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16c343f1 PA |
1 | .\" |
2 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> | |
3 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland | |
4 | .\" All rights reserved | |
5 | .\" | |
6 | .\" As far as I am concerned, the code I have written for this software | |
7 | .\" can be used freely for any purpose. Any derived versions of this | |
8 | .\" software must be clearly marked as such, and if the derived work is | |
9 | .\" incompatible with the protocol description in the RFC file, it must be | |
10 | .\" called by a name other than "ssh" or "Secure Shell". | |
11 | .\" | |
12 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. | |
13 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. | |
14 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. | |
15 | .\" | |
16 | .\" Redistribution and use in source and binary forms, with or without | |
17 | .\" modification, are permitted provided that the following conditions | |
18 | .\" are met: | |
19 | .\" 1. Redistributions of source code must retain the above copyright | |
20 | .\" notice, this list of conditions and the following disclaimer. | |
21 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
22 | .\" notice, this list of conditions and the following disclaimer in the | |
23 | .\" documentation and/or other materials provided with the distribution. | |
24 | .\" | |
25 | .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR | |
26 | .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES | |
27 | .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |
28 | .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, | |
29 | .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT | |
30 | .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
31 | .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
32 | .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
33 | .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF | |
34 | .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
35 | .\" | |
36e94dc5 PA |
36 | .\" $OpenBSD: ssh_config.5,v 1.191 2014/07/15 15:54:14 millert Exp $ |
37 | .Dd $Mdocdate: July 15 2014 $ | |
16c343f1 PA |
38 | .Dt SSH_CONFIG 5 |
39 | .Os | |
40 | .Sh NAME | |
41 | .Nm ssh_config | |
42 | .Nd OpenSSH SSH client configuration files | |
43 | .Sh SYNOPSIS | |
44 | .Nm ~/.ssh/config | |
45 | .Nm /etc/ssh/ssh_config | |
46 | .Sh DESCRIPTION | |
47 | .Xr ssh 1 | |
48 | obtains configuration data from the following sources in | |
49 | the following order: | |
50 | .Pp | |
51 | .Bl -enum -offset indent -compact | |
52 | .It | |
53 | command-line options | |
54 | .It | |
55 | user's configuration file | |
56 | .Pq Pa ~/.ssh/config | |
57 | .It | |
58 | system-wide configuration file | |
59 | .Pq Pa /etc/ssh/ssh_config | |
60 | .El | |
61 | .Pp | |
62 | For each parameter, the first obtained value | |
63 | will be used. | |
64 | The configuration files contain sections separated by | |
65 | .Dq Host | |
66 | specifications, and that section is only applied for hosts that | |
67 | match one of the patterns given in the specification. | |
68 | The matched host name is the one given on the command line. | |
69 | .Pp | |
70 | Since the first obtained value for each parameter is used, more | |
71 | host-specific declarations should be given near the beginning of the | |
72 | file, and general defaults at the end. | |
73 | .Pp | |
74 | The configuration file has the following format: | |
75 | .Pp | |
76 | Empty lines and lines starting with | |
77 | .Ql # | |
78 | are comments. | |
79 | Otherwise a line is of the format | |
80 | .Dq keyword arguments . | |
81 | Configuration options may be separated by whitespace or | |
82 | optional whitespace and exactly one | |
83 | .Ql = ; | |
84 | the latter format is useful to avoid the need to quote whitespace | |
85 | when specifying configuration options using the | |
86 | .Nm ssh , | |
87 | .Nm scp , | |
88 | and | |
89 | .Nm sftp | |
90 | .Fl o | |
91 | option. | |
92 | Arguments may optionally be enclosed in double quotes | |
93 | .Pq \&" | |
94 | in order to represent arguments containing spaces. | |
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 | |
36e94dc5 PA |
103 | or |
104 | .Cm Match | |
16c343f1 PA |
105 | keyword) to be only for those hosts that match one of the patterns |
106 | given after the keyword. | |
cb5eb4f1 | 107 | If more than one pattern is provided, they should be separated by whitespace. |
16c343f1 PA |
108 | A single |
109 | .Ql * | |
110 | as a pattern can be used to provide global | |
111 | defaults for all hosts. | |
112 | The host is the | |
113 | .Ar hostname | |
114 | argument given on the command line (i.e. the name is not converted to | |
115 | a canonicalized host name before matching). | |
116 | .Pp | |
1c188a7f PA |
117 | A pattern entry may be negated by prefixing it with an exclamation mark |
118 | .Pq Sq !\& . | |
119 | If a negated entry is matched, then the | |
120 | .Cm Host | |
121 | entry is ignored, regardless of whether any other patterns on the line | |
122 | match. | |
123 | Negated matches are therefore useful to provide exceptions for wildcard | |
124 | matches. | |
125 | .Pp | |
16c343f1 PA |
126 | See |
127 | .Sx PATTERNS | |
128 | for more information on patterns. | |
36e94dc5 PA |
129 | .It Cm Match |
130 | Restricts the following declarations (up to the next | |
131 | .Cm Host | |
132 | or | |
133 | .Cm Match | |
134 | keyword) to be used only when the conditions following the | |
135 | .Cm Match | |
136 | keyword are satisfied. | |
137 | Match conditions are specified using one or more keyword/criteria pairs | |
138 | or the single token | |
139 | .Cm all | |
140 | which matches all criteria. | |
141 | The available keywords are: | |
142 | .Cm exec , | |
143 | .Cm host , | |
144 | .Cm originalhost , | |
145 | .Cm user , | |
146 | and | |
147 | .Cm localuser . | |
148 | .Pp | |
149 | The | |
150 | .Cm exec | |
151 | keyword executes the specified command under the user's shell. | |
152 | If the command returns a zero exit status then the condition is considered true. | |
153 | Commands containing whitespace characters must be quoted. | |
154 | The following character sequences in the command will be expanded prior to | |
155 | execution: | |
156 | .Ql %L | |
157 | will be substituted by the first component of the local host name, | |
158 | .Ql %l | |
159 | will be substituted by the local host name (including any domain name), | |
160 | .Ql %h | |
161 | will be substituted by the target host name, | |
162 | .Ql %n | |
163 | will be substituted by the original target host name | |
164 | specified on the command-line, | |
165 | .Ql %p | |
166 | the destination port, | |
167 | .Ql %r | |
168 | by the remote login username, and | |
169 | .Ql %u | |
170 | by the username of the user running | |
171 | .Xr ssh 1 . | |
172 | .Pp | |
173 | The other keywords' criteria must be single entries or comma-separated | |
174 | lists and may use the wildcard and negation operators described in the | |
175 | .Sx PATTERNS | |
176 | section. | |
177 | The criteria for the | |
178 | .Cm host | |
179 | keyword are matched against the target hostname, after any substitution | |
180 | by the | |
181 | .Cm Hostname | |
182 | option. | |
183 | The | |
184 | .Cm originalhost | |
185 | keyword matches against the hostname as it was specified on the command-line. | |
186 | The | |
187 | .Cm user | |
188 | keyword matches against the target username on the remote host. | |
189 | The | |
190 | .Cm localuser | |
191 | keyword matches against the name of the local user running | |
192 | .Xr ssh 1 | |
