Annotation of src/usr.bin/ssh/sshd_config.5, Revision 1.34
1.1 stevesk 1: .\" -*- nroff -*-
2: .\"
3: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5: .\" All rights reserved
6: .\"
7: .\" As far as I am concerned, the code I have written for this software
8: .\" can be used freely for any purpose. Any derived versions of this
9: .\" software must be clearly marked as such, and if the derived work is
10: .\" incompatible with the protocol description in the RFC file, it must be
11: .\" called by a name other than "ssh" or "Secure Shell".
12: .\"
13: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
14: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
15: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
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1.34 ! dtucker 37: .\" $OpenBSD: sshd_config.5,v 1.33 2004/05/23 23:59:53 dtucker Exp $
1.1 stevesk 38: .Dd September 25, 1999
39: .Dt SSHD_CONFIG 5
40: .Os
41: .Sh NAME
42: .Nm sshd_config
43: .Nd OpenSSH SSH daemon configuration file
44: .Sh SYNOPSIS
45: .Bl -tag -width Ds -compact
46: .It Pa /etc/ssh/sshd_config
47: .El
48: .Sh DESCRIPTION
49: .Nm sshd
50: reads configuration data from
51: .Pa /etc/ssh/sshd_config
52: (or the file specified with
53: .Fl f
54: on the command line).
55: The file contains keyword-argument pairs, one per line.
56: Lines starting with
57: .Ql #
58: and empty lines are interpreted as comments.
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
75: .Ql \&*
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.
1.1 stevesk 86: .It Cm AllowGroups
87: This keyword can be followed by a list of group name patterns, separated
88: by spaces.
89: If specified, login is allowed only for users whose primary
90: group or supplementary group list matches one of the patterns.
91: .Ql \&*
92: and
1.16 mouring 93: .Ql \&?
1.1 stevesk 94: can be used as
95: wildcards in the patterns.
96: Only group names are valid; a numerical group ID is not recognized.
97: By default, login is allowed for all groups.
98: .It Cm AllowTcpForwarding
99: Specifies whether TCP forwarding is permitted.
100: The default is
101: .Dq yes .
102: Note that disabling TCP forwarding does not improve security unless
103: users are also denied shell access, as they can always install their
104: own forwarders.
105: .It Cm AllowUsers
106: This keyword can be followed by a list of user name patterns, separated
107: by spaces.
1.14 jmc 108: If specified, login is allowed only for user names that
1.1 stevesk 109: match one of the patterns.
110: .Ql \&*
111: and
1.16 mouring 112: .Ql \&?
1.1 stevesk 113: can be used as
114: wildcards in the patterns.
115: Only user names are valid; a numerical user ID is not recognized.
116: By default, login is allowed for all users.
117: If the pattern takes the form USER@HOST then USER and HOST
118: are separately checked, restricting logins to particular
119: users from particular hosts.
120: .It Cm AuthorizedKeysFile
121: Specifies the file that contains the public keys that can be used
122: for user authentication.
123: .Cm AuthorizedKeysFile
124: may contain tokens of the form %T which are substituted during connection
1.17 jmc 125: set-up.
126: The following tokens are defined: %% is replaced by a literal '%',
1.1 stevesk 127: %h is replaced by the home directory of the user being authenticated and
128: %u is replaced by the username of that user.
129: After expansion,
130: .Cm AuthorizedKeysFile
131: is taken to be an absolute path or one relative to the user's home
132: directory.
133: The default is
134: .Dq .ssh/authorized_keys .
135: .It Cm Banner
136: In some jurisdictions, sending a warning message before authentication
137: may be relevant for getting legal protection.
138: The contents of the specified file are sent to the remote user before
139: authentication is allowed.
140: This option is only available for protocol version 2.
141: By default, no banner is displayed.
142: .It Cm ChallengeResponseAuthentication
143: Specifies whether challenge response authentication is allowed.
144: All authentication styles from
145: .Xr login.conf 5
146: are supported.
147: The default is
148: .Dq yes .
149: .It Cm Ciphers
150: Specifies the ciphers allowed for protocol version 2.
151: Multiple ciphers must be comma-separated.
1.34 ! dtucker 152: The supported ciphers are
! 153: .Dq 3des-cbc ,
! 154: .Dq aes128-cbc ,
! 155: .Dq aes192-cbc ,
! 156: .Dq aes256-cbc ,
! 157: .Dq aes128-ctr ,
! 158: .Dq aes192-ctr ,
! 159: .Dq aes256-ctr ,
! 160: .Dq arcfour ,
! 161: .Dq blowfish-cbc ,
! 162: and
! 163: .Dq cast128-cbc .
