Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.59
1.1 stevesk 1: .\" -*- nroff -*-
2: .\"
3: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5: .\" All rights reserved
6: .\"
7: .\" As far as I am concerned, the code I have written for this software
8: .\" can be used freely for any purpose. Any derived versions of this
9: .\" software must be clearly marked as such, and if the derived work is
10: .\" incompatible with the protocol description in the RFC file, it must be
11: .\" called by a name other than "ssh" or "Secure Shell".
12: .\"
13: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
14: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
15: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
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22: .\" 2. Redistributions in binary form must reproduce the above copyright
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1.59 ! jmc 37: .\" $OpenBSD: ssh_config.5,v 1.58 2005/07/04 00:58:43 djm 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 ,
1.54 djm 196: .Dq arcfour128 ,
197: .Dq arcfour256 ,
1.35 dtucker 198: .Dq arcfour ,
199: .Dq blowfish-cbc ,
200: and
201: .Dq cast128-cbc .
1.1 stevesk 202: The default is
203: .Bd -literal
1.54 djm 204: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
205: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
206: aes192-ctr,aes256-ctr''
1.1 stevesk 207: .Ed
208: .It Cm ClearAllForwardings
209: Specifies that all local, remote and dynamic port forwardings
210: specified in the configuration files or on the command line be
1.7 jmc 211: cleared.
212: This option is primarily useful when used from the
1.1 stevesk 213: .Nm ssh
214: command line to clear port forwardings set in
215: configuration files, and is automatically set by
216: .Xr scp 1
217: and
218: .Xr sftp 1 .
219: The argument must be
220: .Dq yes
221: or
222: .Dq no .
223: The default is
224: .Dq no .
225: .It Cm Compression
226: Specifies whether to use compression.
227: The argument must be
228: .Dq yes
229: or
230: .Dq no .
231: The default is
232: .Dq no .
233: .It Cm CompressionLevel
234: Specifies the compression level to use if compression is enabled.
235: The argument must be an integer from 1 (fast) to 9 (slow, best).
236: The default level is 6, which is good for most applications.
237: The meaning of the values is the same as in
238: .Xr gzip 1 .
239: Note that this option applies to protocol version 1 only.
240: .It Cm ConnectionAttempts
241: Specifies the number of tries (one per second) to make before exiting.
242: The argument must be an integer.
243: This may be useful in scripts if the connection sometimes fails.
244: The default is 1.
1.9 djm 245: .It Cm ConnectTimeout
246: Specifies the timeout (in seconds) used when connecting to the ssh
1.11 jmc 247: server, instead of using the default system TCP timeout.
248: This value is used only when the target is down or really unreachable,
249: not when it refuses the connection.
1.36 djm 250: .It Cm ControlMaster
251: Enables the sharing of multiple sessions over a single network connection.
252: When set to
253: .Dq yes
254: .Nm ssh
255: will listen for connections on a control socket specified using the
256: .Cm ControlPath
257: argument.
258: Additional sessions can connect to this socket using the same
259: .Cm ControlPath
260: with
261: .Cm ControlMaster
262: set to
263: .Dq no
1.38 jmc 264: (the default).
1.36 djm 265: These sessions will reuse the master instance's network connection rather
266: than initiating new ones.
1.37 djm 267: Setting this to
268: .Dq ask
269: will cause
270: .Nm ssh
271: to listen for control connections, but require confirmation using the
272: .Ev SSH_ASKPASS
273: program before they are accepted (see
274: .Xr ssh-add 1
1.38 jmc 275: for details).
1.51 jakob 276: If the
277: .Cm ControlPath
278: can not be opened,
279: .Nm ssh
280: will continue without connecting to a master instance.
