blob: 0e1a031e5da5a8e6cff685a0a2dc8fcc259b1967 [file] [log] [blame]
Ben Lindstrom9f049032002-06-21 00:59:05 +00001.\" -*- 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.\"
Damien Miller2234bac2004-06-30 22:38:52 +100037.\" $OpenBSD: ssh_config.5,v 1.38 2004/06/26 09:11:14 jmc Exp $
Ben Lindstrom9f049032002-06-21 00:59:05 +000038.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
51obtains configuration data from the following sources in
52the following order:
Ben Lindstrom479b4762002-08-20 19:04:51 +000053.Bl -enum -offset indent -compact
54.It
55command-line options
56.It
57user's configuration file
58.Pq Pa $HOME/.ssh/config
59.It
60system-wide configuration file
61.Pq Pa /etc/ssh/ssh_config
62.El
Ben Lindstrom9f049032002-06-21 00:59:05 +000063.Pp
64For each parameter, the first obtained value
65will be used.
66The configuration files contain sections bracketed by
67.Dq Host
68specifications, and that section is only applied for hosts that
69match one of the patterns given in the specification.
70The matched host name is the one given on the command line.
71.Pp
72Since the first obtained value for each parameter is used, more
73host-specific declarations should be given near the beginning of the
74file, and general defaults at the end.
75.Pp
76The configuration file has the following format:
77.Pp
78Empty lines and lines starting with
79.Ql #
80are comments.
81.Pp
82Otherwise a line is of the format
83.Dq keyword arguments .
84Configuration options may be separated by whitespace or
85optional whitespace and exactly one
86.Ql = ;
87the latter format is useful to avoid the need to quote whitespace
88when specifying configuration options using the
89.Nm ssh ,
90.Nm scp
91and
92.Nm sftp
93.Fl o
94option.
95.Pp
96The possible
97keywords and their meanings are as follows (note that
98keywords are case-insensitive and arguments are case-sensitive):
99.Bl -tag -width Ds
100.It Cm Host
101Restricts the following declarations (up to the next
102.Cm Host
103keyword) to be only for those hosts that match one of the patterns
104given after the keyword.
105.Ql \&*
106and
Damien Millerc2b98272003-09-03 12:13:30 +1000107.Ql \&?
Ben Lindstrom9f049032002-06-21 00:59:05 +0000108can be used as wildcards in the
109patterns.
110A single
111.Ql \&*
112as a pattern can be used to provide global
113defaults for all hosts.
114The host is the
115.Ar hostname
116argument given on the command line (i.e., the name is not converted to
117a canonicalized host name before matching).
Damien Miller20a8f972003-05-18 20:50:30 +1000118.It Cm AddressFamily
Damien Millerfbf486b2003-05-23 18:44:23 +1000119Specifies which address family to use when connecting.
120Valid arguments are
Damien Miller20a8f972003-05-18 20:50:30 +1000121.Dq any ,
122.Dq inet
123(Use IPv4 only) or
124.Dq inet6
125(Use IPv6 only.)
Ben Lindstrom9f049032002-06-21 00:59:05 +0000126.It Cm BatchMode
127If set to
128.Dq yes ,
129passphrase/password querying will be disabled.
130This option is useful in scripts and other batch jobs where no user
131is present to supply the password.
132The argument must be
133.Dq yes
134or
135.Dq no .
136The default is
137.Dq no .
138.It Cm BindAddress
139Specify the interface to transmit from on machines with multiple
140interfaces or aliased addresses.
141Note that this option does not work if
142.Cm UsePrivilegedPort
143is set to
144.Dq yes .
145.It Cm ChallengeResponseAuthentication
146Specifies whether to use challenge response authentication.
147The argument to this keyword must be
148.Dq yes
149or
150.Dq no .
151The default is
152.Dq yes .
153.It Cm CheckHostIP
154If this flag is set to
155.Dq yes ,
156ssh will additionally check the host IP address in the
157.Pa known_hosts
158file.
159This allows ssh to detect if a host key changed due to DNS spoofing.
160If the option is set to
161.Dq no ,
162the check will not be executed.
