Annotation of src/usr.bin/ssh/sshd_config.5, Revision 1.152
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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1.152 ! markus 36: .\" $OpenBSD: sshd_config.5,v 1.151 2012/12/03 08:33:03 jmc Exp $
! 37: .Dd $Mdocdate: December 3 2012 $
1.1 stevesk 38: .Dt SSHD_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm sshd_config
42: .Nd OpenSSH SSH daemon configuration file
43: .Sh SYNOPSIS
1.71 jmc 44: .Nm /etc/ssh/sshd_config
1.1 stevesk 45: .Sh DESCRIPTION
1.53 jmc 46: .Xr sshd 8
1.1 stevesk 47: reads configuration data from
48: .Pa /etc/ssh/sshd_config
49: (or the file specified with
50: .Fl f
51: on the command line).
52: The file contains keyword-argument pairs, one per line.
53: Lines starting with
54: .Ql #
55: and empty lines are interpreted as comments.
1.56 dtucker 56: Arguments may optionally be enclosed in double quotes
57: .Pq \&"
58: in order to represent arguments containing spaces.
1.1 stevesk 59: .Pp
60: The possible
61: keywords and their meanings are as follows (note that
62: keywords are case-insensitive and arguments are case-sensitive):
63: .Bl -tag -width Ds
1.30 djm 64: .It Cm AcceptEnv
65: Specifies what environment variables sent by the client will be copied into
66: the session's
67: .Xr environ 7 .
68: See
69: .Cm SendEnv
70: in
71: .Xr ssh_config 5
72: for how to configure the client.
1.31 djm 73: Note that environment passing is only supported for protocol 2.
1.30 djm 74: Variables are specified by name, which may contain the wildcard characters
1.51 jmc 75: .Ql *
1.30 djm 76: and
77: .Ql \&? .
1.31 djm 78: Multiple environment variables may be separated by whitespace or spread
1.30 djm 79: across multiple
80: .Cm AcceptEnv
81: directives.
1.31 djm 82: Be warned that some environment variables could be used to bypass restricted
1.30 djm 83: user environments.
84: For this reason, care should be taken in the use of this directive.
85: The default is not to accept any environment variables.
1.37 djm 86: .It Cm AddressFamily
87: Specifies which address family should be used by
1.53 jmc 88: .Xr sshd 8 .
1.37 djm 89: Valid arguments are
90: .Dq any ,
91: .Dq inet
1.52 jmc 92: (use IPv4 only), or
1.37 djm 93: .Dq inet6
94: (use IPv6 only).
95: The default is
96: .Dq any .
1.89 jmc 97: .It Cm AllowAgentForwarding
98: Specifies whether
99: .Xr ssh-agent 1
100: forwarding is permitted.
101: The default is
102: .Dq yes .
103: Note that disabling agent forwarding does not improve security
104: unless users are also denied shell access, as they can always install
105: their own forwarders.
1.1 stevesk 106: .It Cm AllowGroups
107: This keyword can be followed by a list of group name patterns, separated
108: by spaces.
109: If specified, login is allowed only for users whose primary
110: group or supplementary group list matches one of the patterns.
111: Only group names are valid; a numerical group ID is not recognized.
112: By default, login is allowed for all groups.
1.54 jmc 113: The allow/deny directives are processed in the following order:
114: .Cm DenyUsers ,
115: .Cm AllowUsers ,
116: .Cm DenyGroups ,
117: and finally
118: .Cm AllowGroups .
1.49 jmc 119: .Pp
120: See
121: .Sx PATTERNS
122: in
123: .Xr ssh_config 5
124: for more information on patterns.
1.1 stevesk 125: .It Cm AllowTcpForwarding
126: Specifies whether TCP forwarding is permitted.
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 ,
1.43 djm 340: .Dq arcfour128 ,
341: .Dq arcfour256 ,
1.34 dtucker 342: .Dq arcfour ,
343: .Dq blowfish-cbc ,
344: and
345: .Dq cast128-cbc .
1.52 jmc 346: The default is:
347: .Bd -literal -offset 3n
1.100 naddy 348: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
349: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
350: aes256-cbc,arcfour
1.1 stevesk 351: .Ed
352: .It Cm ClientAliveCountMax
1.48 jmc 353: Sets the number of client alive messages (see below) which may be
1.1 stevesk 354: sent without
1.52 jmc 355: .Xr sshd 8
1.17 jmc 356: receiving any messages back from the client.
357: If this threshold is reached while client alive messages are being sent,
1.52 jmc 358: sshd will disconnect the client, terminating the session.
1.17 jmc 359: It is important to note that the use of client alive messages is very
360: different from
1.27 markus 361: .Cm TCPKeepAlive
1.17 jmc 362: (below).
363: The client alive messages are sent through the encrypted channel
364: and therefore will not be spoofable.
365: The TCP keepalive option enabled by
1.27 markus 366: .Cm TCPKeepAlive
1.17 jmc 367: is spoofable.
368: The client alive mechanism is valuable when the client or
1.1 stevesk 369: server depend on knowing when a connection has become inactive.
370: .Pp
1.17 jmc 371: The default value is 3.
