Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.49.2.2
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
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22: .\" 2. Redistributions in binary form must reproduce the above copyright
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27: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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1.49.2.2! brad 37: .\" $OpenBSD: ssh_config.5,v 1.76 2006/01/20 11:21:45 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
1.49.2.1 brad 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
1.49.2.1 brad 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
1.49.2.1 brad 139: Use the specified address on the local machine as the source address of
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 ,
1.49.2.1 brad 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
1.49.2.1 brad 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).
1.49.2.2! brad 266: These sessions will try to reuse the master instance's network connection
! 267: rather than initiating new ones, but will fall back to connecting normally
! 268: if the control socket does not exist, or is not listening.
! 269: .Pp
1.37 djm 270: Setting this to
271: .Dq ask
272: will cause
273: .Nm ssh
274: to listen for control connections, but require confirmation using the
275: .Ev SSH_ASKPASS
276: program before they are accepted (see
277: .Xr ssh-add 1
1.38 jmc 278: for details).
1.49.2.1 brad 279: If the
280: .Cm ControlPath
281: can not be opened,
282: .Nm ssh
283: will continue without connecting to a master instance.
284: .Pp
285: X11 and
286: .Xr ssh-agent 1
287: forwarding is supported over these multiplexed connections, however the
1.49.2.2! brad 288: display and agent forwarded will be the one belonging to the master
1.49.2.1 brad 289: connection i.e. it is not possible to forward multiple displays or agents.
290: .Pp
291: Two additional options allow for opportunistic multiplexing: try to use a
292: master connection but fall back to creating a new one if one does not already
293: exist.
294: These options are:
295: .Dq auto
296: and
297: .Dq autoask .
298: The latter requires confirmation like the
299: .Dq ask
300: option.
1.36 djm 301: .It Cm ControlPath
1.49.2.1 brad 302: Specify the path to the control socket used for connection sharing as described
303: in the
1.36 djm 304: .Cm ControlMaster
1.49.2.1 brad 305: section above or the string
306: .Dq none
307: to disable connection sharing.
308: In the path,
309: .Ql %h
310: will be substituted by the target host name,
311: .Ql %p
312: the port and
313: .Ql %r
314: by the remote login username.
315: It is recommended that any
316: .Cm ControlPath
317: used for opportunistic connection sharing include
318: all three of these escape sequences.
319: This ensures that shared connections are uniquely identified.
1.38 jmc 320: .It Cm DynamicForward
1.49.2.2! brad 321: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 322: over the secure channel, and the application
323: protocol is then used to determine where to connect to from the
324: remote machine.
1.49.2.2! brad 325: .Pp
! 326: The argument must be
! 327: .Sm off
! 328: .Oo Ar bind_address : Oc Ar port .
! 329: .Sm on
! 330: IPv6 addresses can be specified by enclosing addresses in square brackets or
! 331: by using an alternative syntax:
! 332: .Oo Ar bind_address Ns / Oc Ns Ar port .
! 333: By default, the local port is bound in accordance with the
! 334: .Cm GatewayPorts
! 335: setting.
! 336: However, an explicit
! 337: .Ar bind_address
! 338: may be used to bind the connection to a specific address.
! 339: The
! 340: .Ar bind_address
! 341: of
! 342: .Dq localhost
! 343: indicates that the listening port be bound for local use only, while an
! 344: empty address or
! 345: .Sq *
! 346: indicates that the port should be available from all interfaces.
! 347: .Pp
1.38 jmc 348: Currently the SOCKS4 and SOCKS5 protocols are supported, and
349: .Nm ssh
350: will act as a SOCKS server.
351: Multiple forwardings may be specified, and
352: additional forwardings can be given on the command line.
353: Only the superuser can forward privileged ports.
1.14 markus 354: .It Cm EnableSSHKeysign
355: Setting this option to
356: .Dq yes
357: in the global client configuration file
358: .Pa /etc/ssh/ssh_config
359: enables the use of the helper program
360: .Xr ssh-keysign 8
361: during
362: .Cm HostbasedAuthentication .
