man/systemd.special.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="systemd.special" xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>systemd.special</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>systemd.special</refentrytitle>
  15     <manvolnum>7</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>systemd.special</refname>
  20     <refpurpose>Special systemd units</refpurpose>
  21   </refnamediv>
  22
  23   <refsynopsisdiv><para>
  24     <!-- sort alphabetically, targets first --><filename>basic.target</filename>,
  25     <filename>bluetooth.target</filename>,
  26     <filename>cryptsetup-pre.target</filename>,
  27     <filename>cryptsetup.target</filename>,
  28     <filename>veritysetup-pre.target</filename>,
  29     <filename>veritysetup.target</filename>,
  30     <filename>ctrl-alt-del.target</filename>,
  31     <filename>blockdev@.target</filename>,
  32     <filename>boot-complete.target</filename>,
  33     <filename>default.target</filename>,
  34     <filename>emergency.target</filename>,
  35     <filename>exit.target</filename>,
  36     <filename>factory-reset.target</filename>,
  37     <filename>final.target</filename>,
  38     <filename>first-boot-complete.target</filename>,
  39     <filename>getty.target</filename>,
  40     <filename>getty-pre.target</filename>,
  41     <filename>graphical.target</filename>,
  42     <filename>halt.target</filename>,
  43     <filename>hibernate.target</filename>,
  44     <filename>hybrid-sleep.target</filename>,
  45     <filename>suspend-then-hibernate.target</filename>,
  46     <filename>initrd.target</filename>,
  47     <filename>initrd-fs.target</filename>,
  48     <filename>initrd-root-device.target</filename>,
  49     <filename>initrd-root-fs.target</filename>,
  50     <filename>initrd-usr-fs.target</filename>,
  51     <filename>integritysetup-pre.target</filename>,
  52     <filename>integritysetup.target</filename>,
  53     <filename>kbrequest.target</filename>,
  54     <filename>kexec.target</filename>,
  55     <filename>local-fs-pre.target</filename>,
  56     <filename>local-fs.target</filename>,
  57     <filename>machines.target</filename>
  58     <filename>multi-user.target</filename>,
  59     <filename>network-online.target</filename>,
  60     <filename>network-pre.target</filename>,
  61     <filename>network.target</filename>,
  62     <filename>nss-lookup.target</filename>,
  63     <filename>nss-user-lookup.target</filename>,
  64     <filename>paths.target</filename>,
  65     <filename>poweroff.target</filename>,
  66     <filename>printer.target</filename>,
  67     <filename>reboot.target</filename>,
  68     <filename>remote-cryptsetup.target</filename>,
  69     <filename>remote-veritysetup.target</filename>,
  70     <filename>remote-fs-pre.target</filename>,
  71     <filename>remote-fs.target</filename>,
  72     <filename>rescue.target</filename>,
  73     <filename>rpcbind.target</filename>,
  74     <filename>runlevel2.target</filename>,
  75     <filename>runlevel3.target</filename>,
  76     <filename>runlevel4.target</filename>,
  77     <filename>runlevel5.target</filename>,
  78     <filename>shutdown.target</filename>,
  79     <filename>sigpwr.target</filename>,
  80     <filename>sleep.target</filename>,
  81     <filename>slices.target</filename>,
  82     <filename>smartcard.target</filename>,
  83     <filename>sockets.target</filename>,
  84     <filename>soft-reboot.target</filename>,
  85     <filename>sound.target</filename>,
  86     <filename>suspend.target</filename>,
  87     <filename>swap.target</filename>,
  88     <filename>sysinit.target</filename>,
  89     <filename>system-update.target</filename>,
  90     <filename>system-update-pre.target</filename>,
  91     <filename>time-set.target</filename>,
  92     <filename>time-sync.target</filename>,
  93     <filename>timers.target</filename>,
  94     <filename>umount.target</filename>,
  95     <filename>usb-gadget.target</filename>,
  96     <!-- slices --><filename>-.slice</filename>,
  97     <filename>system.slice</filename>,
  98     <filename>user.slice</filename>,
  99     <filename>machine.slice</filename>,
 100     <!-- the rest --><filename>-.mount</filename>,
 101     <filename>dbus.service</filename>,
 102     <filename>dbus.socket</filename>,
 103     <filename>display-manager.service</filename>,
 104     <filename>init.scope</filename>,
 105     <filename>syslog.socket</filename>,
 106     <filename>system-update-cleanup.service</filename>
 107   </para></refsynopsisdiv>
 108
 109   <refsect1>
 110     <title>Description</title>
 111
 112     <para>A few units are treated specially by systemd. Many of them have
 113     special internal semantics and cannot be renamed, while others simply
 114     have a standard meaning and should be present on all systems.</para>
 115   </refsect1>
 116
 117   <refsect1>
 118     <title>Units managed by the system service manager</title>
 119
 120     <refsect2>
 121       <title>Special System Units</title>
 122
 123       <variablelist>
 124         <varlistentry>
 125           <term><filename>-.mount</filename></term>
 126           <listitem>
 127             <para>The root mount point, i.e. the mount unit for the <filename>/</filename>
 128             path. This unit is unconditionally active, during the entire time the system is up, as
 129             this mount point is where the basic userspace is running from.</para>
 130
 131           <xi:include href="version-info.xml" xpointer="v235"/>
 132           </listitem>
 133         </varlistentry>
 134
 135         <varlistentry>
 136           <term><filename>basic.target</filename></term>
 137           <listitem>
 138             <para>A special target unit covering basic boot-up.</para>
 139
 140             <para>systemd automatically adds dependency of the type
 141             <varname>After=</varname> for this target unit to all
 142             services (except for those with
 143             <varname>DefaultDependencies=no</varname>).</para>
 144
 145             <para>Usually, this should pull-in all local mount points plus
 146             <filename>/var/</filename>, <filename>/tmp/</filename> and
 147             <filename>/var/tmp/</filename>, swap devices, sockets, timers,
 148             path units and other basic initialization necessary for general
 149             purpose daemons. The mentioned mount points are special cased
 150             to allow them to be remote.
 151             </para>
 152
 153             <para>This target usually does not pull in any non-target units
 154             directly, but rather does so indirectly via other early boot targets.
 155             It is instead meant as a synchronization point for late boot
 156             services. Refer to
 157             <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 158             for details on the targets involved.
