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3c0ef626 | 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 | .\" | |
9108f8d9 | 37 | .\" $OpenBSD: ssh.1,v 1.263 2006/07/11 18:50:48 markus Exp $ |
3c0ef626 | 38 | .Dd September 25, 1999 |
39 | .Dt SSH 1 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm ssh | |
43 | .Nd OpenSSH SSH client (remote login program) | |
44 | .Sh SYNOPSIS | |
45 | .Nm ssh | |
c9f39d2c | 46 | .Op Fl 1246AaCfgkMNnqsTtVvXxY |
3c0ef626 | 47 | .Op Fl b Ar bind_address |
48 | .Op Fl c Ar cipher_spec | |
2c06c99b | 49 | .Oo Fl D\ \& |
50 | .Sm off | |
51 | .Oo Ar bind_address : Oc | |
52 | .Ar port | |
53 | .Sm on | |
54 | .Oc | |
3c0ef626 | 55 | .Op Fl e Ar escape_char |
9cb1827b | 56 | .Op Fl F Ar configfile |
2c06c99b | 57 | .Bk -words |
cdd66111 | 58 | .Op Fl i Ar identity_file |
2c06c99b | 59 | .Ek |
996d5e62 | 60 | .Oo Fl L\ \& |
3c0ef626 | 61 | .Sm off |
996d5e62 | 62 | .Oo Ar bind_address : Oc |
63 | .Ar port : host : hostport | |
3c0ef626 | 64 | .Sm on |
3c0ef626 | 65 | .Oc |
2c06c99b | 66 | .Bk -words |
cdd66111 | 67 | .Op Fl l Ar login_name |
2c06c99b | 68 | .Ek |
cdd66111 | 69 | .Op Fl m Ar mac_spec |
996d5e62 | 70 | .Op Fl O Ar ctl_cmd |
cdd66111 | 71 | .Op Fl o Ar option |
cdd66111 | 72 | .Op Fl p Ar port |
996d5e62 | 73 | .Oo Fl R\ \& |
3c0ef626 | 74 | .Sm off |
996d5e62 | 75 | .Oo Ar bind_address : Oc |
76 | .Ar port : host : hostport | |
3c0ef626 | 77 | .Sm on |
3c0ef626 | 78 | .Oc |
996d5e62 | 79 | .Op Fl S Ar ctl_path |
2c06c99b | 80 | .Bk -words |
9108f8d9 | 81 | .Oo Fl w Ar local_tun Ns |
82 | .Op : Ns Ar remote_tun Oc | |
cdd66111 | 83 | .Oo Ar user Ns @ Oc Ns Ar hostname |
3c0ef626 | 84 | .Op Ar command |
996d5e62 | 85 | .Ek |
3c0ef626 | 86 | .Sh DESCRIPTION |
87 | .Nm | |
88 | (SSH client) is a program for logging into a remote machine and for | |
89 | executing commands on a remote machine. | |
cdd66111 | 90 | It is intended to replace rlogin and rsh, |
91 | and provide secure encrypted communications between | |
3c0ef626 | 92 | two untrusted hosts over an insecure network. |
2c06c99b | 93 | X11 connections and arbitrary TCP ports |
cdd66111 | 94 | can also be forwarded over the secure channel. |
3c0ef626 | 95 | .Pp |
96 | .Nm | |
97 | connects and logs into the specified | |
cdd66111 | 98 | .Ar hostname |
99 | (with optional | |
100 | .Ar user | |
101 | name). | |
3c0ef626 | 102 | The user must prove |
103 | his/her identity to the remote machine using one of several methods | |
2c06c99b | 104 | depending on the protocol version used (see below). |
3c0ef626 | 105 | .Pp |
cdd66111 | 106 | If |
107 | .Ar command | |
108 | is specified, | |
2c06c99b | 109 | it is executed on the remote host instead of a login shell. |
c9f39d2c | 110 | .Pp |
3c0ef626 | 111 | The options are as follows: |
112 | .Bl -tag -width Ds | |
cdd66111 | 113 | .It Fl 1 |
114 | Forces | |
115 | .Nm | |
116 | to try protocol version 1 only. | |
117 | .It Fl 2 | |
118 | Forces | |
119 | .Nm | |
120 | to try protocol version 2 only. | |
121 | .It Fl 4 | |
122 | Forces | |
123 | .Nm | |
124 | to use IPv4 addresses only. | |
125 | .It Fl 6 | |
126 | Forces | |
127 | .Nm | |
128 | to use IPv6 addresses only. | |
3c0ef626 | 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. | |
41b2f314 | 132 | .Pp |
6a9b3198 | 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, | |
41b2f314 | 138 | however they can perform operations on the keys that enable them to |
139 | authenticate using the identities loaded into the agent. | |
cdd66111 | 140 | .It Fl a |
141 | Disables forwarding of the authentication agent connection. | |
3c0ef626 | 142 | .It Fl b Ar bind_address |
665a873d | 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. | |
cdd66111 | 148 | .It Fl C |
149 | Requests compression of all data (including stdin, stdout, stderr, and | |
2c06c99b | 150 | data for forwarded X11 and TCP connections). |
cdd66111 | 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. | |
c9f39d2c | 164 | .It Fl c Ar cipher_spec |
165 | Selects the cipher specification for encrypting the session. | |
166 | .Pp | |
167 | Protocol version 1 allows specification of a single cipher. | |
2c06c99b | 168 | The supported values are |
c9f39d2c | 169 | .Dq 3des , |
2c06c99b | 170 | .Dq blowfish , |
c9f39d2c | 171 | and |
172 | .Dq des . | |
3c0ef626 | 173 | .Ar 3des |
174 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
c9f39d2c | 175 | It is believed to be secure. |
3c0ef626 | 176 | .Ar blowfish |
cdd66111 | 177 | is a fast block cipher; it appears very secure and is much faster than |
3c0ef626 | 178 | .Ar 3des . |
179 | .Ar des | |
180 | is only supported in the | |
181 | .Nm | |
182 | client for interoperability with legacy protocol 1 implementations | |
183 | that do not support the | |
184 | .Ar 3des | |
6a9b3198 | 185 | cipher. |
186 | Its use is strongly discouraged due to cryptographic weaknesses. | |
c9f39d2c | 187 | The default is |
188 | .Dq 3des . | |
189 | .Pp | |
2c06c99b | 190 | For protocol version 2, |
c9f39d2c | 191 | .Ar cipher_spec |
192 | is a comma-separated list of ciphers | |
193 | listed in order of preference. | |
2c06c99b | 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, | |
c9f39d2c | 206 | and |
2c06c99b | 207 | cast128-cbc. |
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 | |
c9f39d2c | 213 | .Ed |
2c06c99b | 214 | .It Fl D Xo |
215 | .Sm off | |
216 | .Oo Ar bind_address : Oc | |
217 | .Ar port | |
218 | .Sm on | |
219 | .Xc | |
cdd66111 | 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 | |
2c06c99b | 225 | on the local side, optionally bound to the specified |
226 | .Ar bind_address . | |
227 | Whenever a connection is made to this port, the | |
cdd66111 | 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 | |
232 | .Nm | |
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. | |
2c06c99b | 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. | |
260 | .It Fl e Ar escape_char | |
3c0ef626 | 261 | Sets the escape character for sessions with a pty (default: |
262 | .Ql ~ ) . | |
263 | The escape character is only recognized at the beginning of a line. | |
264 | The escape character followed by a dot | |
265 | .Pq Ql \&. | |
cdd66111 | 266 | closes the connection; |
267 | followed by control-Z suspends the connection; | |
268 | and followed by itself sends the escape character once. | |
