summaryrefslogtreecommitdiff
path: root/man/systemd.special.xml
blob: b513a13b5abd7a8541f35258c9d7e0d66d48c434 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<!--
  This file is part of systemd.

  Copyright 2010 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU Lesser General Public License as published by
  the Free Software Foundation; either version 2.1 of the License, or
  (at your option) any later version.

  systemd is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->

<refentry id="systemd.special">

  <refentryinfo>
    <title>systemd.special</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Lennart</firstname>
        <surname>Poettering</surname>
        <email>lennart@poettering.net</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd.special</refentrytitle>
    <manvolnum>7</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd.special</refname>
    <refpurpose>Special systemd units</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>basic.target</filename>,
    <filename>bluetooth.target</filename>,
    <filename>ctrl-alt-del.target</filename>,
    <filename>cryptsetup.target</filename>,
    <filename>cryptsetup-pre.target</filename>,
    <filename>dbus.service</filename>,
    <filename>dbus.socket</filename>,
    <filename>default.target</filename>,
    <filename>display-manager.service</filename>,
    <filename>emergency.target</filename>,
    <filename>exit.target</filename>,
    <filename>final.target</filename>,
    <filename>getty.target</filename>,
    <filename>graphical.target</filename>,
    <filename>halt.target</filename>,
    <filename>hibernate.target</filename>,
    <filename>hybrid-sleep.target</filename>,
    <filename>initrd-fs.target</filename>,
    <filename>kbrequest.target</filename>,
    <filename>kexec.target</filename>,
    <filename>local-fs.target</filename>,
    <filename>local-fs-pre.target</filename>,
    <filename>multi-user.target</filename>,
    <filename>network.target</filename>,
    <filename>network-online.target</filename>,
    <filename>network-pre.target</filename>,
    <filename>nss-lookup.target</filename>,
    <filename>nss-user-lookup.target</filename>,
    <filename>paths.target</filename>,
    <filename>poweroff.target</filename>,
    <filename>printer.target</filename>,
    <filename>reboot.target</filename>,
    <filename>remote-fs.target</filename>,
    <filename>remote-fs-pre.target</filename>,
    <filename>rescue.target</filename>,
    <filename>initrd-root-device.target</filename>,
    <filename>initrd-root-fs.target</filename>,
    <filename>rpcbind.target</filename>,
    <filename>runlevel2.target</filename>,
    <filename>runlevel3.target</filename>,
    <filename>runlevel4.target</filename>,
    <filename>runlevel5.target</filename>,
    <filename>shutdown.target</filename>,
    <filename>sigpwr.target</filename>,
    <filename>sleep.target</filename>,
    <filename>slices.target</filename>,
    <filename>smartcard.target</filename>,
    <filename>sockets.target</filename>,
    <filename>sound.target</filename>,
    <filename>suspend.target</filename>,
    <filename>swap.target</filename>,
    <filename>sysinit.target</filename>,
    <filename>syslog.socket</filename>,
    <filename>system-update.target</filename>,
    <filename>system-update-cleanup.service</filename>,
    <filename>time-sync.target</filename>,
    <filename>timers.target</filename>,
    <filename>umount.target</filename>,
    <filename>-.slice</filename>,
    <filename>system.slice</filename>,
    <filename>user.slice</filename>,
    <filename>machine.slice</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>A few units are treated specially by systemd. They have
    special internal semantics and cannot be renamed.</para>
  </refsect1>

  <refsect1>
    <title>Special System Units</title>

    <variablelist>
      <varlistentry>
        <term><filename>basic.target</filename></term>
        <listitem>
          <para>A special target unit covering basic boot-up.</para>

          <para>systemd automatically adds dependency of the type
          <varname>After=</varname> for this target unit to all
          services (except for those with
          <varname>DefaultDependencies=no</varname>).</para>

          <para>Usually, this should pull-in all local mount points plus
          <filename>/var</filename>, <filename>/tmp</filename> and
          <filename>/var/tmp</filename>, swap devices, sockets, timers,
          path units and other basic initialization necessary for general
          purpose daemons. The mentioned mount points are special cased
          to allow them to be remote.
          </para>

