summaryrefslogtreecommitdiff
path: root/man/systemd.exec.xml
blob: 4a6869534831311b0caffc23569563fef8616e46 (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
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<!--
  This file is part of systemd.

  Copyright 2010 Lennart Poettering

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

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

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

<refentry id="systemd.exec">
  <refentryinfo>
    <title>systemd.exec</title>
    <productname>systemd</productname>

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

  <refmeta>
    <refentrytitle>systemd.exec</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd.exec</refname>
    <refpurpose>Execution environment configuration</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename><replaceable>service</replaceable>.service</filename>,
    <filename><replaceable>socket</replaceable>.socket</filename>,
    <filename><replaceable>mount</replaceable>.mount</filename>,
    <filename><replaceable>swap</replaceable>.swap</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>Unit configuration files for services, sockets, mount
    points, and swap devices share a subset of configuration options
    which define the execution environment of spawned
    processes.</para>

    <para>This man page lists the configuration options shared by
    these four unit types. See
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for the common options of all unit configuration files, and
    <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    and
    <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for more information on the specific unit configuration files. The
    execution specific configuration options are configured in the
    [Service], [Socket], [Mount], or [Swap] sections, depending on the
    unit type.</para>
  </refsect1>

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

    <para>A few execution parameters result in additional, automatic
    dependencies to be added.</para>

    <para>Units with <varname>WorkingDirectory=</varname> or
    <varname>RootDirectory=</varname> set automatically gain
    dependencies of type <varname>Requires=</varname> and
    <varname>After=</varname> on all mount units required to access
    the specified paths. This is equivalent to having them listed
    explicitly in <varname>RequiresMountsFor=</varname>.</para>

    <para>Similar, units with <varname>PrivateTmp=</varname> enabled
    automatically get mount unit dependencies for all mounts
    required to access <filename>/tmp</filename> and
    <filename>/var/tmp</filename>.</para>

    <para>Units whose standard output or error output is connected to <option>journal</option>, <option>syslog</option>
    or <option>kmsg</option> (or their combinations with console output, see below) automatically acquire dependencies
    of type <varname>After=</varname> on <filename>systemd-journald.socket</filename>.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <variablelist class='unit-directives'>

      <varlistentry>
        <term><varname>WorkingDirectory=</varname></term>

        <listitem><para>Takes a directory path relative to the service's root directory specified by
        <varname>RootDirectory=</varname>, or the special value <literal>~</literal>. Sets the working directory for
        executed processes. If set to <literal>~</literal>, the home directory of the user specified in
        <varname>User=</varname> is used. If not set, defaults to the root directory when systemd is running as a
        system instance and the respective user's home directory if run as user. If the setting is prefixed with the
        <literal>-</literal> character, a missing working directory is not considered fatal. If
        <varname>RootDirectory=</varname> is not set, then <varname>WorkingDirectory=</varname> is relative to the root
        of the system running the service manager.  Note that setting this parameter might result in additional
        dependencies to be added to the unit (see above).</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RootDirectory=</varname></term>

        <listitem><para>Takes a directory path relative to the host's root directory (i.e. the root of the system
        running the service manager). Sets the root directory for executed processes, with the <citerefentry
        project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>2</manvolnum></citerefentry> system
        call. If this is used, it must be ensured that the process binary and all its auxiliary files are available in
        the <function>chroot()</function> jail. Note that setting this parameter might result in additional
        dependencies to be added to the unit (see above).</para>

        <para>The <varname>PrivateUsers=</varname> setting is particularly useful in conjunction with
        <varname>RootDirectory=</varname>. For details, see below.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>User=</varname></term>
        <term><varname>Group=</varname></term>

        <listitem><para>Set the UNIX user or group that the processes are executed as, respectively. Takes a single
        user or group name, or numeric ID as argument. If no group is set, the default group of the user is used. This
        setting does not affect commands whose command line is prefixed with <literal>+</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>DynamicUser=</varname></term>

        <listitem><para>Takes a boolean parameter. If set, a UNIX user and group pair is allocated dynamically when the
        unit is started, and released as soon as it is stopped. The user and group will not be added to
        <filename>/etc/passwd</filename> or <filename>/etc/group</filename>, but are managed transiently during
        runtime. The <citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
        glibc NSS module provides integration of these dynamic users/groups into the system's user and group
        databases. The user and group name to use may be configured via <varname>User=</varname> and
        <varname>Group=</varname> (see above). If these options are not used and dynamic user/group allocation is
        enabled for a unit, the name of the dynamic user/group is implicitly derived from the unit name. If the unit
        name without the type suffix qualifies as valid user name it is used directly, otherwise a name incorporating a
        hash of it is used. If a statically allocated user or group of the configured name already exists, it is used
        and no dynamic user/group is allocated. Dynamic users/groups are allocated from the UID/GID range
        61184…65519. It is recommended to avoid this range for regular system or login users.  At any point in time
        each UID/GID from this range is only assigned to zero or one dynamically allocated users/groups in
        use. However, UID/GIDs are recycled after a unit is terminated. Care should be taken that any processes running
        as part of a unit for which dynamic users/groups are enabled do not leave files or directories owned by these
        users/groups around, as a different unit might get the same UID/GID assigned later on, and thus gain access to
        these files or directories. If <varname>DynamicUser=</varname> is enabled, <varname>RemoveIPC=</varname>,
        <varname>PrivateTmp=</varname> are implied. This ensures that the lifetime of IPC objects and temporary files
        created by the executed processes is bound to the runtime of the service, and hence the lifetime of the dynamic
        user/group. Since <filename>/tmp</filename> and <filename>/var/tmp</filename> are usually the only
        world-writable directories on a system this ensures that a unit making use of dynamic user/group allocation
        cannot leave files around after unit termination. Moreover <varname>ProtectSystem=strict</varname> and
        <varname>ProtectHome=read-only</varname> are implied, thus prohibiting the service to write to arbitrary file
        system locations. In order to allow the service to write to certain directories, they have to be whitelisted
        using <varname>ReadWritePaths=</varname>, but care must be taken so that UID/GID recycling doesn't
        create security issues involving files created by the service. Use <varname>RuntimeDirectory=</varname> (see
        below) in order to assign a writable runtime directory to a service, owned by the dynamic user/group and
        removed automatically when the unit is terminated. Defaults to off.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>SupplementaryGroups=</varname></term>

        <listitem><para>Sets the supplementary Unix groups the
        processes are executed as. This takes a space-separated list
        of group names or IDs. This option may be specified more than
        once, in which case all listed groups are set as supplementary
        groups. When the empty string is assigned, the list of
        supplementary groups is reset, and all assignments prior to
        this one will have no effect. In any way, this option does not
        override, but extends the list of supplementary groups
        configured in the system group database for the
        user. This does not affect commands prefixed with <literal>+</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RemoveIPC=</varname></term>

        <listitem><para>Takes a boolean parameter. If set, all System V and POSIX IPC objects owned by the user and
        group the processes of this unit are run as are removed when the unit is stopped. This setting only has an
        effect if at least one of <varname>User=</varname>, <varname>Group=</varname> and
        <varname>DynamicUser=</varname> are used. It has no effect on IPC objects owned by the root user. Specifically,
        this removes System V semaphores, as well as System V and POSIX shared memory segments and message queues. If
        multiple units use the same user or group the IPC objects are removed when the last of these units is
        stopped. This setting is implied if <varname>DynamicUser=</varname> is set.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>Nice=</varname></term>

        <listitem><para>Sets the default nice level (scheduling
        priority) for executed processes. Takes an integer between -20
        (highest priority) and 19 (lowest priority). See
        <citerefentry><refentrytitle>setpriority</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        for details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>OOMScoreAdjust=</varname></term>

        <listitem><para>Sets the adjustment level for the
        Out-Of-Memory killer for executed processes. Takes an integer
        between -1000 (to disable OOM killing for this process) and
        1000 (to make killing of this process under memory pressure
        very likely). See <ulink
        url="https://www.kernel.org/doc/Documentation/filesystems/proc.txt">proc.txt</ulink>
        for details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>IOSchedulingClass=</varname></term>

        <listitem><para>Sets the I/O scheduling class for executed
        processes. Takes an integer between 0 and 3 or one of the
        strings <option>none</option>, <option>realtime</option>,
        <option>best-effort</option> or <option>idle</option>. See
        <citerefentry><refentrytitle>ioprio_set</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        for details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>IOSchedulingPriority=</varname></term>

        <listitem><para>Sets the I/O scheduling priority for executed
        processes. Takes an integer between 0 (highest priority) and 7
        (lowest priority). The available priorities depend on the
        selected I/O scheduling class (see above). See
        <citerefentry><refentrytitle>ioprio_set</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        for details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>CPUSchedulingPolicy=</varname></term>

