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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 | .\" | |
f127d8a4 | 37 | .\" $OpenBSD: ssh_config.5,v 1.94 2006/05/29 16:10:03 jmc Exp $ |
588df31a | 38 | .Dd September 25, 1999 |
39 | .Dt SSH_CONFIG 5 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm ssh_config | |
43 | .Nd OpenSSH SSH client configuration files | |
44 | .Sh SYNOPSIS | |
45 | .Bl -tag -width Ds -compact | |
140e3e97 | 46 | .It Pa ~/.ssh/config |
588df31a | 47 | .It Pa /etc/ssh/ssh_config |
48 | .El | |
49 | .Sh DESCRIPTION | |
c5786b30 | 50 | .Xr ssh 1 |
588df31a | 51 | obtains configuration data from the following sources in |
52 | the following order: | |
922f8f17 | 53 | .Pp |
4dcbbeea | 54 | .Bl -enum -offset indent -compact |
55 | .It | |
56 | command-line options | |
57 | .It | |
58 | user's configuration file | |
140e3e97 | 59 | .Pq Pa ~/.ssh/config |
4dcbbeea | 60 | .It |
61 | system-wide configuration file | |
62 | .Pq Pa /etc/ssh/ssh_config | |
63 | .El | |
588df31a | 64 | .Pp |
65 | For each parameter, the first obtained value | |
66 | will be used. | |
7034edae | 67 | The configuration files contain sections separated by |
588df31a | 68 | .Dq Host |
69 | specifications, and that section is only applied for hosts that | |
70 | match one of the patterns given in the specification. | |
71 | The matched host name is the one given on the command line. | |
72 | .Pp | |
73 | Since the first obtained value for each parameter is used, more | |
74 | host-specific declarations should be given near the beginning of the | |
75 | file, and general defaults at the end. | |
76 | .Pp | |
77 | The configuration file has the following format: | |
78 | .Pp | |
79 | Empty lines and lines starting with | |
80 | .Ql # | |
81 | are comments. | |
588df31a | 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 , | |
c04ba6a6 | 90 | .Nm scp , |
588df31a | 91 | and |
92 | .Nm sftp | |
93 | .Fl o | |
94 | option. | |
533b9133 | 95 | Arguments may optionally be enclosed in double quotes |
96 | .Pq \&" | |
97 | in order to represent arguments containing spaces. | |
588df31a | 98 | .Pp |
99 | The possible | |
100 | keywords and their meanings are as follows (note that | |
101 | keywords are case-insensitive and arguments are case-sensitive): | |
102 | .Bl -tag -width Ds | |
103 | .It Cm Host | |
104 | Restricts the following declarations (up to the next | |
105 | .Cm Host | |
106 | keyword) to be only for those hosts that match one of the patterns | |
107 | given after the keyword. | |
588df31a | 108 | A single |
f09ffbdb | 109 | .Ql * |
588df31a | 110 | as a pattern can be used to provide global |
111 | defaults for all hosts. | |
112 | The host is the | |
113 | .Ar hostname | |
f09ffbdb | 114 | argument given on the command line (i.e. the name is not converted to |
588df31a | 115 | a canonicalized host name before matching). |
436a5ff9 | 116 | .Pp |
117 | See | |
118 | .Sx PATTERNS | |
119 | for more information on patterns. | |
f811e52a | 120 | .It Cm AddressFamily |
3cbc677d | 121 | Specifies which address family to use when connecting. |
122 | Valid arguments are | |
f811e52a | 123 | .Dq any , |
124 | .Dq inet | |
c5786b30 | 125 | (use IPv4 only), or |
f811e52a | 126 | .Dq inet6 |
0d6cbe2c | 127 | (use IPv6 only). |
588df31a | 128 | .It Cm BatchMode |
129 | If set to | |
130 | .Dq yes , | |
131 | passphrase/password querying will be disabled. | |
132 | This option is useful in scripts and other batch jobs where no user | |
133 | is present to supply the password. | |
134 | The argument must be | |
135 | .Dq yes | |
136 | or | |
137 | .Dq no . | |
138 | The default is | |
139 | .Dq no . | |
140 | .It Cm BindAddress | |
1a8521be | 141 | Use the specified address on the local machine as the source address of |
82b7531b | 142 | the connection. |
143 | Only useful on systems with more than one address. | |
588df31a | 144 | Note that this option does not work if |
145 | .Cm UsePrivilegedPort | |
146 | is set to | |
147 | .Dq yes . | |
148 | .It Cm ChallengeResponseAuthentication | |
340a4caf | 149 | Specifies whether to use challenge-response authentication. |
588df31a | 150 | The argument to this keyword must be |
151 | .Dq yes | |
152 | or | |
153 | .Dq no . | |
154 | The default is | |
155 | .Dq yes . | |
156 | .It Cm CheckHostIP | |
157 | If this flag is set to | |
158 | .Dq yes , | |
c5786b30 | 159 | .Xr ssh 1 |
160 | will additionally check the host IP address in the | |
588df31a | 161 | .Pa known_hosts |
162 | file. | |
163 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
164 | If the option is set to | |
165 | .Dq no , | |
166 | the check will not be executed. | |
167 | The default is | |
168 | .Dq yes . | |
169 | .It Cm Cipher | |
170 | Specifies the cipher to use for encrypting the session | |
171 | in protocol version 1. | |
172 | Currently, | |
173 | .Dq blowfish , | |
174 | .Dq 3des , | |
175 | and | |
176 | .Dq des | |
177 | are supported. | |
178 | .Ar des | |
179 | is only supported in the | |
c5786b30 | 180 | .Xr ssh 1 |
588df31a | 181 | client for interoperability with legacy protocol 1 implementations |
182 | that do not support the | |
183 | .Ar 3des | |
a4e5acef | 184 | cipher. |
185 | Its use is strongly discouraged due to cryptographic weaknesses. | |