 159             </para>
 160           </listitem>
 161         </varlistentry>
 162         <varlistentry>
 163           <term><filename>boot-complete.target</filename></term>
 164           <listitem>
 165             <para>This target is intended as generic synchronization point for services that shall determine or act on
 166             whether the boot process completed successfully. Order units that are required to succeed for a boot process
 167             to be considered successful before this unit, and add a <varname>Requires=</varname> dependency from the
 168             target unit to them. Order units that shall only run when the boot process is considered successful after the
 169             target unit and pull in the target from it, also with <varname>Requires=</varname>. Note that by default this
 170             target unit is not part of the initial boot transaction, but is supposed to be pulled in only if required by
 171             units that want to run only on successful boots.</para>
 172
 173             <para>See
 174             <citerefentry><refentrytitle>systemd-boot-check-no-failures.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 175             for a service that implements a generic system health check and orders itself before
 176             <filename>boot-complete.target</filename>.</para>
 177
 178             <para>See
 179             <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 180             for a service that propagates boot success information to the boot loader, and orders itself after
 181             <filename>boot-complete.target</filename>.</para>
 182
 183             <xi:include href="version-info.xml" xpointer="v240"/>
 184           </listitem>
 185         </varlistentry>
 186         <varlistentry>
 187           <term><filename>ctrl-alt-del.target</filename></term>
 188           <listitem>
 189             <para>systemd starts this target whenever Control+Alt+Del is
 190             pressed on the console. Usually, this should be aliased
 191             (symlinked) to <filename>reboot.target</filename>.</para>
 192           </listitem>
 193         </varlistentry>
 194         <varlistentry>
 195           <term><filename>cryptsetup.target</filename></term>
 196           <listitem>
 197             <para>A target that pulls in setup services for all
 198             encrypted block devices.</para>
 199           </listitem>
 200         </varlistentry>
 201         <varlistentry>
 202           <term><filename>veritysetup.target</filename></term>
 203           <listitem>
 204             <para>A target that pulls in setup services for all
 205             verity integrity protected block devices.</para>
 206
 207             <xi:include href="version-info.xml" xpointer="v248"/>
 208           </listitem>
 209         </varlistentry>
 210         <varlistentry>
 211           <term><filename>dbus.service</filename></term>
 212           <listitem>
 213             <para>A special unit for the D-Bus bus daemon. As soon as
 214             this service is fully started up systemd will connect to it
 215             and register its service.</para>
 216           </listitem>
 217         </varlistentry>
 218         <varlistentry>
 219           <term><filename>dbus.socket</filename></term>
 220           <listitem>
 221             <para>A special unit for the D-Bus system bus socket. All
 222             units with <varname>Type=dbus</varname> automatically gain a
 223             dependency on this unit.</para>
 224           </listitem>
 225         </varlistentry>
 226         <varlistentry>
 227           <term><filename>default.target</filename></term>
 228           <listitem>
 229             <para>The default unit systemd starts at bootup. Usually, this should be aliased (symlinked) to
 230             <filename>multi-user.target</filename> or <filename>graphical.target</filename>. See
 231             <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
 232             more discussion.</para>
 233
 234             <para>The default unit systemd starts at bootup can be overridden with the
 235             <varname>systemd.unit=</varname> kernel command line option, or more conveniently, with the short
 236             names like <varname>single</varname>, <varname>rescue</varname>, <varname>1</varname>,
 237             <varname>3</varname>, <varname>5</varname>, …; see
 238             <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
 239           </listitem>
 240         </varlistentry>
 241         <varlistentry>
 242           <term><filename>display-manager.service</filename></term>
 243           <listitem>
 244             <para>The display manager service. Usually, this should be
 245             aliased (symlinked) to <filename>gdm.service</filename> or a
 246             similar display manager service.</para>
 247           </listitem>
 248         </varlistentry>
 249         <varlistentry>
 250           <term><filename>emergency.target</filename></term>
 251           <listitem>
 252             <para>A special target unit that starts an emergency shell on the main console. This
 253             target does not pull in other services or mounts. It is the most minimal version of
 254             starting the system in order to acquire an interactive shell; the only processes running
 255             are usually just the system manager (PID 1) and the shell process. This unit may be used
 256             by specifying <varname>emergency</varname> on the kernel command line; it is
 257             also used when a file system check on a required file system fails and boot-up cannot
 258             continue. Compare with <filename>rescue.target</filename>, which serves a similar
 259             purpose, but also starts the most basic services and mounts all file systems.</para>
 260
 261             <para>In many ways booting into <filename>emergency.target</filename> is similar to the
 262             effect of booting with <literal>init=/bin/sh</literal> on the kernel command line,
 263             except that emergency mode provides you with the full system and service manager, and
 264             allows starting individual units in order to continue the boot process in steps.</para>
 265
 266             <para>Note that depending on how <filename>emergency.target</filename> is reached, the root file
 267             system might be mounted read-only or read-write (no remounting is done specially for this
 268             target). For example, the system may boot with root mounted read-only when <varname>ro</varname>
 269             is used on the kernel command line and remain this way for <filename>emergency.target</filename>,
 270             or the system may transition to <filename>emergency.target</filename> after the system has been
 271             partially booted and disks have already been remounted read-write.</para>
 272           </listitem>
 273         </varlistentry>
 274         <varlistentry>
 275           <term><filename>exit.target</filename></term>
 276           <listitem>
 277             <para>A special service unit for shutting down the system or
 278             user service manager. It is equivalent to
 279             <filename>poweroff.target</filename> on non-container
 280             systems, and also works in containers.</para>
 281
 282             <para>systemd will start this unit when it receives the
 283             <constant>SIGTERM</constant> or <constant>SIGINT</constant>
 284             signal when running as user service daemon.</para>
 285
 286             <para>Normally, this (indirectly) pulls in
 287             <filename>shutdown.target</filename>, which in turn should be
 288             conflicted by all units that want to be scheduled for
 289             shutdown when the service manager starts to exit.</para>
 290
 291             <xi:include href="version-info.xml" xpointer="v186"/>
 292           </listitem>
 293         </varlistentry>
 294         <varlistentry>
 295           <term><filename>factory-reset.target</filename></term>
 296           <listitem>
 297             <para>A special target to trigger a factory reset.</para>
 298
 299           <xi:include href="version-info.xml" xpointer="v250"/>
 300           </listitem>
 301         </varlistentry>
 302         <varlistentry>
 303           <term><filename>final.target</filename></term>
 304           <listitem>
 305             <para>A special target unit that is used during the shutdown
 306             logic and may be used to pull in late services after all
 307             normal services are already terminated and all mounts
 308             unmounted.
 309             </para>
 310           </listitem>
 311         </varlistentry>
 312         <varlistentry>
 313           <term><filename>getty.target</filename></term>
 314           <listitem>
 315             <para>A special target unit that pulls in statically
 316             configured local TTY <filename>getty</filename> instances.
 317             </para>
 318           </listitem>
 319         </varlistentry>
 320         <varlistentry>
 321           <term><filename>graphical.target</filename></term>
 322           <listitem>
 323             <para>A special target unit for setting up a graphical login
 324             screen. This pulls in
 325             <filename>multi-user.target</filename>.</para>
 326
 327             <para>Units that are needed for graphical logins shall add
 328             <varname>Wants=</varname> dependencies for their unit to
 329             this unit (or <filename>multi-user.target</filename>) during
 330             installation. This is best configured via
 331             <varname>WantedBy=graphical.target</varname> in the unit's
 332             [Install] section.</para>
 333           </listitem>
 334         </varlistentry>
 335         <varlistentry>
 336           <term><filename>hibernate.target</filename></term>
 337           <listitem>
 338             <para>A special target unit for hibernating the system. This
 339             pulls in <filename>sleep.target</filename>.</para>
 340           </listitem>
 341         </varlistentry>
 342         <varlistentry>
 343           <term><filename>hybrid-sleep.target</filename></term>
 344           <listitem>
 345             <para>A special target unit for hibernating and suspending
 346             the system at the same time. This pulls in
 347             <filename>sleep.target</filename>.</para>
 348
 349             <xi:include href="version-info.xml" xpointer="v196"/>
 350           </listitem>
 351         </varlistentry>
 352         <varlistentry>
 353           <term><filename>suspend-then-hibernate.target</filename></term>
 354           <listitem>
 355             <para>A special target unit for suspending the system for a period
 356             of time, waking it and putting it into hibernate. This pulls in
 357             <filename>sleep.target</filename>.</para>
 358
 359             <xi:include href="version-info.xml" xpointer="v239"/>
 360           </listitem>
 361         </varlistentry>
 362
 363         <varlistentry>
 364           <term><filename>halt.target</filename></term>
 365           <listitem>
 366             <para>A special target unit for shutting down and halting
 367             the system. Note that this target is distinct from
 368             <filename>poweroff.target</filename> in that it generally
 369             really just halts the system rather than powering it
 370             down.</para>
 371
 372             <para>Applications wanting to halt the system should not start this unit
 373             directly, but should instead execute <command>systemctl halt</command>
 374             (possibly with the <option>--no-block</option> option) or call
 375             <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 376             <command>org.freedesktop.systemd1.Manager.Halt</command> D-Bus method
 377             directly.</para>
 378           </listitem>
 379         </varlistentry>
 380         <varlistentry>
 381           <term><filename>init.scope</filename></term>
 382           <listitem>
 383             <para>This scope unit is where the system and service manager (PID 1) itself resides. It
 384             is active as long as the system is running.</para>
 385
 386             <xi:include href="version-info.xml" xpointer="v235"/>
 387           </listitem>
 388         </varlistentry>
 389         <varlistentry>
 390           <term><filename>initrd.target</filename></term>
 391           <listitem>
 392             <para>This is the default target in the initrd, similar to <filename>default.target</filename> in
 393             the main system. It is used to mount the real root and transition to it. See
 394             <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
 395             more discussion.</para>
 396
 397           <xi:include href="version-info.xml" xpointer="v245"/>
 398           </listitem>
 399         </varlistentry>
 400         <varlistentry>
 401           <term><filename>initrd-fs.target</filename></term>
 402           <listitem>
 403             <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 404             automatically adds dependencies of type <varname>Before=</varname> to
 405             <filename>sysroot-usr.mount</filename> and all mount points found in
 406             <filename>/etc/fstab</filename> that have the <option>x-initrd.mount</option> mount option set
 407             and do not have the <option>noauto</option> mount option set. It is also indirectly ordered after
 408             <filename>sysroot.mount</filename>. Thus, once this target is reached the
 409             <filename>/sysroot/</filename> hierarchy is fully set up, in preparation for the transition to
 410             the host OS.</para>
 411
 412           <xi:include href="version-info.xml" xpointer="v199"/>
 413           </listitem>
 414         </varlistentry>
 415         <varlistentry>
 416           <term><filename>initrd-root-device.target</filename></term>
 417           <listitem>
 418             <para>A special initrd target unit that is reached when the root filesystem device is available, but before
 419             it has been mounted.
