Annotation of src/usr.bin/ssh/sshd_config.5, Revision 1.154
1.1 stevesk 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
18: .\" are met:
19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
22: .\" notice, this list of conditions and the following disclaimer in the
23: .\" documentation and/or other materials provided with the distribution.
24: .\"
25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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1.154 ! djm 36: .\" $OpenBSD: sshd_config.5,v 1.153 2013/01/08 18:49:04 markus Exp $
! 37: .Dd $Mdocdate: January 8 2013 $
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.
1.150 djm 127: The available options are
128: .Dq yes
129: or
130: .Dq all
131: to allow TCP forwarding,
132: .Dq no
133: to prevent all TCP forwarding,
134: .Dq local
135: to allow local (from the perspective of
1.151 jmc 136: .Xr ssh 1 )
137: forwarding only or
1.150 djm 138: .Dq remote
139: to allow remote forwarding only.
1.1 stevesk 140: The default is
141: .Dq yes .
142: Note that disabling TCP forwarding does not improve security unless
143: users are also denied shell access, as they can always install their
144: own forwarders.
145: .It Cm AllowUsers
146: This keyword can be followed by a list of user name patterns, separated
147: by spaces.
1.14 jmc 148: If specified, login is allowed only for user names that
1.1 stevesk 149: match one of the patterns.
150: Only user names are valid; a numerical user ID is not recognized.
151: By default, login is allowed for all users.
152: If the pattern takes the form USER@HOST then USER and HOST
153: are separately checked, restricting logins to particular
154: users from particular hosts.
1.54 jmc 155: The allow/deny directives are processed in the following order:
156: .Cm DenyUsers ,
157: .Cm AllowUsers ,
158: .Cm DenyGroups ,
159: and finally
160: .Cm AllowGroups .
1.49 jmc 161: .Pp
162: See
163: .Sx PATTERNS
164: in
165: .Xr ssh_config 5
166: for more information on patterns.
1.149 djm 167: .It Cm AuthenticationMethods
168: Specifies the authentication methods that must be successfully completed
169: for a user to be granted access.
170: This option must be followed by one or more comma-separated lists of
171: authentication method names.
172: Successful authentication requires completion of every method in at least
173: one of these lists.
174: .Pp
175: For example, an argument of
176: .Dq publickey,password publickey,keyboard-interactive
177: would require the user to complete public key authentication, followed by
178: either password or keyboard interactive authentication.
179: Only methods that are next in one or more lists are offered at each stage,
180: so for this example, it would not be possible to attempt password or
181: keyboard-interactive authentication before public key.
182: .Pp
183: This option is only available for SSH protocol 2 and will yield a fatal
184: error if enabled if protocol 1 is also enabled.
185: Note that each authentication method listed should also be explicitly enabled
186: in the configuration.
187: The default is not to require multiple authentication; successful completion
188: of a single authentication method is sufficient.
1.146 djm 189: .It Cm AuthorizedKeysCommand
1.147 jmc 190: Specifies a program to be used to look up the user's public keys.
1.146 djm 191: The program will be invoked with a single argument of the username
192: being authenticated, and should produce on standard output zero or
1.147 jmc 193: more lines of authorized_keys output (see
194: .Sx AUTHORIZED_KEYS
195: in
196: .Xr sshd 8 ) .
1.146 djm 197: If a key supplied by AuthorizedKeysCommand does not successfully authenticate
198: and authorize the user then public key authentication continues using the usual
199: .Cm AuthorizedKeysFile
200: files.
201: By default, no AuthorizedKeysCommand is run.
202: .It Cm AuthorizedKeysCommandUser
203: Specifies the user under whose account the AuthorizedKeysCommand is run.
204: It is recommended to use a dedicated user that has no other role on the host
205: than running authorized keys commands.
1.1 stevesk 206: .It Cm AuthorizedKeysFile
207: Specifies the file that contains the public keys that can be used
208: for user authentication.
1.124 djm 209: The format is described in the
210: .Sx AUTHORIZED_KEYS FILE FORMAT
211: section of
212: .Xr sshd 8 .
1.1 stevesk 213: .Cm AuthorizedKeysFile
214: may contain tokens of the form %T which are substituted during connection
1.52 jmc 215: setup.
1.17 jmc 216: The following tokens are defined: %% is replaced by a literal '%',
1.52 jmc 217: %h is replaced by the home directory of the user being authenticated, and
1.1 stevesk 218: %u is replaced by the username of that user.
219: After expansion,
220: .Cm AuthorizedKeysFile
221: is taken to be an absolute path or one relative to the user's home
222: directory.
1.133 jmc 223: Multiple files may be listed, separated by whitespace.
224: The default is
225: .Dq .ssh/authorized_keys .ssh/authorized_keys2 .
1.121 djm 226: .It Cm AuthorizedPrincipalsFile
227: Specifies a file that lists principal names that are accepted for
228: certificate authentication.
229: When using certificates signed by a key listed in
230: .Cm TrustedUserCAKeys ,
231: this file lists names, one of which must appear in the certificate for it
232: to be accepted for authentication.
1.125 jmc 233: Names are listed one per line preceded by key options (as described
1.124 djm 234: in
235: .Sx AUTHORIZED_KEYS FILE FORMAT
236: in
1.125 jmc 237: .Xr sshd 8 ) .
1.124 djm 238: Empty lines and comments starting with
1.121 djm 239: .Ql #
240: are ignored.
241: .Pp
242: .Cm AuthorizedPrincipalsFile
243: may contain tokens of the form %T which are substituted during connection
244: setup.
245: The following tokens are defined: %% is replaced by a literal '%',
246: %h is replaced by the home directory of the user being authenticated, and
247: %u is replaced by the username of that user.
248: After expansion,
249: .Cm AuthorizedPrincipalsFile
250: is taken to be an absolute path or one relative to the user's home
251: directory.
252: .Pp
1.138 djm 253: The default is
254: .Dq none ,
255: i.e. not to use a principals file \(en in this case, the username
1.121 djm 256: of the user must appear in a certificate's principals list for it to be
257: accepted.
