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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 | .\" | |
08822d99 | 37 | .\" $OpenBSD: ssh.1,v 1.253 2006/01/30 13:37:49 jmc 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 | |
7e82606e | 46 | .Op Fl 1246AaCfgkMNnqsTtVvXxY |
3c0ef626 | 47 | .Op Fl b Ar bind_address |
48 | .Op Fl c Ar cipher_spec | |
08822d99 | 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 |
3c0ef626 | 56 | .Op Fl F Ar configfile |
08822d99 | 57 | .Bk -words |
540d72c3 | 58 | .Op Fl i Ar identity_file |
08822d99 | 59 | .Ek |
dfddba3d | 60 | .Oo Fl L\ \& |
3c0ef626 | 61 | .Sm off |
dfddba3d | 62 | .Oo Ar bind_address : Oc |
63 | .Ar port : host : hostport | |
3c0ef626 | 64 | .Sm on |
3c0ef626 | 65 | .Oc |
08822d99 | 66 | .Bk -words |
540d72c3 | 67 | .Op Fl l Ar login_name |
08822d99 | 68 | .Ek |
540d72c3 | 69 | .Op Fl m Ar mac_spec |
dfddba3d | 70 | .Op Fl O Ar ctl_cmd |
540d72c3 | 71 | .Op Fl o Ar option |
540d72c3 | 72 | .Op Fl p Ar port |
dfddba3d | 73 | .Oo Fl R\ \& |
3c0ef626 | 74 | .Sm off |
dfddba3d | 75 | .Oo Ar bind_address : Oc |
76 | .Ar port : host : hostport | |
3c0ef626 | 77 | .Sm on |
3c0ef626 | 78 | .Oc |
dfddba3d | 79 | .Op Fl S Ar ctl_path |
08822d99 | 80 | .Bk -words |
81 | .Op Fl w Ar tunnel : Ns Ar tunnel | |
540d72c3 | 82 | .Oo Ar user Ns @ Oc Ns Ar hostname |
3c0ef626 | 83 | .Op Ar command |
dfddba3d | 84 | .Ek |
3c0ef626 | 85 | .Sh DESCRIPTION |
86 | .Nm | |
87 | (SSH client) is a program for logging into a remote machine and for | |
88 | executing commands on a remote machine. | |
540d72c3 | 89 | It is intended to replace rlogin and rsh, |
90 | and provide secure encrypted communications between | |
3c0ef626 | 91 | two untrusted hosts over an insecure network. |
08822d99 | 92 | X11 connections and arbitrary TCP ports |
540d72c3 | 93 | can also be forwarded over the secure channel. |
3c0ef626 | 94 | .Pp |
95 | .Nm | |
96 | connects and logs into the specified | |
540d72c3 | 97 | .Ar hostname |
98 | (with optional | |
99 | .Ar user | |
100 | name). | |
3c0ef626 | 101 | The user must prove |
102 | his/her identity to the remote machine using one of several methods | |
08822d99 | 103 | depending on the protocol version used (see below). |
3c0ef626 | 104 | .Pp |
540d72c3 | 105 | If |
106 | .Ar command | |
107 | is specified, | |
08822d99 | 108 | it is executed on the remote host instead of a login shell. |
7e82606e | 109 | .Pp |
3c0ef626 | 110 | The options are as follows: |
111 | .Bl -tag -width Ds | |
540d72c3 | 112 | .It Fl 1 |
113 | Forces | |
114 | .Nm | |
115 | to try protocol version 1 only. | |
116 | .It Fl 2 | |
117 | Forces | |
118 | .Nm | |
119 | to try protocol version 2 only. | |
120 | .It Fl 4 | |
121 | Forces | |
122 | .Nm | |
123 | to use IPv4 addresses only. | |
124 | .It Fl 6 | |
125 | Forces | |
126 | .Nm | |
127 | to use IPv6 addresses only. | |
3c0ef626 | 128 | .It Fl A |
129 | Enables forwarding of the authentication agent connection. | |
130 | This can also be specified on a per-host basis in a configuration file. | |
d03f4262 | 131 | .Pp |
bfe49944 | 132 | Agent forwarding should be enabled with caution. |
133 | Users with the ability to bypass file permissions on the remote host | |
134 | (for the agent's Unix-domain socket) | |
135 | can access the local agent through the forwarded connection. | |
136 | An attacker cannot obtain key material from the agent, | |
d03f4262 | 137 | however they can perform operations on the keys that enable them to |
138 | authenticate using the identities loaded into the agent. | |
540d72c3 | 139 | .It Fl a |
140 | Disables forwarding of the authentication agent connection. | |
3c0ef626 | 141 | .It Fl b Ar bind_address |
2ce0bfe4 | 142 | Use |
143 | .Ar bind_address | |
144 | on the local machine as the source address | |
145 | of the connection. | |
146 | Only useful on systems with more than one address. | |
540d72c3 | 147 | .It Fl C |
148 | Requests compression of all data (including stdin, stdout, stderr, and | |
08822d99 | 149 | data for forwarded X11 and TCP connections). |
540d72c3 | 150 | The compression algorithm is the same used by |
151 | .Xr gzip 1 , | |
152 | and the | |
153 | .Dq level | |
154 | can be controlled by the | |
155 | .Cm CompressionLevel | |
156 | option for protocol version 1. | |
157 | Compression is desirable on modem lines and other | |
158 | slow connections, but will only slow down things on fast networks. | |
159 | The default value can be set on a host-by-host basis in the | |
160 | configuration files; see the | |
161 | .Cm Compression | |
162 | option. | |
7e82606e | 163 | .It Fl c Ar cipher_spec |
164 | Selects the cipher specification for encrypting the session. | |
165 | .Pp | |
166 | Protocol version 1 allows specification of a single cipher. | |
08822d99 | 167 | The supported values are |
7e82606e | 168 | .Dq 3des , |
08822d99 | 169 | .Dq blowfish , |
7e82606e | 170 | and |
171 | .Dq des . | |
3c0ef626 | 172 | .Ar 3des |
173 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
7e82606e | 174 | It is believed to be secure. |
3c0ef626 | 175 | .Ar blowfish |
540d72c3 | 176 | is a fast block cipher; it appears very secure and is much faster than |
3c0ef626 | 177 | .Ar 3des . |
178 | .Ar des | |
179 | is only supported in the | |
180 | .Nm | |
181 | client for interoperability with legacy protocol 1 implementations | |
182 | that do not support the | |
183 | .Ar 3des | |
bfe49944 | 184 | cipher. |
185 | Its use is strongly discouraged due to cryptographic weaknesses. | |
7e82606e | 186 | The default is |
187 | .Dq 3des . | |
188 | .Pp | |
08822d99 | 189 | For protocol version 2, |
7e82606e | 190 | .Ar cipher_spec |
191 | is a comma-separated list of ciphers | |
192 | listed in order of preference. | |
08822d99 | 193 | The supported ciphers are: |
194 | 3des-cbc, | |
195 | aes128-cbc, | |
196 | aes192-cbc, | |
197 | aes256-cbc, | |
198 | aes128-ctr, | |
199 | aes192-ctr, | |
200 | aes256-ctr, | |
201 | arcfour128, | |
202 | arcfour256, | |
203 | arcfour, | |
204 | blowfish-cbc, | |
7e82606e | 205 | and |
08822d99 | 206 | cast128-cbc. |
207 | The default is: | |
208 | .Bd -literal -offset indent | |
209 | aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, | |
210 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
211 | aes192-ctr,aes256-ctr | |
7e82606e | 212 | .Ed |
08822d99 | 213 | .It Fl D Xo |
214 | .Sm off | |
215 | .Oo Ar bind_address : Oc | |
216 | .Ar port | |
