summaryrefslogtreecommitdiff
path: root/man/systemd.service.xml
blob: 67c68d2f8b5bcd7a98d0604691f38c81374a222e (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
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!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.service">
  <refentryinfo>
    <title>systemd.service</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.service</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd.service</refname>
    <refpurpose>Service unit configuration</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename><replaceable>service</replaceable>.service</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>A unit configuration file whose name ends in
    <filename>.service</filename> encodes information about a process
    controlled and supervised by systemd.</para>

    <para>This man page lists the configuration options specific to
    this unit type. See
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for the common options of all unit configuration files. The common
    configuration items are configured in the generic
    <literal>[Unit]</literal> and <literal>[Install]</literal>
    sections. The service specific configuration options are
    configured in the <literal>[Service]</literal> section.</para>

    <para>Additional options are listed in
    <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    which define the execution environment the commands are executed
    in, and in
    <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    which define the way the processes of the service are terminated,
    and in
    <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    which configure resource control settings for the processes of the
    service.</para>

    <para>If a service is requested under a certain name but no unit
    configuration file is found, systemd looks for a SysV init script
    by the same name (with the <filename>.service</filename> suffix
    removed) and dynamically creates a service unit from that script.
    This is useful for compatibility with SysV. Note that this
    compatibility is quite comprehensive but not 100%. For details
    about the incompatibilities, see the <ulink
    url="http://www.freedesktop.org/wiki/Software/systemd/Incompatibilities">Incompatibilities
    with SysV</ulink> document.</para>
  </refsect1>

  <refsect1>
    <title>Automatic Dependencies</title>

    <para>Services with <varname>Type=dbus</varname> set automatically
    acquire dependencies of type <varname>Requires=</varname> and
    <varname>After=</varname> on
    <filename>dbus.socket</filename>.</para>

    <para>Socket activated services are automatically ordered after
    their activating <filename>.socket</filename> units via an
    automatic <varname>After=</varname> dependency.
    Services also pull in all <filename>.socket</filename> units
    listed in <varname>Sockets=</varname> via automatic
    <varname>Wants=</varname> and <varname>After=</varname> dependencies.</para>

    <para>Unless <varname>DefaultDependencies=</varname> in the <literal>[Unit]</literal> is set to
    <option>false</option>, service units will implicitly have dependencies of type <varname>Requires=</varname> and
    <varname>After=</varname> on <filename>sysinit.target</filename>, a dependency of type <varname>After=</varname> on
    <filename>basic.target</filename> as well as dependencies of type <varname>Conflicts=</varname> and
    <varname>Before=</varname> on <filename>shutdown.target</filename>. These ensure that normal service units pull in
    basic system initialization, and are terminated cleanly prior to system shutdown. Only services involved with early
    boot or late system shutdown should disable this option.</para>

    <para>Instanced service units (i.e. service units with an <literal>@</literal> in their name) are assigned by
    default a per-template slice unit (see
    <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>), named after the
    template unit, containing all instances of the specific template. This slice is normally stopped at shutdown,
    together with all template instances. If that is not desired, set <varname>DefaultDependencies=no</varname> in the
    template unit, and either define your own per-template slice unit file that also sets
    <varname>DefaultDependencies=no</varname>, or set <varname>Slice=system.slice</varname> (or another suitable slice)
    in the template unit. Also see
    <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

    <para>Additional implicit dependencies may be added as result of
    execution and resource control parameters as documented in
    <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    and
    <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>Service files must include a <literal>[Service]</literal>
    section, which carries information about the service and the
    process it supervises. A number of options that may be used in
    this section are shared with other unit types. These options are
    documented in
    <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    and
    <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    The options specific to the <literal>[Service]</literal> section
    of service units are the following:</para>

    <variablelist class='unit-directives'>
      <varlistentry>
        <term><varname>Type=</varname></term>

        <listitem><para>Configures the process start-up type for this
        service unit. One of
        <option>simple</option>,
        <option>forking</option>,
        <option>oneshot</option>,
        <option>dbus</option>,
        <option>notify</option> or
        <option>idle</option>.</para>

        <para>If set to <option>simple</option> (the default if
        neither <varname>Type=</varname> nor
        <varname>BusName=</varname>, but <varname>ExecStart=</varname>
        are specified), it is expected that the process configured
        with <varname>ExecStart=</varname> is the main process of the
        service. In this mode, if the process offers functionality to
        other processes on the system, its communication channels
        should be installed before the daemon is started up (e.g.
        sockets set up by systemd, via socket activation), as systemd
        will immediately proceed starting follow-up units.</para>

        <para>If set to <option>forking</option>, it is expected that
        the process configured with <varname>ExecStart=</varname> will
        call <function>fork()</function> as part of its start-up. The
        parent process is expected to exit when start-up is complete
        and all communication channels are set up. The child continues
        to run as the main daemon process. This is the behavior of
        traditional UNIX daemons. If this setting is used, it is
        recommended to also use the <varname>PIDFile=</varname>
        option, so that systemd can identify the main process of the
        daemon. systemd will proceed with starting follow-up units as
        soon as the parent process exits.</para>

        <para>Behavior of <option>oneshot</option> is similar to
        <option>simple</option>; however, it is expected that the
        process has to exit before systemd starts follow-up units.
        <varname>RemainAfterExit=</varname> is particularly useful for
        this type of service. This is the implied default if neither
        <varname>Type=</varname> or <varname>ExecStart=</varname> are
        specified.</para>

        <para>Behavior of <option>dbus</option> is similar to
        <option>simple</option>; however, it is expected that the
        daemon acquires a name on the D-Bus bus, as configured by
        <varname>BusName=</varname>. systemd will proceed with
        starting follow-up units after the D-Bus bus name has been
        acquired. Service units with this option configured implicitly
        gain dependencies on the <filename>dbus.socket</filename>
        unit. This type is the default if <varname>BusName=</varname>
        is specified.</para>

