Annotation of src/usr.bin/ssh/sshd_config.5, Revision 1.149
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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1.149 ! djm 36: .\" $OpenBSD: sshd_config.5,v 1.148 2012/11/04 10:38:43 djm Exp $
! 37: .Dd $Mdocdate: November 4 2012 $
1.1 stevesk 38: .Dt SSHD_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm sshd_config
42: .Nd OpenSSH SSH daemon configuration file
43: .Sh SYNOPSIS
1.71 jmc 44: .Nm /etc/ssh/sshd_config
1.1 stevesk 45: .Sh DESCRIPTION
1.53 jmc 46: .Xr sshd 8
1.1 stevesk 47: reads configuration data from
48: .Pa /etc/ssh/sshd_config
49: (or the file specified with
50: .Fl f
51: on the command line).
52: The file contains keyword-argument pairs, one per line.
53: Lines starting with
54: .Ql #
55: and empty lines are interpreted as comments.
1.56 dtucker 56: Arguments may optionally be enclosed in double quotes
57: .Pq \&"
58: in order to represent arguments containing spaces.
1.1 stevesk 59: .Pp
60: The possible
61: keywords and their meanings are as follows (note that
62: keywords are case-insensitive and arguments are case-sensitive):
63: .Bl -tag -width Ds
1.30 djm 64: .It Cm AcceptEnv
65: Specifies what environment variables sent by the client will be copied into
66: the session's
67: .Xr environ 7 .
68: See
69: .Cm SendEnv
70: in
71: .Xr ssh_config 5
72: for how to configure the client.
1.31 djm 73: Note that environment passing is only supported for protocol 2.
1.30 djm 74: Variables are specified by name, which may contain the wildcard characters
1.51 jmc 75: .Ql *
1.30 djm 76: and
77: .Ql \&? .
1.31 djm 78: Multiple environment variables may be separated by whitespace or spread
1.30 djm 79: across multiple
80: .Cm AcceptEnv
81: directives.
1.31 djm 82: Be warned that some environment variables could be used to bypass restricted
1.30 djm 83: user environments.
84: For this reason, care should be taken in the use of this directive.
85: The default is not to accept any environment variables.
1.37 djm 86: .It Cm AddressFamily
87: Specifies which address family should be used by
1.53 jmc 88: .Xr sshd 8 .
1.37 djm 89: Valid arguments are
90: .Dq any ,
91: .Dq inet
1.52 jmc 92: (use IPv4 only), or
1.37 djm 93: .Dq inet6
94: (use IPv6 only).
95: The default is
96: .Dq any .
1.89 jmc 97: .It Cm AllowAgentForwarding
98: Specifies whether
99: .Xr ssh-agent 1
100: forwarding is permitted.
101: The default is
102: .Dq yes .
103: Note that disabling agent forwarding does not improve security
104: unless users are also denied shell access, as they can always install
105: their own forwarders.
1.1 stevesk 106: .It Cm AllowGroups
107: This keyword can be followed by a list of group name patterns, separated
108: by spaces.
109: If specified, login is allowed only for users whose primary
110: group or supplementary group list matches one of the patterns.
111: Only group names are valid; a numerical group ID is not recognized.
112: By default, login is allowed for all groups.
1.54 jmc 113: The allow/deny directives are processed in the following order:
114: .Cm DenyUsers ,
115: .Cm AllowUsers ,
116: .Cm DenyGroups ,
117: and finally
118: .Cm AllowGroups .
1.49 jmc 119: .Pp
120: See
121: .Sx PATTERNS
122: in
123: .Xr ssh_config 5
124: for more information on patterns.
1.1 stevesk 125: .It Cm AllowTcpForwarding
126: Specifies whether TCP forwarding is permitted.
127: The default is
128: .Dq yes .
129: Note that disabling TCP forwarding does not improve security unless
130: users are also denied shell access, as they can always install their
131: own forwarders.
132: .It Cm AllowUsers
133: This keyword can be followed by a list of user name patterns, separated
134: by spaces.
1.14 jmc 135: If specified, login is allowed only for user names that
1.1 stevesk 136: match one of the patterns.
137: Only user names are valid; a numerical user ID is not recognized.
138: By default, login is allowed for all users.
139: If the pattern takes the form USER@HOST then USER and HOST
140: are separately checked, restricting logins to particular
141: users from particular hosts.
1.54 jmc 142: The allow/deny directives are processed in the following order:
143: .Cm DenyUsers ,
144: .Cm AllowUsers ,
145: .Cm DenyGroups ,
146: and finally
147: .Cm AllowGroups .
1.49 jmc 148: .Pp
149: See
150: .Sx PATTERNS
151: in
152: .Xr ssh_config 5
153: for more information on patterns.
1.149 ! djm 154: .It Cm AuthenticationMethods
! 155: Specifies the authentication methods that must be successfully completed
! 156: for a user to be granted access.
! 157: This option must be followed by one or more comma-separated lists of
! 158: authentication method names.
! 159: Successful authentication requires completion of every method in at least
! 160: one of these lists.
! 161: .Pp
! 162: For example, an argument of
! 163: .Dq publickey,password publickey,keyboard-interactive
! 164: would require the user to complete public key authentication, followed by
! 165: either password or keyboard interactive authentication.
! 166: Only methods that are next in one or more lists are offered at each stage,
! 167: so for this example, it would not be possible to attempt password or
! 168: keyboard-interactive authentication before public key.
! 169: .Pp
! 170: This option is only available for SSH protocol 2 and will yield a fatal
! 171: error if enabled if protocol 1 is also enabled.
! 172: Note that each authentication method listed should also be explicitly enabled
! 173: in the configuration.
! 174: The default is not to require multiple authentication; successful completion
! 175: of a single authentication method is sufficient.
1.146 djm 176: .It Cm AuthorizedKeysCommand
1.147 jmc 177: Specifies a program to be used to look up the user's public keys.
1.146 djm 178: The program will be invoked with a single argument of the username
179: being authenticated, and should produce on standard output zero or
1.147 jmc 180: more lines of authorized_keys output (see
181: .Sx AUTHORIZED_KEYS
182: in
183: .Xr sshd 8 ) .
