Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.80
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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1.80 ! jmc 37: .\" $OpenBSD: ssh_config.5,v 1.79 2006/02/19 20:12:25 jmc Exp $
1.1 stevesk 38: .Dd September 25, 1999
39: .Dt SSH_CONFIG 5
40: .Os
41: .Sh NAME
42: .Nm ssh_config
43: .Nd OpenSSH SSH client configuration files
44: .Sh SYNOPSIS
45: .Bl -tag -width Ds -compact
1.50 djm 46: .It Pa ~/.ssh/config
1.1 stevesk 47: .It Pa /etc/ssh/ssh_config
48: .El
49: .Sh DESCRIPTION
50: .Nm ssh
51: obtains configuration data from the following sources in
52: the following order:
1.79 jmc 53: .Pp
1.2 stevesk 54: .Bl -enum -offset indent -compact
55: .It
56: command-line options
57: .It
58: user's configuration file
1.50 djm 59: .Pq Pa ~/.ssh/config
1.2 stevesk 60: .It
61: system-wide configuration file
62: .Pq Pa /etc/ssh/ssh_config
63: .El
1.1 stevesk 64: .Pp
65: For each parameter, the first obtained value
66: will be used.
1.41 jmc 67: The configuration files contain sections separated by
1.1 stevesk 68: .Dq Host
69: specifications, and that section is only applied for hosts that
70: match one of the patterns given in the specification.
71: The matched host name is the one given on the command line.
72: .Pp
73: Since the first obtained value for each parameter is used, more
74: host-specific declarations should be given near the beginning of the
75: file, and general defaults at the end.
1.80 ! jmc 76: .Sh PATTERNS
! 77: A
! 78: .Em pattern
! 79: consists of zero or more non-whitespace characters,
! 80: .Sq *
! 81: (a wildcard that matches zero or more characters),
! 82: or
! 83: .Sq ?\&
! 84: (a wildcard that matches exactly one character).
! 85: For example, to specify a set of declarations for any host in the
! 86: .Dq .co.uk
! 87: set of domains,
! 88: the following pattern could be used:
! 89: .Pp
! 90: .Dl Host *.co.uk
! 91: .Pp
! 92: The following pattern
! 93: would match any host in the 192.168.0.[0-9] network range:
! 94: .Pp
! 95: .Dl Host 192.168.0.?
! 96: .Pp
! 97: A
! 98: .Em pattern-list
! 99: is a comma-separated list of patterns.
! 100: Patterns within pattern-lists may be negated
! 101: by preceding them with an exclamation mark
! 102: .Pq Sq !\& .
! 103: For example,
! 104: to allow a key to be used from anywhere within an organisation
! 105: except from the
! 106: .Dq dialup
! 107: pool,
! 108: the following entry (in authorized_keys) could be used:
1.1 stevesk 109: .Pp
1.80 ! jmc 110: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
! 111: .Sh FILE FORMAT
1.1 stevesk 112: The configuration file has the following format:
113: .Pp
114: Empty lines and lines starting with
115: .Ql #
116: are comments.
117: Otherwise a line is of the format
118: .Dq keyword arguments .
119: Configuration options may be separated by whitespace or
120: optional whitespace and exactly one
121: .Ql = ;
122: the latter format is useful to avoid the need to quote whitespace
123: when specifying configuration options using the
124: .Nm ssh ,
125: .Nm scp
126: and
127: .Nm sftp
128: .Fl o
129: option.
130: .Pp
131: The possible
132: keywords and their meanings are as follows (note that
133: keywords are case-insensitive and arguments are case-sensitive):
134: .Bl -tag -width Ds
135: .It Cm Host
136: Restricts the following declarations (up to the next
137: .Cm Host
138: keyword) to be only for those hosts that match one of the patterns
139: given after the keyword.
140: A single
141: .Ql \&*
142: as a pattern can be used to provide global
143: defaults for all hosts.
1.80 ! jmc 144: See
! 145: .Sx PATTERNS
! 146: for more information on patterns.
1.1 stevesk 147: The host is the
148: .Ar hostname
149: argument given on the command line (i.e., the name is not converted to
150: a canonicalized host name before matching).
1.10 djm 151: .It Cm AddressFamily
1.11 jmc 152: Specifies which address family to use when connecting.
153: Valid arguments are
1.10 djm 154: .Dq any ,
155: .Dq inet
1.40 jmc 156: (use IPv4 only) or
1.10 djm 157: .Dq inet6
1.40 jmc 158: (use IPv6 only).
