Annotation of src/usr.bin/ssh/sshd_config.5, Revision 1.146
1.1 stevesk 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
18: .\" are met:
19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
22: .\" notice, this list of conditions and the following disclaimer in the
23: .\" documentation and/or other materials provided with the distribution.
24: .\"
25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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1.146 ! djm 36: .\" $OpenBSD: sshd_config.5,v 1.145 2012/10/04 13:21:50 markus Exp $
! 37: .Dd $Mdocdate: October 4 2012 $
1.1 stevesk 38: .Dt SSHD_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm sshd_config
42: .Nd OpenSSH SSH daemon configuration file
43: .Sh SYNOPSIS
1.71 jmc 44: .Nm /etc/ssh/sshd_config
1.1 stevesk 45: .Sh DESCRIPTION
1.53 jmc 46: .Xr sshd 8
1.1 stevesk 47: reads configuration data from
48: .Pa /etc/ssh/sshd_config
49: (or the file specified with
50: .Fl f
51: on the command line).
52: The file contains keyword-argument pairs, one per line.
53: Lines starting with
54: .Ql #
55: and empty lines are interpreted as comments.
1.56 dtucker 56: Arguments may optionally be enclosed in double quotes
57: .Pq \&"
58: in order to represent arguments containing spaces.
1.1 stevesk 59: .Pp
60: The possible
61: keywords and their meanings are as follows (note that
62: keywords are case-insensitive and arguments are case-sensitive):
63: .Bl -tag -width Ds
1.30 djm 64: .It Cm AcceptEnv
65: Specifies what environment variables sent by the client will be copied into
66: the session's
67: .Xr environ 7 .
68: See
69: .Cm SendEnv
70: in
71: .Xr ssh_config 5
72: for how to configure the client.
1.31 djm 73: Note that environment passing is only supported for protocol 2.
1.30 djm 74: Variables are specified by name, which may contain the wildcard characters
1.51 jmc 75: .Ql *
1.30 djm 76: and
77: .Ql \&? .
1.31 djm 78: Multiple environment variables may be separated by whitespace or spread
1.30 djm 79: across multiple
80: .Cm AcceptEnv
81: directives.
1.31 djm 82: Be warned that some environment variables could be used to bypass restricted
1.30 djm 83: user environments.
84: For this reason, care should be taken in the use of this directive.
85: The default is not to accept any environment variables.
1.37 djm 86: .It Cm AddressFamily
87: Specifies which address family should be used by
1.53 jmc 88: .Xr sshd 8 .
1.37 djm 89: Valid arguments are
90: .Dq any ,
91: .Dq inet
1.52 jmc 92: (use IPv4 only), or
1.37 djm 93: .Dq inet6
94: (use IPv6 only).
95: The default is
96: .Dq any .
1.89 jmc 97: .It Cm AllowAgentForwarding
98: Specifies whether
99: .Xr ssh-agent 1
100: forwarding is permitted.
101: The default is
102: .Dq yes .
103: Note that disabling agent forwarding does not improve security
104: unless users are also denied shell access, as they can always install
105: their own forwarders.
1.1 stevesk 106: .It Cm AllowGroups
107: This keyword can be followed by a list of group name patterns, separated
108: by spaces.
109: If specified, login is allowed only for users whose primary
110: group or supplementary group list matches one of the patterns.
111: Only group names are valid; a numerical group ID is not recognized.
112: By default, login is allowed for all groups.
1.54 jmc 113: The allow/deny directives are processed in the following order:
114: .Cm DenyUsers ,
115: .Cm AllowUsers ,
116: .Cm DenyGroups ,
117: and finally
118: .Cm AllowGroups .
1.49 jmc 119: .Pp
120: See
121: .Sx PATTERNS
122: in
123: .Xr ssh_config 5
124: for more information on patterns.
1.1 stevesk 125: .It Cm AllowTcpForwarding
126: Specifies whether TCP forwarding is permitted.
127: The default is
128: .Dq yes .
129: Note that disabling TCP forwarding does not improve security unless
130: users are also denied shell access, as they can always install their
131: own forwarders.
132: .It Cm AllowUsers
133: This keyword can be followed by a list of user name patterns, separated
134: by spaces.
1.14 jmc 135: If specified, login is allowed only for user names that
1.1 stevesk 136: match one of the patterns.
137: Only user names are valid; a numerical user ID is not recognized.
138: By default, login is allowed for all users.
139: If the pattern takes the form USER@HOST then USER and HOST
140: are separately checked, restricting logins to particular
141: users from particular hosts.
1.54 jmc 142: The allow/deny directives are processed in the following order:
143: .Cm DenyUsers ,
144: .Cm AllowUsers ,
145: .Cm DenyGroups ,
146: and finally
147: .Cm AllowGroups .
1.49 jmc 148: .Pp
149: See
150: .Sx PATTERNS
151: in
152: .Xr ssh_config 5
153: for more information on patterns.
1.146 ! djm 154: .It Cm AuthorizedKeysCommand
! 155: Specifies a program to be used for lookup of the user's public keys.
! 156: The program will be invoked with a single argument of the username
! 157: being authenticated, and should produce on standard output zero or
! 158: more lines of authorized_keys output (see AUTHORIZED_KEYS in
! 159: .Xr sshd 8 )
! 160: If a key supplied by AuthorizedKeysCommand does not successfully authenticate
! 161: and authorize the user then public key authentication continues using the usual
! 162: .Cm AuthorizedKeysFile
! 163: files.
! 164: By default, no AuthorizedKeysCommand is run.
! 165: .It Cm AuthorizedKeysCommandUser
! 166: Specifies the user under whose account the AuthorizedKeysCommand is run.
! 167: The default is the user being authenticated.
! 168: It is recommended to use a dedicated user that has no other role on the host
! 169: than running authorized keys commands.
1.1 stevesk 170: .It Cm AuthorizedKeysFile
171: Specifies the file that contains the public keys that can be used
172: for user authentication.
1.124 djm 173: The format is described in the
174: .Sx AUTHORIZED_KEYS FILE FORMAT
175: section of
176: .Xr sshd 8 .
