aboutsummaryrefslogtreecommitdiffstats
path: root/lib/kernel/doc/src/inet.xml
blob: d4678ca5dbe85179b7eb29aad9cde3f0c3ceb94d (plain) (blame)
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
<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>1997</year><year>2018</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>inet</title>
    <prepared>[email protected]</prepared>
    <docno></docno>
    <date>1998-02-04</date>
    <rev>A</rev>
  </header>
  <module since="">inet</module>
  <modulesummary>Access to TCP/IP protocols.</modulesummary>
  <description>
    <p>This module provides access to TCP/IP protocols.</p>
    <p>See also
      <seealso marker="erts:inet_cfg">ERTS User's Guide:
      Inet Configuration</seealso> for more information about how to
      configure an Erlang runtime system for IP communication.</p>
    <p>The following two Kernel configuration parameters affect the
      behavior of all sockets opened on an Erlang node:</p>
    <list type="bulleted">
      <item><p><c>inet_default_connect_options</c> can contain a list of
        default options used for all sockets returned when doing
        <c>connect</c>.</p></item>
      <item><p><c>inet_default_listen_options</c> can contain a list of
        default options used when issuing a <c>listen</c> call.</p></item>
    </list>
    <p>When <c>accept</c> is issued, the values of the listening socket options
      are inherited. No such application variable is therefore needed for
      <c>accept</c>.</p>
    <p>Using the Kernel configuration parameters above, one
      can set default options for all TCP sockets on a node, but use this
      with care. Options such as <c>{delay_send,true}</c> can be
      specified in this way. The following is an example of starting an Erlang
      node with all sockets using delayed send:</p>
    <pre>
$ <input>erl -sname test -kernel \</input>
<input>inet_default_connect_options '[{delay_send,true}]' \</input>
<input>inet_default_listen_options '[{delay_send,true}]'</input></pre>
    <p>Notice that default option <c>{active, true}</c>
      cannot be changed, for internal reasons.</p>
    <p>Addresses as inputs to functions can be either a string or a
      tuple. For example, the IP address 150.236.20.73 can be passed to
      <c>gethostbyaddr/1</c>, either as string <c>"150.236.20.73"</c>
      or as tuple <c>{150, 236, 20, 73}</c>.</p>
    <p><em>IPv4 address examples:</em></p>
    <code type="none">
Address          ip_address()
-------          ------------
127.0.0.1        {127,0,0,1}
192.168.42.2     {192,168,42,2}</code>
    <p><em>IPv6 address examples:</em></p>
    <code type="none">
Address          ip_address()
-------          ------------
::1             {0,0,0,0,0,0,0,1}
::192.168.42.2  {0,0,0,0,0,0,(192 bsl 8) bor 168,(42 bsl 8) bor 2}
::FFFF:192.168.42.2
                {0,0,0,0,0,16#FFFF,(192 bsl 8) bor 168,(42 bsl 8) bor 2}
3ffe:b80:1f8d:2:204:acff:fe17:bf38
                {16#3ffe,16#b80,16#1f8d,16#2,16#204,16#acff,16#fe17,16#bf38}
fe80::204:acff:fe17:bf38
                {16#fe80,0,0,0,0,16#204,16#acff,16#fe17,16#bf38}</code>
    <p>Function
      <seealso marker="#parse_address/1"><c>parse_address/1</c></seealso>
        can be useful:</p>
    <pre>
1> <input>inet:parse_address("192.168.42.2").</input>
{ok,{192,168,42,2}}
2> <input>inet:parse_address("::FFFF:192.168.42.2").</input>
{ok,{0,0,0,0,0,65535,49320,10754}}</pre>
  </description>

  <datatypes>
    <datatype>
      <name name="hostent"/>
      <desc>
        <p>The record is defined in the Kernel include file
          <c>"inet.hrl"</c>.</p>
        <p>Add the following directive to the module:</p>
        <code>
-include_lib("kernel/include/inet.hrl").</code>
      </desc>
    </datatype>
    <datatype>
      <name name="hostname"/>
    </datatype>
    <datatype>
      <name name="ip_address"/>
    </datatype>
    <datatype>
      <name name="ip4_address"/>
    </datatype>
    <datatype>
      <name name="ip6_address"/>
    </datatype>
    <datatype>
      <name name="port_number"/>
    </datatype>
    <datatype>
      <name name="local_address"/>
      <desc>
	<p>
	  This address family only works on Unix-like systems.
	</p>
	<p>
	  <c><anno>File</anno></c> is normally a file pathname
	  in a local filesystem.  It is limited in length by the
	  operating system, traditionally to 108 bytes.
	</p>
	<p>
	  A <c>binary()</c> is passed as is to the operating system,
	  but a <c>string()</c> is encoded according to the
	  <seealso marker="file#native_name_encoding/0">
	    system filename encoding mode.
	  </seealso>
	</p>
	<p>
	  Other addresses are possible, for example Linux implements
	  "Abstract Addresses".  See the documentation for
	  Unix Domain Sockets on your system,
	  normally <c>unix</c> in manual section 7.
	</p>
	<p>
	  In most API functions where you can use
	  this address family the port number must be <c>0</c>.
	</p>
      </desc>
    </datatype>
    <datatype>
      <name name="socket_address"/>
    </datatype>
    <datatype>
      <name name="socket_getopt"/>
    </datatype>
    <datatype>
      <name name="socket_setopt"/>
    </datatype>
    <datatype>
      <name name="returned_non_ip_address"/>
      <desc>
	<p>
	  Addresses besides
	  <seealso marker="#type-ip_address">
	    <c>ip_address()</c>
	  </seealso>
	  ones that are returned from socket API functions.
	  See in particular
	  <seealso marker="#type-local_address">
	    <c>local_address()</c>.
	  </seealso>
	  The <c>unspec</c> family corresponds to AF_UNSPEC and can
	  occur if the other side has no socket address.
	  The <c>undefined</c> family can only occur in the unlikely
	  event of an address family that the VM does not recognize.
	</p>
      </desc>
    </datatype>
    <datatype>
      <name name="ancillary_data"/>
      <desc>
	<p>
	  Ancillary data received with the data packet
	  or read with the socket option
	  <seealso marker="gen_tcp#type-pktoptions_value">
	    <c>pktoptions</c>
	  </seealso>
	  from a TCP socket.
	</p>
	<p>
	  The value(s) correspond to the currently active socket
	  <seealso marker="#type-socket_setopt">options</seealso>
	  <seealso marker="inet#option-recvtos"><c>recvtos</c></seealso>,
	  <seealso marker="inet#option-recvtclass"><c>recvtclass</c></seealso>
	  and
	  <seealso marker="inet#option-recvttl"><c>recvttl</c></seealso>.
	</p>
      </desc>
    </datatype>
    <datatype>
      <name name="getifaddrs_ifopts"/>
      <desc>
	<p>
	  Interface address description list returned from
	  <seealso marker="#getifaddrs/0"><c>getifaddrs/0,1</c></seealso>
	  for a named interface, translated from the returned
	  data of the POSIX API function <c>getaddrinfo()</c>.
	</p>
        <p>
	  <c><anno>Hwaddr</anno></c> is hardware dependent,
	  for example, on Ethernet interfaces it is
	the 6-byte Ethernet address (MAC address (EUI-48 address)).
	</p>
        <p>
	  The tuples <c>{addr,<anno>Addr</anno>}</c>,
	  <c>{netmask,<anno>Netmask</anno>}</c>, and possibly
	  <c>{broadaddr,<anno>Broadaddr</anno>}</c> or
	  <c>{dstaddr,<anno>Dstaddr</anno>}</c>
	  are repeated in the list
	  if the interface has got multiple addresses.
	  An interface may have multiple <c>{flag,_}</c> tuples
	  for example if it has different flags
	  for different address families.
	  Multiple <c>{hwaddr,<anno>Hwaddr</anno>}</c> tuples
	  is hard to say anything definite about, though.
	  The tuple <c>{flag,<anno>Flags</anno>}</c> is mandatory,
	  all others are optional.
	</p>
        <p>
	  Do not rely too much on the order
	  of <c><anno>Flags</anno></c> atoms
          or the <c><anno>Ifopt</anno></c> tuples.
	  There are however some rules:
	</p>
        <list type="bulleted">
	  <item><p>
	    A <c>{flag,_}</c> tuple applies to all other tuples that follow.
	  </p></item>
          <item><p>
	    Immediately after <c>{addr,_}</c> follows <c>{netmask,_}</c>.
	  </p></item>
          <item><p>
	    Immediately thereafter may <c>{broadaddr,_}</c> follow
	    if <c>broadcast</c> is member of <c><anno>Flags</anno></c>,
	    or <c>{dstaddr,_}</c> if <c>pointtopoint</c>
	    is member of <c><anno>Flags</anno></c>.
	    Both <c>{dstaddr,_}</c> and <c>{broadaddr,_}</c>
	    does not occur for the same <c>{addr,_}</c>.
	  </p></item>
          <item><p>
	    Any <c>{netmask,_}</c>, <c>{broadaddr,_}</c>, or
            <c>{dstaddr,_}</c> tuples that follow an
	    <c>{addr,<anno>Addr</anno>}</c>
            tuple concerns the address <c><anno>Addr</anno></c>.
	  </p></item>
        </list>
        <p>
	  The tuple <c>{hwaddr,_}</c> is not returned on Solaris, as the
          hardware address historically belongs to the link layer
	  and it is not returned by the Solaris API function
	  <c>getaddrinfo()</c>.
	</p>
	<warning>
	  <p>
	    On Windows, the data is fetched from different
	    OS API functions, so the <c><anno>Netmask</anno></c>
	    and <c><anno>Broadaddr</anno></c> values may be calculated,
	    just as some <c><anno>Flags</anno></c> values.
	  </p>
	</warning>
      </desc>
    </datatype>
    <datatype>
      <name name="posix"/>
      <desc>
        <p>An atom that is named from the POSIX error codes used in Unix,
          and in the runtime libraries of most C compilers. See section
          <seealso marker="#error_codes">POSIX Error Codes</seealso>.</p>
      </desc>
    </datatype>
    <datatype>
      <name>socket()</name>
      <desc>
        <p>See
          <seealso marker="gen_tcp#type-socket"><c>gen_tcp:type-socket</c></seealso>
          and
          <seealso marker="gen_udp#type-socket"><c>gen_udp:type-socket</c></seealso>.
        </p>
      </desc>
    </datatype>
    <datatype>
      <name name="address_family"/>
    </datatype>
    <datatype>
      <name name="socket_protocol"/>
    </datatype>
    <datatype>
      <name name="stat_option"/>
    </datatype>
  </datatypes>

