Annotation of src/usr.bin/ssh/sshd_config.5, Revision 1.23
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.
16: .\"
17: .\" Redistribution and use in source and binary forms, with or without
18: .\" modification, are permitted provided that the following conditions
19: .\" are met:
20: .\" 1. Redistributions of source code must retain the above copyright
21: .\" notice, this list of conditions and the following disclaimer.
22: .\" 2. Redistributions in binary form must reproduce the above copyright
23: .\" notice, this list of conditions and the following disclaimer in the
24: .\" documentation and/or other materials provided with the distribution.
25: .\"
26: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
27: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
28: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
29: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
30: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
31: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36: .\"
1.23 ! markus 37: .\" $OpenBSD: sshd_config.5,v 1.22 2003/08/13 08:46:31 markus 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
64: .It Cm AllowGroups
65: This keyword can be followed by a list of group name patterns, separated
66: by spaces.
67: If specified, login is allowed only for users whose primary
68: group or supplementary group list matches one of the patterns.
69: .Ql \&*
70: and
1.16 mouring 71: .Ql \&?
1.1 stevesk 72: can be used as
73: wildcards in the patterns.
74: Only group names are valid; a numerical group ID is not recognized.
75: By default, login is allowed for all groups.
76: .Pp
77: .It Cm AllowTcpForwarding
78: Specifies whether TCP forwarding is permitted.
79: The default is
80: .Dq yes .
81: Note that disabling TCP forwarding does not improve security unless
82: users are also denied shell access, as they can always install their
83: own forwarders.
84: .Pp
85: .It Cm AllowUsers
86: This keyword can be followed by a list of user name patterns, separated
87: by spaces.
1.14 jmc 88: If specified, login is allowed only for user names that
1.1 stevesk 89: match one of the patterns.
90: .Ql \&*
91: and
1.16 mouring 92: .Ql \&?
1.1 stevesk 93: can be used as
94: wildcards in the patterns.
95: Only user names are valid; a numerical user ID is not recognized.
96: By default, login is allowed for all users.
97: If the pattern takes the form USER@HOST then USER and HOST
98: are separately checked, restricting logins to particular
99: users from particular hosts.
100: .Pp
101: .It Cm AuthorizedKeysFile
102: Specifies the file that contains the public keys that can be used
103: for user authentication.
104: .Cm AuthorizedKeysFile
105: may contain tokens of the form %T which are substituted during connection
1.17 jmc 106: set-up.
107: The following tokens are defined: %% is replaced by a literal '%',
1.1 stevesk 108: %h is replaced by the home directory of the user being authenticated and
109: %u is replaced by the username of that user.
110: After expansion,
111: .Cm AuthorizedKeysFile
112: is taken to be an absolute path or one relative to the user's home
113: directory.
114: The default is
115: .Dq .ssh/authorized_keys .
116: .It Cm Banner
117: In some jurisdictions, sending a warning message before authentication
118: may be relevant for getting legal protection.
119: The contents of the specified file are sent to the remote user before
120: authentication is allowed.
121: This option is only available for protocol version 2.
122: By default, no banner is displayed.
123: .Pp
124: .It Cm ChallengeResponseAuthentication
125: Specifies whether challenge response authentication is allowed.
126: All authentication styles from
127: .Xr login.conf 5
128: are supported.
129: The default is
130: .Dq yes .
131: .It Cm Ciphers
132: Specifies the ciphers allowed for protocol version 2.
133: Multiple ciphers must be comma-separated.
134: The default is
135: .Pp
136: .Bd -literal
137: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
1.20 djm 138: aes192-cbc,aes256-cbc,aes128-ctr,aes192-ctr,aes256-ctr''
1.1 stevesk 139: .Ed
140: .It Cm ClientAliveInterval
141: Sets a timeout interval in seconds after which if no data has been received
142: from the client,
143: .Nm sshd
144: will send a message through the encrypted
145: channel to request a response from the client.
146: The default
147: is 0, indicating that these messages will not be sent to the client.
148: This option applies to protocol version 2 only.
149: .It Cm ClientAliveCountMax
150: Sets the number of client alive messages (see above) which may be
151: sent without
152: .Nm sshd
1.17 jmc 153: receiving any messages back from the client.