1.1 stevesk 177: .Cm AuthorizedKeysFile
178: may contain tokens of the form %T which are substituted during connection
1.52 jmc 179: setup.
1.17 jmc 180: The following tokens are defined: %% is replaced by a literal '%',
1.52 jmc 181: %h is replaced by the home directory of the user being authenticated, and
1.1 stevesk 182: %u is replaced by the username of that user.
183: After expansion,
184: .Cm AuthorizedKeysFile
185: is taken to be an absolute path or one relative to the user's home
186: directory.
1.133 jmc 187: Multiple files may be listed, separated by whitespace.
188: The default is
189: .Dq .ssh/authorized_keys .ssh/authorized_keys2 .
1.121 djm 190: .It Cm AuthorizedPrincipalsFile
191: Specifies a file that lists principal names that are accepted for
192: certificate authentication.
193: When using certificates signed by a key listed in
194: .Cm TrustedUserCAKeys ,
195: this file lists names, one of which must appear in the certificate for it
196: to be accepted for authentication.
1.125 jmc 197: Names are listed one per line preceded by key options (as described
1.124 djm 198: in
199: .Sx AUTHORIZED_KEYS FILE FORMAT
200: in
1.125 jmc 201: .Xr sshd 8 ) .
1.124 djm 202: Empty lines and comments starting with
1.121 djm 203: .Ql #
204: are ignored.
205: .Pp
206: .Cm AuthorizedPrincipalsFile
207: may contain tokens of the form %T which are substituted during connection
208: setup.
209: The following tokens are defined: %% is replaced by a literal '%',
210: %h is replaced by the home directory of the user being authenticated, and
211: %u is replaced by the username of that user.
212: After expansion,
213: .Cm AuthorizedPrincipalsFile
214: is taken to be an absolute path or one relative to the user's home
215: directory.
216: .Pp
1.138 djm 217: The default is
218: .Dq none ,
219: i.e. not to use a principals file \(en in this case, the username
1.121 djm 220: of the user must appear in a certificate's principals list for it to be
221: accepted.
222: Note that
223: .Cm AuthorizedPrincipalsFile
224: is only used when authentication proceeds using a CA listed in
225: .Cm TrustedUserCAKeys
226: and is not consulted for certification authorities trusted via
227: .Pa ~/.ssh/authorized_keys ,
228: though the
229: .Cm principals=
230: key option offers a similar facility (see
231: .Xr sshd 8
232: for details).
1.1 stevesk 233: .It Cm Banner
234: The contents of the specified file are sent to the remote user before
235: authentication is allowed.
1.78 djm 236: If the argument is
237: .Dq none
238: then no banner is displayed.
1.1 stevesk 239: This option is only available for protocol version 2.
240: By default, no banner is displayed.
241: .It Cm ChallengeResponseAuthentication
1.50 jmc 242: Specifies whether challenge-response authentication is allowed.
1.1 stevesk 243: All authentication styles from
244: .Xr login.conf 5
245: are supported.
246: The default is
247: .Dq yes .
1.80 djm 248: .It Cm ChrootDirectory
1.113 stevesk 249: Specifies the pathname of a directory to
1.80 djm 250: .Xr chroot 2
251: to after authentication.
1.113 stevesk 252: All components of the pathname must be root-owned directories that are
1.80 djm 253: not writable by any other user or group.
1.106 stevesk 254: After the chroot,
255: .Xr sshd 8
256: changes the working directory to the user's home directory.
1.80 djm 257: .Pp
1.113 stevesk 258: The pathname may contain the following tokens that are expanded at runtime once
1.80 djm 259: the connecting user has been authenticated: %% is replaced by a literal '%',
260: %h is replaced by the home directory of the user being authenticated, and
261: %u is replaced by the username of that user.
262: .Pp
263: The
264: .Cm ChrootDirectory
265: must contain the necessary files and directories to support the
1.103 stevesk 266: user's session.
1.80 djm 267: For an interactive session this requires at least a shell, typically
268: .Xr sh 1 ,
269: and basic
270: .Pa /dev
271: nodes such as
272: .Xr null 4 ,
273: .Xr zero 4 ,
274: .Xr stdin 4 ,
275: .Xr stdout 4 ,
276: .Xr stderr 4 ,
277: .Xr arandom 4
278: and
279: .Xr tty 4
280: devices.
281: For file transfer sessions using
1.105 jmc 282: .Dq sftp ,
1.80 djm 283: no additional configuration of the environment is necessary if the
1.105 jmc 284: in-process sftp server is used,
285: though sessions which use logging do require
1.104 stevesk 286: .Pa /dev/log
287: inside the chroot directory (see
288: .Xr sftp-server 8
1.81 jmc 289: for details).
1.80 djm 290: .Pp
291: The default is not to
292: .Xr chroot 2 .
1.1 stevesk 293: .It Cm Ciphers
294: Specifies the ciphers allowed for protocol version 2.
295: Multiple ciphers must be comma-separated.
1.34 dtucker 296: The supported ciphers are
297: .Dq 3des-cbc ,
298: .Dq aes128-cbc ,
299: .Dq aes192-cbc ,
300: .Dq aes256-cbc ,
301: .Dq aes128-ctr ,
302: .Dq aes192-ctr ,
303: .Dq aes256-ctr ,
1.43 djm 304: .Dq arcfour128 ,
305: .Dq arcfour256 ,
1.34 dtucker 306: .Dq arcfour ,
307: .Dq blowfish-cbc ,
308: and
309: .Dq cast128-cbc .
1.52 jmc 310: The default is:
311: .Bd -literal -offset 3n
1.100 naddy 312: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
313: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
314: aes256-cbc,arcfour
1.1 stevesk 315: .Ed
316: .It Cm ClientAliveCountMax
1.48 jmc 317: Sets the number of client alive messages (see below) which may be
1.1 stevesk 318: sent without
1.52 jmc 319: .Xr sshd 8
1.17 jmc 320: receiving any messages back from the client.
321: If this threshold is reached while client alive messages are being sent,
1.52 jmc 322: sshd will disconnect the client, terminating the session.
