Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.55
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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1.55 ! djm 37: .\" $OpenBSD: ssh_config.5,v 1.54 2005/05/23 23:32:46 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.
1.36 djm 281: .It Cm ControlPath
1.55 ! djm 282: Specify the path to the control socket used for connection sharing as described
! 283: in the
1.36 djm 284: .Cm ControlMaster
1.55 ! djm 285: section above.
! 286: In the path,
! 287: .Ql %h
! 288: will be substituted by the target host name,
! 289: .Ql %p
! 290: the port and
! 291: .Ql %r
! 292: by the remote login username.
1.38 jmc 293: .It Cm DynamicForward
294: Specifies that a TCP/IP port on the local machine be forwarded
295: over the secure channel, and the application
296: protocol is then used to determine where to connect to from the
297: remote machine.
298: The argument must be a port number.
299: Currently the SOCKS4 and SOCKS5 protocols are supported, and
300: .Nm ssh
301: will act as a SOCKS server.
302: Multiple forwardings may be specified, and
303: additional forwardings can be given on the command line.
304: Only the superuser can forward privileged ports.
1.14 markus 305: .It Cm EnableSSHKeysign
306: Setting this option to
307: .Dq yes
308: in the global client configuration file
309: .Pa /etc/ssh/ssh_config
310: enables the use of the helper program
311: .Xr ssh-keysign 8
312: during
313: .Cm HostbasedAuthentication .
314: The argument must be
315: .Dq yes
316: or
317: .Dq no .
318: The default is
319: .Dq no .
1.23 jmc 320: This option should be placed in the non-hostspecific section.
1.14 markus 321: See
322: .Xr ssh-keysign 8
323: for more information.
1.1 stevesk 324: .It Cm EscapeChar
325: Sets the escape character (default:
326: .Ql ~ ) .
327: The escape character can also
328: be set on the command line.
329: The argument should be a single character,
330: .Ql ^
331: followed by a letter, or
332: .Dq none
333: to disable the escape
334: character entirely (making the connection transparent for binary
335: data).
336: .It Cm ForwardAgent
337: Specifies whether the connection to the authentication agent (if any)
338: will be forwarded to the remote machine.
339: The argument must be
340: .Dq yes
341: or
342: .Dq no .
343: The default is
344: .Dq no .
1.3 stevesk 345: .Pp
1.7 jmc 346: Agent forwarding should be enabled with caution.
347: Users with the ability to bypass file permissions on the remote host
348: (for the agent's Unix-domain socket)
349: can access the local agent through the forwarded connection.
350: An attacker cannot obtain key material from the agent,
1.3 stevesk 351: however they can perform operations on the keys that enable them to
352: authenticate using the identities loaded into the agent.
1.1 stevesk 353: .It Cm ForwardX11
354: Specifies whether X11 connections will be automatically redirected
355: over the secure channel and
356: .Ev DISPLAY
357: set.
358: The argument must be
359: .Dq yes
360: or
361: .Dq no .
362: The default is
363: .Dq no .
1.3 stevesk 364: .Pp
1.7 jmc 365: X11 forwarding should be enabled with caution.
366: Users with the ability to bypass file permissions on the remote host
1.22 markus 367: (for the user's X11 authorization database)
1.7 jmc 368: can access the local X11 display through the forwarded connection.
1.22 markus 369: An attacker may then be able to perform activities such as keystroke monitoring
370: if the
371: .Cm ForwardX11Trusted
372: option is also enabled.
373: .It Cm ForwardX11Trusted
1.34 jmc 374: If this option is set to
1.22 markus 375: .Dq yes
376: then remote X11 clients will have full access to the original X11 display.
1.42 djm 377: .Pp
1.22 markus 378: If this option is set to
379: .Dq no
380: then remote X11 clients will be considered untrusted and prevented
381: from stealing or tampering with data belonging to trusted X11
382: clients.
1.42 djm 383: Furthermore, the
384: .Xr xauth 1
385: token used for the session will be set to expire after 20 minutes.
386: Remote clients will be refused access after this time.
1.22 markus 387: .Pp
388: The default is
389: .Dq no .
390: .Pp
391: See the X11 SECURITY extension specification for full details on
392: the restrictions imposed on untrusted clients.
1.1 stevesk 393: .It Cm GatewayPorts
394: Specifies whether remote hosts are allowed to connect to local
395: forwarded ports.
396: By default,
397: .Nm ssh
1.7 jmc 398: binds local port forwardings to the loopback address.
