Annotation of src/usr.bin/ssh/sshd_config.5, Revision 1.268
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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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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1.268 ! jmc 36: .\" $OpenBSD: sshd_config.5,v 1.267 2018/06/01 03:33:53 djm Exp $
! 37: .Dd $Mdocdate: June 1 2018 $
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 DESCRIPTION
1.53 jmc 44: .Xr sshd 8
1.1 stevesk 45: reads configuration data from
46: .Pa /etc/ssh/sshd_config
47: (or the file specified with
48: .Fl f
49: on the command line).
50: The file contains keyword-argument pairs, one per line.
1.254 benno 51: For each keyword, the first obtained value will be used.
1.1 stevesk 52: Lines starting with
53: .Ql #
54: and empty lines are interpreted as comments.
1.56 dtucker 55: Arguments may optionally be enclosed in double quotes
56: .Pq \&"
57: in order to represent arguments containing spaces.
1.1 stevesk 58: .Pp
59: The possible
60: keywords and their meanings are as follows (note that
61: keywords are case-insensitive and arguments are case-sensitive):
62: .Bl -tag -width Ds
1.30 djm 63: .It Cm AcceptEnv
64: Specifies what environment variables sent by the client will be copied into
65: the session's
66: .Xr environ 7 .
67: See
68: .Cm SendEnv
69: in
70: .Xr ssh_config 5
71: for how to configure the client.
1.219 jmc 72: The
1.197 dtucker 73: .Ev TERM
1.199 jmc 74: environment variable is always sent whenever the client
1.204 djm 75: requests a pseudo-terminal as it is required by the protocol.
1.30 djm 76: Variables are specified by name, which may contain the wildcard characters
1.51 jmc 77: .Ql *
1.30 djm 78: and
79: .Ql \&? .
1.31 djm 80: Multiple environment variables may be separated by whitespace or spread
1.30 djm 81: across multiple
82: .Cm AcceptEnv
83: directives.
1.31 djm 84: Be warned that some environment variables could be used to bypass restricted
1.30 djm 85: user environments.
86: For this reason, care should be taken in the use of this directive.
87: The default is not to accept any environment variables.
1.37 djm 88: .It Cm AddressFamily
89: Specifies which address family should be used by
1.53 jmc 90: .Xr sshd 8 .
1.37 djm 91: Valid arguments are
1.237 jmc 92: .Cm any
93: (the default),
94: .Cm inet
1.52 jmc 95: (use IPv4 only), or
1.237 jmc 96: .Cm inet6
1.37 djm 97: (use IPv6 only).
1.89 jmc 98: .It Cm AllowAgentForwarding
99: Specifies whether
100: .Xr ssh-agent 1
101: forwarding is permitted.
102: The default is
1.237 jmc 103: .Cm yes .
1.89 jmc 104: Note that disabling agent forwarding does not improve security
105: unless users are also denied shell access, as they can always install
106: their own forwarders.
1.1 stevesk 107: .It Cm AllowGroups
108: This keyword can be followed by a list of group name patterns, separated
109: by spaces.
110: If specified, login is allowed only for users whose primary
111: group or supplementary group list matches one of the patterns.
112: Only group names are valid; a numerical group ID is not recognized.
113: By default, login is allowed for all groups.
1.54 jmc 114: The allow/deny directives are processed in the following order:
115: .Cm DenyUsers ,
116: .Cm AllowUsers ,
117: .Cm DenyGroups ,
118: and finally
119: .Cm AllowGroups .
1.49 jmc 120: .Pp
1.161 jmc 121: See PATTERNS in
1.49 jmc 122: .Xr ssh_config 5
123: for more information on patterns.
1.231 jmc 124: .It Cm AllowStreamLocalForwarding
125: Specifies whether StreamLocal (Unix-domain socket) forwarding is permitted.
1.150 djm 126: The available options are
1.237 jmc 127: .Cm yes
128: (the default)
1.150 djm 129: or
1.237 jmc 130: .Cm all
1.231 jmc 131: to allow StreamLocal forwarding,
1.237 jmc 132: .Cm no
1.231 jmc 133: to prevent all StreamLocal forwarding,
1.237 jmc 134: .Cm local
1.150 djm 135: to allow local (from the perspective of
1.151 jmc 136: .Xr ssh 1 )
137: forwarding only or
1.237 jmc 138: .Cm remote
1.150 djm 139: to allow remote forwarding only.
1.231 jmc 140: Note that disabling StreamLocal forwarding does not improve security unless
1.1 stevesk 141: users are also denied shell access, as they can always install their
142: own forwarders.
1.231 jmc 143: .It Cm AllowTcpForwarding
144: Specifies whether TCP forwarding is permitted.
1.175 millert 145: The available options are
1.237 jmc 146: .Cm yes
147: (the default)
1.175 millert 148: or
1.237 jmc 149: .Cm all
1.231 jmc 150: to allow TCP forwarding,
1.237 jmc 151: .Cm no
1.231 jmc 152: to prevent all TCP forwarding,
1.237 jmc 153: .Cm local
1.175 millert 154: to allow local (from the perspective of
155: .Xr ssh 1 )
156: forwarding only or
1.237 jmc 157: .Cm remote
1.175 millert 158: to allow remote forwarding only.
1.231 jmc 159: Note that disabling TCP forwarding does not improve security unless
1.175 millert 160: users are also denied shell access, as they can always install their
161: own forwarders.
1.1 stevesk 162: .It Cm AllowUsers
163: This keyword can be followed by a list of user name patterns, separated
164: by spaces.
1.14 jmc 165: If specified, login is allowed only for user names that
1.1 stevesk 166: match one of the patterns.
167: Only user names are valid; a numerical user ID is not recognized.
168: By default, login is allowed for all users.
169: If the pattern takes the form USER@HOST then USER and HOST
170: are separately checked, restricting logins to particular
171: users from particular hosts.
1.222 jmc 172: HOST criteria may additionally contain addresses to match in CIDR
173: address/masklen format.
1.54 jmc 174: The allow/deny directives are processed in the following order:
175: .Cm DenyUsers ,
176: .Cm AllowUsers ,
177: .Cm DenyGroups ,
178: and finally
179: .Cm AllowGroups .
1.49 jmc 180: .Pp
1.161 jmc 181: See PATTERNS in
1.49 jmc 182: .Xr ssh_config 5
183: for more information on patterns.
1.149 djm 184: .It Cm AuthenticationMethods
185: Specifies the authentication methods that must be successfully completed
186: for a user to be granted access.
187: This option must be followed by one or more comma-separated lists of
1.224 djm 188: authentication method names, or by the single string
1.237 jmc 189: .Cm any
1.224 djm 190: to indicate the default behaviour of accepting any single authentication
1.225 jmc 191: method.
1.237 jmc 192: If the default is overridden, then successful authentication requires
1.224 djm 193: completion of every method in at least one of these lists.
1.149 djm 194: .Pp
1.237 jmc 195: For example,
196: .Qq publickey,password publickey,keyboard-interactive
1.149 djm 197: would require the user to complete public key authentication, followed by
198: either password or keyboard interactive authentication.
199: Only methods that are next in one or more lists are offered at each stage,
1.237 jmc 200: so for this example it would not be possible to attempt password or
1.149 djm 201: keyboard-interactive authentication before public key.
1.157 markus 202: .Pp
203: For keyboard interactive authentication it is also possible to
204: restrict authentication to a specific device by appending a
205: colon followed by the device identifier
1.237 jmc 206: .Cm bsdauth ,
207: .Cm pam ,
1.157 markus 208: or
1.237 jmc 209: .Cm skey ,
1.157 markus 210: depending on the server configuration.
211: For example,
1.237 jmc 212: .Qq keyboard-interactive:bsdauth
1.157 markus 213: would restrict keyboard interactive authentication to the
1.237 jmc 214: .Cm bsdauth
1.157 markus 215: device.
1.185 djm 216: .Pp
1.237 jmc 217: If the publickey method is listed more than once,
1.185 djm 218: .Xr sshd 8
219: verifies that keys that have been used successfully are not reused for
220: subsequent authentications.
1.237 jmc 221: For example,
222: .Qq publickey,publickey
223: requires successful authentication using two different public keys.
1.181 djm 224: .Pp
1.149 djm 225: Note that each authentication method listed should also be explicitly enabled
226: in the configuration.
1.251 djm 227: .Pp
228: The available authentication methods are:
229: .Qq gssapi-with-mic ,
230: .Qq hostbased ,
231: .Qq keyboard-interactive ,
232: .Qq none
233: (used for access to password-less accounts when
1.266 jmc 234: .Cm PermitEmptyPasswords
1.251 djm 235: is enabled),
236: .Qq password
237: and
238: .Qq publickey .
1.146 djm 239: .It Cm AuthorizedKeysCommand
1.147 jmc 240: Specifies a program to be used to look up the user's public keys.
1.201 djm 241: The program must be owned by root, not writable by group or others and
242: specified by an absolute path.
243: Arguments to
244: .Cm AuthorizedKeysCommand
1.235 jmc 245: accept the tokens described in the
246: .Sx TOKENS
247: section.