1.17 jmc 323: It is important to note that the use of client alive messages is very
324: different from
1.27 markus 325: .Cm TCPKeepAlive
1.17 jmc 326: (below).
327: The client alive messages are sent through the encrypted channel
328: and therefore will not be spoofable.
329: The TCP keepalive option enabled by
1.27 markus 330: .Cm TCPKeepAlive
1.17 jmc 331: is spoofable.
332: The client alive mechanism is valuable when the client or
1.1 stevesk 333: server depend on knowing when a connection has become inactive.
334: .Pp
1.17 jmc 335: The default value is 3.
336: If
1.1 stevesk 337: .Cm ClientAliveInterval
1.48 jmc 338: (see below) is set to 15, and
1.1 stevesk 339: .Cm ClientAliveCountMax
1.52 jmc 340: is left at the default, unresponsive SSH clients
1.1 stevesk 341: will be disconnected after approximately 45 seconds.
1.57 markus 342: This option applies to protocol version 2 only.
1.42 djm 343: .It Cm ClientAliveInterval
344: Sets a timeout interval in seconds after which if no data has been received
345: from the client,
1.52 jmc 346: .Xr sshd 8
1.42 djm 347: will send a message through the encrypted
348: channel to request a response from the client.
349: The default
350: is 0, indicating that these messages will not be sent to the client.
351: This option applies to protocol version 2 only.
1.3 markus 352: .It Cm Compression
1.44 markus 353: Specifies whether compression is allowed, or delayed until
354: the user has authenticated successfully.
1.3 markus 355: The argument must be
1.44 markus 356: .Dq yes ,
357: .Dq delayed ,
1.3 markus 358: or
359: .Dq no .
360: The default is
1.44 markus 361: .Dq delayed .
1.1 stevesk 362: .It Cm DenyGroups
363: This keyword can be followed by a list of group name patterns, separated
364: by spaces.
365: Login is disallowed for users whose primary group or supplementary
366: group list matches one of the patterns.
367: Only group names are valid; a numerical group ID is not recognized.
368: By default, login is allowed for all groups.
1.54 jmc 369: The allow/deny directives are processed in the following order:
370: .Cm DenyUsers ,
371: .Cm AllowUsers ,
372: .Cm DenyGroups ,
373: and finally
374: .Cm AllowGroups .
1.49 jmc 375: .Pp
376: See
377: .Sx PATTERNS
378: in
379: .Xr ssh_config 5
380: for more information on patterns.
1.1 stevesk 381: .It Cm DenyUsers
382: This keyword can be followed by a list of user name patterns, separated
383: by spaces.
384: Login is disallowed for user names that match one of the patterns.
385: Only user names are valid; a numerical user ID is not recognized.
386: By default, login is allowed for all users.
387: If the pattern takes the form USER@HOST then USER and HOST
388: are separately checked, restricting logins to particular
389: users from particular hosts.
1.54 jmc 390: The allow/deny directives are processed in the following order:
391: .Cm DenyUsers ,
392: .Cm AllowUsers ,
393: .Cm DenyGroups ,
394: and finally
395: .Cm AllowGroups .
1.49 jmc 396: .Pp
397: See
398: .Sx PATTERNS
399: in
400: .Xr ssh_config 5
401: for more information on patterns.
1.67 dtucker 402: .It Cm ForceCommand
403: Forces the execution of the command specified by
404: .Cm ForceCommand ,
1.84 djm 405: ignoring any command supplied by the client and
406: .Pa ~/.ssh/rc
407: if present.
1.67 dtucker 408: The command is invoked by using the user's login shell with the -c option.
409: This applies to shell, command, or subsystem execution.
410: It is most useful inside a
411: .Cm Match
412: block.
413: The command originally supplied by the client is available in the
414: .Ev SSH_ORIGINAL_COMMAND
415: environment variable.
1.82 djm 416: Specifying a command of
417: .Dq internal-sftp
418: will force the use of an in-process sftp server that requires no support
419: files when used with
420: .Cm ChrootDirectory .
1.1 stevesk 421: .It Cm GatewayPorts
422: Specifies whether remote hosts are allowed to connect to ports
423: forwarded for the client.
424: By default,
1.52 jmc 425: .Xr sshd 8
1.15 jmc 426: binds remote port forwardings to the loopback address.
427: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 428: .Cm GatewayPorts
1.52 jmc 429: can be used to specify that sshd
1.39 djm 430: should allow remote port forwardings to bind to non-loopback addresses, thus
431: allowing other hosts to connect.
432: The argument may be
433: .Dq no
434: to force remote port forwardings to be available to the local host only,
1.1 stevesk 435: .Dq yes
1.39 djm 436: to force remote port forwardings to bind to the wildcard address, or
437: .Dq clientspecified
438: to allow the client to select the address to which the forwarding is bound.
1.1 stevesk 439: The default is
440: .Dq no .
1.23 markus 441: .It Cm GSSAPIAuthentication
1.25 markus 442: Specifies whether user authentication based on GSSAPI is allowed.
1.26 djm 443: The default is
1.23 markus 444: .Dq no .
445: Note that this option applies to protocol version 2 only.
446: .It Cm GSSAPICleanupCredentials
447: Specifies whether to automatically destroy the user's credentials cache
448: on logout.
449: The default is
450: .Dq yes .
451: Note that this option applies to protocol version 2 only.
1.1 stevesk 452: .It Cm HostbasedAuthentication
453: Specifies whether rhosts or /etc/hosts.equiv authentication together
454: with successful public key client host authentication is allowed
1.50 jmc 455: (host-based authentication).
1.1 stevesk 456: This option is similar to
457: .Cm RhostsRSAAuthentication
458: and applies to protocol version 2 only.
1.70 dtucker 459: The default is
460: .Dq no .
461: .It Cm HostbasedUsesNameFromPacketOnly
462: Specifies whether or not the server will attempt to perform a reverse
463: name lookup when matching the name in the
464: .Pa ~/.shosts ,
465: .Pa ~/.rhosts ,
466: and
467: .Pa /etc/hosts.equiv
468: files during
469: .Cm HostbasedAuthentication .