1.146 djm 184: If a key supplied by AuthorizedKeysCommand does not successfully authenticate
185: and authorize the user then public key authentication continues using the usual
186: .Cm AuthorizedKeysFile
187: files.
188: By default, no AuthorizedKeysCommand is run.
189: .It Cm AuthorizedKeysCommandUser
190: Specifies the user under whose account the AuthorizedKeysCommand is run.
191: It is recommended to use a dedicated user that has no other role on the host
192: than running authorized keys commands.
1.1 stevesk 193: .It Cm AuthorizedKeysFile
194: Specifies the file that contains the public keys that can be used
195: for user authentication.
1.124 djm 196: The format is described in the
197: .Sx AUTHORIZED_KEYS FILE FORMAT
198: section of
199: .Xr sshd 8 .
1.1 stevesk 200: .Cm AuthorizedKeysFile
201: may contain tokens of the form %T which are substituted during connection
1.52 jmc 202: setup.
1.17 jmc 203: The following tokens are defined: %% is replaced by a literal '%',
1.52 jmc 204: %h is replaced by the home directory of the user being authenticated, and
1.1 stevesk 205: %u is replaced by the username of that user.
206: After expansion,
207: .Cm AuthorizedKeysFile
208: is taken to be an absolute path or one relative to the user's home
209: directory.
1.133 jmc 210: Multiple files may be listed, separated by whitespace.
211: The default is
212: .Dq .ssh/authorized_keys .ssh/authorized_keys2 .
1.121 djm 213: .It Cm AuthorizedPrincipalsFile
214: Specifies a file that lists principal names that are accepted for
215: certificate authentication.
216: When using certificates signed by a key listed in
217: .Cm TrustedUserCAKeys ,
218: this file lists names, one of which must appear in the certificate for it
219: to be accepted for authentication.
1.125 jmc 220: Names are listed one per line preceded by key options (as described
1.124 djm 221: in
222: .Sx AUTHORIZED_KEYS FILE FORMAT
223: in
1.125 jmc 224: .Xr sshd 8 ) .
1.124 djm 225: Empty lines and comments starting with
1.121 djm 226: .Ql #
227: are ignored.
228: .Pp
229: .Cm AuthorizedPrincipalsFile
230: may contain tokens of the form %T which are substituted during connection
231: setup.
232: The following tokens are defined: %% is replaced by a literal '%',
233: %h is replaced by the home directory of the user being authenticated, and
234: %u is replaced by the username of that user.
235: After expansion,
236: .Cm AuthorizedPrincipalsFile
237: is taken to be an absolute path or one relative to the user's home
238: directory.
239: .Pp
1.138 djm 240: The default is
241: .Dq none ,
242: i.e. not to use a principals file \(en in this case, the username
1.121 djm 243: of the user must appear in a certificate's principals list for it to be
244: accepted.
245: Note that
246: .Cm AuthorizedPrincipalsFile
247: is only used when authentication proceeds using a CA listed in
248: .Cm TrustedUserCAKeys
249: and is not consulted for certification authorities trusted via
250: .Pa ~/.ssh/authorized_keys ,
251: though the
252: .Cm principals=
253: key option offers a similar facility (see
254: .Xr sshd 8
255: for details).
1.1 stevesk 256: .It Cm Banner
257: The contents of the specified file are sent to the remote user before
258: authentication is allowed.
1.78 djm 259: If the argument is
260: .Dq none
261: then no banner is displayed.
1.1 stevesk 262: This option is only available for protocol version 2.
263: By default, no banner is displayed.
264: .It Cm ChallengeResponseAuthentication
1.50 jmc 265: Specifies whether challenge-response authentication is allowed.
1.1 stevesk 266: All authentication styles from
267: .Xr login.conf 5
268: are supported.
269: The default is
270: .Dq yes .
1.80 djm 271: .It Cm ChrootDirectory
1.113 stevesk 272: Specifies the pathname of a directory to
1.80 djm 273: .Xr chroot 2
274: to after authentication.
1.113 stevesk 275: All components of the pathname must be root-owned directories that are
1.80 djm 276: not writable by any other user or group.
1.106 stevesk 277: After the chroot,
278: .Xr sshd 8
279: changes the working directory to the user's home directory.
1.80 djm 280: .Pp
1.113 stevesk 281: The pathname may contain the following tokens that are expanded at runtime once
1.80 djm 282: the connecting user has been authenticated: %% is replaced by a literal '%',
283: %h is replaced by the home directory of the user being authenticated, and
284: %u is replaced by the username of that user.
285: .Pp
286: The
287: .Cm ChrootDirectory
288: must contain the necessary files and directories to support the
1.103 stevesk 289: user's session.
1.80 djm 290: For an interactive session this requires at least a shell, typically
291: .Xr sh 1 ,
292: and basic
293: .Pa /dev
294: nodes such as
295: .Xr null 4 ,
296: .Xr zero 4 ,
297: .Xr stdin 4 ,
298: .Xr stdout 4 ,
299: .Xr stderr 4 ,
300: .Xr arandom 4
301: and
302: .Xr tty 4
303: devices.
304: For file transfer sessions using
1.105 jmc 305: .Dq sftp ,
1.80 djm 306: no additional configuration of the environment is necessary if the
1.105 jmc 307: in-process sftp server is used,
308: though sessions which use logging do require
1.104 stevesk 309: .Pa /dev/log
310: inside the chroot directory (see
311: .Xr sftp-server 8
1.81 jmc 312: for details).
1.80 djm 313: .Pp
314: The default is not to
315: .Xr chroot 2 .
1.1 stevesk 316: .It Cm Ciphers
317: Specifies the ciphers allowed for protocol version 2.
318: Multiple ciphers must be comma-separated.
1.34 dtucker 319: The supported ciphers are
320: .Dq 3des-cbc ,
321: .Dq aes128-cbc ,
322: .Dq aes192-cbc ,
323: .Dq aes256-cbc ,
324: .Dq aes128-ctr ,
325: .Dq aes192-ctr ,
326: .Dq aes256-ctr ,
1.43 djm 327: .Dq arcfour128 ,
328: .Dq arcfour256 ,
1.34 dtucker 329: .Dq arcfour ,
330: .Dq blowfish-cbc ,
331: and
332: .Dq cast128-cbc .
