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
|
<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE comref SYSTEM "comref.dtd">
<comref>
<header>
<copyright>
<year>1996</year><year>2016</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
</legalnotice>
<title>erl</title>
<prepared></prepared>
<docno></docno>
<date></date>
<rev></rev>
<file>erl.xml</file>
</header>
<com>erl</com>
<comsummary>The Erlang emulator.</comsummary>
<description>
<p>The <c><![CDATA[erl]]></c> program starts an Erlang runtime system.
The exact details (for example, whether <c><![CDATA[erl]]></c> is a
script or a program and which other programs it calls) are
system-dependent.</p>
<p>Windows users probably want to use the <c><![CDATA[werl]]></c> program
instead, which runs in its own window with scrollbars and supports
command-line editing. The <c><![CDATA[erl]]></c> program on Windows
provides no line editing in its shell, and on Windows 95 there is no way
to scroll back to text that has scrolled off the screen. The
<c><![CDATA[erl]]></c> program must be used, however, in pipelines or if
you want to redirect standard input or output.</p>
<note>
<p>As from ERTS 5.9 (Erlang/OTP R15B) the runtime system does by
default <em>not</em> bind schedulers to logical processors.
For more information, see system flag
<seealso marker="#+sbt"><c>+sbt</c></seealso>.</p>
</note>
</description>
<funcs>
<func>
<name>erl <arguments></name>
<fsummary>Start an Erlang runtime system.</fsummary>
<desc>
<p>Starts an Erlang runtime system.</p>
<p>The arguments can be divided into <em>emulator flags</em>,
<em>flags</em>, and <em>plain arguments</em>:</p>
<list type="bulleted">
<item>
<p>Any argument starting with character <c><![CDATA[+]]></c> is
interpreted as an
<seealso marker="#emu_flags">emulator flag</seealso>.</p>
<p>As indicated by the name, emulator flags control
the behavior of the emulator.</p>
</item>
<item>
<p>Any argument starting with character <c><![CDATA[-]]></c>
(hyphen) is interpreted as a
<seealso marker="#init_flags">flag</seealso>, which is to
be passed to the Erlang part of the runtime system, more
specifically to the <c><![CDATA[init]]></c> system process, see
<seealso marker="init"><c>init(3)</c></seealso>.</p>
<p>The <c><![CDATA[init]]></c> process itself interprets some of
these flags, the <em>init flags</em>. It also stores any
remaining flags, the <em>user flags</em>. The latter can be
retrieved by calling <c><![CDATA[init:get_argument/1]]></c>.</p>
<p>A small number of "-" flags exist, which now actually are
emulator flags, see the description below.</p>
</item>
<item>
<p>Plain arguments are not interpreted in any way. They are also
stored by the <c><![CDATA[init]]></c> process and can be retrieved
by calling <c><![CDATA[init:get_plain_arguments/0]]></c>.
Plain arguments can occur before the first flag, or after a
<c><![CDATA[--]]></c> flag. Also, the <c><![CDATA[-extra]]></c>
flag causes everything that follows to become plain arguments.</p>
</item>
</list>
<p><em>Examples:</em></p>
<pre>
% <input>erl +W w -sname arnie +R 9 -s my_init -extra +bertie</input>
(arnie@host)1> <input>init:get_argument(sname).</input>
{ok,[["arnie"]]}
(arnie@host)2> <input>init:get_plain_arguments().</input>
["+bertie"]</pre>
<p>Here <c><![CDATA[+W w]]></c> and <c><![CDATA[+R 9]]></c> are
emulator flags. <c><![CDATA[-s my_init]]></c> is an init flag,
interpreted by <c><![CDATA[init]]></c>.
<c><![CDATA[-sname arnie]]></c> is a user flag, stored by
<c><![CDATA[init]]></c>. It is read by Kernel and causes the
Erlang runtime system to become distributed. Finally, everything after
<c><![CDATA[-extra]]></c> (that is, <c><![CDATA[+bertie]]></c>) is
considered as plain arguments.</p>
<pre>
% <input>erl -myflag 1</input>
1> <input>init:get_argument(myflag).</input>
{ok,[["1"]]}
2> <input>init:get_plain_arguments().</input>
[]</pre>
<p>Here the user flag <c><![CDATA[-myflag 1]]></c> is passed to and
stored by the <c><![CDATA[init]]></c> process. It is a user-defined
flag, presumably used by some user-defined application.</p>
</desc>
</func>
</funcs>
<section>
<marker id="init_flags"></marker>
<title>Flags</title>
<p>In the following list, init flags are marked "(init flag)".
Unless otherwise specified, all other flags are user flags, for
which the values can be retrieved by calling
<c><![CDATA[init:get_argument/1]]></c>. Notice that the list of user
flags is not exhaustive, there can be more application-specific
flags that instead are described in the corresponding
application documentation.</p>
<taglist>
<tag><c><![CDATA[--]]></c> (init flag)</tag>
<item>
<p>Everything following <c><![CDATA[--]]></c> up to the next flag
(<c><![CDATA[-flag]]></c> or <c><![CDATA[+flag]]></c>) is considered
plain arguments and can be retrieved using
<c><![CDATA[init:get_plain_arguments/0]]></c>.</p>
</item>
<tag><c><![CDATA[-Application Par Val]]></c></tag>
<item>
<p>Sets the application configuration parameter <c><![CDATA[Par]]></c>
to the value <c><![CDATA[Val]]></c> for the application
<c><![CDATA[Application]]></c>; see
<seealso marker="kernel:app"><c>app(4)</c></seealso> and
<seealso marker="kernel:application">
<c>application(3)</c></seealso>.</p>
</item>
<tag><marker id="args_file"/><c><![CDATA[-args_file FileName]]></c></tag>
<item>
<p>Command-line arguments are read from the file
<c><![CDATA[FileName]]></c>. The arguments read from the file replace
flag '<c><![CDATA[-args_file FileName]]></c>' on the resulting
command line.</p>
<p>The file <c><![CDATA[FileName]]></c> is to be a plain text file and
can contain comments and command-line arguments. A comment begins
with a <c>#</c> character and continues until the next end of line
character. Backslash (\\) is used as quoting character. All
command-line arguments accepted by <c><![CDATA[erl]]></c> are allowed,
also flag <c><![CDATA[-args_file FileName]]></c>. Be careful not to
cause circular dependencies between files containing flag
<c><![CDATA[-args_file]]></c>, though.</p>
<p>The flag <c><![CDATA[-extra]]></c> is treated in special way. Its
scope ends at the end of the file. Arguments following an
<c><![CDATA[-extra]]></c> flag are moved on the command line into the
<c><![CDATA[-extra]]></c> section, that is, the end of the command
line following after an <c><![CDATA[-extra]]></c> flag.</p>
</item>
<tag><c><![CDATA[-async_shell_start]]></c></tag>
<item>
<p>The initial Erlang shell does not read user input until
the system boot procedure has been completed (Erlang/OTP 5.4 and
later). This flag disables the start synchronization feature
and lets the shell start in parallel with the rest of
the system.</p>
</item>
<tag><c><![CDATA[-boot File]]></c></tag>
<item>
<p>Specifies the name of the boot file, <c><![CDATA[File.boot]]></c>,
which is used to start the system; see
<seealso marker="init"><c>init(3)</c></seealso>. Unless
<c><![CDATA[File]]></c> contains an absolute path, the system searches
for <c><![CDATA[File.boot]]></c> in the current and
<c><![CDATA[$ROOT/bin]]></c> directories.</p>
<p>Defaults to <c><![CDATA[$ROOT/bin/start.boot]]></c>.</p>
</item>
<tag><c><![CDATA[-boot_var Var Dir]]></c></tag>
<item>
<p>If the boot script contains a path variable <c><![CDATA[Var]]></c>
other than <c><![CDATA[$ROOT]]></c>, this variable is expanded to
<c><![CDATA[Dir]]></c>. Used when applications are installed in
another directory than <c><![CDATA[$ROOT/lib]]></c>; see
<seealso marker="sasl:systools#make_script/1">
<c>systools:make_script/1,2</c></seealso> in SASL.</p>
</item>
<tag><c><![CDATA[-code_path_cache]]></c></tag>
<item>
<p>Enables the code path cache of the code server; see
<seealso marker="kernel:code"><c>code(3)</c></seealso>.</p>
</item>
<tag><c><![CDATA[-compile Mod1 Mod2 ...]]></c></tag>
<item>
<p>Compiles the specified modules and then terminates (with
non-zero exit code if the compilation of some file did not
succeed). Implies <c><![CDATA[-noinput]]></c>.</p>
<p>Not recommended; use <seealso marker="erlc"><c>erlc</c></seealso>
instead.</p>
</item>
<tag><c><![CDATA[-config Config]]></c></tag>
<item>
<p>Specifies the name of a configuration file,
<c><![CDATA[Config.config]]></c>, which is used to configure
applications; see
<seealso marker="kernel:app"><c>app(4)</c></seealso> and
<seealso marker="kernel:application">
<c>application(3)</c></seealso>.</p>
</item>
<tag><marker id="connect_all"/><c><![CDATA[-connect_all false]]></c></tag>
<item>
<p>If this flag is present, <c><![CDATA[global]]></c> does not maintain
a fully connected network of distributed Erlang nodes, and then
global name registration cannot be used; see
<seealso marker="kernel:global"><c>global(3)</c></seealso>.</p>
</item>
<tag><c><![CDATA[-cookie Cookie]]></c></tag>
<item>
<p>Obsolete flag without any effect and common misspelling for
<c><![CDATA[-setcookie]]></c>. Use <c><![CDATA[-setcookie]]></c>
instead.</p>
</item>
<tag><c><![CDATA[-detached]]></c></tag>
<item>
<p>Starts the Erlang runtime system detached from the system
console. Useful for running daemons and backgrounds processes. Implies
<c><![CDATA[-noinput]]></c>.</p>
</item>
<tag><c><![CDATA[-emu_args]]></c></tag>
<item>
<p>Useful for debugging. Prints the arguments sent to the emulator.</p>
</item>
<tag><c><![CDATA[-env Variable Value]]></c></tag>
<item>
<p>Sets the host OS environment variable <c><![CDATA[Variable]]></c> to
the value <c><![CDATA[Value]]></c> for the Erlang runtime system.