1.58 djm 281: .Pp
282: X11 and
1.59 ! jmc 283: .Xr ssh-agent 1
1.58 djm 284: forwarding is supported over these multiplexed connections, however the
285: display and agent fowarded will be the one belonging to the master
1.59 ! jmc 286: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 287: .Pp
288: Two additional options allow for opportunistic multiplexing: try to use a
289: master connection but fall back to creating a new one if one does not already
290: exist.
291: These options are:
292: .Dq auto
293: and
294: .Dq autoask .
295: The latter requires confirmation like the
296: .Dq ask
297: option.
1.36 djm 298: .It Cm ControlPath
1.55 djm 299: Specify the path to the control socket used for connection sharing as described
300: in the
1.36 djm 301: .Cm ControlMaster
1.57 djm 302: section above or the string
303: .Dq none
304: to disable connection sharing.
1.55 djm 305: In the path,
306: .Ql %h
307: will be substituted by the target host name,
308: .Ql %p
309: the port and
310: .Ql %r
311: by the remote login username.
1.56 djm 312: It is recommended that any
313: .Cm ControlPath
314: used for opportunistic connection sharing include
315: all three of these escape sequences.
316: This ensures that shared connections are uniquely identified.
1.38 jmc 317: .It Cm DynamicForward
318: Specifies that a TCP/IP port on the local machine be forwarded
319: over the secure channel, and the application
320: protocol is then used to determine where to connect to from the
321: remote machine.
322: The argument must be a port number.
323: Currently the SOCKS4 and SOCKS5 protocols are supported, and
324: .Nm ssh
325: will act as a SOCKS server.
326: Multiple forwardings may be specified, and
327: additional forwardings can be given on the command line.
328: Only the superuser can forward privileged ports.
1.14 markus 329: .It Cm EnableSSHKeysign
330: Setting this option to
331: .Dq yes
332: in the global client configuration file
333: .Pa /etc/ssh/ssh_config
334: enables the use of the helper program
335: .Xr ssh-keysign 8
336: during
337: .Cm HostbasedAuthentication .
338: The argument must be
339: .Dq yes
340: or
341: .Dq no .
342: The default is
343: .Dq no .
1.23 jmc 344: This option should be placed in the non-hostspecific section.
1.14 markus 345: See
346: .Xr ssh-keysign 8
347: for more information.
1.1 stevesk 348: .It Cm EscapeChar
349: Sets the escape character (default:
350: .Ql ~ ) .
351: The escape character can also
352: be set on the command line.
353: The argument should be a single character,
354: .Ql ^
355: followed by a letter, or
356: .Dq none
357: to disable the escape
358: character entirely (making the connection transparent for binary
359: data).
360: .It Cm ForwardAgent
361: Specifies whether the connection to the authentication agent (if any)
362: will be forwarded to the remote machine.
363: The argument must be
364: .Dq yes
365: or
366: .Dq no .
367: The default is
368: .Dq no .
1.3 stevesk 369: .Pp
1.7 jmc 370: Agent forwarding should be enabled with caution.
371: Users with the ability to bypass file permissions on the remote host
372: (for the agent's Unix-domain socket)
373: can access the local agent through the forwarded connection.
374: An attacker cannot obtain key material from the agent,
1.3 stevesk 375: however they can perform operations on the keys that enable them to
376: authenticate using the identities loaded into the agent.
1.1 stevesk 377: .It Cm ForwardX11
378: Specifies whether X11 connections will be automatically redirected
379: over the secure channel and
380: .Ev DISPLAY
381: set.
382: The argument must be
383: .Dq yes
384: or
385: .Dq no .
386: The default is
387: .Dq no .
1.3 stevesk 388: .Pp
1.7 jmc 389: X11 forwarding should be enabled with caution.
390: Users with the ability to bypass file permissions on the remote host
1.22 markus 391: (for the user's X11 authorization database)
1.7 jmc 392: can access the local X11 display through the forwarded connection.
1.22 markus 393: An attacker may then be able to perform activities such as keystroke monitoring
394: if the
395: .Cm ForwardX11Trusted
396: option is also enabled.
