Annotation of src/usr.bin/ssh/sshd_config.5, Revision 1.147
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.
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1.147 ! jmc 36: .\" $OpenBSD: sshd_config.5,v 1.146 2012/10/30 21:29:55 djm Exp $
! 37: .Dd $Mdocdate: October 30 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
1.147 ! jmc 155: Specifies a program to be used to look up the user's public keys.
1.146 djm 156: The program will be invoked with a single argument of the username
157: being authenticated, and should produce on standard output zero or
1.147 ! jmc 158: more lines of authorized_keys output (see
! 159: .Sx AUTHORIZED_KEYS
! 160: in
! 161: .Xr sshd 8 ) .
1.146 djm 162: If a key supplied by AuthorizedKeysCommand does not successfully authenticate
163: and authorize the user then public key authentication continues using the usual
164: .Cm AuthorizedKeysFile
165: files.
166: By default, no AuthorizedKeysCommand is run.
167: .It Cm AuthorizedKeysCommandUser
168: Specifies the user under whose account the AuthorizedKeysCommand is run.
169: The default is the user being authenticated.
170: It is recommended to use a dedicated user that has no other role on the host
171: than running authorized keys commands.
1.1 stevesk 172: .It Cm AuthorizedKeysFile
173: Specifies the file that contains the public keys that can be used
174: for user authentication.
1.124 djm 175: The format is described in the
176: .Sx AUTHORIZED_KEYS FILE FORMAT
177: section of
178: .Xr sshd 8 .
1.1 stevesk 179: .Cm AuthorizedKeysFile
180: may contain tokens of the form %T which are substituted during connection
1.52 jmc 181: setup.
1.17 jmc 182: The following tokens are defined: %% is replaced by a literal '%',
1.52 jmc 183: %h is replaced by the home directory of the user being authenticated, and
1.1 stevesk 184: %u is replaced by the username of that user.
185: After expansion,
186: .Cm AuthorizedKeysFile
187: is taken to be an absolute path or one relative to the user's home
188: directory.
1.133 jmc 189: Multiple files may be listed, separated by whitespace.
190: The default is
191: .Dq .ssh/authorized_keys .ssh/authorized_keys2 .
1.121 djm 192: .It Cm AuthorizedPrincipalsFile
193: Specifies a file that lists principal names that are accepted for
194: certificate authentication.
195: When using certificates signed by a key listed in
196: .Cm TrustedUserCAKeys ,
197: this file lists names, one of which must appear in the certificate for it
198: to be accepted for authentication.
1.125 jmc 199: Names are listed one per line preceded by key options (as described
1.124 djm 200: in
201: .Sx AUTHORIZED_KEYS FILE FORMAT
202: in
1.125 jmc 203: .Xr sshd 8 ) .
1.124 djm 204: Empty lines and comments starting with
1.121 djm 205: .Ql #
206: are ignored.
207: .Pp
208: .Cm AuthorizedPrincipalsFile
209: may contain tokens of the form %T which are substituted during connection
210: setup.
211: The following tokens are defined: %% is replaced by a literal '%',
212: %h is replaced by the home directory of the user being authenticated, and
213: %u is replaced by the username of that user.
214: After expansion,
215: .Cm AuthorizedPrincipalsFile
216: is taken to be an absolute path or one relative to the user's home
217: directory.
218: .Pp
1.138 djm 219: The default is
220: .Dq none ,
221: i.e. not to use a principals file \(en in this case, the username
1.121 djm 222: of the user must appear in a certificate's principals list for it to be
223: accepted.
224: Note that
225: .Cm AuthorizedPrincipalsFile
226: is only used when authentication proceeds using a CA listed in
227: .Cm TrustedUserCAKeys
228: and is not consulted for certification authorities trusted via
229: .Pa ~/.ssh/authorized_keys ,
230: though the
231: .Cm principals=
232: key option offers a similar facility (see
233: .Xr sshd 8
234: for details).
1.1 stevesk 235: .It Cm Banner
236: The contents of the specified file are sent to the remote user before
237: authentication is allowed.
1.78 djm 238: If the argument is
239: .Dq none
240: then no banner is displayed.
1.1 stevesk 241: This option is only available for protocol version 2.
242: By default, no banner is displayed.
243: .It Cm ChallengeResponseAuthentication
1.50 jmc 244: Specifies whether challenge-response authentication is allowed.
1.1 stevesk 245: All authentication styles from
246: .Xr login.conf 5
247: are supported.
248: The default is
249: .Dq yes .
1.80 djm 250: .It Cm ChrootDirectory
1.113 stevesk 251: Specifies the pathname of a directory to
1.80 djm 252: .Xr chroot 2
253: to after authentication.
1.113 stevesk 254: All components of the pathname must be root-owned directories that are
1.80 djm 255: not writable by any other user or group.
1.106 stevesk 256: After the chroot,
257: .Xr sshd 8
258: changes the working directory to the user's home directory.
1.80 djm 259: .Pp
1.113 stevesk 260: The pathname may contain the following tokens that are expanded at runtime once
1.80 djm 261: the connecting user has been authenticated: %% is replaced by a literal '%',
262: %h is replaced by the home directory of the user being authenticated, and
263: %u is replaced by the username of that user.
264: .Pp
265: The
266: .Cm ChrootDirectory
267: must contain the necessary files and directories to support the
1.103 stevesk 268: user's session.