258: Note that
259: .Cm AuthorizedPrincipalsFile
260: is only used when authentication proceeds using a CA listed in
261: .Cm TrustedUserCAKeys
262: and is not consulted for certification authorities trusted via
263: .Pa ~/.ssh/authorized_keys ,
264: though the
265: .Cm principals=
266: key option offers a similar facility (see
267: .Xr sshd 8
268: for details).
1.1 stevesk 269: .It Cm Banner
270: The contents of the specified file are sent to the remote user before
271: authentication is allowed.
1.78 djm 272: If the argument is
273: .Dq none
274: then no banner is displayed.
1.1 stevesk 275: This option is only available for protocol version 2.
276: By default, no banner is displayed.
277: .It Cm ChallengeResponseAuthentication
1.50 jmc 278: Specifies whether challenge-response authentication is allowed.
1.1 stevesk 279: All authentication styles from
280: .Xr login.conf 5
281: are supported.
282: The default is
283: .Dq yes .
1.80 djm 284: .It Cm ChrootDirectory
1.113 stevesk 285: Specifies the pathname of a directory to
1.80 djm 286: .Xr chroot 2
287: to after authentication.
1.113 stevesk 288: All components of the pathname must be root-owned directories that are
1.80 djm 289: not writable by any other user or group.
1.106 stevesk 290: After the chroot,
291: .Xr sshd 8
292: changes the working directory to the user's home directory.
1.80 djm 293: .Pp
1.113 stevesk 294: The pathname may contain the following tokens that are expanded at runtime once
1.80 djm 295: the connecting user has been authenticated: %% is replaced by a literal '%',
296: %h is replaced by the home directory of the user being authenticated, and
297: %u is replaced by the username of that user.
298: .Pp
299: The
300: .Cm ChrootDirectory
301: must contain the necessary files and directories to support the
1.103 stevesk 302: user's session.
1.80 djm 303: For an interactive session this requires at least a shell, typically
304: .Xr sh 1 ,
305: and basic
306: .Pa /dev
307: nodes such as
308: .Xr null 4 ,
309: .Xr zero 4 ,
310: .Xr stdin 4 ,
311: .Xr stdout 4 ,
312: .Xr stderr 4 ,
313: .Xr arandom 4
314: and
315: .Xr tty 4
316: devices.
317: For file transfer sessions using
1.105 jmc 318: .Dq sftp ,
1.80 djm 319: no additional configuration of the environment is necessary if the
1.105 jmc 320: in-process sftp server is used,
321: though sessions which use logging do require
1.104 stevesk 322: .Pa /dev/log
323: inside the chroot directory (see
324: .Xr sftp-server 8
1.81 jmc 325: for details).
1.80 djm 326: .Pp
327: The default is not to
328: .Xr chroot 2 .
1.1 stevesk 329: .It Cm Ciphers
330: Specifies the ciphers allowed for protocol version 2.
331: Multiple ciphers must be comma-separated.
1.34 dtucker 332: The supported ciphers are
333: .Dq 3des-cbc ,
334: .Dq aes128-cbc ,
335: .Dq aes192-cbc ,
336: .Dq aes256-cbc ,
337: .Dq aes128-ctr ,
338: .Dq aes192-ctr ,
339: .Dq aes256-ctr ,
1.153 markus 340: .Dq aes128-gcm@openssh.com ,
341: .Dq aes256-gcm@openssh.com ,
1.43 djm 342: .Dq arcfour128 ,
343: .Dq arcfour256 ,
1.34 dtucker 344: .Dq arcfour ,
345: .Dq blowfish-cbc ,
346: and
347: .Dq cast128-cbc .
1.52 jmc 348: The default is:
349: .Bd -literal -offset 3n
1.100 naddy 350: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
1.153 markus 351: aes128-gcm@openssh.com,aes256-gcm@openssh.com,
1.100 naddy 352: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
353: aes256-cbc,arcfour
1.1 stevesk 354: .Ed
355: .It Cm ClientAliveCountMax
1.48 jmc 356: Sets the number of client alive messages (see below) which may be
1.1 stevesk 357: sent without
1.52 jmc 358: .Xr sshd 8
1.17 jmc 359: receiving any messages back from the client.
360: If this threshold is reached while client alive messages are being sent,
1.52 jmc 361: sshd will disconnect the client, terminating the session.
1.17 jmc 362: It is important to note that the use of client alive messages is very
363: different from
1.27 markus 364: .Cm TCPKeepAlive
1.17 jmc 365: (below).
366: The client alive messages are sent through the encrypted channel
367: and therefore will not be spoofable.
368: The TCP keepalive option enabled by
1.27 markus 369: .Cm TCPKeepAlive
1.17 jmc 370: is spoofable.
371: The client alive mechanism is valuable when the client or
1.1 stevesk 372: server depend on knowing when a connection has become inactive.
373: .Pp
1.17 jmc 374: The default value is 3.
375: If
1.1 stevesk 376: .Cm ClientAliveInterval
1.48 jmc 377: (see below) is set to 15, and
1.1 stevesk 378: .Cm ClientAliveCountMax
1.52 jmc 379: is left at the default, unresponsive SSH clients
1.1 stevesk 380: will be disconnected after approximately 45 seconds.
1.57 markus 381: This option applies to protocol version 2 only.
1.42 djm 382: .It Cm ClientAliveInterval
383: Sets a timeout interval in seconds after which if no data has been received
384: from the client,
1.52 jmc 385: .Xr sshd 8
1.42 djm 386: will send a message through the encrypted
387: channel to request a response from the client.
388: The default
389: is 0, indicating that these messages will not be sent to the client.
390: This option applies to protocol version 2 only.
1.3 markus 391: .It Cm Compression
1.44 markus 392: Specifies whether compression is allowed, or delayed until
393: the user has authenticated successfully.
1.3 markus 394: The argument must be
1.44 markus 395: .Dq yes ,
396: .Dq delayed ,
1.3 markus 397: or
398: .Dq no .
