Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.52
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: .\"
1.52 ! djm 37: .\" $OpenBSD: ssh_config.5,v 1.51 2005/04/26 13:08:37 jakob 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
139: Specify the interface to transmit from on machines with multiple
140: interfaces or aliased addresses.
141: Note that this option does not work if
142: .Cm UsePrivilegedPort
143: is set to
144: .Dq yes .
145: .It Cm ChallengeResponseAuthentication
146: Specifies whether to use challenge response authentication.
147: The argument to this keyword must be
148: .Dq yes
149: or
150: .Dq no .
151: The default is
152: .Dq yes .
153: .It Cm CheckHostIP
154: If this flag is set to
155: .Dq yes ,
156: ssh will additionally check the host IP address in the
157: .Pa known_hosts
158: file.
159: This allows ssh to detect if a host key changed due to DNS spoofing.
160: If the option is set to
161: .Dq no ,
162: the check will not be executed.
163: The default is
164: .Dq yes .
165: .It Cm Cipher
166: Specifies the cipher to use for encrypting the session
167: in protocol version 1.
168: Currently,
169: .Dq blowfish ,
170: .Dq 3des ,
171: and
172: .Dq des
173: are supported.
174: .Ar des
175: is only supported in the
176: .Nm ssh
177: client for interoperability with legacy protocol 1 implementations
178: that do not support the
179: .Ar 3des
1.7 jmc 180: cipher.
181: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 182: The default is
183: .Dq 3des .
184: .It Cm Ciphers
185: Specifies the ciphers allowed for protocol version 2
186: in order of preference.
187: Multiple ciphers must be comma-separated.
1.35 dtucker 188: The supported ciphers are
189: .Dq 3des-cbc ,
190: .Dq aes128-cbc ,
191: .Dq aes192-cbc ,
192: .Dq aes256-cbc ,
193: .Dq aes128-ctr ,
194: .Dq aes192-ctr ,
195: .Dq aes256-ctr ,
196: .Dq arcfour ,
197: .Dq blowfish-cbc ,
198: and
199: .Dq cast128-cbc .
1.1 stevesk 200: The default is
201: .Bd -literal
202: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
203: aes192-cbc,aes256-cbc''
204: .Ed
205: .It Cm ClearAllForwardings
206: Specifies that all local, remote and dynamic port forwardings
207: specified in the configuration files or on the command line be
1.7 jmc 208: cleared.
209: This option is primarily useful when used from the
1.1 stevesk 210: .Nm ssh
211: command line to clear port forwardings set in
212: configuration files, and is automatically set by
213: .Xr scp 1
214: and
215: .Xr sftp 1 .
216: The argument must be
217: .Dq yes
218: or
219: .Dq no .
220: The default is
221: .Dq no .
222: .It Cm Compression
223: Specifies whether to use compression.
224: The argument must be
225: .Dq yes
226: or
227: .Dq no .
228: The default is
229: .Dq no .
230: .It Cm CompressionLevel
231: Specifies the compression level to use if compression is enabled.
232: The argument must be an integer from 1 (fast) to 9 (slow, best).
233: The default level is 6, which is good for most applications.
234: The meaning of the values is the same as in
235: .Xr gzip 1 .
236: Note that this option applies to protocol version 1 only.
237: .It Cm ConnectionAttempts
238: Specifies the number of tries (one per second) to make before exiting.
239: The argument must be an integer.
240: This may be useful in scripts if the connection sometimes fails.
241: The default is 1.
1.9 djm 242: .It Cm ConnectTimeout
243: Specifies the timeout (in seconds) used when connecting to the ssh
1.11 jmc 244: server, instead of using the default system TCP timeout.
245: This value is used only when the target is down or really unreachable,
246: not when it refuses the connection.
1.36 djm 247: .It Cm ControlMaster
248: Enables the sharing of multiple sessions over a single network connection.