3c0ef626 | 269 | Setting the character to |
270 | .Dq none | |
271 | disables any escapes and makes the session fully transparent. | |
cdd66111 | 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 | |
665a873d | 279 | .Pa ~/.ssh/config . |
3c0ef626 | 280 | .It Fl f |
281 | Requests | |
282 | .Nm | |
283 | to go to background just before command execution. | |
284 | This is useful if | |
285 | .Nm | |
286 | is going to ask for passwords or passphrases, but the user | |
287 | wants it in the background. | |
288 | This implies | |
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 . | |
293 | .It Fl g | |
294 | Allows remote hosts to connect to local forwarded ports. | |
cdd66111 | 295 | .It Fl I Ar smartcard_device |
2c06c99b | 296 | Specify the device |
cdd66111 | 297 | .Nm |
298 | should use to communicate with a smartcard used for storing the user's | |
299 | private RSA key. | |
2c06c99b | 300 | This option is only available if support for smartcard devices |
301 | is compiled in (default is no support). | |
3c0ef626 | 302 | .It Fl i Ar identity_file |
e9a17296 | 303 | Selects a file from which the identity (private key) for |
3c0ef626 | 304 | RSA or DSA authentication is read. |
e9a17296 | 305 | The default is |
665a873d | 306 | .Pa ~/.ssh/identity |
e9a17296 | 307 | for protocol version 1, and |
665a873d | 308 | .Pa ~/.ssh/id_rsa |
e9a17296 | 309 | and |
665a873d | 310 | .Pa ~/.ssh/id_dsa |
e9a17296 | 311 | for protocol version 2. |
3c0ef626 | 312 | Identity files may also be specified on |
313 | a per-host basis in the configuration file. | |
314 | It is possible to have multiple | |
315 | .Fl i | |
316 | options (and multiple identities specified in | |
317 | configuration files). | |
3c0ef626 | 318 | .It Fl k |
cdd66111 | 319 | Disables forwarding (delegation) of GSSAPI credentials to the server. |
320 | .It Fl L Xo | |
321 | .Sm off | |
996d5e62 | 322 | .Oo Ar bind_address : Oc |
cdd66111 | 323 | .Ar port : host : hostport |
324 | .Sm on | |
325 | .Xc | |
326 | Specifies that the given port on the local (client) host is to be | |
327 | forwarded to the given host and port on the remote side. | |
328 | This works by allocating a socket to listen to | |
329 | .Ar port | |
996d5e62 | 330 | on the local side, optionally bound to the specified |
331 | .Ar bind_address . | |
332 | Whenever a connection is made to this port, the | |
cdd66111 | 333 | connection is forwarded over the secure channel, and a connection is |
334 | made to | |
335 | .Ar host | |
336 | port | |
337 | .Ar hostport | |
338 | from the remote machine. | |
339 | Port forwardings can also be specified in the configuration file. | |
cdd66111 | 340 | IPv6 addresses can be specified with an alternative syntax: |
341 | .Sm off | |
342 | .Xo | |
996d5e62 | 343 | .Op Ar bind_address No / |
cdd66111 | 344 | .Ar port No / Ar host No / |
996d5e62 | 345 | .Ar hostport |
cdd66111 | 346 | .Xc |
347 | .Sm on | |
996d5e62 | 348 | or by enclosing the address in square brackets. |
349 | Only the superuser can forward privileged ports. | |
350 | By default, the local port is bound in accordance with the | |
351 | .Cm GatewayPorts | |
352 | setting. | |
353 | However, an explicit | |
354 | .Ar bind_address | |
355 | may be used to bind the connection to a specific address. | |
356 | The | |
357 | .Ar bind_address | |
358 | of | |
359 | .Dq localhost | |
360 | indicates that the listening port be bound for local use only, while an | |
361 | empty address or | |
362 | .Sq * | |
363 | indicates that the port should be available from all interfaces. | |
3c0ef626 | 364 | .It Fl l Ar login_name |
365 | Specifies the user to log in as on the remote machine. | |
366 | This also may be specified on a per-host basis in the configuration file. | |
c9f39d2c | 367 | .It Fl M |
368 | Places the | |
369 | .Nm | |
370 | client into | |
371 | .Dq master | |
372 | mode for connection sharing. | |
2c06c99b | 373 | Multiple |
374 | .Fl M | |
375 | options places | |
376 | .Nm | |
377 | into | |
378 | .Dq master | |
379 | mode with confirmation required before slave connections are accepted. | |
c9f39d2c | 380 | Refer to the description of |
381 | .Cm ControlMaster | |
382 | in | |
383 | .Xr ssh_config 5 | |
384 | for details. | |
3c0ef626 | 385 | .It Fl m Ar mac_spec |
386 | Additionally, for protocol version 2 a comma-separated list of MAC | |
387 | (message authentication code) algorithms can | |
388 | be specified in order of preference. | |
389 | See the | |
390 | .Cm MACs | |
391 | keyword for more information. | |
cdd66111 | 392 | .It Fl N |
393 | Do not execute a remote command. | |
394 | This is useful for just forwarding ports | |
395 | (protocol version 2 only). | |
3c0ef626 | 396 | .It Fl n |
397 | Redirects stdin from | |
398 | .Pa /dev/null | |
399 | (actually, prevents reading from stdin). | |
400 | This must be used when | |
401 | .Nm | |
402 | is run in the background. | |
403 | A common trick is to use this to run X11 programs on a remote machine. | |
404 | For example, | |
405 | .Ic ssh -n shadows.cs.hut.fi emacs & | |
406 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
407 | connection will be automatically forwarded over an encrypted channel. | |
408 | The | |
409 | .Nm | |
410 | program will be put in the background. | |
411 | (This does not work if | |
412 | .Nm | |
413 | needs to ask for a password or passphrase; see also the | |
414 | .Fl f | |
415 | option.) | |
996d5e62 | 416 | .It Fl O Ar ctl_cmd |
417 | Control an active connection multiplexing master process. | |
418 | When the | |
419 | .Fl O | |
420 | option is specified, the | |
421 | .Ar ctl_cmd | |
422 | argument is interpreted and passed to the master process. | |
423 | Valid commands are: | |
424 | .Dq check | |
425 | (check that the master process is running) and | |
426 | .Dq exit | |
427 | (request the master to exit). | |
3c0ef626 | 428 | .It Fl o Ar option |
429 | Can be used to give options in the format used in the configuration file. | |
430 | This is useful for specifying options for which there is no separate | |
431 | command-line flag. | |
cdd66111 | 432 | For full details of the options listed below, and their possible values, see |
433 | .Xr ssh_config 5 . | |
434 | .Pp | |
435 | .Bl -tag -width Ds -offset indent -compact | |
436 | .It AddressFamily | |
437 | .It BatchMode | |
