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884dc78b | 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 | .\" | |
2ce0bfe4 | 37 | .\" $OpenBSD: ssh_config.5,v 1.61 2005/07/08 12:53:10 jmc Exp $ |
884dc78b | 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 | |
2ce0bfe4 | 46 | .It Pa ~/.ssh/config |
884dc78b | 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: | |
d03f4262 | 53 | .Bl -enum -offset indent -compact |
54 | .It | |
55 | command-line options | |
56 | .It | |
44a053a3 | 57 | user's configuration file |
2ce0bfe4 | 58 | .Pq Pa ~/.ssh/config |
d03f4262 | 59 | .It |
d6862c36 | 60 | GSSAPI configuration file |
d03f4262 | 61 | .Pq Pa $HOME/.ssh/config.gssapi |
62 | .It | |
d6862c36 | 63 | Kerberos configuration file |
d03f4262 | 64 | .Pq Pa $HOME/.ssh/config.krb |
65 | .It | |
d03f4262 | 66 | system-wide configuration file |
67 | .Pq Pa /etc/ssh/ssh_config | |
44a053a3 | 68 | .El |
884dc78b | 69 | .Pp |
70 | For each parameter, the first obtained value | |
71 | will be used. | |
dfddba3d | 72 | The configuration files contain sections separated by |
884dc78b | 73 | .Dq Host |
74 | specifications, and that section is only applied for hosts that | |
75 | match one of the patterns given in the specification. | |
76 | The matched host name is the one given on the command line. | |
77 | .Pp | |
78 | Since the first obtained value for each parameter is used, more | |
79 | host-specific declarations should be given near the beginning of the | |
80 | file, and general defaults at the end. | |
81 | .Pp | |
82 | The configuration file has the following format: | |
83 | .Pp | |
84 | Empty lines and lines starting with | |
85 | .Ql # | |
86 | are comments. | |
87 | .Pp | |
88 | Otherwise a line is of the format | |
89 | .Dq keyword arguments . | |
90 | Configuration options may be separated by whitespace or | |
91 | optional whitespace and exactly one | |
92 | .Ql = ; | |
93 | the latter format is useful to avoid the need to quote whitespace | |
94 | when specifying configuration options using the | |
95 | .Nm ssh , | |
96 | .Nm scp | |
97 | and | |
98 | .Nm sftp | |
99 | .Fl o | |
100 | option. | |
101 | .Pp | |
102 | The possible | |
103 | keywords and their meanings are as follows (note that | |
104 | keywords are case-insensitive and arguments are case-sensitive): | |
105 | .Bl -tag -width Ds | |
106 | .It Cm Host | |
107 | Restricts the following declarations (up to the next | |
108 | .Cm Host | |
109 | keyword) to be only for those hosts that match one of the patterns | |
110 | given after the keyword. | |
111 | .Ql \&* | |
112 | and | |
7cac2b65 | 113 | .Ql \&? |
884dc78b | 114 | can be used as wildcards in the |
115 | patterns. | |
116 | A single | |
117 | .Ql \&* | |
118 | as a pattern can be used to provide global | |
119 | defaults for all hosts. | |
120 | The host is the | |
121 | .Ar hostname | |
122 | argument given on the command line (i.e., the name is not converted to | |
123 | a canonicalized host name before matching). | |
7cac2b65 | 124 | .It Cm AddressFamily |
125 | Specifies which address family to use when connecting. | |
126 | Valid arguments are | |
127 | .Dq any , | |
128 | .Dq inet | |
dfddba3d | 129 | (use IPv4 only) or |
7cac2b65 | 130 | .Dq inet6 |
dfddba3d | 131 | (use IPv6 only). |
884dc78b | 132 | .It Cm BatchMode |
133 | If set to | |
134 | .Dq yes , | |
135 | passphrase/password querying will be disabled. | |
136 | This option is useful in scripts and other batch jobs where no user | |
137 | is present to supply the password. | |
138 | The argument must be | |
139 | .Dq yes | |
140 | or | |
141 | .Dq no . | |
142 | The default is | |
143 | .Dq no . | |
144 | .It Cm BindAddress | |
2ce0bfe4 | 145 | Use the specified address on the local machine as the source address of |
146 | the connection. | |
147 | Only useful on systems with more than one address. | |
884dc78b | 148 | Note that this option does not work if |
149 | .Cm UsePrivilegedPort | |
150 | is set to | |
151 | .Dq yes . | |
152 | .It Cm ChallengeResponseAuthentication | |
153 | Specifies whether to use challenge response authentication. | |
154 | The argument to this keyword must be | |
155 | .Dq yes | |
156 | or | |
157 | .Dq no . | |
158 | The default is | |
159 | .Dq yes . | |
160 | .It Cm CheckHostIP | |
161 | If this flag is set to | |
162 | .Dq yes , | |
163 | ssh will additionally check the host IP address in the | |
164 | .Pa known_hosts | |
165 | file. | |
166 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
167 | If the option is set to | |
168 | .Dq no , | |