399: The default is
1.44 markus 400: .Dq delayed .
1.1 stevesk 401: .It Cm DenyGroups
402: This keyword can be followed by a list of group name patterns, separated
403: by spaces.
404: Login is disallowed for users whose primary group or supplementary
405: group list matches one of the patterns.
406: Only group names are valid; a numerical group ID is not recognized.
407: By default, login is allowed for all groups.
1.54 jmc 408: The allow/deny directives are processed in the following order:
409: .Cm DenyUsers ,
410: .Cm AllowUsers ,
411: .Cm DenyGroups ,
412: and finally
413: .Cm AllowGroups .
1.49 jmc 414: .Pp
415: See
416: .Sx PATTERNS
417: in
418: .Xr ssh_config 5
419: for more information on patterns.
1.1 stevesk 420: .It Cm DenyUsers
421: This keyword can be followed by a list of user name patterns, separated
422: by spaces.
423: Login is disallowed for user names that match one of the patterns.
424: Only user names are valid; a numerical user ID is not recognized.
425: By default, login is allowed for all users.
426: If the pattern takes the form USER@HOST then USER and HOST
427: are separately checked, restricting logins to particular
428: users from particular hosts.
1.54 jmc 429: The allow/deny directives are processed in the following order:
430: .Cm DenyUsers ,
431: .Cm AllowUsers ,
432: .Cm DenyGroups ,
433: and finally
434: .Cm AllowGroups .
1.49 jmc 435: .Pp
436: See
437: .Sx PATTERNS
438: in
439: .Xr ssh_config 5
440: for more information on patterns.
1.67 dtucker 441: .It Cm ForceCommand
442: Forces the execution of the command specified by
443: .Cm ForceCommand ,
1.84 djm 444: ignoring any command supplied by the client and
445: .Pa ~/.ssh/rc
446: if present.
1.67 dtucker 447: The command is invoked by using the user's login shell with the -c option.
448: This applies to shell, command, or subsystem execution.
449: It is most useful inside a
450: .Cm Match
451: block.
452: The command originally supplied by the client is available in the
453: .Ev SSH_ORIGINAL_COMMAND
454: environment variable.
1.82 djm 455: Specifying a command of
456: .Dq internal-sftp
457: will force the use of an in-process sftp server that requires no support
458: files when used with
459: .Cm ChrootDirectory .
1.1 stevesk 460: .It Cm GatewayPorts
461: Specifies whether remote hosts are allowed to connect to ports
462: forwarded for the client.
463: By default,
1.52 jmc 464: .Xr sshd 8
1.15 jmc 465: binds remote port forwardings to the loopback address.
466: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 467: .Cm GatewayPorts
1.52 jmc 468: can be used to specify that sshd
1.39 djm 469: should allow remote port forwardings to bind to non-loopback addresses, thus
470: allowing other hosts to connect.
471: The argument may be
472: .Dq no
473: to force remote port forwardings to be available to the local host only,
1.1 stevesk 474: .Dq yes
1.39 djm 475: to force remote port forwardings to bind to the wildcard address, or
476: .Dq clientspecified
477: to allow the client to select the address to which the forwarding is bound.
1.1 stevesk 478: The default is
479: .Dq no .
1.23 markus 480: .It Cm GSSAPIAuthentication
1.25 markus 481: Specifies whether user authentication based on GSSAPI is allowed.
1.26 djm 482: The default is
1.23 markus 483: .Dq no .
484: Note that this option applies to protocol version 2 only.
485: .It Cm GSSAPICleanupCredentials
486: Specifies whether to automatically destroy the user's credentials cache
487: on logout.
488: The default is
489: .Dq yes .
490: Note that this option applies to protocol version 2 only.
1.1 stevesk 491: .It Cm HostbasedAuthentication
492: Specifies whether rhosts or /etc/hosts.equiv authentication together
493: with successful public key client host authentication is allowed
1.50 jmc 494: (host-based authentication).
1.1 stevesk 495: This option is similar to
496: .Cm RhostsRSAAuthentication
497: and applies to protocol version 2 only.
1.70 dtucker 498: The default is
499: .Dq no .
500: .It Cm HostbasedUsesNameFromPacketOnly
501: Specifies whether or not the server will attempt to perform a reverse
502: name lookup when matching the name in the
503: .Pa ~/.shosts ,
504: .Pa ~/.rhosts ,
505: and
506: .Pa /etc/hosts.equiv
507: files during
508: .Cm HostbasedAuthentication .
509: A setting of
510: .Dq yes
511: means that
512: .Xr sshd 8
513: uses the name supplied by the client rather than
514: attempting to resolve the name from the TCP connection itself.
1.1 stevesk 515: The default is
516: .Dq no .
1.117 djm 517: .It Cm HostCertificate
518: Specifies a file containing a public host certificate.
519: The certificate's public key must match a private host key already specified
520: by
521: .Cm HostKey .
522: The default behaviour of
523: .Xr sshd 8
524: is not to load any certificates.
1.1 stevesk 525: .It Cm HostKey
526: Specifies a file containing a private host key
527: used by SSH.
528: The default is
529: .Pa /etc/ssh/ssh_host_key
530: for protocol version 1, and
1.126 djm 531: .Pa /etc/ssh/ssh_host_dsa_key ,
532: .Pa /etc/ssh/ssh_host_ecdsa_key
533: and
1.1 stevesk 534: .Pa /etc/ssh/ssh_host_rsa_key
535: for protocol version 2.
536: Note that
1.52 jmc 537: .Xr sshd 8
1.1 stevesk 538: will refuse to use a file if it is group/world-accessible.
539: It is possible to have multiple host key files.
540: .Dq rsa1
541: keys are used for version 1 and
1.126 djm 542: .Dq dsa ,
543: .Dq ecdsa
1.1 stevesk 544: or
545: .Dq rsa
546: are used for version 2 of the SSH protocol.