1.80 djm 269: For an interactive session this requires at least a shell, typically
270: .Xr sh 1 ,
271: and basic
272: .Pa /dev
273: nodes such as
274: .Xr null 4 ,
275: .Xr zero 4 ,
276: .Xr stdin 4 ,
277: .Xr stdout 4 ,
278: .Xr stderr 4 ,
279: .Xr arandom 4
280: and
281: .Xr tty 4
282: devices.
283: For file transfer sessions using
1.105 jmc 284: .Dq sftp ,
1.80 djm 285: no additional configuration of the environment is necessary if the
1.105 jmc 286: in-process sftp server is used,
287: though sessions which use logging do require
1.104 stevesk 288: .Pa /dev/log
289: inside the chroot directory (see
290: .Xr sftp-server 8
1.81 jmc 291: for details).
1.80 djm 292: .Pp
293: The default is not to
294: .Xr chroot 2 .
1.1 stevesk 295: .It Cm Ciphers
296: Specifies the ciphers allowed for protocol version 2.
297: Multiple ciphers must be comma-separated.
1.34 dtucker 298: The supported ciphers are
299: .Dq 3des-cbc ,
300: .Dq aes128-cbc ,
301: .Dq aes192-cbc ,
302: .Dq aes256-cbc ,
303: .Dq aes128-ctr ,
304: .Dq aes192-ctr ,
305: .Dq aes256-ctr ,
1.43 djm 306: .Dq arcfour128 ,
307: .Dq arcfour256 ,
1.34 dtucker 308: .Dq arcfour ,
309: .Dq blowfish-cbc ,
310: and
311: .Dq cast128-cbc .
1.52 jmc 312: The default is:
313: .Bd -literal -offset 3n
1.100 naddy 314: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
315: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
316: aes256-cbc,arcfour
1.1 stevesk 317: .Ed
318: .It Cm ClientAliveCountMax
1.48 jmc 319: Sets the number of client alive messages (see below) which may be
1.1 stevesk 320: sent without
1.52 jmc 321: .Xr sshd 8
1.17 jmc 322: receiving any messages back from the client.
323: If this threshold is reached while client alive messages are being sent,
1.52 jmc 324: sshd will disconnect the client, terminating the session.
1.17 jmc 325: It is important to note that the use of client alive messages is very
326: different from
1.27 markus 327: .Cm TCPKeepAlive
1.17 jmc 328: (below).
329: The client alive messages are sent through the encrypted channel
330: and therefore will not be spoofable.
331: The TCP keepalive option enabled by
1.27 markus 332: .Cm TCPKeepAlive
1.17 jmc 333: is spoofable.
334: The client alive mechanism is valuable when the client or
1.1 stevesk 335: server depend on knowing when a connection has become inactive.
336: .Pp
1.17 jmc 337: The default value is 3.
338: If
1.1 stevesk 339: .Cm ClientAliveInterval
1.48 jmc 340: (see below) is set to 15, and
1.1 stevesk 341: .Cm ClientAliveCountMax
1.52 jmc 342: is left at the default, unresponsive SSH clients
1.1 stevesk 343: will be disconnected after approximately 45 seconds.
1.57 markus 344: This option applies to protocol version 2 only.
1.42 djm 345: .It Cm ClientAliveInterval
346: Sets a timeout interval in seconds after which if no data has been received
347: from the client,
1.52 jmc 348: .Xr sshd 8
1.42 djm 349: will send a message through the encrypted
350: channel to request a response from the client.
351: The default
352: is 0, indicating that these messages will not be sent to the client.
353: This option applies to protocol version 2 only.
1.3 markus 354: .It Cm Compression
1.44 markus 355: Specifies whether compression is allowed, or delayed until
356: the user has authenticated successfully.
1.3 markus 357: The argument must be
1.44 markus 358: .Dq yes ,
359: .Dq delayed ,
1.3 markus 360: or
361: .Dq no .
362: The default is
1.44 markus 363: .Dq delayed .
1.1 stevesk 364: .It Cm DenyGroups
365: This keyword can be followed by a list of group name patterns, separated
366: by spaces.
367: Login is disallowed for users whose primary group or supplementary
368: group list matches one of the patterns.
369: Only group names are valid; a numerical group ID is not recognized.
370: By default, login is allowed for all groups.
1.54 jmc 371: The allow/deny directives are processed in the following order:
372: .Cm DenyUsers ,
373: .Cm AllowUsers ,
374: .Cm DenyGroups ,
375: and finally
376: .Cm AllowGroups .
1.49 jmc 377: .Pp
378: See
379: .Sx PATTERNS
380: in
381: .Xr ssh_config 5
382: for more information on patterns.
1.1 stevesk 383: .It Cm DenyUsers
384: This keyword can be followed by a list of user name patterns, separated
385: by spaces.
386: Login is disallowed for user names that match one of the patterns.
387: Only user names are valid; a numerical user ID is not recognized.
388: By default, login is allowed for all users.
389: If the pattern takes the form USER@HOST then USER and HOST
390: are separately checked, restricting logins to particular
391: users from particular hosts.
1.54 jmc 392: The allow/deny directives are processed in the following order:
393: .Cm DenyUsers ,
394: .Cm AllowUsers ,
395: .Cm DenyGroups ,
396: and finally
397: .Cm AllowGroups .
1.49 jmc 398: .Pp
399: See
400: .Sx PATTERNS
401: in
402: .Xr ssh_config 5
403: for more information on patterns.
1.67 dtucker 404: .It Cm ForceCommand
405: Forces the execution of the command specified by
406: .Cm ForceCommand ,
1.84 djm 407: ignoring any command supplied by the client and
408: .Pa ~/.ssh/rc
409: if present.