217 | .Sm on | |
218 | .Xc | |
540d72c3 | 219 | Specifies a local |
220 | .Dq dynamic | |
221 | application-level port forwarding. | |
222 | This works by allocating a socket to listen to | |
223 | .Ar port | |
08822d99 | 224 | on the local side, optionally bound to the specified |
225 | .Ar bind_address . | |
226 | Whenever a connection is made to this port, the | |
540d72c3 | 227 | connection is forwarded over the secure channel, and the application |
228 | protocol is then used to determine where to connect to from the | |
229 | remote machine. | |
230 | Currently the SOCKS4 and SOCKS5 protocols are supported, and | |
231 | .Nm | |
232 | will act as a SOCKS server. | |
233 | Only root can forward privileged ports. | |
234 | Dynamic port forwardings can also be specified in the configuration file. | |
08822d99 | 235 | .Pp |
236 | IPv6 addresses can be specified with an alternative syntax: | |
237 | .Sm off | |
238 | .Xo | |
239 | .Op Ar bind_address No / | |
240 | .Ar port | |
241 | .Xc | |
242 | .Sm on | |
243 | or by enclosing the address in square brackets. | |
244 | Only the superuser can forward privileged ports. | |
245 | By default, the local port is bound in accordance with the | |
246 | .Cm GatewayPorts | |
247 | setting. | |
248 | However, an explicit | |
249 | .Ar bind_address | |
250 | may be used to bind the connection to a specific address. | |
251 | The | |
252 | .Ar bind_address | |
253 | of | |
254 | .Dq localhost | |
255 | indicates that the listening port be bound for local use only, while an | |
256 | empty address or | |
257 | .Sq * | |
258 | indicates that the port should be available from all interfaces. | |
259 | .It Fl e Ar escape_char | |
3c0ef626 | 260 | Sets the escape character for sessions with a pty (default: |
261 | .Ql ~ ) . | |
262 | The escape character is only recognized at the beginning of a line. | |
263 | The escape character followed by a dot | |
264 | .Pq Ql \&. | |
540d72c3 | 265 | closes the connection; |
266 | followed by control-Z suspends the connection; | |
267 | and followed by itself sends the escape character once. | |
3c0ef626 | 268 | Setting the character to |
269 | .Dq none | |
270 | disables any escapes and makes the session fully transparent. | |
540d72c3 | 271 | .It Fl F Ar configfile |
272 | Specifies an alternative per-user configuration file. | |
273 | If a configuration file is given on the command line, | |
274 | the system-wide configuration file | |
275 | .Pq Pa /etc/ssh/ssh_config | |
276 | will be ignored. | |
277 | The default for the per-user configuration file is | |
2ce0bfe4 | 278 | .Pa ~/.ssh/config . |
3c0ef626 | 279 | .It Fl f |
280 | Requests | |
281 | .Nm | |
282 | to go to background just before command execution. | |
283 | This is useful if | |
284 | .Nm | |
285 | is going to ask for passwords or passphrases, but the user | |
286 | wants it in the background. | |
287 | This implies | |
288 | .Fl n . | |
289 | The recommended way to start X11 programs at a remote site is with | |
290 | something like | |
291 | .Ic ssh -f host xterm . | |
292 | .It Fl g | |
293 | Allows remote hosts to connect to local forwarded ports. | |
540d72c3 | 294 | .It Fl I Ar smartcard_device |
08822d99 | 295 | Specify the device |
540d72c3 | 296 | .Nm |
297 | should use to communicate with a smartcard used for storing the user's | |
298 | private RSA key. | |
08822d99 | 299 | This option is only available if support for smartcard devices |
300 | is compiled in (default is no support). | |
3c0ef626 | 301 | .It Fl i Ar identity_file |
db32a221 | 302 | Selects a file from which the identity (private key) for |
3c0ef626 | 303 | RSA or DSA authentication is read. |
db32a221 | 304 | The default is |
2ce0bfe4 | 305 | .Pa ~/.ssh/identity |
db32a221 | 306 | for protocol version 1, and |
2ce0bfe4 | 307 | .Pa ~/.ssh/id_rsa |
db32a221 | 308 | and |
2ce0bfe4 | 309 | .Pa ~/.ssh/id_dsa |
db32a221 | 310 | for protocol version 2. |
3c0ef626 | 311 | Identity files may also be specified on |
312 | a per-host basis in the configuration file. | |
313 | It is possible to have multiple | |
314 | .Fl i | |
315 | options (and multiple identities specified in | |
316 | configuration files). | |
3c0ef626 | 317 | .It Fl k |
540d72c3 | 318 | Disables forwarding (delegation) of GSSAPI credentials to the server. |
319 | .It Fl L Xo | |
320 | .Sm off | |
dfddba3d | 321 | .Oo Ar bind_address : Oc |
540d72c3 | 322 | .Ar port : host : hostport |
323 | .Sm on | |
324 | .Xc | |
325 | Specifies that the given port on the local (client) host is to be | |
326 | forwarded to the given host and port on the remote side. | |
327 | This works by allocating a socket to listen to | |
328 | .Ar port | |
dfddba3d | 329 | on the local side, optionally bound to the specified |
330 | .Ar bind_address . | |
331 | Whenever a connection is made to this port, the | |
540d72c3 | 332 | connection is forwarded over the secure channel, and a connection is |
333 | made to | |
334 | .Ar host | |
335 | port | |
336 | .Ar hostport | |
337 | from the remote machine. | |
338 | Port forwardings can also be specified in the configuration file. | |
540d72c3 | 339 | IPv6 addresses can be specified with an alternative syntax: |
340 | .Sm off | |
341 | .Xo | |
dfddba3d | 342 | .Op Ar bind_address No / |
540d72c3 | 343 | .Ar port No / Ar host No / |
dfddba3d | 344 | .Ar hostport |
540d72c3 | 345 | .Xc |
346 | .Sm on | |
dfddba3d | 347 | or by enclosing the address in square brackets. |
348 | Only the superuser can forward privileged ports. | |
349 | By default, the local port is bound in accordance with the | |
350 | .Cm GatewayPorts | |
351 | setting. | |
352 | However, an explicit | |
353 | .Ar bind_address | |
354 | may be used to bind the connection to a specific address. | |
355 | The | |
356 | .Ar bind_address | |
357 | of | |
358 | .Dq localhost | |
359 | indicates that the listening port be bound for local use only, while an | |
360 | empty address or | |
361 | .Sq * | |
362 | indicates that the port should be available from all interfaces. | |
3c0ef626 | 363 | .It Fl l Ar login_name |
364 | Specifies the user to log in as on the remote machine. | |
365 | This also may be specified on a per-host basis in the configuration file. | |
7e82606e | 366 | .It Fl M |
367 | Places the | |
368 | .Nm | |
369 | client into | |
370 | .Dq master | |
371 | mode for connection sharing. | |
08822d99 | 372 | Multiple |
373 | .Fl M | |