193 | (this keyword may be useful in system-wide | |
194 | .Nm | |
195 | files). | |
16c343f1 PA |
196 | .It Cm AddressFamily |
197 | Specifies which address family to use when connecting. | |
198 | Valid arguments are | |
199 | .Dq any , | |
200 | .Dq inet | |
201 | (use IPv4 only), or | |
202 | .Dq inet6 | |
203 | (use IPv6 only). | |
204 | .It Cm BatchMode | |
205 | If set to | |
206 | .Dq yes , | |
207 | passphrase/password querying will be disabled. | |
208 | This option is useful in scripts and other batch jobs where no user | |
209 | is present to supply the password. | |
210 | The argument must be | |
211 | .Dq yes | |
212 | or | |
213 | .Dq no . | |
214 | The default is | |
215 | .Dq no . | |
216 | .It Cm BindAddress | |
217 | Use the specified address on the local machine as the source address of | |
218 | the connection. | |
219 | Only useful on systems with more than one address. | |
220 | Note that this option does not work if | |
221 | .Cm UsePrivilegedPort | |
222 | is set to | |
223 | .Dq yes . | |
36e94dc5 PA |
224 | .It Cm CanonicalDomains |
225 | When | |
226 | .Cm CanonicalizeHostname | |
227 | is enabled, this option specifies the list of domain suffixes in which to | |
228 | search for the specified destination host. | |
229 | .It Cm CanonicalizeFallbackLocal | |
230 | Specifies whether to fail with an error when hostname canonicalization fails. | |
231 | The default, | |
232 | .Dq yes , | |
233 | will attempt to look up the unqualified hostname using the system resolver's | |
234 | search rules. | |
235 | A value of | |
236 | .Dq no | |
237 | will cause | |
238 | .Xr ssh 1 | |
239 | to fail instantly if | |
240 | .Cm CanonicalizeHostname | |
241 | is enabled and the target hostname cannot be found in any of the domains | |
242 | specified by | |
243 | .Cm CanonicalDomains . | |
244 | .It Cm CanonicalizeHostname | |
245 | Controls whether explicit hostname canonicalization is performed. | |
246 | The default, | |
247 | .Dq no , | |
248 | is not to perform any name rewriting and let the system resolver handle all | |
249 | hostname lookups. | |
250 | If set to | |
251 | .Dq yes | |
252 | then, for connections that do not use a | |
253 | .Cm ProxyCommand , | |
254 | .Xr ssh 1 | |
255 | will attempt to canonicalize the hostname specified on the command line | |
256 | using the | |
257 | .Cm CanonicalDomains | |
258 | suffixes and | |
259 | .Cm CanonicalizePermittedCNAMEs | |
260 | rules. | |
261 | If | |
262 | .Cm CanonicalizeHostname | |
263 | is set to | |
264 | .Dq always , | |
265 | then canonicalization is applied to proxied connections too. | |
266 | .Pp | |
267 | If this option is enabled and canonicalisation results in the target hostname | |
268 | changing, then the configuration files are processed again using the new | |
269 | target name to pick up any new configuration in matching | |
270 | .Cm Host | |
271 | stanzas. | |
272 | .It Cm CanonicalizeMaxDots | |
273 | Specifies the maximum number of dot characters in a hostname before | |
274 | canonicalization is disabled. | |
275 | The default, | |
276 | .Dq 1 , | |
277 | allows a single dot (i.e. hostname.subdomain). | |
278 | .It Cm CanonicalizePermittedCNAMEs | |
279 | Specifies rules to determine whether CNAMEs should be followed when | |
280 | canonicalizing hostnames. | |
281 | The rules consist of one or more arguments of | |
282 | .Ar source_domain_list : Ns Ar target_domain_list , | |
283 | where | |
284 | .Ar source_domain_list | |
285 | is a pattern-list of domains that may follow CNAMEs in canonicalization, | |
286 | and | |
287 | .Ar target_domain_list | |
288 | is a pattern-list of domains that they may resolve to. | |
289 | .Pp | |
290 | For example, | |
291 | .Dq *.a.example.com:*.b.example.com,*.c.example.com | |
292 | will allow hostnames matching | |
293 | .Dq *.a.example.com | |
294 | to be canonicalized to names in the | |
295 | .Dq *.b.example.com | |
296 | or | |
297 | .Dq *.c.example.com | |
298 | domains. | |
16c343f1 PA |
299 | .It Cm ChallengeResponseAuthentication |
300 | Specifies whether to use challenge-response authentication. | |
301 | The argument to this keyword must be | |
302 | .Dq yes | |
303 | or | |
304 | .Dq no . | |
305 | The default is | |
306 | .Dq yes . | |
307 | .It Cm CheckHostIP | |
308 | If this flag is set to | |
309 | .Dq yes , | |
310 | .Xr ssh 1 | |
311 | will additionally check the host IP address in the | |
312 | .Pa known_hosts | |
313 | file. | |
314 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
315 | If the option is set to | |
316 | .Dq no , | |
317 | the check will not be executed. | |
318 | The default is | |
40948e2d | 319 | .Dq no . |
16c343f1 PA |
320 | .It Cm Cipher |
321 | Specifies the cipher to use for encrypting the session | |
322 | in protocol version 1. | |
323 | Currently, | |
324 | .Dq blowfish , | |
325 | .Dq 3des , | |
326 | and | |
327 | .Dq des | |
328 | are supported. | |
329 | .Ar des | |
330 | is only supported in the | |
331 | .Xr ssh 1 | |
332 | client for interoperability with legacy protocol 1 implementations | |
333 | that do not support the | |
334 | .Ar 3des | |
335 | cipher. | |
336 | Its use is strongly discouraged due to cryptographic weaknesses. | |
337 | The default is | |
338 | .Dq 3des . | |
339 | .It Cm Ciphers | |
340 | Specifies the ciphers allowed for protocol version 2 | |
341 | in order of preference. | |
342 | Multiple ciphers must be comma-separated. | |
36e94dc5 PA |
343 | The supported ciphers are: |
344 | .Pp | |
345 | .Bl -item -compact -offset indent | |
346 | .It | |
347 | 3des-cbc | |
348 | .It | |
349 | aes128-cbc | |
350 | .It | |
351 | aes192-cbc | |
352 | .It | |
353 | aes256-cbc | |
354 | .It | |
355 | aes128-ctr | |
356 | .It | |
357 | aes192-ctr | |
358 | .It | |
359 | aes256-ctr | |
360 | .It | |
361 | aes128-gcm@openssh.com | |
362 | .It | |
363 | aes256-gcm@openssh.com | |
364 | .It | |
365 | arcfour | |
366 | .It | |
367 | arcfour128 | |
368 | .It | |
369 | arcfour256 | |
370 | .It | |
371 | blowfish-cbc | |
372 | .It | |
373 | cast128-cbc | |
374 | .It | |
375 | chacha20-poly1305@openssh.com | |
376 | .El | |
377 | .Pp | |
16c343f1 | 378 | The default is: |
36e94dc5 PA |
379 | .Bd -literal -offset indent |
380 | aes128-ctr,aes192-ctr,aes256-ctr, | |
381 | aes128-gcm@openssh.com,aes256-gcm@openssh.com, | |
382 | chacha20-poly1305@openssh.com, | |
383 | arcfour256,arcfour128, | |
384 | aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc, | |
385 | aes192-cbc,aes256-cbc,arcfour | |
16c343f1 | 386 | .Ed |
36e94dc5 PA |
387 | .Pp |
388 | The list of available ciphers may also be obtained using the | |
389 | .Fl Q | |
390 | option of | |
391 | .Xr ssh 1 . | |
16c343f1 PA |
392 | .It Cm ClearAllForwardings |
393 | Specifies that all local, remote, and dynamic port forwardings | |
394 | specified in the configuration files or on the command line be | |
395 | cleared. | |
396 | This option is primarily useful when used from the | |
397 | .Xr ssh 1 | |
398 | command line to clear port forwardings set in | |
399 | configuration files, and is automatically set by | |
400 | .Xr scp 1 | |
401 | and | |
402 | .Xr sftp 1 . | |
403 | The argument must be | |
404 | .Dq yes | |
405 | or | |
406 | .Dq no . | |
407 | The default is | |
408 | .Dq no . | |
409 | .It Cm Compression | |
410 | Specifies whether to use compression. | |
411 | The argument must be | |
412 | .Dq yes | |
413 | or | |
414 | .Dq no . | |
415 | The default is | |
416 | .Dq no . | |
417 | .It Cm CompressionLevel | |
418 | Specifies the compression level to use if compression is enabled. | |
419 | The argument must be an integer from 1 (fast) to 9 (slow, best). | |