 420             <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 421             and
 422             <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 423             automatically setup the appropriate dependencies to make this happen.
 424             </para>
 425
 426             <xi:include href="version-info.xml" xpointer="v230"/>
 427           </listitem>
 428         </varlistentry>
 429         <varlistentry>
 430           <term><filename>initrd-root-fs.target</filename></term>
 431           <listitem>
 432             <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 433             automatically adds dependencies of type <varname>Before=</varname> to the
 434             <filename>sysroot.mount</filename> unit, which is generated from the kernel command line's
 435             <varname>root=</varname> setting (or equivalent).</para>
 436
 437           <xi:include href="version-info.xml" xpointer="v199"/>
 438           </listitem>
 439         </varlistentry>
 440         <varlistentry>
 441           <term><filename>initrd-usr-fs.target</filename></term>
 442           <listitem>
 443             <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 444             automatically adds dependencies of type <varname>Before=</varname> to the
 445             <filename>sysusr-usr.mount</filename> unit, which is generated from the kernel command line's
 446             <varname>usr=</varname> switch. Services may order themselves after this target unit in order to
 447             run once the <filename>/sysusr/</filename> hierarchy becomes available, on systems that come up
 448             initially without a root file system, but with an initialized <filename>/usr/</filename> and need
 449             to access that before setting up the root file system to ultimately switch to. On systems where
 450             <varname>usr=</varname> is not used this target is ordered after
 451             <filename>sysroot.mount</filename> and thus mostly equivalent to
 452             <filename>initrd-root-fs.target</filename>. In effect on any system once this target is reached
 453             the file system backing <filename>/usr/</filename> is mounted, though possibly at two different
 454             locations, either below the <filename>/sysusr/</filename> or the <filename>/sysroot/</filename>
 455             hierarchies.</para>
 456
 457           <xi:include href="version-info.xml" xpointer="v249"/>
 458           </listitem>
 459         </varlistentry>
 460         <varlistentry>
 461           <term><filename>kbrequest.target</filename></term>
 462           <listitem>
 463             <para>systemd starts this target whenever Alt+ArrowUp is
 464             pressed on the console. Note that any user with physical access
 465             to the machine will be able to do this, without authentication,
 466             so this should be used carefully.</para>
 467           </listitem>
 468         </varlistentry>
 469         <varlistentry>
 470           <term><filename>kexec.target</filename></term>
 471           <listitem>
 472             <para>A special target unit for shutting down and rebooting the system via kexec.</para>
 473
 474             <para>Applications wanting to reboot the system should not start this unit directly, but should
 475             instead execute <command>systemctl kexec</command> (possibly with the
 476             <option>--no-block</option> option) or call
 477             <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
 478             <function>org.freedesktop.login1.Manager.RebootWithFlags()</function> D-Bus method
 479             directly.</para>
 480
 481             <para>See
 482             <citerefentry><refentrytitle>systemd-kexec.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 483             for further details of the operation this target pulls in.</para>
 484           </listitem>
 485         </varlistentry>
 486         <varlistentry>
 487           <term><filename>local-fs.target</filename></term>
 488           <listitem>
 489             <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 490             automatically adds dependencies of type
 491             <varname>Before=</varname> to all mount units that refer to
 492             local mount points for this target unit. In addition, it
 493             adds dependencies of type <varname>Wants=</varname> to this
 494             target unit for those mounts listed in
 495             <filename>/etc/fstab</filename> that have the
 496             <option>auto</option> mount option set.</para>
 497           </listitem>
 498         </varlistentry>
 499         <varlistentry>
 500           <term><filename>machines.target</filename></term>
 501           <listitem>
 502             <para>A standard target unit for starting all the containers
 503             and other virtual machines. See <filename>systemd-nspawn@.service</filename>
 504             for an example.</para>
 505
 506             <xi:include href="version-info.xml" xpointer="v233"/>
 507           </listitem>
 508         </varlistentry>
 509         <varlistentry>
 510           <term><filename>multi-user.target</filename></term>
 511           <listitem>
 512             <para>A special target unit for setting up a multi-user
 513             system (non-graphical). This is pulled in by
 514             <filename>graphical.target</filename>.</para>
 515
 516             <para>Units that are needed for a multi-user system shall
 517             add <varname>Wants=</varname> dependencies for their unit to
 518             this unit during installation. This is best configured via
 519             <varname>WantedBy=multi-user.target</varname> in the unit's
 520             [Install] section.</para>
 521           </listitem>
 522         </varlistentry>
 523         <varlistentry>
 524           <term><filename>network-online.target</filename></term>
 525           <listitem>
 526             <para>Units that strictly require a configured network
 527             connection should pull in
 528             <filename>network-online.target</filename> (via a
 529             <varname>Wants=</varname> type dependency) and order
 530             themselves after it. This target unit is intended to pull in
 531             a service that delays further execution until the network is
 532             sufficiently set up. What precisely this requires is left to
 533             the implementation of the network managing service.</para>
 534
 535             <para>Note the distinction between this unit and <filename>network.target</filename>. This unit
 536             is an active unit (i.e. pulled in by the consumer rather than the provider of this functionality)
 537             and pulls in a service which possibly adds substantial delays to further execution. In contrast,
 538             <filename>network.target</filename> is a passive unit (i.e. pulled in by the provider of the
 539             functionality, rather than the consumer) that usually does not delay execution much. Usually,
 540             <filename>network.target</filename> is part of the boot of most systems, while
 541             <filename>network-online.target</filename> is not, except when at least one unit requires
 542             it. Also see <ulink url="https://systemd.io/NETWORK_ONLINE">Running Services After the Network Is
 543             Up</ulink> for more information.</para>
 544
 545             <para>All mount units for remote network file systems automatically pull in this unit, and order
 546             themselves after it. Note that networking daemons that simply <emphasis>provide</emphasis>
 547             functionality to other hosts (as opposed to <emphasis>consume</emphasis> functionality of other
 548             hosts) generally do not need to pull this in.</para>
 549
 550             <para>systemd automatically adds dependencies of type <varname>Wants=</varname> and
 551             <varname>After=</varname> for this target unit to all SysV init script service units
 552             with an LSB header referring to the <literal>$network</literal> facility.</para>
 553
 554             <para>Note that this unit is only useful during the original system start-up
 555             logic. After the system has completed booting up, it will not track the online state of
 556             the system anymore. Due to this it cannot be used as a network connection monitor
 557             concept, it is purely a one-time system start-up concept.</para>
 558
 559             <xi:include href="version-info.xml" xpointer="v200"/>
 560             </listitem>
 561         </varlistentry>
 562         <varlistentry>
 563           <term><filename>paths.target</filename></term>
 564           <listitem>
 565             <para>A special target unit that sets up all path units (see
 566             <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 567             for details) that shall be active after boot.</para>
 568
 569             <para>It is recommended that path units installed by
 570             applications get pulled in via <varname>Wants=</varname>
 571             dependencies from this unit. This is best configured via a
 572             <varname>WantedBy=paths.target</varname> in the path unit's
 573             [Install] section.</para>
 574
 575             <xi:include href="version-info.xml" xpointer="v199"/>
 576           </listitem>
 577         </varlistentry>
 578         <varlistentry>
 579           <term><filename>poweroff.target</filename></term>
 580           <listitem>
 581             <para>A special target unit for shutting down and powering
