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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 | .\" | |
9dfd96d6 | 37 | .\" $OpenBSD: ssh_config.5,v 1.56 2005/06/08 11:25:09 djm 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 | |
139 | Specify the interface to transmit from on machines with multiple | |
140 | interfaces or aliased addresses. | |
141 | Note that this option does not work if | |
142 | .Cm UsePrivilegedPort | |
143 | is set to | |
144 | .Dq yes . | |
145 | .It Cm ChallengeResponseAuthentication | |
146 | Specifies whether to use challenge response authentication. | |
147 | The argument to this keyword must be | |
148 | .Dq yes | |
149 | or | |
150 | .Dq no . | |
151 | The default is | |
152 | .Dq yes . | |
153 | .It Cm CheckHostIP | |
154 | If this flag is set to | |
155 | .Dq yes , | |
156 | ssh will additionally check the host IP address in the | |
157 | .Pa known_hosts | |
158 | file. | |
159 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
160 | If the option is set to | |
161 | .Dq no , | |
162 | the check will not be executed. | |
163 | The default is | |
164 | .Dq yes . | |
165 | .It Cm Cipher | |
166 | Specifies the cipher to use for encrypting the session | |
167 | in protocol version 1. | |
168 | Currently, | |
169 | .Dq blowfish , | |
170 | .Dq 3des , | |
171 | and | |
172 | .Dq des | |
173 | are supported. | |
174 | .Ar des | |
175 | is only supported in the | |
176 | .Nm ssh | |
177 | client for interoperability with legacy protocol 1 implementations | |
178 | that do not support the | |
179 | .Ar 3des | |
a4e5acef | 180 | cipher. |
181 | Its use is strongly discouraged due to cryptographic weaknesses. | |
588df31a | 182 | The default is |
183 | .Dq 3des . | |
184 | .It Cm Ciphers | |
185 | Specifies the ciphers allowed for protocol version 2 | |
186 | in order of preference. | |
187 | Multiple ciphers must be comma-separated. | |
3b9baa7b | 188 | The supported ciphers are |
189 | .Dq 3des-cbc , | |
190 | .Dq aes128-cbc , | |
191 | .Dq aes192-cbc , | |
192 | .Dq aes256-cbc , | |
193 | .Dq aes128-ctr , | |
194 | .Dq aes192-ctr , | |
195 | .Dq aes256-ctr , | |
74a66cc8 | 196 | .Dq arcfour128 , |
197 | .Dq arcfour256 , | |
3b9baa7b | 198 | .Dq arcfour , |
199 | .Dq blowfish-cbc , | |
200 | and | |
201 | .Dq cast128-cbc . | |
588df31a | 202 | The default is |
588df31a | 203 | .Bd -literal |
74a66cc8 | 204 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, |
205 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
206 | aes192-ctr,aes256-ctr'' | |
588df31a | 207 | .Ed |
208 | .It Cm ClearAllForwardings | |
209 | Specifies that all local, remote and dynamic port forwardings | |
210 | specified in the configuration files or on the command line be | |
a4e5acef | 211 | cleared. |
212 | This option is primarily useful when used from the | |
588df31a | 213 | .Nm ssh |
214 | command line to clear port forwardings set in | |
215 | configuration files, and is automatically set by | |
216 | .Xr scp 1 | |
217 | and | |
218 | .Xr sftp 1 . | |
219 | The argument must be | |
220 | .Dq yes | |
221 | or | |
222 | .Dq no . | |
223 | The default is | |
224 | .Dq no . | |
225 | .It Cm Compression | |
226 | Specifies whether to use compression. | |
227 | The argument must be | |
228 | .Dq yes | |
229 | or | |
230 | .Dq no . | |
231 | The default is | |
232 | .Dq no . | |
233 | .It Cm CompressionLevel | |
234 | Specifies the compression level to use if compression is enabled. | |
235 | The argument must be an integer from 1 (fast) to 9 (slow, best). | |
236 | The default level is 6, which is good for most applications. | |
237 | The meaning of the values is the same as in | |
238 | .Xr gzip 1 . | |
239 | Note that this option applies to protocol version 1 only. | |
240 | .It Cm ConnectionAttempts | |
241 | Specifies the number of tries (one per second) to make before exiting. | |
242 | The argument must be an integer. | |
243 | This may be useful in scripts if the connection sometimes fails. | |