1.1 stevesk 164: The default is
165: .Bd -literal
166: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
1.20 djm 167: aes192-cbc,aes256-cbc,aes128-ctr,aes192-ctr,aes256-ctr''
1.1 stevesk 168: .Ed
169: .It Cm ClientAliveInterval
170: Sets a timeout interval in seconds after which if no data has been received
171: from the client,
172: .Nm sshd
173: will send a message through the encrypted
174: channel to request a response from the client.
175: The default
176: is 0, indicating that these messages will not be sent to the client.
177: This option applies to protocol version 2 only.
178: .It Cm ClientAliveCountMax
179: Sets the number of client alive messages (see above) which may be
180: sent without
181: .Nm sshd
1.17 jmc 182: receiving any messages back from the client.
183: If this threshold is reached while client alive messages are being sent,
1.1 stevesk 184: .Nm sshd
1.17 jmc 185: will disconnect the client, terminating the session.
186: It is important to note that the use of client alive messages is very
187: different from
1.27 markus 188: .Cm TCPKeepAlive
1.17 jmc 189: (below).
190: The client alive messages are sent through the encrypted channel
191: and therefore will not be spoofable.
192: The TCP keepalive option enabled by
1.27 markus 193: .Cm TCPKeepAlive
1.17 jmc 194: is spoofable.
195: The client alive mechanism is valuable when the client or
1.1 stevesk 196: server depend on knowing when a connection has become inactive.
197: .Pp
1.17 jmc 198: The default value is 3.
199: If
1.1 stevesk 200: .Cm ClientAliveInterval
201: (above) is set to 15, and
202: .Cm ClientAliveCountMax
203: is left at the default, unresponsive ssh clients
204: will be disconnected after approximately 45 seconds.
1.3 markus 205: .It Cm Compression
206: Specifies whether compression is allowed.
207: The argument must be
208: .Dq yes
209: or
210: .Dq no .
211: The default is
212: .Dq yes .
1.1 stevesk 213: .It Cm DenyGroups
214: This keyword can be followed by a list of group name patterns, separated
215: by spaces.
216: Login is disallowed for users whose primary group or supplementary
217: group list matches one of the patterns.
218: .Ql \&*
219: and
1.16 mouring 220: .Ql \&?
1.1 stevesk 221: can be used as
222: wildcards in the patterns.
223: Only group names are valid; a numerical group ID is not recognized.
224: By default, login is allowed for all groups.
225: .It Cm DenyUsers
226: This keyword can be followed by a list of user name patterns, separated
227: by spaces.
228: Login is disallowed for user names that match one of the patterns.
229: .Ql \&*
230: and
1.16 mouring 231: .Ql \&?
1.1 stevesk 232: can be used as wildcards in the patterns.
233: Only user names are valid; a numerical user ID is not recognized.
234: By default, login is allowed for all users.
235: If the pattern takes the form USER@HOST then USER and HOST
236: are separately checked, restricting logins to particular
237: users from particular hosts.
238: .It Cm GatewayPorts
239: Specifies whether remote hosts are allowed to connect to ports
240: forwarded for the client.
241: By default,
242: .Nm sshd
1.15 jmc 243: binds remote port forwardings to the loopback address.
244: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 245: .Cm GatewayPorts
246: can be used to specify that
247: .Nm sshd
248: should bind remote port forwardings to the wildcard address,
249: thus allowing remote hosts to connect to forwarded ports.
250: The argument must be
251: .Dq yes
252: or
253: .Dq no .
254: The default is
255: .Dq no .
1.23 markus 256: .It Cm GSSAPIAuthentication
1.25 markus 257: Specifies whether user authentication based on GSSAPI is allowed.
1.26 djm 258: The default is
1.23 markus 259: .Dq no .
260: Note that this option applies to protocol version 2 only.
261: .It Cm GSSAPICleanupCredentials
262: Specifies whether to automatically destroy the user's credentials cache
263: on logout.
264: The default is
265: .Dq yes .
266: Note that this option applies to protocol version 2 only.
1.1 stevesk 267: .It Cm HostbasedAuthentication
268: Specifies whether rhosts or /etc/hosts.equiv authentication together
269: with successful public key client host authentication is allowed
270: (hostbased authentication).
