blob: 67b6ca72ee8e43e54d772aecadd9b9a6bb849eb8 [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.\"
Darren Tucker43d8e282005-02-09 09:51:08 +110037.\" $OpenBSD: ssh_config.5,v 1.41 2005/01/28 18:14:09 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.
Darren Tucker43d8e282005-02-09 09:51:08 +110066The configuration files contain sections separated by
Ben Lindstrom9f049032002-06-21 00:59:05 +000067.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
Darren Tucker79a7acf2005-02-09 09:48:57 +1100123(use IPv4 only) or
Damien Miller20a8f972003-05-18 20:50:30 +1000124.Dq inet6
Darren Tucker79a7acf2005-02-09 09:48:57 +1100125(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 .
Darren Tucker636ca902004-11-05 20:22:00 +1100470.It Cm KbdInteractiveDevices
471Specifies the list of methods to use in keyboard-interactive authentication.
472Multiple method names must be comma-separated.
473The default is to use the server specified list.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000474.It Cm LocalForward
475Specifies that a TCP/IP port on the local machine be forwarded over
476the secure channel to the specified host and port from the remote machine.
477The first argument must be a port number, and the second must be
478.Ar host:port .
479IPv6 addresses can be specified with an alternative syntax:
480.Ar host/port .
481Multiple forwardings may be specified, and additional
482forwardings can be given on the command line.
483Only the superuser can forward privileged ports.
484.It Cm LogLevel
485Gives the verbosity level that is used when logging messages from
486.Nm ssh .
487The possible values are:
488QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
Damien Miller495dca32003-04-01 21:42:14 +1000489The default is INFO.
490DEBUG and DEBUG1 are equivalent.
491DEBUG2 and DEBUG3 each specify higher levels of verbose output.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000492.It Cm MACs
493Specifies the MAC (message authentication code) algorithms
494in order of preference.
495The MAC algorithm is used in protocol version 2
496for data integrity protection.
497Multiple algorithms must be comma-separated.
498The default is
499.Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
500.It Cm NoHostAuthenticationForLocalhost
501This option can be used if the home directory is shared across machines.
502In this case localhost will refer to a different machine on each of
503the machines and the user will get many warnings about changed host keys.
504However, this option disables host authentication for localhost.
505The argument to this keyword must be
506.Dq yes
507or
508.Dq no .
509The default is to check the host key for localhost.
510.It Cm NumberOfPasswordPrompts
511Specifies the number of password prompts before giving up.
512The argument to this keyword must be an integer.
513Default is 3.
514.It Cm PasswordAuthentication
515Specifies whether to use password authentication.
516The argument to this keyword must be
517.Dq yes
518or
519.Dq no .
520The default is
521.Dq yes .
522.It Cm Port
523Specifies the port number to connect on the remote host.
524Default is 22.
525.It Cm PreferredAuthentications
526Specifies the order in which the client should try protocol 2
Damien Millerfbf486b2003-05-23 18:44:23 +1000527authentication methods.
528This allows a client to prefer one method (e.g.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000529.Cm keyboard-interactive )
530over another method (e.g.
531.Cm password )
532The default for this option is:
533.Dq hostbased,publickey,keyboard-interactive,password .
534.It Cm Protocol
535Specifies the protocol versions
536.Nm ssh
537should support in order of preference.
538The possible values are
539.Dq 1
540and
541.Dq 2 .
542Multiple versions must be comma-separated.
543The default is
544.Dq 2,1 .
545This means that
546.Nm ssh
547tries version 2 and falls back to version 1
548if version 2 is not available.
549.It Cm ProxyCommand
550Specifies the command to use to connect to the server.
551The command
552string extends to the end of the line, and is executed with
553.Pa /bin/sh .
554In the command string,
555.Ql %h
556will be substituted by the host name to
557connect and
558.Ql %p
559by the port.
560The command can be basically anything,
561and should read from its standard input and write to its standard output.
562It should eventually connect an
563.Xr sshd 8
564server running on some machine, or execute
565.Ic sshd -i
566somewhere.
567Host key management will be done using the
568HostName of the host being connected (defaulting to the name typed by
569the user).
Damien Miller495dca32003-04-01 21:42:14 +1000570Setting the command to
571.Dq none
Damien Miller9f1e33a2003-02-24 11:57:32 +1100572disables this option entirely.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000573Note that
574.Cm CheckHostIP
575is not available for connects with a proxy command.
576.Pp
577.It Cm PubkeyAuthentication
578Specifies whether to try public key authentication.
579The argument to this keyword must be
580.Dq yes
581or
582.Dq no .
583The default is
584.Dq yes .