420 | The default level is 6, which is good for most applications. | |
421 | The meaning of the values is the same as in | |
422 | .Xr gzip 1 . | |
423 | Note that this option applies to protocol version 1 only. | |
424 | .It Cm ConnectionAttempts | |
425 | Specifies the number of tries (one per second) to make before exiting. | |
426 | The argument must be an integer. | |
427 | This may be useful in scripts if the connection sometimes fails. | |
428 | The default is 1. | |
429 | .It Cm ConnectTimeout | |
430 | Specifies the timeout (in seconds) used when connecting to the | |
431 | SSH server, instead of using the default system TCP timeout. | |
432 | This value is used only when the target is down or really unreachable, | |
433 | not when it refuses the connection. | |
434 | .It Cm ControlMaster | |
435 | Enables the sharing of multiple sessions over a single network connection. | |
436 | When set to | |
437 | .Dq yes , | |
438 | .Xr ssh 1 | |
439 | will listen for connections on a control socket specified using the | |
440 | .Cm ControlPath | |
441 | argument. | |
442 | Additional sessions can connect to this socket using the same | |
443 | .Cm ControlPath | |
444 | with | |
445 | .Cm ControlMaster | |
446 | set to | |
447 | .Dq no | |
448 | (the default). | |
449 | These sessions will try to reuse the master instance's network connection | |
450 | rather than initiating new ones, but will fall back to connecting normally | |
451 | if the control socket does not exist, or is not listening. | |
452 | .Pp | |
453 | Setting this to | |
454 | .Dq ask | |
455 | will cause ssh | |
456 | to listen for control connections, but require confirmation using the | |
457 | .Ev SSH_ASKPASS | |
458 | program before they are accepted (see | |
459 | .Xr ssh-add 1 | |
460 | for details). | |
461 | If the | |
462 | .Cm ControlPath | |
463 | cannot be opened, | |
464 | ssh will continue without connecting to a master instance. | |
465 | .Pp | |
466 | X11 and | |
467 | .Xr ssh-agent 1 | |
468 | forwarding is supported over these multiplexed connections, however the | |
469 | display and agent forwarded will be the one belonging to the master | |
470 | connection i.e. it is not possible to forward multiple displays or agents. | |
471 | .Pp | |
472 | Two additional options allow for opportunistic multiplexing: try to use a | |
473 | master connection but fall back to creating a new one if one does not already | |
474 | exist. | |
475 | These options are: | |
476 | .Dq auto | |
477 | and | |
478 | .Dq autoask . | |
479 | The latter requires confirmation like the | |
480 | .Dq ask | |
481 | option. | |
482 | .It Cm ControlPath | |
483 | Specify the path to the control socket used for connection sharing as described | |
484 | in the | |
485 | .Cm ControlMaster | |
486 | section above or the string | |
487 | .Dq none | |
488 | to disable connection sharing. | |
489 | In the path, | |
1c188a7f PA |
490 | .Ql %L |
491 | will be substituted by the first component of the local host name, | |
16c343f1 | 492 | .Ql %l |
1c188a7f | 493 | will be substituted by the local host name (including any domain name), |
16c343f1 PA |
494 | .Ql %h |
495 | will be substituted by the target host name, | |
1c188a7f PA |
496 | .Ql %n |
497 | will be substituted by the original target host name | |
498 | specified on the command line, | |
16c343f1 | 499 | .Ql %p |
36e94dc5 | 500 | the destination port, |
16c343f1 | 501 | .Ql %r |
36e94dc5 | 502 | by the remote login username, |
1c188a7f PA |
503 | .Ql %u |
504 | by the username of the user running | |
36e94dc5 PA |
505 | .Xr ssh 1 , and |
506 | .Ql \&%C | |
507 | by a hash of the concatenation: %l%h%p%r. | |
16c343f1 PA |
508 | It is recommended that any |
509 | .Cm ControlPath | |
510 | used for opportunistic connection sharing include | |
36e94dc5 | 511 | at least %h, %p, and %r (or alternatively %C). |
16c343f1 | 512 | This ensures that shared connections are uniquely identified. |
856ea928 PA |
513 | .It Cm ControlPersist |
514 | When used in conjunction with | |
515 | .Cm ControlMaster , | |
516 | specifies that the master connection should remain open | |
517 | in the background (waiting for future client connections) | |
518 | after the initial client connection has been closed. | |
519 | If set to | |
520 | .Dq no , | |
521 | then the master connection will not be placed into the background, | |
522 | and will close as soon as the initial client connection is closed. | |
523 | If set to | |
524 | .Dq yes , | |
525 | then the master connection will remain in the background indefinitely | |
526 | (until killed or closed via a mechanism such as the | |
527 | .Xr ssh 1 | |
528 | .Dq Fl O No exit | |
529 | option). | |
530 | If set to a time in seconds, or a time in any of the formats documented in | |
531 | .Xr sshd_config 5 , | |
532 | then the backgrounded master connection will automatically terminate | |
533 | after it has remained idle (with no client connections) for the | |
534 | specified time. | |
16c343f1 PA |
535 | .It Cm DynamicForward |
536 | Specifies that a TCP port on the local machine be forwarded | |
537 | over the secure channel, and the application | |
538 | protocol is then used to determine where to connect to from the | |
539 | remote machine. | |
540 | .Pp | |
541 | The argument must be | |
542 | .Sm off | |
543 | .Oo Ar bind_address : Oc Ar port . | |
544 | .Sm on | |
856ea928 | 545 | IPv6 addresses can be specified by enclosing addresses in square brackets. |
16c343f1 PA |
546 | By default, the local port is bound in accordance with the |
547 | .Cm GatewayPorts | |
548 | setting. | |
549 | However, an explicit | |
550 | .Ar bind_address | |
551 | may be used to bind the connection to a specific address. | |
552 | The | |
553 | .Ar bind_address | |
554 | of | |
555 | .Dq localhost | |
556 | indicates that the listening port be bound for local use only, while an | |
557 | empty address or | |
558 | .Sq * | |
559 | indicates that the port should be available from all interfaces. | |
560 | .Pp | |
561 | Currently the SOCKS4 and SOCKS5 protocols are supported, and | |
562 | .Xr ssh 1 | |
563 | will act as a SOCKS server. | |
564 | Multiple forwardings may be specified, and | |
565 | additional forwardings can be given on the command line. | |
566 | Only the superuser can forward privileged ports. | |
567 | .It Cm EnableSSHKeysign | |
568 | Setting this option to | |
569 | .Dq yes | |
570 | in the global client configuration file | |
571 | .Pa /etc/ssh/ssh_config | |
572 | enables the use of the helper program | |
573 | .Xr ssh-keysign 8 | |
574 | during | |
575 | .Cm HostbasedAuthentication . | |
576 | The argument must be | |
577 | .Dq yes | |
578 | or | |
579 | .Dq no . | |
580 | The default is | |
581 | .Dq no . | |
582 | This option should be placed in the non-hostspecific section. | |
583 | See | |
584 | .Xr ssh-keysign 8 | |
585 | for more information. | |
586 | .It Cm EscapeChar | |
587 | Sets the escape character (default: | |
588 | .Ql ~ ) . | |
589 | The escape character can also | |
590 | be set on the command line. | |
591 | The argument should be a single character, | |
592 | .Ql ^ | |
593 | followed by a letter, or | |
594 | .Dq none | |
595 | to disable the escape | |
596 | character entirely (making the connection transparent for binary | |
597 | data). | |
598 | .It Cm ExitOnForwardFailure | |
599 | Specifies whether | |
600 | .Xr ssh 1 | |
601 | should terminate the connection if it cannot set up all requested | |
602 | dynamic, tunnel, local, and remote port forwardings. | |
603 | The argument must be | |
604 | .Dq yes | |
