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authorColin Watson <cjwatson@debian.org>2003-09-23 17:49:41 +0000
committerColin Watson <cjwatson@debian.org>2003-09-23 17:49:41 +0000
commit45431c9b4677608680cd071768cbf156b316a7e8 (patch)
tree9dd03d2cda2d52d8457ec7ae06902fbe0496e1e0 /ssh_config.0
parent6dbe10d82295512af03b81649c26841381318996 (diff)
parent9221adce6959801664fd4a340c19e6b69107ad0b (diff)
Import OpenSSH 3.7.1p2.
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1SSH_CONFIG(5) OpenBSD Programmer's Manual SSH_CONFIG(5)
2
3NAME
4 ssh_config - OpenSSH SSH client configuration files
5
6SYNOPSIS
7 $HOME/.ssh/config
8 /etc/ssh/ssh_config
9
10DESCRIPTION
11 ssh obtains configuration data from the following sources in the follow-
12 ing order:
13 1. command-line options
14 2. user's configuration file ($HOME/.ssh/config)
15 3. system-wide configuration file (/etc/ssh/ssh_config)
16
17 For each parameter, the first obtained value will be used. The configu-
18 ration files contain sections bracketed by ``Host'' specifications, and
19 that section is only applied for hosts that match one of the patterns
20 given in the specification. The matched host name is the one given on
21 the command line.
22
23 Since the first obtained value for each parameter is used, more host-spe-
24 cific declarations should be given near the beginning of the file, and
25 general defaults at the end.
26
27 The configuration file has the following format:
28
29 Empty lines and lines starting with `#' are comments.
30
31 Otherwise a line is of the format ``keyword arguments''. Configuration
32 options may be separated by whitespace or optional whitespace and exactly
33 one `='; the latter format is useful to avoid the need to quote whites-
34 pace when specifying configuration options using the ssh, scp and sftp -o
35 option.
36
37 The possible keywords and their meanings are as follows (note that key-
38 words are case-insensitive and arguments are case-sensitive):
39
40 Host Restricts the following declarations (up to the next Host key-
41 word) to be only for those hosts that match one of the patterns
42 given after the keyword. `*' and `?' can be used as wildcards in
43 the patterns. A single `*' as a pattern can be used to provide
44 global defaults for all hosts. The host is the hostname argument
45 given on the command line (i.e., the name is not converted to a
46 canonicalized host name before matching).
47
48 AddressFamily
49 Specifies which address family to use when connecting. Valid ar-
50 guments are ``any'', ``inet'' (Use IPv4 only) or ``inet6'' (Use
51 IPv6 only.)
52
53 BatchMode
54 If set to ``yes'', passphrase/password querying will be disabled.
55 This option is useful in scripts and other batch jobs where no
56 user is present to supply the password. The argument must be
57 ``yes'' or ``no''. The default is ``no''.
58
59 BindAddress
60 Specify the interface to transmit from on machines with multiple
61 interfaces or aliased addresses. Note that this option does not
62 work if UsePrivilegedPort is set to ``yes''.
63
64 ChallengeResponseAuthentication
65 Specifies whether to use challenge response authentication. The
66 argument to this keyword must be ``yes'' or ``no''. The default
67 is ``yes''.
68
69 CheckHostIP
70 If this flag is set to ``yes'', ssh will additionally check the
71 host IP address in the known_hosts file. This allows ssh to de-
72 tect if a host key changed due to DNS spoofing. If the option is
73 set to ``no'', the check will not be executed. The default is
74 ``yes''.
75
76 Cipher Specifies the cipher to use for encrypting the session in proto-
77 col version 1. Currently, ``blowfish'', ``3des'', and ``des''
78 are supported. des is only supported in the ssh client for in-
79 teroperability with legacy protocol 1 implementations that do not
80 support the 3des cipher. Its use is strongly discouraged due to
81 cryptographic weaknesses. The default is ``3des''.
82
83 Ciphers
84 Specifies the ciphers allowed for protocol version 2 in order of
85 preference. Multiple ciphers must be comma-separated. The de-
86 fault is
87
88 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
89 aes192-cbc,aes256-cbc''
90
91 ClearAllForwardings
92 Specifies that all local, remote and dynamic port forwardings
93 specified in the configuration files or on the command line be
94 cleared. This option is primarily useful when used from the ssh
95 command line to clear port forwardings set in configuration
96 files, and is automatically set by scp(1) and sftp(1). The argu-
97 ment must be ``yes'' or ``no''. The default is ``no''.