  <funcs>
    <func>
      <name name="close" arity="1" since=""/>
      <fsummary>Close a socket of any type.</fsummary>
      <desc>
        <p>Closes a socket of any type.</p>
      </desc>
    </func>

    <func>
      <name name="format_error" arity="1" since=""/>
      <fsummary>Return a descriptive string for an error reason.</fsummary>
      <desc>
        <p>Returns a diagnostic error string. For possible POSIX values and
          corresponding strings, see section
          <seealso marker="#error_codes">POSIX Error Codes</seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="get_rc" arity="0" since=""/>
      <fsummary>Return a list of IP configuration parameters.</fsummary>
      <desc>
        <p>
	  Returns the state of the <c>Inet</c> configuration database in
          form of a list of recorded configuration parameters. For more
          information, see <seealso marker="erts:inet_cfg">ERTS User's Guide:
          Inet Configuration</seealso>.
	</p>
        <p>
	  Only actual parameters with other than default values
	  are returned, for example not directives that specify
	  other sources for configuration parameters nor
	  directives that clear parameters.
	</p>
      </desc>
    </func>

    <func>
      <name name="getaddr" arity="2" since=""/>
      <fsummary>Return the IP address for a host.</fsummary>
      <desc>
        <p>Returns the IP address for <c><anno>Host</anno></c> as a tuple of
          integers. <c><anno>Host</anno></c> can be an IP address, a single
          hostname, or a fully qualified hostname.</p>
      </desc>
    </func>

    <func>
      <name name="getaddrs" arity="2" since=""/>
      <fsummary>Return the IP addresses for a host.</fsummary>
      <desc>
        <p>Returns a list of all IP addresses for <c><anno>Host</anno></c>.
          <c><anno>Host</anno></c> can be an IP address, a single hostname, or
          a fully qualified hostname.</p>
      </desc>
    </func>

    <func>
      <name name="gethostbyaddr" arity="1" since=""/>
      <fsummary>Return a hostent record for the host with the specified
        address.</fsummary>
      <desc>
        <p>Returns a <c>hostent</c> record for the host with the specified
          address.</p></desc>
    </func>

    <func>
      <name name="gethostbyname" arity="1" since=""/>
      <fsummary>Return a hostent record for the host with the specified name.
      </fsummary>
      <desc>
        <p>Returns a <c>hostent</c> record for the host with the specified
          hostname.</p>
        <p>If resolver option <c>inet6</c> is <c>true</c>,
          an IPv6 address is looked up.</p>
      </desc>
    </func>

    <func>
      <name name="gethostbyname" arity="2" since=""/>
      <fsummary>Return a hostent record for the host with the specified name.
      </fsummary>
      <desc>
        <p>Returns a <c>hostent</c> record for the host with the specified
          name, restricted to the specified address family.</p>
      </desc>
    </func>

    <func>
      <name name="gethostname" arity="0" since=""/>
      <fsummary>Return the local hostname.</fsummary>
      <desc>
        <p>Returns the local hostname. Never fails.</p>
      </desc>
    </func>

    <func>
      <name name="getifaddrs" arity="0" since="OTP R14B01"/>
      <fsummary>Return a list of interfaces and their addresses.</fsummary>
      <desc>
        <p>
	  Returns a list of 2-tuples containing interface names and
	  the interfaces' addresses. <c><anno>Ifname</anno></c>
	  is a Unicode string and
	  <c><anno>Ifopts</anno></c> is a list of
	  interface address description tuples.
	</p>
        <p>
	  The interface address description tuples
	  are documented under the type of the
          <seealso marker="#type-getifaddrs_ifopts">
	    <c><anno>Ifopts</anno></c>
	  </seealso>
	  value.
	</p>
      </desc>
    </func>

    <func>
      <name since="OTP 21.2">getifaddrs(Opts) ->
        {ok, [{Ifname, Ifopts}]} | {error, Posix}
      </name>
      <fsummary>Return a list of interfaces and their addresses.</fsummary>
      <type>
	<v>
	  Opts = [{netns, Namespace}]
	</v>
	<v>
	  Namespace =
	  <seealso marker="file#type-filename_all">
	    file:filename_all()
	  </seealso>
	</v>
	<v>Ifname = string()</v>
	<v>
	  Ifopts =
	  <seealso marker="#type-getifaddrs_ifopts">
	    getifaddrs_ifopts()
	  </seealso>
	</v>
	<v>Posix = <seealso marker="#type-posix">posix()</seealso></v>
      </type>
      <desc>
	<p>
	  The same as
	  <seealso marker="#getifaddrs/0"><c>getifaddrs/0</c></seealso>
	  but the <c>Option</c>
	  <c>{netns, Namespace}</c> sets a network namespace
	  for the OS call, on platforms that supports that feature.
	</p>
	<p>
	  See the socket option
	  <seealso marker="#option-netns">
	    <c>{netns, Namespace}</c>
	  </seealso>
	  under
	  <seealso marker="#setopts/2"><c>setopts/2</c></seealso>.
	</p>
      </desc>
    </func>

    <func>
      <name name="getopts" arity="2" since=""/>
      <fsummary>Get one or more options for a socket.</fsummary>
      <desc>
        <p>Gets one or more options for a socket. For a list of available
          options, see
          <seealso marker="#setopts/2"><c>setopts/2</c></seealso>.
	  See also the description for the type
          <seealso marker="gen_tcp#type-pktoptions_value">
	    <c>gen_tcp:pktoptions_value()</c>
	  </seealso>.</p>
        <p>The number of elements in the returned
          <c><anno>OptionValues</anno></c>
          list does not necessarily correspond to the number of options
          asked for. If the operating system fails to support an option,
          it is left out in the returned list. An error tuple is returned
          only when getting options for the socket is impossible (that is,
          the socket is closed or the buffer size in a raw request
          is too large). This behavior is kept for backward
          compatibility reasons.</p>
        <p>A raw option request
          <c>RawOptReq = {raw, Protocol, OptionNum, ValueSpec}</c>
          can be used to get information about
          socket options not (explicitly) supported by the emulator. The
          use of raw socket options makes the code non-portable, but
          allows the Erlang programmer to take advantage of unusual features
          present on a particular platform.</p>
        <p><c>RawOptReq</c> consists of tag <c>raw</c> followed
          by the protocol level, the option number, and either a binary
          or the size, in bytes, of the
          buffer in which the option value is to be stored. A binary is to be
          used when the underlying <c>getsockopt</c> requires <em>input</em>
          in the argument field. In this case, the binary size
          is to correspond to the required buffer
          size of the return value. The supplied values in a <c>RawOptReq</c>
          correspond to the second, third, and fourth/fifth parameters to the
          <c>getsockopt</c> call in the C socket API. The value stored
          in the buffer is returned as a binary <c>ValueBin</c>,
          where all values are coded in the native endianess.</p>
        <p>Asking for and inspecting raw socket options require low-level
          information about the current operating system and TCP stack.</p>
        <p><em>Example:</em></p>
        <p>Consider a Linux machine where option
          <c>TCP_INFO</c> can be used to collect TCP statistics
          for a socket. Assume you are interested in field
          <c>tcpi_sacked</c> of <c>struct tcp_info</c>
          filled in when asking for <c>TCP_INFO</c>. To be able to access
          this information, you need to know the following:</p>
        <list type="bulleted">
          <item>The numeric value of protocol level <c>IPPROTO_TCP</c></item>
          <item>The numeric value of option <c>TCP_INFO</c></item>
          <item>The size of <c>struct tcp_info</c></item>
          <item>The size and offset of the specific field</item>
        </list>
        <p>By inspecting the headers or writing a small C program, it is found
          that <c>IPPROTO_TCP</c> is 6, <c>TCP_INFO</c> is 11, the structure
          size is 92 (bytes), the offset of <c>tcpi_sacked</c> is 28 bytes,
          and the value is a 32-bit integer. The following code can be used
          to retrieve the value:</p>
        <code type="none"><![CDATA[
get_tcpi_sacked(Sock) ->
    {ok,[{raw,_,_,Info}]} = inet:getopts(Sock,[{raw,6,11,92}]),
    <<_:28/binary,TcpiSacked:32/native,_/binary>> = Info,
    TcpiSacked.]]></code>
        <p>Preferably, you would check the machine type, the operating system,
          and the Kernel version before executing anything similar to
          this code.</p>
      </desc>
    </func>