1.1 stevesk 159: .It Cm BatchMode
160: If set to
161: .Dq yes ,
162: passphrase/password querying will be disabled.
163: This option is useful in scripts and other batch jobs where no user
164: is present to supply the password.
165: The argument must be
166: .Dq yes
167: or
168: .Dq no .
169: The default is
170: .Dq no .
171: .It Cm BindAddress
1.60 dtucker 172: Use the specified address on the local machine as the source address of
1.61 jmc 173: the connection.
174: Only useful on systems with more than one address.
1.1 stevesk 175: Note that this option does not work if
176: .Cm UsePrivilegedPort
177: is set to
178: .Dq yes .
179: .It Cm ChallengeResponseAuthentication
180: Specifies whether to use challenge response authentication.
181: The argument to this keyword must be
182: .Dq yes
183: or
184: .Dq no .
185: The default is
186: .Dq yes .
187: .It Cm CheckHostIP
188: If this flag is set to
189: .Dq yes ,
190: ssh will additionally check the host IP address in the
191: .Pa known_hosts
192: file.
193: This allows ssh to detect if a host key changed due to DNS spoofing.
194: If the option is set to
195: .Dq no ,
196: the check will not be executed.
197: The default is
198: .Dq yes .
199: .It Cm Cipher
200: Specifies the cipher to use for encrypting the session
201: in protocol version 1.
202: Currently,
203: .Dq blowfish ,
204: .Dq 3des ,
205: and
206: .Dq des
207: are supported.
208: .Ar des
209: is only supported in the
210: .Nm ssh
211: client for interoperability with legacy protocol 1 implementations
212: that do not support the
213: .Ar 3des
1.7 jmc 214: cipher.
215: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 216: The default is
217: .Dq 3des .
218: .It Cm Ciphers
219: Specifies the ciphers allowed for protocol version 2
220: in order of preference.
221: Multiple ciphers must be comma-separated.
1.35 dtucker 222: The supported ciphers are
223: .Dq 3des-cbc ,
224: .Dq aes128-cbc ,
225: .Dq aes192-cbc ,
226: .Dq aes256-cbc ,
227: .Dq aes128-ctr ,
228: .Dq aes192-ctr ,
229: .Dq aes256-ctr ,
1.54 djm 230: .Dq arcfour128 ,
231: .Dq arcfour256 ,
1.35 dtucker 232: .Dq arcfour ,
233: .Dq blowfish-cbc ,
234: and
235: .Dq cast128-cbc .
1.1 stevesk 236: The default is
237: .Bd -literal
1.54 djm 238: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
239: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
240: aes192-ctr,aes256-ctr''
1.1 stevesk 241: .Ed
242: .It Cm ClearAllForwardings
243: Specifies that all local, remote and dynamic port forwardings
244: specified in the configuration files or on the command line be
1.7 jmc 245: cleared.
246: This option is primarily useful when used from the
1.1 stevesk 247: .Nm ssh
248: command line to clear port forwardings set in
249: configuration files, and is automatically set by
250: .Xr scp 1
251: and
252: .Xr sftp 1 .
253: The argument must be
254: .Dq yes
255: or
256: .Dq no .
257: The default is
258: .Dq no .
259: .It Cm Compression
260: Specifies whether to use compression.
261: The argument must be
262: .Dq yes
263: or
264: .Dq no .
265: The default is
266: .Dq no .
267: .It Cm CompressionLevel
268: Specifies the compression level to use if compression is enabled.
269: The argument must be an integer from 1 (fast) to 9 (slow, best).
270: The default level is 6, which is good for most applications.
271: The meaning of the values is the same as in
272: .Xr gzip 1 .
273: Note that this option applies to protocol version 1 only.
274: .It Cm ConnectionAttempts
275: Specifies the number of tries (one per second) to make before exiting.
276: The argument must be an integer.
277: This may be useful in scripts if the connection sometimes fails.
278: The default is 1.
1.9 djm 279: .It Cm ConnectTimeout
280: Specifies the timeout (in seconds) used when connecting to the ssh
1.11 jmc 281: server, instead of using the default system TCP timeout.
282: This value is used only when the target is down or really unreachable,
283: not when it refuses the connection.
1.36 djm 284: .It Cm ControlMaster
285: Enables the sharing of multiple sessions over a single network connection.
286: When set to
287: .Dq yes
288: .Nm ssh
289: will listen for connections on a control socket specified using the
290: .Cm ControlPath
291: argument.