169 | the check will not be executed. | |
170 | The default is | |
171 | .Dq yes . | |
172 | .It Cm Cipher | |
173 | Specifies the cipher to use for encrypting the session | |
174 | in protocol version 1. | |
175 | Currently, | |
176 | .Dq blowfish , | |
177 | .Dq 3des , | |
178 | and | |
179 | .Dq des | |
180 | are supported. | |
181 | .Ar des | |
182 | is only supported in the | |
183 | .Nm ssh | |
184 | client for interoperability with legacy protocol 1 implementations | |
185 | that do not support the | |
186 | .Ar 3des | |
bfe49944 | 187 | cipher. |
188 | Its use is strongly discouraged due to cryptographic weaknesses. | |
884dc78b | 189 | The default is |
190 | .Dq 3des . | |
191 | .It Cm Ciphers | |
192 | Specifies the ciphers allowed for protocol version 2 | |
193 | in order of preference. | |
194 | Multiple ciphers must be comma-separated. | |
7e82606e | 195 | The supported ciphers are |
196 | .Dq 3des-cbc , | |
197 | .Dq aes128-cbc , | |
198 | .Dq aes192-cbc , | |
199 | .Dq aes256-cbc , | |
200 | .Dq aes128-ctr , | |
201 | .Dq aes192-ctr , | |
202 | .Dq aes256-ctr , | |
2ce0bfe4 | 203 | .Dq arcfour128 , |
204 | .Dq arcfour256 , | |
7e82606e | 205 | .Dq arcfour , |
206 | .Dq blowfish-cbc , | |
207 | and | |
208 | .Dq cast128-cbc . | |
884dc78b | 209 | The default is |
884dc78b | 210 | .Bd -literal |
2ce0bfe4 | 211 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, |
212 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
213 | aes192-ctr,aes256-ctr'' | |
884dc78b | 214 | .Ed |
215 | .It Cm ClearAllForwardings | |
216 | Specifies that all local, remote and dynamic port forwardings | |
217 | specified in the configuration files or on the command line be | |
bfe49944 | 218 | cleared. |
219 | This option is primarily useful when used from the | |
884dc78b | 220 | .Nm ssh |
221 | command line to clear port forwardings set in | |
222 | configuration files, and is automatically set by | |
223 | .Xr scp 1 | |
224 | and | |
225 | .Xr sftp 1 . | |
226 | The argument must be | |
227 | .Dq yes | |
228 | or | |
229 | .Dq no . | |
230 | The default is | |
231 | .Dq no . | |
232 | .It Cm Compression | |
233 | Specifies whether to use compression. | |
234 | The argument must be | |
235 | .Dq yes | |
236 | or | |
237 | .Dq no . | |
238 | The default is | |
239 | .Dq no . | |
240 | .It Cm CompressionLevel | |
241 | Specifies the compression level to use if compression is enabled. | |
242 | The argument must be an integer from 1 (fast) to 9 (slow, best). | |
243 | The default level is 6, which is good for most applications. | |
244 | The meaning of the values is the same as in | |
245 | .Xr gzip 1 . | |
246 | Note that this option applies to protocol version 1 only. | |
247 | .It Cm ConnectionAttempts | |
248 | Specifies the number of tries (one per second) to make before exiting. | |
249 | The argument must be an integer. | |
250 | This may be useful in scripts if the connection sometimes fails. | |
251 | The default is 1. | |
7cac2b65 | 252 | .It Cm ConnectTimeout |
253 | Specifies the timeout (in seconds) used when connecting to the ssh | |
254 | server, instead of using the default system TCP timeout. | |
255 | This value is used only when the target is down or really unreachable, | |
256 | not when it refuses the connection. | |
7e82606e | 257 | .It Cm ControlMaster |
258 | Enables the sharing of multiple sessions over a single network connection. | |
259 | When set to | |
260 | .Dq yes | |
261 | .Nm ssh | |
262 | will listen for connections on a control socket specified using the | |
263 | .Cm ControlPath | |
264 | argument. | |
265 | Additional sessions can connect to this socket using the same | |
266 | .Cm ControlPath | |
267 | with | |
268 | .Cm ControlMaster | |
269 | set to | |
270 | .Dq no | |
271 | (the default). | |
272 | These sessions will reuse the master instance's network connection rather | |
273 | than initiating new ones. | |
274 | Setting this to | |
275 | .Dq ask | |
276 | will cause | |
277 | .Nm ssh | |
278 | to listen for control connections, but require confirmation using the | |
279 | .Ev SSH_ASKPASS | |
280 | program before they are accepted (see | |
281 | .Xr ssh-add 1 | |
282 | for details). | |
2ce0bfe4 | 283 | If the |
284 | .Cm ControlPath | |
285 | can not be opened, | |
286 | .Nm ssh | |
287 | will continue without connecting to a master instance. | |
288 | .Pp | |
289 | X11 and | |
290 | .Xr ssh-agent 1 | |
291 | forwarding is supported over these multiplexed connections, however the | |
292 | display and agent fowarded will be the one belonging to the master | |