        <listitem><para>Sets the CPU scheduling policy for executed
        processes. Takes one of
        <option>other</option>,
        <option>batch</option>,
        <option>idle</option>,
        <option>fifo</option> or
        <option>rr</option>. See
        <citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        for details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>CPUSchedulingPriority=</varname></term>

        <listitem><para>Sets the CPU scheduling priority for executed
        processes. The available priority range depends on the
        selected CPU scheduling policy (see above). For real-time
        scheduling policies an integer between 1 (lowest priority) and
        99 (highest priority) can be used. See
        <citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        for details. </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>CPUSchedulingResetOnFork=</varname></term>

        <listitem><para>Takes a boolean argument. If true, elevated
        CPU scheduling priorities and policies will be reset when the
        executed processes fork, and can hence not leak into child
        processes. See
        <citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        for details. Defaults to false.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>CPUAffinity=</varname></term>

        <listitem><para>Controls the CPU affinity of the executed
        processes. Takes a list of CPU indices or ranges separated by
        either whitespace or commas. CPU ranges are specified by the
        lower and upper CPU indices separated by a dash.
        This option may be specified more than once, in which case the
        specified CPU affinity masks are merged. If the empty string
        is assigned, the mask is reset, all assignments prior to this
        will have no effect. See
        <citerefentry><refentrytitle>sched_setaffinity</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        for details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>UMask=</varname></term>

        <listitem><para>Controls the file mode creation mask. Takes an
        access mode in octal notation. See
        <citerefentry><refentrytitle>umask</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        for details. Defaults to 0022.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>Environment=</varname></term>

        <listitem><para>Sets environment variables for executed
        processes. Takes a space-separated list of variable
        assignments. This option may be specified more than once, in
        which case all listed variables will be set. If the same
        variable is set twice, the later setting will override the
        earlier setting. If the empty string is assigned to this
        option, the list of environment variables is reset, all prior
        assignments have no effect. Variable expansion is not
        performed inside the strings, however, specifier expansion is
        possible. The $ character has no special meaning. If you need
        to assign a value containing spaces to a variable, use double
        quotes (") for the assignment.</para>

        <para>Example:
        <programlisting>Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"</programlisting>
        gives three variables <literal>VAR1</literal>,
        <literal>VAR2</literal>, <literal>VAR3</literal>
        with the values <literal>word1 word2</literal>,
        <literal>word3</literal>, <literal>$word 5 6</literal>.
        </para>

        <para>
        See
        <citerefentry project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>
        for details about environment variables.</para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>EnvironmentFile=</varname></term>
        <listitem><para>Similar to <varname>Environment=</varname> but
        reads the environment variables from a text file. The text
        file should contain new-line-separated variable assignments.
        Empty lines, lines without an <literal>=</literal> separator,
        or lines starting with ; or # will be ignored,
        which may be used for commenting. A line ending with a
        backslash will be concatenated with the following one,
        allowing multiline variable definitions. The parser strips
        leading and trailing whitespace from the values of
        assignments, unless you use double quotes (").</para>

        <para>The argument passed should be an absolute filename or
        wildcard expression, optionally prefixed with
        <literal>-</literal>, which indicates that if the file does
        not exist, it will not be read and no error or warning message
        is logged. This option may be specified more than once in
        which case all specified files are read. If the empty string
        is assigned to this option, the list of file to read is reset,
        all prior assignments have no effect.</para>

        <para>The files listed with this directive will be read
        shortly before the process is executed (more specifically,
        after all processes from a previous unit state terminated.
        This means you can generate these files in one unit state, and
        read it with this option in the next).</para>

        <para>Settings from these
        files override settings made with
        <varname>Environment=</varname>. If the same variable is set
        twice from these files, the files will be read in the order
        they are specified and the later setting will override the
        earlier setting.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>PassEnvironment=</varname></term>

        <listitem><para>Pass environment variables from the systemd system
        manager to executed processes. Takes a space-separated list of variable
        names. This option may be specified more than once, in which case all
        listed variables will be set. If the empty string is assigned to this
        option, the list of environment variables is reset, all prior
        assignments have no effect. Variables that are not set in the system
        manager will not be passed and will be silently ignored.</para>

        <para>Variables passed from this setting are overridden by those passed
        from <varname>Environment=</varname> or
        <varname>EnvironmentFile=</varname>.</para>

        <para>Example:
        <programlisting>PassEnvironment=VAR1 VAR2 VAR3</programlisting>
        passes three variables <literal>VAR1</literal>,
        <literal>VAR2</literal>, <literal>VAR3</literal>
        with the values set for those variables in PID1.</para>

        <para>
        See
        <citerefentry project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>
        for details about environment variables.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>StandardInput=</varname></term>
        <listitem><para>Controls where file descriptor 0 (STDIN) of
        the executed processes is connected to. Takes one of
        <option>null</option>,
        <option>tty</option>,
        <option>tty-force</option>,
        <option>tty-fail</option> or
        <option>socket</option>.</para>

        <para>If <option>null</option> is selected, standard input
        will be connected to <filename>/dev/null</filename>, i.e. all
        read attempts by the process will result in immediate
        EOF.</para>

        <para>If <option>tty</option> is selected, standard input is
        connected to a TTY (as configured by
        <varname>TTYPath=</varname>, see below) and the executed
        process becomes the controlling process of the terminal. If
        the terminal is already being controlled by another process,
        the executed process waits until the current controlling
        process releases the terminal.</para>

        <para><option>tty-force</option> is similar to
        <option>tty</option>, but the executed process is forcefully
        and immediately made the controlling process of the terminal,
        potentially removing previous controlling processes from the
        terminal.</para>

        <para><option>tty-fail</option> is similar to
        <option>tty</option> but if the terminal already has a
        controlling process start-up of the executed process
        fails.</para>

        <para>The <option>socket</option> option is only valid in
        socket-activated services, and only when the socket
        configuration file (see
        <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        for details) specifies a single socket only. If this option is
        set, standard input will be connected to the socket the
        service was activated from, which is primarily useful for
        compatibility with daemons designed for use with the
        traditional
        <citerefentry project='freebsd'><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
        daemon.</para>

        <para>This setting defaults to
        <option>null</option>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>StandardOutput=</varname></term>
        <listitem><para>Controls where file descriptor 1 (STDOUT) of
        the executed processes is connected to. Takes one of
        <option>inherit</option>,
        <option>null</option>,
        <option>tty</option>,
        <option>journal</option>,
        <option>syslog</option>,
        <option>kmsg</option>,
        <option>journal+console</option>,
        <option>syslog+console</option>,
        <option>kmsg+console</option> or
        <option>socket</option>.</para>

        <para><option>inherit</option> duplicates the file descriptor
        of standard input for standard output.</para>

        <para><option>null</option> connects standard output to
        <filename>/dev/null</filename>, i.e. everything written to it
        will be lost.</para>

        <para><option>tty</option> connects standard output to a tty
        (as configured via <varname>TTYPath=</varname>, see below). If
        the TTY is used for output only, the executed process will not
        become the controlling process of the terminal, and will not
        fail or wait for other processes to release the
        terminal.</para>

        <para><option>journal</option> connects standard output with
        the journal which is accessible via
        <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
        Note that everything that is written to syslog or kmsg (see
        below) is implicitly stored in the journal as well, the
        specific two options listed below are hence supersets of this
        one.</para>

        <para><option>syslog</option> connects standard output to the
        <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        system syslog service, in addition to the journal. Note that
        the journal daemon is usually configured to forward everything
        it receives to syslog anyway, in which case this option is no
        different from <option>journal</option>.</para>

        <para><option>kmsg</option> connects standard output with the
        kernel log buffer which is accessible via
        <citerefentry project='man-pages'><refentrytitle>dmesg</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
        in addition to the journal. The journal daemon might be
        configured to send all logs to kmsg anyway, in which case this
        option is no different from <option>journal</option>.</para>

        <para><option>journal+console</option>,
        <option>syslog+console</option> and
        <option>kmsg+console</option> work in a similar way as the
        three options above but copy the output to the system console
        as well.</para>

        <para><option>socket</option> connects standard output to a
        socket acquired via socket activation. The semantics are
        similar to the same option of
        <varname>StandardInput=</varname>.</para>

        <para>If the standard output (or error output, see below) of a unit is connected to the journal, syslog or the
        kernel log buffer, the unit will implicitly gain a dependency of type <varname>After=</varname> on
        <filename>systemd-journald.socket</filename> (also see the automatic dependencies section above).</para>

