Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.2
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
19: .\" are met:
20: .\" 1. Redistributions of source code must retain the above copyright
21: .\" notice, this list of conditions and the following disclaimer.
22: .\" 2. Redistributions in binary form must reproduce the above copyright
23: .\" notice, this list of conditions and the following disclaimer in the
24: .\" documentation and/or other materials provided with the distribution.
25: .\"
26: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
27: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
28: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
29: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
30: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
31: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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1.2 ! stevesk 37: .\" $OpenBSD: ssh_config.5,v 1.1 2002/06/20 19:56:07 stevesk 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
46: .It Pa $HOME/.ssh/config
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
! 58: .Pq Pa $HOME/.ssh/config
! 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.
66: The configuration files contain sections bracketed by
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
107: .Ql ?
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).
118: .It Cm AFSTokenPassing
119: Specifies whether to pass AFS tokens to remote host.
120: The argument to this keyword must be
121: .Dq yes
122: or
123: .Dq no .
124: This option applies to protocol version 1 only.
125: .It Cm BatchMode
126: If set to
127: .Dq yes ,
128: passphrase/password querying will be disabled.
129: This option is useful in scripts and other batch jobs where no user
130: is present to supply the password.
131: The argument must be
132: .Dq yes
133: or
134: .Dq no .
135: The default is
136: .Dq no .
137: .It Cm BindAddress
138: Specify the interface to transmit from on machines with multiple
139: interfaces or aliased addresses.
140: Note that this option does not work if
141: .Cm UsePrivilegedPort
142: is set to
143: .Dq yes .
144: .It Cm ChallengeResponseAuthentication
145: Specifies whether to use challenge response authentication.
146: The argument to this keyword must be
147: .Dq yes
148: or
149: .Dq no .
150: The default is
151: .Dq yes .
152: .It Cm CheckHostIP
153: If this flag is set to
154: .Dq yes ,
155: ssh will additionally check the host IP address in the
156: .Pa known_hosts
157: file.
158: This allows ssh to detect if a host key changed due to DNS spoofing.
159: If the option is set to
160: .Dq no ,
161: the check will not be executed.
162: The default is
163: .Dq yes .
164: .It Cm Cipher
165: Specifies the cipher to use for encrypting the session
166: in protocol version 1.
167: Currently,
168: .Dq blowfish ,
169: .Dq 3des ,
170: and
171: .Dq des
172: are supported.
173: .Ar des
174: is only supported in the
175: .Nm ssh
176: client for interoperability with legacy protocol 1 implementations
177: that do not support the
178: .Ar 3des
179: cipher. Its use is strongly discouraged due to cryptographic
180: weaknesses.
181: The default is
182: .Dq 3des .
183: .It Cm Ciphers
184: Specifies the ciphers allowed for protocol version 2
185: in order of preference.
186: Multiple ciphers must be comma-separated.
187: The default is
188: .Pp
189: .Bd -literal
190: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
191: aes192-cbc,aes256-cbc''
192: .Ed
193: .It Cm ClearAllForwardings
194: Specifies that all local, remote and dynamic port forwardings
195: specified in the configuration files or on the command line be
196: cleared. This option is primarily useful when used from the
197: .Nm ssh
198: command line to clear port forwardings set in
199: configuration files, and is automatically set by
200: .Xr scp 1
201: and
202: .Xr sftp 1 .
203: The argument must be
204: .Dq yes
205: or
206: .Dq no .
207: The default is
208: .Dq no .
209: .It Cm Compression
210: Specifies whether to use compression.
211: The argument must be
212: .Dq yes
213: or
214: .Dq no .
215: The default is
216: .Dq no .
217: .It Cm CompressionLevel
218: Specifies the compression level to use if compression is enabled.
219: The argument must be an integer from 1 (fast) to 9 (slow, best).
220: The default level is 6, which is good for most applications.
221: The meaning of the values is the same as in
222: .Xr gzip 1 .
223: Note that this option applies to protocol version 1 only.
224: .It Cm ConnectionAttempts
225: Specifies the number of tries (one per second) to make before exiting.
226: The argument must be an integer.
227: This may be useful in scripts if the connection sometimes fails.
228: The default is 1.
229: .It Cm DynamicForward
230: Specifies that a TCP/IP port on the local machine be forwarded
231: over the secure channel, and the application
232: protocol is then used to determine where to connect to from the
233: remote machine. The argument must be a port number.