    <func>
      <name name="getstat" arity="1" since=""/>
      <name name="getstat" arity="2" since=""/>
      <fsummary>Get one or more statistic options for a socket.</fsummary>
      <type name="stat_option"/>
      <desc>
        <p>Gets one or more statistic options for a socket.</p>
        <p><c>getstat(<anno>Socket</anno>)</c> is equivalent to
          <c>getstat(<anno>Socket</anno>, [recv_avg, recv_cnt, recv_dvi,
          recv_max, recv_oct, send_avg, send_cnt, send_dvi, send_max,
          send_oct])</c>.</p>
        <p>The following options are available:</p>
        <taglist>
          <tag><c>recv_avg</c></tag>
          <item>
            <p>Average size of packets, in bytes, received by the socket.</p>
          </item>
          <tag><c>recv_cnt</c></tag>
          <item>
            <p>Number of packets received by the socket.</p>
          </item>
          <tag><c>recv_dvi</c></tag>
          <item>
            <p>Average packet size deviation, in bytes, received by the socket.</p>
          </item>
          <tag><c>recv_max</c></tag>
          <item>
            <p>Size of the largest packet, in bytes, received by the socket.</p>
          </item>
          <tag><c>recv_oct</c></tag>
          <item>
            <p>Number of bytes received by the socket.</p>
          </item>
          <tag><c>send_avg</c></tag>
          <item>
            <p>Average size of packets, in bytes, sent from the socket.</p>
          </item>
          <tag><c>send_cnt</c></tag>
          <item>
            <p>Number of packets sent from the socket.</p>
          </item>
          <tag><c>send_dvi</c></tag>
          <item>
            <p>Average packet size deviation, in bytes, sent from the socket.</p>
          </item>
          <tag><c>send_max</c></tag>
          <item>
            <p>Size of the largest packet, in bytes, sent from the socket.</p>
          </item>
          <tag><c>send_oct</c></tag>
          <item>
            <p>Number of bytes sent from the socket.</p>
          </item>
        </taglist>
      </desc>
    </func>

    <func>
      <name name="i" arity="0"  since="OTP 21.0"/>
      <name name="i" arity="1"  since="OTP 21.0"/>
      <name name="i" arity="2"  since="OTP 21.0"/>
      <fsummary>Displays information and statistics about sockets on the terminal</fsummary>
      <desc>
        <p>
          Lists all TCP, UDP and SCTP sockets, including those that the Erlang runtime system uses as well as
          those created by the application.
        </p>
        <p>
          The following options are available:
        </p>

        <taglist>
          <tag><c>port</c></tag>
          <item>
            <p>The internal index of the port.</p>
          </item>
          <tag><c>module</c></tag>
          <item>
            <p>The callback module of the socket.</p>
          </item>
          <tag><c>recv</c></tag>
          <item>
            <p>Number of bytes received by the socket.</p>
          </item>
          <tag><c>sent</c></tag>
          <item>
            <p>Number of bytes sent from the socket.</p>
          </item>
          <tag><c>owner</c></tag>
          <item>
            <p>The socket owner process.</p>
          </item>
          <tag><c>local_address</c></tag>
          <item>
            <p>The local address of the socket.</p>
          </item>
          <tag><c>foreign_address</c></tag>
          <item>
            <p>The address and port of the other end of the connection.</p>
          </item>
          <tag><c>state</c></tag>
          <item>
            <p>The connection state.</p>
          </item>
          <tag><c>type</c></tag>
          <item>
            <p>STREAM or DGRAM or SEQPACKET.</p>
          </item>
        </taglist>
      </desc>
    </func>

    <func>
      <name name="ntoa" arity="1"  since="OTP R16B02"/>
      <fsummary>Convert IPv6/IPV4 address to ASCII.</fsummary>
      <desc>
	<p>Parses an
          <seealso marker="#type-ip_address"><c>ip_address()</c></seealso>
          and returns an IPv4 or IPv6 address string.</p>
      </desc>
    </func>

    <func>
      <name name="parse_address" arity="1"  since="OTP R16B"/>
      <fsummary>Parse an IPv4 or IPv6 address.</fsummary>
      <desc>
	<p>Parses an IPv4 or IPv6 address string and returns an
          <seealso marker="#type-ip4_address"><c>ip4_address()</c></seealso> or
          <seealso marker="#type-ip6_address"><c>ip6_address()</c></seealso>.
          Accepts a shortened IPv4 address string.</p>
      </desc>
    </func>

    <func>
      <name name="parse_ipv4_address" arity="1"  since="OTP R16B"/>
      <fsummary>Parse an IPv4 address.</fsummary>
      <desc>
	<p>Parses an IPv4 address string and returns an
          <seealso marker="#type-ip4_address"><c>ip4_address()</c></seealso>.
	  Accepts a shortened IPv4 address string.</p>
      </desc>
    </func>

    <func>
      <name name="parse_ipv4strict_address" arity="1"  since="OTP R16B"/>
      <fsummary>Parse an IPv4 address strict.</fsummary>
      <desc>
	<p>Parses an IPv4 address string containing four fields, that is,
          <em>not</em> shortened, and returns an
          <seealso marker="#type-ip4_address"><c>ip4_address()</c></seealso>.
        </p>
      </desc>
    </func>

    <func>
      <name name="parse_ipv6_address" arity="1"  since="OTP R16B"/>
      <fsummary>Parse an IPv6 address.</fsummary>
      <desc>
	<p>Parses an IPv6 address string and returns an
          <seealso marker="#type-ip6_address"><c>ip6_address()</c></seealso>.
          If an IPv4 address string is specified, an IPv4-mapped IPv6 address
          is returned.</p>
      </desc>
    </func>

    <func>
      <name name="parse_ipv6strict_address" arity="1"  since="OTP R16B"/>
      <fsummary>Parse an IPv6 address strict.</fsummary>
      <desc>
	<p>Parses an IPv6 address string and returns an
          <seealso marker="#type-ip6_address"><c>ip6_address()</c></seealso>.
          Does <em>not</em> accept IPv4 addresses.</p>
      </desc>
    </func>

    <func>
      <name name="ipv4_mapped_ipv6_address" arity="1"  since="OTP 21.0"/>
      <fsummary>Convert to and from IPv4-mapped IPv6 address.</fsummary>
      <desc>
	<p>
	  Convert an IPv4 address to an IPv4-mapped IPv6 address
	  or the reverse.  When converting from an IPv6 address
	  all but the 2 low words are ignored so this function also
	  works on some other types of addresses than IPv4-mapped.
	</p>
      </desc>
    </func>

    <func>
      <name name="parse_strict_address" arity="1"  since="OTP R16B"/>
      <fsummary>Parse an IPv4 or IPv6 address strict.</fsummary>
      <desc>
	<p>Parses an IPv4 or IPv6 address string and returns an
          <seealso marker="#type-ip4_address"><c>ip4_address()</c></seealso> or
          <seealso marker="#type-ip6_address"><c>ip6_address()</c></seealso>.
          Does <em>not</em> accept a shortened IPv4 address string.</p>
      </desc>
    </func>

    <func>
      <name name="peername" arity="1" since=""/>
      <fsummary>Return the address and port for the other end of a connection.
      </fsummary>
      <desc>
        <p>Returns the address and port for the other end of a connection.</p>
	<p>Notice that for SCTP sockets, this function returns only
	  one of the peer addresses of the socket. Function
	  <seealso marker="#peernames/1"><c>peernames/1,2</c></seealso>
	  returns all.</p>
      </desc>
    </func>

    <func>
      <name name="peernames" arity="1" since="OTP R16B03"/>
      <fsummary>Return all address/port numbers for the other end of a
        connection.</fsummary>
      <desc>
	<p>Equivalent to
	  <seealso marker="#peernames/2"><c>peernames(<anno>Socket</anno>, 0)</c></seealso>.
        </p>
        <p>Notice that the behavior of this function for an SCTP
	  one-to-many style socket is not defined by the
	  <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">SCTP Sockets API Extensions</url>.</p>
      </desc>
    </func>