363: The argument must be
364: .Dq yes
365: or
366: .Dq no .
367: The default is
368: .Dq no .
1.23 jmc 369: This option should be placed in the non-hostspecific section.
1.14 markus 370: See
371: .Xr ssh-keysign 8
372: for more information.
1.1 stevesk 373: .It Cm EscapeChar
374: Sets the escape character (default:
375: .Ql ~ ) .
376: The escape character can also
377: be set on the command line.
378: The argument should be a single character,
379: .Ql ^
380: followed by a letter, or
381: .Dq none
382: to disable the escape
383: character entirely (making the connection transparent for binary
384: data).
385: .It Cm ForwardAgent
386: Specifies whether the connection to the authentication agent (if any)
387: will be forwarded to the remote machine.
388: The argument must be
389: .Dq yes
390: or
391: .Dq no .
392: The default is
393: .Dq no .
1.3 stevesk 394: .Pp
1.7 jmc 395: Agent forwarding should be enabled with caution.
396: Users with the ability to bypass file permissions on the remote host
397: (for the agent's Unix-domain socket)
398: can access the local agent through the forwarded connection.
399: An attacker cannot obtain key material from the agent,
1.3 stevesk 400: however they can perform operations on the keys that enable them to
401: authenticate using the identities loaded into the agent.
1.1 stevesk 402: .It Cm ForwardX11
403: Specifies whether X11 connections will be automatically redirected
404: over the secure channel and
405: .Ev DISPLAY
406: set.
407: The argument must be
408: .Dq yes
409: or
410: .Dq no .
411: The default is
412: .Dq no .
1.3 stevesk 413: .Pp
1.7 jmc 414: X11 forwarding should be enabled with caution.
415: Users with the ability to bypass file permissions on the remote host
1.22 markus 416: (for the user's X11 authorization database)
1.7 jmc 417: can access the local X11 display through the forwarded connection.
1.22 markus 418: An attacker may then be able to perform activities such as keystroke monitoring
419: if the
420: .Cm ForwardX11Trusted
421: option is also enabled.
422: .It Cm ForwardX11Trusted
1.34 jmc 423: If this option is set to
1.22 markus 424: .Dq yes
425: then remote X11 clients will have full access to the original X11 display.
1.42 djm 426: .Pp
1.22 markus 427: If this option is set to
428: .Dq no
429: then remote X11 clients will be considered untrusted and prevented
430: from stealing or tampering with data belonging to trusted X11
431: clients.
1.42 djm 432: Furthermore, the
433: .Xr xauth 1
434: token used for the session will be set to expire after 20 minutes.
435: Remote clients will be refused access after this time.
1.22 markus 436: .Pp
437: The default is
438: .Dq no .
439: .Pp
440: See the X11 SECURITY extension specification for full details on
441: the restrictions imposed on untrusted clients.
1.1 stevesk 442: .It Cm GatewayPorts
443: Specifies whether remote hosts are allowed to connect to local
444: forwarded ports.
445: By default,
446: .Nm ssh
1.7 jmc 447: binds local port forwardings to the loopback address.
448: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 449: .Cm GatewayPorts
450: can be used to specify that
451: .Nm ssh
452: should bind local port forwardings to the wildcard address,
453: thus allowing remote hosts to connect to forwarded ports.
454: The argument must be
455: .Dq yes
456: or
457: .Dq no .
458: The default is
459: .Dq no .
460: .It Cm GlobalKnownHostsFile
461: Specifies a file to use for the global
462: host key database instead of
463: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 464: .It Cm GSSAPIAuthentication
1.27 markus 465: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 466: The default is
1.21 markus 467: .Dq no .
1.18 markus 468: Note that this option applies to protocol version 2 only.
469: .It Cm GSSAPIDelegateCredentials
470: Forward (delegate) credentials to the server.
471: The default is
472: .Dq no .