249: When set to
250: .Dq yes
251: .Nm ssh
252: will listen for connections on a control socket specified using the
253: .Cm ControlPath
254: argument.
255: Additional sessions can connect to this socket using the same
256: .Cm ControlPath
257: with
258: .Cm ControlMaster
259: set to
260: .Dq no
1.38 jmc 261: (the default).
1.36 djm 262: These sessions will reuse the master instance's network connection rather
263: than initiating new ones.
1.37 djm 264: Setting this to
265: .Dq ask
266: will cause
267: .Nm ssh
268: to listen for control connections, but require confirmation using the
269: .Ev SSH_ASKPASS
270: program before they are accepted (see
271: .Xr ssh-add 1
1.38 jmc 272: for details).
1.51 jakob 273: If the
274: .Cm ControlPath
275: can not be opened,
276: .Nm ssh
277: will continue without connecting to a master instance.
1.36 djm 278: .It Cm ControlPath
1.38 jmc 279: Specify the path to the control socket used for connection sharing.
1.36 djm 280: See
281: .Cm ControlMaster
282: above.
1.38 jmc 283: .It Cm DynamicForward
284: Specifies that a TCP/IP port on the local machine be forwarded
285: over the secure channel, and the application
286: protocol is then used to determine where to connect to from the
287: remote machine.
288: The argument must be a port number.
289: Currently the SOCKS4 and SOCKS5 protocols are supported, and
290: .Nm ssh
291: will act as a SOCKS server.
292: Multiple forwardings may be specified, and
293: additional forwardings can be given on the command line.
294: Only the superuser can forward privileged ports.
1.14 markus 295: .It Cm EnableSSHKeysign
296: Setting this option to
297: .Dq yes
298: in the global client configuration file
299: .Pa /etc/ssh/ssh_config
300: enables the use of the helper program
301: .Xr ssh-keysign 8
302: during
303: .Cm HostbasedAuthentication .
304: The argument must be
305: .Dq yes
306: or
307: .Dq no .
308: The default is
309: .Dq no .
1.23 jmc 310: This option should be placed in the non-hostspecific section.
1.14 markus 311: See
312: .Xr ssh-keysign 8
313: for more information.
1.1 stevesk 314: .It Cm EscapeChar
315: Sets the escape character (default:
316: .Ql ~ ) .
317: The escape character can also
318: be set on the command line.
319: The argument should be a single character,
320: .Ql ^
321: followed by a letter, or
322: .Dq none
323: to disable the escape
324: character entirely (making the connection transparent for binary
325: data).
326: .It Cm ForwardAgent
327: Specifies whether the connection to the authentication agent (if any)
328: will be forwarded to the remote machine.
329: The argument must be
330: .Dq yes
331: or
332: .Dq no .
333: The default is
334: .Dq no .
1.3 stevesk 335: .Pp
1.7 jmc 336: Agent forwarding should be enabled with caution.
337: Users with the ability to bypass file permissions on the remote host
338: (for the agent's Unix-domain socket)
339: can access the local agent through the forwarded connection.
340: An attacker cannot obtain key material from the agent,
1.3 stevesk 341: however they can perform operations on the keys that enable them to
342: authenticate using the identities loaded into the agent.
1.1 stevesk 343: .It Cm ForwardX11
344: Specifies whether X11 connections will be automatically redirected
345: over the secure channel and
346: .Ev DISPLAY
347: set.
348: The argument must be
349: .Dq yes
350: or
351: .Dq no .
352: The default is
353: .Dq no .
1.3 stevesk 354: .Pp
1.7 jmc 355: X11 forwarding should be enabled with caution.
356: Users with the ability to bypass file permissions on the remote host
1.22 markus 357: (for the user's X11 authorization database)
1.7 jmc 358: can access the local X11 display through the forwarded connection.
1.22 markus 359: An attacker may then be able to perform activities such as keystroke monitoring
360: if the
361: .Cm ForwardX11Trusted
362: option is also enabled.
