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588df31a | 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 | .\" | |
a274ba38 | 37 | .\" $OpenBSD: ssh_config.5,v 1.69 2005/12/08 21:37:50 jmc Exp $ |
588df31a | 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 | |
140e3e97 | 46 | .It Pa ~/.ssh/config |
588df31a | 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: | |
4dcbbeea | 53 | .Bl -enum -offset indent -compact |
54 | .It | |
55 | command-line options | |
56 | .It | |
57 | user's configuration file | |
140e3e97 | 58 | .Pq Pa ~/.ssh/config |
4dcbbeea | 59 | .It |
60 | system-wide configuration file | |
61 | .Pq Pa /etc/ssh/ssh_config | |
62 | .El | |
588df31a | 63 | .Pp |
64 | For each parameter, the first obtained value | |
65 | will be used. | |
7034edae | 66 | The configuration files contain sections separated by |
588df31a | 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 | |
d0445371 | 107 | .Ql \&? |
588df31a | 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). | |
f811e52a | 118 | .It Cm AddressFamily |
3cbc677d | 119 | Specifies which address family to use when connecting. |
120 | Valid arguments are | |
f811e52a | 121 | .Dq any , |
122 | .Dq inet | |
0d6cbe2c | 123 | (use IPv4 only) or |
f811e52a | 124 | .Dq inet6 |
0d6cbe2c | 125 | (use IPv6 only). |
588df31a | 126 | .It Cm BatchMode |
127 | If set to | |
128 | .Dq yes , | |
129 | passphrase/password querying will be disabled. | |
130 | This option is useful in scripts and other batch jobs where no user | |
131 | is present to supply the password. | |
132 | The argument must be | |
133 | .Dq yes | |
134 | or | |
135 | .Dq no . | |
136 | The default is | |
137 | .Dq no . | |
138 | .It Cm BindAddress | |
1a8521be | 139 | Use the specified address on the local machine as the source address of |
82b7531b | 140 | the connection. |
141 | Only useful on systems with more than one address. | |
588df31a | 142 | Note that this option does not work if |
143 | .Cm UsePrivilegedPort | |
144 | is set to | |
145 | .Dq yes . | |
146 | .It Cm ChallengeResponseAuthentication | |
147 | Specifies whether to use challenge response authentication. | |
148 | The argument to this keyword must be | |
149 | .Dq yes | |
150 | or | |
151 | .Dq no . | |
152 | The default is | |
153 | .Dq yes . | |
154 | .It Cm CheckHostIP | |
155 | If this flag is set to | |
156 | .Dq yes , | |
157 | ssh will additionally check the host IP address in the | |
158 | .Pa known_hosts | |
159 | file. | |
160 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
161 | If the option is set to | |
162 | .Dq no , | |
163 | the check will not be executed. | |
164 | The default is | |
165 | .Dq yes . | |
166 | .It Cm Cipher | |
167 | Specifies the cipher to use for encrypting the session | |
168 | in protocol version 1. | |
169 | Currently, | |
170 | .Dq blowfish , | |
171 | .Dq 3des , | |
172 | and | |
173 | .Dq des | |
174 | are supported. | |
175 | .Ar des | |
176 | is only supported in the | |
177 | .Nm ssh | |
178 | client for interoperability with legacy protocol 1 implementations | |
179 | that do not support the | |
180 | .Ar 3des | |
a4e5acef | 181 | cipher. |
182 | Its use is strongly discouraged due to cryptographic weaknesses. | |
588df31a | 183 | The default is |
184 | .Dq 3des . | |
185 | .It Cm Ciphers | |
186 | Specifies the ciphers allowed for protocol version 2 | |
187 | in order of preference. | |
188 | Multiple ciphers must be comma-separated. | |
3b9baa7b | 189 | The supported ciphers are |
190 | .Dq 3des-cbc , | |
191 | .Dq aes128-cbc , | |
192 | .Dq aes192-cbc , | |
193 | .Dq aes256-cbc , | |
194 | .Dq aes128-ctr , | |
195 | .Dq aes192-ctr , | |
196 | .Dq aes256-ctr , | |
74a66cc8 | 197 | .Dq arcfour128 , |
198 | .Dq arcfour256 , | |
3b9baa7b | 199 | .Dq arcfour , |
200 | .Dq blowfish-cbc , | |
201 | and | |
202 | .Dq cast128-cbc . | |
588df31a | 203 | The default is |
588df31a | 204 | .Bd -literal |
74a66cc8 | 205 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, |
206 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
207 | aes192-ctr,aes256-ctr'' | |
588df31a | 208 | .Ed |
209 | .It Cm ClearAllForwardings | |
210 | Specifies that all local, remote and dynamic port forwardings | |
211 | specified in the configuration files or on the command line be | |
a4e5acef | 212 | cleared. |
213 | This option is primarily useful when used from the | |
588df31a | 214 | .Nm ssh |
215 | command line to clear port forwardings set in | |
216 | configuration files, and is automatically set by | |
217 | .Xr scp 1 | |
