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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 | .\" |
a55c1733 | 37 | .\" $OpenBSD: ssh.1,v 1.221 2005/12/16 18:14:40 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 |
a55c1733 | 103 | depending on the protocol version used (see below). |
1d1ffb87 | 104 | .Pp |
5f4a0c58 | 105 | If |
106 | .Ar command | |
107 | is specified, | |
e426efa9 | 108 | it is executed on the remote host instead of a login shell. |
bf740959 | 109 | .Pp |
442c8b33 | 110 | The options are as follows: |
111 | .Bl -tag -width Ds | |
112 | .It Fl 1 | |
113 | Forces | |
bf740959 | 114 | .Nm |
442c8b33 | 115 | to try protocol version 1 only. |
116 | .It Fl 2 | |
117 | Forces | |
bf740959 | 118 | .Nm |
442c8b33 | 119 | to try protocol version 2 only. |
120 | .It Fl 4 | |
121 | Forces | |
bf740959 | 122 | .Nm |
442c8b33 | 123 | to use IPv4 addresses only. |
124 | .It Fl 6 | |
125 | Forces | |
bf740959 | 126 | .Nm |
442c8b33 | 127 | to use IPv6 addresses only. |
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. | |
bf740959 | 131 | .Pp |
442c8b33 | 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, | |
137 | however they can perform operations on the keys that enable them to | |
138 | authenticate using the identities loaded into the agent. | |
139 | .It Fl a | |
140 | Disables forwarding of the authentication agent connection. | |
141 | .It Fl b Ar bind_address | |
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. | |
147 | .It Fl C | |
148 | Requests compression of all data (including stdin, stdout, stderr, and | |
149 | data for forwarded X11 and TCP/IP connections). | |
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. | |
163 | .It Fl c Ar cipher_spec | |
164 | Selects the cipher specification for encrypting the session. | |
bf740959 | 165 | .Pp |
442c8b33 | 166 | Protocol version 1 allows specification of a single cipher. |
167 | The supported values are | |
168 | .Dq 3des , | |
0fe62d3d | 169 | .Dq blowfish , |
442c8b33 | 170 | and |
171 | .Dq des . | |
172 | .Ar 3des | |
173 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
174 | It is believed to be secure. | |
175 | .Ar blowfish | |
176 | is a fast block cipher; it appears very secure and is much faster than | |
177 | .Ar 3des . | |
178 | .Ar des | |
179 | is only supported in the | |
bf740959 | 180 | .Nm |
442c8b33 | 181 | client for interoperability with legacy protocol 1 implementations |
182 | that do not support the | |
183 | .Ar 3des | |
184 | cipher. | |
185 | Its use is strongly discouraged due to cryptographic weaknesses. | |
186 | The default is | |
187 | .Dq 3des . | |
da89cf4d | 188 | .Pp |
442c8b33 | 189 | For protocol version 2 |
190 | .Ar cipher_spec | |
191 | is a comma-separated list of ciphers | |
192 | listed in order of preference. | |
193 | The supported ciphers are | |
194 | .Dq 3des-cbc , | |
195 | .Dq aes128-cbc , | |
196 | .Dq aes192-cbc , | |
197 | .Dq aes256-cbc , | |
198 | .Dq aes128-ctr , | |
199 | .Dq aes192-ctr , | |
200 | .Dq aes256-ctr , | |
201 | .Dq arcfour128 , | |
202 | .Dq arcfour256 , | |
203 | .Dq arcfour , | |
204 | .Dq blowfish-cbc , | |
205 | and | |
206 | .Dq cast128-cbc . | |
0fe62d3d | 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 | |
442c8b33 | 212 | .Ed |
213 | .It Fl D Xo | |
214 | .Sm off | |
215 | .Oo Ar bind_address : Oc | |
216 | .Ar port | |
217 | .Sm on | |
218 | .Xc | |
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 | |
224 | on the local side, optionally bound to the specified | |
225 | .Ar bind_address . | |
226 | Whenever a connection is made to this port, the | |
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 | |
da89cf4d | 231 | .Nm |
442c8b33 | 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. | |
5ddc5eb4 | 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. | |
5f4a0c58 | 259 | .It Fl e Ar ch | ^ch | none |
bf740959 | 260 | Sets the escape character for sessions with a pty (default: |
261 | .Ql ~ ) . | |
610cd5c6 | 262 | The escape character is only recognized at the beginning of a line. |
263 | The escape character followed by a dot | |
bf740959 | 264 | .Pq Ql \&. |
5f4a0c58 | 265 | closes the connection; |
266 | followed by control-Z suspends the connection; | |
267 | and followed by itself sends the escape character once. | |
610cd5c6 | 268 | Setting the character to |
bf740959 | 269 | .Dq none |
270 | disables any escapes and makes the session fully transparent. | |
5f4a0c58 | 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 | |
140e3e97 | 278 | .Pa ~/.ssh/config . |
bf740959 | 279 | .It Fl f |
280 | Requests | |
281 | .Nm | |
610cd5c6 | 282 | to go to background just before command execution. |
283 | This is useful if | |
bf740959 | 284 | .Nm |
285 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 286 | wants it in the background. |
f54651ce | 287 | This implies |
bf740959 | 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 . | |
7b2ea3a1 | 292 | .It Fl g |
293 | Allows remote hosts to connect to local forwarded ports. | |
5f4a0c58 | 294 | .It Fl I Ar smartcard_device |
295 | Specifies which smartcard device to use. | |
296 | The argument is the device | |
297 | .Nm | |
298 | should use to communicate with a smartcard used for storing the user's | |
299 | private RSA key. | |
bf740959 | 300 | .It Fl i Ar identity_file |
cf5a07a8 | 301 | Selects a file from which the identity (private key) for |
fa08c86b | 302 | RSA or DSA authentication is read. |
