summaryrefslogtreecommitdiffstats
path: root/man/systemd.service.xml
blob: 58439dfa6ee7ab6977de5a4ca5349666457d3b42 (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
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="systemd.service" xmlns:xi="http://www.w3.org/2001/XInclude">
  <refentryinfo>
    <title>systemd.service</title>
    <productname>systemd</productname>
  </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
    <literal>.service</literal> 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
    [Unit] and [Install]
    sections. The service specific configuration options are
    configured in the [Service] 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 SysV init compat is enabled, systemd automatically creates service units that wrap SysV init
    scripts (the service name is the same as the name of the script, with a <literal>.service</literal>
    suffix added); see
    <citerefentry><refentrytitle>systemd-sysv-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
    </para>

    <para>The <citerefentry><refentrytitle>systemd-run</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    command allows creating <filename>.service</filename> and <filename>.scope</filename> units dynamically
    and transiently from the command line.</para>
  </refsect1>

  <refsect1>
    <title>Service Templates</title>

    <para>It is possible for <command>systemd</command> services to take a single argument via the
    <literal><replaceable>service</replaceable>@<replaceable>argument</replaceable>.service</literal>
    syntax. Such services are called "instantiated" services, while the unit definition without the
    <replaceable>argument</replaceable> parameter is called a "template". An example could be a
    <filename>dhcpcd@.service</filename> service template which takes a network interface as a
    parameter to form an instantiated service. Within the service file, this parameter or "instance
    name" can be accessed with %-specifiers. See
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for details.</para>
  </refsect1>

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

    <refsect2>
      <title>Implicit Dependencies</title>

      <para>The following dependencies are implicitly added:</para>

      <itemizedlist>
        <listitem><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></listitem>

        <listitem><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></listitem>
      </itemizedlist>

      <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>
    </refsect2>

    <refsect2>
      <title>Default Dependencies</title>

      <para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para>

      <itemizedlist>
        <listitem><para>Service units will 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></listitem>

        <listitem><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></listitem>
      </itemizedlist>
    </refsect2>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>Service unit files may include [Unit] and [Install] sections, which are described in
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    </para>

    <para>Service unit files must include a [Service]
    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>,
    <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    and
    <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    The options specific to the [Service] section
    of service units are the following:</para>

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

        <listitem>
          <para>Configures the mechanism via which the service notifies the manager that the service start-up
          has finished. One of <option>simple</option>, <option>exec</option>, <option>forking</option>,
          <option>oneshot</option>, <option>dbus</option>, <option>notify</option>,
          <option>notify-reload</option>, or <option>idle</option>:</para>

          <itemizedlist>
            <listitem><para>If set to <option>simple</option> (the default if <varname>ExecStart=</varname>
            is specified but neither <varname>Type=</varname> nor <varname>BusName=</varname> are), the
            service manager will consider the unit started immediately after the main service process has
            been forked off (i.e. immediately after <function>fork()</function>, and before various process
            attributes have been configured and in particular before the new process has called
            <function>execve()</function> to invoke the actual service binary). Typically,
            <varname>Type=</varname><option>exec</option> is the better choice, see below.</para>

            <para>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 service is started up
            (e.g. sockets set up by systemd, via socket activation), as the service manager will immediately
            proceed starting follow-up units, right after creating the main service process, and before
            executing the service's binary. Note that this means <command>systemctl start</command> command
            lines for <option>simple</option> services will report success even if the service's binary
            cannot be invoked successfully (for example because the selected <varname>User=</varname> doesn't
            exist, or the service binary is missing).</para></listitem>

            <listitem><para>The <option>exec</option> type is similar to <option>simple</option>, but the
            service manager will consider the unit started immediately after the main service binary has been
            executed. The service manager will delay starting of follow-up units until that point. (Or in
            other words: <option>simple</option> proceeds with further jobs right after
            <function>fork()</function> returns, while <option>exec</option> will not proceed before both
            <function>fork()</function> and <function>execve()</function> in the service process succeeded.)
            Note that this means <command>systemctl start</command> command lines for <option>exec</option>
            services will report failure when the service's binary cannot be invoked successfully (for
            example because the selected <varname>User=</varname> doesn't exist, or the service binary is
            missing).</para></listitem>

            <listitem><para>If set to <option>forking</option>, the manager will consider the unit started
            immediately after the binary that forked off by the manager exits. <emphasis>The use of this type
            is discouraged, use <option>notify</option>, <option>notify-reload</option>, or
            <option>dbus</option> instead.</emphasis></para>

            <para>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 service process, and the service manager will consider the unit started when the parent
            process exits. This is the behavior of traditional UNIX services. If this setting is used, it is
            recommended to also use the <varname>PIDFile=</varname> option, so that systemd can reliably
            identify the main process of the service. The manager will proceed with starting follow-up units
            after the parent process exits.</para></listitem>

            <listitem><para>Behavior of <option>oneshot</option> is similar to <option>simple</option>;
            however, the service manager will consider the unit up after the main process exits. It will then
            start follow-up units. <varname>RemainAfterExit=</varname> is particularly useful for this type
            of service. <varname>Type=</varname><option>oneshot</option> is the implied default if neither
            <varname>Type=</varname> nor <varname>ExecStart=</varname> are specified. Note that if this
            option is used without <varname>RemainAfterExit=</varname> the service will never enter
            <literal>active</literal> unit state, but will directly transition from
            <literal>activating</literal> to <literal>deactivating</literal> or <literal>dead</literal>,
            since no process is configured that shall run continuously. In particular this means that after a
            service of this type ran (and which has <varname>RemainAfterExit=</varname> not set) it will not
            show up as started afterwards, but as dead.</para></listitem>