271: This option is similar to
272: .Cm RhostsRSAAuthentication
273: and applies to protocol version 2 only.
274: The default is
275: .Dq no .
276: .It Cm HostKey
277: Specifies a file containing a private host key
278: used by SSH.
279: The default is
280: .Pa /etc/ssh/ssh_host_key
281: for protocol version 1, and
282: .Pa /etc/ssh/ssh_host_rsa_key
283: and
284: .Pa /etc/ssh/ssh_host_dsa_key
285: for protocol version 2.
286: Note that
287: .Nm sshd
288: will refuse to use a file if it is group/world-accessible.
289: It is possible to have multiple host key files.
290: .Dq rsa1
291: keys are used for version 1 and
292: .Dq dsa
293: or
294: .Dq rsa
295: are used for version 2 of the SSH protocol.
296: .It Cm IgnoreRhosts
297: Specifies that
298: .Pa .rhosts
299: and
300: .Pa .shosts
301: files will not be used in
302: .Cm RhostsRSAAuthentication
303: or
304: .Cm HostbasedAuthentication .
305: .Pp
306: .Pa /etc/hosts.equiv
307: and
308: .Pa /etc/shosts.equiv
309: are still used.
310: The default is
311: .Dq yes .
312: .It Cm IgnoreUserKnownHosts
313: Specifies whether
314: .Nm sshd
315: should ignore the user's
316: .Pa $HOME/.ssh/known_hosts
317: during
318: .Cm RhostsRSAAuthentication
319: or
320: .Cm HostbasedAuthentication .
321: The default is
322: .Dq no .
323: .It Cm KerberosAuthentication
1.24 markus 324: Specifies whether the password provided by the user for
1.1 stevesk 325: .Cm PasswordAuthentication
1.24 markus 326: will be validated through the Kerberos KDC.
1.1 stevesk 327: To use this option, the server needs a
328: Kerberos servtab which allows the verification of the KDC's identity.
1.29 dtucker 329: Default is
330: .Dq no .
331: .It Cm KerberosGetAFSToken
332: If AFS is active and the user has a Kerberos 5 TGT, attempt to aquire
333: an AFS token before accessing the user's home directory.
1.1 stevesk 334: Default is
335: .Dq no .
336: .It Cm KerberosOrLocalPasswd
337: If set then if password authentication through Kerberos fails then
338: the password will be validated via any additional local mechanism
339: such as
340: .Pa /etc/passwd .
341: Default is
342: .Dq yes .
343: .It Cm KerberosTicketCleanup
344: Specifies whether to automatically destroy the user's ticket cache
345: file on logout.
346: Default is
347: .Dq yes .
348: .It Cm KeyRegenerationInterval
349: In protocol version 1, the ephemeral server key is automatically regenerated
350: after this many seconds (if it has been used).
351: The purpose of regeneration is to prevent
352: decrypting captured sessions by later breaking into the machine and
353: stealing the keys.
354: The key is never stored anywhere.
355: If the value is 0, the key is never regenerated.
356: The default is 3600 (seconds).
357: .It Cm ListenAddress
358: Specifies the local addresses
359: .Nm sshd
360: should listen on.
361: The following forms may be used:
362: .Pp
363: .Bl -item -offset indent -compact
364: .It
365: .Cm ListenAddress
366: .Sm off
367: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
368: .Sm on
369: .It
370: .Cm ListenAddress
371: .Sm off
372: .Ar host No | Ar IPv4_addr No : Ar port
373: .Sm on
374: .It
375: .Cm ListenAddress
376: .Sm off
377: .Oo
378: .Ar host No | Ar IPv6_addr Oc : Ar port
379: .Sm on
380: .El
381: .Pp
382: If
383: .Ar port
384: is not specified,
385: .Nm sshd
386: will listen on the address and all prior
387: .Cm Port
1.17 jmc 388: options specified.
389: The default is to listen on all local addresses.
1.15 jmc 390: Multiple
1.1 stevesk 391: .Cm ListenAddress
1.17 jmc 392: options are permitted.
393: Additionally, any
1.1 stevesk 394: .Cm Port
395: options must precede this option for non port qualified addresses.
396: .It Cm LoginGraceTime
397: The server disconnects after this time if the user has not
398: successfully logged in.
399: If the value is 0, there is no time limit.
1.12 stevesk 400: The default is 120 seconds.