470: A setting of
471: .Dq yes
472: means that
473: .Xr sshd 8
474: uses the name supplied by the client rather than
475: attempting to resolve the name from the TCP connection itself.
1.1 stevesk 476: The default is
477: .Dq no .
1.117 djm 478: .It Cm HostCertificate
479: Specifies a file containing a public host certificate.
480: The certificate's public key must match a private host key already specified
481: by
482: .Cm HostKey .
483: The default behaviour of
484: .Xr sshd 8
485: is not to load any certificates.
1.1 stevesk 486: .It Cm HostKey
487: Specifies a file containing a private host key
488: used by SSH.
489: The default is
490: .Pa /etc/ssh/ssh_host_key
491: for protocol version 1, and
1.126 djm 492: .Pa /etc/ssh/ssh_host_dsa_key ,
493: .Pa /etc/ssh/ssh_host_ecdsa_key
494: and
1.1 stevesk 495: .Pa /etc/ssh/ssh_host_rsa_key
496: for protocol version 2.
497: Note that
1.52 jmc 498: .Xr sshd 8
1.1 stevesk 499: will refuse to use a file if it is group/world-accessible.
500: It is possible to have multiple host key files.
501: .Dq rsa1
502: keys are used for version 1 and
1.126 djm 503: .Dq dsa ,
504: .Dq ecdsa
1.1 stevesk 505: or
506: .Dq rsa
507: are used for version 2 of the SSH protocol.
508: .It Cm IgnoreRhosts
509: Specifies that
510: .Pa .rhosts
511: and
512: .Pa .shosts
513: files will not be used in
514: .Cm RhostsRSAAuthentication
515: or
516: .Cm HostbasedAuthentication .
517: .Pp
518: .Pa /etc/hosts.equiv
519: and
520: .Pa /etc/shosts.equiv
521: are still used.
522: The default is
523: .Dq yes .
524: .It Cm IgnoreUserKnownHosts
525: Specifies whether
1.52 jmc 526: .Xr sshd 8
1.1 stevesk 527: should ignore the user's
1.41 djm 528: .Pa ~/.ssh/known_hosts
1.1 stevesk 529: during
530: .Cm RhostsRSAAuthentication
531: or
532: .Cm HostbasedAuthentication .
533: The default is
534: .Dq no .
1.129 djm 535: .It Cm IPQoS
536: Specifies the IPv4 type-of-service or DSCP class for the connection.
537: Accepted values are
538: .Dq af11 ,
539: .Dq af12 ,
540: .Dq af13 ,
1.136 djm 541: .Dq af21 ,
1.129 djm 542: .Dq af22 ,
543: .Dq af23 ,
544: .Dq af31 ,
545: .Dq af32 ,
546: .Dq af33 ,
547: .Dq af41 ,
548: .Dq af42 ,
549: .Dq af43 ,
550: .Dq cs0 ,
551: .Dq cs1 ,
552: .Dq cs2 ,
553: .Dq cs3 ,
554: .Dq cs4 ,
555: .Dq cs5 ,
556: .Dq cs6 ,
557: .Dq cs7 ,
558: .Dq ef ,
559: .Dq lowdelay ,
560: .Dq throughput ,
561: .Dq reliability ,
562: or a numeric value.
1.131 djm 563: This option may take one or two arguments, separated by whitespace.
1.129 djm 564: If one argument is specified, it is used as the packet class unconditionally.
565: If two values are specified, the first is automatically selected for
566: interactive sessions and the second for non-interactive sessions.
567: The default is
568: .Dq lowdelay
569: for interactive sessions and
570: .Dq throughput
571: for non-interactive sessions.
1.1 stevesk 572: .It Cm KerberosAuthentication
1.24 markus 573: Specifies whether the password provided by the user for
1.1 stevesk 574: .Cm PasswordAuthentication
1.24 markus 575: will be validated through the Kerberos KDC.
1.1 stevesk 576: To use this option, the server needs a
577: Kerberos servtab which allows the verification of the KDC's identity.
1.52 jmc 578: The default is
1.29 dtucker 579: .Dq no .
580: .It Cm KerberosGetAFSToken
1.45 djm 581: If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire
1.29 dtucker 582: an AFS token before accessing the user's home directory.
1.52 jmc 583: The default is
1.1 stevesk 584: .Dq no .
585: .It Cm KerberosOrLocalPasswd
1.52 jmc 586: If password authentication through Kerberos fails then
1.1 stevesk 587: the password will be validated via any additional local mechanism
588: such as
589: .Pa /etc/passwd .
1.52 jmc 590: The default is
1.1 stevesk 591: .Dq yes .
592: .It Cm KerberosTicketCleanup
593: Specifies whether to automatically destroy the user's ticket cache
594: file on logout.
1.52 jmc 595: The default is
1.1 stevesk 596: .Dq yes .
1.127 djm 597: .It Cm KexAlgorithms
598: Specifies the available KEX (Key Exchange) algorithms.
599: Multiple algorithms must be comma-separated.
600: The default is
601: .Dq ecdh-sha2-nistp256 ,
602: .Dq ecdh-sha2-nistp384 ,
603: .Dq ecdh-sha2-nistp521 ,
1.130 jmc 604: .Dq diffie-hellman-group-exchange-sha256 ,
1.127 djm 605: .Dq diffie-hellman-group-exchange-sha1 ,
606: .Dq diffie-hellman-group14-sha1 ,
607: .Dq diffie-hellman-group1-sha1 .
1.1 stevesk 608: .It Cm KeyRegenerationInterval
609: In protocol version 1, the ephemeral server key is automatically regenerated
610: after this many seconds (if it has been used).
611: The purpose of regeneration is to prevent
612: decrypting captured sessions by later breaking into the machine and
613: stealing the keys.
614: The key is never stored anywhere.
615: If the value is 0, the key is never regenerated.
616: The default is 3600 (seconds).
617: .It Cm ListenAddress
618: Specifies the local addresses
1.52 jmc 619: .Xr sshd 8
1.1 stevesk 620: should listen on.