234: Currently the SOCKS4 protocol is supported, and
235: .Nm ssh
236: will act as a SOCKS4 server.
237: Multiple forwardings may be specified, and
238: additional forwardings can be given on the command line. Only
239: the superuser can forward privileged ports.
240: .It Cm EscapeChar
241: Sets the escape character (default:
242: .Ql ~ ) .
243: The escape character can also
244: be set on the command line.
245: The argument should be a single character,
246: .Ql ^
247: followed by a letter, or
248: .Dq none
249: to disable the escape
250: character entirely (making the connection transparent for binary
251: data).
252: .It Cm ForwardAgent
253: Specifies whether the connection to the authentication agent (if any)
254: will be forwarded to the remote machine.
255: The argument must be
256: .Dq yes
257: or
258: .Dq no .
259: The default is
260: .Dq no .
261: .It Cm ForwardX11
262: Specifies whether X11 connections will be automatically redirected
263: over the secure channel and
264: .Ev DISPLAY
265: set.
266: The argument must be
267: .Dq yes
268: or
269: .Dq no .
270: The default is
271: .Dq no .
272: .It Cm GatewayPorts
273: Specifies whether remote hosts are allowed to connect to local
274: forwarded ports.
275: By default,
276: .Nm ssh
277: binds local port forwardings to the loopback address. This
278: prevents other remote hosts from connecting to forwarded ports.
279: .Cm GatewayPorts
280: can be used to specify that
281: .Nm ssh
282: should bind local port forwardings to the wildcard address,
283: thus allowing remote hosts to connect to forwarded ports.
284: The argument must be
285: .Dq yes
286: or
287: .Dq no .
288: The default is
289: .Dq no .
290: .It Cm GlobalKnownHostsFile
291: Specifies a file to use for the global
292: host key database instead of
293: .Pa /etc/ssh/ssh_known_hosts .
294: .It Cm HostbasedAuthentication
295: Specifies whether to try rhosts based authentication with public key
296: authentication.
297: The argument must be
298: .Dq yes
299: or
300: .Dq no .
301: The default is
302: .Dq no .
303: This option applies to protocol version 2 only and
304: is similar to
305: .Cm RhostsRSAAuthentication .
306: .It Cm HostKeyAlgorithms
307: Specifies the protocol version 2 host key algorithms
308: that the client wants to use in order of preference.
309: The default for this option is:
310: .Dq ssh-rsa,ssh-dss .
311: .It Cm HostKeyAlias
312: Specifies an alias that should be used instead of the
313: real host name when looking up or saving the host key
314: in the host key database files.
315: This option is useful for tunneling ssh connections
316: or for multiple servers running on a single host.
317: .It Cm HostName
318: Specifies the real host name to log into.
319: This can be used to specify nicknames or abbreviations for hosts.
320: Default is the name given on the command line.
321: Numeric IP addresses are also permitted (both on the command line and in
322: .Cm HostName
323: specifications).
324: .It Cm IdentityFile
325: Specifies a file from which the user's RSA or DSA authentication identity
326: is read. The default is
327: .Pa $HOME/.ssh/identity
328: for protocol version 1, and
329: .Pa $HOME/.ssh/id_rsa
330: and
331: .Pa $HOME/.ssh/id_dsa
332: for protocol version 2.
333: Additionally, any identities represented by the authentication agent
334: will be used for authentication.
335: The file name may use the tilde
336: syntax to refer to a user's home directory.
337: It is possible to have
338: multiple identity files specified in configuration files; all these
339: identities will be tried in sequence.
340: .It Cm KeepAlive
341: Specifies whether the system should send TCP keepalive messages to the
342: other side.
343: If they are sent, death of the connection or crash of one
344: of the machines will be properly noticed.
345: However, this means that
346: connections will die if the route is down temporarily, and some people
347: find it annoying.
348: .Pp
349: The default is
350: .Dq yes
351: (to send keepalives), and the client will notice
352: if the network goes down or the remote host dies.
353: This is important in scripts, and many users want it too.
354: .Pp
355: To disable keepalives, the value should be set to
356: .Dq no .
357: .It Cm KerberosAuthentication
358: Specifies whether Kerberos authentication will be used.
359: The argument to this keyword must be
360: .Dq yes
361: or
362: .Dq no .
363: .It Cm KerberosTgtPassing
364: Specifies whether a Kerberos TGT will be forwarded to the server.