372: If
1.1 stevesk 373: .Cm ClientAliveInterval
1.48 jmc 374: (see below) is set to 15, and
1.1 stevesk 375: .Cm ClientAliveCountMax
1.52 jmc 376: is left at the default, unresponsive SSH clients
1.1 stevesk 377: will be disconnected after approximately 45 seconds.
1.57 markus 378: This option applies to protocol version 2 only.
1.42 djm 379: .It Cm ClientAliveInterval
380: Sets a timeout interval in seconds after which if no data has been received
381: from the client,
1.52 jmc 382: .Xr sshd 8
1.42 djm 383: will send a message through the encrypted
384: channel to request a response from the client.
385: The default
386: is 0, indicating that these messages will not be sent to the client.
387: This option applies to protocol version 2 only.
1.3 markus 388: .It Cm Compression
1.44 markus 389: Specifies whether compression is allowed, or delayed until
390: the user has authenticated successfully.
1.3 markus 391: The argument must be
1.44 markus 392: .Dq yes ,
393: .Dq delayed ,
1.3 markus 394: or
395: .Dq no .
396: The default is
1.44 markus 397: .Dq delayed .
1.1 stevesk 398: .It Cm DenyGroups
399: This keyword can be followed by a list of group name patterns, separated
400: by spaces.
401: Login is disallowed for users whose primary group or supplementary
402: group list matches one of the patterns.
403: Only group names are valid; a numerical group ID is not recognized.
404: By default, login is allowed for all groups.
1.54 jmc 405: The allow/deny directives are processed in the following order:
406: .Cm DenyUsers ,
407: .Cm AllowUsers ,
408: .Cm DenyGroups ,
409: and finally
410: .Cm AllowGroups .
1.49 jmc 411: .Pp
412: See
413: .Sx PATTERNS
414: in
415: .Xr ssh_config 5
416: for more information on patterns.
1.1 stevesk 417: .It Cm DenyUsers
418: This keyword can be followed by a list of user name patterns, separated
419: by spaces.
420: Login is disallowed for user names that match one of the patterns.
421: Only user names are valid; a numerical user ID is not recognized.
422: By default, login is allowed for all users.
423: If the pattern takes the form USER@HOST then USER and HOST
424: are separately checked, restricting logins to particular
425: users from particular hosts.
1.54 jmc 426: The allow/deny directives are processed in the following order:
427: .Cm DenyUsers ,
428: .Cm AllowUsers ,
429: .Cm DenyGroups ,
430: and finally
431: .Cm AllowGroups .
1.49 jmc 432: .Pp
433: See
434: .Sx PATTERNS
435: in
436: .Xr ssh_config 5
437: for more information on patterns.
1.67 dtucker 438: .It Cm ForceCommand
439: Forces the execution of the command specified by
440: .Cm ForceCommand ,
1.84 djm 441: ignoring any command supplied by the client and
442: .Pa ~/.ssh/rc
443: if present.
1.67 dtucker 444: The command is invoked by using the user's login shell with the -c option.
445: This applies to shell, command, or subsystem execution.
446: It is most useful inside a
447: .Cm Match
448: block.
449: The command originally supplied by the client is available in the
450: .Ev SSH_ORIGINAL_COMMAND
451: environment variable.
1.82 djm 452: Specifying a command of
453: .Dq internal-sftp
454: will force the use of an in-process sftp server that requires no support
455: files when used with
456: .Cm ChrootDirectory .
1.1 stevesk 457: .It Cm GatewayPorts
458: Specifies whether remote hosts are allowed to connect to ports
459: forwarded for the client.
460: By default,
1.52 jmc 461: .Xr sshd 8
1.15 jmc 462: binds remote port forwardings to the loopback address.
463: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 464: .Cm GatewayPorts
1.52 jmc 465: can be used to specify that sshd
1.39 djm 466: should allow remote port forwardings to bind to non-loopback addresses, thus
467: allowing other hosts to connect.
468: The argument may be
469: .Dq no
470: to force remote port forwardings to be available to the local host only,
1.1 stevesk 471: .Dq yes
1.39 djm 472: to force remote port forwardings to bind to the wildcard address, or
473: .Dq clientspecified
474: to allow the client to select the address to which the forwarding is bound.
1.1 stevesk 475: The default is
476: .Dq no .
1.23 markus 477: .It Cm GSSAPIAuthentication
1.25 markus 478: Specifies whether user authentication based on GSSAPI is allowed.
1.26 djm 479: The default is
1.23 markus 480: .Dq no .
481: Note that this option applies to protocol version 2 only.
482: .It Cm GSSAPICleanupCredentials
483: Specifies whether to automatically destroy the user's credentials cache
484: on logout.
485: The default is
486: .Dq yes .
487: Note that this option applies to protocol version 2 only.
1.1 stevesk 488: .It Cm HostbasedAuthentication
489: Specifies whether rhosts or /etc/hosts.equiv authentication together
490: with successful public key client host authentication is allowed
1.50 jmc 491: (host-based authentication).
1.1 stevesk 492: This option is similar to
493: .Cm RhostsRSAAuthentication
494: and applies to protocol version 2 only.
1.70 dtucker 495: The default is
496: .Dq no .