98
99 Compression
100 Specifies whether to use compression. The argument must be
101 ``yes'' or ``no''. The default is ``no''.
102
103 CompressionLevel
104 Specifies the compression level to use if compression is enabled.
105 The argument must be an integer from 1 (fast) to 9 (slow, best).
106 The default level is 6, which is good for most applications. The
107 meaning of the values is the same as in gzip(1). Note that this
108 option applies to protocol version 1 only.
109
110 ConnectionAttempts
111 Specifies the number of tries (one per second) to make before ex-
112 iting. The argument must be an integer. This may be useful in
113 scripts if the connection sometimes fails. The default is 1.
114
115 ConnectTimeout
116 Specifies the timeout (in seconds) used when connecting to the
117 ssh server, instead of using the default system TCP timeout.
118 This value is used only when the target is down or really un-
119 reachable, not when it refuses the connection.
120
121 DynamicForward
122 Specifies that a TCP/IP port on the local machine be forwarded
123 over the secure channel, and the application protocol is then
124 used to determine where to connect to from the remote machine.
125 The argument must be a port number. Currently the SOCKS4 and
126 SOCKS5 protocols are supported, and ssh will act as a SOCKS serv-
127 er. Multiple forwardings may be specified, and additional for-
128 wardings can be given on the command line. Only the superuser
129 can forward privileged ports.
130
131 EnableSSHKeysign
132 Setting this option to ``yes'' in the global client configuration
133 file /etc/ssh/ssh_config enables the use of the helper program
134 ssh-keysign(8) during HostbasedAuthentication. The argument must
135 be ``yes'' or ``no''. The default is ``no''. See ssh-keysign(8)
136 for more information.
137
138 EscapeChar
139 Sets the escape character (default: `~'). The escape character
140 can also be set on the command line. The argument should be a
141 single character, `^' followed by a letter, or ``none'' to dis-
142 able the escape character entirely (making the connection trans-
143 parent for binary data).
144
145 ForwardAgent
146 Specifies whether the connection to the authentication agent (if
147 any) will be forwarded to the remote machine. The argument must
148 be ``yes'' or ``no''. The default is ``no''.
149
150 Agent forwarding should be enabled with caution. Users with the
151 ability to bypass file permissions on the remote host (for the
152 agent's Unix-domain socket) can access the local agent through
153 the forwarded connection. An attacker cannot obtain key material
154 from the agent, however they can perform operations on the keys
155 that enable them to authenticate using the identities loaded into
156 the agent.
157
158 ForwardX11
159 Specifies whether X11 connections will be automatically redirect-
160 ed over the secure channel and DISPLAY set. The argument must be
161 ``yes'' or ``no''. The default is ``no''.
162
163 X11 forwarding should be enabled with caution. Users with the
164 ability to bypass file permissions on the remote host (for the
165 user's X authorization database) can access the local X11 display
166 through the forwarded connection. An attacker may then be able
167 to perform activities such as keystroke monitoring.
168
169 GatewayPorts
170 Specifies whether remote hosts are allowed to connect to local
171 forwarded ports. By default, ssh binds local port forwardings to
172 the loopback address. This prevents other remote hosts from con-
173 necting to forwarded ports. GatewayPorts can be used to specify
174 that ssh should bind local port forwardings to the wildcard ad-
175 dress, thus allowing remote hosts to connect to forwarded ports.
176 The argument must be ``yes'' or ``no''. The default is ``no''.
177
178 GlobalKnownHostsFile
179 Specifies a file to use for the global host key database instead
180 of /etc/ssh/ssh_known_hosts.
181
182 GSSAPIAuthentication
183 Specifies whether authentication based on GSSAPI may be used, ei-
184 ther using the result of a successful key exchange, or using GSS-
185 API user authentication. The default is ``yes''. Note that this
186 option applies to protocol version 2 only.
187
188 GSSAPIDelegateCredentials
189 Forward (delegate) credentials to the server. The default is
190 ``no''. Note that this option applies to protocol version 2 on-
191 ly.
192
193 HostbasedAuthentication
194 Specifies whether to try rhosts based authentication with public
195 key authentication. The argument must be ``yes'' or ``no''. The
196 default is ``no''. This option applies to protocol version 2 on-
197 ly and is similar to RhostsRSAAuthentication.