1.67 dtucker 410: The command is invoked by using the user's login shell with the -c option.
411: This applies to shell, command, or subsystem execution.
412: It is most useful inside a
413: .Cm Match
414: block.
415: The command originally supplied by the client is available in the
416: .Ev SSH_ORIGINAL_COMMAND
417: environment variable.
1.82 djm 418: Specifying a command of
419: .Dq internal-sftp
420: will force the use of an in-process sftp server that requires no support
421: files when used with
422: .Cm ChrootDirectory .
1.1 stevesk 423: .It Cm GatewayPorts
424: Specifies whether remote hosts are allowed to connect to ports
425: forwarded for the client.
426: By default,
1.52 jmc 427: .Xr sshd 8
1.15 jmc 428: binds remote port forwardings to the loopback address.
429: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 430: .Cm GatewayPorts
1.52 jmc 431: can be used to specify that sshd
1.39 djm 432: should allow remote port forwardings to bind to non-loopback addresses, thus
433: allowing other hosts to connect.
434: The argument may be
435: .Dq no
436: to force remote port forwardings to be available to the local host only,
1.1 stevesk 437: .Dq yes
1.39 djm 438: to force remote port forwardings to bind to the wildcard address, or
439: .Dq clientspecified
440: to allow the client to select the address to which the forwarding is bound.
1.1 stevesk 441: The default is
442: .Dq no .
1.23 markus 443: .It Cm GSSAPIAuthentication
1.25 markus 444: Specifies whether user authentication based on GSSAPI is allowed.
1.26 djm 445: The default is
1.23 markus 446: .Dq no .
447: Note that this option applies to protocol version 2 only.
448: .It Cm GSSAPICleanupCredentials
449: Specifies whether to automatically destroy the user's credentials cache
450: on logout.
451: The default is
452: .Dq yes .
453: Note that this option applies to protocol version 2 only.
1.1 stevesk 454: .It Cm HostbasedAuthentication
455: Specifies whether rhosts or /etc/hosts.equiv authentication together
456: with successful public key client host authentication is allowed
1.50 jmc 457: (host-based authentication).
1.1 stevesk 458: This option is similar to
459: .Cm RhostsRSAAuthentication
460: and applies to protocol version 2 only.
1.70 dtucker 461: The default is
462: .Dq no .
463: .It Cm HostbasedUsesNameFromPacketOnly
464: Specifies whether or not the server will attempt to perform a reverse
465: name lookup when matching the name in the
466: .Pa ~/.shosts ,
467: .Pa ~/.rhosts ,
468: and
469: .Pa /etc/hosts.equiv
470: files during
471: .Cm HostbasedAuthentication .
472: A setting of
473: .Dq yes
474: means that
475: .Xr sshd 8
476: uses the name supplied by the client rather than
477: attempting to resolve the name from the TCP connection itself.
1.1 stevesk 478: The default is
479: .Dq no .
1.117 djm 480: .It Cm HostCertificate
481: Specifies a file containing a public host certificate.
482: The certificate's public key must match a private host key already specified
483: by
484: .Cm HostKey .
485: The default behaviour of
486: .Xr sshd 8
487: is not to load any certificates.
1.1 stevesk 488: .It Cm HostKey
489: Specifies a file containing a private host key
490: used by SSH.
491: The default is
492: .Pa /etc/ssh/ssh_host_key
493: for protocol version 1, and
1.126 djm 494: .Pa /etc/ssh/ssh_host_dsa_key ,
495: .Pa /etc/ssh/ssh_host_ecdsa_key
496: and
1.1 stevesk 497: .Pa /etc/ssh/ssh_host_rsa_key
498: for protocol version 2.
499: Note that
1.52 jmc 500: .Xr sshd 8
1.1 stevesk 501: will refuse to use a file if it is group/world-accessible.
502: It is possible to have multiple host key files.
503: .Dq rsa1
504: keys are used for version 1 and
1.126 djm 505: .Dq dsa ,
506: .Dq ecdsa
1.1 stevesk 507: or
508: .Dq rsa
509: are used for version 2 of the SSH protocol.
510: .It Cm IgnoreRhosts
511: Specifies that
512: .Pa .rhosts
513: and
514: .Pa .shosts
515: files will not be used in
516: .Cm RhostsRSAAuthentication
517: or
518: .Cm HostbasedAuthentication .
519: .Pp
520: .Pa /etc/hosts.equiv
521: and
522: .Pa /etc/shosts.equiv
523: are still used.
524: The default is
525: .Dq yes .
526: .It Cm IgnoreUserKnownHosts
527: Specifies whether
1.52 jmc 528: .Xr sshd 8
1.1 stevesk 529: should ignore the user's
1.41 djm 530: .Pa ~/.ssh/known_hosts
1.1 stevesk 531: during
532: .Cm RhostsRSAAuthentication
533: or
534: .Cm HostbasedAuthentication .
535: The default is
536: .Dq no .
1.129 djm 537: .It Cm IPQoS
538: Specifies the IPv4 type-of-service or DSCP class for the connection.
539: Accepted values are
540: .Dq af11 ,
541: .Dq af12 ,
542: .Dq af13 ,
1.136 djm 543: .Dq af21 ,
1.129 djm 544: .Dq af22 ,
545: .Dq af23 ,
546: .Dq af31 ,
547: .Dq af32 ,
548: .Dq af33 ,
549: .Dq af41 ,
550: .Dq af42 ,
551: .Dq af43 ,
552: .Dq cs0 ,
553: .Dq cs1 ,
554: .Dq cs2 ,
555: .Dq cs3 ,
556: .Dq cs4 ,
557: .Dq cs5 ,
558: .Dq cs6 ,
559: .Dq cs7 ,
560: .Dq ef ,
561: .Dq lowdelay ,
562: .Dq throughput ,
563: .Dq reliability ,
564: or a numeric value.