218 | and | |
219 | .Xr sftp 1 . | |
220 | The argument must be | |
221 | .Dq yes | |
222 | or | |
223 | .Dq no . | |
224 | The default is | |
225 | .Dq no . | |
226 | .It Cm Compression | |
227 | Specifies whether to use compression. | |
228 | The argument must be | |
229 | .Dq yes | |
230 | or | |
231 | .Dq no . | |
232 | The default is | |
233 | .Dq no . | |
234 | .It Cm CompressionLevel | |
235 | Specifies the compression level to use if compression is enabled. | |
236 | The argument must be an integer from 1 (fast) to 9 (slow, best). | |
237 | The default level is 6, which is good for most applications. | |
238 | The meaning of the values is the same as in | |
239 | .Xr gzip 1 . | |
240 | Note that this option applies to protocol version 1 only. | |
241 | .It Cm ConnectionAttempts | |
242 | Specifies the number of tries (one per second) to make before exiting. | |
243 | The argument must be an integer. | |
244 | This may be useful in scripts if the connection sometimes fails. | |
245 | The default is 1. | |
09ab3296 | 246 | .It Cm ConnectTimeout |
247 | Specifies the timeout (in seconds) used when connecting to the ssh | |
3cbc677d | 248 | server, instead of using the default system TCP timeout. |
249 | This value is used only when the target is down or really unreachable, | |
250 | not when it refuses the connection. | |
5e96b616 | 251 | .It Cm ControlMaster |
252 | Enables the sharing of multiple sessions over a single network connection. | |
253 | When set to | |
254 | .Dq yes | |
255 | .Nm ssh | |
256 | will listen for connections on a control socket specified using the | |
257 | .Cm ControlPath | |
258 | argument. | |
259 | Additional sessions can connect to this socket using the same | |
260 | .Cm ControlPath | |
261 | with | |
262 | .Cm ControlMaster | |
263 | set to | |
264 | .Dq no | |
9a5cfb58 | 265 | (the default). |
db98627d | 266 | These sessions will try to reuse the master instance's network connection |
6b0b0d65 | 267 | rather than initiating new ones, but will fall back to connecting normally |
268 | if the control socket does not exist, or is not listening. | |
269 | .Pp | |
0d34d6ce | 270 | Setting this to |
271 | .Dq ask | |
272 | will cause | |
273 | .Nm ssh | |
274 | to listen for control connections, but require confirmation using the | |
275 | .Ev SSH_ASKPASS | |
276 | program before they are accepted (see | |
277 | .Xr ssh-add 1 | |
9a5cfb58 | 278 | for details). |
cc8ca1e6 | 279 | If the |
280 | .Cm ControlPath | |
281 | can not be opened, | |
282 | .Nm ssh | |
283 | will continue without connecting to a master instance. | |
9dfd96d6 | 284 | .Pp |
ef07103c | 285 | X11 and |
d313869b | 286 | .Xr ssh-agent 1 |
ef07103c | 287 | forwarding is supported over these multiplexed connections, however the |
288 | display and agent fowarded will be the one belonging to the master | |
d313869b | 289 | connection i.e. it is not possible to forward multiple displays or agents. |
ef07103c | 290 | .Pp |
9dfd96d6 | 291 | Two additional options allow for opportunistic multiplexing: try to use a |
292 | master connection but fall back to creating a new one if one does not already | |
293 | exist. | |
294 | These options are: | |
295 | .Dq auto | |
296 | and | |
297 | .Dq autoask . | |
298 | The latter requires confirmation like the | |
299 | .Dq ask | |
300 | option. | |
5e96b616 | 301 | .It Cm ControlPath |
a980cbd7 | 302 | Specify the path to the control socket used for connection sharing as described |
303 | in the | |
5e96b616 | 304 | .Cm ControlMaster |
699255b5 | 305 | section above or the string |
306 | .Dq none | |
307 | to disable connection sharing. | |
a980cbd7 | 308 | In the path, |
309 | .Ql %h | |
310 | will be substituted by the target host name, | |
311 | .Ql %p | |
312 | the port and | |
313 | .Ql %r | |
314 | by the remote login username. | |
9dfd96d6 | 315 | It is recommended that any |
316 | .Cm ControlPath | |
317 | used for opportunistic connection sharing include | |
318 | all three of these escape sequences. | |
319 | This ensures that shared connections are uniquely identified. | |
9a5cfb58 | 320 | .It Cm DynamicForward |
321 | Specifies that a TCP/IP port on the local machine be forwarded | |
322 | over the secure channel, and the application | |
323 | protocol is then used to determine where to connect to from the | |
324 | remote machine. | |
5ddc5eb4 | 325 | .Pp |
326 | The argument must be | |
327 | .Sm off | |
328 | .Oo Ar bind_address : Oc Ar port . | |
329 | .Sm on | |