            <listitem><para>Behavior of <option>dbus</option> is similar to <option>simple</option>; however,
            units of this type must have the <varname>BusName=</varname> specified and the service manager
            will consider the unit up when the specified bus name has been acquired. This type is the default
            if <varname>BusName=</varname> is specified.</para>

            <para>Service units with this option configured implicitly gain dependencies on the
            <filename>dbus.socket</filename> unit. A service unit of this type is considered to be in the
            activating state until the specified bus name is acquired. It is considered activated while the
            bus name is taken. Once the bus name is released the service is considered being no longer
            functional which has the effect that the service manager attempts to terminate any remaining
            processes belonging to the service. Services that drop their bus name as part of their shutdown
            logic thus should be prepared to receive a <constant>SIGTERM</constant> (or whichever signal is
            configured in <varname>KillSignal=</varname>) as result.</para></listitem>

            <listitem><para>Behavior of <option>notify</option> is similar to <option>exec</option>; however,
            it is expected that the service sends a <literal>READY=1</literal> 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>.</para>

            <para>If the service supports reloading, and uses a signal to start the reload, using
            <option>notify-reload</option> instead is recommended.</para></listitem>

            <listitem><para>Behavior of <option>notify-reload</option> is similar to <option>notify</option>,
            with one difference: the <constant>SIGHUP</constant> UNIX process signal is sent to the service's
            main process when the service is asked to reload and the manager will wait for a notification
            about the reload being finished.</para>

            <para>When initiating the reload process the service is expected to reply with a notification
            message via
            <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
            that contains the <literal>RELOADING=1</literal> field in combination with
            <literal>MONOTONIC_USEC=</literal> set to the current monotonic time
            (i.e. <constant>CLOCK_MONOTONIC</constant> in
            <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>)
            in μs, formatted as decimal string. Once reloading is complete another notification message must
            be sent, containing <literal>READY=1</literal>. Using this service type and implementing this
            reload protocol is an efficient alternative to providing an <varname>ExecReload=</varname>
            command for reloading of the service's configuration.</para>

            <para>The signal to send can be tweaked via <varname>ReloadSignal=</varname>, see below.</para>
            </listitem>

            <listitem><para>Behavior of <option>idle</option> is very similar to <option>simple</option>; however,
            actual execution of the service program 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 timeout, after which the service program is invoked
            anyway.</para></listitem>
          </itemizedlist>

          <para>It is recommended to use <varname>Type=</varname><option>exec</option> for long-running
          services, as it ensures that process setup errors (e.g. errors such as a missing service
          executable, or missing user) are properly tracked. However, as this service type won't propagate
          the failures in the service's own startup code (as opposed to failures in the preparatory steps the
          service manager executes before <function>execve()</function>) and doesn't allow ordering of other
          units against completion of initialization of the service code itself (which for example is useful
          if clients need to connect to the service through some form of IPC, and the IPC channel is only
          established by the service itself  in contrast to doing this ahead of time through socket or bus
          activation or similar), it might not be sufficient for many cases. If so, <option>notify</option>,
          <option>notify-reload</option>, or <option>dbus</option> (the latter only in case the service
          provides a D-Bus interface) are the preferred options as they allow service program code to
          precisely schedule when to consider the service started up successfully and when to proceed with
          follow-up units. The <option>notify</option>/<option>notify-reload</option> service types require
          explicit support in the service codebase (as <function>sd_notify()</function> or an equivalent API
          needs to be invoked by the service at the appropriate time)  if it's not supported, then
          <option>forking</option> is an alternative: it supports the traditional heavy-weight UNIX service
          start-up protocol. Note that using any type other than <option>simple</option> possibly delays the
          boot process, as the service manager needs to wait for at least some service initialization to
          complete. (Also note it is generally not recommended to use <option>idle</option> or
          <option>oneshot</option> for long-running services.)</para>

          <para>Note that various service settings (e.g. <varname>User=</varname>, <varname>Group=</varname>
          through libc NSS) might result in "hidden" blocking IPC calls to other services when
          used. Sometimes it might be advisable to use the <option>simple</option> service type to ensure
          that the service manager's transaction logic is not affected by such potentially slow operations
          and hidden dependencies, as this is the only service type where the service manager will not wait
          for such service execution setup operations to complete before proceeding.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ExitType=</varname></term>

        <listitem>
          <para>Specifies when the manager should consider the service to be finished. One of <option>main</option> or
          <option>cgroup</option>:</para>

          <itemizedlist>
            <listitem><para>If set to <option>main</option> (the default), the service manager
            will consider the unit stopped when the main process, which is determined according to the
            <varname>Type=</varname>, exits. Consequently, it cannot be used with
            <varname>Type=</varname><option>oneshot</option>.</para></listitem>

            <listitem><para>If set to <option>cgroup</option>, the service will be considered running as long as at
            least one process in the cgroup has not exited.</para></listitem>
          </itemizedlist>

          <para>It is generally recommended to use <varname>ExitType=</varname><option>main</option> when a service has
          a known forking model and a main process can reliably be determined. <varname>ExitType=</varname>
          <option>cgroup</option> is meant for applications whose forking model is not known ahead of time and which
          might not have a specific main process. It is well suited for transient or automatically generated services,
          such as graphical applications inside of a desktop environment.</para>