 582             off the system.</para>
 583
 584             <para>Applications wanting to power off the system should not start this unit
 585             directly, but should instead execute <command>systemctl poweroff</command>
 586             (possibly with the <option>--no-block</option> option) or call
 587             <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
 588             <command>org.freedesktop.login1.Manager.PowerOff</command> D-Bus method
 589             directly.</para>
 590
 591             <para><filename>runlevel0.target</filename> is an alias for
 592             this target unit, for compatibility with SysV.</para>
 593           </listitem>
 594         </varlistentry>
 595         <varlistentry>
 596           <term><filename>reboot.target</filename></term>
 597           <listitem>
 598             <para>A special target unit for shutting down and rebooting the system.</para>
 599
 600             <para>Applications wanting to reboot the system should not start this unit directly, but should
 601             instead execute <command>systemctl reboot</command> (possibly with the
 602             <option>--no-block</option> option) or call
 603             <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
 604             <function>org.freedesktop.login1.Manager.Reboot()</function> D-Bus method directly.</para>
 605
 606             <para>See
 607             <citerefentry><refentrytitle>systemd-reboot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 608             for further details of the operation this target pulls in.</para>
 609
 610             <para><filename>runlevel6.target</filename> is an alias for this target unit, for compatibility
 611             with SysV.</para>
 612           </listitem>
 613         </varlistentry>
 614         <varlistentry>
 615           <term><filename>remote-cryptsetup.target</filename></term>
 616           <listitem>
 617             <para>Similar to <filename>cryptsetup.target</filename>, but for encrypted
 618             devices which are accessed over the network. It is used for
 619             <citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 620             entries marked with <option>_netdev</option>.</para>
 621
 622           <xi:include href="version-info.xml" xpointer="v235"/>
 623           </listitem>
 624         </varlistentry>
 625         <varlistentry>
 626           <term><filename>remote-veritysetup.target</filename></term>
 627           <listitem>
 628             <para>Similar to <filename>veritysetup.target</filename>, but for verity
 629             integrity protected devices which are accessed over the network. It is used for
 630             <citerefentry><refentrytitle>veritytab</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 631             entries marked with <option>_netdev</option>.</para>
 632
 633           <xi:include href="version-info.xml" xpointer="v248"/>
 634           </listitem>
 635         </varlistentry>
 636         <varlistentry>
 637           <term><filename>remote-fs.target</filename></term>
 638           <listitem>
 639             <para>Similar to <filename>local-fs.target</filename>, but
 640             for remote mount points.</para>
 641
 642             <para>systemd automatically adds dependencies of type
 643             <varname>After=</varname> for this target unit to all SysV
 644             init script service units with an LSB header referring to
 645             the <literal>$remote_fs</literal> facility.</para>
 646           </listitem>
 647         </varlistentry>
 648         <varlistentry>
 649           <term><filename>rescue.target</filename></term>
 650           <listitem>
 651             <para>A special target unit that pulls in the base system (including system mounts) and
 652             spawns a rescue shell. Isolate to this target in order to administer the system in
 653             single-user mode with all file systems mounted but with no services running, except for
 654             the most basic. Compare with <filename>emergency.target</filename>, which is much more
 655             reduced and does not provide the file systems or most basic services. Compare with
 656             <filename>multi-user.target</filename>, this target could be seen as
 657             <filename>single-user.target</filename>.</para>
 658
 659             <para><filename>runlevel1.target</filename> is an alias for this target unit, for
 660             compatibility with SysV.</para>
 661
 662             <para>Use the <literal>systemd.unit=rescue.target</literal> kernel command line option
 663             to boot into this mode. A short alias for this kernel command line option is
 664             <literal>1</literal>, for compatibility with SysV.</para>
 665           </listitem>
 666         </varlistentry>
 667         <varlistentry>
 668           <term><filename>runlevel2.target</filename></term>
 669           <term><filename>runlevel3.target</filename></term>
 670           <term><filename>runlevel4.target</filename></term>
 671           <term><filename>runlevel5.target</filename></term>
 672           <listitem>
 673             <para>These are targets that are called whenever the SysV
 674             compatibility code asks for runlevel 2, 3, 4, 5,
 675             respectively. It is a good idea to make this an alias for
 676             (i.e. symlink to) <filename>graphical.target</filename>
 677             (for runlevel 5) or <filename>multi-user.target</filename>
 678             (the others).</para>
 679           </listitem>
 680         </varlistentry>
 681         <varlistentry>
 682           <term><filename>shutdown.target</filename></term>
 683           <listitem>
 684             <para>A special target unit that terminates the services on
 685             system shutdown.</para>
 686
 687             <para>Services that shall be terminated on system shutdown
 688             shall add <varname>Conflicts=</varname> and
 689             <varname>Before=</varname> dependencies to this unit for
 690             their service unit, which is implicitly done when
 691             <varname>DefaultDependencies=yes</varname> is set (the
 692             default).</para>
 693           </listitem>
 694         </varlistentry>
 695         <varlistentry>
 696           <term><filename>sigpwr.target</filename></term>
 697           <listitem>
 698             <para>A special target that is started when systemd receives
 699             the SIGPWR process signal, which is normally sent by the
 700             kernel or UPS daemons when power fails.</para>
 701           </listitem>
 702         </varlistentry>
 703         <varlistentry>
 704           <term><filename>sleep.target</filename></term>
 705           <listitem>
 706             <para>A special target unit that is pulled in by
 707             <filename>suspend.target</filename>,
 708             <filename>hibernate.target</filename> and
 709             <filename>hybrid-sleep.target</filename> and may be used to
 710             hook units into the sleep state logic.</para>
 711           </listitem>
 712         </varlistentry>
 713         <varlistentry>
 714           <term><filename>slices.target</filename></term>
 715           <listitem>
 716             <para>A special target unit that sets up all slice units (see
 717             <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 718             for details) that shall always be active after boot. By default the generic
 719             <filename>system.slice</filename> slice unit as well as the root slice unit
 720             <filename>-.slice</filename> are pulled in and ordered before this unit (see
 721             below).</para>
 722
 723             <para>Adding slice units to <filename>slices.target</filename> is generally not
 724             necessary. Instead, when some unit that uses <varname>Slice=</varname> is started, the
 725             specified slice will be started automatically. Adding
 726             <varname>WantedBy=slices.target</varname> lines to the [Install]
 727             section should only be done for units that need to be always active. In that case care
 728             needs to be taken to avoid creating a loop through the automatic dependencies on
 729             "parent" slices.</para>
 730
 731             <xi:include href="version-info.xml" xpointer="v229"/>
 732           </listitem>
 733         </varlistentry>
 734         <varlistentry>
 735           <term><filename>sockets.target</filename></term>
 736           <listitem>
 737             <para>A special target unit that sets up all socket
 738             units (see
 739             <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 740             for details) that shall be active after boot.</para>
 741
 742             <para>Services that can be socket-activated shall add
 743             <varname>Wants=</varname> dependencies to this unit for
 744             their socket unit during installation. This is best
 745             configured via a <varname>WantedBy=sockets.target</varname>
 746             in the socket unit's [Install]
 747             section.</para>
 748           </listitem>
 749         </varlistentry>
 750         <varlistentry>
 751           <term><filename>soft-reboot.target</filename></term>
 752           <listitem>
 753             <para>A special target unit for shutting down and rebooting the userspace of the system (leaving
 754             the kernel running).</para>
 755
 756             <para>Applications wanting to reboot the system should not start this unit directly, but should