438 | .It BindAddress | |
439 | .It ChallengeResponseAuthentication | |
440 | .It CheckHostIP | |
441 | .It Cipher | |
442 | .It Ciphers | |
443 | .It ClearAllForwardings | |
444 | .It Compression | |
445 | .It CompressionLevel | |
446 | .It ConnectionAttempts | |
c9f39d2c | 447 | .It ConnectTimeout |
448 | .It ControlMaster | |
449 | .It ControlPath | |
cdd66111 | 450 | .It DynamicForward |
451 | .It EscapeChar | |
9108f8d9 | 452 | .It ExitOnForwardFailure |
cdd66111 | 453 | .It ForwardAgent |
454 | .It ForwardX11 | |
455 | .It ForwardX11Trusted | |
456 | .It GatewayPorts | |
457 | .It GlobalKnownHostsFile | |
458 | .It GSSAPIAuthentication | |
459 | .It GSSAPIDelegateCredentials | |
996d5e62 | 460 | .It HashKnownHosts |
cdd66111 | 461 | .It Host |
462 | .It HostbasedAuthentication | |
463 | .It HostKeyAlgorithms | |
464 | .It HostKeyAlias | |
465 | .It HostName | |
466 | .It IdentityFile | |
99be0775 | 467 | .It IdentitiesOnly |
996d5e62 | 468 | .It KbdInteractiveDevices |
2c06c99b | 469 | .It LocalCommand |
cdd66111 | 470 | .It LocalForward |
471 | .It LogLevel | |
472 | .It MACs | |
473 | .It NoHostAuthenticationForLocalhost | |
474 | .It NumberOfPasswordPrompts | |
475 | .It PasswordAuthentication | |
2c06c99b | 476 | .It PermitLocalCommand |
cdd66111 | 477 | .It Port |
478 | .It PreferredAuthentications | |
479 | .It Protocol | |
480 | .It ProxyCommand | |
481 | .It PubkeyAuthentication | |
2c06c99b | 482 | .It RekeyLimit |
cdd66111 | 483 | .It RemoteForward |
484 | .It RhostsRSAAuthentication | |
485 | .It RSAAuthentication | |
c9f39d2c | 486 | .It SendEnv |
cdd66111 | 487 | .It ServerAliveInterval |
488 | .It ServerAliveCountMax | |
489 | .It SmartcardDevice | |
490 | .It StrictHostKeyChecking | |
491 | .It TCPKeepAlive | |
2c06c99b | 492 | .It Tunnel |
493 | .It TunnelDevice | |
cdd66111 | 494 | .It UsePrivilegedPort |
495 | .It User | |
496 | .It UserKnownHostsFile | |
497 | .It VerifyHostKeyDNS | |
498 | .It XAuthLocation | |
499 | .El | |
3c0ef626 | 500 | .It Fl p Ar port |
501 | Port to connect to on the remote host. | |
502 | This can be specified on a | |
503 | per-host basis in the configuration file. | |
3c0ef626 | 504 | .It Fl q |
505 | Quiet mode. | |
506 | Causes all warning and diagnostic messages to be suppressed. | |
cdd66111 | 507 | .It Fl R Xo |
508 | .Sm off | |
996d5e62 | 509 | .Oo Ar bind_address : Oc |
cdd66111 | 510 | .Ar port : host : hostport |
511 | .Sm on | |
512 | .Xc | |
513 | Specifies that the given port on the remote (server) host is to be | |
514 | forwarded to the given host and port on the local side. | |
515 | This works by allocating a socket to listen to | |
516 | .Ar port | |
517 | on the remote side, and whenever a connection is made to this port, the | |
518 | connection is forwarded over the secure channel, and a connection is | |
519 | made to | |
520 | .Ar host | |
521 | port | |
522 | .Ar hostport | |
523 | from the local machine. | |
996d5e62 | 524 | .Pp |
cdd66111 | 525 | Port forwardings can also be specified in the configuration file. |
526 | Privileged ports can be forwarded only when | |
527 | logging in as root on the remote machine. | |
996d5e62 | 528 | IPv6 addresses can be specified by enclosing the address in square braces or |
529 | using an alternative syntax: | |
cdd66111 | 530 | .Sm off |
531 | .Xo | |
996d5e62 | 532 | .Op Ar bind_address No / |
533 | .Ar host No / Ar port No / | |
534 | .Ar hostport | |
535 | .Xc . | |
cdd66111 | 536 | .Sm on |
996d5e62 | 537 | .Pp |
538 | By default, the listening socket on the server will be bound to the loopback | |
539 | interface only. | |
540 | This may be overriden by specifying a | |
541 | .Ar bind_address . | |
542 | An empty | |
543 | .Ar bind_address , | |
544 | or the address | |
545 | .Ql * , | |
546 | indicates that the remote socket should listen on all interfaces. | |
547 | Specifying a remote | |
548 | .Ar bind_address | |
549 | will only succeed if the server's | |
550 | .Cm GatewayPorts | |
551 | option is enabled (see | |
552 | .Xr sshd_config 5 ) . | |
553 | .It Fl S Ar ctl_path | |
c9f39d2c | 554 | Specifies the location of a control socket for connection sharing. |
555 | Refer to the description of | |
556 | .Cm ControlPath | |
557 | and | |
558 | .Cm ControlMaster | |
559 | in | |
560 | .Xr ssh_config 5 | |
561 | for details. | |
3c0ef626 | 562 | .It Fl s |
0fff78ff | 563 | May be used to request invocation of a subsystem on the remote system. |
564 | Subsystems are a feature of the SSH2 protocol which facilitate the use | |
cdd66111 | 565 | of SSH as a secure transport for other applications (eg.\& |
566 | .Xr sftp 1 ) . | |
0fff78ff | 567 | The subsystem is specified as the remote command. |
cdd66111 | 568 | .It Fl T |
569 | Disable pseudo-tty allocation. | |
3c0ef626 | 570 | .It Fl t |
571 | Force pseudo-tty allocation. | |
572 | This can be used to execute arbitrary | |
573 | screen-based programs on a remote machine, which can be very useful, | |
9108f8d9 | 574 | e.g. when implementing menu services. |
3c0ef626 | 575 | Multiple |
576 | .Fl t | |
577 | options force tty allocation, even if | |
578 | .Nm | |
579 | has no local tty. | |
cdd66111 | 580 | .It Fl V |
581 | Display the version number and exit. | |
3c0ef626 | 582 | .It Fl v |
583 | Verbose mode. | |
584 | Causes | |
585 | .Nm | |
586 | to print debugging messages about its progress. | |
587 | This is helpful in | |
588 | debugging connection, authentication, and configuration problems. | |
589 | Multiple | |
590 | .Fl v | |
0fff78ff | 591 | options increase the verbosity. |
592 | The maximum is 3. | |
9108f8d9 | 593 | .It Fl w Xo |
594 | .Ar local_tun Ns Op : Ns Ar remote_tun | |
595 | .Xc | |
596 | Requests | |
597 | tunnel | |
598 | device forwarding with the specified | |
2c06c99b | 599 | .Xr tun 4 |
9108f8d9 | 600 | devices between the client |
601 | .Pq Ar local_tun | |
602 | and the server | |
603 | .Pq Ar remote_tun . | |
604 | .Pp | |
2c06c99b | 605 | The devices may be specified by numerical ID or the keyword |
606 | .Dq any , | |
607 | which uses the next available tunnel device. | |
9108f8d9 | 608 | If |
609 | .Ar remote_tun | |
610 | is not specified, it defaults to | |
611 | .Dq any . | |
2c06c99b | 612 | See also the |
613 | .Cm Tunnel | |
9108f8d9 | 614 | and |
615 | .Cm TunnelDevice | |
616 | directives in | |
2c06c99b | 617 | .Xr ssh_config 5 . |