363: .It Cm ForwardX11Trusted
1.34 jmc 364: If this option is set to
1.22 markus 365: .Dq yes
366: then remote X11 clients will have full access to the original X11 display.
1.42 djm 367: .Pp
1.22 markus 368: If this option is set to
369: .Dq no
370: then remote X11 clients will be considered untrusted and prevented
371: from stealing or tampering with data belonging to trusted X11
372: clients.
1.42 djm 373: Furthermore, the
374: .Xr xauth 1
375: token used for the session will be set to expire after 20 minutes.
376: Remote clients will be refused access after this time.
1.22 markus 377: .Pp
378: The default is
379: .Dq no .
380: .Pp
381: See the X11 SECURITY extension specification for full details on
382: the restrictions imposed on untrusted clients.
1.1 stevesk 383: .It Cm GatewayPorts
384: Specifies whether remote hosts are allowed to connect to local
385: forwarded ports.
386: By default,
387: .Nm ssh
1.7 jmc 388: binds local port forwardings to the loopback address.
389: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 390: .Cm GatewayPorts
391: can be used to specify that
392: .Nm ssh
393: should bind local port forwardings to the wildcard address,
394: thus allowing remote hosts to connect to forwarded ports.
395: The argument must be
396: .Dq yes
397: or
398: .Dq no .
399: The default is
400: .Dq no .
401: .It Cm GlobalKnownHostsFile
402: Specifies a file to use for the global
403: host key database instead of
404: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 405: .It Cm GSSAPIAuthentication
1.27 markus 406: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 407: The default is
1.21 markus 408: .Dq no .
1.18 markus 409: Note that this option applies to protocol version 2 only.
410: .It Cm GSSAPIDelegateCredentials
411: Forward (delegate) credentials to the server.
412: The default is
413: .Dq no .
414: Note that this option applies to protocol version 2 only.
1.44 djm 415: .It Cm HashKnownHosts
416: Indicates that
417: .Nm ssh
418: should hash host names and addresses when they are added to
1.50 djm 419: .Pa ~/.ssh/known_hosts .
1.44 djm 420: These hashed names may be used normally by
421: .Nm ssh
422: and
423: .Nm sshd ,
424: but they do not reveal identifying information should the file's contents
425: be disclosed.
426: The default is
427: .Dq no .
1.46 jmc 428: Note that hashing of names and addresses will not be retrospectively applied
1.45 djm 429: to existing known hosts files, but these may be manually hashed using
430: .Xr ssh-keygen 1 .
1.1 stevesk 431: .It Cm HostbasedAuthentication
432: Specifies whether to try rhosts based authentication with public key
433: authentication.
434: The argument must be
435: .Dq yes
436: or
437: .Dq no .
438: The default is
439: .Dq no .
440: This option applies to protocol version 2 only and
441: is similar to
442: .Cm RhostsRSAAuthentication .
443: .It Cm HostKeyAlgorithms
444: Specifies the protocol version 2 host key algorithms
445: that the client wants to use in order of preference.
446: The default for this option is:
447: .Dq ssh-rsa,ssh-dss .
448: .It Cm HostKeyAlias
449: Specifies an alias that should be used instead of the
450: real host name when looking up or saving the host key
451: in the host key database files.
452: This option is useful for tunneling ssh connections
453: or for multiple servers running on a single host.
454: .It Cm HostName
455: Specifies the real host name to log into.
456: This can be used to specify nicknames or abbreviations for hosts.
457: Default is the name given on the command line.
458: Numeric IP addresses are also permitted (both on the command line and in
459: .Cm HostName
460: specifications).
461: .It Cm IdentityFile
462: Specifies a file from which the user's RSA or DSA authentication identity
1.11 jmc 463: is read.
464: The default is
1.50 djm 465: .Pa ~/.ssh/identity
1.1 stevesk 466: for protocol version 1, and
1.50 djm 467: .Pa ~/.ssh/id_rsa
1.1 stevesk 468: and
1.50 djm 469: .Pa ~/.ssh/id_dsa
1.1 stevesk 470: for protocol version 2.
