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f5799ae1 | 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 | .\" | |
665a873d | 37 | .\" $OpenBSD: ssh_config.5,v 1.61 2005/07/08 12:53:10 jmc Exp $ |
f5799ae1 | 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 | |
665a873d | 46 | .It Pa ~/.ssh/config |
f5799ae1 | 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: | |
41b2f314 | 53 | .Bl -enum -offset indent -compact |
54 | .It | |
55 | command-line options | |
56 | .It | |
57 | user's configuration file | |
665a873d | 58 | .Pq Pa ~/.ssh/config |
41b2f314 | 59 | .It |
60 | system-wide configuration file | |
61 | .Pq Pa /etc/ssh/ssh_config | |
62 | .El | |
f5799ae1 | 63 | .Pp |
64 | For each parameter, the first obtained value | |
65 | will be used. | |
996d5e62 | 66 | The configuration files contain sections separated by |
f5799ae1 | 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 | |
0fff78ff | 107 | .Ql \&? |
f5799ae1 | 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). | |
0fff78ff | 118 | .It Cm AddressFamily |
119 | Specifies which address family to use when connecting. | |
120 | Valid arguments are | |
121 | .Dq any , | |
122 | .Dq inet | |
996d5e62 | 123 | (use IPv4 only) or |
0fff78ff | 124 | .Dq inet6 |
996d5e62 | 125 | (use IPv6 only). |
f5799ae1 | 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 | |
665a873d | 139 | Use the specified address on the local machine as the source address of |
140 | the connection. | |
141 | Only useful on systems with more than one address. | |
f5799ae1 | 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 | |
6a9b3198 | 181 | cipher. |
182 | Its use is strongly discouraged due to cryptographic weaknesses. | |
f5799ae1 | 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. | |
c9f39d2c | 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 , | |
665a873d | 197 | .Dq arcfour128 , |
198 | .Dq arcfour256 , | |
c9f39d2c | 199 | .Dq arcfour , |
200 | .Dq blowfish-cbc , | |
201 | and | |
202 | .Dq cast128-cbc . | |
f5799ae1 | 203 | The default is |
f5799ae1 | 204 | .Bd -literal |
665a873d | 205 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, |
206 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
207 | aes192-ctr,aes256-ctr'' | |
f5799ae1 | 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 | |
6a9b3198 | 212 | cleared. |
213 | This option is primarily useful when used from the | |
f5799ae1 | 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. | |
0fff78ff | 246 | .It Cm ConnectTimeout |
247 | Specifies the timeout (in seconds) used when connecting to the ssh | |
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. | |
c9f39d2c | 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 | |
265 | (the default). | |
266 | These sessions will reuse the master instance's network connection rather | |
267 | than initiating new ones. | |
268 | Setting this to | |
269 | .Dq ask | |
270 | will cause | |
271 | .Nm ssh | |
272 | to listen for control connections, but require confirmation using the | |
273 | .Ev SSH_ASKPASS | |
274 | program before they are accepted (see | |
275 | .Xr ssh-add 1 | |
276 | for details). | |
665a873d | 277 | If the |
278 | .Cm ControlPath | |
279 | can not be opened, | |
280 | .Nm ssh | |
281 | will continue without connecting to a master instance. | |
282 | .Pp | |
283 | X11 and | |
284 | .Xr ssh-agent 1 | |
285 | forwarding is supported over these multiplexed connections, however the | |
286 | display and agent fowarded will be the one belonging to the master | |
287 | connection i.e. it is not possible to forward multiple displays or agents. | |
288 | .Pp | |
289 | Two additional options allow for opportunistic multiplexing: try to use a | |
