summaryrefslogtreecommitdiffstats
path: root/sshd_config.0
blob: 8b397396c237bf194de863c0c1356267627df6fc (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
SSHD_CONFIG(5)                File Formats Manual               SSHD_CONFIG(5)

NAME
     sshd_config M-bM-^@M-^S OpenSSH daemon configuration file

DESCRIPTION
     sshd(8) reads configuration data from /etc/ssh/sshd_config (or the file
     specified with -f on the command line).  The file contains keyword-
     argument pairs, one per line.  Unless noted otherwise, for each keyword,
     the first obtained value will be used.  Lines starting with M-bM-^@M-^X#M-bM-^@M-^Y and empty
     lines are interpreted as comments.  Arguments may optionally be enclosed
     in double quotes (") in order to represent arguments containing spaces.

     The possible keywords and their meanings are as follows (note that
     keywords are case-insensitive and arguments are case-sensitive):

     AcceptEnv
             Specifies what environment variables sent by the client will be
             copied into the session's environ(7).  See SendEnv and SetEnv in
             ssh_config(5) for how to configure the client.  The TERM
             environment variable is always accepted whenever the client
             requests a pseudo-terminal as it is required by the protocol.
             Variables are specified by name, which may contain the wildcard
             characters M-bM-^@M-^X*M-bM-^@M-^Y and M-bM-^@M-^X?M-bM-^@M-^Y.  Multiple environment variables may be
             separated by whitespace or spread across multiple AcceptEnv
             directives.  Be warned that some environment variables could be
             used to bypass restricted user environments.  For this reason,
             care should be taken in the use of this directive.  The default
             is not to accept any environment variables.

     AddressFamily
             Specifies which address family should be used by sshd(8).  Valid
             arguments are any (the default), inet (use IPv4 only), or inet6
             (use IPv6 only).

     AllowAgentForwarding
             Specifies whether ssh-agent(1) forwarding is permitted.  The
             default is yes.  Note that disabling agent forwarding does not
             improve security unless users are also denied shell access, as
             they can always install their own forwarders.

     AllowGroups
             This keyword can be followed by a list of group name patterns,
             separated by spaces.  If specified, login is allowed only for
             users whose primary group or supplementary group list matches one
             of the patterns.  Only group names are valid; a numerical group
             ID is not recognized.  By default, login is allowed for all
             groups.  The allow/deny groups directives are processed in the
             following order: DenyGroups, AllowGroups.

             See PATTERNS in ssh_config(5) for more information on patterns.
             This keyword may appear multiple times in sshd_config with each
             instance appending to the list.

     AllowStreamLocalForwarding
             Specifies whether StreamLocal (Unix-domain socket) forwarding is
             permitted.  The available options are yes (the default) or all to
             allow StreamLocal forwarding, no to prevent all StreamLocal
             forwarding, local to allow local (from the perspective of ssh(1))
             forwarding only or remote to allow remote forwarding only.  Note
             that disabling StreamLocal forwarding does not improve security
             unless users are also denied shell access, as they can always
             install their own forwarders.

     AllowTcpForwarding
             Specifies whether TCP forwarding is permitted.  The available
             options are yes (the default) or all to allow TCP forwarding, no
             to prevent all TCP forwarding, local to allow local (from the
             perspective of ssh(1)) forwarding only or remote to allow remote
             forwarding only.  Note that disabling TCP forwarding does not
             improve security unless users are also denied shell access, as
             they can always install their own forwarders.

     AllowUsers
             This keyword can be followed by a list of user name patterns,
             separated by spaces.  If specified, login is allowed only for
             user names that match one of the patterns.  Only user names are
             valid; a numerical user ID is not recognized.  By default, login
             is allowed for all users.  If the pattern takes the form
             USER@HOST then USER and HOST are separately checked, restricting
             logins to particular users from particular hosts.  HOST criteria
             may additionally contain addresses to match in CIDR
             address/masklen format.  The allow/deny users directives are
             processed in the following order: DenyUsers, AllowUsers.

             See PATTERNS in ssh_config(5) for more information on patterns.
             This keyword may appear multiple times in sshd_config with each
             instance appending to the list.

     AuthenticationMethods
             Specifies the authentication methods that must be successfully
             completed for a user to be granted access.  This option must be
             followed by one or more lists of comma-separated authentication
             method names, or by the single string any to indicate the default
             behaviour of accepting any single authentication method.  If the
             default is overridden, then successful authentication requires
             completion of every method in at least one of these lists.

             For example, "publickey,password publickey,keyboard-interactive"
             would require the user to complete public key authentication,
             followed by either password or keyboard interactive
             authentication.  Only methods that are next in one or more lists
             are offered at each stage, so for this example it would not be
             possible to attempt password or keyboard-interactive
             authentication before public key.

             For keyboard interactive authentication it is also possible to
             restrict authentication to a specific device by appending a colon
             followed by the device identifier bsdauth or pam.  depending on
             the server configuration.  For example,
             "keyboard-interactive:bsdauth" would restrict keyboard
             interactive authentication to the bsdauth device.

             If the publickey method is listed more than once, sshd(8)
             verifies that keys that have been used successfully are not
             reused for subsequent authentications.  For example,
             "publickey,publickey" requires successful authentication using
             two different public keys.

             Note that each authentication method listed should also be
             explicitly enabled in the configuration.

             The available authentication methods are: "gssapi-with-mic",
             "hostbased", "keyboard-interactive", "none" (used for access to
             password-less accounts when PermitEmptyPasswords is enabled),
             "password" and "publickey".

     AuthorizedKeysCommand
             Specifies a program to be used to look up the user's public keys.
             The program must be owned by root, not writable by group or
             others and specified by an absolute path.  Arguments to
             AuthorizedKeysCommand accept the tokens described in the TOKENS
             section.  If no arguments are specified then the username of the
             target user is used.

             The program should produce on standard output zero or more lines
             of authorized_keys output (see AUTHORIZED_KEYS in sshd(8)).
             AuthorizedKeysCommand is tried after the usual AuthorizedKeysFile
             files and will not be executed if a matching key is found there.
             By default, no AuthorizedKeysCommand is run.

     AuthorizedKeysCommandUser
             Specifies the user under whose account the AuthorizedKeysCommand
             is run.  It is recommended to use a dedicated user that has no
             other role on the host than running authorized keys commands.  If
             AuthorizedKeysCommand is specified but AuthorizedKeysCommandUser
             is not, then sshd(8) will refuse to start.