293 | connection i.e. it is not possible to forward multiple displays or agents. | |
294 | .Pp | |
295 | Two additional options allow for opportunistic multiplexing: try to use a | |
296 | master connection but fall back to creating a new one if one does not already | |
297 | exist. | |
298 | These options are: | |
299 | .Dq auto | |
300 | and | |
301 | .Dq autoask . | |
302 | The latter requires confirmation like the | |
303 | .Dq ask | |
304 | option. | |
7e82606e | 305 | .It Cm ControlPath |
2ce0bfe4 | 306 | Specify the path to the control socket used for connection sharing as described |
307 | in the | |
7e82606e | 308 | .Cm ControlMaster |
2ce0bfe4 | 309 | section above or the string |
310 | .Dq none | |
311 | to disable connection sharing. | |
312 | In the path, | |
313 | .Ql %h | |
314 | will be substituted by the target host name, | |
315 | .Ql %p | |
316 | the port and | |
317 | .Ql %r | |
318 | by the remote login username. | |
319 | It is recommended that any | |
320 | .Cm ControlPath | |
321 | used for opportunistic connection sharing include | |
322 | all three of these escape sequences. | |
323 | This ensures that shared connections are uniquely identified. | |
884dc78b | 324 | .It Cm DynamicForward |
325 | Specifies that a TCP/IP port on the local machine be forwarded | |
326 | over the secure channel, and the application | |
327 | protocol is then used to determine where to connect to from the | |
bfe49944 | 328 | remote machine. |
329 | The argument must be a port number. | |
7cac2b65 | 330 | Currently the SOCKS4 and SOCKS5 protocols are supported, and |
884dc78b | 331 | .Nm ssh |
7cac2b65 | 332 | will act as a SOCKS server. |
884dc78b | 333 | Multiple forwardings may be specified, and |
bfe49944 | 334 | additional forwardings can be given on the command line. |
335 | Only the superuser can forward privileged ports. | |
7cac2b65 | 336 | .It Cm EnableSSHKeysign |
337 | Setting this option to | |
338 | .Dq yes | |
339 | in the global client configuration file | |
340 | .Pa /etc/ssh/ssh_config | |
341 | enables the use of the helper program | |
342 | .Xr ssh-keysign 8 | |
343 | during | |
344 | .Cm HostbasedAuthentication . | |
345 | The argument must be | |
346 | .Dq yes | |
347 | or | |
348 | .Dq no . | |
349 | The default is | |
350 | .Dq no . | |
540d72c3 | 351 | This option should be placed in the non-hostspecific section. |
7cac2b65 | 352 | See |
353 | .Xr ssh-keysign 8 | |
354 | for more information. | |
884dc78b | 355 | .It Cm EscapeChar |
356 | Sets the escape character (default: | |
357 | .Ql ~ ) . | |
358 | The escape character can also | |
359 | be set on the command line. | |
360 | The argument should be a single character, | |
361 | .Ql ^ | |
362 | followed by a letter, or | |
363 | .Dq none | |
364 | to disable the escape | |
365 | character entirely (making the connection transparent for binary | |
366 | data). | |
367 | .It Cm ForwardAgent | |
368 | Specifies whether the connection to the authentication agent (if any) | |
369 | will be forwarded to the remote machine. | |
370 | The argument must be | |
371 | .Dq yes | |
372 | or | |
373 | .Dq no . | |
374 | The default is | |
375 | .Dq no . | |
d03f4262 | 376 | .Pp |
bfe49944 | 377 | Agent forwarding should be enabled with caution. |
378 | Users with the ability to bypass file permissions on the remote host | |
379 | (for the agent's Unix-domain socket) | |
380 | can access the local agent through the forwarded connection. | |
381 | An attacker cannot obtain key material from the agent, | |
d03f4262 | 382 | however they can perform operations on the keys that enable them to |
383 | authenticate using the identities loaded into the agent. | |
884dc78b | 384 | .It Cm ForwardX11 |
385 | Specifies whether X11 connections will be automatically redirected | |
386 | over the secure channel and | |
387 | .Ev DISPLAY | |
388 | set. | |
389 | The argument must be | |
390 | .Dq yes | |
391 | or | |
392 | .Dq no . | |
393 | The default is | |
394 | .Dq no . | |
d03f4262 | 395 | .Pp |
bfe49944 | 396 | X11 forwarding should be enabled with caution. |
397 | Users with the ability to bypass file permissions on the remote host | |
540d72c3 | 398 | (for the user's X11 authorization database) |
bfe49944 | 399 | can access the local X11 display through the forwarded connection. |
540d72c3 | 400 | An attacker may then be able to perform activities such as keystroke monitoring |
401 | if the | |
402 | .Cm ForwardX11Trusted | |
403 | option is also enabled. | |
404 | .It Cm ForwardX11Trusted | |
7e82606e | 405 | If this option is set to |