cf5a07a8 | 303 | The default is |
140e3e97 | 304 | .Pa ~/.ssh/identity |
cf5a07a8 | 305 | for protocol version 1, and |
140e3e97 | 306 | .Pa ~/.ssh/id_rsa |
cf5a07a8 | 307 | and |
140e3e97 | 308 | .Pa ~/.ssh/id_dsa |
cf5a07a8 | 309 | for protocol version 2. |
610cd5c6 | 310 | Identity files may also be specified on |
311 | a per-host basis in the configuration file. | |
312 | It is possible to have multiple | |
bf740959 | 313 | .Fl i |
314 | options (and multiple identities specified in | |
315 | configuration files). | |
bf740959 | 316 | .It Fl k |
f7926e97 | 317 | Disables forwarding (delegation) of GSSAPI credentials to the server. |
5f4a0c58 | 318 | .It Fl L Xo |
319 | .Sm off | |
3867aa0a | 320 | .Oo Ar bind_address : Oc |
5f4a0c58 | 321 | .Ar port : host : hostport |
322 | .Sm on | |
323 | .Xc | |
324 | Specifies that the given port on the local (client) host is to be | |
325 | forwarded to the given host and port on the remote side. | |
326 | This works by allocating a socket to listen to | |
327 | .Ar port | |
3867aa0a | 328 | on the local side, optionally bound to the specified |
329 | .Ar bind_address . | |
330 | Whenever a connection is made to this port, the | |
5f4a0c58 | 331 | connection is forwarded over the secure channel, and a connection is |
332 | made to | |
333 | .Ar host | |
334 | port | |
335 | .Ar hostport | |
336 | from the remote machine. | |
337 | Port forwardings can also be specified in the configuration file. | |
5f4a0c58 | 338 | IPv6 addresses can be specified with an alternative syntax: |
339 | .Sm off | |
340 | .Xo | |
6d7a9e8f | 341 | .Op Ar bind_address No / |
5f4a0c58 | 342 | .Ar port No / Ar host No / |
3867aa0a | 343 | .Ar hostport |
5f4a0c58 | 344 | .Xc |
345 | .Sm on | |
3867aa0a | 346 | or by enclosing the address in square brackets. |
347 | Only the superuser can forward privileged ports. | |
348 | By default, the local port is bound in accordance with the | |
349 | .Cm GatewayPorts | |
350 | setting. | |
351 | However, an explicit | |
352 | .Ar bind_address | |
353 | may be used to bind the connection to a specific address. | |
354 | The | |
355 | .Ar bind_address | |
356 | of | |
357 | .Dq localhost | |
6c7e3b94 | 358 | indicates that the listening port be bound for local use only, while an |
359 | empty address or | |
360 | .Sq * | |
3867aa0a | 361 | indicates that the port should be available from all interfaces. |
bf740959 | 362 | .It Fl l Ar login_name |
610cd5c6 | 363 | Specifies the user to log in as on the remote machine. |
364 | This also may be specified on a per-host basis in the configuration file. | |
5e96b616 | 365 | .It Fl M |
366 | Places the | |
367 | .Nm | |
368 | client into | |
369 | .Dq master | |
370 | mode for connection sharing. | |
371 | Refer to the description of | |
372 | .Cm ControlMaster | |
373 | in | |
374 | .Xr ssh_config 5 | |
375 | for details. | |
9affc5db | 376 | .It Fl m Ar mac_spec |
377 | Additionally, for protocol version 2 a comma-separated list of MAC | |
378 | (message authentication code) algorithms can | |
379 | be specified in order of preference. | |
380 | See the | |
381 | .Cm MACs | |
382 | keyword for more information. | |
5f4a0c58 | 383 | .It Fl N |
384 | Do not execute a remote command. | |
385 | This is useful for just forwarding ports | |
386 | (protocol version 2 only). | |
bf740959 | 387 | .It Fl n |
388 | Redirects stdin from | |
389 | .Pa /dev/null | |
390 | (actually, prevents reading from stdin). | |
391 | This must be used when | |
392 | .Nm | |
610cd5c6 | 393 | is run in the background. |
394 | A common trick is to use this to run X11 programs on a remote machine. | |
395 | For example, | |
bf740959 | 396 | .Ic ssh -n shadows.cs.hut.fi emacs & |
397 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
398 | connection will be automatically forwarded over an encrypted channel. | |
399 | The | |
400 | .Nm | |
401 | program will be put in the background. | |
402 | (This does not work if | |
403 | .Nm | |
404 | needs to ask for a password or passphrase; see also the | |
405 | .Fl f | |
406 | option.) | |
cf848a5e | 407 | .It Fl O Ar ctl_cmd |
408 | Control an active connection multiplexing master process. | |
409 | When the | |
410 | .Fl O | |
411 | option is specified, the | |
412 | .Ar ctl_cmd | |
413 | argument is interpreted and passed to the master process. | |
414 | Valid commands are: | |
415 | .Dq check | |
416 | (check that the master process is running) and | |
417 | .Dq exit | |
418 | (request the master to exit). | |
bf740959 | 419 | .It Fl o Ar option |
38539909 | 420 | Can be used to give options in the format used in the configuration file. |
bf740959 | 421 | This is useful for specifying options for which there is no separate |
610cd5c6 | 422 | command-line flag. |
5f4a0c58 | 423 | For full details of the options listed below, and their possible values, see |
424 | .Xr ssh_config 5 . | |
425 | .Pp | |
426 | .Bl -tag -width Ds -offset indent -compact | |
427 | .It AddressFamily | |
428 | .It BatchMode | |
429 | .It BindAddress | |
430 | .It ChallengeResponseAuthentication | |
431 | .It CheckHostIP | |
432 | .It Cipher | |
433 | .It Ciphers | |
434 | .It ClearAllForwardings | |
435 | .It Compression | |
436 | .It CompressionLevel | |
437 | .It ConnectionAttempts | |
20b267fb | 438 | .It ConnectTimeout |
5e96b616 | 439 | .It ControlMaster |
440 | .It ControlPath | |
5f4a0c58 | 441 | .It DynamicForward |
5f4a0c58 | 442 | .It EscapeChar |
443 | .It ForwardAgent | |
444 | .It ForwardX11 | |
