man/systemd.special.xml

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  10   Copyright 2010 Lennart Poettering
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  25
  26 <refentry id="systemd.special">
  27
  28   <refentryinfo>
  29     <title>systemd.special</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>Developer</contrib>
  35         <firstname>Lennart</firstname>
  36         <surname>Poettering</surname>
  37         <email>lennart@poettering.net</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>systemd.special</refentrytitle>
  44     <manvolnum>7</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>systemd.special</refname>
  49     <refpurpose>Special systemd units</refpurpose>
  50   </refnamediv>
  51
  52   <refsynopsisdiv><para>
  53     <!-- sort alphabetically, targets first --><filename>basic.target</filename>,
  54     <filename>bluetooth.target</filename>,
  55     <filename>cryptsetup-pre.target</filename>,
  56     <filename>cryptsetup.target</filename>,
  57     <filename>ctrl-alt-del.target</filename>,
  58     <filename>default.target</filename>,
  59     <filename>emergency.target</filename>,
  60     <filename>exit.target</filename>,
  61     <filename>final.target</filename>,
  62     <filename>getty.target</filename>,
  63     <filename>getty-pre.target</filename>,
  64     <filename>graphical.target</filename>,
  65     <filename>halt.target</filename>,
  66     <filename>hibernate.target</filename>,
  67     <filename>hybrid-sleep.target</filename>,
  68     <filename>suspend-then-hibernate.target</filename>,
  69     <filename>initrd-fs.target</filename>,
  70     <filename>initrd-root-device.target</filename>,
  71     <filename>initrd-root-fs.target</filename>,
  72     <filename>kbrequest.target</filename>,
  73     <filename>kexec.target</filename>,
  74     <filename>local-fs-pre.target</filename>,
  75     <filename>local-fs.target</filename>,
  76     <filename>machines.target</filename>
  77     <filename>multi-user.target</filename>,
  78     <filename>network-online.target</filename>,
  79     <filename>network-pre.target</filename>,
  80     <filename>network.target</filename>,
  81     <filename>nss-lookup.target</filename>,
  82     <filename>nss-user-lookup.target</filename>,
  83     <filename>paths.target</filename>,
  84     <filename>poweroff.target</filename>,
  85     <filename>printer.target</filename>,
  86     <filename>reboot.target</filename>,
  87     <filename>remote-cryptsetup.target</filename>,
  88     <filename>remote-fs-pre.target</filename>,
  89     <filename>remote-fs.target</filename>,
  90     <filename>rescue.target</filename>,
  91     <filename>rpcbind.target</filename>,
  92     <filename>runlevel2.target</filename>,
  93     <filename>runlevel3.target</filename>,
  94     <filename>runlevel4.target</filename>,
  95     <filename>runlevel5.target</filename>,
  96     <filename>shutdown.target</filename>,
  97     <filename>sigpwr.target</filename>,
  98     <filename>sleep.target</filename>,
  99     <filename>slices.target</filename>,
 100     <filename>smartcard.target</filename>,
 101     <filename>sockets.target</filename>,
 102     <filename>sound.target</filename>,
 103     <filename>suspend.target</filename>,
 104     <filename>swap.target</filename>,
 105     <filename>sysinit.target</filename>,
 106     <filename>system-update.target</filename>,
 107     <filename>time-sync.target</filename>,
 108     <filename>timers.target</filename>,
 109     <filename>umount.target</filename>,
 110     <!-- slices --><filename>-.slice</filename>,
 111     <filename>system.slice</filename>,
 112     <filename>user.slice</filename>,
 113     <filename>machine.slice</filename>,
 114     <!-- the rest --><filename>-.mount</filename>,
 115     <filename>dbus.service</filename>,
 116     <filename>dbus.socket</filename>,
 117     <filename>display-manager.service</filename>,
 118     <filename>init.scope</filename>,
 119     <filename>syslog.socket</filename>,
 120     <filename>system-update-cleanup.service</filename>
 121   </para></refsynopsisdiv>
 122
 123   <refsect1>
 124     <title>Description</title>
 125
 126     <para>A few units are treated specially by systemd. Many of them have
 127     special internal semantics and cannot be renamed, while others simply
 128     have a standard meaning and should be present on all systems.</para>
 129   </refsect1>
 130
 131   <refsect1>
 132     <title>Special System Units</title>
 133
 134     <variablelist>
 135       <varlistentry>
 136         <term><filename>-.mount</filename></term>
 137         <listitem>
 138           <para>The root mount point, i.e. the mount unit for the <filename>/</filename> path. This unit is
 139           unconditionally active, during the entire time the system is up, as this mount point is where the basic
 140           userspace is running from.</para>
 141         </listitem>
 142       </varlistentry>
 143
 144       <varlistentry>
 145         <term><filename>basic.target</filename></term>
 146         <listitem>
 147           <para>A special target unit covering basic boot-up.</para>
 148
 149           <para>systemd automatically adds dependency of the type
 150           <varname>After=</varname> for this target unit to all
 151           services (except for those with
 152           <varname>DefaultDependencies=no</varname>).</para>
 153
 154           <para>Usually, this should pull-in all local mount points plus
 155           <filename>/var</filename>, <filename>/tmp</filename> and
 156           <filename>/var/tmp</filename>, swap devices, sockets, timers,
 157           path units and other basic initialization necessary for general
 158           purpose daemons. The mentioned mount points are special cased
 159           to allow them to be remote.