397: .It Cm ForwardX11Trusted
1.34 jmc 398: If this option is set to
1.22 markus 399: .Dq yes
400: then remote X11 clients will have full access to the original X11 display.
1.42 djm 401: .Pp
1.22 markus 402: If this option is set to
403: .Dq no
404: then remote X11 clients will be considered untrusted and prevented
405: from stealing or tampering with data belonging to trusted X11
406: clients.
1.42 djm 407: Furthermore, the
408: .Xr xauth 1
409: token used for the session will be set to expire after 20 minutes.
410: Remote clients will be refused access after this time.
1.22 markus 411: .Pp
412: The default is
413: .Dq no .
414: .Pp
415: See the X11 SECURITY extension specification for full details on
416: the restrictions imposed on untrusted clients.
1.1 stevesk 417: .It Cm GatewayPorts
418: Specifies whether remote hosts are allowed to connect to local
419: forwarded ports.
420: By default,
421: .Nm ssh
1.7 jmc 422: binds local port forwardings to the loopback address.
423: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 424: .Cm GatewayPorts
425: can be used to specify that
426: .Nm ssh
427: should bind local port forwardings to the wildcard address,
428: thus allowing remote hosts to connect to forwarded ports.
429: The argument must be
430: .Dq yes
431: or
432: .Dq no .
433: The default is
434: .Dq no .
435: .It Cm GlobalKnownHostsFile
436: Specifies a file to use for the global
437: host key database instead of
438: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 439: .It Cm GSSAPIAuthentication
1.27 markus 440: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 441: The default is
1.21 markus 442: .Dq no .
1.18 markus 443: Note that this option applies to protocol version 2 only.
444: .It Cm GSSAPIDelegateCredentials
445: Forward (delegate) credentials to the server.
446: The default is
447: .Dq no .
448: Note that this option applies to protocol version 2 only.
1.44 djm 449: .It Cm HashKnownHosts
450: Indicates that
451: .Nm ssh
452: should hash host names and addresses when they are added to
1.50 djm 453: .Pa ~/.ssh/known_hosts .
1.44 djm 454: These hashed names may be used normally by
455: .Nm ssh
456: and
457: .Nm sshd ,
458: but they do not reveal identifying information should the file's contents
459: be disclosed.
460: The default is
461: .Dq no .
1.46 jmc 462: Note that hashing of names and addresses will not be retrospectively applied
1.45 djm 463: to existing known hosts files, but these may be manually hashed using
464: .Xr ssh-keygen 1 .
1.1 stevesk 465: .It Cm HostbasedAuthentication
466: Specifies whether to try rhosts based authentication with public key
467: authentication.
468: The argument must be
469: .Dq yes
470: or
471: .Dq no .
472: The default is
473: .Dq no .
474: This option applies to protocol version 2 only and
475: is similar to
476: .Cm RhostsRSAAuthentication .
477: .It Cm HostKeyAlgorithms
478: Specifies the protocol version 2 host key algorithms
479: that the client wants to use in order of preference.
480: The default for this option is:
481: .Dq ssh-rsa,ssh-dss .
482: .It Cm HostKeyAlias
483: Specifies an alias that should be used instead of the
484: real host name when looking up or saving the host key
485: in the host key database files.
486: This option is useful for tunneling ssh connections
487: or for multiple servers running on a single host.
488: .It Cm HostName
489: Specifies the real host name to log into.
490: This can be used to specify nicknames or abbreviations for hosts.
491: Default is the name given on the command line.
492: Numeric IP addresses are also permitted (both on the command line and in
493: .Cm HostName
494: specifications).
495: .It Cm IdentityFile
496: Specifies a file from which the user's RSA or DSA authentication identity
1.11 jmc 497: is read.