154: If this threshold is reached while client alive messages are being sent,
1.1 stevesk 155: .Nm sshd
1.17 jmc 156: will disconnect the client, terminating the session.
157: It is important to note that the use of client alive messages is very
158: different from
1.1 stevesk 159: .Cm KeepAlive
1.17 jmc 160: (below).
161: The client alive messages are sent through the encrypted channel
162: and therefore will not be spoofable.
163: The TCP keepalive option enabled by
1.1 stevesk 164: .Cm KeepAlive
1.17 jmc 165: is spoofable.
166: The client alive mechanism is valuable when the client or
1.1 stevesk 167: server depend on knowing when a connection has become inactive.
168: .Pp
1.17 jmc 169: The default value is 3.
170: If
1.1 stevesk 171: .Cm ClientAliveInterval
172: (above) is set to 15, and
173: .Cm ClientAliveCountMax
174: is left at the default, unresponsive ssh clients
175: will be disconnected after approximately 45 seconds.
1.3 markus 176: .It Cm Compression
177: Specifies whether compression is allowed.
178: The argument must be
179: .Dq yes
180: or
181: .Dq no .
182: The default is
183: .Dq yes .
1.1 stevesk 184: .It Cm DenyGroups
185: This keyword can be followed by a list of group name patterns, separated
186: by spaces.
187: Login is disallowed for users whose primary group or supplementary
188: group list matches one of the patterns.
189: .Ql \&*
190: and
1.16 mouring 191: .Ql \&?
1.1 stevesk 192: can be used as
193: wildcards in the patterns.
194: Only group names are valid; a numerical group ID is not recognized.
195: By default, login is allowed for all groups.
196: .Pp
197: .It Cm DenyUsers
198: This keyword can be followed by a list of user name patterns, separated
199: by spaces.
200: Login is disallowed for user names that match one of the patterns.
201: .Ql \&*
202: and
1.16 mouring 203: .Ql \&?
1.1 stevesk 204: can be used as wildcards in the patterns.
205: Only user names are valid; a numerical user ID is not recognized.
206: By default, login is allowed for all users.
207: If the pattern takes the form USER@HOST then USER and HOST
208: are separately checked, restricting logins to particular
209: users from particular hosts.
210: .It Cm GatewayPorts
211: Specifies whether remote hosts are allowed to connect to ports
212: forwarded for the client.
213: By default,
214: .Nm sshd
1.15 jmc 215: binds remote port forwardings to the loopback address.
216: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 217: .Cm GatewayPorts
218: can be used to specify that
219: .Nm sshd
220: should bind remote port forwardings to the wildcard address,
221: thus allowing remote hosts to connect to forwarded ports.
222: The argument must be
223: .Dq yes
224: or
225: .Dq no .
226: The default is
227: .Dq no .
1.23 ! markus 228: .It Cm GSSAPIAuthentication
! 229: Specifies whether authentication based on GSSAPI may be used, either using
! 230: the result of a successful key exchange, or using GSSAPI user
! 231: authentication.
! 232: The default is
! 233: .Dq no .
! 234: Note that this option applies to protocol version 2 only.
! 235: .It Cm GSSAPICleanupCredentials
! 236: Specifies whether to automatically destroy the user's credentials cache
! 237: on logout.
! 238: The default is
! 239: .Dq yes .
! 240: Note that this option applies to protocol version 2 only.
1.1 stevesk 241: .It Cm HostbasedAuthentication
242: Specifies whether rhosts or /etc/hosts.equiv authentication together
243: with successful public key client host authentication is allowed
244: (hostbased authentication).
245: This option is similar to
246: .Cm RhostsRSAAuthentication
247: and applies to protocol version 2 only.
248: The default is
249: .Dq no .
250: .It Cm HostKey
251: Specifies a file containing a private host key
252: used by SSH.
253: The default is
254: .Pa /etc/ssh/ssh_host_key
255: for protocol version 1, and
256: .Pa /etc/ssh/ssh_host_rsa_key
257: and
258: .Pa /etc/ssh/ssh_host_dsa_key
259: for protocol version 2.
260: Note that
261: .Nm sshd
262: will refuse to use a file if it is group/world-accessible.
263: It is possible to have multiple host key files.