330 | IPv6 addresses can be specified by enclosing addresses in square brackets or | |
331 | by using an alternative syntax: | |
332 | .Oo Ar bind_address Ns / Oc Ns Ar port . | |
333 | By default, the local port is bound in accordance with the | |
334 | .Cm GatewayPorts | |
335 | setting. | |
336 | However, an explicit | |
337 | .Ar bind_address | |
338 | may be used to bind the connection to a specific address. | |
339 | The | |
340 | .Ar bind_address | |
341 | of | |
342 | .Dq localhost | |
343 | indicates that the listening port be bound for local use only, while an | |
344 | empty address or | |
345 | .Sq * | |
346 | indicates that the port should be available from all interfaces. | |
347 | .Pp | |
9a5cfb58 | 348 | Currently the SOCKS4 and SOCKS5 protocols are supported, and |
349 | .Nm ssh | |
350 | will act as a SOCKS server. | |
351 | Multiple forwardings may be specified, and | |
352 | additional forwardings can be given on the command line. | |
353 | Only the superuser can forward privileged ports. | |
f0677b69 | 354 | .It Cm EnableSSHKeysign |
355 | Setting this option to | |
356 | .Dq yes | |
357 | in the global client configuration file | |
358 | .Pa /etc/ssh/ssh_config | |
359 | enables the use of the helper program | |
360 | .Xr ssh-keysign 8 | |
361 | during | |
362 | .Cm HostbasedAuthentication . | |
363 | The argument must be | |
364 | .Dq yes | |
365 | or | |
366 | .Dq no . | |
367 | The default is | |
368 | .Dq no . | |
246bb171 | 369 | This option should be placed in the non-hostspecific section. |
f0677b69 | 370 | See |
371 | .Xr ssh-keysign 8 | |
372 | for more information. | |
588df31a | 373 | .It Cm EscapeChar |
374 | Sets the escape character (default: | |
375 | .Ql ~ ) . | |
376 | The escape character can also | |
377 | be set on the command line. | |
378 | The argument should be a single character, | |
379 | .Ql ^ | |
380 | followed by a letter, or | |
381 | .Dq none | |
382 | to disable the escape | |
383 | character entirely (making the connection transparent for binary | |
384 | data). | |
385 | .It Cm ForwardAgent | |
386 | Specifies whether the connection to the authentication agent (if any) | |
387 | will be forwarded to the remote machine. | |
388 | The argument must be | |
389 | .Dq yes | |
390 | or | |
391 | .Dq no . | |
392 | The default is | |
393 | .Dq no . | |
dbcdea68 | 394 | .Pp |
a4e5acef | 395 | Agent forwarding should be enabled with caution. |
396 | Users with the ability to bypass file permissions on the remote host | |
397 | (for the agent's Unix-domain socket) | |
398 | can access the local agent through the forwarded connection. | |
399 | An attacker cannot obtain key material from the agent, | |
dbcdea68 | 400 | however they can perform operations on the keys that enable them to |
401 | authenticate using the identities loaded into the agent. | |
588df31a | 402 | .It Cm ForwardX11 |
403 | Specifies whether X11 connections will be automatically redirected | |
404 | over the secure channel and | |
405 | .Ev DISPLAY | |
406 | set. | |
407 | The argument must be | |
408 | .Dq yes | |
409 | or | |
410 | .Dq no . | |
411 | The default is | |
412 | .Dq no . | |
dbcdea68 | 413 | .Pp |
a4e5acef | 414 | X11 forwarding should be enabled with caution. |
415 | Users with the ability to bypass file permissions on the remote host | |
d73a67d7 | 416 | (for the user's X11 authorization database) |
a4e5acef | 417 | can access the local X11 display through the forwarded connection. |
d73a67d7 | 418 | An attacker may then be able to perform activities such as keystroke monitoring |
419 | if the | |
420 | .Cm ForwardX11Trusted | |
421 | option is also enabled. | |
422 | .It Cm ForwardX11Trusted | |
b2e90ab5 | 423 | If this option is set to |
d73a67d7 | 424 | .Dq yes |
425 | then remote X11 clients will have full access to the original X11 display. | |
9a6b3b7a | 426 | .Pp |
d73a67d7 | 427 | If this option is set to |
428 | .Dq no | |
429 | then remote X11 clients will be considered untrusted and prevented | |
430 | from stealing or tampering with data belonging to trusted X11 | |
431 | clients. | |
9a6b3b7a | 432 | Furthermore, the |
433 | .Xr xauth 1 | |
434 | token used for the session will be set to expire after 20 minutes. | |
435 | Remote clients will be refused access after this time. | |
d73a67d7 | 436 | .Pp |
437 | The default is | |
438 | .Dq no . | |
439 | .Pp | |
440 | See the X11 SECURITY extension specification for full details on | |
441 | the restrictions imposed on untrusted clients. | |
588df31a | 442 | .It Cm GatewayPorts |
