Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.1.4.3
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,
32: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36: .\"
1.1.4.3 ! miod 37: .\" $OpenBSD: ssh_config.5,v 1.7 2003/03/28 10:11:43 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
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:
1.1.4.2 miod 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
1.1.4.3 ! miod 179: cipher.
! 180: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 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
1.1.4.3 ! miod 196: cleared.
! 197: This option is primarily useful when used from the
1.1 stevesk 198: .Nm ssh
199: command line to clear port forwardings set in
200: configuration files, and is automatically set by
201: .Xr scp 1
202: and
203: .Xr sftp 1 .
204: The argument must be
205: .Dq yes
206: or
207: .Dq no .
208: The default is
209: .Dq no .
210: .It Cm Compression
211: Specifies whether to use compression.
212: The argument must be
213: .Dq yes
214: or
215: .Dq no .
216: The default is
217: .Dq no .
218: .It Cm CompressionLevel
219: Specifies the compression level to use if compression is enabled.
220: The argument must be an integer from 1 (fast) to 9 (slow, best).
221: The default level is 6, which is good for most applications.
222: The meaning of the values is the same as in
223: .Xr gzip 1 .
224: Note that this option applies to protocol version 1 only.
225: .It Cm ConnectionAttempts
226: Specifies the number of tries (one per second) to make before exiting.
227: The argument must be an integer.
228: This may be useful in scripts if the connection sometimes fails.
229: The default is 1.
230: .It Cm DynamicForward
231: Specifies that a TCP/IP port on the local machine be forwarded
232: over the secure channel, and the application
233: protocol is then used to determine where to connect to from the
1.1.4.3 ! miod 234: remote machine.
! 235: The argument must be a port number.
1.1 stevesk 236: Currently the SOCKS4 protocol is supported, and
237: .Nm ssh
238: will act as a SOCKS4 server.
239: Multiple forwardings may be specified, and
1.1.4.3 ! miod 240: additional forwardings can be given on the command line.
! 241: Only the superuser can forward privileged ports.
1.1 stevesk 242: .It Cm EscapeChar
243: Sets the escape character (default:
244: .Ql ~ ) .
245: The escape character can also
246: be set on the command line.
247: The argument should be a single character,
248: .Ql ^
249: followed by a letter, or
250: .Dq none
251: to disable the escape
252: character entirely (making the connection transparent for binary
253: data).
254: .It Cm ForwardAgent
255: Specifies whether the connection to the authentication agent (if any)
256: will be forwarded to the remote machine.
257: The argument must be
258: .Dq yes
259: or
260: .Dq no .
261: The default is
262: .Dq no .
1.1.4.2 miod 263: .Pp
1.1.4.3 ! miod 264: Agent forwarding should be enabled with caution.
! 265: Users with the ability to bypass file permissions on the remote host
! 266: (for the agent's Unix-domain socket)
! 267: can access the local agent through the forwarded connection.
! 268: An attacker cannot obtain key material from the agent,
1.1.4.2 miod 269: however they can perform operations on the keys that enable them to
270: authenticate using the identities loaded into the agent.
1.1 stevesk 271: .It Cm ForwardX11
272: Specifies whether X11 connections will be automatically redirected
273: over the secure channel and
274: .Ev DISPLAY
275: set.
276: The argument must be
277: .Dq yes
278: or
279: .Dq no .
280: The default is
281: .Dq no .
1.1.4.2 miod 282: .Pp
1.1.4.3 ! miod 283: X11 forwarding should be enabled with caution.
! 284: Users with the ability to bypass file permissions on the remote host
! 285: (for the user's X authorization database)
! 286: can access the local X11 display through the forwarded connection.
! 287: An attacker may then be able to perform activities such as keystroke monitoring.
1.1 stevesk 288: .It Cm GatewayPorts
289: Specifies whether remote hosts are allowed to connect to local
290: forwarded ports.
291: By default,
292: .Nm ssh
1.1.4.3 ! miod 293: binds local port forwardings to the loopback address.