     AuthorizedKeysFile
             Specifies the file that contains the public keys used for user
             authentication.  The format is described in the AUTHORIZED_KEYS
             FILE FORMAT section of sshd(8).  Arguments to AuthorizedKeysFile
             accept the tokens described in the TOKENS section.  After
             expansion, AuthorizedKeysFile is taken to be an absolute path or
             one relative to the user's home directory.  Multiple files may be
             listed, separated by whitespace.  Alternately this option may be
             set to none to skip checking for user keys in files.  The default
             is ".ssh/authorized_keys .ssh/authorized_keys2".

     AuthorizedPrincipalsCommand
             Specifies a program to be used to generate the list of allowed
             certificate principals as per AuthorizedPrincipalsFile.  The
             program must be owned by root, not writable by group or others
             and specified by an absolute path.  Arguments to
             AuthorizedPrincipalsCommand accept the tokens described in the
             TOKENS section.  If no arguments are specified then the username
             of the target user is used.

             The program should produce on standard output zero or more lines
             of AuthorizedPrincipalsFile output.  If either
             AuthorizedPrincipalsCommand or AuthorizedPrincipalsFile is
             specified, then certificates offered by the client for
             authentication must contain a principal that is listed.  By
             default, no AuthorizedPrincipalsCommand is run.

     AuthorizedPrincipalsCommandUser
             Specifies the user under whose account the
             AuthorizedPrincipalsCommand is run.  It is recommended to use a
             dedicated user that has no other role on the host than running
             authorized principals commands.  If AuthorizedPrincipalsCommand
             is specified but AuthorizedPrincipalsCommandUser is not, then
             sshd(8) will refuse to start.

     AuthorizedPrincipalsFile
             Specifies a file that lists principal names that are accepted for
             certificate authentication.  When using certificates signed by a
             key listed in TrustedUserCAKeys, this file lists names, one of
             which must appear in the certificate for it to be accepted for
             authentication.  Names are listed one per line preceded by key
             options (as described in AUTHORIZED_KEYS FILE FORMAT in sshd(8)).
             Empty lines and comments starting with M-bM-^@M-^X#M-bM-^@M-^Y are ignored.

             Arguments to AuthorizedPrincipalsFile accept the tokens described
             in the TOKENS section.  After expansion, AuthorizedPrincipalsFile
             is taken to be an absolute path or one relative to the user's
             home directory.  The default is none, i.e. not to use a
             principals file M-bM-^@M-^S in this case, the username of the user must
             appear in a certificate's principals list for it to be accepted.

             Note that AuthorizedPrincipalsFile is only used when
             authentication proceeds using a CA listed in TrustedUserCAKeys
             and is not consulted for certification authorities trusted via
             ~/.ssh/authorized_keys, though the principals= key option offers
             a similar facility (see sshd(8) for details).

     Banner  The contents of the specified file are sent to the remote user
             before authentication is allowed.  If the argument is none then
             no banner is displayed.  By default, no banner is displayed.

     CASignatureAlgorithms
             Specifies which algorithms are allowed for signing of
             certificates by certificate authorities (CAs).  The default is:

                   ssh-ed25519,ecdsa-sha2-nistp256,
                   ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                   sk-ssh-ed25519@openssh.com,
                   sk-ecdsa-sha2-nistp256@openssh.com,
                   rsa-sha2-512,rsa-sha2-256

             If the specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the
             specified algorithms will be appended to the default set instead
             of replacing them.  If the specified list begins with a M-bM-^@M-^X-M-bM-^@M-^Y
             character, then the specified algorithms (including wildcards)
             will be removed from the default set instead of replacing them.

             Certificates signed using other algorithms will not be accepted
             for public key or host-based authentication.

     ChannelTimeout
             Specifies whether and how quickly sshd(8) should close inactive
             channels.  Timeouts are specified as one or more M-bM-^@M-^\type=intervalM-bM-^@M-^]
             pairs separated by whitespace, where the M-bM-^@M-^\typeM-bM-^@M-^] must be the
             special keyword M-bM-^@M-^\globalM-bM-^@M-^] or a channel type name from the list
             below, optionally containing wildcard characters.

             The timeout value M-bM-^@M-^\intervalM-bM-^@M-^] is specified in seconds or may use
             any of the units documented in the TIME FORMATS section.  For
             example, M-bM-^@M-^\session=5mM-bM-^@M-^] would cause interactive sessions to
             terminate after five minutes of inactivity.  Specifying a zero
             value disables the inactivity timeout.

             The special timeout M-bM-^@M-^\globalM-bM-^@M-^] applies to all active channels,
             taken together.  Traffic on any active channel will reset the
             timeout, but when the timeout expires then all open channels will
             be closed.  Note that this global timeout is not matched by
             wildcards and must be specified explicitly.

             The available channel type names include:

             agent-connection
                     Open connections to ssh-agent(1).

             direct-tcpip, direct-streamlocal@openssh.com
                     Open TCP or Unix socket (respectively) connections that
                     have been established from a ssh(1) local forwarding,
                     i.e. LocalForward or DynamicForward.

             forwarded-tcpip, forwarded-streamlocal@openssh.com
                     Open TCP or Unix socket (respectively) connections that
                     have been established to a sshd(8) listening on behalf of
                     a ssh(1) remote forwarding, i.e. RemoteForward.

             session
                     The interactive main session, including shell session,
                     command execution, scp(1), sftp(1), etc.

             tun-connection
                     Open TunnelForward connections.

             x11-connection
                     Open X11 forwarding sessions.

             Note that in all the above cases, terminating an inactive session
             does not guarantee to remove all resources associated with the
             session, e.g. shell processes or X11 clients relating to the
             session may continue to execute.

             Moreover, terminating an inactive channel or session does not
             necessarily close the SSH connection, nor does it prevent a
             client from requesting another channel of the same type.  In
             particular, expiring an inactive forwarding session does not
             prevent another identical forwarding from being subsequently
             created.

             The default is not to expire channels of any type for inactivity.

     ChrootDirectory
             Specifies the pathname of a directory to chroot(2) to after
             authentication.  At session startup sshd(8) checks that all
             components of the pathname are root-owned directories which are
             not writable by group or others.  After the chroot, sshd(8)
             changes the working directory to the user's home directory.
             Arguments to ChrootDirectory accept the tokens described in the
             TOKENS section.

             The ChrootDirectory must contain the necessary files and
             directories to support the user's session.  For an interactive
             session this requires at least a shell, typically sh(1), and
             basic /dev nodes such as null(4), zero(4), stdin(4), stdout(4),
             stderr(4), and tty(4) devices.  For file transfer sessions using
             SFTP no additional configuration of the environment is necessary
             if the in-process sftp-server is used, though sessions which use
             logging may require /dev/log inside the chroot directory on some
             operating systems (see sftp-server(8) for details).

             For safety, it is very important that the directory hierarchy be
             prevented from modification by other processes on the system
             (especially those outside the jail).  Misconfiguration can lead
             to unsafe environments which sshd(8) cannot detect.

