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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 | .\" | |
6d7a9e8f | 37 | .\" $OpenBSD: ssh_config.5,v 1.47 2005/03/07 23:41:54 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 | |
46 | .It Pa $HOME/.ssh/config | |
47 | .It Pa /etc/ssh/ssh_config | |
48 | .El | |
49 | .Sh DESCRIPTION | |
50 | .Nm ssh | |
51 | obtains configuration data from the following sources in | |
52 | the following order: | |
4dcbbeea | 53 | .Bl -enum -offset indent -compact |
54 | .It | |
55 | command-line options | |
56 | .It | |
57 | user's configuration file | |
58 | .Pq Pa $HOME/.ssh/config | |
59 | .It | |
60 | system-wide configuration file | |
61 | .Pq Pa /etc/ssh/ssh_config | |
62 | .El | |
588df31a | 63 | .Pp |
64 | For each parameter, the first obtained value | |
65 | will be used. | |
7034edae | 66 | The configuration files contain sections separated by |
588df31a | 67 | .Dq Host |
68 | specifications, and that section is only applied for hosts that | |
69 | match one of the patterns given in the specification. | |
70 | The matched host name is the one given on the command line. | |
71 | .Pp | |
72 | Since the first obtained value for each parameter is used, more | |
73 | host-specific declarations should be given near the beginning of the | |
74 | file, and general defaults at the end. | |
75 | .Pp | |
76 | The configuration file has the following format: | |
77 | .Pp | |
78 | Empty lines and lines starting with | |
79 | .Ql # | |
80 | are comments. | |
81 | .Pp | |
82 | Otherwise a line is of the format | |
83 | .Dq keyword arguments . | |
84 | Configuration options may be separated by whitespace or | |
85 | optional whitespace and exactly one | |
86 | .Ql = ; | |
87 | the latter format is useful to avoid the need to quote whitespace | |
88 | when specifying configuration options using the | |
89 | .Nm ssh , | |
90 | .Nm scp | |
91 | and | |
92 | .Nm sftp | |
93 | .Fl o | |
94 | option. | |
95 | .Pp | |
96 | The possible | |
97 | keywords and their meanings are as follows (note that | |
98 | keywords are case-insensitive and arguments are case-sensitive): | |
99 | .Bl -tag -width Ds | |
100 | .It Cm Host | |
101 | Restricts the following declarations (up to the next | |
102 | .Cm Host | |
103 | keyword) to be only for those hosts that match one of the patterns | |
104 | given after the keyword. | |
105 | .Ql \&* | |
106 | and | |
d0445371 | 107 | .Ql \&? |
588df31a | 108 | can be used as wildcards in the |
109 | patterns. | |
110 | A single | |
111 | .Ql \&* | |
112 | as a pattern can be used to provide global | |
113 | defaults for all hosts. | |
114 | The host is the | |
115 | .Ar hostname | |
116 | argument given on the command line (i.e., the name is not converted to | |
117 | a canonicalized host name before matching). | |
f811e52a | 118 | .It Cm AddressFamily |
3cbc677d | 119 | Specifies which address family to use when connecting. |
120 | Valid arguments are | |
f811e52a | 121 | .Dq any , |
122 | .Dq inet | |
0d6cbe2c | 123 | (use IPv4 only) or |
f811e52a | 124 | .Dq inet6 |
0d6cbe2c | 125 | (use IPv6 only). |
588df31a | 126 | .It Cm BatchMode |
127 | If set to | |
128 | .Dq yes , | |
129 | passphrase/password querying will be disabled. | |
130 | This option is useful in scripts and other batch jobs where no user | |
131 | is present to supply the password. | |
132 | The argument must be | |
133 | .Dq yes | |
134 | or | |
135 | .Dq no . | |
136 | The default is | |
137 | .Dq no . | |
138 | .It Cm BindAddress | |
139 | Specify the interface to transmit from on machines with multiple | |
140 | interfaces or aliased addresses. | |
141 | Note that this option does not work if | |
142 | .Cm UsePrivilegedPort | |
143 | is set to | |
144 | .Dq yes . | |
145 | .It Cm ChallengeResponseAuthentication | |
146 | Specifies whether to use challenge response authentication. | |
147 | The argument to this keyword must be | |
148 | .Dq yes | |
149 | or | |
150 | .Dq no . | |
151 | The default is | |
152 | .Dq yes . | |
153 | .It Cm CheckHostIP | |
154 | If this flag is set to | |
155 | .Dq yes , | |
156 | ssh will additionally check the host IP address in the | |
157 | .Pa known_hosts | |
158 | file. | |