399: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 400: .Cm GatewayPorts
401: can be used to specify that
402: .Nm ssh
403: should bind local port forwardings to the wildcard address,
404: thus allowing remote hosts to connect to forwarded ports.
405: The argument must be
406: .Dq yes
407: or
408: .Dq no .
409: The default is
410: .Dq no .
411: .It Cm GlobalKnownHostsFile
412: Specifies a file to use for the global
413: host key database instead of
414: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 415: .It Cm GSSAPIAuthentication
1.27 markus 416: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 417: The default is
1.21 markus 418: .Dq no .
1.18 markus 419: Note that this option applies to protocol version 2 only.
420: .It Cm GSSAPIDelegateCredentials
421: Forward (delegate) credentials to the server.
422: The default is
423: .Dq no .
424: Note that this option applies to protocol version 2 only.
1.44 djm 425: .It Cm HashKnownHosts
426: Indicates that
427: .Nm ssh
428: should hash host names and addresses when they are added to
1.50 djm 429: .Pa ~/.ssh/known_hosts .
1.44 djm 430: These hashed names may be used normally by
431: .Nm ssh
432: and
433: .Nm sshd ,
434: but they do not reveal identifying information should the file's contents
435: be disclosed.
436: The default is
437: .Dq no .
1.46 jmc 438: Note that hashing of names and addresses will not be retrospectively applied
1.45 djm 439: to existing known hosts files, but these may be manually hashed using
440: .Xr ssh-keygen 1 .
1.1 stevesk 441: .It Cm HostbasedAuthentication
442: Specifies whether to try rhosts based authentication with public key
443: authentication.
444: The argument must be
445: .Dq yes
446: or
447: .Dq no .
448: The default is
449: .Dq no .
450: This option applies to protocol version 2 only and
451: is similar to
452: .Cm RhostsRSAAuthentication .
453: .It Cm HostKeyAlgorithms
454: Specifies the protocol version 2 host key algorithms
455: that the client wants to use in order of preference.
456: The default for this option is:
457: .Dq ssh-rsa,ssh-dss .
458: .It Cm HostKeyAlias
459: Specifies an alias that should be used instead of the
460: real host name when looking up or saving the host key
461: in the host key database files.
462: This option is useful for tunneling ssh connections
463: or for multiple servers running on a single host.
464: .It Cm HostName
465: Specifies the real host name to log into.
466: This can be used to specify nicknames or abbreviations for hosts.
467: Default is the name given on the command line.
468: Numeric IP addresses are also permitted (both on the command line and in
469: .Cm HostName
470: specifications).
471: .It Cm IdentityFile
472: Specifies a file from which the user's RSA or DSA authentication identity
1.11 jmc 473: is read.
474: The default is
1.50 djm 475: .Pa ~/.ssh/identity
1.1 stevesk 476: for protocol version 1, and
1.50 djm 477: .Pa ~/.ssh/id_rsa
1.1 stevesk 478: and
1.50 djm 479: .Pa ~/.ssh/id_dsa
1.1 stevesk 480: for protocol version 2.
481: Additionally, any identities represented by the authentication agent
482: will be used for authentication.
483: The file name may use the tilde
484: syntax to refer to a user's home directory.
485: It is possible to have
486: multiple identity files specified in configuration files; all these
487: identities will be tried in sequence.
1.29 markus 488: .It Cm IdentitiesOnly
489: Specifies that
490: .Nm ssh
491: should only use the authentication identity files configured in the
1.31 jmc 492: .Nm
1.29 markus 493: files,
494: even if the
495: .Nm ssh-agent
496: offers more identities.
497: The argument to this keyword must be
498: .Dq yes
499: or
500: .Dq no .
501: This option is intented for situations where
502: .Nm ssh-agent
503: offers many different identities.
504: The default is
505: .Dq no .
1.39 djm 506: .It Cm KbdInteractiveDevices
507: Specifies the list of methods to use in keyboard-interactive authentication.
508: Multiple method names must be comma-separated.
509: The default is to use the server specified list.
1.1 stevesk 510: .It Cm LocalForward
511: Specifies that a TCP/IP port on the local machine be forwarded over
512: the secure channel to the specified host and port from the remote machine.
1.49 jmc 513: The first argument must be
1.43 djm 514: .Sm off
1.49 jmc 515: .Oo Ar bind_address : Oc Ar port
1.43 djm 516: .Sm on
1.49 jmc 517: and the second argument must be
518: .Ar host : Ns Ar hostport .
1.46 jmc 519: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 520: by using an alternative syntax:
1.49 jmc 521: .Oo Ar bind_address Ns / Oc Ns Ar port
522: and
523: .Ar host Ns / Ns Ar hostport .