498: The default is
1.50 djm 499: .Pa ~/.ssh/identity
1.1 stevesk 500: for protocol version 1, and
1.50 djm 501: .Pa ~/.ssh/id_rsa
1.1 stevesk 502: and
1.50 djm 503: .Pa ~/.ssh/id_dsa
1.1 stevesk 504: for protocol version 2.
505: Additionally, any identities represented by the authentication agent
506: will be used for authentication.
507: The file name may use the tilde
508: syntax to refer to a user's home directory.
509: It is possible to have
510: multiple identity files specified in configuration files; all these
511: identities will be tried in sequence.
1.29 markus 512: .It Cm IdentitiesOnly
513: Specifies that
514: .Nm ssh
515: should only use the authentication identity files configured in the
1.31 jmc 516: .Nm
1.29 markus 517: files,
518: even if the
519: .Nm ssh-agent
520: offers more identities.
521: The argument to this keyword must be
522: .Dq yes
523: or
524: .Dq no .
525: This option is intented for situations where
526: .Nm ssh-agent
527: offers many different identities.
528: The default is
529: .Dq no .
1.39 djm 530: .It Cm KbdInteractiveDevices
531: Specifies the list of methods to use in keyboard-interactive authentication.
532: Multiple method names must be comma-separated.
533: The default is to use the server specified list.
1.1 stevesk 534: .It Cm LocalForward
535: Specifies that a TCP/IP port on the local machine be forwarded over
536: the secure channel to the specified host and port from the remote machine.
1.49 jmc 537: The first argument must be
1.43 djm 538: .Sm off
1.49 jmc 539: .Oo Ar bind_address : Oc Ar port
1.43 djm 540: .Sm on
1.49 jmc 541: and the second argument must be
542: .Ar host : Ns Ar hostport .
1.46 jmc 543: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 544: by using an alternative syntax:
1.49 jmc 545: .Oo Ar bind_address Ns / Oc Ns Ar port
546: and
547: .Ar host Ns / Ns Ar hostport .
1.46 jmc 548: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 549: given on the command line.
1.1 stevesk 550: Only the superuser can forward privileged ports.
1.43 djm 551: By default, the local port is bound in accordance with the
552: .Cm GatewayPorts
553: setting.
554: However, an explicit
555: .Ar bind_address
556: may be used to bind the connection to a specific address.
557: The
558: .Ar bind_address
559: of
560: .Dq localhost
1.46 jmc 561: indicates that the listening port be bound for local use only, while an
562: empty address or
563: .Sq *
1.43 djm 564: indicates that the port should be available from all interfaces.
1.1 stevesk 565: .It Cm LogLevel
566: Gives the verbosity level that is used when logging messages from
567: .Nm ssh .
568: The possible values are:
569: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
1.7 jmc 570: The default is INFO.
571: DEBUG and DEBUG1 are equivalent.
572: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 573: .It Cm MACs
574: Specifies the MAC (message authentication code) algorithms
575: in order of preference.
576: The MAC algorithm is used in protocol version 2
577: for data integrity protection.
578: Multiple algorithms must be comma-separated.
579: The default is
580: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
581: .It Cm NoHostAuthenticationForLocalhost
582: This option can be used if the home directory is shared across machines.
583: In this case localhost will refer to a different machine on each of
584: the machines and the user will get many warnings about changed host keys.
585: However, this option disables host authentication for localhost.
586: The argument to this keyword must be
587: .Dq yes
588: or
589: .Dq no .
590: The default is to check the host key for localhost.
591: .It Cm NumberOfPasswordPrompts
592: Specifies the number of password prompts before giving up.
593: The argument to this keyword must be an integer.
594: Default is 3.
595: .It Cm PasswordAuthentication
596: Specifies whether to use password authentication.
597: The argument to this keyword must be
598: .Dq yes
599: or
600: .Dq no .
601: The default is
602: .Dq yes .
603: .It Cm Port
604: Specifies the port number to connect on the remote host.
605: Default is 22.