374 | options places | |
375 | .Nm | |
376 | into | |
377 | .Dq master | |
378 | mode with confirmation required before slave connections are accepted. | |
7e82606e | 379 | Refer to the description of |
380 | .Cm ControlMaster | |
381 | in | |
382 | .Xr ssh_config 5 | |
383 | for details. | |
3c0ef626 | 384 | .It Fl m Ar mac_spec |
385 | Additionally, for protocol version 2 a comma-separated list of MAC | |
386 | (message authentication code) algorithms can | |
387 | be specified in order of preference. | |
388 | See the | |
389 | .Cm MACs | |
390 | keyword for more information. | |
540d72c3 | 391 | .It Fl N |
392 | Do not execute a remote command. | |
393 | This is useful for just forwarding ports | |
394 | (protocol version 2 only). | |
3c0ef626 | 395 | .It Fl n |
396 | Redirects stdin from | |
397 | .Pa /dev/null | |
398 | (actually, prevents reading from stdin). | |
399 | This must be used when | |
400 | .Nm | |
401 | is run in the background. | |
402 | A common trick is to use this to run X11 programs on a remote machine. | |
403 | For example, | |
404 | .Ic ssh -n shadows.cs.hut.fi emacs & | |
405 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
406 | connection will be automatically forwarded over an encrypted channel. | |
407 | The | |
408 | .Nm | |
409 | program will be put in the background. | |
410 | (This does not work if | |
411 | .Nm | |
412 | needs to ask for a password or passphrase; see also the | |
413 | .Fl f | |
414 | option.) | |
dfddba3d | 415 | .It Fl O Ar ctl_cmd |
416 | Control an active connection multiplexing master process. | |
417 | When the | |
418 | .Fl O | |
419 | option is specified, the | |
420 | .Ar ctl_cmd | |
421 | argument is interpreted and passed to the master process. | |
422 | Valid commands are: | |
423 | .Dq check | |
424 | (check that the master process is running) and | |
425 | .Dq exit | |
426 | (request the master to exit). | |
3c0ef626 | 427 | .It Fl o Ar option |
428 | Can be used to give options in the format used in the configuration file. | |
429 | This is useful for specifying options for which there is no separate | |
430 | command-line flag. | |
540d72c3 | 431 | For full details of the options listed below, and their possible values, see |
432 | .Xr ssh_config 5 . | |
433 | .Pp | |
434 | .Bl -tag -width Ds -offset indent -compact | |
435 | .It AddressFamily | |
436 | .It BatchMode | |
437 | .It BindAddress | |
438 | .It ChallengeResponseAuthentication | |
439 | .It CheckHostIP | |
440 | .It Cipher | |
441 | .It Ciphers | |
442 | .It ClearAllForwardings | |
443 | .It Compression | |
444 | .It CompressionLevel | |
445 | .It ConnectionAttempts | |
7e82606e | 446 | .It ConnectTimeout |
447 | .It ControlMaster | |
448 | .It ControlPath | |
540d72c3 | 449 | .It DynamicForward |
450 | .It EscapeChar | |
451 | .It ForwardAgent | |
452 | .It ForwardX11 | |
453 | .It ForwardX11Trusted | |
454 | .It GatewayPorts | |
455 | .It GlobalKnownHostsFile | |
456 | .It GSSAPIAuthentication | |
457 | .It GSSAPIDelegateCredentials | |
dfddba3d | 458 | .It HashKnownHosts |
540d72c3 | 459 | .It Host |
460 | .It HostbasedAuthentication | |
461 | .It HostKeyAlgorithms | |
462 | .It HostKeyAlias | |
463 | .It HostName | |
464 | .It IdentityFile | |
12a403af | 465 | .It IdentitiesOnly |
dfddba3d | 466 | .It KbdInteractiveDevices |
08822d99 | 467 | .It LocalCommand |
540d72c3 | 468 | .It LocalForward |
469 | .It LogLevel | |
470 | .It MACs | |
471 | .It NoHostAuthenticationForLocalhost | |
472 | .It NumberOfPasswordPrompts | |
473 | .It PasswordAuthentication | |
08822d99 | 474 | .It PermitLocalCommand |
540d72c3 | 475 | .It Port |
476 | .It PreferredAuthentications | |
477 | .It Protocol | |
478 | .It ProxyCommand | |
479 | .It PubkeyAuthentication | |
08822d99 | 480 | .It RekeyLimit |
540d72c3 | 481 | .It RemoteForward |
482 | .It RhostsRSAAuthentication | |
483 | .It RSAAuthentication | |
7e82606e | 484 | .It SendEnv |
540d72c3 | 485 | .It ServerAliveInterval |
486 | .It ServerAliveCountMax | |
487 | .It SmartcardDevice | |
488 | .It StrictHostKeyChecking | |
489 | .It TCPKeepAlive | |
08822d99 | 490 | .It Tunnel |
491 | .It TunnelDevice | |
540d72c3 | 492 | .It UsePrivilegedPort |
493 | .It User | |
494 | .It UserKnownHostsFile | |
495 | .It VerifyHostKeyDNS | |
496 | .It XAuthLocation | |
497 | .El | |
3c0ef626 | 498 | .It Fl p Ar port |
499 | Port to connect to on the remote host. | |
500 | This can be specified on a | |
501 | per-host basis in the configuration file. | |
3c0ef626 | 502 | .It Fl q |
503 | Quiet mode. | |
504 | Causes all warning and diagnostic messages to be suppressed. | |
540d72c3 | 505 | .It Fl R Xo |
506 | .Sm off | |
dfddba3d | 507 | .Oo Ar bind_address : Oc |
540d72c3 | 508 | .Ar port : host : hostport |
509 | .Sm on | |
510 | .Xc | |
511 | Specifies that the given port on the remote (server) host is to be | |
512 | forwarded to the given host and port on the local side. | |
513 | This works by allocating a socket to listen to | |
514 | .Ar port | |
515 | on the remote side, and whenever a connection is made to this port, the | |
516 | connection is forwarded over the secure channel, and a connection is | |
517 | made to | |
518 | .Ar host | |
519 | port | |
520 | .Ar hostport | |
521 | from the local machine. | |
dfddba3d | 522 | .Pp |
540d72c3 | 523 | Port forwardings can also be specified in the configuration file. |
524 | Privileged ports can be forwarded only when | |
525 | logging in as root on the remote machine. | |
dfddba3d | 526 | IPv6 addresses can be specified by enclosing the address in square braces or |
527 | using an alternative syntax: | |
540d72c3 | 528 | .Sm off |
529 | .Xo | |
dfddba3d | 530 | .Op Ar bind_address No / |
531 | .Ar host No / Ar port No / | |
532 | .Ar hostport | |
533 | .Xc . | |
540d72c3 | 534 | .Sm on |
dfddba3d | 535 | .Pp |
536 | By default, the listening socket on the server will be bound to the loopback | |
537 | interface only. | |
538 | This may be overriden by specifying a | |
539 | .Ar bind_address . | |
540 | An empty | |
541 | .Ar bind_address , | |
542 | or the address | |
543 | .Ql * , | |
544 | indicates that the remote socket should listen on all interfaces. | |
545 | Specifying a remote | |
546 | .Ar bind_address | |
547 | will only succeed if the server's | |
548 | .Cm GatewayPorts | |
549 | option is enabled (see | |
550 | .Xr sshd_config 5 ) . | |
551 | .It Fl S Ar ctl_path | |