          <xi:include href="version-info.xml" xpointer="v250"/>
        </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 a path referring to the PID file of the service. Usage of this option is recommended for
        services where <varname>Type=</varname> is set to <option>forking</option>. The path specified typically points
        to a file below <filename>/run/</filename>. If a relative path is specified it is hence prefixed with
        <filename>/run/</filename>. The service manager will read the PID of the main process of the service from this
        file after start-up of the service. The service manager will not write to the file configured here, although it
        will remove the file after the service has shut down if it still exists. The PID file does not need to be owned
        by a privileged user, but if it is owned by an unprivileged user additional safety restrictions are enforced:
        the file may not be a symlink to a file owned by a different user (neither directly nor indirectly), and the
        PID file must refer to a process already belonging to the service.</para>

        <para>Note that PID files should be avoided in modern projects. Use <option>Type=notify</option>,
        <option>Type=notify-reload</option> or <option>Type=simple</option> where possible, which does not
        require use of PID files to determine the main process of a service and avoids needless
        forking.</para></listitem>
      </varlistentry>

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

        <listitem><para>Takes a D-Bus destination name that this service shall use. This option is mandatory
        for services where <varname>Type=</varname> is set to <option>dbus</option>. It is recommended to
        always set this property if known to make it easy to map the service name to the D-Bus destination.
        In particular, <command>systemctl service-log-level/service-log-target</command> verbs make use of
        this.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ExecStart=</varname></term>
        <listitem><para>Commands that are executed when this service is started. The value is split into zero
        or more command lines according to the rules described in the 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> and at least one
        <varname>ExecStop=</varname> line set. (Services lacking both <varname>ExecStart=</varname> and
        <varname>ExecStop=</varname> are not valid.)</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 commands specified in
        <varname>ExecStart=</varname> have been invoked 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 last <varname>ExecStart=</varname> process exited successfully for
        <varname>Type=oneshot</varname>, the initial process exited successfully for
        <varname>Type=forking</varname>, <literal>READY=1</literal> is sent for
        <varname>Type=notify</varname>/<varname>Type=notify-reload</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>

        <para>Note that the execution of <varname>ExecStartPost=</varname> is taken into account for the purpose of
        <varname>Before=</varname>/<varname>After=</varname> ordering constraints.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ExecCondition=</varname></term>
        <listitem><para>Optional commands that are executed before the commands in <varname>ExecStartPre=</varname>.
        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>The behavior is like an <varname>ExecStartPre=</varname> and condition check hybrid: when an
        <varname>ExecCondition=</varname> command exits with exit code 1 through 254 (inclusive), the remaining
        commands are skipped and the unit is <emphasis>not</emphasis> marked as failed. However, if an
        <varname>ExecCondition=</varname> command exits with 255 or abnormally (e.g. timeout, killed by a
        signal, etc.), the unit will be considered failed (and remaining commands will be skipped). Exit code of 0 or
        those matching <varname>SuccessExitStatus=</varname> will continue execution to the next commands.</para>

        <para>The same recommendations about not running long-running processes in <varname>ExecStartPre=</varname>
        also applies to <varname>ExecCondition=</varname>. <varname>ExecCondition=</varname> will also run the commands
        in <varname>ExecStopPost=</varname>, as part of stopping the service, in the case of any non-zero or abnormal
        exits, like the ones described above.</para>

        <xi:include href="version-info.xml" xpointer="v243"/>
        </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>ExecReload=kill -HUP $MAINPID</programlisting>

        <para>Note however that reloading a daemon by enqueuing a signal (as with the example line above) is
        usually not a good choice, because this is an asynchronous operation and hence not suitable when
        ordering reloads of multiple services against each other. It is thus strongly recommended to either
        use <varname>Type=</varname><option>notify-reload</option> in place of
        <varname>ExecReload=</varname>, or 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. For
        example, <citerefentry
        project='mankier'><refentrytitle>dbus-broker</refentrytitle><manvolnum>1</manvolnum></citerefentry>
        uses the following:</para>

        <programlisting>ExecReload=busctl call org.freedesktop.DBus \
        /org/freedesktop/DBus org.freedesktop.DBus \
        ReloadConfig
</programlisting>
        </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, it is implied that the service is stopped, and any
        processes remaining for it 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> or <varname>RestartKillSignal=</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 sending some form of termination signal to it), but does not
        wait for it to do so. Since the remaining processes of the services are killed according to
        <varname>KillMode=</varname> and <varname>KillSignal=</varname> or
        <varname>RestartKillSignal=</varname> as described above immediately after the command exited, this
        may 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. Also note that the stop operation is always
        performed if the service started successfully, even if the processes in the service terminated on their
        own or were killed. The stop commands must be prepared to deal with that case. <varname>$MAINPID</varname>
        will be unset if systemd knows that the main process exited by the time the stop commands are called.</para>

        <para>Service restart requests are implemented as stop operations followed by start operations. This
        means that <varname>ExecStop=</varname> and <varname>ExecStopPost=</varname> are executed during a
        service restart operation.</para>

        <para>It is recommended to use this setting for commands that communicate with the service requesting
        clean termination. 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>

        <para>Note that the execution of <varname>ExecStopPost=</varname> is taken into account for the purpose of
        <varname>Before=</varname>/<varname>After=</varname> ordering constraints.</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>RestartSteps=</varname></term>
        <listitem><para>Configures the number of steps to take to increase the interval
        of auto-restarts from <varname>RestartSec=</varname> to <varname>RestartMaxDelaySec=</varname>.
        Takes a positive integer or 0 to disable it. Defaults to 0.</para>

        <para>This setting is effective only if <varname>RestartMaxDelaySec=</varname> is also set.</para>

        <xi:include href="version-info.xml" xpointer="v254"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RestartMaxDelaySec=</varname></term>
        <listitem><para>Configures the longest time to sleep before restarting a service
        as the interval goes up with <varname>RestartSteps=</varname>. Takes a value
        in the same format as <varname>RestartSec=</varname>, or <literal>infinity</literal>
        to disable the setting. Defaults to <literal>infinity</literal>.</para>