248: If no arguments are specified then the username of the target user is used.
1.201 djm 249: .Pp
250: The program should produce on standard output zero or
1.235 jmc 251: more lines of authorized_keys output (see
252: .Sx AUTHORIZED_KEYS
253: in
1.147 jmc 254: .Xr sshd 8 ) .
1.235 jmc 255: If a key supplied by
256: .Cm AuthorizedKeysCommand
257: does not successfully authenticate
1.146 djm 258: and authorize the user then public key authentication continues using the usual
259: .Cm AuthorizedKeysFile
260: files.
1.237 jmc 261: By default, no
262: .Cm AuthorizedKeysCommand
263: is run.
1.146 djm 264: .It Cm AuthorizedKeysCommandUser
1.237 jmc 265: Specifies the user under whose account the
266: .Cm AuthorizedKeysCommand
267: is run.
1.146 djm 268: It is recommended to use a dedicated user that has no other role on the host
269: than running authorized keys commands.
1.186 djm 270: If
1.181 djm 271: .Cm AuthorizedKeysCommand
1.186 djm 272: is specified but
273: .Cm AuthorizedKeysCommandUser
274: is not, then
275: .Xr sshd 8
276: will refuse to start.
1.1 stevesk 277: .It Cm AuthorizedKeysFile
1.235 jmc 278: Specifies the file that contains the public keys used for user authentication.
1.124 djm 279: The format is described in the
1.235 jmc 280: .Sx AUTHORIZED_KEYS FILE FORMAT
1.124 djm 281: section of
282: .Xr sshd 8 .
1.235 jmc 283: Arguments to
1.1 stevesk 284: .Cm AuthorizedKeysFile
1.235 jmc 285: accept the tokens described in the
286: .Sx TOKENS
287: section.
1.1 stevesk 288: After expansion,
289: .Cm AuthorizedKeysFile
290: is taken to be an absolute path or one relative to the user's home
291: directory.
1.133 jmc 292: Multiple files may be listed, separated by whitespace.
1.212 djm 293: Alternately this option may be set to
1.237 jmc 294: .Cm none
1.212 djm 295: to skip checking for user keys in files.
1.133 jmc 296: The default is
1.237 jmc 297: .Qq .ssh/authorized_keys .ssh/authorized_keys2 .
1.202 djm 298: .It Cm AuthorizedPrincipalsCommand
299: Specifies a program to be used to generate the list of allowed
300: certificate principals as per
301: .Cm AuthorizedPrincipalsFile .
302: The program must be owned by root, not writable by group or others and
303: specified by an absolute path.
304: Arguments to
305: .Cm AuthorizedPrincipalsCommand
1.235 jmc 306: accept the tokens described in the
307: .Sx TOKENS
308: section.
309: If no arguments are specified then the username of the target user is used.
1.202 djm 310: .Pp
311: The program should produce on standard output zero or
312: more lines of
313: .Cm AuthorizedPrincipalsFile
314: output.
315: If either
316: .Cm AuthorizedPrincipalsCommand
317: or
318: .Cm AuthorizedPrincipalsFile
319: is specified, then certificates offered by the client for authentication
320: must contain a principal that is listed.
1.235 jmc 321: By default, no
322: .Cm AuthorizedPrincipalsCommand
323: is run.
1.202 djm 324: .It Cm AuthorizedPrincipalsCommandUser
1.235 jmc 325: Specifies the user under whose account the
326: .Cm AuthorizedPrincipalsCommand
327: is run.
1.202 djm 328: It is recommended to use a dedicated user that has no other role on the host
329: than running authorized principals commands.
330: If
331: .Cm AuthorizedPrincipalsCommand
332: is specified but
333: .Cm AuthorizedPrincipalsCommandUser
334: is not, then
335: .Xr sshd 8
336: will refuse to start.
1.121 djm 337: .It Cm AuthorizedPrincipalsFile
338: Specifies a file that lists principal names that are accepted for
339: certificate authentication.
340: When using certificates signed by a key listed in
341: .Cm TrustedUserCAKeys ,
342: this file lists names, one of which must appear in the certificate for it
343: to be accepted for authentication.
1.235 jmc 344: Names are listed one per line preceded by key options (as described in
345: .Sx AUTHORIZED_KEYS FILE FORMAT
346: in
1.125 jmc 347: .Xr sshd 8 ) .
1.124 djm 348: Empty lines and comments starting with
1.121 djm 349: .Ql #
350: are ignored.
351: .Pp
1.235 jmc 352: Arguments to
1.121 djm 353: .Cm AuthorizedPrincipalsFile
1.235 jmc 354: accept the tokens described in the
355: .Sx TOKENS
356: section.
1.121 djm 357: After expansion,
358: .Cm AuthorizedPrincipalsFile
1.235 jmc 359: is taken to be an absolute path or one relative to the user's home directory.
1.138 djm 360: The default is
1.237 jmc 361: .Cm none ,
1.138 djm 362: i.e. not to use a principals file \(en in this case, the username
1.121 djm 363: of the user must appear in a certificate's principals list for it to be
364: accepted.
1.235 jmc 365: .Pp
1.121 djm 366: Note that
367: .Cm AuthorizedPrincipalsFile
368: is only used when authentication proceeds using a CA listed in
369: .Cm TrustedUserCAKeys
370: and is not consulted for certification authorities trusted via
371: .Pa ~/.ssh/authorized_keys ,
372: though the
373: .Cm principals=
374: key option offers a similar facility (see
375: .Xr sshd 8
376: for details).
1.1 stevesk 377: .It Cm Banner
378: The contents of the specified file are sent to the remote user before
379: authentication is allowed.
1.78 djm 380: If the argument is
1.237 jmc 381: .Cm none
1.78 djm 382: then no banner is displayed.
1.1 stevesk 383: By default, no banner is displayed.
384: .It Cm ChallengeResponseAuthentication
1.50 jmc 385: Specifies whether challenge-response authentication is allowed.
1.1 stevesk 386: All authentication styles from
387: .Xr login.conf 5
388: are supported.
389: The default is
1.237 jmc 390: .Cm yes .
1.80 djm 391: .It Cm ChrootDirectory
1.113 stevesk 392: Specifies the pathname of a directory to
1.80 djm 393: .Xr chroot 2
394: to after authentication.
1.190 deraadt 395: At session startup
396: .Xr sshd 8
397: checks that all components of the pathname are root-owned directories
398: which are not writable by any other user or group.
1.106 stevesk 399: After the chroot,
400: .Xr sshd 8
401: changes the working directory to the user's home directory.
1.235 jmc 402: Arguments to
403: .Cm ChrootDirectory
404: accept the tokens described in the
405: .Sx TOKENS
406: section.
1.80 djm 407: .Pp
408: The
409: .Cm ChrootDirectory
410: must contain the necessary files and directories to support the
1.103 stevesk 411: user's session.
1.80 djm 412: For an interactive session this requires at least a shell, typically
413: .Xr sh 1 ,
414: and basic
415: .Pa /dev
416: nodes such as
417: .Xr null 4 ,
418: .Xr zero 4 ,
419: .Xr stdin 4 ,
420: .Xr stdout 4 ,
421: .Xr stderr 4 ,
1.180 jmc 422: and
1.80 djm 423: .Xr tty 4
424: devices.
1.237 jmc 425: For file transfer sessions using SFTP
426: no additional configuration of the environment is necessary if the in-process
427: sftp-server is used,
1.176 schwarze 428: though sessions which use logging may require
1.104 stevesk 429: .Pa /dev/log
1.176 schwarze 430: inside the chroot directory on some operating systems (see
1.104 stevesk 431: .Xr sftp-server 8
1.81 jmc 432: for details).
1.190 deraadt 433: .Pp
1.191 jmc 434: For safety, it is very important that the directory hierarchy be
1.190 deraadt 435: prevented from modification by other processes on the system (especially
436: those outside the jail).
437: Misconfiguration can lead to unsafe environments which
438: .Xr sshd 8
439: cannot detect.
1.80 djm 440: .Pp
1.215 djm 441: The default is
1.237 jmc 442: .Cm none ,
1.215 djm 443: indicating not to
1.80 djm 444: .Xr chroot 2 .
1.1 stevesk 445: .It Cm Ciphers
1.219 jmc 446: Specifies the ciphers allowed.
1.1 stevesk 447: Multiple ciphers must be comma-separated.
1.208 djm 448: If the specified value begins with a
449: .Sq +
450: character, then the specified ciphers will be appended to the default set
451: instead of replacing them.
1.242 djm 452: If the specified value begins with a
453: .Sq -
454: character, then the specified ciphers (including wildcards) will be removed
455: from the default set instead of replacing them.