605 | or | |
606 | .Dq no . | |
607 | The default is | |
608 | .Dq no . | |
609 | .It Cm ForwardAgent | |
610 | Specifies whether the connection to the authentication agent (if any) | |
611 | will be forwarded to the remote machine. | |
612 | The argument must be | |
613 | .Dq yes | |
614 | or | |
615 | .Dq no . | |
616 | The default is | |
617 | .Dq no . | |
618 | .Pp | |
619 | Agent forwarding should be enabled with caution. | |
620 | Users with the ability to bypass file permissions on the remote host | |
621 | (for the agent's Unix-domain socket) | |
622 | can access the local agent through the forwarded connection. | |
623 | An attacker cannot obtain key material from the agent, | |
624 | however they can perform operations on the keys that enable them to | |
625 | authenticate using the identities loaded into the agent. | |
626 | .It Cm ForwardX11 | |
627 | Specifies whether X11 connections will be automatically redirected | |
628 | over the secure channel and | |
629 | .Ev DISPLAY | |
630 | set. | |
631 | The argument must be | |
632 | .Dq yes | |
633 | or | |
634 | .Dq no . | |
635 | The default is | |
636 | .Dq no . | |
637 | .Pp | |
638 | X11 forwarding should be enabled with caution. | |
639 | Users with the ability to bypass file permissions on the remote host | |
640 | (for the user's X11 authorization database) | |
641 | can access the local X11 display through the forwarded connection. | |
642 | An attacker may then be able to perform activities such as keystroke monitoring | |
643 | if the | |
644 | .Cm ForwardX11Trusted | |
645 | option is also enabled. | |
856ea928 PA |
646 | .It Cm ForwardX11Timeout |
647 | Specify a timeout for untrusted X11 forwarding | |
648 | using the format described in the | |
36e94dc5 | 649 | TIME FORMATS section of |
856ea928 PA |
650 | .Xr sshd_config 5 . |
651 | X11 connections received by | |
652 | .Xr ssh 1 | |
653 | after this time will be refused. | |
654 | The default is to disable untrusted X11 forwarding after twenty minutes has | |
655 | elapsed. | |
16c343f1 PA |
656 | .It Cm ForwardX11Trusted |
657 | If this option is set to | |
658 | .Dq yes , | |
659 | remote X11 clients will have full access to the original X11 display. | |
660 | .Pp | |
661 | If this option is set to | |
662 | .Dq no , | |
663 | remote X11 clients will be considered untrusted and prevented | |
664 | from stealing or tampering with data belonging to trusted X11 | |
665 | clients. | |
666 | Furthermore, the | |
667 | .Xr xauth 1 | |
668 | token used for the session will be set to expire after 20 minutes. | |
669 | Remote clients will be refused access after this time. | |
670 | .Pp | |
671 | The default is | |
672 | .Dq no . | |
673 | .Pp | |
674 | See the X11 SECURITY extension specification for full details on | |
675 | the restrictions imposed on untrusted clients. | |
676 | .It Cm GatewayPorts | |
677 | Specifies whether remote hosts are allowed to connect to local | |
678 | forwarded ports. | |
679 | By default, | |
680 | .Xr ssh 1 | |
681 | binds local port forwardings to the loopback address. | |
682 | This prevents other remote hosts from connecting to forwarded ports. | |
683 | .Cm GatewayPorts | |
684 | can be used to specify that ssh | |
685 | should bind local port forwardings to the wildcard address, | |
686 | thus allowing remote hosts to connect to forwarded ports. | |
687 | The argument must be | |
688 | .Dq yes | |
689 | or | |
690 | .Dq no . | |
691 | The default is | |
692 | .Dq no . | |
693 | .It Cm GlobalKnownHostsFile | |
1c188a7f PA |
694 | Specifies one or more files to use for the global |
695 | host key database, separated by whitespace. | |
696 | The default is | |
697 | .Pa /etc/ssh/ssh_known_hosts , | |
698 | .Pa /etc/ssh/ssh_known_hosts2 . | |
16c343f1 PA |
699 | .It Cm GSSAPIAuthentication |
700 | Specifies whether user authentication based on GSSAPI is allowed. | |
701 | The default is | |
702 | .Dq no . | |
703 | Note that this option applies to protocol version 2 only. | |
704 | .It Cm GSSAPIDelegateCredentials | |
705 | Forward (delegate) credentials to the server. | |
706 | The default is | |
707 | .Dq no . | |
708 | Note that this option applies to protocol version 2 only. | |
709 | .It Cm HashKnownHosts | |
710 | Indicates that | |
711 | .Xr ssh 1 | |
712 | should hash host names and addresses when they are added to | |
713 | .Pa ~/.ssh/known_hosts . | |
714 | These hashed names may be used normally by | |
715 | .Xr ssh 1 | |
716 | and | |
717 | .Xr sshd 8 , | |
718 | but they do not reveal identifying information should the file's contents | |
719 | be disclosed. | |
720 | The default is | |
721 | .Dq no . | |
722 | Note that existing names and addresses in known hosts files | |
723 | will not be converted automatically, | |
724 | but may be manually hashed using | |
725 | .Xr ssh-keygen 1 . | |
726 | .It Cm HostbasedAuthentication | |
727 | Specifies whether to try rhosts based authentication with public key | |
728 | authentication. | |
729 | The argument must be | |
730 | .Dq yes | |
731 | or | |
732 | .Dq no . | |
733 | The default is | |
734 | .Dq no . | |
735 | This option applies to protocol version 2 only and | |
736 | is similar to | |
737 | .Cm RhostsRSAAuthentication . | |
738 | .It Cm HostKeyAlgorithms | |
739 | Specifies the protocol version 2 host key algorithms | |
740 | that the client wants to use in order of preference. | |
741 | The default for this option is: | |
9f304aaf PA |
742 | .Bd -literal -offset 3n |
743 | ecdsa-sha2-nistp256-cert-v01@openssh.com, | |
744 | ecdsa-sha2-nistp384-cert-v01@openssh.com, | |
745 | ecdsa-sha2-nistp521-cert-v01@openssh.com, | |
36e94dc5 | 746 | ssh-ed25519-cert-v01@openssh.com, |
9f304aaf PA |
747 | ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com, |
748 | ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com, | |
749 | ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521, | |
36e94dc5 | 750 | ssh-ed25519,ssh-rsa,ssh-dss |
9f304aaf PA |
751 | .Ed |
752 | .Pp | |
753 | If hostkeys are known for the destination host then this default is modified | |
754 | to prefer their algorithms. | |
16c343f1 PA |
755 | .It Cm HostKeyAlias |
756 | Specifies an alias that should be used instead of the | |
757 | real host name when looking up or saving the host key | |
758 | in the host key database files. | |
759 | This option is useful for tunneling SSH connections | |
760 | or for multiple servers running on a single host. | |
761 | .It Cm HostName | |
762 | Specifies the real host name to log into. | |
763 | This can be used to specify nicknames or abbreviations for hosts. | |
856ea928 PA |
764 | If the hostname contains the character sequence |
765 | .Ql %h , | |
1c188a7f | 766 | then this will be replaced with the host name specified on the command line |
856ea928 | 767 | (this is useful for manipulating unqualified names). |
36e94dc5 PA |
768 | The character sequence |
769 | .Ql %% | |
770 | will be replaced by a single | |
771 | .Ql % | |
772 | character, which may be used when specifying IPv6 link-local addresses. | |
773 | .Pp | |
16c343f1 PA |
774 | The default is the name given on the command line. |
775 | Numeric IP addresses are also permitted (both on the command line and in | |
776 | .Cm HostName | |
777 | specifications). | |
778 | .It Cm IdentitiesOnly | |
779 | Specifies that | |
780 | .Xr ssh 1 | |
781 | should only use the authentication identity files configured in the | |
782 | .Nm | |
783 | files, | |
784 | even if | |
785 | .Xr ssh-agent 1 | |
36e94dc5 PA |
786 | or a |
787 | .Cm PKCS11Provider | |
16c343f1 PA |
788 | offers more identities. |