264: .Dq rsa1
265: keys are used for version 1 and
266: .Dq dsa
267: or
268: .Dq rsa
269: are used for version 2 of the SSH protocol.
270: .It Cm IgnoreRhosts
271: Specifies that
272: .Pa .rhosts
273: and
274: .Pa .shosts
275: files will not be used in
276: .Cm RhostsRSAAuthentication
277: or
278: .Cm HostbasedAuthentication .
279: .Pp
280: .Pa /etc/hosts.equiv
281: and
282: .Pa /etc/shosts.equiv
283: are still used.
284: The default is
285: .Dq yes .
286: .It Cm IgnoreUserKnownHosts
287: Specifies whether
288: .Nm sshd
289: should ignore the user's
290: .Pa $HOME/.ssh/known_hosts
291: during
292: .Cm RhostsRSAAuthentication
293: or
294: .Cm HostbasedAuthentication .
295: The default is
296: .Dq no .
297: .It Cm KeepAlive
298: Specifies whether the system should send TCP keepalive messages to the
299: other side.
300: If they are sent, death of the connection or crash of one
301: of the machines will be properly noticed.
302: However, this means that
303: connections will die if the route is down temporarily, and some people
304: find it annoying.
305: On the other hand, if keepalives are not sent,
306: sessions may hang indefinitely on the server, leaving
307: .Dq ghost
308: users and consuming server resources.
309: .Pp
310: The default is
311: .Dq yes
312: (to send keepalives), and the server will notice
313: if the network goes down or the client host crashes.
314: This avoids infinitely hanging sessions.
315: .Pp
316: To disable keepalives, the value should be set to
317: .Dq no .
318: .It Cm KerberosAuthentication
319: Specifies whether Kerberos authentication is allowed.
320: This can be in the form of a Kerberos ticket, or if
321: .Cm PasswordAuthentication
322: is yes, the password provided by the user will be validated through
323: the Kerberos KDC.
324: To use this option, the server needs a
325: Kerberos servtab which allows the verification of the KDC's identity.
326: Default is
327: .Dq no .
328: .It Cm KerberosOrLocalPasswd
329: If set then if password authentication through Kerberos fails then
330: the password will be validated via any additional local mechanism
331: such as
332: .Pa /etc/passwd .
333: Default is
334: .Dq yes .
335: .It Cm KerberosTgtPassing
336: Specifies whether a Kerberos TGT may be forwarded to the server.
337: Default is
1.21 markus 338: .Dq no .
1.1 stevesk 339: .It Cm KerberosTicketCleanup
340: Specifies whether to automatically destroy the user's ticket cache
341: file on logout.
342: Default is
343: .Dq yes .
344: .It Cm KeyRegenerationInterval
345: In protocol version 1, the ephemeral server key is automatically regenerated
346: after this many seconds (if it has been used).
347: The purpose of regeneration is to prevent
348: decrypting captured sessions by later breaking into the machine and
349: stealing the keys.
350: The key is never stored anywhere.
351: If the value is 0, the key is never regenerated.
352: The default is 3600 (seconds).
353: .It Cm ListenAddress
354: Specifies the local addresses
355: .Nm sshd
356: should listen on.
357: The following forms may be used:
358: .Pp
359: .Bl -item -offset indent -compact
360: .It
361: .Cm ListenAddress
362: .Sm off
363: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
364: .Sm on
365: .It
366: .Cm ListenAddress
367: .Sm off
368: .Ar host No | Ar IPv4_addr No : Ar port
369: .Sm on
370: .It
371: .Cm ListenAddress
372: .Sm off
373: .Oo
374: .Ar host No | Ar IPv6_addr Oc : Ar port
375: .Sm on
376: .El
377: .Pp
378: If
379: .Ar port
380: is not specified,
381: .Nm sshd
382: will listen on the address and all prior
383: .Cm Port
1.17 jmc 384: options specified.
385: The default is to listen on all local addresses.
1.15 jmc 386: Multiple
1.1 stevesk 387: .Cm ListenAddress
1.17 jmc 388: options are permitted.
389: Additionally, any
1.1 stevesk 390: .Cm Port
391: options must precede this option for non port qualified addresses.
392: .It Cm LoginGraceTime
393: The server disconnects after this time if the user has not
394: successfully logged in.
395: If the value is 0, there is no time limit.