        <para>This setting defaults to the value set with
        <option>DefaultStandardOutput=</option> in
        <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        which defaults to <option>journal</option>. Note that setting
        this parameter might result in additional dependencies to be
        added to the unit (see above).</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>StandardError=</varname></term>
        <listitem><para>Controls where file descriptor 2 (STDERR) of
        the executed processes is connected to. The available options
        are identical to those of <varname>StandardOutput=</varname>,
        with one exception: if set to <option>inherit</option> the
        file descriptor used for standard output is duplicated for
        standard error. This setting defaults to the value set with
        <option>DefaultStandardError=</option> in
        <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        which defaults to <option>inherit</option>. Note that setting
        this parameter might result in additional dependencies to be
        added to the unit (see above).</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>TTYPath=</varname></term>
        <listitem><para>Sets the terminal device node to use if
        standard input, output, or error are connected to a TTY (see
        above). Defaults to
        <filename>/dev/console</filename>.</para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>TTYReset=</varname></term>
        <listitem><para>Reset the terminal device specified with
        <varname>TTYPath=</varname> before and after execution.
        Defaults to <literal>no</literal>.</para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>TTYVHangup=</varname></term>
        <listitem><para>Disconnect all clients which have opened the
        terminal device specified with <varname>TTYPath=</varname>
        before and after execution. Defaults to
        <literal>no</literal>.</para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>TTYVTDisallocate=</varname></term>
        <listitem><para>If the terminal device specified with
        <varname>TTYPath=</varname> is a virtual console terminal, try
        to deallocate the TTY before and after execution. This ensures
        that the screen and scrollback buffer is cleared. Defaults to
        <literal>no</literal>.</para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>SyslogIdentifier=</varname></term>
        <listitem><para>Sets the process name to prefix log lines sent
        to the logging system or the kernel log buffer with. If not
        set, defaults to the process name of the executed process.
        This option is only useful when
        <varname>StandardOutput=</varname> or
        <varname>StandardError=</varname> are set to
        <option>syslog</option>, <option>journal</option> or
        <option>kmsg</option> (or to the same settings in combination
        with <option>+console</option>).</para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>SyslogFacility=</varname></term>
        <listitem><para>Sets the syslog facility to use when logging
        to syslog. One of <option>kern</option>,
        <option>user</option>, <option>mail</option>,
        <option>daemon</option>, <option>auth</option>,
        <option>syslog</option>, <option>lpr</option>,
        <option>news</option>, <option>uucp</option>,
        <option>cron</option>, <option>authpriv</option>,
        <option>ftp</option>, <option>local0</option>,
        <option>local1</option>, <option>local2</option>,
        <option>local3</option>, <option>local4</option>,
        <option>local5</option>, <option>local6</option> or
        <option>local7</option>. See
        <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        for details. This option is only useful when
        <varname>StandardOutput=</varname> or
        <varname>StandardError=</varname> are set to
        <option>syslog</option>. Defaults to
        <option>daemon</option>.</para></listitem>
      </varlistentry>
      <varlistentry>
        <term><varname>SyslogLevel=</varname></term>
        <listitem><para>The default syslog level to use when logging to
        syslog or the kernel log buffer. One of
        <option>emerg</option>,
        <option>alert</option>,
        <option>crit</option>,
        <option>err</option>,
        <option>warning</option>,
        <option>notice</option>,
        <option>info</option>,
        <option>debug</option>. See
        <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        for details. This option is only useful when
        <varname>StandardOutput=</varname> or
        <varname>StandardError=</varname> are set to
        <option>syslog</option> or <option>kmsg</option>. Note that
        individual lines output by the daemon might be prefixed with a
        different log level which can be used to override the default
        log level specified here. The interpretation of these prefixes
        may be disabled with <varname>SyslogLevelPrefix=</varname>,
        see below. For details, see
        <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.

        Defaults to
        <option>info</option>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>SyslogLevelPrefix=</varname></term>
        <listitem><para>Takes a boolean argument. If true and
        <varname>StandardOutput=</varname> or
        <varname>StandardError=</varname> are set to
        <option>syslog</option>, <option>kmsg</option> or
        <option>journal</option>, log lines written by the executed
        process that are prefixed with a log level will be passed on
        to syslog with this log level set but the prefix removed. If
        set to false, the interpretation of these prefixes is disabled
        and the logged lines are passed on as-is. For details about
        this prefixing see
        <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
        Defaults to true.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>TimerSlackNSec=</varname></term>
        <listitem><para>Sets the timer slack in nanoseconds for the
        executed processes. The timer slack controls the accuracy of
        wake-ups triggered by timers. See
        <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        for more information. Note that in contrast to most other time
        span definitions this parameter takes an integer value in
        nano-seconds if no unit is specified. The usual time units are
        understood too.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>LimitCPU=</varname></term>
        <term><varname>LimitFSIZE=</varname></term>
        <term><varname>LimitDATA=</varname></term>
        <term><varname>LimitSTACK=</varname></term>
        <term><varname>LimitCORE=</varname></term>
        <term><varname>LimitRSS=</varname></term>
        <term><varname>LimitNOFILE=</varname></term>
        <term><varname>LimitAS=</varname></term>
        <term><varname>LimitNPROC=</varname></term>
        <term><varname>LimitMEMLOCK=</varname></term>
        <term><varname>LimitLOCKS=</varname></term>
        <term><varname>LimitSIGPENDING=</varname></term>
        <term><varname>LimitMSGQUEUE=</varname></term>
        <term><varname>LimitNICE=</varname></term>
        <term><varname>LimitRTPRIO=</varname></term>
        <term><varname>LimitRTTIME=</varname></term>
        <listitem><para>Set soft and hard limits on various resources for executed processes. See
        <citerefentry><refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details on
        the resource limit concept. Resource limits may be specified in two formats: either as single value to set a
        specific soft and hard limit to the same value, or as colon-separated pair <option>soft:hard</option> to set
        both limits individually (e.g. <literal>LimitAS=4G:16G</literal>).  Use the string <varname>infinity</varname>
        to configure no limit on a specific resource. The multiplicative suffixes K, M, G, T, P and E (to the base
        1024) may be used for resource limits measured in bytes (e.g. LimitAS=16G). For the limits referring to time
        values, the usual time units ms, s, min, h and so on may be used (see
        <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
        details). Note that if no time unit is specified for <varname>LimitCPU=</varname> the default unit of seconds
        is implied, while for <varname>LimitRTTIME=</varname> the default unit of microseconds is implied. Also, note
        that the effective granularity of the limits might influence their enforcement. For example, time limits
        specified for <varname>LimitCPU=</varname> will be rounded up implicitly to multiples of 1s. For
        <varname>LimitNICE=</varname> the value may be specified in two syntaxes: if prefixed with <literal>+</literal>
        or <literal>-</literal>, the value is understood as regular Linux nice value in the range -20..19. If not
        prefixed like this the value is understood as raw resource limit parameter in the range 0..40 (with 0 being
        equivalent to 1).</para>

        <para>Note that most process resource limits configured with
        these options are per-process, and processes may fork in order
        to acquire a new set of resources that are accounted
        independently of the original process, and may thus escape
        limits set. Also note that <varname>LimitRSS=</varname> is not
        implemented on Linux, and setting it has no effect. Often it
        is advisable to prefer the resource controls listed in
        <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        over these per-process limits, as they apply to services as a
        whole, may be altered dynamically at runtime, and are
        generally more expressive. For example,
        <varname>MemoryLimit=</varname> is a more powerful (and
        working) replacement for <varname>LimitRSS=</varname>.</para>

        <para>For system units these resource limits may be chosen freely. For user units however (i.e. units run by a
        per-user instance of
        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>), these limits are
        bound by (possibly more restrictive) per-user limits enforced by the OS.</para>

        <para>Resource limits not configured explicitly for a unit default to the value configured in the various
        <varname>DefaultLimitCPU=</varname>, <varname>DefaultLimitFSIZE=</varname>, … options available in
        <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, and –
        if not configured there – the kernel or per-user defaults, as defined by the OS (the latter only for user
        services, see above).</para>

        <table>
          <title>Resource limit directives, their equivalent <command>ulimit</command> shell commands and the unit used</title>