        <para>This setting is effective only if <varname>RestartSteps=</varname> is also set.</para>

        <xi:include href="version-info.xml" xpointer="v254"/></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. The precise action depends on the <varname>TimeoutStartFailureMode=</varname>
        option. 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> set in the manager, 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>

        <para>If a service of <varname>Type=notify</varname>/<varname>Type=notify-reload</varname> sends
        <literal>EXTEND_TIMEOUT_USEC=…</literal>, this may cause the start time to be extended beyond
        <varname>TimeoutStartSec=</varname>. The first receipt of this message must occur before
        <varname>TimeoutStartSec=</varname> is exceeded, and once the start time has extended beyond
        <varname>TimeoutStartSec=</varname>, the service manager will allow the service to continue to start,
        provided the service repeats <literal>EXTEND_TIMEOUT_USEC=…</literal> within the interval specified
        until the service startup status is finished by <literal>READY=1</literal>. (see
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
        </para>

        <xi:include href="version-info.xml" xpointer="v188"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>TimeoutStopSec=</varname></term>
        <listitem><para>This option serves two purposes. First, it configures the time to wait for each
        <varname>ExecStop=</varname> command. If any of them times out, subsequent <varname>ExecStop=</varname> commands
        are skipped and the service will be terminated by <constant>SIGTERM</constant>. If no <varname>ExecStop=</varname>
        commands are specified, the service gets the <constant>SIGTERM</constant> immediately. This default behavior
        can be changed by the <varname>TimeoutStopFailureMode=</varname> option. Second, it configures the time
        to wait for the service itself to stop. If it doesn't terminate in the specified time, it will be forcibly terminated
        by <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>

        <para>If a service of <varname>Type=notify</varname>/<varname>Type=notify-reload</varname> sends
        <literal>EXTEND_TIMEOUT_USEC=…</literal>, this may cause the stop time to be extended beyond
        <varname>TimeoutStopSec=</varname>. The first receipt of this message must occur before
        <varname>TimeoutStopSec=</varname> is exceeded, and once the stop time has extended beyond
        <varname>TimeoutStopSec=</varname>, the service manager will allow the service to continue to stop,
        provided the service repeats <literal>EXTEND_TIMEOUT_USEC=…</literal> within the interval specified,
        or terminates itself (see
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
        </para>

        <xi:include href="version-info.xml" xpointer="v188"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>TimeoutAbortSec=</varname></term>
        <listitem><para>This option configures the time to wait for the service to terminate when it was aborted due to a
        watchdog timeout (see <varname>WatchdogSec=</varname>). If the service has a short <varname>TimeoutStopSec=</varname>
        this option can be used to give the system more time to write a core dump of the service. Upon expiration the service
        will be forcibly terminated by <constant>SIGKILL</constant> (see <varname>KillMode=</varname> in
        <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>). The core file will
        be truncated in this case. Use <varname>TimeoutAbortSec=</varname> to set a sensible timeout for the core dumping per
        service that is large enough to write all expected data while also being short enough to handle the service failure
        in due time.
        </para>

        <para>Takes a unit-less value in seconds, or a time span value such as "5min 20s". Pass an empty value to skip
        the dedicated watchdog abort timeout handling and fall back <varname>TimeoutStopSec=</varname>. Pass
        <literal>infinity</literal> to disable the timeout logic. Defaults to <varname>DefaultTimeoutAbortSec=</varname> from
        the manager configuration file (see
        <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
        </para>

        <para>If a service of <varname>Type=notify</varname>/<varname>Type=notify-reload</varname> handles
        <constant>SIGABRT</constant> itself (instead of relying on the kernel to write a core dump) it can
        send <literal>EXTEND_TIMEOUT_USEC=…</literal> to extended the abort time beyond
        <varname>TimeoutAbortSec=</varname>. The first receipt of this message must occur before
        <varname>TimeoutAbortSec=</varname> is exceeded, and once the abort time has extended beyond
        <varname>TimeoutAbortSec=</varname>, the service manager will allow the service to continue to abort,
        provided the service repeats <literal>EXTEND_TIMEOUT_USEC=…</literal> within the interval specified,
        or terminates itself (see
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
        </para>

        <xi:include href="version-info.xml" xpointer="v243"/></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>TimeoutStartFailureMode=</varname></term>
        <term><varname>TimeoutStopFailureMode=</varname></term>

        <listitem><para>These options configure the action that is taken in case a daemon service does not signal
        start-up within its configured <varname>TimeoutStartSec=</varname>, respectively if it does not stop within
        <varname>TimeoutStopSec=</varname>. Takes one of <option>terminate</option>, <option>abort</option> and
        <option>kill</option>. Both options default to <option>terminate</option>.</para>

        <para>If <option>terminate</option> is set the service will be gracefully terminated by sending the signal
        specified in <varname>KillSignal=</varname> (defaults to <constant>SIGTERM</constant>, see
        <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>). If the
        service does not terminate the <varname>FinalKillSignal=</varname> is sent after
        <varname>TimeoutStopSec=</varname>. If <option>abort</option> is set, <varname>WatchdogSignal=</varname> is sent
        instead and <varname>TimeoutAbortSec=</varname> applies before sending <varname>FinalKillSignal=</varname>.
        This setting may be used to analyze services that fail to start-up or shut-down intermittently.
        By using <option>kill</option> the service is immediately terminated by sending
        <varname>FinalKillSignal=</varname> without any further timeout. This setting can be used to expedite the
        shutdown of failing services.
        </para>

        <xi:include href="version-info.xml" xpointer="v246"/></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>