Example:</p>
<pre>
% <input>erl -env DISPLAY gin:0</input></pre>
<p>In this example, an Erlang runtime system is started with
environment variable <c><![CDATA[DISPLAY]]></c> set to
<c><![CDATA[gin:0]]></c>.</p>
</item>
<tag><c><![CDATA[-epmd_module Module]]></c> (init flag)</tag>
<item>
<p>Configures the module responsible to communicate to
<seealso marker="epmd">epmd</seealso>. Defaults to <c>erl_epmd</c>.</p>
</item>
<tag><c><![CDATA[-eval Expr]]></c> (init flag)</tag>
<item>
<p>Makes <c><![CDATA[init]]></c> evaluate the expression
<c><![CDATA[Expr]]></c>; see
<seealso marker="init"><c>init(3)</c></seealso>.</p>
</item>
<tag><c><![CDATA[-extra]]></c> (init flag)</tag>
<item>
<p>Everything following <c><![CDATA[-extra]]></c> is considered plain
arguments and can be retrieved using
<c><![CDATA[init:get_plain_arguments/0]]></c>.</p>
</item>
<tag><c><![CDATA[-heart]]></c></tag>
<item>
<p>Starts heartbeat monitoring of the Erlang runtime system;
see <seealso marker="kernel:heart">
<c>heart(3)</c></seealso>.</p>
</item>
<tag><c><![CDATA[-hidden]]></c></tag>
<item>
<p>Starts the Erlang runtime system as a hidden node, if it is
run as a distributed node. Hidden nodes always establish
hidden connections to all other nodes except for nodes in the
same global group. Hidden connections are not published on
any of the connected nodes, that is, none of the connected
nodes are part of the result from <c><![CDATA[nodes/0]]></c> on the
other node. See also hidden global groups;
<seealso marker="kernel:global_group">
<c>global_group(3)</c></seealso>.</p>
</item>
<tag><c><![CDATA[-hosts Hosts]]></c></tag>
<item>
<p>Specifies the IP addresses for the hosts on which Erlang boot servers
are running, see <seealso marker="kernel:erl_boot_server">
<c>erl_boot_server(3)</c></seealso>. This flag
is mandatory if flag <c><![CDATA[-loader inet]]></c> is present.</p>
<p>The IP addresses must be specified in the standard form (four
decimal numbers separated by periods, for example,
<c><![CDATA["150.236.20.74"]]></c>. Hosts names are not acceptable,
but a broadcast address (preferably limited to the local network)
is.</p>
</item>
<tag><c><![CDATA[-id Id]]></c></tag>
<item>
<p>Specifies the identity of the Erlang runtime system. If it is
run as a distributed node, <c><![CDATA[Id]]></c> must be identical to
the name supplied together with flag <c><![CDATA[-sname]]></c> or
<c><![CDATA[-name]]></c>.</p>
</item>
<tag><c><![CDATA[-init_debug]]></c></tag>
<item>
<p>Makes <c><![CDATA[init]]></c> write some debug information while
interpreting the boot script.</p>
</item>
<tag><marker id="instr"/><c><![CDATA[-instr]]></c> (emulator flag)</tag>
<item>
<p>Selects an instrumented Erlang runtime system (virtual
machine) to run, instead of the ordinary one. When running an
instrumented runtime system, some resource usage data can be
obtained and analyzed using the <c><![CDATA[instrument]]></c> module.
Functionally, it behaves exactly like an ordinary Erlang
runtime system.</p>
</item>
<tag><c><![CDATA[-loader Loader]]></c></tag>
<item>
<p>Specifies the method used by <c><![CDATA[erl_prim_loader]]></c> to
load Erlang modules into the system; see
<seealso marker="erl_prim_loader"><c>erl_prim_loader(3)</c></seealso>.
Two <c><![CDATA[Loader]]></c> methods are supported:</p>
<list type="bulleted">
<item>
<p><c><![CDATA[efile]]></c>, which means use the local file system,
this is the default.</p>
</item>
<item>
<p><c><![CDATA[inet]]></c>, which means use a boot server on
another machine. The flags <c><![CDATA[-id]]></c>,
<c><![CDATA[-hosts]]></c> and <c><![CDATA[-setcookie]]></c> must
also be specified.</p>
</item>
</list>
<p>If <c><![CDATA[Loader]]></c> is something else, the user-supplied
<c><![CDATA[Loader]]></c> port program is started.</p>
</item>
<tag><c><![CDATA[-make]]></c></tag>
<item>
<p>Makes the Erlang runtime system invoke <c><![CDATA[make:all()]]></c>
in the current working directory and then terminate; see
<seealso marker="tools:make"><c>make(3)</c></seealso>. Implies
<c><![CDATA[-noinput]]></c>.</p>
</item>
<tag><c><![CDATA[-man Module]]></c></tag>
<item>
<p>Displays the manual page for the Erlang module
<c><![CDATA[Module]]></c>. Only supported on Unix.</p>
</item>
<tag><c><![CDATA[-mode interactive | embedded]]></c></tag>
<item>
<p>Indicates if the system is to load code dynamically
(<c><![CDATA[interactive]]></c>), or if all code is to be loaded
during system initialization (<c><![CDATA[embedded]]></c>); see
<seealso marker="kernel:code"><c>code(3)</c></seealso>.
Defaults to <c><![CDATA[interactive]]></c>.</p>
</item>
<tag><c><![CDATA[-name Name]]></c></tag>
<item>
<p>Makes the Erlang runtime system into a distributed node.
This flag invokes all network servers necessary for a node to
become distributed; see <seealso marker="kernel:net_kernel">
<c>net_kernel(3)</c></seealso>. It is also ensured that
<c><![CDATA[epmd]]></c> runs on the current host before Erlang is
started; see <seealso marker="epmd"><c>epmd(1)</c></seealso>.and the
<seealso marker="#start_epmd"><c>-start_epmd</c></seealso> option.</p>
<p>The node name will be <c><![CDATA[Name@Host]]></c>, where
<c><![CDATA[Host]]></c> is the fully qualified host name of the
current host. For short names, use flag <c><![CDATA[-sname]]></c>
instead.</p>
</item>
<tag><c><![CDATA[-noinput]]></c></tag>
<item>
<p>Ensures that the Erlang runtime system never tries to read
any input. Implies <c><![CDATA[-noshell]]></c>.</p>
</item>
<tag><c><![CDATA[-noshell]]></c></tag>
<item>
<p>Starts an Erlang runtime system with no shell. This flag
makes it possible to have the Erlang runtime system as a
component in a series of Unix pipes.</p>
</item>
<tag><c><![CDATA[-nostick]]></c></tag>
<item>
<p>Disables the sticky directory facility of the Erlang code
server; see
<seealso marker="kernel:code"><c>code(3)</c></seealso>.</p>
</item>
<tag><c><![CDATA[-oldshell]]></c></tag>
<item>
<p>Invokes the old Erlang shell from Erlang/OTP 3.3. The old shell
can still be used.</p>
</item>
<tag><c><![CDATA[-pa Dir1 Dir2 ...]]></c></tag>
<item>
<p>Adds the specified directories to the beginning of the code
path, similar to <seealso marker="kernel:code#add_pathsa/1">
<c><![CDATA[code:add_pathsa/1]]></c></seealso>. Note that the
order of the given directories will be reversed in the
resulting path.</p>
<p>As an alternative to <c>-pa</c>, if several directories are
to be prepended to the code path and the directories have a
common parent directory, that parent directory can be
specified in environment variable <c>ERL_LIBS</c>; see
<seealso marker="kernel:code"><c>code(3)</c></seealso>.</p>
</item>
<tag><c><![CDATA[-pz Dir1 Dir2 ...]]></c></tag>
<item>
<p>Adds the specified directories to the end of the code path,
similar to <c><![CDATA[code:add_pathsz/1]]></c>; see
<seealso marker="kernel:code"><c>code(3)</c></seealso>.</p>
</item>
<tag><c><![CDATA[-path Dir1 Dir2 ...]]></c></tag>
<item>
<p>Replaces the path specified in the boot script; see
<seealso marker="sasl:script"><c>script(4)</c></seealso>.</p>
</item>
<tag><c><![CDATA[-proto_dist Proto]]></c></tag>
<item>
<p>Specifies a protocol for Erlang distribution:</p>
<taglist>
<tag><c>inet_tcp</c></tag>
<item>TCP over IPv4 (the default)</item>
<tag><c>inet_tls</c></tag>
<item>Distribution over TLS/SSL</item>
<tag><c>inet6_tcp</c></tag>
<item>TCP over IPv6</item>
</taglist>
<p>For example, to start up IPv6 distributed nodes:</p>
<pre>
% <input>erl -name test@ipv6node.example.com -proto_dist inet6_tcp</input></pre>
</item>
<tag><c><![CDATA[-remsh Node]]></c></tag>
<item>
<p>Starts Erlang with a remote shell connected to
<c><![CDATA[Node]]></c>.</p>
</item>
<tag><c><![CDATA[-rsh Program]]></c></tag>
<item>
<p>Specifies an alternative to <c><![CDATA[rsh]]></c> for starting a
slave node on a remote host; see
<seealso marker="stdlib:slave"><c>slave(3)</c></seealso>.</p>
</item>
<tag><c><![CDATA[-run Mod [Func [Arg1, Arg2, ...]]]]></c> (init
flag)</tag>
<item>
<p>Makes <c><![CDATA[init]]></c> call the specified function.