1.131 djm 565: This option may take one or two arguments, separated by whitespace.
1.129 djm 566: If one argument is specified, it is used as the packet class unconditionally.
567: If two values are specified, the first is automatically selected for
568: interactive sessions and the second for non-interactive sessions.
569: The default is
570: .Dq lowdelay
571: for interactive sessions and
572: .Dq throughput
573: for non-interactive sessions.
1.1 stevesk 574: .It Cm KerberosAuthentication
1.24 markus 575: Specifies whether the password provided by the user for
1.1 stevesk 576: .Cm PasswordAuthentication
1.24 markus 577: will be validated through the Kerberos KDC.
1.1 stevesk 578: To use this option, the server needs a
579: Kerberos servtab which allows the verification of the KDC's identity.
1.52 jmc 580: The default is
1.29 dtucker 581: .Dq no .
582: .It Cm KerberosGetAFSToken
1.45 djm 583: If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire
1.29 dtucker 584: an AFS token before accessing the user's home directory.
1.52 jmc 585: The default is
1.1 stevesk 586: .Dq no .
587: .It Cm KerberosOrLocalPasswd
1.52 jmc 588: If password authentication through Kerberos fails then
1.1 stevesk 589: the password will be validated via any additional local mechanism
590: such as
591: .Pa /etc/passwd .
1.52 jmc 592: The default is
1.1 stevesk 593: .Dq yes .
594: .It Cm KerberosTicketCleanup
595: Specifies whether to automatically destroy the user's ticket cache
596: file on logout.
1.52 jmc 597: The default is
1.1 stevesk 598: .Dq yes .
1.127 djm 599: .It Cm KexAlgorithms
600: Specifies the available KEX (Key Exchange) algorithms.
601: Multiple algorithms must be comma-separated.
602: The default is
603: .Dq ecdh-sha2-nistp256 ,
604: .Dq ecdh-sha2-nistp384 ,
605: .Dq ecdh-sha2-nistp521 ,
1.130 jmc 606: .Dq diffie-hellman-group-exchange-sha256 ,
1.127 djm 607: .Dq diffie-hellman-group-exchange-sha1 ,
608: .Dq diffie-hellman-group14-sha1 ,
609: .Dq diffie-hellman-group1-sha1 .
1.1 stevesk 610: .It Cm KeyRegenerationInterval
611: In protocol version 1, the ephemeral server key is automatically regenerated
612: after this many seconds (if it has been used).
613: The purpose of regeneration is to prevent
614: decrypting captured sessions by later breaking into the machine and
615: stealing the keys.
616: The key is never stored anywhere.
617: If the value is 0, the key is never regenerated.
618: The default is 3600 (seconds).
619: .It Cm ListenAddress
620: Specifies the local addresses
1.52 jmc 621: .Xr sshd 8
1.1 stevesk 622: should listen on.
623: The following forms may be used:
624: .Pp
625: .Bl -item -offset indent -compact
626: .It
627: .Cm ListenAddress
628: .Sm off
629: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
630: .Sm on
631: .It
632: .Cm ListenAddress
633: .Sm off
634: .Ar host No | Ar IPv4_addr No : Ar port
635: .Sm on
636: .It
637: .Cm ListenAddress
638: .Sm off
639: .Oo
640: .Ar host No | Ar IPv6_addr Oc : Ar port
641: .Sm on
642: .El
643: .Pp
644: If
645: .Ar port
646: is not specified,
1.52 jmc 647: sshd will listen on the address and all prior
1.1 stevesk 648: .Cm Port
1.17 jmc 649: options specified.
650: The default is to listen on all local addresses.
1.15 jmc 651: Multiple
1.1 stevesk 652: .Cm ListenAddress
1.17 jmc 653: options are permitted.
654: Additionally, any
1.1 stevesk 655: .Cm Port
1.52 jmc 656: options must precede this option for non-port qualified addresses.
1.1 stevesk 657: .It Cm LoginGraceTime
658: The server disconnects after this time if the user has not
659: successfully logged in.
660: If the value is 0, there is no time limit.
1.12 stevesk 661: The default is 120 seconds.
1.1 stevesk 662: .It Cm LogLevel
663: Gives the verbosity level that is used when logging messages from
1.53 jmc 664: .Xr sshd 8 .
1.1 stevesk 665: The possible values are:
1.52 jmc 666: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.15 jmc 667: The default is INFO.
668: DEBUG and DEBUG1 are equivalent.
669: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
670: Logging with a DEBUG level violates the privacy of users and is not recommended.
1.1 stevesk 671: .It Cm MACs
672: Specifies the available MAC (message authentication code) algorithms.
673: The MAC algorithm is used in protocol version 2
674: for data integrity protection.
675: Multiple algorithms must be comma-separated.
1.52 jmc 676: The default is:
1.77 jmc 677: .Bd -literal -offset indent
1.145 markus 678: hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
1.144 naddy 679: hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
680: hmac-sha1-96,hmac-md5-96
1.77 jmc 681: .Ed
1.60 dtucker 682: .It Cm Match
1.61 jmc 683: Introduces a conditional block.