290 | master connection but fall back to creating a new one if one does not already | |
291 | exist. | |
292 | These options are: | |
293 | .Dq auto | |
294 | and | |
295 | .Dq autoask . | |
296 | The latter requires confirmation like the | |
297 | .Dq ask | |
298 | option. | |
c9f39d2c | 299 | .It Cm ControlPath |
665a873d | 300 | Specify the path to the control socket used for connection sharing as described |
301 | in the | |
c9f39d2c | 302 | .Cm ControlMaster |
665a873d | 303 | section above or the string |
304 | .Dq none | |
305 | to disable connection sharing. | |
306 | In the path, | |
307 | .Ql %h | |
308 | will be substituted by the target host name, | |
309 | .Ql %p | |
310 | the port and | |
311 | .Ql %r | |
312 | by the remote login username. | |
313 | It is recommended that any | |
314 | .Cm ControlPath | |
315 | used for opportunistic connection sharing include | |
316 | all three of these escape sequences. | |
317 | This ensures that shared connections are uniquely identified. | |
f5799ae1 | 318 | .It Cm DynamicForward |
319 | Specifies that a TCP/IP port on the local machine be forwarded | |
320 | over the secure channel, and the application | |
321 | protocol is then used to determine where to connect to from the | |
6a9b3198 | 322 | remote machine. |
323 | The argument must be a port number. | |
0fff78ff | 324 | Currently the SOCKS4 and SOCKS5 protocols are supported, and |
f5799ae1 | 325 | .Nm ssh |
0fff78ff | 326 | will act as a SOCKS server. |
f5799ae1 | 327 | Multiple forwardings may be specified, and |
6a9b3198 | 328 | additional forwardings can be given on the command line. |
329 | Only the superuser can forward privileged ports. | |
0fff78ff | 330 | .It Cm EnableSSHKeysign |
331 | Setting this option to | |
332 | .Dq yes | |
333 | in the global client configuration file | |
334 | .Pa /etc/ssh/ssh_config | |
335 | enables the use of the helper program | |
336 | .Xr ssh-keysign 8 | |
337 | during | |
338 | .Cm HostbasedAuthentication . | |
339 | The argument must be | |
340 | .Dq yes | |
341 | or | |
342 | .Dq no . | |
343 | The default is | |
344 | .Dq no . | |
cdd66111 | 345 | This option should be placed in the non-hostspecific section. |
0fff78ff | 346 | See |
347 | .Xr ssh-keysign 8 | |
348 | for more information. | |
f5799ae1 | 349 | .It Cm EscapeChar |
350 | Sets the escape character (default: | |
351 | .Ql ~ ) . | |
352 | The escape character can also | |
353 | be set on the command line. | |
354 | The argument should be a single character, | |
355 | .Ql ^ | |
356 | followed by a letter, or | |
357 | .Dq none | |
358 | to disable the escape | |
359 | character entirely (making the connection transparent for binary | |
360 | data). | |
361 | .It Cm ForwardAgent | |
362 | Specifies whether the connection to the authentication agent (if any) | |
363 | will be forwarded to the remote machine. | |
364 | The argument must be | |
365 | .Dq yes | |
366 | or | |
367 | .Dq no . | |
368 | The default is | |
369 | .Dq no . | |
41b2f314 | 370 | .Pp |
6a9b3198 | 371 | Agent forwarding should be enabled with caution. |
372 | Users with the ability to bypass file permissions on the remote host | |
373 | (for the agent's Unix-domain socket) | |
374 | can access the local agent through the forwarded connection. | |
375 | An attacker cannot obtain key material from the agent, | |
41b2f314 | 376 | however they can perform operations on the keys that enable them to |
377 | authenticate using the identities loaded into the agent. | |
f5799ae1 | 378 | .It Cm ForwardX11 |
379 | Specifies whether X11 connections will be automatically redirected | |
380 | over the secure channel and | |
381 | .Ev DISPLAY | |
382 | set. | |
383 | The argument must be | |
384 | .Dq yes | |
385 | or | |
386 | .Dq no . | |
387 | The default is | |