<c><![CDATA[Func]]></c> defaults to <c><![CDATA[start]]></c>.
If no arguments are provided, the function is assumed to be of
arity 0. Otherwise it is assumed to be of arity 1, taking the list
<c><![CDATA[[Arg1,Arg2,...]]]></c> as argument. All arguments are
passed as strings. See <seealso marker="init">
<c>init(3)</c></seealso>.</p>
</item>
<tag><c><![CDATA[-s Mod [Func [Arg1, Arg2, ...]]]]></c> (init flag)</tag>
<item>
<p>Makes <c><![CDATA[init]]></c> call the specified function.
<c><![CDATA[Func]]></c> defaults to <c><![CDATA[start]]></c>.
If no arguments are provided, the function is assumed to be of
arity 0. Otherwise it is assumed to be of arity 1, taking the list
<c><![CDATA[[Arg1,Arg2,...]]]></c> as argument. All arguments are
passed as atoms. See <seealso marker="init">
<c>init(3)</c></seealso>.</p>
</item>
<tag><c><![CDATA[-setcookie Cookie]]></c></tag>
<item>
<p>Sets the magic cookie of the node to <c><![CDATA[Cookie]]></c>; see
<seealso marker="erlang#set_cookie/2">
<c>erlang:set_cookie/2</c></seealso>.</p>
</item>
<tag><c><![CDATA[-shutdown_time Time]]></c></tag>
<item>
<p>Specifies how long time (in milliseconds) the <c><![CDATA[init]]></c>
process is allowed to spend shutting down the system. If
<c><![CDATA[Time]]></c> milliseconds have elapsed, all processes still
existing are killed. Defaults to <c><![CDATA[infinity]]></c>.</p>
</item>
<tag><c><![CDATA[-sname Name]]></c></tag>
<item>
<p>Makes the Erlang runtime system into a distributed node, similar to
<c><![CDATA[-name]]></c>, but the host name portion of the node
name <c><![CDATA[Name@Host]]></c> will be the short name, not fully
qualified.</p>
<p>This is sometimes the only way to run distributed Erlang if
the Domain Name System (DNS) is not running. No communication can
exist between nodes running with flag <c><![CDATA[-sname]]></c>
and those running with flag <c><![CDATA[-name]]></c>, as node
names must be unique in distributed Erlang systems.</p>
</item>
<tag><marker id="start_epmd"/><c>-start_epmd true | false</c></tag>
<item>
<p>Specifies whether Erlang should start
<seealso marker="epmd">epmd</seealso> on startup. By default
this is <c>true</c>, but if you prefer to start epmd
manually, set this to <c>false</c>.</p>
<p>This only applies if Erlang is started as a distributed node,
i.e. if <c>-name</c> or <c>-sname</c> is specified. Otherwise,
epmd is not started even if <c>-start_epmd true</c> is given.</p>
<p>Note that a distributed node will fail to start if epmd is
not running.</p>
</item>
<tag><marker id="smp"/><c><![CDATA[-smp [enable|auto|disable]]]></c></tag>
<item>
<p><c>-smp enable</c> and <c>-smp</c> start the Erlang runtime
system with SMP support enabled. This can fail if no runtime
system with SMP support is available. <c>-smp auto</c> starts
the Erlang runtime system with SMP support enabled if it is
available and more than one logical processor is detected.
<c>-smp disable</c> starts a runtime system without SMP support.</p>
<note>
<p>The runtime system with SMP support is not available on all
supported platforms. See also flag
<seealso marker="#+S"><c>+S</c></seealso>.</p>
</note>
</item>
<tag><c><![CDATA[-version]]></c> (emulator flag)</tag>
<item>
<p>Makes the emulator print its version number. The same
as <c><![CDATA[erl +V]]></c>.</p>
</item>
</taglist>
</section>
<section>
<marker id="emu_flags"></marker>
<title>Emulator Flags</title>
<p><c><![CDATA[erl]]></c> invokes the code for the Erlang emulator (virtual
machine), which supports the following flags:</p>
<taglist>
<tag><marker id="async_thread_stack_size"/>
<c><![CDATA[+a size]]></c></tag>
<item>
<p>Suggested stack size, in kilowords, for threads in the
async thread pool. Valid range is 16-8192 kilowords. The
default suggested stack size is 16 kilowords, that is, 64
kilobyte on 32-bit architectures. This small default size
has been chosen because the number of async threads can
be large. The default size is enough for drivers
delivered with Erlang/OTP, but might not be large
enough for other dynamically linked-in drivers that use the
<seealso marker="erl_driver#driver_async">
<c>driver_async()</c></seealso> functionality.
Notice that the value passed is only a suggestion,
and it can even be ignored on some platforms.</p>
</item>
<tag><marker id="async_thread_pool_size"/><c><![CDATA[+A size]]></c></tag>
<item>
<p>Sets the number of threads in async thread pool. Valid range
is 0-1024. Defaults to 10 if thread support is available.</p>
</item>
<tag><c><![CDATA[+B [c | d | i]]]></c></tag>
<item>
<p>Option <c><![CDATA[c]]></c> makes <c><![CDATA[Ctrl-C]]></c>
interrupt the current shell instead of invoking the emulator break
handler. Option <c><![CDATA[d]]></c> (same as specifying
<c><![CDATA[+B]]></c> without an extra option) disables the break
handler. Option <c><![CDATA[i]]></c> makes the emulator ignore any
break signal.</p>
<p>If option <c><![CDATA[c]]></c> is used with
<c><![CDATA[oldshell]]></c> on Unix, <c><![CDATA[Ctrl-C]]></c> will
restart the shell process rather than interrupt it.</p>
<p>Notice that on Windows, this flag is only applicable for
<c><![CDATA[werl]]></c>, not <c><![CDATA[erl]]></c>
(<c><![CDATA[oldshell]]></c>). Notice also that
<c><![CDATA[Ctrl-Break]]></c> is used instead of
<c><![CDATA[Ctrl-C]]></c> on Windows.</p>
</item>
<tag><marker id="+c"/><c><![CDATA[+c true | false]]></c></tag>
<item>
<p>Enables or disables
<seealso marker="time_correction#Time_Correction">time
correction</seealso>:</p>
<taglist>
<tag><c>true</c></tag>
<item>Enables time correction. This is the default if
time correction is supported on the specific platform.</item>
<tag><c>false</c></tag>
<item>Disables time correction.</item>
</taglist>
<p>For backward compatibility, the boolean value can be omitted.
This is interpreted as <c>+c false</c>.</p>
</item>
<tag><marker id="+C_"/><c><![CDATA[+C no_time_warp | single_time_warp |
multi_time_warp]]></c></tag>
<item>
<p>Sets <seealso marker="time_correction#Time_Warp_Modes">time warp
mode</seealso>:</p>
<taglist>
<tag><c>no_time_warp</c></tag>
<item><seealso marker="time_correction#No_Time_Warp_Mode">
No time warp mode</seealso> (the default)</item>
<tag><c>single_time_warp</c></tag>
<item><seealso marker="time_correction#Single_Time_Warp_Mode">
Single time warp mode</seealso></item>
<tag><c>multi_time_warp</c></tag>
<item><seealso marker="time_correction#Multi_Time_Warp_Mode">
Multi-time warp mode</seealso></item>
</taglist>
</item>
<tag><c><![CDATA[+d]]></c></tag>
<item>
<p>If the emulator detects an internal error (or runs out of memory),
it, by default, generates both a crash dump and a core dump.
The core dump is, however, not very useful as the content
of process heaps is destroyed by the crash dump generation.</p>
<p>Option <c>+d</c> instructs the emulator to produce only a
core dump and no crash dump if an internal error is detected.</p>
<p>Calling <seealso marker="erlang:halt/1">
<c>erlang:halt/1</c></seealso> with a string argument still
produces a crash dump. On Unix systems, sending an emulator process
a <c>SIGUSR1</c> signal also forces a crash dump.</p>
</item>
<tag><marker id="+e"/><c><![CDATA[+e Number]]></c></tag>
<item>
<p>Sets the maximum number of ETS tables.</p>
</item>
<tag><c><![CDATA[+ec]]></c></tag>
<item>
<p>Forces option <c>compressed</c> on all ETS tables.