163The default is
164.Dq yes .
165.It Cm Cipher
166Specifies the cipher to use for encrypting the session
167in protocol version 1.
168Currently,
169.Dq blowfish ,
170.Dq 3des ,
171and
172.Dq des
173are supported.
174.Ar des
175is only supported in the
176.Nm ssh
177client for interoperability with legacy protocol 1 implementations
178that do not support the
179.Ar 3des
Damien Miller495dca32003-04-01 21:42:14 +1000180cipher.
181Its use is strongly discouraged due to cryptographic weaknesses.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000182The default is
183.Dq 3des .
184.It Cm Ciphers
185Specifies the ciphers allowed for protocol version 2
186in order of preference.
187Multiple ciphers must be comma-separated.
Damien Miller05202ff2004-06-15 10:30:39 +1000188The 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 ,
196.Dq arcfour ,
197.Dq blowfish-cbc ,
198and
199.Dq cast128-cbc .
Ben Lindstrom9f049032002-06-21 00:59:05 +0000200The default is
Ben Lindstrom9f049032002-06-21 00:59:05 +0000201.Bd -literal
202 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
203 aes192-cbc,aes256-cbc''
204.Ed
205.It Cm ClearAllForwardings
206Specifies that all local, remote and dynamic port forwardings
207specified in the configuration files or on the command line be
Damien Miller495dca32003-04-01 21:42:14 +1000208cleared.
209This option is primarily useful when used from the
Ben Lindstrom9f049032002-06-21 00:59:05 +0000210.Nm ssh
211command line to clear port forwardings set in
212configuration files, and is automatically set by
213.Xr scp 1
214and
215.Xr sftp 1 .
216The argument must be
217.Dq yes
218or
219.Dq no .
220The default is
221.Dq no .
222.It Cm Compression
223Specifies whether to use compression.
224The argument must be
225.Dq yes
226or
227.Dq no .
228The default is
229.Dq no .
230.It Cm CompressionLevel
231Specifies the compression level to use if compression is enabled.
232The argument must be an integer from 1 (fast) to 9 (slow, best).
233The default level is 6, which is good for most applications.
234The meaning of the values is the same as in
235.Xr gzip 1 .
236Note that this option applies to protocol version 1 only.
237.It Cm ConnectionAttempts
238Specifies the number of tries (one per second) to make before exiting.
239The argument must be an integer.
240This may be useful in scripts if the connection sometimes fails.
241The default is 1.
Damien Millerb78d5eb2003-05-16 11:39:04 +1000242.It Cm ConnectTimeout
243Specifies the timeout (in seconds) used when connecting to the ssh
Damien Millerfbf486b2003-05-23 18:44:23 +1000244server, instead of using the default system TCP timeout.
245This value is used only when the target is down or really unreachable,
246not when it refuses the connection.
Damien Miller0e220db2004-06-15 10:34:08 +1000247.It Cm ControlMaster
248Enables the sharing of multiple sessions over a single network connection.
249When set to
250.Dq yes
251.Nm ssh
252will listen for connections on a control socket specified using the
253.Cm ControlPath
254argument.
255Additional sessions can connect to this socket using the same
256.Cm ControlPath
257with
258.Cm ControlMaster
259set to
260.Dq no
Damien Miller2234bac2004-06-30 22:38:52 +1000261(the default).
Damien Miller0e220db2004-06-15 10:34:08 +1000262These sessions will reuse the master instance's network connection rather
263than initiating new ones.
Damien Miller23f07702004-06-18 01:19:03 +1000264Setting this to
265.Dq ask
266will cause
267.Nm ssh
268to listen for control connections, but require confirmation using the
269.Ev SSH_ASKPASS
270program before they are accepted (see
271.Xr ssh-add 1
Damien Miller2234bac2004-06-30 22:38:52 +1000272for details).
Damien Miller0e220db2004-06-15 10:34:08 +1000273.It Cm ControlPath
Damien Miller2234bac2004-06-30 22:38:52 +1000274Specify the path to the control socket used for connection sharing.
Damien Miller0e220db2004-06-15 10:34:08 +1000275See
276.Cm ControlMaster
277above.
