <varlistentry>
 662                                 <term><filename>syslog.socket</filename></term>
 663                                 <listitem>
 664                                         <para>The socket unit
 665                                         syslog implementations should
 666                                         listen on. All userspace log
 667                                         messages will be made
 668                                         available on this socket. For
 669                                         more information about syslog
 670                                         integration, please consult
 671                                         the <ulink
 672                                         url="http://www.freedesktop.org/wiki/Software/systemd/syslog">Syslog
 673                                         Interface</ulink>
 674                                         document.</para>
 675                                 </listitem>
 676                         </varlistentry>
 677                         <varlistentry>
 678                                 <term><filename>system-update.target</filename></term>
 679                                 <listitem>
 680                                         <para>A special target unit
 681                                         that is used for off-line
 682                                         system updates.
 683                                         <citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 684                                         will redirect the boot process
 685                                         to this target if
 686                                         <filename>/system-update</filename>
 687                                         exists. For more information
 688                                         see the <ulink
 689                                         url="http://freedesktop.org/wiki/Software/systemd/SystemUpdates">System
 690                                         Updates
 691                                         Specification</ulink>.</para>
 692                                 </listitem>
 693                         </varlistentry>
 694                         <varlistentry>
 695                                 <term><filename>timers.target</filename></term>
 696                                 <listitem>
 697                                         <para>A special target unit
 698                                         that sets up all timer
 699                                         units (see
 700                                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 701                                         for details) that shall be
 702                                         active after boot.</para>
 703
 704                                         <para>It is recommended that
 705                                         timer units installed by
 706                                         applications get pulled in via
 707                                         <varname>Wants=</varname>
 708                                         dependencies from this
 709                                         unit. This is best configured
 710                                         via
 711                                         <varname>WantedBy=timers.target</varname>
 712                                         in the timer unit's
 713                                         <literal>[Install]</literal>
 714                                         section.</para>
 715                                 </listitem>
 716                         </varlistentry>
 717                         <varlistentry>
 718                                 <term><filename>umount.target</filename></term>
 719                                 <listitem>
 720                                         <para>A special target unit
 721                                         that umounts all mount and
 722                                         automount points on system
 723                                         shutdown.</para>
 724
 725                                         <para>Mounts that shall be
 726                                         unmounted on system shutdown
 727                                         shall add Conflicts
 728                                         dependencies to this unit for
 729                                         their mount unit, which is
 730                                         implicitly done when
 731                                         <varname>DefaultDependencies=yes</varname>
 732                                         is set (the default).</para>
 733                                 </listitem>
 734                         </varlistentry>
 735
 736                 </variablelist>
 737         </refsect1>
 738
 739         <refsect1>
 740                 <title>Special System Units for Devices</title>
 741
 742                 <para>Some target units are automatically pulled in as
 743                 devices of certain kinds show up in the system. These
 744                 may be used to automatically activate various services
 745                 based on the specific type of the available
 746                 hardware.</para>
 747
 748                 <variablelist>
 749                         <varlistentry>
 750                                 <term><filename>bluetooth.target</filename></term>
 751                                 <listitem>
 752                                         <para>This target is started
 753                                         automatically as soon as a
 754                                         Bluetooth controller is
 755                                         plugged in or becomes
 756                                         available at boot.</para>
 757
 758                                         <para>This may be used to pull
 759                                         in Bluetooth management
 760                                         daemons dynamically when
 761                                         Bluetooth hardware is
 762                                         found.</para>
 763                                 </listitem>
 764                         </varlistentry>
 765                         <varlistentry>
 766                                 <term><filename>printer.target</filename></term>
 767                                 <listitem>
 768                                         <para>This target is started
 769                                         automatically as soon as a
 770                                         printer is plugged in or
 771                                         becomes available at
 772                                         boot.</para>
 773
 774                                         <para>This may be used to pull
 775                                         in printer management
 776                                         daemons dynamically when
 777                                         printer hardware is
 778                                         found.</para>
 779                                 </listitem>
 780                         </varlistentry>
 781                         <varlistentry>
 782                                 <term><filename>smartcard.target</filename></term>
 783                                 <listitem>
 784                                         <para>This target is started
 785                                         automatically as soon as a
 786                                         smartcard controller is
 787                                         plugged in or becomes
 788                                         available at boot.</para>
 789
 790                                         <para>This may be used to pull
 791                                         in smartcard management
 792                                         daemons dynamically when
 793                                         smartcard hardware is
 794                                         found.</para>
 795                                 </listitem>
 796                         </varlistentry>
 797                         <varlistentry>
 798                                 <term><filename>sound.target</filename></term>
 799                                 <listitem>
 800                                         <para>This target is started
 801                                         automatically as soon as a
 802                                         sound card is plugged in or
 803                                         becomes available at
 804                                         boot.</para>
 805
 806                                         <para>This may be used to pull