473: Note that this option applies to protocol version 2 only.
1.44 djm 474: .It Cm HashKnownHosts
475: Indicates that
476: .Nm ssh
477: should hash host names and addresses when they are added to
1.49.2.1 brad 478: .Pa ~/.ssh/known_hosts .
1.44 djm 479: These hashed names may be used normally by
480: .Nm ssh
481: and
482: .Nm sshd ,
483: but they do not reveal identifying information should the file's contents
484: be disclosed.
485: The default is
486: .Dq no .
1.46 jmc 487: Note that hashing of names and addresses will not be retrospectively applied
1.45 djm 488: to existing known hosts files, but these may be manually hashed using
489: .Xr ssh-keygen 1 .
1.1 stevesk 490: .It Cm HostbasedAuthentication
491: Specifies whether to try rhosts based authentication with public key
492: authentication.
493: The argument must be
494: .Dq yes
495: or
496: .Dq no .
497: The default is
498: .Dq no .
499: This option applies to protocol version 2 only and
500: is similar to
501: .Cm RhostsRSAAuthentication .
502: .It Cm HostKeyAlgorithms
503: Specifies the protocol version 2 host key algorithms
504: that the client wants to use in order of preference.
505: The default for this option is:
506: .Dq ssh-rsa,ssh-dss .
507: .It Cm HostKeyAlias
508: Specifies an alias that should be used instead of the
509: real host name when looking up or saving the host key
510: in the host key database files.
511: This option is useful for tunneling ssh connections
512: or for multiple servers running on a single host.
513: .It Cm HostName
514: Specifies the real host name to log into.
515: This can be used to specify nicknames or abbreviations for hosts.
516: Default is the name given on the command line.
517: Numeric IP addresses are also permitted (both on the command line and in
518: .Cm HostName
519: specifications).
1.29 markus 520: .It Cm IdentitiesOnly
521: Specifies that
522: .Nm ssh
523: should only use the authentication identity files configured in the
1.31 jmc 524: .Nm
1.29 markus 525: files,
526: even if the
527: .Nm ssh-agent
528: offers more identities.
529: The argument to this keyword must be
530: .Dq yes
531: or
532: .Dq no .
1.49.2.2! brad 533: This option is intended for situations where
1.29 markus 534: .Nm ssh-agent
535: offers many different identities.
536: The default is
537: .Dq no .
1.49.2.2! brad 538: .It Cm IdentityFile
! 539: Specifies a file from which the user's RSA or DSA authentication identity
! 540: is read.
! 541: The default is
! 542: .Pa ~/.ssh/identity
! 543: for protocol version 1, and
! 544: .Pa ~/.ssh/id_rsa
! 545: and
! 546: .Pa ~/.ssh/id_dsa
! 547: for protocol version 2.
! 548: Additionally, any identities represented by the authentication agent
! 549: will be used for authentication.
! 550: The file name may use the tilde
! 551: syntax to refer to a user's home directory.
! 552: It is possible to have
! 553: multiple identity files specified in configuration files; all these
! 554: identities will be tried in sequence.
1.39 djm 555: .It Cm KbdInteractiveDevices
556: Specifies the list of methods to use in keyboard-interactive authentication.
557: Multiple method names must be comma-separated.
558: The default is to use the server specified list.
1.49.2.2! brad 559: .It Cm LocalCommand
! 560: Specifies a command to execute on the local machine after successfully
! 561: connecting to the server.
! 562: The command string extends to the end of the line, and is executed with
! 563: .Pa /bin/sh .
! 564: This directive is ignored unless
! 565: .Cm PermitLocalCommand
! 566: has been enabled.
1.1 stevesk 567: .It Cm LocalForward
1.49.2.2! brad 568: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 569: the secure channel to the specified host and port from the remote machine.
1.49 jmc 570: The first argument must be
1.43 djm 571: .Sm off
1.49 jmc 572: .Oo Ar bind_address : Oc Ar port
1.43 djm 573: .Sm on
1.49 jmc 574: and the second argument must be
575: .Ar host : Ns Ar hostport .