7e82606e | 552 | Specifies the location of a control socket for connection sharing. |
553 | Refer to the description of | |
554 | .Cm ControlPath | |
555 | and | |
556 | .Cm ControlMaster | |
557 | in | |
558 | .Xr ssh_config 5 | |
559 | for details. | |
3c0ef626 | 560 | .It Fl s |
7cac2b65 | 561 | May be used to request invocation of a subsystem on the remote system. |
562 | Subsystems are a feature of the SSH2 protocol which facilitate the use | |
540d72c3 | 563 | of SSH as a secure transport for other applications (eg.\& |
564 | .Xr sftp 1 ) . | |
7cac2b65 | 565 | The subsystem is specified as the remote command. |
540d72c3 | 566 | .It Fl T |
567 | Disable pseudo-tty allocation. | |
3c0ef626 | 568 | .It Fl t |
569 | Force pseudo-tty allocation. | |
570 | This can be used to execute arbitrary | |
571 | screen-based programs on a remote machine, which can be very useful, | |
572 | e.g., when implementing menu services. | |
573 | Multiple | |
574 | .Fl t | |
575 | options force tty allocation, even if | |
576 | .Nm | |
577 | has no local tty. | |
540d72c3 | 578 | .It Fl V |
579 | Display the version number and exit. | |
3c0ef626 | 580 | .It Fl v |
581 | Verbose mode. | |
582 | Causes | |
583 | .Nm | |
584 | to print debugging messages about its progress. | |
585 | This is helpful in | |
586 | debugging connection, authentication, and configuration problems. | |
587 | Multiple | |
588 | .Fl v | |
7cac2b65 | 589 | options increase the verbosity. |
590 | The maximum is 3. | |
08822d99 | 591 | .It Fl w Ar tunnel : Ns Ar tunnel |
592 | Requests a | |
593 | .Xr tun 4 | |
594 | device on the client | |
595 | (first | |
596 | .Ar tunnel | |
597 | arg) | |
598 | and server | |
599 | (second | |
600 | .Ar tunnel | |
601 | arg). | |
602 | The devices may be specified by numerical ID or the keyword | |
603 | .Dq any , | |
604 | which uses the next available tunnel device. | |
605 | See also the | |
606 | .Cm Tunnel | |
607 | directive in | |
608 | .Xr ssh_config 5 . | |
3c0ef626 | 609 | .It Fl X |
610 | Enables X11 forwarding. | |
611 | This can also be specified on a per-host basis in a configuration file. | |
d03f4262 | 612 | .Pp |
bfe49944 | 613 | X11 forwarding should be enabled with caution. |
614 | Users with the ability to bypass file permissions on the remote host | |
615 | (for the user's X authorization database) | |
616 | can access the local X11 display through the forwarded connection. | |
617 | An attacker may then be able to perform activities such as keystroke monitoring. | |
dfddba3d | 618 | .Pp |
619 | For this reason, X11 forwarding is subjected to X11 SECURITY extension | |
620 | restrictions by default. | |
621 | Please refer to the | |
622 | .Nm | |
623 | .Fl Y | |
624 | option and the | |
625 | .Cm ForwardX11Trusted | |
626 | directive in | |
627 | .Xr ssh_config 5 | |
628 | for more information. | |
540d72c3 | 629 | .It Fl x |
630 | Disables X11 forwarding. | |
631 | .It Fl Y | |
632 | Enables trusted X11 forwarding. | |
dfddba3d | 633 | Trusted X11 forwardings are not subjected to the X11 SECURITY extension |
634 | controls. | |
3c0ef626 | 635 | .El |
08822d99 | 636 | .Pp |
3c0ef626 | 637 | .Nm |
44a053a3 | 638 | may additionally obtain configuration data from |
639 | a per-user configuration file and a system-wide configuration file. | |
640 | The file format and configuration options are described in | |
641 | .Xr ssh_config 5 . | |
08822d99 | 642 | .Pp |
643 | .Nm | |
644 | exits with the exit status of the remote command or with 255 | |
645 | if an error occurred. | |
646 | .Sh AUTHENTICATION | |
647 | The OpenSSH SSH client supports SSH protocols 1 and 2. | |
648 | Protocol 2 is the default, with | |
649 | .Nm | |
650 | falling back to protocol 1 if it detects protocol 2 is unsupported. | |
651 | These settings may be altered using the | |
652 | .Cm Protocol | |
653 | option in | |
654 | .Xr ssh_config 5 , | |
655 | or enforced using the | |
656 | .Fl 1 | |
657 | and | |
658 | .Fl 2 | |
659 | options (see above). | |
660 | Both protocols support similar authentication methods, | |
661 | but protocol 2 is preferred since | |
662 | it provides additional mechanisms for confidentiality | |
663 | (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour) | |
664 | and integrity (hmac-md5, hmac-sha1, hmac-ripemd160). | |
665 | Protocol 1 lacks a strong mechanism for ensuring the | |
666 | integrity of the connection. | |
667 | .Pp | |
668 | The methods available for authentication are: | |
669 | host-based authentication, | |
670 | public key authentication, | |
671 | challenge-response authentication, | |
672 | and password authentication. | |
673 | Authentication methods are tried in the order specified above, | |
674 | though protocol 2 has a configuration option to change the default order: | |
675 | .Cm PreferredAuthentications . | |
676 | .Pp | |
677 | Host-based authentication works as follows: | |
678 | If the machine the user logs in from is listed in | |
679 | .Pa /etc/hosts.equiv | |
680 | or | |
681 | .Pa /etc/shosts.equiv | |
682 | on the remote machine, and the user names are | |
683 | the same on both sides, or if the files | |
684 | .Pa ~/.rhosts | |
685 | or | |
686 | .Pa ~/.shosts | |
687 | exist in the user's home directory on the | |
688 | remote machine and contain a line containing the name of the client | |
689 | machine and the name of the user on that machine, the user is | |
690 | considered for login. | |
691 | Additionally, the server | |
692 | .Em must | |
693 | be able to verify the client's | |
694 | host key (see the description of | |
695 | .Pa /etc/ssh/ssh_known_hosts | |
696 | and | |
697 | .Pa ~/.ssh/known_hosts , | |
698 | below) | |
699 | for login to be permitted. | |
700 | This authentication method closes security holes due to IP | |
701 | spoofing, DNS spoofing, and routing spoofing. | |
702 | [Note to the administrator: | |
703 | .Pa /etc/hosts.equiv , | |
704 | .Pa ~/.rhosts , | |
705 | and the rlogin/rsh protocol in general, are inherently insecure and should be | |
706 | disabled if security is desired.] | |
707 | .Pp | |
708 | Public key authentication works as follows: | |
709 | The scheme is based on public-key cryptography, | |
710 | using cryptosystems | |
711 | where encryption and decryption are done using separate keys, | |
712 | and it is unfeasible to derive the decryption key from the encryption key. | |
713 | The idea is that each user creates a public/private | |
714 | key pair for authentication purposes. | |
