Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.62
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: .\"
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22: .\" 2. Redistributions in binary form must reproduce the above copyright
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1.62 ! djm 37: .\" $OpenBSD: ssh_config.5,v 1.61 2005/07/08 12:53:10 jmc Exp $
1.1 stevesk 38: .Dd September 25, 1999
39: .Dt SSH_CONFIG 5
40: .Os
41: .Sh NAME
42: .Nm ssh_config
43: .Nd OpenSSH SSH client configuration files
44: .Sh SYNOPSIS
45: .Bl -tag -width Ds -compact
1.50 djm 46: .It Pa ~/.ssh/config
1.1 stevesk 47: .It Pa /etc/ssh/ssh_config
48: .El
49: .Sh DESCRIPTION
50: .Nm ssh
51: obtains configuration data from the following sources in
52: the following order:
1.2 stevesk 53: .Bl -enum -offset indent -compact
54: .It
55: command-line options
56: .It
57: user's configuration file
1.50 djm 58: .Pq Pa ~/.ssh/config
1.2 stevesk 59: .It
60: system-wide configuration file
61: .Pq Pa /etc/ssh/ssh_config
62: .El
1.1 stevesk 63: .Pp
64: For each parameter, the first obtained value
65: will be used.
1.41 jmc 66: The configuration files contain sections separated by
1.1 stevesk 67: .Dq Host
68: specifications, and that section is only applied for hosts that
69: match one of the patterns given in the specification.
70: The matched host name is the one given on the command line.
71: .Pp
72: Since the first obtained value for each parameter is used, more
73: host-specific declarations should be given near the beginning of the
74: file, and general defaults at the end.
75: .Pp
76: The configuration file has the following format:
77: .Pp
78: Empty lines and lines starting with
79: .Ql #
80: are comments.
81: .Pp
82: Otherwise a line is of the format
83: .Dq keyword arguments .
84: Configuration options may be separated by whitespace or
85: optional whitespace and exactly one
86: .Ql = ;
87: the latter format is useful to avoid the need to quote whitespace
88: when specifying configuration options using the
89: .Nm ssh ,
90: .Nm scp
91: and
92: .Nm sftp
93: .Fl o
94: option.
95: .Pp
96: The possible
97: keywords and their meanings are as follows (note that
98: keywords are case-insensitive and arguments are case-sensitive):
99: .Bl -tag -width Ds
100: .It Cm Host
101: Restricts the following declarations (up to the next
102: .Cm Host
103: keyword) to be only for those hosts that match one of the patterns
104: given after the keyword.
105: .Ql \&*
106: and
1.20 jmc 107: .Ql \&?
1.1 stevesk 108: can be used as wildcards in the
109: patterns.
110: A single
111: .Ql \&*
112: as a pattern can be used to provide global
113: defaults for all hosts.
114: The host is the
115: .Ar hostname
116: argument given on the command line (i.e., the name is not converted to
117: a canonicalized host name before matching).
1.10 djm 118: .It Cm AddressFamily
1.11 jmc 119: Specifies which address family to use when connecting.
120: Valid arguments are
1.10 djm 121: .Dq any ,
122: .Dq inet
1.40 jmc 123: (use IPv4 only) or
1.10 djm 124: .Dq inet6
1.40 jmc 125: (use IPv6 only).
1.1 stevesk 126: .It Cm BatchMode
127: If set to
128: .Dq yes ,
129: passphrase/password querying will be disabled.
130: This option is useful in scripts and other batch jobs where no user
131: is present to supply the password.
132: The argument must be
133: .Dq yes
134: or
135: .Dq no .
136: The default is
137: .Dq no .
138: .It Cm BindAddress
1.60 dtucker 139: Use the specified address on the local machine as the source address of
1.61 jmc 140: the connection.
141: Only useful on systems with more than one address.
1.1 stevesk 142: Note that this option does not work if
143: .Cm UsePrivilegedPort
144: is set to
145: .Dq yes .
146: .It Cm ChallengeResponseAuthentication
147: Specifies whether to use challenge response authentication.
148: The argument to this keyword must be
149: .Dq yes
150: or
151: .Dq no .