547: .It Cm IgnoreRhosts
548: Specifies that
549: .Pa .rhosts
550: and
551: .Pa .shosts
552: files will not be used in
553: .Cm RhostsRSAAuthentication
554: or
555: .Cm HostbasedAuthentication .
556: .Pp
557: .Pa /etc/hosts.equiv
558: and
559: .Pa /etc/shosts.equiv
560: are still used.
561: The default is
562: .Dq yes .
563: .It Cm IgnoreUserKnownHosts
564: Specifies whether
1.52 jmc 565: .Xr sshd 8
1.1 stevesk 566: should ignore the user's
1.41 djm 567: .Pa ~/.ssh/known_hosts
1.1 stevesk 568: during
569: .Cm RhostsRSAAuthentication
570: or
571: .Cm HostbasedAuthentication .
572: The default is
573: .Dq no .
1.129 djm 574: .It Cm IPQoS
575: Specifies the IPv4 type-of-service or DSCP class for the connection.
576: Accepted values are
577: .Dq af11 ,
578: .Dq af12 ,
579: .Dq af13 ,
1.136 djm 580: .Dq af21 ,
1.129 djm 581: .Dq af22 ,
582: .Dq af23 ,
583: .Dq af31 ,
584: .Dq af32 ,
585: .Dq af33 ,
586: .Dq af41 ,
587: .Dq af42 ,
588: .Dq af43 ,
589: .Dq cs0 ,
590: .Dq cs1 ,
591: .Dq cs2 ,
592: .Dq cs3 ,
593: .Dq cs4 ,
594: .Dq cs5 ,
595: .Dq cs6 ,
596: .Dq cs7 ,
597: .Dq ef ,
598: .Dq lowdelay ,
599: .Dq throughput ,
600: .Dq reliability ,
601: or a numeric value.
1.131 djm 602: This option may take one or two arguments, separated by whitespace.
1.129 djm 603: If one argument is specified, it is used as the packet class unconditionally.
604: If two values are specified, the first is automatically selected for
605: interactive sessions and the second for non-interactive sessions.
606: The default is
607: .Dq lowdelay
608: for interactive sessions and
609: .Dq throughput
610: for non-interactive sessions.
1.1 stevesk 611: .It Cm KerberosAuthentication
1.24 markus 612: Specifies whether the password provided by the user for
1.1 stevesk 613: .Cm PasswordAuthentication
1.24 markus 614: will be validated through the Kerberos KDC.
1.1 stevesk 615: To use this option, the server needs a
616: Kerberos servtab which allows the verification of the KDC's identity.
1.52 jmc 617: The default is
1.29 dtucker 618: .Dq no .
619: .It Cm KerberosGetAFSToken
1.45 djm 620: If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire
1.29 dtucker 621: an AFS token before accessing the user's home directory.
1.52 jmc 622: The default is
1.1 stevesk 623: .Dq no .
624: .It Cm KerberosOrLocalPasswd
1.52 jmc 625: If password authentication through Kerberos fails then
1.1 stevesk 626: the password will be validated via any additional local mechanism
627: such as
628: .Pa /etc/passwd .
1.52 jmc 629: The default is
1.1 stevesk 630: .Dq yes .
631: .It Cm KerberosTicketCleanup
632: Specifies whether to automatically destroy the user's ticket cache
633: file on logout.
1.52 jmc 634: The default is
1.1 stevesk 635: .Dq yes .
1.127 djm 636: .It Cm KexAlgorithms
637: Specifies the available KEX (Key Exchange) algorithms.
638: Multiple algorithms must be comma-separated.
639: The default is
640: .Dq ecdh-sha2-nistp256 ,
641: .Dq ecdh-sha2-nistp384 ,
642: .Dq ecdh-sha2-nistp521 ,
1.130 jmc 643: .Dq diffie-hellman-group-exchange-sha256 ,
1.127 djm 644: .Dq diffie-hellman-group-exchange-sha1 ,
645: .Dq diffie-hellman-group14-sha1 ,
646: .Dq diffie-hellman-group1-sha1 .
1.1 stevesk 647: .It Cm KeyRegenerationInterval
648: In protocol version 1, the ephemeral server key is automatically regenerated
649: after this many seconds (if it has been used).
650: The purpose of regeneration is to prevent
651: decrypting captured sessions by later breaking into the machine and
652: stealing the keys.
653: The key is never stored anywhere.
654: If the value is 0, the key is never regenerated.
655: The default is 3600 (seconds).
656: .It Cm ListenAddress
657: Specifies the local addresses
1.52 jmc 658: .Xr sshd 8
1.1 stevesk 659: should listen on.
660: The following forms may be used:
661: .Pp
662: .Bl -item -offset indent -compact
663: .It
664: .Cm ListenAddress
665: .Sm off
666: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
667: .Sm on
668: .It
669: .Cm ListenAddress
670: .Sm off
671: .Ar host No | Ar IPv4_addr No : Ar port
672: .Sm on
673: .It
674: .Cm ListenAddress
675: .Sm off
676: .Oo
677: .Ar host No | Ar IPv6_addr Oc : Ar port
678: .Sm on
679: .El
680: .Pp
681: If
682: .Ar port
683: is not specified,
1.52 jmc 684: sshd will listen on the address and all prior
1.1 stevesk 685: .Cm Port
1.17 jmc 686: options specified.
687: The default is to listen on all local addresses.
1.15 jmc 688: Multiple
1.1 stevesk 689: .Cm ListenAddress
1.17 jmc 690: options are permitted.
691: Additionally, any
1.1 stevesk 692: .Cm Port
1.52 jmc 693: options must precede this option for non-port qualified addresses.
1.1 stevesk 694: .It Cm LoginGraceTime
695: The server disconnects after this time if the user has not
696: successfully logged in.
697: If the value is 0, there is no time limit.
1.12 stevesk 698: The default is 120 seconds.
1.1 stevesk 699: .It Cm LogLevel
700: Gives the verbosity level that is used when logging messages from
1.53 jmc 701: .Xr sshd 8 .