159 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
160 | If the option is set to | |
161 | .Dq no , | |
162 | the check will not be executed. | |
163 | The default is | |
164 | .Dq yes . | |
165 | .It Cm Cipher | |
166 | Specifies the cipher to use for encrypting the session | |
167 | in protocol version 1. | |
168 | Currently, | |
169 | .Dq blowfish , | |
170 | .Dq 3des , | |
171 | and | |
172 | .Dq des | |
173 | are supported. | |
174 | .Ar des | |
175 | is only supported in the | |
176 | .Nm ssh | |
177 | client for interoperability with legacy protocol 1 implementations | |
178 | that do not support the | |
179 | .Ar 3des | |
a4e5acef | 180 | cipher. |
181 | Its use is strongly discouraged due to cryptographic weaknesses. | |
588df31a | 182 | The default is |
183 | .Dq 3des . | |
184 | .It Cm Ciphers | |
185 | Specifies the ciphers allowed for protocol version 2 | |
186 | in order of preference. | |
187 | Multiple ciphers must be comma-separated. | |
3b9baa7b | 188 | The supported ciphers are |
189 | .Dq 3des-cbc , | |
190 | .Dq aes128-cbc , | |
191 | .Dq aes192-cbc , | |
192 | .Dq aes256-cbc , | |
193 | .Dq aes128-ctr , | |
194 | .Dq aes192-ctr , | |
195 | .Dq aes256-ctr , | |
196 | .Dq arcfour , | |
197 | .Dq blowfish-cbc , | |
198 | and | |
199 | .Dq cast128-cbc . | |
588df31a | 200 | The default is |
588df31a | 201 | .Bd -literal |
202 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour, | |
203 | aes192-cbc,aes256-cbc'' | |
204 | .Ed | |
205 | .It Cm ClearAllForwardings | |
206 | Specifies that all local, remote and dynamic port forwardings | |
207 | specified in the configuration files or on the command line be | |
a4e5acef | 208 | cleared. |
209 | This option is primarily useful when used from the | |
588df31a | 210 | .Nm ssh |
211 | command line to clear port forwardings set in | |
212 | configuration files, and is automatically set by | |
213 | .Xr scp 1 | |
214 | and | |
215 | .Xr sftp 1 . | |
216 | The argument must be | |
217 | .Dq yes | |
218 | or | |
219 | .Dq no . | |
220 | The default is | |
221 | .Dq no . | |
222 | .It Cm Compression | |
223 | Specifies whether to use compression. | |
224 | The argument must be | |
225 | .Dq yes | |
226 | or | |
227 | .Dq no . | |
228 | The default is | |
229 | .Dq no . | |
230 | .It Cm CompressionLevel | |
231 | Specifies the compression level to use if compression is enabled. | |
232 | The argument must be an integer from 1 (fast) to 9 (slow, best). | |
233 | The default level is 6, which is good for most applications. | |
234 | The meaning of the values is the same as in | |
235 | .Xr gzip 1 . | |
236 | Note that this option applies to protocol version 1 only. | |
237 | .It Cm ConnectionAttempts | |
238 | Specifies the number of tries (one per second) to make before exiting. | |
239 | The argument must be an integer. | |
240 | This may be useful in scripts if the connection sometimes fails. | |
241 | The default is 1. | |
09ab3296 | 242 | .It Cm ConnectTimeout |
243 | Specifies the timeout (in seconds) used when connecting to the ssh | |
3cbc677d | 244 | server, instead of using the default system TCP timeout. |
245 | This value is used only when the target is down or really unreachable, | |
246 | not when it refuses the connection. | |
5e96b616 | 247 | .It Cm ControlMaster |
248 | Enables the sharing of multiple sessions over a single network connection. | |
249 | When set to | |
250 | .Dq yes | |
251 | .Nm ssh | |
252 | will listen for connections on a control socket specified using the | |
253 | .Cm ControlPath | |
254 | argument. | |
255 | Additional sessions can connect to this socket using the same | |
256 | .Cm ControlPath | |
257 | with | |
258 | .Cm ControlMaster | |
259 | set to | |
260 | .Dq no | |
9a5cfb58 | 261 | (the default). |
5e96b616 | 262 | These sessions will reuse the master instance's network connection rather |
263 | than initiating new ones. | |
0d34d6ce | 264 | Setting this to |
265 | .Dq ask | |
266 | will cause | |
267 | .Nm ssh | |
268 | to listen for control connections, but require confirmation using the | |
269 | .Ev SSH_ASKPASS | |
270 | program before they are accepted (see | |
271 | .Xr ssh-add 1 | |
9a5cfb58 | 272 | for details). |