152: The default is
153: .Dq yes .
154: .It Cm CheckHostIP
155: If this flag is set to
156: .Dq yes ,
157: ssh will additionally check the host IP address in the
158: .Pa known_hosts
159: file.
160: This allows ssh to detect if a host key changed due to DNS spoofing.
161: If the option is set to
162: .Dq no ,
163: the check will not be executed.
164: The default is
165: .Dq yes .
166: .It Cm Cipher
167: Specifies the cipher to use for encrypting the session
168: in protocol version 1.
169: Currently,
170: .Dq blowfish ,
171: .Dq 3des ,
172: and
173: .Dq des
174: are supported.
175: .Ar des
176: is only supported in the
177: .Nm ssh
178: client for interoperability with legacy protocol 1 implementations
179: that do not support the
180: .Ar 3des
1.7 jmc 181: cipher.
182: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 183: The default is
184: .Dq 3des .
185: .It Cm Ciphers
186: Specifies the ciphers allowed for protocol version 2
187: in order of preference.
188: Multiple ciphers must be comma-separated.
1.35 dtucker 189: The supported ciphers are
190: .Dq 3des-cbc ,
191: .Dq aes128-cbc ,
192: .Dq aes192-cbc ,
193: .Dq aes256-cbc ,
194: .Dq aes128-ctr ,
195: .Dq aes192-ctr ,
196: .Dq aes256-ctr ,
1.54 djm 197: .Dq arcfour128 ,
198: .Dq arcfour256 ,
1.35 dtucker 199: .Dq arcfour ,
200: .Dq blowfish-cbc ,
201: and
202: .Dq cast128-cbc .
1.1 stevesk 203: The default is
204: .Bd -literal
1.54 djm 205: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
206: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
207: aes192-ctr,aes256-ctr''
1.1 stevesk 208: .Ed
209: .It Cm ClearAllForwardings
210: Specifies that all local, remote and dynamic port forwardings
211: specified in the configuration files or on the command line be
1.7 jmc 212: cleared.
213: This option is primarily useful when used from the
1.1 stevesk 214: .Nm ssh
215: command line to clear port forwardings set in
216: configuration files, and is automatically set by
217: .Xr scp 1
218: and
219: .Xr sftp 1 .
220: The argument must be
221: .Dq yes
222: or
223: .Dq no .
224: The default is
225: .Dq no .
226: .It Cm Compression
227: Specifies whether to use compression.
228: The argument must be
229: .Dq yes
230: or
231: .Dq no .
232: The default is
233: .Dq no .
234: .It Cm CompressionLevel
235: Specifies the compression level to use if compression is enabled.
236: The argument must be an integer from 1 (fast) to 9 (slow, best).
237: The default level is 6, which is good for most applications.
238: The meaning of the values is the same as in
239: .Xr gzip 1 .
240: Note that this option applies to protocol version 1 only.
241: .It Cm ConnectionAttempts
242: Specifies the number of tries (one per second) to make before exiting.
243: The argument must be an integer.
244: This may be useful in scripts if the connection sometimes fails.
245: The default is 1.
1.9 djm 246: .It Cm ConnectTimeout
247: Specifies the timeout (in seconds) used when connecting to the ssh
1.11 jmc 248: server, instead of using the default system TCP timeout.
249: This value is used only when the target is down or really unreachable,
250: not when it refuses the connection.
1.36 djm 251: .It Cm ControlMaster
252: Enables the sharing of multiple sessions over a single network connection.
253: When set to
254: .Dq yes
255: .Nm ssh
256: will listen for connections on a control socket specified using the
257: .Cm ControlPath
258: argument.
259: Additional sessions can connect to this socket using the same
260: .Cm ControlPath
261: with
262: .Cm ControlMaster
263: set to
264: .Dq no
1.38 jmc 265: (the default).
1.36 djm 266: These sessions will reuse the master instance's network connection rather
267: than initiating new ones.
1.37 djm 268: Setting this to
269: .Dq ask
270: will cause
271: .Nm ssh
272: to listen for control connections, but require confirmation using the
273: .Ev SSH_ASKPASS
274: program before they are accepted (see
275: .Xr ssh-add 1
1.38 jmc 276: for details).