! 294: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 295: .Cm GatewayPorts
296: can be used to specify that
297: .Nm ssh
298: should bind local port forwardings to the wildcard address,
299: thus allowing remote hosts to connect to forwarded ports.
300: The argument must be
301: .Dq yes
302: or
303: .Dq no .
304: The default is
305: .Dq no .
306: .It Cm GlobalKnownHostsFile
307: Specifies a file to use for the global
308: host key database instead of
309: .Pa /etc/ssh/ssh_known_hosts .
310: .It Cm HostbasedAuthentication
311: Specifies whether to try rhosts based authentication with public key
312: authentication.
313: The argument must be
314: .Dq yes
315: or
316: .Dq no .
317: The default is
318: .Dq no .
319: This option applies to protocol version 2 only and
320: is similar to
321: .Cm RhostsRSAAuthentication .
322: .It Cm HostKeyAlgorithms
323: Specifies the protocol version 2 host key algorithms
324: that the client wants to use in order of preference.
325: The default for this option is:
326: .Dq ssh-rsa,ssh-dss .
327: .It Cm HostKeyAlias
328: Specifies an alias that should be used instead of the
329: real host name when looking up or saving the host key
330: in the host key database files.
331: This option is useful for tunneling ssh connections
332: or for multiple servers running on a single host.
333: .It Cm HostName
334: Specifies the real host name to log into.
335: This can be used to specify nicknames or abbreviations for hosts.
336: Default is the name given on the command line.
337: Numeric IP addresses are also permitted (both on the command line and in
338: .Cm HostName
339: specifications).
340: .It Cm IdentityFile
341: Specifies a file from which the user's RSA or DSA authentication identity
342: is read. The default is
343: .Pa $HOME/.ssh/identity
344: for protocol version 1, and
345: .Pa $HOME/.ssh/id_rsa
346: and
347: .Pa $HOME/.ssh/id_dsa
348: for protocol version 2.
349: Additionally, any identities represented by the authentication agent
350: will be used for authentication.
351: The file name may use the tilde
352: syntax to refer to a user's home directory.
353: It is possible to have
354: multiple identity files specified in configuration files; all these
355: identities will be tried in sequence.
356: .It Cm KeepAlive
357: Specifies whether the system should send TCP keepalive messages to the
358: other side.
359: If they are sent, death of the connection or crash of one
360: of the machines will be properly noticed.
361: However, this means that
362: connections will die if the route is down temporarily, and some people
363: find it annoying.
364: .Pp
365: The default is
366: .Dq yes
367: (to send keepalives), and the client will notice
368: if the network goes down or the remote host dies.
369: This is important in scripts, and many users want it too.
370: .Pp
371: To disable keepalives, the value should be set to
372: .Dq no .
373: .It Cm KerberosAuthentication
374: Specifies whether Kerberos authentication will be used.
375: The argument to this keyword must be
376: .Dq yes
377: or
378: .Dq no .
379: .It Cm KerberosTgtPassing
380: Specifies whether a Kerberos TGT will be forwarded to the server.
381: This will only work if the Kerberos server is actually an AFS kaserver.
382: The argument to this keyword must be
383: .Dq yes
384: or
385: .Dq no .
386: .It Cm LocalForward
387: Specifies that a TCP/IP port on the local machine be forwarded over
388: the secure channel to the specified host and port from the remote machine.
389: The first argument must be a port number, and the second must be
390: .Ar host:port .
391: IPv6 addresses can be specified with an alternative syntax:
392: .Ar host/port .
393: Multiple forwardings may be specified, and additional
394: forwardings can be given on the command line.
395: Only the superuser can forward privileged ports.
396: .It Cm LogLevel
397: Gives the verbosity level that is used when logging messages from
398: .Nm ssh .
399: The possible values are:
400: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
1.1.4.3 ! miod 401: The default is INFO.
! 402: DEBUG and DEBUG1 are equivalent.
! 403: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 404: .It Cm MACs
405: Specifies the MAC (message authentication code) algorithms
406: in order of preference.
407: The MAC algorithm is used in protocol version 2
408: for data integrity protection.
409: Multiple algorithms must be comma-separated.
