]>
Commit | Line | Data |
---|---|---|
bf740959 | 1 | .\" -*- nroff -*- |
2 | .\" | |
bf740959 | 3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
bf740959 | 4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
5 | .\" All rights reserved | |
6 | .\" | |
bcbf86ec | 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 | .\" | |
f3c7c613 | 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. | |
bcbf86ec | 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. | |
bf740959 | 25 | .\" |
bcbf86ec | 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. | |
bf740959 | 36 | .\" |
bf793210 | 37 | .\" $OpenBSD: ssh.1,v 1.278 2008/10/08 23:34:03 djm Exp $ |
7b3999b8 | 38 | .Dd $Mdocdate$ |
bf740959 | 39 | .Dt SSH 1 |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm ssh | |
2c86906e | 43 | .Nd OpenSSH SSH client (remote login program) |
bf740959 | 44 | .Sh SYNOPSIS |
45 | .Nm ssh | |
bf793210 | 46 | .Op Fl 1246AaCfgKkMNnqsTtVvXxYy |
3435f5a6 | 47 | .Op Fl b Ar bind_address |
d0c832f3 | 48 | .Op Fl c Ar cipher_spec |
5ddc5eb4 | 49 | .Oo Fl D\ \& |
50 | .Sm off | |
51 | .Oo Ar bind_address : Oc | |
52 | .Ar port | |
53 | .Sm on | |
54 | .Oc | |
bf740959 | 55 | .Op Fl e Ar escape_char |
e591b98a | 56 | .Op Fl F Ar configfile |
37c406a8 | 57 | .Bk -words |
5f4a0c58 | 58 | .Op Fl i Ar identity_file |
37c406a8 | 59 | .Ek |
6c7e3b94 | 60 | .Oo Fl L\ \& |
bf740959 | 61 | .Sm off |
3867aa0a | 62 | .Oo Ar bind_address : Oc |
6c7e3b94 | 63 | .Ar port : host : hostport |
bf740959 | 64 | .Sm on |
bf740959 | 65 | .Oc |
37c406a8 | 66 | .Bk -words |
5f4a0c58 | 67 | .Op Fl l Ar login_name |
37c406a8 | 68 | .Ek |
5f4a0c58 | 69 | .Op Fl m Ar mac_spec |
f8c6db83 | 70 | .Op Fl O Ar ctl_cmd |
5f4a0c58 | 71 | .Op Fl o Ar option |
5f4a0c58 | 72 | .Op Fl p Ar port |
6c7e3b94 | 73 | .Oo Fl R\ \& |
bf740959 | 74 | .Sm off |
3867aa0a | 75 | .Oo Ar bind_address : Oc |
6c7e3b94 | 76 | .Ar port : host : hostport |
bf740959 | 77 | .Sm on |
bf740959 | 78 | .Oc |
f8c6db83 | 79 | .Op Fl S Ar ctl_path |
985bb789 | 80 | .Bk -words |
06fa4ac1 | 81 | .Oo Fl w Ar local_tun Ns |
82 | .Op : Ns Ar remote_tun Oc | |
5f4a0c58 | 83 | .Oo Ar user Ns @ Oc Ns Ar hostname |
bf740959 | 84 | .Op Ar command |
985bb789 | 85 | .Ek |
f54651ce | 86 | .Sh DESCRIPTION |
bf740959 | 87 | .Nm |
2c86906e | 88 | (SSH client) is a program for logging into a remote machine and for |
610cd5c6 | 89 | executing commands on a remote machine. |
5f4a0c58 | 90 | It is intended to replace rlogin and rsh, |
91 | and provide secure encrypted communications between | |
610cd5c6 | 92 | two untrusted hosts over an insecure network. |
5d4e571c | 93 | X11 connections and arbitrary TCP ports |
5f4a0c58 | 94 | can also be forwarded over the secure channel. |
bf740959 | 95 | .Pp |
96 | .Nm | |
f54651ce | 97 | connects and logs into the specified |
5f4a0c58 | 98 | .Ar hostname |
99 | (with optional | |
100 | .Ar user | |
101 | name). | |
bf740959 | 102 | The user must prove |
1d1ffb87 | 103 | his/her identity to the remote machine using one of several methods |
a55c1733 | 104 | depending on the protocol version used (see below). |
1d1ffb87 | 105 | .Pp |
5f4a0c58 | 106 | If |
107 | .Ar command | |
108 | is specified, | |
e426efa9 | 109 | it is executed on the remote host instead of a login shell. |
bf740959 | 110 | .Pp |
442c8b33 | 111 | The options are as follows: |
112 | .Bl -tag -width Ds | |
113 | .It Fl 1 | |
114 | Forces | |
bf740959 | 115 | .Nm |
442c8b33 | 116 | to try protocol version 1 only. |
117 | .It Fl 2 | |
118 | Forces | |
bf740959 | 119 | .Nm |
442c8b33 | 120 | to try protocol version 2 only. |
121 | .It Fl 4 | |
122 | Forces | |
bf740959 | 123 | .Nm |
442c8b33 | 124 | to use IPv4 addresses only. |
125 | .It Fl 6 | |
126 | Forces | |
bf740959 | 127 | .Nm |
442c8b33 | 128 | to use IPv6 addresses only. |
129 | .It Fl A | |
130 | Enables forwarding of the authentication agent connection. | |
131 | This can also be specified on a per-host basis in a configuration file. | |
bf740959 | 132 | .Pp |
442c8b33 | 133 | Agent forwarding should be enabled with caution. |
134 | Users with the ability to bypass file permissions on the remote host | |
135 | (for the agent's Unix-domain socket) | |
136 | can access the local agent through the forwarded connection. | |
137 | An attacker cannot obtain key material from the agent, | |
138 | however they can perform operations on the keys that enable them to | |
139 | authenticate using the identities loaded into the agent. | |
140 | .It Fl a | |
141 | Disables forwarding of the authentication agent connection. | |
142 | .It Fl b Ar bind_address | |
143 | Use | |
144 | .Ar bind_address | |
145 | on the local machine as the source address | |
146 | of the connection. | |
147 | Only useful on systems with more than one address. | |
148 | .It Fl C | |
149 | Requests compression of all data (including stdin, stdout, stderr, and | |
5d4e571c | 150 | data for forwarded X11 and TCP connections). |
442c8b33 | 151 | The compression algorithm is the same used by |
152 | .Xr gzip 1 , | |
153 | and the | |
154 | .Dq level | |
155 | can be controlled by the | |
156 | .Cm CompressionLevel | |
157 | option for protocol version 1. | |
158 | Compression is desirable on modem lines and other | |
159 | slow connections, but will only slow down things on fast networks. | |
160 | The default value can be set on a host-by-host basis in the | |
161 | configuration files; see the | |
162 | .Cm Compression | |
163 | option. | |
164 | .It Fl c Ar cipher_spec | |
165 | Selects the cipher specification for encrypting the session. | |
bf740959 | 166 | .Pp |
442c8b33 | 167 | Protocol version 1 allows specification of a single cipher. |
168 | The supported values are | |
169 | .Dq 3des , | |
0fe62d3d | 170 | .Dq blowfish , |
442c8b33 | 171 | and |
172 | .Dq des . | |
173 | .Ar 3des | |
174 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
175 | It is believed to be secure. | |
176 | .Ar blowfish | |
177 | is a fast block cipher; it appears very secure and is much faster than | |
178 | .Ar 3des . | |
179 | .Ar des | |
180 | is only supported in the | |
bf740959 | 181 | .Nm |
442c8b33 | 182 | client for interoperability with legacy protocol 1 implementations |
183 | that do not support the | |
184 | .Ar 3des | |
185 | cipher. | |
186 | Its use is strongly discouraged due to cryptographic weaknesses. | |
187 | The default is | |
188 | .Dq 3des . | |
da89cf4d | 189 | .Pp |
025fc42e | 190 | For protocol version 2, |
442c8b33 | 191 | .Ar cipher_spec |
192 | is a comma-separated list of ciphers | |
193 | listed in order of preference. | |
025fc42e | 194 | The supported ciphers are: |
195 | 3des-cbc, | |
196 | aes128-cbc, | |
197 | aes192-cbc, | |
198 | aes256-cbc, | |
199 | aes128-ctr, | |
200 | aes192-ctr, | |
201 | aes256-ctr, | |
202 | arcfour128, | |
203 | arcfour256, | |
204 | arcfour, | |
205 | blowfish-cbc, | |
442c8b33 | 206 | and |
025fc42e | 207 | cast128-cbc. |
0fe62d3d | 208 | The default is: |
209 | .Bd -literal -offset indent | |
210 | aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, | |
211 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
212 | aes192-ctr,aes256-ctr | |
442c8b33 | 213 | .Ed |
214 | .It Fl D Xo | |
215 | .Sm off | |
216 | .Oo Ar bind_address : Oc | |
217 | .Ar port | |
218 | .Sm on | |