1.51 jakob 277: If the
278: .Cm ControlPath
279: can not be opened,
280: .Nm ssh
281: will continue without connecting to a master instance.
1.58 djm 282: .Pp
283: X11 and
1.59 jmc 284: .Xr ssh-agent 1
1.58 djm 285: forwarding is supported over these multiplexed connections, however the
286: display and agent fowarded will be the one belonging to the master
1.59 jmc 287: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 288: .Pp
289: Two additional options allow for opportunistic multiplexing: try to use a
290: master connection but fall back to creating a new one if one does not already
291: exist.
292: These options are:
293: .Dq auto
294: and
295: .Dq autoask .
296: The latter requires confirmation like the
297: .Dq ask
298: option.
1.36 djm 299: .It Cm ControlPath
1.55 djm 300: Specify the path to the control socket used for connection sharing as described
301: in the
1.36 djm 302: .Cm ControlMaster
1.57 djm 303: section above or the string
304: .Dq none
305: to disable connection sharing.
1.55 djm 306: In the path,
307: .Ql %h
308: will be substituted by the target host name,
309: .Ql %p
310: the port and
311: .Ql %r
312: by the remote login username.
1.56 djm 313: It is recommended that any
314: .Cm ControlPath
315: used for opportunistic connection sharing include
316: all three of these escape sequences.
317: This ensures that shared connections are uniquely identified.
1.38 jmc 318: .It Cm DynamicForward
319: Specifies that a TCP/IP port on the local machine be forwarded
320: over the secure channel, and the application
321: protocol is then used to determine where to connect to from the
322: remote machine.
1.62 ! djm 323: .Pp
! 324: The argument must be
! 325: .Sm off
! 326: .Oo Ar bind_address : Oc Ar port .
! 327: .Sm on
! 328: IPv6 addresses can be specified by enclosing addresses in square brackets or
! 329: by using an alternative syntax:
! 330: .Oo Ar bind_address Ns / Oc Ns Ar port .
! 331: By default, the local port is bound in accordance with the
! 332: .Cm GatewayPorts
! 333: setting.
! 334: However, an explicit
! 335: .Ar bind_address
! 336: may be used to bind the connection to a specific address.
! 337: The
! 338: .Ar bind_address
! 339: of
! 340: .Dq localhost
! 341: indicates that the listening port be bound for local use only, while an
! 342: empty address or
! 343: .Sq *
! 344: indicates that the port should be available from all interfaces.
! 345: .Pp
1.38 jmc 346: Currently the SOCKS4 and SOCKS5 protocols are supported, and
347: .Nm ssh
348: will act as a SOCKS server.
349: Multiple forwardings may be specified, and
350: additional forwardings can be given on the command line.
351: Only the superuser can forward privileged ports.
1.14 markus 352: .It Cm EnableSSHKeysign
353: Setting this option to
354: .Dq yes
355: in the global client configuration file
356: .Pa /etc/ssh/ssh_config
357: enables the use of the helper program
358: .Xr ssh-keysign 8
359: during
360: .Cm HostbasedAuthentication .
361: The argument must be
362: .Dq yes
363: or
364: .Dq no .
365: The default is
366: .Dq no .
1.23 jmc 367: This option should be placed in the non-hostspecific section.
1.14 markus 368: See
369: .Xr ssh-keysign 8
370: for more information.
1.1 stevesk 371: .It Cm EscapeChar
372: Sets the escape character (default:
373: .Ql ~ ) .
374: The escape character can also
375: be set on the command line.
376: The argument should be a single character,
377: .Ql ^
378: followed by a letter, or
379: .Dq none
380: to disable the escape
381: character entirely (making the connection transparent for binary
382: data).
383: .It Cm ForwardAgent
384: Specifies whether the connection to the authentication agent (if any)
385: will be forwarded to the remote machine.
386: The argument must be
387: .Dq yes
388: or
389: .Dq no .
390: The default is
391: .Dq no .