1.65 dtucker 684: If all of the criteria on the
1.60 dtucker 685: .Cm Match
1.65 dtucker 686: line are satisfied, the keywords on the following lines override those
687: set in the global section of the config file, until either another
1.60 dtucker 688: .Cm Match
1.65 dtucker 689: line or the end of the file.
1.91 djm 690: .Pp
1.61 jmc 691: The arguments to
1.60 dtucker 692: .Cm Match
1.65 dtucker 693: are one or more criteria-pattern pairs.
1.60 dtucker 694: The available criteria are
695: .Cm User ,
1.69 dtucker 696: .Cm Group ,
1.60 dtucker 697: .Cm Host ,
1.139 dtucker 698: .Cm LocalAddress ,
699: .Cm LocalPort ,
1.60 dtucker 700: and
701: .Cm Address .
1.91 djm 702: The match patterns may consist of single entries or comma-separated
703: lists and may use the wildcard and negation operators described in the
1.92 djm 704: .Sx PATTERNS
1.91 djm 705: section of
1.92 djm 706: .Xr ssh_config 5 .
1.91 djm 707: .Pp
708: The patterns in an
709: .Cm Address
710: criteria may additionally contain addresses to match in CIDR
1.93 jmc 711: address/masklen format, e.g.\&
1.91 djm 712: .Dq 192.0.2.0/24
713: or
714: .Dq 3ffe:ffff::/32 .
715: Note that the mask length provided must be consistent with the address -
716: it is an error to specify a mask length that is too long for the address
1.93 jmc 717: or one with bits set in this host portion of the address.
718: For example,
1.91 djm 719: .Dq 192.0.2.0/33
720: and
1.93 jmc 721: .Dq 192.0.2.0/8
1.91 djm 722: respectively.
723: .Pp
1.60 dtucker 724: Only a subset of keywords may be used on the lines following a
725: .Cm Match
726: keyword.
727: Available keywords are
1.142 jmc 728: .Cm AcceptEnv ,
1.99 okan 729: .Cm AllowAgentForwarding ,
1.142 jmc 730: .Cm AllowGroups ,
1.62 dtucker 731: .Cm AllowTcpForwarding ,
1.141 markus 732: .Cm AllowUsers ,
1.146 djm 733: .Cm AuthorizedKeysCommand ,
734: .Cm AuthorizedKeysCommandUser ,
1.147 ! jmc 735: .Cm AuthorizedKeysFile ,
1.123 djm 736: .Cm AuthorizedPrincipalsFile ,
1.72 dtucker 737: .Cm Banner ,
1.85 djm 738: .Cm ChrootDirectory ,
1.141 markus 739: .Cm DenyGroups ,
740: .Cm DenyUsers ,
1.67 dtucker 741: .Cm ForceCommand ,
1.142 jmc 742: .Cm GatewayPorts ,
1.141 markus 743: .Cm GSSAPIAuthentication ,
1.87 djm 744: .Cm HostbasedAuthentication ,
1.123 djm 745: .Cm HostbasedUsesNameFromPacketOnly ,
1.74 jmc 746: .Cm KbdInteractiveAuthentication ,
1.72 dtucker 747: .Cm KerberosAuthentication ,
1.95 dtucker 748: .Cm MaxAuthTries ,
1.94 dtucker 749: .Cm MaxSessions ,
1.72 dtucker 750: .Cm PasswordAuthentication ,
1.97 djm 751: .Cm PermitEmptyPasswords ,
1.66 dtucker 752: .Cm PermitOpen ,
1.79 dtucker 753: .Cm PermitRootLogin ,
1.123 djm 754: .Cm PermitTunnel ,
1.107 dtucker 755: .Cm PubkeyAuthentication ,
1.142 jmc 756: .Cm RhostsRSAAuthentication ,
1.141 markus 757: .Cm RSAAuthentication ,
1.66 dtucker 758: .Cm X11DisplayOffset ,
1.101 djm 759: .Cm X11Forwarding
1.60 dtucker 760: and
1.102 djm 761: .Cm X11UseLocalHost .
1.33 dtucker 762: .It Cm MaxAuthTries
763: Specifies the maximum number of authentication attempts permitted per
1.35 jmc 764: connection.
765: Once the number of failures reaches half this value,
766: additional failures are logged.
767: The default is 6.
1.90 djm 768: .It Cm MaxSessions
769: Specifies the maximum number of open sessions permitted per network connection.
770: The default is 10.
1.1 stevesk 771: .It Cm MaxStartups
772: Specifies the maximum number of concurrent unauthenticated connections to the
1.52 jmc 773: SSH daemon.
1.1 stevesk 774: Additional connections will be dropped until authentication succeeds or the
775: .Cm LoginGraceTime
776: expires for a connection.
777: The default is 10.
778: .Pp
779: Alternatively, random early drop can be enabled by specifying
780: the three colon separated values
781: .Dq start:rate:full
1.51 jmc 782: (e.g. "10:30:60").
1.53 jmc 783: .Xr sshd 8
1.1 stevesk 784: will refuse connection attempts with a probability of
785: .Dq rate/100
786: (30%)
787: if there are currently
788: .Dq start
789: (10)
790: unauthenticated connections.
791: The probability increases linearly and all connection attempts
792: are refused if the number of unauthenticated connections reaches
793: .Dq full
794: (60).
795: .It Cm PasswordAuthentication
796: Specifies whether password authentication is allowed.
797: The default is
798: .Dq yes .
799: .It Cm PermitEmptyPasswords
800: When password authentication is allowed, it specifies whether the
801: server allows login to accounts with empty password strings.
802: The default is
803: .Dq no .