Only intended for test and evaluation.</p>
</item>
<tag><marker id="file_name_encoding"></marker>
<c><![CDATA[+fnl]]></c></tag>
<item>
<p>The virtual machine works with filenames as if they are encoded
using the ISO Latin-1 encoding, disallowing Unicode characters with
code points > 255.</p>
<p>For more information about Unicode filenames, see section
<seealso marker="stdlib:unicode_usage#unicode_file_names">Unicode
Filenames</seealso> in the STDLIB User's Guide. Notice that
this value also applies to command-line parameters and environment
variables (see section <seealso
marker="stdlib:unicode_usage#unicode_in_environment_and_parameters">
Unicode in Enviroment and Parameters</seealso> in the STDLIB
User's Guide).</p>
</item>
<tag><c><![CDATA[+fnu[{w|i|e}]]]></c></tag>
<item>
<p>The virtual machine works with filenames as if they are encoded
using UTF-8 (or some other system-specific Unicode encoding). This is
the default on operating systems that enforce Unicode encoding, that
is, Windows and MacOS X.</p>
<p>The <c>+fnu</c> switch can be followed by <c>w</c>, <c>i</c>, or
<c>e</c> to control how wrongly encoded filenames are to be
reported:</p>
<list type="bulleted">
<item>
<p><c>w</c> means that a warning is sent to the <c>error_logger</c>
whenever a wrongly encoded filename is "skipped" in directory
listings. This is the default.</p>
</item>
<item>
<p><c>i</c> means that those wrongly encoded filenames are silently
ignored.</p>
</item>
<item>
<p><c>e</c> means that the API function returns an error whenever a
wrongly encoded filename (or directory name) is encountered.</p>
</item>
</list>
<p>Notice that <seealso marker="kernel:file#read_link/1">
<c>file:read_link/1</c></seealso> always returns an error if the link
points to an invalid filename.</p>
<p>For more information about Unicode filenames, see section
<seealso marker="stdlib:unicode_usage#unicode_file_names">Unicode
Filenames</seealso> in the STDLIB User's Guide. Notice that
this value also applies to command-line parameters and environment
variables (see section <seealso
marker="stdlib:unicode_usage#unicode_in_environment_and_parameters">
Unicode in Enviroment and Parameters</seealso> in the STDLIB
User's Guide).</p>
</item>
<tag><c><![CDATA[+fna[{w|i|e}]]]></c></tag>
<item>
<p>Selection between <c>+fnl</c> and <c>+fnu</c> is done based
on the current locale settings in the OS. This means that if you
have set your terminal for UTF-8 encoding, the filesystem is
expected to use the same encoding for filenames. This is
default on all operating systems, except MacOS X and Windows.</p>
<p>The <c>+fna</c> switch can be followed by <c>w</c>, <c>i</c>, or
<c>e</c>. This has effect if the locale settings cause the behavior
of <c>+fnu</c> to be selected; see the description of <c>+fnu</c>
above. If the locale settings cause the behavior of <c>+fnl</c> to be
selected, then <c>w</c>, <c>i</c>, or <c>e</c> have no effect.</p>
<p>For more information about Unicode filenames, see section
<seealso marker="stdlib:unicode_usage#unicode_file_names">Unicode
Filenames</seealso> in the STDLIB User's Guide. Notice that
this value also applies to command-line parameters and environment
variables (see section <seealso
marker="stdlib:unicode_usage#unicode_in_environment_and_parameters">
Unicode in Enviroment and Parameters</seealso> in the STDLIB
User's Guide).</p>
</item>
<tag><c><![CDATA[+hms Size]]></c></tag>
<item>
<p>Sets the default heap size of processes to the size
<c><![CDATA[Size]]></c>.</p>
</item>
<tag><c><![CDATA[+hmbs Size]]></c></tag>
<item>
<p>Sets the default binary virtual heap size of processes to the size
<c><![CDATA[Size]]></c>.</p>
</item>
<tag><marker id="+hmax"/><c><![CDATA[+hmax Size]]></c></tag>
<item>
<p>Sets the default maximum heap size of processes to the size
<c><![CDATA[Size]]></c>. Defaults to <c>0</c>, which means that no
maximum heap size is used. For more information, see
<seealso marker="erlang#process_flag_max_heap_size">
<c>process_flag(max_heap_size, MaxHeapSize)</c></seealso>.</p>
</item>
<tag><marker id="+hmaxel"/><c><![CDATA[+hmaxel true|false]]></c></tag>
<item>
<p>Sets whether to send an error logger message or not for processes
reaching the maximum heap size. Defaults to <c>true</c>.
For more information, see
<seealso marker="erlang#process_flag_max_heap_size">
<c>process_flag(max_heap_size, MaxHeapSize)</c></seealso>.</p>
</item>
<tag><marker id="+hmaxk"/><c><![CDATA[+hmaxk true|false]]></c></tag>
<item>
<p>Sets whether to kill processes reaching the maximum heap size or not.
Default to <c>true</c>. For more information, see
<seealso marker="erlang#process_flag_max_heap_size">
<c>process_flag(max_heap_size, MaxHeapSize)</c></seealso>.</p>
</item>
<tag><c><![CDATA[+hpds Size]]></c></tag>
<item>
<p>Sets the initial process dictionary size of processes to the size
<c><![CDATA[Size]]></c>.</p>
</item>
<tag><marker id="+hmqd"/><c>+hmqd off_heap|on_heap</c></tag>
<item>
<p>Sets the default value for process flag <c>message_queue_data</c>.
Defaults to <c>on_heap</c>. If <c>+hmqd</c> is not
passed, <c>on_heap</c> will be the default. For more information, see
<seealso marker="erlang#process_flag_message_queue_data">
<c>process_flag(message_queue_data, MQD)</c></seealso>.</p>
</item>
<tag><c><![CDATA[+K true | false]]></c></tag>
<item>
<p>Enables or disables the kernel poll functionality if supported by
the emulator. Defaults to <c><![CDATA[false]]></c> (disabled).
If the emulator does not support kernel poll, and flag
<c><![CDATA[+K]]></c> is passed to the emulator, a warning is
issued at startup.</p>
</item>
<tag><c><![CDATA[+l]]></c></tag>
<item>
<p>Enables autoload tracing, displaying information while loading
code.</p>
</item>
<tag><c><![CDATA[+L]]></c></tag>
<item>
<p>Prevents loading information about source filenames and line
numbers. This saves some memory, but exceptions do not contain
information about the filenames and line numbers.</p>
</item>
<tag><marker id="erts_alloc"/><c><![CDATA[+MFlag Value]]></c></tag>
<item>
<p>Memory allocator-specific flags. For more information, see
<seealso marker="erts_alloc"><c>erts_alloc(3)</c></seealso>.</p>
</item>
<tag><marker id="+pc"/><marker id="printable_character_range"/>
<c><![CDATA[+pc Range]]></c></tag>
<item>
<p>Sets the range of characters that the system considers printable in
heuristic detection of strings. This typically affects the shell,
debugger, and <c>io:format</c> functions (when <c>~tp</c> is used in
the format string).</p>
<p>Two values are supported for <c>Range</c>:</p>
<taglist>
<tag><c>latin1</c></tag>
<item>The default. Only characters in the ISO Latin-1 range can be
considered printable. This means that a character with a code point
> 255 is never considered printable and that lists containing
such characters are displayed as lists of integers rather than text
strings by tools.</item>
<tag><c>unicode</c></tag>
<item>All printable Unicode characters are considered when
determining if a list of integers is to be displayed in
string syntax. This can give unexpected results if, for
example, your font does not cover all Unicode characters.</item>
</taglist>
<p>See also <seealso marker="stdlib:io#printable_range/0">
<c>io:printable_range/0</c></seealso> in STDLIB.</p>
</item>
<tag><marker id="+P"/><marker id="max_processes"/><c><![CDATA[+P Number]]></c></tag>
<item>
<p>Sets the maximum number of simultaneously existing processes for this
system if a <c>Number</c> is passed as value. Valid range for
<c>Number</c> is <c>[1024-134217727]</c></p>
<p><em>NOTE</em>: The actual maximum chosen may be much larger than
the <c>Number</c> passed. Currently the runtime system often,
but not always, chooses a value that is a power of 2. This might,
however, be changed in the future. The actual value chosen can be
checked by calling
<seealso marker="erlang#system_info_process_limit">erlang:system_info(process_limit)</seealso>.</p>
<p>The default value is <c>262144</c></p>
</item>
<tag><marker id="+Q"/><marker id="max_ports"/><c><![CDATA[+Q Number]]></c></tag>
<item>
<p>Sets the maximum number of simultaneously existing ports for this
system if a Number is passed as value. Valid range for <c>Number</c>
is <c>[1024-134217727]</c></p>
<p><em>NOTE</em>: The actual maximum chosen may be much larger than
the actual <c>Number</c> passed. Currently the runtime system often,
but not always, chooses a value that is a power of 2. This might,
however, be changed in the future. The actual value chosen can be
checked by calling
<seealso marker="erlang#system_info_port_limit">erlang:system_info(port_limit)</seealso>.</p>
<p>The default value used is normally <c>65536</c>. However, if
the runtime system is able to determine maximum amount of file
descriptors that it is allowed to open and this value is larger
than <c>65536</c>, the chosen value will increased to a value
larger or equal to the maximum amount of file descriptors that
can be opened.</p>
<p>On Windows the default value is set to <c>8196</c> because the
normal OS limitations are set higher than most machines can handle.</p>
</item>
<tag><marker id="compat_rel"/><c><![CDATA[+R ReleaseNumber]]></c></tag>
<item>
<p>Sets the compatibility mode.</p>
<p>The distribution mechanism is not backward compatible by
default. This flag sets the emulator in compatibility mode
with an earlier Erlang/OTP release <c><![CDATA[ReleaseNumber]]></c>.