1.3 stevesk 392: .Pp
1.7 jmc 393: Agent forwarding should be enabled with caution.
394: Users with the ability to bypass file permissions on the remote host
395: (for the agent's Unix-domain socket)
396: can access the local agent through the forwarded connection.
397: An attacker cannot obtain key material from the agent,
1.3 stevesk 398: however they can perform operations on the keys that enable them to
399: authenticate using the identities loaded into the agent.
1.1 stevesk 400: .It Cm ForwardX11
401: Specifies whether X11 connections will be automatically redirected
402: over the secure channel and
403: .Ev DISPLAY
404: set.
405: The argument must be
406: .Dq yes
407: or
408: .Dq no .
409: The default is
410: .Dq no .
1.3 stevesk 411: .Pp
1.7 jmc 412: X11 forwarding should be enabled with caution.
413: Users with the ability to bypass file permissions on the remote host
1.22 markus 414: (for the user's X11 authorization database)
1.7 jmc 415: can access the local X11 display through the forwarded connection.
1.22 markus 416: An attacker may then be able to perform activities such as keystroke monitoring
417: if the
418: .Cm ForwardX11Trusted
419: option is also enabled.
420: .It Cm ForwardX11Trusted
1.34 jmc 421: If this option is set to
1.22 markus 422: .Dq yes
423: then remote X11 clients will have full access to the original X11 display.
1.42 djm 424: .Pp
1.22 markus 425: If this option is set to
426: .Dq no
427: then remote X11 clients will be considered untrusted and prevented
428: from stealing or tampering with data belonging to trusted X11
429: clients.
1.42 djm 430: Furthermore, the
431: .Xr xauth 1
432: token used for the session will be set to expire after 20 minutes.
433: Remote clients will be refused access after this time.
1.22 markus 434: .Pp
435: The default is
436: .Dq no .
437: .Pp
438: See the X11 SECURITY extension specification for full details on
439: the restrictions imposed on untrusted clients.
1.1 stevesk 440: .It Cm GatewayPorts
441: Specifies whether remote hosts are allowed to connect to local
442: forwarded ports.
443: By default,
444: .Nm ssh
1.7 jmc 445: binds local port forwardings to the loopback address.
446: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 447: .Cm GatewayPorts
448: can be used to specify that
449: .Nm ssh
450: should bind local port forwardings to the wildcard address,
451: thus allowing remote hosts to connect to forwarded ports.
452: The argument must be
453: .Dq yes
454: or
455: .Dq no .
456: The default is
457: .Dq no .
458: .It Cm GlobalKnownHostsFile
459: Specifies a file to use for the global
460: host key database instead of
461: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 462: .It Cm GSSAPIAuthentication
1.27 markus 463: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 464: The default is
1.21 markus 465: .Dq no .
1.18 markus 466: Note that this option applies to protocol version 2 only.
467: .It Cm GSSAPIDelegateCredentials
468: Forward (delegate) credentials to the server.
469: The default is
470: .Dq no .
471: Note that this option applies to protocol version 2 only.
1.44 djm 472: .It Cm HashKnownHosts
473: Indicates that
474: .Nm ssh
475: should hash host names and addresses when they are added to
1.50 djm 476: .Pa ~/.ssh/known_hosts .
1.44 djm 477: These hashed names may be used normally by
478: .Nm ssh
479: and
480: .Nm sshd ,
481: but they do not reveal identifying information should the file's contents
482: be disclosed.
483: The default is
484: .Dq no .
1.46 jmc 485: Note that hashing of names and addresses will not be retrospectively applied
1.45 djm 486: to existing known hosts files, but these may be manually hashed using
487: .Xr ssh-keygen 1 .
1.1 stevesk 488: .It Cm HostbasedAuthentication
489: Specifies whether to try rhosts based authentication with public key
490: authentication.
491: The argument must be
492: .Dq yes
493: or
494: .Dq no .
495: The default is
496: .Dq no .
497: This option applies to protocol version 2 only and
498: is similar to
499: .Cm RhostsRSAAuthentication .
500: .It Cm HostKeyAlgorithms
501: Specifies the protocol version 2 host key algorithms
502: that the client wants to use in order of preference.