789 | The argument to this keyword must be | |
790 | .Dq yes | |
791 | or | |
792 | .Dq no . | |
793 | This option is intended for situations where ssh-agent | |
794 | offers many different identities. | |
795 | The default is | |
796 | .Dq no . | |
797 | .It Cm IdentityFile | |
36e94dc5 | 798 | Specifies a file from which the user's DSA, ECDSA, ED25519 or RSA authentication |
9f304aaf | 799 | identity is read. |
16c343f1 PA |
800 | The default is |
801 | .Pa ~/.ssh/identity | |
802 | for protocol version 1, and | |
9f304aaf | 803 | .Pa ~/.ssh/id_dsa , |
36e94dc5 PA |
804 | .Pa ~/.ssh/id_ecdsa , |
805 | .Pa ~/.ssh/id_ed25519 | |
16c343f1 | 806 | and |
9f304aaf | 807 | .Pa ~/.ssh/id_rsa |
16c343f1 PA |
808 | for protocol version 2. |
809 | Additionally, any identities represented by the authentication agent | |
36e94dc5 PA |
810 | will be used for authentication unless |
811 | .Cm IdentitiesOnly | |
812 | is set. | |
856ea928 PA |
813 | .Xr ssh 1 |
814 | will try to load certificate information from the filename obtained by | |
815 | appending | |
816 | .Pa -cert.pub | |
817 | to the path of a specified | |
818 | .Cm IdentityFile . | |
16c343f1 PA |
819 | .Pp |
820 | The file name may use the tilde | |
821 | syntax to refer to a user's home directory or one of the following | |
822 | escape characters: | |
823 | .Ql %d | |
824 | (local user's home directory), | |
825 | .Ql %u | |
826 | (local user name), | |
827 | .Ql %l | |
828 | (local host name), | |
829 | .Ql %h | |
830 | (remote host name) or | |
831 | .Ql %r | |
832 | (remote user name). | |
833 | .Pp | |
834 | It is possible to have | |
835 | multiple identity files specified in configuration files; all these | |
836 | identities will be tried in sequence. | |
1c188a7f PA |
837 | Multiple |
838 | .Cm IdentityFile | |
839 | directives will add to the list of identities tried (this behaviour | |
840 | differs from that of other configuration directives). | |
36e94dc5 PA |
841 | .Pp |
842 | .Cm IdentityFile | |
843 | may be used in conjunction with | |
844 | .Cm IdentitiesOnly | |
845 | to select which identities in an agent are offered during authentication. | |
846 | .It Cm IgnoreUnknown | |
847 | Specifies a pattern-list of unknown options to be ignored if they are | |
848 | encountered in configuration parsing. | |
849 | This may be used to suppress errors if | |
850 | .Nm | |
851 | contains options that are unrecognised by | |
852 | .Xr ssh 1 . | |
853 | It is recommended that | |
854 | .Cm IgnoreUnknown | |
855 | be listed early in the configuration file as it will not be applied | |
856 | to unknown options that appear before it. | |
9f304aaf PA |
857 | .It Cm IPQoS |
858 | Specifies the IPv4 type-of-service or DSCP class for connections. | |
859 | Accepted values are | |
860 | .Dq af11 , | |
861 | .Dq af12 , | |
862 | .Dq af13 , | |
99e85e0d | 863 | .Dq af21 , |
9f304aaf PA |
864 | .Dq af22 , |
865 | .Dq af23 , | |
866 | .Dq af31 , | |
867 | .Dq af32 , | |
868 | .Dq af33 , | |
869 | .Dq af41 , | |
870 | .Dq af42 , | |
871 | .Dq af43 , | |
872 | .Dq cs0 , | |
873 | .Dq cs1 , | |
874 | .Dq cs2 , | |
875 | .Dq cs3 , | |
876 | .Dq cs4 , | |
877 | .Dq cs5 , | |
878 | .Dq cs6 , | |
879 | .Dq cs7 , | |
880 | .Dq ef , | |
881 | .Dq lowdelay , | |
882 | .Dq throughput , | |
883 | .Dq reliability , | |
884 | or a numeric value. | |
885 | This option may take one or two arguments, separated by whitespace. | |
886 | If one argument is specified, it is used as the packet class unconditionally. | |
887 | If two values are specified, the first is automatically selected for | |
888 | interactive sessions and the second for non-interactive sessions. | |
889 | The default is | |
890 | .Dq lowdelay | |
891 | for interactive sessions and | |
892 | .Dq throughput | |
893 | for non-interactive sessions. | |
16c343f1 PA |
894 | .It Cm KbdInteractiveAuthentication |
895 | Specifies whether to use keyboard-interactive authentication. | |
896 | The argument to this keyword must be | |
897 | .Dq yes | |
898 | or | |
899 | .Dq no . | |
900 | The default is | |
901 | .Dq yes . | |
902 | .It Cm KbdInteractiveDevices | |
903 | Specifies the list of methods to use in keyboard-interactive authentication. | |
904 | Multiple method names must be comma-separated. | |
905 | The default is to use the server specified list. | |
906 | The methods available vary depending on what the server supports. | |
907 | For an OpenSSH server, | |
908 | it may be zero or more of: | |
909 | .Dq bsdauth , | |
910 | .Dq pam , | |
911 | and | |
912 | .Dq skey . | |
9f304aaf PA |
913 | .It Cm KexAlgorithms |
914 | Specifies the available KEX (Key Exchange) algorithms. | |
915 | Multiple algorithms must be comma-separated. | |
916 | The default is: | |
917 | .Bd -literal -offset indent | |
36e94dc5 | 918 | curve25519-sha256@libssh.org, |
9f304aaf PA |
919 | ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, |
920 | diffie-hellman-group-exchange-sha256, | |
9f304aaf | 921 | diffie-hellman-group14-sha1, |
36e94dc5 | 922 | diffie-hellman-group-exchange-sha1, |
9f304aaf PA |
923 | diffie-hellman-group1-sha1 |
924 | .Ed | |
16c343f1 PA |
925 | .It Cm LocalCommand |
926 | Specifies a command to execute on the local machine after successfully | |
927 | connecting to the server. | |
928 | The command string extends to the end of the line, and is executed with | |
929 | the user's shell. | |
c8c467ee PA |
930 | The following escape character substitutions will be performed: |
931 | .Ql %d | |
932 | (local user's home directory), | |
933 | .Ql %h | |
934 | (remote host name), | |
935 | .Ql %l | |
936 | (local host name), | |
937 | .Ql %n | |
938 | (host name as provided on the command line), | |
939 | .Ql %p | |
940 | (remote port), | |
941 | .Ql %r | |
942 | (remote user name) or | |
943 | .Ql %u | |
36e94dc5 PA |
944 | (local user name) or |
945 | .Ql \&%C | |
946 | by a hash of the concatenation: %l%h%p%r. | |
856ea928 PA |
947 | .Pp |
948 | The command is run synchronously and does not have access to the | |
949 | session of the | |
950 | .Xr ssh 1 | |
951 | that spawned it. | |
952 | It should not be used for interactive commands. | |
953 | .Pp | |
16c343f1 PA |
954 | This directive is ignored unless |
955 | .Cm PermitLocalCommand | |
956 | has been enabled. | |
957 | .It Cm LocalForward | |
958 | Specifies that a TCP port on the local machine be forwarded over | |
959 | the secure channel to the specified host and port from the remote machine. | |
960 | The first argument must be | |
961 | .Sm off | |
962 | .Oo Ar bind_address : Oc Ar port | |
963 | .Sm on | |
964 | and the second argument must be | |
965 | .Ar host : Ns Ar hostport . | |
856ea928 | 966 | IPv6 addresses can be specified by enclosing addresses in square brackets. |
16c343f1 PA |
967 | Multiple forwardings may be specified, and additional forwardings can be |
968 | given on the command line. | |
969 | Only the superuser can forward privileged ports. | |
970 | By default, the local port is bound in accordance with the | |
971 | .Cm GatewayPorts | |
972 | setting. | |
973 | However, an explicit | |
974 | .Ar bind_address | |
975 | may be used to bind the connection to a specific address. | |
976 | The | |
977 | .Ar bind_address | |
978 | of | |
979 | .Dq localhost | |
980 | indicates that the listening port be bound for local use only, while an | |
981 | empty address or | |
982 | .Sq * | |
983 | indicates that the port should be available from all interfaces. | |
984 | .It Cm LogLevel | |
985 | Gives the verbosity level that is used when logging messages from | |
986 | .Xr ssh 1 . | |
987 | The possible values are: | |
988 | QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. | |