588df31a | 186 | The default is |
187 | .Dq 3des . | |
188 | .It Cm Ciphers | |
189 | Specifies the ciphers allowed for protocol version 2 | |
190 | in order of preference. | |
191 | Multiple ciphers must be comma-separated. | |
3b9baa7b | 192 | The supported ciphers are |
193 | .Dq 3des-cbc , | |
194 | .Dq aes128-cbc , | |
195 | .Dq aes192-cbc , | |
196 | .Dq aes256-cbc , | |
197 | .Dq aes128-ctr , | |
198 | .Dq aes192-ctr , | |
199 | .Dq aes256-ctr , | |
74a66cc8 | 200 | .Dq arcfour128 , |
201 | .Dq arcfour256 , | |
3b9baa7b | 202 | .Dq arcfour , |
203 | .Dq blowfish-cbc , | |
204 | and | |
205 | .Dq cast128-cbc . | |
c5786b30 | 206 | The default is: |
207 | .Bd -literal -offset 3n | |
208 | aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, | |
209 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
210 | aes192-ctr,aes256-ctr | |
588df31a | 211 | .Ed |
212 | .It Cm ClearAllForwardings | |
c5786b30 | 213 | Specifies that all local, remote, and dynamic port forwardings |
588df31a | 214 | specified in the configuration files or on the command line be |
a4e5acef | 215 | cleared. |
216 | This option is primarily useful when used from the | |
c5786b30 | 217 | .Xr ssh 1 |
588df31a | 218 | command line to clear port forwardings set in |
219 | configuration files, and is automatically set by | |
220 | .Xr scp 1 | |
221 | and | |
222 | .Xr sftp 1 . | |
223 | The argument must be | |
224 | .Dq yes | |
225 | or | |
226 | .Dq no . | |
227 | The default is | |
228 | .Dq no . | |
229 | .It Cm Compression | |
230 | Specifies whether to use compression. | |
231 | The argument must be | |
232 | .Dq yes | |
233 | or | |
234 | .Dq no . | |
235 | The default is | |
236 | .Dq no . | |
237 | .It Cm CompressionLevel | |
238 | Specifies the compression level to use if compression is enabled. | |
239 | The argument must be an integer from 1 (fast) to 9 (slow, best). | |
240 | The default level is 6, which is good for most applications. | |
241 | The meaning of the values is the same as in | |
242 | .Xr gzip 1 . | |
243 | Note that this option applies to protocol version 1 only. | |
244 | .It Cm ConnectionAttempts | |
245 | Specifies the number of tries (one per second) to make before exiting. | |
246 | The argument must be an integer. | |
247 | This may be useful in scripts if the connection sometimes fails. | |
248 | The default is 1. | |
09ab3296 | 249 | .It Cm ConnectTimeout |
c5786b30 | 250 | Specifies the timeout (in seconds) used when connecting to the |
251 | SSH server, instead of using the default system TCP timeout. | |
3cbc677d | 252 | This value is used only when the target is down or really unreachable, |
253 | not when it refuses the connection. | |
5e96b616 | 254 | .It Cm ControlMaster |
255 | Enables the sharing of multiple sessions over a single network connection. | |
256 | When set to | |
c5786b30 | 257 | .Dq yes , |
258 | .Xr ssh 1 | |
5e96b616 | 259 | will listen for connections on a control socket specified using the |
260 | .Cm ControlPath | |
261 | argument. | |
262 | Additional sessions can connect to this socket using the same | |
263 | .Cm ControlPath | |
264 | with | |
265 | .Cm ControlMaster | |
266 | set to | |
267 | .Dq no | |
9a5cfb58 | 268 | (the default). |
db98627d | 269 | These sessions will try to reuse the master instance's network connection |
6b0b0d65 | 270 | rather than initiating new ones, but will fall back to connecting normally |
271 | if the control socket does not exist, or is not listening. | |
272 | .Pp | |
0d34d6ce | 273 | Setting this to |
274 | .Dq ask | |
c5786b30 | 275 | will cause ssh |
0d34d6ce | 276 | to listen for control connections, but require confirmation using the |
277 | .Ev SSH_ASKPASS | |
278 | program before they are accepted (see | |
279 | .Xr ssh-add 1 | |
9a5cfb58 | 280 | for details). |
cc8ca1e6 | 281 | If the |
282 | .Cm ControlPath | |
c5786b30 | 283 | cannot be opened, |
284 | ssh will continue without connecting to a master instance. | |
9dfd96d6 | 285 | .Pp |
ef07103c | 286 | X11 and |
d313869b | 287 | .Xr ssh-agent 1 |
ef07103c | 288 | forwarding is supported over these multiplexed connections, however the |
8918b906 | 289 | display and agent forwarded will be the one belonging to the master |
d313869b | 290 | connection i.e. it is not possible to forward multiple displays or agents. |
ef07103c | 291 | .Pp |
9dfd96d6 | 292 | Two additional options allow for opportunistic multiplexing: try to use a |
293 | master connection but fall back to creating a new one if one does not already | |
294 | exist. | |
295 | These options are: | |
296 | .Dq auto | |
297 | and | |
298 | .Dq autoask . | |
299 | The latter requires confirmation like the | |
300 | .Dq ask | |
301 | option. | |
5e96b616 | 302 | .It Cm ControlPath |
a980cbd7 | 303 | Specify the path to the control socket used for connection sharing as described |
304 | in the | |
5e96b616 | 305 | .Cm ControlMaster |
699255b5 | 306 | section above or the string |
307 | .Dq none | |
308 | to disable connection sharing. | |
a980cbd7 | 309 | In the path, |
f7b8224d | 310 | .Ql %l |
311 | will be substituted by the local host name, | |
a980cbd7 | 312 | .Ql %h |
313 | will be substituted by the target host name, | |