1.1 stevesk 401: .It Cm LogLevel
402: Gives the verbosity level that is used when logging messages from
403: .Nm sshd .
404: The possible values are:
405: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
1.15 jmc 406: The default is INFO.
407: DEBUG and DEBUG1 are equivalent.
408: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
409: Logging with a DEBUG level violates the privacy of users and is not recommended.
1.1 stevesk 410: .It Cm MACs
411: Specifies the available MAC (message authentication code) algorithms.
412: The MAC algorithm is used in protocol version 2
413: for data integrity protection.
414: Multiple algorithms must be comma-separated.
415: The default is
416: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
1.33 dtucker 417: .It Cm MaxAuthTries
418: Specifies the maximum number of authentication attempts permitted per
419: connection. Once the number of failures reaches half this value, additional
420: failures are logged. The default is 6.
1.1 stevesk 421: .It Cm MaxStartups
422: Specifies the maximum number of concurrent unauthenticated connections to the
423: .Nm sshd
424: daemon.
425: Additional connections will be dropped until authentication succeeds or the
426: .Cm LoginGraceTime
427: expires for a connection.
428: The default is 10.
429: .Pp
430: Alternatively, random early drop can be enabled by specifying
431: the three colon separated values
432: .Dq start:rate:full
433: (e.g., "10:30:60").
434: .Nm sshd
435: will refuse connection attempts with a probability of
436: .Dq rate/100
437: (30%)
438: if there are currently
439: .Dq start
440: (10)
441: unauthenticated connections.
442: The probability increases linearly and all connection attempts
443: are refused if the number of unauthenticated connections reaches
444: .Dq full
445: (60).
446: .It Cm PasswordAuthentication
447: Specifies whether password authentication is allowed.
448: The default is
449: .Dq yes .
450: .It Cm PermitEmptyPasswords
451: When password authentication is allowed, it specifies whether the
452: server allows login to accounts with empty password strings.
453: The default is
454: .Dq no .
455: .It Cm PermitRootLogin
456: Specifies whether root can login using
457: .Xr ssh 1 .
458: The argument must be
459: .Dq yes ,
460: .Dq without-password ,
461: .Dq forced-commands-only
462: or
463: .Dq no .
464: The default is
465: .Dq yes .
466: .Pp
467: If this option is set to
468: .Dq without-password
469: password authentication is disabled for root.
470: .Pp
471: If this option is set to
472: .Dq forced-commands-only
473: root login with public key authentication will be allowed,
474: but only if the
475: .Ar command
476: option has been specified
477: (which may be useful for taking remote backups even if root login is
1.17 jmc 478: normally not allowed).
479: All other authentication methods are disabled for root.
1.1 stevesk 480: .Pp
481: If this option is set to
482: .Dq no
483: root is not allowed to login.
1.6 markus 484: .It Cm PermitUserEnvironment
485: Specifies whether
486: .Pa ~/.ssh/environment
1.9 stevesk 487: and
1.6 markus 488: .Cm environment=
489: options in
490: .Pa ~/.ssh/authorized_keys
1.9 stevesk 491: are processed by
492: .Nm sshd .
1.6 markus 493: The default is
494: .Dq no .
1.9 stevesk 495: Enabling environment processing may enable users to bypass access
496: restrictions in some configurations using mechanisms such as
497: .Ev LD_PRELOAD .
1.1 stevesk 498: .It Cm PidFile
1.4 stevesk 499: Specifies the file that contains the process ID of the
1.1 stevesk 500: .Nm sshd
501: daemon.
502: The default is
503: .Pa /var/run/sshd.pid .
504: .It Cm Port
505: Specifies the port number that
506: .Nm sshd
507: listens on.
508: The default is 22.
509: Multiple options of this type are permitted.
510: See also
511: .Cm ListenAddress .
512: .It Cm PrintLastLog
513: Specifies whether
514: .Nm sshd
515: should print the date and time when the user last logged in.
516: The default is
517: .Dq yes .
518: .It Cm PrintMotd
519: Specifies whether
520: .Nm sshd
521: should print
522: .Pa /etc/motd
523: when a user logs in interactively.
524: (On some systems it is also printed by the shell,
525: .Pa /etc/profile ,
526: or equivalent.)
527: The default is
528: .Dq yes .
529: .It Cm Protocol
530: Specifies the protocol versions
531: .Nm sshd
1.5 stevesk 532: supports.