5e96b616 | 273 | .It Cm ControlPath |
9a5cfb58 | 274 | Specify the path to the control socket used for connection sharing. |
5e96b616 | 275 | See |
276 | .Cm ControlMaster | |
277 | above. | |
9a5cfb58 | 278 | .It Cm DynamicForward |
279 | Specifies that a TCP/IP port on the local machine be forwarded | |
280 | over the secure channel, and the application | |
281 | protocol is then used to determine where to connect to from the | |
282 | remote machine. | |
283 | The argument must be a port number. | |
284 | Currently the SOCKS4 and SOCKS5 protocols are supported, and | |
285 | .Nm ssh | |
286 | will act as a SOCKS server. | |
287 | Multiple forwardings may be specified, and | |
288 | additional forwardings can be given on the command line. | |
289 | Only the superuser can forward privileged ports. | |
f0677b69 | 290 | .It Cm EnableSSHKeysign |
291 | Setting this option to | |
292 | .Dq yes | |
293 | in the global client configuration file | |
294 | .Pa /etc/ssh/ssh_config | |
295 | enables the use of the helper program | |
296 | .Xr ssh-keysign 8 | |
297 | during | |
298 | .Cm HostbasedAuthentication . | |
299 | The argument must be | |
300 | .Dq yes | |
301 | or | |
302 | .Dq no . | |
303 | The default is | |
304 | .Dq no . | |
246bb171 | 305 | This option should be placed in the non-hostspecific section. |
f0677b69 | 306 | See |
307 | .Xr ssh-keysign 8 | |
308 | for more information. | |
588df31a | 309 | .It Cm EscapeChar |
310 | Sets the escape character (default: | |
311 | .Ql ~ ) . | |
312 | The escape character can also | |
313 | be set on the command line. | |
314 | The argument should be a single character, | |
315 | .Ql ^ | |
316 | followed by a letter, or | |
317 | .Dq none | |
318 | to disable the escape | |
319 | character entirely (making the connection transparent for binary | |
320 | data). | |
321 | .It Cm ForwardAgent | |
322 | Specifies whether the connection to the authentication agent (if any) | |
323 | will be forwarded to the remote machine. | |
324 | The argument must be | |
325 | .Dq yes | |
326 | or | |
327 | .Dq no . | |
328 | The default is | |
329 | .Dq no . | |
dbcdea68 | 330 | .Pp |
a4e5acef | 331 | Agent forwarding should be enabled with caution. |
332 | Users with the ability to bypass file permissions on the remote host | |
333 | (for the agent's Unix-domain socket) | |
334 | can access the local agent through the forwarded connection. | |
335 | An attacker cannot obtain key material from the agent, | |
dbcdea68 | 336 | however they can perform operations on the keys that enable them to |
337 | authenticate using the identities loaded into the agent. | |
588df31a | 338 | .It Cm ForwardX11 |
339 | Specifies whether X11 connections will be automatically redirected | |
340 | over the secure channel and | |
341 | .Ev DISPLAY | |
342 | set. | |
343 | The argument must be | |
344 | .Dq yes | |
345 | or | |
346 | .Dq no . | |
347 | The default is | |
348 | .Dq no . | |
dbcdea68 | 349 | .Pp |
a4e5acef | 350 | X11 forwarding should be enabled with caution. |
351 | Users with the ability to bypass file permissions on the remote host | |
d73a67d7 | 352 | (for the user's X11 authorization database) |
a4e5acef | 353 | can access the local X11 display through the forwarded connection. |
d73a67d7 | 354 | An attacker may then be able to perform activities such as keystroke monitoring |
355 | if the | |
356 | .Cm ForwardX11Trusted | |
357 | option is also enabled. | |
358 | .It Cm ForwardX11Trusted | |
b2e90ab5 | 359 | If this option is set to |
d73a67d7 | 360 | .Dq yes |
361 | then remote X11 clients will have full access to the original X11 display. | |
9a6b3b7a | 362 | .Pp |
d73a67d7 | 363 | If this option is set to |
364 | .Dq no | |
365 | then remote X11 clients will be considered untrusted and prevented | |
366 | from stealing or tampering with data belonging to trusted X11 | |
367 | clients. | |
9a6b3b7a | 368 | Furthermore, the |
369 | .Xr xauth 1 | |
370 | token used for the session will be set to expire after 20 minutes. | |
371 | Remote clients will be refused access after this time. | |
d73a67d7 | 372 | .Pp |
373 | The default is | |
374 | .Dq no . | |
375 | .Pp | |
376 | See the X11 SECURITY extension specification for full details on | |