621: The following forms may be used:
622: .Pp
623: .Bl -item -offset indent -compact
624: .It
625: .Cm ListenAddress
626: .Sm off
627: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
628: .Sm on
629: .It
630: .Cm ListenAddress
631: .Sm off
632: .Ar host No | Ar IPv4_addr No : Ar port
633: .Sm on
634: .It
635: .Cm ListenAddress
636: .Sm off
637: .Oo
638: .Ar host No | Ar IPv6_addr Oc : Ar port
639: .Sm on
640: .El
641: .Pp
642: If
643: .Ar port
644: is not specified,
1.52 jmc 645: sshd will listen on the address and all prior
1.1 stevesk 646: .Cm Port
1.17 jmc 647: options specified.
648: The default is to listen on all local addresses.
1.15 jmc 649: Multiple
1.1 stevesk 650: .Cm ListenAddress
1.17 jmc 651: options are permitted.
652: Additionally, any
1.1 stevesk 653: .Cm Port
1.52 jmc 654: options must precede this option for non-port qualified addresses.
1.1 stevesk 655: .It Cm LoginGraceTime
656: The server disconnects after this time if the user has not
657: successfully logged in.
658: If the value is 0, there is no time limit.
1.12 stevesk 659: The default is 120 seconds.
1.1 stevesk 660: .It Cm LogLevel
661: Gives the verbosity level that is used when logging messages from
1.53 jmc 662: .Xr sshd 8 .
1.1 stevesk 663: The possible values are:
1.52 jmc 664: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.15 jmc 665: The default is INFO.
666: DEBUG and DEBUG1 are equivalent.
667: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
668: Logging with a DEBUG level violates the privacy of users and is not recommended.
1.1 stevesk 669: .It Cm MACs
670: Specifies the available MAC (message authentication code) algorithms.
671: The MAC algorithm is used in protocol version 2
672: for data integrity protection.
673: Multiple algorithms must be comma-separated.
1.52 jmc 674: The default is:
1.77 jmc 675: .Bd -literal -offset indent
1.145 markus 676: hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
1.144 naddy 677: hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
678: hmac-sha1-96,hmac-md5-96
1.77 jmc 679: .Ed
1.60 dtucker 680: .It Cm Match
1.61 jmc 681: Introduces a conditional block.
1.65 dtucker 682: If all of the criteria on the
1.60 dtucker 683: .Cm Match
1.65 dtucker 684: line are satisfied, the keywords on the following lines override those
685: set in the global section of the config file, until either another
1.60 dtucker 686: .Cm Match
1.65 dtucker 687: line or the end of the file.
1.91 djm 688: .Pp
1.61 jmc 689: The arguments to
1.60 dtucker 690: .Cm Match
1.65 dtucker 691: are one or more criteria-pattern pairs.
1.60 dtucker 692: The available criteria are
693: .Cm User ,
1.69 dtucker 694: .Cm Group ,
1.60 dtucker 695: .Cm Host ,
1.139 dtucker 696: .Cm LocalAddress ,
697: .Cm LocalPort ,
1.60 dtucker 698: and
699: .Cm Address .
1.91 djm 700: The match patterns may consist of single entries or comma-separated
701: lists and may use the wildcard and negation operators described in the
1.92 djm 702: .Sx PATTERNS
1.91 djm 703: section of
1.92 djm 704: .Xr ssh_config 5 .
1.91 djm 705: .Pp
706: The patterns in an
707: .Cm Address
708: criteria may additionally contain addresses to match in CIDR
1.93 jmc 709: address/masklen format, e.g.\&
1.91 djm 710: .Dq 192.0.2.0/24
711: or
712: .Dq 3ffe:ffff::/32 .
713: Note that the mask length provided must be consistent with the address -
714: it is an error to specify a mask length that is too long for the address
1.93 jmc 715: or one with bits set in this host portion of the address.
716: For example,
1.91 djm 717: .Dq 192.0.2.0/33
718: and
1.93 jmc 719: .Dq 192.0.2.0/8
1.91 djm 720: respectively.
721: .Pp
1.60 dtucker 722: Only a subset of keywords may be used on the lines following a
723: .Cm Match
724: keyword.
725: Available keywords are
1.142 jmc 726: .Cm AcceptEnv ,
1.99 okan 727: .Cm AllowAgentForwarding ,
1.142 jmc 728: .Cm AllowGroups ,
1.62 dtucker 729: .Cm AllowTcpForwarding ,
1.141 markus 730: .Cm AllowUsers ,
1.123 djm 731: .Cm AuthorizedKeysFile ,
1.146 ! djm 732: .Cm AuthorizedKeysCommand ,
! 733: .Cm AuthorizedKeysCommandUser ,
1.123 djm 734: .Cm AuthorizedPrincipalsFile ,
1.72 dtucker 735: .Cm Banner ,
1.85 djm 736: .Cm ChrootDirectory ,
1.141 markus 737: .Cm DenyGroups ,
738: .Cm DenyUsers ,
1.67 dtucker 739: .Cm ForceCommand ,
1.142 jmc 740: .Cm GatewayPorts ,
1.141 markus 741: .Cm GSSAPIAuthentication ,
1.87 djm 742: .Cm HostbasedAuthentication ,
1.123 djm 743: .Cm HostbasedUsesNameFromPacketOnly ,
1.74 jmc 744: .Cm KbdInteractiveAuthentication ,
1.72 dtucker 745: .Cm KerberosAuthentication ,
1.95 dtucker 746: .Cm MaxAuthTries ,
1.94 dtucker 747: .Cm MaxSessions ,
1.72 dtucker 748: .Cm PasswordAuthentication ,
1.97 djm 749: .Cm PermitEmptyPasswords ,
1.66 dtucker 750: .Cm PermitOpen ,
1.79 dtucker 751: .Cm PermitRootLogin ,
1.123 djm 752: .Cm PermitTunnel ,
1.107 dtucker 753: .Cm PubkeyAuthentication ,
1.142 jmc 754: .Cm RhostsRSAAuthentication ,
1.141 markus 755: .Cm RSAAuthentication ,
1.66 dtucker 756: .Cm X11DisplayOffset ,
1.101 djm 757: .Cm X11Forwarding
1.60 dtucker 758: and
1.102 djm 759: .Cm X11UseLocalHost .