989 | The default is INFO. | |
990 | DEBUG and DEBUG1 are equivalent. | |
991 | DEBUG2 and DEBUG3 each specify higher levels of verbose output. | |
992 | .It Cm MACs | |
993 | Specifies the MAC (message authentication code) algorithms | |
994 | in order of preference. | |
995 | The MAC algorithm is used in protocol version 2 | |
996 | for data integrity protection. | |
997 | Multiple algorithms must be comma-separated. | |
36e94dc5 PA |
998 | The algorithms that contain |
999 | .Dq -etm | |
1000 | calculate the MAC after encryption (encrypt-then-mac). | |
1001 | These are considered safer and their use recommended. | |
16c343f1 PA |
1002 | The default is: |
1003 | .Bd -literal -offset indent | |
36e94dc5 PA |
1004 | umac-64-etm@openssh.com,umac-128-etm@openssh.com, |
1005 | hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com, | |
1006 | umac-64@openssh.com,umac-128@openssh.com, | |
1007 | hmac-sha2-256,hmac-sha2-512, | |
1008 | hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com, | |
1009 | hmac-ripemd160-etm@openssh.com, | |
1010 | hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com, | |
1011 | hmac-md5,hmac-sha1,hmac-ripemd160, | |
99e85e0d | 1012 | hmac-sha1-96,hmac-md5-96 |
16c343f1 PA |
1013 | .Ed |
1014 | .It Cm NoHostAuthenticationForLocalhost | |
1015 | This option can be used if the home directory is shared across machines. | |
1016 | In this case localhost will refer to a different machine on each of | |
1017 | the machines and the user will get many warnings about changed host keys. | |
1018 | However, this option disables host authentication for localhost. | |
1019 | The argument to this keyword must be | |
1020 | .Dq yes | |
1021 | or | |
1022 | .Dq no . | |
1023 | The default is to check the host key for localhost. | |
1024 | .It Cm NumberOfPasswordPrompts | |
1025 | Specifies the number of password prompts before giving up. | |
1026 | The argument to this keyword must be an integer. | |
1027 | The default is 3. | |
1028 | .It Cm PasswordAuthentication | |
1029 | Specifies whether to use password authentication. | |
1030 | The argument to this keyword must be | |
1031 | .Dq yes | |
1032 | or | |
1033 | .Dq no . | |
1034 | The default is | |
1035 | .Dq yes . | |
1036 | .It Cm PermitLocalCommand | |
1037 | Allow local command execution via the | |
1038 | .Ic LocalCommand | |
1039 | option or using the | |
1040 | .Ic !\& Ns Ar command | |
1041 | escape sequence in | |
1042 | .Xr ssh 1 . | |
1043 | The argument must be | |
1044 | .Dq yes | |
1045 | or | |
1046 | .Dq no . | |
1047 | The default is | |
1048 | .Dq no . | |
856ea928 PA |
1049 | .It Cm PKCS11Provider |
1050 | Specifies which PKCS#11 provider to use. | |
9f304aaf | 1051 | The argument to this keyword is the PKCS#11 shared library |
856ea928 PA |
1052 | .Xr ssh 1 |
1053 | should use to communicate with a PKCS#11 token providing the user's | |
1054 | private RSA key. | |
16c343f1 PA |
1055 | .It Cm Port |
1056 | Specifies the port number to connect on the remote host. | |
1057 | The default is 22. | |
1058 | .It Cm PreferredAuthentications | |
1059 | Specifies the order in which the client should try protocol 2 | |
1060 | authentication methods. | |
1061 | This allows a client to prefer one method (e.g.\& | |
1062 | .Cm keyboard-interactive ) | |
1063 | over another method (e.g.\& | |
856ea928 PA |
1064 | .Cm password ) . |
1065 | The default is: | |
1066 | .Bd -literal -offset indent | |
1067 | gssapi-with-mic,hostbased,publickey, | |
1068 | keyboard-interactive,password | |
1069 | .Ed | |
16c343f1 PA |
1070 | .It Cm Protocol |
1071 | Specifies the protocol versions | |
1072 | .Xr ssh 1 | |
1073 | should support in order of preference. | |
1074 | The possible values are | |
1075 | .Sq 1 | |
1076 | and | |
1077 | .Sq 2 . | |
1078 | Multiple versions must be comma-separated. | |
856ea928 PA |
1079 | When this option is set to |
1080 | .Dq 2,1 | |
1081 | .Nm ssh | |
1082 | will try version 2 and fall back to version 1 | |
16c343f1 | 1083 | if version 2 is not available. |
856ea928 PA |
1084 | The default is |
1085 | .Sq 2 . | |
16c343f1 PA |
1086 | .It Cm ProxyCommand |
1087 | Specifies the command to use to connect to the server. | |
1088 | The command | |
36e94dc5 PA |
1089 | string extends to the end of the line, and is executed |
1090 | using the user's shell | |
1091 | .Ql exec | |
1092 | directive to avoid a lingering shell process. | |
1093 | .Pp | |
856ea928 | 1094 | In the command string, any occurrence of |
16c343f1 PA |
1095 | .Ql %h |
1096 | will be substituted by the host name to | |
856ea928 | 1097 | connect, |
16c343f1 | 1098 | .Ql %p |
856ea928 PA |
1099 | by the port, and |
1100 | .Ql %r | |
1101 | by the remote user name. | |
16c343f1 PA |
1102 | The command can be basically anything, |
1103 | and should read from its standard input and write to its standard output. | |
1104 | It should eventually connect an | |
1105 | .Xr sshd 8 | |
1106 | server running on some machine, or execute | |
1107 | .Ic sshd -i | |
1108 | somewhere. | |
1109 | Host key management will be done using the | |
1110 | HostName of the host being connected (defaulting to the name typed by | |
1111 | the user). | |
1112 | Setting the command to | |
1113 | .Dq none | |
1114 | disables this option entirely. | |
1115 | Note that | |
1116 | .Cm CheckHostIP | |
1117 | is not available for connects with a proxy command. | |
1118 | .Pp | |
1119 | This directive is useful in conjunction with | |
1120 | .Xr nc 1 | |
1121 | and its proxy support. | |
1122 | For example, the following directive would connect via an HTTP proxy at | |
1123 | 192.0.2.0: | |
1124 | .Bd -literal -offset 3n | |
1125 | ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p | |
1126 | .Ed | |
36e94dc5 PA |
1127 | .It Cm ProxyUseFdpass |
1128 | Specifies that | |
1129 | .Cm ProxyCommand | |
1130 | will pass a connected file descriptor back to | |
1131 | .Xr ssh 1 | |
1132 | instead of continuing to execute and pass data. | |
1133 | The default is | |
1134 | .Dq no . | |
16c343f1 PA |
1135 | .It Cm PubkeyAuthentication |
1136 | Specifies whether to try public key authentication. | |
1137 | The argument to this keyword must be | |
1138 | .Dq yes | |
1139 | or | |
1140 | .Dq no . | |
1141 | The default is | |
1142 | .Dq yes . | |
1143 | This option applies to protocol version 2 only. | |
1144 | .It Cm RekeyLimit | |
1145 | Specifies the maximum amount of data that may be transmitted before the | |
36e94dc5 PA |
1146 | session key is renegotiated, optionally followed a maximum amount of |
1147 | time that may pass before the session key is renegotiated. | |
1148 | The first argument is specified in bytes and may have a suffix of | |
16c343f1 PA |
1149 | .Sq K , |
1150 | .Sq M , | |
1151 | or | |
1152 | .Sq G | |
1153 | to indicate Kilobytes, Megabytes, or Gigabytes, respectively. | |
1154 | The default is between | |
1155 | .Sq 1G | |
1156 | and | |
1157 | .Sq 4G , | |
1158 | depending on the cipher. | |
36e94dc5 PA |
1159 | The optional second value is specified in seconds and may use any of the |
1160 | units documented in the | |
1161 | TIME FORMATS section of | |
1162 | .Xr sshd_config 5 . | |
1163 | The default value for | |
1164 | .Cm RekeyLimit | |
1165 | is | |
1166 | .Dq default none , | |
1167 | which means that rekeying is performed after the cipher's default amount | |
1168 | of data has been sent or received and no time based rekeying is done. | |
16c343f1 PA |
1169 | This option applies to protocol version 2 only. |
1170 | .It Cm RemoteForward | |
1171 | Specifies that a TCP port on the remote machine be forwarded over | |