1.52 jmc 333: The default is:
334: .Bd -literal -offset 3n
1.100 naddy 335: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
336: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
337: aes256-cbc,arcfour
1.1 stevesk 338: .Ed
339: .It Cm ClientAliveCountMax
1.48 jmc 340: Sets the number of client alive messages (see below) which may be
1.1 stevesk 341: sent without
1.52 jmc 342: .Xr sshd 8
1.17 jmc 343: receiving any messages back from the client.
344: If this threshold is reached while client alive messages are being sent,
1.52 jmc 345: sshd will disconnect the client, terminating the session.
1.17 jmc 346: It is important to note that the use of client alive messages is very
347: different from
1.27 markus 348: .Cm TCPKeepAlive
1.17 jmc 349: (below).
350: The client alive messages are sent through the encrypted channel
351: and therefore will not be spoofable.
352: The TCP keepalive option enabled by
1.27 markus 353: .Cm TCPKeepAlive
1.17 jmc 354: is spoofable.
355: The client alive mechanism is valuable when the client or
1.1 stevesk 356: server depend on knowing when a connection has become inactive.
357: .Pp
1.17 jmc 358: The default value is 3.
359: If
1.1 stevesk 360: .Cm ClientAliveInterval
1.48 jmc 361: (see below) is set to 15, and
1.1 stevesk 362: .Cm ClientAliveCountMax
1.52 jmc 363: is left at the default, unresponsive SSH clients
1.1 stevesk 364: will be disconnected after approximately 45 seconds.
1.57 markus 365: This option applies to protocol version 2 only.
1.42 djm 366: .It Cm ClientAliveInterval
367: Sets a timeout interval in seconds after which if no data has been received
368: from the client,
1.52 jmc 369: .Xr sshd 8
1.42 djm 370: will send a message through the encrypted
371: channel to request a response from the client.
372: The default
373: is 0, indicating that these messages will not be sent to the client.
374: This option applies to protocol version 2 only.
1.3 markus 375: .It Cm Compression
1.44 markus 376: Specifies whether compression is allowed, or delayed until
377: the user has authenticated successfully.
1.3 markus 378: The argument must be
1.44 markus 379: .Dq yes ,
380: .Dq delayed ,
1.3 markus 381: or
382: .Dq no .
383: The default is
1.44 markus 384: .Dq delayed .
1.1 stevesk 385: .It Cm DenyGroups
386: This keyword can be followed by a list of group name patterns, separated
387: by spaces.
388: Login is disallowed for users whose primary group or supplementary
389: group list matches one of the patterns.
390: Only group names are valid; a numerical group ID is not recognized.
391: By default, login is allowed for all groups.
1.54 jmc 392: The allow/deny directives are processed in the following order:
393: .Cm DenyUsers ,
394: .Cm AllowUsers ,
395: .Cm DenyGroups ,
396: and finally
397: .Cm AllowGroups .
1.49 jmc 398: .Pp
399: See
400: .Sx PATTERNS
401: in
402: .Xr ssh_config 5
403: for more information on patterns.
1.1 stevesk 404: .It Cm DenyUsers
405: This keyword can be followed by a list of user name patterns, separated
406: by spaces.
407: Login is disallowed for user names that match one of the patterns.
408: Only user names are valid; a numerical user ID is not recognized.
409: By default, login is allowed for all users.
410: If the pattern takes the form USER@HOST then USER and HOST
411: are separately checked, restricting logins to particular
412: users from particular hosts.
1.54 jmc 413: The allow/deny directives are processed in the following order:
414: .Cm DenyUsers ,
415: .Cm AllowUsers ,
416: .Cm DenyGroups ,
417: and finally
418: .Cm AllowGroups .
1.49 jmc 419: .Pp
420: See
421: .Sx PATTERNS
422: in
423: .Xr ssh_config 5
424: for more information on patterns.
1.67 dtucker 425: .It Cm ForceCommand
426: Forces the execution of the command specified by
427: .Cm ForceCommand ,
1.84 djm 428: ignoring any command supplied by the client and
429: .Pa ~/.ssh/rc
430: if present.
1.67 dtucker 431: The command is invoked by using the user's login shell with the -c option.
432: This applies to shell, command, or subsystem execution.
433: It is most useful inside a
434: .Cm Match
435: block.
436: The command originally supplied by the client is available in the
437: .Ev SSH_ORIGINAL_COMMAND
438: environment variable.
1.82 djm 439: Specifying a command of
440: .Dq internal-sftp
441: will force the use of an in-process sftp server that requires no support
442: files when used with
443: .Cm ChrootDirectory .
1.1 stevesk 444: .It Cm GatewayPorts
445: Specifies whether remote hosts are allowed to connect to ports
446: forwarded for the client.
447: By default,
1.52 jmc 448: .Xr sshd 8
1.15 jmc 449: binds remote port forwardings to the loopback address.
450: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 451: .Cm GatewayPorts
1.52 jmc 452: can be used to specify that sshd
1.39 djm 453: should allow remote port forwardings to bind to non-loopback addresses, thus
454: allowing other hosts to connect.
455: The argument may be
456: .Dq no
457: to force remote port forwardings to be available to the local host only,
1.1 stevesk 458: .Dq yes
1.39 djm 459: to force remote port forwardings to bind to the wildcard address, or
460: .Dq clientspecified
461: to allow the client to select the address to which the forwarding is bound.
1.1 stevesk 462: The default is
463: .Dq no .
1.23 markus 464: .It Cm GSSAPIAuthentication
1.25 markus 465: Specifies whether user authentication based on GSSAPI is allowed.
1.26 djm 466: The default is
1.23 markus 467: .Dq no .
468: Note that this option applies to protocol version 2 only.
469: .It Cm GSSAPICleanupCredentials
470: Specifies whether to automatically destroy the user's credentials cache
471: on logout.
472: The default is
473: .Dq yes .
474: Note that this option applies to protocol version 2 only.
1.1 stevesk 475: .It Cm HostbasedAuthentication
476: Specifies whether rhosts or /etc/hosts.equiv authentication together
477: with successful public key client host authentication is allowed
1.50 jmc 478: (host-based authentication).