        <para>Behavior of <option>notify</option> is similar to
        <option>simple</option>; however, it is expected that the
        daemon sends a notification message via
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        or an equivalent call when it has finished starting up.
        systemd will proceed with starting follow-up units after this
        notification message has been sent. If this option is used,
        <varname>NotifyAccess=</varname> (see below) should be set to
        open access to the notification socket provided by systemd. If
        <varname>NotifyAccess=</varname> is missing or set to
        <option>none</option>, it will be forcibly set to
        <option>main</option>. Note that currently
        <varname>Type=</varname><option>notify</option> will not work
        if used in combination with
        <varname>PrivateNetwork=</varname><option>yes</option>.</para>

        <para>Behavior of <option>idle</option> is very similar to <option>simple</option>; however, actual execution
        of the service binary is delayed until all active jobs are dispatched. This may be used to avoid interleaving
        of output of shell services with the status output on the console. Note that this type is useful only to
        improve console output, it is not useful as a general unit ordering tool, and the effect of this service type
        is subject to a 5s time-out, after which the service binary is invoked anyway.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RemainAfterExit=</varname></term>

        <listitem><para>Takes a boolean value that specifies whether
        the service shall be considered active even when all its
        processes exited. Defaults to <option>no</option>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>GuessMainPID=</varname></term>

        <listitem><para>Takes a boolean value that specifies whether
        systemd should try to guess the main PID of a service if it
        cannot be determined reliably. This option is ignored unless
        <option>Type=forking</option> is set and
        <option>PIDFile=</option> is unset because for the other types
        or with an explicitly configured PID file, the main PID is
        always known. The guessing algorithm might come to incorrect
        conclusions if a daemon consists of more than one process. If
        the main PID cannot be determined, failure detection and
        automatic restarting of a service will not work reliably.
        Defaults to <option>yes</option>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>PIDFile=</varname></term>

        <listitem><para>Takes an absolute file name pointing to the
        PID file of this daemon. Use of this option is recommended for
        services where <varname>Type=</varname> is set to
        <option>forking</option>. systemd will read the PID of the
        main process of the daemon after start-up of the service.
        systemd will not write to the file configured here, although
        it will remove the file after the service has shut down if it
        still exists.
        </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>BusName=</varname></term>

        <listitem><para>Takes a D-Bus bus name that this service is
        reachable as. This option is mandatory for services where
        <varname>Type=</varname> is set to
        <option>dbus</option>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ExecStart=</varname></term>
        <listitem><para>Commands with their arguments that are
        executed when this service is started. The value is split into
        zero or more command lines according to the rules described
        below (see section "Command Lines" below).
        </para>

        <para>Unless <varname>Type=</varname> is <option>oneshot</option>, exactly one command must be given. When
        <varname>Type=oneshot</varname> is used, zero or more commands may be specified. Commands may be specified by
        providing multiple command lines in the same directive, or alternatively, this directive may be specified more
        than once with the same effect. If the empty string is assigned to this option, the list of commands to start
        is reset, prior assignments of this option will have no effect. If no <varname>ExecStart=</varname> is
        specified, then the service must have <varname>RemainAfterExit=yes</varname> set.</para>

        <para>For each of the specified commands, the first argument must be an absolute path to an
        executable. Optionally, if this file name is prefixed with <literal>@</literal>, the second token will be
        passed as <literal>argv[0]</literal> to the executed process, followed by the further arguments specified.  If
        the absolute filename is prefixed with <literal>-</literal>, an exit code of the command normally considered a
        failure (i.e. non-zero exit status or abnormal exit due to signal) is ignored and considered success.  If the
        absolute path is prefixed with <literal>+</literal> then it is executed with full
        privileges. <literal>@</literal>, <literal>-</literal>, and <literal>+</literal> may be used together and they
        can appear in any order.</para>

        <para>If more than one command is specified, the commands are
        invoked sequentially in the order they appear in the unit
        file. If one of the commands fails (and is not prefixed with
        <literal>-</literal>), other lines are not executed, and the
        unit is considered failed.</para>

        <para>Unless <varname>Type=forking</varname> is set, the
        process started via this command line will be considered the
        main process of the daemon.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ExecStartPre=</varname></term>
        <term><varname>ExecStartPost=</varname></term>
        <listitem><para>Additional commands that are executed before
        or after the command in <varname>ExecStart=</varname>,
        respectively. Syntax is the same as for
        <varname>ExecStart=</varname>, except that multiple command
        lines are allowed and the commands are executed one after the
        other, serially.</para>

        <para>If any of those commands (not prefixed with
        <literal>-</literal>) fail, the rest are not executed and the
        unit is considered failed.</para>

        <para><varname>ExecStart=</varname> commands are only run after
        all <varname>ExecStartPre=</varname> commands that were not prefixed
        with a <literal>-</literal> exit successfully.</para>

        <para><varname>ExecStartPost=</varname> commands are only run after
        the service has started successfully, as determined by <varname>Type=</varname>
        (i.e. the process has been started for <varname>Type=simple</varname>
        or <varname>Type=idle</varname>, the process exits successfully for
        <varname>Type=oneshot</varname>, the initial process exits successfully
        for <varname>Type=forking</varname>, <literal>READY=1</literal> is sent
        for <varname>Type=notify</varname>, or the <varname>BusName=</varname>
        has been taken for <varname>Type=dbus</varname>).</para>

        <para>Note that <varname>ExecStartPre=</varname> may not be
        used to start long-running processes. All processes forked
        off by processes invoked via <varname>ExecStartPre=</varname> will
        be killed before the next service process is run.</para>