1.62 dtucker 804: .It Cm PermitOpen
805: Specifies the destinations to which TCP port forwarding is permitted.
806: The forwarding specification must be one of the following forms:
807: .Pp
808: .Bl -item -offset indent -compact
809: .It
810: .Cm PermitOpen
811: .Sm off
812: .Ar host : port
813: .Sm on
814: .It
815: .Cm PermitOpen
816: .Sm off
817: .Ar IPv4_addr : port
818: .Sm on
819: .It
820: .Cm PermitOpen
821: .Sm off
822: .Ar \&[ IPv6_addr \&] : port
823: .Sm on
824: .El
825: .Pp
1.68 dtucker 826: Multiple forwards may be specified by separating them with whitespace.
1.62 dtucker 827: An argument of
828: .Dq any
829: can be used to remove all restrictions and permit any forwarding requests.
1.140 dtucker 830: An argument of
831: .Dq none
832: can be used to prohibit all forwarding requests.
1.63 jmc 833: By default all port forwarding requests are permitted.
1.1 stevesk 834: .It Cm PermitRootLogin
1.38 jmc 835: Specifies whether root can log in using
1.1 stevesk 836: .Xr ssh 1 .
837: The argument must be
838: .Dq yes ,
839: .Dq without-password ,
1.52 jmc 840: .Dq forced-commands-only ,
1.1 stevesk 841: or
842: .Dq no .
843: The default is
844: .Dq yes .
845: .Pp
846: If this option is set to
1.52 jmc 847: .Dq without-password ,
1.1 stevesk 848: password authentication is disabled for root.
849: .Pp
850: If this option is set to
1.52 jmc 851: .Dq forced-commands-only ,
1.1 stevesk 852: root login with public key authentication will be allowed,
853: but only if the
854: .Ar command
855: option has been specified
856: (which may be useful for taking remote backups even if root login is
1.17 jmc 857: normally not allowed).
858: All other authentication methods are disabled for root.
1.1 stevesk 859: .Pp
860: If this option is set to
1.52 jmc 861: .Dq no ,
1.38 jmc 862: root is not allowed to log in.
1.46 reyk 863: .It Cm PermitTunnel
864: Specifies whether
865: .Xr tun 4
866: device forwarding is allowed.
1.47 reyk 867: The argument must be
868: .Dq yes ,
1.58 stevesk 869: .Dq point-to-point
870: (layer 3),
871: .Dq ethernet
872: (layer 2), or
1.47 reyk 873: .Dq no .
1.58 stevesk 874: Specifying
875: .Dq yes
876: permits both
877: .Dq point-to-point
878: and
879: .Dq ethernet .
1.46 reyk 880: The default is
881: .Dq no .
1.6 markus 882: .It Cm PermitUserEnvironment
883: Specifies whether
884: .Pa ~/.ssh/environment
1.9 stevesk 885: and
1.6 markus 886: .Cm environment=
887: options in
888: .Pa ~/.ssh/authorized_keys
1.9 stevesk 889: are processed by
1.52 jmc 890: .Xr sshd 8 .
1.6 markus 891: The default is
892: .Dq no .
1.9 stevesk 893: Enabling environment processing may enable users to bypass access
894: restrictions in some configurations using mechanisms such as
895: .Ev LD_PRELOAD .
1.1 stevesk 896: .It Cm PidFile
1.4 stevesk 897: Specifies the file that contains the process ID of the
1.53 jmc 898: SSH daemon.
1.1 stevesk 899: The default is
900: .Pa /var/run/sshd.pid .
901: .It Cm Port
902: Specifies the port number that
1.52 jmc 903: .Xr sshd 8
1.1 stevesk 904: listens on.
905: The default is 22.
906: Multiple options of this type are permitted.
907: See also
908: .Cm ListenAddress .
909: .It Cm PrintLastLog
910: Specifies whether
1.52 jmc 911: .Xr sshd 8
1.36 jaredy 912: should print the date and time of the last user login when a user logs
913: in interactively.
1.1 stevesk 914: The default is
915: .Dq yes .
916: .It Cm PrintMotd
917: Specifies whether
1.52 jmc 918: .Xr sshd 8
1.1 stevesk 919: should print
920: .Pa /etc/motd
921: when a user logs in interactively.
922: (On some systems it is also printed by the shell,
923: .Pa /etc/profile ,
924: or equivalent.)
925: The default is
926: .Dq yes .
927: .It Cm Protocol
928: Specifies the protocol versions
1.52 jmc 929: .Xr sshd 8
1.5 stevesk 930: supports.
1.1 stevesk 931: The possible values are
1.52 jmc 932: .Sq 1
1.1 stevesk 933: and
1.52 jmc 934: .Sq 2 .
1.1 stevesk 935: Multiple versions must be comma-separated.
936: The default is
1.109 jmc 937: .Sq 2 .
1.5 stevesk 938: Note that the order of the protocol list does not indicate preference,
939: because the client selects among multiple protocol versions offered
940: by the server.
941: Specifying
942: .Dq 2,1
943: is identical to
944: .Dq 1,2 .
1.1 stevesk 945: .It Cm PubkeyAuthentication
946: Specifies whether public key authentication is allowed.
947: The default is
948: .Dq yes .
949: Note that this option applies to protocol version 2 only.
1.118 djm 950: .It Cm RevokedKeys
951: Specifies a list of revoked public keys.
952: Keys listed in this file will be refused for public key authentication.
953: Note that if this file is not readable, then public key authentication will
954: be refused for all users.