             The default is none, indicating not to chroot(2).

     Ciphers
             Specifies the ciphers allowed.  Multiple ciphers must be comma-
             separated.  If the specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character,
             then the specified ciphers will be appended to the default set
             instead of replacing them.  If the specified list begins with a
             M-bM-^@M-^X-M-bM-^@M-^Y character, then the specified ciphers (including wildcards)
             will be removed from the default set instead of replacing them.
             If the specified list begins with a M-bM-^@M-^X^M-bM-^@M-^Y character, then the
             specified ciphers will be placed at the head of the default set.

             The supported ciphers are:

                   3des-cbc
                   aes128-cbc
                   aes192-cbc
                   aes256-cbc
                   aes128-ctr
                   aes192-ctr
                   aes256-ctr
                   aes128-gcm@openssh.com
                   aes256-gcm@openssh.com
                   chacha20-poly1305@openssh.com

             The default is:

                   chacha20-poly1305@openssh.com,
                   aes128-ctr,aes192-ctr,aes256-ctr,
                   aes128-gcm@openssh.com,aes256-gcm@openssh.com

             The list of available ciphers may also be obtained using "ssh -Q
             cipher".

     ClientAliveCountMax
             Sets the number of client alive messages which may be sent
             without sshd(8) receiving any messages back from the client.  If
             this threshold is reached while client alive messages are being
             sent, sshd will disconnect the client, terminating the session.
             It is important to note that the use of client alive messages is
             very different from TCPKeepAlive.  The client alive messages are
             sent through the encrypted channel and therefore will not be
             spoofable.  The TCP keepalive option enabled by TCPKeepAlive is
             spoofable.  The client alive mechanism is valuable when the
             client or server depend on knowing when a connection has become
             unresponsive.

             The default value is 3.  If ClientAliveInterval is set to 15, and
             ClientAliveCountMax is left at the default, unresponsive SSH
             clients will be disconnected after approximately 45 seconds.
             Setting a zero ClientAliveCountMax disables connection
             termination.

     ClientAliveInterval
             Sets a timeout interval in seconds after which if no data has
             been received from the client, sshd(8) will send a message
             through the encrypted channel to request a response from the
             client.  The default is 0, indicating that these messages will
             not be sent to the client.

     Compression
             Specifies whether compression is enabled after the user has
             authenticated successfully.  The argument must be yes, delayed (a
             legacy synonym for yes) or no.  The default is yes.

     DenyGroups
             This keyword can be followed by a list of group name patterns,
             separated by spaces.  Login is disallowed for users whose primary
             group or supplementary group list matches one of the patterns.
             Only group names are valid; a numerical group ID is not
             recognized.  By default, login is allowed for all groups.  The
             allow/deny groups directives are processed in the following
             order: DenyGroups, AllowGroups.

             See PATTERNS in ssh_config(5) for more information on patterns.
             This keyword may appear multiple times in sshd_config with each
             instance appending to the list.

     DenyUsers
             This keyword can be followed by a list of user name patterns,
             separated by spaces.  Login is disallowed for user names that
             match one of the patterns.  Only user names are valid; a
             numerical user ID is not recognized.  By default, login is
             allowed for all users.  If the pattern takes the form USER@HOST
             then USER and HOST are separately checked, restricting logins to
             particular users from particular hosts.  HOST criteria may
             additionally contain addresses to match in CIDR address/masklen
             format.  The allow/deny users directives are processed in the
             following order: DenyUsers, AllowUsers.

             See PATTERNS in ssh_config(5) for more information on patterns.
             This keyword may appear multiple times in sshd_config with each
             instance appending to the list.

     DisableForwarding
             Disables all forwarding features, including X11, ssh-agent(1),
             TCP and StreamLocal.  This option overrides all other forwarding-
             related options and may simplify restricted configurations.

     ExposeAuthInfo
             Writes a temporary file containing a list of authentication
             methods and public credentials (e.g. keys) used to authenticate
             the user.  The location of the file is exposed to the user
             session through the SSH_USER_AUTH environment variable.  The
             default is no.

     FingerprintHash
             Specifies the hash algorithm used when logging key fingerprints.
             Valid options are: md5 and sha256.  The default is sha256.

     ForceCommand
             Forces the execution of the command specified by ForceCommand,
             ignoring any command supplied by the client and ~/.ssh/rc if
             present.  The command is invoked by using the user's login shell
             with the -c option.  This applies to shell, command, or subsystem
             execution.  It is most useful inside a Match block.  The command
             originally supplied by the client is available in the
             SSH_ORIGINAL_COMMAND environment variable.  Specifying a command
             of internal-sftp will force the use of an in-process SFTP server
             that requires no support files when used with ChrootDirectory.
             The default is none.

     GatewayPorts
             Specifies whether remote hosts are allowed to connect to ports
             forwarded for the client.  By default, sshd(8) binds remote port
             forwardings to the loopback address.  This prevents other remote
             hosts from connecting to forwarded ports.  GatewayPorts can be
             used to specify that sshd should allow remote port forwardings to
             bind to non-loopback addresses, thus allowing other hosts to
             connect.  The argument may be no to force remote port forwardings
             to be available to the local host only, yes to force remote port
             forwardings to bind to the wildcard address, or clientspecified
             to allow the client to select the address to which the forwarding
             is bound.  The default is no.

     GSSAPIAuthentication
             Specifies whether user authentication based on GSSAPI is allowed.
             The default is no.

     GSSAPICleanupCredentials
             Specifies whether to automatically destroy the user's credentials
             cache on logout.  The default is yes.

     GSSAPIStrictAcceptorCheck
             Determines whether to be strict about the identity of the GSSAPI
             acceptor a client authenticates against.  If set to yes then the
             client must authenticate against the host service on the current
             hostname.  If set to no then the client may authenticate against
             any service key stored in the machine's default store.  This
             facility is provided to assist with operation on multi homed
             machines.  The default is yes.

