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bf740959 | 1 | .\" -*- nroff -*- |
2 | .\" | |
bf740959 | 3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
bf740959 | 4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
5 | .\" All rights reserved | |
6 | .\" | |
bcbf86ec | 7 | .\" As far as I am concerned, the code I have written for this software |
8 | .\" can be used freely for any purpose. Any derived versions of this | |
9 | .\" software must be clearly marked as such, and if the derived work is | |
10 | .\" incompatible with the protocol description in the RFC file, it must be | |
11 | .\" called by a name other than "ssh" or "Secure Shell". | |
12 | .\" | |
f3c7c613 | 13 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. |
14 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. | |
15 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. | |
bcbf86ec | 16 | .\" |
17 | .\" Redistribution and use in source and binary forms, with or without | |
18 | .\" modification, are permitted provided that the following conditions | |
19 | .\" are met: | |
20 | .\" 1. Redistributions of source code must retain the above copyright | |
21 | .\" notice, this list of conditions and the following disclaimer. | |
22 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
23 | .\" notice, this list of conditions and the following disclaimer in the | |
24 | .\" documentation and/or other materials provided with the distribution. | |
bf740959 | 25 | .\" |
bcbf86ec | 26 | .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
27 | .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES | |
28 | .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |
29 | .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, | |
30 | .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT | |
31 | .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
32 | .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
33 | .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
34 | .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF | |
35 | .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
bf740959 | 36 | .\" |
442c8b33 | 37 | .\" $OpenBSD: ssh.1,v 1.218 2005/12/16 18:07:08 jmc Exp $ |
bf740959 | 38 | .Dd September 25, 1999 |
39 | .Dt SSH 1 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm ssh | |
2c86906e | 43 | .Nd OpenSSH SSH client (remote login program) |
bf740959 | 44 | .Sh SYNOPSIS |
45 | .Nm ssh | |
0e19494c | 46 | .Op Fl 1246AaCfgkMNnqsTtVvXxY |
3435f5a6 | 47 | .Op Fl b Ar bind_address |
d0c832f3 | 48 | .Op Fl c Ar cipher_spec |
5ddc5eb4 | 49 | .Oo Fl D\ \& |
50 | .Sm off | |
51 | .Oo Ar bind_address : Oc | |
52 | .Ar port | |
53 | .Sm on | |
54 | .Oc | |
bf740959 | 55 | .Op Fl e Ar escape_char |
e591b98a | 56 | .Op Fl F Ar configfile |
37c406a8 | 57 | .Bk -words |
5f4a0c58 | 58 | .Op Fl i Ar identity_file |
37c406a8 | 59 | .Ek |
6c7e3b94 | 60 | .Oo Fl L\ \& |
bf740959 | 61 | .Sm off |
3867aa0a | 62 | .Oo Ar bind_address : Oc |
6c7e3b94 | 63 | .Ar port : host : hostport |
bf740959 | 64 | .Sm on |
bf740959 | 65 | .Oc |
37c406a8 | 66 | .Bk -words |
5f4a0c58 | 67 | .Op Fl l Ar login_name |
37c406a8 | 68 | .Ek |
5f4a0c58 | 69 | .Op Fl m Ar mac_spec |
f8c6db83 | 70 | .Op Fl O Ar ctl_cmd |
5f4a0c58 | 71 | .Op Fl o Ar option |
5f4a0c58 | 72 | .Op Fl p Ar port |
6c7e3b94 | 73 | .Oo Fl R\ \& |
bf740959 | 74 | .Sm off |
3867aa0a | 75 | .Oo Ar bind_address : Oc |
6c7e3b94 | 76 | .Ar port : host : hostport |
bf740959 | 77 | .Sm on |
bf740959 | 78 | .Oc |
f8c6db83 | 79 | .Op Fl S Ar ctl_path |
985bb789 | 80 | .Bk -words |
81 | .Op Fl w Ar tunnel : Ns Ar tunnel | |
5f4a0c58 | 82 | .Oo Ar user Ns @ Oc Ns Ar hostname |
bf740959 | 83 | .Op Ar command |
985bb789 | 84 | .Ek |
f54651ce | 85 | .Sh DESCRIPTION |
bf740959 | 86 | .Nm |
2c86906e | 87 | (SSH client) is a program for logging into a remote machine and for |
610cd5c6 | 88 | executing commands on a remote machine. |
5f4a0c58 | 89 | It is intended to replace rlogin and rsh, |
90 | and provide secure encrypted communications between | |
610cd5c6 | 91 | two untrusted hosts over an insecure network. |
5f4a0c58 | 92 | X11 connections and arbitrary TCP/IP ports |
93 | can also be forwarded over the secure channel. | |
bf740959 | 94 | .Pp |
95 | .Nm | |
f54651ce | 96 | connects and logs into the specified |
5f4a0c58 | 97 | .Ar hostname |
98 | (with optional | |
99 | .Ar user | |
100 | name). | |
bf740959 | 101 | The user must prove |
1d1ffb87 | 102 | his/her identity to the remote machine using one of several methods |
5f4a0c58 | 103 | depending on the protocol version used. |
1d1ffb87 | 104 | .Pp |
5f4a0c58 | 105 | If |
106 | .Ar command | |
107 | is specified, | |
108 | .Ar command | |
109 | is executed on the remote host instead of a login shell. | |
bf740959 | 110 | .Pp |
442c8b33 | 111 | The options are as follows: |
112 | .Bl -tag -width Ds | |
113 | .It Fl 1 | |
114 | Forces | |
bf740959 | 115 | .Nm |
442c8b33 | 116 | to try protocol version 1 only. |
117 | .It Fl 2 | |
118 | Forces | |
bf740959 | 119 | .Nm |
442c8b33 | 120 | to try protocol version 2 only. |
121 | .It Fl 4 | |
122 | Forces | |
bf740959 | 123 | .Nm |
442c8b33 | 124 | to use IPv4 addresses only. |
125 | .It Fl 6 | |
126 | Forces | |
bf740959 | 127 | .Nm |
442c8b33 | 128 | to use IPv6 addresses only. |
129 | .It Fl A | |
130 | Enables forwarding of the authentication agent connection. | |
131 | This can also be specified on a per-host basis in a configuration file. | |
bf740959 | 132 | .Pp |
442c8b33 | 133 | Agent forwarding should be enabled with caution. |
134 | Users with the ability to bypass file permissions on the remote host | |
135 | (for the agent's Unix-domain socket) | |
136 | can access the local agent through the forwarded connection. | |
137 | An attacker cannot obtain key material from the agent, | |
138 | however they can perform operations on the keys that enable them to | |
139 | authenticate using the identities loaded into the agent. | |
140 | .It Fl a | |
141 | Disables forwarding of the authentication agent connection. | |
142 | .It Fl b Ar bind_address | |
143 | Use | |
144 | .Ar bind_address | |
145 | on the local machine as the source address | |
146 | of the connection. | |
147 | Only useful on systems with more than one address. | |
148 | .It Fl C | |
149 | Requests compression of all data (including stdin, stdout, stderr, and | |