 160           </para>
 161
 162           <para>This target usually does not pull in any non-target units
 163           directly, but rather does so indirectly via other early boot targets.
 164           It is instead meant as a synchronization point for late boot
 165           services. Refer to
 166           <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 167           for details on the targets involved.
 168           </para>
 169
 170         </listitem>
 171       </varlistentry>
 172       <varlistentry>
 173         <term><filename>ctrl-alt-del.target</filename></term>
 174         <listitem>
 175           <para>systemd starts this target whenever Control+Alt+Del is
 176           pressed on the console. Usually, this should be aliased
 177           (symlinked) to <filename>reboot.target</filename>.</para>
 178         </listitem>
 179       </varlistentry>
 180       <varlistentry>
 181         <term><filename>cryptsetup.target</filename></term>
 182         <listitem>
 183           <para>A target that pulls in setup services for all
 184           encrypted block devices.</para>
 185         </listitem>
 186       </varlistentry>
 187       <varlistentry>
 188         <term><filename>dbus.service</filename></term>
 189         <listitem>
 190           <para>A special unit for the D-Bus bus daemon. As soon as
 191           this service is fully started up systemd will connect to it
 192           and register its service.</para>
 193         </listitem>
 194       </varlistentry>
 195       <varlistentry>
 196         <term><filename>dbus.socket</filename></term>
 197         <listitem>
 198           <para>A special unit for the D-Bus system bus socket. All
 199           units with <varname>Type=dbus</varname> automatically gain a
 200           dependency on this unit.</para>
 201         </listitem>
 202       </varlistentry>
 203       <varlistentry>
 204         <term><filename>default.target</filename></term>
 205         <listitem>
 206           <para>The default unit systemd starts at bootup. Usually,
 207           this should be aliased (symlinked) to
 208           <filename>multi-user.target</filename> or
 209           <filename>graphical.target</filename>.</para>
 210
 211           <para>The default unit systemd starts at bootup can be
 212           overridden with the <varname>systemd.unit=</varname> kernel
 213           command line option.</para>
 214         </listitem>
 215       </varlistentry>
 216       <varlistentry>
 217         <term><filename>display-manager.service</filename></term>
 218         <listitem>
 219           <para>The display manager service. Usually, this should be
 220           aliased (symlinked) to <filename>gdm.service</filename> or a
 221           similar display manager service.</para>
 222         </listitem>
 223       </varlistentry>
 224       <varlistentry>
 225         <term><filename>emergency.target</filename></term>
 226         <listitem>
 227           <para>A special target unit that starts an emergency shell on the main console. This target does not pull in
 228           any services or mounts. It is the most minimal version of starting the system in order to acquire an
 229           interactive shell; the only processes running are usually just the system manager (PID 1) and the shell
 230           process. This unit is supposed to be used with the kernel command line option
 231           <varname>systemd.unit=</varname>; it is also used when a file system check on a required file system fails,
 232           and boot-up cannot continue. Compare with <filename>rescue.target</filename>, which serves a similar purpose,
 233           but also starts the most basic services and mounts all file systems.</para>
 234
 235           <para>Use the <literal>systemd.unit=emergency.target</literal> kernel command line option to boot into this
 236           mode. A short alias for this kernel command line option is <literal>emergency</literal>, for compatibility
 237           with SysV.</para>
 238
 239           <para>In many ways booting into <filename>emergency.target</filename> is similar to the effect of booting
 240           with <literal>init=/bin/sh</literal> on the kernel command line, except that emergency mode provides you with
 241           the full system and service manager, and allows starting individual units in order to continue the boot
 242           process in steps.</para>
 243         </listitem>
 244       </varlistentry>
 245       <varlistentry>
 246         <term><filename>exit.target</filename></term>
 247         <listitem>
 248           <para>A special service unit for shutting down the system or
 249           user service manager. It is equivalent to
 250           <filename>poweroff.target</filename> on non-container
 251           systems, and also works in containers.</para>
 252
 253           <para>systemd will start this unit when it receives the
 254           <constant>SIGTERM</constant> or <constant>SIGINT</constant>
 255           signal when running as user service daemon.</para>
 256
 257           <para>Normally, this (indirectly) pulls in
 258           <filename>shutdown.target</filename>, which in turn should be
 259           conflicted by all units that want to be scheduled for
 260           shutdown when the service manager starts to exit.</para>
 261         </listitem>
 262       </varlistentry>
 263       <varlistentry>
 264         <term><filename>final.target</filename></term>
 265         <listitem>
 266           <para>A special target unit that is used during the shutdown
 267           logic and may be used to pull in late services after all
 268           normal services are already terminated and all mounts
 269           unmounted.
 270           </para>
 271         </listitem>
 272       </varlistentry>
 273       <varlistentry>
 274         <term><filename>getty.target</filename></term>
 275         <listitem>
 276           <para>A special target unit that pulls in statically
 277           configured local TTY <filename>getty</filename> instances.