715 | The server knows the public key, and only the user knows the private key. | |
716 | .Nm | |
717 | implements public key authentication protocol automatically, | |
718 | using either the RSA or DSA algorithms. | |
719 | Protocol 1 is restricted to using only RSA keys, | |
720 | but protocol 2 may use either. | |
721 | The | |
722 | .Sx HISTORY | |
723 | section of | |
724 | .Xr ssl 8 | |
725 | contains a brief discussion of the two algorithms. | |
726 | .Pp | |
727 | The file | |
728 | .Pa ~/.ssh/authorized_keys | |
729 | lists the public keys that are permitted for logging in. | |
730 | When the user logs in, the | |
731 | .Nm | |
732 | program tells the server which key pair it would like to use for | |
733 | authentication. | |
734 | The client proves that it has access to the private key | |
735 | and the server checks that the corresponding public key | |
736 | is authorized to accept the account. | |
737 | .Pp | |
738 | The user creates his/her key pair by running | |
739 | .Xr ssh-keygen 1 . | |
740 | This stores the private key in | |
741 | .Pa ~/.ssh/identity | |
742 | (protocol 1), | |
743 | .Pa ~/.ssh/id_dsa | |
744 | (protocol 2 DSA), | |
745 | or | |
746 | .Pa ~/.ssh/id_rsa | |
747 | (protocol 2 RSA) | |
748 | and stores the public key in | |
749 | .Pa ~/.ssh/identity.pub | |
750 | (protocol 1), | |
751 | .Pa ~/.ssh/id_dsa.pub | |
752 | (protocol 2 DSA), | |
753 | or | |
754 | .Pa ~/.ssh/id_rsa.pub | |
755 | (protocol 2 RSA) | |
756 | in the user's home directory. | |
757 | The user should then copy the public key | |
758 | to | |
759 | .Pa ~/.ssh/authorized_keys | |
760 | in his/her home directory on the remote machine. | |
761 | The | |
762 | .Pa authorized_keys | |
763 | file corresponds to the conventional | |
764 | .Pa ~/.rhosts | |
765 | file, and has one key | |
766 | per line, though the lines can be very long. | |
767 | After this, the user can log in without giving the password. | |
768 | .Pp | |
769 | The most convenient way to use public key authentication may be with an | |
770 | authentication agent. | |
771 | See | |
772 | .Xr ssh-agent 1 | |
773 | for more information. | |
774 | .Pp | |
775 | Challenge-response authentication works as follows: | |
776 | The server sends an arbitrary | |
777 | .Qq challenge | |
778 | text, and prompts for a response. | |
779 | Protocol 2 allows multiple challenges and responses; | |
780 | protocol 1 is restricted to just one challenge/response. | |
781 | Examples of challenge-response authentication include | |
782 | BSD Authentication (see | |
783 | .Xr login.conf 5 ) | |
784 | and PAM (some non-OpenBSD systems). | |
785 | .Pp | |
786 | Finally, if other authentication methods fail, | |
787 | .Nm | |
788 | prompts the user for a password. | |
789 | The password is sent to the remote | |
790 | host for checking; however, since all communications are encrypted, | |
791 | the password cannot be seen by someone listening on the network. | |
792 | .Pp | |
793 | .Nm | |
794 | automatically maintains and checks a database containing | |
795 | identification for all hosts it has ever been used with. | |
796 | Host keys are stored in | |
797 | .Pa ~/.ssh/known_hosts | |
798 | in the user's home directory. | |
799 | Additionally, the file | |
800 | .Pa /etc/ssh/ssh_known_hosts | |
801 | is automatically checked for known hosts. | |
802 | Any new hosts are automatically added to the user's file. | |
803 | If a host's identification ever changes, | |
804 | .Nm | |
805 | warns about this and disables password authentication to prevent | |
806 | server spoofing or man-in-the-middle attacks, | |
807 | which could otherwise be used to circumvent the encryption. | |
808 | The | |
809 | .Cm StrictHostKeyChecking | |
810 | option can be used to control logins to machines whose | |
811 | host key is not known or has changed. | |
812 | .Pp | |
813 | When the user's identity has been accepted by the server, the server | |
814 | either executes the given command, or logs into the machine and gives | |
815 | the user a normal shell on the remote machine. | |
816 | All communication with | |
817 | the remote command or shell will be automatically encrypted. | |
818 | .Pp | |
819 | If a pseudo-terminal has been allocated (normal login session), the | |
820 | user may use the escape characters noted below. | |
821 | .Pp | |
822 | If no pseudo-tty has been allocated, | |
823 | the session is transparent and can be used to reliably transfer binary data. | |
824 | On most systems, setting the escape character to | |
825 | .Dq none | |
826 | will also make the session transparent even if a tty is used. | |
827 | .Pp | |
828 | The session terminates when the command or shell on the remote | |
829 | machine exits and all X11 and TCP connections have been closed. | |
830 | .Sh ESCAPE CHARACTERS | |
831 | When a pseudo-terminal has been requested, | |
832 | .Nm | |
833 | supports a number of functions through the use of an escape character. | |
834 | .Pp | |
835 | A single tilde character can be sent as | |
836 | .Ic ~~ | |
837 | or by following the tilde by a character other than those described below. | |
838 | The escape character must always follow a newline to be interpreted as | |
839 | special. | |
840 | The escape character can be changed in configuration files using the | |
841 | .Cm EscapeChar | |
842 | configuration directive or on the command line by the | |
843 | .Fl e | |
844 | option. | |
845 | .Pp | |
846 | The supported escapes (assuming the default | |
847 | .Ql ~ ) | |
848 | are: | |
849 | .Bl -tag -width Ds | |
850 | .It Cm ~. | |
851 | Disconnect. | |
852 | .It Cm ~^Z | |
853 | Background | |
854 | .Nm . | |
855 | .It Cm ~# | |
856 | List forwarded connections. | |
857 | .It Cm ~& | |
858 | Background | |
859 | .Nm | |
860 | at logout when waiting for forwarded connection / X11 sessions to terminate. | |
861 | .It Cm ~? | |
862 | Display a list of escape characters. | |
863 | .It Cm ~B | |
864 | Send a BREAK to the remote system | |
865 | (only useful for SSH protocol version 2 and if the peer supports it). | |
866 | .It Cm ~C | |
867 | Open command line. | |
868 | Currently this allows the addition of port forwardings using the | |
869 | .Fl L | |
870 | and | |
871 | .Fl R | |
872 | options (see above). | |
873 | It also allows the cancellation of existing remote port-forwardings | |
874 | using | |
875 | .Fl KR Ar hostport . | |