1.208 djm 456: .Pp
1.167 djm 457: The supported ciphers are:
458: .Pp
1.173 naddy 459: .Bl -item -compact -offset indent
460: .It
461: 3des-cbc
462: .It
463: aes128-cbc
464: .It
465: aes192-cbc
466: .It
467: aes256-cbc
468: .It
469: aes128-ctr
470: .It
471: aes192-ctr
472: .It
473: aes256-ctr
474: .It
475: aes128-gcm@openssh.com
476: .It
477: aes256-gcm@openssh.com
478: .It
479: chacha20-poly1305@openssh.com
480: .El
1.167 djm 481: .Pp
1.52 jmc 482: The default is:
1.173 naddy 483: .Bd -literal -offset indent
1.211 jmc 484: chacha20-poly1305@openssh.com,
1.173 naddy 485: aes128-ctr,aes192-ctr,aes256-ctr,
1.211 jmc 486: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 487: .Ed
1.167 djm 488: .Pp
1.237 jmc 489: The list of available ciphers may also be obtained using
490: .Qq ssh -Q cipher .
1.1 stevesk 491: .It Cm ClientAliveCountMax
1.237 jmc 492: Sets the number of client alive messages which may be sent without
1.52 jmc 493: .Xr sshd 8
1.17 jmc 494: receiving any messages back from the client.
495: If this threshold is reached while client alive messages are being sent,
1.52 jmc 496: sshd will disconnect the client, terminating the session.
1.17 jmc 497: It is important to note that the use of client alive messages is very
498: different from
1.237 jmc 499: .Cm TCPKeepAlive .
1.17 jmc 500: The client alive messages are sent through the encrypted channel
501: and therefore will not be spoofable.
502: The TCP keepalive option enabled by
1.27 markus 503: .Cm TCPKeepAlive
1.17 jmc 504: is spoofable.
505: The client alive mechanism is valuable when the client or
1.1 stevesk 506: server depend on knowing when a connection has become inactive.
507: .Pp
1.17 jmc 508: The default value is 3.
509: If
1.1 stevesk 510: .Cm ClientAliveInterval
1.237 jmc 511: is set to 15, and
1.1 stevesk 512: .Cm ClientAliveCountMax
1.52 jmc 513: is left at the default, unresponsive SSH clients
1.1 stevesk 514: will be disconnected after approximately 45 seconds.
1.42 djm 515: .It Cm ClientAliveInterval
516: Sets a timeout interval in seconds after which if no data has been received
517: from the client,
1.52 jmc 518: .Xr sshd 8
1.42 djm 519: will send a message through the encrypted
520: channel to request a response from the client.
521: The default
522: is 0, indicating that these messages will not be sent to the client.
1.3 markus 523: .It Cm Compression
1.236 djm 524: Specifies whether compression is enabled after
1.44 markus 525: the user has authenticated successfully.
1.3 markus 526: The argument must be
1.237 jmc 527: .Cm yes ,
528: .Cm delayed
1.236 djm 529: (a legacy synonym for
1.237 jmc 530: .Cm yes )
1.3 markus 531: or
1.237 jmc 532: .Cm no .
1.3 markus 533: The default is
1.237 jmc 534: .Cm yes .
1.1 stevesk 535: .It Cm DenyGroups
536: This keyword can be followed by a list of group name patterns, separated
537: by spaces.
538: Login is disallowed for users whose primary group or supplementary
539: group list matches one of the patterns.
540: Only group names are valid; a numerical group ID is not recognized.
541: By default, login is allowed for all groups.
1.54 jmc 542: The allow/deny directives are processed in the following order:
543: .Cm DenyUsers ,
544: .Cm AllowUsers ,
545: .Cm DenyGroups ,
546: and finally
547: .Cm AllowGroups .
1.49 jmc 548: .Pp
1.161 jmc 549: See PATTERNS in
1.49 jmc 550: .Xr ssh_config 5
551: for more information on patterns.
1.1 stevesk 552: .It Cm DenyUsers
553: This keyword can be followed by a list of user name patterns, separated
554: by spaces.
555: Login is disallowed for user names that match one of the patterns.
556: Only user names are valid; a numerical user ID is not recognized.
557: By default, login is allowed for all users.
558: If the pattern takes the form USER@HOST then USER and HOST
559: are separately checked, restricting logins to particular
560: users from particular hosts.
1.222 jmc 561: HOST criteria may additionally contain addresses to match in CIDR
562: address/masklen format.
1.54 jmc 563: The allow/deny directives are processed in the following order:
564: .Cm DenyUsers ,
565: .Cm AllowUsers ,
566: .Cm DenyGroups ,
567: and finally
568: .Cm AllowGroups .
1.49 jmc 569: .Pp
1.161 jmc 570: See PATTERNS in
1.49 jmc 571: .Xr ssh_config 5
572: for more information on patterns.
1.239 djm 573: .It Cm DisableForwarding
574: Disables all forwarding features, including X11,
575: .Xr ssh-agent 1 ,
576: TCP and StreamLocal.
577: This option overrides all other forwarding-related options and may
578: simplify restricted configurations.
1.246 djm 579: .It Cm ExposeAuthInfo
1.253 jmc 580: Writes a temporary file containing a list of authentication methods and
1.246 djm 581: public credentials (e.g. keys) used to authenticate the user.
1.247 jmc 582: The location of the file is exposed to the user session through the
1.248 djm 583: .Ev SSH_USER_AUTH
1.247 jmc 584: environment variable.
1.253 jmc 585: The default is
586: .Cm no .
1.183 djm 587: .It Cm FingerprintHash
588: Specifies the hash algorithm used when logging key fingerprints.
589: Valid options are:
1.237 jmc 590: .Cm md5
1.183 djm 591: and
1.237 jmc 592: .Cm sha256 .
1.183 djm 593: The default is
1.237 jmc 594: .Cm sha256 .
1.67 dtucker 595: .It Cm ForceCommand
596: Forces the execution of the command specified by
597: .Cm ForceCommand ,
1.84 djm 598: ignoring any command supplied by the client and
599: .Pa ~/.ssh/rc
600: if present.
1.67 dtucker 601: The command is invoked by using the user's login shell with the -c option.
602: This applies to shell, command, or subsystem execution.
603: It is most useful inside a
604: .Cm Match
605: block.
606: The command originally supplied by the client is available in the
607: .Ev SSH_ORIGINAL_COMMAND
608: environment variable.
1.82 djm 609: Specifying a command of
1.237 jmc 610: .Cm internal-sftp
611: will force the use of an in-process SFTP server that requires no support
1.82 djm 612: files when used with
613: .Cm ChrootDirectory .
1.215 djm 614: The default is
1.237 jmc 615: .Cm none .
1.1 stevesk 616: .It Cm GatewayPorts
617: Specifies whether remote hosts are allowed to connect to ports
618: forwarded for the client.
619: By default,
1.52 jmc 620: .Xr sshd 8
1.15 jmc 621: binds remote port forwardings to the loopback address.
622: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 623: .Cm GatewayPorts
1.52 jmc 624: can be used to specify that sshd
1.39 djm 625: should allow remote port forwardings to bind to non-loopback addresses, thus
626: allowing other hosts to connect.
627: The argument may be
1.237 jmc 628: .Cm no
1.39 djm 629: to force remote port forwardings to be available to the local host only,
1.237 jmc 630: .Cm yes
1.39 djm 631: to force remote port forwardings to bind to the wildcard address, or
1.237 jmc 632: .Cm clientspecified
1.39 djm 633: to allow the client to select the address to which the forwarding is bound.
1.1 stevesk 634: The default is
1.237 jmc 635: .Cm no .
1.23 markus 636: .It Cm GSSAPIAuthentication
1.25 markus 637: Specifies whether user authentication based on GSSAPI is allowed.
1.26 djm 638: The default is
1.237 jmc 639: .Cm no .
1.23 markus 640: .It Cm GSSAPICleanupCredentials
641: Specifies whether to automatically destroy the user's credentials cache
642: on logout.
643: The default is
1.237 jmc 644: .Cm yes .
1.203 djm 645: .It Cm GSSAPIStrictAcceptorCheck
646: Determines whether to be strict about the identity of the GSSAPI acceptor
647: a client authenticates against.
648: If set to
1.237 jmc 649: .Cm yes
650: then the client must authenticate against the host
1.203 djm 651: service on the current hostname.
652: If set to
1.237 jmc 653: .Cm no
1.203 djm 654: then the client may authenticate against any service key stored in the
655: machine's default store.
656: This facility is provided to assist with operation on multi homed machines.
657: The default is
1.237 jmc 658: .Cm yes .
1.189 djm 659: .It Cm HostbasedAcceptedKeyTypes
660: Specifies the key types that will be accepted for hostbased authentication
661: as a comma-separated pattern list.
1.208 djm 662: Alternately if the specified value begins with a
663: .Sq +
664: character, then the specified key types will be appended to the default set
665: instead of replacing them.
1.242 djm 666: If the specified value begins with a
667: .Sq -
668: character, then the specified key types (including wildcards) will be removed
669: from the default set instead of replacing them.