 278           </para>
 279         </listitem>
 280       </varlistentry>
 281       <varlistentry>
 282         <term><filename>graphical.target</filename></term>
 283         <listitem>
 284           <para>A special target unit for setting up a graphical login
 285           screen. This pulls in
 286           <filename>multi-user.target</filename>.</para>
 287
 288           <para>Units that are needed for graphical logins shall add
 289           <varname>Wants=</varname> dependencies for their unit to
 290           this unit (or <filename>multi-user.target</filename>) during
 291           installation. This is best configured via
 292           <varname>WantedBy=graphical.target</varname> in the unit's
 293           <literal>[Install]</literal> section.</para>
 294         </listitem>
 295       </varlistentry>
 296       <varlistentry>
 297         <term><filename>hibernate.target</filename></term>
 298         <listitem>
 299           <para>A special target unit for hibernating the system. This
 300           pulls in <filename>sleep.target</filename>.</para>
 301         </listitem>
 302       </varlistentry>
 303       <varlistentry>
 304         <term><filename>hybrid-sleep.target</filename></term>
 305         <listitem>
 306           <para>A special target unit for hibernating and suspending
 307           the system at the same time. This pulls in
 308           <filename>sleep.target</filename>.</para>
 309         </listitem>
 310       </varlistentry>
 311       <varlistentry>
 312         <term><filename>suspend-then-hibernate.target</filename></term>
 313         <listitem>
 314           <para>A special target unit for suspending the system for a period
 315           of time, waking it and putting it into hibernate. This pulls in
 316           <filename>sleep.target</filename>.</para>
 317         </listitem>
 318       </varlistentry>
 319
 320       <varlistentry>
 321         <term><filename>halt.target</filename></term>
 322         <listitem>
 323           <para>A special target unit for shutting down and halting
 324           the system. Note that this target is distinct from
 325           <filename>poweroff.target</filename> in that it generally
 326           really just halts the system rather than powering it
 327           down.</para>
 328
 329           <para>Applications wanting to halt the system should not start this unit
 330           directly, but should instead execute <command>systemctl halt</command>
 331           (possibly with the <option>--no-block</option> option) or call
 332           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 333           <command>org.freedesktop.systemd1.Manager.Halt</command> D-Bus method
 334           directly.</para>
 335         </listitem>
 336       </varlistentry>
 337       <varlistentry>
 338         <term><filename>init.scope</filename></term>
 339         <listitem>
 340           <para>This scope unit is where the system and service manager (PID 1) itself resides. It is active as long as
 341           the system is running.</para>
 342         </listitem>
 343       </varlistentry>
 344       <varlistentry>
 345         <term><filename>initrd-fs.target</filename></term>
 346         <listitem>
 347           <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 348           automatically adds dependencies of type
 349           <varname>Before=</varname> to
 350           <filename>sysroot-usr.mount</filename> and all mount points
 351           found in <filename>/etc/fstab</filename> that have
 352           <option>x-initrd.mount</option> and not have
 353           <option>noauto</option> mount options set.</para>
 354         </listitem>
 355       </varlistentry>
 356       <varlistentry>
 357         <term><filename>initrd-root-device.target</filename></term>
 358         <listitem>
 359           <para>A special initrd target unit that is reached when the root filesystem device is available, but before
 360           it has been mounted.
 361           <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 362           and
 363           <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 364           automatically setup the appropriate dependencies to make this happen.
 365           </para>
 366         </listitem>
 367       </varlistentry>
 368       <varlistentry>
 369         <term><filename>initrd-root-fs.target</filename></term>
 370         <listitem>
 371           <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 372           automatically adds dependencies of type
 373           <varname>Before=</varname> to the
 374           <filename>sysroot.mount</filename> unit, which is generated
 375           from the kernel command line.
 376           </para>
 377         </listitem>
 378       </varlistentry>
 379       <varlistentry>
 380         <term><filename>kbrequest.target</filename></term>
 381         <listitem>
 382           <para>systemd starts this target whenever Alt+ArrowUp is
 383           pressed on the console. Note that any user with physical access
 384           to the machine will be able to do this, without authentication,
 385           so this should be used carefully.</para>
 386         </listitem>
 387       </varlistentry>
 388       <varlistentry>
 389         <term><filename>kexec.target</filename></term>
 390         <listitem>
 391           <para>A special target unit for shutting down and rebooting
 392           the system via kexec.</para>
 393
 394           <para>Applications wanting to reboot the system should not start this unit
 395           directly, but should instead execute <command>systemctl kexec</command>
 396           (possibly with the <option>--no-block</option> option) or call
 397           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 398           <command>org.freedesktop.systemd1.Manager.KExec</command> D-Bus method
 399           directly.</para>
 400         </listitem>
 401       </varlistentry>
 402       <varlistentry>
 403         <term><filename>local-fs.target</filename></term>
 404         <listitem>
 405           <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 406           automatically adds dependencies of type
 407           <varname>Before=</varname> to all mount units that refer to
 408           local mount points for this target unit. In addition, it
 409           adds dependencies of type <varname>Wants=</varname> to this
 410           target unit for those mounts listed in
 411           <filename>/etc/fstab</filename> that have the
 412           <option>auto</option> mount option set.</para>
 413         </listitem>
 414       </varlistentry>
 415       <varlistentry>
 416         <term><filename>machines.target</filename></term>
 417         <listitem>
 418           <para>A standard target unit for starting all the containers
 419           and other virtual machines. See <filename>systemd-nspawn@.service</filename>
 420           for an example.</para>
 421         </listitem>
 422       </varlistentry>