Damien Miller2234bac2004-06-30 22:38:52 +1000278.It Cm DynamicForward
279Specifies that a TCP/IP port on the local machine be forwarded
280over the secure channel, and the application
281protocol is then used to determine where to connect to from the
282remote machine.
283The argument must be a port number.
284Currently the SOCKS4 and SOCKS5 protocols are supported, and
285.Nm ssh
286will act as a SOCKS server.
287Multiple forwardings may be specified, and
288additional forwardings can be given on the command line.
289Only the superuser can forward privileged ports.
Darren Tucker674f71d2003-06-28 12:33:12 +1000290.It Cm EnableSSHKeysign
291Setting this option to
292.Dq yes
293in the global client configuration file
294.Pa /etc/ssh/ssh_config
295enables the use of the helper program
296.Xr ssh-keysign 8
297during
298.Cm HostbasedAuthentication .
299The argument must be
300.Dq yes
301or
302.Dq no .
303The default is
304.Dq no .
Darren Tuckerf132c672003-10-15 15:58:18 +1000305This option should be placed in the non-hostspecific section.
Darren Tucker674f71d2003-06-28 12:33:12 +1000306See
307.Xr ssh-keysign 8
308for more information.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000309.It Cm EscapeChar
310Sets the escape character (default:
311.Ql ~ ) .
312The escape character can also
313be set on the command line.
314The argument should be a single character,
315.Ql ^
316followed by a letter, or
317.Dq none
318to disable the escape
319character entirely (making the connection transparent for binary
320data).
321.It Cm ForwardAgent
322Specifies whether the connection to the authentication agent (if any)
323will be forwarded to the remote machine.
324The argument must be
325.Dq yes
326or
327.Dq no .
328The default is
329.Dq no .
Damien Milleraf653042002-09-04 16:40:37 +1000330.Pp
Damien Miller495dca32003-04-01 21:42:14 +1000331Agent forwarding should be enabled with caution.
332Users with the ability to bypass file permissions on the remote host
333(for the agent's Unix-domain socket)
334can access the local agent through the forwarded connection.
335An attacker cannot obtain key material from the agent,
Damien Milleraf653042002-09-04 16:40:37 +1000336however they can perform operations on the keys that enable them to
337authenticate using the identities loaded into the agent.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000338.It Cm ForwardX11
339Specifies whether X11 connections will be automatically redirected
340over the secure channel and
341.Ev DISPLAY
342set.
343The argument must be
344.Dq yes
345or
346.Dq no .
347The default is
348.Dq no .
Damien Milleraf653042002-09-04 16:40:37 +1000349.Pp
Damien Miller495dca32003-04-01 21:42:14 +1000350X11 forwarding should be enabled with caution.
351Users with the ability to bypass file permissions on the remote host
Darren Tucker0a118da2003-10-15 15:54:32 +1000352(for the user's X11 authorization database)
Damien Miller495dca32003-04-01 21:42:14 +1000353can access the local X11 display through the forwarded connection.
Darren Tucker0a118da2003-10-15 15:54:32 +1000354An attacker may then be able to perform activities such as keystroke monitoring
355if the
356.Cm ForwardX11Trusted
357option is also enabled.
358.It Cm ForwardX11Trusted
Darren Tuckerdcf6ec42004-05-13 13:03:56 +1000359If this option is set to
Darren Tucker0a118da2003-10-15 15:54:32 +1000360.Dq yes
361then remote X11 clients will have full access to the original X11 display.
362If this option is set to
363.Dq no
364then remote X11 clients will be considered untrusted and prevented
365from stealing or tampering with data belonging to trusted X11
366clients.
367.Pp
368The default is
369.Dq no .
370.Pp
371See the X11 SECURITY extension specification for full details on
372the restrictions imposed on untrusted clients.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000373.It Cm GatewayPorts
374Specifies whether remote hosts are allowed to connect to local
375forwarded ports.
376By default,
377.Nm ssh
Damien Miller495dca32003-04-01 21:42:14 +1000378binds local port forwardings to the loopback address.