292: Additional sessions can connect to this socket using the same
293: .Cm ControlPath
294: with
295: .Cm ControlMaster
296: set to
297: .Dq no
1.38 jmc 298: (the default).
1.64 jmc 299: These sessions will try to reuse the master instance's network connection
1.63 djm 300: rather than initiating new ones, but will fall back to connecting normally
301: if the control socket does not exist, or is not listening.
302: .Pp
1.37 djm 303: Setting this to
304: .Dq ask
305: will cause
306: .Nm ssh
307: to listen for control connections, but require confirmation using the
308: .Ev SSH_ASKPASS
309: program before they are accepted (see
310: .Xr ssh-add 1
1.38 jmc 311: for details).
1.51 jakob 312: If the
313: .Cm ControlPath
314: can not be opened,
315: .Nm ssh
316: will continue without connecting to a master instance.
1.58 djm 317: .Pp
318: X11 and
1.59 jmc 319: .Xr ssh-agent 1
1.58 djm 320: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 321: display and agent forwarded will be the one belonging to the master
1.59 jmc 322: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 323: .Pp
324: Two additional options allow for opportunistic multiplexing: try to use a
325: master connection but fall back to creating a new one if one does not already
326: exist.
327: These options are:
328: .Dq auto
329: and
330: .Dq autoask .
331: The latter requires confirmation like the
332: .Dq ask
333: option.
1.36 djm 334: .It Cm ControlPath
1.55 djm 335: Specify the path to the control socket used for connection sharing as described
336: in the
1.36 djm 337: .Cm ControlMaster
1.57 djm 338: section above or the string
339: .Dq none
340: to disable connection sharing.
1.55 djm 341: In the path,
1.77 djm 342: .Ql %l
343: will be substituted by the local host name,
1.55 djm 344: .Ql %h
345: will be substituted by the target host name,
346: .Ql %p
347: the port and
348: .Ql %r
349: by the remote login username.
1.56 djm 350: It is recommended that any
351: .Cm ControlPath
352: used for opportunistic connection sharing include
1.78 jmc 353: at least %h, %p, and %r.
1.56 djm 354: This ensures that shared connections are uniquely identified.
1.38 jmc 355: .It Cm DynamicForward
1.74 jmc 356: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 357: over the secure channel, and the application
358: protocol is then used to determine where to connect to from the
359: remote machine.
1.62 djm 360: .Pp
361: The argument must be
362: .Sm off
363: .Oo Ar bind_address : Oc Ar port .
364: .Sm on
365: IPv6 addresses can be specified by enclosing addresses in square brackets or
366: by using an alternative syntax:
367: .Oo Ar bind_address Ns / Oc Ns Ar port .
368: By default, the local port is bound in accordance with the
369: .Cm GatewayPorts
370: setting.
371: However, an explicit
372: .Ar bind_address
373: may be used to bind the connection to a specific address.
374: The
375: .Ar bind_address
376: of
377: .Dq localhost
378: indicates that the listening port be bound for local use only, while an
379: empty address or
380: .Sq *
381: indicates that the port should be available from all interfaces.
382: .Pp
1.38 jmc 383: Currently the SOCKS4 and SOCKS5 protocols are supported, and
384: .Nm ssh
385: will act as a SOCKS server.
386: Multiple forwardings may be specified, and
387: additional forwardings can be given on the command line.
388: Only the superuser can forward privileged ports.
1.14 markus 389: .It Cm EnableSSHKeysign
390: Setting this option to
391: .Dq yes
392: in the global client configuration file
393: .Pa /etc/ssh/ssh_config
394: enables the use of the helper program
395: .Xr ssh-keysign 8
396: during
397: .Cm HostbasedAuthentication .
398: The argument must be
399: .Dq yes
400: or
401: .Dq no .
402: The default is
403: .Dq no .
1.23 jmc 404: This option should be placed in the non-hostspecific section.
1.14 markus 405: See
406: .Xr ssh-keysign 8
407: for more information.
1.1 stevesk 408: .It Cm EscapeChar
409: Sets the escape character (default:
410: .Ql ~ ) .
411: The escape character can also
412: be set on the command line.
413: The argument should be a single character,
414: .Ql ^
415: followed by a letter, or
416: .Dq none
417: to disable the escape
418: character entirely (making the connection transparent for binary
419: data).
420: .It Cm ForwardAgent
421: Specifies whether the connection to the authentication agent (if any)
422: will be forwarded to the remote machine.
423: The argument must be
424: .Dq yes
425: or
426: .Dq no .
427: The default is
428: .Dq no .