150 | data for forwarded X11 and TCP/IP connections). | |
151 | The compression algorithm is the same used by | |
152 | .Xr gzip 1 , | |
153 | and the | |
154 | .Dq level | |
155 | can be controlled by the | |
156 | .Cm CompressionLevel | |
157 | option for protocol version 1. | |
158 | Compression is desirable on modem lines and other | |
159 | slow connections, but will only slow down things on fast networks. | |
160 | The default value can be set on a host-by-host basis in the | |
161 | configuration files; see the | |
162 | .Cm Compression | |
163 | option. | |
164 | .It Fl c Ar cipher_spec | |
165 | Selects the cipher specification for encrypting the session. | |
bf740959 | 166 | .Pp |
442c8b33 | 167 | Protocol version 1 allows specification of a single cipher. |
168 | The supported values are | |
169 | .Dq 3des , | |
170 | .Dq blowfish | |
171 | and | |
172 | .Dq des . | |
173 | .Ar 3des | |
174 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
175 | It is believed to be secure. | |
176 | .Ar blowfish | |
177 | is a fast block cipher; it appears very secure and is much faster than | |
178 | .Ar 3des . | |
179 | .Ar des | |
180 | is only supported in the | |
bf740959 | 181 | .Nm |
442c8b33 | 182 | client for interoperability with legacy protocol 1 implementations |
183 | that do not support the | |
184 | .Ar 3des | |
185 | cipher. | |
186 | Its use is strongly discouraged due to cryptographic weaknesses. | |
187 | The default is | |
188 | .Dq 3des . | |
da89cf4d | 189 | .Pp |
442c8b33 | 190 | For protocol version 2 |
191 | .Ar cipher_spec | |
192 | is a comma-separated list of ciphers | |
193 | listed in order of preference. | |
194 | The supported ciphers are | |
195 | .Dq 3des-cbc , | |
196 | .Dq aes128-cbc , | |
197 | .Dq aes192-cbc , | |
198 | .Dq aes256-cbc , | |
199 | .Dq aes128-ctr , | |
200 | .Dq aes192-ctr , | |
201 | .Dq aes256-ctr , | |
202 | .Dq arcfour128 , | |
203 | .Dq arcfour256 , | |
204 | .Dq arcfour , | |
205 | .Dq blowfish-cbc , | |
206 | and | |
207 | .Dq cast128-cbc . | |
208 | The default is | |
209 | .Bd -literal | |
210 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, | |
211 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
212 | aes192-ctr,aes256-ctr'' | |
213 | .Ed | |
214 | .It Fl D Xo | |
215 | .Sm off | |
216 | .Oo Ar bind_address : Oc | |
217 | .Ar port | |
218 | .Sm on | |
219 | .Xc | |
220 | Specifies a local | |
221 | .Dq dynamic | |
222 | application-level port forwarding. | |
223 | This works by allocating a socket to listen to | |
224 | .Ar port | |
225 | on the local side, optionally bound to the specified | |
226 | .Ar bind_address . | |
227 | Whenever a connection is made to this port, the | |
228 | connection is forwarded over the secure channel, and the application | |
229 | protocol is then used to determine where to connect to from the | |
230 | remote machine. | |
231 | Currently the SOCKS4 and SOCKS5 protocols are supported, and | |
da89cf4d | 232 | .Nm |
442c8b33 | 233 | will act as a SOCKS server. |
234 | Only root can forward privileged ports. | |
235 | Dynamic port forwardings can also be specified in the configuration file. | |
5ddc5eb4 | 236 | .Pp |
237 | IPv6 addresses can be specified with an alternative syntax: | |
238 | .Sm off | |
239 | .Xo | |
240 | .Op Ar bind_address No / | |
241 | .Ar port | |
242 | .Xc | |
243 | .Sm on | |
244 | or by enclosing the address in square brackets. | |
245 | Only the superuser can forward privileged ports. | |
246 | By default, the local port is bound in accordance with the | |
247 | .Cm GatewayPorts | |
248 | setting. | |
249 | However, an explicit | |
250 | .Ar bind_address | |
251 | may be used to bind the connection to a specific address. | |
252 | The | |
253 | .Ar bind_address | |
254 | of | |
255 | .Dq localhost | |
256 | indicates that the listening port be bound for local use only, while an | |
257 | empty address or | |
258 | .Sq * | |
259 | indicates that the port should be available from all interfaces. | |
5f4a0c58 | 260 | .It Fl e Ar ch | ^ch | none |
bf740959 | 261 | Sets the escape character for sessions with a pty (default: |
262 | .Ql ~ ) . | |
610cd5c6 | 263 | The escape character is only recognized at the beginning of a line. |
264 | The escape character followed by a dot | |
bf740959 | 265 | .Pq Ql \&. |
5f4a0c58 | 266 | closes the connection; |
267 | followed by control-Z suspends the connection; | |
268 | and followed by itself sends the escape character once. | |
610cd5c6 | 269 | Setting the character to |
bf740959 | 270 | .Dq none |
271 | disables any escapes and makes the session fully transparent. | |
5f4a0c58 | 272 | .It Fl F Ar configfile |
273 | Specifies an alternative per-user configuration file. | |
274 | If a configuration file is given on the command line, | |
275 | the system-wide configuration file | |
276 | .Pq Pa /etc/ssh/ssh_config | |
277 | will be ignored. | |
278 | The default for the per-user configuration file is | |
140e3e97 | 279 | .Pa ~/.ssh/config . |
bf740959 | 280 | .It Fl f |
281 | Requests | |
282 | .Nm | |
610cd5c6 | 283 | to go to background just before command execution. |
284 | This is useful if | |
bf740959 | 285 | .Nm |
286 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 287 | wants it in the background. |
f54651ce | 288 | This implies |
bf740959 | 289 | .Fl n . |
290 | The recommended way to start X11 programs at a remote site is with | |
291 | something like | |
292 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 293 | .It Fl g |
294 | Allows remote hosts to connect to local forwarded ports. | |
5f4a0c58 | 295 | .It Fl I Ar smartcard_device |
296 | Specifies which smartcard device to use. | |
297 | The argument is the device | |
298 | .Nm | |
299 | should use to communicate with a smartcard used for storing the user's | |
300 | private RSA key. | |
bf740959 | 301 | .It Fl i Ar identity_file |
cf5a07a8 | 302 | Selects a file from which the identity (private key) for |
fa08c86b | 303 | RSA or DSA authentication is read. |
cf5a07a8 | 304 | The default is |
140e3e97 | 305 | .Pa ~/.ssh/identity |
cf5a07a8 | 306 | for protocol version 1, and |
140e3e97 | 307 | .Pa ~/.ssh/id_rsa |
cf5a07a8 | 308 | and |
140e3e97 | 309 | .Pa ~/.ssh/id_dsa |
cf5a07a8 | 310 | for protocol version 2. |
610cd5c6 | 311 | Identity files may also be specified on |
312 | a per-host basis in the configuration file. | |
313 | It is possible to have multiple | |