9108f8d9 | 618 | If the |
619 | .Cm Tunnel | |
620 | directive is unset, it is set to the default tunnel mode, which is | |
621 | .Dq point-to-point . | |
3c0ef626 | 622 | .It Fl X |
623 | Enables X11 forwarding. | |
624 | This can also be specified on a per-host basis in a configuration file. | |
41b2f314 | 625 | .Pp |
6a9b3198 | 626 | X11 forwarding should be enabled with caution. |
627 | Users with the ability to bypass file permissions on the remote host | |
628 | (for the user's X authorization database) | |
629 | can access the local X11 display through the forwarded connection. | |
630 | An attacker may then be able to perform activities such as keystroke monitoring. | |
996d5e62 | 631 | .Pp |
632 | For this reason, X11 forwarding is subjected to X11 SECURITY extension | |
633 | restrictions by default. | |
634 | Please refer to the | |
635 | .Nm | |
636 | .Fl Y | |
637 | option and the | |
638 | .Cm ForwardX11Trusted | |
639 | directive in | |
640 | .Xr ssh_config 5 | |
641 | for more information. | |
cdd66111 | 642 | .It Fl x |
643 | Disables X11 forwarding. | |
644 | .It Fl Y | |
645 | Enables trusted X11 forwarding. | |
996d5e62 | 646 | Trusted X11 forwardings are not subjected to the X11 SECURITY extension |
647 | controls. | |
3c0ef626 | 648 | .El |
2c06c99b | 649 | .Pp |
3c0ef626 | 650 | .Nm |
f5799ae1 | 651 | may additionally obtain configuration data from |
652 | a per-user configuration file and a system-wide configuration file. | |
653 | The file format and configuration options are described in | |
654 | .Xr ssh_config 5 . | |
2c06c99b | 655 | .Pp |
656 | .Nm | |
657 | exits with the exit status of the remote command or with 255 | |
658 | if an error occurred. | |
659 | .Sh AUTHENTICATION | |
660 | The OpenSSH SSH client supports SSH protocols 1 and 2. | |
661 | Protocol 2 is the default, with | |
662 | .Nm | |
663 | falling back to protocol 1 if it detects protocol 2 is unsupported. | |
664 | These settings may be altered using the | |
665 | .Cm Protocol | |
666 | option in | |
667 | .Xr ssh_config 5 , | |
668 | or enforced using the | |
669 | .Fl 1 | |
670 | and | |
671 | .Fl 2 | |
672 | options (see above). | |
673 | Both protocols support similar authentication methods, | |
674 | but protocol 2 is preferred since | |
675 | it provides additional mechanisms for confidentiality | |
676 | (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour) | |
677 | and integrity (hmac-md5, hmac-sha1, hmac-ripemd160). | |
678 | Protocol 1 lacks a strong mechanism for ensuring the | |
679 | integrity of the connection. | |
680 | .Pp | |
681 | The methods available for authentication are: | |
9108f8d9 | 682 | GSSAPI-based authentication, |
2c06c99b | 683 | host-based authentication, |
684 | public key authentication, | |
685 | challenge-response authentication, | |
686 | and password authentication. | |
687 | Authentication methods are tried in the order specified above, | |
688 | though protocol 2 has a configuration option to change the default order: | |
689 | .Cm PreferredAuthentications . | |
690 | .Pp | |
691 | Host-based authentication works as follows: | |
692 | If the machine the user logs in from is listed in | |
693 | .Pa /etc/hosts.equiv | |
694 | or | |
695 | .Pa /etc/shosts.equiv | |
696 | on the remote machine, and the user names are | |
697 | the same on both sides, or if the files | |
698 | .Pa ~/.rhosts | |
699 | or | |
700 | .Pa ~/.shosts | |
701 | exist in the user's home directory on the | |
702 | remote machine and contain a line containing the name of the client | |
703 | machine and the name of the user on that machine, the user is | |
704 | considered for login. | |
705 | Additionally, the server | |
706 | .Em must | |
707 | be able to verify the client's | |
708 | host key (see the description of | |
709 | .Pa /etc/ssh/ssh_known_hosts | |
710 | and | |
711 | .Pa ~/.ssh/known_hosts , | |
712 | below) | |
713 | for login to be permitted. | |
714 | This authentication method closes security holes due to IP | |
715 | spoofing, DNS spoofing, and routing spoofing. | |
716 | [Note to the administrator: | |
717 | .Pa /etc/hosts.equiv , | |
718 | .Pa ~/.rhosts , | |
719 | and the rlogin/rsh protocol in general, are inherently insecure and should be | |
720 | disabled if security is desired.] | |
721 | .Pp | |
722 | Public key authentication works as follows: | |
723 | The scheme is based on public-key cryptography, | |
724 | using cryptosystems | |
725 | where encryption and decryption are done using separate keys, | |
726 | and it is unfeasible to derive the decryption key from the encryption key. | |
727 | The idea is that each user creates a public/private | |
728 | key pair for authentication purposes. | |
729 | The server knows the public key, and only the user knows the private key. | |
730 | .Nm | |
731 | implements public key authentication protocol automatically, | |
732 | using either the RSA or DSA algorithms. | |
733 | Protocol 1 is restricted to using only RSA keys, | |
734 | but protocol 2 may use either. | |
735 | The | |
736 | .Sx HISTORY | |
737 | section of | |
738 | .Xr ssl 8 | |
739 | contains a brief discussion of the two algorithms. | |
740 | .Pp | |
741 | The file | |
742 | .Pa ~/.ssh/authorized_keys | |
743 | lists the public keys that are permitted for logging in. | |
744 | When the user logs in, the | |
745 | .Nm | |
746 | program tells the server which key pair it would like to use for | |
747 | authentication. | |
748 | The client proves that it has access to the private key | |
749 | and the server checks that the corresponding public key | |
750 | is authorized to accept the account. | |
751 | .Pp | |
752 | The user creates his/her key pair by running | |
753 | .Xr ssh-keygen 1 . | |
754 | This stores the private key in | |
755 | .Pa ~/.ssh/identity | |
756 | (protocol 1), | |
757 | .Pa ~/.ssh/id_dsa | |
758 | (protocol 2 DSA), | |
759 | or | |
760 | .Pa ~/.ssh/id_rsa | |
761 | (protocol 2 RSA) | |
762 | and stores the public key in | |
763 | .Pa ~/.ssh/identity.pub | |
764 | (protocol 1), | |
765 | .Pa ~/.ssh/id_dsa.pub | |
766 | (protocol 2 DSA), | |
767 | or | |
768 | .Pa ~/.ssh/id_rsa.pub | |
769 | (protocol 2 RSA) | |
770 | in the user's home directory. | |
771 | The user should then copy the public key | |
772 | to | |
773 | .Pa ~/.ssh/authorized_keys | |