471: Additionally, any identities represented by the authentication agent
472: will be used for authentication.
473: The file name may use the tilde
474: syntax to refer to a user's home directory.
475: It is possible to have
476: multiple identity files specified in configuration files; all these
477: identities will be tried in sequence.
1.29 markus 478: .It Cm IdentitiesOnly
479: Specifies that
480: .Nm ssh
481: should only use the authentication identity files configured in the
1.31 jmc 482: .Nm
1.29 markus 483: files,
484: even if the
485: .Nm ssh-agent
486: offers more identities.
487: The argument to this keyword must be
488: .Dq yes
489: or
490: .Dq no .
491: This option is intented for situations where
492: .Nm ssh-agent
493: offers many different identities.
494: The default is
495: .Dq no .
1.39 djm 496: .It Cm KbdInteractiveDevices
497: Specifies the list of methods to use in keyboard-interactive authentication.
498: Multiple method names must be comma-separated.
499: The default is to use the server specified list.
1.1 stevesk 500: .It Cm LocalForward
501: Specifies that a TCP/IP port on the local machine be forwarded over
502: the secure channel to the specified host and port from the remote machine.
1.49 jmc 503: The first argument must be
1.43 djm 504: .Sm off
1.49 jmc 505: .Oo Ar bind_address : Oc Ar port
1.43 djm 506: .Sm on
1.49 jmc 507: and the second argument must be
508: .Ar host : Ns Ar hostport .
1.46 jmc 509: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 510: by using an alternative syntax:
1.49 jmc 511: .Oo Ar bind_address Ns / Oc Ns Ar port
512: and
513: .Ar host Ns / Ns Ar hostport .
1.46 jmc 514: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 515: given on the command line.
1.1 stevesk 516: Only the superuser can forward privileged ports.
1.43 djm 517: By default, the local port is bound in accordance with the
518: .Cm GatewayPorts
519: setting.
520: However, an explicit
521: .Ar bind_address
522: may be used to bind the connection to a specific address.
523: The
524: .Ar bind_address
525: of
526: .Dq localhost
1.46 jmc 527: indicates that the listening port be bound for local use only, while an
528: empty address or
529: .Sq *
1.43 djm 530: indicates that the port should be available from all interfaces.
1.1 stevesk 531: .It Cm LogLevel
532: Gives the verbosity level that is used when logging messages from
533: .Nm ssh .
534: The possible values are:
535: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
1.7 jmc 536: The default is INFO.
537: DEBUG and DEBUG1 are equivalent.
538: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 539: .It Cm MACs
540: Specifies the MAC (message authentication code) algorithms
541: in order of preference.
542: The MAC algorithm is used in protocol version 2
543: for data integrity protection.
544: Multiple algorithms must be comma-separated.
545: The default is
546: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
547: .It Cm NoHostAuthenticationForLocalhost
548: This option can be used if the home directory is shared across machines.
549: In this case localhost will refer to a different machine on each of
550: the machines and the user will get many warnings about changed host keys.
551: However, this option disables host authentication for localhost.
552: The argument to this keyword must be
553: .Dq yes
554: or
555: .Dq no .
556: The default is to check the host key for localhost.
557: .It Cm NumberOfPasswordPrompts
558: Specifies the number of password prompts before giving up.
559: The argument to this keyword must be an integer.
560: Default is 3.
561: .It Cm PasswordAuthentication
562: Specifies whether to use password authentication.
563: The argument to this keyword must be
564: .Dq yes
565: or
566: .Dq no .
567: The default is
568: .Dq yes .
569: .It Cm Port
570: Specifies the port number to connect on the remote host.
571: Default is 22.
572: .It Cm PreferredAuthentications
573: Specifies the order in which the client should try protocol 2
1.11 jmc 574: authentication methods.