          <tgroup cols='3'>
            <colspec colname='directive' />
            <colspec colname='equivalent' />
            <colspec colname='unit' />
            <thead>
              <row>
                <entry>Directive</entry>
                <entry><command>ulimit</command> equivalent</entry>
                <entry>Unit</entry>
              </row>
            </thead>
            <tbody>
              <row>
                <entry>LimitCPU=</entry>
                <entry>ulimit -t</entry>
                <entry>Seconds</entry>
              </row>
              <row>
                <entry>LimitFSIZE=</entry>
                <entry>ulimit -f</entry>
                <entry>Bytes</entry>
              </row>
              <row>
                <entry>LimitDATA=</entry>
                <entry>ulimit -d</entry>
                <entry>Bytes</entry>
              </row>
              <row>
                <entry>LimitSTACK=</entry>
                <entry>ulimit -s</entry>
                <entry>Bytes</entry>
              </row>
              <row>
                <entry>LimitCORE=</entry>
                <entry>ulimit -c</entry>
                <entry>Bytes</entry>
              </row>
              <row>
                <entry>LimitRSS=</entry>
                <entry>ulimit -m</entry>
                <entry>Bytes</entry>
              </row>
              <row>
                <entry>LimitNOFILE=</entry>
                <entry>ulimit -n</entry>
                <entry>Number of File Descriptors</entry>
              </row>
              <row>
                <entry>LimitAS=</entry>
                <entry>ulimit -v</entry>
                <entry>Bytes</entry>
              </row>
              <row>
                <entry>LimitNPROC=</entry>
                <entry>ulimit -u</entry>
                <entry>Number of Processes</entry>
              </row>
              <row>
                <entry>LimitMEMLOCK=</entry>
                <entry>ulimit -l</entry>
                <entry>Bytes</entry>
              </row>
              <row>
                <entry>LimitLOCKS=</entry>
                <entry>ulimit -x</entry>
                <entry>Number of Locks</entry>
              </row>
              <row>
                <entry>LimitSIGPENDING=</entry>
                <entry>ulimit -i</entry>
                <entry>Number of Queued Signals</entry>
              </row>
              <row>
                <entry>LimitMSGQUEUE=</entry>
                <entry>ulimit -q</entry>
                <entry>Bytes</entry>
              </row>
              <row>
                <entry>LimitNICE=</entry>
                <entry>ulimit -e</entry>
                <entry>Nice Level</entry>
              </row>
              <row>
                <entry>LimitRTPRIO=</entry>
                <entry>ulimit -r</entry>
                <entry>Realtime Priority</entry>
              </row>
              <row>
                <entry>LimitRTTIME=</entry>
                <entry>No equivalent</entry>
                <entry>Microseconds</entry>
              </row>
            </tbody>
          </tgroup>
        </table></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>PAMName=</varname></term>
        <listitem><para>Sets the PAM service name to set up a session
        as. If set, the executed process will be registered as a PAM
        session under the specified service name. This is only useful
        in conjunction with the <varname>User=</varname> setting. If
        not set, no PAM session will be opened for the executed
        processes. See
        <citerefentry project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>
        for details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>CapabilityBoundingSet=</varname></term>

        <listitem><para>Controls which capabilities to include in the capability bounding set for the executed
        process. See <citerefentry
        project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
        details. Takes a whitespace-separated list of capability names, e.g. <constant>CAP_SYS_ADMIN</constant>,
        <constant>CAP_DAC_OVERRIDE</constant>, <constant>CAP_SYS_PTRACE</constant>. Capabilities listed will be
        included in the bounding set, all others are removed. If the list of capabilities is prefixed with
        <literal>~</literal>, all but the listed capabilities will be included, the effect of the assignment
        inverted. Note that this option also affects the respective capabilities in the effective, permitted and
        inheritable capability sets. If this option is not used, the capability bounding set is not modified on process
        execution, hence no limits on the capabilities of the process are enforced. This option may appear more than
        once, in which case the bounding sets are merged. If the empty string is assigned to this option, the bounding
        set is reset to the empty capability set, and all prior settings have no effect.  If set to
        <literal>~</literal> (without any further argument), the bounding set is reset to the full set of available
        capabilities, also undoing any previous settings. This does not affect commands prefixed with
        <literal>+</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>AmbientCapabilities=</varname></term>

        <listitem><para>Controls which capabilities to include in the ambient capability set for the executed
        process. Takes a whitespace-separated list of capability names, e.g. <constant>CAP_SYS_ADMIN</constant>,
        <constant>CAP_DAC_OVERRIDE</constant>, <constant>CAP_SYS_PTRACE</constant>. This option may appear more than
        once in which case the ambient capability sets are merged.  If the list of capabilities is prefixed with
        <literal>~</literal>, all but the listed capabilities will be included, the effect of the assignment
        inverted. If the empty string is assigned to this option, the ambient capability set is reset to the empty
        capability set, and all prior settings have no effect.  If set to <literal>~</literal> (without any further
        argument), the ambient capability set is reset to the full set of available capabilities, also undoing any
        previous settings. Note that adding capabilities to ambient capability set adds them to the process's inherited
        capability set.  </para><para> Ambient capability sets are useful if you want to execute a process as a
        non-privileged user but still want to give it some capabilities.  Note that in this case option
        <constant>keep-caps</constant> is automatically added to <varname>SecureBits=</varname> to retain the
        capabilities over the user change. <varname>AmbientCapabilities=</varname> does not affect commands prefixed
        with <literal>+</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>SecureBits=</varname></term>
        <listitem><para>Controls the secure bits set for the executed
        process. Takes a space-separated combination of options from
        the following list:
        <option>keep-caps</option>,
        <option>keep-caps-locked</option>,
        <option>no-setuid-fixup</option>,
        <option>no-setuid-fixup-locked</option>,
        <option>noroot</option>, and
        <option>noroot-locked</option>.
        This option may appear more than once, in which case the secure
        bits are ORed. If the empty string is assigned to this option,
        the bits are reset to 0. This does not affect commands prefixed with <literal>+</literal>.
        See <citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
        for details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ReadWritePaths=</varname></term>
        <term><varname>ReadOnlyPaths=</varname></term>
        <term><varname>InaccessiblePaths=</varname></term>

        <listitem><para>Sets up a new file system namespace for executed processes. These options may be used to limit
        access a process might have to the file system hierarchy. Each setting takes a space-separated list of paths
        relative to the host's root directory (i.e. the system running the service manager).  Note that if paths
        contain symlinks, they are resolved relative to the root directory set with
        <varname>RootDirectory=</varname>.</para>

        <para>Paths listed in <varname>ReadWritePaths=</varname> are accessible from within the namespace with the same
        access modes as from outside of it. Paths listed in <varname>ReadOnlyPaths=</varname> are accessible for
        reading only, writing will be refused even if the usual file access controls would permit this. Nest
        <varname>ReadWritePaths=</varname> inside of <varname>ReadOnlyPaths=</varname> in order to provide writable
        subdirectories within read-only directories. Use <varname>ReadWritePaths=</varname> in order to whitelist
        specific paths for write access if <varname>ProtectSystem=strict</varname> is used. Paths listed in
        <varname>InaccessiblePaths=</varname> will be made inaccessible for processes inside the namespace (along with
        everything below them in the file system hierarchy).</para>

        <para>Note that restricting access with these options does not extend to submounts of a directory that are
        created later on.  Non-directory paths may be specified as well. These options may be specified more than once,
        in which case all paths listed will have limited access from within the namespace. If the empty string is
        assigned to this option, the specific list is reset, and all prior assignments have no effect.</para>

        <para>Paths in <varname>ReadWritePaths=</varname>, <varname>ReadOnlyPaths=</varname> and
        <varname>InaccessiblePaths=</varname> may be prefixed with <literal>-</literal>, in which case they will be ignored
        when they do not exist. Note that using this setting will disconnect propagation of mounts from the service to
        the host (propagation in the opposite direction continues to work). This means that this setting may not be used
        for services which shall be able to install mount points in the main mount namespace. Note that the effect of
        these settings may be undone by privileged processes. In order to set up an effective sandboxed environment for
        a unit it is thus recommended to combine these settings with either
        <varname>CapabilityBoundingSet=~CAP_SYS_ADMIN</varname> or <varname>SystemCallFilter=~@mount</varname>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>PrivateTmp=</varname></term>

        <listitem><para>Takes a boolean argument. If true, sets up a new file system namespace for the executed
        processes and mounts private <filename>/tmp</filename> and <filename>/var/tmp</filename> directories inside it
        that is not shared by processes outside of the namespace. This is useful to secure access to temporary files of
        the process, but makes sharing between processes via <filename>/tmp</filename> or <filename>/var/tmp</filename>
        impossible. If this is enabled, all temporary files created by a service in these directories will be removed
        after the service is stopped.  Defaults to false. It is possible to run two or more units within the same
        private <filename>/tmp</filename> and <filename>/var/tmp</filename> namespace by using the
        <varname>JoinsNamespaceOf=</varname> directive, see
        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
        details. This setting is implied if <varname>DynamicUser=</varname> is set. For this setting the same
        restrictions regarding mount propagation and privileges apply as for <varname>ReadOnlyPaths=</varname> and
        related calls, see above.</para></listitem>

      </varlistentry>

      <varlistentry>
        <term><varname>PrivateDevices=</varname></term>

        <listitem><para>Takes a boolean argument. If true, sets up a new /dev namespace for the executed processes and
        only adds API pseudo devices such as <filename>/dev/null</filename>, <filename>/dev/zero</filename> or
        <filename>/dev/random</filename> (as well as the pseudo TTY subsystem) to it, but no physical devices such as
        <filename>/dev/sda</filename>, system memory <filename>/dev/mem</filename>, system ports
        <filename>/dev/port</filename> and others. This is useful to securely turn off physical device access by the
        executed process. Defaults to false. Enabling this option will install a system call filter to block low-level
        I/O system calls that are grouped in the <varname>@raw-io</varname> set, will also remove
        <constant>CAP_MKNOD</constant> and <constant>CAP_SYS_RAWIO</constant> from the capability bounding set for
        the unit (see above), and set <varname>DevicePolicy=closed</varname> (see
        <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        for details). Note that using this setting will disconnect propagation of mounts from the service to the host
        (propagation in the opposite direction continues to work).  This means that this setting may not be used for
        services which shall be able to install mount points in the main mount namespace. The /dev namespace will be
        mounted read-only and 'noexec'.  The latter may break old programs which try to set up executable memory by
        using <citerefentry><refentrytitle>mmap</refentrytitle><manvolnum>2</manvolnum></citerefentry> of
        <filename>/dev/zero</filename> instead of using <constant>MAP_ANON</constant>. This setting is implied if
        <varname>DynamicUser=</varname> is set. For this setting the same restrictions regarding mount propagation and
        privileges apply as for <varname>ReadOnlyPaths=</varname> and related calls, see above.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>PrivateNetwork=</varname></term>