        <para>Note that if any of the commands specified in <varname>ExecStartPre=</varname>,
        <varname>ExecStart=</varname>, or <varname>ExecStartPost=</varname> fail (and are not prefixed with
        <literal>-</literal>, see above) or time out before the service is fully up, execution continues with commands
        specified in <varname>ExecStopPost=</varname>, the commands in <varname>ExecStop=</varname> are skipped.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ExecReload=</varname></term>
        <listitem><para>Commands to execute to trigger a configuration
        reload in the service. This argument takes multiple command
        lines, following the same scheme as described for
        <varname>ExecStart=</varname> above. Use of this setting is
        optional. Specifier and environment variable substitution is
        supported here following the same scheme as for
        <varname>ExecStart=</varname>.</para>

        <para>One additional, special environment variable is set: if
        known, <varname>$MAINPID</varname> is set to the main process
        of the daemon, and may be used for command lines like the
        following:</para>

        <programlisting>/bin/kill -HUP $MAINPID</programlisting>

        <para>Note however that reloading a daemon by sending a signal
        (as with the example line above) is usually not a good choice,
        because this is an asynchronous operation and hence not
        suitable to order reloads of multiple services against each
        other. It is strongly recommended to set
        <varname>ExecReload=</varname> to a command that not only
        triggers a configuration reload of the daemon, but also
        synchronously waits for it to complete.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ExecStop=</varname></term>
        <listitem><para>Commands to execute to stop the service
        started via <varname>ExecStart=</varname>. This argument takes
        multiple command lines, following the same scheme as described
        for <varname>ExecStart=</varname> above. Use of this setting
        is optional. After the commands configured in this option are
        run, all processes remaining for a service are terminated
        according to the <varname>KillMode=</varname> setting (see
        <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
        If this option is not specified, the process is terminated by
        sending the signal specified in <varname>KillSignal=</varname>
        when service stop is requested. Specifier and environment
        variable substitution is supported (including
        <varname>$MAINPID</varname>, see above).</para>

        <para>Note that it is usually not sufficient to specify a
        command for this setting that only asks the service to
        terminate (for example, by queuing some form of termination
        signal for it), but does not wait for it to do so. Since the
        remaining processes of the services are killed using
        <constant>SIGKILL</constant> immediately after the command
        exited, this would not result in a clean stop. The specified
        command should hence be a synchronous operation, not an
        asynchronous one.</para>

        <para>Note that the commands specified in <varname>ExecStop=</varname> are only executed when the service
        started successfully first. They are not invoked if the service was never started at all, or in case its
        start-up failed, for example because any of the commands specified in <varname>ExecStart=</varname>,
        <varname>ExecStartPre=</varname> or <varname>ExecStartPost=</varname> failed (and weren't prefixed with
        <literal>-</literal>, see above) or timed out. Use <varname>ExecStopPost=</varname> to invoke commands when a
        service failed to start up correctly and is shut down again.</para>

        <para>It is recommended to use this setting for commands that communicate with the service requesting clean
        termination. When the commands specified with this option are executed it should be assumed that the service is
        still fully up and is able to react correctly to all commands. For post-mortem clean-up steps use
        <varname>ExecStopPost=</varname> instead.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ExecStopPost=</varname></term>
        <listitem><para>Additional commands that are executed after the service is stopped. This includes cases where
        the commands configured in <varname>ExecStop=</varname> were used, where the service does not have any
        <varname>ExecStop=</varname> defined, or where the service exited unexpectedly. This argument takes multiple
        command lines, following the same scheme as described for <varname>ExecStart=</varname>. Use of these settings
        is optional. Specifier and environment variable substitution is supported. Note that – unlike
        <varname>ExecStop=</varname> – commands specified with this setting are invoked when a service failed to start
        up correctly and is shut down again.</para>

        <para>It is recommended to use this setting for clean-up operations that shall be executed even when the
        service failed to start up correctly. Commands configured with this setting need to be able to operate even if
        the service failed starting up half-way and left incompletely initialized data around. As the service's
        processes have been terminated already when the commands specified with this setting are executed they should
        not attempt to communicate with them.</para>

        <para>Note that all commands that are configured with this setting are invoked with the result code of the
        service, as well as the main process' exit code and status, set in the <varname>$SERVICE_RESULT</varname>,
        <varname>$EXIT_CODE</varname> and <varname>$EXIT_STATUS</varname> environment variables, see
        <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
        details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RestartSec=</varname></term>
        <listitem><para>Configures the time to sleep before restarting
        a service (as configured with <varname>Restart=</varname>).
        Takes a unit-less value in seconds, or a time span value such
        as "5min 20s". Defaults to 100ms.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>TimeoutStartSec=</varname></term>
        <listitem><para>Configures the time to wait for start-up. If a
        daemon service does not signal start-up completion within the
        configured time, the service will be considered failed and
        will be shut down again. Takes a unit-less value in seconds,
        or a time span value such as "5min 20s". Pass
        <literal>infinity</literal> to disable the timeout logic. Defaults to
        <varname>DefaultTimeoutStartSec=</varname> from the manager
        configuration file, except when
        <varname>Type=oneshot</varname> is used, in which case the
        timeout is disabled by default (see
        <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>TimeoutStopSec=</varname></term>
        <listitem><para>Configures the time to wait for stop. If a
        service is asked to stop, but does not terminate in the
        specified time, it will be terminated forcibly via
        <constant>SIGTERM</constant>, and after another timeout of
        equal duration with <constant>SIGKILL</constant> (see
        <varname>KillMode=</varname> in
        <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
        Takes a unit-less value in seconds, or a time span value such
        as "5min 20s". Pass <literal>infinity</literal> to disable the
        timeout logic. Defaults to
        <varname>DefaultTimeoutStopSec=</varname> from the manager
        configuration file (see
        <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>TimeoutSec=</varname></term>
        <listitem><para>A shorthand for configuring both
        <varname>TimeoutStartSec=</varname> and
        <varname>TimeoutStopSec=</varname> to the specified value.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RuntimeMaxSec=</varname></term>