377 | the restrictions imposed on untrusted clients. | |
588df31a | 378 | .It Cm GatewayPorts |
379 | Specifies whether remote hosts are allowed to connect to local | |
380 | forwarded ports. | |
381 | By default, | |
382 | .Nm ssh | |
a4e5acef | 383 | binds local port forwardings to the loopback address. |
384 | This prevents other remote hosts from connecting to forwarded ports. | |
588df31a | 385 | .Cm GatewayPorts |
386 | can be used to specify that | |
387 | .Nm ssh | |
388 | should bind local port forwardings to the wildcard address, | |
389 | thus allowing remote hosts to connect to forwarded ports. | |
390 | The argument must be | |
391 | .Dq yes | |
392 | or | |
393 | .Dq no . | |
394 | The default is | |
395 | .Dq no . | |
396 | .It Cm GlobalKnownHostsFile | |
397 | Specifies a file to use for the global | |
398 | host key database instead of | |
399 | .Pa /etc/ssh/ssh_known_hosts . | |
7364bd04 | 400 | .It Cm GSSAPIAuthentication |
e8dd24a8 | 401 | Specifies whether user authentication based on GSSAPI is allowed. |
d0445371 | 402 | The default is |
2ecb78df | 403 | .Dq no . |
7364bd04 | 404 | Note that this option applies to protocol version 2 only. |
405 | .It Cm GSSAPIDelegateCredentials | |
406 | Forward (delegate) credentials to the server. | |
407 | The default is | |
408 | .Dq no . | |
409 | Note that this option applies to protocol version 2 only. | |
5c63c2ab | 410 | .It Cm HashKnownHosts |
411 | Indicates that | |
412 | .Nm ssh | |
413 | should hash host names and addresses when they are added to | |
414 | .Pa $HOME/.ssh/known_hosts . | |
415 | These hashed names may be used normally by | |
416 | .Nm ssh | |
417 | and | |
418 | .Nm sshd , | |
419 | but they do not reveal identifying information should the file's contents | |
420 | be disclosed. | |
421 | The default is | |
422 | .Dq no . | |
cd8f998c | 423 | Note that hashing of names and addresses will not be retrospectively applied |
bdffbcdc | 424 | to existing known hosts files, but these may be manually hashed using |
425 | .Xr ssh-keygen 1 . | |
588df31a | 426 | .It Cm HostbasedAuthentication |
427 | Specifies whether to try rhosts based authentication with public key | |
428 | authentication. | |
429 | The argument must be | |
430 | .Dq yes | |
431 | or | |
432 | .Dq no . | |
433 | The default is | |
434 | .Dq no . | |
435 | This option applies to protocol version 2 only and | |
436 | is similar to | |
437 | .Cm RhostsRSAAuthentication . | |
438 | .It Cm HostKeyAlgorithms | |
439 | Specifies the protocol version 2 host key algorithms | |
440 | that the client wants to use in order of preference. | |
441 | The default for this option is: | |
442 | .Dq ssh-rsa,ssh-dss . | |
443 | .It Cm HostKeyAlias | |
444 | Specifies an alias that should be used instead of the | |
445 | real host name when looking up or saving the host key | |
446 | in the host key database files. | |
447 | This option is useful for tunneling ssh connections | |
448 | or for multiple servers running on a single host. | |
449 | .It Cm HostName | |
450 | Specifies the real host name to log into. | |
451 | This can be used to specify nicknames or abbreviations for hosts. | |
452 | Default is the name given on the command line. | |
453 | Numeric IP addresses are also permitted (both on the command line and in | |
454 | .Cm HostName | |
455 | specifications). | |
456 | .It Cm IdentityFile | |
457 | Specifies a file from which the user's RSA or DSA authentication identity | |
3cbc677d | 458 | is read. |
459 | The default is | |
588df31a | 460 | .Pa $HOME/.ssh/identity |
461 | for protocol version 1, and | |
462 | .Pa $HOME/.ssh/id_rsa | |
463 | and | |
464 | .Pa $HOME/.ssh/id_dsa | |
465 | for protocol version 2. | |
466 | Additionally, any identities represented by the authentication agent | |
467 | will be used for authentication. | |
468 | The file name may use the tilde | |
469 | syntax to refer to a user's home directory. | |
470 | It is possible to have | |
471 | multiple identity files specified in configuration files; all these | |
472 | identities will be tried in sequence. | |
3a065ed0 | 473 | .It Cm IdentitiesOnly |
474 | Specifies that | |
475 | .Nm ssh | |