        <para>If a service of <varname>Type=notify</varname>/<varname>Type=notify-reload</varname> sends
        <literal>EXTEND_TIMEOUT_USEC=…</literal>, this may cause the runtime to be extended beyond
        <varname>RuntimeMaxSec=</varname>. The first receipt of this message must occur before
        <varname>RuntimeMaxSec=</varname> is exceeded, and once the runtime has extended beyond
        <varname>RuntimeMaxSec=</varname>, the service manager will allow the service to continue to run,
        provided the service repeats <literal>EXTEND_TIMEOUT_USEC=…</literal> within the interval specified
        until the service shutdown is achieved by <literal>STOPPING=1</literal> (or termination). (see
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
        </para>

        <xi:include href="version-info.xml" xpointer="v229"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RuntimeRandomizedExtraSec=</varname></term>

        <listitem><para>This option modifies <varname>RuntimeMaxSec=</varname> by increasing the maximum runtime by an
        evenly distributed duration between 0 and the specified value (in seconds). If <varname>RuntimeMaxSec=</varname> is
        unspecified, then this feature will be disabled.
        </para>

        <xi:include href="version-info.xml" xpointer="v250"/></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> (or the signal specified by
        <varname>WatchdogSignal=</varname>). 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 any of the following:
        <itemizedlist>
            <listitem><simpara>exit code of 0;</simpara></listitem>
            <listitem><simpara>for types other than <varname>Type=oneshot</varname>, one of the signals
                <constant>SIGHUP</constant>, <constant>SIGINT</constant>,
                <constant>SIGTERM</constant>, or <constant>SIGPIPE</constant>;
            </simpara></listitem>
            <listitem><simpara>exit statuses and signals specified in
                <varname>SuccessExitStatus=</varname>.</simpara></listitem>
        </itemizedlist>
        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. Note that <varname>Type=oneshot</varname> services will never be restarted
        on a clean exit status, i.e. <option>always</option> and <option>on-success</option> are rejected
        for them.</para>

        <table>
          <title>Exit causes and the effect of the <varname>Restart=</varname> settings</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) or
        the service is stopped with <command>systemctl stop</command>
        or an equivalent operation. 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>RestartMode=</varname></term>

        <listitem>
          <para>Takes a string value that specifies how a service should restart:
            <itemizedlist>
              <listitem><para>If set to <option>normal</option> (the default), the service restarts by
              going through a failed/inactive state.</para></listitem>

              <listitem><para>If set to <option>direct</option>, the service transitions to the activating
              state directly during auto-restart, skipping failed/inactive state.
              <varname>ExecStopPost=</varname> is invoked.
              <varname>OnSuccess=</varname> and <varname>OnFailure=</varname> are skipped.</para></listitem>
            </itemizedlist>
          </para>

          <para>This option is useful in cases where a dependency can fail temporarily
          but we don't want these temporary failures to make the dependent units fail.
          When this option is set to <option>direct</option>, dependent units are not notified of these temporary failures.</para>

          <xi:include href="version-info.xml" xpointer="v254"/>
        </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 status
        0 and, except for <varname>Type=oneshot</varname>, the signals <constant>SIGHUP</constant>, <constant>SIGINT</constant>,
        <constant>SIGTERM</constant>, and <constant>SIGPIPE</constant>. Exit status definitions can be
        numeric termination statuses, termination status names, or termination signal names, separated by
        spaces. See the Process Exit Codes section in
        <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
        a list of termination status names (for this setting only the part without the
        <literal>EXIT_</literal> or <literal>EX_</literal> prefix should be used). See <citerefentry
        project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
        a list of signal names.</para>

        <para>Note that this setting does not change the mapping between numeric exit statuses and their
        names, i.e. regardless how this setting is used 0 will still be mapped to <literal>SUCCESS</literal>
        (and thus typically shown as <literal>0/SUCCESS</literal> in tool outputs) and 1 to
        <literal>FAILURE</literal> (and thus typically shown as <literal>1/FAILURE</literal>), and so on. It
        only controls what happens as effect of these exit statuses, and how it propagates to the state of
        the service as a whole.</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>

        <example>
          <title>A service with the <varname>SuccessExitStatus=</varname> setting</title>

          <programlisting>SuccessExitStatus=TEMPFAIL 250 SIGKILL</programlisting>

          <para>Exit status 75 (<constant>TEMPFAIL</constant>), 250, and the termination signal
          <constant>SIGKILL</constant> are considered clean service terminations.</para>
        </example>

        <para>Note: <command>systemd-analyze exit-status</command> may be used to list exit statuses and
        translate between numerical status values and names.</para>

        <xi:include href="version-info.xml" xpointer="v189"/></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 be numeric termination statuses, termination
        status names, or termination signal names, separated by spaces. Defaults to the empty list, so that,
        by default, no exit status is excluded from the configured restart logic.

        <example>
          <title>A service with the <varname>RestartPreventExitStatus=</varname> setting</title>

          <programlisting>RestartPreventExitStatus=TEMPFAIL 250 SIGKILL</programlisting>

          <para>Exit status 75 (<constant>TEMPFAIL</constant>), 250, and the termination signal
          <constant>SIGKILL</constant> will not result in automatic service restarting.</para>
        </example>

        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>

        <para>Note that this setting has no effect on processes configured via
        <varname>ExecStartPre=</varname>, <varname>ExecStartPost=</varname>, <varname>ExecStop=</varname>,
        <varname>ExecStopPost=</varname> or <varname>ExecReload=</varname>, but only on the main service
        process, i.e. either the one invoked by <varname>ExecStart=</varname> or (depending on
        <varname>Type=</varname>, <varname>PIDFile=</varname>, …) the otherwise configured main
        process.</para>