 757             instead execute <command>systemctl soft-reboot</command> (possibly with the
 758             <option>--no-block</option> option) or call
 759             <citerefentry><refentrytitle>systemd-logind</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
 760             <function>org.freedesktop.login1.Manager.RebootWithFlags()</function> D-Bus method
 761             directly.</para>
 762
 763             <para>See
 764             <citerefentry><refentrytitle>systemd-soft-reboot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 765             for further details of the operation this target pulls in.</para>
 766
 767             <xi:include href="version-info.xml" xpointer="v254"/>
 768           </listitem>
 769         </varlistentry>
 770         <varlistentry>
 771           <term><filename>suspend.target</filename></term>
 772           <listitem>
 773             <para>A special target unit for suspending the system. This
 774             pulls in <filename>sleep.target</filename>.</para>
 775           </listitem>
 776         </varlistentry>
 777         <varlistentry>
 778           <term><filename>swap.target</filename></term>
 779           <listitem>
 780             <para>Similar to <filename>local-fs.target</filename>, but
 781             for swap partitions and swap files.</para>
 782           </listitem>
 783         </varlistentry>
 784         <varlistentry>
 785           <term><filename>sysinit.target</filename></term>
 786           <listitem>
 787             <para>systemd automatically adds dependencies of the types
 788             <varname>Requires=</varname> and <varname>After=</varname>
 789             for this target unit to all services (except for those with
 790             <varname>DefaultDependencies=no</varname>).</para>
 791
 792             <para>This target pulls in the services required for system
 793             initialization. System services pulled in by this target should
 794             declare <varname>DefaultDependencies=no</varname> and specify
 795             all their dependencies manually, including access to anything
 796             more than a read only root filesystem. For details on the
 797             dependencies of this target, refer to
 798             <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 799             </para>
 800           </listitem>
 801         </varlistentry>
 802         <varlistentry>
 803           <term><filename>syslog.socket</filename></term>
 804           <listitem>
 805             <para>The socket unit syslog implementations should listen
 806             on. All userspace log messages will be made available on
 807             this socket. For more information about syslog integration,
 808             please consult the <ulink
 809             url="https://www.freedesktop.org/wiki/Software/systemd/syslog">Syslog
 810             Interface</ulink> document.</para>
 811           </listitem>
 812         </varlistentry>
 813         <varlistentry>
 814           <term><filename>system-update.target</filename></term>
 815           <term><filename>system-update-pre.target</filename></term>
 816           <term><filename>system-update-cleanup.service</filename></term>
 817           <listitem>
 818             <para>A special target unit that is used for offline system updates.
 819             <citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 820             will redirect the boot process to this target if <filename>/system-update</filename> or
 821             <filename>/etc/system-update</filename> exists. For more information see
 822             <citerefentry><refentrytitle>systemd.offline-updates</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 823             </para>
 824
 825             <para>Updates should happen before the <filename>system-update.target</filename> is
 826             reached, and the services which implement them should cause the machine to reboot. The
 827             main units executing the update should order themselves after
 828             <filename>system-update-pre.target</filename> but not pull it in. Services which want to
 829             run during system updates only, but before the actual system update is executed should
 830             order themselves before this unit and pull it in. As a safety measure, if this does not
 831             happen, and <filename>/system-update</filename> or
 832             <filename>/etc/system-update</filename> still exists after
 833             <filename>system-update.target</filename> is reached,
 834             <filename>system-update-cleanup.service</filename> will remove the symlinks and reboot
 835             the machine.</para>
 836
 837             <xi:include href="version-info.xml" xpointer="v186"/>
 838           </listitem>
 839         </varlistentry>
 840         <varlistentry>
 841           <term><filename>timers.target</filename></term>
 842           <listitem>
 843             <para>A special target unit that sets up all timer units
 844             (see
 845             <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 846             for details) that shall be active after boot.</para>
 847
 848             <para>It is recommended that timer units installed by
 849             applications get pulled in via <varname>Wants=</varname>
 850             dependencies from this unit. This is best configured via
 851             <varname>WantedBy=timers.target</varname> in the timer
 852             unit's [Install] section.</para>
 853
 854             <xi:include href="version-info.xml" xpointer="v199"/>
 855           </listitem>
 856         </varlistentry>
 857         <varlistentry>
 858           <term><filename>umount.target</filename></term>
 859           <listitem>
 860             <para>A special target unit that unmounts all mount and
 861             automount points on system shutdown.</para>
 862
 863             <para>Mounts that shall be unmounted on system shutdown
 864             shall add Conflicts dependencies to this unit for their
 865             mount unit, which is implicitly done when
 866             <varname>DefaultDependencies=yes</varname> is set (the
 867             default).</para>
 868           </listitem>
 869         </varlistentry>
 870
 871       </variablelist>
 872     </refsect2>
 873
 874     <refsect2>
 875       <title>Special System Units for Devices</title>
 876
 877       <para>Some target units are automatically pulled in as devices of
 878       certain kinds show up in the system. These may be used to
 879       automatically activate various services based on the specific type
 880       of the available hardware.</para>
 881
 882       <variablelist>
 883         <varlistentry>
 884           <term><filename>bluetooth.target</filename></term>
 885           <listitem>
 886             <para>This target is started automatically as soon as a
 887             Bluetooth controller is plugged in or becomes available at
 888             boot.</para>
 889
 890             <para>This may be used to pull in Bluetooth management
 891             daemons dynamically when Bluetooth hardware is found.</para>
 892           </listitem>
 893         </varlistentry>
 894         <varlistentry>
 895           <term><filename>printer.target</filename></term>
 896           <listitem>
 897             <para>This target is started automatically as soon as a
 898             printer is plugged in or becomes available at boot.</para>
 899
 900             <para>This may be used to pull in printer management daemons
 901             dynamically when printer hardware is found.</para>
 902           </listitem>
 903         </varlistentry>
 904         <varlistentry>
 905           <term><filename>smartcard.target</filename></term>
 906           <listitem>
 907             <para>This target is started automatically as soon as a
 908             smartcard controller is plugged in or becomes available at
 909             boot.</para>
 910
 911             <para>This may be used to pull in smartcard management
 912             daemons dynamically when smartcard hardware is found.</para>
 913           </listitem>
 914         </varlistentry>
 915         <varlistentry>
 916           <term><filename>sound.target</filename></term>
 917           <listitem>
 918             <para>This target is started automatically as soon as a
 919             sound card is plugged in or becomes available at
 920             boot.</para>
 921
 922             <para>This may be used to pull in audio management daemons
 923             dynamically when audio hardware is found.</para>
 924           </listitem>
 925         </varlistentry>
 926         <varlistentry>
 927           <term><filename>usb-gadget.target</filename></term>
 928           <listitem>
 929             <para>This target is started automatically as soon as a
 930             USB Device Controller becomes available at boot.</para>
 931
 932             <para>This may be used to pull in usb gadget
 933             dynamically when UDC hardware is found.</para>
 934
 935             <xi:include href="version-info.xml" xpointer="v242"/>
 936           </listitem>
 937         </varlistentry>
 938       </variablelist>
 939     </refsect2>
 940
 941     <refsect2>
 942       <title>Special Passive System Units </title>
 943
 944       <para>A number of special system targets are defined that can be
 945       used to properly order boot-up of optional services. These targets
 946       are generally not part of the initial boot transaction, unless
 947       they are explicitly pulled in by one of the implementing services.