410: The default is
411: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
412: .It Cm NoHostAuthenticationForLocalhost
413: This option can be used if the home directory is shared across machines.
414: In this case localhost will refer to a different machine on each of
415: the machines and the user will get many warnings about changed host keys.
416: However, this option disables host authentication for localhost.
417: The argument to this keyword must be
418: .Dq yes
419: or
420: .Dq no .
421: The default is to check the host key for localhost.
422: .It Cm NumberOfPasswordPrompts
423: Specifies the number of password prompts before giving up.
424: The argument to this keyword must be an integer.
425: Default is 3.
426: .It Cm PasswordAuthentication
427: Specifies whether to use password authentication.
428: The argument to this keyword must be
429: .Dq yes
430: or
431: .Dq no .
432: The default is
433: .Dq yes .
434: .It Cm Port
435: Specifies the port number to connect on the remote host.
436: Default is 22.
437: .It Cm PreferredAuthentications
438: Specifies the order in which the client should try protocol 2
439: authentication methods. This allows a client to prefer one method (e.g.
440: .Cm keyboard-interactive )
441: over another method (e.g.
442: .Cm password )
443: The default for this option is:
444: .Dq hostbased,publickey,keyboard-interactive,password .
445: .It Cm Protocol
446: Specifies the protocol versions
447: .Nm ssh
448: should support in order of preference.
449: The possible values are
450: .Dq 1
451: and
452: .Dq 2 .
453: Multiple versions must be comma-separated.
454: The default is
455: .Dq 2,1 .
456: This means that
457: .Nm ssh
458: tries version 2 and falls back to version 1
459: if version 2 is not available.
460: .It Cm ProxyCommand
461: Specifies the command to use to connect to the server.
462: The command
463: string extends to the end of the line, and is executed with
464: .Pa /bin/sh .
465: In the command string,
466: .Ql %h
467: will be substituted by the host name to
468: connect and
469: .Ql %p
470: by the port.
471: The command can be basically anything,
472: and should read from its standard input and write to its standard output.
473: It should eventually connect an
474: .Xr sshd 8
475: server running on some machine, or execute
476: .Ic sshd -i
477: somewhere.
478: Host key management will be done using the
479: HostName of the host being connected (defaulting to the name typed by
480: the user).
1.1.4.3 ! miod 481: Setting the command to
! 482: .Dq none
! 483: disables this option entirely.
1.1 stevesk 484: Note that
485: .Cm CheckHostIP
486: is not available for connects with a proxy command.
487: .Pp
488: .It Cm PubkeyAuthentication
489: Specifies whether to try public key authentication.
490: The argument to this keyword must be
491: .Dq yes
492: or
493: .Dq no .
494: The default is
495: .Dq yes .
496: This option applies to protocol version 2 only.
497: .It Cm RemoteForward
498: Specifies that a TCP/IP port on the remote machine be forwarded over
499: the secure channel to the specified host and port from the local machine.
500: The first argument must be a port number, and the second must be
501: .Ar host:port .
502: IPv6 addresses can be specified with an alternative syntax:
503: .Ar host/port .
504: Multiple forwardings may be specified, and additional
505: forwardings can be given on the command line.
506: Only the superuser can forward privileged ports.
507: .It Cm RhostsAuthentication
508: Specifies whether to try rhosts based authentication.
509: Note that this
510: declaration only affects the client side and has no effect whatsoever
511: on security.
512: Most servers do not permit RhostsAuthentication because it
513: is not secure (see
514: .Cm RhostsRSAAuthentication ) .
515: The argument to this keyword must be
516: .Dq yes
517: or
518: .Dq no .
519: The default is
520: .Dq no .
1.1.4.2 miod 521: This option applies to protocol version 1 only and requires
522: .Nm ssh
523: to be setuid root and
524: .Cm UsePrivilegedPort
525: to be set to
526: .Dq yes .
1.1 stevesk 527: .It Cm RhostsRSAAuthentication
528: Specifies whether to try rhosts based authentication with RSA host
529: authentication.
530: The argument must be
531: .Dq yes
532: or
533: .Dq no .