314 | .Ql %p | |
c5786b30 | 315 | the port, and |
a980cbd7 | 316 | .Ql %r |
317 | by the remote login username. | |
9dfd96d6 | 318 | It is recommended that any |
319 | .Cm ControlPath | |
320 | used for opportunistic connection sharing include | |
5e7007ea | 321 | at least %h, %p, and %r. |
9dfd96d6 | 322 | This ensures that shared connections are uniquely identified. |
9a5cfb58 | 323 | .It Cm DynamicForward |
0b3950af | 324 | Specifies that a TCP port on the local machine be forwarded |
9a5cfb58 | 325 | over the secure channel, and the application |
326 | protocol is then used to determine where to connect to from the | |
327 | remote machine. | |
5ddc5eb4 | 328 | .Pp |
329 | The argument must be | |
330 | .Sm off | |
331 | .Oo Ar bind_address : Oc Ar port . | |
332 | .Sm on | |
333 | IPv6 addresses can be specified by enclosing addresses in square brackets or | |
334 | by using an alternative syntax: | |
335 | .Oo Ar bind_address Ns / Oc Ns Ar port . | |
336 | By default, the local port is bound in accordance with the | |
337 | .Cm GatewayPorts | |
338 | setting. | |
339 | However, an explicit | |
340 | .Ar bind_address | |
341 | may be used to bind the connection to a specific address. | |
342 | The | |
343 | .Ar bind_address | |
344 | of | |
345 | .Dq localhost | |
346 | indicates that the listening port be bound for local use only, while an | |
347 | empty address or | |
348 | .Sq * | |
349 | indicates that the port should be available from all interfaces. | |
350 | .Pp | |
9a5cfb58 | 351 | Currently the SOCKS4 and SOCKS5 protocols are supported, and |
c5786b30 | 352 | .Xr ssh 1 |
9a5cfb58 | 353 | will act as a SOCKS server. |
354 | Multiple forwardings may be specified, and | |
355 | additional forwardings can be given on the command line. | |
356 | Only the superuser can forward privileged ports. | |
f0677b69 | 357 | .It Cm EnableSSHKeysign |
358 | Setting this option to | |
359 | .Dq yes | |
360 | in the global client configuration file | |
361 | .Pa /etc/ssh/ssh_config | |
362 | enables the use of the helper program | |
363 | .Xr ssh-keysign 8 | |
364 | during | |
365 | .Cm HostbasedAuthentication . | |
366 | The argument must be | |
367 | .Dq yes | |
368 | or | |
369 | .Dq no . | |
370 | The default is | |
371 | .Dq no . | |
246bb171 | 372 | This option should be placed in the non-hostspecific section. |
f0677b69 | 373 | See |
374 | .Xr ssh-keysign 8 | |
375 | for more information. | |
588df31a | 376 | .It Cm EscapeChar |
377 | Sets the escape character (default: | |
378 | .Ql ~ ) . | |
379 | The escape character can also | |
380 | be set on the command line. | |
381 | The argument should be a single character, | |
382 | .Ql ^ | |
383 | followed by a letter, or | |
384 | .Dq none | |
385 | to disable the escape | |
386 | character entirely (making the connection transparent for binary | |
387 | data). | |
388 | .It Cm ForwardAgent | |
389 | Specifies whether the connection to the authentication agent (if any) | |
390 | will be forwarded to the remote machine. | |
391 | The argument must be | |
392 | .Dq yes | |
393 | or | |
394 | .Dq no . | |
395 | The default is | |
396 | .Dq no . | |
dbcdea68 | 397 | .Pp |
a4e5acef | 398 | Agent forwarding should be enabled with caution. |
399 | Users with the ability to bypass file permissions on the remote host | |
400 | (for the agent's Unix-domain socket) | |
401 | can access the local agent through the forwarded connection. | |
402 | An attacker cannot obtain key material from the agent, | |
dbcdea68 | 403 | however they can perform operations on the keys that enable them to |
404 | authenticate using the identities loaded into the agent. | |
588df31a | 405 | .It Cm ForwardX11 |
406 | Specifies whether X11 connections will be automatically redirected | |
407 | over the secure channel and | |
408 | .Ev DISPLAY | |
409 | set. | |
410 | The argument must be | |
411 | .Dq yes | |
412 | or | |
413 | .Dq no . | |
414 | The default is | |
415 | .Dq no . | |
dbcdea68 | 416 | .Pp |
a4e5acef | 417 | X11 forwarding should be enabled with caution. |
418 | Users with the ability to bypass file permissions on the remote host | |
d73a67d7 | 419 | (for the user's X11 authorization database) |
a4e5acef | 420 | can access the local X11 display through the forwarded connection. |
d73a67d7 | 421 | An attacker may then be able to perform activities such as keystroke monitoring |
422 | if the | |
423 | .Cm ForwardX11Trusted | |
424 | option is also enabled. | |
425 | .It Cm ForwardX11Trusted | |
b2e90ab5 | 426 | If this option is set to |
c5786b30 | 427 | .Dq yes , |
428 | remote X11 clients will have full access to the original X11 display. | |
9a6b3b7a | 429 | .Pp |
d73a67d7 | 430 | If this option is set to |
c5786b30 | 431 | .Dq no , |
432 | remote X11 clients will be considered untrusted and prevented | |
d73a67d7 | 433 | from stealing or tampering with data belonging to trusted X11 |
434 | clients. | |
9a6b3b7a | 435 | Furthermore, the |
436 | .Xr xauth 1 | |
437 | token used for the session will be set to expire after 20 minutes. | |
438 | Remote clients will be refused access after this time. | |
d73a67d7 | 439 | .Pp |
440 | The default is | |
441 | .Dq no . | |
442 | .Pp | |
443 | See the X11 SECURITY extension specification for full details on | |