774 | in his/her home directory on the remote machine. | |
775 | The | |
776 | .Pa authorized_keys | |
777 | file corresponds to the conventional | |
778 | .Pa ~/.rhosts | |
779 | file, and has one key | |
780 | per line, though the lines can be very long. | |
781 | After this, the user can log in without giving the password. | |
782 | .Pp | |
783 | The most convenient way to use public key authentication may be with an | |
784 | authentication agent. | |
785 | See | |
786 | .Xr ssh-agent 1 | |
787 | for more information. | |
788 | .Pp | |
789 | Challenge-response authentication works as follows: | |
790 | The server sends an arbitrary | |
791 | .Qq challenge | |
792 | text, and prompts for a response. | |
793 | Protocol 2 allows multiple challenges and responses; | |
794 | protocol 1 is restricted to just one challenge/response. | |
795 | Examples of challenge-response authentication include | |
796 | BSD Authentication (see | |
797 | .Xr login.conf 5 ) | |
798 | and PAM (some non-OpenBSD systems). | |
799 | .Pp | |
800 | Finally, if other authentication methods fail, | |
801 | .Nm | |
802 | prompts the user for a password. | |
803 | The password is sent to the remote | |
804 | host for checking; however, since all communications are encrypted, | |
805 | the password cannot be seen by someone listening on the network. | |
806 | .Pp | |
807 | .Nm | |
808 | automatically maintains and checks a database containing | |
809 | identification for all hosts it has ever been used with. | |
810 | Host keys are stored in | |
811 | .Pa ~/.ssh/known_hosts | |
812 | in the user's home directory. | |
813 | Additionally, the file | |
814 | .Pa /etc/ssh/ssh_known_hosts | |
815 | is automatically checked for known hosts. | |
816 | Any new hosts are automatically added to the user's file. | |
817 | If a host's identification ever changes, | |
818 | .Nm | |
819 | warns about this and disables password authentication to prevent | |
820 | server spoofing or man-in-the-middle attacks, | |
821 | which could otherwise be used to circumvent the encryption. | |
822 | The | |
823 | .Cm StrictHostKeyChecking | |
824 | option can be used to control logins to machines whose | |
825 | host key is not known or has changed. | |
826 | .Pp | |
827 | When the user's identity has been accepted by the server, the server | |
828 | either executes the given command, or logs into the machine and gives | |
829 | the user a normal shell on the remote machine. | |
830 | All communication with | |
831 | the remote command or shell will be automatically encrypted. | |
832 | .Pp | |
833 | If a pseudo-terminal has been allocated (normal login session), the | |
834 | user may use the escape characters noted below. | |
835 | .Pp | |
836 | If no pseudo-tty has been allocated, | |
837 | the session is transparent and can be used to reliably transfer binary data. | |
838 | On most systems, setting the escape character to | |
839 | .Dq none | |
840 | will also make the session transparent even if a tty is used. | |
841 | .Pp | |
842 | The session terminates when the command or shell on the remote | |
843 | machine exits and all X11 and TCP connections have been closed. | |
844 | .Sh ESCAPE CHARACTERS | |
845 | When a pseudo-terminal has been requested, | |
846 | .Nm | |
847 | supports a number of functions through the use of an escape character. | |
848 | .Pp | |
849 | A single tilde character can be sent as | |
850 | .Ic ~~ | |
851 | or by following the tilde by a character other than those described below. | |
852 | The escape character must always follow a newline to be interpreted as | |
853 | special. | |
854 | The escape character can be changed in configuration files using the | |
855 | .Cm EscapeChar | |
856 | configuration directive or on the command line by the | |
857 | .Fl e | |
858 | option. | |
859 | .Pp | |
860 | The supported escapes (assuming the default | |
861 | .Ql ~ ) | |
862 | are: | |
863 | .Bl -tag -width Ds | |
864 | .It Cm ~. | |
865 | Disconnect. | |
866 | .It Cm ~^Z | |
867 | Background | |
868 | .Nm . | |
869 | .It Cm ~# | |
870 | List forwarded connections. | |
871 | .It Cm ~& | |
872 | Background | |
873 | .Nm | |
874 | at logout when waiting for forwarded connection / X11 sessions to terminate. | |
875 | .It Cm ~? | |
876 | Display a list of escape characters. | |
877 | .It Cm ~B | |
878 | Send a BREAK to the remote system | |
879 | (only useful for SSH protocol version 2 and if the peer supports it). | |
880 | .It Cm ~C | |
881 | Open command line. | |
882 | Currently this allows the addition of port forwardings using the | |
883 | .Fl L | |
884 | and | |
885 | .Fl R | |
886 | options (see above). | |
887 | It also allows the cancellation of existing remote port-forwardings | |
888 | using | |
9108f8d9 | 889 | .Sm off |
890 | .Fl KR Oo Ar bind_address : Oc Ar port . | |
891 | .Sm on | |
2c06c99b | 892 | .Ic !\& Ns Ar command |
893 | allows the user to execute a local command if the | |
894 | .Ic PermitLocalCommand | |
895 | option is enabled in | |
896 | .Xr ssh_config 5 . | |
897 | Basic help is available, using the | |
898 | .Fl h | |
899 | option. | |
900 | .It Cm ~R | |
901 | Request rekeying of the connection | |
902 | (only useful for SSH protocol version 2 and if the peer supports it). | |
903 | .El | |
904 | .Sh TCP FORWARDING | |
905 | Forwarding of arbitrary TCP connections over the secure channel can | |
906 | be specified either on the command line or in a configuration file. | |
907 | One possible application of TCP forwarding is a secure connection to a | |
908 | mail server; another is going through firewalls. | |
909 | .Pp | |
910 | In the example below, we look at encrypting communication between | |
911 | an IRC client and server, even though the IRC server does not directly | |
912 | support encrypted communications. | |
913 | This works as follows: | |
914 | the user connects to the remote host using | |
915 | .Nm , | |
916 | specifying a port to be used to forward connections | |
917 | to the remote server. | |
918 | After that it is possible to start the service which is to be encrypted | |
919 | on the client machine, | |
920 | connecting to the same local port, | |
921 | and | |
922 | .Nm | |
923 | will encrypt and forward the connection. | |
924 | .Pp | |
925 | The following example tunnels an IRC session from client machine | |
926 | .Dq 127.0.0.1 | |