443 | Specifies whether remote hosts are allowed to connect to local | |
444 | forwarded ports. | |
445 | By default, | |
446 | .Nm ssh | |
a4e5acef | 447 | binds local port forwardings to the loopback address. |
448 | This prevents other remote hosts from connecting to forwarded ports. | |
588df31a | 449 | .Cm GatewayPorts |
450 | can be used to specify that | |
451 | .Nm ssh | |
452 | should bind local port forwardings to the wildcard address, | |
453 | thus allowing remote hosts to connect to forwarded ports. | |
454 | The argument must be | |
455 | .Dq yes | |
456 | or | |
457 | .Dq no . | |
458 | The default is | |
459 | .Dq no . | |
460 | .It Cm GlobalKnownHostsFile | |
461 | Specifies a file to use for the global | |
462 | host key database instead of | |
463 | .Pa /etc/ssh/ssh_known_hosts . | |
7364bd04 | 464 | .It Cm GSSAPIAuthentication |
e8dd24a8 | 465 | Specifies whether user authentication based on GSSAPI is allowed. |
d0445371 | 466 | The default is |
2ecb78df | 467 | .Dq no . |
7364bd04 | 468 | Note that this option applies to protocol version 2 only. |
469 | .It Cm GSSAPIDelegateCredentials | |
470 | Forward (delegate) credentials to the server. | |
471 | The default is | |
472 | .Dq no . | |
473 | Note that this option applies to protocol version 2 only. | |
5c63c2ab | 474 | .It Cm HashKnownHosts |
475 | Indicates that | |
476 | .Nm ssh | |
477 | should hash host names and addresses when they are added to | |
140e3e97 | 478 | .Pa ~/.ssh/known_hosts . |
5c63c2ab | 479 | These hashed names may be used normally by |
480 | .Nm ssh | |
481 | and | |
482 | .Nm sshd , | |
483 | but they do not reveal identifying information should the file's contents | |
484 | be disclosed. | |
485 | The default is | |
486 | .Dq no . | |
cd8f998c | 487 | Note that hashing of names and addresses will not be retrospectively applied |
bdffbcdc | 488 | to existing known hosts files, but these may be manually hashed using |
489 | .Xr ssh-keygen 1 . | |
588df31a | 490 | .It Cm HostbasedAuthentication |
491 | Specifies whether to try rhosts based authentication with public key | |
492 | authentication. | |
493 | The argument must be | |
494 | .Dq yes | |
495 | or | |
496 | .Dq no . | |
497 | The default is | |
498 | .Dq no . | |
499 | This option applies to protocol version 2 only and | |
500 | is similar to | |
501 | .Cm RhostsRSAAuthentication . | |
502 | .It Cm HostKeyAlgorithms | |
503 | Specifies the protocol version 2 host key algorithms | |
504 | that the client wants to use in order of preference. | |
505 | The default for this option is: | |
506 | .Dq ssh-rsa,ssh-dss . | |
507 | .It Cm HostKeyAlias | |
508 | Specifies an alias that should be used instead of the | |
509 | real host name when looking up or saving the host key | |
510 | in the host key database files. | |
511 | This option is useful for tunneling ssh connections | |
512 | or for multiple servers running on a single host. | |
513 | .It Cm HostName | |
514 | Specifies the real host name to log into. | |
515 | This can be used to specify nicknames or abbreviations for hosts. | |
516 | Default is the name given on the command line. | |
517 | Numeric IP addresses are also permitted (both on the command line and in | |
518 | .Cm HostName | |
519 | specifications). | |
3a065ed0 | 520 | .It Cm IdentitiesOnly |
521 | Specifies that | |
522 | .Nm ssh | |
523 | should only use the authentication identity files configured in the | |
1e9b1b82 | 524 | .Nm |
3a065ed0 | 525 | files, |
526 | even if the | |
527 | .Nm ssh-agent | |
528 | offers more identities. | |
529 | The argument to this keyword must be | |
530 | .Dq yes | |
531 | or | |
532 | .Dq no . | |
533 | This option is intented for situations where | |
534 | .Nm ssh-agent | |
535 | offers many different identities. | |
536 | The default is | |
537 | .Dq no . | |
030723f9 | 538 | .It Cm IdentityFile |
539 | Specifies a file from which the user's RSA or DSA authentication identity | |
540 | is read. | |
541 | The default is | |
542 | .Pa ~/.ssh/identity | |
543 | for protocol version 1, and | |
544 | .Pa ~/.ssh/id_rsa | |
545 | and | |
546 | .Pa ~/.ssh/id_dsa | |
547 | for protocol version 2. | |
548 | Additionally, any identities represented by the authentication agent | |
549 | will be used for authentication. | |
550 | The file name may use the tilde | |
551 | syntax to refer to a user's home directory. | |
552 | It is possible to have | |
553 | multiple identity files specified in configuration files; all these | |
554 | identities will be tried in sequence. | |