540d72c3 | 406 | .Dq yes |
407 | then remote X11 clients will have full access to the original X11 display. | |
dfddba3d | 408 | .Pp |
540d72c3 | 409 | If this option is set to |
410 | .Dq no | |
411 | then remote X11 clients will be considered untrusted and prevented | |
412 | from stealing or tampering with data belonging to trusted X11 | |
413 | clients. | |
dfddba3d | 414 | Furthermore, the |
415 | .Xr xauth 1 | |
416 | token used for the session will be set to expire after 20 minutes. | |
417 | Remote clients will be refused access after this time. | |
540d72c3 | 418 | .Pp |
419 | The default is | |
420 | .Dq no . | |
421 | .Pp | |
422 | See the X11 SECURITY extension specification for full details on | |
423 | the restrictions imposed on untrusted clients. | |
884dc78b | 424 | .It Cm GatewayPorts |
425 | Specifies whether remote hosts are allowed to connect to local | |
426 | forwarded ports. | |
427 | By default, | |
428 | .Nm ssh | |
bfe49944 | 429 | binds local port forwardings to the loopback address. |
430 | This prevents other remote hosts from connecting to forwarded ports. | |
884dc78b | 431 | .Cm GatewayPorts |
432 | can be used to specify that | |
433 | .Nm ssh | |
434 | should bind local port forwardings to the wildcard address, | |
435 | thus allowing remote hosts to connect to forwarded ports. | |
436 | The argument must be | |
437 | .Dq yes | |
438 | or | |
439 | .Dq no . | |
440 | The default is | |
441 | .Dq no . | |
442 | .It Cm GlobalKnownHostsFile | |
443 | Specifies a file to use for the global | |
444 | host key database instead of | |
445 | .Pa /etc/ssh/ssh_known_hosts . | |
7cac2b65 | 446 | .It Cm GSSAPIAuthentication |
540d72c3 | 447 | Specifies whether user authentication based on GSSAPI is allowed. |
44a053a3 | 448 | The default is |
449 | .Dq yes . | |
85740ad2 | 450 | Note that this option applies to protocol version 2 only. |
7cac2b65 | 451 | .It Cm GSSAPIKeyExchange |
7a056ed1 | 452 | Specifies whether key exchange based on GSSAPI may be used. When using |
453 | GSSAPI key exchange the server need not have a host key. | |
454 | The default is | |
455 | .Dq yes . | |
85740ad2 | 456 | Note that this option applies to protocol version 2 only. |
7cac2b65 | 457 | .It Cm GSSAPIDelegateCredentials |
85740ad2 | 458 | Forward (delegate) credentials to the server. |
44a053a3 | 459 | The default is |
460 | .Dq yes . | |
85740ad2 | 461 | Note that this option applies to protocol version 2 only. |
fe4ad273 | 462 | .It Cm GSSAPITrustDns |
463 | Set to | |
464 | .Dq yes to indicate that the DNS is trusted to securely canonicalize | |
465 | the name of the host being connected to. If | |
466 | .Dq no, the hostname entered on the | |
467 | command line will be passed untouched to the GSSAPI library. | |
468 | The default is | |
469 | .Dq yes . | |
470 | This option only applies to protocol version 2 connections using GSSAPI | |
471 | key exchange. | |
dfddba3d | 472 | .It Cm HashKnownHosts |
473 | Indicates that | |
474 | .Nm ssh | |
475 | should hash host names and addresses when they are added to | |
2ce0bfe4 | 476 | .Pa ~/.ssh/known_hosts . |
dfddba3d | 477 | These hashed names may be used normally by |
478 | .Nm ssh | |
479 | and | |
480 | .Nm sshd , | |
481 | but they do not reveal identifying information should the file's contents | |
482 | be disclosed. | |
483 | The default is | |
484 | .Dq no . | |
485 | Note that hashing of names and addresses will not be retrospectively applied | |
486 | to existing known hosts files, but these may be manually hashed using | |
487 | .Xr ssh-keygen 1 . | |
884dc78b | 488 | .It Cm HostbasedAuthentication |
489 | Specifies whether to try rhosts based authentication with public key | |
490 | authentication. | |
491 | The argument must be | |
492 | .Dq yes | |
493 | or | |
494 | .Dq no . | |
495 | The default is | |
496 | .Dq no . | |
497 | This option applies to protocol version 2 only and | |
498 | is similar to | |
499 | .Cm RhostsRSAAuthentication . | |
500 | .It Cm HostKeyAlgorithms | |
501 | Specifies the protocol version 2 host key algorithms | |
502 | that the client wants to use in order of preference. | |
503 | The default for this option is: | |
504 | .Dq ssh-rsa,ssh-dss . | |
505 | .It Cm HostKeyAlias | |
506 | Specifies an alias that should be used instead of the | |
507 | real host name when looking up or saving the host key | |
508 | in the host key database files. | |
509 | This option is useful for tunneling ssh connections | |
510 | or for multiple servers running on a single host. | |
511 | .It Cm HostName | |