244 | The default is 1. | |
09ab3296 | 245 | .It Cm ConnectTimeout |
246 | Specifies the timeout (in seconds) used when connecting to the ssh | |
3cbc677d | 247 | server, instead of using the default system TCP timeout. |
248 | This value is used only when the target is down or really unreachable, | |
249 | not when it refuses the connection. | |
5e96b616 | 250 | .It Cm ControlMaster |
251 | Enables the sharing of multiple sessions over a single network connection. | |
252 | When set to | |
253 | .Dq yes | |
254 | .Nm ssh | |
255 | will listen for connections on a control socket specified using the | |
256 | .Cm ControlPath | |
257 | argument. | |
258 | Additional sessions can connect to this socket using the same | |
259 | .Cm ControlPath | |
260 | with | |
261 | .Cm ControlMaster | |
262 | set to | |
263 | .Dq no | |
9a5cfb58 | 264 | (the default). |
5e96b616 | 265 | These sessions will reuse the master instance's network connection rather |
266 | than initiating new ones. | |
0d34d6ce | 267 | Setting this to |
268 | .Dq ask | |
269 | will cause | |
270 | .Nm ssh | |
271 | to listen for control connections, but require confirmation using the | |
272 | .Ev SSH_ASKPASS | |
273 | program before they are accepted (see | |
274 | .Xr ssh-add 1 | |
9a5cfb58 | 275 | for details). |
cc8ca1e6 | 276 | If the |
277 | .Cm ControlPath | |
278 | can not be opened, | |
279 | .Nm ssh | |
280 | will continue without connecting to a master instance. | |
9dfd96d6 | 281 | .Pp |
282 | Two additional options allow for opportunistic multiplexing: try to use a | |
283 | master connection but fall back to creating a new one if one does not already | |
284 | exist. | |
285 | These options are: | |
286 | .Dq auto | |
287 | and | |
288 | .Dq autoask . | |
289 | The latter requires confirmation like the | |
290 | .Dq ask | |
291 | option. | |
5e96b616 | 292 | .It Cm ControlPath |
a980cbd7 | 293 | Specify the path to the control socket used for connection sharing as described |
294 | in the | |
5e96b616 | 295 | .Cm ControlMaster |
a980cbd7 | 296 | section above. |
297 | In the path, | |
298 | .Ql %h | |
299 | will be substituted by the target host name, | |
300 | .Ql %p | |
301 | the port and | |
302 | .Ql %r | |
303 | by the remote login username. | |
9dfd96d6 | 304 | It is recommended that any |
305 | .Cm ControlPath | |
306 | used for opportunistic connection sharing include | |
307 | all three of these escape sequences. | |
308 | This ensures that shared connections are uniquely identified. | |
9a5cfb58 | 309 | .It Cm DynamicForward |
310 | Specifies that a TCP/IP port on the local machine be forwarded | |
311 | over the secure channel, and the application | |
312 | protocol is then used to determine where to connect to from the | |
313 | remote machine. | |
314 | The argument must be a port number. | |
315 | Currently the SOCKS4 and SOCKS5 protocols are supported, and | |
316 | .Nm ssh | |
317 | will act as a SOCKS server. | |
318 | Multiple forwardings may be specified, and | |
319 | additional forwardings can be given on the command line. | |
320 | Only the superuser can forward privileged ports. | |
f0677b69 | 321 | .It Cm EnableSSHKeysign |
322 | Setting this option to | |
323 | .Dq yes | |
324 | in the global client configuration file | |
325 | .Pa /etc/ssh/ssh_config | |
326 | enables the use of the helper program | |
327 | .Xr ssh-keysign 8 | |
328 | during | |
329 | .Cm HostbasedAuthentication . | |
330 | The argument must be | |
331 | .Dq yes | |
332 | or | |
333 | .Dq no . | |
334 | The default is | |
335 | .Dq no . | |
246bb171 | 336 | This option should be placed in the non-hostspecific section. |
f0677b69 | 337 | See |
338 | .Xr ssh-keysign 8 | |
339 | for more information. | |
588df31a | 340 | .It Cm EscapeChar |
341 | Sets the escape character (default: | |
342 | .Ql ~ ) . | |
343 | The escape character can also | |
344 | be set on the command line. | |
345 | The argument should be a single character, | |
346 | .Ql ^ | |