        <listitem><para>Configures a maximum time for the service to run. If this is used and the service has been
        active for longer than the specified time it is terminated and put into a failure state. Note that this setting
        does not have any effect on <varname>Type=oneshot</varname> services, as they terminate immediately after
        activation completed. Pass <literal>infinity</literal> (the default) to configure no runtime
        limit.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>WatchdogSec=</varname></term>
        <listitem><para>Configures the watchdog timeout for a service.
        The watchdog is activated when the start-up is completed. The
        service must call
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        regularly with <literal>WATCHDOG=1</literal> (i.e. the
        "keep-alive ping"). If the time between two such calls is
        larger than the configured time, then the service is placed in
        a failed state and it will be terminated with
        <constant>SIGABRT</constant>. By setting
        <varname>Restart=</varname> to <option>on-failure</option>,
        <option>on-watchdog</option>, <option>on-abnormal</option> or
        <option>always</option>, the service will be automatically
        restarted. The time configured here will be passed to the
        executed service process in the
        <varname>WATCHDOG_USEC=</varname> environment variable. This
        allows daemons to automatically enable the keep-alive pinging
        logic if watchdog support is enabled for the service. If this
        option is used, <varname>NotifyAccess=</varname> (see below)
        should be set to open access to the notification socket
        provided by systemd. If <varname>NotifyAccess=</varname> is
        not set, it will be implicitly set to <option>main</option>.
        Defaults to 0, which disables this feature. The service can
        check whether the service manager expects watchdog keep-alive
        notifications. See
        <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        for details.
        <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        may be used to enable automatic watchdog notification support.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>Restart=</varname></term>
        <listitem><para>Configures whether the service shall be
        restarted when the service process exits, is killed, or a
        timeout is reached. The service process may be the main
        service process, but it may also be one of the processes
        specified with <varname>ExecStartPre=</varname>,
        <varname>ExecStartPost=</varname>,
        <varname>ExecStop=</varname>,
        <varname>ExecStopPost=</varname>, or
        <varname>ExecReload=</varname>. When the death of the process
        is a result of systemd operation (e.g. service stop or
        restart), the service will not be restarted. Timeouts include
        missing the watchdog "keep-alive ping" deadline and a service
        start, reload, and stop operation timeouts.</para>

        <para>Takes one of
        <option>no</option>,
        <option>on-success</option>,
        <option>on-failure</option>,
        <option>on-abnormal</option>,
        <option>on-watchdog</option>,
        <option>on-abort</option>, or
        <option>always</option>.
        If set to <option>no</option> (the default), the service will
        not be restarted. If set to <option>on-success</option>, it
        will be restarted only when the service process exits cleanly.
        In this context, a clean exit means an exit code of 0, or one
        of the signals
        <constant>SIGHUP</constant>,
        <constant>SIGINT</constant>,
        <constant>SIGTERM</constant> or
        <constant>SIGPIPE</constant>, and
        additionally, exit statuses and signals specified in
        <varname>SuccessExitStatus=</varname>. If set to
        <option>on-failure</option>, the service will be restarted
        when the process exits with a non-zero exit code, is
        terminated by a signal (including on core dump, but excluding
        the aforementioned four signals), when an operation (such as
        service reload) times out, and when the configured watchdog
        timeout is triggered. If set to <option>on-abnormal</option>,
        the service will be restarted when the process is terminated
        by a signal (including on core dump, excluding the
        aforementioned four signals), when an operation times out, or
        when the watchdog timeout is triggered. If set to
        <option>on-abort</option>, the service will be restarted only
        if the service process exits due to an uncaught signal not
        specified as a clean exit status. If set to
        <option>on-watchdog</option>, the service will be restarted
        only if the watchdog timeout for the service expires. If set
        to <option>always</option>, the service will be restarted
        regardless of whether it exited cleanly or not, got terminated
        abnormally by a signal, or hit a timeout.</para>

        <table>
          <title>Exit causes and the effect of the <varname>Restart=</varname> settings on them</title>

          <tgroup cols='2'>
            <colspec colname='path' />
            <colspec colname='expl' />
            <thead>
              <row>
                <entry>Restart settings/Exit causes</entry>
                <entry><option>no</option></entry>
                <entry><option>always</option></entry>
                <entry><option>on-success</option></entry>
                <entry><option>on-failure</option></entry>
                <entry><option>on-abnormal</option></entry>
                <entry><option>on-abort</option></entry>
                <entry><option>on-watchdog</option></entry>
              </row>
            </thead>
            <tbody>
              <row>
                <entry>Clean exit code or signal</entry>
                <entry/>
                <entry>X</entry>
                <entry>X</entry>
                <entry/>
                <entry/>
                <entry/>
                <entry/>
              </row>
              <row>
                <entry>Unclean exit code</entry>
                <entry/>
                <entry>X</entry>
                <entry/>
                <entry>X</entry>
                <entry/>
                <entry/>
                <entry/>
              </row>
              <row>
                <entry>Unclean signal</entry>
                <entry/>
                <entry>X</entry>
                <entry/>
                <entry>X</entry>
                <entry>X</entry>
                <entry>X</entry>
                <entry/>
              </row>
              <row>
                <entry>Timeout</entry>
                <entry/>
                <entry>X</entry>
                <entry/>
                <entry>X</entry>
                <entry>X</entry>
                <entry/>
                <entry/>
              </row>
              <row>
                <entry>Watchdog</entry>
                <entry/>
                <entry>X</entry>
                <entry/>
                <entry>X</entry>
                <entry>X</entry>
                <entry/>
                <entry>X</entry>
              </row>
            </tbody>
          </tgroup>
        </table>