365: This will only work if the Kerberos server is actually an AFS kaserver.
366: The argument to this keyword must be
367: .Dq yes
368: or
369: .Dq no .
370: .It Cm LocalForward
371: Specifies that a TCP/IP port on the local machine be forwarded over
372: the secure channel to the specified host and port from the remote machine.
373: The first argument must be a port number, and the second must be
374: .Ar host:port .
375: IPv6 addresses can be specified with an alternative syntax:
376: .Ar host/port .
377: Multiple forwardings may be specified, and additional
378: forwardings can be given on the command line.
379: Only the superuser can forward privileged ports.
380: .It Cm LogLevel
381: Gives the verbosity level that is used when logging messages from
382: .Nm ssh .
383: The possible values are:
384: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
385: The default is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2
386: and DEBUG3 each specify higher levels of verbose output.
387: .It Cm MACs
388: Specifies the MAC (message authentication code) algorithms
389: in order of preference.
390: The MAC algorithm is used in protocol version 2
391: for data integrity protection.
392: Multiple algorithms must be comma-separated.
393: The default is
394: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
395: .It Cm NoHostAuthenticationForLocalhost
396: This option can be used if the home directory is shared across machines.
397: In this case localhost will refer to a different machine on each of
398: the machines and the user will get many warnings about changed host keys.
399: However, this option disables host authentication for localhost.
400: The argument to this keyword must be
401: .Dq yes
402: or
403: .Dq no .
404: The default is to check the host key for localhost.
405: .It Cm NumberOfPasswordPrompts
406: Specifies the number of password prompts before giving up.
407: The argument to this keyword must be an integer.
408: Default is 3.
409: .It Cm PasswordAuthentication
410: Specifies whether to use password authentication.
411: The argument to this keyword must be
412: .Dq yes
413: or
414: .Dq no .
415: The default is
416: .Dq yes .
417: .It Cm Port
418: Specifies the port number to connect on the remote host.
419: Default is 22.
420: .It Cm PreferredAuthentications
421: Specifies the order in which the client should try protocol 2
422: authentication methods. This allows a client to prefer one method (e.g.
423: .Cm keyboard-interactive )
424: over another method (e.g.
425: .Cm password )
426: The default for this option is:
427: .Dq hostbased,publickey,keyboard-interactive,password .
428: .It Cm Protocol
429: Specifies the protocol versions
430: .Nm ssh
431: should support in order of preference.
432: The possible values are
433: .Dq 1
434: and
435: .Dq 2 .
436: Multiple versions must be comma-separated.
437: The default is
438: .Dq 2,1 .
439: This means that
440: .Nm ssh
441: tries version 2 and falls back to version 1
442: if version 2 is not available.
443: .It Cm ProxyCommand
444: Specifies the command to use to connect to the server.
445: The command
446: string extends to the end of the line, and is executed with
447: .Pa /bin/sh .
448: In the command string,
449: .Ql %h
450: will be substituted by the host name to
451: connect and
452: .Ql %p
453: by the port.
454: The command can be basically anything,
455: and should read from its standard input and write to its standard output.
456: It should eventually connect an
457: .Xr sshd 8
458: server running on some machine, or execute
459: .Ic sshd -i
460: somewhere.
461: Host key management will be done using the
462: HostName of the host being connected (defaulting to the name typed by
463: the user).
464: Note that
465: .Cm CheckHostIP
466: is not available for connects with a proxy command.
467: .Pp
468: .It Cm PubkeyAuthentication
469: Specifies whether to try public key authentication.
470: The argument to this keyword must be
471: .Dq yes
472: or
473: .Dq no .
474: The default is
475: .Dq yes .
476: This option applies to protocol version 2 only.
477: .It Cm RemoteForward
478: Specifies that a TCP/IP port on the remote machine be forwarded over
479: the secure channel to the specified host and port from the local machine.
480: The first argument must be a port number, and the second must be
481: .Ar host:port .
482: IPv6 addresses can be specified with an alternative syntax:
483: .Ar host/port .
484: Multiple forwardings may be specified, and additional
485: forwardings can be given on the command line.
486: Only the superuser can forward privileged ports.
487: .It Cm RhostsAuthentication
488: Specifies whether to try rhosts based authentication.
489: Note that this
490: declaration only affects the client side and has no effect whatsoever
491: on security.