347 | followed by a letter, or | |
348 | .Dq none | |
349 | to disable the escape | |
350 | character entirely (making the connection transparent for binary | |
351 | data). | |
352 | .It Cm ForwardAgent | |
353 | Specifies whether the connection to the authentication agent (if any) | |
354 | will be forwarded to the remote machine. | |
355 | The argument must be | |
356 | .Dq yes | |
357 | or | |
358 | .Dq no . | |
359 | The default is | |
360 | .Dq no . | |
dbcdea68 | 361 | .Pp |
a4e5acef | 362 | Agent forwarding should be enabled with caution. |
363 | Users with the ability to bypass file permissions on the remote host | |
364 | (for the agent's Unix-domain socket) | |
365 | can access the local agent through the forwarded connection. | |
366 | An attacker cannot obtain key material from the agent, | |
dbcdea68 | 367 | however they can perform operations on the keys that enable them to |
368 | authenticate using the identities loaded into the agent. | |
588df31a | 369 | .It Cm ForwardX11 |
370 | Specifies whether X11 connections will be automatically redirected | |
371 | over the secure channel and | |
372 | .Ev DISPLAY | |
373 | set. | |
374 | The argument must be | |
375 | .Dq yes | |
376 | or | |
377 | .Dq no . | |
378 | The default is | |
379 | .Dq no . | |
dbcdea68 | 380 | .Pp |
a4e5acef | 381 | X11 forwarding should be enabled with caution. |
382 | Users with the ability to bypass file permissions on the remote host | |
d73a67d7 | 383 | (for the user's X11 authorization database) |
a4e5acef | 384 | can access the local X11 display through the forwarded connection. |
d73a67d7 | 385 | An attacker may then be able to perform activities such as keystroke monitoring |
386 | if the | |
387 | .Cm ForwardX11Trusted | |
388 | option is also enabled. | |
389 | .It Cm ForwardX11Trusted | |
b2e90ab5 | 390 | If this option is set to |
d73a67d7 | 391 | .Dq yes |
392 | then remote X11 clients will have full access to the original X11 display. | |
9a6b3b7a | 393 | .Pp |
d73a67d7 | 394 | If this option is set to |
395 | .Dq no | |
396 | then remote X11 clients will be considered untrusted and prevented | |
397 | from stealing or tampering with data belonging to trusted X11 | |
398 | clients. | |
9a6b3b7a | 399 | Furthermore, the |
400 | .Xr xauth 1 | |
401 | token used for the session will be set to expire after 20 minutes. | |
402 | Remote clients will be refused access after this time. | |
d73a67d7 | 403 | .Pp |
404 | The default is | |
405 | .Dq no . | |
406 | .Pp | |
407 | See the X11 SECURITY extension specification for full details on | |
408 | the restrictions imposed on untrusted clients. | |
588df31a | 409 | .It Cm GatewayPorts |
410 | Specifies whether remote hosts are allowed to connect to local | |
411 | forwarded ports. | |
412 | By default, | |
413 | .Nm ssh | |
a4e5acef | 414 | binds local port forwardings to the loopback address. |
415 | This prevents other remote hosts from connecting to forwarded ports. | |
588df31a | 416 | .Cm GatewayPorts |
417 | can be used to specify that | |
418 | .Nm ssh | |
419 | should bind local port forwardings to the wildcard address, | |
420 | thus allowing remote hosts to connect to forwarded ports. | |
421 | The argument must be | |
422 | .Dq yes | |
423 | or | |
424 | .Dq no . | |
425 | The default is | |
426 | .Dq no . | |
427 | .It Cm GlobalKnownHostsFile | |
428 | Specifies a file to use for the global | |
429 | host key database instead of | |
430 | .Pa /etc/ssh/ssh_known_hosts . | |
7364bd04 | 431 | .It Cm GSSAPIAuthentication |
e8dd24a8 | 432 | Specifies whether user authentication based on GSSAPI is allowed. |
d0445371 | 433 | The default is |
2ecb78df | 434 | .Dq no . |
7364bd04 | 435 | Note that this option applies to protocol version 2 only. |
436 | .It Cm GSSAPIDelegateCredentials | |
437 | Forward (delegate) credentials to the server. | |
438 | The default is | |
439 | .Dq no . | |
440 | Note that this option applies to protocol version 2 only. | |
5c63c2ab | 441 | .It Cm HashKnownHosts |