396070f8 | 555 | .It Cm KbdInteractiveDevices |
556 | Specifies the list of methods to use in keyboard-interactive authentication. | |
557 | Multiple method names must be comma-separated. | |
558 | The default is to use the server specified list. | |
d20f3c9e | 559 | .It Cm LocalCommand |
560 | Specifies a command to execute on the local machine after successfully | |
561 | connecting to the server. | |
562 | The command string extends to the end of the line, and is executed with | |
563 | .Pa /bin/sh . | |
564 | This directive is ignored unless | |
565 | .Cm PermitLocalCommand | |
566 | has been enabled. | |
588df31a | 567 | .It Cm LocalForward |
568 | Specifies that a TCP/IP port on the local machine be forwarded over | |
569 | the secure channel to the specified host and port from the remote machine. | |
ecda4ffb | 570 | The first argument must be |
3867aa0a | 571 | .Sm off |
ecda4ffb | 572 | .Oo Ar bind_address : Oc Ar port |
3867aa0a | 573 | .Sm on |
ecda4ffb | 574 | and the second argument must be |
575 | .Ar host : Ns Ar hostport . | |
cd8f998c | 576 | IPv6 addresses can be specified by enclosing addresses in square brackets or |
3867aa0a | 577 | by using an alternative syntax: |
ecda4ffb | 578 | .Oo Ar bind_address Ns / Oc Ns Ar port |
579 | and | |
580 | .Ar host Ns / Ns Ar hostport . | |
cd8f998c | 581 | Multiple forwardings may be specified, and additional forwardings can be |
3867aa0a | 582 | given on the command line. |
588df31a | 583 | Only the superuser can forward privileged ports. |
3867aa0a | 584 | By default, the local port is bound in accordance with the |
585 | .Cm GatewayPorts | |
586 | setting. | |
587 | However, an explicit | |
588 | .Ar bind_address | |
589 | may be used to bind the connection to a specific address. | |
590 | The | |
591 | .Ar bind_address | |
592 | of | |
593 | .Dq localhost | |
cd8f998c | 594 | indicates that the listening port be bound for local use only, while an |
595 | empty address or | |
596 | .Sq * | |
3867aa0a | 597 | indicates that the port should be available from all interfaces. |
588df31a | 598 | .It Cm LogLevel |
599 | Gives the verbosity level that is used when logging messages from | |
600 | .Nm ssh . | |
601 | The possible values are: | |
602 | QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3. | |
a4e5acef | 603 | The default is INFO. |
604 | DEBUG and DEBUG1 are equivalent. | |
605 | DEBUG2 and DEBUG3 each specify higher levels of verbose output. | |
588df31a | 606 | .It Cm MACs |
607 | Specifies the MAC (message authentication code) algorithms | |
608 | in order of preference. | |
609 | The MAC algorithm is used in protocol version 2 | |
610 | for data integrity protection. | |
611 | Multiple algorithms must be comma-separated. | |
612 | The default is | |
613 | .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 . | |
614 | .It Cm NoHostAuthenticationForLocalhost | |
615 | This option can be used if the home directory is shared across machines. | |
616 | In this case localhost will refer to a different machine on each of | |
617 | the machines and the user will get many warnings about changed host keys. | |
618 | However, this option disables host authentication for localhost. | |
619 | The argument to this keyword must be | |
620 | .Dq yes | |
621 | or | |
622 | .Dq no . | |
623 | The default is to check the host key for localhost. | |
624 | .It Cm NumberOfPasswordPrompts | |
625 | Specifies the number of password prompts before giving up. | |
626 | The argument to this keyword must be an integer. | |
627 | Default is 3. | |
628 | .It Cm PasswordAuthentication | |
629 | Specifies whether to use password authentication. | |
630 | The argument to this keyword must be | |
631 | .Dq yes | |
632 | or | |
633 | .Dq no . | |
634 | The default is | |
635 | .Dq yes . | |
d20f3c9e | 636 | .It Cm PermitLocalCommand |
637 | Allow local command execution via the | |
638 | .Ic LocalCommand | |
639 | option or using the | |
64925c6d | 640 | .Ic !\& Ns Ar command |
d20f3c9e | 641 | escape sequence in |
642 | .Xr ssh 1 . | |
643 | The argument must be | |
644 | .Dq yes | |
645 | or | |
646 | .Dq no . | |
647 | The default is | |
648 | .Dq no . | |
030723f9 | 649 | .It Cm Port |
650 | Specifies the port number to connect on the remote host. | |
651 | Default is 22. | |
588df31a | 652 | .It Cm PreferredAuthentications |
653 | Specifies the order in which the client should try protocol 2 | |
3cbc677d | 654 | authentication methods. |
4e5038f7 | 655 | This allows a client to prefer one method (e.g.\& |