476 | should only use the authentication identity files configured in the | |
1e9b1b82 | 477 | .Nm |
3a065ed0 | 478 | files, |
479 | even if the | |
480 | .Nm ssh-agent | |
481 | offers more identities. | |
482 | The argument to this keyword must be | |
483 | .Dq yes | |
484 | or | |
485 | .Dq no . | |
486 | This option is intented for situations where | |
487 | .Nm ssh-agent | |
488 | offers many different identities. | |
489 | The default is | |
490 | .Dq no . | |
396070f8 | 491 | .It Cm KbdInteractiveDevices |
492 | Specifies the list of methods to use in keyboard-interactive authentication. | |
493 | Multiple method names must be comma-separated. | |
494 | The default is to use the server specified list. | |
588df31a | 495 | .It Cm LocalForward |
496 | Specifies that a TCP/IP port on the local machine be forwarded over | |
497 | the secure channel to the specified host and port from the remote machine. | |
498 | The first argument must be a port number, and the second must be | |
3867aa0a | 499 | .Xo |
500 | .Sm off | |
501 | .Oo Ar bind_address : Oc | |
cd8f998c | 502 | .Ar host : port |
3867aa0a | 503 | .Sm on |
504 | .Xc . | |
cd8f998c | 505 | IPv6 addresses can be specified by enclosing addresses in square brackets or |
3867aa0a | 506 | by using an alternative syntax: |
3867aa0a | 507 | .Sm off |
6d7a9e8f | 508 | .Xo |
509 | .Op Ar bind_address No / | |
cd8f998c | 510 | .Ar host No / Ar port |
3867aa0a | 511 | .Xc . |
6d7a9e8f | 512 | .Sm on |
cd8f998c | 513 | Multiple forwardings may be specified, and additional forwardings can be |
3867aa0a | 514 | given on the command line. |
588df31a | 515 | Only the superuser can forward privileged ports. |
3867aa0a | 516 | By default, the local port is bound in accordance with the |
517 | .Cm GatewayPorts | |
518 | setting. | |
519 | However, an explicit | |
520 | .Ar bind_address | |
521 | may be used to bind the connection to a specific address. | |
522 | The | |
523 | .Ar bind_address | |
524 | of | |
525 | .Dq localhost | |
cd8f998c | 526 | indicates that the listening port be bound for local use only, while an |
527 | empty address or | |
528 | .Sq * | |
3867aa0a | 529 | indicates that the port should be available from all interfaces. |
588df31a | 530 | .It Cm LogLevel |
531 | Gives the verbosity level that is used when logging messages from | |
532 | .Nm ssh . | |
533 | The possible values are: | |
534 | QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3. | |
a4e5acef | 535 | The default is INFO. |
536 | DEBUG and DEBUG1 are equivalent. | |
537 | DEBUG2 and DEBUG3 each specify higher levels of verbose output. | |
588df31a | 538 | .It Cm MACs |
539 | Specifies the MAC (message authentication code) algorithms | |
540 | in order of preference. | |
541 | The MAC algorithm is used in protocol version 2 | |
542 | for data integrity protection. | |
543 | Multiple algorithms must be comma-separated. | |
544 | The default is | |
545 | .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 . | |
546 | .It Cm NoHostAuthenticationForLocalhost | |
547 | This option can be used if the home directory is shared across machines. | |
548 | In this case localhost will refer to a different machine on each of | |
549 | the machines and the user will get many warnings about changed host keys. | |
550 | However, this option disables host authentication for localhost. | |
551 | The argument to this keyword must be | |
552 | .Dq yes | |
553 | or | |
554 | .Dq no . | |
555 | The default is to check the host key for localhost. | |
556 | .It Cm NumberOfPasswordPrompts | |
557 | Specifies the number of password prompts before giving up. | |
558 | The argument to this keyword must be an integer. | |
559 | Default is 3. | |
560 | .It Cm PasswordAuthentication | |
561 | Specifies whether to use password authentication. | |
562 | The argument to this keyword must be | |
563 | .Dq yes | |
564 | or | |
565 | .Dq no . | |
566 | The default is | |
567 | .Dq yes . | |
568 | .It Cm Port | |
569 | Specifies the port number to connect on the remote host. | |
570 | Default is 22. | |
571 | .It Cm PreferredAuthentications | |
572 | Specifies the order in which the client should try protocol 2 | |
3cbc677d | 573 | authentication methods. |