497: .It Cm HostbasedUsesNameFromPacketOnly
498: Specifies whether or not the server will attempt to perform a reverse
499: name lookup when matching the name in the
500: .Pa ~/.shosts ,
501: .Pa ~/.rhosts ,
502: and
503: .Pa /etc/hosts.equiv
504: files during
505: .Cm HostbasedAuthentication .
506: A setting of
507: .Dq yes
508: means that
509: .Xr sshd 8
510: uses the name supplied by the client rather than
511: attempting to resolve the name from the TCP connection itself.
1.1 stevesk 512: The default is
513: .Dq no .
1.117 djm 514: .It Cm HostCertificate
515: Specifies a file containing a public host certificate.
516: The certificate's public key must match a private host key already specified
517: by
518: .Cm HostKey .
519: The default behaviour of
520: .Xr sshd 8
521: is not to load any certificates.
1.1 stevesk 522: .It Cm HostKey
523: Specifies a file containing a private host key
524: used by SSH.
525: The default is
526: .Pa /etc/ssh/ssh_host_key
527: for protocol version 1, and
1.126 djm 528: .Pa /etc/ssh/ssh_host_dsa_key ,
529: .Pa /etc/ssh/ssh_host_ecdsa_key
530: and
1.1 stevesk 531: .Pa /etc/ssh/ssh_host_rsa_key
532: for protocol version 2.
533: Note that
1.52 jmc 534: .Xr sshd 8
1.1 stevesk 535: will refuse to use a file if it is group/world-accessible.
536: It is possible to have multiple host key files.
537: .Dq rsa1
538: keys are used for version 1 and
1.126 djm 539: .Dq dsa ,
540: .Dq ecdsa
1.1 stevesk 541: or
542: .Dq rsa
543: are used for version 2 of the SSH protocol.
544: .It Cm IgnoreRhosts
545: Specifies that
546: .Pa .rhosts
547: and
548: .Pa .shosts
549: files will not be used in
550: .Cm RhostsRSAAuthentication
551: or
552: .Cm HostbasedAuthentication .
553: .Pp
554: .Pa /etc/hosts.equiv
555: and
556: .Pa /etc/shosts.equiv
557: are still used.
558: The default is
559: .Dq yes .
560: .It Cm IgnoreUserKnownHosts
561: Specifies whether
1.52 jmc 562: .Xr sshd 8
1.1 stevesk 563: should ignore the user's
1.41 djm 564: .Pa ~/.ssh/known_hosts
1.1 stevesk 565: during
566: .Cm RhostsRSAAuthentication
567: or
568: .Cm HostbasedAuthentication .
569: The default is
570: .Dq no .
1.129 djm 571: .It Cm IPQoS
572: Specifies the IPv4 type-of-service or DSCP class for the connection.
573: Accepted values are
574: .Dq af11 ,
575: .Dq af12 ,
576: .Dq af13 ,
1.136 djm 577: .Dq af21 ,
1.129 djm 578: .Dq af22 ,
579: .Dq af23 ,
580: .Dq af31 ,
581: .Dq af32 ,
582: .Dq af33 ,
583: .Dq af41 ,
584: .Dq af42 ,
585: .Dq af43 ,
586: .Dq cs0 ,
587: .Dq cs1 ,
588: .Dq cs2 ,
589: .Dq cs3 ,
590: .Dq cs4 ,
591: .Dq cs5 ,
592: .Dq cs6 ,
593: .Dq cs7 ,
594: .Dq ef ,
595: .Dq lowdelay ,
596: .Dq throughput ,
597: .Dq reliability ,
598: or a numeric value.
1.131 djm 599: This option may take one or two arguments, separated by whitespace.
1.129 djm 600: If one argument is specified, it is used as the packet class unconditionally.
601: If two values are specified, the first is automatically selected for
602: interactive sessions and the second for non-interactive sessions.
603: The default is
604: .Dq lowdelay
605: for interactive sessions and
606: .Dq throughput
607: for non-interactive sessions.
1.1 stevesk 608: .It Cm KerberosAuthentication
1.24 markus 609: Specifies whether the password provided by the user for
1.1 stevesk 610: .Cm PasswordAuthentication
1.24 markus 611: will be validated through the Kerberos KDC.
1.1 stevesk 612: To use this option, the server needs a
613: Kerberos servtab which allows the verification of the KDC's identity.
1.52 jmc 614: The default is
1.29 dtucker 615: .Dq no .
616: .It Cm KerberosGetAFSToken
1.45 djm 617: If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire
1.29 dtucker 618: an AFS token before accessing the user's home directory.
1.52 jmc 619: The default is
1.1 stevesk 620: .Dq no .
621: .It Cm KerberosOrLocalPasswd
1.52 jmc 622: If password authentication through Kerberos fails then
1.1 stevesk 623: the password will be validated via any additional local mechanism
624: such as
625: .Pa /etc/passwd .
1.52 jmc 626: The default is
1.1 stevesk 627: .Dq yes .
628: .It Cm KerberosTicketCleanup
629: Specifies whether to automatically destroy the user's ticket cache
630: file on logout.
1.52 jmc 631: The default is
1.1 stevesk 632: .Dq yes .
1.127 djm 633: .It Cm KexAlgorithms
634: Specifies the available KEX (Key Exchange) algorithms.
635: Multiple algorithms must be comma-separated.