bf740959 | 314 | .Fl i |
315 | options (and multiple identities specified in | |
316 | configuration files). | |
bf740959 | 317 | .It Fl k |
f7926e97 | 318 | Disables forwarding (delegation) of GSSAPI credentials to the server. |
5f4a0c58 | 319 | .It Fl L Xo |
320 | .Sm off | |
3867aa0a | 321 | .Oo Ar bind_address : Oc |
5f4a0c58 | 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 | |
3867aa0a | 329 | on the local side, optionally bound to the specified |
330 | .Ar bind_address . | |
331 | Whenever a connection is made to this port, the | |
5f4a0c58 | 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. | |
5f4a0c58 | 339 | IPv6 addresses can be specified with an alternative syntax: |
340 | .Sm off | |
341 | .Xo | |
6d7a9e8f | 342 | .Op Ar bind_address No / |
5f4a0c58 | 343 | .Ar port No / Ar host No / |
3867aa0a | 344 | .Ar hostport |
5f4a0c58 | 345 | .Xc |
346 | .Sm on | |
3867aa0a | 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 | |
6c7e3b94 | 359 | indicates that the listening port be bound for local use only, while an |
360 | empty address or | |
361 | .Sq * | |
3867aa0a | 362 | indicates that the port should be available from all interfaces. |
bf740959 | 363 | .It Fl l Ar login_name |
610cd5c6 | 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. | |
5e96b616 | 366 | .It Fl M |
367 | Places the | |
368 | .Nm | |
369 | client into | |
370 | .Dq master | |
371 | mode for connection sharing. | |
372 | Refer to the description of | |
373 | .Cm ControlMaster | |
374 | in | |
375 | .Xr ssh_config 5 | |
376 | for details. | |
9affc5db | 377 | .It Fl m Ar mac_spec |
378 | Additionally, for protocol version 2 a comma-separated list of MAC | |
379 | (message authentication code) algorithms can | |
380 | be specified in order of preference. | |
381 | See the | |
382 | .Cm MACs | |
383 | keyword for more information. | |
5f4a0c58 | 384 | .It Fl N |
385 | Do not execute a remote command. | |
386 | This is useful for just forwarding ports | |
387 | (protocol version 2 only). | |
bf740959 | 388 | .It Fl n |
389 | Redirects stdin from | |
390 | .Pa /dev/null | |
391 | (actually, prevents reading from stdin). | |
392 | This must be used when | |
393 | .Nm | |
610cd5c6 | 394 | is run in the background. |
395 | A common trick is to use this to run X11 programs on a remote machine. | |
396 | For example, | |
bf740959 | 397 | .Ic ssh -n shadows.cs.hut.fi emacs & |
398 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
399 | connection will be automatically forwarded over an encrypted channel. | |
400 | The | |
401 | .Nm | |
402 | program will be put in the background. | |
403 | (This does not work if | |
404 | .Nm | |
405 | needs to ask for a password or passphrase; see also the | |
406 | .Fl f | |
407 | option.) | |
cf848a5e | 408 | .It Fl O Ar ctl_cmd |
409 | Control an active connection multiplexing master process. | |
410 | When the | |
411 | .Fl O | |
412 | option is specified, the | |
413 | .Ar ctl_cmd | |
414 | argument is interpreted and passed to the master process. | |
415 | Valid commands are: | |
416 | .Dq check | |
417 | (check that the master process is running) and | |
418 | .Dq exit | |
419 | (request the master to exit). | |
bf740959 | 420 | .It Fl o Ar option |
38539909 | 421 | Can be used to give options in the format used in the configuration file. |
bf740959 | 422 | This is useful for specifying options for which there is no separate |
610cd5c6 | 423 | command-line flag. |
5f4a0c58 | 424 | For full details of the options listed below, and their possible values, see |
425 | .Xr ssh_config 5 . | |
426 | .Pp | |
427 | .Bl -tag -width Ds -offset indent -compact | |
428 | .It AddressFamily | |
429 | .It BatchMode | |
430 | .It BindAddress | |
431 | .It ChallengeResponseAuthentication | |
432 | .It CheckHostIP | |
433 | .It Cipher | |
434 | .It Ciphers | |
435 | .It ClearAllForwardings | |
436 | .It Compression | |
437 | .It CompressionLevel | |
438 | .It ConnectionAttempts | |
20b267fb | 439 | .It ConnectTimeout |
5e96b616 | 440 | .It ControlMaster |
441 | .It ControlPath | |
5f4a0c58 | 442 | .It DynamicForward |
5f4a0c58 | 443 | .It EscapeChar |
444 | .It ForwardAgent | |
445 | .It ForwardX11 | |
d73a67d7 | 446 | .It ForwardX11Trusted |
5f4a0c58 | 447 | .It GatewayPorts |
448 | .It GlobalKnownHostsFile | |
449 | .It GSSAPIAuthentication | |
450 | .It GSSAPIDelegateCredentials | |
5c63c2ab | 451 | .It HashKnownHosts |
5f4a0c58 | 452 | .It Host |
453 | .It HostbasedAuthentication | |
454 | .It HostKeyAlgorithms | |
455 | .It HostKeyAlias | |
456 | .It HostName | |
457 | .It IdentityFile | |
3a065ed0 | 458 | .It IdentitiesOnly |
396070f8 | 459 | .It KbdInteractiveDevices |
d20f3c9e | 460 | .It LocalCommand |
5f4a0c58 | 461 | .It LocalForward |
462 | .It LogLevel | |
463 | .It MACs | |
464 | .It NoHostAuthenticationForLocalhost | |
465 | .It NumberOfPasswordPrompts | |
466 | .It PasswordAuthentication | |
d20f3c9e | 467 | .It PermitLocalCommand |
5f4a0c58 | 468 | .It Port |
469 | .It PreferredAuthentications | |
470 | .It Protocol | |
471 | .It ProxyCommand | |
472 | .It PubkeyAuthentication | |
473 | .It RemoteForward | |
474 | .It RhostsRSAAuthentication | |
475 | .It RSAAuthentication | |
8e99a198 | 476 | .It SendEnv |
5d8d32a3 | 477 | .It ServerAliveInterval |
478 | .It ServerAliveCountMax | |
5f4a0c58 | 479 | .It SmartcardDevice |
480 | .It StrictHostKeyChecking | |
fd573618 | 481 | .It TCPKeepAlive |
d20f3c9e | 482 | .It Tunnel |
483 | .It TunnelDevice | |
5f4a0c58 | 484 | .It UsePrivilegedPort |
485 | .It User | |
486 | .It UserKnownHostsFile | |
487 | .It VerifyHostKeyDNS | |
488 | .It XAuthLocation | |
489 | .El | |
bf740959 | 490 | .It Fl p Ar port |
610cd5c6 | 491 | Port to connect to on the remote host. |
492 | This can be specified on a | |
bf740959 | 493 | per-host basis in the configuration file. |
bf740959 | 494 | .It Fl q |
610cd5c6 | 495 | Quiet mode. |
496 | Causes all warning and diagnostic messages to be suppressed. | |
5f4a0c58 | 497 | .It Fl R Xo |
498 | .Sm off | |
3867aa0a | 499 | .Oo Ar bind_address : Oc |
5f4a0c58 | 500 | .Ar port : host : hostport |
501 | .Sm on | |
502 | .Xc | |
503 | Specifies that the given port on the remote (server) host is to be | |
504 | forwarded to the given host and port on the local side. | |
505 | This works by allocating a socket to listen to | |
506 | .Ar port | |