534: The default is
535: .Dq no .
536: This option applies to protocol version 1 only and requires
537: .Nm ssh
538: to be setuid root.
539: .It Cm RSAAuthentication
540: Specifies whether to try RSA authentication.
541: The argument to this keyword must be
542: .Dq yes
543: or
544: .Dq no .
545: RSA authentication will only be
546: attempted if the identity file exists, or an authentication agent is
547: running.
548: The default is
549: .Dq yes .
550: Note that this option applies to protocol version 1 only.
551: .It Cm SmartcardDevice
552: Specifies which smartcard device to use. The argument to this keyword is
553: the device
554: .Nm ssh
555: should use to communicate with a smartcard used for storing the user's
556: private RSA key. By default, no device is specified and smartcard support
557: is not activated.
558: .It Cm StrictHostKeyChecking
559: If this flag is set to
560: .Dq yes ,
561: .Nm ssh
562: will never automatically add host keys to the
563: .Pa $HOME/.ssh/known_hosts
564: file, and refuses to connect to hosts whose host key has changed.
565: This provides maximum protection against trojan horse attacks,
566: however, can be annoying when the
567: .Pa /etc/ssh/ssh_known_hosts
568: file is poorly maintained, or connections to new hosts are
569: frequently made.
570: This option forces the user to manually
571: add all new hosts.
572: If this flag is set to
573: .Dq no ,
574: .Nm ssh
575: will automatically add new host keys to the
576: user known hosts files.
577: If this flag is set to
578: .Dq ask ,
579: new host keys
580: will be added to the user known host files only after the user
581: has confirmed that is what they really want to do, and
582: .Nm ssh
583: will refuse to connect to hosts whose host key has changed.
584: The host keys of
585: known hosts will be verified automatically in all cases.
586: The argument must be
587: .Dq yes ,
588: .Dq no
589: or
590: .Dq ask .
591: The default is
592: .Dq ask .
593: .It Cm UsePrivilegedPort
594: Specifies whether to use a privileged port for outgoing connections.
595: The argument must be
596: .Dq yes
597: or
598: .Dq no .
599: The default is
600: .Dq no .
1.1.4.2 miod 601: If set to
602: .Dq yes
603: .Nm ssh
604: must be setuid root.
1.1 stevesk 605: Note that this option must be set to
606: .Dq yes
607: if
608: .Cm RhostsAuthentication
609: and
610: .Cm RhostsRSAAuthentication
611: authentications are needed with older servers.
612: .It Cm User
613: Specifies the user to log in as.
614: This can be useful when a different user name is used on different machines.
615: This saves the trouble of
616: having to remember to give the user name on the command line.
617: .It Cm UserKnownHostsFile
618: Specifies a file to use for the user
619: host key database instead of
620: .Pa $HOME/.ssh/known_hosts .
621: .It Cm XAuthLocation
1.1.4.2 miod 622: Specifies the full pathname of the
1.1 stevesk 623: .Xr xauth 1
624: program.
625: The default is
626: .Pa /usr/X11R6/bin/xauth .
627: .El
628: .Sh FILES
629: .Bl -tag -width Ds
630: .It Pa $HOME/.ssh/config
631: This is the per-user configuration file.
632: The format of this file is described above.
633: This file is used by the
634: .Nm ssh
635: client.
636: This file does not usually contain any sensitive information,
637: but the recommended permissions are read/write for the user, and not
638: accessible by others.
639: .It Pa /etc/ssh/ssh_config
640: Systemwide configuration file.
641: This file provides defaults for those
642: values that are not specified in the user's configuration file, and
643: for those users who do not have a configuration file.
644: This file must be world-readable.
645: .El
646: .Sh AUTHORS
647: OpenSSH is a derivative of the original and free
648: ssh 1.2.12 release by Tatu Ylonen.
649: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
650: Theo de Raadt and Dug Song
651: removed many bugs, re-added newer features and
652: created OpenSSH.
653: Markus Friedl contributed the support for SSH
654: protocol versions 1.5 and 2.0.
655: .Sh SEE ALSO
656: .Xr ssh 1
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