219 | .Xc | |
220 | Specifies a local | |
221 | .Dq dynamic | |
222 | application-level port forwarding. | |
223 | This works by allocating a socket to listen to | |
224 | .Ar port | |
225 | on the local side, optionally bound to the specified | |
226 | .Ar bind_address . | |
227 | Whenever a connection is made to this port, the | |
228 | connection is forwarded over the secure channel, and the application | |
229 | protocol is then used to determine where to connect to from the | |
230 | remote machine. | |
231 | Currently the SOCKS4 and SOCKS5 protocols are supported, and | |
da89cf4d | 232 | .Nm |
442c8b33 | 233 | will act as a SOCKS server. |
234 | Only root can forward privileged ports. | |
235 | Dynamic port forwardings can also be specified in the configuration file. | |
5ddc5eb4 | 236 | .Pp |
237 | IPv6 addresses can be specified with an alternative syntax: | |
238 | .Sm off | |
239 | .Xo | |
240 | .Op Ar bind_address No / | |
241 | .Ar port | |
242 | .Xc | |
243 | .Sm on | |
244 | or by enclosing the address in square brackets. | |
245 | Only the superuser can forward privileged ports. | |
246 | By default, the local port is bound in accordance with the | |
247 | .Cm GatewayPorts | |
248 | setting. | |
249 | However, an explicit | |
250 | .Ar bind_address | |
251 | may be used to bind the connection to a specific address. | |
252 | The | |
253 | .Ar bind_address | |
254 | of | |
255 | .Dq localhost | |
256 | indicates that the listening port be bound for local use only, while an | |
257 | empty address or | |
258 | .Sq * | |
259 | indicates that the port should be available from all interfaces. | |
86131206 | 260 | .It Fl e Ar escape_char |
bf740959 | 261 | Sets the escape character for sessions with a pty (default: |
262 | .Ql ~ ) . | |
610cd5c6 | 263 | The escape character is only recognized at the beginning of a line. |
264 | The escape character followed by a dot | |
bf740959 | 265 | .Pq Ql \&. |
5f4a0c58 | 266 | closes the connection; |
267 | followed by control-Z suspends the connection; | |
268 | and followed by itself sends the escape character once. | |
610cd5c6 | 269 | Setting the character to |
bf740959 | 270 | .Dq none |
271 | disables any escapes and makes the session fully transparent. | |
5f4a0c58 | 272 | .It Fl F Ar configfile |
273 | Specifies an alternative per-user configuration file. | |
274 | If a configuration file is given on the command line, | |
275 | the system-wide configuration file | |
276 | .Pq Pa /etc/ssh/ssh_config | |
277 | will be ignored. | |
278 | The default for the per-user configuration file is | |
140e3e97 | 279 | .Pa ~/.ssh/config . |
bf740959 | 280 | .It Fl f |
281 | Requests | |
282 | .Nm | |
610cd5c6 | 283 | to go to background just before command execution. |
284 | This is useful if | |
bf740959 | 285 | .Nm |
286 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 287 | wants it in the background. |
f54651ce | 288 | This implies |
bf740959 | 289 | .Fl n . |
290 | The recommended way to start X11 programs at a remote site is with | |
291 | something like | |
292 | .Ic ssh -f host xterm . | |
6c777090 | 293 | .Pp |
294 | If the | |
295 | .Cm ExitOnForwardFailure | |
296 | configuration option is set to | |
297 | .Dq yes , | |
298 | then a client started with | |
299 | .Fl f | |
300 | will wait for all remote port forwards to be successfully established | |
301 | before placing itself in the background. | |
7b2ea3a1 | 302 | .It Fl g |
303 | Allows remote hosts to connect to local forwarded ports. | |
5f4a0c58 | 304 | .It Fl I Ar smartcard_device |
86131206 | 305 | Specify the device |
5f4a0c58 | 306 | .Nm |
307 | should use to communicate with a smartcard used for storing the user's | |
308 | private RSA key. | |
86131206 | 309 | This option is only available if support for smartcard devices |
310 | is compiled in (default is no support). | |
bf740959 | 311 | .It Fl i Ar identity_file |
cf5a07a8 | 312 | Selects a file from which the identity (private key) for |
fa08c86b | 313 | RSA or DSA authentication is read. |
cf5a07a8 | 314 | The default is |
140e3e97 | 315 | .Pa ~/.ssh/identity |
cf5a07a8 | 316 | for protocol version 1, and |
140e3e97 | 317 | .Pa ~/.ssh/id_rsa |
cf5a07a8 | 318 | and |
140e3e97 | 319 | .Pa ~/.ssh/id_dsa |
cf5a07a8 | 320 | for protocol version 2. |
610cd5c6 | 321 | Identity files may also be specified on |
322 | a per-host basis in the configuration file. | |
323 | It is possible to have multiple | |
bf740959 | 324 | .Fl i |
325 | options (and multiple identities specified in | |
326 | configuration files). | |
b2f4d5cc | 327 | .It Fl K |
328 | Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI | |
329 | credentials to the server. | |
bf740959 | 330 | .It Fl k |
f7926e97 | 331 | Disables forwarding (delegation) of GSSAPI credentials to the server. |
5f4a0c58 | 332 | .It Fl L Xo |
333 | .Sm off | |
3867aa0a | 334 | .Oo Ar bind_address : Oc |
5f4a0c58 | 335 | .Ar port : host : hostport |
336 | .Sm on | |
337 | .Xc | |
338 | Specifies that the given port on the local (client) host is to be | |
339 | forwarded to the given host and port on the remote side. | |
340 | This works by allocating a socket to listen to | |
341 | .Ar port | |
3867aa0a | 342 | on the local side, optionally bound to the specified |
343 | .Ar bind_address . | |
344 | Whenever a connection is made to this port, the | |
5f4a0c58 | 345 | connection is forwarded over the secure channel, and a connection is |
346 | made to | |
347 | .Ar host | |
348 | port | |
349 | .Ar hostport | |
350 | from the remote machine. | |
351 | Port forwardings can also be specified in the configuration file. | |
5f4a0c58 | 352 | IPv6 addresses can be specified with an alternative syntax: |
353 | .Sm off | |
354 | .Xo | |
6d7a9e8f | 355 | .Op Ar bind_address No / |
5f4a0c58 | 356 | .Ar port No / Ar host No / |
3867aa0a | 357 | .Ar hostport |
5f4a0c58 | 358 | .Xc |
359 | .Sm on | |
3867aa0a | 360 | or by enclosing the address in square brackets. |
361 | Only the superuser can forward privileged ports. | |
362 | By default, the local port is bound in accordance with the | |
363 | .Cm GatewayPorts | |
364 | setting. | |
365 | However, an explicit | |
366 | .Ar bind_address | |
367 | may be used to bind the connection to a specific address. | |
368 | The | |
369 | .Ar bind_address | |
370 | of | |
371 | .Dq localhost | |
6c7e3b94 | 372 | indicates that the listening port be bound for local use only, while an |
373 | empty address or | |
374 | .Sq * | |
3867aa0a | 375 | indicates that the port should be available from all interfaces. |
bf740959 | 376 | .It Fl l Ar login_name |
610cd5c6 | 377 | Specifies the user to log in as on the remote machine. |
378 | This also may be specified on a per-host basis in the configuration file. | |
5e96b616 | 379 | .It Fl M |
380 | Places the | |
381 | .Nm | |
382 | client into | |
383 | .Dq master | |
384 | mode for connection sharing. | |
f470cf48 | 385 | Multiple |
386 | .Fl M | |
387 | options places | |
388 | .Nm | |
389 | into | |
390 | .Dq master | |
391 | mode with confirmation required before slave connections are accepted. | |
5e96b616 | 392 | Refer to the description of |
393 | .Cm ControlMaster | |
394 | in | |
395 | .Xr ssh_config 5 | |
396 | for details. | |
9affc5db | 397 | .It Fl m Ar mac_spec |