1.206 markus 670: The default for this option is:
671: .Bd -literal -offset 3n
672: ecdsa-sha2-nistp256-cert-v01@openssh.com,
673: ecdsa-sha2-nistp384-cert-v01@openssh.com,
674: ecdsa-sha2-nistp521-cert-v01@openssh.com,
675: ssh-ed25519-cert-v01@openssh.com,
676: ssh-rsa-cert-v01@openssh.com,
677: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.220 djm 678: ssh-ed25519,ssh-rsa
1.206 markus 679: .Ed
680: .Pp
1.237 jmc 681: The list of available key types may also be obtained using
682: .Qq ssh -Q key .
1.1 stevesk 683: .It Cm HostbasedAuthentication
684: Specifies whether rhosts or /etc/hosts.equiv authentication together
685: with successful public key client host authentication is allowed
1.50 jmc 686: (host-based authentication).
1.70 dtucker 687: The default is
1.237 jmc 688: .Cm no .
1.70 dtucker 689: .It Cm HostbasedUsesNameFromPacketOnly
690: Specifies whether or not the server will attempt to perform a reverse
691: name lookup when matching the name in the
692: .Pa ~/.shosts ,
693: .Pa ~/.rhosts ,
694: and
695: .Pa /etc/hosts.equiv
696: files during
697: .Cm HostbasedAuthentication .
698: A setting of
1.237 jmc 699: .Cm yes
1.70 dtucker 700: means that
701: .Xr sshd 8
702: uses the name supplied by the client rather than
703: attempting to resolve the name from the TCP connection itself.
1.1 stevesk 704: The default is
1.237 jmc 705: .Cm no .
1.117 djm 706: .It Cm HostCertificate
707: Specifies a file containing a public host certificate.
708: The certificate's public key must match a private host key already specified
709: by
710: .Cm HostKey .
711: The default behaviour of
712: .Xr sshd 8
713: is not to load any certificates.
1.1 stevesk 714: .It Cm HostKey
715: Specifies a file containing a private host key
716: used by SSH.
1.229 naddy 717: The defaults are
1.169 naddy 718: .Pa /etc/ssh/ssh_host_ecdsa_key ,
719: .Pa /etc/ssh/ssh_host_ed25519_key
1.126 djm 720: and
1.229 naddy 721: .Pa /etc/ssh/ssh_host_rsa_key .
1.206 markus 722: .Pp
1.1 stevesk 723: Note that
1.52 jmc 724: .Xr sshd 8
1.206 markus 725: will refuse to use a file if it is group/world-accessible
726: and that the
727: .Cm HostKeyAlgorithms
728: option restricts which of the keys are actually used by
729: .Xr sshd 8 .
730: .Pp
1.1 stevesk 731: It is possible to have multiple host key files.
1.162 markus 732: It is also possible to specify public host key files instead.
733: In this case operations on the private key will be delegated
734: to an
735: .Xr ssh-agent 1 .
736: .It Cm HostKeyAgent
737: Identifies the UNIX-domain socket used to communicate
738: with an agent that has access to the private host keys.
1.223 markus 739: If the string
1.237 jmc 740: .Qq SSH_AUTH_SOCK
1.162 markus 741: is specified, the location of the socket will be read from the
742: .Ev SSH_AUTH_SOCK
743: environment variable.
1.206 markus 744: .It Cm HostKeyAlgorithms
1.219 jmc 745: Specifies the host key algorithms
1.206 markus 746: that the server offers.
747: The default for this option is:
748: .Bd -literal -offset 3n
749: ecdsa-sha2-nistp256-cert-v01@openssh.com,
750: ecdsa-sha2-nistp384-cert-v01@openssh.com,
751: ecdsa-sha2-nistp521-cert-v01@openssh.com,
752: ssh-ed25519-cert-v01@openssh.com,
753: ssh-rsa-cert-v01@openssh.com,
754: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.220 djm 755: ssh-ed25519,ssh-rsa
1.206 markus 756: .Ed
757: .Pp
1.237 jmc 758: The list of available key types may also be obtained using
759: .Qq ssh -Q key .
1.1 stevesk 760: .It Cm IgnoreRhosts
761: Specifies that
762: .Pa .rhosts
763: and
764: .Pa .shosts
765: files will not be used in
766: .Cm HostbasedAuthentication .
767: .Pp
768: .Pa /etc/hosts.equiv
769: and
770: .Pa /etc/shosts.equiv
771: are still used.
772: The default is
1.237 jmc 773: .Cm yes .
1.1 stevesk 774: .It Cm IgnoreUserKnownHosts
775: Specifies whether
1.52 jmc 776: .Xr sshd 8
1.1 stevesk 777: should ignore the user's
1.41 djm 778: .Pa ~/.ssh/known_hosts
1.1 stevesk 779: during
1.261 djm 780: .Cm HostbasedAuthentication
781: and use only the system-wide known hosts file
782: .Pa /etc/ssh/known_hosts .
1.1 stevesk 783: The default is
1.237 jmc 784: .Cm no .
1.129 djm 785: .It Cm IPQoS
786: Specifies the IPv4 type-of-service or DSCP class for the connection.
787: Accepted values are
1.237 jmc 788: .Cm af11 ,
789: .Cm af12 ,
790: .Cm af13 ,
791: .Cm af21 ,
792: .Cm af22 ,
793: .Cm af23 ,
794: .Cm af31 ,
795: .Cm af32 ,
796: .Cm af33 ,
797: .Cm af41 ,
798: .Cm af42 ,
799: .Cm af43 ,
800: .Cm cs0 ,
801: .Cm cs1 ,
802: .Cm cs2 ,
803: .Cm cs3 ,
804: .Cm cs4 ,
805: .Cm cs5 ,
806: .Cm cs6 ,
807: .Cm cs7 ,
808: .Cm ef ,
809: .Cm lowdelay ,
810: .Cm throughput ,
811: .Cm reliability ,
1.250 djm 812: a numeric value, or
813: .Cm none
814: to use the operating system default.
1.131 djm 815: This option may take one or two arguments, separated by whitespace.
1.129 djm 816: If one argument is specified, it is used as the packet class unconditionally.
817: If two values are specified, the first is automatically selected for
818: interactive sessions and the second for non-interactive sessions.
819: The default is
1.264 job 820: .Cm af21
1.265 jmc 821: (Low-Latency Data)
1.129 djm 822: for interactive sessions and
1.264 job 823: .Cm cs1
1.265 jmc 824: (Lower Effort)
1.129 djm 825: for non-interactive sessions.
1.171 jmc 826: .It Cm KbdInteractiveAuthentication
827: Specifies whether to allow keyboard-interactive authentication.
828: The argument to this keyword must be
1.237 jmc 829: .Cm yes
1.171 jmc 830: or
1.237 jmc 831: .Cm no .
1.171 jmc 832: The default is to use whatever value
833: .Cm ChallengeResponseAuthentication
834: is set to
835: (by default
1.237 jmc 836: .Cm yes ) .
1.1 stevesk 837: .It Cm KerberosAuthentication
1.24 markus 838: Specifies whether the password provided by the user for
1.1 stevesk 839: .Cm PasswordAuthentication
1.24 markus 840: will be validated through the Kerberos KDC.
1.1 stevesk 841: To use this option, the server needs a
842: Kerberos servtab which allows the verification of the KDC's identity.
1.52 jmc 843: The default is
1.237 jmc 844: .Cm no .
1.29 dtucker 845: .It Cm KerberosGetAFSToken
1.45 djm 846: If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire
1.29 dtucker 847: an AFS token before accessing the user's home directory.
1.52 jmc 848: The default is
1.237 jmc 849: .Cm no .
1.1 stevesk 850: .It Cm KerberosOrLocalPasswd
1.52 jmc 851: If password authentication through Kerberos fails then
1.1 stevesk 852: the password will be validated via any additional local mechanism
853: such as
854: .Pa /etc/passwd .
1.52 jmc 855: The default is
1.237 jmc 856: .Cm yes .
1.1 stevesk 857: .It Cm KerberosTicketCleanup
858: Specifies whether to automatically destroy the user's ticket cache
859: file on logout.
1.52 jmc 860: The default is
1.237 jmc 861: .Cm yes .
1.127 djm 862: .It Cm KexAlgorithms
863: Specifies the available KEX (Key Exchange) algorithms.
864: Multiple algorithms must be comma-separated.
1.208 djm 865: Alternately if the specified value begins with a
866: .Sq +
867: character, then the specified methods will be appended to the default set
868: instead of replacing them.
1.242 djm 869: If the specified value begins with a
870: .Sq -
871: character, then the specified methods (including wildcards) will be removed
872: from the default set instead of replacing them.