1.1 stevesk 479: This option is similar to
480: .Cm RhostsRSAAuthentication
481: and applies to protocol version 2 only.
1.70 dtucker 482: The default is
483: .Dq no .
484: .It Cm HostbasedUsesNameFromPacketOnly
485: Specifies whether or not the server will attempt to perform a reverse
486: name lookup when matching the name in the
487: .Pa ~/.shosts ,
488: .Pa ~/.rhosts ,
489: and
490: .Pa /etc/hosts.equiv
491: files during
492: .Cm HostbasedAuthentication .
493: A setting of
494: .Dq yes
495: means that
496: .Xr sshd 8
497: uses the name supplied by the client rather than
498: attempting to resolve the name from the TCP connection itself.
1.1 stevesk 499: The default is
500: .Dq no .
1.117 djm 501: .It Cm HostCertificate
502: Specifies a file containing a public host certificate.
503: The certificate's public key must match a private host key already specified
504: by
505: .Cm HostKey .
506: The default behaviour of
507: .Xr sshd 8
508: is not to load any certificates.
1.1 stevesk 509: .It Cm HostKey
510: Specifies a file containing a private host key
511: used by SSH.
512: The default is
513: .Pa /etc/ssh/ssh_host_key
514: for protocol version 1, and
1.126 djm 515: .Pa /etc/ssh/ssh_host_dsa_key ,
516: .Pa /etc/ssh/ssh_host_ecdsa_key
517: and
1.1 stevesk 518: .Pa /etc/ssh/ssh_host_rsa_key
519: for protocol version 2.
520: Note that
1.52 jmc 521: .Xr sshd 8
1.1 stevesk 522: will refuse to use a file if it is group/world-accessible.
523: It is possible to have multiple host key files.
524: .Dq rsa1
525: keys are used for version 1 and
1.126 djm 526: .Dq dsa ,
527: .Dq ecdsa
1.1 stevesk 528: or
529: .Dq rsa
530: are used for version 2 of the SSH protocol.
531: .It Cm IgnoreRhosts
532: Specifies that
533: .Pa .rhosts
534: and
535: .Pa .shosts
536: files will not be used in
537: .Cm RhostsRSAAuthentication
538: or
539: .Cm HostbasedAuthentication .
540: .Pp
541: .Pa /etc/hosts.equiv
542: and
543: .Pa /etc/shosts.equiv
544: are still used.
545: The default is
546: .Dq yes .
547: .It Cm IgnoreUserKnownHosts
548: Specifies whether
1.52 jmc 549: .Xr sshd 8
1.1 stevesk 550: should ignore the user's
1.41 djm 551: .Pa ~/.ssh/known_hosts
1.1 stevesk 552: during
553: .Cm RhostsRSAAuthentication
554: or
555: .Cm HostbasedAuthentication .
556: The default is
557: .Dq no .
1.129 djm 558: .It Cm IPQoS
559: Specifies the IPv4 type-of-service or DSCP class for the connection.
560: Accepted values are
561: .Dq af11 ,
562: .Dq af12 ,
563: .Dq af13 ,
1.136 djm 564: .Dq af21 ,
1.129 djm 565: .Dq af22 ,
566: .Dq af23 ,
567: .Dq af31 ,
568: .Dq af32 ,
569: .Dq af33 ,
570: .Dq af41 ,
571: .Dq af42 ,
572: .Dq af43 ,
573: .Dq cs0 ,
574: .Dq cs1 ,
575: .Dq cs2 ,
576: .Dq cs3 ,
577: .Dq cs4 ,
578: .Dq cs5 ,
579: .Dq cs6 ,
580: .Dq cs7 ,
581: .Dq ef ,
582: .Dq lowdelay ,
583: .Dq throughput ,
584: .Dq reliability ,
585: or a numeric value.
1.131 djm 586: This option may take one or two arguments, separated by whitespace.
1.129 djm 587: If one argument is specified, it is used as the packet class unconditionally.
588: If two values are specified, the first is automatically selected for
589: interactive sessions and the second for non-interactive sessions.
590: The default is
591: .Dq lowdelay
592: for interactive sessions and
593: .Dq throughput
594: for non-interactive sessions.
1.1 stevesk 595: .It Cm KerberosAuthentication
1.24 markus 596: Specifies whether the password provided by the user for
1.1 stevesk 597: .Cm PasswordAuthentication
1.24 markus 598: will be validated through the Kerberos KDC.
1.1 stevesk 599: To use this option, the server needs a
600: Kerberos servtab which allows the verification of the KDC's identity.
1.52 jmc 601: The default is
1.29 dtucker 602: .Dq no .
603: .It Cm KerberosGetAFSToken
1.45 djm 604: If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire
1.29 dtucker 605: an AFS token before accessing the user's home directory.
1.52 jmc 606: The default is
1.1 stevesk 607: .Dq no .
608: .It Cm KerberosOrLocalPasswd
1.52 jmc 609: If password authentication through Kerberos fails then
1.1 stevesk 610: the password will be validated via any additional local mechanism
611: such as
612: .Pa /etc/passwd .
1.52 jmc 613: The default is
1.1 stevesk 614: .Dq yes .
615: .It Cm KerberosTicketCleanup
616: Specifies whether to automatically destroy the user's ticket cache
617: file on logout.
1.52 jmc 618: The default is
1.1 stevesk 619: .Dq yes .
1.127 djm 620: .It Cm KexAlgorithms
621: Specifies the available KEX (Key Exchange) algorithms.
622: Multiple algorithms must be comma-separated.
623: The default is
624: .Dq ecdh-sha2-nistp256 ,
625: .Dq ecdh-sha2-nistp384 ,
626: .Dq ecdh-sha2-nistp521 ,
1.130 jmc 627: .Dq diffie-hellman-group-exchange-sha256 ,
1.127 djm 628: .Dq diffie-hellman-group-exchange-sha1 ,
629: .Dq diffie-hellman-group14-sha1 ,
630: .Dq diffie-hellman-group1-sha1 .
1.1 stevesk 631: .It Cm KeyRegenerationInterval
632: In protocol version 1, the ephemeral server key is automatically regenerated
633: after this many seconds (if it has been used).
634: The purpose of regeneration is to prevent
635: decrypting captured sessions by later breaking into the machine and
636: stealing the keys.