379This prevents other remote hosts from connecting to forwarded ports.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000380.Cm GatewayPorts
381can be used to specify that
382.Nm ssh
383should bind local port forwardings to the wildcard address,
384thus allowing remote hosts to connect to forwarded ports.
385The argument must be
386.Dq yes
387or
388.Dq no .
389The default is
390.Dq no .
391.It Cm GlobalKnownHostsFile
392Specifies a file to use for the global
393host key database instead of
394.Pa /etc/ssh/ssh_known_hosts .
Darren Tucker0efd1552003-08-26 11:49:55 +1000395.It Cm GSSAPIAuthentication
Damien Millerbaafb982003-12-17 16:32:23 +1100396Specifies whether user authentication based on GSSAPI is allowed.
Damien Millerc2b98272003-09-03 12:13:30 +1000397The default is
Darren Tuckera044f472003-10-15 15:52:03 +1000398.Dq no .
Darren Tucker0efd1552003-08-26 11:49:55 +1000399Note that this option applies to protocol version 2 only.
400.It Cm GSSAPIDelegateCredentials
401Forward (delegate) credentials to the server.
402The default is
403.Dq no .
404Note that this option applies to protocol version 2 only.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000405.It Cm HostbasedAuthentication
406Specifies whether to try rhosts based authentication with public key
407authentication.
408The argument must be
409.Dq yes
410or
411.Dq no .
412The default is
413.Dq no .
414This option applies to protocol version 2 only and
415is similar to
416.Cm RhostsRSAAuthentication .
417.It Cm HostKeyAlgorithms
418Specifies the protocol version 2 host key algorithms
419that the client wants to use in order of preference.
420The default for this option is:
421.Dq ssh-rsa,ssh-dss .
422.It Cm HostKeyAlias
423Specifies an alias that should be used instead of the
424real host name when looking up or saving the host key
425in the host key database files.
426This option is useful for tunneling ssh connections
427or for multiple servers running on a single host.
428.It Cm HostName
429Specifies the real host name to log into.
430This can be used to specify nicknames or abbreviations for hosts.
431Default is the name given on the command line.
432Numeric IP addresses are also permitted (both on the command line and in
433.Cm HostName
434specifications).
435.It Cm IdentityFile
436Specifies a file from which the user's RSA or DSA authentication identity
Damien Millerfbf486b2003-05-23 18:44:23 +1000437is read.
438The default is
Ben Lindstrom9f049032002-06-21 00:59:05 +0000439.Pa $HOME/.ssh/identity
440for protocol version 1, and
441.Pa $HOME/.ssh/id_rsa
442and
443.Pa $HOME/.ssh/id_dsa
444for protocol version 2.
445Additionally, any identities represented by the authentication agent
446will be used for authentication.
447The file name may use the tilde
448syntax to refer to a user's home directory.
449It is possible to have
450multiple identity files specified in configuration files; all these
451identities will be tried in sequence.
Damien Millerbd394c32004-03-08 23:12:36 +1100452.It Cm IdentitiesOnly
453Specifies that
454.Nm ssh
455should only use the authentication identity files configured in the
Damien Miller1a812582004-04-20 20:13:32 +1000456.Nm
Damien Millerbd394c32004-03-08 23:12:36 +1100457files,
458even if the
459.Nm ssh-agent
460offers more identities.
461The argument to this keyword must be
462.Dq yes
463or
464.Dq no .
465This option is intented for situations where
466.Nm ssh-agent
467offers many different identities.
468The default is
469.Dq no .
Ben Lindstrom9f049032002-06-21 00:59:05 +0000470.It Cm LocalForward
471Specifies that a TCP/IP port on the local machine be forwarded over
472the secure channel to the specified host and port from the remote machine.
473The first argument must be a port number, and the second must be
474.Ar host:port .
475IPv6 addresses can be specified with an alternative syntax:
476.Ar host/port .
477Multiple forwardings may be specified, and additional
478forwardings can be given on the command line.
479Only the superuser can forward privileged ports.
480.It Cm LogLevel
481Gives the verbosity level that is used when logging messages from
482.Nm ssh .