1.48 jmc 575: This allows a client to prefer one method (e.g.\&
1.1 stevesk 576: .Cm keyboard-interactive )
1.48 jmc 577: over another method (e.g.\&
1.1 stevesk 578: .Cm password )
579: The default for this option is:
580: .Dq hostbased,publickey,keyboard-interactive,password .
581: .It Cm Protocol
582: Specifies the protocol versions
583: .Nm ssh
584: should support in order of preference.
585: The possible values are
586: .Dq 1
587: and
588: .Dq 2 .
589: Multiple versions must be comma-separated.
590: The default is
591: .Dq 2,1 .
592: This means that
593: .Nm ssh
594: tries version 2 and falls back to version 1
595: if version 2 is not available.
596: .It Cm ProxyCommand
597: Specifies the command to use to connect to the server.
598: The command
599: string extends to the end of the line, and is executed with
600: .Pa /bin/sh .
601: In the command string,
602: .Ql %h
603: will be substituted by the host name to
604: connect and
605: .Ql %p
606: by the port.
607: The command can be basically anything,
608: and should read from its standard input and write to its standard output.
609: It should eventually connect an
610: .Xr sshd 8
611: server running on some machine, or execute
612: .Ic sshd -i
613: somewhere.
614: Host key management will be done using the
615: HostName of the host being connected (defaulting to the name typed by
616: the user).
1.7 jmc 617: Setting the command to
618: .Dq none
1.6 markus 619: disables this option entirely.
1.1 stevesk 620: Note that
621: .Cm CheckHostIP
622: is not available for connects with a proxy command.
1.52 ! djm 623: .Pp
! 624: This directive is useful in conjunction with
! 625: .Xr nc 1
! 626: and its proxy support.
! 627: For example, the following directive would connect via a HTTP proxy at
! 628: 192.0.2.0:
! 629: .Bd -literal -offset 3n
! 630: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
! 631: .Ed
1.1 stevesk 632: .Pp
633: .It Cm PubkeyAuthentication
634: Specifies whether to try public key authentication.
635: The argument to this keyword must be
636: .Dq yes
637: or
638: .Dq no .
639: The default is
640: .Dq yes .
641: This option applies to protocol version 2 only.
642: .It Cm RemoteForward
643: Specifies that a TCP/IP port on the remote machine be forwarded over
644: the secure channel to the specified host and port from the local machine.
1.49 jmc 645: The first argument must be
1.43 djm 646: .Sm off
1.49 jmc 647: .Oo Ar bind_address : Oc Ar port
1.43 djm 648: .Sm on
1.49 jmc 649: and the second argument must be
650: .Ar host : Ns Ar hostport .
651: IPv6 addresses can be specified by enclosing addresses in square brackets
652: or by using an alternative syntax:
653: .Oo Ar bind_address Ns / Oc Ns Ar port
654: and
655: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 656: Multiple forwardings may be specified, and additional
657: forwardings can be given on the command line.
658: Only the superuser can forward privileged ports.
1.43 djm 659: .Pp
660: If the
661: .Ar bind_address
662: is not specified, the default is to only bind to loopback addresses.
663: If the
664: .Ar bind_address
665: is
666: .Ql *
667: or an empty string, then the forwarding is requested to listen on all
668: interfaces.
669: Specifying a remote
670: .Ar bind_address
1.46 jmc 671: will only succeed if the server's
672: .Cm GatewayPorts
1.43 djm 673: option is enabled (see
1.46 jmc 674: .Xr sshd_config 5 ) .
1.1 stevesk 675: .It Cm RhostsRSAAuthentication
676: Specifies whether to try rhosts based authentication with RSA host
677: authentication.
678: The argument must be
679: .Dq yes
680: or
681: .Dq no .
682: The default is
683: .Dq no .
684: This option applies to protocol version 1 only and requires
685: .Nm ssh
686: to be setuid root.
687: .It Cm RSAAuthentication
688: Specifies whether to try RSA authentication.