1.12 stevesk 396: The default is 120 seconds.
1.1 stevesk 397: .It Cm LogLevel
398: Gives the verbosity level that is used when logging messages from
399: .Nm sshd .
400: The possible values are:
401: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
1.15 jmc 402: The default is INFO.
403: DEBUG and DEBUG1 are equivalent.
404: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
405: Logging with a DEBUG level violates the privacy of users and is not recommended.
1.1 stevesk 406: .It Cm MACs
407: Specifies the available MAC (message authentication code) algorithms.
408: The MAC algorithm is used in protocol version 2
409: for data integrity protection.
410: Multiple algorithms must be comma-separated.
411: The default is
412: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
413: .It Cm MaxStartups
414: Specifies the maximum number of concurrent unauthenticated connections to the
415: .Nm sshd
416: daemon.
417: Additional connections will be dropped until authentication succeeds or the
418: .Cm LoginGraceTime
419: expires for a connection.
420: The default is 10.
421: .Pp
422: Alternatively, random early drop can be enabled by specifying
423: the three colon separated values
424: .Dq start:rate:full
425: (e.g., "10:30:60").
426: .Nm sshd
427: will refuse connection attempts with a probability of
428: .Dq rate/100
429: (30%)
430: if there are currently
431: .Dq start
432: (10)
433: unauthenticated connections.
434: The probability increases linearly and all connection attempts
435: are refused if the number of unauthenticated connections reaches
436: .Dq full
437: (60).
438: .It Cm PasswordAuthentication
439: Specifies whether password authentication is allowed.
440: The default is
441: .Dq yes .
442: .It Cm PermitEmptyPasswords
443: When password authentication is allowed, it specifies whether the
444: server allows login to accounts with empty password strings.
445: The default is
446: .Dq no .
447: .It Cm PermitRootLogin
448: Specifies whether root can login using
449: .Xr ssh 1 .
450: The argument must be
451: .Dq yes ,
452: .Dq without-password ,
453: .Dq forced-commands-only
454: or
455: .Dq no .
456: The default is
457: .Dq yes .
458: .Pp
459: If this option is set to
460: .Dq without-password
461: password authentication is disabled for root.
462: .Pp
463: If this option is set to
464: .Dq forced-commands-only
465: root login with public key authentication will be allowed,
466: but only if the
467: .Ar command
468: option has been specified
469: (which may be useful for taking remote backups even if root login is
1.17 jmc 470: normally not allowed).
471: All other authentication methods are disabled for root.
1.1 stevesk 472: .Pp
473: If this option is set to
474: .Dq no
475: root is not allowed to login.
1.6 markus 476: .It Cm PermitUserEnvironment
477: Specifies whether
478: .Pa ~/.ssh/environment
1.9 stevesk 479: and
1.6 markus 480: .Cm environment=
481: options in
482: .Pa ~/.ssh/authorized_keys
1.9 stevesk 483: are processed by
484: .Nm sshd .
1.6 markus 485: The default is
486: .Dq no .
1.9 stevesk 487: Enabling environment processing may enable users to bypass access
488: restrictions in some configurations using mechanisms such as
489: .Ev LD_PRELOAD .
1.1 stevesk 490: .It Cm PidFile
1.4 stevesk 491: Specifies the file that contains the process ID of the
1.1 stevesk 492: .Nm sshd
493: daemon.
494: The default is
495: .Pa /var/run/sshd.pid .
496: .It Cm Port
497: Specifies the port number that
498: .Nm sshd
499: listens on.
500: The default is 22.
501: Multiple options of this type are permitted.
502: See also
503: .Cm ListenAddress .
504: .It Cm PrintLastLog
505: Specifies whether
506: .Nm sshd
507: should print the date and time when the user last logged in.
508: The default is
509: .Dq yes .
510: .It Cm PrintMotd
511: Specifies whether
512: .Nm sshd
513: should print
514: .Pa /etc/motd
515: when a user logs in interactively.
516: (On some systems it is also printed by the shell,
517: .Pa /etc/profile ,
518: or equivalent.)
519: The default is
520: .Dq yes .
521: .It Cm Protocol
522: Specifies the protocol versions
523: .Nm sshd
1.5 stevesk 524: supports.