388 | .Dq no . | |
41b2f314 | 389 | .Pp |
6a9b3198 | 390 | X11 forwarding should be enabled with caution. |
391 | Users with the ability to bypass file permissions on the remote host | |
cdd66111 | 392 | (for the user's X11 authorization database) |
6a9b3198 | 393 | can access the local X11 display through the forwarded connection. |
cdd66111 | 394 | An attacker may then be able to perform activities such as keystroke monitoring |
395 | if the | |
396 | .Cm ForwardX11Trusted | |
397 | option is also enabled. | |
398 | .It Cm ForwardX11Trusted | |
c9f39d2c | 399 | If this option is set to |
cdd66111 | 400 | .Dq yes |
401 | then remote X11 clients will have full access to the original X11 display. | |
996d5e62 | 402 | .Pp |
cdd66111 | 403 | If this option is set to |
404 | .Dq no | |
405 | then remote X11 clients will be considered untrusted and prevented | |
406 | from stealing or tampering with data belonging to trusted X11 | |
407 | clients. | |
996d5e62 | 408 | Furthermore, the |
409 | .Xr xauth 1 | |
410 | token used for the session will be set to expire after 20 minutes. | |
411 | Remote clients will be refused access after this time. | |
cdd66111 | 412 | .Pp |
413 | The default is | |
414 | .Dq no . | |
415 | .Pp | |
416 | See the X11 SECURITY extension specification for full details on | |
417 | the restrictions imposed on untrusted clients. | |
f5799ae1 | 418 | .It Cm GatewayPorts |
419 | Specifies whether remote hosts are allowed to connect to local | |
420 | forwarded ports. | |
421 | By default, | |
422 | .Nm ssh | |
6a9b3198 | 423 | binds local port forwardings to the loopback address. |
424 | This prevents other remote hosts from connecting to forwarded ports. | |
f5799ae1 | 425 | .Cm GatewayPorts |
426 | can be used to specify that | |
427 | .Nm ssh | |
428 | should bind local port forwardings to the wildcard address, | |
429 | thus allowing remote hosts to connect to forwarded ports. | |
430 | The argument must be | |
431 | .Dq yes | |
432 | or | |
433 | .Dq no . | |
434 | The default is | |
435 | .Dq no . | |
436 | .It Cm GlobalKnownHostsFile | |
437 | Specifies a file to use for the global | |
438 | host key database instead of | |
439 | .Pa /etc/ssh/ssh_known_hosts . | |
0fff78ff | 440 | .It Cm GSSAPIAuthentication |
cdd66111 | 441 | Specifies whether user authentication based on GSSAPI is allowed. |
0fff78ff | 442 | The default is |
cdd66111 | 443 | .Dq no . |
0fff78ff | 444 | Note that this option applies to protocol version 2 only. |
445 | .It Cm GSSAPIDelegateCredentials | |
446 | Forward (delegate) credentials to the server. | |
447 | The default is | |
448 | .Dq no . | |
449 | Note that this option applies to protocol version 2 only. | |
996d5e62 | 450 | .It Cm HashKnownHosts |
451 | Indicates that | |
452 | .Nm ssh | |
453 | should hash host names and addresses when they are added to | |
665a873d | 454 | .Pa ~/.ssh/known_hosts . |
996d5e62 | 455 | These hashed names may be used normally by |
456 | .Nm ssh | |
457 | and | |
458 | .Nm sshd , | |
459 | but they do not reveal identifying information should the file's contents | |
460 | be disclosed. | |
461 | The default is | |
462 | .Dq no . | |
463 | Note that hashing of names and addresses will not be retrospectively applied | |
464 | to existing known hosts files, but these may be manually hashed using | |
465 | .Xr ssh-keygen 1 . | |
f5799ae1 | 466 | .It Cm HostbasedAuthentication |
467 | Specifies whether to try rhosts based authentication with public key | |
468 | authentication. | |
469 | The argument must be | |
470 | .Dq yes | |
471 | or | |
472 | .Dq no . | |
473 | The default is | |
474 | .Dq no . | |
475 | This option applies to protocol version 2 only and | |
476 | is similar to | |
477 | .Cm RhostsRSAAuthentication . | |