636: The default is
637: .Dq ecdh-sha2-nistp256 ,
638: .Dq ecdh-sha2-nistp384 ,
639: .Dq ecdh-sha2-nistp521 ,
1.130 jmc 640: .Dq diffie-hellman-group-exchange-sha256 ,
1.127 djm 641: .Dq diffie-hellman-group-exchange-sha1 ,
642: .Dq diffie-hellman-group14-sha1 ,
643: .Dq diffie-hellman-group1-sha1 .
1.1 stevesk 644: .It Cm KeyRegenerationInterval
645: In protocol version 1, the ephemeral server key is automatically regenerated
646: after this many seconds (if it has been used).
647: The purpose of regeneration is to prevent
648: decrypting captured sessions by later breaking into the machine and
649: stealing the keys.
650: The key is never stored anywhere.
651: If the value is 0, the key is never regenerated.
652: The default is 3600 (seconds).
653: .It Cm ListenAddress
654: Specifies the local addresses
1.52 jmc 655: .Xr sshd 8
1.1 stevesk 656: should listen on.
657: The following forms may be used:
658: .Pp
659: .Bl -item -offset indent -compact
660: .It
661: .Cm ListenAddress
662: .Sm off
663: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
664: .Sm on
665: .It
666: .Cm ListenAddress
667: .Sm off
668: .Ar host No | Ar IPv4_addr No : Ar port
669: .Sm on
670: .It
671: .Cm ListenAddress
672: .Sm off
673: .Oo
674: .Ar host No | Ar IPv6_addr Oc : Ar port
675: .Sm on
676: .El
677: .Pp
678: If
679: .Ar port
680: is not specified,
1.52 jmc 681: sshd will listen on the address and all prior
1.1 stevesk 682: .Cm Port
1.17 jmc 683: options specified.
684: The default is to listen on all local addresses.
1.15 jmc 685: Multiple
1.1 stevesk 686: .Cm ListenAddress
1.17 jmc 687: options are permitted.
688: Additionally, any
1.1 stevesk 689: .Cm Port
1.52 jmc 690: options must precede this option for non-port qualified addresses.
1.1 stevesk 691: .It Cm LoginGraceTime
692: The server disconnects after this time if the user has not
693: successfully logged in.
694: If the value is 0, there is no time limit.
1.12 stevesk 695: The default is 120 seconds.
1.1 stevesk 696: .It Cm LogLevel
697: Gives the verbosity level that is used when logging messages from
1.53 jmc 698: .Xr sshd 8 .
1.1 stevesk 699: The possible values are:
1.52 jmc 700: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.15 jmc 701: The default is INFO.
702: DEBUG and DEBUG1 are equivalent.
703: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
704: Logging with a DEBUG level violates the privacy of users and is not recommended.
1.1 stevesk 705: .It Cm MACs
706: Specifies the available MAC (message authentication code) algorithms.
707: The MAC algorithm is used in protocol version 2
708: for data integrity protection.
709: Multiple algorithms must be comma-separated.
1.152 ! markus 710: The algorithms that contain
! 711: .Dq -etm
! 712: calculate the MAC after encryption (encrypt-then-mac).
! 713: These are considered safer and their use recommended.
1.52 jmc 714: The default is:
1.77 jmc 715: .Bd -literal -offset indent
1.152 ! markus 716: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
! 717: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
! 718: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
! 719: hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,
! 720: hmac-md5-96-etm@openssh.com,
1.145 markus 721: hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
1.144 naddy 722: hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
723: hmac-sha1-96,hmac-md5-96
1.77 jmc 724: .Ed
1.60 dtucker 725: .It Cm Match
1.61 jmc 726: Introduces a conditional block.
1.65 dtucker 727: If all of the criteria on the
1.60 dtucker 728: .Cm Match
1.65 dtucker 729: line are satisfied, the keywords on the following lines override those
730: set in the global section of the config file, until either another
1.60 dtucker 731: .Cm Match
1.65 dtucker 732: line or the end of the file.
1.91 djm 733: .Pp
1.61 jmc 734: The arguments to
1.60 dtucker 735: .Cm Match
1.65 dtucker 736: are one or more criteria-pattern pairs.
1.60 dtucker 737: The available criteria are
738: .Cm User ,
1.69 dtucker 739: .Cm Group ,
1.60 dtucker 740: .Cm Host ,
1.139 dtucker 741: .Cm LocalAddress ,
742: .Cm LocalPort ,
1.60 dtucker 743: and
744: .Cm Address .
1.91 djm 745: The match patterns may consist of single entries or comma-separated
746: lists and may use the wildcard and negation operators described in the
1.92 djm 747: .Sx PATTERNS
1.91 djm 748: section of
1.92 djm 749: .Xr ssh_config 5 .
1.91 djm 750: .Pp
751: The patterns in an
752: .Cm Address
753: criteria may additionally contain addresses to match in CIDR
1.93 jmc 754: address/masklen format, e.g.\&
1.91 djm 755: .Dq 192.0.2.0/24
756: or
757: .Dq 3ffe:ffff::/32 .
758: Note that the mask length provided must be consistent with the address -
759: it is an error to specify a mask length that is too long for the address
1.93 jmc 760: or one with bits set in this host portion of the address.