d73a67d7 | 445 | .It ForwardX11Trusted |
5f4a0c58 | 446 | .It GatewayPorts |
447 | .It GlobalKnownHostsFile | |
448 | .It GSSAPIAuthentication | |
449 | .It GSSAPIDelegateCredentials | |
5c63c2ab | 450 | .It HashKnownHosts |
5f4a0c58 | 451 | .It Host |
452 | .It HostbasedAuthentication | |
453 | .It HostKeyAlgorithms | |
454 | .It HostKeyAlias | |
455 | .It HostName | |
456 | .It IdentityFile | |
3a065ed0 | 457 | .It IdentitiesOnly |
396070f8 | 458 | .It KbdInteractiveDevices |
d20f3c9e | 459 | .It LocalCommand |
5f4a0c58 | 460 | .It LocalForward |
461 | .It LogLevel | |
462 | .It MACs | |
463 | .It NoHostAuthenticationForLocalhost | |
464 | .It NumberOfPasswordPrompts | |
465 | .It PasswordAuthentication | |
d20f3c9e | 466 | .It PermitLocalCommand |
5f4a0c58 | 467 | .It Port |
468 | .It PreferredAuthentications | |
469 | .It Protocol | |
470 | .It ProxyCommand | |
471 | .It PubkeyAuthentication | |
472 | .It RemoteForward | |
473 | .It RhostsRSAAuthentication | |
474 | .It RSAAuthentication | |
8e99a198 | 475 | .It SendEnv |
5d8d32a3 | 476 | .It ServerAliveInterval |
477 | .It ServerAliveCountMax | |
5f4a0c58 | 478 | .It SmartcardDevice |
479 | .It StrictHostKeyChecking | |
fd573618 | 480 | .It TCPKeepAlive |
d20f3c9e | 481 | .It Tunnel |
482 | .It TunnelDevice | |
5f4a0c58 | 483 | .It UsePrivilegedPort |
484 | .It User | |
485 | .It UserKnownHostsFile | |
486 | .It VerifyHostKeyDNS | |
487 | .It XAuthLocation | |
488 | .El | |
bf740959 | 489 | .It Fl p Ar port |
610cd5c6 | 490 | Port to connect to on the remote host. |
491 | This can be specified on a | |
bf740959 | 492 | per-host basis in the configuration file. |
bf740959 | 493 | .It Fl q |
610cd5c6 | 494 | Quiet mode. |
495 | Causes all warning and diagnostic messages to be suppressed. | |
5f4a0c58 | 496 | .It Fl R Xo |
497 | .Sm off | |
3867aa0a | 498 | .Oo Ar bind_address : Oc |
5f4a0c58 | 499 | .Ar port : host : hostport |
500 | .Sm on | |
501 | .Xc | |
502 | Specifies that the given port on the remote (server) host is to be | |
503 | forwarded to the given host and port on the local side. | |
504 | This works by allocating a socket to listen to | |
505 | .Ar port | |
506 | on the remote side, and whenever a connection is made to this port, the | |
507 | connection is forwarded over the secure channel, and a connection is | |
508 | made to | |
509 | .Ar host | |
510 | port | |
511 | .Ar hostport | |
512 | from the local machine. | |
3867aa0a | 513 | .Pp |
5f4a0c58 | 514 | Port forwardings can also be specified in the configuration file. |
515 | Privileged ports can be forwarded only when | |
516 | logging in as root on the remote machine. | |
3867aa0a | 517 | IPv6 addresses can be specified by enclosing the address in square braces or |
518 | using an alternative syntax: | |
3867aa0a | 519 | .Sm off |
6c7e3b94 | 520 | .Xo |
6d7a9e8f | 521 | .Op Ar bind_address No / |
6c7e3b94 | 522 | .Ar host No / Ar port No / |
523 | .Ar hostport | |
3867aa0a | 524 | .Xc . |
6c7e3b94 | 525 | .Sm on |
3867aa0a | 526 | .Pp |
527 | By default, the listening socket on the server will be bound to the loopback | |
528 | interface only. | |
529 | This may be overriden by specifying a | |
530 | .Ar bind_address . | |
6c7e3b94 | 531 | An empty |
532 | .Ar bind_address , | |
3867aa0a | 533 | or the address |
6c7e3b94 | 534 | .Ql * , |
3867aa0a | 535 | indicates that the remote socket should listen on all interfaces. |
536 | Specifying a remote | |
537 | .Ar bind_address | |
6c7e3b94 | 538 | will only succeed if the server's |
539 | .Cm GatewayPorts | |
3867aa0a | 540 | option is enabled (see |
6c7e3b94 | 541 | .Xr sshd_config 5 ) . |
f8c6db83 | 542 | .It Fl S Ar ctl_path |
9affc5db | 543 | Specifies the location of a control socket for connection sharing. |
5e96b616 | 544 | Refer to the description of |
0e19494c | 545 | .Cm ControlPath |
546 | and | |
5e96b616 | 547 | .Cm ControlMaster |
548 | in | |
549 | .Xr ssh_config 5 | |
550 | for details. | |
ae810de7 | 551 | .It Fl s |
3cbc677d | 552 | May be used to request invocation of a subsystem on the remote system. |
553 | Subsystems are a feature of the SSH2 protocol which facilitate the use | |
5f4a0c58 | 554 | of SSH as a secure transport for other applications (eg.\& |
555 | .Xr sftp 1 ) . | |
3cbc677d | 556 | The subsystem is specified as the remote command. |
5f4a0c58 | 557 | .It Fl T |
558 | Disable pseudo-tty allocation. | |
bf740959 | 559 | .It Fl t |
610cd5c6 | 560 | Force pseudo-tty allocation. |
4fe2af09 | 561 | This can be used to execute arbitrary |
610cd5c6 | 562 | screen-based programs on a remote machine, which can be very useful, |
563 | e.g., when implementing menu services. | |
8abcdba4 | 564 | Multiple |
565 | .Fl t | |
566 | options force tty allocation, even if | |
567 | .Nm | |
568 | has no local tty. | |
5f4a0c58 | 569 | .It Fl V |
570 | Display the version number and exit. | |
bf740959 | 571 | .It Fl v |
610cd5c6 | 572 | Verbose mode. |
573 | Causes | |
bf740959 | 574 | .Nm |
442c8b33 | 575 | to print debugging messages about its progress. |
576 | This is helpful in | |
577 | debugging connection, authentication, and configuration problems. | |
578 | Multiple | |
579 | .Fl v | |
580 | options increase the verbosity. | |
581 | The maximum is 3. | |
582 | .It Fl w Ar tunnel : Ns Ar tunnel | |
583 | Requests a | |
584 | .Xr tun 4 | |
585 | device on the client and server like the | |
586 | .Cm Tunnel | |
587 | directive in | |
588 | .Xr ssh_config 5 . | |
589 | .It Fl X | |