 423       <varlistentry>
 424         <term><filename>multi-user.target</filename></term>
 425         <listitem>
 426           <para>A special target unit for setting up a multi-user
 427           system (non-graphical). This is pulled in by
 428           <filename>graphical.target</filename>.</para>
 429
 430           <para>Units that are needed for a multi-user system shall
 431           add <varname>Wants=</varname> dependencies for their unit to
 432           this unit during installation. This is best configured via
 433           <varname>WantedBy=multi-user.target</varname> in the unit's
 434           <literal>[Install]</literal> section.</para>
 435         </listitem>
 436       </varlistentry>
 437       <varlistentry>
 438         <term><filename>network-online.target</filename></term>
 439         <listitem>
 440           <para>Units that strictly require a configured network
 441           connection should pull in
 442           <filename>network-online.target</filename> (via a
 443           <varname>Wants=</varname> type dependency) and order
 444           themselves after it. This target unit is intended to pull in
 445           a service that delays further execution until the network is
 446           sufficiently set up. What precisely this requires is left to
 447           the implementation of the network managing service.</para>
 448
 449           <para>Note the distinction between this unit and
 450           <filename>network.target</filename>. This unit is an active
 451           unit (i.e. pulled in by the consumer rather than the
 452           provider of this functionality) and pulls in a service which
 453           possibly adds substantial delays to further execution. In
 454           contrast, <filename>network.target</filename> is a passive
 455           unit (i.e. pulled in by the provider of the functionality,
 456           rather than the consumer) that usually does not delay
 457           execution much. Usually, <filename>network.target</filename>
 458           is part of the boot of most systems, while
 459           <filename>network-online.target</filename> is not, except
 460           when at least one unit requires it. Also see <ulink
 461           url="https://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 462           Services After the Network is up</ulink> for more
 463           information.</para>
 464
 465           <para>All mount units for remote network file systems
 466           automatically pull in this unit, and order themselves after
 467           it. Note that networking daemons that simply provide
 468           functionality to other hosts generally do not need to pull
 469           this in.</para>
 470
 471           <para>Note that this unit is only useful during the original system start-up logic. After the system has
 472           completed booting up, it will not track the online state of the system anymore. Due to this it cannot be used
 473           as a network connection monitor concept, it is purely a one-time system start-up concept.</para>
 474           </listitem>
 475       </varlistentry>
 476       <varlistentry>
 477         <term><filename>paths.target</filename></term>
 478         <listitem>
 479           <para>A special target unit that sets up all path units (see
 480           <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 481           for details) that shall be active after boot.</para>
 482
 483           <para>It is recommended that path units installed by
 484           applications get pulled in via <varname>Wants=</varname>
 485           dependencies from this unit. This is best configured via a
 486           <varname>WantedBy=paths.target</varname> in the path unit's
 487           <literal>[Install]</literal> section.</para>
 488         </listitem>
 489       </varlistentry>
 490       <varlistentry>
 491         <term><filename>poweroff.target</filename></term>
 492         <listitem>
 493           <para>A special target unit for shutting down and powering
 494           off the system.</para>
 495
 496           <para>Applications wanting to power off the system should not start this unit
 497           directly, but should instead execute <command>systemctl poweroff</command>
 498           (possibly with the <option>--no-block</option> option) or call
 499           <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
 500           <command>org.freedesktop.login1.Manager.PowerOff</command> D-Bus method
 501           directly.</para>
 502
 503           <para><filename>runlevel0.target</filename> is an alias for
 504           this target unit, for compatibility with SysV.</para>
 505         </listitem>
 506       </varlistentry>
 507       <varlistentry>
 508         <term><filename>reboot.target</filename></term>
 509         <listitem>
 510           <para>A special target unit for shutting down and rebooting
 511           the system.</para>
 512
 513           <para>Applications wanting to reboot the system should not start this unit
 514           directly, but should instead execute <command>systemctl reboot</command>
 515           (possibly with the <option>--no-block</option> option) or call
 516           <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
 517           <command>org.freedesktop.login1.Manager.Reboot</command> D-Bus method
 518           directly.</para>
 519
 520           <para><filename>runlevel6.target</filename> is an alias for
 521           this target unit, for compatibility with SysV.</para>
 522         </listitem>
 523       </varlistentry>
 524       <varlistentry>
 525         <term><filename>remote-cryptsetup.target</filename></term>
 526         <listitem>
 527           <para>Similar to <filename>cryptsetup.target</filename>, but for encrypted
 528           devices which are accessed over the network. It is used for
 529           <citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 530           entries marked with <option>_netdev</option>.</para>
 531         </listitem>
 532       </varlistentry>
 533       <varlistentry>
 534         <term><filename>remote-fs.target</filename></term>
 535         <listitem>
 536           <para>Similar to <filename>local-fs.target</filename>, but
 537           for remote mount points.</para>
 538
 539           <para>systemd automatically adds dependencies of type
 540           <varname>After=</varname> for this target unit to all SysV
 541           init script service units with an LSB header referring to
 542           the <literal>$remote_fs</literal> facility.</para>
 543         </listitem>
 544       </varlistentry>
 545       <varlistentry>
 546         <term><filename>rescue.target</filename></term>
 547         <listitem>
 548           <para>A special target unit that pulls in the base system (including system mounts) and spawns a rescue
 549           shell. Isolate to this target in order to administer the system in single-user mode with all file systems