1.173 naddy 873: The supported algorithms are:
874: .Pp
875: .Bl -item -compact -offset indent
876: .It
1.234 djm 877: curve25519-sha256
878: .It
1.173 naddy 879: curve25519-sha256@libssh.org
880: .It
881: diffie-hellman-group1-sha1
882: .It
883: diffie-hellman-group14-sha1
884: .It
1.263 djm 885: diffie-hellman-group14-sha256
886: .It
887: diffie-hellman-group16-sha512
888: .It
889: diffie-hellman-group18-sha512
890: .It
1.173 naddy 891: diffie-hellman-group-exchange-sha1
892: .It
893: diffie-hellman-group-exchange-sha256
894: .It
895: ecdh-sha2-nistp256
896: .It
897: ecdh-sha2-nistp384
898: .It
899: ecdh-sha2-nistp521
900: .El
901: .Pp
902: The default is:
1.170 dtucker 903: .Bd -literal -offset indent
1.234 djm 904: curve25519-sha256,curve25519-sha256@libssh.org,
1.170 dtucker 905: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
906: diffie-hellman-group-exchange-sha256,
1.263 djm 907: diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,
908: diffie-hellman-group14-sha256,diffie-hellman-group14-sha1
1.170 dtucker 909: .Ed
1.188 djm 910: .Pp
1.237 jmc 911: The list of available key exchange algorithms may also be obtained using
912: .Qq ssh -Q kex .
1.1 stevesk 913: .It Cm ListenAddress
914: Specifies the local addresses
1.52 jmc 915: .Xr sshd 8
1.1 stevesk 916: should listen on.
917: The following forms may be used:
918: .Pp
919: .Bl -item -offset indent -compact
920: .It
921: .Cm ListenAddress
922: .Sm off
1.259 jmc 923: .Ar hostname | address
1.1 stevesk 924: .Sm on
1.260 jmc 925: .Op Cm rdomain Ar domain
1.1 stevesk 926: .It
927: .Cm ListenAddress
928: .Sm off
1.259 jmc 929: .Ar hostname : port
1.1 stevesk 930: .Sm on
1.260 jmc 931: .Op Cm rdomain Ar domain
1.256 djm 932: .It
933: .Cm ListenAddress
934: .Sm off
1.259 jmc 935: .Ar IPv4_address : port
1.256 djm 936: .Sm on
1.260 jmc 937: .Op Cm rdomain Ar domain
1.1 stevesk 938: .It
939: .Cm ListenAddress
940: .Sm off
1.259 jmc 941: .Oo Ar hostname | address Oc : Ar port
1.1 stevesk 942: .Sm on
1.260 jmc 943: .Op Cm rdomain Ar domain
1.1 stevesk 944: .El
945: .Pp
1.256 djm 946: The optional
947: .Cm rdomain
948: qualifier requests
949: .Xr sshd 8
950: listen in an explicit routing domain.
1.1 stevesk 951: If
952: .Ar port
953: is not specified,
1.200 dtucker 954: sshd will listen on the address and all
1.1 stevesk 955: .Cm Port
1.17 jmc 956: options specified.
1.256 djm 957: The default is to listen on all local addresses on the current default
958: routing domain.
1.15 jmc 959: Multiple
1.1 stevesk 960: .Cm ListenAddress
1.17 jmc 961: options are permitted.
1.256 djm 962: For more information on routing domains, see
1.259 jmc 963: .Xr rdomain 4 .
1.1 stevesk 964: .It Cm LoginGraceTime
965: The server disconnects after this time if the user has not
966: successfully logged in.
967: If the value is 0, there is no time limit.
1.12 stevesk 968: The default is 120 seconds.
1.1 stevesk 969: .It Cm LogLevel
970: Gives the verbosity level that is used when logging messages from
1.53 jmc 971: .Xr sshd 8 .
1.1 stevesk 972: The possible values are:
1.52 jmc 973: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.15 jmc 974: The default is INFO.
975: DEBUG and DEBUG1 are equivalent.
976: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
977: Logging with a DEBUG level violates the privacy of users and is not recommended.
1.1 stevesk 978: .It Cm MACs
979: Specifies the available MAC (message authentication code) algorithms.
1.219 jmc 980: The MAC algorithm is used for data integrity protection.
1.1 stevesk 981: Multiple algorithms must be comma-separated.
1.208 djm 982: If the specified value begins with a
983: .Sq +
984: character, then the specified algorithms will be appended to the default set
985: instead of replacing them.
1.242 djm 986: If the specified value begins with a
987: .Sq -
988: character, then the specified algorithms (including wildcards) will be removed
989: from the default set instead of replacing them.
1.208 djm 990: .Pp
1.152 markus 991: The algorithms that contain
1.237 jmc 992: .Qq -etm
1.152 markus 993: calculate the MAC after encryption (encrypt-then-mac).
994: These are considered safer and their use recommended.
1.173 naddy 995: The supported MACs are:
996: .Pp
997: .Bl -item -compact -offset indent
998: .It
999: hmac-md5
1000: .It
1001: hmac-md5-96
1002: .It
1003: hmac-sha1
1004: .It
1005: hmac-sha1-96
1006: .It
1007: hmac-sha2-256
1008: .It
1009: hmac-sha2-512
1010: .It
1011: umac-64@openssh.com
1012: .It
1013: umac-128@openssh.com
1014: .It
1015: hmac-md5-etm@openssh.com
1016: .It
1017: hmac-md5-96-etm@openssh.com
1018: .It
1019: hmac-sha1-etm@openssh.com
1020: .It
1021: hmac-sha1-96-etm@openssh.com
1022: .It
1023: hmac-sha2-256-etm@openssh.com
1024: .It
1025: hmac-sha2-512-etm@openssh.com
1026: .It
1027: umac-64-etm@openssh.com
1028: .It
1029: umac-128-etm@openssh.com
1030: .El
1031: .Pp
1.52 jmc 1032: The default is:
1.77 jmc 1033: .Bd -literal -offset indent
1.152 markus 1034: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1035: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.217 djm 1036: hmac-sha1-etm@openssh.com,
1.173 naddy 1037: umac-64@openssh.com,umac-128@openssh.com,
1.217 djm 1038: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.77 jmc 1039: .Ed
1.188 djm 1040: .Pp
1.237 jmc 1041: The list of available MAC algorithms may also be obtained using
1042: .Qq ssh -Q mac .
1.60 dtucker 1043: .It Cm Match
1.61 jmc 1044: Introduces a conditional block.
1.65 dtucker 1045: If all of the criteria on the
1.60 dtucker 1046: .Cm Match
1.65 dtucker 1047: line are satisfied, the keywords on the following lines override those
1048: set in the global section of the config file, until either another
1.60 dtucker 1049: .Cm Match
1.65 dtucker 1050: line or the end of the file.
1.172 djm 1051: If a keyword appears in multiple
1052: .Cm Match
1.177 sobrado 1053: blocks that are satisfied, only the first instance of the keyword is
1.172 djm 1054: applied.
1.91 djm 1055: .Pp
1.61 jmc 1056: The arguments to
1.60 dtucker 1057: .Cm Match
1.163 dtucker 1058: are one or more criteria-pattern pairs or the single token
1059: .Cm All
1060: which matches all criteria.
1.60 dtucker 1061: The available criteria are
1062: .Cm User ,
1.69 dtucker 1063: .Cm Group ,
1.60 dtucker 1064: .Cm Host ,
1.139 dtucker 1065: .Cm LocalAddress ,
1066: .Cm LocalPort ,
1.258 djm 1067: .Cm RDomain ,
1.60 dtucker 1068: and
1.258 djm 1069: .Cm Address
1070: (with
1071: .Cm RDomain
1072: representing the
1073: .Xr rdomain 4
1074: on which the connection was received.)
1075: .Pp
1.91 djm 1076: The match patterns may consist of single entries or comma-separated
1077: lists and may use the wildcard and negation operators described in the
1.237 jmc 1078: .Sx PATTERNS
1079: section of
1.92 djm 1080: .Xr ssh_config 5 .
1.91 djm 1081: .Pp
1082: The patterns in an
1083: .Cm Address
1084: criteria may additionally contain addresses to match in CIDR
1.237 jmc 1085: address/masklen format,
1086: such as 192.0.2.0/24 or 2001:db8::/32.
1.91 djm 1087: Note that the mask length provided must be consistent with the address -
1088: it is an error to specify a mask length that is too long for the address
1.93 jmc 1089: or one with bits set in this host portion of the address.
1.237 jmc 1090: For example, 192.0.2.0/33 and 192.0.2.0/8, respectively.
1.91 djm 1091: .Pp
1.60 dtucker 1092: Only a subset of keywords may be used on the lines following a
1093: .Cm Match
1094: keyword.