1.1 stevesk 702: The possible values are:
1.52 jmc 703: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.15 jmc 704: The default is INFO.
705: DEBUG and DEBUG1 are equivalent.
706: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
707: Logging with a DEBUG level violates the privacy of users and is not recommended.
1.1 stevesk 708: .It Cm MACs
709: Specifies the available MAC (message authentication code) algorithms.
710: The MAC algorithm is used in protocol version 2
711: for data integrity protection.
712: Multiple algorithms must be comma-separated.
1.152 markus 713: The algorithms that contain
714: .Dq -etm
715: calculate the MAC after encryption (encrypt-then-mac).
716: These are considered safer and their use recommended.
1.52 jmc 717: The default is:
1.77 jmc 718: .Bd -literal -offset indent
1.152 markus 719: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
720: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
721: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
722: hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,
723: hmac-md5-96-etm@openssh.com,
1.145 markus 724: hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
1.144 naddy 725: hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
726: hmac-sha1-96,hmac-md5-96
1.77 jmc 727: .Ed
1.60 dtucker 728: .It Cm Match
1.61 jmc 729: Introduces a conditional block.
1.65 dtucker 730: If all of the criteria on the
1.60 dtucker 731: .Cm Match
1.65 dtucker 732: line are satisfied, the keywords on the following lines override those
733: set in the global section of the config file, until either another
1.60 dtucker 734: .Cm Match
1.65 dtucker 735: line or the end of the file.
1.91 djm 736: .Pp
1.61 jmc 737: The arguments to
1.60 dtucker 738: .Cm Match
1.65 dtucker 739: are one or more criteria-pattern pairs.
1.60 dtucker 740: The available criteria are
741: .Cm User ,
1.69 dtucker 742: .Cm Group ,
1.60 dtucker 743: .Cm Host ,
1.139 dtucker 744: .Cm LocalAddress ,
745: .Cm LocalPort ,
1.60 dtucker 746: and
747: .Cm Address .
1.91 djm 748: The match patterns may consist of single entries or comma-separated
749: lists and may use the wildcard and negation operators described in the
1.92 djm 750: .Sx PATTERNS
1.91 djm 751: section of
1.92 djm 752: .Xr ssh_config 5 .
1.91 djm 753: .Pp
754: The patterns in an
755: .Cm Address
756: criteria may additionally contain addresses to match in CIDR
1.93 jmc 757: address/masklen format, e.g.\&
1.91 djm 758: .Dq 192.0.2.0/24
759: or
760: .Dq 3ffe:ffff::/32 .
761: Note that the mask length provided must be consistent with the address -
762: it is an error to specify a mask length that is too long for the address
1.93 jmc 763: or one with bits set in this host portion of the address.
764: For example,
1.91 djm 765: .Dq 192.0.2.0/33
766: and
1.93 jmc 767: .Dq 192.0.2.0/8
1.91 djm 768: respectively.
769: .Pp
1.60 dtucker 770: Only a subset of keywords may be used on the lines following a
771: .Cm Match
772: keyword.
773: Available keywords are
1.142 jmc 774: .Cm AcceptEnv ,
1.99 okan 775: .Cm AllowAgentForwarding ,
1.142 jmc 776: .Cm AllowGroups ,
1.62 dtucker 777: .Cm AllowTcpForwarding ,
1.141 markus 778: .Cm AllowUsers ,
1.149 djm 779: .Cm AuthenticationMethods ,
1.146 djm 780: .Cm AuthorizedKeysCommand ,
781: .Cm AuthorizedKeysCommandUser ,
1.147 jmc 782: .Cm AuthorizedKeysFile ,
1.123 djm 783: .Cm AuthorizedPrincipalsFile ,
1.72 dtucker 784: .Cm Banner ,
1.85 djm 785: .Cm ChrootDirectory ,
1.141 markus 786: .Cm DenyGroups ,
787: .Cm DenyUsers ,
1.67 dtucker 788: .Cm ForceCommand ,
1.142 jmc 789: .Cm GatewayPorts ,
1.141 markus 790: .Cm GSSAPIAuthentication ,
1.87 djm 791: .Cm HostbasedAuthentication ,
1.123 djm 792: .Cm HostbasedUsesNameFromPacketOnly ,
1.74 jmc 793: .Cm KbdInteractiveAuthentication ,
1.72 dtucker 794: .Cm KerberosAuthentication ,
1.95 dtucker 795: .Cm MaxAuthTries ,
1.94 dtucker 796: .Cm MaxSessions ,
1.72 dtucker 797: .Cm PasswordAuthentication ,
1.97 djm 798: .Cm PermitEmptyPasswords ,
1.66 dtucker 799: .Cm PermitOpen ,
1.79 dtucker 800: .Cm PermitRootLogin ,
1.123 djm 801: .Cm PermitTunnel ,
1.107 dtucker 802: .Cm PubkeyAuthentication ,
1.142 jmc 803: .Cm RhostsRSAAuthentication ,
1.141 markus 804: .Cm RSAAuthentication ,
1.66 dtucker 805: .Cm X11DisplayOffset ,
1.101 djm 806: .Cm X11Forwarding
1.60 dtucker 807: and
1.102 djm 808: .Cm X11UseLocalHost .
1.33 dtucker 809: .It Cm MaxAuthTries
810: Specifies the maximum number of authentication attempts permitted per
1.35 jmc 811: connection.
812: Once the number of failures reaches half this value,
813: additional failures are logged.
814: The default is 6.
1.90 djm 815: .It Cm MaxSessions
816: Specifies the maximum number of open sessions permitted per network connection.
817: The default is 10.
1.1 stevesk 818: .It Cm MaxStartups
819: Specifies the maximum number of concurrent unauthenticated connections to the
1.52 jmc 820: SSH daemon.
1.1 stevesk 821: Additional connections will be dropped until authentication succeeds or the
822: .Cm LoginGraceTime
823: expires for a connection.
824: The default is 10.