512 | Specifies the real host name to log into. | |
513 | This can be used to specify nicknames or abbreviations for hosts. | |
514 | Default is the name given on the command line. | |
515 | Numeric IP addresses are also permitted (both on the command line and in | |
516 | .Cm HostName | |
517 | specifications). | |
518 | .It Cm IdentityFile | |
519 | Specifies a file from which the user's RSA or DSA authentication identity | |
7cac2b65 | 520 | is read. |
521 | The default is | |
2ce0bfe4 | 522 | .Pa ~/.ssh/identity |
884dc78b | 523 | for protocol version 1, and |
2ce0bfe4 | 524 | .Pa ~/.ssh/id_rsa |
884dc78b | 525 | and |
2ce0bfe4 | 526 | .Pa ~/.ssh/id_dsa |
884dc78b | 527 | for protocol version 2. |
528 | Additionally, any identities represented by the authentication agent | |
529 | will be used for authentication. | |
530 | The file name may use the tilde | |
531 | syntax to refer to a user's home directory. | |
532 | It is possible to have | |
533 | multiple identity files specified in configuration files; all these | |
534 | identities will be tried in sequence. | |
12a403af | 535 | .It Cm IdentitiesOnly |
536 | Specifies that | |
537 | .Nm ssh | |
538 | should only use the authentication identity files configured in the | |
7e82606e | 539 | .Nm |
12a403af | 540 | files, |
541 | even if the | |
542 | .Nm ssh-agent | |
543 | offers more identities. | |
544 | The argument to this keyword must be | |
545 | .Dq yes | |
546 | or | |
547 | .Dq no . | |
548 | This option is intented for situations where | |
549 | .Nm ssh-agent | |
550 | offers many different identities. | |
551 | The default is | |
552 | .Dq no . | |
dfddba3d | 553 | .It Cm KbdInteractiveDevices |
554 | Specifies the list of methods to use in keyboard-interactive authentication. | |
555 | Multiple method names must be comma-separated. | |
556 | The default is to use the server specified list. | |
884dc78b | 557 | .It Cm LocalForward |
558 | Specifies that a TCP/IP port on the local machine be forwarded over | |
559 | the secure channel to the specified host and port from the remote machine. | |
8b32eddc | 560 | The first argument must be |
dfddba3d | 561 | .Sm off |
8b32eddc | 562 | .Oo Ar bind_address : Oc Ar port |
dfddba3d | 563 | .Sm on |
8b32eddc | 564 | and the second argument must be |
565 | .Ar host : Ns Ar hostport . | |
dfddba3d | 566 | IPv6 addresses can be specified by enclosing addresses in square brackets or |
567 | by using an alternative syntax: | |
8b32eddc | 568 | .Oo Ar bind_address Ns / Oc Ns Ar port |
569 | and | |
570 | .Ar host Ns / Ns Ar hostport . | |
dfddba3d | 571 | Multiple forwardings may be specified, and additional forwardings can be |
572 | given on the command line. | |
884dc78b | 573 | Only the superuser can forward privileged ports. |
dfddba3d | 574 | By default, the local port is bound in accordance with the |
575 | .Cm GatewayPorts | |
576 | setting. | |
577 | However, an explicit | |
578 | .Ar bind_address | |
579 | may be used to bind the connection to a specific address. | |
580 | The | |
581 | .Ar bind_address | |
582 | of | |
583 | .Dq localhost | |
584 | indicates that the listening port be bound for local use only, while an | |
585 | empty address or | |
586 | .Sq * | |
587 | indicates that the port should be available from all interfaces. | |
884dc78b | 588 | .It Cm LogLevel |
589 | Gives the verbosity level that is used when logging messages from | |
590 | .Nm ssh . | |
591 | The possible values are: | |
592 | QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3. | |
bfe49944 | 593 | The default is INFO. |
594 | DEBUG and DEBUG1 are equivalent. | |
595 | DEBUG2 and DEBUG3 each specify higher levels of verbose output. | |
884dc78b | 596 | .It Cm MACs |
597 | Specifies the MAC (message authentication code) algorithms | |
598 | in order of preference. | |
599 | The MAC algorithm is used in protocol version 2 | |
600 | for data integrity protection. | |
601 | Multiple algorithms must be comma-separated. | |
602 | The default is | |
603 | .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 . | |
604 | .It Cm NoHostAuthenticationForLocalhost | |
605 | This option can be used if the home directory is shared across machines. | |
606 | In this case localhost will refer to a different machine on each of | |
607 | the machines and the user will get many warnings about changed host keys. | |
608 | However, this option disables host authentication for localhost. | |
609 | The argument to this keyword must be | |
610 | .Dq yes | |
611 | or | |
612 | .Dq no . | |