507 | on the remote side, and whenever a connection is made to this port, the | |
508 | connection is forwarded over the secure channel, and a connection is | |
509 | made to | |
510 | .Ar host | |
511 | port | |
512 | .Ar hostport | |
513 | from the local machine. | |
3867aa0a | 514 | .Pp |
5f4a0c58 | 515 | Port forwardings can also be specified in the configuration file. |
516 | Privileged ports can be forwarded only when | |
517 | logging in as root on the remote machine. | |
3867aa0a | 518 | IPv6 addresses can be specified by enclosing the address in square braces or |
519 | using an alternative syntax: | |
3867aa0a | 520 | .Sm off |
6c7e3b94 | 521 | .Xo |
6d7a9e8f | 522 | .Op Ar bind_address No / |
6c7e3b94 | 523 | .Ar host No / Ar port No / |
524 | .Ar hostport | |
3867aa0a | 525 | .Xc . |
6c7e3b94 | 526 | .Sm on |
3867aa0a | 527 | .Pp |
528 | By default, the listening socket on the server will be bound to the loopback | |
529 | interface only. | |
530 | This may be overriden by specifying a | |
531 | .Ar bind_address . | |
6c7e3b94 | 532 | An empty |
533 | .Ar bind_address , | |
3867aa0a | 534 | or the address |
6c7e3b94 | 535 | .Ql * , |
3867aa0a | 536 | indicates that the remote socket should listen on all interfaces. |
537 | Specifying a remote | |
538 | .Ar bind_address | |
6c7e3b94 | 539 | will only succeed if the server's |
540 | .Cm GatewayPorts | |
3867aa0a | 541 | option is enabled (see |
6c7e3b94 | 542 | .Xr sshd_config 5 ) . |
f8c6db83 | 543 | .It Fl S Ar ctl_path |
9affc5db | 544 | Specifies the location of a control socket for connection sharing. |
5e96b616 | 545 | Refer to the description of |
0e19494c | 546 | .Cm ControlPath |
547 | and | |
5e96b616 | 548 | .Cm ControlMaster |
549 | in | |
550 | .Xr ssh_config 5 | |
551 | for details. | |
ae810de7 | 552 | .It Fl s |
3cbc677d | 553 | May be used to request invocation of a subsystem on the remote system. |
554 | Subsystems are a feature of the SSH2 protocol which facilitate the use | |
5f4a0c58 | 555 | of SSH as a secure transport for other applications (eg.\& |
556 | .Xr sftp 1 ) . | |
3cbc677d | 557 | The subsystem is specified as the remote command. |
5f4a0c58 | 558 | .It Fl T |
559 | Disable pseudo-tty allocation. | |
bf740959 | 560 | .It Fl t |
610cd5c6 | 561 | Force pseudo-tty allocation. |
4fe2af09 | 562 | This can be used to execute arbitrary |
610cd5c6 | 563 | screen-based programs on a remote machine, which can be very useful, |
564 | e.g., when implementing menu services. | |
8abcdba4 | 565 | Multiple |
566 | .Fl t | |
567 | options force tty allocation, even if | |
568 | .Nm | |
569 | has no local tty. | |
5f4a0c58 | 570 | .It Fl V |
571 | Display the version number and exit. | |
bf740959 | 572 | .It Fl v |
610cd5c6 | 573 | Verbose mode. |
574 | Causes | |
bf740959 | 575 | .Nm |
442c8b33 | 576 | to print debugging messages about its progress. |
577 | This is helpful in | |
578 | debugging connection, authentication, and configuration problems. | |
579 | Multiple | |
580 | .Fl v | |
581 | options increase the verbosity. | |
582 | The maximum is 3. | |
583 | .It Fl w Ar tunnel : Ns Ar tunnel | |
584 | Requests a | |
585 | .Xr tun 4 | |
586 | device on the client and server like the | |
587 | .Cm Tunnel | |
588 | directive in | |
589 | .Xr ssh_config 5 . | |
590 | .It Fl X | |
591 | Enables X11 forwarding. | |
592 | This can also be specified on a per-host basis in a configuration file. | |
593 | .Pp | |
594 | X11 forwarding should be enabled with caution. | |
595 | Users with the ability to bypass file permissions on the remote host | |
596 | (for the user's X authorization database) | |
597 | can access the local X11 display through the forwarded connection. | |
598 | An attacker may then be able to perform activities such as keystroke monitoring. | |
599 | .Pp | |
600 | For this reason, X11 forwarding is subjected to X11 SECURITY extension | |
601 | restrictions by default. | |
602 | Please refer to the | |
603 | .Nm | |
604 | .Fl Y | |
605 | option and the | |
606 | .Cm ForwardX11Trusted | |
607 | directive in | |
608 | .Xr ssh_config 5 | |
609 | for more information. | |
610 | .It Fl x | |
611 | Disables X11 forwarding. | |
612 | .It Fl Y | |
613 | Enables trusted X11 forwarding. | |
614 | Trusted X11 forwardings are not subjected to the X11 SECURITY extension | |
615 | controls. | |
616 | .El | |
617 | .Ss SSH protocol version 1 | |
618 | The first authentication method is the | |
619 | .Em rhosts | |
620 | or | |
621 | .Em hosts.equiv | |
622 | method combined with RSA-based host authentication. | |
623 | If the machine the user logs in from is listed in | |
624 | .Pa /etc/hosts.equiv | |
625 | or | |
626 | .Pa /etc/shosts.equiv | |
627 | on the remote machine, and the user names are | |
628 | the same on both sides, or if the files | |
629 | .Pa ~/.rhosts | |
630 | or | |
631 | .Pa ~/.shosts | |
632 | exist in the user's home directory on the | |
633 | remote machine and contain a line containing the name of the client | |
634 | machine and the name of the user on that machine, the user is | |
635 | considered for log in. | |
636 | Additionally, if the server can verify the client's | |
637 | host key (see | |
638 | .Pa /etc/ssh/ssh_known_hosts | |
639 | and | |
640 | .Pa ~/.ssh/known_hosts | |
641 | in the | |
642 | .Sx FILES | |
643 | section), only then is login permitted. | |
644 | This authentication method closes security holes due to IP | |
645 | spoofing, DNS spoofing and routing spoofing. | |
646 | [Note to the administrator: | |
647 | .Pa /etc/hosts.equiv , | |
648 | .Pa ~/.rhosts , | |
649 | and the rlogin/rsh protocol in general, are inherently insecure and should be | |
650 | disabled if security is desired.] | |
651 | .Pp | |
652 | As a second authentication method, | |
653 | .Nm | |
654 | supports RSA based authentication. | |
655 | The scheme is based on public-key cryptography: there are cryptosystems | |
656 | where encryption and decryption are done using separate keys, and it | |
657 | is not possible to derive the decryption key from the encryption key. | |
658 | RSA is one such system. | |
659 | The idea is that each user creates a public/private | |
660 | key pair for authentication purposes. | |
661 | The server knows the public key, and only the user knows the private key. | |
662 | .Pp | |
663 | The file | |
664 | .Pa ~/.ssh/authorized_keys | |