     HostbasedAcceptedAlgorithms
             Specifies the signature algorithms that will be accepted for
             hostbased authentication as a list of comma-separated patterns.
             Alternately if the specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character,
             then the specified signature algorithms will be appended to the
             default set instead of replacing them.  If the specified list
             begins with a M-bM-^@M-^X-M-bM-^@M-^Y character, then the specified signature
             algorithms (including wildcards) will be removed from the default
             set instead of replacing them.  If the specified list begins with
             a M-bM-^@M-^X^M-bM-^@M-^Y character, then the specified signature algorithms will be
             placed at the head of the default set.  The default for this
             option is:

                ssh-ed25519-cert-v01@openssh.com,
                ecdsa-sha2-nistp256-cert-v01@openssh.com,
                ecdsa-sha2-nistp384-cert-v01@openssh.com,
                ecdsa-sha2-nistp521-cert-v01@openssh.com,
                sk-ssh-ed25519-cert-v01@openssh.com,
                sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
                rsa-sha2-512-cert-v01@openssh.com,
                rsa-sha2-256-cert-v01@openssh.com,
                ssh-ed25519,
                ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                sk-ssh-ed25519@openssh.com,
                sk-ecdsa-sha2-nistp256@openssh.com,
                rsa-sha2-512,rsa-sha2-256

             The list of available signature algorithms may also be obtained
             using "ssh -Q HostbasedAcceptedAlgorithms".  This was formerly
             named HostbasedAcceptedKeyTypes.

     HostbasedAuthentication
             Specifies whether rhosts or /etc/hosts.equiv authentication
             together with successful public key client host authentication is
             allowed (host-based authentication).  The default is no.

     HostbasedUsesNameFromPacketOnly
             Specifies whether or not the server will attempt to perform a
             reverse name lookup when matching the name in the ~/.shosts,
             ~/.rhosts, and /etc/hosts.equiv files during
             HostbasedAuthentication.  A setting of yes means that sshd(8)
             uses the name supplied by the client rather than attempting to
             resolve the name from the TCP connection itself.  The default is
             no.

     HostCertificate
             Specifies a file containing a public host certificate.  The
             certificate's public key must match a private host key already
             specified by HostKey.  The default behaviour of sshd(8) is not to
             load any certificates.

     HostKey
             Specifies a file containing a private host key used by SSH.  The
             defaults are /etc/ssh/ssh_host_ecdsa_key,
             /etc/ssh/ssh_host_ed25519_key and /etc/ssh/ssh_host_rsa_key.

             Note that sshd(8) will refuse to use a file if it is group/world-
             accessible and that the HostKeyAlgorithms option restricts which
             of the keys are actually used by sshd(8).

             It is possible to have multiple host key files.  It is also
             possible to specify public host key files instead.  In this case
             operations on the private key will be delegated to an
             ssh-agent(1).

     HostKeyAgent
             Identifies the UNIX-domain socket used to communicate with an
             agent that has access to the private host keys.  If the string
             "SSH_AUTH_SOCK" is specified, the location of the socket will be
             read from the SSH_AUTH_SOCK environment variable.

     HostKeyAlgorithms
             Specifies the host key signature algorithms that the server
             offers.  The default for this option is:

                ssh-ed25519-cert-v01@openssh.com,
                ecdsa-sha2-nistp256-cert-v01@openssh.com,
                ecdsa-sha2-nistp384-cert-v01@openssh.com,
                ecdsa-sha2-nistp521-cert-v01@openssh.com,
                sk-ssh-ed25519-cert-v01@openssh.com,
                sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
                rsa-sha2-512-cert-v01@openssh.com,
                rsa-sha2-256-cert-v01@openssh.com,
                ssh-ed25519,
                ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                sk-ssh-ed25519@openssh.com,
                sk-ecdsa-sha2-nistp256@openssh.com,
                rsa-sha2-512,rsa-sha2-256

             The list of available signature algorithms may also be obtained
             using "ssh -Q HostKeyAlgorithms".

     IgnoreRhosts
             Specifies whether to ignore per-user .rhosts and .shosts files
             during HostbasedAuthentication.  The system-wide /etc/hosts.equiv
             and /etc/shosts.equiv are still used regardless of this setting.

             Accepted values are yes (the default) to ignore all per-user
             files, shosts-only to allow the use of .shosts but to ignore
             .rhosts or no to allow both .shosts and rhosts.

     IgnoreUserKnownHosts
             Specifies whether sshd(8) should ignore the user's
             ~/.ssh/known_hosts during HostbasedAuthentication and use only
             the system-wide known hosts file /etc/ssh/ssh_known_hosts.  The
             default is M-bM-^@M-^\noM-bM-^@M-^].

     Include
             Include the specified configuration file(s).  Multiple pathnames
             may be specified and each pathname may contain glob(7) wildcards
             that will be expanded and processed in lexical order.  Files
             without absolute paths are assumed to be in /etc/ssh.  An Include
             directive may appear inside a Match block to perform conditional
             inclusion.

     IPQoS   Specifies the IPv4 type-of-service or DSCP class for the
             connection.  Accepted values are af11, af12, af13, af21, af22,
             af23, af31, af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3,
             cs4, cs5, cs6, cs7, ef, le, lowdelay, throughput, reliability, a
             numeric value, or none to use the operating system default.  This
             option may take one or two arguments, separated by whitespace.
             If one argument is specified, it is used as the packet class
             unconditionally.  If two values are specified, the first is
             automatically selected for interactive sessions and the second
             for non-interactive sessions.  The default is af21 (Low-Latency
             Data) for interactive sessions and cs1 (Lower Effort) for non-
             interactive sessions.

     KbdInteractiveAuthentication
             Specifies whether to allow keyboard-interactive authentication.
             All authentication styles from login.conf(5) are supported.  The
             default is yes.  The argument to this keyword must be yes or no.
             ChallengeResponseAuthentication is a deprecated alias for this.

     KerberosAuthentication
             Specifies whether the password provided by the user for
             PasswordAuthentication will be validated through the Kerberos
             KDC.  To use this option, the server needs a Kerberos servtab
             which allows the verification of the KDC's identity.  The default
             is no.

     KerberosGetAFSToken
             If AFS is active and the user has a Kerberos 5 TGT, attempt to
             acquire an AFS token before accessing the user's home directory.
             The default is no.

     KerberosOrLocalPasswd
             If password authentication through Kerberos fails then the
             password will be validated via any additional local mechanism
             such as /etc/passwd.  The default is yes.

     KerberosTicketCleanup
             Specifies whether to automatically destroy the user's ticket
             cache file on logout.  The default is yes.

     KexAlgorithms
             Specifies the available KEX (Key Exchange) algorithms.  Multiple
             algorithms must be comma-separated.  Alternately if the specified
             list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified algorithms
             will be appended to the default set instead of replacing them.
             If the specified list begins with a M-bM-^@M-^X-M-bM-^@M-^Y character, then the
             specified algorithms (including wildcards) will be removed from
             the default set instead of replacing them.  If the specified list
             begins with a M-bM-^@M-^X^M-bM-^@M-^Y character, then the specified algorithms will
             be placed at the head of the default set.  The supported
             algorithms are:

                   curve25519-sha256
                   curve25519-sha256@libssh.org
                   diffie-hellman-group1-sha1
                   diffie-hellman-group14-sha1
                   diffie-hellman-group14-sha256
                   diffie-hellman-group16-sha512
                   diffie-hellman-group18-sha512
                   diffie-hellman-group-exchange-sha1
                   diffie-hellman-group-exchange-sha256
                   ecdh-sha2-nistp256
                   ecdh-sha2-nistp384
                   ecdh-sha2-nistp521
                   sntrup761x25519-sha512@openssh.com

             The default is:

                   sntrup761x25519-sha512@openssh.com,
                   curve25519-sha256,curve25519-sha256@libssh.org,
                   ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
                   diffie-hellman-group-exchange-sha256,
                   diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,
                   diffie-hellman-group14-sha256

             The list of available key exchange algorithms may also be
             obtained using "ssh -Q KexAlgorithms".