825: .Pp
826: Alternatively, random early drop can be enabled by specifying
827: the three colon separated values
828: .Dq start:rate:full
1.51 jmc 829: (e.g. "10:30:60").
1.53 jmc 830: .Xr sshd 8
1.1 stevesk 831: will refuse connection attempts with a probability of
832: .Dq rate/100
833: (30%)
834: if there are currently
835: .Dq start
836: (10)
837: unauthenticated connections.
838: The probability increases linearly and all connection attempts
839: are refused if the number of unauthenticated connections reaches
840: .Dq full
841: (60).
842: .It Cm PasswordAuthentication
843: Specifies whether password authentication is allowed.
844: The default is
845: .Dq yes .
846: .It Cm PermitEmptyPasswords
847: When password authentication is allowed, it specifies whether the
848: server allows login to accounts with empty password strings.
849: The default is
850: .Dq no .
1.62 dtucker 851: .It Cm PermitOpen
852: Specifies the destinations to which TCP port forwarding is permitted.
853: The forwarding specification must be one of the following forms:
854: .Pp
855: .Bl -item -offset indent -compact
856: .It
857: .Cm PermitOpen
858: .Sm off
859: .Ar host : port
860: .Sm on
861: .It
862: .Cm PermitOpen
863: .Sm off
864: .Ar IPv4_addr : port
865: .Sm on
866: .It
867: .Cm PermitOpen
868: .Sm off
869: .Ar \&[ IPv6_addr \&] : port
870: .Sm on
871: .El
872: .Pp
1.68 dtucker 873: Multiple forwards may be specified by separating them with whitespace.
1.62 dtucker 874: An argument of
875: .Dq any
876: can be used to remove all restrictions and permit any forwarding requests.
1.140 dtucker 877: An argument of
878: .Dq none
879: can be used to prohibit all forwarding requests.
1.63 jmc 880: By default all port forwarding requests are permitted.
1.1 stevesk 881: .It Cm PermitRootLogin
1.38 jmc 882: Specifies whether root can log in using
1.1 stevesk 883: .Xr ssh 1 .
884: The argument must be
885: .Dq yes ,
886: .Dq without-password ,
1.52 jmc 887: .Dq forced-commands-only ,
1.1 stevesk 888: or
889: .Dq no .
890: The default is
891: .Dq yes .
892: .Pp
893: If this option is set to
1.52 jmc 894: .Dq without-password ,
1.1 stevesk 895: password authentication is disabled for root.
896: .Pp
897: If this option is set to
1.52 jmc 898: .Dq forced-commands-only ,
1.1 stevesk 899: root login with public key authentication will be allowed,
900: but only if the
901: .Ar command
902: option has been specified
903: (which may be useful for taking remote backups even if root login is
1.17 jmc 904: normally not allowed).
905: All other authentication methods are disabled for root.
1.1 stevesk 906: .Pp
907: If this option is set to
1.52 jmc 908: .Dq no ,
1.38 jmc 909: root is not allowed to log in.
1.46 reyk 910: .It Cm PermitTunnel
911: Specifies whether
912: .Xr tun 4
913: device forwarding is allowed.
1.47 reyk 914: The argument must be
915: .Dq yes ,
1.58 stevesk 916: .Dq point-to-point
917: (layer 3),
918: .Dq ethernet
919: (layer 2), or
1.47 reyk 920: .Dq no .
1.58 stevesk 921: Specifying
922: .Dq yes
923: permits both
924: .Dq point-to-point
925: and
926: .Dq ethernet .
1.46 reyk 927: The default is
928: .Dq no .
1.6 markus 929: .It Cm PermitUserEnvironment
930: Specifies whether
931: .Pa ~/.ssh/environment
1.9 stevesk 932: and
1.6 markus 933: .Cm environment=
934: options in
935: .Pa ~/.ssh/authorized_keys
1.9 stevesk 936: are processed by
1.52 jmc 937: .Xr sshd 8 .
1.6 markus 938: The default is
939: .Dq no .
1.9 stevesk 940: Enabling environment processing may enable users to bypass access
941: restrictions in some configurations using mechanisms such as
942: .Ev LD_PRELOAD .
1.1 stevesk 943: .It Cm PidFile
1.4 stevesk 944: Specifies the file that contains the process ID of the
1.53 jmc 945: SSH daemon.
1.1 stevesk 946: The default is
947: .Pa /var/run/sshd.pid .
948: .It Cm Port
949: Specifies the port number that
1.52 jmc 950: .Xr sshd 8
1.1 stevesk 951: listens on.
952: The default is 22.
953: Multiple options of this type are permitted.
954: See also
955: .Cm ListenAddress .
956: .It Cm PrintLastLog
957: Specifies whether
1.52 jmc 958: .Xr sshd 8
1.36 jaredy 959: should print the date and time of the last user login when a user logs
960: in interactively.
1.1 stevesk 961: The default is
962: .Dq yes .
963: .It Cm PrintMotd
964: Specifies whether
1.52 jmc 965: .Xr sshd 8
1.1 stevesk 966: should print
967: .Pa /etc/motd
968: when a user logs in interactively.
969: (On some systems it is also printed by the shell,
970: .Pa /etc/profile ,
971: or equivalent.)
972: The default is
973: .Dq yes .
974: .It Cm Protocol
975: Specifies the protocol versions
1.52 jmc 976: .Xr sshd 8
1.5 stevesk 977: supports.
1.1 stevesk 978: The possible values are
1.52 jmc 979: .Sq 1
1.1 stevesk 980: and
1.52 jmc 981: .Sq 2 .
1.1 stevesk 982: Multiple versions must be comma-separated.
983: The default is
1.109 jmc 984: .Sq 2 .
1.5 stevesk 985: Note that the order of the protocol list does not indicate preference,
986: because the client selects among multiple protocol versions offered
987: by the server.
988: Specifying
989: .Dq 2,1
990: is identical to
991: .Dq 1,2 .
1.1 stevesk 992: .It Cm PubkeyAuthentication
993: Specifies whether public key authentication is allowed.