1.3 stevesk 429: .Pp
1.7 jmc 430: Agent forwarding should be enabled with caution.
431: Users with the ability to bypass file permissions on the remote host
432: (for the agent's Unix-domain socket)
433: can access the local agent through the forwarded connection.
434: An attacker cannot obtain key material from the agent,
1.3 stevesk 435: however they can perform operations on the keys that enable them to
436: authenticate using the identities loaded into the agent.
1.1 stevesk 437: .It Cm ForwardX11
438: Specifies whether X11 connections will be automatically redirected
439: over the secure channel and
440: .Ev DISPLAY
441: set.
442: The argument must be
443: .Dq yes
444: or
445: .Dq no .
446: The default is
447: .Dq no .
1.3 stevesk 448: .Pp
1.7 jmc 449: X11 forwarding should be enabled with caution.
450: Users with the ability to bypass file permissions on the remote host
1.22 markus 451: (for the user's X11 authorization database)
1.7 jmc 452: can access the local X11 display through the forwarded connection.
1.22 markus 453: An attacker may then be able to perform activities such as keystroke monitoring
454: if the
455: .Cm ForwardX11Trusted
456: option is also enabled.
457: .It Cm ForwardX11Trusted
1.34 jmc 458: If this option is set to
1.22 markus 459: .Dq yes
460: then remote X11 clients will have full access to the original X11 display.
1.42 djm 461: .Pp
1.22 markus 462: If this option is set to
463: .Dq no
464: then remote X11 clients will be considered untrusted and prevented
465: from stealing or tampering with data belonging to trusted X11
466: clients.
1.42 djm 467: Furthermore, the
468: .Xr xauth 1
469: token used for the session will be set to expire after 20 minutes.
470: Remote clients will be refused access after this time.
1.22 markus 471: .Pp
472: The default is
473: .Dq no .
474: .Pp
475: See the X11 SECURITY extension specification for full details on
476: the restrictions imposed on untrusted clients.
1.1 stevesk 477: .It Cm GatewayPorts
478: Specifies whether remote hosts are allowed to connect to local
479: forwarded ports.
480: By default,
481: .Nm ssh
1.7 jmc 482: binds local port forwardings to the loopback address.
483: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 484: .Cm GatewayPorts
485: can be used to specify that
486: .Nm ssh
487: should bind local port forwardings to the wildcard address,
488: thus allowing remote hosts to connect to forwarded ports.
489: The argument must be
490: .Dq yes
491: or
492: .Dq no .
493: The default is
494: .Dq no .
495: .It Cm GlobalKnownHostsFile
496: Specifies a file to use for the global
497: host key database instead of
498: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 499: .It Cm GSSAPIAuthentication
1.27 markus 500: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 501: The default is
1.21 markus 502: .Dq no .
1.18 markus 503: Note that this option applies to protocol version 2 only.
504: .It Cm GSSAPIDelegateCredentials
505: Forward (delegate) credentials to the server.
506: The default is
507: .Dq no .
508: Note that this option applies to protocol version 2 only.
1.44 djm 509: .It Cm HashKnownHosts
510: Indicates that
511: .Nm ssh
512: should hash host names and addresses when they are added to
1.50 djm 513: .Pa ~/.ssh/known_hosts .
1.44 djm 514: These hashed names may be used normally by
515: .Nm ssh
516: and
517: .Nm sshd ,
518: but they do not reveal identifying information should the file's contents
519: be disclosed.
520: The default is
521: .Dq no .
1.46 jmc 522: Note that hashing of names and addresses will not be retrospectively applied
1.45 djm 523: to existing known hosts files, but these may be manually hashed using
524: .Xr ssh-keygen 1 .
1.1 stevesk 525: .It Cm HostbasedAuthentication
526: Specifies whether to try rhosts based authentication with public key
527: authentication.
528: The argument must be
529: .Dq yes
530: or
531: .Dq no .
532: The default is
533: .Dq no .
534: This option applies to protocol version 2 only and
535: is similar to
536: .Cm RhostsRSAAuthentication .
537: .It Cm HostKeyAlgorithms
538: Specifies the protocol version 2 host key algorithms
539: that the client wants to use in order of preference.
540: The default for this option is:
541: .Dq ssh-rsa,ssh-dss .
542: .It Cm HostKeyAlias
543: Specifies an alias that should be used instead of the
544: real host name when looking up or saving the host key
545: in the host key database files.
546: This option is useful for tunneling ssh connections
547: or for multiple servers running on a single host.