590 | Enables X11 forwarding. | |
591 | This can also be specified on a per-host basis in a configuration file. | |
592 | .Pp | |
593 | X11 forwarding should be enabled with caution. | |
594 | Users with the ability to bypass file permissions on the remote host | |
595 | (for the user's X authorization database) | |
596 | can access the local X11 display through the forwarded connection. | |
597 | An attacker may then be able to perform activities such as keystroke monitoring. | |
598 | .Pp | |
599 | For this reason, X11 forwarding is subjected to X11 SECURITY extension | |
600 | restrictions by default. | |
601 | Please refer to the | |
602 | .Nm | |
603 | .Fl Y | |
604 | option and the | |
605 | .Cm ForwardX11Trusted | |
606 | directive in | |
607 | .Xr ssh_config 5 | |
608 | for more information. | |
609 | .It Fl x | |
610 | Disables X11 forwarding. | |
611 | .It Fl Y | |
612 | Enables trusted X11 forwarding. | |
613 | Trusted X11 forwardings are not subjected to the X11 SECURITY extension | |
614 | controls. | |
615 | .El | |
616 | .Ss SSH protocol version 1 | |
617 | The first authentication method is the | |
618 | .Em rhosts | |
619 | or | |
620 | .Em hosts.equiv | |
621 | method combined with RSA-based host authentication. | |
622 | If the machine the user logs in from is listed in | |
623 | .Pa /etc/hosts.equiv | |
624 | or | |
625 | .Pa /etc/shosts.equiv | |
626 | on the remote machine, and the user names are | |
627 | the same on both sides, or if the files | |
628 | .Pa ~/.rhosts | |
629 | or | |
630 | .Pa ~/.shosts | |
631 | exist in the user's home directory on the | |
632 | remote machine and contain a line containing the name of the client | |
633 | machine and the name of the user on that machine, the user is | |
634 | considered for log in. | |
635 | Additionally, if the server can verify the client's | |
636 | host key (see | |
637 | .Pa /etc/ssh/ssh_known_hosts | |
638 | and | |
639 | .Pa ~/.ssh/known_hosts | |
640 | in the | |
641 | .Sx FILES | |
642 | section), only then is login permitted. | |
643 | This authentication method closes security holes due to IP | |
644 | spoofing, DNS spoofing and routing spoofing. | |
645 | [Note to the administrator: | |
646 | .Pa /etc/hosts.equiv , | |
647 | .Pa ~/.rhosts , | |
648 | and the rlogin/rsh protocol in general, are inherently insecure and should be | |
649 | disabled if security is desired.] | |
650 | .Pp | |
651 | As a second authentication method, | |
652 | .Nm | |
653 | supports RSA based authentication. | |
654 | The scheme is based on public-key cryptography: there are cryptosystems | |
655 | where encryption and decryption are done using separate keys, and it | |
656 | is not possible to derive the decryption key from the encryption key. | |
657 | RSA is one such system. | |
658 | The idea is that each user creates a public/private | |
659 | key pair for authentication purposes. | |
660 | The server knows the public key, and only the user knows the private key. | |
661 | .Pp | |
662 | The file | |
663 | .Pa ~/.ssh/authorized_keys | |
664 | lists the public keys that are permitted for logging in. | |
665 | When the user logs in, the | |
666 | .Nm | |
667 | program tells the server which key pair it would like to use for | |
668 | authentication. | |
669 | The server checks if this key is permitted, and if so, | |
670 | sends the user (actually the | |
671 | .Nm | |
672 | program running on behalf of the user) a challenge, a random number, | |
673 | encrypted by the user's public key. | |
674 | The challenge can only be decrypted using the proper private key. | |
675 | The user's client then decrypts the challenge using the private key, | |
676 | proving that he/she knows the private key | |
677 | but without disclosing it to the server. | |
678 | .Pp | |
679 | .Nm | |
680 | implements the RSA authentication protocol automatically. | |
681 | The user creates his/her RSA key pair by running | |
682 | .Xr ssh-keygen 1 . | |
683 | This stores the private key in | |
684 | .Pa ~/.ssh/identity | |
685 | and stores the public key in | |
686 | .Pa ~/.ssh/identity.pub | |
687 | in the user's home directory. | |
688 | The user should then copy the | |
689 | .Pa identity.pub | |
690 | to | |
691 | .Pa ~/.ssh/authorized_keys | |
692 | in his/her home directory on the remote machine (the | |
693 | .Pa authorized_keys | |
694 | file corresponds to the conventional | |
695 | .Pa ~/.rhosts | |
696 | file, and has one key | |
697 | per line, though the lines can be very long). | |
698 | After this, the user can log in without giving the password. | |
699 | .Pp | |
700 | The most convenient way to use RSA authentication may be with an | |
701 | authentication agent. | |
702 | See | |
703 | .Xr ssh-agent 1 | |
704 | for more information. | |
705 | .Pp | |
706 | If other authentication methods fail, | |
707 | .Nm | |
708 | prompts the user for a password. | |
709 | The password is sent to the remote | |
710 | host for checking; however, since all communications are encrypted, | |
711 | the password cannot be seen by someone listening on the network. | |
712 | .Ss SSH protocol version 2 | |
713 | When a user connects using protocol version 2, | |
714 | similar authentication methods are available. | |
715 | Using the default values for | |
716 | .Cm PreferredAuthentications , | |
717 | the client will try to authenticate first using the hostbased method; | |
718 | if this method fails, public key authentication is attempted, | |