606: .It Cm PreferredAuthentications
607: Specifies the order in which the client should try protocol 2
1.11 jmc 608: authentication methods.
1.48 jmc 609: This allows a client to prefer one method (e.g.\&
1.1 stevesk 610: .Cm keyboard-interactive )
1.48 jmc 611: over another method (e.g.\&
1.1 stevesk 612: .Cm password )
613: The default for this option is:
614: .Dq hostbased,publickey,keyboard-interactive,password .
615: .It Cm Protocol
616: Specifies the protocol versions
617: .Nm ssh
618: should support in order of preference.
619: The possible values are
620: .Dq 1
621: and
622: .Dq 2 .
623: Multiple versions must be comma-separated.
624: The default is
625: .Dq 2,1 .
626: This means that
627: .Nm ssh
628: tries version 2 and falls back to version 1
629: if version 2 is not available.
630: .It Cm ProxyCommand
631: Specifies the command to use to connect to the server.
632: The command
633: string extends to the end of the line, and is executed with
634: .Pa /bin/sh .
635: In the command string,
636: .Ql %h
637: will be substituted by the host name to
638: connect and
639: .Ql %p
640: by the port.
641: The command can be basically anything,
642: and should read from its standard input and write to its standard output.
643: It should eventually connect an
644: .Xr sshd 8
645: server running on some machine, or execute
646: .Ic sshd -i
647: somewhere.
648: Host key management will be done using the
649: HostName of the host being connected (defaulting to the name typed by
650: the user).
1.7 jmc 651: Setting the command to
652: .Dq none
1.6 markus 653: disables this option entirely.
1.1 stevesk 654: Note that
655: .Cm CheckHostIP
656: is not available for connects with a proxy command.
1.52 djm 657: .Pp
658: This directive is useful in conjunction with
659: .Xr nc 1
660: and its proxy support.
1.53 jmc 661: For example, the following directive would connect via an HTTP proxy at
1.52 djm 662: 192.0.2.0:
663: .Bd -literal -offset 3n
664: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
665: .Ed
1.1 stevesk 666: .It Cm PubkeyAuthentication
667: Specifies whether to try public key authentication.
668: The argument to this keyword must be
669: .Dq yes
670: or
671: .Dq no .
672: The default is
673: .Dq yes .
674: This option applies to protocol version 2 only.
675: .It Cm RemoteForward
676: Specifies that a TCP/IP port on the remote machine be forwarded over
677: the secure channel to the specified host and port from the local machine.
1.49 jmc 678: The first argument must be
1.43 djm 679: .Sm off
1.49 jmc 680: .Oo Ar bind_address : Oc Ar port
1.43 djm 681: .Sm on
1.49 jmc 682: and the second argument must be
683: .Ar host : Ns Ar hostport .
684: IPv6 addresses can be specified by enclosing addresses in square brackets
685: or by using an alternative syntax:
686: .Oo Ar bind_address Ns / Oc Ns Ar port
687: and
688: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 689: Multiple forwardings may be specified, and additional
690: forwardings can be given on the command line.
691: Only the superuser can forward privileged ports.
1.43 djm 692: .Pp
693: If the
694: .Ar bind_address
695: is not specified, the default is to only bind to loopback addresses.
696: If the
697: .Ar bind_address
698: is
699: .Ql *
700: or an empty string, then the forwarding is requested to listen on all
701: interfaces.
702: Specifying a remote
703: .Ar bind_address
1.46 jmc 704: will only succeed if the server's
705: .Cm GatewayPorts
1.43 djm 706: option is enabled (see
1.46 jmc 707: .Xr sshd_config 5 ) .
1.1 stevesk 708: .It Cm RhostsRSAAuthentication
709: Specifies whether to try rhosts based authentication with RSA host
710: authentication.
711: The argument must be
712: .Dq yes
713: or
714: .Dq no .
715: The default is
716: .Dq no .