637: The key is never stored anywhere.
638: If the value is 0, the key is never regenerated.
639: The default is 3600 (seconds).
640: .It Cm ListenAddress
641: Specifies the local addresses
1.52 jmc 642: .Xr sshd 8
1.1 stevesk 643: should listen on.
644: The following forms may be used:
645: .Pp
646: .Bl -item -offset indent -compact
647: .It
648: .Cm ListenAddress
649: .Sm off
650: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
651: .Sm on
652: .It
653: .Cm ListenAddress
654: .Sm off
655: .Ar host No | Ar IPv4_addr No : Ar port
656: .Sm on
657: .It
658: .Cm ListenAddress
659: .Sm off
660: .Oo
661: .Ar host No | Ar IPv6_addr Oc : Ar port
662: .Sm on
663: .El
664: .Pp
665: If
666: .Ar port
667: is not specified,
1.52 jmc 668: sshd will listen on the address and all prior
1.1 stevesk 669: .Cm Port
1.17 jmc 670: options specified.
671: The default is to listen on all local addresses.
1.15 jmc 672: Multiple
1.1 stevesk 673: .Cm ListenAddress
1.17 jmc 674: options are permitted.
675: Additionally, any
1.1 stevesk 676: .Cm Port
1.52 jmc 677: options must precede this option for non-port qualified addresses.
1.1 stevesk 678: .It Cm LoginGraceTime
679: The server disconnects after this time if the user has not
680: successfully logged in.
681: If the value is 0, there is no time limit.
1.12 stevesk 682: The default is 120 seconds.
1.1 stevesk 683: .It Cm LogLevel
684: Gives the verbosity level that is used when logging messages from
1.53 jmc 685: .Xr sshd 8 .
1.1 stevesk 686: The possible values are:
1.52 jmc 687: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.15 jmc 688: The default is INFO.
689: DEBUG and DEBUG1 are equivalent.
690: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
691: Logging with a DEBUG level violates the privacy of users and is not recommended.
1.1 stevesk 692: .It Cm MACs
693: Specifies the available MAC (message authentication code) algorithms.
694: The MAC algorithm is used in protocol version 2
695: for data integrity protection.
696: Multiple algorithms must be comma-separated.
1.52 jmc 697: The default is:
1.77 jmc 698: .Bd -literal -offset indent
1.145 markus 699: hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
1.144 naddy 700: hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
701: hmac-sha1-96,hmac-md5-96
1.77 jmc 702: .Ed
1.60 dtucker 703: .It Cm Match
1.61 jmc 704: Introduces a conditional block.
1.65 dtucker 705: If all of the criteria on the
1.60 dtucker 706: .Cm Match
1.65 dtucker 707: line are satisfied, the keywords on the following lines override those
708: set in the global section of the config file, until either another
1.60 dtucker 709: .Cm Match
1.65 dtucker 710: line or the end of the file.
1.91 djm 711: .Pp
1.61 jmc 712: The arguments to
1.60 dtucker 713: .Cm Match
1.65 dtucker 714: are one or more criteria-pattern pairs.
1.60 dtucker 715: The available criteria are
716: .Cm User ,
1.69 dtucker 717: .Cm Group ,
1.60 dtucker 718: .Cm Host ,
1.139 dtucker 719: .Cm LocalAddress ,
720: .Cm LocalPort ,
1.60 dtucker 721: and
722: .Cm Address .
1.91 djm 723: The match patterns may consist of single entries or comma-separated
724: lists and may use the wildcard and negation operators described in the
1.92 djm 725: .Sx PATTERNS
1.91 djm 726: section of
1.92 djm 727: .Xr ssh_config 5 .
1.91 djm 728: .Pp
729: The patterns in an
730: .Cm Address
731: criteria may additionally contain addresses to match in CIDR
1.93 jmc 732: address/masklen format, e.g.\&
1.91 djm 733: .Dq 192.0.2.0/24
734: or
735: .Dq 3ffe:ffff::/32 .
736: Note that the mask length provided must be consistent with the address -
737: it is an error to specify a mask length that is too long for the address
1.93 jmc 738: or one with bits set in this host portion of the address.
739: For example,
1.91 djm 740: .Dq 192.0.2.0/33
741: and
1.93 jmc 742: .Dq 192.0.2.0/8
1.91 djm 743: respectively.
744: .Pp
1.60 dtucker 745: Only a subset of keywords may be used on the lines following a
746: .Cm Match
747: keyword.
748: Available keywords are
1.142 jmc 749: .Cm AcceptEnv ,
1.99 okan 750: .Cm AllowAgentForwarding ,
1.142 jmc 751: .Cm AllowGroups ,
1.62 dtucker 752: .Cm AllowTcpForwarding ,
1.141 markus 753: .Cm AllowUsers ,
1.149 ! djm 754: .Cm AuthenticationMethods ,
1.146 djm 755: .Cm AuthorizedKeysCommand ,
756: .Cm AuthorizedKeysCommandUser ,
1.147 jmc 757: .Cm AuthorizedKeysFile ,
1.123 djm 758: .Cm AuthorizedPrincipalsFile ,
1.72 dtucker 759: .Cm Banner ,
1.85 djm 760: .Cm ChrootDirectory ,
1.141 markus 761: .Cm DenyGroups ,
762: .Cm DenyUsers ,
1.67 dtucker 763: .Cm ForceCommand ,
1.142 jmc 764: .Cm GatewayPorts ,
1.141 markus 765: .Cm GSSAPIAuthentication ,
1.87 djm 766: .Cm HostbasedAuthentication ,
1.123 djm 767: .Cm HostbasedUsesNameFromPacketOnly ,
1.74 jmc 768: .Cm KbdInteractiveAuthentication ,
1.72 dtucker 769: .Cm KerberosAuthentication ,
1.95 dtucker 770: .Cm MaxAuthTries ,
1.94 dtucker 771: .Cm MaxSessions ,
1.72 dtucker 772: .Cm PasswordAuthentication ,
1.97 djm 773: .Cm PermitEmptyPasswords ,
1.66 dtucker 774: .Cm PermitOpen ,
1.79 dtucker 775: .Cm PermitRootLogin ,
1.123 djm 776: .Cm PermitTunnel ,
1.107 dtucker 777: .Cm PubkeyAuthentication ,
1.142 jmc 778: .Cm RhostsRSAAuthentication ,
1.141 markus 779: .Cm RSAAuthentication ,
1.66 dtucker 780: .Cm X11DisplayOffset ,
1.101 djm 781: .Cm X11Forwarding
1.60 dtucker 782: and
1.102 djm 783: .Cm X11UseLocalHost .