     ListenAddress
             Specifies the local addresses sshd(8) should listen on.  The
             following forms may be used:

                   ListenAddress hostname|address [rdomain domain]
                   ListenAddress hostname:port [rdomain domain]
                   ListenAddress IPv4_address:port [rdomain domain]
                   ListenAddress [hostname|address]:port [rdomain domain]

             The optional rdomain qualifier requests sshd(8) listen in an
             explicit routing domain.  If port is not specified, sshd will
             listen on the address and all Port options specified.  The
             default is to listen on all local addresses on the current
             default routing domain.  Multiple ListenAddress options are
             permitted.  For more information on routing domains, see
             rdomain(4).

     LoginGraceTime
             The server disconnects after this time if the user has not
             successfully logged in.  If the value is 0, there is no time
             limit.  The default is 120 seconds.

     LogLevel
             Gives the verbosity level that is used when logging messages from
             sshd(8).  The possible values are: QUIET, FATAL, ERROR, INFO,
             VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.  The default is INFO.
             DEBUG and DEBUG1 are equivalent.  DEBUG2 and DEBUG3 each specify
             higher levels of debugging output.  Logging with a DEBUG level
             violates the privacy of users and is not recommended.

     LogVerbose
             Specify one or more overrides to LogLevel.  An override consists
             of a pattern lists that matches the source file, function and
             line number to force detailed logging for.  For example, an
             override pattern of:

                   kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*

             would enable detailed logging for line 1000 of kex.c, everything
             in the kex_exchange_identification() function, and all code in
             the packet.c file.  This option is intended for debugging and no
             overrides are enabled by default.

     MACs    Specifies the available MAC (message authentication code)
             algorithms.  The MAC algorithm is used for data integrity
             protection.  Multiple algorithms must be comma-separated.  If the
             specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified
             algorithms will be appended to the default set instead of
             replacing them.  If the specified list begins with a M-bM-^@M-^X-M-bM-^@M-^Y
             character, then the specified algorithms (including wildcards)
             will be removed from the default set instead of replacing them.
             If the specified list begins with a M-bM-^@M-^X^M-bM-^@M-^Y character, then the
             specified algorithms will be placed at the head of the default
             set.

             The algorithms that contain "-etm" calculate the MAC after
             encryption (encrypt-then-mac).  These are considered safer and
             their use recommended.  The supported MACs are:

                   hmac-md5
                   hmac-md5-96
                   hmac-sha1
                   hmac-sha1-96
                   hmac-sha2-256
                   hmac-sha2-512
                   umac-64@openssh.com
                   umac-128@openssh.com
                   hmac-md5-etm@openssh.com
                   hmac-md5-96-etm@openssh.com
                   hmac-sha1-etm@openssh.com
                   hmac-sha1-96-etm@openssh.com
                   hmac-sha2-256-etm@openssh.com
                   hmac-sha2-512-etm@openssh.com
                   umac-64-etm@openssh.com
                   umac-128-etm@openssh.com

             The default is:

                   umac-64-etm@openssh.com,umac-128-etm@openssh.com,
                   hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
                   hmac-sha1-etm@openssh.com,
                   umac-64@openssh.com,umac-128@openssh.com,
                   hmac-sha2-256,hmac-sha2-512,hmac-sha1

             The list of available MAC algorithms may also be obtained using
             "ssh -Q mac".

     Match   Introduces a conditional block.  If all of the criteria on the
             Match line are satisfied, the keywords on the following lines
             override those set in the global section of the config file,
             until either another Match line or the end of the file.  If a
             keyword appears in multiple Match blocks that are satisfied, only
             the first instance of the keyword is applied.

             The arguments to Match are one or more criteria-pattern pairs or
             the single token All which matches all criteria.  The available
             criteria are User, Group, Host, LocalAddress, LocalPort, RDomain,
             and Address (with RDomain representing the rdomain(4) on which
             the connection was received).

             The match patterns may consist of single entries or comma-
             separated lists and may use the wildcard and negation operators
             described in the PATTERNS section of ssh_config(5).

             The patterns in an Address criteria may additionally contain
             addresses to match in CIDR address/masklen format, such as
             192.0.2.0/24 or 2001:db8::/32.  Note that the mask length
             provided must be consistent with the address - it is an error to
             specify a mask length that is too long for the address or one
             with bits set in this host portion of the address.  For example,
             192.0.2.0/33 and 192.0.2.0/8, respectively.

             Only a subset of keywords may be used on the lines following a
             Match keyword.  Available keywords are AcceptEnv,
             AllowAgentForwarding, AllowGroups, AllowStreamLocalForwarding,
             AllowTcpForwarding, AllowUsers, AuthenticationMethods,
             AuthorizedKeysCommand, AuthorizedKeysCommandUser,
             AuthorizedKeysFile, AuthorizedPrincipalsCommand,
             AuthorizedPrincipalsCommandUser, AuthorizedPrincipalsFile,
             Banner, CASignatureAlgorithms, ChannelTimeout, ChrootDirectory,
             ClientAliveCountMax, ClientAliveInterval, DenyGroups, DenyUsers,
             DisableForwarding, ExposeAuthInfo, ForceCommand, GatewayPorts,
             GSSAPIAuthentication, HostbasedAcceptedAlgorithms,
             HostbasedAuthentication, HostbasedUsesNameFromPacketOnly,
             IgnoreRhosts, Include, IPQoS, KbdInteractiveAuthentication,
             KerberosAuthentication, LogLevel, MaxAuthTries, MaxSessions,
             PasswordAuthentication, PermitEmptyPasswords, PermitListen,
             PermitOpen, PermitRootLogin, PermitTTY, PermitTunnel,
             PermitUserRC, PubkeyAcceptedAlgorithms, PubkeyAuthentication,
             PubkeyAuthOptions, RekeyLimit, RevokedKeys, RDomain, SetEnv,
             StreamLocalBindMask, StreamLocalBindUnlink, TrustedUserCAKeys,
             UnusedConnectionTimeout, X11DisplayOffset, X11Forwarding and
             X11UseLocalhost.