 550           mounted but with no services running, except for the most basic. Compare with
 551           <filename>emergency.target</filename>, which is much more reduced and does not provide the file systems or
 552           most basic services. Compare with <filename>multi-user.target</filename>, this target could be seen as
 553           <filename>single-user.target</filename>.</para>
 554
 555           <para><filename>runlevel1.target</filename> is an alias for this target unit, for compatibility with
 556           SysV.</para>
 557
 558           <para>Use the <literal>systemd.unit=rescue.target</literal> kernel command line option to boot into this
 559           mode. A short alias for this kernel command line option is <literal>1</literal>, for compatibility with
 560           SysV.</para>
 561         </listitem>
 562       </varlistentry>
 563       <varlistentry>
 564         <term><filename>runlevel2.target</filename></term>
 565         <term><filename>runlevel3.target</filename></term>
 566         <term><filename>runlevel4.target</filename></term>
 567         <term><filename>runlevel5.target</filename></term>
 568         <listitem>
 569           <para>These are targets that are called whenever the SysV
 570           compatibility code asks for runlevel 2, 3, 4, 5,
 571           respectively. It is a good idea to make this an alias for
 572           (i.e. symlink to) <filename>graphical.target</filename>
 573           (for runlevel 5) or <filename>multi-user.target</filename>
 574           (the others).</para>
 575         </listitem>
 576       </varlistentry>
 577       <varlistentry>
 578         <term><filename>shutdown.target</filename></term>
 579         <listitem>
 580           <para>A special target unit that terminates the services on
 581           system shutdown.</para>
 582
 583           <para>Services that shall be terminated on system shutdown
 584           shall add <varname>Conflicts=</varname> and
 585           <varname>Before=</varname> dependencies to this unit for
 586           their service unit, which is implicitly done when
 587           <varname>DefaultDependencies=yes</varname> is set (the
 588           default).</para>
 589         </listitem>
 590       </varlistentry>
 591       <varlistentry>
 592         <term><filename>sigpwr.target</filename></term>
 593         <listitem>
 594           <para>A special target that is started when systemd receives
 595           the SIGPWR process signal, which is normally sent by the
 596           kernel or UPS daemons when power fails.</para>
 597         </listitem>
 598       </varlistentry>
 599       <varlistentry>
 600         <term><filename>sleep.target</filename></term>
 601         <listitem>
 602           <para>A special target unit that is pulled in by
 603           <filename>suspend.target</filename>,
 604           <filename>hibernate.target</filename> and
 605           <filename>hybrid-sleep.target</filename> and may be used to
 606           hook units into the sleep state logic.</para>
 607         </listitem>
 608       </varlistentry>
 609       <varlistentry>
 610         <term><filename>slices.target</filename></term>
 611         <listitem>
 612           <para>A special target unit that sets up all slice units (see
 613           <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 614           details) that shall be active after boot. By default the generic <filename>system.slice</filename>
 615           slice unit, as well as the root slice unit <filename>-.slice</filename>, is pulled in and ordered before
 616           this unit (see below).</para>
 617
 618           <para>It's a good idea to add <varname>WantedBy=slices.target</varname> lines to the <literal>[Install]</literal>
 619           section of all slices units that may be installed dynamically.</para>
 620         </listitem>
 621       </varlistentry>
 622       <varlistentry>
 623         <term><filename>sockets.target</filename></term>
 624         <listitem>
 625           <para>A special target unit that sets up all socket
 626           units (see
 627           <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 628           for details) that shall be active after boot.</para>
 629
 630           <para>Services that can be socket-activated shall add
 631           <varname>Wants=</varname> dependencies to this unit for
 632           their socket unit during installation. This is best
 633           configured via a <varname>WantedBy=sockets.target</varname>
 634           in the socket unit's <literal>[Install]</literal>
 635           section.</para>
 636         </listitem>
 637       </varlistentry>
 638       <varlistentry>
 639         <term><filename>suspend.target</filename></term>
 640         <listitem>
 641           <para>A special target unit for suspending the system. This
 642           pulls in <filename>sleep.target</filename>.</para>
 643         </listitem>
 644       </varlistentry>
 645       <varlistentry>
 646         <term><filename>swap.target</filename></term>
 647         <listitem>
 648           <para>Similar to <filename>local-fs.target</filename>, but
 649           for swap partitions and swap files.</para>
 650         </listitem>
 651       </varlistentry>
 652       <varlistentry>
 653         <term><filename>sysinit.target</filename></term>
 654         <listitem>
 655           <para>systemd automatically adds dependencies of the types
 656           <varname>Requires=</varname> and <varname>After=</varname>
 657           for this target unit to all services (except for those with
 658           <varname>DefaultDependencies=no</varname>).</para>
 659
 660           <para>This target pulls in the services required for system
 661           initialization. System services pulled in by this target should
 662           declare <varname>DefaultDependencies=no</varname> and specify
 663           all their dependencies manually, including access to anything
 664           more than a read only root filesystem. For details on the
 665           dependencies of this target, refer to
 666           <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 667           </para>
 668         </listitem>
 669       </varlistentry>
 670       <varlistentry>
 671         <term><filename>syslog.socket</filename></term>
 672         <listitem>
 673           <para>The socket unit syslog implementations should listen
 674           on. All userspace log messages will be made available on
 675           this socket. For more information about syslog integration,
 676           please consult the <ulink
 677           url="https://www.freedesktop.org/wiki/Software/systemd/syslog">Syslog
 678           Interface</ulink> document.</para>
 679         </listitem>
 680       </varlistentry>
 681       <varlistentry>
 682         <term><filename>system-update.target</filename></term>
 683         <term><filename>system-update-cleanup.service</filename></term>
 684         <listitem>
 685           <para>A special target unit that is used for offline system updates.