478 | .It Cm HostKeyAlgorithms | |
479 | Specifies the protocol version 2 host key algorithms | |
480 | that the client wants to use in order of preference. | |
481 | The default for this option is: | |
482 | .Dq ssh-rsa,ssh-dss . | |
483 | .It Cm HostKeyAlias | |
484 | Specifies an alias that should be used instead of the | |
485 | real host name when looking up or saving the host key | |
486 | in the host key database files. | |
487 | This option is useful for tunneling ssh connections | |
488 | or for multiple servers running on a single host. | |
489 | .It Cm HostName | |
490 | Specifies the real host name to log into. | |
491 | This can be used to specify nicknames or abbreviations for hosts. | |
492 | Default is the name given on the command line. | |
493 | Numeric IP addresses are also permitted (both on the command line and in | |
494 | .Cm HostName | |
495 | specifications). | |
496 | .It Cm IdentityFile | |
497 | Specifies a file from which the user's RSA or DSA authentication identity | |
0fff78ff | 498 | is read. |
499 | The default is | |
665a873d | 500 | .Pa ~/.ssh/identity |
f5799ae1 | 501 | for protocol version 1, and |
665a873d | 502 | .Pa ~/.ssh/id_rsa |
f5799ae1 | 503 | and |
665a873d | 504 | .Pa ~/.ssh/id_dsa |
f5799ae1 | 505 | for protocol version 2. |
506 | Additionally, any identities represented by the authentication agent | |
507 | will be used for authentication. | |
508 | The file name may use the tilde | |
509 | syntax to refer to a user's home directory. | |
510 | It is possible to have | |
511 | multiple identity files specified in configuration files; all these | |
512 | identities will be tried in sequence. | |
99be0775 | 513 | .It Cm IdentitiesOnly |
514 | Specifies that | |
515 | .Nm ssh | |
516 | should only use the authentication identity files configured in the | |
c9f39d2c | 517 | .Nm |
99be0775 | 518 | files, |
519 | even if the | |
520 | .Nm ssh-agent | |
521 | offers more identities. | |
522 | The argument to this keyword must be | |
523 | .Dq yes | |
524 | or | |
525 | .Dq no . | |
526 | This option is intented for situations where | |
527 | .Nm ssh-agent | |
528 | offers many different identities. | |
529 | The default is | |
530 | .Dq no . | |
996d5e62 | 531 | .It Cm KbdInteractiveDevices |
532 | Specifies the list of methods to use in keyboard-interactive authentication. | |
533 | Multiple method names must be comma-separated. | |
534 | The default is to use the server specified list. | |
f5799ae1 | 535 | .It Cm LocalForward |
536 | Specifies that a TCP/IP port on the local machine be forwarded over | |
537 | the secure channel to the specified host and port from the remote machine. | |
dec6d9fe | 538 | The first argument must be |
996d5e62 | 539 | .Sm off |
dec6d9fe | 540 | .Oo Ar bind_address : Oc Ar port |
996d5e62 | 541 | .Sm on |
dec6d9fe | 542 | and the second argument must be |
543 | .Ar host : Ns Ar hostport . | |
996d5e62 | 544 | IPv6 addresses can be specified by enclosing addresses in square brackets or |
545 | by using an alternative syntax: | |
dec6d9fe | 546 | .Oo Ar bind_address Ns / Oc Ns Ar port |
547 | and | |
548 | .Ar host Ns / Ns Ar hostport . | |
996d5e62 | 549 | Multiple forwardings may be specified, and additional forwardings can be |
550 | given on the command line. | |
f5799ae1 | 551 | Only the superuser can forward privileged ports. |
996d5e62 | 552 | By default, the local port is bound in accordance with the |
553 | .Cm GatewayPorts | |
554 | setting. | |
555 | However, an explicit | |
556 | .Ar bind_address | |
557 | may be used to bind the connection to a specific address. | |
558 | The | |
559 | .Ar bind_address | |
560 | of | |
561 | .Dq localhost | |
562 | indicates that the listening port be bound for local use only, while an | |
