summaryrefslogtreecommitdiff
path: root/man/systemd.special.xml
blob: b7340ed978a4e93800e47fca1bdd723eaa559c14 (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
<?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>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>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>remote-fs-setup.target</filename>,
                <filename>rescue.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>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>time-sync.target</filename>,
                <filename>timers.target</filename>,
                <filename>umount.target</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 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>Usually this should
                                        pull-in all mount points, swap
                                        devices, sockets, timers, and
                                        path units and other basic
                                        initialization necessary for
                                        general purpose
                                        daemons.</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 unit is supposed
                                        to be used with the kernel
                                        command line option
                                        <varname>systemd.unit=</varname>
                                        and has otherwise little use.
                                        </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 fround in
                                        <filename>/etc/fstab</filename>
                                        that have the
                                        <option>auto</option> and
                                        <option>x-initrd.mount</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-uer.target</varname>
                                        in the unit's
                                        <literal>[Install]</literal>
                                        section.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>network.target</filename></term>
                                <listitem>
                                        <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>

                                        <para>This unit is supposed to
                                        indicate when the network is
                                        "up", but it is only very
                                        loosely defined what that is
                                        supposed to mean. Also see <ulink
                                        url="http://www.freedesktop.org/wiki/Software/systemd/NetworkTarget">Running
                                        Services After the Network is
                                        up</ulink> for more
                                        information.</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>remote-fs-setup.target</filename></term>
                                <listitem>
                                        <para>This target unit is
                                        automatically pulled in (by a
                                        <varname>Wants=</varname> type
                                        dependency) by all remote
                                        mount points. It can be used
                                        to run certain units when at
                                        least one remote file system
                                        is to be mounted. Note that
                                        this target is not ordered
                                        against the remote mounts, use
                                        <filename>remote-fs-pre.target</filename>
                                        for that (see below).</para>

                                        <para>Again, this target unit
                                        is <emphasis>not</emphasis>
                                        suitable for ordering, it is
                                        only useful for pulling in
                                        other units.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>rescue.target</filename></term>
                                <listitem>
                                        <para>A special target unit
                                        for setting up the base system
                                        and a rescue shell.</para>

                                        <para><filename>runlevel1.target</filename>
                                        is an alias for this target
                                        unit, for compatibility with SysV.</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>multi-user.target</filename>
                                        (for runlevel 2) or
                                        <filename>graphical.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>
                                        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>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>A special target unit
                                        covering early boot-up scripts.</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>
                                <listitem>
                                        <para>A special target unit
                                        that is used for off-line
                                        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 the <ulink
                                        url="http://freedesktop.org/wiki/Software/systemd/SystemUpdates">System
                                        Updates
                                        Specification</ulink>.</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 umounts 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 printer 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 printer
                                        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>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>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. 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. </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>remote-fs-setup.target</filename>
                                        (see above).</para>

                                        <para>Again, this target unit
                                        is <emphasis>not</emphasis>
                                        suitable for pulling in other
                                        units, it is only useful for
                                        ordering.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>rpcbind.target</filename></term>
                                <listitem>
                                        <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>$portmap</literal>
                                        facility.</para>
                                </listitem>
                        </varlistentry>
                        <varlistentry>
                                <term><filename>time-sync.target</filename></term>
                                <listitem>
                                        <para>systemd automatically
                                        adds dependencies of type
                                        <varname>After=</varname> for
                                        this target unit to all SysV
                                        init script service units with
                                        an LSB header referring to the
                                        <literal>$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>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>

                <para>In addition the following special unit is
                understood only when systemd runs as service instance:</para>

                <variablelist>
                        <varlistentry>
                                <term><filename>exit.target</filename></term>
                                <listitem>
                                        <para>A special service unit
                                        for shutting down the
                                        user service manager.</para>

                                        <para>Applications wanting to
                                        terminate the user service
                                        manager should start this
                                        unit. If systemd receives
                                        SIGTERM or SIGINT when running
                                        as user service daemon it will
                                        start this unit.</para>

                                        <para>Normally, this pulls in
                                        <filename>shutdown.target</filename>
                                        which in turn should be
                                        conflicted by all units that
                                        want to be shut down on
                                        user service manager exit.</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>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
                  </para>
        </refsect1>

</refentry>