574 | This allows a client to prefer one method (e.g. | |
588df31a | 575 | .Cm keyboard-interactive ) |
576 | over another method (e.g. | |
577 | .Cm password ) | |
578 | The default for this option is: | |
579 | .Dq hostbased,publickey,keyboard-interactive,password . | |
580 | .It Cm Protocol | |
581 | Specifies the protocol versions | |
582 | .Nm ssh | |
583 | should support in order of preference. | |
584 | The possible values are | |
585 | .Dq 1 | |
586 | and | |
587 | .Dq 2 . | |
588 | Multiple versions must be comma-separated. | |
589 | The default is | |
590 | .Dq 2,1 . | |
591 | This means that | |
592 | .Nm ssh | |
593 | tries version 2 and falls back to version 1 | |
594 | if version 2 is not available. | |
595 | .It Cm ProxyCommand | |
596 | Specifies the command to use to connect to the server. | |
597 | The command | |
598 | string extends to the end of the line, and is executed with | |
599 | .Pa /bin/sh . | |
600 | In the command string, | |
601 | .Ql %h | |
602 | will be substituted by the host name to | |
603 | connect and | |
604 | .Ql %p | |
605 | by the port. | |
606 | The command can be basically anything, | |
607 | and should read from its standard input and write to its standard output. | |
608 | It should eventually connect an | |
609 | .Xr sshd 8 | |
610 | server running on some machine, or execute | |
611 | .Ic sshd -i | |
612 | somewhere. | |
613 | Host key management will be done using the | |
614 | HostName of the host being connected (defaulting to the name typed by | |
615 | the user). | |
a4e5acef | 616 | Setting the command to |
617 | .Dq none | |
f78bde70 | 618 | disables this option entirely. |
588df31a | 619 | Note that |
620 | .Cm CheckHostIP | |
621 | is not available for connects with a proxy command. | |
622 | .Pp | |
623 | .It Cm PubkeyAuthentication | |
624 | Specifies whether to try public key authentication. | |
625 | The argument to this keyword must be | |
626 | .Dq yes | |
627 | or | |
628 | .Dq no . | |
629 | The default is | |
630 | .Dq yes . | |
631 | This option applies to protocol version 2 only. | |
632 | .It Cm RemoteForward | |
633 | Specifies that a TCP/IP port on the remote machine be forwarded over | |
634 | the secure channel to the specified host and port from the local machine. | |
635 | The first argument must be a port number, and the second must be | |
3867aa0a | 636 | .Xo |
637 | .Sm off | |
638 | .Oo Ar bind_address : Oc | |
cd8f998c | 639 | .Ar host : port |
3867aa0a | 640 | .Sm on |
641 | .Xc . | |
642 | IPv6 addresses can be specified by enclosing any addresses in square brackets | |
643 | or by using the alternative syntax: | |
3867aa0a | 644 | .Sm off |
6d7a9e8f | 645 | .Xo |
646 | .Op Ar bind_address No / | |
cd8f998c | 647 | .Ar host No / Ar port |
3867aa0a | 648 | .Xc . |
6d7a9e8f | 649 | .Sm on |
588df31a | 650 | Multiple forwardings may be specified, and additional |
651 | forwardings can be given on the command line. | |
652 | Only the superuser can forward privileged ports. | |
3867aa0a | 653 | .Pp |
654 | If the | |
655 | .Ar bind_address | |
656 | is not specified, the default is to only bind to loopback addresses. | |
657 | If the | |
658 | .Ar bind_address | |
659 | is | |
660 | .Ql * | |
661 | or an empty string, then the forwarding is requested to listen on all | |
662 | interfaces. | |
663 | Specifying a remote | |
664 | .Ar bind_address | |
cd8f998c | 665 | will only succeed if the server's |
666 | .Cm GatewayPorts | |
3867aa0a | 667 | option is enabled (see |
cd8f998c | 668 | .Xr sshd_config 5 ) . |
588df31a | 669 | .It Cm RhostsRSAAuthentication |
670 | Specifies whether to try rhosts based authentication with RSA host | |
671 | authentication. | |
672 | The argument must be | |
673 | .Dq yes | |
674 | or | |
675 | .Dq no . | |
676 | The default is | |
677 | .Dq no . | |
678 | This option applies to protocol version 1 only and requires | |
679 | .Nm ssh | |
680 | to be setuid root. | |
681 | .It Cm RSAAuthentication | |
682 | Specifies whether to try RSA authentication. | |
683 | The argument to this keyword must be | |
684 | .Dq yes | |
685 | or | |
686 | .Dq no . | |
687 | RSA authentication will only be | |
688 | attempted if the identity file exists, or an authentication agent is | |