198
199 HostKeyAlgorithms
200 Specifies the protocol version 2 host key algorithms that the
201 client wants to use in order of preference. The default for this
202 option is: ``ssh-rsa,ssh-dss''.
203
204 HostKeyAlias
205 Specifies an alias that should be used instead of the real host
206 name when looking up or saving the host key in the host key
207 database files. This option is useful for tunneling ssh connec-
208 tions or for multiple servers running on a single host.
209
210 HostName
211 Specifies the real host name to log into. This can be used to
212 specify nicknames or abbreviations for hosts. Default is the
213 name given on the command line. Numeric IP addresses are also
214 permitted (both on the command line and in HostName specifica-
215 tions).
216
217 IdentityFile
218 Specifies a file from which the user's RSA or DSA authentication
219 identity is read. The default is $HOME/.ssh/identity for proto-
220 col version 1, and $HOME/.ssh/id_rsa and $HOME/.ssh/id_dsa for
221 protocol version 2. Additionally, any identities represented by
222 the authentication agent will be used for authentication. The
223 file name may use the tilde syntax to refer to a user's home di-
224 rectory. It is possible to have multiple identity files speci-
225 fied in configuration files; all these identities will be tried
226 in sequence.
227
228 KeepAlive
229 Specifies whether the system should send TCP keepalive messages
230 to the other side. If they are sent, death of the connection or
231 crash of one of the machines will be properly noticed. However,
232 this means that connections will die if the route is down tem-
233 porarily, and some people find it annoying.
234
235 The default is ``yes'' (to send keepalives), and the client will
236 notice if the network goes down or the remote host dies. This is
237 important in scripts, and many users want it too.
238
239 To disable keepalives, the value should be set to ``no''.
240
241 LocalForward
242 Specifies that a TCP/IP port on the local machine be forwarded
243 over the secure channel to the specified host and port from the
244 remote machine. The first argument must be a port number, and
245 the second must be host:port. IPv6 addresses can be specified
246 with an alternative syntax: host/port. Multiple forwardings may
247 be specified, and additional forwardings can be given on the com-
248 mand line. Only the superuser can forward privileged ports.
249
250 LogLevel
251 Gives the verbosity level that is used when logging messages from
252 ssh. The possible values are: QUIET, FATAL, ERROR, INFO, VER-
253 BOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3. The default is INFO.
254 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
255 higher levels of verbose output.
256
257 MACs Specifies the MAC (message authentication code) algorithms in or-
258 der of preference. The MAC algorithm is used in protocol version
259 2 for data integrity protection. Multiple algorithms must be
260 comma-separated. The default is ``hmac-md5,hmac-sha1,hmac-
261 ripemd160,hmac-sha1-96,hmac-md5-96''.
262
263 NoHostAuthenticationForLocalhost
264 This option can be used if the home directory is shared across
265 machines. In this case localhost will refer to a different ma-
266 chine on each of the machines and the user will get many warnings
267 about changed host keys. However, this option disables host au-
268 thentication for localhost. The argument to this keyword must be
269 ``yes'' or ``no''. The default is to check the host key for lo-
270 calhost.
271
272 NumberOfPasswordPrompts
273 Specifies the number of password prompts before giving up. The
274 argument to this keyword must be an integer. Default is 3.
275
276 PasswordAuthentication
277 Specifies whether to use password authentication. The argument
278 to this keyword must be ``yes'' or ``no''. The default is
279 ``yes''.
280
281 Port Specifies the port number to connect on the remote host. Default
282 is 22.
283
284 PreferredAuthentications
285 Specifies the order in which the client should try protocol 2 au-
286 thentication methods. This allows a client to prefer one method
287 (e.g. keyboard-interactive) over another method (e.g. password)
288 The default for this option is: ``hostbased,publickey,keyboard-
289 interactive,password''.
290
291 Protocol
292 Specifies the protocol versions ssh should support in order of
293 preference. The possible values are ``1'' and ``2''. Multiple
294 versions must be comma-separated. The default is ``2,1''. This
295 means that ssh tries version 2 and falls back to version 1 if
296 version 2 is not available.
297
298 ProxyCommand
299 Specifies the command to use to connect to the server. The com-
300 mand string extends to the end of the line, and is executed with
301 /bin/sh. In the command string, `%h' will be substituted by the
302 host name to connect and `%p' by the port. The command can be
303 basically anything, and should read from its standard input and
304 write to its standard output. It should eventually connect an
305 sshd(8) server running on some machine, or execute sshd -i some-
306 where. Host key management will be done using the HostName of
307 the host being connected (defaulting to the name typed by the us-
308 er). Setting the command to ``none'' disables this option en-
309 tirely. Note that CheckHostIP is not available for connects with
310 a proxy command.