442 | Indicates that | |
443 | .Nm ssh | |
444 | should hash host names and addresses when they are added to | |
140e3e97 | 445 | .Pa ~/.ssh/known_hosts . |
5c63c2ab | 446 | These hashed names may be used normally by |
447 | .Nm ssh | |
448 | and | |
449 | .Nm sshd , | |
450 | but they do not reveal identifying information should the file's contents | |
451 | be disclosed. | |
452 | The default is | |
453 | .Dq no . | |
cd8f998c | 454 | Note that hashing of names and addresses will not be retrospectively applied |
bdffbcdc | 455 | to existing known hosts files, but these may be manually hashed using |
456 | .Xr ssh-keygen 1 . | |
588df31a | 457 | .It Cm HostbasedAuthentication |
458 | Specifies whether to try rhosts based authentication with public key | |
459 | authentication. | |
460 | The argument must be | |
461 | .Dq yes | |
462 | or | |
463 | .Dq no . | |
464 | The default is | |
465 | .Dq no . | |
466 | This option applies to protocol version 2 only and | |
467 | is similar to | |
468 | .Cm RhostsRSAAuthentication . | |
469 | .It Cm HostKeyAlgorithms | |
470 | Specifies the protocol version 2 host key algorithms | |
471 | that the client wants to use in order of preference. | |
472 | The default for this option is: | |
473 | .Dq ssh-rsa,ssh-dss . | |
474 | .It Cm HostKeyAlias | |
475 | Specifies an alias that should be used instead of the | |
476 | real host name when looking up or saving the host key | |
477 | in the host key database files. | |
478 | This option is useful for tunneling ssh connections | |
479 | or for multiple servers running on a single host. | |
480 | .It Cm HostName | |
481 | Specifies the real host name to log into. | |
482 | This can be used to specify nicknames or abbreviations for hosts. | |
483 | Default is the name given on the command line. | |
484 | Numeric IP addresses are also permitted (both on the command line and in | |
485 | .Cm HostName | |
486 | specifications). | |
487 | .It Cm IdentityFile | |
488 | Specifies a file from which the user's RSA or DSA authentication identity | |
3cbc677d | 489 | is read. |
490 | The default is | |
140e3e97 | 491 | .Pa ~/.ssh/identity |
588df31a | 492 | for protocol version 1, and |
140e3e97 | 493 | .Pa ~/.ssh/id_rsa |
588df31a | 494 | and |
140e3e97 | 495 | .Pa ~/.ssh/id_dsa |
588df31a | 496 | for protocol version 2. |
497 | Additionally, any identities represented by the authentication agent | |
498 | will be used for authentication. | |
499 | The file name may use the tilde | |
500 | syntax to refer to a user's home directory. | |
501 | It is possible to have | |
502 | multiple identity files specified in configuration files; all these | |
503 | identities will be tried in sequence. | |
3a065ed0 | 504 | .It Cm IdentitiesOnly |
505 | Specifies that | |
506 | .Nm ssh | |
507 | should only use the authentication identity files configured in the | |
1e9b1b82 | 508 | .Nm |
3a065ed0 | 509 | files, |
510 | even if the | |
511 | .Nm ssh-agent | |
512 | offers more identities. | |
513 | The argument to this keyword must be | |
514 | .Dq yes | |
515 | or | |
516 | .Dq no . | |
517 | This option is intented for situations where | |
518 | .Nm ssh-agent | |
519 | offers many different identities. | |
520 | The default is | |
521 | .Dq no . | |
396070f8 | 522 | .It Cm KbdInteractiveDevices |
523 | Specifies the list of methods to use in keyboard-interactive authentication. | |
524 | Multiple method names must be comma-separated. | |
525 | The default is to use the server specified list. | |
588df31a | 526 | .It Cm LocalForward |
527 | Specifies that a TCP/IP port on the local machine be forwarded over | |
528 | the secure channel to the specified host and port from the remote machine. | |
ecda4ffb | 529 | The first argument must be |
3867aa0a | 530 | .Sm off |
ecda4ffb | 531 | .Oo Ar bind_address : Oc Ar port |
3867aa0a | 532 | .Sm on |
ecda4ffb | 533 | and the second argument must be |
534 | .Ar host : Ns Ar hostport . | |