563 | empty address or | |
564 | .Sq * | |
565 | indicates that the port should be available from all interfaces. | |
f5799ae1 | 566 | .It Cm LogLevel |
567 | Gives the verbosity level that is used when logging messages from | |
568 | .Nm ssh . | |
569 | The possible values are: | |
570 | QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3. | |
6a9b3198 | 571 | The default is INFO. |
572 | DEBUG and DEBUG1 are equivalent. | |
573 | DEBUG2 and DEBUG3 each specify higher levels of verbose output. | |
f5799ae1 | 574 | .It Cm MACs |
575 | Specifies the MAC (message authentication code) algorithms | |
576 | in order of preference. | |
577 | The MAC algorithm is used in protocol version 2 | |
578 | for data integrity protection. | |
579 | Multiple algorithms must be comma-separated. | |
580 | The default is | |
581 | .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 . | |
582 | .It Cm NoHostAuthenticationForLocalhost | |
583 | This option can be used if the home directory is shared across machines. | |
584 | In this case localhost will refer to a different machine on each of | |
585 | the machines and the user will get many warnings about changed host keys. | |
586 | However, this option disables host authentication for localhost. | |
587 | The argument to this keyword must be | |
588 | .Dq yes | |
589 | or | |
590 | .Dq no . | |
591 | The default is to check the host key for localhost. | |
592 | .It Cm NumberOfPasswordPrompts | |
593 | Specifies the number of password prompts before giving up. | |
594 | The argument to this keyword must be an integer. | |
595 | Default is 3. | |
596 | .It Cm PasswordAuthentication | |
597 | Specifies whether to use password authentication. | |
598 | The argument to this keyword must be | |
599 | .Dq yes | |
600 | or | |
601 | .Dq no . | |
602 | The default is | |
603 | .Dq yes . | |
604 | .It Cm Port | |
605 | Specifies the port number to connect on the remote host. | |
606 | Default is 22. | |
607 | .It Cm PreferredAuthentications | |
608 | Specifies the order in which the client should try protocol 2 | |
0fff78ff | 609 | authentication methods. |
dec6d9fe | 610 | This allows a client to prefer one method (e.g.\& |
f5799ae1 | 611 | .Cm keyboard-interactive ) |
dec6d9fe | 612 | over another method (e.g.\& |
f5799ae1 | 613 | .Cm password ) |
614 | The default for this option is: | |
615 | .Dq hostbased,publickey,keyboard-interactive,password . | |
616 | .It Cm Protocol | |
617 | Specifies the protocol versions | |
618 | .Nm ssh | |
619 | should support in order of preference. | |
620 | The possible values are | |
621 | .Dq 1 | |
622 | and | |
623 | .Dq 2 . | |
624 | Multiple versions must be comma-separated. | |
625 | The default is | |
626 | .Dq 2,1 . | |
627 | This means that | |
628 | .Nm ssh | |
629 | tries version 2 and falls back to version 1 | |
630 | if version 2 is not available. | |
631 | .It Cm ProxyCommand | |
632 | Specifies the command to use to connect to the server. | |
633 | The command | |
634 | string extends to the end of the line, and is executed with | |
635 | .Pa /bin/sh . | |
636 | In the command string, | |
637 | .Ql %h | |
638 | will be substituted by the host name to | |
639 | connect and | |
640 | .Ql %p | |
641 | by the port. | |
642 | The command can be basically anything, | |
643 | and should read from its standard input and write to its standard output. | |
644 | It should eventually connect an | |
645 | .Xr sshd 8 | |
646 | server running on some machine, or execute | |
647 | .Ic sshd -i | |
648 | somewhere. | |
649 | Host key management will be done using the | |
650 | HostName of the host being connected (defaulting to the name typed by | |
651 | the user). | |
6a9b3198 | 652 | Setting the command to |