588df31a | 656 | .Cm keyboard-interactive ) |
4e5038f7 | 657 | over another method (e.g.\& |
588df31a | 658 | .Cm password ) |
659 | The default for this option is: | |
660 | .Dq hostbased,publickey,keyboard-interactive,password . | |
661 | .It Cm Protocol | |
662 | Specifies the protocol versions | |
663 | .Nm ssh | |
664 | should support in order of preference. | |
665 | The possible values are | |
666 | .Dq 1 | |
667 | and | |
668 | .Dq 2 . | |
669 | Multiple versions must be comma-separated. | |
670 | The default is | |
671 | .Dq 2,1 . | |
672 | This means that | |
673 | .Nm ssh | |
674 | tries version 2 and falls back to version 1 | |
675 | if version 2 is not available. | |
676 | .It Cm ProxyCommand | |
677 | Specifies the command to use to connect to the server. | |
678 | The command | |
679 | string extends to the end of the line, and is executed with | |
680 | .Pa /bin/sh . | |
681 | In the command string, | |
682 | .Ql %h | |
683 | will be substituted by the host name to | |
684 | connect and | |
685 | .Ql %p | |
686 | by the port. | |
687 | The command can be basically anything, | |
688 | and should read from its standard input and write to its standard output. | |
689 | It should eventually connect an | |
690 | .Xr sshd 8 | |
691 | server running on some machine, or execute | |
692 | .Ic sshd -i | |
693 | somewhere. | |
694 | Host key management will be done using the | |
695 | HostName of the host being connected (defaulting to the name typed by | |
696 | the user). | |
a4e5acef | 697 | Setting the command to |
698 | .Dq none | |
f78bde70 | 699 | disables this option entirely. |
588df31a | 700 | Note that |
701 | .Cm CheckHostIP | |
702 | is not available for connects with a proxy command. | |
703 | .Pp | |
2b610872 | 704 | This directive is useful in conjunction with |
705 | .Xr nc 1 | |
706 | and its proxy support. | |
9fa42d41 | 707 | For example, the following directive would connect via an HTTP proxy at |
2b610872 | 708 | 192.0.2.0: |
709 | .Bd -literal -offset 3n | |
710 | ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p | |
711 | .Ed | |
588df31a | 712 | .It Cm PubkeyAuthentication |
713 | Specifies whether to try public key authentication. | |
714 | The argument to this keyword must be | |
715 | .Dq yes | |
716 | or | |
717 | .Dq no . | |
718 | The default is | |
719 | .Dq yes . | |
720 | This option applies to protocol version 2 only. | |
721 | .It Cm RemoteForward | |
722 | Specifies that a TCP/IP port on the remote machine be forwarded over | |
723 | the secure channel to the specified host and port from the local machine. | |
ecda4ffb | 724 | The first argument must be |
3867aa0a | 725 | .Sm off |
ecda4ffb | 726 | .Oo Ar bind_address : Oc Ar port |
6d7a9e8f | 727 | .Sm on |
ecda4ffb | 728 | and the second argument must be |
729 | .Ar host : Ns Ar hostport . | |
730 | IPv6 addresses can be specified by enclosing addresses in square brackets | |
731 | or by using an alternative syntax: | |
732 | .Oo Ar bind_address Ns / Oc Ns Ar port | |
733 | and | |
734 | .Ar host Ns / Ns Ar hostport . | |
588df31a | 735 | Multiple forwardings may be specified, and additional |
736 | forwardings can be given on the command line. | |
737 | Only the superuser can forward privileged ports. | |
3867aa0a | 738 | .Pp |
739 | If the | |
740 | .Ar bind_address | |
741 | is not specified, the default is to only bind to loopback addresses. | |
742 | If the | |
743 | .Ar bind_address | |
744 | is | |
745 | .Ql * | |
746 | or an empty string, then the forwarding is requested to listen on all | |
747 | interfaces. | |
748 | Specifying a remote | |
749 | .Ar bind_address | |
cd8f998c | 750 | will only succeed if the server's |
751 | .Cm GatewayPorts | |
3867aa0a | 752 | option is enabled (see |
cd8f998c | 753 | .Xr sshd_config 5 ) . |
588df31a | 754 | .It Cm RhostsRSAAuthentication |
755 | Specifies whether to try rhosts based authentication with RSA host | |
756 | authentication. | |
757 | The argument must be | |
758 | .Dq yes | |
759 | or | |
760 | .Dq no . | |
761 | The default is | |
762 | .Dq no . | |
763 | This option applies to protocol version 1 only and requires | |
764 | .Nm ssh | |
765 | to be setuid root. | |
766 | .It Cm RSAAuthentication | |
767 | Specifies whether to try RSA authentication. | |
768 | The argument to this keyword must be | |
769 | .Dq yes | |
770 | or | |
771 | .Dq no . | |
772 | RSA authentication will only be | |
773 | attempted if the identity file exists, or an authentication agent is | |
774 | running. | |
775 | The default is | |