1.46 jmc 524: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 525: given on the command line.
1.1 stevesk 526: Only the superuser can forward privileged ports.
1.43 djm 527: By default, the local port is bound in accordance with the
528: .Cm GatewayPorts
529: setting.
530: However, an explicit
531: .Ar bind_address
532: may be used to bind the connection to a specific address.
533: The
534: .Ar bind_address
535: of
536: .Dq localhost
1.46 jmc 537: indicates that the listening port be bound for local use only, while an
538: empty address or
539: .Sq *
1.43 djm 540: indicates that the port should be available from all interfaces.
1.1 stevesk 541: .It Cm LogLevel
542: Gives the verbosity level that is used when logging messages from
543: .Nm ssh .
544: The possible values are:
545: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
1.7 jmc 546: The default is INFO.
547: DEBUG and DEBUG1 are equivalent.
548: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 549: .It Cm MACs
550: Specifies the MAC (message authentication code) algorithms
551: in order of preference.
552: The MAC algorithm is used in protocol version 2
553: for data integrity protection.
554: Multiple algorithms must be comma-separated.
555: The default is
556: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
557: .It Cm NoHostAuthenticationForLocalhost
558: This option can be used if the home directory is shared across machines.
559: In this case localhost will refer to a different machine on each of
560: the machines and the user will get many warnings about changed host keys.
561: However, this option disables host authentication for localhost.
562: The argument to this keyword must be
563: .Dq yes
564: or
565: .Dq no .
566: The default is to check the host key for localhost.
567: .It Cm NumberOfPasswordPrompts
568: Specifies the number of password prompts before giving up.
569: The argument to this keyword must be an integer.
570: Default is 3.
571: .It Cm PasswordAuthentication
572: Specifies whether to use password authentication.
573: The argument to this keyword must be
574: .Dq yes
575: or
576: .Dq no .
577: The default is
578: .Dq yes .
579: .It Cm Port
580: Specifies the port number to connect on the remote host.
581: Default is 22.
582: .It Cm PreferredAuthentications
583: Specifies the order in which the client should try protocol 2
1.11 jmc 584: authentication methods.
1.48 jmc 585: This allows a client to prefer one method (e.g.\&
1.1 stevesk 586: .Cm keyboard-interactive )
1.48 jmc 587: over another method (e.g.\&
1.1 stevesk 588: .Cm password )
589: The default for this option is:
590: .Dq hostbased,publickey,keyboard-interactive,password .
591: .It Cm Protocol
592: Specifies the protocol versions
593: .Nm ssh
594: should support in order of preference.
595: The possible values are
596: .Dq 1
597: and
598: .Dq 2 .
599: Multiple versions must be comma-separated.
600: The default is
601: .Dq 2,1 .
602: This means that
603: .Nm ssh
604: tries version 2 and falls back to version 1
605: if version 2 is not available.
606: .It Cm ProxyCommand
607: Specifies the command to use to connect to the server.
608: The command
609: string extends to the end of the line, and is executed with
610: .Pa /bin/sh .
611: In the command string,
612: .Ql %h
613: will be substituted by the host name to
614: connect and
615: .Ql %p
616: by the port.
617: The command can be basically anything,
618: and should read from its standard input and write to its standard output.
619: It should eventually connect an
620: .Xr sshd 8
621: server running on some machine, or execute
622: .Ic sshd -i
623: somewhere.
624: Host key management will be done using the
625: HostName of the host being connected (defaulting to the name typed by
626: the user).
1.7 jmc 627: Setting the command to
628: .Dq none
1.6 markus 629: disables this option entirely.
1.1 stevesk 630: Note that
631: .Cm CheckHostIP
632: is not available for connects with a proxy command.
1.52 djm 633: .Pp
634: This directive is useful in conjunction with
635: .Xr nc 1
636: and its proxy support.
1.53 jmc 637: For example, the following directive would connect via an HTTP proxy at
1.52 djm 638: 192.0.2.0:
639: .Bd -literal -offset 3n
640: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
641: .Ed
1.1 stevesk 642: .It Cm PubkeyAuthentication
643: Specifies whether to try public key authentication.
644: The argument to this keyword must be
645: .Dq yes
646: or
647: .Dq no .
648: The default is
649: .Dq yes .
650: This option applies to protocol version 2 only.
651: .It Cm RemoteForward
652: Specifies that a TCP/IP port on the remote machine be forwarded over
653: the secure channel to the specified host and port from the local machine.