1.33 dtucker 760: .It Cm MaxAuthTries
761: Specifies the maximum number of authentication attempts permitted per
1.35 jmc 762: connection.
763: Once the number of failures reaches half this value,
764: additional failures are logged.
765: The default is 6.
1.90 djm 766: .It Cm MaxSessions
767: Specifies the maximum number of open sessions permitted per network connection.
768: The default is 10.
1.1 stevesk 769: .It Cm MaxStartups
770: Specifies the maximum number of concurrent unauthenticated connections to the
1.52 jmc 771: SSH daemon.
1.1 stevesk 772: Additional connections will be dropped until authentication succeeds or the
773: .Cm LoginGraceTime
774: expires for a connection.
775: The default is 10.
776: .Pp
777: Alternatively, random early drop can be enabled by specifying
778: the three colon separated values
779: .Dq start:rate:full
1.51 jmc 780: (e.g. "10:30:60").
1.53 jmc 781: .Xr sshd 8
1.1 stevesk 782: will refuse connection attempts with a probability of
783: .Dq rate/100
784: (30%)
785: if there are currently
786: .Dq start
787: (10)
788: unauthenticated connections.
789: The probability increases linearly and all connection attempts
790: are refused if the number of unauthenticated connections reaches
791: .Dq full
792: (60).
793: .It Cm PasswordAuthentication
794: Specifies whether password authentication is allowed.
795: The default is
796: .Dq yes .
797: .It Cm PermitEmptyPasswords
798: When password authentication is allowed, it specifies whether the
799: server allows login to accounts with empty password strings.
800: The default is
801: .Dq no .
1.62 dtucker 802: .It Cm PermitOpen
803: Specifies the destinations to which TCP port forwarding is permitted.
804: The forwarding specification must be one of the following forms:
805: .Pp
806: .Bl -item -offset indent -compact
807: .It
808: .Cm PermitOpen
809: .Sm off
810: .Ar host : port
811: .Sm on
812: .It
813: .Cm PermitOpen
814: .Sm off
815: .Ar IPv4_addr : port
816: .Sm on
817: .It
818: .Cm PermitOpen
819: .Sm off
820: .Ar \&[ IPv6_addr \&] : port
821: .Sm on
822: .El
823: .Pp
1.68 dtucker 824: Multiple forwards may be specified by separating them with whitespace.
1.62 dtucker 825: An argument of
826: .Dq any
827: can be used to remove all restrictions and permit any forwarding requests.
1.140 dtucker 828: An argument of
829: .Dq none
830: can be used to prohibit all forwarding requests.
1.63 jmc 831: By default all port forwarding requests are permitted.
1.1 stevesk 832: .It Cm PermitRootLogin
1.38 jmc 833: Specifies whether root can log in using
1.1 stevesk 834: .Xr ssh 1 .
835: The argument must be
836: .Dq yes ,
837: .Dq without-password ,
1.52 jmc 838: .Dq forced-commands-only ,
1.1 stevesk 839: or
840: .Dq no .
841: The default is
842: .Dq yes .
843: .Pp
844: If this option is set to
1.52 jmc 845: .Dq without-password ,
1.1 stevesk 846: password authentication is disabled for root.
847: .Pp
848: If this option is set to
1.52 jmc 849: .Dq forced-commands-only ,
1.1 stevesk 850: root login with public key authentication will be allowed,
851: but only if the
852: .Ar command
853: option has been specified
854: (which may be useful for taking remote backups even if root login is
1.17 jmc 855: normally not allowed).
856: All other authentication methods are disabled for root.
1.1 stevesk 857: .Pp
858: If this option is set to
1.52 jmc 859: .Dq no ,
1.38 jmc 860: root is not allowed to log in.
1.46 reyk 861: .It Cm PermitTunnel
862: Specifies whether
863: .Xr tun 4
864: device forwarding is allowed.
1.47 reyk 865: The argument must be
866: .Dq yes ,
1.58 stevesk 867: .Dq point-to-point
868: (layer 3),
869: .Dq ethernet
870: (layer 2), or
1.47 reyk 871: .Dq no .
1.58 stevesk 872: Specifying
873: .Dq yes
874: permits both
875: .Dq point-to-point
876: and
877: .Dq ethernet .
1.46 reyk 878: The default is
879: .Dq no .
1.6 markus 880: .It Cm PermitUserEnvironment
881: Specifies whether
882: .Pa ~/.ssh/environment
1.9 stevesk 883: and
1.6 markus 884: .Cm environment=
885: options in
886: .Pa ~/.ssh/authorized_keys
1.9 stevesk 887: are processed by
1.52 jmc 888: .Xr sshd 8 .
1.6 markus 889: The default is
890: .Dq no .
1.9 stevesk 891: Enabling environment processing may enable users to bypass access
892: restrictions in some configurations using mechanisms such as
893: .Ev LD_PRELOAD .
1.1 stevesk 894: .It Cm PidFile
1.4 stevesk 895: Specifies the file that contains the process ID of the
1.53 jmc 896: SSH daemon.
1.1 stevesk 897: The default is
898: .Pa /var/run/sshd.pid .
899: .It Cm Port
900: Specifies the port number that
1.52 jmc 901: .Xr sshd 8
1.1 stevesk 902: listens on.
903: The default is 22.
904: Multiple options of this type are permitted.
905: See also
906: .Cm ListenAddress .
907: .It Cm PrintLastLog
908: Specifies whether
1.52 jmc 909: .Xr sshd 8
1.36 jaredy 910: should print the date and time of the last user login when a user logs
911: in interactively.
1.1 stevesk 912: The default is
913: .Dq yes .
914: .It Cm PrintMotd
915: Specifies whether
1.52 jmc 916: .Xr sshd 8
1.1 stevesk 917: should print
918: .Pa /etc/motd
919: when a user logs in interactively.
920: (On some systems it is also printed by the shell,
921: .Pa /etc/profile ,
922: or equivalent.)
923: The default is
924: .Dq yes .