503: The default for this option is:
504: .Dq ssh-rsa,ssh-dss .
505: .It Cm HostKeyAlias
506: Specifies an alias that should be used instead of the
507: real host name when looking up or saving the host key
508: in the host key database files.
509: This option is useful for tunneling ssh connections
510: or for multiple servers running on a single host.
511: .It Cm HostName
512: Specifies the real host name to log into.
513: This can be used to specify nicknames or abbreviations for hosts.
514: Default is the name given on the command line.
515: Numeric IP addresses are also permitted (both on the command line and in
516: .Cm HostName
517: specifications).
518: .It Cm IdentityFile
519: Specifies a file from which the user's RSA or DSA authentication identity
1.11 jmc 520: is read.
521: The default is
1.50 djm 522: .Pa ~/.ssh/identity
1.1 stevesk 523: for protocol version 1, and
1.50 djm 524: .Pa ~/.ssh/id_rsa
1.1 stevesk 525: and
1.50 djm 526: .Pa ~/.ssh/id_dsa
1.1 stevesk 527: for protocol version 2.
528: Additionally, any identities represented by the authentication agent
529: will be used for authentication.
530: The file name may use the tilde
531: syntax to refer to a user's home directory.
532: It is possible to have
533: multiple identity files specified in configuration files; all these
534: identities will be tried in sequence.
1.29 markus 535: .It Cm IdentitiesOnly
536: Specifies that
537: .Nm ssh
538: should only use the authentication identity files configured in the
1.31 jmc 539: .Nm
1.29 markus 540: files,
541: even if the
542: .Nm ssh-agent
543: offers more identities.
544: The argument to this keyword must be
545: .Dq yes
546: or
547: .Dq no .
548: This option is intented for situations where
549: .Nm ssh-agent
550: offers many different identities.
551: The default is
552: .Dq no .
1.39 djm 553: .It Cm KbdInteractiveDevices
554: Specifies the list of methods to use in keyboard-interactive authentication.
555: Multiple method names must be comma-separated.
556: The default is to use the server specified list.
1.1 stevesk 557: .It Cm LocalForward
558: Specifies that a TCP/IP port on the local machine be forwarded over
559: the secure channel to the specified host and port from the remote machine.
1.49 jmc 560: The first argument must be
1.43 djm 561: .Sm off
1.49 jmc 562: .Oo Ar bind_address : Oc Ar port
1.43 djm 563: .Sm on
1.49 jmc 564: and the second argument must be
565: .Ar host : Ns Ar hostport .
1.46 jmc 566: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 567: by using an alternative syntax:
1.49 jmc 568: .Oo Ar bind_address Ns / Oc Ns Ar port
569: and
570: .Ar host Ns / Ns Ar hostport .
1.46 jmc 571: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 572: given on the command line.
1.1 stevesk 573: Only the superuser can forward privileged ports.
1.43 djm 574: By default, the local port is bound in accordance with the
575: .Cm GatewayPorts
576: setting.
577: However, an explicit
578: .Ar bind_address
579: may be used to bind the connection to a specific address.
580: The
581: .Ar bind_address
582: of
583: .Dq localhost
1.46 jmc 584: indicates that the listening port be bound for local use only, while an
585: empty address or
586: .Sq *
1.43 djm 587: indicates that the port should be available from all interfaces.
1.1 stevesk 588: .It Cm LogLevel
589: Gives the verbosity level that is used when logging messages from
590: .Nm ssh .
591: The possible values are:
592: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
1.7 jmc 593: The default is INFO.
594: DEBUG and DEBUG1 are equivalent.
595: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 596: .It Cm MACs
597: Specifies the MAC (message authentication code) algorithms
598: in order of preference.
599: The MAC algorithm is used in protocol version 2
600: for data integrity protection.
601: Multiple algorithms must be comma-separated.
602: The default is
603: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
604: .It Cm NoHostAuthenticationForLocalhost
605: This option can be used if the home directory is shared across machines.
606: In this case localhost will refer to a different machine on each of
607: the machines and the user will get many warnings about changed host keys.