689: The argument to this keyword must be
690: .Dq yes
691: or
692: .Dq no .
693: RSA authentication will only be
694: attempted if the identity file exists, or an authentication agent is
695: running.
696: The default is
697: .Dq yes .
698: Note that this option applies to protocol version 1 only.
1.32 djm 699: .It Cm SendEnv
700: Specifies what variables from the local
701: .Xr environ 7
702: should be sent to the server.
703: Note that environment passing is only supported for protocol 2, the
1.33 djm 704: server must also support it, and the server must be configured to
705: accept these environment variables.
1.32 djm 706: Refer to
707: .Cm AcceptEnv
708: in
709: .Xr sshd_config 5
710: for how to configure the server.
711: Variables are specified by name, which may contain the wildcard characters
712: .Ql \&*
713: and
714: .Ql \&? .
1.33 djm 715: Multiple environment variables may be separated by whitespace or spread
1.32 djm 716: across multiple
717: .Cm SendEnv
718: directives.
719: The default is not to send any environment variables.
1.28 markus 720: .It Cm ServerAliveInterval
721: Sets a timeout interval in seconds after which if no data has been received
722: from the server,
723: .Nm ssh
724: will send a message through the encrypted
725: channel to request a response from the server.
726: The default
727: is 0, indicating that these messages will not be sent to the server.
728: This option applies to protocol version 2 only.
729: .It Cm ServerAliveCountMax
730: Sets the number of server alive messages (see above) which may be
731: sent without
732: .Nm ssh
733: receiving any messages back from the server.
734: If this threshold is reached while server alive messages are being sent,
735: .Nm ssh
736: will disconnect from the server, terminating the session.
737: It is important to note that the use of server alive messages is very
738: different from
739: .Cm TCPKeepAlive
740: (below).
741: The server alive messages are sent through the encrypted channel
742: and therefore will not be spoofable.
743: The TCP keepalive option enabled by
744: .Cm TCPKeepAlive
745: is spoofable.
746: The server alive mechanism is valuable when the client or
747: server depend on knowing when a connection has become inactive.
748: .Pp
749: The default value is 3.
750: If, for example,
751: .Cm ServerAliveInterval
752: (above) is set to 15, and
753: .Cm ServerAliveCountMax
754: is left at the default, if the server becomes unresponsive ssh
755: will disconnect after approximately 45 seconds.
1.1 stevesk 756: .It Cm SmartcardDevice
1.11 jmc 757: Specifies which smartcard device to use.
758: The argument to this keyword is the device
1.1 stevesk 759: .Nm ssh
760: should use to communicate with a smartcard used for storing the user's
1.11 jmc 761: private RSA key.
762: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 763: .It Cm StrictHostKeyChecking
764: If this flag is set to
765: .Dq yes ,
766: .Nm ssh
767: will never automatically add host keys to the
1.50 djm 768: .Pa ~/.ssh/known_hosts
1.1 stevesk 769: file, and refuses to connect to hosts whose host key has changed.
770: This provides maximum protection against trojan horse attacks,
771: however, can be annoying when the
772: .Pa /etc/ssh/ssh_known_hosts
773: file is poorly maintained, or connections to new hosts are
774: frequently made.
775: This option forces the user to manually
776: add all new hosts.
777: If this flag is set to
778: .Dq no ,
779: .Nm ssh
780: will automatically add new host keys to the
781: user known hosts files.
782: If this flag is set to
783: .Dq ask ,
784: new host keys
785: will be added to the user known host files only after the user
786: has confirmed that is what they really want to do, and
787: .Nm ssh
788: will refuse to connect to hosts whose host key has changed.
789: The host keys of
790: known hosts will be verified automatically in all cases.
791: The argument must be
792: .Dq yes ,
793: .Dq no
794: or
795: .Dq ask .
796: The default is
797: .Dq ask .
1.26 markus 798: .It Cm TCPKeepAlive
799: Specifies whether the system should send TCP keepalive messages to the
800: other side.