cd8f998c | 535 | IPv6 addresses can be specified by enclosing addresses in square brackets or |
3867aa0a | 536 | by using an alternative syntax: |
ecda4ffb | 537 | .Oo Ar bind_address Ns / Oc Ns Ar port |
538 | and | |
539 | .Ar host Ns / Ns Ar hostport . | |
cd8f998c | 540 | Multiple forwardings may be specified, and additional forwardings can be |
3867aa0a | 541 | given on the command line. |
588df31a | 542 | Only the superuser can forward privileged ports. |
3867aa0a | 543 | By default, the local port is bound in accordance with the |
544 | .Cm GatewayPorts | |
545 | setting. | |
546 | However, an explicit | |
547 | .Ar bind_address | |
548 | may be used to bind the connection to a specific address. | |
549 | The | |
550 | .Ar bind_address | |
551 | of | |
552 | .Dq localhost | |
cd8f998c | 553 | indicates that the listening port be bound for local use only, while an |
554 | empty address or | |
555 | .Sq * | |
3867aa0a | 556 | indicates that the port should be available from all interfaces. |
588df31a | 557 | .It Cm LogLevel |
558 | Gives the verbosity level that is used when logging messages from | |
559 | .Nm ssh . | |
560 | The possible values are: | |
561 | QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3. | |
a4e5acef | 562 | The default is INFO. |
563 | DEBUG and DEBUG1 are equivalent. | |
564 | DEBUG2 and DEBUG3 each specify higher levels of verbose output. | |
588df31a | 565 | .It Cm MACs |
566 | Specifies the MAC (message authentication code) algorithms | |
567 | in order of preference. | |
568 | The MAC algorithm is used in protocol version 2 | |
569 | for data integrity protection. | |
570 | Multiple algorithms must be comma-separated. | |
571 | The default is | |
572 | .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 . | |
573 | .It Cm NoHostAuthenticationForLocalhost | |
574 | This option can be used if the home directory is shared across machines. | |
575 | In this case localhost will refer to a different machine on each of | |
576 | the machines and the user will get many warnings about changed host keys. | |
577 | However, this option disables host authentication for localhost. | |
578 | The argument to this keyword must be | |
579 | .Dq yes | |
580 | or | |
581 | .Dq no . | |
582 | The default is to check the host key for localhost. | |
583 | .It Cm NumberOfPasswordPrompts | |
584 | Specifies the number of password prompts before giving up. | |
585 | The argument to this keyword must be an integer. | |
586 | Default is 3. | |
587 | .It Cm PasswordAuthentication | |
588 | Specifies whether to use password authentication. | |
589 | The argument to this keyword must be | |
590 | .Dq yes | |
591 | or | |
592 | .Dq no . | |
593 | The default is | |
594 | .Dq yes . | |
595 | .It Cm Port | |
596 | Specifies the port number to connect on the remote host. | |
597 | Default is 22. | |
598 | .It Cm PreferredAuthentications | |
599 | Specifies the order in which the client should try protocol 2 | |
3cbc677d | 600 | authentication methods. |
4e5038f7 | 601 | This allows a client to prefer one method (e.g.\& |
588df31a | 602 | .Cm keyboard-interactive ) |
4e5038f7 | 603 | over another method (e.g.\& |
588df31a | 604 | .Cm password ) |
605 | The default for this option is: | |
606 | .Dq hostbased,publickey,keyboard-interactive,password . | |
607 | .It Cm Protocol | |
608 | Specifies the protocol versions | |
609 | .Nm ssh | |
610 | should support in order of preference. | |
611 | The possible values are | |
612 | .Dq 1 | |
613 | and | |
614 | .Dq 2 . | |
615 | Multiple versions must be comma-separated. | |
616 | The default is | |
617 | .Dq 2,1 . | |
618 | This means that | |
619 | .Nm ssh | |
620 | tries version 2 and falls back to version 1 | |
621 | if version 2 is not available. | |
622 | .It Cm ProxyCommand | |
623 | Specifies the command to use to connect to the server. | |
624 | The command | |
625 | string extends to the end of the line, and is executed with | |
626 | .Pa /bin/sh . | |
627 | In the command string, | |
628 | .Ql %h | |