          <para>This target usually does not pull in any non-target units
          directly, but rather does so indirectly via other early boot targets.
          It is instead meant as a synchronization point for late boot
          services. Refer to
          <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>
          for details on the targets involved.
          </para>

        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>ctrl-alt-del.target</filename></term>
        <listitem>
          <para>systemd starts this target whenever Control+Alt+Del is
          pressed on the console. Usually, this should be aliased
          (symlinked) to <filename>reboot.target</filename>.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>cryptsetup.target</filename></term>
        <listitem>
          <para>A target that pulls in setup services for all
          encrypted block devices.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>dbus.service</filename></term>
        <listitem>
          <para>A special unit for the D-Bus bus daemon. As soon as
          this service is fully started up systemd will connect to it
          and register its service.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>dbus.socket</filename></term>
        <listitem>
          <para>A special unit for the D-Bus system bus socket. All
          units with <varname>Type=dbus</varname> automatically gain a
          dependency on this unit.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>default.target</filename></term>
        <listitem>
          <para>The default unit systemd starts at bootup. Usually,
          this should be aliased (symlinked) to
          <filename>multi-user.target</filename> or
          <filename>graphical.target</filename>.</para>

          <para>The default unit systemd starts at bootup can be
          overridden with the <varname>systemd.unit=</varname> kernel
          command line option.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>display-manager.service</filename></term>
        <listitem>
          <para>The display manager service. Usually, this should be
          aliased (symlinked) to <filename>gdm.service</filename> or a
          similar display manager service.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>emergency.target</filename></term>
        <listitem>
          <para>A special target unit that starts an emergency shell on the main console. This target does not pull in
          any services or mounts. It is the most minimal version of starting the system in order to acquire an
          interactive shell; the only processes running are usually just the system manager (PID 1) and the shell
          process. This unit is supposed to be used with the kernel command line option
          <varname>systemd.unit=</varname>; it is also used when a file system check on a required file system fails,
          and boot-up cannot continue. Compare with <filename>rescue.target</filename>, which serves a similar purpose,
          but also starts the most basic services and mounts all file systems.</para>

          <para>Use the <literal>systemd.unit=emergency.target</literal> kernel command line option to boot into this
          mode. A short alias for this kernel command line option is <literal>emergency</literal>, for compatibility
          with SysV.</para>

          <para>In many ways booting into <filename>emergency.target</filename> is similar to the effect of booting
          with <literal>init=/bin/sh</literal> on the kernel command line, except that emergency mode provides you with
          the full system and service manager, and allows starting individual units in order to continue the boot
          process in steps.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>exit.target</filename></term>
        <listitem>
          <para>A special service unit for shutting down the system or
          user service manager. It is equivalent to
          <filename>poweroff.target</filename> on non-container
          systems, and also works in containers.</para>

          <para>systemd will start this unit when it receives a
          request to shut down over D-Bus or a
          <constant>SIGTERM</constant> or <constant>SIGINT</constant>
          signal when running as user service daemon.</para>

          <para>Normally, this (indirectly) pulls in
          <filename>shutdown.target</filename>, which in turn should be
          conflicted by all units that want to be scheduled for
          shutdown when the service manager starts to exit.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>final.target</filename></term>
        <listitem>
          <para>A special target unit that is used during the shutdown
          logic and may be used to pull in late services after all
          normal services are already terminated and all mounts
          unmounted.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>getty.target</filename></term>
        <listitem>
          <para>A special target unit that pulls in statically
          configured local TTY <filename>getty</filename> instances.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>graphical.target</filename></term>
        <listitem>
          <para>A special target unit for setting up a graphical login
          screen. This pulls in
          <filename>multi-user.target</filename>.</para>