613 | The default is to check the host key for localhost. | |
614 | .It Cm NumberOfPasswordPrompts | |
615 | Specifies the number of password prompts before giving up. | |
616 | The argument to this keyword must be an integer. | |
617 | Default is 3. | |
618 | .It Cm PasswordAuthentication | |
619 | Specifies whether to use password authentication. | |
620 | The argument to this keyword must be | |
621 | .Dq yes | |
622 | or | |
623 | .Dq no . | |
624 | The default is | |
625 | .Dq yes . | |
626 | .It Cm Port | |
627 | Specifies the port number to connect on the remote host. | |
628 | Default is 22. | |
629 | .It Cm PreferredAuthentications | |
630 | Specifies the order in which the client should try protocol 2 | |
7cac2b65 | 631 | authentication methods. |
8b32eddc | 632 | This allows a client to prefer one method (e.g.\& |
884dc78b | 633 | .Cm keyboard-interactive ) |
8b32eddc | 634 | over another method (e.g.\& |
884dc78b | 635 | .Cm password ) |
636 | The default for this option is: | |
fe4ad273 | 637 | .Dq publickey,gssapi-keyex,external-keyx,gssapi-with-mic,gssapi,password,keyboard-interactive . |
884dc78b | 638 | .It Cm Protocol |
639 | Specifies the protocol versions | |
640 | .Nm ssh | |
641 | should support in order of preference. | |
642 | The possible values are | |
643 | .Dq 1 | |
644 | and | |
645 | .Dq 2 . | |
646 | Multiple versions must be comma-separated. | |
647 | The default is | |
648 | .Dq 2,1 . | |
649 | This means that | |
650 | .Nm ssh | |
651 | tries version 2 and falls back to version 1 | |
652 | if version 2 is not available. | |
653 | .It Cm ProxyCommand | |
654 | Specifies the command to use to connect to the server. | |
655 | The command | |
656 | string extends to the end of the line, and is executed with | |
657 | .Pa /bin/sh . | |
658 | In the command string, | |
659 | .Ql %h | |
660 | will be substituted by the host name to | |
661 | connect and | |
662 | .Ql %p | |
663 | by the port. | |
664 | The command can be basically anything, | |
665 | and should read from its standard input and write to its standard output. | |
666 | It should eventually connect an | |
667 | .Xr sshd 8 | |
668 | server running on some machine, or execute | |
669 | .Ic sshd -i | |
670 | somewhere. | |
671 | Host key management will be done using the | |
672 | HostName of the host being connected (defaulting to the name typed by | |
673 | the user). | |
bfe49944 | 674 | Setting the command to |
675 | .Dq none | |
676 | disables this option entirely. | |
884dc78b | 677 | Note that |
678 | .Cm CheckHostIP | |
679 | is not available for connects with a proxy command. | |
680 | .Pp | |
2ce0bfe4 | 681 | This directive is useful in conjunction with |
682 | .Xr nc 1 | |
683 | and its proxy support. | |
684 | For example, the following directive would connect via an HTTP proxy at | |
685 | 192.0.2.0: | |
686 | .Bd -literal -offset 3n | |
687 | ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p | |
688 | .Ed | |
884dc78b | 689 | .It Cm PubkeyAuthentication |
690 | Specifies whether to try public key authentication. | |
691 | The argument to this keyword must be | |
692 | .Dq yes | |
693 | or | |
694 | .Dq no . | |
695 | The default is | |
696 | .Dq yes . | |
697 | This option applies to protocol version 2 only. | |
698 | .It Cm RemoteForward | |
699 | Specifies that a TCP/IP port on the remote machine be forwarded over | |
700 | the secure channel to the specified host and port from the local machine. | |
8b32eddc | 701 | The first argument must be |
dfddba3d | 702 | .Sm off |
8b32eddc | 703 | .Oo Ar bind_address : Oc Ar port |
dfddba3d | 704 | .Sm on |
8b32eddc | 705 | and the second argument must be |
706 | .Ar host : Ns Ar hostport . | |
707 | IPv6 addresses can be specified by enclosing addresses in square brackets | |
708 | or by using an alternative syntax: | |
709 | .Oo Ar bind_address Ns / Oc Ns Ar port | |
710 | and | |
711 | .Ar host Ns / Ns Ar hostport . | |
884dc78b | 712 | Multiple forwardings may be specified, and additional |
713 | forwardings can be given on the command line. | |
714 | Only the superuser can forward privileged ports. | |
dfddba3d | 715 | .Pp |
716 | If the | |
717 | .Ar bind_address | |
718 | is not specified, the default is to only bind to loopback addresses. | |
719 | If the | |
720 | .Ar bind_address | |
721 | is | |
722 | .Ql * | |
723 | or an empty string, then the forwarding is requested to listen on all | |
724 | interfaces. | |
725 | Specifying a remote | |
726 | .Ar bind_address | |
727 | will only succeed if the server's | |
728 | .Cm GatewayPorts | |