1172 | the secure channel to the specified host and port from the local machine. | |
1173 | The first argument must be | |
1174 | .Sm off | |
1175 | .Oo Ar bind_address : Oc Ar port | |
1176 | .Sm on | |
1177 | and the second argument must be | |
1178 | .Ar host : Ns Ar hostport . | |
856ea928 | 1179 | IPv6 addresses can be specified by enclosing addresses in square brackets. |
16c343f1 PA |
1180 | Multiple forwardings may be specified, and additional |
1181 | forwardings can be given on the command line. | |
cb5eb4f1 PA |
1182 | Privileged ports can be forwarded only when |
1183 | logging in as root on the remote machine. | |
1184 | .Pp | |
1185 | If the | |
1186 | .Ar port | |
1187 | argument is | |
1188 | .Ql 0 , | |
1189 | the listen port will be dynamically allocated on the server and reported | |
1190 | to the client at run time. | |
16c343f1 PA |
1191 | .Pp |
1192 | If the | |
1193 | .Ar bind_address | |
1194 | is not specified, the default is to only bind to loopback addresses. | |
1195 | If the | |
1196 | .Ar bind_address | |
1197 | is | |
1198 | .Ql * | |
1199 | or an empty string, then the forwarding is requested to listen on all | |
1200 | interfaces. | |
1201 | Specifying a remote | |
1202 | .Ar bind_address | |
1203 | will only succeed if the server's | |
1204 | .Cm GatewayPorts | |
1205 | option is enabled (see | |
1206 | .Xr sshd_config 5 ) . | |
1c188a7f PA |
1207 | .It Cm RequestTTY |
1208 | Specifies whether to request a pseudo-tty for the session. | |
1209 | The argument may be one of: | |
1210 | .Dq no | |
1211 | (never request a TTY), | |
1212 | .Dq yes | |
1213 | (always request a TTY when standard input is a TTY), | |
1214 | .Dq force | |
1215 | (always request a TTY) or | |
1216 | .Dq auto | |
1217 | (request a TTY when opening a login session). | |
1218 | This option mirrors the | |
1219 | .Fl t | |
1220 | and | |
1221 | .Fl T | |
1222 | flags for | |
1223 | .Xr ssh 1 . | |
16c343f1 PA |
1224 | .It Cm RhostsRSAAuthentication |
1225 | Specifies whether to try rhosts based authentication with RSA host | |
1226 | authentication. | |
1227 | The argument must be | |
1228 | .Dq yes | |
1229 | or | |
1230 | .Dq no . | |
1231 | The default is | |
1232 | .Dq no . | |
1233 | This option applies to protocol version 1 only and requires | |
1234 | .Xr ssh 1 | |
1235 | to be setuid root. | |
1236 | .It Cm RSAAuthentication | |
1237 | Specifies whether to try RSA authentication. | |
1238 | The argument to this keyword must be | |
1239 | .Dq yes | |
1240 | or | |
1241 | .Dq no . | |
1242 | RSA authentication will only be | |
1243 | attempted if the identity file exists, or an authentication agent is | |
1244 | running. | |
1245 | The default is | |
1246 | .Dq yes . | |
1247 | Note that this option applies to protocol version 1 only. | |
1248 | .It Cm SendEnv | |
1249 | Specifies what variables from the local | |
1250 | .Xr environ 7 | |
1251 | should be sent to the server. | |
1252 | Note that environment passing is only supported for protocol 2. | |
1253 | The server must also support it, and the server must be configured to | |
1254 | accept these environment variables. | |
1255 | Refer to | |
1256 | .Cm AcceptEnv | |
1257 | in | |
1258 | .Xr sshd_config 5 | |
1259 | for how to configure the server. | |
1260 | Variables are specified by name, which may contain wildcard characters. | |
1261 | Multiple environment variables may be separated by whitespace or spread | |
1262 | across multiple | |
1263 | .Cm SendEnv | |
1264 | directives. | |
1265 | The default is not to send any environment variables. | |
1266 | .Pp | |
1267 | See | |
1268 | .Sx PATTERNS | |
1269 | for more information on patterns. | |
1270 | .It Cm ServerAliveCountMax | |
1271 | Sets the number of server alive messages (see below) which may be | |
1272 | sent without | |
1273 | .Xr ssh 1 | |
1274 | receiving any messages back from the server. | |
1275 | If this threshold is reached while server alive messages are being sent, | |
1276 | ssh will disconnect from the server, terminating the session. | |
1277 | It is important to note that the use of server alive messages is very | |
1278 | different from | |
1279 | .Cm TCPKeepAlive | |
1280 | (below). | |
1281 | The server alive messages are sent through the encrypted channel | |
1282 | and therefore will not be spoofable. | |
1283 | The TCP keepalive option enabled by | |
1284 | .Cm TCPKeepAlive | |
1285 | is spoofable. | |
1286 | The server alive mechanism is valuable when the client or | |
1287 | server depend on knowing when a connection has become inactive. | |
1288 | .Pp | |
1289 | The default value is 3. | |
1290 | If, for example, | |
1291 | .Cm ServerAliveInterval | |
1292 | (see below) is set to 15 and | |
1293 | .Cm ServerAliveCountMax | |
1294 | is left at the default, if the server becomes unresponsive, | |
1295 | ssh will disconnect after approximately 45 seconds. | |
1296 | This option applies to protocol version 2 only. | |
1297 | .It Cm ServerAliveInterval | |
1298 | Sets a timeout interval in seconds after which if no data has been received | |
1299 | from the server, | |
1300 | .Xr ssh 1 | |
1301 | will send a message through the encrypted | |
1302 | channel to request a response from the server. | |
1303 | The default | |
1304 | is 0, indicating that these messages will not be sent to the server. | |
1305 | This option applies to protocol version 2 only. | |
36e94dc5 PA |
1306 | .It Cm StreamLocalBindMask |
1307 | Sets the octal file creation mode mask | |
1308 | .Pq umask | |
1309 | used when creating a Unix-domain socket file for local or remote | |
1310 | port forwarding. | |
1311 | This option is only used for port forwarding to a Unix-domain socket file. | |
1312 | .Pp | |
1313 | The default value is 0177, which creates a Unix-domain socket file that is | |
1314 | readable and writable only by the owner. | |
1315 | Note that not all operating systems honor the file mode on Unix-domain | |
1316 | socket files. | |
1317 | .It Cm StreamLocalBindUnlink | |
1318 | Specifies whether to remove an existing Unix-domain socket file for local | |
1319 | or remote port forwarding before creating a new one. | |
1320 | If the socket file already exists and | |
1321 | .Cm StreamLocalBindUnlink | |
1322 | is not enabled, | |
1323 | .Nm ssh | |
1324 | will be unable to forward the port to the Unix-domain socket file. | |
1325 | This option is only used for port forwarding to a Unix-domain socket file. | |
1326 | .Pp | |
1327 | The argument must be | |
1328 | .Dq yes | |
1329 | or | |
1330 | .Dq no . | |
1331 | The default is | |
1332 | .Dq no . | |
16c343f1 PA |
1333 | .It Cm StrictHostKeyChecking |
1334 | If this flag is set to | |
1335 | .Dq yes , | |
1336 | .Xr ssh 1 | |
1337 | will never automatically add host keys to the | |
1338 | .Pa ~/.ssh/known_hosts | |
1339 | file, and refuses to connect to hosts whose host key has changed. | |
1340 | This provides maximum protection against trojan horse attacks, | |
1341 | though it can be annoying when the | |
1342 | .Pa /etc/ssh/ssh_known_hosts | |
1343 | file is poorly maintained or when connections to new hosts are | |
1344 | frequently made. | |
1345 | This option forces the user to manually | |
1346 | add all new hosts. | |
1347 | If this flag is set to | |
1348 | .Dq no , | |
1349 | ssh will automatically add new host keys to the | |
1350 | user known hosts files. | |
1351 | If this flag is set to | |
1352 | .Dq ask , | |
1353 | new host keys | |
1354 | will be added to the user known host files only after the user | |
1355 | has confirmed that is what they really want to do, and | |
1356 | ssh will refuse to connect to hosts whose host key has changed. | |