653 | .Dq none | |
654 | disables this option entirely. | |
f5799ae1 | 655 | Note that |
656 | .Cm CheckHostIP | |
657 | is not available for connects with a proxy command. | |
658 | .Pp | |
665a873d | 659 | This directive is useful in conjunction with |
660 | .Xr nc 1 | |
661 | and its proxy support. | |
662 | For example, the following directive would connect via an HTTP proxy at | |
663 | 192.0.2.0: | |
664 | .Bd -literal -offset 3n | |
665 | ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p | |
666 | .Ed | |
f5799ae1 | 667 | .It Cm PubkeyAuthentication |
668 | Specifies whether to try public key authentication. | |
669 | The argument to this keyword must be | |
670 | .Dq yes | |
671 | or | |
672 | .Dq no . | |
673 | The default is | |
674 | .Dq yes . | |
675 | This option applies to protocol version 2 only. | |
676 | .It Cm RemoteForward | |
677 | Specifies that a TCP/IP port on the remote machine be forwarded over | |
678 | the secure channel to the specified host and port from the local machine. | |
dec6d9fe | 679 | The first argument must be |
996d5e62 | 680 | .Sm off |
dec6d9fe | 681 | .Oo Ar bind_address : Oc Ar port |
996d5e62 | 682 | .Sm on |
dec6d9fe | 683 | and the second argument must be |
684 | .Ar host : Ns Ar hostport . | |
685 | IPv6 addresses can be specified by enclosing addresses in square brackets | |
686 | or by using an alternative syntax: | |
687 | .Oo Ar bind_address Ns / Oc Ns Ar port | |
688 | and | |
689 | .Ar host Ns / Ns Ar hostport . | |
f5799ae1 | 690 | Multiple forwardings may be specified, and additional |
691 | forwardings can be given on the command line. | |
692 | Only the superuser can forward privileged ports. | |
996d5e62 | 693 | .Pp |
694 | If the | |
695 | .Ar bind_address | |
696 | is not specified, the default is to only bind to loopback addresses. | |
697 | If the | |
698 | .Ar bind_address | |
699 | is | |
700 | .Ql * | |
701 | or an empty string, then the forwarding is requested to listen on all | |
702 | interfaces. | |
703 | Specifying a remote | |
704 | .Ar bind_address | |
705 | will only succeed if the server's | |
706 | .Cm GatewayPorts | |
707 | option is enabled (see | |
708 | .Xr sshd_config 5 ) . | |
f5799ae1 | 709 | .It Cm RhostsRSAAuthentication |
710 | Specifies whether to try rhosts based authentication with RSA host | |
711 | authentication. | |
712 | The argument must be | |
713 | .Dq yes | |
714 | or | |
715 | .Dq no . | |
716 | The default is | |
717 | .Dq no . | |
718 | This option applies to protocol version 1 only and requires | |
719 | .Nm ssh | |
720 | to be setuid root. | |
721 | .It Cm RSAAuthentication | |
722 | Specifies whether to try RSA authentication. | |
723 | The argument to this keyword must be | |
724 | .Dq yes | |
725 | or | |
726 | .Dq no . | |
727 | RSA authentication will only be | |
728 | attempted if the identity file exists, or an authentication agent is | |
729 | running. | |
730 | The default is | |
731 | .Dq yes . | |
732 | Note that this option applies to protocol version 1 only. | |
c9f39d2c | 733 | .It Cm SendEnv |
734 | Specifies what variables from the local | |
735 | .Xr environ 7 | |
736 | should be sent to the server. | |
737 | Note that environment passing is only supported for protocol 2, the | |
738 | server must also support it, and the server must be configured to | |
739 | accept these environment variables. | |
740 | Refer to | |
741 | .Cm AcceptEnv | |
742 | in | |
743 | .Xr sshd_config 5 | |
744 | for how to configure the server. | |
745 | Variables are specified by name, which may contain the wildcard characters | |
746 | .Ql \&* | |
747 | and | |
748 | .Ql \&? . | |
749 | Multiple environment variables may be separated by whitespace or spread | |
750 | across multiple | |