629 | will be substituted by the host name to | |
630 | connect and | |
631 | .Ql %p | |
632 | by the port. | |
633 | The command can be basically anything, | |
634 | and should read from its standard input and write to its standard output. | |
635 | It should eventually connect an | |
636 | .Xr sshd 8 | |
637 | server running on some machine, or execute | |
638 | .Ic sshd -i | |
639 | somewhere. | |
640 | Host key management will be done using the | |
641 | HostName of the host being connected (defaulting to the name typed by | |
642 | the user). | |
a4e5acef | 643 | Setting the command to |
644 | .Dq none | |
f78bde70 | 645 | disables this option entirely. |
588df31a | 646 | Note that |
647 | .Cm CheckHostIP | |
648 | is not available for connects with a proxy command. | |
649 | .Pp | |
2b610872 | 650 | This directive is useful in conjunction with |
651 | .Xr nc 1 | |
652 | and its proxy support. | |
9fa42d41 | 653 | For example, the following directive would connect via an HTTP proxy at |
2b610872 | 654 | 192.0.2.0: |
655 | .Bd -literal -offset 3n | |
656 | ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p | |
657 | .Ed | |
588df31a | 658 | .It Cm PubkeyAuthentication |
659 | Specifies whether to try public key authentication. | |
660 | The argument to this keyword must be | |
661 | .Dq yes | |
662 | or | |
663 | .Dq no . | |
664 | The default is | |
665 | .Dq yes . | |
666 | This option applies to protocol version 2 only. | |
667 | .It Cm RemoteForward | |
668 | Specifies that a TCP/IP port on the remote machine be forwarded over | |
669 | the secure channel to the specified host and port from the local machine. | |
ecda4ffb | 670 | The first argument must be |
3867aa0a | 671 | .Sm off |
ecda4ffb | 672 | .Oo Ar bind_address : Oc Ar port |
6d7a9e8f | 673 | .Sm on |
ecda4ffb | 674 | and the second argument must be |
675 | .Ar host : Ns Ar hostport . | |
676 | IPv6 addresses can be specified by enclosing addresses in square brackets | |
677 | or by using an alternative syntax: | |
678 | .Oo Ar bind_address Ns / Oc Ns Ar port | |
679 | and | |
680 | .Ar host Ns / Ns Ar hostport . | |
588df31a | 681 | Multiple forwardings may be specified, and additional |
682 | forwardings can be given on the command line. | |
683 | Only the superuser can forward privileged ports. | |
3867aa0a | 684 | .Pp |
685 | If the | |
686 | .Ar bind_address | |
687 | is not specified, the default is to only bind to loopback addresses. | |
688 | If the | |
689 | .Ar bind_address | |
690 | is | |
691 | .Ql * | |
692 | or an empty string, then the forwarding is requested to listen on all | |
693 | interfaces. | |
694 | Specifying a remote | |
695 | .Ar bind_address | |
cd8f998c | 696 | will only succeed if the server's |
697 | .Cm GatewayPorts | |
3867aa0a | 698 | option is enabled (see |
cd8f998c | 699 | .Xr sshd_config 5 ) . |
588df31a | 700 | .It Cm RhostsRSAAuthentication |
701 | Specifies whether to try rhosts based authentication with RSA host | |
702 | authentication. | |
703 | The argument must be | |
704 | .Dq yes | |
705 | or | |
706 | .Dq no . | |
707 | The default is | |
708 | .Dq no . | |
709 | This option applies to protocol version 1 only and requires | |
710 | .Nm ssh | |
711 | to be setuid root. | |
712 | .It Cm RSAAuthentication | |
713 | Specifies whether to try RSA authentication. | |
714 | The argument to this keyword must be | |
715 | .Dq yes | |
716 | or | |
717 | .Dq no . | |
718 | RSA authentication will only be | |
719 | attempted if the identity file exists, or an authentication agent is | |
720 | running. | |
721 | The default is | |
722 | .Dq yes . | |
723 | Note that this option applies to protocol version 1 only. | |
61a2c1da | 724 | .It Cm SendEnv |
725 | Specifies what variables from the local | |
726 | .Xr environ 7 | |
727 | should be sent to the server. | |
728 | Note that environment passing is only supported for protocol 2, the | |
b8b9f2e6 | 729 | server must also support it, and the server must be configured to |