 807                                         in audio management daemons
 808                                         dynamically when audio
 809                                         hardware is found.</para>
 810                                 </listitem>
 811                         </varlistentry>
 812                 </variablelist>
 813         </refsect1>
 814
 815         <refsect1>
 816                 <title>Special Passive System Units </title>
 817
 818                 <para>A number of special system targets are defined
 819                 that can be used to properly order boot-up of optional
 820                 services. These targets are generally not part of the
 821                 initial boot transaction, unless they are explicitly
 822                 pulled in by one of the implementing services. Note
 823                 specifically that these <emphasis>passive</emphasis>
 824                 target units are generally not pulled in by the
 825                 consumer of a service, but by the provider of the
 826                 service. This means: a consuming service should order
 827                 itself after these targets (as appropriate), but not
 828                 pull it in. A providing service should order itself
 829                 before these targets (as appropriate) and pull it in
 830                 (via a <varname>Wants=</varname> type
 831                 dependency).</para>
 832
 833                 <para>Note that these passive units cannot be started
 834                 manually, i.e. <literal>systemctl start
 835                 time-sync.target</literal> will fail with an
 836                 error. They can only be pulled in by dependency. This
 837                 is enforced since they exist for ordering purposes
 838                 only and thus are not useful as only unit within a
 839                 transaction.</para>
 840
 841                 <variablelist>
 842                         <varlistentry>
 843                                 <term><filename>local-fs-pre.target</filename></term>
 844                                 <listitem>
 845                                         <para>This target unit is
 846                                         automatically ordered before
 847                                         all local mount points marked
 848                                         with <option>auto</option>
 849                                         (see above). It can be used to
 850                                         execute certain units before
 851                                         all local mounts.</para>
 852                                 </listitem>
 853                         </varlistentry>
 854                         <varlistentry>
 855                                 <term><filename>network.target</filename></term>
 856                                 <listitem>
 857                                         <para>This unit is supposed to
 858                                         indicate when network
 859                                         functionality is available,
 860                                         but it is only very weakly
 861                                         defined what that is supposed
 862                                         to mean, with one exception:
 863                                         at shutdown, a unit that is
 864                                         ordered after
 865                                         <filename>network.target</filename>
 866                                         will be stopped before the
 867                                         network -- to whatever level
 868                                         it might be set up then -- is
 869                                         shut down. Also see <ulink
 870                                         url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 871                                         Services After the Network is
 872                                         up</ulink> for more
 873                                         information. Also see
 874                                         <filename>network-online.target</filename>
 875                                         described above.</para>
 876
 877                                         <para>systemd automatically
 878                                         adds dependencies of type
 879                                         <varname>After=</varname> for
 880                                         this target unit to all SysV
 881                                         init script service units with
 882                                         an LSB header referring to the
 883                                         <literal>$network</literal>
 884                                         facility.</para>
 885
 886                                 </listitem>
 887                         </varlistentry>
 888                         <varlistentry>
 889                                 <term><filename>nss-lookup.target</filename></term>
 890                                 <listitem>
 891                                         <para>A target that should be
 892                                         used as synchronization point
 893                                         for all host/network name
 894                                         service lookups. Note that
 895                                         this is independent of
 896                                         user/group name lookups for
 897                                         which
 898                                         <filename>nss-user-lookup.target</filename>
 899                                         should be used. systemd
 900                                         automatically adds
 901                                         dependencies of type
 902                                         <varname>After=</varname> for
 903                                         this target unit to all SysV
 904                                         init script service units with
 905                                         an LSB header referring to the
 906                                         <literal>$named</literal>
 907                                         facility.</para>
 908                                 </listitem>
 909                         </varlistentry>
 910                         <varlistentry>
 911                                 <term><filename>nss-user-lookup.target</filename></term>
 912                                 <listitem>
 913                                         <para>A target that should be
 914                                         used as synchronization point
 915                                         for all user/group name
 916                                         service lookups. Note that
 917                                         this is independent of
 918                                         host/network name lookups for
 919                                         which
 920                                         <filename>nss-lookup.target</filename>
 921                                         should be used. </para>
 922                                 </listitem>
 923                         </varlistentry>
 924                         <varlistentry>
 925                                 <term><filename>remote-fs-pre.target</filename></term>
 926                                 <listitem>
 927                                         <para>This target unit is
 928                                         automatically ordered before
 929                                         all remote mount point units
 930                                         (see above). It can be used to
 931                                         run certain units before the
 932                                         remote mounts are
 933                                         established. Note that this
 934                                         unit is generally not part of
 935                                         the initial transaction,
 936                                         unless the unit that wants to
 937                                         be ordered before all remote
 938                                         mounts pulls it in via a
 939                                         <varname>Wants=</varname> type
 940                                         dependency. If the unit wants
 941                                         to be pulled in by the first
 942                                         remote mount showing up, it
 943                                         should use