719 | and finally if this method fails, keyboard-interactive and | |
720 | password authentication are tried. | |
07d688d5 | 721 | .Pp |
442c8b33 | 722 | The public key method is similar to RSA authentication described |
723 | in the previous section and allows the RSA or DSA algorithm to be used: | |
724 | The client uses his private key, | |
725 | .Pa ~/.ssh/id_dsa | |
726 | or | |
727 | .Pa ~/.ssh/id_rsa , | |
728 | to sign the session identifier and sends the result to the server. | |
729 | The server checks whether the matching public key is listed in | |
730 | .Pa ~/.ssh/authorized_keys | |
731 | and grants access if both the key is found and the signature is correct. | |
732 | The session identifier is derived from a shared Diffie-Hellman value | |
733 | and is only known to the client and the server. | |
82966fe8 | 734 | .Pp |
442c8b33 | 735 | If public key authentication fails or is not available, a password |
736 | can be sent encrypted to the remote host to prove the user's identity. | |
737 | .Pp | |
738 | Additionally, | |
82966fe8 | 739 | .Nm |
442c8b33 | 740 | supports hostbased or challenge response authentication. |
741 | .Pp | |
742 | Protocol 2 provides additional mechanisms for confidentiality | |
743 | (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour) | |
744 | and integrity (hmac-md5, hmac-sha1, hmac-ripemd160). | |
745 | Note that protocol 1 lacks a strong mechanism for ensuring the | |
746 | integrity of the connection. | |
747 | .Ss Login session and remote execution | |
748 | When the user's identity has been accepted by the server, the server | |
749 | either executes the given command, or logs into the machine and gives | |
750 | the user a normal shell on the remote machine. | |
751 | All communication with | |
752 | the remote command or shell will be automatically encrypted. | |
753 | .Pp | |
754 | If a pseudo-terminal has been allocated (normal login session), the | |
755 | user may use the escape characters noted below. | |
756 | .Pp | |
757 | If no pseudo-tty has been allocated, | |
758 | the session is transparent and can be used to reliably transfer binary data. | |
759 | On most systems, setting the escape character to | |
760 | .Dq none | |
761 | will also make the session transparent even if a tty is used. | |
762 | .Pp | |
763 | The session terminates when the command or shell on the remote | |
764 | machine exits and all X11 and TCP/IP connections have been closed. | |
765 | The exit status of the remote program is returned as the exit status of | |
766 | .Nm ssh . | |
767 | .Pp | |
bf740959 | 768 | .Nm |
588df31a | 769 | may additionally obtain configuration data from |
770 | a per-user configuration file and a system-wide configuration file. | |
771 | The file format and configuration options are described in | |
772 | .Xr ssh_config 5 . | |
442c8b33 | 773 | .Ss Escape Characters |
774 | When a pseudo-terminal has been requested, | |
775 | .Nm | |
776 | supports a number of functions through the use of an escape character. | |
777 | .Pp | |
778 | A single tilde character can be sent as | |
779 | .Ic ~~ | |
780 | or by following the tilde by a character other than those described below. | |
781 | The escape character must always follow a newline to be interpreted as | |
782 | special. | |
783 | The escape character can be changed in configuration files using the | |
784 | .Cm EscapeChar | |
785 | configuration directive or on the command line by the | |
786 | .Fl e | |
787 | option. | |
788 | .Pp | |
789 | The supported escapes (assuming the default | |
790 | .Ql ~ ) | |
791 | are: | |
792 | .Bl -tag -width Ds | |
793 | .It Cm ~. | |
794 | Disconnect. | |
795 | .It Cm ~^Z | |
796 | Background | |
797 | .Nm ssh . | |
798 | .It Cm ~# | |
799 | List forwarded connections. | |
800 | .It Cm ~& | |
801 | Background | |
802 | .Nm | |
803 | at logout when waiting for forwarded connection / X11 sessions to terminate. | |
804 | .It Cm ~? | |
805 | Display a list of escape characters. | |
806 | .It Cm ~B | |
807 | Send a BREAK to the remote system | |
808 | (only useful for SSH protocol version 2 and if the peer supports it). | |
809 | .It Cm ~C | |
810 | Open command line. | |
811 | Currently this allows the addition of port forwardings using the | |
812 | .Fl L | |
813 | and | |
814 | .Fl R | |
815 | options (see below). | |
816 | It also allows the cancellation of existing remote port-forwardings | |
817 | using | |
818 | .Fl KR Ar hostport . | |
819 | .Ic !\& Ns Ar command | |
820 | allows the user to execute a local command if the | |
821 | .Ic PermitLocalCommand | |
822 | option is enabled in | |
823 | .Xr ssh_config 5 . | |
824 | Basic help is available, using the | |
825 | .Fl h | |
826 | option. | |
827 | .It Cm ~R | |
828 | Request rekeying of the connection | |
829 | (only useful for SSH protocol version 2 and if the peer supports it). | |
830 | .El | |
831 | .Ss X11 and TCP forwarding | |
832 | If the | |
833 | .Cm ForwardX11 | |
834 | variable is set to | |
835 | .Dq yes | |
836 | (or see the description of the | |
837 | .Fl X | |
838 | and | |
839 | .Fl x | |
840 | options described later) | |
841 | and the user is using X11 (the | |
842 | .Ev DISPLAY | |
843 | environment variable is set), the connection to the X11 display is | |
844 | automatically forwarded to the remote side in such a way that any X11 | |
845 | programs started from the shell (or command) will go through the | |
846 | encrypted channel, and the connection to the real X server will be made | |