          <para>Units that are needed for graphical logins shall add
          <varname>Wants=</varname> dependencies for their unit to
          this unit (or <filename>multi-user.target</filename>) during
          installation. This is best configured via
          <varname>WantedBy=graphical.target</varname> in the unit's
          <literal>[Install]</literal> section.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>hibernate.target</filename></term>
        <listitem>
          <para>A special target unit for hibernating the system. This
          pulls in <filename>sleep.target</filename>.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>hybrid-sleep.target</filename></term>
        <listitem>
          <para>A special target unit for hibernating and suspending
          the system at the same time. This pulls in
          <filename>sleep.target</filename>.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>halt.target</filename></term>
        <listitem>
          <para>A special target unit for shutting down and halting
          the system. Note that this target is distinct from
          <filename>poweroff.target</filename> in that it generally
          really just halts the system rather than powering it
          down.</para>

          <para>Applications wanting to halt the system should start
          this unit.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>initrd-fs.target</filename></term>
        <listitem>
          <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
          automatically adds dependencies of type
          <varname>Before=</varname> to
          <filename>sysroot-usr.mount</filename> and all mount points
          found in <filename>/etc/fstab</filename> that have
          <option>x-initrd.mount</option> and not have
          <option>noauto</option> mount options set.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>kbrequest.target</filename></term>
        <listitem>
          <para>systemd starts this target whenever Alt+ArrowUp is
          pressed on the console. This is a good candidate to be
          aliased (symlinked) to
          <filename>rescue.target</filename>.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>kexec.target</filename></term>
        <listitem>
          <para>A special target unit for shutting down and rebooting
          the system via kexec.</para>

          <para>Applications wanting to reboot the system with kexec
          should start this unit.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>local-fs.target</filename></term>
        <listitem>
          <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
          automatically adds dependencies of type
          <varname>Before=</varname> to all mount units that refer to
          local mount points for this target unit. In addition, it
          adds dependencies of type <varname>Wants=</varname> to this
          target unit for those mounts listed in
          <filename>/etc/fstab</filename> that have the
          <option>auto</option> mount option set.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>multi-user.target</filename></term>
        <listitem>
          <para>A special target unit for setting up a multi-user
          system (non-graphical). This is pulled in by
          <filename>graphical.target</filename>.</para>

          <para>Units that are needed for a multi-user system shall
          add <varname>Wants=</varname> dependencies for their unit to
          this unit during installation. This is best configured via
          <varname>WantedBy=multi-user.target</varname> in the unit's
          <literal>[Install]</literal> section.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>network-online.target</filename></term>
        <listitem>
          <para>Units that strictly require a configured network
          connection should pull in
          <filename>network-online.target</filename> (via a
          <varname>Wants=</varname> type dependency) and order
          themselves after it. This target unit is intended to pull in
          a service that delays further execution until the network is
          sufficiently set up. What precisely this requires is left to
          the implementation of the network managing service.</para>

          <para>Note the distinction between this unit and
          <filename>network.target</filename>. This unit is an active
          unit (i.e. pulled in by the consumer rather than the
          provider of this functionality) and pulls in a service which
          possibly adds substantial delays to further execution. In
          contrast, <filename>network.target</filename> is a passive
          unit (i.e. pulled in by the provider of the functionality,
          rather than the consumer) that usually does not delay
          execution much. Usually, <filename>network.target</filename>
          is part of the boot of most systems, while
          <filename>network-online.target</filename> is not, except
          when at least one unit requires it. Also see <ulink
          url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
          Services After the Network is up</ulink> for more
          information.</para>

          <para>All mount units for remote network file systems
          automatically pull in this unit, and order themselves after
          it. Note that networking daemons that simply provide
          functionality to other hosts generally do not need to pull
          this in.</para>
          </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>paths.target</filename></term>
        <listitem>
          <para>A special target unit that sets up all path units (see
          <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>
          for details) that shall be active after boot.</para>

          <para>It is recommended that path units installed by
          applications get pulled in via <varname>Wants=</varname>
          dependencies from this unit. This is best configured via a
          <varname>WantedBy=paths.target</varname> in the path unit's
          <literal>[Install]</literal> section.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>poweroff.target</filename></term>
        <listitem>
          <para>A special target unit for shutting down and powering
          off the system.</para>

          <para>Applications wanting to power off the system should
          start this unit.</para>

          <para><filename>runlevel0.target</filename> is an alias for
          this target unit, for compatibility with SysV.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>reboot.target</filename></term>
        <listitem>
          <para>A special target unit for shutting down and rebooting
          the system.</para>