1.49 jmc 654: The first argument must be
1.43 djm 655: .Sm off
1.49 jmc 656: .Oo Ar bind_address : Oc Ar port
1.43 djm 657: .Sm on
1.49 jmc 658: and the second argument must be
659: .Ar host : Ns Ar hostport .
660: IPv6 addresses can be specified by enclosing addresses in square brackets
661: or by using an alternative syntax:
662: .Oo Ar bind_address Ns / Oc Ns Ar port
663: and
664: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 665: Multiple forwardings may be specified, and additional
666: forwardings can be given on the command line.
667: Only the superuser can forward privileged ports.
1.43 djm 668: .Pp
669: If the
670: .Ar bind_address
671: is not specified, the default is to only bind to loopback addresses.
672: If the
673: .Ar bind_address
674: is
675: .Ql *
676: or an empty string, then the forwarding is requested to listen on all
677: interfaces.
678: Specifying a remote
679: .Ar bind_address
1.46 jmc 680: will only succeed if the server's
681: .Cm GatewayPorts
1.43 djm 682: option is enabled (see
1.46 jmc 683: .Xr sshd_config 5 ) .
1.1 stevesk 684: .It Cm RhostsRSAAuthentication
685: Specifies whether to try rhosts based authentication with RSA host
686: authentication.
687: The argument must be
688: .Dq yes
689: or
690: .Dq no .
691: The default is
692: .Dq no .
693: This option applies to protocol version 1 only and requires
694: .Nm ssh
695: to be setuid root.
696: .It Cm RSAAuthentication
697: Specifies whether to try RSA authentication.
698: The argument to this keyword must be
699: .Dq yes
700: or
701: .Dq no .
702: RSA authentication will only be
703: attempted if the identity file exists, or an authentication agent is
704: running.
705: The default is
706: .Dq yes .
707: Note that this option applies to protocol version 1 only.
1.32 djm 708: .It Cm SendEnv
709: Specifies what variables from the local
710: .Xr environ 7
711: should be sent to the server.
712: Note that environment passing is only supported for protocol 2, the
1.33 djm 713: server must also support it, and the server must be configured to
714: accept these environment variables.
1.32 djm 715: Refer to
716: .Cm AcceptEnv
717: in
718: .Xr sshd_config 5
719: for how to configure the server.
720: Variables are specified by name, which may contain the wildcard characters
721: .Ql \&*
722: and
723: .Ql \&? .
1.33 djm 724: Multiple environment variables may be separated by whitespace or spread
1.32 djm 725: across multiple
726: .Cm SendEnv
727: directives.
728: The default is not to send any environment variables.
1.28 markus 729: .It Cm ServerAliveInterval
730: Sets a timeout interval in seconds after which if no data has been received
731: from the server,
732: .Nm ssh
733: will send a message through the encrypted
734: channel to request a response from the server.
735: The default
736: is 0, indicating that these messages will not be sent to the server.
737: This option applies to protocol version 2 only.
738: .It Cm ServerAliveCountMax
739: Sets the number of server alive messages (see above) which may be
740: sent without
741: .Nm ssh
742: receiving any messages back from the server.
743: If this threshold is reached while server alive messages are being sent,
744: .Nm ssh
745: will disconnect from the server, terminating the session.
746: It is important to note that the use of server alive messages is very
747: different from
748: .Cm TCPKeepAlive
749: (below).
750: The server alive messages are sent through the encrypted channel
751: and therefore will not be spoofable.
752: The TCP keepalive option enabled by
753: .Cm TCPKeepAlive
754: is spoofable.
755: The server alive mechanism is valuable when the client or
756: server depend on knowing when a connection has become inactive.
757: .Pp
758: The default value is 3.
759: If, for example,
760: .Cm ServerAliveInterval
761: (above) is set to 15, and
762: .Cm ServerAliveCountMax
763: is left at the default, if the server becomes unresponsive ssh
764: will disconnect after approximately 45 seconds.
1.1 stevesk 765: .It Cm SmartcardDevice
1.11 jmc 766: Specifies which smartcard device to use.
767: The argument to this keyword is the device
1.1 stevesk 768: .Nm ssh
769: should use to communicate with a smartcard used for storing the user's
1.11 jmc 770: private RSA key.
771: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 772: .It Cm StrictHostKeyChecking
773: If this flag is set to
774: .Dq yes ,
775: .Nm ssh
776: will never automatically add host keys to the
1.50 djm 777: .Pa ~/.ssh/known_hosts
1.1 stevesk 778: file, and refuses to connect to hosts whose host key has changed.