751 | .Cm SendEnv | |
752 | directives. | |
753 | The default is not to send any environment variables. | |
cdd66111 | 754 | .It Cm ServerAliveInterval |
755 | Sets a timeout interval in seconds after which if no data has been received | |
756 | from the server, | |
757 | .Nm ssh | |
758 | will send a message through the encrypted | |
759 | channel to request a response from the server. | |
760 | The default | |
761 | is 0, indicating that these messages will not be sent to the server. | |
762 | This option applies to protocol version 2 only. | |
763 | .It Cm ServerAliveCountMax | |
764 | Sets the number of server alive messages (see above) which may be | |
765 | sent without | |
766 | .Nm ssh | |
767 | receiving any messages back from the server. | |
768 | If this threshold is reached while server alive messages are being sent, | |
769 | .Nm ssh | |
770 | will disconnect from the server, terminating the session. | |
771 | It is important to note that the use of server alive messages is very | |
772 | different from | |
773 | .Cm TCPKeepAlive | |
774 | (below). | |
775 | The server alive messages are sent through the encrypted channel | |
776 | and therefore will not be spoofable. | |
777 | The TCP keepalive option enabled by | |
778 | .Cm TCPKeepAlive | |
779 | is spoofable. | |
780 | The server alive mechanism is valuable when the client or | |
781 | server depend on knowing when a connection has become inactive. | |
782 | .Pp | |
783 | The default value is 3. | |
784 | If, for example, | |
785 | .Cm ServerAliveInterval | |
786 | (above) is set to 15, and | |
787 | .Cm ServerAliveCountMax | |
788 | is left at the default, if the server becomes unresponsive ssh | |
789 | will disconnect after approximately 45 seconds. | |
f5799ae1 | 790 | .It Cm SmartcardDevice |
0fff78ff | 791 | Specifies which smartcard device to use. |
792 | The argument to this keyword is the device | |
f5799ae1 | 793 | .Nm ssh |
794 | should use to communicate with a smartcard used for storing the user's | |
0fff78ff | 795 | private RSA key. |
796 | By default, no device is specified and smartcard support is not activated. | |
f5799ae1 | 797 | .It Cm StrictHostKeyChecking |
798 | If this flag is set to | |
799 | .Dq yes , | |
800 | .Nm ssh | |
801 | will never automatically add host keys to the | |
665a873d | 802 | .Pa ~/.ssh/known_hosts |
f5799ae1 | 803 | file, and refuses to connect to hosts whose host key has changed. |
804 | This provides maximum protection against trojan horse attacks, | |
805 | however, can be annoying when the | |
806 | .Pa /etc/ssh/ssh_known_hosts | |
807 | file is poorly maintained, or connections to new hosts are | |
808 | frequently made. | |
809 | This option forces the user to manually | |
810 | add all new hosts. | |
811 | If this flag is set to | |
812 | .Dq no , | |
813 | .Nm ssh | |
814 | will automatically add new host keys to the | |
815 | user known hosts files. | |
816 | If this flag is set to | |
817 | .Dq ask , | |
818 | new host keys | |
819 | will be added to the user known host files only after the user | |
820 | has confirmed that is what they really want to do, and | |
821 | .Nm ssh | |
822 | will refuse to connect to hosts whose host key has changed. | |
823 | The host keys of | |
824 | known hosts will be verified automatically in all cases. | |
825 | The argument must be | |
826 | .Dq yes , | |
827 | .Dq no | |
828 | or | |
829 | .Dq ask . | |
830 | The default is | |
831 | .Dq ask . | |
cdd66111 | 832 | .It Cm TCPKeepAlive |
833 | Specifies whether the system should send TCP keepalive messages to the | |
834 | other side. | |
835 | If they are sent, death of the connection or crash of one | |
836 | of the machines will be properly noticed. | |
837 | However, this means that | |