        <para>As exceptions to the setting above, the service will not
        be restarted if the exit code or signal is specified in
        <varname>RestartPreventExitStatus=</varname> (see below).
        Also, the services will always be restarted if the exit code
        or signal is specified in
        <varname>RestartForceExitStatus=</varname> (see below).</para>

        <para>Note that service restart is subject to unit start rate
        limiting configured with <varname>StartLimitIntervalSec=</varname>
        and <varname>StartLimitBurst=</varname>, see
        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        for details.</para>

        <para>Setting this to <option>on-failure</option> is the
        recommended choice for long-running services, in order to
        increase reliability by attempting automatic recovery from
        errors. For services that shall be able to terminate on their
        own choice (and avoid immediate restarting),
        <option>on-abnormal</option> is an alternative choice.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>SuccessExitStatus=</varname></term>
        <listitem><para>Takes a list of exit status definitions that,
        when returned by the main service process, will be considered
        successful termination, in addition to the normal successful
        exit code 0 and the signals <constant>SIGHUP</constant>,
        <constant>SIGINT</constant>, <constant>SIGTERM</constant>, and
        <constant>SIGPIPE</constant>. Exit status definitions can
        either be numeric exit codes or termination signal names,
        separated by spaces. For example:

        <programlisting>SuccessExitStatus=1 2 8 SIGKILL</programlisting>

        ensures that exit codes 1, 2, 8 and
        the termination signal <constant>SIGKILL</constant> are
        considered clean service terminations.
        </para>

        <para>Note that if a process has a signal handler installed
        and exits by calling
        <citerefentry><refentrytitle>_exit</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        in response to a signal, the information about the signal is
        lost. Programs should instead perform cleanup and kill
        themselves with the same signal instead. See
        <ulink url="http://www.cons.org/cracauer/sigint.html">Proper
        handling of SIGINT/SIGQUIT — How to be a proper
        program</ulink>.</para>

        <para>This option may appear more than once, in which case the
        list of successful exit statuses is merged. If the empty
        string is assigned to this option, the list is reset, all
        prior assignments of this option will have no
        effect.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RestartPreventExitStatus=</varname></term>
        <listitem><para>Takes a list of exit status definitions that,
        when returned by the main service process, will prevent
        automatic service restarts, regardless of the restart setting
        configured with <varname>Restart=</varname>. Exit status
        definitions can either be numeric exit codes or termination
        signal names, and are separated by spaces. Defaults to the
        empty list, so that, by default, no exit status is excluded
        from the configured restart logic. For example:

        <programlisting>RestartPreventExitStatus=1 6 SIGABRT</programlisting>

        ensures that exit codes 1 and 6 and the termination signal
        <constant>SIGABRT</constant> will not result in automatic
        service restarting. This option may appear more than once, in
        which case the list of restart-preventing statuses is
        merged. If the empty string is assigned to this option, the
        list is reset and all prior assignments of this option will
        have no effect.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RestartForceExitStatus=</varname></term>
        <listitem><para>Takes a list of exit status definitions that,
        when returned by the main service process, will force automatic
        service restarts, regardless of the restart setting configured
        with <varname>Restart=</varname>. The argument format is
        similar to
        <varname>RestartPreventExitStatus=</varname>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>PermissionsStartOnly=</varname></term>
        <listitem><para>Takes a boolean argument. If true, the
        permission-related execution options, as configured with
        <varname>User=</varname> and similar options (see
        <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        for more information), are only applied to the process started
        with
        <varname>ExecStart=</varname>, and not to the various other
        <varname>ExecStartPre=</varname>,
        <varname>ExecStartPost=</varname>,
        <varname>ExecReload=</varname>,
        <varname>ExecStop=</varname>, and
        <varname>ExecStopPost=</varname>
        commands. If false, the setting is applied to all configured
        commands the same way. Defaults to false.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RootDirectoryStartOnly=</varname></term>
        <listitem><para>Takes a boolean argument. If true, the root
        directory, as configured with the
        <varname>RootDirectory=</varname> option (see
        <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        for more information), is only applied to the process started
        with <varname>ExecStart=</varname>, and not to the various
        other <varname>ExecStartPre=</varname>,
        <varname>ExecStartPost=</varname>,
        <varname>ExecReload=</varname>, <varname>ExecStop=</varname>,
        and <varname>ExecStopPost=</varname> commands. If false, the
        setting is applied to all configured commands the same way.
        Defaults to false.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>NonBlocking=</varname></term>
        <listitem><para>Set the <constant>O_NONBLOCK</constant> flag
        for all file descriptors passed via socket-based activation.
        If true, all file descriptors >= 3 (i.e. all except stdin,
        stdout, and stderr) will have the
        <constant>O_NONBLOCK</constant> flag set and hence are in
        non-blocking mode. This option is only useful in conjunction
        with a socket unit, as described in
        <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
        Defaults to false.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>NotifyAccess=</varname></term>
        <listitem><para>Controls access to the service status
        notification socket, as accessible via the
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        call. Takes one of <option>none</option> (the default),
        <option>main</option>, <option>exec</option> or
        <option>all</option>. If <option>none</option>, no daemon status
        updates are accepted from the service processes, all status
        update messages are ignored. If <option>main</option>, only
        service updates sent from the main process of the service are
        accepted. If <option>exec</option>, only service updates sent
        from any of the control processes originating from one of the
        <varname>Exec*=</varname> commands are accepted. If
        <option>all</option>, all services updates from all members of
        the service's control group are accepted. This option should
        be set to open access to the notification socket when using
        <varname>Type=notify</varname> or
        <varname>WatchdogSec=</varname> (see above). If those options
        are used but <varname>NotifyAccess=</varname> is not
        configured, it will be implicitly set to
        <option>main</option>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>Sockets=</varname></term>
        <listitem><para>Specifies the name of the socket units this
        service shall inherit socket file descriptors from when the
        service is started. Normally, it should not be necessary to use
        this setting, as all socket file descriptors whose unit shares
        the same name as the service (subject to the different unit
        name suffix of course) are passed to the spawned
        process.</para>