 686           <citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 687           will redirect the boot process to this target if <filename>/system-update</filename>
 688           exists. For more information see
 689           <citerefentry><refentrytitle>systemd.offline-updates</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 690           </para>
 691
 692           <para>Updates should happen before the <filename>system-update.target</filename> is
 693           reached, and the services which implement them should cause the machine to reboot. As
 694           a safety measure, if this does not happen, and <filename>/system-update</filename>
 695           still exists after <filename>system-update.target</filename> is reached,
 696           <filename>system-update-cleanup.service</filename> will remove this symlink and
 697           reboot the machine.</para>
 698         </listitem>
 699       </varlistentry>
 700       <varlistentry>
 701         <term><filename>timers.target</filename></term>
 702         <listitem>
 703           <para>A special target unit that sets up all timer units
 704           (see
 705           <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 706           for details) that shall be active after boot.</para>
 707
 708           <para>It is recommended that timer units installed by
 709           applications get pulled in via <varname>Wants=</varname>
 710           dependencies from this unit. This is best configured via
 711           <varname>WantedBy=timers.target</varname> in the timer
 712           unit's <literal>[Install]</literal> section.</para>
 713         </listitem>
 714       </varlistentry>
 715       <varlistentry>
 716         <term><filename>umount.target</filename></term>
 717         <listitem>
 718           <para>A special target unit that unmounts all mount and
 719           automount points on system shutdown.</para>
 720
 721           <para>Mounts that shall be unmounted on system shutdown
 722           shall add Conflicts dependencies to this unit for their
 723           mount unit, which is implicitly done when
 724           <varname>DefaultDependencies=yes</varname> is set (the
 725           default).</para>
 726         </listitem>
 727       </varlistentry>
 728
 729     </variablelist>
 730   </refsect1>
 731
 732   <refsect1>
 733     <title>Special System Units for Devices</title>
 734
 735     <para>Some target units are automatically pulled in as devices of
 736     certain kinds show up in the system. These may be used to
 737     automatically activate various services based on the specific type
 738     of the available hardware.</para>
 739
 740     <variablelist>
 741       <varlistentry>
 742         <term><filename>bluetooth.target</filename></term>
 743         <listitem>
 744           <para>This target is started automatically as soon as a
 745           Bluetooth controller is plugged in or becomes available at
 746           boot.</para>
 747
 748           <para>This may be used to pull in Bluetooth management
 749           daemons dynamically when Bluetooth hardware is found.</para>
 750         </listitem>
 751       </varlistentry>
 752       <varlistentry>
 753         <term><filename>printer.target</filename></term>
 754         <listitem>
 755           <para>This target is started automatically as soon as a
 756           printer is plugged in or becomes available at boot.</para>
 757
 758           <para>This may be used to pull in printer management daemons
 759           dynamically when printer hardware is found.</para>
 760         </listitem>
 761       </varlistentry>
 762       <varlistentry>
 763         <term><filename>smartcard.target</filename></term>
 764         <listitem>
 765           <para>This target is started automatically as soon as a
 766           smartcard controller is plugged in or becomes available at
 767           boot.</para>
 768
 769           <para>This may be used to pull in smartcard management
 770           daemons dynamically when smartcard hardware is found.</para>
 771         </listitem>
 772       </varlistentry>
 773       <varlistentry>
 774         <term><filename>sound.target</filename></term>
 775         <listitem>
 776           <para>This target is started automatically as soon as a
 777           sound card is plugged in or becomes available at
 778           boot.</para>
 779
 780           <para>This may be used to pull in audio management daemons
 781           dynamically when audio hardware is found.</para>
 782         </listitem>
 783       </varlistentry>
 784     </variablelist>
 785   </refsect1>
 786
 787   <refsect1>
 788     <title>Special Passive System Units </title>
 789
 790     <para>A number of special system targets are defined that can be
 791     used to properly order boot-up of optional services. These targets
 792     are generally not part of the initial boot transaction, unless
 793     they are explicitly pulled in by one of the implementing services.
 794     Note specifically that these <emphasis>passive</emphasis> target
 795     units are generally not pulled in by the consumer of a service,
 796     but by the provider of the service. This means: a consuming
 797     service should order itself after these targets (as appropriate),
 798     but not pull it in. A providing service should order itself before
 799     these targets (as appropriate) and pull it in (via a
 800     <varname>Wants=</varname> type dependency).</para>
 801
 802     <para>Note that these passive units cannot be started manually,
 803     i.e. <literal>systemctl start time-sync.target</literal> will fail
 804     with an error. They can only be pulled in by dependency. This is
 805     enforced since they exist for ordering purposes only and thus are
 806     not useful as only unit within a transaction.</para>
 807
 808     <variablelist>
 809       <varlistentry>
 810         <term><filename>cryptsetup-pre.target</filename></term>
 811         <listitem>
 812           <para>This passive target unit may be pulled in by services
 813           that want to run before any encrypted block device is set
 814           up. All encrypted block devices are set up after this target
 815           has been reached. Since the shutdown order is implicitly the
 816           reverse start-up order between units, this target is
 817           particularly useful to ensure that a service is shut down
 818           only after all encrypted block devices are fully
 819           stopped.</para>
 820         </listitem>
 821       </varlistentry>
 822       <varlistentry>
 823         <term><filename>getty-pre.target</filename></term>
 824         <listitem>
 825           <para>A special passive target unit. Users of this target
 826           are expected to pull it in the boot transaction via
 827           a dependency (e.g. <varname>Wants=</varname>). Order your
 828           unit before this unit if you want to make use of the console
 829           just before <filename>getty</filename> is started.