925: .It Cm Protocol
926: Specifies the protocol versions
1.52 jmc 927: .Xr sshd 8
1.5 stevesk 928: supports.
1.1 stevesk 929: The possible values are
1.52 jmc 930: .Sq 1
1.1 stevesk 931: and
1.52 jmc 932: .Sq 2 .
1.1 stevesk 933: Multiple versions must be comma-separated.
934: The default is
1.109 jmc 935: .Sq 2 .
1.5 stevesk 936: Note that the order of the protocol list does not indicate preference,
937: because the client selects among multiple protocol versions offered
938: by the server.
939: Specifying
940: .Dq 2,1
941: is identical to
942: .Dq 1,2 .
1.1 stevesk 943: .It Cm PubkeyAuthentication
944: Specifies whether public key authentication is allowed.
945: The default is
946: .Dq yes .
947: Note that this option applies to protocol version 2 only.
1.118 djm 948: .It Cm RevokedKeys
949: Specifies a list of revoked public keys.
950: Keys listed in this file will be refused for public key authentication.
951: Note that if this file is not readable, then public key authentication will
952: be refused for all users.
1.1 stevesk 953: .It Cm RhostsRSAAuthentication
954: Specifies whether rhosts or /etc/hosts.equiv authentication together
955: with successful RSA host authentication is allowed.
956: The default is
957: .Dq no .
958: This option applies to protocol version 1 only.
959: .It Cm RSAAuthentication
960: Specifies whether pure RSA authentication is allowed.
961: The default is
962: .Dq yes .
963: This option applies to protocol version 1 only.
964: .It Cm ServerKeyBits
965: Defines the number of bits in the ephemeral protocol version 1 server key.
1.96 djm 966: The minimum value is 512, and the default is 1024.
1.1 stevesk 967: .It Cm StrictModes
968: Specifies whether
1.52 jmc 969: .Xr sshd 8
1.1 stevesk 970: should check file modes and ownership of the
971: user's files and home directory before accepting login.
972: This is normally desirable because novices sometimes accidentally leave their
973: directory or files world-writable.
974: The default is
975: .Dq yes .
1.112 djm 976: Note that this does not apply to
977: .Cm ChrootDirectory ,
978: whose permissions and ownership are checked unconditionally.
1.1 stevesk 979: .It Cm Subsystem
1.51 jmc 980: Configures an external subsystem (e.g. file transfer daemon).
1.59 djm 981: Arguments should be a subsystem name and a command (with optional arguments)
982: to execute upon subsystem request.
1.80 djm 983: .Pp
1.1 stevesk 984: The command
985: .Xr sftp-server 8
986: implements the
987: .Dq sftp
988: file transfer subsystem.
1.80 djm 989: .Pp
990: Alternately the name
991: .Dq internal-sftp
992: implements an in-process
993: .Dq sftp
994: server.
995: This may simplify configurations using
996: .Cm ChrootDirectory
997: to force a different filesystem root on clients.
998: .Pp
1.1 stevesk 999: By default no subsystems are defined.
1000: Note that this option applies to protocol version 2 only.
1001: .It Cm SyslogFacility
1002: Gives the facility code that is used when logging messages from
1.53 jmc 1003: .Xr sshd 8 .
1.1 stevesk 1004: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1005: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1006: The default is AUTH.
1.27 markus 1007: .It Cm TCPKeepAlive
1008: Specifies whether the system should send TCP keepalive messages to the
1009: other side.
1010: If they are sent, death of the connection or crash of one
1011: of the machines will be properly noticed.
1012: However, this means that
1013: connections will die if the route is down temporarily, and some people
1014: find it annoying.
1015: On the other hand, if TCP keepalives are not sent,
1016: sessions may hang indefinitely on the server, leaving
1017: .Dq ghost
1018: users and consuming server resources.
1019: .Pp
1020: The default is
1021: .Dq yes
1022: (to send TCP keepalive messages), and the server will notice
1023: if the network goes down or the client host crashes.
1024: This avoids infinitely hanging sessions.
1025: .Pp
1026: To disable TCP keepalive messages, the value should be set to
1027: .Dq no .
1.118 djm 1028: .It Cm TrustedUserCAKeys
1029: Specifies a file containing public keys of certificate authorities that are
1.120 djm 1030: trusted to sign user certificates for authentication.
1.119 jmc 1031: Keys are listed one per line; empty lines and comments starting with
1.118 djm 1032: .Ql #
1033: are allowed.
1034: If a certificate is presented for authentication and has its signing CA key
1035: listed in this file, then it may be used for authentication for any user
1036: listed in the certificate's principals list.
1037: Note that certificates that lack a list of principals will not be permitted
1038: for authentication using
1039: .Cm TrustedUserCAKeys .
1.119 jmc 1040: For more details on certificates, see the
1.118 djm 1041: .Sx CERTIFICATES
1042: section in
1043: .Xr ssh-keygen 1 .
1.18 markus 1044: .It Cm UseDNS
1045: Specifies whether
1.52 jmc 1046: .Xr sshd 8
1.40 jmc 1047: should look up the remote host name and check that
1.18 markus 1048: the resolved host name for the remote IP address maps back to the
1049: very same IP address.
1050: The default is
1051: .Dq yes .
1.1 stevesk 1052: .It Cm UseLogin
1053: Specifies whether
1054: .Xr login 1
1055: is used for interactive login sessions.
1056: The default is
1057: .Dq no .
1058: Note that
1059: .Xr login 1
1060: is never used for remote command execution.
1061: Note also, that if this is enabled,
1062: .Cm X11Forwarding
1063: will be disabled because
1064: .Xr login 1
1065: does not know how to handle
1066: .Xr xauth 1
1.15 jmc 1067: cookies.
1068: If
1.1 stevesk 1069: .Cm UsePrivilegeSeparation
1070: is specified, it will be disabled after authentication.
1071: .It Cm UsePrivilegeSeparation
1072: Specifies whether
1.52 jmc 1073: .Xr sshd 8
1.2 stevesk 1074: separates privileges by creating an unprivileged child process
1.15 jmc 1075: to deal with incoming network traffic.