1.1 stevesk 533: The possible values are
534: .Dq 1
535: and
536: .Dq 2 .
537: Multiple versions must be comma-separated.
538: The default is
539: .Dq 2,1 .
1.5 stevesk 540: Note that the order of the protocol list does not indicate preference,
541: because the client selects among multiple protocol versions offered
542: by the server.
543: Specifying
544: .Dq 2,1
545: is identical to
546: .Dq 1,2 .
1.1 stevesk 547: .It Cm PubkeyAuthentication
548: Specifies whether public key authentication is allowed.
549: The default is
550: .Dq yes .
551: Note that this option applies to protocol version 2 only.
552: .It Cm RhostsRSAAuthentication
553: Specifies whether rhosts or /etc/hosts.equiv authentication together
554: with successful RSA host authentication is allowed.
555: The default is
556: .Dq no .
557: This option applies to protocol version 1 only.
558: .It Cm RSAAuthentication
559: Specifies whether pure RSA authentication is allowed.
560: The default is
561: .Dq yes .
562: This option applies to protocol version 1 only.
563: .It Cm ServerKeyBits
564: Defines the number of bits in the ephemeral protocol version 1 server key.
565: The minimum value is 512, and the default is 768.
566: .It Cm StrictModes
567: Specifies whether
568: .Nm sshd
569: should check file modes and ownership of the
570: user's files and home directory before accepting login.
571: This is normally desirable because novices sometimes accidentally leave their
572: directory or files world-writable.
573: The default is
574: .Dq yes .
575: .It Cm Subsystem
576: Configures an external subsystem (e.g., file transfer daemon).
577: Arguments should be a subsystem name and a command to execute upon subsystem
578: request.
579: The command
580: .Xr sftp-server 8
581: implements the
582: .Dq sftp
583: file transfer subsystem.
584: By default no subsystems are defined.
585: Note that this option applies to protocol version 2 only.
586: .It Cm SyslogFacility
587: Gives the facility code that is used when logging messages from
588: .Nm sshd .
589: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
590: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
591: The default is AUTH.
1.27 markus 592: .It Cm TCPKeepAlive
593: Specifies whether the system should send TCP keepalive messages to the
594: other side.
595: If they are sent, death of the connection or crash of one
596: of the machines will be properly noticed.
597: However, this means that
598: connections will die if the route is down temporarily, and some people
599: find it annoying.
600: On the other hand, if TCP keepalives are not sent,
601: sessions may hang indefinitely on the server, leaving
602: .Dq ghost
603: users and consuming server resources.
604: .Pp
605: The default is
606: .Dq yes
607: (to send TCP keepalive messages), and the server will notice
608: if the network goes down or the client host crashes.
609: This avoids infinitely hanging sessions.
610: .Pp
611: To disable TCP keepalive messages, the value should be set to
612: .Dq no .
1.18 markus 613: .It Cm UseDNS
614: Specifies whether
615: .Nm sshd
616: should lookup the remote host name and check that
617: the resolved host name for the remote IP address maps back to the
618: very same IP address.
619: The default is
620: .Dq yes .
1.1 stevesk 621: .It Cm UseLogin
622: Specifies whether
623: .Xr login 1
624: is used for interactive login sessions.
625: The default is
626: .Dq no .
627: Note that
628: .Xr login 1
629: is never used for remote command execution.
630: Note also, that if this is enabled,
631: .Cm X11Forwarding
632: will be disabled because
633: .Xr login 1
634: does not know how to handle
635: .Xr xauth 1
1.15 jmc 636: cookies.
637: If
1.1 stevesk 638: .Cm UsePrivilegeSeparation
639: is specified, it will be disabled after authentication.
640: .It Cm UsePrivilegeSeparation
641: Specifies whether
642: .Nm sshd
1.2 stevesk 643: separates privileges by creating an unprivileged child process
1.15 jmc 644: to deal with incoming network traffic.
645: After successful authentication, another process will be created that has
646: the privilege of the authenticated user.
647: The goal of privilege separation is to prevent privilege
1.1 stevesk 648: escalation by containing any corruption within the unprivileged processes.
649: The default is
650: .Dq yes .
651: .It Cm X11DisplayOffset
652: Specifies the first display number available for
653: .Nm sshd Ns 's
654: X11 forwarding.
655: This prevents
656: .Nm sshd
657: from interfering with real X11 servers.
658: The default is 10.