927 | (localhost) | |
928 | to remote server | |
929 | .Dq server.example.com : | |
930 | .Bd -literal -offset 4n | |
931 | $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10 | |
932 | $ irc -c '#users' -p 1234 pinky 127.0.0.1 | |
933 | .Ed | |
934 | .Pp | |
935 | This tunnels a connection to IRC server | |
936 | .Dq server.example.com , | |
937 | joining channel | |
938 | .Dq #users , | |
939 | nickname | |
940 | .Dq pinky , | |
941 | using port 1234. | |
942 | It doesn't matter which port is used, | |
943 | as long as it's greater than 1023 | |
944 | (remember, only root can open sockets on privileged ports) | |
945 | and doesn't conflict with any ports already in use. | |
946 | The connection is forwarded to port 6667 on the remote server, | |
947 | since that's the standard port for IRC services. | |
948 | .Pp | |
949 | The | |
950 | .Fl f | |
951 | option backgrounds | |
952 | .Nm | |
953 | and the remote command | |
954 | .Dq sleep 10 | |
955 | is specified to allow an amount of time | |
956 | (10 seconds, in the example) | |
957 | to start the service which is to be tunnelled. | |
958 | If no connections are made within the time specified, | |
959 | .Nm | |
960 | will exit. | |
961 | .Sh X11 FORWARDING | |
962 | If the | |
963 | .Cm ForwardX11 | |
964 | variable is set to | |
965 | .Dq yes | |
966 | (or see the description of the | |
967 | .Fl X , | |
968 | .Fl x , | |
969 | and | |
970 | .Fl Y | |
971 | options above) | |
972 | and the user is using X11 (the | |
973 | .Ev DISPLAY | |
974 | environment variable is set), the connection to the X11 display is | |
975 | automatically forwarded to the remote side in such a way that any X11 | |
976 | programs started from the shell (or command) will go through the | |
977 | encrypted channel, and the connection to the real X server will be made | |
978 | from the local machine. | |
979 | The user should not manually set | |
980 | .Ev DISPLAY . | |
981 | Forwarding of X11 connections can be | |
982 | configured on the command line or in configuration files. | |
983 | .Pp | |
984 | The | |
985 | .Ev DISPLAY | |
986 | value set by | |
987 | .Nm | |
988 | will point to the server machine, but with a display number greater than zero. | |
989 | This is normal, and happens because | |
990 | .Nm | |
991 | creates a | |
992 | .Dq proxy | |
993 | X server on the server machine for forwarding the | |
994 | connections over the encrypted channel. | |
995 | .Pp | |
996 | .Nm | |
997 | will also automatically set up Xauthority data on the server machine. | |
998 | For this purpose, it will generate a random authorization cookie, | |
999 | store it in Xauthority on the server, and verify that any forwarded | |
1000 | connections carry this cookie and replace it by the real cookie when | |
1001 | the connection is opened. | |
1002 | The real authentication cookie is never | |
1003 | sent to the server machine (and no cookies are sent in the plain). | |
1004 | .Pp | |
1005 | If the | |
1006 | .Cm ForwardAgent | |
1007 | variable is set to | |
1008 | .Dq yes | |
1009 | (or see the description of the | |
1010 | .Fl A | |
1011 | and | |
1012 | .Fl a | |
1013 | options above) and | |
1014 | the user is using an authentication agent, the connection to the agent | |
1015 | is automatically forwarded to the remote side. | |
1016 | .Sh VERIFYING HOST KEYS | |
1017 | When connecting to a server for the first time, | |
1018 | a fingerprint of the server's public key is presented to the user | |
1019 | (unless the option | |
1020 | .Cm StrictHostKeyChecking | |
1021 | has been disabled). | |
1022 | Fingerprints can be determined using | |
1023 | .Xr ssh-keygen 1 : | |
1024 | .Pp | |
1025 | .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key | |
1026 | .Pp | |
1027 | If the fingerprint is already known, | |
1028 | it can be matched and verified, | |
1029 | and the key can be accepted. | |
1030 | If the fingerprint is unknown, | |
1031 | an alternative method of verification is available: | |
1032 | SSH fingerprints verified by DNS. | |
1033 | An additional resource record (RR), | |
1034 | SSHFP, | |
1035 | is added to a zonefile | |
1036 | and the connecting client is able to match the fingerprint | |
1037 | with that of the key presented. | |
1038 | .Pp | |
1039 | In this example, we are connecting a client to a server, | |
1040 | .Dq host.example.com . | |
1041 | The SSHFP resource records should first be added to the zonefile for | |
1042 | host.example.com: | |
1043 | .Bd -literal -offset indent | |
9108f8d9 | 1044 | $ ssh-keygen -r host.example.com. |
2c06c99b | 1045 | .Ed |
1046 | .Pp | |
1047 | The output lines will have to be added to the zonefile. | |
1048 | To check that the zone is answering fingerprint queries: | |
1049 | .Pp | |
1050 | .Dl $ dig -t SSHFP host.example.com | |
1051 | .Pp | |
1052 | Finally the client connects: | |
1053 | .Bd -literal -offset indent | |
1054 | $ ssh -o "VerifyHostKeyDNS ask" host.example.com | |
1055 | [...] | |
1056 | Matching host key fingerprint found in DNS. | |
1057 | Are you sure you want to continue connecting (yes/no)? | |
1058 | .Ed | |
1059 | .Pp | |
1060 | See the | |
1061 | .Cm VerifyHostKeyDNS | |
1062 | option in | |
1063 | .Xr ssh_config 5 | |
1064 | for more information. | |
1065 | .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS | |
1066 | .Nm | |
1067 | contains support for Virtual Private Network (VPN) tunnelling | |
1068 | using the | |
1069 | .Xr tun 4 | |
1070 | network pseudo-device, | |
1071 | allowing two networks to be joined securely. | |
1072 | The | |
1073 | .Xr sshd_config 5 | |
1074 | configuration option | |
1075 | .Cm PermitTunnel | |
1076 | controls whether the server supports this, | |
1077 | and at what level (layer 2 or 3 traffic). | |
1078 | .Pp | |
1079 | The following example would connect client network 10.0.50.0/24 | |
1080 | with remote network 10.0.99.0/24, provided that the SSH server | |
1081 | running on the gateway to the remote network, | |
1082 | at 192.168.1.15, allows it: | |
1083 | .Bd -literal -offset indent | |
1084 | # ssh -f -w 0:1 192.168.1.15 true | |
1085 | # ifconfig tun0 10.0.50.1 10.0.99.1 netmask 255.255.255.252 | |
1086 | .Ed | |
1087 | .Pp | |
1088 | Client access may be more finely tuned via the | |
1089 | .Pa /root/.ssh/authorized_keys | |
1090 | file (see below) and the | |