1.1 stevesk 525: The possible values are
526: .Dq 1
527: and
528: .Dq 2 .
529: Multiple versions must be comma-separated.
530: The default is
531: .Dq 2,1 .
1.5 stevesk 532: Note that the order of the protocol list does not indicate preference,
533: because the client selects among multiple protocol versions offered
534: by the server.
535: Specifying
536: .Dq 2,1
537: is identical to
538: .Dq 1,2 .
1.1 stevesk 539: .It Cm PubkeyAuthentication
540: Specifies whether public key authentication is allowed.
541: The default is
542: .Dq yes .
543: Note that this option applies to protocol version 2 only.
544: .Cm RhostsRSAAuthentication
545: should be used
546: instead, because it performs RSA-based host authentication in addition
547: to normal rhosts or /etc/hosts.equiv authentication.
548: The default is
549: .Dq no .
550: This option applies to protocol version 1 only.
551: .It Cm RhostsRSAAuthentication
552: Specifies whether rhosts or /etc/hosts.equiv authentication together
553: with successful RSA host authentication is allowed.
554: The default is
555: .Dq no .
556: This option applies to protocol version 1 only.
557: .It Cm RSAAuthentication
558: Specifies whether pure RSA authentication is allowed.
559: The default is
560: .Dq yes .
561: This option applies to protocol version 1 only.
562: .It Cm ServerKeyBits
563: Defines the number of bits in the ephemeral protocol version 1 server key.
564: The minimum value is 512, and the default is 768.
565: .It Cm StrictModes
566: Specifies whether
567: .Nm sshd
568: should check file modes and ownership of the
569: user's files and home directory before accepting login.
570: This is normally desirable because novices sometimes accidentally leave their
571: directory or files world-writable.
572: The default is
573: .Dq yes .
574: .It Cm Subsystem
575: Configures an external subsystem (e.g., file transfer daemon).
576: Arguments should be a subsystem name and a command to execute upon subsystem
577: request.
578: The command
579: .Xr sftp-server 8
580: implements the
581: .Dq sftp
582: file transfer subsystem.
583: By default no subsystems are defined.
584: Note that this option applies to protocol version 2 only.
585: .It Cm SyslogFacility
586: Gives the facility code that is used when logging messages from
587: .Nm sshd .
588: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
589: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
590: The default is AUTH.
1.18 markus 591: .It Cm UseDNS
592: Specifies whether
593: .Nm sshd
594: should lookup the remote host name and check that
595: the resolved host name for the remote IP address maps back to the
596: very same IP address.
597: The default is
598: .Dq yes .
1.1 stevesk 599: .It Cm UseLogin
600: Specifies whether
601: .Xr login 1
602: is used for interactive login sessions.
603: The default is
604: .Dq no .
605: Note that
606: .Xr login 1
607: is never used for remote command execution.
608: Note also, that if this is enabled,
609: .Cm X11Forwarding
610: will be disabled because
611: .Xr login 1
612: does not know how to handle
613: .Xr xauth 1
1.15 jmc 614: cookies.
615: If
1.1 stevesk 616: .Cm UsePrivilegeSeparation
617: is specified, it will be disabled after authentication.
618: .It Cm UsePrivilegeSeparation
619: Specifies whether
620: .Nm sshd
1.2 stevesk 621: separates privileges by creating an unprivileged child process
1.15 jmc 622: to deal with incoming network traffic.
623: After successful authentication, another process will be created that has
624: the privilege of the authenticated user.
625: The goal of privilege separation is to prevent privilege
1.1 stevesk 626: escalation by containing any corruption within the unprivileged processes.
627: The default is
628: .Dq yes .
629: .It Cm X11DisplayOffset
630: Specifies the first display number available for
631: .Nm sshd Ns 's
632: X11 forwarding.
633: This prevents
634: .Nm sshd
635: from interfering with real X11 servers.
636: The default is 10.
637: .It Cm X11Forwarding
638: Specifies whether X11 forwarding is permitted.
1.13 stevesk 639: The argument must be
640: .Dq yes
641: or
642: .Dq no .
1.1 stevesk 643: The default is
644: .Dq no .
1.13 stevesk 645: .Pp
646: When X11 forwarding is enabled, there may be additional exposure to
647: the server and to client displays if the
648: .Nm sshd
649: proxy display is configured to listen on the wildcard address (see
650: .Cm X11UseLocalhost
651: below), however this is not the default.