        <xi:include href="version-info.xml" xpointer="v189"/></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>

        <para>Note that for <varname>Type=oneshot</varname> services, a success exit status will prevent
        them from auto-restarting, no matter whether the corresponding exit statuses are listed in this
        option or not.</para>

        <xi:include href="version-info.xml" xpointer="v215"/></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, stderr),
        excluding those passed in via the file descriptor storage logic (see
        <varname>FileDescriptorStoreMax=</varname> for details), 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>
        and has no effect on file descriptors which were previously saved in the file-descriptor store for
        example.  Defaults to false.</para>

        <para>Note that if the same socket unit is configured to be passed to multiple service units (via the
        <varname>Sockets=</varname> setting, see below), and these services have different
        <varname>NonBlocking=</varname> configurations, the precise state of <constant>O_NONBLOCK</constant>
        depends on the order in which these services are invoked, and will possibly change after service code
        already took possession of the socket file descriptor, simply because the
        <constant>O_NONBLOCK</constant> state of a socket is shared by all file descriptors referencing
        it. Hence it is essential that all services sharing the same socket use the same
        <varname>NonBlocking=</varname> configuration, and do not change the flag in service code
        either.</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 main or 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>/<varname>Type=notify-reload</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>

        <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if
        either the sending process is still around at the time PID 1 processes the message, or if the sending process
        is explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally
        forked off the process, i.e. on all processes that match <option>main</option> or
        <option>exec</option>. Conversely, if an auxiliary process of the unit sends an
        <function>sd_notify()</function> message and immediately exits, the service manager might not be able to
        properly attribute the message to the unit, and thus will ignore it, even if
        <varname>NotifyAccess=</varname><option>all</option> is set for it.</para>

        <para>Hence, to eliminate all race conditions involving lookup of the client's unit and attribution of notifications
        to units correctly, <function>sd_notify_barrier()</function> may be used. This call acts as a synchronization point
        and ensures all notifications sent before this call have been picked up by the service manager when it returns
        successfully. Use of <function>sd_notify_barrier()</function> is needed for clients which are not invoked by the
        service manager, otherwise this synchronization mechanism is unnecessary for attribution of notifications to the
        unit.</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. Note
        that once set, clearing the list of sockets again (for example, by assigning the empty string to this
        option) is not supported.</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 services that can restart
        after an explicit request or a crash without losing state. Any open sockets and other file
        descriptors which should not be closed during the restart may be stored this way. Application state
        can either be serialized to a file in <varname>RuntimeDirectory=</varname>, or stored in a
        <citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        memory file descriptor. 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 (see
        <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
        details about the precise protocol used and the order in which the file descriptors are passed). Any
        file descriptors passed to the service manager are automatically closed when
        <constant>POLLHUP</constant> or <constant>POLLERR</constant> is seen on them, or when the service is
        fully stopped and no job is queued or being executed for it (the latter can be tweaked with
        <varname>FileDescriptorStorePreserve=</varname>, see below). If this option is used,
        <varname>NotifyAccess=</varname> (see above) 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>.</para>

        <para>The <command>fdstore</command> command of
        <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>
        may be used to list the current contents of a service's file descriptor store.</para>

        <para>Note that the service manager will only pass file descriptors contained in the file descriptor
        store to the service's own processes, never to other clients via IPC or similar. However, it does
        allow unprivileged clients to query the list of currently open file descriptors of a
        service. Sensitive data may hence be safely placed inside the referenced files, but should not be
        attached to the metadata (e.g. included in filenames) of the stored file
        descriptors.</para>

        <para>If this option is set to a non-zero value the <varname>$FDSTORE</varname> environment variable
        will be set for processes invoked for this service. See
        <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
        details.</para>

        <para>For further information on the file descriptor store see the <ulink
        url="https://systemd.io/FILE_DESCRIPTOR_STORE">File Descriptor Store</ulink> overview.</para>

        <xi:include href="version-info.xml" xpointer="v219"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>FileDescriptorStorePreserve=</varname></term>
        <listitem><para>Takes one of <constant>no</constant>, <constant>yes</constant>,
        <constant>restart</constant> and controls when to release the service's file descriptor store
        (i.e. when to close the contained file descriptors, if any). If set to <constant>no</constant> the
        file descriptor store is automatically released when the service is stopped; if
        <constant>restart</constant> (the default) it is kept around as long as the unit is neither inactive
        nor failed, or a job is queued for the service, or the service is expected to be restarted. If
        <constant>yes</constant> the file descriptor store is kept around until the unit is removed from
        memory (i.e. is not referenced anymore and inactive). The latter is useful to keep entries in the
        file descriptor store pinned until the service manager exits.</para>

        <para>Use <command>systemctl clean --what=fdstore </command> to release the file descriptor store
        explicitly.</para>

        <xi:include href="version-info.xml" xpointer="v254"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>USBFunctionDescriptors=</varname></term>
        <listitem><para>Configure the location of a file containing
        <ulink
        url="https://docs.kernel.org/usb/functionfs.html">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>

        <xi:include href="version-info.xml" xpointer="v227"/></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>

        <xi:include href="version-info.xml" xpointer="v227"/></listitem>
      </varlistentry>

      <varlistentry id='oom-policy'>
        <term><varname>OOMPolicy=</varname></term>

        <listitem><para>Configure the out-of-memory (OOM) killing policy for the kernel and the userspace OOM
        killer
        <citerefentry><refentrytitle>systemd-oomd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
        On Linux, when memory becomes scarce to the point that the kernel has trouble allocating memory for
        itself, it might decide to kill a running process in order to free up memory and reduce memory
        pressure. Note that <filename>systemd-oomd.service</filename> is a more flexible solution that aims
        to prevent out-of-memory situations for the userspace too, not just the kernel, by attempting to
        terminate services earlier, before the kernel would have to act.</para>