779: This provides maximum protection against trojan horse attacks,
780: however, can be annoying when the
781: .Pa /etc/ssh/ssh_known_hosts
782: file is poorly maintained, or connections to new hosts are
783: frequently made.
784: This option forces the user to manually
785: add all new hosts.
786: If this flag is set to
787: .Dq no ,
788: .Nm ssh
789: will automatically add new host keys to the
790: user known hosts files.
791: If this flag is set to
792: .Dq ask ,
793: new host keys
794: will be added to the user known host files only after the user
795: has confirmed that is what they really want to do, and
796: .Nm ssh
797: will refuse to connect to hosts whose host key has changed.
798: The host keys of
799: known hosts will be verified automatically in all cases.
800: The argument must be
801: .Dq yes ,
802: .Dq no
803: or
804: .Dq ask .
805: The default is
806: .Dq ask .
1.26 markus 807: .It Cm TCPKeepAlive
808: Specifies whether the system should send TCP keepalive messages to the
809: other side.
810: If they are sent, death of the connection or crash of one
811: of the machines will be properly noticed.
812: However, this means that
813: connections will die if the route is down temporarily, and some people
814: find it annoying.
815: .Pp
816: The default is
817: .Dq yes
818: (to send TCP keepalive messages), and the client will notice
819: if the network goes down or the remote host dies.
820: This is important in scripts, and many users want it too.
821: .Pp
822: To disable TCP keepalive messages, the value should be set to
823: .Dq no .
1.1 stevesk 824: .It Cm UsePrivilegedPort
825: Specifies whether to use a privileged port for outgoing connections.
826: The argument must be
827: .Dq yes
828: or
829: .Dq no .
830: The default is
831: .Dq no .
1.4 stevesk 832: If set to
833: .Dq yes
834: .Nm ssh
835: must be setuid root.
1.1 stevesk 836: Note that this option must be set to
837: .Dq yes
1.17 markus 838: for
1.1 stevesk 839: .Cm RhostsRSAAuthentication
1.17 markus 840: with older servers.
1.1 stevesk 841: .It Cm User
842: Specifies the user to log in as.
843: This can be useful when a different user name is used on different machines.
844: This saves the trouble of
845: having to remember to give the user name on the command line.
846: .It Cm UserKnownHostsFile
847: Specifies a file to use for the user
848: host key database instead of
1.50 djm 849: .Pa ~/.ssh/known_hosts .
1.8 jakob 850: .It Cm VerifyHostKeyDNS
851: Specifies whether to verify the remote key using DNS and SSHFP resource
852: records.
1.24 jakob 853: If this option is set to
854: .Dq yes ,
1.25 jmc 855: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 856: from DNS.
857: Insecure fingerprints will be handled as if this option was set to
858: .Dq ask .
859: If this option is set to
860: .Dq ask ,
861: information on fingerprint match will be displayed, but the user will still
862: need to confirm new host keys according to the
863: .Cm StrictHostKeyChecking
864: option.
865: The argument must be
866: .Dq yes ,
867: .Dq no
1.25 jmc 868: or
869: .Dq ask .
1.8 jakob 870: The default is
871: .Dq no .
1.12 jakob 872: Note that this option applies to protocol version 2 only.
1.1 stevesk 873: .It Cm XAuthLocation
1.5 stevesk 874: Specifies the full pathname of the
1.1 stevesk 875: .Xr xauth 1
876: program.
877: The default is
878: .Pa /usr/X11R6/bin/xauth .
879: .El
880: .Sh FILES
881: .Bl -tag -width Ds
1.50 djm 882: .It Pa ~/.ssh/config
1.1 stevesk 883: This is the per-user configuration file.
884: The format of this file is described above.
885: This file is used by the
886: .Nm ssh
887: client.
1.30 djm 888: Because of the potential for abuse, this file must have strict permissions:
889: read/write for the user, and not accessible by others.
1.1 stevesk 890: .It Pa /etc/ssh/ssh_config
891: Systemwide configuration file.
892: This file provides defaults for those
893: values that are not specified in the user's configuration file, and
894: for those users who do not have a configuration file.
895: This file must be world-readable.
896: .El
1.13 jmc 897: .Sh SEE ALSO
898: .Xr ssh 1
1.1 stevesk 899: .Sh AUTHORS
900: OpenSSH is a derivative of the original and free
901: ssh 1.2.12 release by Tatu Ylonen.
902: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
903: Theo de Raadt and Dug Song
904: removed many bugs, re-added newer features and
905: created OpenSSH.
906: Markus Friedl contributed the support for SSH
907: protocol versions 1.5 and 2.0.
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