    <func>
      <name name="peernames" arity="2" since="OTP R16B03"/>
      <fsummary>Return all address/port numbers for the other end of a
        connection.</fsummary>
      <desc>
	<p>Returns a list of all address/port number pairs for the other end
	  of an association <c><anno>Assoc</anno></c> of a socket.</p>
	<p>This function can return multiple addresses for multihomed
	  sockets, such as SCTP sockets. For other sockets it
	  returns a one-element list.</p>
	<p>Notice that parameter <c><anno>Assoc</anno></c> is by the
	  <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">SCTP Sockets API Extensions</url>
	  defined to be ignored for
	  one-to-one style sockets. What the special value <c>0</c>
	  means, hence its behavior for one-to-many style sockets,
	  is unfortunately undefined.</p>
      </desc>
    </func>

    <func>
      <name name="port" arity="1" since=""/>
      <fsummary>Return the local port number for a socket.</fsummary>
      <desc>
        <p>Returns the local port number for a socket.</p>
      </desc>
    </func>

    <func>
      <name name="setopts" arity="2" since=""/>
      <fsummary>Set one or more options for a socket.</fsummary>
      <desc>
        <p>Sets one or more options for a socket.</p>
        <p>The following options are available:</p>
        <taglist>
          <tag><c>{active, true | false | once | N}</c></tag>
          <item>
            <p>If the value is <c>true</c>, which is the default,
              everything received from the socket is sent as
              messages to the receiving process.</p>
            <p>If the value is <c>false</c> (passive mode), the process must
              explicitly receive incoming data by calling
              <seealso marker="gen_tcp#recv/2"><c>gen_tcp:recv/2,3</c></seealso>,
              <seealso marker="gen_udp#recv/2"><c>gen_udp:recv/2,3</c></seealso>,
              or <seealso marker="gen_sctp#recv/1"><c>gen_sctp:recv/1,2</c></seealso>
              (depending on the type of socket).</p>
            <p>If the value is <c>once</c> (<c>{active, once}</c>),
              <em>one</em> data message from the socket is sent
              to the process. To receive one more message,
              <c>setopts/2</c> must be called again with option
              <c>{active, once}</c>.</p>
            <p>If the value is an integer <c>N</c> in the range -32768 to 32767
              (inclusive), the value is added to the socket's count of data
              messages sent to the controlling process. A socket's default
              message count is <c>0</c>. If a negative value is specified, and
              its magnitude is equal to or greater than the socket's current
              message count, the socket's message count is set to <c>0</c>.
              Once the socket's message count reaches <c>0</c>, either because
              of sending
              received data messages to the process or by being explicitly set,
              the process is then notified by a special message, specific to
              the type of socket, that the socket has entered passive
              mode. Once the socket enters passive mode, to receive more
              messages <c>setopts/2</c> must be called again to set the
              socket back into an active mode.</p>
            <p>When using <c>{active, once}</c> or <c>{active, N}</c>, the
              socket changes behavior automatically when data is received.
              This can be confusing in combination with connection-oriented
              sockets (that is, <c>gen_tcp</c>), as a socket
              with <c>{active, false}</c> behavior reports closing
              differently than a socket with <c>{active, true}</c>
              behavior. To simplify programming, a socket where
              the peer closed, and this is detected while in
              <c>{active, false}</c> mode, still generates message
              <c>{tcp_closed,Socket}</c> when set to <c>{active, once}</c>,
              <c>{active, true}</c>, or <c>{active, N}</c> mode.
              It is therefore safe to assume that message
              <c>{tcp_closed,Socket}</c>, possibly followed by socket port
              termination (depending on option <c>exit_on_close</c>)
              eventually appears when a socket changes
              back and forth between <c>{active, true}</c> and
              <c>{active, false}</c> mode. However,
              <em>when</em> peer closing is detected it is all up to the
              underlying TCP/IP stack and protocol.</p>
            <p>Notice that <c>{active, true}</c> mode provides no flow
              control; a fast sender can easily overflow the
              receiver with incoming messages. The same is true for
              <c>{active, N}</c> mode, while the message count is greater
              than zero.</p>
            <p>Use active mode only if
              your high-level protocol provides its own flow control
              (for example, acknowledging received messages) or the
              amount of data exchanged is small. <c>{active, false}</c>
              mode, use of the <c>{active, once}</c> mode, or <c>{active, N}</c>
              mode with values of <c>N</c> appropriate for the application
              provides flow control. The other side cannot send
              faster than the receiver can read.</p>
          </item>
          <tag><c>{broadcast, Boolean}</c> (UDP sockets)</tag>
          <item>
            <p>Enables/disables permission to send broadcasts.</p>
            <marker id="option-buffer"></marker>
          </item>
          <tag><c>{buffer, Size}</c></tag>
          <item>
            <p>The size of the user-level buffer used by
              the driver. Not to be confused with options <c>sndbuf</c>
              and <c>recbuf</c>, which correspond to the
              Kernel socket buffers. For TCP it is recommended
              to have <c>val(buffer) &gt;= val(recbuf)</c> to
              avoid performance issues because of unnecessary copying.
              For UDP the same recommendation applies, but the max should
              not be larger than the MTU of the network path.
              <c>val(buffer)</c> is automatically set to the above
              maximum when <c>recbuf</c> is set.
              However, as the size set for <c>recbuf</c>
              usually become larger, you are encouraged to use
              <seealso marker="#getopts/2"><c>getopts/2</c></seealso>
              to analyze the behavior of your operating system.</p>
            <p>Note that this is also the maximum amount of data that can be
	       received from a single recv call. If you are using higher than
	       normal MTU consider setting buffer higher.</p>
          </item>
          <tag><c>{delay_send, Boolean}</c></tag>
          <item>
            <p>Normally, when an Erlang process sends to a socket,
              the driver tries to send the data immediately. If that
              fails, the driver uses any means available to queue
              up the message to be sent whenever the operating system
              says it can handle it. Setting <c>{delay_send, true}</c>
              makes <em>all</em> messages queue up. The messages sent
              to the network are then larger but fewer.
              The option affects the scheduling of send
              requests versus Erlang processes instead of changing any
              real property of the socket. The option is
              implementation-specific. Defaults to <c>false</c>.</p>
          </item>
          <tag><c>{deliver, port | term}</c></tag>
          <item>
            <p>When <c>{active, true}</c>, data is delivered on the form
              <c>port</c> : <c>{S, {data, [H1,..Hsz | Data]}}</c> or
              <c>term</c> : <c>{tcp, S, [H1..Hsz | Data]}</c>.</p>
          </item>
          <tag><c>{dontroute, Boolean}</c></tag>
          <item>
            <p>Enables/disables routing bypass for outgoing messages.</p>
          </item>
          <tag><c>{exit_on_close, Boolean}</c></tag>
          <item>
            <p>This option is set to <c>true</c> by default.</p>
            <p>The only reason to set it to <c>false</c> is if you want
              to continue sending data to the socket after a close is
              detected, for example, if the peer uses
              <seealso marker="gen_tcp#shutdown/2"><c>gen_tcp:shutdown/2</c></seealso>
              to shut down the write side.</p>
          </item>
          <tag><c>{header, Size}</c></tag>
          <item>
            <p>This option is only meaningful if option <c>binary</c>
              was specified when the socket was created. If option
              <c>header</c> is specified, the first
              <c>Size</c> number bytes of data received from the socket
              are elements of a list, and the remaining data is
              a binary specified as the tail of the same list. For example,
              if <c>Size == 2</c>, the data received matches
              <c>[Byte1,Byte2|Binary]</c>.</p>
          </item>
          <tag><c>{high_msgq_watermark, Size}</c></tag>
          <item>
	    <p>The socket message queue is set to a busy
	      state when the amount of data on the message
	      queue reaches this limit. Notice that this limit only
	      concerns data that has not yet reached the ERTS internal
	      socket implementation. Defaults to 8 kB.</p>
	    <p>Senders of data to the socket are suspended if
	      either the socket message queue is busy or the socket
	      itself is busy.</p>
	    <p>For more information, see options <c>low_msgq_watermark</c>,
	      <c>high_watermark</c>, and <c>low_watermark</c>.</p>
	    <p>Notice that distribution sockets disable the use of
	      <c>high_msgq_watermark</c> and <c>low_msgq_watermark</c>.
	      Instead use the
	      <seealso marker="erts:erlang#system_info_dist_buf_busy_limit">distribution buffer busy limit</seealso>,
              which is a similar feature.</p>
          </item>
          <tag><c>{high_watermark, Size}</c> (TCP/IP sockets)</tag>
          <item>
	    <p>The socket is set to a busy state when the amount
	      of data queued internally by the ERTS socket implementation
	      reaches this limit. Defaults to 8 kB.</p>
	    <p>Senders of data to the socket are suspended if
	      either the socket message queue is busy or the socket
	      itself is busy.</p>
	    <p>For more information, see options <c>low_watermark</c>,
	      <c>high_msgq_watermark</c>, and <c>low_msqg_watermark</c>.</p>
          </item>
	  <tag><c>{ipv6_v6only, Boolean}</c></tag>
	  <item>
	    <p>Restricts the socket to use only IPv6, prohibiting any
	      IPv4 connections. This is only applicable for
	      IPv6 sockets (option <c>inet6</c>).</p>
            <p>On most platforms this option must be set on the socket
	      before associating it to an address. It is therefore only
	      reasonable to specify it when creating the socket and not
	      to use it when calling function
	      (<seealso marker="#setopts/2"><c>setopts/2</c></seealso>)
	      containing this description.</p>
	    <p>The behavior of a socket with this option set to
	      <c>true</c> is the only portable one. The original
	      idea when IPv6 was new of using IPv6 for all traffic
	      is now not recommended by FreeBSD (you can use
	      <c>{ipv6_v6only,false}</c> to override the recommended
	      system default value),
	      forbidden by OpenBSD (the supported GENERIC kernel),
	      and impossible on Windows (which has separate
	      IPv4 and IPv6 protocol stacks). Most Linux distros
	      still have a system default value of <c>false</c>.
	      This policy shift among operating systems to
	      separate IPv6 from IPv4 traffic has evolved, as
	      it gradually proved hard and complicated to get
	      a dual stack implementation correct and secure.</p>
	    <p>On some platforms, the only allowed value for this option
	      is <c>true</c>, for example, OpenBSD and Windows. Trying to set
	      this option to <c>false</c>, when creating the socket, fails
	      in this case.</p>
	    <p>Setting this option on platforms where it does not exist
	      is ignored. Getting this option with
	      <seealso marker="#getopts/2"><c>getopts/2</c></seealso>
	      returns no value, that is, the returned list does not contain an
	      <c>{ipv6_v6only,_}</c> tuple. On Windows, the option
	      does not exist, but it is emulated as a
	      read-only option with value <c>true</c>.</p>
	    <p>Therefore, setting this option to <c>true</c>
	      when creating a socket never fails, except possibly on a