1.1 stevesk 955: .It Cm RhostsRSAAuthentication
956: Specifies whether rhosts or /etc/hosts.equiv authentication together
957: with successful RSA host authentication is allowed.
958: The default is
959: .Dq no .
960: This option applies to protocol version 1 only.
961: .It Cm RSAAuthentication
962: Specifies whether pure RSA authentication is allowed.
963: The default is
964: .Dq yes .
965: This option applies to protocol version 1 only.
966: .It Cm ServerKeyBits
967: Defines the number of bits in the ephemeral protocol version 1 server key.
1.96 djm 968: The minimum value is 512, and the default is 1024.
1.1 stevesk 969: .It Cm StrictModes
970: Specifies whether
1.52 jmc 971: .Xr sshd 8
1.1 stevesk 972: should check file modes and ownership of the
973: user's files and home directory before accepting login.
974: This is normally desirable because novices sometimes accidentally leave their
975: directory or files world-writable.
976: The default is
977: .Dq yes .
1.112 djm 978: Note that this does not apply to
979: .Cm ChrootDirectory ,
980: whose permissions and ownership are checked unconditionally.
1.1 stevesk 981: .It Cm Subsystem
1.51 jmc 982: Configures an external subsystem (e.g. file transfer daemon).
1.59 djm 983: Arguments should be a subsystem name and a command (with optional arguments)
984: to execute upon subsystem request.
1.80 djm 985: .Pp
1.1 stevesk 986: The command
987: .Xr sftp-server 8
988: implements the
989: .Dq sftp
990: file transfer subsystem.
1.80 djm 991: .Pp
992: Alternately the name
993: .Dq internal-sftp
994: implements an in-process
995: .Dq sftp
996: server.
997: This may simplify configurations using
998: .Cm ChrootDirectory
999: to force a different filesystem root on clients.
1000: .Pp
1.1 stevesk 1001: By default no subsystems are defined.
1002: Note that this option applies to protocol version 2 only.
1003: .It Cm SyslogFacility
1004: Gives the facility code that is used when logging messages from
1.53 jmc 1005: .Xr sshd 8 .
1.1 stevesk 1006: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1007: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1008: The default is AUTH.
1.27 markus 1009: .It Cm TCPKeepAlive
1010: Specifies whether the system should send TCP keepalive messages to the
1011: other side.
1012: If they are sent, death of the connection or crash of one
1013: of the machines will be properly noticed.
1014: However, this means that
1015: connections will die if the route is down temporarily, and some people
1016: find it annoying.
1017: On the other hand, if TCP keepalives are not sent,
1018: sessions may hang indefinitely on the server, leaving
1019: .Dq ghost
1020: users and consuming server resources.
1021: .Pp
1022: The default is
1023: .Dq yes
1024: (to send TCP keepalive messages), and the server will notice
1025: if the network goes down or the client host crashes.
1026: This avoids infinitely hanging sessions.
1027: .Pp
1028: To disable TCP keepalive messages, the value should be set to
1029: .Dq no .
1.118 djm 1030: .It Cm TrustedUserCAKeys
1031: Specifies a file containing public keys of certificate authorities that are
1.120 djm 1032: trusted to sign user certificates for authentication.
1.119 jmc 1033: Keys are listed one per line; empty lines and comments starting with
1.118 djm 1034: .Ql #
1035: are allowed.
1036: If a certificate is presented for authentication and has its signing CA key
1037: listed in this file, then it may be used for authentication for any user
1038: listed in the certificate's principals list.
1039: Note that certificates that lack a list of principals will not be permitted
1040: for authentication using
1041: .Cm TrustedUserCAKeys .
1.119 jmc 1042: For more details on certificates, see the
1.118 djm 1043: .Sx CERTIFICATES
1044: section in
1045: .Xr ssh-keygen 1 .
1.18 markus 1046: .It Cm UseDNS
1047: Specifies whether
1.52 jmc 1048: .Xr sshd 8
1.40 jmc 1049: should look up the remote host name and check that
1.18 markus 1050: the resolved host name for the remote IP address maps back to the
1051: very same IP address.
1052: The default is
1053: .Dq yes .
1.1 stevesk 1054: .It Cm UseLogin
1055: Specifies whether
1056: .Xr login 1
1057: is used for interactive login sessions.
1058: The default is
1059: .Dq no .
1060: Note that
1061: .Xr login 1
1062: is never used for remote command execution.
1063: Note also, that if this is enabled,
1064: .Cm X11Forwarding
1065: will be disabled because
1066: .Xr login 1
1067: does not know how to handle
1068: .Xr xauth 1
1.15 jmc 1069: cookies.
1070: If
1.1 stevesk 1071: .Cm UsePrivilegeSeparation
1072: is specified, it will be disabled after authentication.
1073: .It Cm UsePrivilegeSeparation
1074: Specifies whether
1.52 jmc 1075: .Xr sshd 8
1.2 stevesk 1076: separates privileges by creating an unprivileged child process
1.15 jmc 1077: to deal with incoming network traffic.
1078: After successful authentication, another process will be created that has
1079: the privilege of the authenticated user.
1080: The goal of privilege separation is to prevent privilege
1.1 stevesk 1081: escalation by containing any corruption within the unprivileged processes.
1082: The default is
1083: .Dq yes .
1.134 djm 1084: If
1085: .Cm UsePrivilegeSeparation
1086: is set to
1087: .Dq sandbox
1088: then the pre-authentication unprivileged process is subject to additional
1089: restrictions.
1.137 djm 1090: .It Cm VersionAddendum
1091: Optionally specifies additional text to append to the SSH protocol banner
1092: sent by the server upon connection.