1091 | .Cm PermitRootLogin | |
1092 | server option. | |
9108f8d9 | 1093 | The following entry would permit connections on |
2c06c99b | 1094 | .Xr tun 4 |
9108f8d9 | 1095 | device 1 from user |
2c06c99b | 1096 | .Dq jane |
9108f8d9 | 1097 | and on tun device 2 from user |
2c06c99b | 1098 | .Dq john , |
1099 | if | |
1100 | .Cm PermitRootLogin | |
1101 | is set to | |
1102 | .Dq forced-commands-only : | |
1103 | .Bd -literal -offset 2n | |
1104 | tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane | |
9108f8d9 | 1105 | tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john |
2c06c99b | 1106 | .Ed |
1107 | .Pp | |
1108 | Since a SSH-based setup entails a fair amount of overhead, | |
1109 | it may be more suited to temporary setups, | |
1110 | such as for wireless VPNs. | |
1111 | More permanent VPNs are better provided by tools such as | |
1112 | .Xr ipsecctl 8 | |
1113 | and | |
1114 | .Xr isakmpd 8 . | |
3c0ef626 | 1115 | .Sh ENVIRONMENT |
1116 | .Nm | |
1117 | will normally set the following environment variables: | |
2c06c99b | 1118 | .Bl -tag -width "SSH_ORIGINAL_COMMAND" |
3c0ef626 | 1119 | .It Ev DISPLAY |
1120 | The | |
1121 | .Ev DISPLAY | |
1122 | variable indicates the location of the X11 server. | |
1123 | It is automatically set by | |
1124 | .Nm | |
1125 | to point to a value of the form | |
2c06c99b | 1126 | .Dq hostname:n , |
1127 | where | |
1128 | .Dq hostname | |
1129 | indicates the host where the shell runs, and | |
1130 | .Sq n | |
1131 | is an integer \*(Ge 1. | |
3c0ef626 | 1132 | .Nm |
1133 | uses this special value to forward X11 connections over the secure | |
1134 | channel. | |
1135 | The user should normally not set | |
1136 | .Ev DISPLAY | |
1137 | explicitly, as that | |
1138 | will render the X11 connection insecure (and will require the user to | |
1139 | manually copy any required authorization cookies). | |
1140 | .It Ev HOME | |
1141 | Set to the path of the user's home directory. | |
1142 | .It Ev LOGNAME | |
1143 | Synonym for | |
1144 | .Ev USER ; | |
1145 | set for compatibility with systems that use this variable. | |
1146 | .It Ev MAIL | |
1147 | Set to the path of the user's mailbox. | |
1148 | .It Ev PATH | |
1149 | Set to the default | |
1150 | .Ev PATH , | |
1151 | as specified when compiling | |
2c06c99b | 1152 | .Nm . |
3c0ef626 | 1153 | .It Ev SSH_ASKPASS |
1154 | If | |
1155 | .Nm | |
1156 | needs a passphrase, it will read the passphrase from the current | |
1157 | terminal if it was run from a terminal. | |
1158 | If | |
1159 | .Nm | |
1160 | does not have a terminal associated with it but | |
1161 | .Ev DISPLAY | |
1162 | and | |
1163 | .Ev SSH_ASKPASS | |
1164 | are set, it will execute the program specified by | |
1165 | .Ev SSH_ASKPASS | |
1166 | and open an X11 window to read the passphrase. | |
1167 | This is particularly useful when calling | |
1168 | .Nm | |
1169 | from a | |
996d5e62 | 1170 | .Pa .xsession |
3c0ef626 | 1171 | or related script. |
1172 | (Note that on some machines it | |
1173 | may be necessary to redirect the input from | |
1174 | .Pa /dev/null | |
1175 | to make this work.) | |
1176 | .It Ev SSH_AUTH_SOCK | |
2c06c99b | 1177 | Identifies the path of a |
1178 | .Ux Ns -domain | |
1179 | socket used to communicate with the agent. | |
41b2f314 | 1180 | .It Ev SSH_CONNECTION |
1181 | Identifies the client and server ends of the connection. | |
3c0ef626 | 1182 | The variable contains |
2c06c99b | 1183 | four space-separated values: client IP address, client port number, |
1184 | server IP address, and server port number. | |
3c0ef626 | 1185 | .It Ev SSH_ORIGINAL_COMMAND |
2c06c99b | 1186 | This variable contains the original command line if a forced command |
3c0ef626 | 1187 | is executed. |
1188 | It can be used to extract the original arguments. | |
1189 | .It Ev SSH_TTY | |
1190 | This is set to the name of the tty (path to the device) associated | |
1191 | with the current shell or command. | |
1192 | If the current session has no tty, | |
1193 | this variable is not set. | |
1194 | .It Ev TZ | |
2c06c99b | 1195 | This variable is set to indicate the present time zone if it |
9108f8d9 | 1196 | was set when the daemon was started (i.e. the daemon passes the value |
3c0ef626 | 1197 | on to new connections). |
1198 | .It Ev USER | |
1199 | Set to the name of the user logging in. | |
1200 | .El | |
1201 | .Pp | |
1202 | Additionally, | |
1203 | .Nm | |
1204 | reads | |
665a873d | 1205 | .Pa ~/.ssh/environment , |
3c0ef626 | 1206 | and adds lines of the format |
1207 | .Dq VARNAME=value | |
2c06c99b | 1208 | to the environment if the file exists and users are allowed to |
41b2f314 | 1209 | change their environment. |
cdd66111 | 1210 | For more information, see the |
41b2f314 | 1211 | .Cm PermitUserEnvironment |
1212 | option in | |
1213 | .Xr sshd_config 5 . | |
3c0ef626 | 1214 | .Sh FILES |
2c06c99b | 1215 | .Bl -tag -width Ds -compact |
1216 | .It ~/.rhosts | |
1217 | This file is used for host-based authentication (see above). | |
1218 | On some machines this file may need to be | |
1219 | world-readable if the user's home directory is on an NFS partition, | |
1220 | because | |
1221 | .Xr sshd 8 | |
1222 | reads it as root. | |
1223 | Additionally, this file must be owned by the user, | |
1224 | and must not have write permissions for anyone else. | |
1225 | The recommended | |
1226 | permission for most machines is read/write for the user, and not | |
1227 | accessible by others. | |
1228 | .Pp | |
1229 | .It ~/.shosts | |
1230 | This file is used in exactly the same way as | |
1231 | .Pa .rhosts , | |
1232 | but allows host-based authentication without permitting login with | |
1233 | rlogin/rsh. | |
1234 | .Pp | |
1235 | .It ~/.ssh/authorized_keys | |
1236 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. | |
1237 | The format of this file is described in the | |
1238 | .Xr sshd 8 | |
1239 | manual page. | |
1240 | This file is not highly sensitive, but the recommended | |
1241 | permissions are read/write for the user, and not accessible by others. | |
1242 | .Pp | |
1243 | .It ~/.ssh/config | |
1244 | This is the per-user configuration file. | |
1245 | The file format and configuration options are described in | |
1246 | .Xr ssh_config 5 . | |
1247 | Because of the potential for abuse, this file must have strict permissions: | |