              platform where you
	      have customized the kernel to only allow <c>false</c>,
	      which can be doable (but awkward) on, for example, OpenBSD.</p>
	    <p>If you read back the option value using
	      <seealso marker="#getopts/2"><c>getopts/2</c></seealso>
	      and get no value, the option does not exist in the host
              operating system. The behavior of both an IPv6 and an IPv4
	      socket listening on the same port, and for an IPv6 socket
	      getting IPv4 traffic is then no longer predictable.</p>
	  </item>
          <tag><c>{keepalive, Boolean}</c>(TCP/IP sockets)</tag>
          <item>
            <p>Enables/disables periodic transmission on a connected
              socket when no other data is exchanged. If
              the other end does not respond, the connection is
              considered broken and an error message is sent to
              the controlling process. Defaults to <c>disabled</c>.</p>
            <marker id="option-linger"></marker>
          </item>
          <tag><c>{linger, {true|false, Seconds}}</c></tag>
	  <item>
            <p>Determines the time-out, in seconds, for flushing unsent data
              in the <c>close/1</c> socket call. </p>
	    <p>The first component is if linger is enabled, the second component
	    is the flushing time-out, in seconds. There are 3 alternatives:</p>
	    <taglist>
	      <tag><c>{false, _}</c></tag>
	      <item>
		<p>close/1 or shutdown/2 returns immediately,
		not waiting for data to be flushed, with closing
		happening in the background.</p>
	      </item>
	      <tag><c>{true, 0}</c></tag>
	      <item>
		<p>Aborts the connection when it is closed.
		Discards any data still remaining in the send buffers
		and sends RST to the peer.</p>
		<p>This avoids TCP's TIME_WAIT state, but leaves open
		the possibility that another "incarnation" of this connection
		being created.</p>
	      </item>
	      <tag><c>{true, Time} when Time > 0</c></tag>
	      <item>
		<p>close/1 or shutdown/2 will not return until
		all queued messages for the socket have been successfully
		sent or the linger timeout (Time) has been reached.</p>
	      </item>
	    </taglist>
          </item>
          <tag><c>{low_msgq_watermark, Size}</c></tag>
          <item>
	    <p>If the socket message queue is in a busy state, the
	      socket message queue is set in a not busy state when
	      the amount of data queued in the message queue falls
	      below this limit. Notice that this limit only concerns data
	      that has not yet reached the ERTS internal socket
	      implementation. Defaults to 4 kB.</p>
	    <p>Senders that are suspended because of either a
	      busy message queue or a busy socket are resumed
	      when the socket message queue and the socket
	      are not busy.</p>
	    <p>For more information, see options <c>high_msgq_watermark</c>,
	      <c>high_watermark</c>, and <c>low_watermark</c>.</p>
	    <p>Notice that distribution sockets disable the use of
	      <c>high_msgq_watermark</c> and <c>low_msgq_watermark</c>.
	      Instead they use the
	      <seealso marker="erts:erlang#system_info_dist_buf_busy_limit">distribution
	      buffer busy limit</seealso>, which is a similar feature.</p>
          </item>
          <tag><c>{low_watermark, Size}</c> (TCP/IP sockets)</tag>
          <item>
	    <p>If the socket is in a busy state, the socket is
	      set in a not busy state when the amount of data
	      queued internally by the ERTS socket implementation
	      falls below this limit. Defaults to 4 kB.</p>
	    <p>Senders that are suspended because of a
	      busy message queue or a busy socket are resumed
	      when the socket message queue and the socket are not busy.</p>
	    <p>For more information, see options <c>high_watermark</c>,
	      <c>high_msgq_watermark</c>, and <c>low_msgq_watermark</c>.</p>
          </item>
          <tag><c>{mode, Mode :: binary | list}</c></tag>
          <item>
            <p>
	      Received <c>Packet</c> is delivered as defined by <c>Mode</c>.
            </p>
          </item>
	  <tag>
	    <marker id="option-netns"/>
	    <c>{netns, Namespace :: file:filename_all()}</c>
	  </tag>
	  <item>
	    <p>
	      Sets a network namespace for the socket. Parameter
	      <c>Namespace</c> is a filename defining the namespace, for
	      example, <c>"/var/run/netns/example"</c>, typically created by
	      command <c>ip netns add example</c>. This option must be used in
	      a function call that creates a socket, that is,
	      <seealso marker="gen_tcp#connect/3"><c>gen_tcp:connect/3,4</c></seealso>,
	      <seealso marker="gen_tcp#listen/2"><c>gen_tcp:listen/2</c></seealso>,
	      <seealso marker="gen_udp#open/1"><c>gen_udp:open/1,2</c></seealso>
	      or
	      <seealso marker="gen_sctp#open/0"><c>gen_sctp:open/0,1,2</c></seealso>,
	      and also
	      <seealso marker="#getifaddrs/1"><c>getifaddrs/1</c></seealso>.
	    </p>
	    <p>This option uses the Linux-specific syscall
	      <c>setns()</c>, such as in Linux kernel 3.0 or later,
	      and therefore only exists when the runtime system
	      is compiled for such an operating system.</p>
	    <p>The virtual machine also needs elevated privileges, either
	      running as superuser or (for Linux) having capability
	      <c>CAP_SYS_ADMIN</c> according to the documentation for
	      <c>setns(2)</c>.
	      However, during testing also <c>CAP_SYS_PTRACE</c>
	      and <c>CAP_DAC_READ_SEARCH</c> have proven to be necessary.</p>
            <p><em>Example:</em></p>
	    <code>
setcap cap_sys_admin,cap_sys_ptrace,cap_dac_read_search+epi beam.smp</code>
            <p>Notice that the filesystem containing the virtual machine
	      executable (<c>beam.smp</c> in the example) must be local,
	      mounted without flag <c>nosetuid</c>,
	      support extended attributes, and
	      the kernel must support file capabilities.
	      All this runs out of the box on at least Ubuntu 12.04 LTS,
	      except that SCTP sockets appear to not support
	      network namespaces.</p>
	    <p><c>Namespace</c> is a filename and is encoded
	      and decoded as discussed in module
	      <seealso marker="file">file</seealso>, with the
              following exceptions:</p>
	    <list type="bulleted">
	      <item><p>Emulator flag <c>+fnu</c> is ignored.</p></item>
	      <item><p><seealso marker="#getopts/2"><c>getopts/2</c></seealso>
	      for this option returns a binary for the filename if the stored
	      filename cannot be decoded. This is only to occur if you set the
	      option using a binary that cannot be decoded with the emulator's
	      filename encoding:
	      <seealso marker="file#native_name_encoding/0"><c>file:native_name_encoding/0</c></seealso>.</p></item>
	    </list>
          </item>
	  <tag><c>{bind_to_device, Ifname :: binary()}</c></tag>
	  <item>
	    <p>Binds a socket to a specific network interface. This option
	      must be used in a function call that creates a socket, that is,
	      <seealso marker="gen_tcp#connect/3"><c>gen_tcp:connect/3,4</c></seealso>,
	      <seealso marker="gen_tcp#listen/2"><c>gen_tcp:listen/2</c></seealso>,
	      <seealso marker="gen_udp#open/1"><c>gen_udp:open/1,2</c></seealso>, or
	      <seealso marker="gen_sctp#open/0"><c>gen_sctp:open/0,1,2</c></seealso>.</p>
	    <p>Unlike <seealso marker="#getifaddrs/0"><c>getifaddrs/0</c></seealso>, Ifname
	      is encoded a binary. In the unlikely case that a system is using
	      non-7-bit-ASCII characters in network device names, special care
	      has to be taken when encoding this argument.</p>
	    <p>This option uses the Linux-specific socket option
	      <c>SO_BINDTODEVICE</c>, such as in Linux kernel 2.0.30 or later,
	      and therefore only exists when the runtime system
	      is compiled for such an operating system.</p>
	    <p>Before Linux 3.8, this socket option could be set, but could not retrieved
	      with <seealso marker="#getopts/2"><c>getopts/2</c></seealso>. Since Linux 3.8,
	      it is readable.</p>
	    <p>The virtual machine also needs elevated privileges, either
	      running as superuser or (for Linux) having capability
	    <c>CAP_NET_RAW</c>.</p>
	    <p>The primary use case for this option is to bind sockets into
	      <url href="http://www.kernel.org/doc/Documentation/networking/vrf.txt">Linux VRF instances</url>.
	    </p>
	  </item>
          <tag><c>list</c></tag>
          <item>
            <p>Received <c>Packet</c> is delivered as a list.</p>
          </item>
          <tag><c>binary</c></tag>
          <item>
            <p>Received <c>Packet</c> is delivered as a binary.</p>
          </item>
          <tag><c>{nodelay, Boolean}</c>(TCP/IP sockets)</tag>
          <item>
            <p>If <c>Boolean == true</c>, option <c>TCP_NODELAY</c>
              is turned on for the socket, which means that also small
              amounts of data are sent immediately.</p>
          </item>
          <tag><c>{nopush, Boolean}</c>(TCP/IP sockets)</tag>
          <item>
            <p>This translates to <c>TCP_NOPUSH</c> on BSD and
              to <c>TCP_CORK</c> on Linux.</p>
            <p>If <c>Boolean == true</c>, the corresponding option
              is turned on for the socket, which means that small
              amounts of data are accumulated until a full MSS-worth
              of data is available or this option is turned off.</p>
            <p>Note that while <c>TCP_NOPUSH</c> socket option is available on OSX, its semantics
              is very different (e.g., unsetting it does not cause immediate send
              of accumulated data). Hence, <c>nopush</c> option is intentionally ignored on OSX.</p>
          </item>
          <tag><c>{packet, PacketType}</c>(TCP/IP sockets)</tag>
          <item>
            <p><marker id="packet"/>Defines the type of packets to use for a socket.
	      Possible values:</p>
            <taglist>
              <tag><c>raw | 0</c></tag>
              <item>
                <p>No packaging is done.</p>
              </item>
              <tag><c>1 | 2 | 4</c></tag>
              <item>
                <p>Packets consist of a header specifying the number of
                  bytes in the packet, followed by that number of bytes.
                  The header length can be one, two, or four bytes, and
                  containing an unsigned integer in big-endian byte order.
                  Each send operation generates the header, and the header
                  is stripped off on each receive operation.</p>
                <p>The 4-byte header is limited to 2Gb.</p>
              </item>
              <tag><c>asn1 | cdr | sunrm | fcgi | tpkt | line</c></tag>
              <item>
                <p>These packet types only have effect on receiving.
                  When sending a packet, it is the responsibility of
                  the application to supply a correct header. On
                  receiving, however, one message is sent to
                  the controlling process for each complete packet
                  received, and, similarly, each call to
                  <c>gen_tcp:recv/2,3</c> returns one complete packet.
                  The header is <em>not</em> stripped off.</p>
                <p>The meanings of the packet types are as follows:</p>
		<list type="bulleted">
		  <item><c>asn1</c> - ASN.1 BER</item>
		  <item><c>sunrm</c> - Sun's RPC encoding</item>
		  <item><c>cdr</c> - CORBA (GIOP 1.1)</item>
		  <item><c>fcgi</c> - Fast CGI</item>
		  <item><c>tpkt</c> - TPKT format [RFC1006]</item>
		  <item><c>line</c> - Line mode, a packet is a line-terminated
		    with newline, lines longer than the receive buffer are
		    truncated</item>
		</list>
	      </item>
              <tag><c>http | http_bin</c></tag>
              <item>
                <p>The Hypertext Transfer Protocol. The packets
                 are returned with the format according to <c>HttpPacket</c>
                 described in
                 <seealso marker="erts:erlang#decode_packet/3">
                 <c>erlang:decode_packet/3</c></seealso> in ERTS.
                 A socket in passive
                 mode returns <c>{ok, HttpPacket}</c> from <c>gen_tcp:recv</c>
                 while an active socket sends messages like
		 <c>{http, Socket, HttpPacket}</c>.</p>
              </item>
              <tag><c>httph | httph_bin</c></tag>
              <item>
                <p>These two types are often not needed, as the socket
		automatically switches from <c>http</c>/<c>http_bin</c> to
		<c>httph</c>/<c>httph_bin</c> internally after the first line