 948       Note specifically that these <emphasis>passive</emphasis> target
 949       units are generally not pulled in by the consumer of a service,
 950       but by the provider of the service. This means: a consuming
 951       service should order itself after these targets (as appropriate),
 952       but not pull it in. A providing service should order itself before
 953       these targets (as appropriate) and pull it in (via a
 954       <varname>Wants=</varname> type dependency).</para>
 955
 956       <para>Note that these passive units cannot be started manually,
 957       i.e. <literal>systemctl start time-sync.target</literal> will fail
 958       with an error. They can only be pulled in by dependency. This is
 959       enforced since they exist for ordering purposes only and thus are
 960       not useful as only unit within a transaction.</para>
 961
 962       <variablelist>
 963         <varlistentry>
 964           <term><filename>blockdev@.target</filename></term>
 965           <listitem><para>This template unit is used to order mount units and other consumers of block
 966           devices after services that synthesize these block devices. In particular, this is intended to be
 967           used with storage services (such as
 968           <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>/
 969           <citerefentry><refentrytitle>systemd-veritysetup@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>)
 970           that allocate and manage a virtual block device. Storage services are ordered before an instance of
 971           <filename>blockdev@.target</filename>, and the consumer units after it. The ordering is
 972           particularly relevant during shutdown, as it ensures that the mount is deactivated first and the
 973           service backing the mount later. The <filename>blockdev@.target</filename> instance should be
 974           pulled in via a <option>Wants=</option> dependency of the storage daemon and thus generally not be
 975           part of any transaction unless a storage daemon is used. The instance name for instances of this
 976           template unit must be a properly escaped block device node path, e.g.
 977           <filename index="false">blockdev@dev-mapper-foobar.target</filename> for the storage device
 978           <filename index="false">/dev/mapper/foobar</filename>.</para>
 979
 980           <xi:include href="version-info.xml" xpointer="v245"/></listitem>
 981         </varlistentry>
 982         <varlistentry>
 983           <term><filename>cryptsetup-pre.target</filename></term>
 984           <listitem>
 985             <para>This passive target unit may be pulled in by services
 986             that want to run before any encrypted block device is set
 987             up. All encrypted block devices are set up after this target
 988             has been reached. Since the shutdown order is implicitly the
 989             reverse start-up order between units, this target is
 990             particularly useful to ensure that a service is shut down
 991             only after all encrypted block devices are fully
 992             stopped.</para>
 993
 994             <xi:include href="version-info.xml" xpointer="v215"/>
 995           </listitem>
 996         </varlistentry>
 997         <varlistentry>
 998           <term><filename>veritysetup-pre.target</filename></term>
 999           <listitem>
1000             <para>This passive target unit may be pulled in by services
1001             that want to run before any verity integrity protected block
1002             device is set up. All verity integrity protected block
1003             devices are set up after this target has been reached. Since
1004             the shutdown order is implicitly the reverse start-up order
1005             between units, this target is particularly useful to ensure
1006             that a service is shut down only after all verity integrity
1007             protected block devices are fully stopped.</para>
1008
1009             <xi:include href="version-info.xml" xpointer="v248"/>
1010           </listitem>
1011         </varlistentry>
1012         <varlistentry>
1013           <term><filename>first-boot-complete.target</filename></term>
1014           <listitem>
1015             <para>This passive target is intended as a synchronization point for units that need to run once
1016             during the first boot.  Only after all units ordered before this target have finished, will the
1017             <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1018             be committed to disk, marking the first boot as completed.  If the boot is aborted at any time
1019             before that, the next boot will re-run any units with <varname>ConditionFirstBoot=yes</varname>.
1020             </para>
1021
1022             <xi:include href="version-info.xml" xpointer="v247"/>
1023           </listitem>
1024         </varlistentry>
1025         <varlistentry>
1026           <term><filename>getty-pre.target</filename></term>
1027           <listitem>
1028             <para>A special passive target unit. Users of this target
1029             are expected to pull it in the boot transaction via
1030             a dependency (e.g. <varname>Wants=</varname>). Order your
1031             unit before this unit if you want to make use of the console
1032             just before <filename>getty</filename> is started.
1033             </para>
1034
1035             <xi:include href="version-info.xml" xpointer="v235"/>
1036           </listitem>
1037         </varlistentry>
1038         <varlistentry>
1039           <term><filename>local-fs-pre.target</filename></term>
1040           <listitem>
1041             <para>This target unit is
1042             automatically ordered before
1043             all local mount points marked
1044             with <option>auto</option>
1045             (see above). It can be used to
1046             execute certain units before
1047             all local mounts.</para>
1048           </listitem>
1049         </varlistentry>
1050         <varlistentry>
1051           <term><filename>network.target</filename></term>
1052           <listitem>
1053             <para>This unit is supposed to indicate when network functionality is available, but it is only
1054             very weakly defined what that is supposed to mean. However, the following should apply at
1055             minimum:</para>
1056
1057             <itemizedlist>
1058               <listitem><para>At start-up, any configured synthetic network devices (i.e. not physical ones
1059               that require hardware to show up and be probed, but virtual ones like bridge devices and
1060               similar which are created programmatically) that do not depend on any underlying hardware
1061               should be allocated by the time this target is reached. It is not necessary for these
1062               interfaces to also have completed IP level configuration by the time
1063               <filename>network.target</filename> is reached.</para></listitem>
1064
1065               <listitem><para>At shutdown, a unit that is ordered after <filename>network.target</filename>
1066               will be stopped before the network — to whatever level it might be set up by then — is shut
1067               down. It is hence useful when writing service files that require network access on shutdown,
1068               which should order themselves after this target, but not pull it in. Also see <ulink
1069               url="https://systemd.io/NETWORK_ONLINE">Running Services After the Network Is Up</ulink> for
1070               more information.</para></listitem>
1071             </itemizedlist>
1072
1073             <para>It must emphasized that at start-up there's no guarantee that hardware-based devices have
1074             shown up by the time this target is reached, or even acquired complete IP configuration. For that
1075             purpose use <filename>network-online.target</filename> as described above.</para>
1076           </listitem>
1077         </varlistentry>
1078         <varlistentry>
1079           <term><filename>network-pre.target</filename></term>
1080           <listitem>
1081             <para>This passive target unit may be pulled in by services that want to run before any network
1082             is set up, for example for the purpose of setting up a firewall. All network management software
1083             orders itself after this target, but does not pull it in. Also see <ulink
1084             url="https://systemd.io/NETWORK_ONLINE">Running Services After the Network Is Up</ulink> for more
1085             information.</para>
1086
1087             <xi:include href="version-info.xml" xpointer="v214"/>
1088           </listitem>
1089         </varlistentry>
1090         <varlistentry>
1091           <term><filename>nss-lookup.target</filename></term>
1092           <listitem>
1093             <para>A target that should be used as synchronization point for all host/network name
1094             service lookups. Note that this is independent of UNIX user/group name lookups for which
1095             <filename>nss-user-lookup.target</filename> should be used.  All services for which the
1096             availability of full host/network name resolution is essential should be ordered after
1097             this target, but not pull it in. systemd automatically adds dependencies of type
1098             <varname>After=</varname> for this target unit to all SysV init script service units
1099             with an LSB header referring to the <literal>$named</literal> facility.</para>
1100           </listitem>
1101         </varlistentry>
1102         <varlistentry>
1103           <term><filename>nss-user-lookup.target</filename></term>
1104           <listitem>
1105             <para>A target that should be used as synchronization point for all regular UNIX
1106             user/group name service lookups. Note that this is independent of host/network name
1107             lookups for which <filename>nss-lookup.target</filename> should be used. All services
1108             for which the availability of the full user/group database is essential should be
1109             ordered after this target, but not pull it in. All services which provide parts of the
1110             user/group database should be ordered before this target, and pull it in. Note that this
1111             unit is only relevant for regular users and groups — system users and groups are
1112             required to be resolvable during earliest boot already, and hence do not need any
1113             special ordering against this target.</para>
1114           </listitem>
1115         </varlistentry>
1116         <varlistentry>
1117           <term><filename>remote-fs-pre.target</filename></term>
1118           <listitem>
1119             <para>This target unit is automatically ordered before all
1120             mount point units (see above) and cryptsetup/veritysetup devices
1121             marked with the <option>_netdev</option>. It can be used to run
1122             certain units before remote encrypted devices and mounts are established.