847 | from the local machine. | |
848 | The user should not manually set | |
849 | .Ev DISPLAY . | |
850 | Forwarding of X11 connections can be | |
851 | configured on the command line or in configuration files. | |
852 | .Pp | |
853 | The | |
854 | .Ev DISPLAY | |
855 | value set by | |
856 | .Nm | |
857 | will point to the server machine, but with a display number greater than zero. | |
858 | This is normal, and happens because | |
859 | .Nm | |
860 | creates a | |
861 | .Dq proxy | |
862 | X server on the server machine for forwarding the | |
863 | connections over the encrypted channel. | |
864 | .Pp | |
865 | .Nm | |
866 | will also automatically set up Xauthority data on the server machine. | |
867 | For this purpose, it will generate a random authorization cookie, | |
868 | store it in Xauthority on the server, and verify that any forwarded | |
869 | connections carry this cookie and replace it by the real cookie when | |
870 | the connection is opened. | |
871 | The real authentication cookie is never | |
872 | sent to the server machine (and no cookies are sent in the plain). | |
873 | .Pp | |
874 | If the | |
875 | .Cm ForwardAgent | |
876 | variable is set to | |
877 | .Dq yes | |
878 | (or see the description of the | |
879 | .Fl A | |
880 | and | |
881 | .Fl a | |
882 | options described later) and | |
883 | the user is using an authentication agent, the connection to the agent | |
884 | is automatically forwarded to the remote side. | |
885 | .Pp | |
886 | Forwarding of arbitrary TCP/IP connections over the secure channel can | |
887 | be specified either on the command line or in a configuration file. | |
888 | One possible application of TCP/IP forwarding is a secure connection to an | |
889 | electronic purse; another is going through firewalls. | |
890 | .Ss Server authentication | |
891 | .Nm | |
892 | automatically maintains and checks a database containing | |
893 | identifications for all hosts it has ever been used with. | |
894 | Host keys are stored in | |
895 | .Pa ~/.ssh/known_hosts | |
896 | in the user's home directory. | |
897 | Additionally, the file | |
898 | .Pa /etc/ssh/ssh_known_hosts | |
899 | is automatically checked for known hosts. | |
900 | Any new hosts are automatically added to the user's file. | |
901 | If a host's identification ever changes, | |
902 | .Nm | |
903 | warns about this and disables password authentication to prevent a | |
904 | trojan horse from getting the user's password. | |
905 | Another purpose of this mechanism is to prevent man-in-the-middle attacks | |
906 | which could otherwise be used to circumvent the encryption. | |
907 | The | |
908 | .Cm StrictHostKeyChecking | |
909 | option can be used to prevent logins to machines whose | |
910 | host key is not known or has changed. | |
911 | .Pp | |
912 | .Nm | |
913 | can be configured to verify host identification using fingerprint resource | |
914 | records (SSHFP) published in DNS. | |
915 | The | |
916 | .Cm VerifyHostKeyDNS | |
917 | option can be used to control how DNS lookups are performed. | |
918 | SSHFP resource records can be generated using | |
919 | .Xr ssh-keygen 1 . | |
bf740959 | 920 | .Sh ENVIRONMENT |
921 | .Nm | |
922 | will normally set the following environment variables: | |
5f4a0c58 | 923 | .Bl -tag -width LOGNAME |
bf740959 | 924 | .It Ev DISPLAY |
925 | The | |
926 | .Ev DISPLAY | |
610cd5c6 | 927 | variable indicates the location of the X11 server. |
f54651ce | 928 | It is automatically set by |
bf740959 | 929 | .Nm |
930 | to point to a value of the form | |
931 | .Dq hostname:n | |
932 | where hostname indicates | |
5f4a0c58 | 933 | the host where the shell runs, and n is an integer \*(Ge 1. |
610cd5c6 | 934 | .Nm |
935 | uses this special value to forward X11 connections over the secure | |
936 | channel. | |
da89cf4d | 937 | The user should normally not set |
938 | .Ev DISPLAY | |
939 | explicitly, as that | |
bf740959 | 940 | will render the X11 connection insecure (and will require the user to |
941 | manually copy any required authorization cookies). | |
942 | .It Ev HOME | |
943 | Set to the path of the user's home directory. | |
944 | .It Ev LOGNAME | |
945 | Synonym for | |
946 | .Ev USER ; | |
947 | set for compatibility with systems that use this variable. | |
948 | .It Ev MAIL | |
ae897d7c | 949 | Set to the path of the user's mailbox. |
610cd5c6 | 950 | .It Ev PATH |
bf740959 | 951 | Set to the default |
952 | .Ev PATH , | |
953 | as specified when compiling | |
954 | .Nm ssh . | |
3474b2b4 | 955 | .It Ev SSH_ASKPASS |
956 | If | |
957 | .Nm | |
958 | needs a passphrase, it will read the passphrase from the current | |
959 | terminal if it was run from a terminal. | |
960 | If | |
961 | .Nm | |
962 | does not have a terminal associated with it but | |
963 | .Ev DISPLAY | |
964 | and | |
965 | .Ev SSH_ASKPASS | |
966 | are set, it will execute the program specified by | |
967 | .Ev SSH_ASKPASS | |
968 | and open an X11 window to read the passphrase. | |
969 | This is particularly useful when calling | |
970 | .Nm | |
971 | from a | |
caeffafb | 972 | .Pa .xsession |
3474b2b4 | 973 | or related script. |
974 | (Note that on some machines it | |
975 | may be necessary to redirect the input from | |
976 | .Pa /dev/null | |
977 | to make this work.) | |
bf740959 | 978 | .It Ev SSH_AUTH_SOCK |
ae897d7c | 979 | Identifies the path of a unix-domain socket used to communicate with the |
bf740959 | 980 | agent. |