729 | option is enabled (see | |
730 | .Xr sshd_config 5 ) . | |
884dc78b | 731 | .It Cm RhostsRSAAuthentication |
732 | Specifies whether to try rhosts based authentication with RSA host | |
733 | authentication. | |
734 | The argument must be | |
735 | .Dq yes | |
736 | or | |
737 | .Dq no . | |
738 | The default is | |
739 | .Dq no . | |
740 | This option applies to protocol version 1 only and requires | |
741 | .Nm ssh | |
742 | to be setuid root. | |
743 | .It Cm RSAAuthentication | |
744 | Specifies whether to try RSA authentication. | |
745 | The argument to this keyword must be | |
746 | .Dq yes | |
747 | or | |
748 | .Dq no . | |
749 | RSA authentication will only be | |
750 | attempted if the identity file exists, or an authentication agent is | |
751 | running. | |
752 | The default is | |
753 | .Dq yes . | |
754 | Note that this option applies to protocol version 1 only. | |
7e82606e | 755 | .It Cm SendEnv |
756 | Specifies what variables from the local | |
757 | .Xr environ 7 | |
758 | should be sent to the server. | |
759 | Note that environment passing is only supported for protocol 2, the | |
760 | server must also support it, and the server must be configured to | |
761 | accept these environment variables. | |
762 | Refer to | |
763 | .Cm AcceptEnv | |
764 | in | |
765 | .Xr sshd_config 5 | |
766 | for how to configure the server. | |
767 | Variables are specified by name, which may contain the wildcard characters | |
768 | .Ql \&* | |
769 | and | |
770 | .Ql \&? . | |
771 | Multiple environment variables may be separated by whitespace or spread | |
772 | across multiple | |
773 | .Cm SendEnv | |
774 | directives. | |
775 | The default is not to send any environment variables. | |
540d72c3 | 776 | .It Cm ServerAliveInterval |
777 | Sets a timeout interval in seconds after which if no data has been received | |
778 | from the server, | |
779 | .Nm ssh | |
780 | will send a message through the encrypted | |
781 | channel to request a response from the server. | |
782 | The default | |
783 | is 0, indicating that these messages will not be sent to the server. | |
784 | This option applies to protocol version 2 only. | |
785 | .It Cm ServerAliveCountMax | |
786 | Sets the number of server alive messages (see above) which may be | |
787 | sent without | |
788 | .Nm ssh | |
789 | receiving any messages back from the server. | |
790 | If this threshold is reached while server alive messages are being sent, | |
791 | .Nm ssh | |
792 | will disconnect from the server, terminating the session. | |
793 | It is important to note that the use of server alive messages is very | |
794 | different from | |
795 | .Cm TCPKeepAlive | |
796 | (below). | |
797 | The server alive messages are sent through the encrypted channel | |
798 | and therefore will not be spoofable. | |
799 | The TCP keepalive option enabled by | |
800 | .Cm TCPKeepAlive | |
801 | is spoofable. | |
802 | The server alive mechanism is valuable when the client or | |
803 | server depend on knowing when a connection has become inactive. | |
804 | .Pp | |
805 | The default value is 3. | |
806 | If, for example, | |
807 | .Cm ServerAliveInterval | |
808 | (above) is set to 15, and | |
809 | .Cm ServerAliveCountMax | |
810 | is left at the default, if the server becomes unresponsive ssh | |
811 | will disconnect after approximately 45 seconds. | |
884dc78b | 812 | .It Cm SmartcardDevice |
7cac2b65 | 813 | Specifies which smartcard device to use. |
814 | The argument to this keyword is the device | |
884dc78b | 815 | .Nm ssh |
816 | should use to communicate with a smartcard used for storing the user's | |
7cac2b65 | 817 | private RSA key. |
818 | By default, no device is specified and smartcard support is not activated. | |
884dc78b | 819 | .It Cm StrictHostKeyChecking |
820 | If this flag is set to | |
821 | .Dq yes , | |
822 | .Nm ssh | |
823 | will never automatically add host keys to the | |
2ce0bfe4 | 824 | .Pa ~/.ssh/known_hosts |
884dc78b | 825 | file, and refuses to connect to hosts whose host key has changed. |
826 | This provides maximum protection against trojan horse attacks, | |
827 | however, can be annoying when the | |
828 | .Pa /etc/ssh/ssh_known_hosts | |
829 | file is poorly maintained, or connections to new hosts are | |
830 | frequently made. | |
831 | This option forces the user to manually | |
832 | add all new hosts. | |
833 | If this flag is set to | |
834 | .Dq no , | |
835 | .Nm ssh | |
836 | will automatically add new host keys to the | |
837 | user known hosts files. | |
838 | If this flag is set to | |