1123             Note that this unit is generally not part of the initial
1124             transaction, unless the unit that wants to be ordered before
1125             all remote mounts pulls it in via a
1126             <varname>Wants=</varname> type dependency. If the unit wants
1127             to be pulled in by the first remote mount showing up, it
1128             should use <filename>network-online.target</filename> (see
1129             above).</para>
1130           </listitem>
1131         </varlistentry>
1132         <varlistentry>
1133           <term><filename>rpcbind.target</filename></term>
1134           <listitem>
1135             <para>The portmapper/rpcbind pulls in this target and orders
1136             itself before it, to indicate its availability. systemd
1137             automatically adds dependencies of type
1138             <varname>After=</varname> for this target unit to all SysV
1139             init script service units with an LSB header referring to
1140             the <literal>$portmap</literal> facility.</para>
1141           </listitem>
1142         </varlistentry>
1143         <varlistentry>
1144           <term><filename>time-set.target</filename></term>
1145           <listitem>
1146             <para>Services responsible for setting the system clock (<constant>CLOCK_REALTIME</constant>)
1147             from a local source (such as a maintained timestamp file or imprecise real-time clock) should
1148             pull in this target and order themselves before it. Services where approximate, roughly monotonic
1149             time is desired should be ordered after this unit, but not pull it in.</para>
1150
1151             <para>This target does not provide the accuracy guarantees of
1152             <filename>time-sync.target</filename> (see below), however does not depend on remote clock
1153             sources to be reachable, i.e. the target is typically not delayed by network problems and
1154             similar. Use of this target is recommended for services where approximate clock accuracy and
1155             rough monotonicity is desired but activation shall not be delayed for possibly unreliable network
1156             communication.</para>
1157
1158             <para>The service manager automatically adds dependencies of type <varname>After=</varname> for
1159             this target unit to all timer units with at least one <varname>OnCalendar=</varname>
1160             directive.</para>
1161
1162             <para>The
1163             <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1164             service is a simple daemon that pulls in this target and orders itself before it. Besides
1165             implementing the SNTP network protocol it maintains a timestamp file on disk whose modification
1166             time is regularly updated. At service start-up the local system clock is set from that modification time,
1167             ensuring it increases roughly monotonically.</para>
1168
1169             <para>Note that ordering a unit after <filename>time-set.target</filename> only has effect if
1170             there's actually a service ordered before it that delays it until the clock is adjusted for rough
1171             monotonicity. Otherwise, this target might get reached before the clock is adjusted to be roughly
1172             monotonic. Enable
1173             <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1174             or an alternative NTP implementation to delay the target.</para>
1175
1176             <xi:include href="version-info.xml" xpointer="v242"/>
1177           </listitem>
1178         </varlistentry>
1179         <varlistentry>
1180           <term><filename>time-sync.target</filename></term>
1181           <listitem>
1182             <para>Services indicating completed synchronization of the system clock
1183             (<constant>CLOCK_REALTIME</constant>) to a remote source should pull in this target and order
1184             themselves before it. Services where accurate time is essential should be ordered after this
1185             unit, but not pull it in.</para>
1186
1187             <para>The service manager automatically adds dependencies of type <varname>After=</varname> for
1188             this target unit to all SysV init script service units with an LSB header referring to the
1189             <literal>$time</literal> facility, as well to all timer units with at least one
1190             <varname>OnCalendar=</varname> directive.</para>
1191
1192             <para>This target provides stricter clock accuracy guarantees than
1193             <filename>time-set.target</filename> (see above), but likely requires
1194             network communication and thus introduces unpredictable delays.
1195             Services that require clock accuracy and where network
1196             communication delays are acceptable should use this target. Services that require a less accurate
1197             clock, and only approximate and roughly monotonic clock behaviour should use
1198             <filename>time-set.target</filename> instead.</para>
1199
1200             <para>Note that ordering a unit after <filename>time-sync.target</filename> only has effect if
1201             there's actually a service ordered before it that delays it until clock synchronization is
1202             reached. Otherwise, this target might get reached before the clock is synchronized to any remote
1203             accurate reference clock. When using
1204             <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1205             enable
1206             <citerefentry><refentrytitle>systemd-time-wait-sync.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1207             to delay the target; or use an equivalent service for other NTP implementations.</para>
1208
1209             <table>
1210               <title>Comparison</title>
1211               <tgroup cols='2' align='left' colsep='1' rowsep='1'>
1212                 <colspec colname="time-set" />
1213                 <colspec colname="time-sync" />
1214                 <thead>
1215                   <row>
1216                     <entry><filename>time-set.target</filename></entry>
1217                     <entry><filename>time-sync.target</filename></entry>
1218                   </row>
1219                 </thead>
1220                 <tbody>
1221                   <row>
1222                     <entry>"quick" to reach</entry>
1223                     <entry>"slow" to reach</entry>
1224                   </row>
1225                   <row>
1226                     <entry>typically uses local clock sources, boot process not affected by availability of external resources</entry>
1227                     <entry>typically uses remote clock sources, inserts dependencies on remote resources into boot process</entry>
1228                   </row>
1229                   <row>
1230                     <entry>reliable, because local</entry>
1231                     <entry>unreliable, because typically network involved</entry>
1232                   </row>
1233                   <row>
1234                     <entry>typically guarantees an approximate and roughly monotonic clock only</entry>
1235                     <entry>typically guarantees an accurate clock</entry>
1236                   </row>
1237                   <row>
1238                     <entry>implemented by <filename>systemd-timesyncd.service</filename></entry>
1239                     <entry>implemented by <filename>systemd-time-wait-sync.service</filename></entry>
1240                   </row>
1241                 </tbody>
1242               </tgroup>
1243             </table>
1244
1245           </listitem>
1246         </varlistentry>
1247       </variablelist>
1248     </refsect2>
1249
1250     <refsect2>
1251       <title>Special Slice Units</title>
1252
1253       <para>There are four <literal>.slice</literal> units which form the basis of the hierarchy for
1254       assignment of resources for services, users, and virtual machines or containers. See
1255       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1256       for details about slice units.</para>
1257
1258       <variablelist>
1259         <varlistentry>
1260           <term><filename>-.slice</filename></term>
1261           <listitem>
1262             <para>The root slice is the root of the slice hierarchy. It usually does not contain
1263             units directly, but may be used to set defaults for the whole tree.</para>
1264
1265             <xi:include href="version-info.xml" xpointer="v206"/>
1266           </listitem>
1267         </varlistentry>
1268
1269         <varlistentry>
1270           <term><filename>system.slice</filename></term>
1271           <listitem>
1272             <para>By default, all system services started by
1273             <command>systemd</command> are found in this slice.</para>
1274
1275             <xi:include href="version-info.xml" xpointer="v206"/>
1276           </listitem>
1277         </varlistentry>
1278
1279         <varlistentry>
1280           <term><filename>user.slice</filename></term>
1281           <listitem>
1282             <para>By default, all user processes and services started on
1283             behalf of the user, including the per-user systemd instance
1284             are found in this slice.  This is pulled in by
1285             <filename>systemd-logind.service</filename>.</para>
1286
1287             <xi:include href="version-info.xml" xpointer="v206"/>
1288           </listitem>
1289         </varlistentry>
1290
1291         <varlistentry>
1292           <term><filename>machine.slice</filename></term>
1293           <listitem>
1294             <para>By default, all virtual machines and containers
1295             registered with <command>systemd-machined</command> are