 830           </para>
 831         </listitem>
 832       </varlistentry>
 833       <varlistentry>
 834         <term><filename>local-fs-pre.target</filename></term>
 835         <listitem>
 836           <para>This target unit is
 837           automatically ordered before
 838           all local mount points marked
 839           with <option>auto</option>
 840           (see above). It can be used to
 841           execute certain units before
 842           all local mounts.</para>
 843         </listitem>
 844       </varlistentry>
 845       <varlistentry>
 846         <term><filename>network.target</filename></term>
 847         <listitem>
 848           <para>This unit is supposed to indicate when network
 849           functionality is available, but it is only very weakly
 850           defined what that is supposed to mean, with one exception:
 851           at shutdown, a unit that is ordered after
 852           <filename>network.target</filename> will be stopped before
 853           the network — to whatever level it might be set up then —
 854           is shut down. It is hence useful when writing service files
 855           that require network access on shutdown, which should order
 856           themselves after this target, but not pull it in. Also see
 857           <ulink url="https://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
 858           Services After the Network is up</ulink> for more
 859           information. Also see
 860           <filename>network-online.target</filename> described
 861           above.</para>
 862
 863           <para>systemd automatically adds dependencies of type
 864           <varname>After=</varname> for this target unit to all SysV
 865           init script service units with an LSB header referring to
 866           the <literal>$network</literal> facility.</para>
 867         </listitem>
 868       </varlistentry>
 869       <varlistentry>
 870         <term><filename>network-pre.target</filename></term>
 871         <listitem>
 872           <para>This passive target unit may be pulled in by services
 873           that want to run before any network is set up, for example
 874           for the purpose of setting up a firewall. All network
 875           management software orders itself after this target, but
 876           does not pull it in.</para>
 877         </listitem>
 878       </varlistentry>
 879       <varlistentry>
 880         <term><filename>nss-lookup.target</filename></term>
 881         <listitem>
 882           <para>A target that should be used as synchronization point
 883           for all host/network name service lookups. Note that this is
 884           independent of user/group name lookups for which
 885           <filename>nss-user-lookup.target</filename> should be used.
 886           All services for which the availability of full host/network
 887           name resolution is essential should be ordered after this
 888           target, but not pull it in. systemd automatically adds
 889           dependencies of type <varname>After=</varname> for this
 890           target unit to all SysV init script service units with an
 891           LSB header referring to the <literal>$named</literal>
 892           facility.</para>
 893         </listitem>
 894       </varlistentry>
 895       <varlistentry>
 896         <term><filename>nss-user-lookup.target</filename></term>
 897         <listitem>
 898           <para>A target that should be used as synchronization point
 899           for all user/group name service lookups. Note that this is
 900           independent of host/network name lookups for which
 901           <filename>nss-lookup.target</filename> should be used. All
 902           services for which the availability of the full user/group
 903           database is essential should be ordered after this target,
 904           but not pull it in. Note that system users are always
 905           resolvable, and hence do not require any special ordering
 906           against this target.</para>
 907         </listitem>
 908       </varlistentry>
 909       <varlistentry>
 910         <term><filename>remote-fs-pre.target</filename></term>
 911         <listitem>
 912           <para>This target unit is automatically ordered before all
 913           mount point units (see above) and cryptsetup devices
 914           marked with the <option>_netdev</option>. It can be used to run
 915           certain units before remote encrypted devices and mounts are established.