665 | lists the public keys that are permitted for logging in. | |
666 | When the user logs in, the | |
667 | .Nm | |
668 | program tells the server which key pair it would like to use for | |
669 | authentication. | |
670 | The server checks if this key is permitted, and if so, | |
671 | sends the user (actually the | |
672 | .Nm | |
673 | program running on behalf of the user) a challenge, a random number, | |
674 | encrypted by the user's public key. | |
675 | The challenge can only be decrypted using the proper private key. | |
676 | The user's client then decrypts the challenge using the private key, | |
677 | proving that he/she knows the private key | |
678 | but without disclosing it to the server. | |
679 | .Pp | |
680 | .Nm | |
681 | implements the RSA authentication protocol automatically. | |
682 | The user creates his/her RSA key pair by running | |
683 | .Xr ssh-keygen 1 . | |
684 | This stores the private key in | |
685 | .Pa ~/.ssh/identity | |
686 | and stores the public key in | |
687 | .Pa ~/.ssh/identity.pub | |
688 | in the user's home directory. | |
689 | The user should then copy the | |
690 | .Pa identity.pub | |
691 | to | |
692 | .Pa ~/.ssh/authorized_keys | |
693 | in his/her home directory on the remote machine (the | |
694 | .Pa authorized_keys | |
695 | file corresponds to the conventional | |
696 | .Pa ~/.rhosts | |
697 | file, and has one key | |
698 | per line, though the lines can be very long). | |
699 | After this, the user can log in without giving the password. | |
700 | .Pp | |
701 | The most convenient way to use RSA authentication may be with an | |
702 | authentication agent. | |
703 | See | |
704 | .Xr ssh-agent 1 | |
705 | for more information. | |
706 | .Pp | |
707 | If other authentication methods fail, | |
708 | .Nm | |
709 | prompts the user for a password. | |
710 | The password is sent to the remote | |
711 | host for checking; however, since all communications are encrypted, | |
712 | the password cannot be seen by someone listening on the network. | |
713 | .Ss SSH protocol version 2 | |
714 | When a user connects using protocol version 2, | |
715 | similar authentication methods are available. | |
716 | Using the default values for | |
717 | .Cm PreferredAuthentications , | |
718 | the client will try to authenticate first using the hostbased method; | |
719 | if this method fails, public key authentication is attempted, | |
720 | and finally if this method fails, keyboard-interactive and | |
721 | password authentication are tried. | |
07d688d5 | 722 | .Pp |
442c8b33 | 723 | The public key method is similar to RSA authentication described |
724 | in the previous section and allows the RSA or DSA algorithm to be used: | |
725 | The client uses his private key, | |
726 | .Pa ~/.ssh/id_dsa | |
727 | or | |
728 | .Pa ~/.ssh/id_rsa , | |
729 | to sign the session identifier and sends the result to the server. | |
730 | The server checks whether the matching public key is listed in | |
731 | .Pa ~/.ssh/authorized_keys | |
732 | and grants access if both the key is found and the signature is correct. | |
733 | The session identifier is derived from a shared Diffie-Hellman value | |
734 | and is only known to the client and the server. | |
82966fe8 | 735 | .Pp |
442c8b33 | 736 | If public key authentication fails or is not available, a password |
737 | can be sent encrypted to the remote host to prove the user's identity. | |
738 | .Pp | |
739 | Additionally, | |
82966fe8 | 740 | .Nm |
442c8b33 | 741 | supports hostbased or challenge response authentication. |
742 | .Pp | |
743 | Protocol 2 provides additional mechanisms for confidentiality | |
744 | (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour) | |
745 | and integrity (hmac-md5, hmac-sha1, hmac-ripemd160). | |
746 | Note that protocol 1 lacks a strong mechanism for ensuring the | |
747 | integrity of the connection. | |
748 | .Ss Login session and remote execution | |
749 | When the user's identity has been accepted by the server, the server | |
750 | either executes the given command, or logs into the machine and gives | |
751 | the user a normal shell on the remote machine. | |
752 | All communication with | |
753 | the remote command or shell will be automatically encrypted. | |
754 | .Pp | |
755 | If a pseudo-terminal has been allocated (normal login session), the | |
756 | user may use the escape characters noted below. | |
757 | .Pp | |
758 | If no pseudo-tty has been allocated, | |
759 | the session is transparent and can be used to reliably transfer binary data. | |
760 | On most systems, setting the escape character to | |
761 | .Dq none | |
762 | will also make the session transparent even if a tty is used. | |
763 | .Pp | |
764 | The session terminates when the command or shell on the remote | |
765 | machine exits and all X11 and TCP/IP connections have been closed. | |
766 | The exit status of the remote program is returned as the exit status of | |
767 | .Nm ssh . | |
768 | .Pp | |
bf740959 | 769 | .Nm |
588df31a | 770 | may additionally obtain configuration data from |
771 | a per-user configuration file and a system-wide configuration file. | |
772 | The file format and configuration options are described in | |
773 | .Xr ssh_config 5 . | |
442c8b33 | 774 | .Ss Escape Characters |
775 | When a pseudo-terminal has been requested, | |
776 | .Nm | |
777 | supports a number of functions through the use of an escape character. | |
778 | .Pp | |
779 | A single tilde character can be sent as | |
780 | .Ic ~~ | |
781 | or by following the tilde by a character other than those described below. | |
782 | The escape character must always follow a newline to be interpreted as | |
783 | special. | |
784 | The escape character can be changed in configuration files using the | |
785 | .Cm EscapeChar | |
786 | configuration directive or on the command line by the | |
787 | .Fl e | |
788 | option. | |
789 | .Pp | |
790 | The supported escapes (assuming the default | |
791 | .Ql ~ ) | |
792 | are: | |
793 | .Bl -tag -width Ds | |
794 | .It Cm ~. | |
795 | Disconnect. | |
796 | .It Cm ~^Z | |
797 | Background | |
798 | .Nm ssh . | |
799 | .It Cm ~# | |
800 | List forwarded connections. | |
801 | .It Cm ~& | |
802 | Background | |
803 | .Nm | |
804 | at logout when waiting for forwarded connection / X11 sessions to terminate. | |
805 | .It Cm ~? | |
806 | Display a list of escape characters. | |