585This option applies to protocol version 2 only.
586.It Cm RemoteForward
587Specifies that a TCP/IP port on the remote machine be forwarded over
588the secure channel to the specified host and port from the local machine.
589The first argument must be a port number, and the second must be
590.Ar host:port .
591IPv6 addresses can be specified with an alternative syntax:
592.Ar host/port .
593Multiple forwardings may be specified, and additional
594forwardings can be given on the command line.
595Only the superuser can forward privileged ports.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000596.It Cm RhostsRSAAuthentication
597Specifies whether to try rhosts based authentication with RSA host
598authentication.
599The argument must be
600.Dq yes
601or
602.Dq no .
603The default is
604.Dq no .
605This option applies to protocol version 1 only and requires
606.Nm ssh
607to be setuid root.
608.It Cm RSAAuthentication
609Specifies whether to try RSA authentication.
610The argument to this keyword must be
611.Dq yes
612or
613.Dq no .
614RSA authentication will only be
615attempted if the identity file exists, or an authentication agent is
616running.
617The default is
618.Dq yes .
619Note that this option applies to protocol version 1 only.
Darren Tucker46bc0752004-05-02 22:11:30 +1000620.It Cm SendEnv
621Specifies what variables from the local
622.Xr environ 7
623should be sent to the server.
624Note that environment passing is only supported for protocol 2, the
Darren Tucker1e0c9bf2004-05-02 22:12:48 +1000625server must also support it, and the server must be configured to
626accept these environment variables.
Darren Tucker46bc0752004-05-02 22:11:30 +1000627Refer to
628.Cm AcceptEnv
629in
630.Xr sshd_config 5
631for how to configure the server.
632Variables are specified by name, which may contain the wildcard characters
633.Ql \&*
634and
635.Ql \&? .
Darren Tucker1e0c9bf2004-05-02 22:12:48 +1000636Multiple environment variables may be separated by whitespace or spread
Darren Tucker46bc0752004-05-02 22:11:30 +1000637across multiple
638.Cm SendEnv
639directives.
640The default is not to send any environment variables.
Damien Miller509b0102003-12-17 16:33:10 +1100641.It Cm ServerAliveInterval
642Sets a timeout interval in seconds after which if no data has been received
643from the server,
644.Nm ssh
645will send a message through the encrypted
646channel to request a response from the server.
647The default
648is 0, indicating that these messages will not be sent to the server.
649This option applies to protocol version 2 only.
650.It Cm ServerAliveCountMax
651Sets the number of server alive messages (see above) which may be
652sent without
653.Nm ssh
654receiving any messages back from the server.
655If this threshold is reached while server alive messages are being sent,
656.Nm ssh
657will disconnect from the server, terminating the session.
658It is important to note that the use of server alive messages is very
659different from
660.Cm TCPKeepAlive
661(below).
662The server alive messages are sent through the encrypted channel
663and therefore will not be spoofable.
664The TCP keepalive option enabled by
665.Cm TCPKeepAlive
666is spoofable.
667The server alive mechanism is valuable when the client or
668server depend on knowing when a connection has become inactive.
669.Pp
670The default value is 3.
671If, for example,
672.Cm ServerAliveInterval
673(above) is set to 15, and
674.Cm ServerAliveCountMax
675is left at the default, if the server becomes unresponsive ssh
676will disconnect after approximately 45 seconds.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000677.It Cm SmartcardDevice
Damien Millerfbf486b2003-05-23 18:44:23 +1000678Specifies which smartcard device to use.
679The argument to this keyword is the device
Ben Lindstrom9f049032002-06-21 00:59:05 +0000680.Nm ssh
681should use to communicate with a smartcard used for storing the user's
Damien Millerfbf486b2003-05-23 18:44:23 +1000682private RSA key.
683By default, no device is specified and smartcard support is not activated.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000684.It Cm StrictHostKeyChecking
685If this flag is set to
686.Dq yes ,
687.Nm ssh
688will never automatically add host keys to the
689.Pa $HOME/.ssh/known_hosts
690file, and refuses to connect to hosts whose host key has changed.
691This provides maximum protection against trojan horse attacks,
692however, can be annoying when the
693.Pa /etc/ssh/ssh_known_hosts
694file is poorly maintained, or connections to new hosts are
695frequently made.
696This option forces the user to manually
697add all new hosts.
698If this flag is set to
699.Dq no ,
700.Nm ssh
701will automatically add new host keys to the
702user known hosts files.
703If this flag is set to
704.Dq ask ,
705new host keys
706will be added to the user known host files only after the user
707has confirmed that is what they really want to do, and
708.Nm ssh
709will refuse to connect to hosts whose host key has changed.
