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