da0561eb | 981 | .It Ev SSH_CONNECTION |
982 | Identifies the client and server ends of the connection. | |
610cd5c6 | 983 | The variable contains |
da0561eb | 984 | four space-separated values: client ip-address, client port number, |
985 | server ip-address and server port number. | |
8abcdba4 | 986 | .It Ev SSH_ORIGINAL_COMMAND |
987 | The variable contains the original command line if a forced command | |
988 | is executed. | |
989 | It can be used to extract the original arguments. | |
bf740959 | 990 | .It Ev SSH_TTY |
991 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 992 | with the current shell or command. |
993 | If the current session has no tty, | |
bf740959 | 994 | this variable is not set. |
995 | .It Ev TZ | |
04ac3e62 | 996 | This variable is set to indicate the present time zone if it |
c345cf9d | 997 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 998 | on to new connections). |
999 | .It Ev USER | |
1000 | Set to the name of the user logging in. | |
1001 | .El | |
1002 | .Pp | |
f54651ce | 1003 | Additionally, |
bf740959 | 1004 | .Nm |
f54651ce | 1005 | reads |
140e3e97 | 1006 | .Pa ~/.ssh/environment , |
bf740959 | 1007 | and adds lines of the format |
1008 | .Dq VARNAME=value | |
6a342527 | 1009 | to the environment if the file exists and if users are allowed to |
1010 | change their environment. | |
5f4a0c58 | 1011 | For more information, see the |
6a342527 | 1012 | .Cm PermitUserEnvironment |
35453849 | 1013 | option in |
6a342527 | 1014 | .Xr sshd_config 5 . |
bf740959 | 1015 | .Sh FILES |
c8d54615 | 1016 | .Bl -tag -width Ds |
140e3e97 | 1017 | .It Pa ~/.ssh/known_hosts |
ae897d7c | 1018 | Records host keys for all hosts the user has logged into that are not |
bf740959 | 1019 | in |
2a8a6488 | 1020 | .Pa /etc/ssh/ssh_known_hosts . |
bf740959 | 1021 | See |
1022 | .Xr sshd 8 . | |
140e3e97 | 1023 | .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa |
c0ecc314 | 1024 | Contains the authentication identity of the user. |
1025 | They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. | |
1d1ffb87 | 1026 | These files |
1027 | contain sensitive data and should be readable by the user but not | |
bf740959 | 1028 | accessible by others (read/write/execute). |
1029 | Note that | |
1030 | .Nm | |
1d1ffb87 | 1031 | ignores a private key file if it is accessible by others. |
bf740959 | 1032 | It is possible to specify a passphrase when |
1033 | generating the key; the passphrase will be used to encrypt the | |
1034 | sensitive part of this file using 3DES. | |
140e3e97 | 1035 | .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub |
bf740959 | 1036 | Contains the public key for authentication (public part of the |
610cd5c6 | 1037 | identity file in human-readable form). |
1d1ffb87 | 1038 | The contents of the |
140e3e97 | 1039 | .Pa ~/.ssh/identity.pub |
5f4a0c58 | 1040 | file should be added to the file |
140e3e97 | 1041 | .Pa ~/.ssh/authorized_keys |
bf740959 | 1042 | on all machines |
91789042 | 1043 | where the user wishes to log in using protocol version 1 RSA authentication. |
1d1ffb87 | 1044 | The contents of the |
140e3e97 | 1045 | .Pa ~/.ssh/id_dsa.pub |
c0ecc314 | 1046 | and |
140e3e97 | 1047 | .Pa ~/.ssh/id_rsa.pub |
1d1ffb87 | 1048 | file should be added to |
140e3e97 | 1049 | .Pa ~/.ssh/authorized_keys |
1d1ffb87 | 1050 | on all machines |
91789042 | 1051 | where the user wishes to log in using protocol version 2 DSA/RSA authentication. |
1d1ffb87 | 1052 | These files are not |
610cd5c6 | 1053 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 1054 | These files are |
c44559d2 | 1055 | never used automatically and are not necessary; they are only provided for |
bf740959 | 1056 | the convenience of the user. |
140e3e97 | 1057 | .It Pa ~/.ssh/config |
610cd5c6 | 1058 | This is the per-user configuration file. |
588df31a | 1059 | The file format and configuration options are described in |
1060 | .Xr ssh_config 5 . | |
e1520719 | 1061 | Because of the potential for abuse, this file must have strict permissions: |
1062 | read/write for the user, and not accessible by others. | |
140e3e97 | 1063 | .It Pa ~/.ssh/authorized_keys |
96a7b0cc | 1064 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. |
610cd5c6 | 1065 | The format of this file is described in the |
bf740959 | 1066 | .Xr sshd 8 |
610cd5c6 | 1067 | manual page. |
5f4a0c58 | 1068 | In the simplest form the format is the same as the |
1069 | .Pa .pub | |
f49bc4f7 | 1070 | identity files. |
1d1ffb87 | 1071 | This file is not highly sensitive, but the recommended |
1072 | permissions are read/write for the user, and not accessible by others. | |
2a8a6488 | 1073 | .It Pa /etc/ssh/ssh_known_hosts |
610cd5c6 | 1074 | Systemwide list of known host keys. |
f49bc4f7 | 1075 | This file should be prepared by the |
bf740959 | 1076 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1077 | organization. |
1078 | This file should be world-readable. | |
1079 | This file contains | |
bf740959 | 1080 | public keys, one per line, in the following format (fields separated |
f49bc4f7 | 1081 | by spaces): system name, public key and optional comment field. |
610cd5c6 | 1082 | When different names are used |
bf740959 | 1083 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1084 | commas. |
5f4a0c58 | 1085 | The format is described in the |
bf740959 | 1086 | .Xr sshd 8 |
1087 | manual page. | |
1088 | .Pp | |
1089 | The canonical system name (as returned by name servers) is used by | |