     MaxAuthTries
             Specifies the maximum number of authentication attempts permitted
             per connection.  Once the number of failures reaches half this
             value, additional failures are logged.  The default is 6.

     MaxSessions
             Specifies the maximum number of open shell, login or subsystem
             (e.g. sftp) sessions permitted per network connection.  Multiple
             sessions may be established by clients that support connection
             multiplexing.  Setting MaxSessions to 1 will effectively disable
             session multiplexing, whereas setting it to 0 will prevent all
             shell, login and subsystem sessions while still permitting
             forwarding.  The default is 10.

     MaxStartups
             Specifies the maximum number of concurrent unauthenticated
             connections to the SSH daemon.  Additional connections will be
             dropped until authentication succeeds or the LoginGraceTime
             expires for a connection.  The default is 10:30:100.

             Alternatively, random early drop can be enabled by specifying the
             three colon separated values start:rate:full (e.g. "10:30:60").
             sshd(8) will refuse connection attempts with a probability of
             rate/100 (30%) if there are currently start (10) unauthenticated
             connections.  The probability increases linearly and all
             connection attempts are refused if the number of unauthenticated
             connections reaches full (60).

     ModuliFile
             Specifies the moduli(5) file that contains the Diffie-Hellman
             groups used for the M-bM-^@M-^\diffie-hellman-group-exchange-sha1M-bM-^@M-^] and
             M-bM-^@M-^\diffie-hellman-group-exchange-sha256M-bM-^@M-^] key exchange methods.  The
             default is /etc/moduli.

     PasswordAuthentication
             Specifies whether password authentication is allowed.  The
             default is yes.

     PermitEmptyPasswords
             When password authentication is allowed, it specifies whether the
             server allows login to accounts with empty password strings.  The
             default is no.

     PermitListen
             Specifies the addresses/ports on which a remote TCP port
             forwarding may listen.  The listen specification must be one of
             the following forms:

                   PermitListen port
                   PermitListen host:port

             Multiple permissions may be specified by separating them with
             whitespace.  An argument of any can be used to remove all
             restrictions and permit any listen requests.  An argument of none
             can be used to prohibit all listen requests.  The host name may
             contain wildcards as described in the PATTERNS section in
             ssh_config(5).  The wildcard M-bM-^@M-^X*M-bM-^@M-^Y can also be used in place of a
             port number to allow all ports.  By default all port forwarding
             listen requests are permitted.  Note that the GatewayPorts option
             may further restrict which addresses may be listened on.  Note
             also that ssh(1) will request a listen host of M-bM-^@M-^\localhostM-bM-^@M-^] if no
             listen host was specifically requested, and this name is treated
             differently to explicit localhost addresses of M-bM-^@M-^\127.0.0.1M-bM-^@M-^] and
             M-bM-^@M-^\::1M-bM-^@M-^].

     PermitOpen
             Specifies the destinations to which TCP port forwarding is
             permitted.  The forwarding specification must be one of the
             following forms:

                   PermitOpen host:port
                   PermitOpen IPv4_addr:port
                   PermitOpen [IPv6_addr]:port

             Multiple forwards may be specified by separating them with
             whitespace.  An argument of any can be used to remove all
             restrictions and permit any forwarding requests.  An argument of
             none can be used to prohibit all forwarding requests.  The
             wildcard M-bM-^@M-^X*M-bM-^@M-^Y can be used for host or port to allow all hosts or
             ports respectively.  Otherwise, no pattern matching or address
             lookups are performed on supplied names.  By default all port
             forwarding requests are permitted.

     PermitRootLogin
             Specifies whether root can log in using ssh(1).  The argument
             must be yes, prohibit-password, forced-commands-only, or no.  The
             default is prohibit-password.

             If this option is set to prohibit-password (or its deprecated
             alias, without-password), password and keyboard-interactive
             authentication are disabled for root.

             If this option is set to forced-commands-only, root login with
             public key authentication will be allowed, but only if the
             command option has been specified (which may be useful for taking
             remote backups even if root login is normally not allowed).  All
             other authentication methods are disabled for root.

             If this option is set to no, root is not allowed to log in.

     PermitTTY
             Specifies whether pty(4) allocation is permitted.  The default is
             yes.

     PermitTunnel
             Specifies whether tun(4) device forwarding is allowed.  The
             argument must be yes, point-to-point (layer 3), ethernet (layer
             2), or no.  Specifying yes permits both point-to-point and
             ethernet.  The default is no.

             Independent of this setting, the permissions of the selected
             tun(4) device must allow access to the user.

     PermitUserEnvironment
             Specifies whether ~/.ssh/environment and environment= options in
             ~/.ssh/authorized_keys are processed by sshd(8).  Valid options
             are yes, no or a pattern-list specifying which environment
             variable names to accept (for example "LANG,LC_*").  The default
             is no.  Enabling environment processing may enable users to
             bypass access restrictions in some configurations using
             mechanisms such as LD_PRELOAD.

     PermitUserRC
             Specifies whether any ~/.ssh/rc file is executed.  The default is
             yes.

     PerSourceMaxStartups
             Specifies the number of unauthenticated connections allowed from
             a given source address, or M-bM-^@M-^\noneM-bM-^@M-^] if there is no limit.  This
             limit is applied in addition to MaxStartups, whichever is lower.
             The default is none.

     PerSourceNetBlockSize
             Specifies the number of bits of source address that are grouped
             together for the purposes of applying PerSourceMaxStartups
             limits.  Values for IPv4 and optionally IPv6 may be specified,
             separated by a colon.  The default is 32:128, which means each
             address is considered individually.

     PidFile
             Specifies the file that contains the process ID of the SSH
             daemon, or none to not write one.  The default is
             /var/run/sshd.pid.

     Port    Specifies the port number that sshd(8) listens on.  The default
             is 22.  Multiple options of this type are permitted.  See also
             ListenAddress.

     PrintLastLog
             Specifies whether sshd(8) should print the date and time of the
             last user login when a user logs in interactively.  The default
             is yes.

     PrintMotd
             Specifies whether sshd(8) should print /etc/motd when a user logs
             in interactively.  (On some systems it is also printed by the
             shell, /etc/profile, or equivalent.)  The default is yes.