The release number must be in the range
<c><![CDATA[<current release>-2..<current release>]]></c>. This
limits the emulator, making it possible for it to communicate
with Erlang nodes (as well as C- and Java nodes) running that
earlier release.</p>
<note>
<p>Ensure that all nodes (Erlang-, C-, and Java nodes) of
a distributed Erlang system is of the same Erlang/OTP release,
or from two different Erlang/OTP releases X and Y, where
<em>all</em> Y nodes have compatibility mode X.</p>
</note>
</item>
<tag><c><![CDATA[+r]]></c></tag>
<item>
<p>Forces ETS memory block to be moved on realloc.</p>
</item>
<tag><marker id="+rg"/><c><![CDATA[+rg ReaderGroupsLimit]]></c></tag>
<item>
<p>Limits the number of reader groups used by read/write locks
optimized for read operations in the Erlang runtime system. By
default the reader groups limit is 64.</p>
<p>When the number of schedulers is less than or equal to the reader
groups limit, each scheduler has its own reader group. When the
number of schedulers is larger than the reader groups limit,
schedulers share reader groups. Shared reader groups degrade
read lock and read unlock performance while many
reader groups degrade write lock performance. So, the limit is a
tradeoff between performance for read operations and performance
for write operations. Each reader group consumes 64 byte
in each read/write lock.</p>
<p>Notice that a runtime system using shared reader groups benefits from
<seealso marker="#+sbt">binding schedulers to logical
processors</seealso>, as the reader groups are distributed better
between schedulers.</p>
</item>
<tag><marker id="+S"/>
<c><![CDATA[+S Schedulers:SchedulerOnline]]></c></tag>
<item>
<p>Sets the number of scheduler threads to create and scheduler threads
to set online when SMP support has been enabled. The maximum for both
values is 1024. If the Erlang runtime system is able to determine the
number of logical processors configured and logical processors
available, <c>Schedulers</c> defaults to logical processors
configured, and <c>SchedulersOnline</c> defaults to logical processors
available; otherwise the default values are 1. <c>Schedulers</c> can
be omitted if <c>:SchedulerOnline</c> is not and conversely. The
number of schedulers online can be changed at runtime through
<seealso marker="erlang#system_flag_schedulers_online">
<c>erlang:system_flag(schedulers_online,
SchedulersOnline)</c></seealso>.</p>
<p>If <c>Schedulers</c> or <c>SchedulersOnline</c> is specified as a
negative number, the value is subtracted from the default number of
logical processors configured or logical processors available,
respectively.</p>
<p>Specifying value <c>0</c> for <c>Schedulers</c> or
<c>SchedulersOnline</c> resets the number of scheduler threads or
scheduler threads online, respectively, to its default value.</p>
<p>This option is ignored if the emulator does not have SMP support
enabled (see flag <seealso marker="#smp"><c>-smp</c></seealso>).</p>
</item>
<tag><marker id="+SP"/><c><![CDATA[+SP
SchedulersPercentage:SchedulersOnlinePercentage]]></c></tag>
<item>
<p>Similar to <seealso marker="#+S"><c>+S</c></seealso> but uses
percentages to set the number of scheduler threads to create, based
on logical processors configured, and scheduler threads to set online,
based on logical processors available, when SMP support has been
enabled. Specified values must be > 0. For example,
<c>+SP 50:25</c> sets the number of scheduler threads to 50% of the
logical processors configured, and the number of scheduler threads
online to 25% of the logical processors available.
<c>SchedulersPercentage</c> can be omitted if
<c>:SchedulersOnlinePercentage</c> is not and conversely. The number
of schedulers online can be changed at runtime through
<seealso marker="erlang#system_flag_schedulers_online">
<c>erlang:system_flag(schedulers_online,
SchedulersOnline)</c></seealso>.</p>
<p>This option interacts with <seealso marker="#+S"><c>+S</c></seealso>
settings. For example, on a system with 8 logical cores configured
and 8 logical cores available, the combination of the options
<c>+S 4:4 +SP 50:25</c> (in either order) results in 2 scheduler
threads (50% of 4) and 1 scheduler thread online (25% of 4).</p>
<p>This option is ignored if the emulator does not have SMP support
enabled (see flag <seealso marker="#smp"><c>-smp</c></seealso>).</p>
</item>
<tag><marker id="+SDcpu"/><c><![CDATA[+SDcpu
DirtyCPUSchedulers:DirtyCPUSchedulersOnline]]></c></tag>
<item>
<p>Sets the number of dirty CPU scheduler threads to create and dirty
CPU scheduler threads to set online when threading support has been
enabled. The maximum for both values is 1024, and each value is
further limited by the settings for normal schedulers:</p>
<list type="bulleted">
<item>The number of dirty CPU scheduler threads created cannot exceed
the number of normal scheduler threads created.</item>
<item>The number of dirty CPU scheduler threads online cannot exceed
the number of normal scheduler threads online.</item>
</list>
<p>For details, see the <seealso marker="#+S"><c>+S</c></seealso> and
<seealso marker="#+SP"><c>+SP</c></seealso>. By default, the number
of dirty CPU scheduler threads created equals the number of normal
scheduler threads created, and the number of dirty CPU scheduler
threads online equals the number of normal scheduler threads online.
<c>DirtyCPUSchedulers</c> can be omitted if
<c>:DirtyCPUSchedulersOnline</c> is not and conversely. The number of
dirty CPU schedulers online can be changed at runtime through
<seealso marker="erlang#system_flag_dirty_cpu_schedulers_online">
<c>erlang:system_flag(dirty_cpu_schedulers_online,
DirtyCPUSchedulersOnline)</c></seealso>.</p>
<p>The amount of dirty CPU schedulers is limited by the amount of
normal schedulers in order to limit the effect on processes
executing on ordinary schedulers. If the amount of dirty CPU
schedulers was allowed to be unlimited, dirty CPU bound jobs would
potentially starve normal jobs.</p>
<p>This option is ignored if the emulator does not have threading
support enabled. <em>This option is experimental</em> and
is supported only if the emulator was configured and built with
support for dirty schedulers enabled (it is disabled by default).</p>
</item>
<tag><marker id="+SDPcpu"/><c><![CDATA[+SDPcpu
DirtyCPUSchedulersPercentage:DirtyCPUSchedulersOnlinePercentage]]></c></tag>
<item>
<p>Similar to <seealso marker="#+SDcpu"><c>+SDcpu</c></seealso> but
uses percentages to set the number of dirty CPU scheduler threads to
create and the number of dirty CPU scheduler threads to set online
when threading support has been enabled. Specified values must be
> 0. For example, <c>+SDPcpu 50:25</c> sets the number of dirty
CPU scheduler threads to 50% of the logical processors configured
and the number of dirty CPU scheduler threads online to 25% of the
logical processors available. <c>DirtyCPUSchedulersPercentage</c> can
be omitted if <c>:DirtyCPUSchedulersOnlinePercentage</c> is not and
conversely. The number of dirty CPU schedulers online can be changed
at runtime through
<seealso marker="erlang#system_flag_dirty_cpu_schedulers_online">
<c>erlang:system_flag(dirty_cpu_schedulers_online,
DirtyCPUSchedulersOnline)</c></seealso>.</p>
<p>This option interacts with <seealso
marker="#+SDcpu"><c>+SDcpu</c></seealso> settings. For example, on a
system with 8 logical cores configured and 8 logical cores available,
the combination of the options <c>+SDcpu 4:4 +SDPcpu 50:25</c> (in
either order) results in 2 dirty CPU scheduler threads (50% of 4) and
1 dirty CPU scheduler thread online (25% of 4).</p>
<p>This option is ignored if the emulator does not have threading
support enabled. <em>This option is experimental</em> and
is supported only if the emulator was configured and built with
support for dirty schedulers enabled (it is disabled by default).</p>
</item>
<tag><marker id="+SDio"/><c><![CDATA[+SDio DirtyIOSchedulers]]></c></tag>
<item>
<p>Sets the number of dirty I/O scheduler threads to create when
threading support has been enabled. Valid range is 0-1024. By
default, the number of dirty I/O scheduler threads created is 10,
same as the default number of threads in the <seealso
marker="#async_thread_pool_size">async thread pool</seealso>.</p>
<p>The amount of dirty IO schedulers is not limited by the amount of
normal schedulers <seealso marker="#+SDcpu">like the amount of
dirty CPU schedulers</seealso>. This since only I/O bound work is
expected to execute on dirty I/O schedulers. If the user should schedule CPU
bound jobs on dirty I/O schedulers, these jobs might starve ordinary
jobs executing on ordinary schedulers.</p>
<p>This option is ignored if the emulator does not have threading
support enabled. <em>This option is experimental</em> and
is supported only if the emulator was configured and built with
support for dirty schedulers enabled (it is disabled by default).</p>
</item>
<tag><c><![CDATA[+sFlag Value]]></c></tag>
<item>
<p>Scheduling specific flags.</p>
<taglist>
<tag><marker id="+sbt"/><c>+sbt BindType</c></tag>
<item>
<p>Sets scheduler bind type.</p>
<p>Schedulers can also be bound using flag
<seealso marker="#+stbt"><c>+stbt</c></seealso>. The only
difference between these two flags is how the following errors
are handled:</p>
<list type="bulleted">
<item>Binding of schedulers is not supported on the specific
platform.</item>
<item>No available CPU topology. That is, the runtime system was
not able to detect the CPU topology automatically, and no
<seealso marker="#+sct">user-defined CPU topology</seealso>
was set.</item>
</list>
<p>If any of these errors occur when <c>+sbt</c> has been passed,
the runtime system prints an error message, and refuses to
start. If any of these errors occur when <c>+stbt</c> has been
passed, the runtime system silently ignores the error, and
start up using unbound schedulers.</p>
<p>Valid <c>BindType</c>s:</p>
<taglist>
<tag><c>u</c></tag>
<item><c>unbound</c> - Schedulers are not bound to logical
processors, that is, the operating system decides where the
scheduler threads execute, and when to migrate them. This is
the default.