        <para>Note that the same socket file descriptors may be passed
        to multiple processes simultaneously. Also note that a
        different service may be activated on incoming socket traffic
        than the one which is ultimately configured to inherit the
        socket file descriptors. Or, in other words: the
        <varname>Service=</varname> setting of
        <filename>.socket</filename> units does not have to match the
        inverse of the <varname>Sockets=</varname> setting of the
        <filename>.service</filename> it refers to.</para>

        <para>This option may appear more than once, in which case the
        list of socket units is merged. If the empty string is
        assigned to this option, the list of sockets is reset, and all
        prior uses of this setting will have no
        effect.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>FailureAction=</varname></term>
        <listitem><para>Configure the action to take when the service enters a failed state. Takes the same values as
        the unit setting <varname>StartLimitAction=</varname> and executes the same actions (see
        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>). Defaults to
        <option>none</option>. </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>FileDescriptorStoreMax=</varname></term>
        <listitem><para>Configure how many file descriptors may be
        stored in the service manager for the service using
        <citerefentry><refentrytitle>sd_pid_notify_with_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>'s
        <literal>FDSTORE=1</literal> messages. This is useful for
        implementing service restart schemes where the state is
        serialized to <filename>/run</filename> and the file
        descriptors passed to the service manager, to allow restarts
        without losing state. Defaults to 0, i.e. no file descriptors
        may be stored in the service manager. All file
        descriptors passed to the service manager from a specific
        service are passed back to the service's main process on the
        next service restart. Any file descriptors passed to the
        service manager are automatically closed when POLLHUP or
        POLLERR is seen on them, or when the service is fully stopped
        and no job is queued or being executed for it.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>USBFunctionDescriptors=</varname></term>
        <listitem><para>Configure the location of a file containing
        <ulink
        url="https://www.kernel.org/doc/Documentation/usb/functionfs.txt">USB
        FunctionFS</ulink> descriptors, for implementation of USB
        gadget functions. This is used only in conjunction with a
        socket unit with <varname>ListenUSBFunction=</varname>
        configured. The contents of this file are written to the
        <filename>ep0</filename> file after it is
        opened.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>USBFunctionStrings=</varname></term>
        <listitem><para>Configure the location of a file containing
        USB FunctionFS strings.  Behavior is similar to
        <varname>USBFunctionDescriptors=</varname>
        above.</para></listitem>
      </varlistentry>

    </variablelist>

    <para>Check
    <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    and
    <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for more settings.</para>

  </refsect1>

  <refsect1>
    <title>Command lines</title>

    <para>This section describes command line parsing and
    variable and specifier substitutions for
    <varname>ExecStart=</varname>,
    <varname>ExecStartPre=</varname>,
    <varname>ExecStartPost=</varname>,
    <varname>ExecReload=</varname>,
    <varname>ExecStop=</varname>, and
    <varname>ExecStopPost=</varname> options.</para>

    <para>Multiple command lines may be concatenated in a single
    directive by separating them with semicolons (these semicolons
    must be passed as separate words). Lone semicolons may be escaped
    as <literal>\;</literal>.</para>

    <para>Each command line is split on whitespace, with the first
    item being the command to execute, and the subsequent items being
    the arguments. Double quotes ("...") and single quotes ('...') may
    be used, in which case everything until the next matching quote
    becomes part of the same argument. C-style escapes are also
    supported. The table below contains the list of allowed escape
    patterns. Only patterns which match the syntax in the table are
    allowed; others will result in an error, and must be escaped by
    doubling the backslash. Quotes themselves are removed after
    parsing and escape sequences substituted. In addition, a trailing
    backslash (<literal>\</literal>) may be used to merge lines.
    </para>

    <para>This syntax is intended to be very similar to shell syntax,
    but only the meta-characters and expansions described in the
    following paragraphs are understood. Specifically, redirection
    using
    <literal>&lt;</literal>,
    <literal>&lt;&lt;</literal>,
    <literal>&gt;</literal>, and
    <literal>&gt;&gt;</literal>, pipes using
    <literal>|</literal>, running programs in the background using
    <literal>&amp;</literal>, and <emphasis>other elements of shell
    syntax are not supported</emphasis>.</para>

    <para>The command to execute must be an absolute path name. It may
    contain spaces, but control characters are not allowed.</para>

    <para>The command line accepts <literal>%</literal> specifiers as
    described in
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    Note that the first argument of the command line (i.e. the program
    to execute) may not include specifiers.</para>

    <para>Basic environment variable substitution is supported. Use
    <literal>${FOO}</literal> as part of a word, or as a word of its
    own, on the command line, in which case it will be replaced by the
    value of the environment variable including all whitespace it
    contains, resulting in a single argument. Use
    <literal>$FOO</literal> as a separate word on the command line, in
    which case it will be replaced by the value of the environment
    variable split at whitespace, resulting in zero or more arguments.
    For this type of expansion, quotes are respected when splitting
    into words, and afterwards removed.</para>

    <para>Example:</para>

    <programlisting>Environment="ONE=one" 'TWO=two two'
ExecStart=/bin/echo $ONE $TWO ${TWO}</programlisting>

    <para>This will execute <command>/bin/echo</command> with four
    arguments: <literal>one</literal>, <literal>two</literal>,
    <literal>two</literal>, and <literal>two two</literal>.</para>

    <para>Example:</para>
    <programlisting>Environment=ONE='one' "TWO='two two' too" THREE=
ExecStart=/bin/echo ${ONE} ${TWO} ${THREE}
ExecStart=/bin/echo $ONE $TWO $THREE</programlisting>
    <para>This results in <filename>echo</filename> being
    called twice, the first time with arguments
    <literal>'one'</literal>,
    <literal>'two two' too</literal>, <literal></literal>,
    and the second time with arguments
    <literal>one</literal>, <literal>two two</literal>,
    <literal>too</literal>.
    </para>