689 | running. | |
690 | The default is | |
691 | .Dq yes . | |
692 | Note that this option applies to protocol version 1 only. | |
61a2c1da | 693 | .It Cm SendEnv |
694 | Specifies what variables from the local | |
695 | .Xr environ 7 | |
696 | should be sent to the server. | |
697 | Note that environment passing is only supported for protocol 2, the | |
b8b9f2e6 | 698 | server must also support it, and the server must be configured to |
699 | accept these environment variables. | |
61a2c1da | 700 | Refer to |
701 | .Cm AcceptEnv | |
702 | in | |
703 | .Xr sshd_config 5 | |
704 | for how to configure the server. | |
705 | Variables are specified by name, which may contain the wildcard characters | |
706 | .Ql \&* | |
707 | and | |
708 | .Ql \&? . | |
b8b9f2e6 | 709 | Multiple environment variables may be separated by whitespace or spread |
61a2c1da | 710 | across multiple |
711 | .Cm SendEnv | |
712 | directives. | |
713 | The default is not to send any environment variables. | |
5d8d32a3 | 714 | .It Cm ServerAliveInterval |
715 | Sets a timeout interval in seconds after which if no data has been received | |
716 | from the server, | |
717 | .Nm ssh | |
718 | will send a message through the encrypted | |
719 | channel to request a response from the server. | |
720 | The default | |
721 | is 0, indicating that these messages will not be sent to the server. | |
722 | This option applies to protocol version 2 only. | |
723 | .It Cm ServerAliveCountMax | |
724 | Sets the number of server alive messages (see above) which may be | |
725 | sent without | |
726 | .Nm ssh | |
727 | receiving any messages back from the server. | |
728 | If this threshold is reached while server alive messages are being sent, | |
729 | .Nm ssh | |
730 | will disconnect from the server, terminating the session. | |
731 | It is important to note that the use of server alive messages is very | |
732 | different from | |
733 | .Cm TCPKeepAlive | |
734 | (below). | |
735 | The server alive messages are sent through the encrypted channel | |
736 | and therefore will not be spoofable. | |
737 | The TCP keepalive option enabled by | |
738 | .Cm TCPKeepAlive | |
739 | is spoofable. | |
740 | The server alive mechanism is valuable when the client or | |
741 | server depend on knowing when a connection has become inactive. | |
742 | .Pp | |
743 | The default value is 3. | |
744 | If, for example, | |
745 | .Cm ServerAliveInterval | |
746 | (above) is set to 15, and | |
747 | .Cm ServerAliveCountMax | |
748 | is left at the default, if the server becomes unresponsive ssh | |
749 | will disconnect after approximately 45 seconds. | |
588df31a | 750 | .It Cm SmartcardDevice |
3cbc677d | 751 | Specifies which smartcard device to use. |
752 | The argument to this keyword is the device | |
588df31a | 753 | .Nm ssh |
754 | should use to communicate with a smartcard used for storing the user's | |
3cbc677d | 755 | private RSA key. |
756 | By default, no device is specified and smartcard support is not activated. | |
588df31a | 757 | .It Cm StrictHostKeyChecking |
758 | If this flag is set to | |
759 | .Dq yes , | |
760 | .Nm ssh | |
761 | will never automatically add host keys to the | |
762 | .Pa $HOME/.ssh/known_hosts | |
763 | file, and refuses to connect to hosts whose host key has changed. | |
764 | This provides maximum protection against trojan horse attacks, | |
765 | however, can be annoying when the | |
766 | .Pa /etc/ssh/ssh_known_hosts | |
767 | file is poorly maintained, or connections to new hosts are | |
768 | frequently made. | |
769 | This option forces the user to manually | |
770 | add all new hosts. | |
771 | If this flag is set to | |
772 | .Dq no , | |
773 | .Nm ssh | |
774 | will automatically add new host keys to the | |
775 | user known hosts files. | |
776 | If this flag is set to | |
777 | .Dq ask , | |
778 | new host keys | |
779 | will be added to the user known host files only after the user | |
780 | has confirmed that is what they really want to do, and | |
781 | .Nm ssh | |
782 | will refuse to connect to hosts whose host key has changed. | |
783 | The host keys of | |
784 | known hosts will be verified automatically in all cases. | |