		is read. However, there can be occasions when they are
		useful, such as parsing trailers from chunked encoding.</p>
              </item>
            </taglist>
          </item>
          <tag><c>{packet_size, Integer}</c>(TCP/IP sockets)</tag>
          <item>
            <p>Sets the maximum allowed length of the packet body. If
              the packet header indicates that the length of the packet
              is longer than the maximum allowed length, the packet is
              considered invalid. The same occurs if the packet header
              is too large for the socket receive buffer.</p>
	    <p>For line-oriented protocols (<c>line</c>, <c>http*</c>),
	      option <c>packet_size</c> also guarantees that lines up to the
	      indicated length are accepted and not considered invalid
	      because of internal buffer limitations.</p>
          </item>
          <tag><c>{line_delimiter, Char}</c>(TCP/IP sockets)</tag>
          <item>
            <p>Sets the line delimiting character for line-oriented protocols
              (<c>line</c>). Defaults to <c>$\n</c>.</p>
          </item>
          <tag><c>{raw, Protocol, OptionNum, ValueBin}</c></tag>
          <item>
            <p>See below.</p>
          </item>
          <tag><c>{read_packets, Integer}</c>(UDP sockets)</tag>
          <item>
            <p>Sets the maximum number of UDP packets to read without
              intervention from the socket when data is available.
              When this many packets have been read and delivered
              to the destination process, new packets are not read
              until a new notification of available data has arrived.
              Defaults to <c>5</c>. If this parameter is set too
              high, the system can become unresponsive because of
              UDP packet flooding.</p>
          </item>
          <tag><c>{recbuf, Size}</c></tag>
          <item>
            <p>The minimum size of the receive buffer to use for
              the socket. You are encouraged to use
              <seealso marker="#getopts/2"><c>getopts/2</c></seealso>
              to retrieve the size set by your operating system.</p>
	    <marker id="option-recvtclass"></marker>
          </item>
          <tag><c>{recvtclass, Boolean}</c></tag>
          <item>
            <p>
	      If set to <c>true</c> activates returning the received
	      <c>TCLASS</c> value on platforms that implements
	      the protocol <c>IPPROTO_IPV6</c>
	      option <c>IPV6_RECVTCLASS</c> or <c>IPV6_2292RECVTCLASS</c>
	      for the socket.
	      The value is returned as a <c>{tclass,TCLASS}</c> tuple
	      regardless of if the platform returns an <c>IPV6_TCLASS</c>
	      or an <c>IPV6_RECVTCLASS</c> CMSG value.
	    </p>
	    <p>
	      For packet oriented sockets that supports receiving
	      ancillary data with the payload data
	      (<c>gen_udp</c> and <c>gen_sctp</c>),
	      the <c>TCLASS</c> value is returned
	      in an extended return tuple contained in an
	      <seealso marker="inet#type-ancillary_data">
		ancillary data
	      </seealso>
	      list.
	      For stream oriented sockets (<c>gen_tcp</c>)
	      the only way to get the <c>TCLASS</c>
	      value is if the platform supports the
	      <seealso marker="gen_tcp#type-pktoptions_value">
		<c>pktoptions</c>
	      </seealso>
	      option.
	    </p>
	    <marker id="option-recvtos"></marker>
          </item>
          <tag><c>{recvtos, Boolean}</c></tag>
          <item>
            <p>
	      If set to <c>true</c> activates returning the received
	      <c>TOS</c> value on platforms that implements
	      the protocol <c>IPPROTO_IP</c> option <c>IP_RECVTOS</c>
	      for the socket.
	      The value is returned as a <c>{tos,TOS}</c> tuple
	      regardless of if the platform returns an <c>IP_TOS</c>
	      or an <c>IP_RECVTOS</c> CMSG value.
	    </p>
	    <p>
	      For packet oriented sockets that supports receiving
	      ancillary data with the payload data
	      (<c>gen_udp</c> and <c>gen_sctp</c>),
	      the <c>TOS</c> value is returned
	      in an extended return tuple contained in an
	      <seealso marker="inet#type-ancillary_data">
		ancillary data
	      </seealso>
	      list.
	      For stream oriented sockets (<c>gen_tcp</c>)
	      the only way to get the <c>TOS</c>
	      value is if the platform supports the
	      <seealso marker="gen_tcp#type-pktoptions_value">
		<c>pktoptions</c>
	      </seealso>
	      option.
	    </p>
	    <marker id="option-recvttl"></marker>
          </item>
          <tag><c>{recvttl, Boolean}</c></tag>
          <item>
            <p>
	      If set to <c>true</c> activates returning the received
	      <c>TTL</c> value on platforms that implements
	      the protocol <c>IPPROTO_IP</c> option <c>IP_RECVTTL</c>
	      for the socket.
	      The value is returned as a <c>{ttl,TTL}</c> tuple
	      regardless of if the platform returns an <c>IP_TTL</c>
	      or an <c>IP_RECVTTL</c> CMSG value.
	    </p>
	    <p>
	      For packet oriented sockets that supports receiving
	      ancillary data with the payload data
	      (<c>gen_udp</c> and <c>gen_sctp</c>),
	      the <c>TTL</c> value is returned
	      in an extended return tuple contained in an
	      <seealso marker="inet#type-ancillary_data">
		ancillary data
	      </seealso>
	      list.
	      For stream oriented sockets (<c>gen_tcp</c>)
	      the only way to get the <c>TTL</c>
	      value is if the platform supports the
	      <seealso marker="gen_tcp#type-pktoptions_value">
		<c>pktoptions</c>
	      </seealso>
	      option.
	    </p>
          </item>
          <tag><c>{reuseaddr, Boolean}</c></tag>
          <item>
            <p>Allows or disallows local reuse of port numbers. By
              default, reuse is disallowed.</p>
          </item>
          <tag><c>{send_timeout, Integer}</c></tag>
          <item>
            <p>Only allowed for connection-oriented sockets.</p>
            <p>Specifies a longest time to wait for a send operation to
              be accepted by the underlying TCP stack. When the limit is
              exceeded, the send operation returns
              <c>{error,timeout}</c>. How much of a packet that
              got sent is unknown; the socket is therefore to be closed
              whenever a time-out has occurred (see <c>send_timeout_close</c>
              below). Defaults to <c>infinity</c>.</p>
          </item>
          <tag><c>{send_timeout_close, Boolean}</c></tag>
          <item>
            <p>Only allowed for connection-oriented sockets.</p>
            <p>Used together with <c>send_timeout</c> to specify whether
              the socket is to be automatically closed when the send operation
              returns <c>{error,timeout}</c>. The recommended setting is
              <c>true</c>, which automatically closes the socket.
              Defaults to <c>false</c> because of backward compatibility.</p>
            <marker id="option-sndbuf"></marker>
          </item>
          <tag><c>{show_econnreset, Boolean}</c>(TCP/IP sockets)</tag>
          <item>
            <p>When this option is set to <c>false</c>, which is
              default, an RST received from the TCP peer is treated
              as a normal close (as though an FIN was sent). A caller to
              <seealso marker="gen_tcp#recv/2"><c>gen_tcp:recv/2</c></seealso>
              gets <c>{error, closed}</c>. In active
              mode, the controlling process receives a
              <c>{tcp_closed, Socket}</c> message, indicating that the
              peer has closed the connection.</p>
            <p>Setting this option to <c>true</c> allows you to
              distinguish between a connection that was closed normally,
              and one that was aborted (intentionally or unintentionally)
              by the TCP peer. A call to
              <seealso marker="gen_tcp#recv/2"><c>gen_tcp:recv/2</c></seealso>
              returns <c>{error, econnreset}</c>. In
              active mode, the controlling process receives a
              <c>{tcp_error, Socket, econnreset}</c> message
              before the usual <c>{tcp_closed, Socket}</c>, as is
              the case for any other socket error. Calls to
              <seealso marker="gen_tcp#send/2"><c>gen_tcp:send/2</c></seealso>
              also returns <c>{error, econnreset}</c> when it
              is detected that a TCP peer has sent an RST.</p>
            <p>A connected socket returned from
              <seealso marker="gen_tcp#accept/1"><c>gen_tcp:accept/1</c></seealso>
              inherits the <c>show_econnreset</c> setting from the
              listening socket.</p>
            <marker id="option-show_econnreset"></marker>
          </item>
          <tag><c>{sndbuf, Size}</c></tag>
          <item>
            <p>The minimum size of the send buffer to use for the socket.
              You are encouraged to use
              <seealso marker="#getopts/2"><c>getopts/2</c></seealso>,
              to retrieve the size set by your operating system.</p>
          </item>
          <tag><c>{priority, Integer}</c></tag>
          <item>
            <p>Sets the <c>SO_PRIORITY</c> socket level option on platforms
              where this is implemented. The behavior and allowed range varies
              between different systems.
              The option is ignored on platforms where it
              is not implemented. Use with caution.</p>
          </item>
          <tag><c>{tos, Integer}</c></tag>
          <item>
            <p>Sets <c>IP_TOS IP</c> level options on platforms where this is
              implemented. The behavior and allowed range varies between
              different systems.
              The option is ignored on platforms where it is not
              implemented. Use with caution.</p>
          </item>
          <tag><c>{tclass, Integer}</c></tag>
          <item>
            <p>
	      Sets <c>IPV6_TCLASS IP</c> level options on platforms
	      where this is implemented. The behavior and allowed range
	      varies between different systems.
              The option is ignored on platforms where it is not
              implemented. Use with caution.</p>
          </item>
        </taglist>
        <p>In addition to these options, <em>raw</em>
          option specifications can be used. The raw options are
          specified as a tuple of arity four, beginning with tag
          <c>raw</c>, followed by the protocol level, the option number,
          and the option value specified as a binary. This
          corresponds to the second, third, and fourth arguments to the
          <c>setsockopt</c> call in the C socket API. The option value
          must be coded in the native endianess of the platform and,
          if a structure is required, must follow the structure
          alignment conventions on the specific platform.</p>
        <p>Using raw socket options requires detailed knowledge about
          the current operating system and TCP stack.</p>
        <p><em>Example:</em></p>
        <p>This example concerns the use of raw options. Consider a Linux
          system where you want to set option <c>TCP_LINGER2</c> on
          protocol level <c>IPPROTO_TCP</c> in the stack. You know
          that on this particular system it defaults to 60 (seconds),
          but you want to lower it to 30 for a particular
          socket. Option <c>TCP_LINGER2</c> is not explicitly
          supported by <c>inet</c>, but you know that the protocol level
          translates to number 6, the option number to number 8,
          and the value is to be specified as a 32-bit integer. You can use
          this code line to set the option for the socket named
          <c>Sock</c>:</p>
        <code type="none"><![CDATA[
inet:setopts(Sock,[{raw,6,8,<<30:32/native>>}]),]]></code>
        <p>As many options are silently discarded by the stack if they
          are specified out of range; it can be a good idea to check that
          a raw option is accepted. The following code places the value
          in variable <c>TcpLinger2:</c></p>
        <code type="none"><![CDATA[
{ok,[{raw,6,8,<<TcpLinger2:32/native>>}]}=inet:getopts(Sock,[{raw,6,8,4}]),]]></code>
        <p>Code such as these examples is inherently non-portable,
          even different versions of the same OS on the same platform
          can respond differently to this kind of option
          manipulation. Use with care.</p>
        <p>Notice that the default options for TCP/IP sockets can be
          changed with the Kernel configuration parameters mentioned in
          the beginning of this manual page.</p>
      </desc>
    </func>