548: .It Cm HostName
549: Specifies the real host name to log into.
550: This can be used to specify nicknames or abbreviations for hosts.
551: Default is the name given on the command line.
552: Numeric IP addresses are also permitted (both on the command line and in
553: .Cm HostName
554: specifications).
1.29 markus 555: .It Cm IdentitiesOnly
556: Specifies that
557: .Nm ssh
558: should only use the authentication identity files configured in the
1.31 jmc 559: .Nm
1.29 markus 560: files,
561: even if the
562: .Nm ssh-agent
563: offers more identities.
564: The argument to this keyword must be
565: .Dq yes
566: or
567: .Dq no .
1.71 stevesk 568: This option is intended for situations where
1.29 markus 569: .Nm ssh-agent
570: offers many different identities.
571: The default is
572: .Dq no .
1.67 jmc 573: .It Cm IdentityFile
574: Specifies a file from which the user's RSA or DSA authentication identity
575: is read.
576: The default is
577: .Pa ~/.ssh/identity
578: for protocol version 1, and
579: .Pa ~/.ssh/id_rsa
580: and
581: .Pa ~/.ssh/id_dsa
582: for protocol version 2.
583: Additionally, any identities represented by the authentication agent
584: will be used for authentication.
585: The file name may use the tilde
586: syntax to refer to a user's home directory.
587: It is possible to have
588: multiple identity files specified in configuration files; all these
589: identities will be tried in sequence.
1.39 djm 590: .It Cm KbdInteractiveDevices
591: Specifies the list of methods to use in keyboard-interactive authentication.
592: Multiple method names must be comma-separated.
593: The default is to use the server specified list.
1.65 reyk 594: .It Cm LocalCommand
595: Specifies a command to execute on the local machine after successfully
596: connecting to the server.
597: The command string extends to the end of the line, and is executed with
598: .Pa /bin/sh .
599: This directive is ignored unless
600: .Cm PermitLocalCommand
601: has been enabled.
1.1 stevesk 602: .It Cm LocalForward
1.74 jmc 603: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 604: the secure channel to the specified host and port from the remote machine.
1.49 jmc 605: The first argument must be
1.43 djm 606: .Sm off
1.49 jmc 607: .Oo Ar bind_address : Oc Ar port
1.43 djm 608: .Sm on
1.49 jmc 609: and the second argument must be
610: .Ar host : Ns Ar hostport .
1.46 jmc 611: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 612: by using an alternative syntax:
1.49 jmc 613: .Oo Ar bind_address Ns / Oc Ns Ar port
614: and
615: .Ar host Ns / Ns Ar hostport .
1.46 jmc 616: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 617: given on the command line.
1.1 stevesk 618: Only the superuser can forward privileged ports.
1.43 djm 619: By default, the local port is bound in accordance with the
620: .Cm GatewayPorts
621: setting.
622: However, an explicit
623: .Ar bind_address
624: may be used to bind the connection to a specific address.
625: The
626: .Ar bind_address
627: of
628: .Dq localhost
1.46 jmc 629: indicates that the listening port be bound for local use only, while an
630: empty address or
631: .Sq *
1.43 djm 632: indicates that the port should be available from all interfaces.
1.1 stevesk 633: .It Cm LogLevel
634: Gives the verbosity level that is used when logging messages from
635: .Nm ssh .
636: The possible values are:
637: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
1.7 jmc 638: The default is INFO.
639: DEBUG and DEBUG1 are equivalent.
640: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 641: .It Cm MACs
642: Specifies the MAC (message authentication code) algorithms
643: in order of preference.
644: The MAC algorithm is used in protocol version 2
645: for data integrity protection.
646: Multiple algorithms must be comma-separated.
647: The default is
648: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
649: .It Cm NoHostAuthenticationForLocalhost
650: This option can be used if the home directory is shared across machines.
651: In this case localhost will refer to a different machine on each of
652: the machines and the user will get many warnings about changed host keys.
653: However, this option disables host authentication for localhost.
654: The argument to this keyword must be
655: .Dq yes
656: or
657: .Dq no .
658: The default is to check the host key for localhost.
659: .It Cm NumberOfPasswordPrompts
660: Specifies the number of password prompts before giving up.
661: The argument to this keyword must be an integer.
662: Default is 3.
663: .It Cm PasswordAuthentication
664: Specifies whether to use password authentication.
665: The argument to this keyword must be
666: .Dq yes
667: or
668: .Dq no .
669: The default is
670: .Dq yes .