        <para>This setting takes one of <constant>continue</constant>, <constant>stop</constant> or
        <constant>kill</constant>. If set to <constant>continue</constant> and a process in the unit is
        killed by the OOM killer, this is logged but the unit continues running. If set to
        <constant>stop</constant> the event is logged but the unit is terminated cleanly by the service
        manager. If set to <constant>kill</constant> and one of the unit's processes is killed by the OOM
        killer the kernel is instructed to kill all remaining processes of the unit too, by setting the
        <filename>memory.oom.group</filename> attribute to <constant>1</constant>; also see kernel
        page <ulink url="https://docs.kernel.org/admin-guide/cgroup-v2.html">Control Group v2</ulink>.
        </para>

        <para>Defaults to the setting <varname>DefaultOOMPolicy=</varname> in
        <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        is set to, except for units where <varname>Delegate=</varname> is turned on, where it defaults to
        <constant>continue</constant>.</para>

        <para>Use the <varname>OOMScoreAdjust=</varname> setting to configure whether processes of the unit
        shall be considered preferred or less preferred candidates for process termination by the Linux OOM
        killer logic. See
        <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
        details.</para>

        <para>This setting also applies to
        <citerefentry><refentrytitle>systemd-oomd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
        Similarly to the kernel OOM kills performed by the kernel, this setting determines the state of the
        unit after <command>systemd-oomd</command> kills a cgroup associated with it.</para>

        <xi:include href="version-info.xml" xpointer="v243"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>OpenFile=</varname></term>
        <listitem><para>Takes an argument of the form <literal>path<optional><replaceable>:fd-name:options</replaceable></optional></literal>,
        where:
        <itemizedlist>
            <listitem><simpara><literal>path</literal> is a path to a file or an <constant>AF_UNIX</constant> socket in the file system;</simpara></listitem>
            <listitem><simpara><literal>fd-name</literal> is a name that will be associated with the file descriptor;
            the name may contain any ASCII character, but must exclude control characters and ":", and must be at most 255 characters in length;
            it is optional and, if not provided, defaults to the file name;</simpara></listitem>
            <listitem><simpara><literal>options</literal> is a comma-separated list of access options;
            possible values are
            <literal>read-only</literal>,
            <literal>append</literal>,
            <literal>truncate</literal>,
            <literal>graceful</literal>;
            if not specified, files will be opened in <constant>rw</constant> mode;
            if <literal>graceful</literal> is specified, errors during file/socket opening are ignored.
            Specifying the same option several times is treated as an error.</simpara></listitem>
        </itemizedlist>
        The file or socket is opened by the service manager and the file descriptor is passed to the service.
        If the path is a socket, we call <function>connect()</function> on it.
        See <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        for more details on how to retrieve these file descriptors.</para>

        <para>This setting is useful to allow services to access files/sockets that they can't access themselves
        (due to running in a separate mount namespace, not having privileges, ...).</para>

        <para>This setting can be specified multiple times, in which case all the specified paths are opened and the file descriptors passed to the service.
        If the empty string is assigned, the entire list of open files defined prior to this is reset.</para>

        <xi:include href="version-info.xml" xpointer="v253"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ReloadSignal=</varname></term>
        <listitem><para>Configures the UNIX process signal to send to the service's main process when asked
        to reload the service's configuration. Defaults to <constant>SIGHUP</constant>. This option has no
        effect unless <varname>Type=</varname><option>notify-reload</option> is used, see
        above.</para>

        <xi:include href="version-info.xml" xpointer="v253"/></listitem>
      </varlistentry>

    </variablelist>

    <para id='shared-unit-options'>Check
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    <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>,
    <varname>ExecStopPost=</varname>, and
    <varname>ExecCondition=</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 unquoted using the rules described in "Quoting" section in
    <citerefentry><refentrytitle>systemd.syntax</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The
    first item becomes the command to execute, and the subsequent items the arguments.</para>

    <para>This syntax is inspired by shell syntax, but only the meta-characters and expansions
    described in the following paragraphs are understood, and the expansion of variables is
    different. 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 may contain spaces, but control characters are not allowed.</para>

    <para>Each command may be prefixed with a number of special characters:</para>

    <table>
      <title>Special executable prefixes</title>

      <tgroup cols='2'>
        <colspec colname='prefix'/>
        <colspec colname='meaning'/>

        <thead>
          <row>
            <entry>Prefix</entry>
            <entry>Effect</entry>
          </row>
        </thead>
        <tbody>
          <row>
            <entry><literal>@</literal></entry>
            <entry>If the executable path is prefixed with <literal>@</literal>, the second specified token will be passed as <constant>argv[0]</constant> to the executed process (instead of the actual filename), followed by the further arguments specified.</entry>
          </row>

          <row>
            <entry><literal>-</literal></entry>
            <entry>If the executable path 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 recorded, but has no further effect and is considered equivalent to success.</entry>
          </row>

          <row>
            <entry><literal>:</literal></entry>
            <entry>If the executable path is prefixed with <literal>:</literal>, environment variable substitution (as described below this table) is not applied.</entry>
          </row>

          <row>
            <entry><literal>+</literal></entry>
            <entry>If the executable path is prefixed with <literal>+</literal> then the process is executed with full privileges. In this mode privilege restrictions configured with <varname>User=</varname>, <varname>Group=</varname>, <varname>CapabilityBoundingSet=</varname> or the various file system namespacing options (such as <varname>PrivateDevices=</varname>, <varname>PrivateTmp=</varname>) are not applied to the invoked command line (but still affect any other <varname>ExecStart=</varname>, <varname>ExecStop=</varname>,  lines). However, note that this will not bypass options that apply to the whole control group, such as <varname>DevicePolicy=</varname>, see <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry> for the full list.</entry>
          </row>