801: If they are sent, death of the connection or crash of one
802: of the machines will be properly noticed.
803: However, this means that
804: connections will die if the route is down temporarily, and some people
805: find it annoying.
806: .Pp
807: The default is
808: .Dq yes
809: (to send TCP keepalive messages), and the client will notice
810: if the network goes down or the remote host dies.
811: This is important in scripts, and many users want it too.
812: .Pp
813: To disable TCP keepalive messages, the value should be set to
814: .Dq no .
1.1 stevesk 815: .It Cm UsePrivilegedPort
816: Specifies whether to use a privileged port for outgoing connections.
817: The argument must be
818: .Dq yes
819: or
820: .Dq no .
821: The default is
822: .Dq no .
1.4 stevesk 823: If set to
824: .Dq yes
825: .Nm ssh
826: must be setuid root.
1.1 stevesk 827: Note that this option must be set to
828: .Dq yes
1.17 markus 829: for
1.1 stevesk 830: .Cm RhostsRSAAuthentication
1.17 markus 831: with older servers.
1.1 stevesk 832: .It Cm User
833: Specifies the user to log in as.
834: This can be useful when a different user name is used on different machines.
835: This saves the trouble of
836: having to remember to give the user name on the command line.
837: .It Cm UserKnownHostsFile
838: Specifies a file to use for the user
839: host key database instead of
1.50 djm 840: .Pa ~/.ssh/known_hosts .
1.8 jakob 841: .It Cm VerifyHostKeyDNS
842: Specifies whether to verify the remote key using DNS and SSHFP resource
843: records.
1.24 jakob 844: If this option is set to
845: .Dq yes ,
1.25 jmc 846: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 847: from DNS.
848: Insecure fingerprints will be handled as if this option was set to
849: .Dq ask .
850: If this option is set to
851: .Dq ask ,
852: information on fingerprint match will be displayed, but the user will still
853: need to confirm new host keys according to the
854: .Cm StrictHostKeyChecking
855: option.
856: The argument must be
857: .Dq yes ,
858: .Dq no
1.25 jmc 859: or
860: .Dq ask .
1.8 jakob 861: The default is
862: .Dq no .
1.12 jakob 863: Note that this option applies to protocol version 2 only.
1.1 stevesk 864: .It Cm XAuthLocation
1.5 stevesk 865: Specifies the full pathname of the
1.1 stevesk 866: .Xr xauth 1
867: program.
868: The default is
869: .Pa /usr/X11R6/bin/xauth .
870: .El
871: .Sh FILES
872: .Bl -tag -width Ds
1.50 djm 873: .It Pa ~/.ssh/config
1.1 stevesk 874: This is the per-user configuration file.
875: The format of this file is described above.
876: This file is used by the
877: .Nm ssh
878: client.
1.30 djm 879: Because of the potential for abuse, this file must have strict permissions:
880: read/write for the user, and not accessible by others.
1.1 stevesk 881: .It Pa /etc/ssh/ssh_config
882: Systemwide configuration file.
883: This file provides defaults for those
884: values that are not specified in the user's configuration file, and
885: for those users who do not have a configuration file.
886: This file must be world-readable.
887: .El
1.13 jmc 888: .Sh SEE ALSO
889: .Xr ssh 1
1.1 stevesk 890: .Sh AUTHORS
891: OpenSSH is a derivative of the original and free
892: ssh 1.2.12 release by Tatu Ylonen.
893: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
894: Theo de Raadt and Dug Song
895: removed many bugs, re-added newer features and
896: created OpenSSH.
897: Markus Friedl contributed the support for SSH
898: protocol versions 1.5 and 2.0.
![[BACK]](/icons/back.gif){kind=icon}
Return to ssh_config.5 CVS log ![[TXT]](/icons/text.gif){kind=icon}
![[DIR]](/icons/dir.gif){kind=icon}
Up to [local] / src / usr.bin / ssh