1095: Available keywords are
1.142 jmc 1096: .Cm AcceptEnv ,
1.99 okan 1097: .Cm AllowAgentForwarding ,
1.142 jmc 1098: .Cm AllowGroups ,
1.193 djm 1099: .Cm AllowStreamLocalForwarding ,
1.62 dtucker 1100: .Cm AllowTcpForwarding ,
1.141 markus 1101: .Cm AllowUsers ,
1.149 djm 1102: .Cm AuthenticationMethods ,
1.146 djm 1103: .Cm AuthorizedKeysCommand ,
1104: .Cm AuthorizedKeysCommandUser ,
1.147 jmc 1105: .Cm AuthorizedKeysFile ,
1.214 djm 1106: .Cm AuthorizedPrincipalsCommand ,
1107: .Cm AuthorizedPrincipalsCommandUser ,
1.123 djm 1108: .Cm AuthorizedPrincipalsFile ,
1.72 dtucker 1109: .Cm Banner ,
1.85 djm 1110: .Cm ChrootDirectory ,
1.238 markus 1111: .Cm ClientAliveCountMax ,
1112: .Cm ClientAliveInterval ,
1.141 markus 1113: .Cm DenyGroups ,
1114: .Cm DenyUsers ,
1.67 dtucker 1115: .Cm ForceCommand ,
1.194 djm 1116: .Cm GatewayPorts ,
1.193 djm 1117: .Cm GSSAPIAuthentication ,
1.189 djm 1118: .Cm HostbasedAcceptedKeyTypes ,
1.87 djm 1119: .Cm HostbasedAuthentication ,
1.123 djm 1120: .Cm HostbasedUsesNameFromPacketOnly ,
1.193 djm 1121: .Cm IPQoS ,
1.74 jmc 1122: .Cm KbdInteractiveAuthentication ,
1.72 dtucker 1123: .Cm KerberosAuthentication ,
1.245 djm 1124: .Cm LogLevel ,
1.95 dtucker 1125: .Cm MaxAuthTries ,
1.94 dtucker 1126: .Cm MaxSessions ,
1.72 dtucker 1127: .Cm PasswordAuthentication ,
1.97 djm 1128: .Cm PermitEmptyPasswords ,
1.66 dtucker 1129: .Cm PermitOpen ,
1.79 dtucker 1130: .Cm PermitRootLogin ,
1.164 djm 1131: .Cm PermitTTY ,
1.123 djm 1132: .Cm PermitTunnel ,
1.174 djm 1133: .Cm PermitUserRC ,
1.189 djm 1134: .Cm PubkeyAcceptedKeyTypes ,
1.107 dtucker 1135: .Cm PubkeyAuthentication ,
1.159 dtucker 1136: .Cm RekeyLimit ,
1.193 djm 1137: .Cm RevokedKeys ,
1.257 djm 1138: .Cm RDomain ,
1.193 djm 1139: .Cm StreamLocalBindMask ,
1140: .Cm StreamLocalBindUnlink ,
1141: .Cm TrustedUserCAKeys ,
1.66 dtucker 1142: .Cm X11DisplayOffset ,
1.101 djm 1143: .Cm X11Forwarding
1.60 dtucker 1144: and
1.102 djm 1145: .Cm X11UseLocalHost .
1.33 dtucker 1146: .It Cm MaxAuthTries
1147: Specifies the maximum number of authentication attempts permitted per
1.35 jmc 1148: connection.
1149: Once the number of failures reaches half this value,
1150: additional failures are logged.
1151: The default is 6.
1.90 djm 1152: .It Cm MaxSessions
1.216 djm 1153: Specifies the maximum number of open shell, login or subsystem (e.g. sftp)
1154: sessions permitted per network connection.
1155: Multiple sessions may be established by clients that support connection
1156: multiplexing.
1157: Setting
1158: .Cm MaxSessions
1159: to 1 will effectively disable session multiplexing, whereas setting it to 0
1160: will prevent all shell, login and subsystem sessions while still permitting
1161: forwarding.
1.90 djm 1162: The default is 10.
1.1 stevesk 1163: .It Cm MaxStartups
1164: Specifies the maximum number of concurrent unauthenticated connections to the
1.52 jmc 1165: SSH daemon.
1.1 stevesk 1166: Additional connections will be dropped until authentication succeeds or the
1167: .Cm LoginGraceTime
1168: expires for a connection.
1.156 dtucker 1169: The default is 10:30:100.
1.1 stevesk 1170: .Pp
1171: Alternatively, random early drop can be enabled by specifying
1172: the three colon separated values
1.237 jmc 1173: start:rate:full (e.g. "10:30:60").
1.53 jmc 1174: .Xr sshd 8
1.237 jmc 1175: will refuse connection attempts with a probability of rate/100 (30%)
1176: if there are currently start (10) unauthenticated connections.
1.1 stevesk 1177: The probability increases linearly and all connection attempts
1.237 jmc 1178: are refused if the number of unauthenticated connections reaches full (60).
1.1 stevesk 1179: .It Cm PasswordAuthentication
1180: Specifies whether password authentication is allowed.
1181: The default is
1.237 jmc 1182: .Cm yes .
1.1 stevesk 1183: .It Cm PermitEmptyPasswords
1184: When password authentication is allowed, it specifies whether the
1185: server allows login to accounts with empty password strings.
1186: The default is
1.237 jmc 1187: .Cm no .
1.62 dtucker 1188: .It Cm PermitOpen
1189: Specifies the destinations to which TCP port forwarding is permitted.
1190: The forwarding specification must be one of the following forms:
1191: .Pp
1192: .Bl -item -offset indent -compact
1193: .It
1194: .Cm PermitOpen
1195: .Sm off
1196: .Ar host : port
1197: .Sm on
1198: .It
1199: .Cm PermitOpen
1200: .Sm off
1201: .Ar IPv4_addr : port
1202: .Sm on
1203: .It
1204: .Cm PermitOpen
1205: .Sm off
1206: .Ar \&[ IPv6_addr \&] : port
1207: .Sm on
1208: .El
1209: .Pp
1.68 dtucker 1210: Multiple forwards may be specified by separating them with whitespace.
1.62 dtucker 1211: An argument of
1.237 jmc 1212: .Cm any
1.62 dtucker 1213: can be used to remove all restrictions and permit any forwarding requests.
1.140 dtucker 1214: An argument of
1.237 jmc 1215: .Cm none
1.140 dtucker 1216: can be used to prohibit all forwarding requests.
1.227 jmc 1217: The wildcard
1.237 jmc 1218: .Sq *
1.227 jmc 1219: can be used for host or port to allow all hosts or ports, respectively.
1.63 jmc 1220: By default all port forwarding requests are permitted.
1.1 stevesk 1221: .It Cm PermitRootLogin
1.38 jmc 1222: Specifies whether root can log in using
1.1 stevesk 1223: .Xr ssh 1 .
1224: The argument must be
1.237 jmc 1225: .Cm yes ,
1226: .Cm prohibit-password ,
1227: .Cm forced-commands-only ,
1.1 stevesk 1228: or
1.237 jmc 1229: .Cm no .
1.1 stevesk 1230: The default is
1.237 jmc 1231: .Cm prohibit-password .
1.1 stevesk 1232: .Pp
1233: If this option is set to
1.237 jmc 1234: .Cm prohibit-password
1.255 jmc 1235: (or its deprecated alias,
1236: .Cm without-password ) ,
1.210 deraadt 1237: password and keyboard-interactive authentication are disabled for root.
1.1 stevesk 1238: .Pp
1239: If this option is set to
1.237 jmc 1240: .Cm forced-commands-only ,
1.1 stevesk 1241: root login with public key authentication will be allowed,
1242: but only if the
1243: .Ar command
1244: option has been specified
1245: (which may be useful for taking remote backups even if root login is
1.17 jmc 1246: normally not allowed).
1247: All other authentication methods are disabled for root.
1.1 stevesk 1248: .Pp
1249: If this option is set to
1.237 jmc 1250: .Cm no ,
1.38 jmc 1251: root is not allowed to log in.
1.231 jmc 1252: .It Cm PermitTTY
1253: Specifies whether
1254: .Xr pty 4
1255: allocation is permitted.
1256: The default is
1.237 jmc 1257: .Cm yes .
1.46 reyk 1258: .It Cm PermitTunnel
1259: Specifies whether
1260: .Xr tun 4
1261: device forwarding is allowed.
1.47 reyk 1262: The argument must be
1.237 jmc 1263: .Cm yes ,
1264: .Cm point-to-point
1.58 stevesk 1265: (layer 3),
1.237 jmc 1266: .Cm ethernet
1.58 stevesk 1267: (layer 2), or
1.237 jmc 1268: .Cm no .
1.58 stevesk 1269: Specifying
1.237 jmc 1270: .Cm yes
1.58 stevesk 1271: permits both
1.237 jmc 1272: .Cm point-to-point
1.58 stevesk 1273: and
1.237 jmc 1274: .Cm ethernet .
1.46 reyk 1275: The default is
1.237 jmc 1276: .Cm no .
1.178 djm 1277: .Pp
1278: Independent of this setting, the permissions of the selected
1279: .Xr tun 4
1280: device must allow access to the user.
1.6 markus 1281: .It Cm PermitUserEnvironment
1282: Specifies whether
1283: .Pa ~/.ssh/environment
1.9 stevesk 1284: and
1.6 markus 1285: .Cm environment=
1286: options in
1287: .Pa ~/.ssh/authorized_keys
1.9 stevesk 1288: are processed by
1.52 jmc 1289: .Xr sshd 8 .
1.6 markus 1290: The default is
1.237 jmc 1291: .Cm no .
1.9 stevesk 1292: Enabling environment processing may enable users to bypass access
1293: restrictions in some configurations using mechanisms such as
1294: .Ev LD_PRELOAD .
1.174 djm 1295: .It Cm PermitUserRC
1296: Specifies whether any
1297: .Pa ~/.ssh/rc
1298: file is executed.
1299: The default is
1.237 jmc 1300: .Cm yes .