876 | .Ic !\& Ns Ar command | |
877 | allows the user to execute a local command if the | |
878 | .Ic PermitLocalCommand | |
879 | option is enabled in | |
880 | .Xr ssh_config 5 . | |
881 | Basic help is available, using the | |
882 | .Fl h | |
883 | option. | |
884 | .It Cm ~R | |
885 | Request rekeying of the connection | |
886 | (only useful for SSH protocol version 2 and if the peer supports it). | |
887 | .El | |
888 | .Sh TCP FORWARDING | |
889 | Forwarding of arbitrary TCP connections over the secure channel can | |
890 | be specified either on the command line or in a configuration file. | |
891 | One possible application of TCP forwarding is a secure connection to a | |
892 | mail server; another is going through firewalls. | |
893 | .Pp | |
894 | In the example below, we look at encrypting communication between | |
895 | an IRC client and server, even though the IRC server does not directly | |
896 | support encrypted communications. | |
897 | This works as follows: | |
898 | the user connects to the remote host using | |
899 | .Nm , | |
900 | specifying a port to be used to forward connections | |
901 | to the remote server. | |
902 | After that it is possible to start the service which is to be encrypted | |
903 | on the client machine, | |
904 | connecting to the same local port, | |
905 | and | |
906 | .Nm | |
907 | will encrypt and forward the connection. | |
908 | .Pp | |
909 | The following example tunnels an IRC session from client machine | |
910 | .Dq 127.0.0.1 | |
911 | (localhost) | |
912 | to remote server | |
913 | .Dq server.example.com : | |
914 | .Bd -literal -offset 4n | |
915 | $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10 | |
916 | $ irc -c '#users' -p 1234 pinky 127.0.0.1 | |
917 | .Ed | |
918 | .Pp | |
919 | This tunnels a connection to IRC server | |
920 | .Dq server.example.com , | |
921 | joining channel | |
922 | .Dq #users , | |
923 | nickname | |
924 | .Dq pinky , | |
925 | using port 1234. | |
926 | It doesn't matter which port is used, | |
927 | as long as it's greater than 1023 | |
928 | (remember, only root can open sockets on privileged ports) | |
929 | and doesn't conflict with any ports already in use. | |
930 | The connection is forwarded to port 6667 on the remote server, | |
931 | since that's the standard port for IRC services. | |
932 | .Pp | |
933 | The | |
934 | .Fl f | |
935 | option backgrounds | |
936 | .Nm | |
937 | and the remote command | |
938 | .Dq sleep 10 | |
939 | is specified to allow an amount of time | |
940 | (10 seconds, in the example) | |
941 | to start the service which is to be tunnelled. | |
942 | If no connections are made within the time specified, | |
943 | .Nm | |
944 | will exit. | |
945 | .Sh X11 FORWARDING | |
946 | If the | |
947 | .Cm ForwardX11 | |
948 | variable is set to | |
949 | .Dq yes | |
950 | (or see the description of the | |
951 | .Fl X , | |
952 | .Fl x , | |
953 | and | |
954 | .Fl Y | |
955 | options above) | |
956 | and the user is using X11 (the | |
957 | .Ev DISPLAY | |
958 | environment variable is set), the connection to the X11 display is | |
959 | automatically forwarded to the remote side in such a way that any X11 | |
960 | programs started from the shell (or command) will go through the | |
961 | encrypted channel, and the connection to the real X server will be made | |
962 | from the local machine. | |
963 | The user should not manually set | |
964 | .Ev DISPLAY . | |
965 | Forwarding of X11 connections can be | |
966 | configured on the command line or in configuration files. | |
967 | .Pp | |
968 | The | |
969 | .Ev DISPLAY | |
970 | value set by | |
971 | .Nm | |
972 | will point to the server machine, but with a display number greater than zero. | |
973 | This is normal, and happens because | |
974 | .Nm | |
975 | creates a | |
976 | .Dq proxy | |
977 | X server on the server machine for forwarding the | |
978 | connections over the encrypted channel. | |
979 | .Pp | |
980 | .Nm | |
981 | will also automatically set up Xauthority data on the server machine. | |
982 | For this purpose, it will generate a random authorization cookie, | |
983 | store it in Xauthority on the server, and verify that any forwarded | |
984 | connections carry this cookie and replace it by the real cookie when | |
985 | the connection is opened. | |
986 | The real authentication cookie is never | |
987 | sent to the server machine (and no cookies are sent in the plain). | |
988 | .Pp | |
989 | If the | |
990 | .Cm ForwardAgent | |
991 | variable is set to | |
992 | .Dq yes | |
993 | (or see the description of the | |
994 | .Fl A | |
995 | and | |
996 | .Fl a | |
997 | options above) and | |
998 | the user is using an authentication agent, the connection to the agent | |
999 | is automatically forwarded to the remote side. | |
1000 | .Sh VERIFYING HOST KEYS | |
1001 | When connecting to a server for the first time, | |
1002 | a fingerprint of the server's public key is presented to the user | |
1003 | (unless the option | |
1004 | .Cm StrictHostKeyChecking | |
1005 | has been disabled). | |
1006 | Fingerprints can be determined using | |
1007 | .Xr ssh-keygen 1 : | |
1008 | .Pp | |
1009 | .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key | |
1010 | .Pp | |
1011 | If the fingerprint is already known, | |
1012 | it can be matched and verified, | |
1013 | and the key can be accepted. | |
1014 | If the fingerprint is unknown, | |
1015 | an alternative method of verification is available: | |
1016 | SSH fingerprints verified by DNS. | |
1017 | An additional resource record (RR), | |
1018 | SSHFP, | |
1019 | is added to a zonefile | |
1020 | and the connecting client is able to match the fingerprint | |
1021 | with that of the key presented. | |
1022 | .Pp | |
1023 | In this example, we are connecting a client to a server, | |
1024 | .Dq host.example.com . | |
1025 | The SSHFP resource records should first be added to the zonefile for | |
1026 | host.example.com: | |
1027 | .Bd -literal -offset indent | |
1028 | $ ssh-keygen -f /etc/ssh/ssh_host_rsa_key.pub -r host.example.com. | |
1029 | $ ssh-keygen -f /etc/ssh/ssh_host_dsa_key.pub -r host.example.com. | |
1030 | .Ed | |
1031 | .Pp | |
1032 | The output lines will have to be added to the zonefile. | |
1033 | To check that the zone is answering fingerprint queries: | |
1034 | .Pp | |
1035 | .Dl $ dig -t SSHFP host.example.com | |
1036 | .Pp | |
1037 | Finally the client connects: | |