659: .It Cm X11Forwarding
660: Specifies whether X11 forwarding is permitted.
1.13 stevesk 661: The argument must be
662: .Dq yes
663: or
664: .Dq no .
1.1 stevesk 665: The default is
666: .Dq no .
1.13 stevesk 667: .Pp
668: When X11 forwarding is enabled, there may be additional exposure to
669: the server and to client displays if the
670: .Nm sshd
671: proxy display is configured to listen on the wildcard address (see
672: .Cm X11UseLocalhost
673: below), however this is not the default.
674: Additionally, the authentication spoofing and authentication data
675: verification and substitution occur on the client side.
676: The security risk of using X11 forwarding is that the client's X11
677: display server may be exposed to attack when the ssh client requests
678: forwarding (see the warnings for
679: .Cm ForwardX11
680: in
1.19 jmc 681: .Xr ssh_config 5 ) .
1.13 stevesk 682: A system administrator may have a stance in which they want to
683: protect clients that may expose themselves to attack by unwittingly
684: requesting X11 forwarding, which can warrant a
685: .Dq no
686: setting.
687: .Pp
688: Note that disabling X11 forwarding does not prevent users from
689: forwarding X11 traffic, as users can always install their own forwarders.
1.1 stevesk 690: X11 forwarding is automatically disabled if
691: .Cm UseLogin
692: is enabled.
693: .It Cm X11UseLocalhost
694: Specifies whether
695: .Nm sshd
696: should bind the X11 forwarding server to the loopback address or to
1.15 jmc 697: the wildcard address.
698: By default,
1.1 stevesk 699: .Nm sshd
700: binds the forwarding server to the loopback address and sets the
701: hostname part of the
702: .Ev DISPLAY
703: environment variable to
704: .Dq localhost .
1.8 stevesk 705: This prevents remote hosts from connecting to the proxy display.
1.1 stevesk 706: However, some older X11 clients may not function with this
707: configuration.
708: .Cm X11UseLocalhost
709: may be set to
710: .Dq no
711: to specify that the forwarding server should be bound to the wildcard
712: address.
713: The argument must be
714: .Dq yes
715: or
716: .Dq no .
717: The default is
718: .Dq yes .
719: .It Cm XAuthLocation
1.11 stevesk 720: Specifies the full pathname of the
1.1 stevesk 721: .Xr xauth 1
722: program.
723: The default is
724: .Pa /usr/X11R6/bin/xauth .
725: .El
726: .Ss Time Formats
727: .Nm sshd
728: command-line arguments and configuration file options that specify time
729: may be expressed using a sequence of the form:
730: .Sm off
1.7 stevesk 731: .Ar time Op Ar qualifier ,
1.1 stevesk 732: .Sm on
733: where
734: .Ar time
735: is a positive integer value and
736: .Ar qualifier
737: is one of the following:
738: .Pp
739: .Bl -tag -width Ds -compact -offset indent
740: .It Cm <none>
741: seconds
742: .It Cm s | Cm S
743: seconds
744: .It Cm m | Cm M
745: minutes
746: .It Cm h | Cm H
747: hours
748: .It Cm d | Cm D
749: days
750: .It Cm w | Cm W
751: weeks
752: .El
753: .Pp
754: Each member of the sequence is added together to calculate
755: the total time value.
756: .Pp
757: Time format examples:
758: .Pp
759: .Bl -tag -width Ds -compact -offset indent
760: .It 600
761: 600 seconds (10 minutes)
762: .It 10m
763: 10 minutes
764: .It 1h30m
765: 1 hour 30 minutes (90 minutes)
766: .El
767: .Sh FILES
768: .Bl -tag -width Ds
769: .It Pa /etc/ssh/sshd_config
770: Contains configuration data for
771: .Nm sshd .
772: This file should be writable by root only, but it is recommended
773: (though not necessary) that it be world-readable.
774: .El
1.19 jmc 775: .Sh SEE ALSO
776: .Xr sshd 8
1.1 stevesk 777: .Sh AUTHORS
778: OpenSSH is a derivative of the original and free
779: ssh 1.2.12 release by Tatu Ylonen.
780: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
781: Theo de Raadt and Dug Song
782: removed many bugs, re-added newer features and
783: created OpenSSH.
784: Markus Friedl contributed the support for SSH
785: protocol versions 1.5 and 2.0.
786: Niels Provos and Markus Friedl contributed support
787: for privilege separation.
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