730 | accept these environment variables. | |
61a2c1da | 731 | Refer to |
732 | .Cm AcceptEnv | |
733 | in | |
734 | .Xr sshd_config 5 | |
735 | for how to configure the server. | |
736 | Variables are specified by name, which may contain the wildcard characters | |
737 | .Ql \&* | |
738 | and | |
739 | .Ql \&? . | |
b8b9f2e6 | 740 | Multiple environment variables may be separated by whitespace or spread |
61a2c1da | 741 | across multiple |
742 | .Cm SendEnv | |
743 | directives. | |
744 | The default is not to send any environment variables. | |
5d8d32a3 | 745 | .It Cm ServerAliveInterval |
746 | Sets a timeout interval in seconds after which if no data has been received | |
747 | from the server, | |
748 | .Nm ssh | |
749 | will send a message through the encrypted | |
750 | channel to request a response from the server. | |
751 | The default | |
752 | is 0, indicating that these messages will not be sent to the server. | |
753 | This option applies to protocol version 2 only. | |
754 | .It Cm ServerAliveCountMax | |
755 | Sets the number of server alive messages (see above) which may be | |
756 | sent without | |
757 | .Nm ssh | |
758 | receiving any messages back from the server. | |
759 | If this threshold is reached while server alive messages are being sent, | |
760 | .Nm ssh | |
761 | will disconnect from the server, terminating the session. | |
762 | It is important to note that the use of server alive messages is very | |
763 | different from | |
764 | .Cm TCPKeepAlive | |
765 | (below). | |
766 | The server alive messages are sent through the encrypted channel | |
767 | and therefore will not be spoofable. | |
768 | The TCP keepalive option enabled by | |
769 | .Cm TCPKeepAlive | |
770 | is spoofable. | |
771 | The server alive mechanism is valuable when the client or | |
772 | server depend on knowing when a connection has become inactive. | |
773 | .Pp | |
774 | The default value is 3. | |
775 | If, for example, | |
776 | .Cm ServerAliveInterval | |
777 | (above) is set to 15, and | |
778 | .Cm ServerAliveCountMax | |
779 | is left at the default, if the server becomes unresponsive ssh | |
780 | will disconnect after approximately 45 seconds. | |
588df31a | 781 | .It Cm SmartcardDevice |
3cbc677d | 782 | Specifies which smartcard device to use. |
783 | The argument to this keyword is the device | |
588df31a | 784 | .Nm ssh |
785 | should use to communicate with a smartcard used for storing the user's | |
3cbc677d | 786 | private RSA key. |
787 | By default, no device is specified and smartcard support is not activated. | |
588df31a | 788 | .It Cm StrictHostKeyChecking |
789 | If this flag is set to | |
790 | .Dq yes , | |
791 | .Nm ssh | |
792 | will never automatically add host keys to the | |
140e3e97 | 793 | .Pa ~/.ssh/known_hosts |
588df31a | 794 | file, and refuses to connect to hosts whose host key has changed. |
795 | This provides maximum protection against trojan horse attacks, | |
796 | however, can be annoying when the | |
797 | .Pa /etc/ssh/ssh_known_hosts | |
798 | file is poorly maintained, or connections to new hosts are | |
799 | frequently made. | |
800 | This option forces the user to manually | |
801 | add all new hosts. | |
802 | If this flag is set to | |
803 | .Dq no , | |
804 | .Nm ssh | |
805 | will automatically add new host keys to the | |
806 | user known hosts files. | |
807 | If this flag is set to | |
808 | .Dq ask , | |
809 | new host keys | |
810 | will be added to the user known host files only after the user | |
811 | has confirmed that is what they really want to do, and | |
812 | .Nm ssh | |
813 | will refuse to connect to hosts whose host key has changed. | |
814 | The host keys of | |
815 | known hosts will be verified automatically in all cases. | |
816 | The argument must be | |
817 | .Dq yes , | |
818 | .Dq no | |
819 | or | |
820 | .Dq ask . | |
821 | The default is | |
822 | .Dq ask . | |
fd573618 | 823 | .It Cm TCPKeepAlive |
824 | Specifies whether the system should send TCP keepalive messages to the | |