398 | Additionally, for protocol version 2 a comma-separated list of MAC | |
399 | (message authentication code) algorithms can | |
400 | be specified in order of preference. | |
401 | See the | |
402 | .Cm MACs | |
403 | keyword for more information. | |
5f4a0c58 | 404 | .It Fl N |
405 | Do not execute a remote command. | |
406 | This is useful for just forwarding ports | |
407 | (protocol version 2 only). | |
bf740959 | 408 | .It Fl n |
409 | Redirects stdin from | |
410 | .Pa /dev/null | |
411 | (actually, prevents reading from stdin). | |
412 | This must be used when | |
413 | .Nm | |
610cd5c6 | 414 | is run in the background. |
415 | A common trick is to use this to run X11 programs on a remote machine. | |
416 | For example, | |
bf740959 | 417 | .Ic ssh -n shadows.cs.hut.fi emacs & |
418 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
419 | connection will be automatically forwarded over an encrypted channel. | |
420 | The | |
421 | .Nm | |
422 | program will be put in the background. | |
423 | (This does not work if | |
424 | .Nm | |
425 | needs to ask for a password or passphrase; see also the | |
426 | .Fl f | |
427 | option.) | |
cf848a5e | 428 | .It Fl O Ar ctl_cmd |
429 | Control an active connection multiplexing master process. | |
430 | When the | |
431 | .Fl O | |
432 | option is specified, the | |
433 | .Ar ctl_cmd | |
434 | argument is interpreted and passed to the master process. | |
435 | Valid commands are: | |
436 | .Dq check | |
437 | (check that the master process is running) and | |
438 | .Dq exit | |
439 | (request the master to exit). | |
bf740959 | 440 | .It Fl o Ar option |
38539909 | 441 | Can be used to give options in the format used in the configuration file. |
bf740959 | 442 | This is useful for specifying options for which there is no separate |
610cd5c6 | 443 | command-line flag. |
5f4a0c58 | 444 | For full details of the options listed below, and their possible values, see |
445 | .Xr ssh_config 5 . | |
446 | .Pp | |
447 | .Bl -tag -width Ds -offset indent -compact | |
448 | .It AddressFamily | |
449 | .It BatchMode | |
450 | .It BindAddress | |
451 | .It ChallengeResponseAuthentication | |
452 | .It CheckHostIP | |
453 | .It Cipher | |
454 | .It Ciphers | |
455 | .It ClearAllForwardings | |
456 | .It Compression | |
457 | .It CompressionLevel | |
458 | .It ConnectionAttempts | |
20b267fb | 459 | .It ConnectTimeout |
5e96b616 | 460 | .It ControlMaster |
461 | .It ControlPath | |
5f4a0c58 | 462 | .It DynamicForward |
5f4a0c58 | 463 | .It EscapeChar |
42ea6f5e | 464 | .It ExitOnForwardFailure |
5f4a0c58 | 465 | .It ForwardAgent |
466 | .It ForwardX11 | |
d73a67d7 | 467 | .It ForwardX11Trusted |
5f4a0c58 | 468 | .It GatewayPorts |
469 | .It GlobalKnownHostsFile | |
470 | .It GSSAPIAuthentication | |
471 | .It GSSAPIDelegateCredentials | |
5c63c2ab | 472 | .It HashKnownHosts |
5f4a0c58 | 473 | .It Host |
474 | .It HostbasedAuthentication | |
475 | .It HostKeyAlgorithms | |
476 | .It HostKeyAlias | |
477 | .It HostName | |
478 | .It IdentityFile | |
3a065ed0 | 479 | .It IdentitiesOnly |
396070f8 | 480 | .It KbdInteractiveDevices |
d20f3c9e | 481 | .It LocalCommand |
5f4a0c58 | 482 | .It LocalForward |
483 | .It LogLevel | |
484 | .It MACs | |
485 | .It NoHostAuthenticationForLocalhost | |
486 | .It NumberOfPasswordPrompts | |
487 | .It PasswordAuthentication | |
d20f3c9e | 488 | .It PermitLocalCommand |
5f4a0c58 | 489 | .It Port |
490 | .It PreferredAuthentications | |
491 | .It Protocol | |
492 | .It ProxyCommand | |
493 | .It PubkeyAuthentication | |
db175906 | 494 | .It RekeyLimit |
5f4a0c58 | 495 | .It RemoteForward |
496 | .It RhostsRSAAuthentication | |
497 | .It RSAAuthentication | |
8e99a198 | 498 | .It SendEnv |
5d8d32a3 | 499 | .It ServerAliveInterval |
500 | .It ServerAliveCountMax | |
5f4a0c58 | 501 | .It SmartcardDevice |
502 | .It StrictHostKeyChecking | |
fd573618 | 503 | .It TCPKeepAlive |
d20f3c9e | 504 | .It Tunnel |
505 | .It TunnelDevice | |
5f4a0c58 | 506 | .It UsePrivilegedPort |
507 | .It User | |
508 | .It UserKnownHostsFile | |
509 | .It VerifyHostKeyDNS | |
2e8d3306 | 510 | .It VisualHostKey |
5f4a0c58 | 511 | .It XAuthLocation |
512 | .El | |
bf740959 | 513 | .It Fl p Ar port |
610cd5c6 | 514 | Port to connect to on the remote host. |
515 | This can be specified on a | |
bf740959 | 516 | per-host basis in the configuration file. |
bf740959 | 517 | .It Fl q |
610cd5c6 | 518 | Quiet mode. |
05841f5b | 519 | Causes most warning and diagnostic messages to be suppressed. |
5f4a0c58 | 520 | .It Fl R Xo |
521 | .Sm off | |
3867aa0a | 522 | .Oo Ar bind_address : Oc |
5f4a0c58 | 523 | .Ar port : host : hostport |
524 | .Sm on | |
525 | .Xc | |
526 | Specifies that the given port on the remote (server) host is to be | |
527 | forwarded to the given host and port on the local side. | |
528 | This works by allocating a socket to listen to | |
529 | .Ar port | |
530 | on the remote side, and whenever a connection is made to this port, the | |
531 | connection is forwarded over the secure channel, and a connection is | |
532 | made to | |
533 | .Ar host | |
534 | port | |
535 | .Ar hostport | |
536 | from the local machine. | |
3867aa0a | 537 | .Pp |
5f4a0c58 | 538 | Port forwardings can also be specified in the configuration file. |
539 | Privileged ports can be forwarded only when | |
540 | logging in as root on the remote machine. | |
3867aa0a | 541 | IPv6 addresses can be specified by enclosing the address in square braces or |
542 | using an alternative syntax: | |
3867aa0a | 543 | .Sm off |
6c7e3b94 | 544 | .Xo |
6d7a9e8f | 545 | .Op Ar bind_address No / |
6c7e3b94 | 546 | .Ar host No / Ar port No / |
547 | .Ar hostport | |
3867aa0a | 548 | .Xc . |
6c7e3b94 | 549 | .Sm on |
3867aa0a | 550 | .Pp |
551 | By default, the listening socket on the server will be bound to the loopback | |
552 | interface only. | |
553 | This may be overriden by specifying a | |
554 | .Ar bind_address . | |
6c7e3b94 | 555 | An empty |
556 | .Ar bind_address , | |
3867aa0a | 557 | or the address |
6c7e3b94 | 558 | .Ql * , |
3867aa0a | 559 | indicates that the remote socket should listen on all interfaces. |
560 | Specifying a remote | |
561 | .Ar bind_address | |
6c7e3b94 | 562 | will only succeed if the server's |
563 | .Cm GatewayPorts | |
3867aa0a | 564 | option is enabled (see |
6c7e3b94 | 565 | .Xr sshd_config 5 ) . |
f8c6db83 | 566 | .It Fl S Ar ctl_path |
9affc5db | 567 | Specifies the location of a control socket for connection sharing. |
5e96b616 | 568 | Refer to the description of |
0e19494c | 569 | .Cm ControlPath |
570 | and | |
5e96b616 | 571 | .Cm ControlMaster |
572 | in | |
573 | .Xr ssh_config 5 | |
574 | for details. | |
ae810de7 | 575 | .It Fl s |
3cbc677d | 576 | May be used to request invocation of a subsystem on the remote system. |
577 | Subsystems are a feature of the SSH2 protocol which facilitate the use | |
5f4a0c58 | 578 | of SSH as a secure transport for other applications (eg.\& |
579 | .Xr sftp 1 ) . | |
3cbc677d | 580 | The subsystem is specified as the remote command. |
5f4a0c58 | 581 | .It Fl T |
582 | Disable pseudo-tty allocation. | |
bf740959 | 583 | .It Fl t |
610cd5c6 | 584 | Force pseudo-tty allocation. |
4fe2af09 | 585 | This can be used to execute arbitrary |
610cd5c6 | 586 | screen-based programs on a remote machine, which can be very useful, |