     PubkeyAcceptedAlgorithms
             Specifies the signature algorithms that will be accepted for
             public key authentication as a list of comma-separated patterns.
             Alternately if the specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character,
             then the specified algorithms will be appended to the default set
             instead of replacing them.  If the specified list begins with a
             M-bM-^@M-^X-M-bM-^@M-^Y character, then the specified algorithms (including
             wildcards) will be removed from the default set instead of
             replacing them.  If the specified list begins with a M-bM-^@M-^X^M-bM-^@M-^Y
             character, then the specified algorithms will be placed at the
             head of the default set.  The default for this option is:

                ssh-ed25519-cert-v01@openssh.com,
                ecdsa-sha2-nistp256-cert-v01@openssh.com,
                ecdsa-sha2-nistp384-cert-v01@openssh.com,
                ecdsa-sha2-nistp521-cert-v01@openssh.com,
                sk-ssh-ed25519-cert-v01@openssh.com,
                sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
                rsa-sha2-512-cert-v01@openssh.com,
                rsa-sha2-256-cert-v01@openssh.com,
                ssh-ed25519,
                ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                sk-ssh-ed25519@openssh.com,
                sk-ecdsa-sha2-nistp256@openssh.com,
                rsa-sha2-512,rsa-sha2-256

             The list of available signature algorithms may also be obtained
             using "ssh -Q PubkeyAcceptedAlgorithms".

     PubkeyAuthOptions
             Sets one or more public key authentication options.  The
             supported keywords are: none (the default; indicating no
             additional options are enabled), touch-required and
             verify-required.

             The touch-required option causes public key authentication using
             a FIDO authenticator algorithm (i.e. ecdsa-sk or ed25519-sk) to
             always require the signature to attest that a physically present
             user explicitly confirmed the authentication (usually by touching
             the authenticator).  By default, sshd(8) requires user presence
             unless overridden with an authorized_keys option.  The
             touch-required flag disables this override.

             The verify-required option requires a FIDO key signature attest
             that the user was verified, e.g. via a PIN.

             Neither the touch-required or verify-required options have any
             effect for other, non-FIDO, public key types.

     PubkeyAuthentication
             Specifies whether public key authentication is allowed.  The
             default is yes.

     RekeyLimit
             Specifies the maximum amount of data that may be transmitted or
             received before the session key is renegotiated, optionally
             followed by a maximum amount of time that may pass before the
             session key is renegotiated.  The first argument is specified in
             bytes and may have a suffix of M-bM-^@M-^XKM-bM-^@M-^Y, M-bM-^@M-^XMM-bM-^@M-^Y, or M-bM-^@M-^XGM-bM-^@M-^Y to indicate
             Kilobytes, Megabytes, or Gigabytes, respectively.  The default is
             between M-bM-^@M-^X1GM-bM-^@M-^Y and M-bM-^@M-^X4GM-bM-^@M-^Y, depending on the cipher.  The optional
             second value is specified in seconds and may use any of the units
             documented in the TIME FORMATS section.  The default value for
             RekeyLimit is default none, which means that rekeying is
             performed after the cipher's default amount of data has been sent
             or received and no time based rekeying is done.

     RequiredRSASize
             Specifies the minimum RSA key size (in bits) that sshd(8) will
             accept.  User and host-based authentication keys smaller than
             this limit will be refused.  The default is 1024 bits.  Note that
             this limit may only be raised from the default.

     RevokedKeys
             Specifies revoked public keys file, or none to not use one.  Keys
             listed in this file will be refused for public key
             authentication.  Note that if this file is not readable, then
             public key authentication will be refused for all users.  Keys
             may be specified as a text file, listing one public key per line,
             or as an OpenSSH Key Revocation List (KRL) as generated by
             ssh-keygen(1).  For more information on KRLs, see the KEY
             REVOCATION LISTS section in ssh-keygen(1).

     RDomain
             Specifies an explicit routing domain that is applied after
             authentication has completed.  The user session, as well as any
             forwarded or listening IP sockets, will be bound to this
             rdomain(4).  If the routing domain is set to %D, then the domain
             in which the incoming connection was received will be applied.

     SecurityKeyProvider
             Specifies a path to a library that will be used when loading FIDO
             authenticator-hosted keys, overriding the default of using the
             built-in USB HID support.

     SetEnv  Specifies one or more environment variables to set in child
             sessions started by sshd(8) as M-bM-^@M-^\NAME=VALUEM-bM-^@M-^].  The environment
             value may be quoted (e.g. if it contains whitespace characters).
             Environment variables set by SetEnv override the default
             environment and any variables specified by the user via AcceptEnv
             or PermitUserEnvironment.

     StreamLocalBindMask
             Sets the octal file creation mode mask (umask) used when creating
             a Unix-domain socket file for local or remote port forwarding.
             This option is only used for port forwarding to a Unix-domain
             socket file.

             The default value is 0177, which creates a Unix-domain socket
             file that is readable and writable only by the owner.  Note that
             not all operating systems honor the file mode on Unix-domain
             socket files.

     StreamLocalBindUnlink
             Specifies whether to remove an existing Unix-domain socket file
             for local or remote port forwarding before creating a new one.
             If the socket file already exists and StreamLocalBindUnlink is
             not enabled, sshd will be unable to forward the port to the Unix-
             domain socket file.  This option is only used for port forwarding
             to a Unix-domain socket file.

             The argument must be yes or no.  The default is no.

     StrictModes
             Specifies whether sshd(8) should check file modes and ownership
             of the user's files and home directory before accepting login.
             This is normally desirable because novices sometimes accidentally
             leave their directory or files world-writable.  The default is
             yes.  Note that this does not apply to ChrootDirectory, whose
             permissions and ownership are checked unconditionally.

     Subsystem
             Configures an external subsystem (e.g. file transfer daemon).
             Arguments should be a subsystem name and a command (with optional
             arguments) to execute upon subsystem request.

             The command sftp-server implements the SFTP file transfer
             subsystem.

             Alternately the name internal-sftp implements an in-process SFTP
             server.  This may simplify configurations using ChrootDirectory
             to force a different filesystem root on clients.  It accepts the
             same command line arguments as sftp-server and even though it is
             in-process, settings such as LogLevel or SyslogFacility do not
             apply to it and must be set explicitly via command line
             arguments.

             By default no subsystems are defined.

     SyslogFacility
             Gives the facility code that is used when logging messages from
             sshd(8).  The possible values are: DAEMON, USER, AUTH, LOCAL0,
             LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.  The
             default is AUTH.

     TCPKeepAlive
             Specifies whether the system should send TCP keepalive messages
             to the other side.  If they are sent, death of the connection or
             crash of one of the machines will be properly noticed.  However,
             this means that connections will die if the route is down
             temporarily, and some people find it annoying.  On the other
             hand, if TCP keepalives are not sent, sessions may hang
             indefinitely on the server, leaving "ghost" users and consuming
             server resources.

             The default is yes (to send TCP keepalive messages), and the
             server will notice if the network goes down or the client host
             crashes.  This avoids infinitely hanging sessions.

             To disable TCP keepalive messages, the value should be set to no.