1296             found in this slice. This is pulled in by
1297             <filename>systemd-machined.service</filename>.</para>
1298
1299             <xi:include href="version-info.xml" xpointer="v206"/>
1300           </listitem>
1301         </varlistentry>
1302       </variablelist>
1303     </refsect2>
1304   </refsect1>
1305
1306   <refsect1>
1307     <title>Units managed by the user service manager</title>
1308
1309     <refsect2>
1310       <title>Special User Units</title>
1311
1312       <para>When systemd runs as a user instance, the following special
1313       units are available:</para>
1314
1315       <variablelist>
1316         <varlistentry>
1317           <term><filename>default.target</filename></term>
1318           <listitem>
1319             <para>This is the main target of the user session, started by default. Various services that
1320             compose the normal user session should be pulled into this target. In this regard,
1321             <filename>default.target</filename> is similar to <filename>multi-user.target</filename> in the
1322             system instance, but it is a real unit, not an alias.</para>
1323
1324             <xi:include href="version-info.xml" xpointer="v242"/>
1325           </listitem>
1326         </varlistentry>
1327       </variablelist>
1328
1329       <para>In addition, the following units are available which have definitions similar to their
1330       system counterparts:
1331       <filename>exit.target</filename>,
1332       <filename>shutdown.target</filename>,
1333       <filename>sockets.target</filename>,
1334       <filename>timers.target</filename>,
1335       <filename>paths.target</filename>,
1336       <filename>bluetooth.target</filename>,
1337       <filename>printer.target</filename>,
1338       <filename>smartcard.target</filename>,
1339       <filename>sound.target</filename>.</para>
1340     </refsect2>
1341
1342     <refsect2>
1343       <title>Special Passive User Units</title>
1344
1345       <variablelist>
1346         <varlistentry>
1347           <term><filename>graphical-session.target</filename></term>
1348           <listitem>
1349             <para>This target is active whenever any graphical session is running. It is used to
1350             stop user services which only apply to a graphical (X, Wayland, etc.) session when the
1351             session is terminated. Such services should have
1352             <literal>PartOf=graphical-session.target</literal> in their [Unit]
1353             section. A target for a particular session (e. g.
1354             <filename>gnome-session.target</filename>) starts and stops
1355             <literal>graphical-session.target</literal> with
1356             <literal>BindsTo=graphical-session.target</literal>.</para>
1357
1358             <para>Which services are started by a session target is determined by the
1359             <literal>Wants=</literal> and <literal>Requires=</literal> dependencies.  For services
1360             that can be enabled independently, symlinks in <literal>.wants/</literal> and
1361             <literal>.requires/</literal> should be used, see
1362             <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
1363             Those symlinks should either be shipped in packages, or should be added dynamically
1364             after installation, for example using <literal>systemctl add-wants</literal>, see
1365             <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
1366             </para>
1367
1368             <example>
1369               <title>Nautilus as part of a GNOME session</title>
1370
1371               <para><literal>gnome-session.target</literal> pulls in Nautilus as top-level service:</para>
1372
1373               <programlisting>[Unit]
1374 Description=User systemd services for GNOME graphical session
1375 Wants=nautilus.service
1376 BindsTo=graphical-session.target</programlisting>
1377
1378               <para><literal>nautilus.service</literal> gets stopped when the session stops:</para>
1379
1380               <programlisting>[Unit]
1381 Description=Render the desktop icons with Nautilus
1382 PartOf=graphical-session.target
1383
1384 [Service]
1385 …</programlisting>
1386             </example>
1387
1388               <xi:include href="version-info.xml" xpointer="v234"/>
1389           </listitem>
1390         </varlistentry>
1391
1392         <varlistentry>
1393           <term><filename>graphical-session-pre.target</filename></term>
1394           <listitem>
1395             <para>This target contains services which set up the environment or global configuration
1396             of a graphical session, such as SSH/GPG agents (which need to export an environment
1397             variable into all desktop processes) or migration of obsolete d-conf keys after an OS
1398             upgrade (which needs to happen before starting any process that might use them). This
1399             target must be started before starting a graphical session like
1400             <filename>gnome-session.target</filename>.</para>
1401
1402             <xi:include href="version-info.xml" xpointer="v234"/>
1403           </listitem>
1404         </varlistentry>
1405
1406         <varlistentry>
1407           <term><filename>xdg-desktop-autostart.target</filename></term>
1408           <listitem>
1409             <para>The XDG specification defines a way to autostart applications using XDG desktop files.
1410             systemd ships
1411             <citerefentry><refentrytitle>systemd-xdg-autostart-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1412             for the XDG desktop files in autostart directories. Desktop Environments can opt-in to use this
1413             service by adding a <varname>Wants=</varname> dependency on
1414             <filename>xdg-desktop-autostart.target</filename>.</para>
1415
1416             <xi:include href="version-info.xml" xpointer="v246"/>
1417           </listitem>
1418         </varlistentry>
1419       </variablelist>
1420     </refsect2>
1421
1422     <refsect2>
1423       <title>Special User Slice Units</title>
1424
1425       <para>There are four <literal>.slice</literal> units which form the basis of the user hierarchy for
1426       assignment of resources for user applications and services. See
1427       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1428       for details about slice units and the documentation about
1429       <ulink url="https://systemd.io/DESKTOP_ENVIRONMENTS">Desktop Environments</ulink>
1430       for further information.</para>
1431
1432       <variablelist>
1433         <varlistentry>
1434           <term><filename>-.slice</filename></term>
1435           <listitem>
1436             <para>The root slice is the root of the user's slice hierarchy.
1437             It usually does not contain units directly, but may be used to set defaults for the whole tree.</para>
1438
1439             <xi:include href="version-info.xml" xpointer="v247"/>
1440           </listitem>
1441         </varlistentry>
1442
1443         <varlistentry>
1444           <term><filename>app.slice</filename></term>
1445           <listitem>
1446             <para>By default, all user services and applications managed by
1447             <command>systemd</command> are found in this slice.
1448             All interactively launched applications like web browsers and text editors
1449             as well as non-critical services should be placed into this slice.</para>
1450
1451             <xi:include href="version-info.xml" xpointer="v247"/>
1452           </listitem>
1453         </varlistentry>
1454
1455         <varlistentry>
1456           <term><filename>session.slice</filename></term>
1457           <listitem>
1458             <para>All essential services and applications required for the
1459             session should use this slice.
1460             These are services that either cannot be restarted easily
1461             or where latency issues may affect the interactivity of the system and applications.
1462             This includes the display server, screen readers and other services such as DBus or XDG portals.
1463             Such services should be configured to be part of this slice by
1464             adding <varname>Slice=session.slice</varname> to their unit files.</para>
1465
1466             <xi:include href="version-info.xml" xpointer="v247"/>
1467           </listitem>
1468         </varlistentry>
1469
1470         <varlistentry>
1471           <term><filename>background.slice</filename></term>
1472           <listitem>
1473             <para>All services running low-priority background tasks should use this slice.
1474             This permits resources to be preferentially assigned to the other slices.
1475             Examples include non-interactive tasks like file indexing or backup operations
1476             where latency is not important.</para>
1477
1478             <xi:include href="version-info.xml" xpointer="v247"/>
1479           </listitem>
1480         </varlistentry>
1481       </variablelist>
1482     </refsect2>
1483   </refsect1>
1484
1485   <refsect1>
1486       <title>See Also</title>
1487       <para>
1488         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1489         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1490         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1491         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1492         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1493         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1494         <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1495         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1496         <citerefentry><refentrytitle>user@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1497       </para>
1498   </refsect1>
1499
1500 </refentry>