f09ffbdb | 587 | e.g. when implementing menu services. |
8abcdba4 | 588 | Multiple |
589 | .Fl t | |
590 | options force tty allocation, even if | |
591 | .Nm | |
592 | has no local tty. | |
5f4a0c58 | 593 | .It Fl V |
594 | Display the version number and exit. | |
bf740959 | 595 | .It Fl v |
610cd5c6 | 596 | Verbose mode. |
597 | Causes | |
bf740959 | 598 | .Nm |
442c8b33 | 599 | to print debugging messages about its progress. |
600 | This is helpful in | |
601 | debugging connection, authentication, and configuration problems. | |
602 | Multiple | |
603 | .Fl v | |
604 | options increase the verbosity. | |
605 | The maximum is 3. | |
06fa4ac1 | 606 | .It Fl w Xo |
607 | .Ar local_tun Ns Op : Ns Ar remote_tun | |
608 | .Xc | |
609 | Requests | |
610 | tunnel | |
611 | device forwarding with the specified | |
442c8b33 | 612 | .Xr tun 4 |
06fa4ac1 | 613 | devices between the client |
614 | .Pq Ar local_tun | |
615 | and the server | |
616 | .Pq Ar remote_tun . | |
617 | .Pp | |
9bf41db3 | 618 | The devices may be specified by numerical ID or the keyword |
619 | .Dq any , | |
620 | which uses the next available tunnel device. | |
06fa4ac1 | 621 | If |
622 | .Ar remote_tun | |
623 | is not specified, it defaults to | |
624 | .Dq any . | |
9bf41db3 | 625 | See also the |
442c8b33 | 626 | .Cm Tunnel |
06fa4ac1 | 627 | and |
628 | .Cm TunnelDevice | |
629 | directives in | |
442c8b33 | 630 | .Xr ssh_config 5 . |
06fa4ac1 | 631 | If the |
632 | .Cm Tunnel | |
633 | directive is unset, it is set to the default tunnel mode, which is | |
634 | .Dq point-to-point . | |
442c8b33 | 635 | .It Fl X |
636 | Enables X11 forwarding. | |
637 | This can also be specified on a per-host basis in a configuration file. | |
638 | .Pp | |
639 | X11 forwarding should be enabled with caution. | |
640 | Users with the ability to bypass file permissions on the remote host | |
641 | (for the user's X authorization database) | |
642 | can access the local X11 display through the forwarded connection. | |
643 | An attacker may then be able to perform activities such as keystroke monitoring. | |
644 | .Pp | |
645 | For this reason, X11 forwarding is subjected to X11 SECURITY extension | |
646 | restrictions by default. | |
647 | Please refer to the | |
648 | .Nm | |
649 | .Fl Y | |
650 | option and the | |
651 | .Cm ForwardX11Trusted | |
652 | directive in | |
653 | .Xr ssh_config 5 | |
654 | for more information. | |
655 | .It Fl x | |
656 | Disables X11 forwarding. | |
657 | .It Fl Y | |
658 | Enables trusted X11 forwarding. | |
659 | Trusted X11 forwardings are not subjected to the X11 SECURITY extension | |
660 | controls. | |
bf793210 | 661 | .It Fl y |
662 | Send log information using the | |
663 | .Xr syslog 3 | |
664 | system module. | |
665 | By default this information is sent to stderr. | |
442c8b33 | 666 | .El |
e6c7c03e | 667 | .Pp |
668 | .Nm | |
669 | may additionally obtain configuration data from | |
670 | a per-user configuration file and a system-wide configuration file. | |
671 | The file format and configuration options are described in | |
672 | .Xr ssh_config 5 . | |
673 | .Pp | |
674 | .Nm | |
675 | exits with the exit status of the remote command or with 255 | |
676 | if an error occurred. | |
6b0117fd | 677 | .Sh AUTHENTICATION |
16ad260d | 678 | The OpenSSH SSH client supports SSH protocols 1 and 2. |
6b0117fd | 679 | Protocol 2 is the default, with |
680 | .Nm | |
681 | falling back to protocol 1 if it detects protocol 2 is unsupported. | |
682 | These settings may be altered using the | |
683 | .Cm Protocol | |
684 | option in | |
685 | .Xr ssh_config 5 , | |
686 | or enforced using the | |
687 | .Fl 1 | |
688 | and | |
689 | .Fl 2 | |
690 | options (see above). | |
691 | Both protocols support similar authentication methods, | |
692 | but protocol 2 is preferred since | |
693 | it provides additional mechanisms for confidentiality | |
694 | (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour) | |
f444d0f8 | 695 | and integrity (hmac-md5, hmac-sha1, umac-64, hmac-ripemd160). |
6b0117fd | 696 | Protocol 1 lacks a strong mechanism for ensuring the |
697 | integrity of the connection. | |
698 | .Pp | |
699 | The methods available for authentication are: | |
ed277f5e | 700 | GSSAPI-based authentication, |
6b0117fd | 701 | host-based authentication, |
702 | public key authentication, | |
703 | challenge-response authentication, | |
704 | and password authentication. | |
705 | Authentication methods are tried in the order specified above, | |
706 | though protocol 2 has a configuration option to change the default order: | |
707 | .Cm PreferredAuthentications . | |
708 | .Pp | |
709 | Host-based authentication works as follows: | |
442c8b33 | 710 | If the machine the user logs in from is listed in |
711 | .Pa /etc/hosts.equiv | |
712 | or | |
713 | .Pa /etc/shosts.equiv | |
714 | on the remote machine, and the user names are | |
715 | the same on both sides, or if the files | |
716 | .Pa ~/.rhosts | |
717 | or | |
718 | .Pa ~/.shosts | |
719 | exist in the user's home directory on the | |
720 | remote machine and contain a line containing the name of the client | |
721 | machine and the name of the user on that machine, the user is | |
6b0117fd | 722 | considered for login. |
723 | Additionally, the server | |
724 | .Em must | |
725 | be able to verify the client's | |
726 | host key (see the description of | |
442c8b33 | 727 | .Pa /etc/ssh/ssh_known_hosts |
728 | and | |
6b0117fd | 729 | .Pa ~/.ssh/known_hosts , |
730 | below) | |
731 | for login to be permitted. | |
442c8b33 | 732 | This authentication method closes security holes due to IP |
6b0117fd | 733 | spoofing, DNS spoofing, and routing spoofing. |
442c8b33 | 734 | [Note to the administrator: |
735 | .Pa /etc/hosts.equiv , | |
736 | .Pa ~/.rhosts , | |
737 | and the rlogin/rsh protocol in general, are inherently insecure and should be | |
738 | disabled if security is desired.] | |
739 | .Pp | |
6b0117fd | 740 | Public key authentication works as follows: |
741 | The scheme is based on public-key cryptography, | |
742 | using cryptosystems | |
743 | where encryption and decryption are done using separate keys, | |
744 | and it is unfeasible to derive the decryption key from the encryption key. | |
442c8b33 | 745 | The idea is that each user creates a public/private |
746 | key pair for authentication purposes. | |
747 | The server knows the public key, and only the user knows the private key. | |
6b0117fd | 748 | .Nm |
749 | implements public key authentication protocol automatically, | |
750 | using either the RSA or DSA algorithms. | |
751 | Protocol 1 is restricted to using only RSA keys, | |
752 | but protocol 2 may use either. | |
753 | The | |
754 | .Sx HISTORY | |
755 | section of | |
756 | .Xr ssl 8 | |
757 | contains a brief discussion of the two algorithms. | |
442c8b33 | 758 | .Pp |
759 | The file | |
760 | .Pa ~/.ssh/authorized_keys | |
761 | lists the public keys that are permitted for logging in. | |
762 | When the user logs in, the | |
763 | .Nm | |
764 | program tells the server which key pair it would like to use for | |
765 | authentication. | |
6b0117fd | 766 | The client proves that it has access to the private key |
767 | and the server checks that the corresponding public key | |