807 | .It Cm ~B | |
808 | Send a BREAK to the remote system | |
809 | (only useful for SSH protocol version 2 and if the peer supports it). | |
810 | .It Cm ~C | |
811 | Open command line. | |
812 | Currently this allows the addition of port forwardings using the | |
813 | .Fl L | |
814 | and | |
815 | .Fl R | |
816 | options (see below). | |
817 | It also allows the cancellation of existing remote port-forwardings | |
818 | using | |
819 | .Fl KR Ar hostport . | |
820 | .Ic !\& Ns Ar command | |
821 | allows the user to execute a local command if the | |
822 | .Ic PermitLocalCommand | |
823 | option is enabled in | |
824 | .Xr ssh_config 5 . | |
825 | Basic help is available, using the | |
826 | .Fl h | |
827 | option. | |
828 | .It Cm ~R | |
829 | Request rekeying of the connection | |
830 | (only useful for SSH protocol version 2 and if the peer supports it). | |
831 | .El | |
832 | .Ss X11 and TCP forwarding | |
833 | If the | |
834 | .Cm ForwardX11 | |
835 | variable is set to | |
836 | .Dq yes | |
837 | (or see the description of the | |
838 | .Fl X | |
839 | and | |
840 | .Fl x | |
841 | options described later) | |
842 | and the user is using X11 (the | |
843 | .Ev DISPLAY | |
844 | environment variable is set), the connection to the X11 display is | |
845 | automatically forwarded to the remote side in such a way that any X11 | |
846 | programs started from the shell (or command) will go through the | |
847 | encrypted channel, and the connection to the real X server will be made | |
848 | from the local machine. | |
849 | The user should not manually set | |
850 | .Ev DISPLAY . | |
851 | Forwarding of X11 connections can be | |
852 | configured on the command line or in configuration files. | |
853 | .Pp | |
854 | The | |
855 | .Ev DISPLAY | |
856 | value set by | |
857 | .Nm | |
858 | will point to the server machine, but with a display number greater than zero. | |
859 | This is normal, and happens because | |
860 | .Nm | |
861 | creates a | |
862 | .Dq proxy | |
863 | X server on the server machine for forwarding the | |
864 | connections over the encrypted channel. | |
865 | .Pp | |
866 | .Nm | |
867 | will also automatically set up Xauthority data on the server machine. | |
868 | For this purpose, it will generate a random authorization cookie, | |
869 | store it in Xauthority on the server, and verify that any forwarded | |
870 | connections carry this cookie and replace it by the real cookie when | |
871 | the connection is opened. | |
872 | The real authentication cookie is never | |
873 | sent to the server machine (and no cookies are sent in the plain). | |
874 | .Pp | |
875 | If the | |
876 | .Cm ForwardAgent | |
877 | variable is set to | |
878 | .Dq yes | |
879 | (or see the description of the | |
880 | .Fl A | |
881 | and | |
882 | .Fl a | |
883 | options described later) and | |
884 | the user is using an authentication agent, the connection to the agent | |
885 | is automatically forwarded to the remote side. | |
886 | .Pp | |
887 | Forwarding of arbitrary TCP/IP connections over the secure channel can | |
888 | be specified either on the command line or in a configuration file. | |
889 | One possible application of TCP/IP forwarding is a secure connection to an | |
890 | electronic purse; another is going through firewalls. | |
891 | .Ss Server authentication | |
892 | .Nm | |
893 | automatically maintains and checks a database containing | |
894 | identifications for all hosts it has ever been used with. | |
895 | Host keys are stored in | |
896 | .Pa ~/.ssh/known_hosts | |
897 | in the user's home directory. | |
898 | Additionally, the file | |
899 | .Pa /etc/ssh/ssh_known_hosts | |
900 | is automatically checked for known hosts. | |
901 | Any new hosts are automatically added to the user's file. | |
902 | If a host's identification ever changes, | |
903 | .Nm | |
904 | warns about this and disables password authentication to prevent a | |
905 | trojan horse from getting the user's password. | |
906 | Another purpose of this mechanism is to prevent man-in-the-middle attacks | |
907 | which could otherwise be used to circumvent the encryption. | |
908 | The | |
909 | .Cm StrictHostKeyChecking | |
910 | option can be used to prevent logins to machines whose | |
911 | host key is not known or has changed. | |
912 | .Pp | |
913 | .Nm | |
914 | can be configured to verify host identification using fingerprint resource | |
915 | records (SSHFP) published in DNS. | |
916 | The | |
917 | .Cm VerifyHostKeyDNS | |
918 | option can be used to control how DNS lookups are performed. | |
919 | SSHFP resource records can be generated using | |
920 | .Xr ssh-keygen 1 . | |
bf740959 | 921 | .Sh ENVIRONMENT |
922 | .Nm | |
923 | will normally set the following environment variables: | |
5f4a0c58 | 924 | .Bl -tag -width LOGNAME |
bf740959 | 925 | .It Ev DISPLAY |
926 | The | |
927 | .Ev DISPLAY | |
610cd5c6 | 928 | variable indicates the location of the X11 server. |
f54651ce | 929 | It is automatically set by |
bf740959 | 930 | .Nm |
931 | to point to a value of the form | |
932 | .Dq hostname:n | |
933 | where hostname indicates | |
5f4a0c58 | 934 | the host where the shell runs, and n is an integer \*(Ge 1. |
610cd5c6 | 935 | .Nm |
936 | uses this special value to forward X11 connections over the secure | |
937 | channel. | |
da89cf4d | 938 | The user should normally not set |
939 | .Ev DISPLAY | |
940 | explicitly, as that | |
bf740959 | 941 | will render the X11 connection insecure (and will require the user to |
942 | manually copy any required authorization cookies). | |
943 | .It Ev HOME | |
944 | Set to the path of the user's home directory. | |
945 | .It Ev LOGNAME | |
946 | Synonym for | |
947 | .Ev USER ; | |
948 | set for compatibility with systems that use this variable. | |
949 | .It Ev MAIL | |
ae897d7c | 950 | Set to the path of the user's mailbox. |
610cd5c6 | 951 | .It Ev PATH |
bf740959 | 952 | Set to the default |
953 | .Ev PATH , | |
954 | as specified when compiling | |
955 | .Nm ssh . | |
3474b2b4 | 956 | .It Ev SSH_ASKPASS |
957 | If | |
958 | .Nm | |
959 | needs a passphrase, it will read the passphrase from the current | |
960 | terminal if it was run from a terminal. | |
961 | If | |
962 | .Nm | |
963 | does not have a terminal associated with it but | |
964 | .Ev DISPLAY | |
965 | and | |
966 | .Ev SSH_ASKPASS | |