</item>
<tag><c>ns</c></tag>
<item><c>no_spread</c> - Schedulers with close scheduler
identifiers are bound as close as possible in hardware.
</item>
<tag><c>ts</c></tag>
<item><c>thread_spread</c> - Thread refers to hardware threads
(such as Intel's hyper-threads). Schedulers with low scheduler
identifiers, are bound to the first hardware thread of
each core, then schedulers with higher scheduler identifiers
are bound to the second hardware thread of each core,and so on.
</item>
<tag><c>ps</c></tag>
<item><c>processor_spread</c> - Schedulers are spread like
<c>thread_spread</c>, but also over physical processor chips.
</item>
<tag><c>s</c></tag>
<item><c>spread</c> - Schedulers are spread as much as possible.
</item>
<tag><c>nnts</c></tag>
<item><c>no_node_thread_spread</c> - Like <c>thread_spread</c>,
but if multiple Non-Uniform Memory Access (NUMA) nodes exist,
schedulers are spread over one NUMA node at a time,
that is, all logical processors of one NUMA node are bound
to schedulers in sequence.
</item>
<tag><c>nnps</c></tag>
<item><c>no_node_processor_spread</c> - Like
<c>processor_spread</c>, but if multiple NUMA nodes exist,
schedulers are spread over one NUMA node at a time, that is,
all logical processors of one NUMA node are bound to
schedulers in sequence.
</item>
<tag><c>tnnps</c></tag>
<item><c>thread_no_node_processor_spread</c> - A combination of
<c>thread_spread</c>, and <c>no_node_processor_spread</c>.
Schedulers are spread over hardware threads across NUMA
nodes, but schedulers are only spread over processors
internally in one NUMA node at a time.
</item>
<tag><c>db</c></tag>
<item><c>default_bind</c> - Binds schedulers the default way.
Defaults to <c>thread_no_node_processor_spread</c>
(which can change in the future).
</item>
</taglist>
<p>Binding of schedulers is only supported on newer
Linux, Solaris, FreeBSD, and Windows systems.</p>
<p>If no CPU topology is available when flag <c>+sbt</c>
is processed and <c>BindType</c> is any other type than
<c>u</c>, the runtime system fails to start. CPU
topology can be defined using flag
<seealso marker="#+sct"><c>+sct</c></seealso>. Notice
that flag <c>+sct</c> can have to be passed before flag
<c>+sbt</c> on the command line (if no CPU topology
has been automatically detected).</p>
<p>The runtime system does by default <em>not</em> bind schedulers
to logical processors.</p>
<note>
<p>If the Erlang runtime system is the only operating system
process that binds threads to logical processors, this
improves the performance of the runtime system. However,
if other operating system processes (for example
another Erlang runtime system) also bind threads to
logical processors, there can be a performance penalty
instead. This performance penalty can sometimes be
severe. If so, you are advised not to
bind the schedulers.</p>
</note>
<p>How schedulers are bound matters. For example, in
situations when there are fewer running processes than
schedulers online, the runtime system tries to migrate
processes to schedulers with low scheduler identifiers.
The more the schedulers are spread over the hardware,
the more resources are available to the runtime
system in such situations.</p>
<note>
<p>If a scheduler fails to bind, this is
often silently ignored, as it is not always
possible to verify valid logical processor identifiers. If
an error is reported, it is reported to the
<c>error_logger</c>. If you want to verify that the
schedulers have bound as requested, call
<seealso marker="erlang#system_info_scheduler_bindings">
<c>erlang:system_info(scheduler_bindings)</c></seealso>.</p>
</note>
</item>
<tag><marker id="+sbwt"/>
<c>+sbwt none|very_short|short|medium|long|very_long</c></tag>
<item>
<p>Sets scheduler busy wait threshold. Defaults to <c>medium</c>.
The threshold determines how long schedulers are to busy
wait when running out of work before going to sleep.</p>
<note>
<p>This flag can be removed or changed at any time
without prior notice.</p>
</note>
</item>
<tag><marker id="+scl"/><c>+scl true|false</c></tag>
<item>
<p>Enables or disables scheduler compaction of load. By default
scheduler compaction of load is enabled. When enabled, load
balancing strives for a load distribution, which causes
as many scheduler threads as possible to be fully loaded (that is,
not run out of work). This is accomplished by migrating load
(for example, runnable processes) into a smaller set of schedulers
when schedulers frequently run out of work. When disabled,
the frequency with which schedulers run out of work is
not taken into account by the load balancing logic.</p>
<p><c>+scl false</c> is similar to
<seealso marker="#+sub"><c>+sub true</c></seealso>, but
<c>+sub true</c> also balances scheduler utilization
between schedulers.</p>
</item>
<tag><marker id="+sct"/><c>+sct CpuTopology</c></tag>
<item>
<list type="bulleted">
<item><c><![CDATA[<Id> = integer(); when 0 =< <Id> =< 65535]]></c>
</item>
<item><c><![CDATA[<IdRange> = <Id>-<Id>]]></c></item>
<item><c><![CDATA[<IdOrIdRange> = <Id> | <IdRange>]]></c></item>
<item><c><![CDATA[<IdList> = <IdOrIdRange>,<IdOrIdRange> |
<IdOrIdRange>]]></c></item>
<item><c><![CDATA[<LogicalIds> = L<IdList>]]></c></item>
<item><c><![CDATA[<ThreadIds> = T<IdList> | t<IdList>]]></c>
</item>
<item><c><![CDATA[<CoreIds> = C<IdList> | c<IdList>]]></c></item>
<item><c><![CDATA[<ProcessorIds> = P<IdList> | p<IdList>]]></c>
</item>
<item><c><![CDATA[<NodeIds> = N<IdList> | n<IdList>]]></c></item>
<item><c><![CDATA[<IdDefs> =
<LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds> |
<LogicalIds><ThreadIds><CoreIds><NodeIds><ProcessorIds>]]></c>
</item>
<item><c><![CDATA[CpuTopology = <IdDefs>:<IdDefs> |
<IdDefs>]]></c></item>
</list>
<p>Sets a user-defined CPU topology. The user-defined
CPU topology overrides any automatically detected
CPU topology. The CPU topology is used when
<seealso marker="#+sbt">binding schedulers to logical
processors</seealso>.</p>
<p>Uppercase letters signify real identifiers and lowercase
letters signify fake identifiers only used for description
of the topology. Identifiers passed as real identifiers can
be used by the runtime system when trying to access specific
hardware; if they are incorrect the behavior is
undefined. Faked logical CPU identifiers are not accepted,
as there is no point in defining the CPU topology without
real logical CPU identifiers. Thread, core, processor, and
node identifiers can be omitted. If omitted, the thread ID
defaults to <c>t0</c>, the core ID defaults to <c>c0</c>,
the processor ID defaults to <c>p0</c>, and the node ID is
left undefined. Either each logical processor must
belong to only one NUMA node, or no logical
processors must belong to any NUMA nodes.</p>
<p>Both increasing and decreasing <c><![CDATA[<IdRange>]]></c>s
are allowed.</p>
<p>NUMA node identifiers are system wide. That is, each NUMA
node on the system must have a unique identifier. Processor
identifiers are also system wide. Core identifiers are
processor wide. Thread identifiers are core wide.</p>
<p>The order of the identifier types implies the hierarchy of the
CPU topology. The valid orders are as follows:</p>
<list type="bulleted">
<item>
<p><c><![CDATA[<LogicalIds><ThreadIds><CoreIds><ProcessorIds><NodeIds>]]></c>,
that is, thread is part of a core that is part of a processor,
which is part of a NUMA node.</p>
</item>
<item>
<p><c><![CDATA[<LogicalIds><ThreadIds><CoreIds><NodeIds><ProcessorIds>]]></c>,
that is, thread is part of a core that is part of a NUMA node,
which is part of a processor.</p>
</item>
</list>
<p>A CPU topology can consist of both processor external, and
processor internal NUMA nodes as long as each logical processor
belongs to only one NUMA node. If
<c><![CDATA[<ProcessorIds>]]></c> is omitted, its default position
is before <c><![CDATA[<NodeIds>]]></c>. That is, the default is
processor external NUMA nodes.</p>
<p>If a list of identifiers is used in an
<c><![CDATA[<IdDefs>]]></c>:</p>
<list type="bulleted">
<item><c><![CDATA[<LogicalIds>]]></c> must be a list
of identifiers.</item>
<item>At least one other identifier type besides
<c><![CDATA[<LogicalIds>]]></c> must also have a
list of identifiers.</item>
<item>All lists of identifiers must produce the
same number of identifiers.</item>
</list>
<p>A simple example. A single quad core processor can be
described as follows:</p>
<pre>
% <input>erl +sct L0-3c0-3</input>
1> <input>erlang:system_info(cpu_topology).</input>
[{processor,[{core,{logical,0}},
{core,{logical,1}},
{core,{logical,2}},
{core,{logical,3}}]}]</pre>
<p>A more complicated example with two quad core
processors, each processor in its own NUMA node.
The ordering of logical processors is a bit weird.