994: The default is
995: .Dq yes .
996: Note that this option applies to protocol version 2 only.
1.118 djm 997: .It Cm RevokedKeys
1.154 ! djm 998: Specifies revoked public keys.
1.118 djm 999: Keys listed in this file will be refused for public key authentication.
1000: Note that if this file is not readable, then public key authentication will
1001: be refused for all users.
1.154 ! djm 1002: Keys may be specified as a text file, listing one public key per line, or as
! 1003: an OpenSSH Key Revocation List (KRL) as generated by
! 1004: .Xr ssh-keygen 1
! 1005: For more information on KRLs, see the
! 1006: .Sx KEY REVOCATION LISTS
! 1007: section in
! 1008: .Xr ssh-keygen 1 .
1.1 stevesk 1009: .It Cm RhostsRSAAuthentication
1010: Specifies whether rhosts or /etc/hosts.equiv authentication together
1011: with successful RSA host authentication is allowed.
1012: The default is
1013: .Dq no .
1014: This option applies to protocol version 1 only.
1015: .It Cm RSAAuthentication
1016: Specifies whether pure RSA authentication is allowed.
1017: The default is
1018: .Dq yes .
1019: This option applies to protocol version 1 only.
1020: .It Cm ServerKeyBits
1021: Defines the number of bits in the ephemeral protocol version 1 server key.
1.96 djm 1022: The minimum value is 512, and the default is 1024.
1.1 stevesk 1023: .It Cm StrictModes
1024: Specifies whether
1.52 jmc 1025: .Xr sshd 8
1.1 stevesk 1026: should check file modes and ownership of the
1027: user's files and home directory before accepting login.
1028: This is normally desirable because novices sometimes accidentally leave their
1029: directory or files world-writable.
1030: The default is
1031: .Dq yes .
1.112 djm 1032: Note that this does not apply to
1033: .Cm ChrootDirectory ,
1034: whose permissions and ownership are checked unconditionally.
1.1 stevesk 1035: .It Cm Subsystem
1.51 jmc 1036: Configures an external subsystem (e.g. file transfer daemon).
1.59 djm 1037: Arguments should be a subsystem name and a command (with optional arguments)
1038: to execute upon subsystem request.
1.80 djm 1039: .Pp
1.1 stevesk 1040: The command
1041: .Xr sftp-server 8
1042: implements the
1043: .Dq sftp
1044: file transfer subsystem.
1.80 djm 1045: .Pp
1046: Alternately the name
1047: .Dq internal-sftp
1048: implements an in-process
1049: .Dq sftp
1050: server.
1051: This may simplify configurations using
1052: .Cm ChrootDirectory
1053: to force a different filesystem root on clients.
1054: .Pp
1.1 stevesk 1055: By default no subsystems are defined.
1056: Note that this option applies to protocol version 2 only.
1057: .It Cm SyslogFacility
1058: Gives the facility code that is used when logging messages from
1.53 jmc 1059: .Xr sshd 8 .
1.1 stevesk 1060: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1061: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1062: The default is AUTH.
1.27 markus 1063: .It Cm TCPKeepAlive
1064: Specifies whether the system should send TCP keepalive messages to the
1065: other side.
1066: If they are sent, death of the connection or crash of one
1067: of the machines will be properly noticed.
1068: However, this means that
1069: connections will die if the route is down temporarily, and some people
1070: find it annoying.
1071: On the other hand, if TCP keepalives are not sent,
1072: sessions may hang indefinitely on the server, leaving
1073: .Dq ghost
1074: users and consuming server resources.
1075: .Pp
1076: The default is
1077: .Dq yes
1078: (to send TCP keepalive messages), and the server will notice
1079: if the network goes down or the client host crashes.
1080: This avoids infinitely hanging sessions.
1081: .Pp
1082: To disable TCP keepalive messages, the value should be set to
1083: .Dq no .
1.118 djm 1084: .It Cm TrustedUserCAKeys
1085: Specifies a file containing public keys of certificate authorities that are
1.120 djm 1086: trusted to sign user certificates for authentication.
1.119 jmc 1087: Keys are listed one per line; empty lines and comments starting with
1.118 djm 1088: .Ql #
1089: are allowed.
1090: If a certificate is presented for authentication and has its signing CA key
1091: listed in this file, then it may be used for authentication for any user
1092: listed in the certificate's principals list.
1093: Note that certificates that lack a list of principals will not be permitted
1094: for authentication using
1095: .Cm TrustedUserCAKeys .
1.119 jmc 1096: For more details on certificates, see the
1.118 djm 1097: .Sx CERTIFICATES
1098: section in
1099: .Xr ssh-keygen 1 .
1.18 markus 1100: .It Cm UseDNS
1101: Specifies whether
1.52 jmc 1102: .Xr sshd 8
1.40 jmc 1103: should look up the remote host name and check that
1.18 markus 1104: the resolved host name for the remote IP address maps back to the
1105: very same IP address.
1106: The default is
1107: .Dq yes .
1.1 stevesk 1108: .It Cm UseLogin
1109: Specifies whether
1110: .Xr login 1
1111: is used for interactive login sessions.
1112: The default is
1113: .Dq no .
1114: Note that
1115: .Xr login 1
1116: is never used for remote command execution.
1117: Note also, that if this is enabled,
1118: .Cm X11Forwarding
1119: will be disabled because
1120: .Xr login 1
1121: does not know how to handle
1122: .Xr xauth 1
1.15 jmc 1123: cookies.
1124: If
1.1 stevesk 1125: .Cm UsePrivilegeSeparation
1126: is specified, it will be disabled after authentication.
1127: .It Cm UsePrivilegeSeparation
1128: Specifies whether
1.52 jmc 1129: .Xr sshd 8
1.2 stevesk 1130: separates privileges by creating an unprivileged child process
1.15 jmc 1131: to deal with incoming network traffic.
1132: After successful authentication, another process will be created that has
1133: the privilege of the authenticated user.