967 | are set, it will execute the program specified by | |
968 | .Ev SSH_ASKPASS | |
969 | and open an X11 window to read the passphrase. | |
970 | This is particularly useful when calling | |
971 | .Nm | |
972 | from a | |
caeffafb | 973 | .Pa .xsession |
3474b2b4 | 974 | or related script. |
975 | (Note that on some machines it | |
976 | may be necessary to redirect the input from | |
977 | .Pa /dev/null | |
978 | to make this work.) | |
bf740959 | 979 | .It Ev SSH_AUTH_SOCK |
ae897d7c | 980 | Identifies the path of a unix-domain socket used to communicate with the |
bf740959 | 981 | agent. |
da0561eb | 982 | .It Ev SSH_CONNECTION |
983 | Identifies the client and server ends of the connection. | |
610cd5c6 | 984 | The variable contains |
da0561eb | 985 | four space-separated values: client ip-address, client port number, |
986 | server ip-address and server port number. | |
8abcdba4 | 987 | .It Ev SSH_ORIGINAL_COMMAND |
988 | The variable contains the original command line if a forced command | |
989 | is executed. | |
990 | It can be used to extract the original arguments. | |
bf740959 | 991 | .It Ev SSH_TTY |
992 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 993 | with the current shell or command. |
994 | If the current session has no tty, | |
bf740959 | 995 | this variable is not set. |
996 | .It Ev TZ | |
04ac3e62 | 997 | This variable is set to indicate the present time zone if it |
c345cf9d | 998 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 999 | on to new connections). |
1000 | .It Ev USER | |
1001 | Set to the name of the user logging in. | |
1002 | .El | |
1003 | .Pp | |
f54651ce | 1004 | Additionally, |
bf740959 | 1005 | .Nm |
f54651ce | 1006 | reads |
140e3e97 | 1007 | .Pa ~/.ssh/environment , |
bf740959 | 1008 | and adds lines of the format |
1009 | .Dq VARNAME=value | |
6a342527 | 1010 | to the environment if the file exists and if users are allowed to |
1011 | change their environment. | |
5f4a0c58 | 1012 | For more information, see the |
6a342527 | 1013 | .Cm PermitUserEnvironment |
35453849 | 1014 | option in |
6a342527 | 1015 | .Xr sshd_config 5 . |
bf740959 | 1016 | .Sh FILES |
c8d54615 | 1017 | .Bl -tag -width Ds |
140e3e97 | 1018 | .It Pa ~/.ssh/known_hosts |
ae897d7c | 1019 | Records host keys for all hosts the user has logged into that are not |
bf740959 | 1020 | in |
2a8a6488 | 1021 | .Pa /etc/ssh/ssh_known_hosts . |
bf740959 | 1022 | See |
1023 | .Xr sshd 8 . | |
140e3e97 | 1024 | .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa |
c0ecc314 | 1025 | Contains the authentication identity of the user. |
1026 | They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. | |
1d1ffb87 | 1027 | These files |
1028 | contain sensitive data and should be readable by the user but not | |
bf740959 | 1029 | accessible by others (read/write/execute). |
1030 | Note that | |
1031 | .Nm | |
1d1ffb87 | 1032 | ignores a private key file if it is accessible by others. |
bf740959 | 1033 | It is possible to specify a passphrase when |
1034 | generating the key; the passphrase will be used to encrypt the | |
1035 | sensitive part of this file using 3DES. | |
140e3e97 | 1036 | .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub |
bf740959 | 1037 | Contains the public key for authentication (public part of the |
610cd5c6 | 1038 | identity file in human-readable form). |
1d1ffb87 | 1039 | The contents of the |
140e3e97 | 1040 | .Pa ~/.ssh/identity.pub |
5f4a0c58 | 1041 | file should be added to the file |
140e3e97 | 1042 | .Pa ~/.ssh/authorized_keys |
bf740959 | 1043 | on all machines |
91789042 | 1044 | where the user wishes to log in using protocol version 1 RSA authentication. |
1d1ffb87 | 1045 | The contents of the |
140e3e97 | 1046 | .Pa ~/.ssh/id_dsa.pub |
c0ecc314 | 1047 | and |
140e3e97 | 1048 | .Pa ~/.ssh/id_rsa.pub |
1d1ffb87 | 1049 | file should be added to |
140e3e97 | 1050 | .Pa ~/.ssh/authorized_keys |
1d1ffb87 | 1051 | on all machines |
91789042 | 1052 | where the user wishes to log in using protocol version 2 DSA/RSA authentication. |
1d1ffb87 | 1053 | These files are not |
610cd5c6 | 1054 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 1055 | These files are |
c44559d2 | 1056 | never used automatically and are not necessary; they are only provided for |
bf740959 | 1057 | the convenience of the user. |
140e3e97 | 1058 | .It Pa ~/.ssh/config |
610cd5c6 | 1059 | This is the per-user configuration file. |
588df31a | 1060 | The file format and configuration options are described in |
1061 | .Xr ssh_config 5 . | |
e1520719 | 1062 | Because of the potential for abuse, this file must have strict permissions: |
1063 | read/write for the user, and not accessible by others. | |
140e3e97 | 1064 | .It Pa ~/.ssh/authorized_keys |
96a7b0cc | 1065 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. |
610cd5c6 | 1066 | The format of this file is described in the |
bf740959 | 1067 | .Xr sshd 8 |
610cd5c6 | 1068 | manual page. |
5f4a0c58 | 1069 | In the simplest form the format is the same as the |
1070 | .Pa .pub | |
f49bc4f7 | 1071 | identity files. |
1d1ffb87 | 1072 | This file is not highly sensitive, but the recommended |
1073 | permissions are read/write for the user, and not accessible by others. | |
2a8a6488 | 1074 | .It Pa /etc/ssh/ssh_known_hosts |
610cd5c6 | 1075 | Systemwide list of known host keys. |
f49bc4f7 | 1076 | This file should be prepared by the |
bf740959 | 1077 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1078 | organization. |
1079 | This file should be world-readable. | |
1080 | This file contains | |
bf740959 | 1081 | public keys, one per line, in the following format (fields separated |
f49bc4f7 | 1082 | by spaces): system name, public key and optional comment field. |
610cd5c6 | 1083 | When different names are used |
bf740959 | 1084 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1085 | commas. |
5f4a0c58 | 1086 | The format is described in the |
bf740959 | 1087 | .Xr sshd 8 |
1088 | manual page. | |
1089 | .Pp | |
1090 | The canonical system name (as returned by name servers) is used by | |
1091 | .Xr sshd 8 | |
1092 | to verify the client host when logging in; other names are needed because | |
1093 | .Nm | |
1094 | does not convert the user-supplied name to a canonical name before | |
1095 | checking the key, because someone with access to the name servers | |
1096 | would then be able to fool host authentication. | |