1357 | The host keys of | |
1358 | known hosts will be verified automatically in all cases. | |
1359 | The argument must be | |
1360 | .Dq yes , | |
1361 | .Dq no , | |
1362 | or | |
1363 | .Dq ask . | |
1364 | The default is | |
1365 | .Dq ask . | |
1366 | .It Cm TCPKeepAlive | |
1367 | Specifies whether the system should send TCP keepalive messages to the | |
1368 | other side. | |
1369 | If they are sent, death of the connection or crash of one | |
1370 | of the machines will be properly noticed. | |
1371 | However, this means that | |
1372 | connections will die if the route is down temporarily, and some people | |
1373 | find it annoying. | |
1374 | .Pp | |
1375 | The default is | |
1376 | .Dq yes | |
1377 | (to send TCP keepalive messages), and the client will notice | |
1378 | if the network goes down or the remote host dies. | |
1379 | This is important in scripts, and many users want it too. | |
1380 | .Pp | |
1381 | To disable TCP keepalive messages, the value should be set to | |
1382 | .Dq no . | |
1383 | .It Cm Tunnel | |
1384 | Request | |
1385 | .Xr tun 4 | |
1386 | device forwarding between the client and the server. | |
1387 | The argument must be | |
1388 | .Dq yes , | |
1389 | .Dq point-to-point | |
1390 | (layer 3), | |
1391 | .Dq ethernet | |
1392 | (layer 2), | |
1393 | or | |
1394 | .Dq no . | |
1395 | Specifying | |
1396 | .Dq yes | |
1397 | requests the default tunnel mode, which is | |
1398 | .Dq point-to-point . | |
1399 | The default is | |
1400 | .Dq no . | |
1401 | .It Cm TunnelDevice | |
1402 | Specifies the | |
1403 | .Xr tun 4 | |
1404 | devices to open on the client | |
1405 | .Pq Ar local_tun | |
1406 | and the server | |
1407 | .Pq Ar remote_tun . | |
1408 | .Pp | |
1409 | The argument must be | |
1410 | .Sm off | |
1411 | .Ar local_tun Op : Ar remote_tun . | |
1412 | .Sm on | |
1413 | The devices may be specified by numerical ID or the keyword | |
1414 | .Dq any , | |
1415 | which uses the next available tunnel device. | |
1416 | If | |
1417 | .Ar remote_tun | |
1418 | is not specified, it defaults to | |
1419 | .Dq any . | |
1420 | The default is | |
1421 | .Dq any:any . | |
1422 | .It Cm UsePrivilegedPort | |
1423 | Specifies whether to use a privileged port for outgoing connections. | |
1424 | The argument must be | |
1425 | .Dq yes | |
1426 | or | |
1427 | .Dq no . | |
1428 | The default is | |
1429 | .Dq no . | |
1430 | If set to | |
1431 | .Dq yes , | |
1432 | .Xr ssh 1 | |
1433 | must be setuid root. | |
1434 | Note that this option must be set to | |
1435 | .Dq yes | |
1436 | for | |
1437 | .Cm RhostsRSAAuthentication | |
1438 | with older servers. | |
1439 | .It Cm User | |
1440 | Specifies the user to log in as. | |
1441 | This can be useful when a different user name is used on different machines. | |
1442 | This saves the trouble of | |
1443 | having to remember to give the user name on the command line. | |
1444 | .It Cm UserKnownHostsFile | |
1c188a7f PA |
1445 | Specifies one or more files to use for the user |
1446 | host key database, separated by whitespace. | |
1447 | The default is | |
1448 | .Pa ~/.ssh/known_hosts , | |
1449 | .Pa ~/.ssh/known_hosts2 . | |
16c343f1 PA |
1450 | .It Cm VerifyHostKeyDNS |
1451 | Specifies whether to verify the remote key using DNS and SSHFP resource | |
1452 | records. | |
1453 | If this option is set to | |
1454 | .Dq yes , | |
1455 | the client will implicitly trust keys that match a secure fingerprint | |
1456 | from DNS. | |
1457 | Insecure fingerprints will be handled as if this option was set to | |
1458 | .Dq ask . | |
1459 | If this option is set to | |
1460 | .Dq ask , | |
1461 | information on fingerprint match will be displayed, but the user will still | |
1462 | need to confirm new host keys according to the | |
1463 | .Cm StrictHostKeyChecking | |
1464 | option. | |
1465 | The argument must be | |
1466 | .Dq yes , | |
1467 | .Dq no , | |
1468 | or | |
1469 | .Dq ask . | |
1470 | The default is | |
1471 | .Dq no . | |
1472 | Note that this option applies to protocol version 2 only. | |
1473 | .Pp | |
36e94dc5 | 1474 | See also VERIFYING HOST KEYS in |
16c343f1 | 1475 | .Xr ssh 1 . |
40948e2d PA |
1476 | .It Cm VersionAddendum |
1477 | Specifies a string to append to the regular version string to identify | |
1478 | OS- or site-specific modifications. | |
1479 | The default is | |
3e3d7280 | 1480 | .Dq DragonFly-20150122 . |
c8c467ee PA |
1481 | .It Cm VisualHostKey |
1482 | If this flag is set to | |
1483 | .Dq yes , | |
1484 | an ASCII art representation of the remote host key fingerprint is | |
cb5eb4f1 PA |
1485 | printed in addition to the hex fingerprint string at login and |
1486 | for unknown host keys. | |
c8c467ee PA |
1487 | If this flag is set to |
1488 | .Dq no , | |
cb5eb4f1 PA |
1489 | no fingerprint strings are printed at login and |
1490 | only the hex fingerprint string will be printed for unknown host keys. | |
c8c467ee PA |
1491 | The default is |
1492 | .Dq no . | |
16c343f1 PA |
1493 | .It Cm XAuthLocation |
1494 | Specifies the full pathname of the | |
1495 | .Xr xauth 1 | |
1496 | program. | |
1497 | The default is | |
1498 | .Pa /usr/X11R6/bin/xauth . | |
1499 | .El | |
1500 | .Sh PATTERNS | |
1501 | A | |
1502 | .Em pattern | |
1503 | consists of zero or more non-whitespace characters, | |
1504 | .Sq * | |
1505 | (a wildcard that matches zero or more characters), | |
1506 | or | |
1507 | .Sq ?\& | |
1508 | (a wildcard that matches exactly one character). | |
1509 | For example, to specify a set of declarations for any host in the | |
1510 | .Dq .co.uk | |
1511 | set of domains, | |
1512 | the following pattern could be used: | |
1513 | .Pp | |
1514 | .Dl Host *.co.uk | |
1515 | .Pp | |
1516 | The following pattern | |
1517 | would match any host in the 192.168.0.[0-9] network range: | |
1518 | .Pp | |
1519 | .Dl Host 192.168.0.? | |
1520 | .Pp | |
1521 | A | |
1522 | .Em pattern-list | |
1523 | is a comma-separated list of patterns. | |
1524 | Patterns within pattern-lists may be negated | |
1525 | by preceding them with an exclamation mark | |
1526 | .Pq Sq !\& . | |
1527 | For example, | |
36e94dc5 | 1528 | to allow a key to be used from anywhere within an organization |
16c343f1 PA |
1529 | except from the |
1530 | .Dq dialup | |
1531 | pool, | |
1532 | the following entry (in authorized_keys) could be used: | |
1533 | .Pp | |
1534 | .Dl from=\&"!*.dialup.example.com,*.example.com\&" | |
1535 | .Sh FILES | |
1536 | .Bl -tag -width Ds | |
1537 | .It Pa ~/.ssh/config | |
1538 | This is the per-user configuration file. | |
1539 | The format of this file is described above. | |
1540 | This file is used by the SSH client. | |
1541 | Because of the potential for abuse, this file must have strict permissions: | |
1542 | read/write for the user, and not accessible by others. | |
1543 | .It Pa /etc/ssh/ssh_config | |
1544 | Systemwide configuration file. | |
1545 | This file provides defaults for those | |
1546 | values that are not specified in the user's configuration file, and | |
1547 | for those users who do not have a configuration file. | |
1548 | This file must be world-readable. | |
1549 | .El | |
1550 | .Sh SEE ALSO | |
1551 | .Xr ssh 1 | |
1552 | .Sh AUTHORS | |
1553 | OpenSSH is a derivative of the original and free | |
1554 | ssh 1.2.12 release by Tatu Ylonen. | |
1555 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1556 | Theo de Raadt and Dug Song | |
1557 | removed many bugs, re-added newer features and | |
1558 | created OpenSSH. | |
1559 | Markus Friedl contributed the support for SSH | |
1560 | protocol versions 1.5 and 2.0. |