1.46 jmc 576: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 577: by using an alternative syntax:
1.49 jmc 578: .Oo Ar bind_address Ns / Oc Ns Ar port
579: and
580: .Ar host Ns / Ns Ar hostport .
1.46 jmc 581: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 582: given on the command line.
1.1 stevesk 583: Only the superuser can forward privileged ports.
1.43 djm 584: By default, the local port is bound in accordance with the
585: .Cm GatewayPorts
586: setting.
587: However, an explicit
588: .Ar bind_address
589: may be used to bind the connection to a specific address.
590: The
591: .Ar bind_address
592: of
593: .Dq localhost
1.46 jmc 594: indicates that the listening port be bound for local use only, while an
595: empty address or
596: .Sq *
1.43 djm 597: indicates that the port should be available from all interfaces.
1.1 stevesk 598: .It Cm LogLevel
599: Gives the verbosity level that is used when logging messages from
600: .Nm ssh .
601: The possible values are:
602: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
1.7 jmc 603: The default is INFO.
604: DEBUG and DEBUG1 are equivalent.
605: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 606: .It Cm MACs
607: Specifies the MAC (message authentication code) algorithms
608: in order of preference.
609: The MAC algorithm is used in protocol version 2
610: for data integrity protection.
611: Multiple algorithms must be comma-separated.
612: The default is
613: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
614: .It Cm NoHostAuthenticationForLocalhost
615: This option can be used if the home directory is shared across machines.
616: In this case localhost will refer to a different machine on each of
617: the machines and the user will get many warnings about changed host keys.
618: However, this option disables host authentication for localhost.
619: The argument to this keyword must be
620: .Dq yes
621: or
622: .Dq no .
623: The default is to check the host key for localhost.
624: .It Cm NumberOfPasswordPrompts
625: Specifies the number of password prompts before giving up.
626: The argument to this keyword must be an integer.
627: Default is 3.
628: .It Cm PasswordAuthentication
629: Specifies whether to use password authentication.
630: The argument to this keyword must be
631: .Dq yes
632: or
633: .Dq no .
634: The default is
635: .Dq yes .
1.49.2.2! brad 636: .It Cm PermitLocalCommand
! 637: Allow local command execution via the
! 638: .Ic LocalCommand
! 639: option or using the
! 640: .Ic !\& Ns Ar command
! 641: escape sequence in
! 642: .Xr ssh 1 .
! 643: The argument must be
! 644: .Dq yes
! 645: or
! 646: .Dq no .
! 647: The default is
! 648: .Dq no .
1.1 stevesk 649: .It Cm Port
650: Specifies the port number to connect on the remote host.
651: Default is 22.
652: .It Cm PreferredAuthentications
653: Specifies the order in which the client should try protocol 2
1.11 jmc 654: authentication methods.
1.48 jmc 655: This allows a client to prefer one method (e.g.\&
1.1 stevesk 656: .Cm keyboard-interactive )
1.48 jmc 657: over another method (e.g.\&
1.1 stevesk 658: .Cm password )
659: The default for this option is:
660: .Dq hostbased,publickey,keyboard-interactive,password .
661: .It Cm Protocol
662: Specifies the protocol versions
663: .Nm ssh
664: should support in order of preference.
665: The possible values are
666: .Dq 1
667: and
668: .Dq 2 .
669: Multiple versions must be comma-separated.
670: The default is
671: .Dq 2,1 .
672: This means that
673: .Nm ssh
674: tries version 2 and falls back to version 1
675: if version 2 is not available.
676: .It Cm ProxyCommand
677: Specifies the command to use to connect to the server.
678: The command
679: string extends to the end of the line, and is executed with
680: .Pa /bin/sh .
681: In the command string,
682: .Ql %h
683: will be substituted by the host name to
684: connect and
685: .Ql %p
686: by the port.