444 | the restrictions imposed on untrusted clients. | |
588df31a | 445 | .It Cm GatewayPorts |
446 | Specifies whether remote hosts are allowed to connect to local | |
447 | forwarded ports. | |
448 | By default, | |
c5786b30 | 449 | .Xr ssh 1 |
a4e5acef | 450 | binds local port forwardings to the loopback address. |
451 | This prevents other remote hosts from connecting to forwarded ports. | |
588df31a | 452 | .Cm GatewayPorts |
c5786b30 | 453 | can be used to specify that ssh |
588df31a | 454 | should bind local port forwardings to the wildcard address, |
455 | thus allowing remote hosts to connect to forwarded ports. | |
456 | The argument must be | |
457 | .Dq yes | |
458 | or | |
459 | .Dq no . | |
460 | The default is | |
461 | .Dq no . | |
462 | .It Cm GlobalKnownHostsFile | |
463 | Specifies a file to use for the global | |
464 | host key database instead of | |
465 | .Pa /etc/ssh/ssh_known_hosts . | |
7364bd04 | 466 | .It Cm GSSAPIAuthentication |
e8dd24a8 | 467 | Specifies whether user authentication based on GSSAPI is allowed. |
d0445371 | 468 | The default is |
2ecb78df | 469 | .Dq no . |
7364bd04 | 470 | Note that this option applies to protocol version 2 only. |
471 | .It Cm GSSAPIDelegateCredentials | |
472 | Forward (delegate) credentials to the server. | |
473 | The default is | |
474 | .Dq no . | |
475 | Note that this option applies to protocol version 2 only. | |
5c63c2ab | 476 | .It Cm HashKnownHosts |
477 | Indicates that | |
c5786b30 | 478 | .Xr ssh 1 |
5c63c2ab | 479 | should hash host names and addresses when they are added to |
140e3e97 | 480 | .Pa ~/.ssh/known_hosts . |
5c63c2ab | 481 | These hashed names may be used normally by |
c5786b30 | 482 | .Xr ssh 1 |
5c63c2ab | 483 | and |
c5786b30 | 484 | .Xr sshd 8 , |
5c63c2ab | 485 | but they do not reveal identifying information should the file's contents |
486 | be disclosed. | |
487 | The default is | |
488 | .Dq no . | |
cd8f998c | 489 | Note that hashing of names and addresses will not be retrospectively applied |
bdffbcdc | 490 | to existing known hosts files, but these may be manually hashed using |
491 | .Xr ssh-keygen 1 . | |
588df31a | 492 | .It Cm HostbasedAuthentication |
493 | Specifies whether to try rhosts based authentication with public key | |
494 | authentication. | |
495 | The argument must be | |
496 | .Dq yes | |
497 | or | |
498 | .Dq no . | |
499 | The default is | |
500 | .Dq no . | |
501 | This option applies to protocol version 2 only and | |
502 | is similar to | |
503 | .Cm RhostsRSAAuthentication . | |
504 | .It Cm HostKeyAlgorithms | |
505 | Specifies the protocol version 2 host key algorithms | |
506 | that the client wants to use in order of preference. | |
507 | The default for this option is: | |
508 | .Dq ssh-rsa,ssh-dss . | |
509 | .It Cm HostKeyAlias | |
510 | Specifies an alias that should be used instead of the | |
511 | real host name when looking up or saving the host key | |
512 | in the host key database files. | |
c5786b30 | 513 | This option is useful for tunneling SSH connections |
588df31a | 514 | or for multiple servers running on a single host. |
515 | .It Cm HostName | |
516 | Specifies the real host name to log into. | |
517 | This can be used to specify nicknames or abbreviations for hosts. | |
c5786b30 | 518 | The default is the name given on the command line. |
588df31a | 519 | Numeric IP addresses are also permitted (both on the command line and in |
520 | .Cm HostName | |
521 | specifications). | |
3a065ed0 | 522 | .It Cm IdentitiesOnly |
523 | Specifies that | |
c5786b30 | 524 | .Xr ssh 1 |
3a065ed0 | 525 | should only use the authentication identity files configured in the |
1e9b1b82 | 526 | .Nm |
3a065ed0 | 527 | files, |
c5786b30 | 528 | even if |
529 | .Xr ssh-agent 1 | |
3a065ed0 | 530 | offers more identities. |
531 | The argument to this keyword must be | |
532 | .Dq yes | |
533 | or | |
534 | .Dq no . | |
c5786b30 | 535 | This option is intended for situations where ssh-agent |
3a065ed0 | 536 | offers many different identities. |
537 | The default is | |
538 | .Dq no . | |
030723f9 | 539 | .It Cm IdentityFile |
540 | Specifies a file from which the user's RSA or DSA authentication identity | |
541 | is read. | |
542 | The default is | |
543 | .Pa ~/.ssh/identity | |
544 | for protocol version 1, and | |
545 | .Pa ~/.ssh/id_rsa | |
546 | and | |
547 | .Pa ~/.ssh/id_dsa | |
548 | for protocol version 2. | |
549 | Additionally, any identities represented by the authentication agent | |
550 | will be used for authentication. | |
8cffe22a | 551 | .Pp |
030723f9 | 552 | The file name may use the tilde |
99d18e3e | 553 | syntax to refer to a user's home directory or one of the following |
8cffe22a | 554 | escape characters: |
555 | .Ql %d | |
556 | (local user's home directory), | |
557 | .Ql %u | |
558 | (local user name), | |
559 | .Ql %l | |
560 | (local host name), | |
561 | .Ql %h | |
562 | (remote host name) or | |
b4d7dedd | 563 | .Ql %r |
8cffe22a | 564 | (remote user name). |
565 | .Pp | |
030723f9 | 566 | It is possible to have |
567 | multiple identity files specified in configuration files; all these | |
568 | identities will be tried in sequence. | |
396070f8 | 569 | .It Cm KbdInteractiveDevices |