          <para>Applications wanting to reboot the system should start
          this unit.</para>

          <para><filename>runlevel6.target</filename> is an alias for
          this target unit, for compatibility with SysV.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>remote-fs.target</filename></term>
        <listitem>
          <para>Similar to <filename>local-fs.target</filename>, but
          for remote mount points.</para>

          <para>systemd automatically adds dependencies of type
          <varname>After=</varname> for this target unit to all SysV
          init script service units with an LSB header referring to
          the <literal>$remote_fs</literal> facility.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>rescue.target</filename></term>
        <listitem>
          <para>A special target unit that pulls in the base system (including system mounts) and spawns a rescue
          shell. Isolate to this target in order to administer the system in single-user mode with all file systems
          mounted but with no services running, except for the most basic. Compare with
          <filename>emergency.target</filename>, which is much more reduced and does not provide the file systems or
          most basic services.</para>

          <para><filename>runlevel1.target</filename> is an alias for this target unit, for compatibility with
          SysV.</para>

          <para>Use the <literal>systemd.unit=rescue.target</literal> kernel command line option to boot into this
          mode. A short alias for this kernel command line option is <literal>1</literal>, for compatibility with
          SysV.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>initrd-root-device.target</filename></term>
        <listitem>
          <para>A special initrd target unit that is reached when the root filesystem device is available, but before
          it has been mounted.
          <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
          and
          <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
          automatically setup the appropriate dependencies to make this happen.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>initrd-root-fs.target</filename></term>
        <listitem>
          <para><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>3</manvolnum></citerefentry>
          automatically adds dependencies of type
          <varname>Before=</varname> to the
          <filename>sysroot.mount</filename> unit, which is generated
          from the kernel command line.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>runlevel2.target</filename></term>
        <term><filename>runlevel3.target</filename></term>
        <term><filename>runlevel4.target</filename></term>
        <term><filename>runlevel5.target</filename></term>
        <listitem>
          <para>These are targets that are called whenever the SysV
          compatibility code asks for runlevel 2, 3, 4, 5,
          respectively. It is a good idea to make this an alias for
          (i.e. symlink to) <filename>graphical.target</filename>
          (for runlevel 5) or <filename>multi-user.target</filename>
          (the others).</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>shutdown.target</filename></term>
        <listitem>
          <para>A special target unit that terminates the services on
          system shutdown.</para>

          <para>Services that shall be terminated on system shutdown
          shall add <varname>Conflicts=</varname> and
          <varname>Before=</varname> dependencies to this unit for
          their service unit, which is implicitly done when
          <varname>DefaultDependencies=yes</varname> is set (the
          default).</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>sigpwr.target</filename></term>
        <listitem>
          <para>A special target that is started when systemd receives
          the SIGPWR process signal, which is normally sent by the
          kernel or UPS daemons when power fails.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>sleep.target</filename></term>
        <listitem>
          <para>A special target unit that is pulled in by
          <filename>suspend.target</filename>,
          <filename>hibernate.target</filename> and
          <filename>hybrid-sleep.target</filename> and may be used to
          hook units into the sleep state logic.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>slices.target</filename></term>
        <listitem>
          <para>A special target unit that sets up all slice units (see
          <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
          details) that shall be active after boot. By default the generic <filename>user.slice</filename>,
          <filename>system.slice</filename>, <filename>machines.slice</filename> slice units, as well as the root
          slice unit <filename>-.slice</filename> are pulled in and ordered before this unit (see below).</para>

          <para>It's a good idea to add <varname>WantedBy=slices.target</varname> lines to the <literal>[Install]</literal>
          section of all slices units that may be installed dynamically.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>sockets.target</filename></term>
        <listitem>
          <para>A special target unit that sets up all socket
          units (see
          <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
          for details) that shall be active after boot.</para>