652: Additionally, the authentication spoofing and authentication data
653: verification and substitution occur on the client side.
654: The security risk of using X11 forwarding is that the client's X11
655: display server may be exposed to attack when the ssh client requests
656: forwarding (see the warnings for
657: .Cm ForwardX11
658: in
1.19 jmc 659: .Xr ssh_config 5 ) .
1.13 stevesk 660: A system administrator may have a stance in which they want to
661: protect clients that may expose themselves to attack by unwittingly
662: requesting X11 forwarding, which can warrant a
663: .Dq no
664: setting.
665: .Pp
666: Note that disabling X11 forwarding does not prevent users from
667: forwarding X11 traffic, as users can always install their own forwarders.
1.1 stevesk 668: X11 forwarding is automatically disabled if
669: .Cm UseLogin
670: is enabled.
671: .It Cm X11UseLocalhost
672: Specifies whether
673: .Nm sshd
674: should bind the X11 forwarding server to the loopback address or to
1.15 jmc 675: the wildcard address.
676: By default,
1.1 stevesk 677: .Nm sshd
678: binds the forwarding server to the loopback address and sets the
679: hostname part of the
680: .Ev DISPLAY
681: environment variable to
682: .Dq localhost .
1.8 stevesk 683: This prevents remote hosts from connecting to the proxy display.
1.1 stevesk 684: However, some older X11 clients may not function with this
685: configuration.
686: .Cm X11UseLocalhost
687: may be set to
688: .Dq no
689: to specify that the forwarding server should be bound to the wildcard
690: address.
691: The argument must be
692: .Dq yes
693: or
694: .Dq no .
695: The default is
696: .Dq yes .
697: .It Cm XAuthLocation
1.11 stevesk 698: Specifies the full pathname of the
1.1 stevesk 699: .Xr xauth 1
700: program.
701: The default is
702: .Pa /usr/X11R6/bin/xauth .
703: .El
704: .Ss Time Formats
705: .Nm sshd
706: command-line arguments and configuration file options that specify time
707: may be expressed using a sequence of the form:
708: .Sm off
1.7 stevesk 709: .Ar time Op Ar qualifier ,
1.1 stevesk 710: .Sm on
711: where
712: .Ar time
713: is a positive integer value and
714: .Ar qualifier
715: is one of the following:
716: .Pp
717: .Bl -tag -width Ds -compact -offset indent
718: .It Cm <none>
719: seconds
720: .It Cm s | Cm S
721: seconds
722: .It Cm m | Cm M
723: minutes
724: .It Cm h | Cm H
725: hours
726: .It Cm d | Cm D
727: days
728: .It Cm w | Cm W
729: weeks
730: .El
731: .Pp
732: Each member of the sequence is added together to calculate
733: the total time value.
734: .Pp
735: Time format examples:
736: .Pp
737: .Bl -tag -width Ds -compact -offset indent
738: .It 600
739: 600 seconds (10 minutes)
740: .It 10m
741: 10 minutes
742: .It 1h30m
743: 1 hour 30 minutes (90 minutes)
744: .El
745: .Sh FILES
746: .Bl -tag -width Ds
747: .It Pa /etc/ssh/sshd_config
748: Contains configuration data for
749: .Nm sshd .
750: This file should be writable by root only, but it is recommended
751: (though not necessary) that it be world-readable.
752: .El
1.19 jmc 753: .Sh SEE ALSO
754: .Xr sshd 8
1.1 stevesk 755: .Sh AUTHORS
756: OpenSSH is a derivative of the original and free
757: ssh 1.2.12 release by Tatu Ylonen.
758: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
759: Theo de Raadt and Dug Song
760: removed many bugs, re-added newer features and
761: created OpenSSH.
762: Markus Friedl contributed the support for SSH
763: protocol versions 1.5 and 2.0.
764: Niels Provos and Markus Friedl contributed support
765: for privilege separation.
![[BACK]](/icons/back.gif){kind=icon}
Return to sshd_config.5 CVS log ![[TXT]](/icons/text.gif){kind=icon}
![[DIR]](/icons/dir.gif){kind=icon}
Up to [local] / src / usr.bin / ssh