570 | Specifies the list of methods to use in keyboard-interactive authentication. | |
571 | Multiple method names must be comma-separated. | |
572 | The default is to use the server specified list. | |
2963b207 | 573 | The methods available vary depending on what the server supports. |
574 | For an OpenSSH server, | |
575 | it may be zero or more of: | |
576 | .Dq bsdauth , | |
577 | .Dq pam , | |
578 | and | |
579 | .Dq skey . | |
d20f3c9e | 580 | .It Cm LocalCommand |
581 | Specifies a command to execute on the local machine after successfully | |
582 | connecting to the server. | |
583 | The command string extends to the end of the line, and is executed with | |
584 | .Pa /bin/sh . | |
585 | This directive is ignored unless | |
586 | .Cm PermitLocalCommand | |
587 | has been enabled. | |
588df31a | 588 | .It Cm LocalForward |
0b3950af | 589 | Specifies that a TCP port on the local machine be forwarded over |
588df31a | 590 | the secure channel to the specified host and port from the remote machine. |
ecda4ffb | 591 | The first argument must be |
3867aa0a | 592 | .Sm off |
ecda4ffb | 593 | .Oo Ar bind_address : Oc Ar port |
3867aa0a | 594 | .Sm on |
ecda4ffb | 595 | and the second argument must be |
596 | .Ar host : Ns Ar hostport . | |
cd8f998c | 597 | IPv6 addresses can be specified by enclosing addresses in square brackets or |
3867aa0a | 598 | by using an alternative syntax: |
ecda4ffb | 599 | .Oo Ar bind_address Ns / Oc Ns Ar port |
600 | and | |
601 | .Ar host Ns / Ns Ar hostport . | |
cd8f998c | 602 | Multiple forwardings may be specified, and additional forwardings can be |
3867aa0a | 603 | given on the command line. |
588df31a | 604 | Only the superuser can forward privileged ports. |
3867aa0a | 605 | By default, the local port is bound in accordance with the |
606 | .Cm GatewayPorts | |
607 | setting. | |
608 | However, an explicit | |
609 | .Ar bind_address | |
610 | may be used to bind the connection to a specific address. | |
611 | The | |
612 | .Ar bind_address | |
613 | of | |
614 | .Dq localhost | |
cd8f998c | 615 | indicates that the listening port be bound for local use only, while an |
616 | empty address or | |
617 | .Sq * | |
3867aa0a | 618 | indicates that the port should be available from all interfaces. |
588df31a | 619 | .It Cm LogLevel |
620 | Gives the verbosity level that is used when logging messages from | |
c5786b30 | 621 | .Xr ssh 1 . |
588df31a | 622 | The possible values are: |
c5786b30 | 623 | QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. |
a4e5acef | 624 | The default is INFO. |
625 | DEBUG and DEBUG1 are equivalent. | |
626 | DEBUG2 and DEBUG3 each specify higher levels of verbose output. | |
588df31a | 627 | .It Cm MACs |
628 | Specifies the MAC (message authentication code) algorithms | |
629 | in order of preference. | |
630 | The MAC algorithm is used in protocol version 2 | |
631 | for data integrity protection. | |
632 | Multiple algorithms must be comma-separated. | |
c5786b30 | 633 | The default is: |
588df31a | 634 | .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 . |
635 | .It Cm NoHostAuthenticationForLocalhost | |
636 | This option can be used if the home directory is shared across machines. | |
637 | In this case localhost will refer to a different machine on each of | |
638 | the machines and the user will get many warnings about changed host keys. | |
639 | However, this option disables host authentication for localhost. | |
640 | The argument to this keyword must be | |
641 | .Dq yes | |
642 | or | |
643 | .Dq no . | |
644 | The default is to check the host key for localhost. | |
645 | .It Cm NumberOfPasswordPrompts | |
646 | Specifies the number of password prompts before giving up. | |
647 | The argument to this keyword must be an integer. | |
c5786b30 | 648 | The default is 3. |
588df31a | 649 | .It Cm PasswordAuthentication |
650 | Specifies whether to use password authentication. | |
651 | The argument to this keyword must be | |
652 | .Dq yes | |
653 | or | |
654 | .Dq no . | |
655 | The default is | |
656 | .Dq yes . | |
d20f3c9e | 657 | .It Cm PermitLocalCommand |
658 | Allow local command execution via the | |
659 | .Ic LocalCommand | |
660 | option or using the | |
64925c6d | 661 | .Ic !\& Ns Ar command |
d20f3c9e | 662 | escape sequence in |
663 | .Xr ssh 1 . | |
664 | The argument must be | |
665 | .Dq yes | |
666 | or | |
667 | .Dq no . | |
668 | The default is | |
669 | .Dq no . | |
030723f9 | 670 | .It Cm Port |
671 | Specifies the port number to connect on the remote host. | |
c5786b30 | 672 | The default is 22. |
588df31a | 673 | .It Cm PreferredAuthentications |
674 | Specifies the order in which the client should try protocol 2 | |
3cbc677d | 675 | authentication methods. |
4e5038f7 | 676 | This allows a client to prefer one method (e.g.\& |
588df31a | 677 | .Cm keyboard-interactive ) |
4e5038f7 | 678 | over another method (e.g.\& |
588df31a | 679 | .Cm password ) |
680 | The default for this option is: | |
f127d8a4 | 681 | .Do gssapi-with-mic , |
682 | hostbased, | |
683 | publickey, | |
684 | keyboard-interactive, | |
685 | password | |
686 | .Dc . | |
588df31a | 687 | .It Cm Protocol |
688 | Specifies the protocol versions | |
c5786b30 | 689 | .Xr ssh 1 |