1.33 dtucker 784: .It Cm MaxAuthTries
785: Specifies the maximum number of authentication attempts permitted per
1.35 jmc 786: connection.
787: Once the number of failures reaches half this value,
788: additional failures are logged.
789: The default is 6.
1.90 djm 790: .It Cm MaxSessions
791: Specifies the maximum number of open sessions permitted per network connection.
792: The default is 10.
1.1 stevesk 793: .It Cm MaxStartups
794: Specifies the maximum number of concurrent unauthenticated connections to the
1.52 jmc 795: SSH daemon.
1.1 stevesk 796: Additional connections will be dropped until authentication succeeds or the
797: .Cm LoginGraceTime
798: expires for a connection.
799: The default is 10.
800: .Pp
801: Alternatively, random early drop can be enabled by specifying
802: the three colon separated values
803: .Dq start:rate:full
1.51 jmc 804: (e.g. "10:30:60").
1.53 jmc 805: .Xr sshd 8
1.1 stevesk 806: will refuse connection attempts with a probability of
807: .Dq rate/100
808: (30%)
809: if there are currently
810: .Dq start
811: (10)
812: unauthenticated connections.
813: The probability increases linearly and all connection attempts
814: are refused if the number of unauthenticated connections reaches
815: .Dq full
816: (60).
817: .It Cm PasswordAuthentication
818: Specifies whether password authentication is allowed.
819: The default is
820: .Dq yes .
821: .It Cm PermitEmptyPasswords
822: When password authentication is allowed, it specifies whether the
823: server allows login to accounts with empty password strings.
824: The default is
825: .Dq no .
1.62 dtucker 826: .It Cm PermitOpen
827: Specifies the destinations to which TCP port forwarding is permitted.
828: The forwarding specification must be one of the following forms:
829: .Pp
830: .Bl -item -offset indent -compact
831: .It
832: .Cm PermitOpen
833: .Sm off
834: .Ar host : port
835: .Sm on
836: .It
837: .Cm PermitOpen
838: .Sm off
839: .Ar IPv4_addr : port
840: .Sm on
841: .It
842: .Cm PermitOpen
843: .Sm off
844: .Ar \&[ IPv6_addr \&] : port
845: .Sm on
846: .El
847: .Pp
1.68 dtucker 848: Multiple forwards may be specified by separating them with whitespace.
1.62 dtucker 849: An argument of
850: .Dq any
851: can be used to remove all restrictions and permit any forwarding requests.
1.140 dtucker 852: An argument of
853: .Dq none
854: can be used to prohibit all forwarding requests.
1.63 jmc 855: By default all port forwarding requests are permitted.
1.1 stevesk 856: .It Cm PermitRootLogin
1.38 jmc 857: Specifies whether root can log in using
1.1 stevesk 858: .Xr ssh 1 .
859: The argument must be
860: .Dq yes ,
861: .Dq without-password ,
1.52 jmc 862: .Dq forced-commands-only ,
1.1 stevesk 863: or
864: .Dq no .
865: The default is
866: .Dq yes .
867: .Pp
868: If this option is set to
1.52 jmc 869: .Dq without-password ,
1.1 stevesk 870: password authentication is disabled for root.
871: .Pp
872: If this option is set to
1.52 jmc 873: .Dq forced-commands-only ,
1.1 stevesk 874: root login with public key authentication will be allowed,
875: but only if the
876: .Ar command
877: option has been specified
878: (which may be useful for taking remote backups even if root login is
1.17 jmc 879: normally not allowed).
880: All other authentication methods are disabled for root.
1.1 stevesk 881: .Pp
882: If this option is set to
1.52 jmc 883: .Dq no ,
1.38 jmc 884: root is not allowed to log in.
1.46 reyk 885: .It Cm PermitTunnel
886: Specifies whether
887: .Xr tun 4
888: device forwarding is allowed.
1.47 reyk 889: The argument must be
890: .Dq yes ,
1.58 stevesk 891: .Dq point-to-point
892: (layer 3),
893: .Dq ethernet
894: (layer 2), or
1.47 reyk 895: .Dq no .
1.58 stevesk 896: Specifying
897: .Dq yes
898: permits both
899: .Dq point-to-point
900: and
901: .Dq ethernet .
1.46 reyk 902: The default is
903: .Dq no .
1.6 markus 904: .It Cm PermitUserEnvironment
905: Specifies whether
906: .Pa ~/.ssh/environment
1.9 stevesk 907: and
1.6 markus 908: .Cm environment=
909: options in
910: .Pa ~/.ssh/authorized_keys
1.9 stevesk 911: are processed by
1.52 jmc 912: .Xr sshd 8 .
1.6 markus 913: The default is
914: .Dq no .
1.9 stevesk 915: Enabling environment processing may enable users to bypass access
916: restrictions in some configurations using mechanisms such as
917: .Ev LD_PRELOAD .
1.1 stevesk 918: .It Cm PidFile
1.4 stevesk 919: Specifies the file that contains the process ID of the
1.53 jmc 920: SSH daemon.
1.1 stevesk 921: The default is
922: .Pa /var/run/sshd.pid .
923: .It Cm Port
924: Specifies the port number that
1.52 jmc 925: .Xr sshd 8
1.1 stevesk 926: listens on.
927: The default is 22.
928: Multiple options of this type are permitted.
929: See also
930: .Cm ListenAddress .
931: .It Cm PrintLastLog
932: Specifies whether
1.52 jmc 933: .Xr sshd 8
1.36 jaredy 934: should print the date and time of the last user login when a user logs
935: in interactively.
1.1 stevesk 936: The default is
937: .Dq yes .
938: .It Cm PrintMotd
939: Specifies whether
1.52 jmc 940: .Xr sshd 8
1.1 stevesk 941: should print
942: .Pa /etc/motd
943: when a user logs in interactively.