608: However, this option disables host authentication for localhost.
609: The argument to this keyword must be
610: .Dq yes
611: or
612: .Dq no .
613: The default is to check the host key for localhost.
614: .It Cm NumberOfPasswordPrompts
615: Specifies the number of password prompts before giving up.
616: The argument to this keyword must be an integer.
617: Default is 3.
618: .It Cm PasswordAuthentication
619: Specifies whether to use password authentication.
620: The argument to this keyword must be
621: .Dq yes
622: or
623: .Dq no .
624: The default is
625: .Dq yes .
626: .It Cm Port
627: Specifies the port number to connect on the remote host.
628: Default is 22.
629: .It Cm PreferredAuthentications
630: Specifies the order in which the client should try protocol 2
1.11 jmc 631: authentication methods.
1.48 jmc 632: This allows a client to prefer one method (e.g.\&
1.1 stevesk 633: .Cm keyboard-interactive )
1.48 jmc 634: over another method (e.g.\&
1.1 stevesk 635: .Cm password )
636: The default for this option is:
637: .Dq hostbased,publickey,keyboard-interactive,password .
638: .It Cm Protocol
639: Specifies the protocol versions
640: .Nm ssh
641: should support in order of preference.
642: The possible values are
643: .Dq 1
644: and
645: .Dq 2 .
646: Multiple versions must be comma-separated.
647: The default is
648: .Dq 2,1 .
649: This means that
650: .Nm ssh
651: tries version 2 and falls back to version 1
652: if version 2 is not available.
653: .It Cm ProxyCommand
654: Specifies the command to use to connect to the server.
655: The command
656: string extends to the end of the line, and is executed with
657: .Pa /bin/sh .
658: In the command string,
659: .Ql %h
660: will be substituted by the host name to
661: connect and
662: .Ql %p
663: by the port.
664: The command can be basically anything,
665: and should read from its standard input and write to its standard output.
666: It should eventually connect an
667: .Xr sshd 8
668: server running on some machine, or execute
669: .Ic sshd -i
670: somewhere.
671: Host key management will be done using the
672: HostName of the host being connected (defaulting to the name typed by
673: the user).
1.7 jmc 674: Setting the command to
675: .Dq none
1.6 markus 676: disables this option entirely.
1.1 stevesk 677: Note that
678: .Cm CheckHostIP
679: is not available for connects with a proxy command.
1.52 djm 680: .Pp
681: This directive is useful in conjunction with
682: .Xr nc 1
683: and its proxy support.
1.53 jmc 684: For example, the following directive would connect via an HTTP proxy at
1.52 djm 685: 192.0.2.0:
686: .Bd -literal -offset 3n
687: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
688: .Ed
1.1 stevesk 689: .It Cm PubkeyAuthentication
690: Specifies whether to try public key authentication.
691: The argument to this keyword must be
692: .Dq yes
693: or
694: .Dq no .
695: The default is
696: .Dq yes .
697: This option applies to protocol version 2 only.
698: .It Cm RemoteForward
699: Specifies that a TCP/IP port on the remote machine be forwarded over
700: the secure channel to the specified host and port from the local machine.
1.49 jmc 701: The first argument must be
1.43 djm 702: .Sm off
1.49 jmc 703: .Oo Ar bind_address : Oc Ar port
1.43 djm 704: .Sm on
1.49 jmc 705: and the second argument must be
706: .Ar host : Ns Ar hostport .
707: IPv6 addresses can be specified by enclosing addresses in square brackets
708: or by using an alternative syntax:
709: .Oo Ar bind_address Ns / Oc Ns Ar port
710: and
711: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 712: Multiple forwardings may be specified, and additional
713: forwardings can be given on the command line.
714: Only the superuser can forward privileged ports.
1.43 djm 715: .Pp
716: If the
717: .Ar bind_address
718: is not specified, the default is to only bind to loopback addresses.
719: If the
720: .Ar bind_address
721: is
722: .Ql *
723: or an empty string, then the forwarding is requested to listen on all
724: interfaces.