761: For example,
1.91 djm 762: .Dq 192.0.2.0/33
763: and
1.93 jmc 764: .Dq 192.0.2.0/8
1.91 djm 765: respectively.
766: .Pp
1.60 dtucker 767: Only a subset of keywords may be used on the lines following a
768: .Cm Match
769: keyword.
770: Available keywords are
1.142 jmc 771: .Cm AcceptEnv ,
1.99 okan 772: .Cm AllowAgentForwarding ,
1.142 jmc 773: .Cm AllowGroups ,
1.62 dtucker 774: .Cm AllowTcpForwarding ,
1.141 markus 775: .Cm AllowUsers ,
1.149 djm 776: .Cm AuthenticationMethods ,
1.146 djm 777: .Cm AuthorizedKeysCommand ,
778: .Cm AuthorizedKeysCommandUser ,
1.147 jmc 779: .Cm AuthorizedKeysFile ,
1.123 djm 780: .Cm AuthorizedPrincipalsFile ,
1.72 dtucker 781: .Cm Banner ,
1.85 djm 782: .Cm ChrootDirectory ,
1.141 markus 783: .Cm DenyGroups ,
784: .Cm DenyUsers ,
1.67 dtucker 785: .Cm ForceCommand ,
1.142 jmc 786: .Cm GatewayPorts ,
1.141 markus 787: .Cm GSSAPIAuthentication ,
1.87 djm 788: .Cm HostbasedAuthentication ,
1.123 djm 789: .Cm HostbasedUsesNameFromPacketOnly ,
1.74 jmc 790: .Cm KbdInteractiveAuthentication ,
1.72 dtucker 791: .Cm KerberosAuthentication ,
1.95 dtucker 792: .Cm MaxAuthTries ,
1.94 dtucker 793: .Cm MaxSessions ,
1.72 dtucker 794: .Cm PasswordAuthentication ,
1.97 djm 795: .Cm PermitEmptyPasswords ,
1.66 dtucker 796: .Cm PermitOpen ,
1.79 dtucker 797: .Cm PermitRootLogin ,
1.123 djm 798: .Cm PermitTunnel ,
1.107 dtucker 799: .Cm PubkeyAuthentication ,
1.142 jmc 800: .Cm RhostsRSAAuthentication ,
1.141 markus 801: .Cm RSAAuthentication ,
1.66 dtucker 802: .Cm X11DisplayOffset ,
1.101 djm 803: .Cm X11Forwarding
1.60 dtucker 804: and
1.102 djm 805: .Cm X11UseLocalHost .
1.33 dtucker 806: .It Cm MaxAuthTries
807: Specifies the maximum number of authentication attempts permitted per
1.35 jmc 808: connection.
809: Once the number of failures reaches half this value,
810: additional failures are logged.
811: The default is 6.
1.90 djm 812: .It Cm MaxSessions
813: Specifies the maximum number of open sessions permitted per network connection.
814: The default is 10.
1.1 stevesk 815: .It Cm MaxStartups
816: Specifies the maximum number of concurrent unauthenticated connections to the
1.52 jmc 817: SSH daemon.
1.1 stevesk 818: Additional connections will be dropped until authentication succeeds or the
819: .Cm LoginGraceTime
820: expires for a connection.
821: The default is 10.
822: .Pp
823: Alternatively, random early drop can be enabled by specifying
824: the three colon separated values
825: .Dq start:rate:full
1.51 jmc 826: (e.g. "10:30:60").
1.53 jmc 827: .Xr sshd 8
1.1 stevesk 828: will refuse connection attempts with a probability of
829: .Dq rate/100
830: (30%)
831: if there are currently
832: .Dq start
833: (10)
834: unauthenticated connections.
835: The probability increases linearly and all connection attempts
836: are refused if the number of unauthenticated connections reaches
837: .Dq full
838: (60).
839: .It Cm PasswordAuthentication
840: Specifies whether password authentication is allowed.
841: The default is
842: .Dq yes .
843: .It Cm PermitEmptyPasswords
844: When password authentication is allowed, it specifies whether the
845: server allows login to accounts with empty password strings.
846: The default is
847: .Dq no .
1.62 dtucker 848: .It Cm PermitOpen
849: Specifies the destinations to which TCP port forwarding is permitted.
850: The forwarding specification must be one of the following forms:
851: .Pp
852: .Bl -item -offset indent -compact
853: .It
854: .Cm PermitOpen
855: .Sm off
856: .Ar host : port
857: .Sm on
858: .It
859: .Cm PermitOpen
860: .Sm off
861: .Ar IPv4_addr : port
862: .Sm on
863: .It
864: .Cm PermitOpen
865: .Sm off
866: .Ar \&[ IPv6_addr \&] : port
867: .Sm on
868: .El
869: .Pp
1.68 dtucker 870: Multiple forwards may be specified by separating them with whitespace.
1.62 dtucker 871: An argument of
872: .Dq any
873: can be used to remove all restrictions and permit any forwarding requests.
1.140 dtucker 874: An argument of
875: .Dq none
876: can be used to prohibit all forwarding requests.
1.63 jmc 877: By default all port forwarding requests are permitted.