717: This option applies to protocol version 1 only and requires
718: .Nm ssh
719: to be setuid root.
720: .It Cm RSAAuthentication
721: Specifies whether to try RSA authentication.
722: The argument to this keyword must be
723: .Dq yes
724: or
725: .Dq no .
726: RSA authentication will only be
727: attempted if the identity file exists, or an authentication agent is
728: running.
729: The default is
730: .Dq yes .
731: Note that this option applies to protocol version 1 only.
1.32 djm 732: .It Cm SendEnv
733: Specifies what variables from the local
734: .Xr environ 7
735: should be sent to the server.
736: Note that environment passing is only supported for protocol 2, the
1.33 djm 737: server must also support it, and the server must be configured to
738: accept these environment variables.
1.32 djm 739: Refer to
740: .Cm AcceptEnv
741: in
742: .Xr sshd_config 5
743: for how to configure the server.
744: Variables are specified by name, which may contain the wildcard characters
745: .Ql \&*
746: and
747: .Ql \&? .
1.33 djm 748: Multiple environment variables may be separated by whitespace or spread
1.32 djm 749: across multiple
750: .Cm SendEnv
751: directives.
752: The default is not to send any environment variables.
1.28 markus 753: .It Cm ServerAliveInterval
754: Sets a timeout interval in seconds after which if no data has been received
755: from the server,
756: .Nm ssh
757: will send a message through the encrypted
758: channel to request a response from the server.
759: The default
760: is 0, indicating that these messages will not be sent to the server.
761: This option applies to protocol version 2 only.
762: .It Cm ServerAliveCountMax
763: Sets the number of server alive messages (see above) which may be
764: sent without
765: .Nm ssh
766: receiving any messages back from the server.
767: If this threshold is reached while server alive messages are being sent,
768: .Nm ssh
769: will disconnect from the server, terminating the session.
770: It is important to note that the use of server alive messages is very
771: different from
772: .Cm TCPKeepAlive
773: (below).
774: The server alive messages are sent through the encrypted channel
775: and therefore will not be spoofable.
776: The TCP keepalive option enabled by
777: .Cm TCPKeepAlive
778: is spoofable.
779: The server alive mechanism is valuable when the client or
780: server depend on knowing when a connection has become inactive.
781: .Pp
782: The default value is 3.
783: If, for example,
784: .Cm ServerAliveInterval
785: (above) is set to 15, and
786: .Cm ServerAliveCountMax
787: is left at the default, if the server becomes unresponsive ssh
788: will disconnect after approximately 45 seconds.
1.1 stevesk 789: .It Cm SmartcardDevice
1.11 jmc 790: Specifies which smartcard device to use.
791: The argument to this keyword is the device
1.1 stevesk 792: .Nm ssh
793: should use to communicate with a smartcard used for storing the user's
1.11 jmc 794: private RSA key.
795: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 796: .It Cm StrictHostKeyChecking
797: If this flag is set to
798: .Dq yes ,
799: .Nm ssh
800: will never automatically add host keys to the
1.50 djm 801: .Pa ~/.ssh/known_hosts
1.1 stevesk 802: file, and refuses to connect to hosts whose host key has changed.
803: This provides maximum protection against trojan horse attacks,
804: however, can be annoying when the
805: .Pa /etc/ssh/ssh_known_hosts
806: file is poorly maintained, or connections to new hosts are
807: frequently made.
808: This option forces the user to manually
809: add all new hosts.
810: If this flag is set to
811: .Dq no ,
812: .Nm ssh
813: will automatically add new host keys to the
814: user known hosts files.
815: If this flag is set to
816: .Dq ask ,
817: new host keys
818: will be added to the user known host files only after the user
819: has confirmed that is what they really want to do, and
820: .Nm ssh
821: will refuse to connect to hosts whose host key has changed.
822: The host keys of
823: known hosts will be verified automatically in all cases.