768 | is authorized to accept the account. | |
442c8b33 | 769 | .Pp |
6b0117fd | 770 | The user creates his/her key pair by running |
442c8b33 | 771 | .Xr ssh-keygen 1 . |
772 | This stores the private key in | |
773 | .Pa ~/.ssh/identity | |
6b0117fd | 774 | (protocol 1), |
775 | .Pa ~/.ssh/id_dsa | |
776 | (protocol 2 DSA), | |
777 | or | |
778 | .Pa ~/.ssh/id_rsa | |
779 | (protocol 2 RSA) | |
442c8b33 | 780 | and stores the public key in |
781 | .Pa ~/.ssh/identity.pub | |
6b0117fd | 782 | (protocol 1), |
783 | .Pa ~/.ssh/id_dsa.pub | |
784 | (protocol 2 DSA), | |
785 | or | |
786 | .Pa ~/.ssh/id_rsa.pub | |
787 | (protocol 2 RSA) | |
442c8b33 | 788 | in the user's home directory. |
6b0117fd | 789 | The user should then copy the public key |
442c8b33 | 790 | to |
791 | .Pa ~/.ssh/authorized_keys | |
6b0117fd | 792 | in his/her home directory on the remote machine. |
793 | The | |
442c8b33 | 794 | .Pa authorized_keys |
795 | file corresponds to the conventional | |
796 | .Pa ~/.rhosts | |
797 | file, and has one key | |
6b0117fd | 798 | per line, though the lines can be very long. |
442c8b33 | 799 | After this, the user can log in without giving the password. |
800 | .Pp | |
6b0117fd | 801 | The most convenient way to use public key authentication may be with an |
442c8b33 | 802 | authentication agent. |
803 | See | |
804 | .Xr ssh-agent 1 | |
805 | for more information. | |
806 | .Pp | |
6b0117fd | 807 | Challenge-response authentication works as follows: |
808 | The server sends an arbitrary | |
809 | .Qq challenge | |
810 | text, and prompts for a response. | |
811 | Protocol 2 allows multiple challenges and responses; | |
812 | protocol 1 is restricted to just one challenge/response. | |
813 | Examples of challenge-response authentication include | |
814 | BSD Authentication (see | |
815 | .Xr login.conf 5 ) | |
816 | and PAM (some non-OpenBSD systems). | |
817 | .Pp | |
818 | Finally, if other authentication methods fail, | |
442c8b33 | 819 | .Nm |
820 | prompts the user for a password. | |
821 | The password is sent to the remote | |
822 | host for checking; however, since all communications are encrypted, | |
823 | the password cannot be seen by someone listening on the network. | |
4b5e6c81 | 824 | .Pp |
825 | .Nm | |
826 | automatically maintains and checks a database containing | |
827 | identification for all hosts it has ever been used with. | |
828 | Host keys are stored in | |
829 | .Pa ~/.ssh/known_hosts | |
830 | in the user's home directory. | |
831 | Additionally, the file | |
832 | .Pa /etc/ssh/ssh_known_hosts | |
833 | is automatically checked for known hosts. | |
834 | Any new hosts are automatically added to the user's file. | |
835 | If a host's identification ever changes, | |
836 | .Nm | |
837 | warns about this and disables password authentication to prevent | |
838 | server spoofing or man-in-the-middle attacks, | |
839 | which could otherwise be used to circumvent the encryption. | |
840 | The | |
841 | .Cm StrictHostKeyChecking | |
842 | option can be used to control logins to machines whose | |
843 | host key is not known or has changed. | |
844 | .Pp | |
442c8b33 | 845 | When the user's identity has been accepted by the server, the server |
846 | either executes the given command, or logs into the machine and gives | |
847 | the user a normal shell on the remote machine. | |
848 | All communication with | |
849 | the remote command or shell will be automatically encrypted. | |
850 | .Pp | |
851 | If a pseudo-terminal has been allocated (normal login session), the | |
852 | user may use the escape characters noted below. | |
853 | .Pp | |
854 | If no pseudo-tty has been allocated, | |
855 | the session is transparent and can be used to reliably transfer binary data. | |
856 | On most systems, setting the escape character to | |
857 | .Dq none | |
858 | will also make the session transparent even if a tty is used. | |
859 | .Pp | |
860 | The session terminates when the command or shell on the remote | |
5d4e571c | 861 | machine exits and all X11 and TCP connections have been closed. |
5c5546be | 862 | .Sh ESCAPE CHARACTERS |
442c8b33 | 863 | When a pseudo-terminal has been requested, |
864 | .Nm | |
865 | supports a number of functions through the use of an escape character. | |
866 | .Pp | |
867 | A single tilde character can be sent as | |
868 | .Ic ~~ | |
869 | or by following the tilde by a character other than those described below. | |
870 | The escape character must always follow a newline to be interpreted as | |
871 | special. | |
872 | The escape character can be changed in configuration files using the | |
873 | .Cm EscapeChar | |
874 | configuration directive or on the command line by the | |
875 | .Fl e | |
876 | option. | |
877 | .Pp | |
878 | The supported escapes (assuming the default | |
879 | .Ql ~ ) | |
880 | are: | |
881 | .Bl -tag -width Ds | |
882 | .It Cm ~. | |
883 | Disconnect. | |
884 | .It Cm ~^Z | |
885 | Background | |
20892533 | 886 | .Nm . |
442c8b33 | 887 | .It Cm ~# |
888 | List forwarded connections. | |
889 | .It Cm ~& | |
890 | Background | |
891 | .Nm | |
892 | at logout when waiting for forwarded connection / X11 sessions to terminate. | |
893 | .It Cm ~? | |
894 | Display a list of escape characters. | |
895 | .It Cm ~B | |
896 | Send a BREAK to the remote system | |
897 | (only useful for SSH protocol version 2 and if the peer supports it). | |
898 | .It Cm ~C | |
899 | Open command line. | |
900 | Currently this allows the addition of port forwardings using the | |
901 | .Fl L | |
902 | and | |
903 | .Fl R | |
e49f7abd | 904 | options (see above). |
442c8b33 | 905 | It also allows the cancellation of existing remote port-forwardings |
906 | using | |
33f13fa5 | 907 | .Sm off |
908 | .Fl KR Oo Ar bind_address : Oc Ar port . | |
909 | .Sm on | |
442c8b33 | 910 | .Ic !\& Ns Ar command |
911 | allows the user to execute a local command if the | |
912 | .Ic PermitLocalCommand | |
913 | option is enabled in | |
914 | .Xr ssh_config 5 . | |
915 | Basic help is available, using the | |
916 | .Fl h | |
917 | option. | |
918 | .It Cm ~R | |
919 | Request rekeying of the connection | |
920 | (only useful for SSH protocol version 2 and if the peer supports it). | |
921 | .El | |
dbb3bf96 | 922 | .Sh TCP FORWARDING |
923 | Forwarding of arbitrary TCP connections over the secure channel can | |
924 | be specified either on the command line or in a configuration file. | |
925 | One possible application of TCP forwarding is a secure connection to a | |
926 | mail server; another is going through firewalls. | |
927 | .Pp | |
928 | In the example below, we look at encrypting communication between | |
929 | an IRC client and server, even though the IRC server does not directly | |
930 | support encrypted communications. | |
931 | This works as follows: | |
932 | the user connects to the remote host using | |
933 | .Nm , | |
934 | specifying a port to be used to forward connections | |
935 | to the remote server. | |
936 | After that it is possible to start the service which is to be encrypted | |
937 | on the client machine, | |
938 | connecting to the same local port, | |
939 | and | |
940 | .Nm | |
941 | will encrypt and forward the connection. | |
942 | .Pp | |