1076: After successful authentication, another process will be created that has
1077: the privilege of the authenticated user.
1078: The goal of privilege separation is to prevent privilege
1.1 stevesk 1079: escalation by containing any corruption within the unprivileged processes.
1080: The default is
1081: .Dq yes .
1.134 djm 1082: If
1083: .Cm UsePrivilegeSeparation
1084: is set to
1085: .Dq sandbox
1086: then the pre-authentication unprivileged process is subject to additional
1087: restrictions.
1.137 djm 1088: .It Cm VersionAddendum
1089: Optionally specifies additional text to append to the SSH protocol banner
1090: sent by the server upon connection.
1091: The default is
1092: .Dq none .
1.1 stevesk 1093: .It Cm X11DisplayOffset
1094: Specifies the first display number available for
1.52 jmc 1095: .Xr sshd 8 Ns 's
1.1 stevesk 1096: X11 forwarding.
1.52 jmc 1097: This prevents sshd from interfering with real X11 servers.
1.1 stevesk 1098: The default is 10.
1099: .It Cm X11Forwarding
1100: Specifies whether X11 forwarding is permitted.
1.13 stevesk 1101: The argument must be
1102: .Dq yes
1103: or
1104: .Dq no .
1.1 stevesk 1105: The default is
1106: .Dq no .
1.13 stevesk 1107: .Pp
1108: When X11 forwarding is enabled, there may be additional exposure to
1109: the server and to client displays if the
1.52 jmc 1110: .Xr sshd 8
1.13 stevesk 1111: proxy display is configured to listen on the wildcard address (see
1112: .Cm X11UseLocalhost
1.52 jmc 1113: below), though this is not the default.
1.13 stevesk 1114: Additionally, the authentication spoofing and authentication data
1115: verification and substitution occur on the client side.
1116: The security risk of using X11 forwarding is that the client's X11
1.52 jmc 1117: display server may be exposed to attack when the SSH client requests
1.13 stevesk 1118: forwarding (see the warnings for
1119: .Cm ForwardX11
1120: in
1.19 jmc 1121: .Xr ssh_config 5 ) .
1.13 stevesk 1122: A system administrator may have a stance in which they want to
1123: protect clients that may expose themselves to attack by unwittingly
1124: requesting X11 forwarding, which can warrant a
1125: .Dq no
1126: setting.
1127: .Pp
1128: Note that disabling X11 forwarding does not prevent users from
1129: forwarding X11 traffic, as users can always install their own forwarders.
1.1 stevesk 1130: X11 forwarding is automatically disabled if
1131: .Cm UseLogin
1132: is enabled.
1133: .It Cm X11UseLocalhost
1134: Specifies whether
1.52 jmc 1135: .Xr sshd 8
1.1 stevesk 1136: should bind the X11 forwarding server to the loopback address or to
1.15 jmc 1137: the wildcard address.
1138: By default,
1.52 jmc 1139: sshd binds the forwarding server to the loopback address and sets the
1.1 stevesk 1140: hostname part of the
1141: .Ev DISPLAY
1142: environment variable to
1143: .Dq localhost .
1.8 stevesk 1144: This prevents remote hosts from connecting to the proxy display.
1.1 stevesk 1145: However, some older X11 clients may not function with this
1146: configuration.
1147: .Cm X11UseLocalhost
1148: may be set to
1149: .Dq no
1150: to specify that the forwarding server should be bound to the wildcard
1151: address.
1152: The argument must be
1153: .Dq yes
1154: or
1155: .Dq no .
1156: The default is
1157: .Dq yes .
1158: .It Cm XAuthLocation
1.11 stevesk 1159: Specifies the full pathname of the
1.1 stevesk 1160: .Xr xauth 1
1161: program.
1162: The default is
1163: .Pa /usr/X11R6/bin/xauth .
1164: .El
1.55 jmc 1165: .Sh TIME FORMATS
1.53 jmc 1166: .Xr sshd 8
1.1 stevesk 1167: command-line arguments and configuration file options that specify time
1168: may be expressed using a sequence of the form:
1169: .Sm off
1.7 stevesk 1170: .Ar time Op Ar qualifier ,
1.1 stevesk 1171: .Sm on
1172: where
1173: .Ar time
1174: is a positive integer value and
1175: .Ar qualifier
1176: is one of the following:
1177: .Pp
1178: .Bl -tag -width Ds -compact -offset indent
1.64 jmc 1179: .It Aq Cm none
1.1 stevesk 1180: seconds
1181: .It Cm s | Cm S
1182: seconds
1183: .It Cm m | Cm M
1184: minutes
1185: .It Cm h | Cm H
1186: hours
1187: .It Cm d | Cm D
1188: days
1189: .It Cm w | Cm W
1190: weeks
1191: .El
1192: .Pp
1193: Each member of the sequence is added together to calculate
1194: the total time value.
1195: .Pp
1196: Time format examples:
1197: .Pp
1198: .Bl -tag -width Ds -compact -offset indent
1199: .It 600
1200: 600 seconds (10 minutes)
1201: .It 10m
1202: 10 minutes
1203: .It 1h30m
1204: 1 hour 30 minutes (90 minutes)
1205: .El
1206: .Sh FILES
1207: .Bl -tag -width Ds
1208: .It Pa /etc/ssh/sshd_config
1209: Contains configuration data for
1.53 jmc 1210: .Xr sshd 8 .
1.1 stevesk 1211: This file should be writable by root only, but it is recommended
1212: (though not necessary) that it be world-readable.
1213: .El
1.19 jmc 1214: .Sh SEE ALSO
1215: .Xr sshd 8
1.1 stevesk 1216: .Sh AUTHORS
1217: OpenSSH is a derivative of the original and free
1218: ssh 1.2.12 release by Tatu Ylonen.
1219: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1220: Theo de Raadt and Dug Song
1221: removed many bugs, re-added newer features and
1222: created OpenSSH.
1223: Markus Friedl contributed the support for SSH
1224: protocol versions 1.5 and 2.0.
1225: Niels Provos and Markus Friedl contributed support
1226: for privilege separation.
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