1.1 stevesk 878: .It Cm PermitRootLogin
1.38 jmc 879: Specifies whether root can log in using
1.1 stevesk 880: .Xr ssh 1 .
881: The argument must be
882: .Dq yes ,
883: .Dq without-password ,
1.52 jmc 884: .Dq forced-commands-only ,
1.1 stevesk 885: or
886: .Dq no .
887: The default is
888: .Dq yes .
889: .Pp
890: If this option is set to
1.52 jmc 891: .Dq without-password ,
1.1 stevesk 892: password authentication is disabled for root.
893: .Pp
894: If this option is set to
1.52 jmc 895: .Dq forced-commands-only ,
1.1 stevesk 896: root login with public key authentication will be allowed,
897: but only if the
898: .Ar command
899: option has been specified
900: (which may be useful for taking remote backups even if root login is
1.17 jmc 901: normally not allowed).
902: All other authentication methods are disabled for root.
1.1 stevesk 903: .Pp
904: If this option is set to
1.52 jmc 905: .Dq no ,
1.38 jmc 906: root is not allowed to log in.
1.46 reyk 907: .It Cm PermitTunnel
908: Specifies whether
909: .Xr tun 4
910: device forwarding is allowed.
1.47 reyk 911: The argument must be
912: .Dq yes ,
1.58 stevesk 913: .Dq point-to-point
914: (layer 3),
915: .Dq ethernet
916: (layer 2), or
1.47 reyk 917: .Dq no .
1.58 stevesk 918: Specifying
919: .Dq yes
920: permits both
921: .Dq point-to-point
922: and
923: .Dq ethernet .
1.46 reyk 924: The default is
925: .Dq no .
1.6 markus 926: .It Cm PermitUserEnvironment
927: Specifies whether
928: .Pa ~/.ssh/environment
1.9 stevesk 929: and
1.6 markus 930: .Cm environment=
931: options in
932: .Pa ~/.ssh/authorized_keys
1.9 stevesk 933: are processed by
1.52 jmc 934: .Xr sshd 8 .
1.6 markus 935: The default is
936: .Dq no .
1.9 stevesk 937: Enabling environment processing may enable users to bypass access
938: restrictions in some configurations using mechanisms such as
939: .Ev LD_PRELOAD .
1.1 stevesk 940: .It Cm PidFile
1.4 stevesk 941: Specifies the file that contains the process ID of the
1.53 jmc 942: SSH daemon.
1.1 stevesk 943: The default is
944: .Pa /var/run/sshd.pid .
945: .It Cm Port
946: Specifies the port number that
1.52 jmc 947: .Xr sshd 8
1.1 stevesk 948: listens on.
949: The default is 22.
950: Multiple options of this type are permitted.
951: See also
952: .Cm ListenAddress .
953: .It Cm PrintLastLog
954: Specifies whether
1.52 jmc 955: .Xr sshd 8
1.36 jaredy 956: should print the date and time of the last user login when a user logs
957: in interactively.
1.1 stevesk 958: The default is
959: .Dq yes .
960: .It Cm PrintMotd
961: Specifies whether
1.52 jmc 962: .Xr sshd 8
1.1 stevesk 963: should print
964: .Pa /etc/motd
965: when a user logs in interactively.
966: (On some systems it is also printed by the shell,
967: .Pa /etc/profile ,
968: or equivalent.)
969: The default is
970: .Dq yes .
971: .It Cm Protocol
972: Specifies the protocol versions
1.52 jmc 973: .Xr sshd 8
1.5 stevesk 974: supports.
1.1 stevesk 975: The possible values are
1.52 jmc 976: .Sq 1
1.1 stevesk 977: and
1.52 jmc 978: .Sq 2 .
1.1 stevesk 979: Multiple versions must be comma-separated.
980: The default is
1.109 jmc 981: .Sq 2 .
1.5 stevesk 982: Note that the order of the protocol list does not indicate preference,
983: because the client selects among multiple protocol versions offered
984: by the server.
985: Specifying
986: .Dq 2,1
987: is identical to
988: .Dq 1,2 .
1.1 stevesk 989: .It Cm PubkeyAuthentication
990: Specifies whether public key authentication is allowed.
991: The default is
992: .Dq yes .
993: Note that this option applies to protocol version 2 only.
1.118 djm 994: .It Cm RevokedKeys
995: Specifies a list of revoked public keys.
996: Keys listed in this file will be refused for public key authentication.
997: Note that if this file is not readable, then public key authentication will
998: be refused for all users.
1.1 stevesk 999: .It Cm RhostsRSAAuthentication
1000: Specifies whether rhosts or /etc/hosts.equiv authentication together
1001: with successful RSA host authentication is allowed.
1002: The default is
1003: .Dq no .
1004: This option applies to protocol version 1 only.
1005: .It Cm RSAAuthentication
1006: Specifies whether pure RSA authentication is allowed.
1007: The default is
1008: .Dq yes .
1009: This option applies to protocol version 1 only.
1010: .It Cm ServerKeyBits
1011: Defines the number of bits in the ephemeral protocol version 1 server key.
1.96 djm 1012: The minimum value is 512, and the default is 1024.
1.1 stevesk 1013: .It Cm StrictModes
1014: Specifies whether
1.52 jmc 1015: .Xr sshd 8
1.1 stevesk 1016: should check file modes and ownership of the
1017: user's files and home directory before accepting login.