    <func>
      <name name="sockname" arity="1" since=""/>
      <fsummary>Return the local address and port number for a socket.
      </fsummary>
      <desc>
        <p>Returns the local address and port number for a socket.</p>
	<p>Notice that for SCTP sockets this function returns only
	  one of the socket addresses. Function
	  <seealso marker="#socknames/1"><c>socknames/1,2</c></seealso>
	  returns all.</p>
      </desc>
    </func>

    <func>
      <name name="socknames" arity="1" since="OTP R16B03"/>
      <fsummary>Return all local address/port numbers for a socket.</fsummary>
      <desc>
	<p>Equivalent to
	  <seealso marker="#socknames/2"><c>socknames(<anno>Socket</anno>, 0)</c></seealso>.
        </p>
      </desc>
    </func>

    <func>
      <name name="socknames" arity="2" since="OTP R16B03"/>
      <fsummary>Return all local address/port numbers for a socket.</fsummary>
      <desc>
	<p>Returns a list of all local address/port number pairs for a socket
	  for the specified association <c><anno>Assoc</anno></c>.</p>
	<p>This function can return multiple addresses for multihomed
	  sockets, such as SCTP sockets. For other sockets it
	  returns a one-element list.</p>
	<p>Notice that parameter <c><anno>Assoc</anno></c> is by the
	  <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">SCTP Sockets API Extensions</url>
	  defined to be ignored for one-to-one style sockets.
	  For one-to-many style sockets, the special value <c>0</c>
	  is defined to mean that the returned addresses must be
	  without any particular association.
	  How different SCTP implementations interpret this varies somewhat.
        </p>
      </desc>
    </func>
  </funcs>