943 | The following example tunnels an IRC session from client machine | |
944 | .Dq 127.0.0.1 | |
945 | (localhost) | |
946 | to remote server | |
947 | .Dq server.example.com : | |
948 | .Bd -literal -offset 4n | |
949 | $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10 | |
950 | $ irc -c '#users' -p 1234 pinky 127.0.0.1 | |
951 | .Ed | |
952 | .Pp | |
953 | This tunnels a connection to IRC server | |
954 | .Dq server.example.com , | |
955 | joining channel | |
956 | .Dq #users , | |
957 | nickname | |
958 | .Dq pinky , | |
959 | using port 1234. | |
960 | It doesn't matter which port is used, | |
961 | as long as it's greater than 1023 | |
962 | (remember, only root can open sockets on privileged ports) | |
963 | and doesn't conflict with any ports already in use. | |
964 | The connection is forwarded to port 6667 on the remote server, | |
965 | since that's the standard port for IRC services. | |
966 | .Pp | |
967 | The | |
968 | .Fl f | |
969 | option backgrounds | |
970 | .Nm | |
971 | and the remote command | |
972 | .Dq sleep 10 | |
973 | is specified to allow an amount of time | |
974 | (10 seconds, in the example) | |
975 | to start the service which is to be tunnelled. | |
976 | If no connections are made within the time specified, | |
977 | .Nm | |
978 | will exit. | |
dbb3bf96 | 979 | .Sh X11 FORWARDING |
442c8b33 | 980 | If the |
981 | .Cm ForwardX11 | |
982 | variable is set to | |
983 | .Dq yes | |
984 | (or see the description of the | |
6cd6c442 | 985 | .Fl X , |
986 | .Fl x , | |
442c8b33 | 987 | and |
6cd6c442 | 988 | .Fl Y |
8770ef76 | 989 | options above) |
442c8b33 | 990 | and the user is using X11 (the |
991 | .Ev DISPLAY | |
992 | environment variable is set), the connection to the X11 display is | |
993 | automatically forwarded to the remote side in such a way that any X11 | |
994 | programs started from the shell (or command) will go through the | |
995 | encrypted channel, and the connection to the real X server will be made | |
996 | from the local machine. | |
997 | The user should not manually set | |
998 | .Ev DISPLAY . | |
999 | Forwarding of X11 connections can be | |
1000 | configured on the command line or in configuration files. | |
1001 | .Pp | |
1002 | The | |
1003 | .Ev DISPLAY | |
1004 | value set by | |
1005 | .Nm | |
1006 | will point to the server machine, but with a display number greater than zero. | |
1007 | This is normal, and happens because | |
1008 | .Nm | |
1009 | creates a | |
1010 | .Dq proxy | |
1011 | X server on the server machine for forwarding the | |
1012 | connections over the encrypted channel. | |
1013 | .Pp | |
1014 | .Nm | |
1015 | will also automatically set up Xauthority data on the server machine. | |
1016 | For this purpose, it will generate a random authorization cookie, | |
1017 | store it in Xauthority on the server, and verify that any forwarded | |
1018 | connections carry this cookie and replace it by the real cookie when | |
1019 | the connection is opened. | |
1020 | The real authentication cookie is never | |
1021 | sent to the server machine (and no cookies are sent in the plain). | |
1022 | .Pp | |
1023 | If the | |
1024 | .Cm ForwardAgent | |
1025 | variable is set to | |
1026 | .Dq yes | |
1027 | (or see the description of the | |
1028 | .Fl A | |
1029 | and | |
1030 | .Fl a | |
8770ef76 | 1031 | options above) and |
442c8b33 | 1032 | the user is using an authentication agent, the connection to the agent |
1033 | is automatically forwarded to the remote side. | |
b661b7fb | 1034 | .Sh VERIFYING HOST KEYS |
1035 | When connecting to a server for the first time, | |
1036 | a fingerprint of the server's public key is presented to the user | |
1037 | (unless the option | |
1038 | .Cm StrictHostKeyChecking | |
1039 | has been disabled). | |
1040 | Fingerprints can be determined using | |
1041 | .Xr ssh-keygen 1 : | |
1042 | .Pp | |
1043 | .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key | |
1044 | .Pp | |
990ada29 | 1045 | If the fingerprint is already known, it can be matched |
1046 | and the key can be accepted or rejected. | |
1047 | Because of the difficulty of comparing host keys | |
1048 | just by looking at hex strings, | |
1049 | there is also support to compare host keys visually, | |
1050 | using | |
1051 | .Em random art . | |
1052 | By setting the | |
7b3999b8 | 1053 | .Cm VisualHostKey |
990ada29 | 1054 | option to |
7b3999b8 | 1055 | .Dq yes , |
990ada29 | 1056 | a small ASCII graphic gets displayed on every login to a server, no matter |
1057 | if the session itself is interactive or not. | |
1058 | By learning the pattern a known server produces, a user can easily | |
1059 | find out that the host key has changed when a completely different pattern | |
1060 | is displayed. | |
1061 | Because these patterns are not unambiguous however, a pattern that looks | |
1062 | similar to the pattern remembered only gives a good probability that the | |
1063 | host key is the same, not guaranteed proof. | |
1064 | .Pp | |
1065 | To get a listing of the fingerprints along with their random art for | |
1066 | all known hosts, the following command line can be used: | |
1067 | .Pp | |
1068 | .Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts | |
1069 | .Pp | |
b661b7fb | 1070 | If the fingerprint is unknown, |
1071 | an alternative method of verification is available: | |
1072 | SSH fingerprints verified by DNS. | |
1073 | An additional resource record (RR), | |
1074 | SSHFP, | |
1075 | is added to a zonefile | |
1076 | and the connecting client is able to match the fingerprint | |
1077 | with that of the key presented. | |
1078 | .Pp | |
1079 | In this example, we are connecting a client to a server, | |
1080 | .Dq host.example.com . | |
1081 | The SSHFP resource records should first be added to the zonefile for | |
1082 | host.example.com: | |
1083 | .Bd -literal -offset indent | |
f0eea41f | 1084 | $ ssh-keygen -r host.example.com. |
b661b7fb | 1085 | .Ed |
1086 | .Pp | |
1087 | The output lines will have to be added to the zonefile. | |
1088 | To check that the zone is answering fingerprint queries: | |
1089 | .Pp | |
1090 | .Dl $ dig -t SSHFP host.example.com | |
1091 | .Pp | |
1092 | Finally the client connects: | |
1093 | .Bd -literal -offset indent | |
1094 | $ ssh -o "VerifyHostKeyDNS ask" host.example.com | |
1095 | [...] | |
1096 | Matching host key fingerprint found in DNS. | |
1097 | Are you sure you want to continue connecting (yes/no)? | |
1098 | .Ed | |
1099 | .Pp | |
1100 | See the | |
1101 | .Cm VerifyHostKeyDNS | |
1102 | option in | |
1103 | .Xr ssh_config 5 | |
1104 | for more information. | |
43a7d9e7 | 1105 | .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS |
1106 | .Nm | |
1107 | contains support for Virtual Private Network (VPN) tunnelling | |
1108 | using the | |
1109 | .Xr tun 4 | |
1110 | network pseudo-device, | |
1111 | allowing two networks to be joined securely. | |
1112 | The | |
1113 | .Xr sshd_config 5 | |
1114 | configuration option | |
1115 | .Cm PermitTunnel | |
1116 | controls whether the server supports this, | |
1117 | and at what level (layer 2 or 3 traffic). | |
1118 | .Pp | |
1119 | The following example would connect client network 10.0.50.0/24 | |
b8e51e81 | 1120 | with remote network 10.0.99.0/24 using a point-to-point connection |