1.65 reyk 671: .It Cm PermitLocalCommand
672: Allow local command execution via the
673: .Ic LocalCommand
674: option or using the
1.66 jmc 675: .Ic !\& Ns Ar command
1.65 reyk 676: escape sequence in
677: .Xr ssh 1 .
678: The argument must be
679: .Dq yes
680: or
681: .Dq no .
682: The default is
683: .Dq no .
1.67 jmc 684: .It Cm Port
685: Specifies the port number to connect on the remote host.
686: Default is 22.
1.1 stevesk 687: .It Cm PreferredAuthentications
688: Specifies the order in which the client should try protocol 2
1.11 jmc 689: authentication methods.
1.48 jmc 690: This allows a client to prefer one method (e.g.\&
1.1 stevesk 691: .Cm keyboard-interactive )
1.48 jmc 692: over another method (e.g.\&
1.1 stevesk 693: .Cm password )
694: The default for this option is:
695: .Dq hostbased,publickey,keyboard-interactive,password .
696: .It Cm Protocol
697: Specifies the protocol versions
698: .Nm ssh
699: should support in order of preference.
700: The possible values are
701: .Dq 1
702: and
703: .Dq 2 .
704: Multiple versions must be comma-separated.
705: The default is
706: .Dq 2,1 .
707: This means that
708: .Nm ssh
709: tries version 2 and falls back to version 1
710: if version 2 is not available.
711: .It Cm ProxyCommand
712: Specifies the command to use to connect to the server.
713: The command
714: string extends to the end of the line, and is executed with
715: .Pa /bin/sh .
716: In the command string,
717: .Ql %h
718: will be substituted by the host name to
719: connect and
720: .Ql %p
721: by the port.
722: The command can be basically anything,
723: and should read from its standard input and write to its standard output.
724: It should eventually connect an
725: .Xr sshd 8
726: server running on some machine, or execute
727: .Ic sshd -i
728: somewhere.
729: Host key management will be done using the
730: HostName of the host being connected (defaulting to the name typed by
731: the user).
1.7 jmc 732: Setting the command to
733: .Dq none
1.6 markus 734: disables this option entirely.
1.1 stevesk 735: Note that
736: .Cm CheckHostIP
737: is not available for connects with a proxy command.
1.52 djm 738: .Pp
739: This directive is useful in conjunction with
740: .Xr nc 1
741: and its proxy support.
1.53 jmc 742: For example, the following directive would connect via an HTTP proxy at
1.52 djm 743: 192.0.2.0:
744: .Bd -literal -offset 3n
745: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
746: .Ed
1.1 stevesk 747: .It Cm PubkeyAuthentication
748: Specifies whether to try public key authentication.
749: The argument to this keyword must be
750: .Dq yes
751: or
752: .Dq no .
753: The default is
754: .Dq yes .
755: This option applies to protocol version 2 only.
1.75 dtucker 756: .It Cm RekeyLimit
757: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 758: session key is renegotiated.
1.75 dtucker 759: The argument is the number of bytes, with an optional suffix of
1.76 jmc 760: .Sq K ,
761: .Sq M ,
1.75 dtucker 762: or
1.76 jmc 763: .Sq G
1.75 dtucker 764: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
765: The default is between
766: .Dq 1G
767: and
768: .Dq 4G ,
769: depending on the cipher.
1.76 jmc 770: This option applies to protocol version 2 only.
1.1 stevesk 771: .It Cm RemoteForward
1.74 jmc 772: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 773: the secure channel to the specified host and port from the local machine.
1.49 jmc 774: The first argument must be
1.43 djm 775: .Sm off
1.49 jmc 776: .Oo Ar bind_address : Oc Ar port
1.43 djm 777: .Sm on
1.49 jmc 778: and the second argument must be
779: .Ar host : Ns Ar hostport .
780: IPv6 addresses can be specified by enclosing addresses in square brackets
781: or by using an alternative syntax:
782: .Oo Ar bind_address Ns / Oc Ns Ar port
783: and
784: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 785: Multiple forwardings may be specified, and additional
786: forwardings can be given on the command line.
787: Only the superuser can forward privileged ports.
1.43 djm 788: .Pp
789: If the
790: .Ar bind_address
791: is not specified, the default is to only bind to loopback addresses.
792: If the
793: .Ar bind_address
794: is
795: .Ql *
796: or an empty string, then the forwarding is requested to listen on all
797: interfaces.