1.1 stevesk 1301: .It Cm PidFile
1.4 stevesk 1302: Specifies the file that contains the process ID of the
1.195 dtucker 1303: SSH daemon, or
1.237 jmc 1304: .Cm none
1.195 dtucker 1305: to not write one.
1.1 stevesk 1306: The default is
1307: .Pa /var/run/sshd.pid .
1308: .It Cm Port
1309: Specifies the port number that
1.52 jmc 1310: .Xr sshd 8
1.1 stevesk 1311: listens on.
1312: The default is 22.
1313: Multiple options of this type are permitted.
1314: See also
1315: .Cm ListenAddress .
1316: .It Cm PrintLastLog
1317: Specifies whether
1.52 jmc 1318: .Xr sshd 8
1.36 jaredy 1319: should print the date and time of the last user login when a user logs
1320: in interactively.
1.1 stevesk 1321: The default is
1.237 jmc 1322: .Cm yes .
1.1 stevesk 1323: .It Cm PrintMotd
1324: Specifies whether
1.52 jmc 1325: .Xr sshd 8
1.1 stevesk 1326: should print
1327: .Pa /etc/motd
1328: when a user logs in interactively.
1329: (On some systems it is also printed by the shell,
1330: .Pa /etc/profile ,
1331: or equivalent.)
1332: The default is
1.237 jmc 1333: .Cm yes .
1.189 djm 1334: .It Cm PubkeyAcceptedKeyTypes
1335: Specifies the key types that will be accepted for public key authentication
1336: as a comma-separated pattern list.
1.208 djm 1337: Alternately if the specified value begins with a
1338: .Sq +
1339: character, then the specified key types will be appended to the default set
1340: instead of replacing them.
1.242 djm 1341: If the specified value begins with a
1342: .Sq -
1343: character, then the specified key types (including wildcards) will be removed
1344: from the default set instead of replacing them.
1.206 markus 1345: The default for this option is:
1346: .Bd -literal -offset 3n
1347: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1348: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1349: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1350: ssh-ed25519-cert-v01@openssh.com,
1351: ssh-rsa-cert-v01@openssh.com,
1352: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.220 djm 1353: ssh-ed25519,ssh-rsa
1.206 markus 1354: .Ed
1355: .Pp
1.237 jmc 1356: The list of available key types may also be obtained using
1357: .Qq ssh -Q key .
1.1 stevesk 1358: .It Cm PubkeyAuthentication
1359: Specifies whether public key authentication is allowed.
1360: The default is
1.237 jmc 1361: .Cm yes .
1.159 dtucker 1362: .It Cm RekeyLimit
1363: Specifies the maximum amount of data that may be transmitted before the
1364: session key is renegotiated, optionally followed a maximum amount of
1365: time that may pass before the session key is renegotiated.
1366: The first argument is specified in bytes and may have a suffix of
1367: .Sq K ,
1368: .Sq M ,
1369: or
1370: .Sq G
1371: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1372: The default is between
1373: .Sq 1G
1374: and
1375: .Sq 4G ,
1376: depending on the cipher.
1377: The optional second value is specified in seconds and may use any of the
1378: units documented in the
1379: .Sx TIME FORMATS
1.160 jmc 1380: section.
1.159 dtucker 1381: The default value for
1382: .Cm RekeyLimit
1383: is
1.237 jmc 1384: .Cm default none ,
1.159 dtucker 1385: which means that rekeying is performed after the cipher's default amount
1386: of data has been sent or received and no time based rekeying is done.
1.118 djm 1387: .It Cm RevokedKeys
1.195 dtucker 1388: Specifies revoked public keys file, or
1.237 jmc 1389: .Cm none
1.195 dtucker 1390: to not use one.
1.118 djm 1391: Keys listed in this file will be refused for public key authentication.
1392: Note that if this file is not readable, then public key authentication will
1393: be refused for all users.
1.154 djm 1394: Keys may be specified as a text file, listing one public key per line, or as
1395: an OpenSSH Key Revocation List (KRL) as generated by
1.155 jmc 1396: .Xr ssh-keygen 1 .
1.161 jmc 1397: For more information on KRLs, see the KEY REVOCATION LISTS section in
1.154 djm 1398: .Xr ssh-keygen 1 .
1.257 djm 1399: .It Cm RDomain
1400: Specifies an explicit routing domain that is applied after authentication
1401: has completed.
1.259 jmc 1402: The user session, as well and any forwarded or listening IP sockets,
1403: will be bound to this
1.257 djm 1404: .Xr rdomain 4 .
1405: If the routing domain is set to
1406: .Cm \&%D ,
1.259 jmc 1407: then the domain in which the incoming connection was received will be applied.
1.175 millert 1408: .It Cm StreamLocalBindMask
1409: Sets the octal file creation mode mask
1410: .Pq umask
1411: used when creating a Unix-domain socket file for local or remote
1412: port forwarding.
1413: This option is only used for port forwarding to a Unix-domain socket file.
1414: .Pp
1415: The default value is 0177, which creates a Unix-domain socket file that is
1416: readable and writable only by the owner.
1417: Note that not all operating systems honor the file mode on Unix-domain
1418: socket files.
1419: .It Cm StreamLocalBindUnlink
1420: Specifies whether to remove an existing Unix-domain socket file for local
1421: or remote port forwarding before creating a new one.
1422: If the socket file already exists and
1423: .Cm StreamLocalBindUnlink
1424: is not enabled,
1425: .Nm sshd
1426: will be unable to forward the port to the Unix-domain socket file.
1427: This option is only used for port forwarding to a Unix-domain socket file.
1428: .Pp
1429: The argument must be
1.237 jmc 1430: .Cm yes
1.175 millert 1431: or
1.237 jmc 1432: .Cm no .
1.175 millert 1433: The default is
1.237 jmc 1434: .Cm no .
1.1 stevesk 1435: .It Cm StrictModes
1436: Specifies whether
1.52 jmc 1437: .Xr sshd 8
1.1 stevesk 1438: should check file modes and ownership of the
1439: user's files and home directory before accepting login.
1440: This is normally desirable because novices sometimes accidentally leave their
1441: directory or files world-writable.
1442: The default is
1.237 jmc 1443: .Cm yes .
1.112 djm 1444: Note that this does not apply to
1445: .Cm ChrootDirectory ,
1446: whose permissions and ownership are checked unconditionally.
1.1 stevesk 1447: .It Cm Subsystem
1.51 jmc 1448: Configures an external subsystem (e.g. file transfer daemon).
1.59 djm 1449: Arguments should be a subsystem name and a command (with optional arguments)
1450: to execute upon subsystem request.
1.80 djm 1451: .Pp
1.1 stevesk 1452: The command
1.237 jmc 1453: .Cm sftp-server
1454: implements the SFTP file transfer subsystem.
1.80 djm 1455: .Pp
1456: Alternately the name
1.237 jmc 1457: .Cm internal-sftp
1458: implements an in-process SFTP server.
1.80 djm 1459: This may simplify configurations using
1460: .Cm ChrootDirectory
1461: to force a different filesystem root on clients.
1462: .Pp
1.1 stevesk 1463: By default no subsystems are defined.
1464: .It Cm SyslogFacility
1465: Gives the facility code that is used when logging messages from
1.53 jmc 1466: .Xr sshd 8 .
1.1 stevesk 1467: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1468: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1469: The default is AUTH.
1.27 markus 1470: .It Cm TCPKeepAlive
1471: Specifies whether the system should send TCP keepalive messages to the
1472: other side.
1473: If they are sent, death of the connection or crash of one
1474: of the machines will be properly noticed.
1475: However, this means that
1476: connections will die if the route is down temporarily, and some people
1477: find it annoying.
1478: On the other hand, if TCP keepalives are not sent,
1479: sessions may hang indefinitely on the server, leaving
1.237 jmc 1480: .Qq ghost
1.27 markus 1481: users and consuming server resources.
1482: .Pp
1483: The default is
1.237 jmc 1484: .Cm yes
1.27 markus 1485: (to send TCP keepalive messages), and the server will notice
1486: if the network goes down or the client host crashes.
1487: This avoids infinitely hanging sessions.
1488: .Pp
1489: To disable TCP keepalive messages, the value should be set to
1.237 jmc 1490: .Cm no .
1.118 djm 1491: .It Cm TrustedUserCAKeys
1492: Specifies a file containing public keys of certificate authorities that are
1.195 dtucker 1493: trusted to sign user certificates for authentication, or
1.237 jmc 1494: .Cm none
1.195 dtucker 1495: to not use one.
1.119 jmc 1496: Keys are listed one per line; empty lines and comments starting with
1.118 djm 1497: .Ql #
1498: are allowed.
1499: If a certificate is presented for authentication and has its signing CA key
1500: listed in this file, then it may be used for authentication for any user
1501: listed in the certificate's principals list.
1502: Note that certificates that lack a list of principals will not be permitted
1503: for authentication using
1504: .Cm TrustedUserCAKeys .
1.161 jmc 1505: For more details on certificates, see the CERTIFICATES section in
1.118 djm 1506: .Xr ssh-keygen 1 .