        <listitem><para>Takes a boolean argument. If true, sets up a
        new network namespace for the executed processes and
        configures only the loopback network device
        <literal>lo</literal> inside it. No other network devices will
        be available to the executed process. This is useful to
        securely turn off network access by the executed process.
        Defaults to false. It is possible to run two or more units
        within the same private network namespace by using the
        <varname>JoinsNamespaceOf=</varname> directive, see
        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        for details. Note that this option will disconnect all socket
        families from the host, this includes AF_NETLINK and AF_UNIX.
        The latter has the effect that AF_UNIX sockets in the abstract
        socket namespace will become unavailable to the processes
        (however, those located in the file system will continue to be
        accessible).</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>PrivateUsers=</varname></term>

        <listitem><para>Takes a boolean argument. If true, sets up a new user namespace for the executed processes and
        configures a minimal user and group mapping, that maps the <literal>root</literal> user and group as well as
        the unit's own user and group to themselves and everything else to the <literal>nobody</literal> user and
        group. This is useful to securely detach the user and group databases used by the unit from the rest of the
        system, and thus to create an effective sandbox environment. All files, directories, processes, IPC objects and
        other resources owned by users/groups not equalling <literal>root</literal> or the unit's own will stay visible
        from within the unit but appear owned by the <literal>nobody</literal> user and group. If this mode is enabled,
        all unit processes are run without privileges in the host user namespace (regardless if the unit's own
        user/group is <literal>root</literal> or not). Specifically this means that the process will have zero process
        capabilities on the host's user namespace, but full capabilities within the service's user namespace. Settings
        such as <varname>CapabilityBoundingSet=</varname> will affect only the latter, and there's no way to acquire
        additional capabilities in the host's user namespace. Defaults to off.</para>

        <para>This setting is particularly useful in conjunction with <varname>RootDirectory=</varname>, as the need to
        synchronize the user and group databases in the root directory and on the host is reduced, as the only users
        and groups who need to be matched are <literal>root</literal>, <literal>nobody</literal> and the unit's own
        user and group.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ProtectSystem=</varname></term>

        <listitem><para>Takes a boolean argument or the special values <literal>full</literal> or
        <literal>strict</literal>. If true, mounts the <filename>/usr</filename> and <filename>/boot</filename>
        directories read-only for processes invoked by this unit. If set to <literal>full</literal>, the
        <filename>/etc</filename> directory is mounted read-only, too. If set to <literal>strict</literal> the entire
        file system hierarchy is mounted read-only, except for the API file system subtrees <filename>/dev</filename>,
        <filename>/proc</filename> and <filename>/sys</filename> (protect these directories using
        <varname>PrivateDevices=</varname>, <varname>ProtectKernelTunables=</varname>,
        <varname>ProtectControlGroups=</varname>). This setting ensures that any modification of the vendor-supplied
        operating system (and optionally its configuration, and local mounts) is prohibited for the service.  It is
        recommended to enable this setting for all long-running services, unless they are involved with system updates
        or need to modify the operating system in other ways. If this option is used,
        <varname>ReadWritePaths=</varname> may be used to exclude specific directories from being made read-only. This
        setting is implied if <varname>DynamicUser=</varname> is set. For this setting the same restrictions regarding
        mount propagation and privileges apply as for <varname>ReadOnlyPaths=</varname> and related calls, see
        above. Defaults to off.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ProtectHome=</varname></term>

        <listitem><para>Takes a boolean argument or <literal>read-only</literal>. If true, the directories
        <filename>/home</filename>, <filename>/root</filename> and <filename>/run/user</filename> are made inaccessible
        and empty for processes invoked by this unit. If set to <literal>read-only</literal>, the three directories are
        made read-only instead. It is recommended to enable this setting for all long-running services (in particular
        network-facing ones), to ensure they cannot get access to private user data, unless the services actually
        require access to the user's private data. This setting is implied if <varname>DynamicUser=</varname> is
        set. For this setting the same restrictions regarding mount propagation and privileges apply as for
        <varname>ReadOnlyPaths=</varname> and related calls, see above.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ProtectKernelTunables=</varname></term>

        <listitem><para>Takes a boolean argument. If true, kernel variables accessible through
        <filename>/proc/sys</filename>, <filename>/sys</filename>, <filename>/proc/sysrq-trigger</filename>,
        <filename>/proc/latency_stats</filename>, <filename>/proc/acpi</filename>,
        <filename>/proc/timer_stats</filename>, <filename>/proc/fs</filename> and <filename>/proc/irq</filename> will
        be made read-only to all processes of the unit. Usually, tunable kernel variables should only be written at
        boot-time, with the <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        mechanism. Almost no services need to write to these at runtime; it is hence recommended to turn this on for
        most services. For this setting the same restrictions regarding mount propagation and privileges apply as for
        <varname>ReadOnlyPaths=</varname> and related calls, see above. Defaults to off.
        Note that this option does not prevent kernel tuning through IPC interfaces and exeternal programs. However
        <varname>InaccessiblePaths=</varname> can be used to make some IPC file system objects
        inaccessible.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ProtectControlGroups=</varname></term>

        <listitem><para>Takes a boolean argument. If true, the Linux Control Groups (<citerefentry
        project='man-pages'><refentrytitle>cgroups</refentrytitle><manvolnum>7</manvolnum></citerefentry>) hierarchies
        accessible through <filename>/sys/fs/cgroup</filename> will be made read-only to all processes of the
        unit. Except for container managers no services should require write access to the control groups hierarchies;
        it is hence recommended to turn this on for most services. For this setting the same restrictions regarding
        mount propagation and privileges apply as for <varname>ReadOnlyPaths=</varname> and related calls, see
        above. Defaults to off.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>MountFlags=</varname></term>

        <listitem><para>Takes a mount propagation flag: <option>shared</option>, <option>slave</option> or
        <option>private</option>, which control whether mounts in the file system namespace set up for this unit's
        processes will receive or propagate mounts or unmounts. See <citerefentry
        project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
        details. Defaults to <option>shared</option>. Use <option>shared</option> to ensure that mounts and unmounts
        are propagated from the host to the container and vice versa. Use <option>slave</option> to run processes so
        that none of their mounts and unmounts will propagate to the host. Use <option>private</option> to also ensure
        that no mounts and unmounts from the host will propagate into the unit processes' namespace. Note that
        <option>slave</option> means that file systems mounted on the host might stay mounted continuously in the
        unit's namespace, and thus keep the device busy. Note that the file system namespace related options
        (<varname>PrivateTmp=</varname>, <varname>PrivateDevices=</varname>, <varname>ProtectSystem=</varname>,
        <varname>ProtectHome=</varname>, <varname>ProtectKernelTunables=</varname>,
        <varname>ProtectControlGroups=</varname>, <varname>ReadOnlyPaths=</varname>,
        <varname>InaccessiblePaths=</varname>, <varname>ReadWritePaths=</varname>) require that mount and unmount
        propagation from the unit's file system namespace is disabled, and hence downgrade <option>shared</option> to
        <option>slave</option>. </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>UtmpIdentifier=</varname></term>

        <listitem><para>Takes a four character identifier string for
        an <citerefentry
        project='man-pages'><refentrytitle>utmp</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        and wtmp entry for this service. This should only be
        set for services such as <command>getty</command>
        implementations (such as <citerefentry
        project='die-net'><refentrytitle>agetty</refentrytitle><manvolnum>8</manvolnum></citerefentry>)
        where utmp/wtmp entries must be created and cleared before and
        after execution, or for services that shall be executed as if
        they were run by a <command>getty</command> process (see
        below). If the configured string is longer than four
        characters, it is truncated and the terminal four characters
        are used. This setting interprets %I style string
        replacements. This setting is unset by default, i.e. no
        utmp/wtmp entries are created or cleaned up for this
        service.</para></listitem>
      </varlistentry>