824: The argument must be
825: .Dq yes ,
826: .Dq no
827: or
828: .Dq ask .
829: The default is
830: .Dq ask .
1.26 markus 831: .It Cm TCPKeepAlive
832: Specifies whether the system should send TCP keepalive messages to the
833: other side.
834: If they are sent, death of the connection or crash of one
835: of the machines will be properly noticed.
836: However, this means that
837: connections will die if the route is down temporarily, and some people
838: find it annoying.
839: .Pp
840: The default is
841: .Dq yes
842: (to send TCP keepalive messages), and the client will notice
843: if the network goes down or the remote host dies.
844: This is important in scripts, and many users want it too.
845: .Pp
846: To disable TCP keepalive messages, the value should be set to
847: .Dq no .
1.1 stevesk 848: .It Cm UsePrivilegedPort
849: Specifies whether to use a privileged port for outgoing connections.
850: The argument must be
851: .Dq yes
852: or
853: .Dq no .
854: The default is
855: .Dq no .
1.4 stevesk 856: If set to
857: .Dq yes
858: .Nm ssh
859: must be setuid root.
1.1 stevesk 860: Note that this option must be set to
861: .Dq yes
1.17 markus 862: for
1.1 stevesk 863: .Cm RhostsRSAAuthentication
1.17 markus 864: with older servers.
1.1 stevesk 865: .It Cm User
866: Specifies the user to log in as.
867: This can be useful when a different user name is used on different machines.
868: This saves the trouble of
869: having to remember to give the user name on the command line.
870: .It Cm UserKnownHostsFile
871: Specifies a file to use for the user
872: host key database instead of
1.50 djm 873: .Pa ~/.ssh/known_hosts .
1.8 jakob 874: .It Cm VerifyHostKeyDNS
875: Specifies whether to verify the remote key using DNS and SSHFP resource
876: records.
1.24 jakob 877: If this option is set to
878: .Dq yes ,
1.25 jmc 879: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 880: from DNS.
881: Insecure fingerprints will be handled as if this option was set to
882: .Dq ask .
883: If this option is set to
884: .Dq ask ,
885: information on fingerprint match will be displayed, but the user will still
886: need to confirm new host keys according to the
887: .Cm StrictHostKeyChecking
888: option.
889: The argument must be
890: .Dq yes ,
891: .Dq no
1.25 jmc 892: or
893: .Dq ask .
1.8 jakob 894: The default is
895: .Dq no .
1.12 jakob 896: Note that this option applies to protocol version 2 only.
1.1 stevesk 897: .It Cm XAuthLocation
1.5 stevesk 898: Specifies the full pathname of the
1.1 stevesk 899: .Xr xauth 1
900: program.
901: The default is
902: .Pa /usr/X11R6/bin/xauth .
903: .El
904: .Sh FILES
905: .Bl -tag -width Ds
1.50 djm 906: .It Pa ~/.ssh/config
1.1 stevesk 907: This is the per-user configuration file.
908: The format of this file is described above.
909: This file is used by the
910: .Nm ssh
911: client.
1.30 djm 912: Because of the potential for abuse, this file must have strict permissions:
913: read/write for the user, and not accessible by others.
1.1 stevesk 914: .It Pa /etc/ssh/ssh_config
915: Systemwide configuration file.
916: This file provides defaults for those
917: values that are not specified in the user's configuration file, and
918: for those users who do not have a configuration file.
919: This file must be world-readable.
920: .El
1.13 jmc 921: .Sh SEE ALSO
922: .Xr ssh 1
1.1 stevesk 923: .Sh AUTHORS
924: OpenSSH is a derivative of the original and free
925: ssh 1.2.12 release by Tatu Ylonen.
926: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
927: Theo de Raadt and Dug Song
928: removed many bugs, re-added newer features and
929: created OpenSSH.
930: Markus Friedl contributed the support for SSH
931: protocol versions 1.5 and 2.0.
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