492: Most servers do not permit RhostsAuthentication because it
493: is not secure (see
494: .Cm RhostsRSAAuthentication ) .
495: The argument to this keyword must be
496: .Dq yes
497: or
498: .Dq no .
499: The default is
500: .Dq no .
501: This option applies to protocol version 1 only.
502: .It Cm RhostsRSAAuthentication
503: Specifies whether to try rhosts based authentication with RSA host
504: authentication.
505: The argument must be
506: .Dq yes
507: or
508: .Dq no .
509: The default is
510: .Dq no .
511: This option applies to protocol version 1 only and requires
512: .Nm ssh
513: to be setuid root.
514: .It Cm RSAAuthentication
515: Specifies whether to try RSA authentication.
516: The argument to this keyword must be
517: .Dq yes
518: or
519: .Dq no .
520: RSA authentication will only be
521: attempted if the identity file exists, or an authentication agent is
522: running.
523: The default is
524: .Dq yes .
525: Note that this option applies to protocol version 1 only.
526: .It Cm SmartcardDevice
527: Specifies which smartcard device to use. The argument to this keyword is
528: the device
529: .Nm ssh
530: should use to communicate with a smartcard used for storing the user's
531: private RSA key. By default, no device is specified and smartcard support
532: is not activated.
533: .It Cm StrictHostKeyChecking
534: If this flag is set to
535: .Dq yes ,
536: .Nm ssh
537: will never automatically add host keys to the
538: .Pa $HOME/.ssh/known_hosts
539: file, and refuses to connect to hosts whose host key has changed.
540: This provides maximum protection against trojan horse attacks,
541: however, can be annoying when the
542: .Pa /etc/ssh/ssh_known_hosts
543: file is poorly maintained, or connections to new hosts are
544: frequently made.
545: This option forces the user to manually
546: add all new hosts.
547: If this flag is set to
548: .Dq no ,
549: .Nm ssh
550: will automatically add new host keys to the
551: user known hosts files.
552: If this flag is set to
553: .Dq ask ,
554: new host keys
555: will be added to the user known host files only after the user
556: has confirmed that is what they really want to do, and
557: .Nm ssh
558: will refuse to connect to hosts whose host key has changed.
559: The host keys of
560: known hosts will be verified automatically in all cases.
561: The argument must be
562: .Dq yes ,
563: .Dq no
564: or
565: .Dq ask .
566: The default is
567: .Dq ask .
568: .It Cm UsePrivilegedPort
569: Specifies whether to use a privileged port for outgoing connections.
570: The argument must be
571: .Dq yes
572: or
573: .Dq no .
574: The default is
575: .Dq no .
576: Note that this option must be set to
577: .Dq yes
578: if
579: .Cm RhostsAuthentication
580: and
581: .Cm RhostsRSAAuthentication
582: authentications are needed with older servers.
583: .It Cm User
584: Specifies the user to log in as.
585: This can be useful when a different user name is used on different machines.
586: This saves the trouble of
587: having to remember to give the user name on the command line.
588: .It Cm UserKnownHostsFile
589: Specifies a file to use for the user
590: host key database instead of
591: .Pa $HOME/.ssh/known_hosts .
592: .It Cm XAuthLocation
593: Specifies the location of the
594: .Xr xauth 1
595: program.
596: The default is
597: .Pa /usr/X11R6/bin/xauth .
598: .El
599: .Sh FILES
600: .Bl -tag -width Ds
601: .It Pa $HOME/.ssh/config
602: This is the per-user configuration file.
603: The format of this file is described above.
604: This file is used by the
605: .Nm ssh
606: client.
607: This file does not usually contain any sensitive information,
608: but the recommended permissions are read/write for the user, and not
609: accessible by others.
610: .It Pa /etc/ssh/ssh_config
611: Systemwide configuration file.
612: This file provides defaults for those
613: values that are not specified in the user's configuration file, and
614: for those users who do not have a configuration file.
615: This file must be world-readable.
616: .El
617: .Sh AUTHORS
618: OpenSSH is a derivative of the original and free
619: ssh 1.2.12 release by Tatu Ylonen.
620: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
621: Theo de Raadt and Dug Song
622: removed many bugs, re-added newer features and
623: created OpenSSH.
624: Markus Friedl contributed the support for SSH
625: protocol versions 1.5 and 2.0.
626: .Sh SEE ALSO
627: .Xr ssh 1
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