      <varlistentry>
         <term><varname>UtmpMode=</varname></term>

         <listitem><para>Takes one of <literal>init</literal>,
         <literal>login</literal> or <literal>user</literal>. If
         <varname>UtmpIdentifier=</varname> is set, controls which
         type of <citerefentry
         project='man-pages'><refentrytitle>utmp</refentrytitle><manvolnum>5</manvolnum></citerefentry>/wtmp
         entries for this service are generated. This setting has no
         effect unless <varname>UtmpIdentifier=</varname> is set
         too. If <literal>init</literal> is set, only an
         <constant>INIT_PROCESS</constant> entry is generated and the
         invoked process must implement a
         <command>getty</command>-compatible utmp/wtmp logic. If
         <literal>login</literal> is set, first an
         <constant>INIT_PROCESS</constant> entry, followed by a
         <constant>LOGIN_PROCESS</constant> entry is generated. In
         this case, the invoked process must implement a <citerefentry
         project='die-net'><refentrytitle>login</refentrytitle><manvolnum>1</manvolnum></citerefentry>-compatible
         utmp/wtmp logic. If <literal>user</literal> is set, first an
         <constant>INIT_PROCESS</constant> entry, then a
         <constant>LOGIN_PROCESS</constant> entry and finally a
         <constant>USER_PROCESS</constant> entry is generated. In this
         case, the invoked process may be any process that is suitable
         to be run as session leader. Defaults to
         <literal>init</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>SELinuxContext=</varname></term>

        <listitem><para>Set the SELinux security context of the
        executed process. If set, this will override the automated
        domain transition. However, the policy still needs to
        authorize the transition. This directive is ignored if SELinux
        is disabled. If prefixed by <literal>-</literal>, all errors
        will be ignored. This does not affect commands prefixed with <literal>+</literal>.
        See <citerefentry project='die-net'><refentrytitle>setexeccon</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        for details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>AppArmorProfile=</varname></term>

        <listitem><para>Takes a profile name as argument. The process
        executed by the unit will switch to this profile when started.
        Profiles must already be loaded in the kernel, or the unit
        will fail. This result in a non operation if AppArmor is not
        enabled. If prefixed by <literal>-</literal>, all errors will
        be ignored. This does not affect commands prefixed with <literal>+</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>SmackProcessLabel=</varname></term>

        <listitem><para>Takes a <option>SMACK64</option> security
        label as argument. The process executed by the unit will be
        started under this label and SMACK will decide whether the
        process is allowed to run or not, based on it. The process
        will continue to run under the label specified here unless the
        executable has its own <option>SMACK64EXEC</option> label, in
        which case the process will transition to run under that
        label. When not specified, the label that systemd is running
        under is used. This directive is ignored if SMACK is
        disabled.</para>

        <para>The value may be prefixed by <literal>-</literal>, in
        which case all errors will be ignored. An empty value may be
        specified to unset previous assignments. This does not affect
        commands prefixed with <literal>+</literal>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>IgnoreSIGPIPE=</varname></term>

        <listitem><para>Takes a boolean argument. If true, causes
        <constant>SIGPIPE</constant> to be ignored in the executed
        process. Defaults to true because <constant>SIGPIPE</constant>
        generally is useful only in shell pipelines.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>NoNewPrivileges=</varname></term>

        <listitem><para>Takes a boolean argument. If true, ensures
        that the service process and all its children can never gain
        new privileges. This option is more powerful than the
        respective secure bits flags (see above), as it also prohibits
        UID changes of any kind. This is the simplest, most effective
        way to ensure that a process and its children can never
        elevate privileges again.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>SystemCallFilter=</varname></term>

        <listitem><para>Takes a space-separated list of system call
        names. If this setting is used, all system calls executed by
        the unit processes except for the listed ones will result in
        immediate process termination with the
        <constant>SIGSYS</constant> signal (whitelisting). If the
        first character of the list is <literal>~</literal>, the
        effect is inverted: only the listed system calls will result
        in immediate process termination (blacklisting). If running in
        user mode, or in system mode, but without the
        <constant>CAP_SYS_ADMIN</constant> capability (e.g. setting
        <varname>User=nobody</varname>),
        <varname>NoNewPrivileges=yes</varname> is implied. This
        feature makes use of the Secure Computing Mode 2 interfaces of
        the kernel ('seccomp filtering') and is useful for enforcing a
        minimal sandboxing environment. Note that the
        <function>execve</function>,
        <function>rt_sigreturn</function>,
        <function>sigreturn</function>,
        <function>exit_group</function>, <function>exit</function>
        system calls are implicitly whitelisted and do not need to be
        listed explicitly. This option may be specified more than once,
        in which case the filter masks are merged. If the empty string
        is assigned, the filter is reset, all prior assignments will
        have no effect. This does not affect commands prefixed with <literal>+</literal>.</para>

        <para>If you specify both types of this option (i.e.
        whitelisting and blacklisting), the first encountered will
        take precedence and will dictate the default action
        (termination or approval of a system call). Then the next
        occurrences of this option will add or delete the listed
        system calls from the set of the filtered system calls,
        depending of its type and the default action. (For example, if
        you have started with a whitelisting of
        <function>read</function> and <function>write</function>, and
        right after it add a blacklisting of
        <function>write</function>, then <function>write</function>
        will be removed from the set.)</para>

        <para>As the number of possible system
        calls is large, predefined sets of system calls are provided.
        A set starts with <literal>@</literal> character, followed by
        name of the set.

        <table>
          <title>Currently predefined system call sets</title>

          <tgroup cols='2'>
            <colspec colname='set' />
            <colspec colname='description' />
            <thead>
              <row>
                <entry>Set</entry>
                <entry>Description</entry>
              </row>
            </thead>
            <tbody>
              <row>
                <entry>@clock</entry>
                <entry>System calls for changing the system clock (<citerefentry project='man-pages'><refentrytitle>adjtimex</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>settimeofday</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)</entry>
              </row>
              <row>
                <entry>@cpu-emulation</entry>
                <entry>System calls for CPU emulation functionality (<citerefentry project='man-pages'><refentrytitle>vm86</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)</entry>
              </row>
              <row>
                <entry>@debug</entry>
                <entry>Debugging, performance monitoring and tracing functionality (<citerefentry project='man-pages'><refentrytitle>ptrace</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>perf_event_open</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)</entry>
              </row>
              <row>
                <entry>@io-event</entry>
                <entry>Event loop system calls (<citerefentry project='man-pages'><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>select</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>eventfd</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)</entry>
              </row>
              <row>
                <entry>@ipc</entry>
                <entry>SysV IPC, POSIX Message Queues or other IPC (<citerefentry project='man-pages'><refentrytitle>mq_overview</refentrytitle><manvolnum>7</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>svipc</refentrytitle><manvolnum>7</manvolnum></citerefentry>)</entry>
              </row>
              <row>
                <entry>@keyring</entry>
                <entry>Kernel keyring access (<citerefentry project='man-pages'><refentrytitle>keyctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)</entry>
              </row>
              <row>
                <entry>@module</entry>
                <entry>Kernel module control (<citerefentry project='man-pages'><refentrytitle>init_module</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>delete_module</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)</entry>
              </row>
              <row>
                <entry>@mount</entry>
                <entry>File system mounting and unmounting (<citerefentry project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)</entry>
              </row>
              <row>
                <entry>@network-io</entry>
                <entry>Socket I/O (including local AF_UNIX): <citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>unix</refentrytitle><manvolnum>7</manvolnum></citerefentry></entry>
              </row>
              <row>
                <entry>@obsolete</entry>
                <entry>Unusual, obsolete or unimplemented (<citerefentry project='man-pages'><refentrytitle>create_module</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>gtty</refentrytitle><manvolnum>2</manvolnum></citerefentry>, …)</entry>
              </row>
              <row>
                <entry>@privileged</entry>
                <entry>All system calls which need super-user capabilities (<citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>)</entry>
              </row>
              <row>
                <entry>@process</entry>
                <entry>Process control, execution, namespaces (<citerefentry project='man-pages'><refentrytitle>execve</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>kill</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>namespaces</refentrytitle><manvolnum>7</manvolnum></citerefentry>, …</entry>
              </row>
              <row>
                <entry>@raw-io</entry>
                <entry>Raw I/O port access (<citerefentry project='man-pages'><refentrytitle>ioperm</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>iopl</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <function>pciconfig_read()</function>, …</entry>
              </row>
            </tbody>
          </tgroup>
        </table>

        Note, that as new system calls are added to the kernel, additional system calls might be added to the groups
        above, so the contents of the sets may change between systemd versions.</para>

        <para>It is recommended to combine the file system namespacing related options with
        <varname>SystemCallFilter=~@mount</varname>, in order to prohibit the unit's processes to undo the
        mappings. Specifically these are the options <varname>PrivateTmp=</varname>,
        <varname>PrivateDevices=</varname>, <varname>ProtectSystem=</varname>, <varname>ProtectHome=</varname>,
        <varname>ProtectKernelTunables=</varname>, <varname>ProtectControlGroups=</varname>,
        <varname>ReadOnlyPaths=</varname>, <varname>InaccessiblePaths=</varname> and
        <varname>ReadWritePaths=</varname>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>SystemCallErrorNumber=</varname></term>