 944                                         <filename>network-online.target</filename>
 945                                         (see above).</para>
 946
 947                                         <para>Again, this target unit
 948                                         is <emphasis>not</emphasis>
 949                                         suitable for pulling in other
 950                                         units, it is only useful for
 951                                         ordering.</para>
 952                                 </listitem>
 953                         </varlistentry>
 954                         <varlistentry>
 955                                 <term><filename>rpcbind.target</filename></term>
 956                                 <listitem>
 957                                         <para>systemd automatically
 958                                         adds dependencies of type
 959                                         <varname>After=</varname> for
 960                                         this target unit to all SysV
 961                                         init script service units with
 962                                         an LSB header referring to the
 963                                         <literal>$portmap</literal>
 964                                         facility.</para>
 965                                 </listitem>
 966                         </varlistentry>
 967                         <varlistentry>
 968                                 <term><filename>time-sync.target</filename></term>
 969                                 <listitem>
 970                                         <para>systemd automatically
 971                                         adds dependencies of type
 972                                         <varname>After=</varname> for
 973                                         this target unit to all SysV
 974                                         init script service units with
 975                                         an LSB header referring to the
 976                                         <literal>$time</literal>
 977                                         facility.</para>
 978                                 </listitem>
 979                         </varlistentry>
 980                 </variablelist>
 981         </refsect1>
 982
 983         <refsect1>
 984                 <title>Special User Units</title>
 985
 986                 <para>When systemd runs as a user instance, the
 987                 following special units are available, which have
 988                 similar definitions as their system counterparts:
 989                 <filename>default.target</filename>,
 990                 <filename>shutdown.target</filename>,
 991                 <filename>sockets.target</filename>,
 992                 <filename>timers.target</filename>,
 993                 <filename>paths.target</filename>,
 994                 <filename>bluetooth.target</filename>,
 995                 <filename>printer.target</filename>,
 996                 <filename>smartcard.target</filename>,
 997                 <filename>sound.target</filename>.</para>
 998
 999                 <para>In addition, the following special unit is
1000                 understood only when systemd runs as service instance:</para>
1001
1002                 <variablelist>
1003                         <varlistentry>
1004                                 <term><filename>exit.target</filename></term>
1005                                 <listitem>
1006                                         <para>A special service unit
1007                                         for shutting down the
1008                                         user service manager.</para>
1009
1010                                         <para>Applications wanting to
1011                                         terminate the user service
1012                                         manager should start this
1013                                         unit. If systemd receives
1014                                         <constant>SIGTERM</constant> or <constant>SIGINT</constant> when running
1015                                         as user service daemon, it will
1016                                         start this unit.</para>
1017
1018                                         <para>Normally, this pulls in
1019                                         <filename>shutdown.target</filename>
1020                                         which in turn should be
1021                                         conflicted by all units that
1022                                         want to be shut down on
1023                                         user service manager exit.</para>
1024                                 </listitem>
1025                         </varlistentry>
1026                 </variablelist>
1027         </refsect1>
1028
1029         <refsect1>
1030                 <title>Special Slice Units</title>
1031
1032                 <para>There are four <literal>.slice</literal> units
1033                 which form the basis of the hierarchy for assignment
1034                 of resources for services, users, and virtual machines
1035                 or containers.</para>
1036
1037                 <variablelist>
1038                         <varlistentry>
1039                                 <term><filename>-.slice</filename></term>
1040                                 <listitem>
1041                                         <para>The root slice is the
1042                                         root of the hierarchy. It
1043                                         usually does not contain units
1044                                         directly, but may be used to
1045                                         set defaults for the whole
1046                                         tree.</para>
1047                                 </listitem>
1048                         </varlistentry>
1049
1050                         <varlistentry>
1051                                 <term><filename>system.slice</filename></term>
1052                                 <listitem>
1053                                         <para>By default, all services
1054                                         services started by
1055                                         <command>systemd</command> are
1056                                         found in this slice.</para>
1057                                 </listitem>
1058                         </varlistentry>
1059
1060                         <varlistentry>
1061                                 <term><filename>user.slice</filename></term>
1062                                 <listitem>
1063                                         <para>By default, all user
1064                                         processes and services started
1065                                         on behalf of the user,
1066                                         including the per-user systemd
1067                                         instance are found in this
1068                                         slice.</para>
1069                                 </listitem>
1070                         </varlistentry>
1071
1072                         <varlistentry>
1073                                 <term><filename>machine.slice</filename></term>
1074                                 <listitem>
1075                                         <para>By defalt, all virtual
1076                                         machines and containers
1077                                         registered with
1078                                         <command>systemd-machined</command>
1079                                         are found in this slice.
1080                                         </para>
1081                                 </listitem>
1082                         </varlistentry>
1083                 </variablelist>
1084         </refsect1>
1085
1086         <refsect1>
1087                   <title>See Also</title>
1088                   <para>
1089                           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1090                           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1091                           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1092                           <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1093                           <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1094                           <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1095                           <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1096                           <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1097                   </para>
1098         </refsect1>
1099
1100 </refentry>