687: The command can be basically anything,
688: and should read from its standard input and write to its standard output.
689: It should eventually connect an
690: .Xr sshd 8
691: server running on some machine, or execute
692: .Ic sshd -i
693: somewhere.
694: Host key management will be done using the
695: HostName of the host being connected (defaulting to the name typed by
696: the user).
1.7 jmc 697: Setting the command to
698: .Dq none
1.6 markus 699: disables this option entirely.
1.1 stevesk 700: Note that
701: .Cm CheckHostIP
702: is not available for connects with a proxy command.
703: .Pp
1.49.2.1 brad 704: This directive is useful in conjunction with
705: .Xr nc 1
706: and its proxy support.
707: For example, the following directive would connect via an HTTP proxy at
708: 192.0.2.0:
709: .Bd -literal -offset 3n
710: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
711: .Ed
1.1 stevesk 712: .It Cm PubkeyAuthentication
713: Specifies whether to try public key authentication.
714: The argument to this keyword must be
715: .Dq yes
716: or
717: .Dq no .
718: The default is
719: .Dq yes .
720: This option applies to protocol version 2 only.
1.49.2.2! brad 721: .It Cm RekeyLimit
! 722: Specifies the maximum amount of data that may be transmitted before the
! 723: session key is renegotiated.
! 724: The argument is the number of bytes, with an optional suffix of
! 725: .Sq K ,
! 726: .Sq M ,
! 727: or
! 728: .Sq G
! 729: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
! 730: The default is between
! 731: .Dq 1G
! 732: and
! 733: .Dq 4G ,
! 734: depending on the cipher.
! 735: This option applies to protocol version 2 only.
1.1 stevesk 736: .It Cm RemoteForward
1.49.2.2! brad 737: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 738: the secure channel to the specified host and port from the local machine.
1.49 jmc 739: The first argument must be
1.43 djm 740: .Sm off
1.49 jmc 741: .Oo Ar bind_address : Oc Ar port
1.43 djm 742: .Sm on
1.49 jmc 743: and the second argument must be
744: .Ar host : Ns Ar hostport .
745: IPv6 addresses can be specified by enclosing addresses in square brackets
746: or by using an alternative syntax:
747: .Oo Ar bind_address Ns / Oc Ns Ar port
748: and
749: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 750: Multiple forwardings may be specified, and additional
751: forwardings can be given on the command line.
752: Only the superuser can forward privileged ports.
1.43 djm 753: .Pp
754: If the
755: .Ar bind_address
756: is not specified, the default is to only bind to loopback addresses.
757: If the
758: .Ar bind_address
759: is
760: .Ql *
761: or an empty string, then the forwarding is requested to listen on all
762: interfaces.
763: Specifying a remote
764: .Ar bind_address
1.46 jmc 765: will only succeed if the server's
766: .Cm GatewayPorts
1.43 djm 767: option is enabled (see
1.46 jmc 768: .Xr sshd_config 5 ) .
1.1 stevesk 769: .It Cm RhostsRSAAuthentication
770: Specifies whether to try rhosts based authentication with RSA host
771: authentication.
772: The argument must be
773: .Dq yes
774: or
775: .Dq no .
776: The default is
777: .Dq no .
778: This option applies to protocol version 1 only and requires
779: .Nm ssh
780: to be setuid root.
781: .It Cm RSAAuthentication
782: Specifies whether to try RSA authentication.
783: The argument to this keyword must be
784: .Dq yes
785: or
786: .Dq no .
787: RSA authentication will only be
788: attempted if the identity file exists, or an authentication agent is
789: running.
790: The default is
791: .Dq yes .
792: Note that this option applies to protocol version 1 only.
1.32 djm 793: .It Cm SendEnv
794: Specifies what variables from the local
795: .Xr environ 7
796: should be sent to the server.
797: Note that environment passing is only supported for protocol 2, the
1.33 djm 798: server must also support it, and the server must be configured to
799: accept these environment variables.