          <para>Services that can be socket-activated shall add
          <varname>Wants=</varname> dependencies to this unit for
          their socket unit during installation. This is best
          configured via a <varname>WantedBy=sockets.target</varname>
          in the socket unit's <literal>[Install]</literal>
          section.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>suspend.target</filename></term>
        <listitem>
          <para>A special target unit for suspending the system. This
          pulls in <filename>sleep.target</filename>.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>swap.target</filename></term>
        <listitem>
          <para>Similar to <filename>local-fs.target</filename>, but
          for swap partitions and swap files.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>sysinit.target</filename></term>
        <listitem>
          <para>systemd automatically adds dependencies of the types
          <varname>Requires=</varname> and <varname>After=</varname>
          for this target unit to all services (except for those with
          <varname>DefaultDependencies=no</varname>).</para>

          <para>This target pulls in the services required for system
          initialization. System services pulled in by this target should
          declare <varname>DefaultDependencies=no</varname> and specify
          all their dependencies manually, including access to anything
          more than a read only root filesystem. For details on the
          dependencies of this target, refer to
          <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
          </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>syslog.socket</filename></term>
        <listitem>
          <para>The socket unit syslog implementations should listen
          on. All userspace log messages will be made available on
          this socket. For more information about syslog integration,
          please consult the <ulink
          url="http://www.freedesktop.org/wiki/Software/systemd/syslog">Syslog
          Interface</ulink> document.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>system-update.target</filename></term>
        <term><filename>system-update-cleanup.service</filename></term>
        <listitem>
          <para>A special target unit that is used for offline system updates.
          <citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
          will redirect the boot process to this target if <filename>/system-update</filename>
          exists. For more information see
          <citerefentry><refentrytitle>systemd.offline-updates</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
          </para>

          <para>Updates should happen before the <filename>system-update.target</filename> is
          reached, and the services which implement them should cause the machine to reboot. As
          a safety measure, if this does not happen, and <filename>/system-update</filename>
          still exists after <filename>system-update.target</filename> is reached,
          <filename>system-update-cleanup.service</filename> will remove this symlink and
          reboot the machine.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>timers.target</filename></term>
        <listitem>
          <para>A special target unit that sets up all timer units
          (see
          <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
          for details) that shall be active after boot.</para>

          <para>It is recommended that timer units installed by
          applications get pulled in via <varname>Wants=</varname>
          dependencies from this unit. This is best configured via
          <varname>WantedBy=timers.target</varname> in the timer
          unit's <literal>[Install]</literal> section.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>umount.target</filename></term>
        <listitem>
          <para>A special target unit that unmounts all mount and
          automount points on system shutdown.</para>

          <para>Mounts that shall be unmounted on system shutdown
          shall add Conflicts dependencies to this unit for their
          mount unit, which is implicitly done when
          <varname>DefaultDependencies=yes</varname> is set (the
          default).</para>
        </listitem>
      </varlistentry>

    </variablelist>
  </refsect1>

  <refsect1>
    <title>Special System Units for Devices</title>

    <para>Some target units are automatically pulled in as devices of
    certain kinds show up in the system. These may be used to
    automatically activate various services based on the specific type
    of the available hardware.</para>

    <variablelist>
      <varlistentry>
        <term><filename>bluetooth.target</filename></term>
        <listitem>
          <para>This target is started automatically as soon as a
          Bluetooth controller is plugged in or becomes available at
          boot.</para>

          <para>This may be used to pull in Bluetooth management
          daemons dynamically when Bluetooth hardware is found.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>printer.target</filename></term>
        <listitem>
          <para>This target is started automatically as soon as a
          printer is plugged in or becomes available at boot.</para>

          <para>This may be used to pull in printer management daemons
          dynamically when printer hardware is found.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>smartcard.target</filename></term>
        <listitem>
          <para>This target is started automatically as soon as a
          smartcard controller is plugged in or becomes available at
          boot.</para>

          <para>This may be used to pull in smartcard management
          daemons dynamically when smartcard hardware is found.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>sound.target</filename></term>
        <listitem>
          <para>This target is started automatically as soon as a
          sound card is plugged in or becomes available at
          boot.</para>

          <para>This may be used to pull in audio management daemons
          dynamically when audio hardware is found.</para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Special Passive System Units </title>