588df31a | 690 | should support in order of preference. |
691 | The possible values are | |
c5786b30 | 692 | .Sq 1 |
588df31a | 693 | and |
c5786b30 | 694 | .Sq 2 . |
588df31a | 695 | Multiple versions must be comma-separated. |
696 | The default is | |
697 | .Dq 2,1 . | |
c5786b30 | 698 | This means that ssh |
588df31a | 699 | tries version 2 and falls back to version 1 |
700 | if version 2 is not available. | |
701 | .It Cm ProxyCommand | |
702 | Specifies the command to use to connect to the server. | |
703 | The command | |
704 | string extends to the end of the line, and is executed with | |
705 | .Pa /bin/sh . | |
706 | In the command string, | |
707 | .Ql %h | |
708 | will be substituted by the host name to | |
709 | connect and | |
710 | .Ql %p | |
711 | by the port. | |
712 | The command can be basically anything, | |
713 | and should read from its standard input and write to its standard output. | |
714 | It should eventually connect an | |
715 | .Xr sshd 8 | |
716 | server running on some machine, or execute | |
717 | .Ic sshd -i | |
718 | somewhere. | |
719 | Host key management will be done using the | |
720 | HostName of the host being connected (defaulting to the name typed by | |
721 | the user). | |
a4e5acef | 722 | Setting the command to |
723 | .Dq none | |
f78bde70 | 724 | disables this option entirely. |
588df31a | 725 | Note that |
726 | .Cm CheckHostIP | |
727 | is not available for connects with a proxy command. | |
728 | .Pp | |
2b610872 | 729 | This directive is useful in conjunction with |
730 | .Xr nc 1 | |
731 | and its proxy support. | |
9fa42d41 | 732 | For example, the following directive would connect via an HTTP proxy at |
2b610872 | 733 | 192.0.2.0: |
734 | .Bd -literal -offset 3n | |
735 | ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p | |
736 | .Ed | |
588df31a | 737 | .It Cm PubkeyAuthentication |
738 | Specifies whether to try public key authentication. | |
739 | The argument to this keyword must be | |
740 | .Dq yes | |
741 | or | |
742 | .Dq no . | |
743 | The default is | |
744 | .Dq yes . | |
745 | This option applies to protocol version 2 only. | |
db175906 | 746 | .It Cm RekeyLimit |
747 | Specifies the maximum amount of data that may be transmitted before the | |
0ce89457 | 748 | session key is renegotiated. |
db175906 | 749 | The argument is the number of bytes, with an optional suffix of |
0ce89457 | 750 | .Sq K , |
751 | .Sq M , | |
db175906 | 752 | or |
0ce89457 | 753 | .Sq G |
db175906 | 754 | to indicate Kilobytes, Megabytes, or Gigabytes, respectively. |
755 | The default is between | |
c5786b30 | 756 | .Sq 1G |
db175906 | 757 | and |
c5786b30 | 758 | .Sq 4G , |
db175906 | 759 | depending on the cipher. |
0ce89457 | 760 | This option applies to protocol version 2 only. |
588df31a | 761 | .It Cm RemoteForward |
0b3950af | 762 | Specifies that a TCP port on the remote machine be forwarded over |
588df31a | 763 | the secure channel to the specified host and port from the local machine. |
ecda4ffb | 764 | The first argument must be |
3867aa0a | 765 | .Sm off |
ecda4ffb | 766 | .Oo Ar bind_address : Oc Ar port |
6d7a9e8f | 767 | .Sm on |
ecda4ffb | 768 | and the second argument must be |
769 | .Ar host : Ns Ar hostport . | |
770 | IPv6 addresses can be specified by enclosing addresses in square brackets | |
771 | or by using an alternative syntax: | |
772 | .Oo Ar bind_address Ns / Oc Ns Ar port | |
773 | and | |
774 | .Ar host Ns / Ns Ar hostport . | |
588df31a | 775 | Multiple forwardings may be specified, and additional |
776 | forwardings can be given on the command line. | |
777 | Only the superuser can forward privileged ports. | |
3867aa0a | 778 | .Pp |
779 | If the | |
780 | .Ar bind_address | |
781 | is not specified, the default is to only bind to loopback addresses. | |
782 | If the | |
783 | .Ar bind_address | |
784 | is | |
785 | .Ql * | |
786 | or an empty string, then the forwarding is requested to listen on all | |
787 | interfaces. | |
788 | Specifying a remote | |
789 | .Ar bind_address | |
cd8f998c | 790 | will only succeed if the server's |
791 | .Cm GatewayPorts | |
3867aa0a | 792 | option is enabled (see |
cd8f998c | 793 | .Xr sshd_config 5 ) . |
588df31a | 794 | .It Cm RhostsRSAAuthentication |
795 | Specifies whether to try rhosts based authentication with RSA host | |
796 | authentication. | |
797 | The argument must be | |
798 | .Dq yes | |
799 | or | |
800 | .Dq no . | |
801 | The default is | |
802 | .Dq no . | |
803 | This option applies to protocol version 1 only and requires | |
c5786b30 | 804 | .Xr ssh 1 |
588df31a | 805 | to be setuid root. |
806 | .It Cm RSAAuthentication | |
807 | Specifies whether to try RSA authentication. | |
808 | The argument to this keyword must be | |
809 | .Dq yes | |
810 | or | |
811 | .Dq no . | |
812 | RSA authentication will only be | |
813 | attempted if the identity file exists, or an authentication agent is | |
814 | running. | |
815 | The default is | |
816 | .Dq yes . | |
817 | Note that this option applies to protocol version 1 only. | |
61a2c1da | 818 | .It Cm SendEnv |
819 | Specifies what variables from the local | |
820 | .Xr environ 7 | |
821 | should be sent to the server. | |
c5786b30 | 822 | Note that environment passing is only supported for protocol 2. |