1121 | from 10.1.1.1 to 10.1.1.2, | |
1122 | provided that the SSH server running on the gateway to the remote network, | |
1123 | at 192.168.1.15, allows it. | |
1124 | .Pp | |
1125 | On the client: | |
43a7d9e7 | 1126 | .Bd -literal -offset indent |
1127 | # ssh -f -w 0:1 192.168.1.15 true | |
b8e51e81 | 1128 | # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252 |
1129 | # route add 10.0.99.0/24 10.1.1.2 | |
1130 | .Ed | |
1131 | .Pp | |
1132 | On the server: | |
1133 | .Bd -literal -offset indent | |
1134 | # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252 | |
1135 | # route add 10.0.50.0/24 10.1.1.1 | |
43a7d9e7 | 1136 | .Ed |
1137 | .Pp | |
1138 | Client access may be more finely tuned via the | |
1139 | .Pa /root/.ssh/authorized_keys | |
1140 | file (see below) and the | |
1141 | .Cm PermitRootLogin | |
1142 | server option. | |
260c414c | 1143 | The following entry would permit connections on |
43a7d9e7 | 1144 | .Xr tun 4 |
260c414c | 1145 | device 1 from user |
43a7d9e7 | 1146 | .Dq jane |
260c414c | 1147 | and on tun device 2 from user |
43a7d9e7 | 1148 | .Dq john , |
1149 | if | |
1150 | .Cm PermitRootLogin | |
1151 | is set to | |
1152 | .Dq forced-commands-only : | |
1153 | .Bd -literal -offset 2n | |
1154 | tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane | |
0ac58ab4 | 1155 | tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john |
43a7d9e7 | 1156 | .Ed |
1157 | .Pp | |
525251b0 | 1158 | Since an SSH-based setup entails a fair amount of overhead, |
43a7d9e7 | 1159 | it may be more suited to temporary setups, |
1160 | such as for wireless VPNs. | |
1161 | More permanent VPNs are better provided by tools such as | |
1162 | .Xr ipsecctl 8 | |
1163 | and | |
1164 | .Xr isakmpd 8 . | |
bf740959 | 1165 | .Sh ENVIRONMENT |
1166 | .Nm | |
1167 | will normally set the following environment variables: | |
0502727e | 1168 | .Bl -tag -width "SSH_ORIGINAL_COMMAND" |
bf740959 | 1169 | .It Ev DISPLAY |
1170 | The | |
1171 | .Ev DISPLAY | |
610cd5c6 | 1172 | variable indicates the location of the X11 server. |
f54651ce | 1173 | It is automatically set by |
bf740959 | 1174 | .Nm |
1175 | to point to a value of the form | |
b92605e1 | 1176 | .Dq hostname:n , |
1177 | where | |
1178 | .Dq hostname | |
1179 | indicates the host where the shell runs, and | |
1180 | .Sq n | |
1181 | is an integer \*(Ge 1. | |
610cd5c6 | 1182 | .Nm |
1183 | uses this special value to forward X11 connections over the secure | |
1184 | channel. | |
da89cf4d | 1185 | The user should normally not set |
1186 | .Ev DISPLAY | |
1187 | explicitly, as that | |
bf740959 | 1188 | will render the X11 connection insecure (and will require the user to |
1189 | manually copy any required authorization cookies). | |
1190 | .It Ev HOME | |
1191 | Set to the path of the user's home directory. | |
1192 | .It Ev LOGNAME | |
1193 | Synonym for | |
1194 | .Ev USER ; | |
1195 | set for compatibility with systems that use this variable. | |
1196 | .It Ev MAIL | |
ae897d7c | 1197 | Set to the path of the user's mailbox. |
610cd5c6 | 1198 | .It Ev PATH |
bf740959 | 1199 | Set to the default |
1200 | .Ev PATH , | |
1201 | as specified when compiling | |
20892533 | 1202 | .Nm . |
3474b2b4 | 1203 | .It Ev SSH_ASKPASS |
1204 | If | |
1205 | .Nm | |
1206 | needs a passphrase, it will read the passphrase from the current | |
1207 | terminal if it was run from a terminal. | |
1208 | If | |
1209 | .Nm | |
1210 | does not have a terminal associated with it but | |
1211 | .Ev DISPLAY | |
1212 | and | |
1213 | .Ev SSH_ASKPASS | |
1214 | are set, it will execute the program specified by | |
1215 | .Ev SSH_ASKPASS | |
1216 | and open an X11 window to read the passphrase. | |
1217 | This is particularly useful when calling | |
1218 | .Nm | |
1219 | from a | |
caeffafb | 1220 | .Pa .xsession |
3474b2b4 | 1221 | or related script. |
1222 | (Note that on some machines it | |
1223 | may be necessary to redirect the input from | |
1224 | .Pa /dev/null | |
1225 | to make this work.) | |
bf740959 | 1226 | .It Ev SSH_AUTH_SOCK |
b92605e1 | 1227 | Identifies the path of a |
1228 | .Ux Ns -domain | |
1229 | socket used to communicate with the agent. | |
da0561eb | 1230 | .It Ev SSH_CONNECTION |
1231 | Identifies the client and server ends of the connection. | |
610cd5c6 | 1232 | The variable contains |
b92605e1 | 1233 | four space-separated values: client IP address, client port number, |
1234 | server IP address, and server port number. | |
8abcdba4 | 1235 | .It Ev SSH_ORIGINAL_COMMAND |
b92605e1 | 1236 | This variable contains the original command line if a forced command |
8abcdba4 | 1237 | is executed. |
1238 | It can be used to extract the original arguments. | |
bf740959 | 1239 | .It Ev SSH_TTY |
1240 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 1241 | with the current shell or command. |
1242 | If the current session has no tty, | |
bf740959 | 1243 | this variable is not set. |
1244 | .It Ev TZ | |
04ac3e62 | 1245 | This variable is set to indicate the present time zone if it |
f09ffbdb | 1246 | was set when the daemon was started (i.e. the daemon passes the value |
bf740959 | 1247 | on to new connections). |
1248 | .It Ev USER | |
1249 | Set to the name of the user logging in. | |
1250 | .El | |
1251 | .Pp | |
f54651ce | 1252 | Additionally, |
bf740959 | 1253 | .Nm |
f54651ce | 1254 | reads |
140e3e97 | 1255 | .Pa ~/.ssh/environment , |
bf740959 | 1256 | and adds lines of the format |
1257 | .Dq VARNAME=value | |
b92605e1 | 1258 | to the environment if the file exists and users are allowed to |
6a342527 | 1259 | change their environment. |
5f4a0c58 | 1260 | For more information, see the |
6a342527 | 1261 | .Cm PermitUserEnvironment |
35453849 | 1262 | option in |
6a342527 | 1263 | .Xr sshd_config 5 . |
bf740959 | 1264 | .Sh FILES |
0624a70b | 1265 | .Bl -tag -width Ds -compact |
0624a70b | 1266 | .It ~/.rhosts |
f3119772 | 1267 | This file is used for host-based authentication (see above). |
e91c60f2 | 1268 | On some machines this file may need to be |
f3119772 | 1269 | world-readable if the user's home directory is on an NFS partition, |
bf740959 | 1270 | because |
1271 | .Xr sshd 8 | |
610cd5c6 | 1272 | reads it as root. |
1273 | Additionally, this file must be owned by the user, | |
1274 | and must not have write permissions for anyone else. | |
1275 | The recommended | |
bf740959 | 1276 | permission for most machines is read/write for the user, and not |
1277 | accessible by others. | |
1278 | .Pp | |
0624a70b | 1279 | .It ~/.shosts |
f3119772 | 1280 | This file is used in exactly the same way as |
1281 | .Pa .rhosts , | |
1282 | but allows host-based authentication without permitting login with | |
1283 | rlogin/rsh. | |
0624a70b | 1284 | .Pp |
7c36e880 | 1285 | .It ~/.ssh/ |
1286 | This directory is the default location for all user-specific configuration | |
1287 | and authentication information. | |
1288 | There is no general requirement to keep the entire contents of this directory | |
1289 | secret, but the recommended permissions are read/write/execute for the user, | |
1290 | and not accessible by others. | |
1291 | .Pp | |
f403d7b5 | 1292 | .It ~/.ssh/authorized_keys |
1293 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. | |
1294 | The format of this file is described in the | |