    <para>To pass a literal dollar sign, use <literal>$$</literal>.
    Variables whose value is not known at expansion time are treated
    as empty strings. Note that the first argument (i.e. the program
    to execute) may not be a variable.</para>

    <para>Variables to be used in this fashion may be defined through
    <varname>Environment=</varname> and
    <varname>EnvironmentFile=</varname>. In addition, variables listed
    in the section "Environment variables in spawned processes" in
    <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    which are considered "static configuration", may be used (this
    includes e.g. <varname>$USER</varname>, but not
    <varname>$TERM</varname>).</para>

    <para>Note that shell command lines are not directly supported. If
    shell command lines are to be used, they need to be passed
    explicitly to a shell implementation of some kind. Example:</para>
    <programlisting>ExecStart=/bin/sh -c 'dmesg | tac'</programlisting>

    <para>Example:</para>

    <programlisting>ExecStart=/bin/echo one ; /bin/echo "two two"</programlisting>

    <para>This will execute <command>/bin/echo</command> two times,
    each time with one argument: <literal>one</literal> and
    <literal>two two</literal>, respectively. Because two commands are
    specified, <varname>Type=oneshot</varname> must be used.</para>

    <para>Example:</para>

    <programlisting>ExecStart=/bin/echo / &gt;/dev/null &amp; \; \
/bin/ls</programlisting>

    <para>This will execute <command>/bin/echo</command>
    with five arguments: <literal>/</literal>,
    <literal>&gt;/dev/null</literal>,
    <literal>&amp;</literal>, <literal>;</literal>, and
    <literal>/bin/ls</literal>.</para>

    <table>
      <title>C escapes supported in command lines and environment variables</title>
      <tgroup cols='2'>
        <colspec colname='escape' />
        <colspec colname='meaning' />
        <thead>
          <row>
            <entry>Literal</entry>
            <entry>Actual value</entry>
          </row>
        </thead>
        <tbody>
          <row>
            <entry><literal>\a</literal></entry>
            <entry>bell</entry>
          </row>
          <row>
            <entry><literal>\b</literal></entry>
            <entry>backspace</entry>
          </row>
          <row>
            <entry><literal>\f</literal></entry>
            <entry>form feed</entry>
          </row>
          <row>
            <entry><literal>\n</literal></entry>
            <entry>newline</entry>
          </row>
          <row>
            <entry><literal>\r</literal></entry>
            <entry>carriage return</entry>
          </row>
          <row>
            <entry><literal>\t</literal></entry>
            <entry>tab</entry>
          </row>
          <row>
            <entry><literal>\v</literal></entry>
            <entry>vertical tab</entry>
          </row>
          <row>
            <entry><literal>\\</literal></entry>
            <entry>backslash</entry>
          </row>
          <row>
            <entry><literal>\"</literal></entry>
            <entry>double quotation mark</entry>
          </row>
          <row>
            <entry><literal>\'</literal></entry>
            <entry>single quotation mark</entry>
          </row>
          <row>
            <entry><literal>\s</literal></entry>
            <entry>space</entry>
          </row>
          <row>
            <entry><literal>\x<replaceable>xx</replaceable></literal></entry>
            <entry>character number <replaceable>xx</replaceable> in hexadecimal encoding</entry>
          </row>
          <row>
            <entry><literal>\<replaceable>nnn</replaceable></literal></entry>
            <entry>character number <replaceable>nnn</replaceable> in octal encoding</entry>
          </row>
        </tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    <title>Examples</title>

    <example>
      <title>Simple service</title>

      <para>The following unit file creates a service that will
      execute <filename>/usr/sbin/foo-daemon</filename>. Since no
      <varname>Type=</varname> is specified, the default
      <varname>Type=</varname><option>simple</option> will be assumed.
      systemd will assume the unit to be started immediately after the
      program has begun executing.</para>

      <programlisting>[Unit]
Description=Foo

[Service]
ExecStart=/usr/sbin/foo-daemon

[Install]
WantedBy=multi-user.target</programlisting>

      <para>Note that systemd assumes here that the process started by
      systemd will continue running until the service terminates. If
      the program daemonizes itself (i.e. forks), please use
      <varname>Type=</varname><option>forking</option> instead.</para>

      <para>Since no <varname>ExecStop=</varname> was specified,
      systemd will send SIGTERM to all processes started from this
      service, and after a timeout also SIGKILL. This behavior can be
      modified, see
      <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
      for details.</para>

      <para>Note that this unit type does not include any type of
      notification when a service has completed initialization. For
      this, you should use other unit types, such as
      <varname>Type=</varname><option>notify</option> if the service
      understands systemd's notification protocol,
      <varname>Type=</varname><option>forking</option> if the service
      can background itself or
      <varname>Type=</varname><option>dbus</option> if the unit
      acquires a DBus name once initialization is complete. See
      below.</para>
    </example>

    <example>
      <title>Oneshot service</title>

      <para>Sometimes, units should just execute an action without
      keeping active processes, such as a filesystem check or a
      cleanup action on boot. For this,
      <varname>Type=</varname><option>oneshot</option> exists. Units
      of this type will wait until the process specified terminates
      and then fall back to being inactive. The following unit will
      perform a cleanup action:</para>

      <programlisting>[Unit]
Description=Cleanup old Foo data

[Service]
Type=oneshot
ExecStart=/usr/sbin/foo-cleanup

[Install]
WantedBy=multi-user.target</programlisting>

      <para>Note that systemd will consider the unit to be in the
      state "starting" until the program has terminated, so ordered
      dependencies will wait for the program to finish before starting
      themselves. The unit will revert to the "inactive" state after
      the execution is done, never reaching the "active" state. That
      means another request to start the unit will perform the action
      again.</para>