785 | The argument must be | |
786 | .Dq yes , | |
787 | .Dq no | |
788 | or | |
789 | .Dq ask . | |
790 | The default is | |
791 | .Dq ask . | |
fd573618 | 792 | .It Cm TCPKeepAlive |
793 | Specifies whether the system should send TCP keepalive messages to the | |
794 | other side. | |
795 | If they are sent, death of the connection or crash of one | |
796 | of the machines will be properly noticed. | |
797 | However, this means that | |
798 | connections will die if the route is down temporarily, and some people | |
799 | find it annoying. | |
800 | .Pp | |
801 | The default is | |
802 | .Dq yes | |
803 | (to send TCP keepalive messages), and the client will notice | |
804 | if the network goes down or the remote host dies. | |
805 | This is important in scripts, and many users want it too. | |
806 | .Pp | |
807 | To disable TCP keepalive messages, the value should be set to | |
808 | .Dq no . | |
588df31a | 809 | .It Cm UsePrivilegedPort |
810 | Specifies whether to use a privileged port for outgoing connections. | |
811 | The argument must be | |
812 | .Dq yes | |
813 | or | |
814 | .Dq no . | |
815 | The default is | |
816 | .Dq no . | |
878b8992 | 817 | If set to |
818 | .Dq yes | |
819 | .Nm ssh | |
820 | must be setuid root. | |
588df31a | 821 | Note that this option must be set to |
822 | .Dq yes | |
0598d99d | 823 | for |
588df31a | 824 | .Cm RhostsRSAAuthentication |
0598d99d | 825 | with older servers. |
588df31a | 826 | .It Cm User |
827 | Specifies the user to log in as. | |
828 | This can be useful when a different user name is used on different machines. | |
829 | This saves the trouble of | |
830 | having to remember to give the user name on the command line. | |
831 | .It Cm UserKnownHostsFile | |
832 | Specifies a file to use for the user | |
833 | host key database instead of | |
834 | .Pa $HOME/.ssh/known_hosts . | |
21289cd0 | 835 | .It Cm VerifyHostKeyDNS |
836 | Specifies whether to verify the remote key using DNS and SSHFP resource | |
837 | records. | |
0161a13d | 838 | If this option is set to |
839 | .Dq yes , | |
dd376e92 | 840 | the client will implicitly trust keys that match a secure fingerprint |
0161a13d | 841 | from DNS. |
842 | Insecure fingerprints will be handled as if this option was set to | |
843 | .Dq ask . | |
844 | If this option is set to | |
845 | .Dq ask , | |
846 | information on fingerprint match will be displayed, but the user will still | |
847 | need to confirm new host keys according to the | |
848 | .Cm StrictHostKeyChecking | |
849 | option. | |
850 | The argument must be | |
851 | .Dq yes , | |
852 | .Dq no | |
dd376e92 | 853 | or |
854 | .Dq ask . | |
21289cd0 | 855 | The default is |
856 | .Dq no . | |
0f92946c | 857 | Note that this option applies to protocol version 2 only. |
588df31a | 858 | .It Cm XAuthLocation |
57ff5eeb | 859 | Specifies the full pathname of the |
588df31a | 860 | .Xr xauth 1 |
861 | program. | |
862 | The default is | |
863 | .Pa /usr/X11R6/bin/xauth . | |
864 | .El | |
865 | .Sh FILES | |
866 | .Bl -tag -width Ds | |
867 | .It Pa $HOME/.ssh/config | |
868 | This is the per-user configuration file. | |
869 | The format of this file is described above. | |
870 | This file is used by the | |
871 | .Nm ssh | |
872 | client. | |
e1520719 | 873 | Because of the potential for abuse, this file must have strict permissions: |
874 | read/write for the user, and not accessible by others. | |
588df31a | 875 | .It Pa /etc/ssh/ssh_config |
876 | Systemwide configuration file. | |
877 | This file provides defaults for those | |
878 | values that are not specified in the user's configuration file, and | |
879 | for those users who do not have a configuration file. | |
880 | This file must be world-readable. | |
881 | .El | |
be193d89 | 882 | .Sh SEE ALSO |
883 | .Xr ssh 1 | |
588df31a | 884 | .Sh AUTHORS |
885 | OpenSSH is a derivative of the original and free | |
886 | ssh 1.2.12 release by Tatu Ylonen. | |
887 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
888 | Theo de Raadt and Dug Song | |
889 | removed many bugs, re-added newer features and | |
890 | created OpenSSH. | |
891 | Markus Friedl contributed the support for SSH | |
892 | protocol versions 1.5 and 2.0. |