  <section>
    <marker id="error_codes"></marker>
    <title>POSIX Error Codes</title>
    <list type="bulleted">
      <item><c>e2big</c> - Too long argument list</item>
      <item><c>eacces</c> - Permission denied</item>
      <item><c>eaddrinuse</c> - Address already in use</item>
      <item><c>eaddrnotavail</c> - Cannot assign requested address</item>
      <item><c>eadv</c> - Advertise error</item>
      <item><c>eafnosupport</c> - Address family not supported by
        protocol family</item>
      <item><c>eagain</c> - Resource temporarily unavailable</item>
      <item><c>ealign</c> - EALIGN</item>
      <item><c>ealready</c> - Operation already in progress</item>
      <item><c>ebade</c> - Bad exchange descriptor</item>
      <item><c>ebadf</c> - Bad file number</item>
      <item><c>ebadfd</c> - File descriptor in bad state</item>
      <item><c>ebadmsg</c> - Not a data message</item>
      <item><c>ebadr</c> - Bad request descriptor</item>
      <item><c>ebadrpc</c> - Bad RPC structure</item>
      <item><c>ebadrqc</c> - Bad request code</item>
      <item><c>ebadslt</c> - Invalid slot</item>
      <item><c>ebfont</c> - Bad font file format</item>
      <item><c>ebusy</c> - File busy</item>
      <item><c>echild</c> - No children</item>
      <item><c>echrng</c> - Channel number out of range</item>
      <item><c>ecomm</c> - Communication error on send</item>
      <item><c>econnaborted</c> - Software caused connection abort</item>
      <item><c>econnrefused</c> - Connection refused</item>
      <item><c>econnreset</c> - Connection reset by peer</item>
      <item><c>edeadlk</c> - Resource deadlock avoided</item>
      <item><c>edeadlock</c> - Resource deadlock avoided</item>
      <item><c>edestaddrreq</c> - Destination address required</item>
      <item><c>edirty</c> - Mounting a dirty fs without force</item>
      <item><c>edom</c> - Math argument out of range</item>
      <item><c>edotdot</c> - Cross mount point</item>
      <item><c>edquot</c> - Disk quota exceeded</item>
      <item><c>eduppkg</c> - Duplicate package name</item>
      <item><c>eexist</c> - File already exists</item>
      <item><c>efault</c> - Bad address in system call argument</item>
      <item><c>efbig</c> - File too large</item>
      <item><c>ehostdown</c> - Host is down</item>
      <item><c>ehostunreach</c> - Host is unreachable</item>
      <item><c>eidrm</c> - Identifier removed</item>
      <item><c>einit</c> - Initialization error</item>
      <item><c>einprogress</c> - Operation now in progress</item>
      <item><c>eintr</c> - Interrupted system call</item>
      <item><c>einval</c> - Invalid argument</item>
      <item><c>eio</c> - I/O error</item>
      <item><c>eisconn</c> - Socket is already connected</item>
      <item><c>eisdir</c> - Illegal operation on a directory</item>
      <item><c>eisnam</c> - Is a named file</item>
      <item><c>el2hlt</c> - Level 2 halted</item>
      <item><c>el2nsync</c> - Level 2 not synchronized</item>
      <item><c>el3hlt</c> - Level 3 halted</item>
      <item><c>el3rst</c> - Level 3 reset</item>
      <item><c>elbin</c> - ELBIN</item>
      <item><c>elibacc</c> - Cannot access a needed shared library</item>
      <item><c>elibbad</c> - Accessing a corrupted shared library</item>
      <item><c>elibexec</c> - Cannot exec a shared library directly</item>
      <item><c>elibmax</c> - Attempting to link in more shared
        libraries than system limit</item>
      <item><c>elibscn</c> - <c>.lib</c> section in <c>a.out</c>
        corrupted</item>
      <item><c>elnrng</c> - Link number out of range</item>
      <item><c>eloop</c> - Too many levels of symbolic links</item>
      <item><c>emfile</c> - Too many open files</item>
      <item><c>emlink</c> - Too many links</item>
      <item><c>emsgsize</c> - Message too long</item>
      <item><c>emultihop</c> - Multihop attempted</item>
      <item><c>enametoolong</c> - Filename too long</item>
      <item><c>enavail</c> - Unavailable</item>
      <item><c>enet</c> - ENET</item>
      <item><c>enetdown</c> - Network is down</item>
      <item><c>enetreset</c> - Network dropped connection on reset</item>
      <item><c>enetunreach</c> - Network is unreachable</item>
      <item><c>enfile</c> - File table overflow</item>
      <item><c>enoano</c> - Anode table overflow</item>
      <item><c>enobufs</c> - No buffer space available</item>
      <item><c>enocsi</c> - No CSI structure available</item>
      <item><c>enodata</c> - No data available</item>
      <item><c>enodev</c> - No such device</item>
      <item><c>enoent</c> - No such file or directory</item>
      <item><c>enoexec</c> - Exec format error</item>
      <item><c>enolck</c> - No locks available</item>
      <item><c>enolink</c> - Link has been severed</item>
      <item><c>enomem</c> - Not enough memory</item>
      <item><c>enomsg</c> - No message of desired type</item>
      <item><c>enonet</c> - Machine is not on the network</item>
      <item><c>enopkg</c> - Package not installed</item>
      <item><c>enoprotoopt</c> - Bad protocol option</item>
      <item><c>enospc</c> - No space left on device</item>
      <item><c>enosr</c> - Out of stream resources or not a stream device</item>
      <item><c>enosym</c> - Unresolved symbol name</item>
      <item><c>enosys</c> - Function not implemented</item>
      <item><c>enotblk</c> - Block device required</item>
      <item><c>enotconn</c> - Socket is not connected</item>
      <item><c>enotdir</c> - Not a directory</item>
      <item><c>enotempty</c> - Directory not empty</item>
      <item><c>enotnam</c> - Not a named file</item>
      <item><c>enotsock</c> - Socket operation on non-socket</item>
      <item><c>enotsup</c> - Operation not supported</item>
      <item><c>enotty</c> - Inappropriate device for <c>ioctl</c></item>
      <item><c>enotuniq</c> - Name not unique on network</item>
      <item><c>enxio</c> - No such device or address</item>
      <item><c>eopnotsupp</c> - Operation not supported on socket</item>
      <item><c>eperm</c> - Not owner</item>
      <item><c>epfnosupport</c> - Protocol family not supported</item>
      <item><c>epipe</c> - Broken pipe</item>
      <item><c>eproclim</c> - Too many processes</item>
      <item><c>eprocunavail</c> - Bad procedure for program</item>
      <item><c>eprogmismatch</c> - Wrong program version</item>
      <item><c>eprogunavail</c> - RPC program unavailable</item>
      <item><c>eproto</c> - Protocol error</item>
      <item><c>eprotonosupport</c> - Protocol not supported</item>
      <item><c>eprototype</c> - Wrong protocol type for socket</item>
      <item><c>erange</c> - Math result unrepresentable</item>
      <item><c>erefused</c> - EREFUSED</item>
      <item><c>eremchg</c> - Remote address changed</item>
      <item><c>eremdev</c> - Remote device</item>
      <item><c>eremote</c> - Pathname hit remote filesystem</item>
      <item><c>eremoteio</c> - Remote I/O error</item>
      <item><c>eremoterelease</c> - EREMOTERELEASE</item>
      <item><c>erofs</c> - Read-only filesystem</item>
      <item><c>erpcmismatch</c> - Wrong RPC version</item>
      <item><c>erremote</c> - Object is remote</item>
      <item><c>eshutdown</c> - Cannot send after socket shutdown</item>
      <item><c>esocktnosupport</c> - Socket type not supported</item>
      <item><c>espipe</c> - Invalid seek</item>
      <item><c>esrch</c> - No such process</item>
      <item><c>esrmnt</c> - Srmount error</item>
      <item><c>estale</c> - Stale remote file handle</item>
      <item><c>esuccess</c> - Error 0</item>
      <item><c>etime</c> - Timer expired</item>
      <item><c>etimedout</c> - Connection timed out</item>
      <item><c>etoomanyrefs</c> - Too many references</item>
      <item><c>etxtbsy</c> - Text file or pseudo-device busy</item>
      <item><c>euclean</c> - Structure needs cleaning</item>
      <item><c>eunatch</c> - Protocol driver not attached</item>
      <item><c>eusers</c> - Too many users</item>
      <item><c>eversion</c> - Version mismatch</item>
      <item><c>ewouldblock</c> - Operation would block</item>
      <item><c>exdev</c> - Cross-domain link</item>
      <item><c>exfull</c> - Message tables full</item>
      <item><c>nxdomain</c> - Hostname or domain name cannot be found</item>
    </list>
  </section>
</erlref>