311
312 PubkeyAuthentication
313 Specifies whether to try public key authentication. The argument
314 to this keyword must be ``yes'' or ``no''. The default is
315 ``yes''. This option applies to protocol version 2 only.
316
317 RemoteForward
318 Specifies that a TCP/IP port on the remote machine be forwarded
319 over the secure channel to the specified host and port from the
320 local machine. The first argument must be a port number, and the
321 second must be host:port. IPv6 addresses can be specified with
322 an alternative syntax: host/port. Multiple forwardings may be
323 specified, and additional forwardings can be given on the command
324 line. Only the superuser can forward privileged ports.
325
326 RhostsRSAAuthentication
327 Specifies whether to try rhosts based authentication with RSA
328 host authentication. The argument must be ``yes'' or ``no''.
329 The default is ``no''. This option applies to protocol version 1
330 only and requires ssh to be setuid root.
331
332 RSAAuthentication
333 Specifies whether to try RSA authentication. The argument to
334 this keyword must be ``yes'' or ``no''. RSA authentication will
335 only be attempted if the identity file exists, or an authentica-
336 tion agent is running. The default is ``yes''. Note that this
337 option applies to protocol version 1 only.
338
339 SmartcardDevice
340 Specifies which smartcard device to use. The argument to this
341 keyword is the device ssh should use to communicate with a smart-
342 card used for storing the user's private RSA key. By default, no
343 device is specified and smartcard support is not activated.
344
345 StrictHostKeyChecking
346 If this flag is set to ``yes'', ssh will never automatically add
347 host keys to the $HOME/.ssh/known_hosts file, and refuses to con-
348 nect to hosts whose host key has changed. This provides maximum
349 protection against trojan horse attacks, however, can be annoying
350 when the /etc/ssh/ssh_known_hosts file is poorly maintained, or
351 connections to new hosts are frequently made. This option forces
352 the user to manually add all new hosts. If this flag is set to
353 ``no'', ssh will automatically add new host keys to the user
354 known hosts files. If this flag is set to ``ask'', new host keys
355 will be added to the user known host files only after the user
356 has confirmed that is what they really want to do, and ssh will
357 refuse to connect to hosts whose host key has changed. The host
358 keys of known hosts will be verified automatically in all cases.
359 The argument must be ``yes'', ``no'' or ``ask''. The default is
360 ``ask''.
361
362 UsePrivilegedPort
363 Specifies whether to use a privileged port for outgoing connec-
364 tions. The argument must be ``yes'' or ``no''. The default is
365 ``no''. If set to ``yes'' ssh must be setuid root. Note that
366 this option must be set to ``yes'' for RhostsRSAAuthentication
367 with older servers.
368
369 User Specifies the user to log in as. This can be useful when a dif-
370 ferent user name is used on different machines. This saves the
371 trouble of having to remember to give the user name on the com-
372 mand line.
373
374 UserKnownHostsFile
375 Specifies a file to use for the user host key database instead of
376 $HOME/.ssh/known_hosts.
377
378 VerifyHostKeyDNS
379 Specifies whether to verify the remote key using DNS and SSHFP
380 resource records. The default is ``no''. Note that this option
381 applies to protocol version 2 only.
382
383 XAuthLocation
384 Specifies the full pathname of the xauth(1) program. The default
385 is /usr/X11R6/bin/xauth.
386
387FILES
388 $HOME/.ssh/config
389 This is the per-user configuration file. The format of this file
390 is described above. This file is used by the ssh client. This
391 file does not usually contain any sensitive information, but the
392 recommended permissions are read/write for the user, and not ac-
393 cessible by others.
394
395 /etc/ssh/ssh_config
396 Systemwide configuration file. This file provides defaults for
397 those values that are not specified in the user's configuration
398 file, and for those users who do not have a configuration file.
399 This file must be world-readable.
400
401SEE ALSO
402 ssh(1)
403
404AUTHORS
405 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
406 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
407 de Raadt and Dug Song removed many bugs, re-added newer features and cre-
408 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
409 versions 1.5 and 2.0.
410
411OpenBSD 3.4 September 25, 1999 7