1134: The goal of privilege separation is to prevent privilege
1.1 stevesk 1135: escalation by containing any corruption within the unprivileged processes.
1136: The default is
1137: .Dq yes .
1.134 djm 1138: If
1139: .Cm UsePrivilegeSeparation
1140: is set to
1141: .Dq sandbox
1142: then the pre-authentication unprivileged process is subject to additional
1143: restrictions.
1.137 djm 1144: .It Cm VersionAddendum
1145: Optionally specifies additional text to append to the SSH protocol banner
1146: sent by the server upon connection.
1147: The default is
1148: .Dq none .
1.1 stevesk 1149: .It Cm X11DisplayOffset
1150: Specifies the first display number available for
1.52 jmc 1151: .Xr sshd 8 Ns 's
1.1 stevesk 1152: X11 forwarding.
1.52 jmc 1153: This prevents sshd from interfering with real X11 servers.
1.1 stevesk 1154: The default is 10.
1155: .It Cm X11Forwarding
1156: Specifies whether X11 forwarding is permitted.
1.13 stevesk 1157: The argument must be
1158: .Dq yes
1159: or
1160: .Dq no .
1.1 stevesk 1161: The default is
1162: .Dq no .
1.13 stevesk 1163: .Pp
1164: When X11 forwarding is enabled, there may be additional exposure to
1165: the server and to client displays if the
1.52 jmc 1166: .Xr sshd 8
1.13 stevesk 1167: proxy display is configured to listen on the wildcard address (see
1168: .Cm X11UseLocalhost
1.52 jmc 1169: below), though this is not the default.
1.13 stevesk 1170: Additionally, the authentication spoofing and authentication data
1171: verification and substitution occur on the client side.
1172: The security risk of using X11 forwarding is that the client's X11
1.52 jmc 1173: display server may be exposed to attack when the SSH client requests
1.13 stevesk 1174: forwarding (see the warnings for
1175: .Cm ForwardX11
1176: in
1.19 jmc 1177: .Xr ssh_config 5 ) .
1.13 stevesk 1178: A system administrator may have a stance in which they want to
1179: protect clients that may expose themselves to attack by unwittingly
1180: requesting X11 forwarding, which can warrant a
1181: .Dq no
1182: setting.
1183: .Pp
1184: Note that disabling X11 forwarding does not prevent users from
1185: forwarding X11 traffic, as users can always install their own forwarders.
1.1 stevesk 1186: X11 forwarding is automatically disabled if
1187: .Cm UseLogin
1188: is enabled.
1189: .It Cm X11UseLocalhost
1190: Specifies whether
1.52 jmc 1191: .Xr sshd 8
1.1 stevesk 1192: should bind the X11 forwarding server to the loopback address or to
1.15 jmc 1193: the wildcard address.
1194: By default,
1.52 jmc 1195: sshd binds the forwarding server to the loopback address and sets the
1.1 stevesk 1196: hostname part of the
1197: .Ev DISPLAY
1198: environment variable to
1199: .Dq localhost .
1.8 stevesk 1200: This prevents remote hosts from connecting to the proxy display.
1.1 stevesk 1201: However, some older X11 clients may not function with this
1202: configuration.
1203: .Cm X11UseLocalhost
1204: may be set to
1205: .Dq no
1206: to specify that the forwarding server should be bound to the wildcard
1207: address.
1208: The argument must be
1209: .Dq yes
1210: or
1211: .Dq no .
1212: The default is
1213: .Dq yes .
1214: .It Cm XAuthLocation
1.11 stevesk 1215: Specifies the full pathname of the
1.1 stevesk 1216: .Xr xauth 1
1217: program.
1218: The default is
1219: .Pa /usr/X11R6/bin/xauth .
1220: .El
1.55 jmc 1221: .Sh TIME FORMATS
1.53 jmc 1222: .Xr sshd 8
1.1 stevesk 1223: command-line arguments and configuration file options that specify time
1224: may be expressed using a sequence of the form:
1225: .Sm off
1.7 stevesk 1226: .Ar time Op Ar qualifier ,
1.1 stevesk 1227: .Sm on
1228: where
1229: .Ar time
1230: is a positive integer value and
1231: .Ar qualifier
1232: is one of the following:
1233: .Pp
1234: .Bl -tag -width Ds -compact -offset indent
1.64 jmc 1235: .It Aq Cm none
1.1 stevesk 1236: seconds
1237: .It Cm s | Cm S
1238: seconds
1239: .It Cm m | Cm M
1240: minutes
1241: .It Cm h | Cm H
1242: hours
1243: .It Cm d | Cm D
1244: days
1245: .It Cm w | Cm W
1246: weeks
1247: .El
1248: .Pp
1249: Each member of the sequence is added together to calculate
1250: the total time value.
1251: .Pp
1252: Time format examples:
1253: .Pp
1254: .Bl -tag -width Ds -compact -offset indent
1255: .It 600
1256: 600 seconds (10 minutes)
1257: .It 10m
1258: 10 minutes
1259: .It 1h30m
1260: 1 hour 30 minutes (90 minutes)
1261: .El
1262: .Sh FILES
1263: .Bl -tag -width Ds
1264: .It Pa /etc/ssh/sshd_config
1265: Contains configuration data for
1.53 jmc 1266: .Xr sshd 8 .
1.1 stevesk 1267: This file should be writable by root only, but it is recommended
1268: (though not necessary) that it be world-readable.
1269: .El
1.19 jmc 1270: .Sh SEE ALSO
1271: .Xr sshd 8
1.1 stevesk 1272: .Sh AUTHORS
1273: OpenSSH is a derivative of the original and free
1274: ssh 1.2.12 release by Tatu Ylonen.
1275: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1276: Theo de Raadt and Dug Song
1277: removed many bugs, re-added newer features and
1278: created OpenSSH.
1279: Markus Friedl contributed the support for SSH
1280: protocol versions 1.5 and 2.0.
1281: Niels Provos and Markus Friedl contributed support
1282: for privilege separation.
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