1248 | read/write for the user, and not accessible by others. | |
1249 | .Pp | |
1250 | .It ~/.ssh/environment | |
1251 | Contains additional definitions for environment variables; see | |
1252 | .Sx ENVIRONMENT , | |
1253 | above. | |
1254 | .Pp | |
1255 | .It ~/.ssh/identity | |
1256 | .It ~/.ssh/id_dsa | |
1257 | .It ~/.ssh/id_rsa | |
1258 | Contains the private key for authentication. | |
3c0ef626 | 1259 | These files |
1260 | contain sensitive data and should be readable by the user but not | |
1261 | accessible by others (read/write/execute). | |
3c0ef626 | 1262 | .Nm |
2c06c99b | 1263 | will simply ignore a private key file if it is accessible by others. |
3c0ef626 | 1264 | It is possible to specify a passphrase when |
2c06c99b | 1265 | generating the key which will be used to encrypt the |
3c0ef626 | 1266 | sensitive part of this file using 3DES. |
2c06c99b | 1267 | .Pp |
1268 | .It ~/.ssh/identity.pub | |
1269 | .It ~/.ssh/id_dsa.pub | |
1270 | .It ~/.ssh/id_rsa.pub | |
1271 | Contains the public key for authentication. | |
3c0ef626 | 1272 | These files are not |
1273 | sensitive and can (but need not) be readable by anyone. | |
3c0ef626 | 1274 | .Pp |
2c06c99b | 1275 | .It ~/.ssh/known_hosts |
1276 | Contains a list of host keys for all hosts the user has logged into | |
1277 | that are not already in the systemwide list of known host keys. | |
1278 | See | |
3c0ef626 | 1279 | .Xr sshd 8 |
2c06c99b | 1280 | for further details of the format of this file. |
1281 | .Pp | |
1282 | .It ~/.ssh/rc | |
1283 | Commands in this file are executed by | |
3c0ef626 | 1284 | .Nm |
2c06c99b | 1285 | when the user logs in, just before the user's shell (or command) is |
1286 | started. | |
1287 | See the | |
1288 | .Xr sshd 8 | |
1289 | manual page for more information. | |
1290 | .Pp | |
1291 | .It /etc/hosts.equiv | |
1292 | This file is for host-based authentication (see above). | |
1293 | It should only be writable by root. | |
1294 | .Pp | |
1295 | .It /etc/shosts.equiv | |
1296 | This file is used in exactly the same way as | |
1297 | .Pa hosts.equiv , | |
1298 | but allows host-based authentication without permitting login with | |
1299 | rlogin/rsh. | |
1300 | .Pp | |
e9a17296 | 1301 | .It Pa /etc/ssh/ssh_config |
3c0ef626 | 1302 | Systemwide configuration file. |
f5799ae1 | 1303 | The file format and configuration options are described in |
1304 | .Xr ssh_config 5 . | |
2c06c99b | 1305 | .Pp |
1306 | .It /etc/ssh/ssh_host_key | |
1307 | .It /etc/ssh/ssh_host_dsa_key | |
1308 | .It /etc/ssh/ssh_host_rsa_key | |
3c0ef626 | 1309 | These three files contain the private parts of the host keys |
2c06c99b | 1310 | and are used for host-based authentication. |
1311 | If protocol version 1 is used, | |
f5799ae1 | 1312 | .Nm |
1313 | must be setuid root, since the host key is readable only by root. | |
1314 | For protocol version 2, | |
1315 | .Nm | |
1316 | uses | |
1317 | .Xr ssh-keysign 8 | |
2c06c99b | 1318 | to access the host keys, |
1319 | eliminating the requirement that | |
f5799ae1 | 1320 | .Nm |
2c06c99b | 1321 | be setuid root when host-based authentication is used. |
f5799ae1 | 1322 | By default |
3c0ef626 | 1323 | .Nm |
f5799ae1 | 1324 | is not setuid root. |
3c0ef626 | 1325 | .Pp |
2c06c99b | 1326 | .It /etc/ssh/ssh_known_hosts |
1327 | Systemwide list of known host keys. | |
1328 | This file should be prepared by the | |
1329 | system administrator to contain the public host keys of all machines in the | |
1330 | organization. | |
1331 | It should be world-readable. | |
1332 | See | |
3c0ef626 | 1333 | .Xr sshd 8 |
2c06c99b | 1334 | for further details of the format of this file. |
1335 | .Pp | |
1336 | .It /etc/ssh/sshrc | |
3c0ef626 | 1337 | Commands in this file are executed by |
1338 | .Nm | |
2c06c99b | 1339 | when the user logs in, just before the user's shell (or command) is started. |
3c0ef626 | 1340 | See the |
1341 | .Xr sshd 8 | |
1342 | manual page for more information. | |
3c0ef626 | 1343 | .El |
3c0ef626 | 1344 | .Sh SEE ALSO |
3c0ef626 | 1345 | .Xr scp 1 , |
1346 | .Xr sftp 1 , | |
1347 | .Xr ssh-add 1 , | |
1348 | .Xr ssh-agent 1 , | |
1349 | .Xr ssh-keygen 1 , | |
2c06c99b | 1350 | .Xr ssh-keyscan 1 , |
1351 | .Xr tun 4 , | |
cdd66111 | 1352 | .Xr hosts.equiv 5 , |
680cee3b | 1353 | .Xr ssh_config 5 , |
1354 | .Xr ssh-keysign 8 , | |
3c0ef626 | 1355 | .Xr sshd 8 |
1356 | .Rs | |
9108f8d9 | 1357 | .%R RFC 4250 |
1358 | .%T "The Secure Shell (SSH) Protocol Assigned Numbers" | |
1359 | .%D 2006 | |
1360 | .Re | |
1361 | .Rs | |
1362 | .%R RFC 4251 | |
1363 | .%T "The Secure Shell (SSH) Protocol Architecture" | |
1364 | .%D 2006 | |
1365 | .Re | |
1366 | .Rs | |
1367 | .%R RFC 4252 | |
1368 | .%T "The Secure Shell (SSH) Authentication Protocol" | |
1369 | .%D 2006 | |
1370 | .Re | |
1371 | .Rs | |
1372 | .%R RFC 4253 | |
1373 | .%T "The Secure Shell (SSH) Transport Layer Protocol" | |
1374 | .%D 2006 | |
1375 | .Re | |
1376 | .Rs | |
1377 | .%R RFC 4254 | |
1378 | .%T "The Secure Shell (SSH) Connection Protocol" | |
1379 | .%D 2006 | |
1380 | .Re | |
1381 | .Rs | |
1382 | .%R RFC 4255 | |
1383 | .%T "Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints" | |
1384 | .%D 2006 | |
1385 | .Re | |
1386 | .Rs | |
1387 | .%R RFC 4256 | |
1388 | .%T "Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)" | |
1389 | .%D 2006 | |
1390 | .Re | |
1391 | .Rs | |
1392 | .%R RFC 4335 | |
1393 | .%T "The Secure Shell (SSH) Session Channel Break Extension" | |
1394 | .%D 2006 | |
1395 | .Re | |
1396 | .Rs | |
1397 | .%R RFC 4344 | |
1398 | .%T "The Secure Shell (SSH) Transport Layer Encryption Modes" | |
1399 | .%D 2006 | |
1400 | .Re | |
1401 | .Rs | |
1402 | .%R RFC 4345 | |
1403 | .%T "Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol" | |
1404 | .%D 2006 | |
1405 | .Re | |
1406 | .Rs | |
1407 | .%R RFC 4419 | |
1408 | .%T "Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol" | |
1409 | .%D 2006 | |
3c0ef626 | 1410 | .Re |
0fff78ff | 1411 | .Sh AUTHORS |
1412 | OpenSSH is a derivative of the original and free | |
1413 | ssh 1.2.12 release by Tatu Ylonen. | |
1414 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1415 | Theo de Raadt and Dug Song | |
1416 | removed many bugs, re-added newer features and | |
1417 | created OpenSSH. | |
1418 | Markus Friedl contributed the support for SSH | |
1419 | protocol versions 1.5 and 2.0. |