710The host keys of
711known hosts will be verified automatically in all cases.
712The argument must be
713.Dq yes ,
714.Dq no
715or
716.Dq ask .
717The default is
718.Dq ask .
Damien Miller12c150e2003-12-17 16:31:10 +1100719.It Cm TCPKeepAlive
720Specifies whether the system should send TCP keepalive messages to the
721other side.
722If they are sent, death of the connection or crash of one
723of the machines will be properly noticed.
724However, this means that
725connections will die if the route is down temporarily, and some people
726find it annoying.
727.Pp
728The default is
729.Dq yes
730(to send TCP keepalive messages), and the client will notice
731if the network goes down or the remote host dies.
732This is important in scripts, and many users want it too.
733.Pp
734To disable TCP keepalive messages, the value should be set to
735.Dq no .
Ben Lindstrom9f049032002-06-21 00:59:05 +0000736.It Cm UsePrivilegedPort
737Specifies whether to use a privileged port for outgoing connections.
738The argument must be
739.Dq yes
740or
741.Dq no .
742The default is
743.Dq no .
Damien Miller9b1dacd2002-09-04 16:47:35 +1000744If set to
745.Dq yes
746.Nm ssh
747must be setuid root.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000748Note that this option must be set to
749.Dq yes
Darren Tuckerec960f22003-08-13 20:37:05 +1000750for
Ben Lindstrom9f049032002-06-21 00:59:05 +0000751.Cm RhostsRSAAuthentication
Darren Tuckerec960f22003-08-13 20:37:05 +1000752with older servers.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000753.It Cm User
754Specifies the user to log in as.
755This can be useful when a different user name is used on different machines.
756This saves the trouble of
757having to remember to give the user name on the command line.
758.It Cm UserKnownHostsFile
759Specifies a file to use for the user
760host key database instead of
761.Pa $HOME/.ssh/known_hosts .
Damien Miller37876e92003-05-15 10:19:46 +1000762.It Cm VerifyHostKeyDNS
763Specifies whether to verify the remote key using DNS and SSHFP resource
764records.
Damien Miller150b5572003-11-17 21:19:29 +1100765If this option is set to
766.Dq yes ,
Damien Millerfe448472003-11-17 21:19:49 +1100767the client will implicitly trust keys that match a secure fingerprint
Damien Miller150b5572003-11-17 21:19:29 +1100768from DNS.
769Insecure fingerprints will be handled as if this option was set to
770.Dq ask .
771If this option is set to
772.Dq ask ,
773information on fingerprint match will be displayed, but the user will still
774need to confirm new host keys according to the
775.Cm StrictHostKeyChecking
776option.
777The argument must be
778.Dq yes ,
779.Dq no
Damien Millerfe448472003-11-17 21:19:49 +1100780or
781.Dq ask .
Damien Miller37876e92003-05-15 10:19:46 +1000782The default is
783.Dq no .
Damien Millereacbb4f2003-06-02 19:10:41 +1000784Note that this option applies to protocol version 2 only.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000785.It Cm XAuthLocation
Damien Miller05913ba2002-09-04 16:51:03 +1000786Specifies the full pathname of the
Ben Lindstrom9f049032002-06-21 00:59:05 +0000787.Xr xauth 1
788program.
789The default is
790.Pa /usr/X11R6/bin/xauth .
791.El
792.Sh FILES
793.Bl -tag -width Ds
794.It Pa $HOME/.ssh/config
795This is the per-user configuration file.
796The format of this file is described above.
797This file is used by the
798.Nm ssh
799client.
Damien Millerc970cb92004-04-20 20:12:53 +1000800Because of the potential for abuse, this file must have strict permissions:
801read/write for the user, and not accessible by others.
Ben Lindstrom9f049032002-06-21 00:59:05 +0000802.It Pa /etc/ssh/ssh_config
803Systemwide configuration file.
804This file provides defaults for those
805values that are not specified in the user's configuration file, and
806for those users who do not have a configuration file.
807This file must be world-readable.
808.El
Damien Millerf1ce5052003-06-11 22:04:39 +1000809.Sh SEE ALSO
810.Xr ssh 1
Ben Lindstrom9f049032002-06-21 00:59:05 +0000811.Sh AUTHORS
812OpenSSH is a derivative of the original and free
813ssh 1.2.12 release by Tatu Ylonen.
814Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
815Theo de Raadt and Dug Song
816removed many bugs, re-added newer features and
817created OpenSSH.
818Markus Friedl contributed the support for SSH
819protocol versions 1.5 and 2.0.