1.18 markus 1507: .It Cm UseDNS
1508: Specifies whether
1.52 jmc 1509: .Xr sshd 8
1.207 djm 1510: should look up the remote host name, and to check that
1.18 markus 1511: the resolved host name for the remote IP address maps back to the
1512: very same IP address.
1.207 djm 1513: .Pp
1514: If this option is set to
1.237 jmc 1515: .Cm no
1.207 djm 1516: (the default) then only addresses and not host names may be used in
1.221 djm 1517: .Pa ~/.ssh/authorized_keys
1.207 djm 1518: .Cm from
1519: and
1.211 jmc 1520: .Nm
1.207 djm 1521: .Cm Match
1522: .Cm Host
1523: directives.
1.137 djm 1524: .It Cm VersionAddendum
1525: Optionally specifies additional text to append to the SSH protocol banner
1526: sent by the server upon connection.
1527: The default is
1.237 jmc 1528: .Cm none .
1.1 stevesk 1529: .It Cm X11DisplayOffset
1530: Specifies the first display number available for
1.52 jmc 1531: .Xr sshd 8 Ns 's
1.1 stevesk 1532: X11 forwarding.
1.52 jmc 1533: This prevents sshd from interfering with real X11 servers.
1.1 stevesk 1534: The default is 10.
1535: .It Cm X11Forwarding
1536: Specifies whether X11 forwarding is permitted.
1.13 stevesk 1537: The argument must be
1.237 jmc 1538: .Cm yes
1.13 stevesk 1539: or
1.237 jmc 1540: .Cm no .
1.1 stevesk 1541: The default is
1.237 jmc 1542: .Cm no .
1.13 stevesk 1543: .Pp
1544: When X11 forwarding is enabled, there may be additional exposure to
1545: the server and to client displays if the
1.52 jmc 1546: .Xr sshd 8
1.13 stevesk 1547: proxy display is configured to listen on the wildcard address (see
1.237 jmc 1548: .Cm X11UseLocalhost ) ,
1549: though this is not the default.
1.13 stevesk 1550: Additionally, the authentication spoofing and authentication data
1551: verification and substitution occur on the client side.
1552: The security risk of using X11 forwarding is that the client's X11
1.52 jmc 1553: display server may be exposed to attack when the SSH client requests
1.13 stevesk 1554: forwarding (see the warnings for
1555: .Cm ForwardX11
1556: in
1.19 jmc 1557: .Xr ssh_config 5 ) .
1.13 stevesk 1558: A system administrator may have a stance in which they want to
1559: protect clients that may expose themselves to attack by unwittingly
1560: requesting X11 forwarding, which can warrant a
1.237 jmc 1561: .Cm no
1.13 stevesk 1562: setting.
1563: .Pp
1564: Note that disabling X11 forwarding does not prevent users from
1565: forwarding X11 traffic, as users can always install their own forwarders.
1.1 stevesk 1566: .It Cm X11UseLocalhost
1567: Specifies whether
1.52 jmc 1568: .Xr sshd 8
1.1 stevesk 1569: should bind the X11 forwarding server to the loopback address or to
1.15 jmc 1570: the wildcard address.
1571: By default,
1.52 jmc 1572: sshd binds the forwarding server to the loopback address and sets the
1.1 stevesk 1573: hostname part of the
1574: .Ev DISPLAY
1575: environment variable to
1.237 jmc 1576: .Cm localhost .
1.8 stevesk 1577: This prevents remote hosts from connecting to the proxy display.
1.1 stevesk 1578: However, some older X11 clients may not function with this
1579: configuration.
1580: .Cm X11UseLocalhost
1581: may be set to
1.237 jmc 1582: .Cm no
1.1 stevesk 1583: to specify that the forwarding server should be bound to the wildcard
1584: address.
1585: The argument must be
1.237 jmc 1586: .Cm yes
1.1 stevesk 1587: or
1.237 jmc 1588: .Cm no .
1.1 stevesk 1589: The default is
1.237 jmc 1590: .Cm yes .
1.1 stevesk 1591: .It Cm XAuthLocation
1.11 stevesk 1592: Specifies the full pathname of the
1.1 stevesk 1593: .Xr xauth 1
1.195 dtucker 1594: program, or
1.237 jmc 1595: .Cm none
1.195 dtucker 1596: to not use one.
1.1 stevesk 1597: The default is
1598: .Pa /usr/X11R6/bin/xauth .
1599: .El
1.55 jmc 1600: .Sh TIME FORMATS
1.53 jmc 1601: .Xr sshd 8
1.1 stevesk 1602: command-line arguments and configuration file options that specify time
1603: may be expressed using a sequence of the form:
1604: .Sm off
1.7 stevesk 1605: .Ar time Op Ar qualifier ,
1.1 stevesk 1606: .Sm on
1607: where
1608: .Ar time
1609: is a positive integer value and
1610: .Ar qualifier
1611: is one of the following:
1612: .Pp
1613: .Bl -tag -width Ds -compact -offset indent
1.64 jmc 1614: .It Aq Cm none
1.1 stevesk 1615: seconds
1616: .It Cm s | Cm S
1617: seconds
1618: .It Cm m | Cm M
1619: minutes
1620: .It Cm h | Cm H
1621: hours
1622: .It Cm d | Cm D
1623: days
1624: .It Cm w | Cm W
1625: weeks
1626: .El
1627: .Pp
1628: Each member of the sequence is added together to calculate
1629: the total time value.
1630: .Pp
1631: Time format examples:
1632: .Pp
1633: .Bl -tag -width Ds -compact -offset indent
1634: .It 600
1635: 600 seconds (10 minutes)
1636: .It 10m
1637: 10 minutes
1638: .It 1h30m
1639: 1 hour 30 minutes (90 minutes)
1640: .El
1.235 jmc 1641: .Sh TOKENS
1642: Arguments to some keywords can make use of tokens,
1643: which are expanded at runtime:
1644: .Pp
1645: .Bl -tag -width XXXX -offset indent -compact
1646: .It %%
1647: A literal
1648: .Sq % .
1.257 djm 1649: .It \&%D
1650: The routing domain in which the incoming connection was received.
1.235 jmc 1651: .It %F
1652: The fingerprint of the CA key.
1653: .It %f
1654: The fingerprint of the key or certificate.
1655: .It %h
1656: The home directory of the user.
1657: .It %i
1658: The key ID in the certificate.
1659: .It %K
1660: The base64-encoded CA key.
1661: .It %k
1662: The base64-encoded key or certificate for authentication.
1663: .It %s
1664: The serial number of the certificate.
1665: .It \&%T
1666: The type of the CA key.
1667: .It %t
1668: The key or certificate type.
1.268 ! jmc 1669: .It \&%U
! 1670: The numeric user ID of the target user.
1.235 jmc 1671: .It %u
1672: The username.
1673: .El
1674: .Pp
1675: .Cm AuthorizedKeysCommand
1.267 djm 1676: accepts the tokens %%, %f, %h, %k, %t, %U and %u.
1.235 jmc 1677: .Pp
1678: .Cm AuthorizedKeysFile
1.267 djm 1679: accepts the tokens %%, %h, %U and %u.
1.235 jmc 1680: .Pp
1681: .Cm AuthorizedPrincipalsCommand
1.267 djm 1682: accepts the tokens %%, %F, %f, %h, %i, %K, %k, %s, %T, %t, %U and %u.
1.235 jmc 1683: .Pp
1684: .Cm AuthorizedPrincipalsFile
1.267 djm 1685: accepts the tokens %%, %h, and %U %u.
1.235 jmc 1686: .Pp
1687: .Cm ChrootDirectory
1.267 djm 1688: accepts the tokens %%, %h, and %U %u.
1.257 djm 1689: .Pp
1690: .Cm RoutingDomain
1691: accepts the token %D.
1.1 stevesk 1692: .Sh FILES
1693: .Bl -tag -width Ds
1694: .It Pa /etc/ssh/sshd_config
1695: Contains configuration data for
1.53 jmc 1696: .Xr sshd 8 .
1.1 stevesk 1697: This file should be writable by root only, but it is recommended
1698: (though not necessary) that it be world-readable.
1699: .El
1.19 jmc 1700: .Sh SEE ALSO
1.237 jmc 1701: .Xr sftp-server 8 ,
1.19 jmc 1702: .Xr sshd 8
1.1 stevesk 1703: .Sh AUTHORS
1.237 jmc 1704: .An -nosplit
1.1 stevesk 1705: OpenSSH is a derivative of the original and free
1.237 jmc 1706: ssh 1.2.12 release by
1707: .An Tatu Ylonen .
1708: .An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos ,
1709: .An Theo de Raadt
1710: and
1711: .An Dug Song
1.1 stevesk 1712: removed many bugs, re-added newer features and
1713: created OpenSSH.
1.237 jmc 1714: .An Markus Friedl
1715: contributed the support for SSH protocol versions 1.5 and 2.0.
1716: .An Niels Provos
1717: and
1718: .An Markus Friedl
1719: contributed support for privilege separation.
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