1038 | .Bd -literal -offset indent | |
1039 | $ ssh -o "VerifyHostKeyDNS ask" host.example.com | |
1040 | [...] | |
1041 | Matching host key fingerprint found in DNS. | |
1042 | Are you sure you want to continue connecting (yes/no)? | |
1043 | .Ed | |
1044 | .Pp | |
1045 | See the | |
1046 | .Cm VerifyHostKeyDNS | |
1047 | option in | |
1048 | .Xr ssh_config 5 | |
1049 | for more information. | |
1050 | .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS | |
1051 | .Nm | |
1052 | contains support for Virtual Private Network (VPN) tunnelling | |
1053 | using the | |
1054 | .Xr tun 4 | |
1055 | network pseudo-device, | |
1056 | allowing two networks to be joined securely. | |
1057 | The | |
1058 | .Xr sshd_config 5 | |
1059 | configuration option | |
1060 | .Cm PermitTunnel | |
1061 | controls whether the server supports this, | |
1062 | and at what level (layer 2 or 3 traffic). | |
1063 | .Pp | |
1064 | The following example would connect client network 10.0.50.0/24 | |
1065 | with remote network 10.0.99.0/24, provided that the SSH server | |
1066 | running on the gateway to the remote network, | |
1067 | at 192.168.1.15, allows it: | |
1068 | .Bd -literal -offset indent | |
1069 | # ssh -f -w 0:1 192.168.1.15 true | |
1070 | # ifconfig tun0 10.0.50.1 10.0.99.1 netmask 255.255.255.252 | |
1071 | .Ed | |
1072 | .Pp | |
1073 | Client access may be more finely tuned via the | |
1074 | .Pa /root/.ssh/authorized_keys | |
1075 | file (see below) and the | |
1076 | .Cm PermitRootLogin | |
1077 | server option. | |
1078 | The following entry would permit connections on the first | |
1079 | .Xr tun 4 | |
1080 | device from user | |
1081 | .Dq jane | |
1082 | and on the second device from user | |
1083 | .Dq john , | |
1084 | if | |
1085 | .Cm PermitRootLogin | |
1086 | is set to | |
1087 | .Dq forced-commands-only : | |
1088 | .Bd -literal -offset 2n | |
1089 | tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane | |
1090 | tunnel="2",command="sh /etc/netstart tun1" ssh-rsa ... john | |
1091 | .Ed | |
1092 | .Pp | |
1093 | Since a SSH-based setup entails a fair amount of overhead, | |
1094 | it may be more suited to temporary setups, | |
1095 | such as for wireless VPNs. | |
1096 | More permanent VPNs are better provided by tools such as | |
1097 | .Xr ipsecctl 8 | |
1098 | and | |
1099 | .Xr isakmpd 8 . | |
3c0ef626 | 1100 | .Sh ENVIRONMENT |
1101 | .Nm | |
1102 | will normally set the following environment variables: | |
08822d99 | 1103 | .Bl -tag -width "SSH_ORIGINAL_COMMAND" |
3c0ef626 | 1104 | .It Ev DISPLAY |
1105 | The | |
1106 | .Ev DISPLAY | |
1107 | variable indicates the location of the X11 server. | |
1108 | It is automatically set by | |
1109 | .Nm | |
1110 | to point to a value of the form | |
08822d99 | 1111 | .Dq hostname:n , |
1112 | where | |
1113 | .Dq hostname | |
1114 | indicates the host where the shell runs, and | |
1115 | .Sq n | |
1116 | is an integer \*(Ge 1. | |
3c0ef626 | 1117 | .Nm |
1118 | uses this special value to forward X11 connections over the secure | |
1119 | channel. | |
1120 | The user should normally not set | |
1121 | .Ev DISPLAY | |
1122 | explicitly, as that | |
1123 | will render the X11 connection insecure (and will require the user to | |
1124 | manually copy any required authorization cookies). | |
1125 | .It Ev HOME | |
1126 | Set to the path of the user's home directory. | |
1127 | .It Ev LOGNAME | |
1128 | Synonym for | |
1129 | .Ev USER ; | |
1130 | set for compatibility with systems that use this variable. | |
1131 | .It Ev MAIL | |
1132 | Set to the path of the user's mailbox. | |
1133 | .It Ev PATH | |
1134 | Set to the default | |
1135 | .Ev PATH , | |
1136 | as specified when compiling | |
08822d99 | 1137 | .Nm . |
3c0ef626 | 1138 | .It Ev SSH_ASKPASS |
1139 | If | |
1140 | .Nm | |
1141 | needs a passphrase, it will read the passphrase from the current | |
1142 | terminal if it was run from a terminal. | |
1143 | If | |
1144 | .Nm | |
1145 | does not have a terminal associated with it but | |
1146 | .Ev DISPLAY | |
1147 | and | |
1148 | .Ev SSH_ASKPASS | |
1149 | are set, it will execute the program specified by | |
1150 | .Ev SSH_ASKPASS | |
1151 | and open an X11 window to read the passphrase. | |
1152 | This is particularly useful when calling | |
1153 | .Nm | |
1154 | from a | |
dfddba3d | 1155 | .Pa .xsession |
3c0ef626 | 1156 | or related script. |
1157 | (Note that on some machines it | |
1158 | may be necessary to redirect the input from | |
1159 | .Pa /dev/null | |
1160 | to make this work.) | |
1161 | .It Ev SSH_AUTH_SOCK | |
08822d99 | 1162 | Identifies the path of a |
1163 | .Ux Ns -domain | |
1164 | socket used to communicate with the agent. | |
d03f4262 | 1165 | .It Ev SSH_CONNECTION |
1166 | Identifies the client and server ends of the connection. | |
3c0ef626 | 1167 | The variable contains |
08822d99 | 1168 | four space-separated values: client IP address, client port number, |
1169 | server IP address, and server port number. | |
3c0ef626 | 1170 | .It Ev SSH_ORIGINAL_COMMAND |
08822d99 | 1171 | This variable contains the original command line if a forced command |
3c0ef626 | 1172 | is executed. |
1173 | It can be used to extract the original arguments. | |
1174 | .It Ev SSH_TTY | |
1175 | This is set to the name of the tty (path to the device) associated | |
1176 | with the current shell or command. | |
1177 | If the current session has no tty, | |
1178 | this variable is not set. | |
1179 | .It Ev TZ | |
08822d99 | 1180 | This variable is set to indicate the present time zone if it |
3c0ef626 | 1181 | was set when the daemon was started (i.e., the daemon passes the value |
1182 | on to new connections). | |
1183 | .It Ev USER | |
1184 | Set to the name of the user logging in. | |
1185 | .El | |
1186 | .Pp | |
1187 | Additionally, | |
1188 | .Nm | |
1189 | reads | |
2ce0bfe4 | 1190 | .Pa ~/.ssh/environment , |
3c0ef626 | 1191 | and adds lines of the format |
1192 | .Dq VARNAME=value | |
08822d99 | 1193 | to the environment if the file exists and users are allowed to |
d03f4262 | 1194 | change their environment. |
540d72c3 | 1195 | For more information, see the |
d03f4262 | 1196 | .Cm PermitUserEnvironment |
1197 | option in | |
1198 | .Xr sshd_config 5 . | |
3c0ef626 | 1199 | .Sh FILES |
08822d99 | 1200 | .Bl -tag -width Ds -compact |
1201 | .It ~/.rhosts | |
1202 | This file is used for host-based authentication (see above). | |