823 | The server must also support it, and the server must be configured to | |
b8b9f2e6 | 824 | accept these environment variables. |
61a2c1da | 825 | Refer to |
826 | .Cm AcceptEnv | |
827 | in | |
828 | .Xr sshd_config 5 | |
829 | for how to configure the server. | |
95d46d8f | 830 | Variables are specified by name, which may contain wildcard characters. |
b8b9f2e6 | 831 | Multiple environment variables may be separated by whitespace or spread |
61a2c1da | 832 | across multiple |
833 | .Cm SendEnv | |
834 | directives. | |
835 | The default is not to send any environment variables. | |
436a5ff9 | 836 | .Pp |
837 | See | |
838 | .Sx PATTERNS | |
839 | for more information on patterns. | |
5d8d32a3 | 840 | .It Cm ServerAliveCountMax |
79e46360 | 841 | Sets the number of server alive messages (see below) which may be |
5d8d32a3 | 842 | sent without |
c5786b30 | 843 | .Xr ssh 1 |
5d8d32a3 | 844 | receiving any messages back from the server. |
845 | If this threshold is reached while server alive messages are being sent, | |
c5786b30 | 846 | ssh will disconnect from the server, terminating the session. |
5d8d32a3 | 847 | It is important to note that the use of server alive messages is very |
848 | different from | |
849 | .Cm TCPKeepAlive | |
850 | (below). | |
851 | The server alive messages are sent through the encrypted channel | |
852 | and therefore will not be spoofable. | |
853 | The TCP keepalive option enabled by | |
854 | .Cm TCPKeepAlive | |
855 | is spoofable. | |
856 | The server alive mechanism is valuable when the client or | |
857 | server depend on knowing when a connection has become inactive. | |
858 | .Pp | |
859 | The default value is 3. | |
860 | If, for example, | |
861 | .Cm ServerAliveInterval | |
c5786b30 | 862 | (see below) is set to 15 and |
5d8d32a3 | 863 | .Cm ServerAliveCountMax |
c5786b30 | 864 | is left at the default, if the server becomes unresponsive, |
865 | ssh will disconnect after approximately 45 seconds. | |
2d762582 | 866 | This option applies to protocol version 2 only. |
030723f9 | 867 | .It Cm ServerAliveInterval |
868 | Sets a timeout interval in seconds after which if no data has been received | |
869 | from the server, | |
c5786b30 | 870 | .Xr ssh 1 |
030723f9 | 871 | will send a message through the encrypted |
872 | channel to request a response from the server. | |
873 | The default | |
874 | is 0, indicating that these messages will not be sent to the server. | |
875 | This option applies to protocol version 2 only. | |
588df31a | 876 | .It Cm SmartcardDevice |
3cbc677d | 877 | Specifies which smartcard device to use. |
878 | The argument to this keyword is the device | |
c5786b30 | 879 | .Xr ssh 1 |
588df31a | 880 | should use to communicate with a smartcard used for storing the user's |
3cbc677d | 881 | private RSA key. |
882 | By default, no device is specified and smartcard support is not activated. | |
588df31a | 883 | .It Cm StrictHostKeyChecking |
884 | If this flag is set to | |
885 | .Dq yes , | |
c5786b30 | 886 | .Xr ssh 1 |
588df31a | 887 | will never automatically add host keys to the |
140e3e97 | 888 | .Pa ~/.ssh/known_hosts |
588df31a | 889 | file, and refuses to connect to hosts whose host key has changed. |
890 | This provides maximum protection against trojan horse attacks, | |
c5786b30 | 891 | though it can be annoying when the |
588df31a | 892 | .Pa /etc/ssh/ssh_known_hosts |
c5786b30 | 893 | file is poorly maintained or when connections to new hosts are |
588df31a | 894 | frequently made. |
895 | This option forces the user to manually | |
896 | add all new hosts. | |
897 | If this flag is set to | |
898 | .Dq no , | |
c5786b30 | 899 | ssh will automatically add new host keys to the |
588df31a | 900 | user known hosts files. |
901 | If this flag is set to | |
902 | .Dq ask , | |
903 | new host keys | |
904 | will be added to the user known host files only after the user | |
905 | has confirmed that is what they really want to do, and | |
c5786b30 | 906 | ssh will refuse to connect to hosts whose host key has changed. |
588df31a | 907 | The host keys of |
908 | known hosts will be verified automatically in all cases. | |
909 | The argument must be | |
910 | .Dq yes , | |
c5786b30 | 911 | .Dq no , |
588df31a | 912 | or |
913 | .Dq ask . | |
914 | The default is | |
915 | .Dq ask . | |
fd573618 | 916 | .It Cm TCPKeepAlive |
917 | Specifies whether the system should send TCP keepalive messages to the | |
918 | other side. | |
919 | If they are sent, death of the connection or crash of one | |
920 | of the machines will be properly noticed. | |
921 | However, this means that | |
922 | connections will die if the route is down temporarily, and some people | |
923 | find it annoying. | |
924 | .Pp | |
925 | The default is | |
926 | .Dq yes | |
927 | (to send TCP keepalive messages), and the client will notice | |
928 | if the network goes down or the remote host dies. | |
929 | This is important in scripts, and many users want it too. | |
930 | .Pp | |
931 | To disable TCP keepalive messages, the value should be set to | |
932 | .Dq no . | |
d20f3c9e | 933 | .It Cm Tunnel |
934 | Request starting | |
935 | .Xr tun 4 | |
a274ba38 | 936 | device forwarding between the client and the server. |