1295 | .Xr sshd 8 | |
1296 | manual page. | |
f403d7b5 | 1297 | This file is not highly sensitive, but the recommended |
1298 | permissions are read/write for the user, and not accessible by others. | |
1299 | .Pp | |
1300 | .It ~/.ssh/config | |
1301 | This is the per-user configuration file. | |
1302 | The file format and configuration options are described in | |
1303 | .Xr ssh_config 5 . | |
1304 | Because of the potential for abuse, this file must have strict permissions: | |
1305 | read/write for the user, and not accessible by others. | |
1306 | .Pp | |
1307 | .It ~/.ssh/environment | |
c0907b37 | 1308 | Contains additional definitions for environment variables; see |
1309 | .Sx ENVIRONMENT , | |
f403d7b5 | 1310 | above. |
1311 | .Pp | |
1312 | .It ~/.ssh/identity | |
1313 | .It ~/.ssh/id_dsa | |
1314 | .It ~/.ssh/id_rsa | |
1315 | Contains the private key for authentication. | |
1316 | These files | |
1317 | contain sensitive data and should be readable by the user but not | |
1318 | accessible by others (read/write/execute). | |
1319 | .Nm | |
1320 | will simply ignore a private key file if it is accessible by others. | |
1321 | It is possible to specify a passphrase when | |
1322 | generating the key which will be used to encrypt the | |
1323 | sensitive part of this file using 3DES. | |
1324 | .Pp | |
1325 | .It ~/.ssh/identity.pub | |
1326 | .It ~/.ssh/id_dsa.pub | |
1327 | .It ~/.ssh/id_rsa.pub | |
1328 | Contains the public key for authentication. | |
1329 | These files are not | |
1330 | sensitive and can (but need not) be readable by anyone. | |
f403d7b5 | 1331 | .Pp |
1332 | .It ~/.ssh/known_hosts | |
aaa18db9 | 1333 | Contains a list of host keys for all hosts the user has logged into |
1334 | that are not already in the systemwide list of known host keys. | |
f403d7b5 | 1335 | See |
aaa18db9 | 1336 | .Xr sshd 8 |
1337 | for further details of the format of this file. | |
f403d7b5 | 1338 | .Pp |
1339 | .It ~/.ssh/rc | |
1340 | Commands in this file are executed by | |
1341 | .Nm | |
5d7b356f | 1342 | when the user logs in, just before the user's shell (or command) is |
f403d7b5 | 1343 | started. |
1344 | See the | |
1345 | .Xr sshd 8 | |
1346 | manual page for more information. | |
1347 | .Pp | |
0624a70b | 1348 | .It /etc/hosts.equiv |
f3119772 | 1349 | This file is for host-based authentication (see above). |
1350 | It should only be writable by root. | |
0624a70b | 1351 | .Pp |
1352 | .It /etc/shosts.equiv | |
f3119772 | 1353 | This file is used in exactly the same way as |
1354 | .Pa hosts.equiv , | |
1355 | but allows host-based authentication without permitting login with | |
1356 | rlogin/rsh. | |
0624a70b | 1357 | .Pp |
f403d7b5 | 1358 | .It Pa /etc/ssh/ssh_config |
1359 | Systemwide configuration file. | |
1360 | The file format and configuration options are described in | |
1361 | .Xr ssh_config 5 . | |
1362 | .Pp | |
1363 | .It /etc/ssh/ssh_host_key | |
1364 | .It /etc/ssh/ssh_host_dsa_key | |
1365 | .It /etc/ssh/ssh_host_rsa_key | |
1366 | These three files contain the private parts of the host keys | |
5d7b356f | 1367 | and are used for host-based authentication. |
1368 | If protocol version 1 is used, | |
bf740959 | 1369 | .Nm |
f403d7b5 | 1370 | must be setuid root, since the host key is readable only by root. |
1371 | For protocol version 2, | |
1372 | .Nm | |
1373 | uses | |
1374 | .Xr ssh-keysign 8 | |
5d7b356f | 1375 | to access the host keys, |
1376 | eliminating the requirement that | |
f403d7b5 | 1377 | .Nm |
5d7b356f | 1378 | be setuid root when host-based authentication is used. |
f403d7b5 | 1379 | By default |
1380 | .Nm | |
1381 | is not setuid root. | |
1382 | .Pp | |
1383 | .It /etc/ssh/ssh_known_hosts | |
1384 | Systemwide list of known host keys. | |
1385 | This file should be prepared by the | |
1386 | system administrator to contain the public host keys of all machines in the | |
1387 | organization. | |
aaa18db9 | 1388 | It should be world-readable. |
1389 | See | |
f403d7b5 | 1390 | .Xr sshd 8 |
aaa18db9 | 1391 | for further details of the format of this file. |
f403d7b5 | 1392 | .Pp |
1393 | .It /etc/ssh/sshrc | |
bf740959 | 1394 | Commands in this file are executed by |
1395 | .Nm | |
5d7b356f | 1396 | when the user logs in, just before the user's shell (or command) is started. |
f54651ce | 1397 | See the |
bf740959 | 1398 | .Xr sshd 8 |
1399 | manual page for more information. | |
b5e300c2 | 1400 | .El |
bf740959 | 1401 | .Sh SEE ALSO |
bf740959 | 1402 | .Xr scp 1 , |
61e96248 | 1403 | .Xr sftp 1 , |
bf740959 | 1404 | .Xr ssh-add 1 , |
1405 | .Xr ssh-agent 1 , | |
1406 | .Xr ssh-keygen 1 , | |
926f6a7a | 1407 | .Xr ssh-keyscan 1 , |
43a7d9e7 | 1408 | .Xr tun 4 , |
5f4a0c58 | 1409 | .Xr hosts.equiv 5 , |
1ae02182 | 1410 | .Xr ssh_config 5 , |
b2843ec6 | 1411 | .Xr ssh-keysign 8 , |
9afadca8 | 1412 | .Xr sshd 8 |
2cad6cef | 1413 | .Rs |
0e505e42 | 1414 | .%R RFC 4250 |
1415 | .%T "The Secure Shell (SSH) Protocol Assigned Numbers" | |
1416 | .%D 2006 | |
1417 | .Re | |
1418 | .Rs | |
1419 | .%R RFC 4251 | |
1420 | .%T "The Secure Shell (SSH) Protocol Architecture" | |
1421 | .%D 2006 | |
1422 | .Re | |
1423 | .Rs | |
1424 | .%R RFC 4252 | |
1425 | .%T "The Secure Shell (SSH) Authentication Protocol" | |
1426 | .%D 2006 | |
1427 | .Re | |
1428 | .Rs | |
1429 | .%R RFC 4253 | |
1430 | .%T "The Secure Shell (SSH) Transport Layer Protocol" | |
1431 | .%D 2006 | |
1432 | .Re | |
1433 | .Rs | |
1434 | .%R RFC 4254 | |
1435 | .%T "The Secure Shell (SSH) Connection Protocol" | |
1436 | .%D 2006 | |
1437 | .Re | |
1438 | .Rs | |
1439 | .%R RFC 4255 | |
1440 | .%T "Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints" | |
1441 | .%D 2006 | |
1442 | .Re | |
1443 | .Rs | |
1444 | .%R RFC 4256 | |
1445 | .%T "Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)" | |
1446 | .%D 2006 | |
1447 | .Re | |
1448 | .Rs | |
1449 | .%R RFC 4335 | |
1450 | .%T "The Secure Shell (SSH) Session Channel Break Extension" | |
1451 | .%D 2006 | |
1452 | .Re | |
1453 | .Rs | |
1454 | .%R RFC 4344 | |
1455 | .%T "The Secure Shell (SSH) Transport Layer Encryption Modes" | |
1456 | .%D 2006 | |
1457 | .Re | |
1458 | .Rs | |
1459 | .%R RFC 4345 | |
1460 | .%T "Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol" | |
1461 | .%D 2006 | |
2cad6cef | 1462 | .Re |
df938409 | 1463 | .Rs |
1464 | .%R RFC 4419 | |
1465 | .%T "Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol" | |
1466 | .%D 2006 | |
1467 | .Re | |
4e3c0053 | 1468 | .Rs |
1469 | .%R RFC 4716 | |
1470 | .%T "The Secure Shell (SSH) Public Key File Format" | |
1471 | .%D 2006 | |
1472 | .Re | |
990ada29 | 1473 | .Rs |
1474 | .%T "Hash Visualization: a New Technique to improve Real-World Security" | |
1475 | .%A A. Perrig | |
1476 | .%A D. Song | |
1477 | .%D 1999 | |
1478 | .%O "International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)" | |
1479 | .Re | |
be193d89 | 1480 | .Sh AUTHORS |
1481 | OpenSSH is a derivative of the original and free | |
1482 | ssh 1.2.12 release by Tatu Ylonen. | |
1483 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1484 | Theo de Raadt and Dug Song | |
1485 | removed many bugs, re-added newer features and | |
1486 | created OpenSSH. | |
1487 | Markus Friedl contributed the support for SSH | |
1488 | protocol versions 1.5 and 2.0. |