483The possible values are:
484QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
Damien Miller495dca32003-04-01 21:42:14 +1000485The default is INFO.
486DEBUG and DEBUG1 are equivalent.
487DEBUG2 and DEBUG3 each specify higher levels of verbose output.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000488.It Cm MACs
489Specifies the MAC (message authentication code) algorithms
490in order of preference.
491The MAC algorithm is used in protocol version 2
492for data integrity protection.
493Multiple algorithms must be comma-separated.
494The default is
495.Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
496.It Cm NoHostAuthenticationForLocalhost
497This option can be used if the home directory is shared across machines.
498In this case localhost will refer to a different machine on each of
499the machines and the user will get many warnings about changed host keys.
500However, this option disables host authentication for localhost.
501The argument to this keyword must be
502.Dq yes
503or
504.Dq no .
505The default is to check the host key for localhost.
506.It Cm NumberOfPasswordPrompts
507Specifies the number of password prompts before giving up.
508The argument to this keyword must be an integer.
509Default is 3.
510.It Cm PasswordAuthentication
511Specifies whether to use password authentication.
512The argument to this keyword must be
513.Dq yes
514or
515.Dq no .
516The default is
517.Dq yes .
518.It Cm Port
519Specifies the port number to connect on the remote host.
520Default is 22.
521.It Cm PreferredAuthentications
522Specifies the order in which the client should try protocol 2
Damien Millerfbf486b2003-05-23 18:44:23 +1000523authentication methods.
524This allows a client to prefer one method (e.g.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000525.Cm keyboard-interactive )
526over another method (e.g.
527.Cm password )
528The default for this option is:
529.Dq hostbased,publickey,keyboard-interactive,password .
530.It Cm Protocol
531Specifies the protocol versions
532.Nm ssh
533should support in order of preference.
534The possible values are
535.Dq 1
536and
537.Dq 2 .
538Multiple versions must be comma-separated.
539The default is
540.Dq 2,1 .
541This means that
542.Nm ssh
543tries version 2 and falls back to version 1
544if version 2 is not available.
545.It Cm ProxyCommand
546Specifies the command to use to connect to the server.
547The command
548string extends to the end of the line, and is executed with
549.Pa /bin/sh .
550In the command string,
551.Ql %h
552will be substituted by the host name to
553connect and
554.Ql %p
555by the port.
556The command can be basically anything,
557and should read from its standard input and write to its standard output.
558It should eventually connect an
559.Xr sshd 8
560server running on some machine, or execute
561.Ic sshd -i
562somewhere.
563Host key management will be done using the
564HostName of the host being connected (defaulting to the name typed by
565the user).
Damien Miller495dca32003-04-01 21:42:14 +1000566Setting the command to
567.Dq none
Damien Miller9f1e33a2003-02-24 11:57:32 +1100568disables this option entirely.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000569Note that
570.Cm CheckHostIP
571is not available for connects with a proxy command.
572.Pp
573.It Cm PubkeyAuthentication
574Specifies whether to try public key authentication.
575The argument to this keyword must be
576.Dq yes
577or
578.Dq no .
579The default is
580.Dq yes .
581This option applies to protocol version 2 only.
582.It Cm RemoteForward
583Specifies that a TCP/IP port on the remote machine be forwarded over
584the secure channel to the specified host and port from the local machine.
585The first argument must be a port number, and the second must be
586.Ar host:port .
587IPv6 addresses can be specified with an alternative syntax:
588.Ar host/port .
589Multiple forwardings may be specified, and additional
590forwardings can be given on the command line.
591Only the superuser can forward privileged ports.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000592.It Cm RhostsRSAAuthentication
593Specifies whether to try rhosts based authentication with RSA host
594authentication.
595The argument must be
596.Dq yes
597or
598.Dq no .
599The default is
600.Dq no .
601This option applies to protocol version 1 only and requires
602.Nm ssh
603to be setuid root.
604.It Cm RSAAuthentication
605Specifies whether to try RSA authentication.
606The argument to this keyword must be
607.Dq yes
608or
609.Dq no .