776 | .Dq yes . | |
777 | Note that this option applies to protocol version 1 only. | |
61a2c1da | 778 | .It Cm SendEnv |
779 | Specifies what variables from the local | |
780 | .Xr environ 7 | |
781 | should be sent to the server. | |
782 | Note that environment passing is only supported for protocol 2, the | |
b8b9f2e6 | 783 | server must also support it, and the server must be configured to |
784 | accept these environment variables. | |
61a2c1da | 785 | Refer to |
786 | .Cm AcceptEnv | |
787 | in | |
788 | .Xr sshd_config 5 | |
789 | for how to configure the server. | |
790 | Variables are specified by name, which may contain the wildcard characters | |
791 | .Ql \&* | |
792 | and | |
793 | .Ql \&? . | |
b8b9f2e6 | 794 | Multiple environment variables may be separated by whitespace or spread |
61a2c1da | 795 | across multiple |
796 | .Cm SendEnv | |
797 | directives. | |
798 | The default is not to send any environment variables. | |
5d8d32a3 | 799 | .It Cm ServerAliveCountMax |
800 | Sets the number of server alive messages (see above) which may be | |
801 | sent without | |
802 | .Nm ssh | |
803 | receiving any messages back from the server. | |
804 | If this threshold is reached while server alive messages are being sent, | |
805 | .Nm ssh | |
806 | will disconnect from the server, terminating the session. | |
807 | It is important to note that the use of server alive messages is very | |
808 | different from | |
809 | .Cm TCPKeepAlive | |
810 | (below). | |
811 | The server alive messages are sent through the encrypted channel | |
812 | and therefore will not be spoofable. | |
813 | The TCP keepalive option enabled by | |
814 | .Cm TCPKeepAlive | |
815 | is spoofable. | |
816 | The server alive mechanism is valuable when the client or | |
817 | server depend on knowing when a connection has become inactive. | |
818 | .Pp | |
819 | The default value is 3. | |
820 | If, for example, | |
821 | .Cm ServerAliveInterval | |
822 | (above) is set to 15, and | |
823 | .Cm ServerAliveCountMax | |
824 | is left at the default, if the server becomes unresponsive ssh | |
825 | will disconnect after approximately 45 seconds. | |
030723f9 | 826 | .It Cm ServerAliveInterval |
827 | Sets a timeout interval in seconds after which if no data has been received | |
828 | from the server, | |
829 | .Nm ssh | |
830 | will send a message through the encrypted | |
831 | channel to request a response from the server. | |
832 | The default | |
833 | is 0, indicating that these messages will not be sent to the server. | |
834 | This option applies to protocol version 2 only. | |
588df31a | 835 | .It Cm SmartcardDevice |
3cbc677d | 836 | Specifies which smartcard device to use. |
837 | The argument to this keyword is the device | |
588df31a | 838 | .Nm ssh |
839 | should use to communicate with a smartcard used for storing the user's | |
3cbc677d | 840 | private RSA key. |
841 | By default, no device is specified and smartcard support is not activated. | |
588df31a | 842 | .It Cm StrictHostKeyChecking |
843 | If this flag is set to | |
844 | .Dq yes , | |
845 | .Nm ssh | |
846 | will never automatically add host keys to the | |
140e3e97 | 847 | .Pa ~/.ssh/known_hosts |
588df31a | 848 | file, and refuses to connect to hosts whose host key has changed. |
849 | This provides maximum protection against trojan horse attacks, | |
850 | however, can be annoying when the | |
851 | .Pa /etc/ssh/ssh_known_hosts | |
852 | file is poorly maintained, or connections to new hosts are | |
853 | frequently made. | |
854 | This option forces the user to manually | |
855 | add all new hosts. | |
856 | If this flag is set to | |
857 | .Dq no , | |
858 | .Nm ssh | |
859 | will automatically add new host keys to the | |
860 | user known hosts files. | |
861 | If this flag is set to | |
862 | .Dq ask , | |
863 | new host keys | |
864 | will be added to the user known host files only after the user | |
865 | has confirmed that is what they really want to do, and | |
866 | .Nm ssh | |
867 | will refuse to connect to hosts whose host key has changed. | |
868 | The host keys of | |
869 | known hosts will be verified automatically in all cases. | |
870 | The argument must be | |
871 | .Dq yes , | |
872 | .Dq no | |
873 | or | |
874 | .Dq ask . | |
875 | The default is | |
876 | .Dq ask . | |
fd573618 | 877 | .It Cm TCPKeepAlive |
878 | Specifies whether the system should send TCP keepalive messages to the | |
879 | other side. | |
880 | If they are sent, death of the connection or crash of one | |