     TrustedUserCAKeys
             Specifies a file containing public keys of certificate
             authorities that are trusted to sign user certificates for
             authentication, or none to not use one.  Keys are listed one per
             line; empty lines and comments starting with M-bM-^@M-^X#M-bM-^@M-^Y are allowed.  If
             a certificate is presented for authentication and has its signing
             CA key listed in this file, then it may be used for
             authentication for any user listed in the certificate's
             principals list.  Note that certificates that lack a list of
             principals will not be permitted for authentication using
             TrustedUserCAKeys.  For more details on certificates, see the
             CERTIFICATES section in ssh-keygen(1).

     UnusedConnectionTimeout
             Specifies whether and how quickly sshd(8) should close client
             connections with no open channels.  Open channels include active
             shell, command execution or subsystem sessions, connected
             network, socket, agent or X11 forwardings.  Forwarding listeners,
             such as those from the ssh(1) -R flag, are not considered as open
             channels and do not prevent the timeout.  The timeout value is
             specified in seconds or may use any of the units documented in
             the TIME FORMATS section.

             Note that this timeout starts when the client connection
             completes user authentication but before the client has an
             opportunity to open any channels.  Caution should be used when
             using short timeout values, as they may not provide sufficient
             time for the client to request and open its channels before
             terminating the connection.

             The default none is to never expire connections for having no
             open channels.  This option may be useful in conjunction with
             ChannelTimeout.

     UseDNS  Specifies whether sshd(8) should look up the remote host name,
             and to check that the resolved host name for the remote IP
             address maps back to the very same IP address.

             If this option is set to no (the default) then only addresses and
             not host names may be used in ~/.ssh/authorized_keys from and
             sshd_config Match Host directives.

     UsePAM  Enables the Pluggable Authentication Module interface.  If set to
             yes this will enable PAM authentication using
             KbdInteractiveAuthentication and PasswordAuthentication in
             addition to PAM account and session module processing for all
             authentication types.

             Because PAM keyboard-interactive authentication usually serves an
             equivalent role to password authentication, you should disable
             either PasswordAuthentication or KbdInteractiveAuthentication.

             If UsePAM is enabled, you will not be able to run sshd(8) as a
             non-root user.  The default is no.

     VersionAddendum
             Optionally specifies additional text to append to the SSH
             protocol banner sent by the server upon connection.  The default
             is none.

     X11DisplayOffset
             Specifies the first display number available for sshd(8)'s X11
             forwarding.  This prevents sshd from interfering with real X11
             servers.  The default is 10.

     X11Forwarding
             Specifies whether X11 forwarding is permitted.  The argument must
             be yes or no.  The default is no.

             When X11 forwarding is enabled, there may be additional exposure
             to the server and to client displays if the sshd(8) proxy display
             is configured to listen on the wildcard address (see
             X11UseLocalhost), though this is not the default.  Additionally,
             the authentication spoofing and authentication data verification
             and substitution occur on the client side.  The security risk of
             using X11 forwarding is that the client's X11 display server may
             be exposed to attack when the SSH client requests forwarding (see
             the warnings for ForwardX11 in ssh_config(5)).  A system
             administrator may have a stance in which they want to protect
             clients that may expose themselves to attack by unwittingly
             requesting X11 forwarding, which can warrant a no setting.

             Note that disabling X11 forwarding does not prevent users from
             forwarding X11 traffic, as users can always install their own
             forwarders.

     X11UseLocalhost
             Specifies whether sshd(8) should bind the X11 forwarding server
             to the loopback address or to the wildcard address.  By default,
             sshd binds the forwarding server to the loopback address and sets
             the hostname part of the DISPLAY environment variable to
             localhost.  This prevents remote hosts from connecting to the
             proxy display.  However, some older X11 clients may not function
             with this configuration.  X11UseLocalhost may be set to no to
             specify that the forwarding server should be bound to the
             wildcard address.  The argument must be yes or no.  The default
             is yes.

     XAuthLocation
             Specifies the full pathname of the xauth(1) program, or none to
             not use one.  The default is /usr/X11R6/bin/xauth.

TIME FORMATS
     sshd(8) command-line arguments and configuration file options that
     specify time may be expressed using a sequence of the form:
     time[qualifier], where time is a positive integer value and qualifier is
     one of the following:

           M-bM-^_M-(noneM-bM-^_M-)  seconds
           s | S   seconds
           m | M   minutes
           h | H   hours
           d | D   days
           w | W   weeks

     Each member of the sequence is added together to calculate the total time
     value.

     Time format examples:

           600     600 seconds (10 minutes)
           10m     10 minutes
           1h30m   1 hour 30 minutes (90 minutes)

TOKENS
     Arguments to some keywords can make use of tokens, which are expanded at
     runtime:

           %%    A literal M-bM-^@M-^X%M-bM-^@M-^Y.
           %C    Identifies the connection endpoints, containing four space-
                 separated values: client address, client port number, server
                 address, and server port number.
           %D    The routing domain in which the incoming connection was
                 received.
           %F    The fingerprint of the CA key.
           %f    The fingerprint of the key or certificate.
           %h    The home directory of the user.
           %i    The key ID in the certificate.
           %K    The base64-encoded CA key.
           %k    The base64-encoded key or certificate for authentication.
           %s    The serial number of the certificate.
           %T    The type of the CA key.
           %t    The key or certificate type.
           %U    The numeric user ID of the target user.
           %u    The username.

     AuthorizedKeysCommand accepts the tokens %%, %C, %D, %f, %h, %k, %t, %U,
     and %u.

     AuthorizedKeysFile accepts the tokens %%, %h, %U, and %u.

     AuthorizedPrincipalsCommand accepts the tokens %%, %C, %D, %F, %f, %h,
     %i, %K, %k, %s, %T, %t, %U, and %u.

     AuthorizedPrincipalsFile accepts the tokens %%, %h, %U, and %u.

     ChrootDirectory accepts the tokens %%, %h, %U, and %u.

     RoutingDomain accepts the token %D.

FILES
     /etc/ssh/sshd_config
             Contains configuration data for sshd(8).  This file should be
             writable by root only, but it is recommended (though not
             necessary) that it be world-readable.

SEE ALSO
     sftp-server(8), sshd(8)

AUTHORS
     OpenSSH is a derivative of the original and free ssh 1.2.12 release by
     Tatu Ylonen.  Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
     de Raadt and Dug Song removed many bugs, re-added newer features and
     created OpenSSH.  Markus Friedl contributed the support for SSH protocol
     versions 1.5 and 2.0.  Niels Provos and Markus Friedl contributed support
     for privilege separation.

OpenBSD 7.5                    February 21, 2024                   OpenBSD 7.5