798: Specifying a remote
799: .Ar bind_address
1.46 jmc 800: will only succeed if the server's
801: .Cm GatewayPorts
1.43 djm 802: option is enabled (see
1.46 jmc 803: .Xr sshd_config 5 ) .
1.1 stevesk 804: .It Cm RhostsRSAAuthentication
805: Specifies whether to try rhosts based authentication with RSA host
806: authentication.
807: The argument must be
808: .Dq yes
809: or
810: .Dq no .
811: The default is
812: .Dq no .
813: This option applies to protocol version 1 only and requires
814: .Nm ssh
815: to be setuid root.
816: .It Cm RSAAuthentication
817: Specifies whether to try RSA authentication.
818: The argument to this keyword must be
819: .Dq yes
820: or
821: .Dq no .
822: RSA authentication will only be
823: attempted if the identity file exists, or an authentication agent is
824: running.
825: The default is
826: .Dq yes .
827: Note that this option applies to protocol version 1 only.
1.32 djm 828: .It Cm SendEnv
829: Specifies what variables from the local
830: .Xr environ 7
831: should be sent to the server.
832: Note that environment passing is only supported for protocol 2, the
1.33 djm 833: server must also support it, and the server must be configured to
834: accept these environment variables.
1.32 djm 835: Refer to
836: .Cm AcceptEnv
837: in
838: .Xr sshd_config 5
839: for how to configure the server.
1.80 ! jmc 840: Variables are specified by name, which may contain wildcard characters.
! 841: See
! 842: .Sx PATTERNS
! 843: for more information on patterns.
1.33 djm 844: Multiple environment variables may be separated by whitespace or spread
1.32 djm 845: across multiple
846: .Cm SendEnv
847: directives.
848: The default is not to send any environment variables.
1.28 markus 849: .It Cm ServerAliveCountMax
1.73 jmc 850: Sets the number of server alive messages (see below) which may be
1.28 markus 851: sent without
852: .Nm ssh
853: receiving any messages back from the server.
854: If this threshold is reached while server alive messages are being sent,
855: .Nm ssh
856: will disconnect from the server, terminating the session.
857: It is important to note that the use of server alive messages is very
858: different from
859: .Cm TCPKeepAlive
860: (below).
861: The server alive messages are sent through the encrypted channel
862: and therefore will not be spoofable.
863: The TCP keepalive option enabled by
864: .Cm TCPKeepAlive
865: is spoofable.
866: The server alive mechanism is valuable when the client or
867: server depend on knowing when a connection has become inactive.
868: .Pp
869: The default value is 3.
870: If, for example,
871: .Cm ServerAliveInterval
1.73 jmc 872: (see below) is set to 15, and
1.28 markus 873: .Cm ServerAliveCountMax
874: is left at the default, if the server becomes unresponsive ssh
875: will disconnect after approximately 45 seconds.
1.67 jmc 876: .It Cm ServerAliveInterval
877: Sets a timeout interval in seconds after which if no data has been received
878: from the server,
879: .Nm ssh
880: will send a message through the encrypted
881: channel to request a response from the server.
882: The default
883: is 0, indicating that these messages will not be sent to the server.
884: This option applies to protocol version 2 only.
1.1 stevesk 885: .It Cm SmartcardDevice
1.11 jmc 886: Specifies which smartcard device to use.
887: The argument to this keyword is the device
1.1 stevesk 888: .Nm ssh
889: should use to communicate with a smartcard used for storing the user's
1.11 jmc 890: private RSA key.
891: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 892: .It Cm StrictHostKeyChecking
893: If this flag is set to
894: .Dq yes ,
895: .Nm ssh
896: will never automatically add host keys to the
1.50 djm 897: .Pa ~/.ssh/known_hosts
1.1 stevesk 898: file, and refuses to connect to hosts whose host key has changed.
899: This provides maximum protection against trojan horse attacks,
900: however, can be annoying when the
901: .Pa /etc/ssh/ssh_known_hosts
902: file is poorly maintained, or connections to new hosts are
903: frequently made.
904: This option forces the user to manually
905: add all new hosts.
906: If this flag is set to
907: .Dq no ,
908: .Nm ssh
909: will automatically add new host keys to the
910: user known hosts files.
911: If this flag is set to
912: .Dq ask ,
913: new host keys
914: will be added to the user known host files only after the user
915: has confirmed that is what they really want to do, and
916: .Nm ssh
917: will refuse to connect to hosts whose host key has changed.
918: The host keys of
919: known hosts will be verified automatically in all cases.
920: The argument must be
921: .Dq yes ,
922: .Dq no
923: or
924: .Dq ask .