This to give a better example of identifier lists:</p>
<pre>
% <input>erl +sct L0-1,3-2c0-3p0N0:L7,4,6-5c0-3p1N1</input>
1> <input>erlang:system_info(cpu_topology).</input>
[{node,[{processor,[{core,{logical,0}},
{core,{logical,1}},
{core,{logical,3}},
{core,{logical,2}}]}]},
{node,[{processor,[{core,{logical,7}},
{core,{logical,4}},
{core,{logical,6}},
{core,{logical,5}}]}]}]</pre>
<p>As long as real identifiers are correct, it is OK
to pass a CPU topology that is not a correct
description of the CPU topology. When used with
care this can be very useful. This
to trick the emulator to bind its schedulers
as you want. For example, if you want to run multiple
Erlang runtime systems on the same machine, you
want to reduce the number of schedulers used and
manipulate the CPU topology so that they bind to
different logical CPUs. An example, with two Erlang
runtime systems on a quad core machine:</p>
<pre>
% <input>erl +sct L0-3c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname one</input>
% <input>erl +sct L3-0c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname two</input></pre>
<p>In this example, each runtime system have two
schedulers each online, and all schedulers online
will run on different cores. If we change to one
scheduler online on one runtime system, and three
schedulers online on the other, all schedulers
online will still run on different cores.</p>
<p>Notice that a faked CPU topology that does not reflect
how the real CPU topology looks like is likely to
decrease the performance of the runtime system.</p>
<p>For more information, see
<seealso marker="erlang#system_info_cpu_topology">
<c>erlang:system_info(cpu_topology)</c></seealso>.</p>
</item>
<tag><marker id="+secio"/><c>+secio true|false</c></tag>
<item>
<p>Enables or disables eager check I/O scheduling. Defaults
to <c>true</c>. The default was changed from <c>false</c>
as from ERTS 7.0. The behavior before this
flag was introduced corresponds to <c>+secio false</c>.</p>
<p>The flag effects when schedulers will check for I/O
operations possible to execute, and when such I/O operations
will execute. As the parameter name implies,
schedulers are more eager to check for I/O when
<c>true</c> is passed. This, however, also implies that
execution of outstanding I/O operation is not
prioritized to the same extent as when <c>false</c> is
passed.</p>
<p><seealso marker="erlang#system_info_eager_check_io">
<c>erlang:system_info(eager_check_io)</c></seealso>
returns the value of this parameter used when starting
the virtual machine.</p>
</item>
<tag><marker id="+sfwi"/><c>+sfwi Interval</c></tag>
<item>
<p>Sets scheduler-forced wakeup interval. All run queues are
scanned each <c>Interval</c> milliseconds. While there are
sleeping schedulers in the system, one scheduler is woken
for each non-empty run queue found. <c>Interval</c> default
to <c>0</c>, meaning this feature is disabled.</p>
<note>
<p>This feature has been introduced as a temporary workaround
for long-executing native code, and native code that does not
bump reductions properly in OTP. When these bugs have be fixed,
this flag will be removed.</p>
</note>
</item>
<tag><marker id="+spp"/><c>+spp Bool</c></tag>
<item>
<p>Sets default scheduler hint for port parallelism. If set to
<c>true</c>, the virtual machine schedules port tasks when it
improves parallelism in the system. If set to <c>false</c>, the
virtual machine tries to perform port tasks immediately,
improving latency at the expense of parallelism. Default to
<c>false</c>. The default used can be inspected in runtime by
calling <seealso marker="erlang#system_info_port_parallelism">
<c>erlang:system_info(port_parallelism)</c></seealso>.
The default can be overridden on port creation by passing option
<seealso marker="erlang#open_port_parallelism">
<c>parallelism</c></seealso> to
<seealso marker="erlang#open_port/2">
<c>erlang:open_port/2</c></seealso></p>.
</item>
<tag><marker id="sched_thread_stack_size"/>
<c><![CDATA[+sss size]]></c></tag>
<item>
<p>Suggested stack size, in kilowords, for scheduler threads.
Valid range is 4-8192 kilowords. The default stack size is
OS-dependent.</p>
</item>
<tag><marker id="+stbt"/><c>+stbt BindType</c></tag>
<item>
<p>Tries to set the scheduler bind type. The same as flag
<seealso marker="#+sbt"><c>+sbt</c></seealso> except
how some errors are handled. For more information, see
<seealso marker="#+sbt"><c>+sbt</c></seealso>.</p>
</item>
<tag><marker id="+sub"/><c>+sub true|false</c></tag>
<item>
<p>Enables or disables
<seealso marker="erts:erlang#statistics_scheduler_wall_time">
scheduler utilization</seealso> balancing of load. By default
scheduler utilization balancing is disabled and instead scheduler
compaction of load is enabled, which strives for a load
distribution that causes as many scheduler threads as possible
to be fully loaded (that is, not run out of work). When scheduler
utilization balancing is enabled, the system instead tries to
balance scheduler utilization between schedulers. That is,
strive for equal scheduler utilization on all schedulers.</p>
<p><c>+sub true</c> is only supported on systems where the runtime
system detects and uses a monotonically increasing high-resolution
clock. On other systems, the runtime system fails to start.</p>
<p><c>+sub true</c> implies <seealso marker="#+scl">
<c>+scl false</c></seealso>. The difference between
<c>+sub true</c> and <c>+scl false</c> is that <c>+scl false</c>
does not try to balance the scheduler utilization.</p>
</item>
<tag><marker id="+swct"/>
<c>+swct very_eager|eager|medium|lazy|very_lazy</c></tag>
<item>
<p>Sets scheduler wake cleanup threshold. Defaults to <c>medium</c>.
Controls how eager schedulers are to be requesting
wakeup because of certain cleanup operations. When a lazy setting
is used, more outstanding cleanup operations can be left undone
while a scheduler is idling. When an eager setting is used,
schedulers are more frequently woken, potentially increasing
CPU-utilization.</p>
<note>
<p>This flag can be removed or changed at any time without prior
notice.</p>
</note>
</item>
<tag><marker id="+sws"/><c>+sws default|legacy</c></tag>
<item>
<p>Sets scheduler wakeup strategy. Default strategy changed in
ERTS 5.10 (Erlang/OTP R16A). This strategy was known as
<c>proposal</c> in Erlang/OTP R15. The <c>legacy</c> strategy
was used as default from R13 up to and including R15.</p>
<note>
<p>This flag can be removed or changed at any time without prior
notice.</p>
</note>
</item>
<tag><marker id="+swt"/>
<c>+swt very_low|low|medium|high|very_high</c></tag>
<item>
<p>Sets scheduler wakeup threshold. Defaults to <c>medium</c>.
The threshold determines when to wake up sleeping schedulers
when more work than can be handled by currently awake schedulers
exists. A low threshold causes earlier wakeups, and a high
threshold causes later wakeups. Early wakeups distribute work
over multiple schedulers faster, but work does more easily bounce
between schedulers.</p>
<note>
<p>This flag can be removed or changed at any time without prior
notice.</p>
</note>
</item>
</taglist>
</item>
<tag><marker id="+t"/><c><![CDATA[+t size]]></c></tag>
<item>
<p>Sets the maximum number of atoms the virtual machine can handle.
Defaults to 1,048,576.</p>
</item>
<tag><marker id="+T"/><c><![CDATA[+T Level]]></c></tag>
<item>
<p>Enables modified timing and sets the modified timing level. Valid
range is 0-9. The timing of the runtime system is changed. A high
level usually means a greater change than a low level. Changing the
timing can be very useful for finding timing-related bugs.</p>
<p>Modified timing affects the following:</p>
<taglist>
<tag>Process spawning</tag>
<item>A process calling <c><![CDATA[spawn]]></c>,
<c><![CDATA[spawn_link]]></c>, <c><![CDATA[spawn_monitor]]></c>,
or <c><![CDATA[spawn_opt]]></c> is scheduled out immediately
after completing the call. When higher modified timing levels are
used, the caller also sleeps for a while after it is scheduled out.
</item>
<tag>Context reductions</tag>
<item>The number of reductions a process is allowed to use before it
is scheduled out is increased or reduced.
</item>
<tag>Input reductions</tag>
<item>The number of reductions performed before checking I/O is
increased or reduced.
</item>
</taglist>
<note>
<p>Performance suffers when modified timing is enabled. This flag is
<em>only</em> intended for testing and debugging.</p>
<p><c><![CDATA[return_to]]></c> and <c><![CDATA[return_from]]></c>
trace messages are lost when tracing on the spawn BIFs.</p>
<p>This flag can be removed or changed at any time without prior
notice.</p>
</note>
</item>
<tag><c><![CDATA[+v]]></c></tag>
<item>
<p>Verbose.</p>
</item>
<tag><c><![CDATA[+V]]></c></tag>
<item>
<p>Makes the emulator print its version number.</p>
</item>
<tag><c><![CDATA[+W w | i | e]]></c></tag>
<item>
<p>Sets the mapping of warning messages for
<c><![CDATA[error_logger]]></c>. Messages sent to the error logger
using one of the warning routines can be mapped to errors
(<c><![CDATA[+W e]]></c>), warnings (<c><![CDATA[+W w]]></c>), or
information reports (<c><![CDATA[+W i]]></c>). Defaults to warnings.