838 | connections will die if the route is down temporarily, and some people | |
839 | find it annoying. | |
840 | .Pp | |
841 | The default is | |
842 | .Dq yes | |
843 | (to send TCP keepalive messages), and the client will notice | |
844 | if the network goes down or the remote host dies. | |
845 | This is important in scripts, and many users want it too. | |
846 | .Pp | |
847 | To disable TCP keepalive messages, the value should be set to | |
848 | .Dq no . | |
f5799ae1 | 849 | .It Cm UsePrivilegedPort |
850 | Specifies whether to use a privileged port for outgoing connections. | |
851 | The argument must be | |
852 | .Dq yes | |
853 | or | |
854 | .Dq no . | |
855 | The default is | |
856 | .Dq no . | |
41b2f314 | 857 | If set to |
858 | .Dq yes | |
859 | .Nm ssh | |
860 | must be setuid root. | |
f5799ae1 | 861 | Note that this option must be set to |
862 | .Dq yes | |
0fff78ff | 863 | for |
f5799ae1 | 864 | .Cm RhostsRSAAuthentication |
0fff78ff | 865 | with older servers. |
f5799ae1 | 866 | .It Cm User |
867 | Specifies the user to log in as. | |
868 | This can be useful when a different user name is used on different machines. | |
869 | This saves the trouble of | |
870 | having to remember to give the user name on the command line. | |
871 | .It Cm UserKnownHostsFile | |
872 | Specifies a file to use for the user | |
873 | host key database instead of | |
665a873d | 874 | .Pa ~/.ssh/known_hosts . |
0fff78ff | 875 | .It Cm VerifyHostKeyDNS |
876 | Specifies whether to verify the remote key using DNS and SSHFP resource | |
877 | records. | |
cdd66111 | 878 | If this option is set to |
879 | .Dq yes , | |
880 | the client will implicitly trust keys that match a secure fingerprint | |
881 | from DNS. | |
882 | Insecure fingerprints will be handled as if this option was set to | |
883 | .Dq ask . | |
884 | If this option is set to | |
885 | .Dq ask , | |
886 | information on fingerprint match will be displayed, but the user will still | |
887 | need to confirm new host keys according to the | |
888 | .Cm StrictHostKeyChecking | |
889 | option. | |
890 | The argument must be | |
891 | .Dq yes , | |
892 | .Dq no | |
893 | or | |
894 | .Dq ask . | |
0fff78ff | 895 | The default is |
896 | .Dq no . | |
897 | Note that this option applies to protocol version 2 only. | |
f5799ae1 | 898 | .It Cm XAuthLocation |
41b2f314 | 899 | Specifies the full pathname of the |
f5799ae1 | 900 | .Xr xauth 1 |
901 | program. | |
902 | The default is | |
903 | .Pa /usr/X11R6/bin/xauth . | |
904 | .El | |
905 | .Sh FILES | |
906 | .Bl -tag -width Ds | |
665a873d | 907 | .It Pa ~/.ssh/config |
f5799ae1 | 908 | This is the per-user configuration file. |
909 | The format of this file is described above. | |
910 | This file is used by the | |
911 | .Nm ssh | |
912 | client. | |
c9f39d2c | 913 | Because of the potential for abuse, this file must have strict permissions: |
914 | read/write for the user, and not accessible by others. | |
f5799ae1 | 915 | .It Pa /etc/ssh/ssh_config |
916 | Systemwide configuration file. | |
917 | This file provides defaults for those | |
918 | values that are not specified in the user's configuration file, and | |
919 | for those users who do not have a configuration file. | |
920 | This file must be world-readable. | |
921 | .El | |
0fff78ff | 922 | .Sh SEE ALSO |
923 | .Xr ssh 1 | |
f5799ae1 | 924 | .Sh AUTHORS |
925 | OpenSSH is a derivative of the original and free | |
926 | ssh 1.2.12 release by Tatu Ylonen. | |
927 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
928 | Theo de Raadt and Dug Song | |
929 | removed many bugs, re-added newer features and | |
930 | created OpenSSH. | |
931 | Markus Friedl contributed the support for SSH | |
932 | protocol versions 1.5 and 2.0. |