839 | .Dq ask , | |
840 | new host keys | |
841 | will be added to the user known host files only after the user | |
842 | has confirmed that is what they really want to do, and | |
843 | .Nm ssh | |
844 | will refuse to connect to hosts whose host key has changed. | |
845 | The host keys of | |
846 | known hosts will be verified automatically in all cases. | |
847 | The argument must be | |
848 | .Dq yes , | |
849 | .Dq no | |
850 | or | |
851 | .Dq ask . | |
852 | The default is | |
853 | .Dq ask . | |
540d72c3 | 854 | .It Cm TCPKeepAlive |
855 | Specifies whether the system should send TCP keepalive messages to the | |
856 | other side. | |
857 | If they are sent, death of the connection or crash of one | |
858 | of the machines will be properly noticed. | |
859 | However, this means that | |
860 | connections will die if the route is down temporarily, and some people | |
861 | find it annoying. | |
862 | .Pp | |
863 | The default is | |
864 | .Dq yes | |
865 | (to send TCP keepalive messages), and the client will notice | |
866 | if the network goes down or the remote host dies. | |
867 | This is important in scripts, and many users want it too. | |
868 | .Pp | |
869 | To disable TCP keepalive messages, the value should be set to | |
870 | .Dq no . | |
884dc78b | 871 | .It Cm UsePrivilegedPort |
872 | Specifies whether to use a privileged port for outgoing connections. | |
873 | The argument must be | |
874 | .Dq yes | |
875 | or | |
876 | .Dq no . | |
877 | The default is | |
878 | .Dq no . | |
d03f4262 | 879 | If set to |
880 | .Dq yes | |
881 | .Nm ssh | |
882 | must be setuid root. | |
884dc78b | 883 | Note that this option must be set to |
884 | .Dq yes | |
7cac2b65 | 885 | for |
884dc78b | 886 | .Cm RhostsRSAAuthentication |
7cac2b65 | 887 | with older servers. |
884dc78b | 888 | .It Cm User |
889 | Specifies the user to log in as. | |
890 | This can be useful when a different user name is used on different machines. | |
891 | This saves the trouble of | |
892 | having to remember to give the user name on the command line. | |
893 | .It Cm UserKnownHostsFile | |
894 | Specifies a file to use for the user | |
895 | host key database instead of | |
2ce0bfe4 | 896 | .Pa ~/.ssh/known_hosts . |
7cac2b65 | 897 | .It Cm VerifyHostKeyDNS |
898 | Specifies whether to verify the remote key using DNS and SSHFP resource | |
899 | records. | |
540d72c3 | 900 | If this option is set to |
901 | .Dq yes , | |
902 | the client will implicitly trust keys that match a secure fingerprint | |
903 | from DNS. | |
904 | Insecure fingerprints will be handled as if this option was set to | |
905 | .Dq ask . | |
906 | If this option is set to | |
907 | .Dq ask , | |
908 | information on fingerprint match will be displayed, but the user will still | |
909 | need to confirm new host keys according to the | |
910 | .Cm StrictHostKeyChecking | |
911 | option. | |
912 | The argument must be | |
913 | .Dq yes , | |
914 | .Dq no | |
915 | or | |
916 | .Dq ask . | |
7cac2b65 | 917 | The default is |
918 | .Dq no . | |
919 | Note that this option applies to protocol version 2 only. | |
884dc78b | 920 | .It Cm XAuthLocation |
d03f4262 | 921 | Specifies the full pathname of the |
884dc78b | 922 | .Xr xauth 1 |
923 | program. | |
924 | The default is | |
925 | .Pa /usr/X11R6/bin/xauth . | |
926 | .El | |
927 | .Sh FILES | |
928 | .Bl -tag -width Ds | |
2ce0bfe4 | 929 | .It Pa ~/.ssh/config |
884dc78b | 930 | This is the per-user configuration file. |
931 | The format of this file is described above. | |
932 | This file is used by the | |
933 | .Nm ssh | |
934 | client. | |
7e82606e | 935 | Because of the potential for abuse, this file must have strict permissions: |
936 | read/write for the user, and not accessible by others. | |
884dc78b | 937 | .It Pa /etc/ssh/ssh_config |
938 | Systemwide configuration file. | |
939 | This file provides defaults for those | |
940 | values that are not specified in the user's configuration file, and | |
941 | for those users who do not have a configuration file. | |
942 | This file must be world-readable. | |
943 | .El | |
7cac2b65 | 944 | .Sh SEE ALSO |
945 | .Xr ssh 1 | |
884dc78b | 946 | .Sh AUTHORS |
947 | OpenSSH is a derivative of the original and free | |
948 | ssh 1.2.12 release by Tatu Ylonen. | |
949 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
950 | Theo de Raadt and Dug Song | |
951 | removed many bugs, re-added newer features and | |
952 | created OpenSSH. | |
953 | Markus Friedl contributed the support for SSH | |
954 | protocol versions 1.5 and 2.0. |