 916           Note that this unit is generally not part of the initial
 917           transaction, unless the unit that wants to be ordered before
 918           all remote mounts pulls it in via a
 919           <varname>Wants=</varname> type dependency. If the unit wants
 920           to be pulled in by the first remote mount showing up, it
 921           should use <filename>network-online.target</filename> (see
 922           above).</para>
 923         </listitem>
 924       </varlistentry>
 925       <varlistentry>
 926         <term><filename>rpcbind.target</filename></term>
 927         <listitem>
 928           <para>The portmapper/rpcbind pulls in this target and orders
 929           itself before it, to indicate its availability. systemd
 930           automatically adds dependencies of type
 931           <varname>After=</varname> for this target unit to all SysV
 932           init script service units with an LSB header referring to
 933           the <literal>$portmap</literal> facility.</para>
 934         </listitem>
 935       </varlistentry>
 936       <varlistentry>
 937         <term><filename>time-sync.target</filename></term>
 938         <listitem>
 939           <para>Services responsible for synchronizing the system
 940           clock from a remote source (such as NTP client
 941           implementations) should pull in this target and order
 942           themselves before it. All services where correct time is
 943           essential should be ordered after this unit, but not pull it
 944           in. systemd automatically adds dependencies of type
 945           <varname>After=</varname> for this target unit to all SysV
 946           init script service units with an LSB header referring to
 947           the <literal>$time</literal> facility. </para>
 948         </listitem>
 949       </varlistentry>
 950     </variablelist>
 951   </refsect1>
 952
 953   <refsect1>
 954     <title>Special User Units</title>
 955
 956     <para>When systemd runs as a user instance, the following special
 957     units are available, which have similar definitions as their
 958     system counterparts:
 959     <filename>exit.target</filename>,
 960     <filename>default.target</filename>,
 961     <filename>shutdown.target</filename>,
 962     <filename>sockets.target</filename>,
 963     <filename>timers.target</filename>,
 964     <filename>paths.target</filename>,
 965     <filename>bluetooth.target</filename>,
 966     <filename>printer.target</filename>,
 967     <filename>smartcard.target</filename>,
 968     <filename>sound.target</filename>.</para>
 969   </refsect1>
 970
 971   <refsect1>
 972     <title>Special Passive User Units</title>
 973
 974     <variablelist>
 975       <varlistentry>
 976         <term><filename>graphical-session.target</filename></term>
 977         <listitem>
 978           <para>This target is active whenever any graphical session is running. It is used to stop user services which
 979           only apply to a graphical (X, Wayland, etc.) session when the session is terminated. Such services should
 980           have <literal>PartOf=graphical-session.target</literal> in their <literal>[Unit]</literal> section. A target
 981           for a particular session (e. g.  <filename>gnome-session.target</filename>) starts and stops
 982           <literal>graphical-session.target</literal> with <literal>BindsTo=graphical-session.target</literal>.</para>
 983
 984           <para>Which services are started by a session target is determined by the <literal>Wants=</literal> and
 985           <literal>Requires=</literal> dependencies.  For services that can be enabled independently, symlinks in
 986           <literal>.wants/</literal> and <literal>.requires/</literal> should be used, see
 987           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.  Those
 988           symlinks should either be shipped in packages, or should be added dynamically after installation, for example
 989           using <literal>systemctl add-wants</literal>, see
 990           <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
 991           </para>
 992
 993           <example>
 994             <title>Nautilus as part of a GNOME session</title>
 995
 996             <para><literal>gnome-session.target</literal> pulls in Nautilus as top-level service:</para>
 997
 998             <programlisting>[Unit]
 999 Description=User systemd services for GNOME graphical session
1000 Wants=nautilus.service
1001 BindsTo=graphical-session.target</programlisting>
1002
1003             <para><literal>nautilus.service</literal> gets stopped when the session stops:</para>
1004
1005             <programlisting>[Unit]
1006 Description=Render the desktop icons with Nautilus
1007 PartOf=graphical-session.target
1008
1009 [Service]
1010 …</programlisting>
1011           </example>
1012         </listitem>
1013       </varlistentry>
1014
1015       <varlistentry>
1016         <term><filename>graphical-session-pre.target</filename></term>
1017         <listitem>
1018           <para>This target contains services which set up the environment or global configuration of a graphical
1019           session, such as SSH/GPG agents (which need to export an environment variable into all desktop processes) or
1020           migration of obsolete d-conf keys after an OS upgrade (which needs to happen before starting any process that
1021           might use them). This target must be started before starting a graphical session like
1022           <filename>gnome-session.target</filename>.</para>
1023         </listitem>
1024       </varlistentry>
1025     </variablelist>
1026
1027   </refsect1>
1028
1029   <refsect1>
1030     <title>Special Slice Units</title>
1031
1032     <para>There are four <literal>.slice</literal> units which form the basis of the hierarchy for assignment of
1033     resources for services, users, and virtual machines or containers. See
1034     <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details about slice
1035     units.</para>
1036
1037     <variablelist>
1038       <varlistentry>
1039         <term><filename>-.slice</filename></term>
1040         <listitem>
1041           <para>The root slice is the root of the slice hierarchy. It usually does not contain units directly, but may
1042           be used to set defaults for the whole tree.</para>
1043         </listitem>
1044       </varlistentry>
1045
1046       <varlistentry>
1047         <term><filename>system.slice</filename></term>
1048         <listitem>
1049           <para>By default, all system services started by
1050           <command>systemd</command> are found in this slice.</para>
1051         </listitem>
1052       </varlistentry>
1053
1054       <varlistentry>
1055         <term><filename>user.slice</filename></term>
1056         <listitem>
1057           <para>By default, all user processes and services started on
1058           behalf of the user, including the per-user systemd instance
1059           are found in this slice.  This is pulled in by
1060           <filename>systemd-logind.service</filename></para>
1061         </listitem>
1062       </varlistentry>
1063
1064       <varlistentry>
1065         <term><filename>machine.slice</filename></term>
1066         <listitem>
1067           <para>By default, all virtual machines and containers
1068           registered with <command>systemd-machined</command> are
1069           found in this slice.  This is pulled in by
1070           <filename>systemd-machined.service</filename></para>
1071         </listitem>
1072       </varlistentry>
1073     </variablelist>
1074   </refsect1>
1075
1076   <refsect1>
1077       <title>See Also</title>
1078       <para>
1079         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1080         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1081         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1082         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1083         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1084         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1085         <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1086         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1087       </para>
1088   </refsect1>
1089
1090 </refentry>