937 | This option also allows requesting layer 2 (ethernet) | |
938 | instead of layer 3 (point-to-point) tunneling from the server. | |
d20f3c9e | 939 | The argument must be |
a4f24bf8 | 940 | .Dq yes , |
941 | .Dq point-to-point , | |
c5786b30 | 942 | .Dq ethernet , |
d20f3c9e | 943 | or |
944 | .Dq no . | |
945 | The default is | |
946 | .Dq no . | |
947 | .It Cm TunnelDevice | |
948 | Force a specified | |
949 | .Xr tun 4 | |
950 | device on the client. | |
951 | Without this option, the next available device will be used. | |
0c9851b1 | 952 | .It Cm UsePrivilegedPort |
953 | Specifies whether to use a privileged port for outgoing connections. | |
954 | The argument must be | |
955 | .Dq yes | |
956 | or | |
957 | .Dq no . | |
958 | The default is | |
959 | .Dq no . | |
960 | If set to | |
c5786b30 | 961 | .Dq yes , |
962 | .Xr ssh 1 | |
0c9851b1 | 963 | must be setuid root. |
964 | Note that this option must be set to | |
965 | .Dq yes | |
966 | for | |
967 | .Cm RhostsRSAAuthentication | |
968 | with older servers. | |
588df31a | 969 | .It Cm User |
970 | Specifies the user to log in as. | |
971 | This can be useful when a different user name is used on different machines. | |
972 | This saves the trouble of | |
973 | having to remember to give the user name on the command line. | |
974 | .It Cm UserKnownHostsFile | |
975 | Specifies a file to use for the user | |
976 | host key database instead of | |
140e3e97 | 977 | .Pa ~/.ssh/known_hosts . |
21289cd0 | 978 | .It Cm VerifyHostKeyDNS |
979 | Specifies whether to verify the remote key using DNS and SSHFP resource | |
980 | records. | |
0161a13d | 981 | If this option is set to |
982 | .Dq yes , | |
dd376e92 | 983 | the client will implicitly trust keys that match a secure fingerprint |
0161a13d | 984 | from DNS. |
985 | Insecure fingerprints will be handled as if this option was set to | |
986 | .Dq ask . | |
987 | If this option is set to | |
988 | .Dq ask , | |
989 | information on fingerprint match will be displayed, but the user will still | |
990 | need to confirm new host keys according to the | |
991 | .Cm StrictHostKeyChecking | |
992 | option. | |
993 | The argument must be | |
994 | .Dq yes , | |
c5786b30 | 995 | .Dq no , |
dd376e92 | 996 | or |
997 | .Dq ask . | |
21289cd0 | 998 | The default is |
999 | .Dq no . | |
0f92946c | 1000 | Note that this option applies to protocol version 2 only. |
c5786b30 | 1001 | .Pp |
1002 | See also | |
1003 | .Sx VERIFYING HOST KEYS | |
1004 | in | |
1005 | .Xr ssh 1 . | |
588df31a | 1006 | .It Cm XAuthLocation |
57ff5eeb | 1007 | Specifies the full pathname of the |
588df31a | 1008 | .Xr xauth 1 |
1009 | program. | |
1010 | The default is | |
1011 | .Pa /usr/X11R6/bin/xauth . | |
1012 | .El | |
de4f5093 | 1013 | .Sh PATTERNS |
1014 | A | |
1015 | .Em pattern | |
1016 | consists of zero or more non-whitespace characters, | |
1017 | .Sq * | |
1018 | (a wildcard that matches zero or more characters), | |
1019 | or | |
1020 | .Sq ?\& | |
1021 | (a wildcard that matches exactly one character). | |
1022 | For example, to specify a set of declarations for any host in the | |
1023 | .Dq .co.uk | |
1024 | set of domains, | |
1025 | the following pattern could be used: | |
1026 | .Pp | |
1027 | .Dl Host *.co.uk | |
1028 | .Pp | |
1029 | The following pattern | |
1030 | would match any host in the 192.168.0.[0-9] network range: | |
1031 | .Pp | |
1032 | .Dl Host 192.168.0.? | |
1033 | .Pp | |
1034 | A | |
1035 | .Em pattern-list | |
1036 | is a comma-separated list of patterns. | |
1037 | Patterns within pattern-lists may be negated | |
1038 | by preceding them with an exclamation mark | |
1039 | .Pq Sq !\& . | |
1040 | For example, | |
1041 | to allow a key to be used from anywhere within an organisation | |
1042 | except from the | |
1043 | .Dq dialup | |
1044 | pool, | |
1045 | the following entry (in authorized_keys) could be used: | |
1046 | .Pp | |
1047 | .Dl from=\&"!*.dialup.example.com,*.example.com\&" | |
588df31a | 1048 | .Sh FILES |
1049 | .Bl -tag -width Ds | |
140e3e97 | 1050 | .It Pa ~/.ssh/config |
588df31a | 1051 | This is the per-user configuration file. |
1052 | The format of this file is described above. | |
c5786b30 | 1053 | This file is used by the SSH client. |
e1520719 | 1054 | Because of the potential for abuse, this file must have strict permissions: |
1055 | read/write for the user, and not accessible by others. | |
588df31a | 1056 | .It Pa /etc/ssh/ssh_config |
1057 | Systemwide configuration file. | |
1058 | This file provides defaults for those | |
1059 | values that are not specified in the user's configuration file, and | |
1060 | for those users who do not have a configuration file. | |
1061 | This file must be world-readable. | |
1062 | .El | |
be193d89 | 1063 | .Sh SEE ALSO |
1064 | .Xr ssh 1 | |
588df31a | 1065 | .Sh AUTHORS |
1066 | OpenSSH is a derivative of the original and free | |
1067 | ssh 1.2.12 release by Tatu Ylonen. | |
1068 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1069 | Theo de Raadt and Dug Song | |
1070 | removed many bugs, re-added newer features and | |
1071 | created OpenSSH. | |
1072 | Markus Friedl contributed the support for SSH | |
1073 | protocol versions 1.5 and 2.0. |