1018: This is normally desirable because novices sometimes accidentally leave their
1019: directory or files world-writable.
1020: The default is
1021: .Dq yes .
1.112 djm 1022: Note that this does not apply to
1023: .Cm ChrootDirectory ,
1024: whose permissions and ownership are checked unconditionally.
1.1 stevesk 1025: .It Cm Subsystem
1.51 jmc 1026: Configures an external subsystem (e.g. file transfer daemon).
1.59 djm 1027: Arguments should be a subsystem name and a command (with optional arguments)
1028: to execute upon subsystem request.
1.80 djm 1029: .Pp
1.1 stevesk 1030: The command
1031: .Xr sftp-server 8
1032: implements the
1033: .Dq sftp
1034: file transfer subsystem.
1.80 djm 1035: .Pp
1036: Alternately the name
1037: .Dq internal-sftp
1038: implements an in-process
1039: .Dq sftp
1040: server.
1041: This may simplify configurations using
1042: .Cm ChrootDirectory
1043: to force a different filesystem root on clients.
1044: .Pp
1.1 stevesk 1045: By default no subsystems are defined.
1046: Note that this option applies to protocol version 2 only.
1047: .It Cm SyslogFacility
1048: Gives the facility code that is used when logging messages from
1.53 jmc 1049: .Xr sshd 8 .
1.1 stevesk 1050: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1051: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1052: The default is AUTH.
1.27 markus 1053: .It Cm TCPKeepAlive
1054: Specifies whether the system should send TCP keepalive messages to the
1055: other side.
1056: If they are sent, death of the connection or crash of one
1057: of the machines will be properly noticed.
1058: However, this means that
1059: connections will die if the route is down temporarily, and some people
1060: find it annoying.
1061: On the other hand, if TCP keepalives are not sent,
1062: sessions may hang indefinitely on the server, leaving
1063: .Dq ghost
1064: users and consuming server resources.
1065: .Pp
1066: The default is
1067: .Dq yes
1068: (to send TCP keepalive messages), and the server will notice
1069: if the network goes down or the client host crashes.
1070: This avoids infinitely hanging sessions.
1071: .Pp
1072: To disable TCP keepalive messages, the value should be set to
1073: .Dq no .
1.118 djm 1074: .It Cm TrustedUserCAKeys
1075: Specifies a file containing public keys of certificate authorities that are
1.120 djm 1076: trusted to sign user certificates for authentication.
1.119 jmc 1077: Keys are listed one per line; empty lines and comments starting with
1.118 djm 1078: .Ql #
1079: are allowed.
1080: If a certificate is presented for authentication and has its signing CA key
1081: listed in this file, then it may be used for authentication for any user
1082: listed in the certificate's principals list.
1083: Note that certificates that lack a list of principals will not be permitted
1084: for authentication using
1085: .Cm TrustedUserCAKeys .
1.119 jmc 1086: For more details on certificates, see the
1.118 djm 1087: .Sx CERTIFICATES
1088: section in
1089: .Xr ssh-keygen 1 .
1.18 markus 1090: .It Cm UseDNS
1091: Specifies whether
1.52 jmc 1092: .Xr sshd 8
1.40 jmc 1093: should look up the remote host name and check that
1.18 markus 1094: the resolved host name for the remote IP address maps back to the
1095: very same IP address.
1096: The default is
1097: .Dq yes .
1.1 stevesk 1098: .It Cm UseLogin
1099: Specifies whether
1100: .Xr login 1
1101: is used for interactive login sessions.
1102: The default is
1103: .Dq no .
1104: Note that
1105: .Xr login 1
1106: is never used for remote command execution.
1107: Note also, that if this is enabled,
1108: .Cm X11Forwarding
1109: will be disabled because
1110: .Xr login 1
1111: does not know how to handle
1112: .Xr xauth 1
1.15 jmc 1113: cookies.
1114: If
1.1 stevesk 1115: .Cm UsePrivilegeSeparation
1116: is specified, it will be disabled after authentication.
1117: .It Cm UsePrivilegeSeparation
1118: Specifies whether
1.52 jmc 1119: .Xr sshd 8
1.2 stevesk 1120: separates privileges by creating an unprivileged child process
1.15 jmc 1121: to deal with incoming network traffic.
1122: After successful authentication, another process will be created that has
1123: the privilege of the authenticated user.
1124: The goal of privilege separation is to prevent privilege
1.1 stevesk 1125: escalation by containing any corruption within the unprivileged processes.
1126: The default is
1127: .Dq yes .
1.134 djm 1128: If
1129: .Cm UsePrivilegeSeparation
1130: is set to
1131: .Dq sandbox
1132: then the pre-authentication unprivileged process is subject to additional
1133: restrictions.
1.137 djm 1134: .It Cm VersionAddendum
1135: Optionally specifies additional text to append to the SSH protocol banner
1136: sent by the server upon connection.
1137: The default is
1138: .Dq none .
1.1 stevesk 1139: .It Cm X11DisplayOffset
1140: Specifies the first display number available for
1.52 jmc 1141: .Xr sshd 8 Ns 's
1.1 stevesk 1142: X11 forwarding.