1093: The default is
1094: .Dq none .
1.1 stevesk 1095: .It Cm X11DisplayOffset
1096: Specifies the first display number available for
1.52 jmc 1097: .Xr sshd 8 Ns 's
1.1 stevesk 1098: X11 forwarding.
1.52 jmc 1099: This prevents sshd from interfering with real X11 servers.
1.1 stevesk 1100: The default is 10.
1101: .It Cm X11Forwarding
1102: Specifies whether X11 forwarding is permitted.
1.13 stevesk 1103: The argument must be
1104: .Dq yes
1105: or
1106: .Dq no .
1.1 stevesk 1107: The default is
1108: .Dq no .
1.13 stevesk 1109: .Pp
1110: When X11 forwarding is enabled, there may be additional exposure to
1111: the server and to client displays if the
1.52 jmc 1112: .Xr sshd 8
1.13 stevesk 1113: proxy display is configured to listen on the wildcard address (see
1114: .Cm X11UseLocalhost
1.52 jmc 1115: below), though this is not the default.
1.13 stevesk 1116: Additionally, the authentication spoofing and authentication data
1117: verification and substitution occur on the client side.
1118: The security risk of using X11 forwarding is that the client's X11
1.52 jmc 1119: display server may be exposed to attack when the SSH client requests
1.13 stevesk 1120: forwarding (see the warnings for
1121: .Cm ForwardX11
1122: in
1.19 jmc 1123: .Xr ssh_config 5 ) .
1.13 stevesk 1124: A system administrator may have a stance in which they want to
1125: protect clients that may expose themselves to attack by unwittingly
1126: requesting X11 forwarding, which can warrant a
1127: .Dq no
1128: setting.
1129: .Pp
1130: Note that disabling X11 forwarding does not prevent users from
1131: forwarding X11 traffic, as users can always install their own forwarders.
1.1 stevesk 1132: X11 forwarding is automatically disabled if
1133: .Cm UseLogin
1134: is enabled.
1135: .It Cm X11UseLocalhost
1136: Specifies whether
1.52 jmc 1137: .Xr sshd 8
1.1 stevesk 1138: should bind the X11 forwarding server to the loopback address or to
1.15 jmc 1139: the wildcard address.
1140: By default,
1.52 jmc 1141: sshd binds the forwarding server to the loopback address and sets the
1.1 stevesk 1142: hostname part of the
1143: .Ev DISPLAY
1144: environment variable to
1145: .Dq localhost .
1.8 stevesk 1146: This prevents remote hosts from connecting to the proxy display.
1.1 stevesk 1147: However, some older X11 clients may not function with this
1148: configuration.
1149: .Cm X11UseLocalhost
1150: may be set to
1151: .Dq no
1152: to specify that the forwarding server should be bound to the wildcard
1153: address.
1154: The argument must be
1155: .Dq yes
1156: or
1157: .Dq no .
1158: The default is
1159: .Dq yes .
1160: .It Cm XAuthLocation
1.11 stevesk 1161: Specifies the full pathname of the
1.1 stevesk 1162: .Xr xauth 1
1163: program.
1164: The default is
1165: .Pa /usr/X11R6/bin/xauth .
1166: .El
1.55 jmc 1167: .Sh TIME FORMATS
1.53 jmc 1168: .Xr sshd 8
1.1 stevesk 1169: command-line arguments and configuration file options that specify time
1170: may be expressed using a sequence of the form:
1171: .Sm off
1.7 stevesk 1172: .Ar time Op Ar qualifier ,
1.1 stevesk 1173: .Sm on
1174: where
1175: .Ar time
1176: is a positive integer value and
1177: .Ar qualifier
1178: is one of the following:
1179: .Pp
1180: .Bl -tag -width Ds -compact -offset indent
1.64 jmc 1181: .It Aq Cm none
1.1 stevesk 1182: seconds
1183: .It Cm s | Cm S
1184: seconds
1185: .It Cm m | Cm M
1186: minutes
1187: .It Cm h | Cm H
1188: hours
1189: .It Cm d | Cm D
1190: days
1191: .It Cm w | Cm W
1192: weeks
1193: .El
1194: .Pp
1195: Each member of the sequence is added together to calculate
1196: the total time value.
1197: .Pp
1198: Time format examples:
1199: .Pp
1200: .Bl -tag -width Ds -compact -offset indent
1201: .It 600
1202: 600 seconds (10 minutes)
1203: .It 10m
1204: 10 minutes
1205: .It 1h30m
1206: 1 hour 30 minutes (90 minutes)
1207: .El
1208: .Sh FILES
1209: .Bl -tag -width Ds
1210: .It Pa /etc/ssh/sshd_config
1211: Contains configuration data for
1.53 jmc 1212: .Xr sshd 8 .
1.1 stevesk 1213: This file should be writable by root only, but it is recommended
1214: (though not necessary) that it be world-readable.
1215: .El
1.19 jmc 1216: .Sh SEE ALSO
1217: .Xr sshd 8
1.1 stevesk 1218: .Sh AUTHORS
1219: OpenSSH is a derivative of the original and free
1220: ssh 1.2.12 release by Tatu Ylonen.
1221: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1222: Theo de Raadt and Dug Song
1223: removed many bugs, re-added newer features and
1224: created OpenSSH.
1225: Markus Friedl contributed the support for SSH
1226: protocol versions 1.5 and 2.0.
1227: Niels Provos and Markus Friedl contributed support
1228: for privilege separation.