        <listitem><para>Takes an <literal>errno</literal> error number
        name to return when the system call filter configured with
        <varname>SystemCallFilter=</varname> is triggered, instead of
        terminating the process immediately. Takes an error name such
        as <constant>EPERM</constant>, <constant>EACCES</constant> or
        <constant>EUCLEAN</constant>. When this setting is not used,
        or when the empty string is assigned, the process will be
        terminated immediately when the filter is
        triggered.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>SystemCallArchitectures=</varname></term>

        <listitem><para>Takes a space-separated list of architecture
        identifiers to include in the system call filter. The known
        architecture identifiers are <constant>x86</constant>,
        <constant>x86-64</constant>, <constant>x32</constant>,
        <constant>arm</constant>, <constant>s390</constant>,
        <constant>s390x</constant> as well as the special identifier
        <constant>native</constant>. Only system calls of the
        specified architectures will be permitted to processes of this
        unit. This is an effective way to disable compatibility with
        non-native architectures for processes, for example to
        prohibit execution of 32-bit x86 binaries on 64-bit x86-64
        systems. The special <constant>native</constant> identifier
        implicitly maps to the native architecture of the system (or
        more strictly: to the architecture the system manager is
        compiled for). If running in user mode, or in system mode,
        but without the <constant>CAP_SYS_ADMIN</constant>
        capability (e.g. setting <varname>User=nobody</varname>),
        <varname>NoNewPrivileges=yes</varname> is implied. Note
        that setting this option to a non-empty list implies that
        <constant>native</constant> is included too. By default, this
        option is set to the empty list, i.e. no architecture system
        call filtering is applied.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RestrictAddressFamilies=</varname></term>

        <listitem><para>Restricts the set of socket address families
        accessible to the processes of this unit. Takes a
        space-separated list of address family names to whitelist,
        such as
        <constant>AF_UNIX</constant>,
        <constant>AF_INET</constant> or
        <constant>AF_INET6</constant>. When
        prefixed with <constant>~</constant> the listed address
        families will be applied as blacklist, otherwise as whitelist.
        Note that this restricts access to the
        <citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        system call only. Sockets passed into the process by other
        means (for example, by using socket activation with socket
        units, see
        <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>)
        are unaffected. Also, sockets created with
        <function>socketpair()</function> (which creates connected
        AF_UNIX sockets only) are unaffected. Note that this option
        has no effect on 32-bit x86 and is ignored (but works
        correctly on x86-64). If running in user mode, or in system
        mode, but without the <constant>CAP_SYS_ADMIN</constant>
        capability (e.g. setting <varname>User=nobody</varname>),
        <varname>NoNewPrivileges=yes</varname> is implied. By
        default, no restriction applies, all address families are
        accessible to processes. If assigned the empty string, any
        previous list changes are undone.</para>

        <para>Use this option to limit exposure of processes to remote
        systems, in particular via exotic network protocols. Note that
        in most cases, the local <constant>AF_UNIX</constant> address
        family should be included in the configured whitelist as it is
        frequently used for local communication, including for
        <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        logging. This does not affect commands prefixed with <literal>+</literal>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ProtectKernelModules=</varname></term>

        <listitem><para>Takes a boolean argument. If true, explicit module loading will
        be denied. This allows to turn off module load and unload operations on modular
        kernels. It is recomended to turn this on for most services that do not need special
        file systems or extra kernel modules to work. Default to off. Enabling this option
        removes <constant>CAP_SYS_MODULE</constant> from the capability bounding set for
        the unit, and installs a system call filter to block module system calls.
        Note that limited automatic module loading due to user configuration or kernel
        mapping tables might still happen as side effect of requested user operations,
        both privileged and unprivileged. To disable module auto-load feature please see
        <citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        <constant>kernel.modules_disabled</constant> mechanism and
        <filename>/proc/sys/kernel/modules_disabled</filename> documentation.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>Personality=</varname></term>

        <listitem><para>Controls which kernel architecture <citerefentry
        project='man-pages'><refentrytitle>uname</refentrytitle><manvolnum>2</manvolnum></citerefentry> shall report,
        when invoked by unit processes. Takes one of the architecture identifiers <constant>x86</constant>,
        <constant>x86-64</constant>, <constant>ppc</constant>, <constant>ppc-le</constant>, <constant>ppc64</constant>,
        <constant>ppc64-le</constant>, <constant>s390</constant> or <constant>s390x</constant>. Which personality
        architectures are supported depends on the system architecture. Usually the 64bit versions of the various
        system architectures support their immediate 32bit personality architecture counterpart, but no others. For
        example, <constant>x86-64</constant> systems support the <constant>x86-64</constant> and
        <constant>x86</constant> personalities but no others. The personality feature is useful when running 32-bit
        services on a 64-bit host system. If not specified, the personality is left unmodified and thus reflects the
        personality of the host system's kernel.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RuntimeDirectory=</varname></term>
        <term><varname>RuntimeDirectoryMode=</varname></term>

        <listitem><para>Takes a list of directory names. If set, one
        or more directories by the specified names will be created
        below <filename>/run</filename> (for system services) or below
        <varname>$XDG_RUNTIME_DIR</varname> (for user services) when
        the unit is started, and removed when the unit is stopped. The
        directories will have the access mode specified in
        <varname>RuntimeDirectoryMode=</varname>, and will be owned by
        the user and group specified in <varname>User=</varname> and
        <varname>Group=</varname>. Use this to manage one or more
        runtime directories of the unit and bind their lifetime to the
        daemon runtime. The specified directory names must be
        relative, and may not include a <literal>/</literal>, i.e.
        must refer to simple directories to create or remove. This is
        particularly useful for unprivileged daemons that cannot
        create runtime directories in <filename>/run</filename> due to
        lack of privileges, and to make sure the runtime directory is
        cleaned up automatically after use. For runtime directories
        that require more complex or different configuration or
        lifetime guarantees, please consider using
        <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>MemoryDenyWriteExecute=</varname></term>

        <listitem><para>Takes a boolean argument. If set, attempts to create memory mappings that are writable and
        executable at the same time, or to change existing memory mappings to become executable are prohibited.
        Specifically, a system call filter is added that rejects
        <citerefentry><refentrytitle>mmap</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        system calls with both <constant>PROT_EXEC</constant> and <constant>PROT_WRITE</constant> set
        and <citerefentry><refentrytitle>mprotect</refentrytitle><manvolnum>2</manvolnum></citerefentry>
        system calls with <constant>PROT_EXEC</constant> set. Note that this option is incompatible with programs
        that generate program code dynamically at runtime, such as JIT execution engines, or programs compiled making
        use of the code "trampoline" feature of various C compilers. This option improves service security, as it makes
        harder for software exploits to change running code dynamically.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RestrictRealtime=</varname></term>

        <listitem><para>Takes a boolean argument. If set, any attempts to enable realtime scheduling in a process of
        the unit are refused. This restricts access to realtime task scheduling policies such as
        <constant>SCHED_FIFO</constant>, <constant>SCHED_RR</constant> or <constant>SCHED_DEADLINE</constant>. See
        <citerefentry project='man-pages'><refentrytitle>sched</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details about
        these scheduling policies. Realtime scheduling policies may be used to monopolize CPU time for longer periods
        of time, and may hence be used to lock up or otherwise trigger Denial-of-Service situations on the system. It
        is hence recommended to restrict access to realtime scheduling to the few programs that actually require
        them. Defaults to off.</para></listitem>
      </varlistentry>

    </variablelist>
  </refsect1>

  <refsect1>
    <title>Environment variables in spawned processes</title>

    <para>Processes started by the system are executed in a clean
    environment in which select variables listed below are set. System
    processes started by systemd do not inherit variables from PID 1,
    but processes started by user systemd instances inherit all
    environment variables from the user systemd instance.
    </para>

    <variablelist class='environment-variables'>
      <varlistentry>
        <term><varname>$PATH</varname></term>

        <listitem><para>Colon-separated list of directories to use
        when launching executables. Systemd uses a fixed value of
        <filename>/usr/local/sbin</filename>:<filename>/usr/local/bin</filename>:<filename>/usr/sbin</filename>:<filename>/usr/bin</filename>:<filename>/sbin</filename>:<filename>/bin</filename>.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$LANG</varname></term>

        <listitem><para>Locale. Can be set in
        <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
        or on the kernel command line (see
        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
        and
        <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$USER</varname></term>
        <term><varname>$LOGNAME</varname></term>
        <term><varname>$HOME</varname></term>
        <term><varname>$SHELL</varname></term>

        <listitem><para>User name (twice), home directory, and the
        login shell. The variables are set for the units that have
        <varname>User=</varname> set, which includes user
        <command>systemd</command> instances. See
        <citerefentry project='die-net'><refentrytitle>passwd</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$INVOCATION_ID</varname></term>