925: The default is
926: .Dq ask .
1.26 markus 927: .It Cm TCPKeepAlive
928: Specifies whether the system should send TCP keepalive messages to the
929: other side.
930: If they are sent, death of the connection or crash of one
931: of the machines will be properly noticed.
932: However, this means that
933: connections will die if the route is down temporarily, and some people
934: find it annoying.
935: .Pp
936: The default is
937: .Dq yes
938: (to send TCP keepalive messages), and the client will notice
939: if the network goes down or the remote host dies.
940: This is important in scripts, and many users want it too.
941: .Pp
942: To disable TCP keepalive messages, the value should be set to
943: .Dq no .
1.65 reyk 944: .It Cm Tunnel
945: Request starting
946: .Xr tun 4
1.69 jmc 947: device forwarding between the client and the server.
948: This option also allows requesting layer 2 (ethernet)
949: instead of layer 3 (point-to-point) tunneling from the server.
1.65 reyk 950: The argument must be
1.68 reyk 951: .Dq yes ,
952: .Dq point-to-point ,
953: .Dq ethernet
1.65 reyk 954: or
955: .Dq no .
956: The default is
957: .Dq no .
958: .It Cm TunnelDevice
959: Force a specified
960: .Xr tun 4
961: device on the client.
962: Without this option, the next available device will be used.
1.72 jmc 963: .It Cm UsePrivilegedPort
964: Specifies whether to use a privileged port for outgoing connections.
965: The argument must be
966: .Dq yes
967: or
968: .Dq no .
969: The default is
970: .Dq no .
971: If set to
972: .Dq yes
973: .Nm ssh
974: must be setuid root.
975: Note that this option must be set to
976: .Dq yes
977: for
978: .Cm RhostsRSAAuthentication
979: with older servers.
1.1 stevesk 980: .It Cm User
981: Specifies the user to log in as.
982: This can be useful when a different user name is used on different machines.
983: This saves the trouble of
984: having to remember to give the user name on the command line.
985: .It Cm UserKnownHostsFile
986: Specifies a file to use for the user
987: host key database instead of
1.50 djm 988: .Pa ~/.ssh/known_hosts .
1.8 jakob 989: .It Cm VerifyHostKeyDNS
990: Specifies whether to verify the remote key using DNS and SSHFP resource
991: records.
1.24 jakob 992: If this option is set to
993: .Dq yes ,
1.25 jmc 994: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 995: from DNS.
996: Insecure fingerprints will be handled as if this option was set to
997: .Dq ask .
998: If this option is set to
999: .Dq ask ,
1000: information on fingerprint match will be displayed, but the user will still
1001: need to confirm new host keys according to the
1002: .Cm StrictHostKeyChecking
1003: option.
1004: The argument must be
1005: .Dq yes ,
1006: .Dq no
1.25 jmc 1007: or
1008: .Dq ask .
1.8 jakob 1009: The default is
1010: .Dq no .
1.12 jakob 1011: Note that this option applies to protocol version 2 only.
1.1 stevesk 1012: .It Cm XAuthLocation
1.5 stevesk 1013: Specifies the full pathname of the
1.1 stevesk 1014: .Xr xauth 1
1015: program.
1016: The default is
1017: .Pa /usr/X11R6/bin/xauth .
1018: .El
1019: .Sh FILES
1020: .Bl -tag -width Ds
1.50 djm 1021: .It Pa ~/.ssh/config
1.1 stevesk 1022: This is the per-user configuration file.
1023: The format of this file is described above.
1024: This file is used by the
1025: .Nm ssh
1026: client.
1.30 djm 1027: Because of the potential for abuse, this file must have strict permissions:
1028: read/write for the user, and not accessible by others.
1.1 stevesk 1029: .It Pa /etc/ssh/ssh_config
1030: Systemwide configuration file.
1031: This file provides defaults for those
1032: values that are not specified in the user's configuration file, and
1033: for those users who do not have a configuration file.
1034: This file must be world-readable.
1035: .El
1.13 jmc 1036: .Sh SEE ALSO
1037: .Xr ssh 1
1.1 stevesk 1038: .Sh AUTHORS
1039: OpenSSH is a derivative of the original and free
1040: ssh 1.2.12 release by Tatu Ylonen.
1041: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1042: Theo de Raadt and Dug Song
1043: removed many bugs, re-added newer features and
1044: created OpenSSH.
1045: Markus Friedl contributed the support for SSH
1046: protocol versions 1.5 and 2.0.
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