          <row>
            <entry><literal>!</literal></entry>

            <entry>Similar to the <literal>+</literal> character discussed above this permits invoking command lines with elevated privileges. However, unlike <literal>+</literal> the <literal>!</literal> character exclusively alters the effect of <varname>User=</varname>, <varname>Group=</varname> and <varname>SupplementaryGroups=</varname>, i.e. only the stanzas that affect user and group credentials. Note that this setting may be combined with <varname>DynamicUser=</varname>, in which case a dynamic user/group pair is allocated before the command is invoked, but credential changing is left to the executed process itself.</entry>
          </row>

          <row>
            <entry><literal>!!</literal></entry>

            <entry>This prefix is very similar to <literal>!</literal>, however it only has an effect on systems lacking support for ambient process capabilities, i.e. without support for <varname>AmbientCapabilities=</varname>. It's intended to be used for unit files that take benefit of ambient capabilities to run processes with minimal privileges wherever possible while remaining compatible with systems that lack ambient capabilities support. Note that when <literal>!!</literal> is used, and a system lacking ambient capability support is detected any configured <varname>SystemCallFilter=</varname> and <varname>CapabilityBoundingSet=</varname> stanzas are implicitly modified, in order to permit spawned processes to drop credentials and capabilities themselves, even if this is configured to not be allowed. Moreover, if this prefix is used and a system lacking ambient capability support is detected <varname>AmbientCapabilities=</varname> will be skipped and not be applied. On systems supporting ambient capabilities, <literal>!!</literal> has no effect and is redundant.</entry>
          </row>
        </tbody>
      </tgroup>
    </table>

    <para><literal>@</literal>, <literal>-</literal>, <literal>:</literal>, and one of
    <literal>+</literal>/<literal>!</literal>/<literal>!!</literal> may be used together and they can appear in any
    order. However, only one of <literal>+</literal>, <literal>!</literal>, <literal>!!</literal> may be used at a
    time.</para>

    <para>For each command, the first argument must be either an absolute path to an executable or a simple
    file name without any slashes. If the command is not a full (absolute) path, it will be resolved to a
    full path using a fixed search path determined at compilation time. Searched directories include
    <filename>/usr/local/bin/</filename>, <filename>/usr/bin/</filename>, <filename>/bin/</filename> on
    systems using split <filename>/usr/bin/</filename> and <filename>/bin/</filename> directories, and their
    <filename>sbin/</filename> counterparts on systems using split <filename>bin/</filename> and
    <filename>sbin/</filename>. It is thus safe to use just the executable name in case of executables
    located in any of the "standard" directories, and an absolute path must be used in other cases.
    Hint: this search path may be queried using <command>systemd-path search-binaries-default</command>.
    </para>

    <para>The command line accepts <literal>%</literal> specifiers as described in
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

    <para>Basic environment variable substitution is supported. Use
    <literal>${FOO}</literal> as part of a word, or as a word of its
    own, on the command line, in which case it will be erased and replaced
    by the exact value of the environment variable (if any) including all
    whitespace it contains, always resulting in exactly a single argument.
    Use <literal>$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=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>/bin/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=sh -c 'dmesg | tac'</programlisting>

    <para>Example:</para>

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

    <para>This will execute <command>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>Type=oneshot
ExecStart=:echo $USER ; -false ; +:@true $TEST</programlisting>

    <para>This will execute <command>/usr/bin/echo</command> with the literal argument
    <literal>$USER</literal> (<literal>:</literal> suppresses variable expansion), and then
    <command>/usr/bin/false</command> (the return value will be ignored because <literal>-</literal>
    suppresses checking of the return value), and <command>/usr/bin/true</command> (with elevated privileges,
    with <literal>$TEST</literal> as <constant>argv[0]</constant>).</para>

    <para>Example:</para>

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

    <para>This will execute <command>echo</command>
    with five arguments: <literal>/</literal>,
    <literal>&gt;/dev/null</literal>,
    <literal>&amp;</literal>, <literal>;</literal>, and
    <literal>ls</literal>.</para>
  </refsect1>

  <refsect1>
    <title>Examples</title>

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

      <para>The following unit file creates a service that will
      execute <filename index="false">/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>/<varname>Type=</varname><option>notify-reload</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. For units with multiple
      commands (<varname index="false">Type=oneshot</varname>), all commands will be run again.</para>
      <para> For <varname index="false">Type=oneshot</varname>, <varname>Restart=</varname><option>always</option>
      and <varname>Restart=</varname><option>on-success</option> are <emphasis>not</emphasis> allowed.</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 [Install] 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> or
      <varname>Type=</varname><option>notify-reload</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-reload
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>

      <para>To avoid code duplication, it is preferable to use
      <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
      when possible, especially when other APIs provided by
      <citerefentry><refentrytitle>libsystemd</refentrytitle><manvolnum>3</manvolnum></citerefentry> are
      also used, but note that the notification protocol is very simple and guaranteed to be stable as per
      the <ulink url="https://systemd.io/PORTABILITY_AND_STABILITY/">Interface Portability and Stability
      Promise</ulink>, so it can be reimplemented by services with no external dependencies. For a
      self-contained example, see
      <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
    </example>
  </refsect1>

  <refsect1>
      <title>See Also</title>
      <para><simplelist type="inline">
        <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemd-run</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      </simplelist></para>
  </refsect1>

</refentry>