The current mapping can be retrieved using
<c><![CDATA[error_logger:warning_map/0]]></c>. For more information,
see <seealso marker="kernel:error_logger#warning_map/0">
<c>error_logger:warning_map/0</c></seealso> in Kernel.</p>
</item>
<tag><c><![CDATA[+zFlag Value]]></c></tag>
<item>
<p>Miscellaneous flags:</p>
<taglist>
<tag><marker id="+zdbbl"/><c>+zdbbl size</c></tag>
<item>
<p>Sets the distribution buffer busy limit
(<seealso marker="erlang#system_info_dist_buf_busy_limit">
<c>dist_buf_busy_limit</c></seealso>)
in kilobytes. Valid range is 1-2097151. Defaults to 1024.</p>
<p>A larger buffer limit allows processes to buffer
more outgoing messages over the distribution. When the
buffer limit has been reached, sending processes will be
suspended until the buffer size has shrunk. The buffer
limit is per distribution channel. A higher limit
gives lower latency and higher throughput at the expense
of higher memory use.</p>
</item>
<tag><marker id="+zdntgc"/><c>+zdntgc time</c></tag>
<item>
<p>Sets the delayed node table garbage collection time
(<seealso marker="erlang#system_info_delayed_node_table_gc">
<c>delayed_node_table_gc</c></seealso>)
in seconds. Valid values are either <c>infinity</c> or
an integer in the range 0-100000000. Defaults to 60.</p>
<p>Node table entries that are not referred linger
in the table for at least the amount of time that this
parameter determines. The lingering prevents repeated
deletions and insertions in the tables from occurring.</p>
</item>
</taglist>
</item>
</taglist>
</section>
<section>
<marker id="environment_variables"></marker>
<title>Environment Variables</title>
<taglist>
<tag><c><![CDATA[ERL_CRASH_DUMP]]></c></tag>
<item>
<p>If the emulator needs to write a crash dump, the value of this
variable is the filename of the crash dump file.
If the variable is not set, the name of the crash dump file is
<c><![CDATA[erl_crash.dump]]></c> in the current directory.</p>
</item>
<tag><c><![CDATA[ERL_CRASH_DUMP_NICE]]></c></tag>
<item>
<p><em>Unix systems</em>: If the emulator needs to write a crash dump,
it uses the value of this variable to set the nice value
for the process, thus lowering its priority. Valid range is
1-39 (higher values are replaced with 39). The highest
value, 39, gives the process the lowest priority.</p>
</item>
<tag><c><![CDATA[ERL_CRASH_DUMP_SECONDS]]></c></tag>
<item>
<p><em>Unix systems</em>: This variable gives the number of seconds
that the emulator is allowed to spend writing a crash dump. When the
given number of seconds have elapsed, the emulator is terminated by a
<c>SIGALRM</c> signal.</p>
<p>If the variable is <em>not</em> set or set to <c>0</c> seconds
(<c><![CDATA[ERL_CRASH_DUMP_SECONDS=0]]></c>), the runtime system does
not even attempt to write the crash dump file. It only terminates.</p>
<p>If the variable is set to negative value, such as
<c><![CDATA[ERL_CRASH_DUMP_SECONDS=-1]]></c>, the runtime system
waits indefinitely for the crash dump file to be written.</p>
<p>This variable is used with <seealso marker="kernel:heart">
<c>heart(3)</c></seealso> if <c>heart</c> is running:</p>
<taglist>
<tag><c><![CDATA[ERL_CRASH_DUMP_SECONDS=0]]></c></tag>
<item>Suppresses the writing a crash dump file entirely, thus
rebooting the runtime system immediately. This is the same as not
setting the environment variable.
</item>
<tag><c><![CDATA[ERL_CRASH_DUMP_SECONDS=-1]]></c></tag>
<item>Setting the environment variable to a negative value causes the
termination of the runtime system to wait until the crash dump file
has been completly written.
</item>
<tag><c><![CDATA[ERL_CRASH_DUMP_SECONDS=S]]></c></tag>
<item>Waits for <c>S</c> seconds to complete the crash dump file and
then terminates the runtime system.
</item>
</taglist>
</item>
<tag><c><![CDATA[ERL_CRASH_DUMP_BYTES]]></c></tag>
<item>
<p>This variable sets the maximum size of a crash dump file in bytes.
The crash dump will be truncated if this limit is exceeded. If the
variable is not set, no size limit is enforced by default. If the
variable is set to <c>0</c>, the runtime system does not even attempt
to write a crash dump file.</p>
<p>Introduced in ERTS 8.1.2 (Erlang/OTP 19.2).</p>
</item>
<tag><marker id="ERL_AFLAGS"/><c><![CDATA[ERL_AFLAGS]]></c></tag>
<item>
<p>The content of this variable is added to the beginning of the
command line for <c><![CDATA[erl]]></c>.</p>
<p>Flag <c><![CDATA[-extra]]></c> is treated in a special way. Its
scope ends at the end of the environment variable content. Arguments
following an <c><![CDATA[-extra]]></c> flag are moved on the command
line into section <c><![CDATA[-extra]]></c>, that is, the end of the
command line following an <c><![CDATA[-extra]]></c> flag.</p>
</item>
<tag><marker id="ERL_ZFLAGS"/><c><![CDATA[ERL_ZFLAGS]]></c> and
<marker id="ERL_FLAGS"/><c><![CDATA[ERL_FLAGS]]></c></tag>
<item>
<p>The content of these variables are added to the end of the command
line for <c><![CDATA[erl]]></c>.</p>
<p>Flag <c><![CDATA[-extra]]></c> is treated in a special way. Its
scope ends at the end of the environment variable content. Arguments
following an <c><![CDATA[-extra]]></c> flag are moved on the command
line into section <c><![CDATA[-extra]]></c>, that is, the end of the
command line following an <c><![CDATA[-extra]]></c> flag.</p>
</item>
<tag><c><![CDATA[ERL_LIBS]]></c></tag>
<item>
<p>Contains a list of additional library directories that the code
server searches for applications and adds to the code path; see
<seealso marker="kernel:code"><c>code(3)</c></seealso>.</p>
</item>
<tag><c><![CDATA[ERL_EPMD_ADDRESS]]></c></tag>
<item>
<p>Can be set to a comma-separated list of IP addresses, in which case
the <seealso marker="epmd"><c>epmd</c></seealso> daemon listens only
on the specified address(es) and on the loopback address (which is
implicitly added to the list if it has not been specified).</p>
</item>
<tag><c><![CDATA[ERL_EPMD_PORT]]></c></tag>
<item>
<p>Can contain the port number to use when communicating with
<seealso marker="epmd"><c>epmd</c></seealso>. The default port works
fine in most cases. A different port can be specified
to allow nodes of independent clusters to co-exist on the same host.
All nodes in a cluster must use the same <c>epmd</c> port number.</p>
</item>
</taglist>
</section>
<section>
<marker id="signals"></marker>
<title>Signals</title>
<p>On Unix systems, the Erlang runtime will interpret two types of signals.</p>
<taglist>
<tag><c>SIGUSR1</c></tag>
<item>
<p>A <c>SIGUSR1</c> signal forces a crash dump.</p>
</item>
<tag><c>SIGTERM</c></tag>
<item>
<p>A <c>SIGTERM</c> will produce a <c>stop</c> message to the <c>init</c> process.
This is equivalent to a <c>init:stop/0</c> call.</p>
<p>Introduced in ERTS 8.3 (Erlang/OTP 19.3)</p>
</item>
</taglist>
<p>The signal <c>SIGUSR2</c> is reserved for internal usage. No other signals are handled.</p>
</section>
<section>
<marker id="configuration"></marker>
<title>Configuration</title>
<p>The standard Erlang/OTP system can be reconfigured to change the default
behavior on startup.</p>
<taglist>
<tag>The <c>.erlang</c> startup file</tag>
<item>
<p>When Erlang/OTP is started, the system searches for a file named
<c>.erlang</c> in the directory where Erlang/OTP is started. If not
found, the user's home directory is searched for an <c>.erlang</c>
file.</p>
<p>If an <c>.erlang</c> file is found, it is assumed to contain valid
Erlang expressions. These expressions are evaluated as if they were
input to the shell.</p>
<p>A typical <c>.erlang</c> file contains a set of search paths, for
example:</p>
<code type="none"><![CDATA[
io:format("executing user profile in HOME/.erlang\n",[]).
code:add_path("/home/calvin/test/ebin").
code:add_path("/home/hobbes/bigappl-1.2/ebin").
io:format(".erlang rc finished\n",[]). ]]></code>
</item>
<tag>user_default and shell_default</tag>
<item>
<p>Functions in the shell that are not prefixed by a module name are
assumed to be functional objects (funs), built-in functions (BIFs),
or belong to the module <c>user_default</c> or
<c>shell_default</c>.</p>
<p>To include private shell commands, define them in a module
<c>user_default</c> and add the following argument as the first line
in the <c>.erlang</c> file:</p>
<code type="none"><![CDATA[
code:load_abs("..../user_default"). ]]></code>
</item>
<tag>erl</tag>
<item>
<p>If the contents of <c>.erlang</c> are changed and a private version
of <c>user_default</c> is defined, the Erlang/OTP environment can be
customized. More powerful changes can be made by supplying
command-line arguments in the startup script <c>erl</c>. For more
information, see <seealso marker="init"><c>init(3)</c></seealso>.</p>
</item>
</taglist>
</section>
<section>
<title>See Also</title>
<p><seealso marker="epmd"><c>epmd(1)</c></seealso>,
<seealso marker="erl_prim_loader"><c>erl_prim_loader(3)</c></seealso>,
<seealso marker="erts_alloc"><c>erts_alloc(3)</c></seealso>,
<seealso marker="init"><c>init(3)</c></seealso>,
<seealso marker="kernel:application">
<c>application(3)</c></seealso>,
<seealso marker="kernel:auth"><c>auth(3)</c></seealso>,
<seealso marker="kernel:code"><c>code(3)</c></seealso>,
<seealso marker="kernel:erl_boot_server">
<c>erl_boot_server(3)</c></seealso>,
<seealso marker="kernel:heart"><c>heart(3)</c></seealso>,
<seealso marker="kernel:net_kernel"><c>net_kernel(3)</c></seealso>,
<seealso marker="tools:make"><c>make(3)</c></seealso></p>
</section>
</comref>
|