725: Specifying a remote
726: .Ar bind_address
1.46 jmc 727: will only succeed if the server's
728: .Cm GatewayPorts
1.43 djm 729: option is enabled (see
1.46 jmc 730: .Xr sshd_config 5 ) .
1.1 stevesk 731: .It Cm RhostsRSAAuthentication
732: Specifies whether to try rhosts based authentication with RSA host
733: authentication.
734: The argument must be
735: .Dq yes
736: or
737: .Dq no .
738: The default is
739: .Dq no .
740: This option applies to protocol version 1 only and requires
741: .Nm ssh
742: to be setuid root.
743: .It Cm RSAAuthentication
744: Specifies whether to try RSA authentication.
745: The argument to this keyword must be
746: .Dq yes
747: or
748: .Dq no .
749: RSA authentication will only be
750: attempted if the identity file exists, or an authentication agent is
751: running.
752: The default is
753: .Dq yes .
754: Note that this option applies to protocol version 1 only.
1.32 djm 755: .It Cm SendEnv
756: Specifies what variables from the local
757: .Xr environ 7
758: should be sent to the server.
759: Note that environment passing is only supported for protocol 2, the
1.33 djm 760: server must also support it, and the server must be configured to
761: accept these environment variables.
1.32 djm 762: Refer to
763: .Cm AcceptEnv
764: in
765: .Xr sshd_config 5
766: for how to configure the server.
767: Variables are specified by name, which may contain the wildcard characters
768: .Ql \&*
769: and
770: .Ql \&? .
1.33 djm 771: Multiple environment variables may be separated by whitespace or spread
1.32 djm 772: across multiple
773: .Cm SendEnv
774: directives.
775: The default is not to send any environment variables.
1.28 markus 776: .It Cm ServerAliveInterval
777: Sets a timeout interval in seconds after which if no data has been received
778: from the server,
779: .Nm ssh
780: will send a message through the encrypted
781: channel to request a response from the server.
782: The default
783: is 0, indicating that these messages will not be sent to the server.
784: This option applies to protocol version 2 only.
785: .It Cm ServerAliveCountMax
786: Sets the number of server alive messages (see above) which may be
787: sent without
788: .Nm ssh
789: receiving any messages back from the server.
790: If this threshold is reached while server alive messages are being sent,
791: .Nm ssh
792: will disconnect from the server, terminating the session.
793: It is important to note that the use of server alive messages is very
794: different from
795: .Cm TCPKeepAlive
796: (below).
797: The server alive messages are sent through the encrypted channel
798: and therefore will not be spoofable.
799: The TCP keepalive option enabled by
800: .Cm TCPKeepAlive
801: is spoofable.
802: The server alive mechanism is valuable when the client or
803: server depend on knowing when a connection has become inactive.
804: .Pp
805: The default value is 3.
806: If, for example,
807: .Cm ServerAliveInterval
808: (above) is set to 15, and
809: .Cm ServerAliveCountMax
810: is left at the default, if the server becomes unresponsive ssh
811: will disconnect after approximately 45 seconds.
1.1 stevesk 812: .It Cm SmartcardDevice
1.11 jmc 813: Specifies which smartcard device to use.
814: The argument to this keyword is the device
1.1 stevesk 815: .Nm ssh
816: should use to communicate with a smartcard used for storing the user's
1.11 jmc 817: private RSA key.
818: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 819: .It Cm StrictHostKeyChecking
820: If this flag is set to
821: .Dq yes ,
822: .Nm ssh
823: will never automatically add host keys to the
1.50 djm 824: .Pa ~/.ssh/known_hosts
1.1 stevesk 825: file, and refuses to connect to hosts whose host key has changed.
826: This provides maximum protection against trojan horse attacks,
827: however, can be annoying when the
828: .Pa /etc/ssh/ssh_known_hosts
829: file is poorly maintained, or connections to new hosts are
830: frequently made.
831: This option forces the user to manually
832: add all new hosts.
833: If this flag is set to
834: .Dq no ,
835: .Nm ssh
836: will automatically add new host keys to the
837: user known hosts files.