944: (On some systems it is also printed by the shell,
945: .Pa /etc/profile ,
946: or equivalent.)
947: The default is
948: .Dq yes .
949: .It Cm Protocol
950: Specifies the protocol versions
1.52 jmc 951: .Xr sshd 8
1.5 stevesk 952: supports.
1.1 stevesk 953: The possible values are
1.52 jmc 954: .Sq 1
1.1 stevesk 955: and
1.52 jmc 956: .Sq 2 .
1.1 stevesk 957: Multiple versions must be comma-separated.
958: The default is
1.109 jmc 959: .Sq 2 .
1.5 stevesk 960: Note that the order of the protocol list does not indicate preference,
961: because the client selects among multiple protocol versions offered
962: by the server.
963: Specifying
964: .Dq 2,1
965: is identical to
966: .Dq 1,2 .
1.1 stevesk 967: .It Cm PubkeyAuthentication
968: Specifies whether public key authentication is allowed.
969: The default is
970: .Dq yes .
971: Note that this option applies to protocol version 2 only.
1.118 djm 972: .It Cm RevokedKeys
973: Specifies a list of revoked public keys.
974: Keys listed in this file will be refused for public key authentication.
975: Note that if this file is not readable, then public key authentication will
976: be refused for all users.
1.1 stevesk 977: .It Cm RhostsRSAAuthentication
978: Specifies whether rhosts or /etc/hosts.equiv authentication together
979: with successful RSA host authentication is allowed.
980: The default is
981: .Dq no .
982: This option applies to protocol version 1 only.
983: .It Cm RSAAuthentication
984: Specifies whether pure RSA authentication is allowed.
985: The default is
986: .Dq yes .
987: This option applies to protocol version 1 only.
988: .It Cm ServerKeyBits
989: Defines the number of bits in the ephemeral protocol version 1 server key.
1.96 djm 990: The minimum value is 512, and the default is 1024.
1.1 stevesk 991: .It Cm StrictModes
992: Specifies whether
1.52 jmc 993: .Xr sshd 8
1.1 stevesk 994: should check file modes and ownership of the
995: user's files and home directory before accepting login.
996: This is normally desirable because novices sometimes accidentally leave their
997: directory or files world-writable.
998: The default is
999: .Dq yes .
1.112 djm 1000: Note that this does not apply to
1001: .Cm ChrootDirectory ,
1002: whose permissions and ownership are checked unconditionally.
1.1 stevesk 1003: .It Cm Subsystem
1.51 jmc 1004: Configures an external subsystem (e.g. file transfer daemon).
1.59 djm 1005: Arguments should be a subsystem name and a command (with optional arguments)
1006: to execute upon subsystem request.
1.80 djm 1007: .Pp
1.1 stevesk 1008: The command
1009: .Xr sftp-server 8
1010: implements the
1011: .Dq sftp
1012: file transfer subsystem.
1.80 djm 1013: .Pp
1014: Alternately the name
1015: .Dq internal-sftp
1016: implements an in-process
1017: .Dq sftp
1018: server.
1019: This may simplify configurations using
1020: .Cm ChrootDirectory
1021: to force a different filesystem root on clients.
1022: .Pp
1.1 stevesk 1023: By default no subsystems are defined.
1024: Note that this option applies to protocol version 2 only.
1025: .It Cm SyslogFacility
1026: Gives the facility code that is used when logging messages from
1.53 jmc 1027: .Xr sshd 8 .
1.1 stevesk 1028: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1029: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1030: The default is AUTH.
1.27 markus 1031: .It Cm TCPKeepAlive
1032: Specifies whether the system should send TCP keepalive messages to the
1033: other side.
1034: If they are sent, death of the connection or crash of one
1035: of the machines will be properly noticed.
1036: However, this means that
1037: connections will die if the route is down temporarily, and some people
1038: find it annoying.
1039: On the other hand, if TCP keepalives are not sent,
1040: sessions may hang indefinitely on the server, leaving
1041: .Dq ghost
1042: users and consuming server resources.
1043: .Pp
1044: The default is
1045: .Dq yes
1046: (to send TCP keepalive messages), and the server will notice
1047: if the network goes down or the client host crashes.
1048: This avoids infinitely hanging sessions.
1049: .Pp
1050: To disable TCP keepalive messages, the value should be set to
1051: .Dq no .
1.118 djm 1052: .It Cm TrustedUserCAKeys
1053: Specifies a file containing public keys of certificate authorities that are
1.120 djm 1054: trusted to sign user certificates for authentication.
1.119 jmc 1055: Keys are listed one per line; empty lines and comments starting with
1.118 djm 1056: .Ql #
1057: are allowed.
1058: If a certificate is presented for authentication and has its signing CA key
1059: listed in this file, then it may be used for authentication for any user
1060: listed in the certificate's principals list.
1061: Note that certificates that lack a list of principals will not be permitted
1062: for authentication using
1063: .Cm TrustedUserCAKeys .
1.119 jmc 1064: For more details on certificates, see the
1.118 djm 1065: .Sx CERTIFICATES
1066: section in
1067: .Xr ssh-keygen 1 .
1.18 markus 1068: .It Cm UseDNS
1069: Specifies whether
1.52 jmc 1070: .Xr sshd 8
1.40 jmc 1071: should look up the remote host name and check that
1.18 markus 1072: the resolved host name for the remote IP address maps back to the
1073: very same IP address.
1074: The default is
1075: .Dq yes .
1.1 stevesk 1076: .It Cm UseLogin
1077: Specifies whether
1078: .Xr login 1
1079: is used for interactive login sessions.
1080: The default is
1081: .Dq no .
1082: Note that
1083: .Xr login 1
1084: is never used for remote command execution.
1085: Note also, that if this is enabled,
1086: .Cm X11Forwarding
1087: will be disabled because
1088: .Xr login 1
1089: does not know how to handle
1090: .Xr xauth 1
1.15 jmc 1091: cookies.
1092: If
1.1 stevesk 1093: .Cm UsePrivilegeSeparation
1094: is specified, it will be disabled after authentication.