    <para>A number of special system targets are defined that can be
    used to properly order boot-up of optional services. These targets
    are generally not part of the initial boot transaction, unless
    they are explicitly pulled in by one of the implementing services.
    Note specifically that these <emphasis>passive</emphasis> target
    units are generally not pulled in by the consumer of a service,
    but by the provider of the service. This means: a consuming
    service should order itself after these targets (as appropriate),
    but not pull it in. A providing service should order itself before
    these targets (as appropriate) and pull it in (via a
    <varname>Wants=</varname> type dependency).</para>

    <para>Note that these passive units cannot be started manually,
    i.e. <literal>systemctl start time-sync.target</literal> will fail
    with an error. They can only be pulled in by dependency. This is
    enforced since they exist for ordering purposes only and thus are
    not useful as only unit within a transaction.</para>

    <variablelist>
      <varlistentry>
        <term><filename>cryptsetup-pre.target</filename></term>
        <listitem>
          <para>This passive target unit may be pulled in by services
          that want to run before any encrypted block device is set
          up. All encrypted block devices are set up after this target
          has been reached. Since the shutdown order is implicitly the
          reverse start-up order between units, this target is
          particularly useful to ensure that a service is shut down
          only after all encrypted block devices are fully
          stopped.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>local-fs-pre.target</filename></term>
        <listitem>
          <para>This target unit is
          automatically ordered before
          all local mount points marked
          with <option>auto</option>
          (see above). It can be used to
          execute certain units before
          all local mounts.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>network.target</filename></term>
        <listitem>
          <para>This unit is supposed to indicate when network
          functionality is available, but it is only very weakly
          defined what that is supposed to mean, with one exception:
          at shutdown, a unit that is ordered after
          <filename>network.target</filename> will be stopped before
          the network — to whatever level it might be set up then —
          is shut down. It is hence useful when writing service files
          that require network access on shutdown, which should order
          themselves after this target, but not pull it in. Also see
          <ulink url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
          Services After the Network is up</ulink> for more
          information. Also see
          <filename>network-online.target</filename> described
          above.</para>

          <para>systemd automatically adds dependencies of type
          <varname>After=</varname> for this target unit to all SysV
          init script service units with an LSB header referring to
          the <literal>$network</literal> facility.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>network-pre.target</filename></term>
        <listitem>
          <para>This passive target unit may be pulled in by services
          that want to run before any network is set up, for example
          for the purpose of setting up a firewall. All network
          management software orders itself after this target, but
          does not pull it in.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>nss-lookup.target</filename></term>
        <listitem>
          <para>A target that should be used as synchronization point
          for all host/network name service lookups. Note that this is
          independent of user/group name lookups for which
          <filename>nss-user-lookup.target</filename> should be used.
          All services for which the availability of full host/network
          name resolution is essential should be ordered after this
          target, but not pull it in. systemd automatically adds
          dependencies of type <varname>After=</varname> for this
          target unit to all SysV init script service units with an
          LSB header referring to the <literal>$named</literal>
          facility.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>nss-user-lookup.target</filename></term>
        <listitem>
          <para>A target that should be used as synchronization point
          for all user/group name service lookups. Note that this is
          independent of host/network name lookups for which
          <filename>nss-lookup.target</filename> should be used. All
          services for which the availability of the full user/group
          database is essential should be ordered after this target,
          but not pull it in. Note that system users are always
          resolvable, and hence do not require any special ordering
          against this target.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>remote-fs-pre.target</filename></term>
        <listitem>
          <para>This target unit is automatically ordered before all
          remote mount point units (see above). It can be used to run
          certain units before the remote mounts are established. Note
          that this unit is generally not part of the initial
          transaction, unless the unit that wants to be ordered before
          all remote mounts pulls it in via a
          <varname>Wants=</varname> type dependency. If the unit wants
          to be pulled in by the first remote mount showing up, it
          should use <filename>network-online.target</filename> (see
          above).</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>rpcbind.target</filename></term>
        <listitem>
          <para>The portmapper/rpcbind pulls in this target and orders
          itself before it, to indicate its availability. systemd
          automatically adds dependencies of type
          <varname>After=</varname> for this target unit to all SysV
          init script service units with an LSB header referring to
          the <literal>$portmap</literal> facility.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term><filename>time-sync.target</filename></term>
        <listitem>
          <para>Services responsible for synchronizing the system
          clock from a remote source (such as NTP client
          implementations) should pull in this target and order
          themselves before it. All services where correct time is
          essential should be ordered after this unit, but not pull it
          in. systemd automatically adds dependencies of type
          <varname>After=</varname> for this target unit to all SysV
          init script service units with an LSB header referring to
          the <literal>$time</literal> facility. </para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Special User Units</title>