825 | other side. | |
826 | If they are sent, death of the connection or crash of one | |
827 | of the machines will be properly noticed. | |
828 | However, this means that | |
829 | connections will die if the route is down temporarily, and some people | |
830 | find it annoying. | |
831 | .Pp | |
832 | The default is | |
833 | .Dq yes | |
834 | (to send TCP keepalive messages), and the client will notice | |
835 | if the network goes down or the remote host dies. | |
836 | This is important in scripts, and many users want it too. | |
837 | .Pp | |
838 | To disable TCP keepalive messages, the value should be set to | |
839 | .Dq no . | |
588df31a | 840 | .It Cm UsePrivilegedPort |
841 | Specifies whether to use a privileged port for outgoing connections. | |
842 | The argument must be | |
843 | .Dq yes | |
844 | or | |
845 | .Dq no . | |
846 | The default is | |
847 | .Dq no . | |
878b8992 | 848 | If set to |
849 | .Dq yes | |
850 | .Nm ssh | |
851 | must be setuid root. | |
588df31a | 852 | Note that this option must be set to |
853 | .Dq yes | |
0598d99d | 854 | for |
588df31a | 855 | .Cm RhostsRSAAuthentication |
0598d99d | 856 | with older servers. |
588df31a | 857 | .It Cm User |
858 | Specifies the user to log in as. | |
859 | This can be useful when a different user name is used on different machines. | |
860 | This saves the trouble of | |
861 | having to remember to give the user name on the command line. | |
862 | .It Cm UserKnownHostsFile | |
863 | Specifies a file to use for the user | |
864 | host key database instead of | |
140e3e97 | 865 | .Pa ~/.ssh/known_hosts . |
21289cd0 | 866 | .It Cm VerifyHostKeyDNS |
867 | Specifies whether to verify the remote key using DNS and SSHFP resource | |
868 | records. | |
0161a13d | 869 | If this option is set to |
870 | .Dq yes , | |
dd376e92 | 871 | the client will implicitly trust keys that match a secure fingerprint |
0161a13d | 872 | from DNS. |
873 | Insecure fingerprints will be handled as if this option was set to | |
874 | .Dq ask . | |
875 | If this option is set to | |
876 | .Dq ask , | |
877 | information on fingerprint match will be displayed, but the user will still | |
878 | need to confirm new host keys according to the | |
879 | .Cm StrictHostKeyChecking | |
880 | option. | |
881 | The argument must be | |
882 | .Dq yes , | |
883 | .Dq no | |
dd376e92 | 884 | or |
885 | .Dq ask . | |
21289cd0 | 886 | The default is |
887 | .Dq no . | |
0f92946c | 888 | Note that this option applies to protocol version 2 only. |
588df31a | 889 | .It Cm XAuthLocation |
57ff5eeb | 890 | Specifies the full pathname of the |
588df31a | 891 | .Xr xauth 1 |
892 | program. | |
893 | The default is | |
894 | .Pa /usr/X11R6/bin/xauth . | |
895 | .El | |
896 | .Sh FILES | |
897 | .Bl -tag -width Ds | |
140e3e97 | 898 | .It Pa ~/.ssh/config |
588df31a | 899 | This is the per-user configuration file. |
900 | The format of this file is described above. | |
901 | This file is used by the | |
902 | .Nm ssh | |
903 | client. | |
e1520719 | 904 | Because of the potential for abuse, this file must have strict permissions: |
905 | read/write for the user, and not accessible by others. | |
588df31a | 906 | .It Pa /etc/ssh/ssh_config |
907 | Systemwide configuration file. | |
908 | This file provides defaults for those | |
909 | values that are not specified in the user's configuration file, and | |
910 | for those users who do not have a configuration file. | |
911 | This file must be world-readable. | |
912 | .El | |
be193d89 | 913 | .Sh SEE ALSO |
914 | .Xr ssh 1 | |
588df31a | 915 | .Sh AUTHORS |
916 | OpenSSH is a derivative of the original and free | |
917 | ssh 1.2.12 release by Tatu Ylonen. | |
918 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
919 | Theo de Raadt and Dug Song | |
920 | removed many bugs, re-added newer features and | |
921 | created OpenSSH. | |
922 | Markus Friedl contributed the support for SSH | |
923 | protocol versions 1.5 and 2.0. |