610RSA authentication will only be
611attempted if the identity file exists, or an authentication agent is
612running.
613The default is
614.Dq yes .
615Note that this option applies to protocol version 1 only.
Darren Tucker46bc0752004-05-02 22:11:30 +1000616.It Cm SendEnv
617Specifies what variables from the local
618.Xr environ 7
619should be sent to the server.
620Note that environment passing is only supported for protocol 2, the
Darren Tucker1e0c9bf2004-05-02 22:12:48 +1000621server must also support it, and the server must be configured to
622accept these environment variables.
Darren Tucker46bc0752004-05-02 22:11:30 +1000623Refer to
624.Cm AcceptEnv
625in
626.Xr sshd_config 5
627for how to configure the server.
628Variables are specified by name, which may contain the wildcard characters
629.Ql \&*
630and
631.Ql \&? .
Darren Tucker1e0c9bf2004-05-02 22:12:48 +1000632Multiple environment variables may be separated by whitespace or spread
Darren Tucker46bc0752004-05-02 22:11:30 +1000633across multiple
634.Cm SendEnv
635directives.
636The default is not to send any environment variables.
Damien Miller509b0102003-12-17 16:33:10 +1100637.It Cm ServerAliveInterval
638Sets a timeout interval in seconds after which if no data has been received
639from the server,
640.Nm ssh
641will send a message through the encrypted
642channel to request a response from the server.
643The default
644is 0, indicating that these messages will not be sent to the server.
645This option applies to protocol version 2 only.
646.It Cm ServerAliveCountMax
647Sets the number of server alive messages (see above) which may be
648sent without
649.Nm ssh
650receiving any messages back from the server.
651If this threshold is reached while server alive messages are being sent,
652.Nm ssh
653will disconnect from the server, terminating the session.
654It is important to note that the use of server alive messages is very
655different from
656.Cm TCPKeepAlive
657(below).
658The server alive messages are sent through the encrypted channel
659and therefore will not be spoofable.
660The TCP keepalive option enabled by
661.Cm TCPKeepAlive
662is spoofable.
663The server alive mechanism is valuable when the client or
664server depend on knowing when a connection has become inactive.
665.Pp
666The default value is 3.
667If, for example,
668.Cm ServerAliveInterval
669(above) is set to 15, and
670.Cm ServerAliveCountMax
671is left at the default, if the server becomes unresponsive ssh
672will disconnect after approximately 45 seconds.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000673.It Cm SmartcardDevice
Damien Millerfbf486b2003-05-23 18:44:23 +1000674Specifies which smartcard device to use.
675The argument to this keyword is the device
Ben Lindstrom9f049032002-06-21 00:59:05 +0000676.Nm ssh
677should use to communicate with a smartcard used for storing the user's
Damien Millerfbf486b2003-05-23 18:44:23 +1000678private RSA key.
679By default, no device is specified and smartcard support is not activated.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000680.It Cm StrictHostKeyChecking
681If this flag is set to
682.Dq yes ,
683.Nm ssh
684will never automatically add host keys to the
685.Pa $HOME/.ssh/known_hosts
686file, and refuses to connect to hosts whose host key has changed.
687This provides maximum protection against trojan horse attacks,
688however, can be annoying when the
689.Pa /etc/ssh/ssh_known_hosts
690file is poorly maintained, or connections to new hosts are
691frequently made.
692This option forces the user to manually
693add all new hosts.
694If this flag is set to
695.Dq no ,
696.Nm ssh
697will automatically add new host keys to the
698user known hosts files.
699If this flag is set to
700.Dq ask ,
701new host keys
702will be added to the user known host files only after the user
703has confirmed that is what they really want to do, and
704.Nm ssh
705will refuse to connect to hosts whose host key has changed.
706The host keys of
707known hosts will be verified automatically in all cases.
708The argument must be
709.Dq yes ,
710.Dq no
711or
712.Dq ask .
713The default is
714.Dq ask .
Damien Miller12c150e2003-12-17 16:31:10 +1100715.It Cm TCPKeepAlive
716Specifies whether the system should send TCP keepalive messages to the
717other side.