        <listitem><para>Contains a randomized, unique 128bit ID identifying each runtime cycle of the unit, formatted
        as 32 character hexadecimal string. A new ID is assigned each time the unit changes from an inactive state into
        an activating or active state, and may be used to identify this specific runtime cycle, in particular in data
        stored offline, such as the journal. The same ID is passed to all processes run as part of the
        unit.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$XDG_RUNTIME_DIR</varname></term>

        <listitem><para>The directory for volatile state. Set for the
        user <command>systemd</command> instance, and also in user
        sessions. See
        <citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$XDG_SESSION_ID</varname></term>
        <term><varname>$XDG_SEAT</varname></term>
        <term><varname>$XDG_VTNR</varname></term>

        <listitem><para>The identifier of the session, the seat name,
        and virtual terminal of the session. Set by
        <citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
        for login sessions. <varname>$XDG_SEAT</varname> and
        <varname>$XDG_VTNR</varname> will only be set when attached to
        a seat and a tty.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$MAINPID</varname></term>

        <listitem><para>The PID of the units main process if it is
        known. This is only set for control processes as invoked by
        <varname>ExecReload=</varname> and similar. </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$MANAGERPID</varname></term>

        <listitem><para>The PID of the user <command>systemd</command>
        instance, set for processes spawned by it. </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$LISTEN_FDS</varname></term>
        <term><varname>$LISTEN_PID</varname></term>
        <term><varname>$LISTEN_FDNAMES</varname></term>

        <listitem><para>Information about file descriptors passed to a
        service for socket activation. See
        <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$NOTIFY_SOCKET</varname></term>

        <listitem><para>The socket
        <function>sd_notify()</function> talks to. See
        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$WATCHDOG_PID</varname></term>
        <term><varname>$WATCHDOG_USEC</varname></term>

        <listitem><para>Information about watchdog keep-alive notifications. See
        <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$TERM</varname></term>

        <listitem><para>Terminal type, set only for units connected to
        a terminal (<varname>StandardInput=tty</varname>,
        <varname>StandardOutput=tty</varname>, or
        <varname>StandardError=tty</varname>). See
        <citerefentry project='man-pages'><refentrytitle>termcap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
        </para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$JOURNAL_STREAM</varname></term>

        <listitem><para>If the standard output or standard error output of the executed processes are connected to the
        journal (for example, by setting <varname>StandardError=journal</varname>) <varname>$JOURNAL_STREAM</varname>
        contains the device and inode numbers of the connection file descriptor, formatted in decimal, separated by a
        colon (<literal>:</literal>). This permits invoked processes to safely detect whether their standard output or
        standard error output are connected to the journal. The device and inode numbers of the file descriptors should
        be compared with the values set in the environment variable to determine whether the process output is still
        connected to the journal. Note that it is generally not sufficient to only check whether
        <varname>$JOURNAL_STREAM</varname> is set at all as services might invoke external processes replacing their
        standard output or standard error output, without unsetting the environment variable.</para>

        <para>This environment variable is primarily useful to allow services to optionally upgrade their used log
        protocol to the native journal protocol (using
        <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry> and other
        functions) if their standard output or standard error output is connected to the journal anyway, thus enabling
        delivery of structured metadata along with logged messages.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$SERVICE_RESULT</varname></term>

        <listitem><para>Only defined for the service unit type, this environment variable is passed to all
        <varname>ExecStop=</varname> and <varname>ExecStopPost=</varname> processes, and encodes the service
        "result". Currently, the following values are defined: <literal>timeout</literal> (in case of an operation
        timeout), <literal>exit-code</literal> (if a service process exited with a non-zero exit code; see
        <varname>$EXIT_CODE</varname> below for the actual exit code returned), <literal>signal</literal> (if a
        service process was terminated abnormally by a signal; see <varname>$EXIT_CODE</varname> below for the actual
        signal used for the termination), <literal>core-dump</literal> (if a service process terminated abnormally and
        dumped core), <literal>watchdog</literal> (if the watchdog keep-alive ping was enabled for the service but it
        missed the deadline), or <literal>resources</literal> (a catch-all condition in case a system operation
        failed).</para>

        <para>This environment variable is useful to monitor failure or successful termination of a service. Even
        though this variable is available in both <varname>ExecStop=</varname> and <varname>ExecStopPost=</varname>, it
        is usually a better choice to place monitoring tools in the latter, as the former is only invoked for services
        that managed to start up correctly, and the latter covers both services that failed during their start-up and
        those which failed during their runtime.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$EXIT_CODE</varname></term>
        <term><varname>$EXIT_STATUS</varname></term>

        <listitem><para>Only defined for the service unit type, these environment variables are passed to all
        <varname>ExecStop=</varname>, <varname>ExecStopPost=</varname> processes and contain exit status/code
        information of the main process of the service. For the precise definition of the exit code and status, see
        <citerefentry><refentrytitle>wait</refentrytitle><manvolnum>2</manvolnum></citerefentry>. <varname>$EXIT_CODE</varname>
        is one of <literal>exited</literal>, <literal>killed</literal>,
        <literal>dumped</literal>. <varname>$EXIT_STATUS</varname> contains the numeric exit code formatted as string
        if <varname>$EXIT_CODE</varname> is <literal>exited</literal>, and the signal name in all other cases. Note
        that these environment variables are only set if the service manager succeeded to start and identify the main
        process of the service.</para>

        <table>
          <title>Summary of possible service result variable values</title>
          <tgroup cols='3'>
            <colspec colname='result' />
            <colspec colname='status' />
            <colspec colname='code' />
            <thead>
              <row>
                <entry><varname>$SERVICE_RESULT</varname></entry>
                <entry><varname>$EXIT_STATUS</varname></entry>
                <entry><varname>$EXIT_CODE</varname></entry>
              </row>
            </thead>

            <tbody>
              <row>
                <entry morerows="1" valign="top"><literal>timeout</literal></entry>
                <entry valign="top"><literal>killed</literal></entry>
                <entry><literal>TERM</literal>, <literal>KILL</literal></entry>
              </row>

              <row>
                <entry valign="top"><literal>exited</literal></entry>
                <entry><literal>0</literal>, <literal>1</literal>, <literal>2</literal>, <literal
                >3</literal>, …, <literal>255</literal></entry>
              </row>

              <row>
                <entry valign="top"><literal>exit-code</literal></entry>
                <entry valign="top"><literal>exited</literal></entry>
                <entry><literal>0</literal>, <literal>1</literal>, <literal>2</literal>, <literal
                >3</literal>, …, <literal>255</literal></entry>
              </row>

              <row>
                <entry valign="top"><literal>signal</literal></entry>
                <entry valign="top"><literal>killed</literal></entry>
                <entry><literal>HUP</literal>, <literal>INT</literal>, <literal>KILL</literal>, …</entry>
              </row>

              <row>
                <entry valign="top"><literal>core-dump</literal></entry>
                <entry valign="top"><literal>dumped</literal></entry>
                <entry><literal>ABRT</literal>, <literal>SEGV</literal>, <literal>QUIT</literal>, …</entry>
              </row>

              <row>
                <entry morerows="2" valign="top"><literal>watchdog</literal></entry>
                <entry><literal>dumped</literal></entry>
                <entry><literal>ABRT</literal></entry>
              </row>
              <row>
                <entry><literal>killed</literal></entry>
                <entry><literal>TERM</literal>, <literal>KILL</literal></entry>
              </row>
              <row>
                <entry><literal>exited</literal></entry>
                <entry><literal>0</literal>, <literal>1</literal>, <literal>2</literal>, <literal
                >3</literal>, …, <literal>255</literal></entry>
              </row>

              <row>
                <entry><literal>resources</literal></entry>
                <entry>any of the above</entry>
                <entry>any of the above</entry>
              </row>

              <row>
                <entry namest="results" nameend="code">Note: the process may be also terminated by a signal not sent by systemd. In particular the process may send an arbitrary signal to itself in a handler for any of the non-maskable signals. Nevertheless, in the <literal>timeout</literal> and <literal>watchdog</literal> rows above only the signals that systemd sends have been included.</entry>
              </row>
            </tbody>
          </tgroup>
        </table>

        </listitem>
      </varlistentry>
    </variablelist>

    <para>Additional variables may be configured by the following
    means: for processes spawned in specific units, use the
    <varname>Environment=</varname>, <varname>EnvironmentFile=</varname>
    and <varname>PassEnvironment=</varname> options above; to specify
    variables globally, use <varname>DefaultEnvironment=</varname>
    (see
    <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>)
    or the kernel option <varname>systemd.setenv=</varname> (see
    <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>).
    Additional variables may also be set through PAM,
    cf. <citerefentry project='man-pages'><refentrytitle>pam_env</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
  </refsect1>

  <refsect1>
      <title>See Also</title>
      <para>
        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
        <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
        <citerefentry project='man-pages'><refentrytitle>exec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
      </para>
  </refsect1>


</refentry>