1203 | On some machines this file may need to be | |
1204 | world-readable if the user's home directory is on an NFS partition, | |
1205 | because | |
1206 | .Xr sshd 8 | |
1207 | reads it as root. | |
1208 | Additionally, this file must be owned by the user, | |
1209 | and must not have write permissions for anyone else. | |
1210 | The recommended | |
1211 | permission for most machines is read/write for the user, and not | |
1212 | accessible by others. | |
1213 | .Pp | |
1214 | .It ~/.shosts | |
1215 | This file is used in exactly the same way as | |
1216 | .Pa .rhosts , | |
1217 | but allows host-based authentication without permitting login with | |
1218 | rlogin/rsh. | |
1219 | .Pp | |
1220 | .It ~/.ssh/authorized_keys | |
1221 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. | |
1222 | The format of this file is described in the | |
1223 | .Xr sshd 8 | |
1224 | manual page. | |
1225 | This file is not highly sensitive, but the recommended | |
1226 | permissions are read/write for the user, and not accessible by others. | |
1227 | .Pp | |
1228 | .It ~/.ssh/config | |
1229 | This is the per-user configuration file. | |
1230 | The file format and configuration options are described in | |
1231 | .Xr ssh_config 5 . | |
1232 | Because of the potential for abuse, this file must have strict permissions: | |
1233 | read/write for the user, and not accessible by others. | |
1234 | .Pp | |
1235 | .It ~/.ssh/environment | |
1236 | Contains additional definitions for environment variables; see | |
1237 | .Sx ENVIRONMENT , | |
1238 | above. | |
1239 | .Pp | |
1240 | .It ~/.ssh/identity | |
1241 | .It ~/.ssh/id_dsa | |
1242 | .It ~/.ssh/id_rsa | |
1243 | Contains the private key for authentication. | |
3c0ef626 | 1244 | These files |
1245 | contain sensitive data and should be readable by the user but not | |
1246 | accessible by others (read/write/execute). | |
3c0ef626 | 1247 | .Nm |
08822d99 | 1248 | will simply ignore a private key file if it is accessible by others. |
3c0ef626 | 1249 | It is possible to specify a passphrase when |
08822d99 | 1250 | generating the key which will be used to encrypt the |
3c0ef626 | 1251 | sensitive part of this file using 3DES. |
08822d99 | 1252 | .Pp |
1253 | .It ~/.ssh/identity.pub | |
1254 | .It ~/.ssh/id_dsa.pub | |
1255 | .It ~/.ssh/id_rsa.pub | |
1256 | Contains the public key for authentication. | |
3c0ef626 | 1257 | These files are not |
1258 | sensitive and can (but need not) be readable by anyone. | |
3c0ef626 | 1259 | .Pp |
08822d99 | 1260 | .It ~/.ssh/known_hosts |
1261 | Contains a list of host keys for all hosts the user has logged into | |
1262 | that are not already in the systemwide list of known host keys. | |
1263 | See | |
3c0ef626 | 1264 | .Xr sshd 8 |
08822d99 | 1265 | for further details of the format of this file. |
1266 | .Pp | |
1267 | .It ~/.ssh/rc | |
1268 | Commands in this file are executed by | |
3c0ef626 | 1269 | .Nm |
08822d99 | 1270 | when the user logs in, just before the user's shell (or command) is |
1271 | started. | |
1272 | See the | |
1273 | .Xr sshd 8 | |
1274 | manual page for more information. | |
1275 | .Pp | |
1276 | .It /etc/hosts.equiv | |
1277 | This file is for host-based authentication (see above). | |
1278 | It should only be writable by root. | |
1279 | .Pp | |
1280 | .It /etc/shosts.equiv | |
1281 | This file is used in exactly the same way as | |
1282 | .Pa hosts.equiv , | |
1283 | but allows host-based authentication without permitting login with | |
1284 | rlogin/rsh. | |
1285 | .Pp | |
db32a221 | 1286 | .It Pa /etc/ssh/ssh_config |
3c0ef626 | 1287 | Systemwide configuration file. |
44a053a3 | 1288 | The file format and configuration options are described in |
1289 | .Xr ssh_config 5 . | |
08822d99 | 1290 | .Pp |
1291 | .It /etc/ssh/ssh_host_key | |
1292 | .It /etc/ssh/ssh_host_dsa_key | |
1293 | .It /etc/ssh/ssh_host_rsa_key | |
3c0ef626 | 1294 | These three files contain the private parts of the host keys |
08822d99 | 1295 | and are used for host-based authentication. |
1296 | If protocol version 1 is used, | |
44a053a3 | 1297 | .Nm |
1298 | must be setuid root, since the host key is readable only by root. | |
1299 | For protocol version 2, | |
1300 | .Nm | |
1301 | uses | |
1302 | .Xr ssh-keysign 8 | |
08822d99 | 1303 | to access the host keys, |
1304 | eliminating the requirement that | |
44a053a3 | 1305 | .Nm |
08822d99 | 1306 | be setuid root when host-based authentication is used. |
44a053a3 | 1307 | By default |
3c0ef626 | 1308 | .Nm |
44a053a3 | 1309 | is not setuid root. |
3c0ef626 | 1310 | .Pp |
08822d99 | 1311 | .It /etc/ssh/ssh_known_hosts |
1312 | Systemwide list of known host keys. | |
1313 | This file should be prepared by the | |
1314 | system administrator to contain the public host keys of all machines in the | |
1315 | organization. | |
1316 | It should be world-readable. | |
1317 | See | |
3c0ef626 | 1318 | .Xr sshd 8 |
08822d99 | 1319 | for further details of the format of this file. |
1320 | .Pp | |
1321 | .It /etc/ssh/sshrc | |
3c0ef626 | 1322 | Commands in this file are executed by |
1323 | .Nm | |
08822d99 | 1324 | when the user logs in, just before the user's shell (or command) is started. |
3c0ef626 | 1325 | See the |
1326 | .Xr sshd 8 | |
1327 | manual page for more information. | |
3c0ef626 | 1328 | .El |
3c0ef626 | 1329 | .Sh SEE ALSO |
3c0ef626 | 1330 | .Xr scp 1 , |
1331 | .Xr sftp 1 , | |
1332 | .Xr ssh-add 1 , | |
1333 | .Xr ssh-agent 1 , | |
1334 | .Xr ssh-keygen 1 , | |
08822d99 | 1335 | .Xr ssh-keyscan 1 , |
1336 | .Xr tun 4 , | |
540d72c3 | 1337 | .Xr hosts.equiv 5 , |
276b07a3 | 1338 | .Xr ssh_config 5 , |
1339 | .Xr ssh-keysign 8 , | |
3c0ef626 | 1340 | .Xr sshd 8 |
1341 | .Rs | |
1342 | .%A T. Ylonen | |
1343 | .%A T. Kivinen | |
1344 | .%A M. Saarinen | |
1345 | .%A T. Rinne | |
1346 | .%A S. Lehtinen | |
1347 | .%T "SSH Protocol Architecture" | |
db32a221 | 1348 | .%N draft-ietf-secsh-architecture-12.txt |
1349 | .%D January 2002 | |
3c0ef626 | 1350 | .%O work in progress material |
1351 | .Re | |
7cac2b65 | 1352 | .Sh AUTHORS |
1353 | OpenSSH is a derivative of the original and free | |
1354 | ssh 1.2.12 release by Tatu Ylonen. | |
1355 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1356 | Theo de Raadt and Dug Song | |
1357 | removed many bugs, re-added newer features and | |
1358 | created OpenSSH. | |
1359 | Markus Friedl contributed the support for SSH | |
1360 | protocol versions 1.5 and 2.0. |