1095: .It Cm UsePrivilegeSeparation
1096: Specifies whether
1.52 jmc 1097: .Xr sshd 8
1.2 stevesk 1098: separates privileges by creating an unprivileged child process
1.15 jmc 1099: to deal with incoming network traffic.
1100: After successful authentication, another process will be created that has
1101: the privilege of the authenticated user.
1102: The goal of privilege separation is to prevent privilege
1.1 stevesk 1103: escalation by containing any corruption within the unprivileged processes.
1104: The default is
1105: .Dq yes .
1.134 djm 1106: If
1107: .Cm UsePrivilegeSeparation
1108: is set to
1109: .Dq sandbox
1110: then the pre-authentication unprivileged process is subject to additional
1111: restrictions.
1.137 djm 1112: .It Cm VersionAddendum
1113: Optionally specifies additional text to append to the SSH protocol banner
1114: sent by the server upon connection.
1115: The default is
1116: .Dq none .
1.1 stevesk 1117: .It Cm X11DisplayOffset
1118: Specifies the first display number available for
1.52 jmc 1119: .Xr sshd 8 Ns 's
1.1 stevesk 1120: X11 forwarding.
1.52 jmc 1121: This prevents sshd from interfering with real X11 servers.
1.1 stevesk 1122: The default is 10.
1123: .It Cm X11Forwarding
1124: Specifies whether X11 forwarding is permitted.
1.13 stevesk 1125: The argument must be
1126: .Dq yes
1127: or
1128: .Dq no .
1.1 stevesk 1129: The default is
1130: .Dq no .
1.13 stevesk 1131: .Pp
1132: When X11 forwarding is enabled, there may be additional exposure to
1133: the server and to client displays if the
1.52 jmc 1134: .Xr sshd 8
1.13 stevesk 1135: proxy display is configured to listen on the wildcard address (see
1136: .Cm X11UseLocalhost
1.52 jmc 1137: below), though this is not the default.
1.13 stevesk 1138: Additionally, the authentication spoofing and authentication data
1139: verification and substitution occur on the client side.
1140: The security risk of using X11 forwarding is that the client's X11
1.52 jmc 1141: display server may be exposed to attack when the SSH client requests
1.13 stevesk 1142: forwarding (see the warnings for
1143: .Cm ForwardX11
1144: in
1.19 jmc 1145: .Xr ssh_config 5 ) .
1.13 stevesk 1146: A system administrator may have a stance in which they want to
1147: protect clients that may expose themselves to attack by unwittingly
1148: requesting X11 forwarding, which can warrant a
1149: .Dq no
1150: setting.
1151: .Pp
1152: Note that disabling X11 forwarding does not prevent users from
1153: forwarding X11 traffic, as users can always install their own forwarders.
1.1 stevesk 1154: X11 forwarding is automatically disabled if
1155: .Cm UseLogin
1156: is enabled.
1157: .It Cm X11UseLocalhost
1158: Specifies whether
1.52 jmc 1159: .Xr sshd 8
1.1 stevesk 1160: should bind the X11 forwarding server to the loopback address or to
1.15 jmc 1161: the wildcard address.
1162: By default,
1.52 jmc 1163: sshd binds the forwarding server to the loopback address and sets the
1.1 stevesk 1164: hostname part of the
1165: .Ev DISPLAY
1166: environment variable to
1167: .Dq localhost .
1.8 stevesk 1168: This prevents remote hosts from connecting to the proxy display.
1.1 stevesk 1169: However, some older X11 clients may not function with this
1170: configuration.
1171: .Cm X11UseLocalhost
1172: may be set to
1173: .Dq no
1174: to specify that the forwarding server should be bound to the wildcard
1175: address.
1176: The argument must be
1177: .Dq yes
1178: or
1179: .Dq no .
1180: The default is
1181: .Dq yes .
1182: .It Cm XAuthLocation
1.11 stevesk 1183: Specifies the full pathname of the
1.1 stevesk 1184: .Xr xauth 1
1185: program.
1186: The default is
1187: .Pa /usr/X11R6/bin/xauth .
1188: .El
1.55 jmc 1189: .Sh TIME FORMATS
1.53 jmc 1190: .Xr sshd 8
1.1 stevesk 1191: command-line arguments and configuration file options that specify time
1192: may be expressed using a sequence of the form:
1193: .Sm off
1.7 stevesk 1194: .Ar time Op Ar qualifier ,
1.1 stevesk 1195: .Sm on
1196: where
1197: .Ar time
1198: is a positive integer value and
1199: .Ar qualifier
1200: is one of the following:
1201: .Pp
1202: .Bl -tag -width Ds -compact -offset indent
1.64 jmc 1203: .It Aq Cm none
1.1 stevesk 1204: seconds
1205: .It Cm s | Cm S
1206: seconds
1207: .It Cm m | Cm M
1208: minutes
1209: .It Cm h | Cm H
1210: hours
1211: .It Cm d | Cm D
1212: days
1213: .It Cm w | Cm W
1214: weeks
1215: .El
1216: .Pp
1217: Each member of the sequence is added together to calculate
1218: the total time value.
1219: .Pp
1220: Time format examples:
1221: .Pp
1222: .Bl -tag -width Ds -compact -offset indent
1223: .It 600
1224: 600 seconds (10 minutes)
1225: .It 10m
1226: 10 minutes
1227: .It 1h30m
1228: 1 hour 30 minutes (90 minutes)
1229: .El
1230: .Sh FILES
1231: .Bl -tag -width Ds
1232: .It Pa /etc/ssh/sshd_config
1233: Contains configuration data for
1.53 jmc 1234: .Xr sshd 8 .
1.1 stevesk 1235: This file should be writable by root only, but it is recommended
1236: (though not necessary) that it be world-readable.
1237: .El
1.19 jmc 1238: .Sh SEE ALSO
1239: .Xr sshd 8
1.1 stevesk 1240: .Sh AUTHORS
1241: OpenSSH is a derivative of the original and free
1242: ssh 1.2.12 release by Tatu Ylonen.
1243: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1244: Theo de Raadt and Dug Song
1245: removed many bugs, re-added newer features and
1246: created OpenSSH.
1247: Markus Friedl contributed the support for SSH
1248: protocol versions 1.5 and 2.0.
1249: Niels Provos and Markus Friedl contributed support
1250: for privilege separation.
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