    <para>When systemd runs as a user instance, the following special
    units are available, which have similar definitions as their
    system counterparts:
    <filename>exit.target</filename>,
    <filename>default.target</filename>,
    <filename>shutdown.target</filename>,
    <filename>sockets.target</filename>,
    <filename>timers.target</filename>,
    <filename>paths.target</filename>,
    <filename>bluetooth.target</filename>,
    <filename>printer.target</filename>,
    <filename>smartcard.target</filename>,
    <filename>sound.target</filename>.</para>
  </refsect1>

  <refsect1>
    <title>Special Passive User Units</title>

    <refsect2>
      <title>graphical-session.target</title>

      <para>This target is active whenever any graphical session is running. It
      is used to stop user services which only apply to a graphical (X,
      Wayland, etc.) session when the session is terminated. Such services
      should have <literal>PartOf=graphical-session.target</literal> in their
      <literal>[Unit]</literal> section. A target for a particular session
      (e. g.  <filename>gnome-session.target</filename>) starts and stops
      <literal>graphical-session.target</literal> with
      <literal>BindsTo=graphical-session.target</literal>.</para>

      <para>Which services are started by a session target is determined by the
      <literal>Wants=</literal> and <literal>Requires=</literal> dependencies.
      For services that can be enabled independently, symlinks in
      <literal>.wants/</literal> and <literal>.requires/</literal> should be
      used, see
      <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
      Those symlinks should either be shipped in packages, or should be added
      dynamically after installation, for example using <literal>systemctl add-wants</literal>, see
      <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
      </para>

      <example>
        <title>Nautilus as part of a GNOME session</title>

        <para><literal>gnome-session.target</literal> pulls in Nautilus as
        top-level service:</para>

        <programlisting>[Unit]
Description=User systemd services for GNOME graphical session
Wants=nautilus.service
BindsTo=graphical-session.target
        </programlisting>

        <para><literal>nautilus.service</literal> gets stopped when the session stops:</para>

        <programlisting>[Unit]
Description=Render the desktop icons with Nautilus
PartOf=graphical-session.target

[Service]
...
        </programlisting>
      </example>
    </refsect2>

    <refsect2>
      <title>graphical-session-pre.target</title>

      <para>This target contains services which set up the environment or
      global configuration of a graphical session, such as SSH/GPG agents
      (which need to export an environment variable into all desktop processes)
      or migration of obsolete d-conf keys after an OS upgrade (which needs to
      happen before starting any process that might use them). This target must
      be started before starting a graphical session
      like <filename>gnome-session.target</filename>.</para>
    </refsect2>

  </refsect1>

  <refsect1>
    <title>Special Slice Units</title>

    <para>There are four <literal>.slice</literal> units which form
    the basis of the hierarchy for assignment of resources for
    services, users, and virtual machines or containers.</para>

    <variablelist>
      <varlistentry>
        <term><filename>-.slice</filename></term>
        <listitem>
          <para>The root slice is the root of the hierarchy. It
          usually does not contain units directly, but may be used to
          set defaults for the whole tree.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><filename>system.slice</filename></term>
        <listitem>
          <para>By default, all system services started by
          <command>systemd</command> are found in this slice.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><filename>user.slice</filename></term>
        <listitem>
          <para>By default, all user processes and services started on
          behalf of the user, including the per-user systemd instance
          are found in this slice.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><filename>machine.slice</filename></term>
        <listitem>
          <para>By default, all virtual machines and containers
          registered with <command>systemd-machined</command> are
          found in this slice.
          </para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
      <title>See Also</title>
      <para>
        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
      </para>
  </refsect1>

</refentry>