718If they are sent, death of the connection or crash of one
719of the machines will be properly noticed.
720However, this means that
721connections will die if the route is down temporarily, and some people
722find it annoying.
723.Pp
724The default is
725.Dq yes
726(to send TCP keepalive messages), and the client will notice
727if the network goes down or the remote host dies.
728This is important in scripts, and many users want it too.
729.Pp
730To disable TCP keepalive messages, the value should be set to
731.Dq no .
Ben Lindstrom9f049032002-06-21 00:59:05 +0000732.It Cm UsePrivilegedPort
733Specifies whether to use a privileged port for outgoing connections.
734The argument must be
735.Dq yes
736or
737.Dq no .
738The default is
739.Dq no .
Damien Miller9b1dacd2002-09-04 16:47:35 +1000740If set to
741.Dq yes
742.Nm ssh
743must be setuid root.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000744Note that this option must be set to
745.Dq yes
Darren Tuckerec960f22003-08-13 20:37:05 +1000746for
Ben Lindstrom9f049032002-06-21 00:59:05 +0000747.Cm RhostsRSAAuthentication
Darren Tuckerec960f22003-08-13 20:37:05 +1000748with older servers.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000749.It Cm User
750Specifies the user to log in as.
751This can be useful when a different user name is used on different machines.
752This saves the trouble of
753having to remember to give the user name on the command line.
754.It Cm UserKnownHostsFile
755Specifies a file to use for the user
756host key database instead of
757.Pa $HOME/.ssh/known_hosts .
Damien Miller37876e92003-05-15 10:19:46 +1000758.It Cm VerifyHostKeyDNS
759Specifies whether to verify the remote key using DNS and SSHFP resource
760records.
Damien Miller150b5572003-11-17 21:19:29 +1100761If this option is set to
762.Dq yes ,
Damien Millerfe448472003-11-17 21:19:49 +1100763the client will implicitly trust keys that match a secure fingerprint
Damien Miller150b5572003-11-17 21:19:29 +1100764from DNS.
765Insecure fingerprints will be handled as if this option was set to
766.Dq ask .
767If this option is set to
768.Dq ask ,
769information on fingerprint match will be displayed, but the user will still
770need to confirm new host keys according to the
771.Cm StrictHostKeyChecking
772option.
773The argument must be
774.Dq yes ,
775.Dq no
Damien Millerfe448472003-11-17 21:19:49 +1100776or
777.Dq ask .
Damien Miller37876e92003-05-15 10:19:46 +1000778The default is
779.Dq no .
Damien Millereacbb4f2003-06-02 19:10:41 +1000780Note that this option applies to protocol version 2 only.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000781.It Cm XAuthLocation
Damien Miller05913ba2002-09-04 16:51:03 +1000782Specifies the full pathname of the
Ben Lindstrom9f049032002-06-21 00:59:05 +0000783.Xr xauth 1
784program.
785The default is
786.Pa /usr/X11R6/bin/xauth .
787.El
788.Sh FILES
789.Bl -tag -width Ds
790.It Pa $HOME/.ssh/config
791This is the per-user configuration file.
792The format of this file is described above.
793This file is used by the
794.Nm ssh
795client.
Damien Millerc970cb92004-04-20 20:12:53 +1000796Because of the potential for abuse, this file must have strict permissions:
797read/write for the user, and not accessible by others.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000798.It Pa /etc/ssh/ssh_config
799Systemwide configuration file.
800This file provides defaults for those
801values that are not specified in the user's configuration file, and
802for those users who do not have a configuration file.
803This file must be world-readable.
804.El
Damien Millerf1ce5052003-06-11 22:04:39 +1000805.Sh SEE ALSO
806.Xr ssh 1
Ben Lindstrom9f049032002-06-21 00:59:05 +0000807.Sh AUTHORS
808OpenSSH is a derivative of the original and free
809ssh 1.2.12 release by Tatu Ylonen.
810Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
811Theo de Raadt and Dug Song
812removed many bugs, re-added newer features and
813created OpenSSH.
814Markus Friedl contributed the support for SSH
815protocol versions 1.5 and 2.0.