      <para><varname>Type=</varname><option>oneshot</option> are the
      only service units that may have more than one
      <varname>ExecStart=</varname> specified. They will be executed
      in order until either they are all successful or one of them
      fails.</para>
    </example>

    <example>
      <title>Stoppable oneshot service</title>

      <para>Similarly to the oneshot services, there are sometimes
      units that need to execute a program to set up something and
      then execute another to shut it down, but no process remains
      active while they are considered "started". Network
      configuration can sometimes fall into this category. Another use
      case is if a oneshot service shall not be executed each time
      when they are pulled in as a dependency, but only the first
      time.</para>

      <para>For this, systemd knows the setting
      <varname>RemainAfterExit=</varname><option>yes</option>, which
      causes systemd to consider the unit to be active if the start
      action exited successfully. This directive can be used with all
      types, but is most useful with
      <varname>Type=</varname><option>oneshot</option> and
      <varname>Type=</varname><option>simple</option>. With
      <varname>Type=</varname><option>oneshot</option>, systemd waits
      until the start action has completed before it considers the
      unit to be active, so dependencies start only after the start
      action has succeeded. With
      <varname>Type=</varname><option>simple</option>, dependencies
      will start immediately after the start action has been
      dispatched. The following unit provides an example for a simple
      static firewall.</para>

      <programlisting>[Unit]
Description=Simple firewall

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/local/sbin/simple-firewall-start
ExecStop=/usr/local/sbin/simple-firewall-stop

[Install]
WantedBy=multi-user.target</programlisting>

      <para>Since the unit is considered to be running after the start
      action has exited, invoking <command>systemctl start</command>
      on that unit again will cause no action to be taken.</para>
    </example>

    <example>
      <title>Traditional forking services</title>

      <para>Many traditional daemons/services background (i.e. fork,
      daemonize) themselves when starting. Set
      <varname>Type=</varname><option>forking</option> in the
      service's unit file to support this mode of operation. systemd
      will consider the service to be in the process of initialization
      while the original program is still running. Once it exits
      successfully and at least a process remains (and
      <varname>RemainAfterExit=</varname><option>no</option>), the
      service is considered started.</para>

      <para>Often, a traditional daemon only consists of one process.
      Therefore, if only one process is left after the original
      process terminates, systemd will consider that process the main
      process of the service. In that case, the
      <varname>$MAINPID</varname> variable will be available in
      <varname>ExecReload=</varname>, <varname>ExecStop=</varname>,
      etc.</para>

      <para>In case more than one process remains, systemd will be
      unable to determine the main process, so it will not assume
      there is one. In that case, <varname>$MAINPID</varname> will not
      expand to anything. However, if the process decides to write a
      traditional PID file, systemd will be able to read the main PID
      from there. Please set <varname>PIDFile=</varname> accordingly.
      Note that the daemon should write that file before finishing
      with its initialization. Otherwise, systemd might try to read the
      file before it exists.</para>

      <para>The following example shows a simple daemon that forks and
      just starts one process in the background:</para>

      <programlisting>[Unit]
Description=Some simple daemon

[Service]
Type=forking
ExecStart=/usr/sbin/my-simple-daemon -d

[Install]
WantedBy=multi-user.target</programlisting>

      <para>Please see
      <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
      for details on how you can influence the way systemd terminates
      the service.</para>
    </example>

    <example>
      <title>DBus services</title>

      <para>For services that acquire a name on the DBus system bus,
      use <varname>Type=</varname><option>dbus</option> and set
      <varname>BusName=</varname> accordingly. The service should not
      fork (daemonize). systemd will consider the service to be
      initialized once the name has been acquired on the system bus.
      The following example shows a typical DBus service:</para>

      <programlisting>[Unit]
Description=Simple DBus service

[Service]
Type=dbus
BusName=org.example.simple-dbus-service
ExecStart=/usr/sbin/simple-dbus-service

[Install]
WantedBy=multi-user.target</programlisting>

      <para>For <emphasis>bus-activatable</emphasis> services, do not
      include a <literal>[Install]</literal> section in the systemd
      service file, but use the <varname>SystemdService=</varname>
      option in the corresponding DBus service file, for example
      (<filename>/usr/share/dbus-1/system-services/org.example.simple-dbus-service.service</filename>):</para>

      <programlisting>[D-BUS Service]
Name=org.example.simple-dbus-service
Exec=/usr/sbin/simple-dbus-service
User=root
SystemdService=simple-dbus-service.service</programlisting>

      <para>Please see
      <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
      for details on how you can influence the way systemd terminates
      the service.</para>
    </example>

    <example>
      <title>Services that notify systemd about their initialization</title>

      <para><varname>Type=</varname><option>simple</option> services
      are really easy to write, but have the major disadvantage of
      systemd not being able to tell when initialization of the given
      service is complete. For this reason, systemd supports a simple
      notification protocol that allows daemons to make systemd aware
      that they are done initializing. Use
      <varname>Type=</varname><option>notify</option> for this. A
      typical service file for such a daemon would look like
      this:</para>

      <programlisting>[Unit]
Description=Simple notifying service

[Service]
Type=notify
ExecStart=/usr/sbin/simple-notifying-service

[Install]
WantedBy=multi-user.target</programlisting>

      <para>Note that the daemon has to support systemd's notification
      protocol, else systemd will think the service has not started yet
      and kill it after a timeout. For an example of how to update
      daemons to support this protocol transparently, take a look at
      <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
      systemd will consider the unit to be in the 'starting' state
      until a readiness notification has arrived.</para>

      <para>Please see
      <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
      for details on how you can influence the way systemd terminates
      the service.</para>
    </example>
  </refsect1>

  <refsect1>
      <title>See Also</title>
      <para>
        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
      </para>
  </refsect1>

</refentry>