1.32 djm 800: Refer to
801: .Cm AcceptEnv
802: in
803: .Xr sshd_config 5
804: for how to configure the server.
805: Variables are specified by name, which may contain the wildcard characters
806: .Ql \&*
807: and
808: .Ql \&? .
1.33 djm 809: Multiple environment variables may be separated by whitespace or spread
1.32 djm 810: across multiple
811: .Cm SendEnv
812: directives.
813: The default is not to send any environment variables.
1.28 markus 814: .It Cm ServerAliveCountMax
1.49.2.2! brad 815: Sets the number of server alive messages (see below) which may be
1.28 markus 816: sent without
817: .Nm ssh
818: receiving any messages back from the server.
819: If this threshold is reached while server alive messages are being sent,
820: .Nm ssh
821: will disconnect from the server, terminating the session.
822: It is important to note that the use of server alive messages is very
823: different from
824: .Cm TCPKeepAlive
825: (below).
826: The server alive messages are sent through the encrypted channel
827: and therefore will not be spoofable.
828: The TCP keepalive option enabled by
829: .Cm TCPKeepAlive
830: is spoofable.
831: The server alive mechanism is valuable when the client or
832: server depend on knowing when a connection has become inactive.
833: .Pp
834: The default value is 3.
835: If, for example,
836: .Cm ServerAliveInterval
1.49.2.2! brad 837: (see below) is set to 15, and
1.28 markus 838: .Cm ServerAliveCountMax
839: is left at the default, if the server becomes unresponsive ssh
840: will disconnect after approximately 45 seconds.
1.49.2.2! brad 841: .It Cm ServerAliveInterval
! 842: Sets a timeout interval in seconds after which if no data has been received
! 843: from the server,
! 844: .Nm ssh
! 845: will send a message through the encrypted
! 846: channel to request a response from the server.
! 847: The default
! 848: is 0, indicating that these messages will not be sent to the server.
! 849: This option applies to protocol version 2 only.
1.1 stevesk 850: .It Cm SmartcardDevice
1.11 jmc 851: Specifies which smartcard device to use.
852: The argument to this keyword is the device
1.1 stevesk 853: .Nm ssh
854: should use to communicate with a smartcard used for storing the user's
1.11 jmc 855: private RSA key.
856: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 857: .It Cm StrictHostKeyChecking
858: If this flag is set to
859: .Dq yes ,
860: .Nm ssh
861: will never automatically add host keys to the
1.49.2.1 brad 862: .Pa ~/.ssh/known_hosts
1.1 stevesk 863: file, and refuses to connect to hosts whose host key has changed.
864: This provides maximum protection against trojan horse attacks,
865: however, can be annoying when the
866: .Pa /etc/ssh/ssh_known_hosts
867: file is poorly maintained, or connections to new hosts are
868: frequently made.
869: This option forces the user to manually
870: add all new hosts.
871: If this flag is set to
872: .Dq no ,
873: .Nm ssh
874: will automatically add new host keys to the
875: user known hosts files.
876: If this flag is set to
877: .Dq ask ,
878: new host keys
879: will be added to the user known host files only after the user
880: has confirmed that is what they really want to do, and
881: .Nm ssh
882: will refuse to connect to hosts whose host key has changed.
883: The host keys of
884: known hosts will be verified automatically in all cases.
885: The argument must be
886: .Dq yes ,
887: .Dq no
888: or
889: .Dq ask .
890: The default is
891: .Dq ask .
1.26 markus 892: .It Cm TCPKeepAlive
893: Specifies whether the system should send TCP keepalive messages to the
894: other side.
895: If they are sent, death of the connection or crash of one
896: of the machines will be properly noticed.
897: However, this means that
898: connections will die if the route is down temporarily, and some people
899: find it annoying.
900: .Pp
901: The default is
902: .Dq yes
903: (to send TCP keepalive messages), and the client will notice
904: if the network goes down or the remote host dies.
905: This is important in scripts, and many users want it too.