881 | of the machines will be properly noticed. | |
882 | However, this means that | |
883 | connections will die if the route is down temporarily, and some people | |
884 | find it annoying. | |
885 | .Pp | |
886 | The default is | |
887 | .Dq yes | |
888 | (to send TCP keepalive messages), and the client will notice | |
889 | if the network goes down or the remote host dies. | |
890 | This is important in scripts, and many users want it too. | |
891 | .Pp | |
892 | To disable TCP keepalive messages, the value should be set to | |
893 | .Dq no . | |
588df31a | 894 | .It Cm UsePrivilegedPort |
895 | Specifies whether to use a privileged port for outgoing connections. | |
896 | The argument must be | |
897 | .Dq yes | |
898 | or | |
899 | .Dq no . | |
900 | The default is | |
901 | .Dq no . | |
878b8992 | 902 | If set to |
903 | .Dq yes | |
904 | .Nm ssh | |
905 | must be setuid root. | |
588df31a | 906 | Note that this option must be set to |
907 | .Dq yes | |
0598d99d | 908 | for |
588df31a | 909 | .Cm RhostsRSAAuthentication |
0598d99d | 910 | with older servers. |
d20f3c9e | 911 | .It Cm Tunnel |
912 | Request starting | |
913 | .Xr tun 4 | |
a274ba38 | 914 | device forwarding between the client and the server. |
915 | This option also allows requesting layer 2 (ethernet) | |
916 | instead of layer 3 (point-to-point) tunneling from the server. | |
d20f3c9e | 917 | The argument must be |
a4f24bf8 | 918 | .Dq yes , |
919 | .Dq point-to-point , | |
920 | .Dq ethernet | |
d20f3c9e | 921 | or |
922 | .Dq no . | |
923 | The default is | |
924 | .Dq no . | |
925 | .It Cm TunnelDevice | |
926 | Force a specified | |
927 | .Xr tun 4 | |
928 | device on the client. | |
929 | Without this option, the next available device will be used. | |
588df31a | 930 | .It Cm User |
931 | Specifies the user to log in as. | |
932 | This can be useful when a different user name is used on different machines. | |
933 | This saves the trouble of | |
934 | having to remember to give the user name on the command line. | |
935 | .It Cm UserKnownHostsFile | |
936 | Specifies a file to use for the user | |
937 | host key database instead of | |
140e3e97 | 938 | .Pa ~/.ssh/known_hosts . |
21289cd0 | 939 | .It Cm VerifyHostKeyDNS |
940 | Specifies whether to verify the remote key using DNS and SSHFP resource | |
941 | records. | |
0161a13d | 942 | If this option is set to |
943 | .Dq yes , | |
dd376e92 | 944 | the client will implicitly trust keys that match a secure fingerprint |
0161a13d | 945 | from DNS. |
946 | Insecure fingerprints will be handled as if this option was set to | |
947 | .Dq ask . | |
948 | If this option is set to | |
949 | .Dq ask , | |
950 | information on fingerprint match will be displayed, but the user will still | |
951 | need to confirm new host keys according to the | |
952 | .Cm StrictHostKeyChecking | |
953 | option. | |
954 | The argument must be | |
955 | .Dq yes , | |
956 | .Dq no | |
dd376e92 | 957 | or |
958 | .Dq ask . | |
21289cd0 | 959 | The default is |
960 | .Dq no . | |
0f92946c | 961 | Note that this option applies to protocol version 2 only. |
588df31a | 962 | .It Cm XAuthLocation |
57ff5eeb | 963 | Specifies the full pathname of the |
588df31a | 964 | .Xr xauth 1 |
965 | program. | |
966 | The default is | |
967 | .Pa /usr/X11R6/bin/xauth . | |
968 | .El | |
969 | .Sh FILES | |
970 | .Bl -tag -width Ds | |
140e3e97 | 971 | .It Pa ~/.ssh/config |
588df31a | 972 | This is the per-user configuration file. |
973 | The format of this file is described above. | |
974 | This file is used by the | |
975 | .Nm ssh | |
976 | client. | |
e1520719 | 977 | Because of the potential for abuse, this file must have strict permissions: |
978 | read/write for the user, and not accessible by others. | |
588df31a | 979 | .It Pa /etc/ssh/ssh_config |
980 | Systemwide configuration file. | |
981 | This file provides defaults for those | |
982 | values that are not specified in the user's configuration file, and | |
983 | for those users who do not have a configuration file. | |
984 | This file must be world-readable. | |
985 | .El | |
be193d89 | 986 | .Sh SEE ALSO |
987 | .Xr ssh 1 | |
588df31a | 988 | .Sh AUTHORS |
989 | OpenSSH is a derivative of the original and free | |
990 | ssh 1.2.12 release by Tatu Ylonen. | |
991 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
992 | Theo de Raadt and Dug Song | |
993 | removed many bugs, re-added newer features and | |
994 | created OpenSSH. | |
995 | Markus Friedl contributed the support for SSH | |
996 | protocol versions 1.5 and 2.0. |