838: If this flag is set to
839: .Dq ask ,
840: new host keys
841: will be added to the user known host files only after the user
842: has confirmed that is what they really want to do, and
843: .Nm ssh
844: will refuse to connect to hosts whose host key has changed.
845: The host keys of
846: known hosts will be verified automatically in all cases.
847: The argument must be
848: .Dq yes ,
849: .Dq no
850: or
851: .Dq ask .
852: The default is
853: .Dq ask .
1.26 markus 854: .It Cm TCPKeepAlive
855: Specifies whether the system should send TCP keepalive messages to the
856: other side.
857: If they are sent, death of the connection or crash of one
858: of the machines will be properly noticed.
859: However, this means that
860: connections will die if the route is down temporarily, and some people
861: find it annoying.
862: .Pp
863: The default is
864: .Dq yes
865: (to send TCP keepalive messages), and the client will notice
866: if the network goes down or the remote host dies.
867: This is important in scripts, and many users want it too.
868: .Pp
869: To disable TCP keepalive messages, the value should be set to
870: .Dq no .
1.1 stevesk 871: .It Cm UsePrivilegedPort
872: Specifies whether to use a privileged port for outgoing connections.
873: The argument must be
874: .Dq yes
875: or
876: .Dq no .
877: The default is
878: .Dq no .
1.4 stevesk 879: If set to
880: .Dq yes
881: .Nm ssh
882: must be setuid root.
1.1 stevesk 883: Note that this option must be set to
884: .Dq yes
1.17 markus 885: for
1.1 stevesk 886: .Cm RhostsRSAAuthentication
1.17 markus 887: with older servers.
1.1 stevesk 888: .It Cm User
889: Specifies the user to log in as.
890: This can be useful when a different user name is used on different machines.
891: This saves the trouble of
892: having to remember to give the user name on the command line.
893: .It Cm UserKnownHostsFile
894: Specifies a file to use for the user
895: host key database instead of
1.50 djm 896: .Pa ~/.ssh/known_hosts .
1.8 jakob 897: .It Cm VerifyHostKeyDNS
898: Specifies whether to verify the remote key using DNS and SSHFP resource
899: records.
1.24 jakob 900: If this option is set to
901: .Dq yes ,
1.25 jmc 902: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 903: from DNS.
904: Insecure fingerprints will be handled as if this option was set to
905: .Dq ask .
906: If this option is set to
907: .Dq ask ,
908: information on fingerprint match will be displayed, but the user will still
909: need to confirm new host keys according to the
910: .Cm StrictHostKeyChecking
911: option.
912: The argument must be
913: .Dq yes ,
914: .Dq no
1.25 jmc 915: or
916: .Dq ask .
1.8 jakob 917: The default is
918: .Dq no .
1.12 jakob 919: Note that this option applies to protocol version 2 only.
1.1 stevesk 920: .It Cm XAuthLocation
1.5 stevesk 921: Specifies the full pathname of the
1.1 stevesk 922: .Xr xauth 1
923: program.
924: The default is
925: .Pa /usr/X11R6/bin/xauth .
926: .El
927: .Sh FILES
928: .Bl -tag -width Ds
1.50 djm 929: .It Pa ~/.ssh/config
1.1 stevesk 930: This is the per-user configuration file.
931: The format of this file is described above.
932: This file is used by the
933: .Nm ssh
934: client.
1.30 djm 935: Because of the potential for abuse, this file must have strict permissions:
936: read/write for the user, and not accessible by others.
1.1 stevesk 937: .It Pa /etc/ssh/ssh_config
938: Systemwide configuration file.
939: This file provides defaults for those
940: values that are not specified in the user's configuration file, and
941: for those users who do not have a configuration file.
942: This file must be world-readable.
943: .El
1.13 jmc 944: .Sh SEE ALSO
945: .Xr ssh 1
1.1 stevesk 946: .Sh AUTHORS
947: OpenSSH is a derivative of the original and free
948: ssh 1.2.12 release by Tatu Ylonen.
949: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
950: Theo de Raadt and Dug Song
951: removed many bugs, re-added newer features and
952: created OpenSSH.
953: Markus Friedl contributed the support for SSH
954: protocol versions 1.5 and 2.0.
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