906: .Pp
907: To disable TCP keepalive messages, the value should be set to
908: .Dq no .
1.49.2.2! brad 909: .It Cm Tunnel
! 910: Request starting
! 911: .Xr tun 4
! 912: device forwarding between the client and the server.
! 913: This option also allows requesting layer 2 (ethernet)
! 914: instead of layer 3 (point-to-point) tunneling from the server.
! 915: The argument must be
! 916: .Dq yes ,
! 917: .Dq point-to-point ,
! 918: .Dq ethernet
! 919: or
! 920: .Dq no .
! 921: The default is
! 922: .Dq no .
! 923: .It Cm TunnelDevice
! 924: Force a specified
! 925: .Xr tun 4
! 926: device on the client.
! 927: Without this option, the next available device will be used.
1.1 stevesk 928: .It Cm UsePrivilegedPort
929: Specifies whether to use a privileged port for outgoing connections.
930: The argument must be
931: .Dq yes
932: or
933: .Dq no .
934: The default is
935: .Dq no .
1.4 stevesk 936: If set to
937: .Dq yes
938: .Nm ssh
939: must be setuid root.
1.1 stevesk 940: Note that this option must be set to
941: .Dq yes
1.17 markus 942: for
1.1 stevesk 943: .Cm RhostsRSAAuthentication
1.17 markus 944: with older servers.
1.1 stevesk 945: .It Cm User
946: Specifies the user to log in as.
947: This can be useful when a different user name is used on different machines.
948: This saves the trouble of
949: having to remember to give the user name on the command line.
950: .It Cm UserKnownHostsFile
951: Specifies a file to use for the user
952: host key database instead of
1.49.2.1 brad 953: .Pa ~/.ssh/known_hosts .
1.8 jakob 954: .It Cm VerifyHostKeyDNS
955: Specifies whether to verify the remote key using DNS and SSHFP resource
956: records.
1.24 jakob 957: If this option is set to
958: .Dq yes ,
1.25 jmc 959: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 960: from DNS.
961: Insecure fingerprints will be handled as if this option was set to
962: .Dq ask .
963: If this option is set to
964: .Dq ask ,
965: information on fingerprint match will be displayed, but the user will still
966: need to confirm new host keys according to the
967: .Cm StrictHostKeyChecking
968: option.
969: The argument must be
970: .Dq yes ,
971: .Dq no
1.25 jmc 972: or
973: .Dq ask .
1.8 jakob 974: The default is
975: .Dq no .
1.12 jakob 976: Note that this option applies to protocol version 2 only.
1.1 stevesk 977: .It Cm XAuthLocation
1.5 stevesk 978: Specifies the full pathname of the
1.1 stevesk 979: .Xr xauth 1
980: program.
981: The default is
982: .Pa /usr/X11R6/bin/xauth .
983: .El
984: .Sh FILES
985: .Bl -tag -width Ds
1.49.2.1 brad 986: .It Pa ~/.ssh/config
1.1 stevesk 987: This is the per-user configuration file.
988: The format of this file is described above.
989: This file is used by the
990: .Nm ssh
991: client.
1.30 djm 992: Because of the potential for abuse, this file must have strict permissions:
993: read/write for the user, and not accessible by others.
1.1 stevesk 994: .It Pa /etc/ssh/ssh_config
995: Systemwide configuration file.
996: This file provides defaults for those
997: values that are not specified in the user's configuration file, and
998: for those users who do not have a configuration file.
999: This file must be world-readable.
1000: .El
1.13 jmc 1001: .Sh SEE ALSO
1002: .Xr ssh 1
1.1 stevesk 1003: .Sh AUTHORS
1004: OpenSSH is a derivative of the original and free
1005: ssh 1.2.12 release by Tatu Ylonen.
1006: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1007: Theo de Raadt and Dug Song
1008: removed many bugs, re-added newer features and
1009: created OpenSSH.
1010: Markus Friedl contributed the support for SSH
1011: protocol versions 1.5 and 2.0.
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