2a8a6488 | 1097 | .It Pa /etc/ssh/ssh_config |
610cd5c6 | 1098 | Systemwide configuration file. |
588df31a | 1099 | The file format and configuration options are described in |
1100 | .Xr ssh_config 5 . | |
2a8a6488 | 1101 | .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key |
dd58cb5e | 1102 | These three files contain the private parts of the host keys |
1103 | and are used for | |
1104 | .Cm RhostsRSAAuthentication | |
1105 | and | |
1106 | .Cm HostbasedAuthentication . | |
d83cbdc3 | 1107 | If the protocol version 1 |
1108 | .Cm RhostsRSAAuthentication | |
7203d6bb | 1109 | method is used, |
d83cbdc3 | 1110 | .Nm |
1111 | must be setuid root, since the host key is readable only by root. | |
1112 | For protocol version 2, | |
1113 | .Nm | |
1114 | uses | |
1115 | .Xr ssh-keysign 8 | |
1116 | to access the host keys for | |
1117 | .Cm HostbasedAuthentication . | |
1118 | This eliminates the requirement that | |
1119 | .Nm | |
1120 | be setuid root when that authentication method is used. | |
1121 | By default | |
dd58cb5e | 1122 | .Nm |
d83cbdc3 | 1123 | is not setuid root. |
140e3e97 | 1124 | .It Pa ~/.rhosts |
bf740959 | 1125 | This file is used in |
6f5abc1e | 1126 | .Cm RhostsRSAAuthentication |
1127 | and | |
1128 | .Cm HostbasedAuthentication | |
bf740959 | 1129 | authentication to list the |
610cd5c6 | 1130 | host/user pairs that are permitted to log in. |
1131 | (Note that this file is | |
bf740959 | 1132 | also used by rlogin and rsh, which makes using this file insecure.) |
1133 | Each line of the file contains a host name (in the canonical form | |
1134 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1135 | separated by a space. |
e91c60f2 | 1136 | On some machines this file may need to be |
bf740959 | 1137 | world-readable if the user's home directory is on a NFS partition, |
1138 | because | |
1139 | .Xr sshd 8 | |
610cd5c6 | 1140 | reads it as root. |
1141 | Additionally, this file must be owned by the user, | |
1142 | and must not have write permissions for anyone else. | |
1143 | The recommended | |
bf740959 | 1144 | permission for most machines is read/write for the user, and not |
1145 | accessible by others. | |
1146 | .Pp | |
6f5abc1e | 1147 | Note that |
bf740959 | 1148 | .Xr sshd 8 |
6f5abc1e | 1149 | allows authentication only in combination with client host key |
1150 | authentication before permitting log in. | |
91789042 | 1151 | If the server machine does not have the client's host key in |
2a8a6488 | 1152 | .Pa /etc/ssh/ssh_known_hosts , |
91789042 | 1153 | it can be stored in |
140e3e97 | 1154 | .Pa ~/.ssh/known_hosts . |
bf740959 | 1155 | The easiest way to do this is to |
1156 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1157 | will automatically add the host key to |
140e3e97 | 1158 | .Pa ~/.ssh/known_hosts . |
1159 | .It Pa ~/.shosts | |
bf740959 | 1160 | This file is used exactly the same way as |
5f4a0c58 | 1161 | .Pa .rhosts . |
bf740959 | 1162 | The purpose for |
6f5abc1e | 1163 | having this file is to be able to use |
1164 | .Cm RhostsRSAAuthentication | |
1165 | and | |
1166 | .Cm HostbasedAuthentication | |
1167 | authentication without permitting login with | |
5f4a0c58 | 1168 | .Xr rlogin |
bf740959 | 1169 | or |
1170 | .Xr rsh 1 . | |
1171 | .It Pa /etc/hosts.equiv | |
1172 | This file is used during | |
6f5abc1e | 1173 | .Cm RhostsRSAAuthentication |
1174 | and | |
1175 | .Cm HostbasedAuthentication | |
be193d89 | 1176 | authentication. |
610cd5c6 | 1177 | It contains |
5f4a0c58 | 1178 | canonical hosts names, one per line (the full format is described in the |
bf740959 | 1179 | .Xr sshd 8 |
610cd5c6 | 1180 | manual page). |
1181 | If the client host is found in this file, login is | |
bf740959 | 1182 | automatically permitted provided client and server user names are the |
610cd5c6 | 1183 | same. |
6f5abc1e | 1184 | Additionally, successful client host key authentication is required. |
610cd5c6 | 1185 | This file should only be writable by root. |
5f4fdfae | 1186 | .It Pa /etc/shosts.equiv |
f54651ce | 1187 | This file is processed exactly as |
bf740959 | 1188 | .Pa /etc/hosts.equiv . |
1189 | This file may be useful to permit logins using | |
1190 | .Nm | |
1191 | but not using rsh/rlogin. | |
2a8a6488 | 1192 | .It Pa /etc/ssh/sshrc |
bf740959 | 1193 | Commands in this file are executed by |
1194 | .Nm | |
1195 | when the user logs in just before the user's shell (or command) is started. | |
1196 | See the | |
1197 | .Xr sshd 8 | |
1198 | manual page for more information. | |
140e3e97 | 1199 | .It Pa ~/.ssh/rc |
bf740959 | 1200 | Commands in this file are executed by |
1201 | .Nm | |
1202 | when the user logs in just before the user's shell (or command) is | |
1203 | started. | |
f54651ce | 1204 | See the |
bf740959 | 1205 | .Xr sshd 8 |
1206 | manual page for more information. | |
140e3e97 | 1207 | .It Pa ~/.ssh/environment |
83b7f649 | 1208 | Contains additional definitions for environment variables, see section |
1209 | .Sx ENVIRONMENT | |
1210 | above. | |
b5e300c2 | 1211 | .El |
16210ef7 | 1212 | .Sh DIAGNOSTICS |
1213 | .Nm | |
1214 | exits with the exit status of the remote command or with 255 | |
1215 | if an error occurred. | |
bf740959 | 1216 | .Sh SEE ALSO |
5f4a0c58 | 1217 | .Xr gzip 1 , |
bf740959 | 1218 | .Xr rsh 1 , |
1219 | .Xr scp 1 , | |
61e96248 | 1220 | .Xr sftp 1 , |
bf740959 | 1221 | .Xr ssh-add 1 , |
1222 | .Xr ssh-agent 1 , | |
1223 | .Xr ssh-keygen 1 , | |
1224 | .Xr telnet 1 , | |
5f4a0c58 | 1225 | .Xr hosts.equiv 5 , |
1ae02182 | 1226 | .Xr ssh_config 5 , |
b2843ec6 | 1227 | .Xr ssh-keysign 8 , |
9afadca8 | 1228 | .Xr sshd 8 |
2cad6cef | 1229 | .Rs |
1230 | .%A T. Ylonen | |
1231 | .%A T. Kivinen | |
1232 | .%A M. Saarinen | |
1233 | .%A T. Rinne | |
1234 | .%A S. Lehtinen | |
1235 | .%T "SSH Protocol Architecture" | |
17f5e68a | 1236 | .%N draft-ietf-secsh-architecture-12.txt |
1237 | .%D January 2002 | |
2cad6cef | 1238 | .%O work in progress material |
1239 | .Re | |
be193d89 | 1240 | .Sh AUTHORS |
1241 | OpenSSH is a derivative of the original and free | |
1242 | ssh 1.2.12 release by Tatu Ylonen. | |
1243 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1244 | Theo de Raadt and Dug Song | |
1245 | removed many bugs, re-added newer features and | |
1246 | created OpenSSH. | |
1247 | Markus Friedl contributed the support for SSH | |
1248 | protocol versions 1.5 and 2.0. |