1.52 jmc 1143: This prevents sshd from interfering with real X11 servers.
1.1 stevesk 1144: The default is 10.
1145: .It Cm X11Forwarding
1146: Specifies whether X11 forwarding is permitted.
1.13 stevesk 1147: The argument must be
1148: .Dq yes
1149: or
1150: .Dq no .
1.1 stevesk 1151: The default is
1152: .Dq no .
1.13 stevesk 1153: .Pp
1154: When X11 forwarding is enabled, there may be additional exposure to
1155: the server and to client displays if the
1.52 jmc 1156: .Xr sshd 8
1.13 stevesk 1157: proxy display is configured to listen on the wildcard address (see
1158: .Cm X11UseLocalhost
1.52 jmc 1159: below), though this is not the default.
1.13 stevesk 1160: Additionally, the authentication spoofing and authentication data
1161: verification and substitution occur on the client side.
1162: The security risk of using X11 forwarding is that the client's X11
1.52 jmc 1163: display server may be exposed to attack when the SSH client requests
1.13 stevesk 1164: forwarding (see the warnings for
1165: .Cm ForwardX11
1166: in
1.19 jmc 1167: .Xr ssh_config 5 ) .
1.13 stevesk 1168: A system administrator may have a stance in which they want to
1169: protect clients that may expose themselves to attack by unwittingly
1170: requesting X11 forwarding, which can warrant a
1171: .Dq no
1172: setting.
1173: .Pp
1174: Note that disabling X11 forwarding does not prevent users from
1175: forwarding X11 traffic, as users can always install their own forwarders.
1.1 stevesk 1176: X11 forwarding is automatically disabled if
1177: .Cm UseLogin
1178: is enabled.
1179: .It Cm X11UseLocalhost
1180: Specifies whether
1.52 jmc 1181: .Xr sshd 8
1.1 stevesk 1182: should bind the X11 forwarding server to the loopback address or to
1.15 jmc 1183: the wildcard address.
1184: By default,
1.52 jmc 1185: sshd binds the forwarding server to the loopback address and sets the
1.1 stevesk 1186: hostname part of the
1187: .Ev DISPLAY
1188: environment variable to
1189: .Dq localhost .
1.8 stevesk 1190: This prevents remote hosts from connecting to the proxy display.
1.1 stevesk 1191: However, some older X11 clients may not function with this
1192: configuration.
1193: .Cm X11UseLocalhost
1194: may be set to
1195: .Dq no
1196: to specify that the forwarding server should be bound to the wildcard
1197: address.
1198: The argument must be
1199: .Dq yes
1200: or
1201: .Dq no .
1202: The default is
1203: .Dq yes .
1204: .It Cm XAuthLocation
1.11 stevesk 1205: Specifies the full pathname of the
1.1 stevesk 1206: .Xr xauth 1
1207: program.
1208: The default is
1209: .Pa /usr/X11R6/bin/xauth .
1210: .El
1.55 jmc 1211: .Sh TIME FORMATS
1.53 jmc 1212: .Xr sshd 8
1.1 stevesk 1213: command-line arguments and configuration file options that specify time
1214: may be expressed using a sequence of the form:
1215: .Sm off
1.7 stevesk 1216: .Ar time Op Ar qualifier ,
1.1 stevesk 1217: .Sm on
1218: where
1219: .Ar time
1220: is a positive integer value and
1221: .Ar qualifier
1222: is one of the following:
1223: .Pp
1224: .Bl -tag -width Ds -compact -offset indent
1.64 jmc 1225: .It Aq Cm none
1.1 stevesk 1226: seconds
1227: .It Cm s | Cm S
1228: seconds
1229: .It Cm m | Cm M
1230: minutes
1231: .It Cm h | Cm H
1232: hours
1233: .It Cm d | Cm D
1234: days
1235: .It Cm w | Cm W
1236: weeks
1237: .El
1238: .Pp
1239: Each member of the sequence is added together to calculate
1240: the total time value.
1241: .Pp
1242: Time format examples:
1243: .Pp
1244: .Bl -tag -width Ds -compact -offset indent
1245: .It 600
1246: 600 seconds (10 minutes)
1247: .It 10m
1248: 10 minutes
1249: .It 1h30m
1250: 1 hour 30 minutes (90 minutes)
1251: .El
1252: .Sh FILES
1253: .Bl -tag -width Ds
1254: .It Pa /etc/ssh/sshd_config
1255: Contains configuration data for
1.53 jmc 1256: .Xr sshd 8 .
1.1 stevesk 1257: This file should be writable by root only, but it is recommended
1258: (though not necessary) that it be world-readable.
1259: .El
1.19 jmc 1260: .Sh SEE ALSO
1261: .Xr sshd 8
1.1 stevesk 1262: .Sh AUTHORS
1263: OpenSSH is a derivative of the original and free
1264: ssh 1.2.12 release by Tatu Ylonen.
1265: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1266: Theo de Raadt and Dug Song
1267: removed many bugs, re-added newer features and
1268: created OpenSSH.
1269: Markus Friedl contributed the support for SSH
1270: protocol versions 1.5 and 2.0.
1271: Niels Provos and Markus Friedl contributed support
1272: for privilege separation.
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