1090 | .Xr sshd 8 | |
1091 | to verify the client host when logging in; other names are needed because | |
1092 | .Nm | |
1093 | does not convert the user-supplied name to a canonical name before | |
1094 | checking the key, because someone with access to the name servers | |
1095 | would then be able to fool host authentication. | |
2a8a6488 | 1096 | .It Pa /etc/ssh/ssh_config |
610cd5c6 | 1097 | Systemwide configuration file. |
588df31a | 1098 | The file format and configuration options are described in |
1099 | .Xr ssh_config 5 . | |
2a8a6488 | 1100 | .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key |
dd58cb5e | 1101 | These three files contain the private parts of the host keys |
1102 | and are used for | |
1103 | .Cm RhostsRSAAuthentication | |
1104 | and | |
1105 | .Cm HostbasedAuthentication . | |
d83cbdc3 | 1106 | If the protocol version 1 |
1107 | .Cm RhostsRSAAuthentication | |
7203d6bb | 1108 | method is used, |
d83cbdc3 | 1109 | .Nm |
1110 | must be setuid root, since the host key is readable only by root. | |
1111 | For protocol version 2, | |
1112 | .Nm | |
1113 | uses | |
1114 | .Xr ssh-keysign 8 | |
1115 | to access the host keys for | |
1116 | .Cm HostbasedAuthentication . | |
1117 | This eliminates the requirement that | |
1118 | .Nm | |
1119 | be setuid root when that authentication method is used. | |
1120 | By default | |
dd58cb5e | 1121 | .Nm |
d83cbdc3 | 1122 | is not setuid root. |
140e3e97 | 1123 | .It Pa ~/.rhosts |
bf740959 | 1124 | This file is used in |
6f5abc1e | 1125 | .Cm RhostsRSAAuthentication |
1126 | and | |
1127 | .Cm HostbasedAuthentication | |
bf740959 | 1128 | authentication to list the |
610cd5c6 | 1129 | host/user pairs that are permitted to log in. |
1130 | (Note that this file is | |
bf740959 | 1131 | also used by rlogin and rsh, which makes using this file insecure.) |
1132 | Each line of the file contains a host name (in the canonical form | |
1133 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1134 | separated by a space. |
e91c60f2 | 1135 | On some machines this file may need to be |
bf740959 | 1136 | world-readable if the user's home directory is on a NFS partition, |
1137 | because | |
1138 | .Xr sshd 8 | |
610cd5c6 | 1139 | reads it as root. |
1140 | Additionally, this file must be owned by the user, | |
1141 | and must not have write permissions for anyone else. | |
1142 | The recommended | |
bf740959 | 1143 | permission for most machines is read/write for the user, and not |
1144 | accessible by others. | |
1145 | .Pp | |
6f5abc1e | 1146 | Note that |
bf740959 | 1147 | .Xr sshd 8 |
6f5abc1e | 1148 | allows authentication only in combination with client host key |
1149 | authentication before permitting log in. | |
91789042 | 1150 | If the server machine does not have the client's host key in |
2a8a6488 | 1151 | .Pa /etc/ssh/ssh_known_hosts , |
91789042 | 1152 | it can be stored in |
140e3e97 | 1153 | .Pa ~/.ssh/known_hosts . |
bf740959 | 1154 | The easiest way to do this is to |
1155 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1156 | will automatically add the host key to |
140e3e97 | 1157 | .Pa ~/.ssh/known_hosts . |
1158 | .It Pa ~/.shosts | |
bf740959 | 1159 | This file is used exactly the same way as |
5f4a0c58 | 1160 | .Pa .rhosts . |
bf740959 | 1161 | The purpose for |
6f5abc1e | 1162 | having this file is to be able to use |
1163 | .Cm RhostsRSAAuthentication | |
1164 | and | |
1165 | .Cm HostbasedAuthentication | |
1166 | authentication without permitting login with | |
5f4a0c58 | 1167 | .Xr rlogin |
bf740959 | 1168 | or |
1169 | .Xr rsh 1 . | |
1170 | .It Pa /etc/hosts.equiv | |
1171 | This file is used during | |
6f5abc1e | 1172 | .Cm RhostsRSAAuthentication |
1173 | and | |
1174 | .Cm HostbasedAuthentication | |
be193d89 | 1175 | authentication. |
610cd5c6 | 1176 | It contains |
5f4a0c58 | 1177 | canonical hosts names, one per line (the full format is described in the |
bf740959 | 1178 | .Xr sshd 8 |
610cd5c6 | 1179 | manual page). |
1180 | If the client host is found in this file, login is | |
bf740959 | 1181 | automatically permitted provided client and server user names are the |
610cd5c6 | 1182 | same. |
6f5abc1e | 1183 | Additionally, successful client host key authentication is required. |
610cd5c6 | 1184 | This file should only be writable by root. |
5f4fdfae | 1185 | .It Pa /etc/shosts.equiv |
f54651ce | 1186 | This file is processed exactly as |
bf740959 | 1187 | .Pa /etc/hosts.equiv . |
1188 | This file may be useful to permit logins using | |
1189 | .Nm | |
1190 | but not using rsh/rlogin. | |
2a8a6488 | 1191 | .It Pa /etc/ssh/sshrc |
bf740959 | 1192 | Commands in this file are executed by |
1193 | .Nm | |
1194 | when the user logs in just before the user's shell (or command) is started. | |
1195 | See the | |
1196 | .Xr sshd 8 | |
1197 | manual page for more information. | |
140e3e97 | 1198 | .It Pa ~/.ssh/rc |
bf740959 | 1199 | Commands in this file are executed by |
1200 | .Nm | |
1201 | when the user logs in just before the user's shell (or command) is | |
1202 | started. | |
f54651ce | 1203 | See the |
bf740959 | 1204 | .Xr sshd 8 |
1205 | manual page for more information. | |
140e3e97 | 1206 | .It Pa ~/.ssh/environment |
83b7f649 | 1207 | Contains additional definitions for environment variables, see section |
1208 | .Sx ENVIRONMENT | |
1209 | above. | |
b5e300c2 | 1210 | .El |
16210ef7 | 1211 | .Sh DIAGNOSTICS |
1212 | .Nm | |
1213 | exits with the exit status of the remote command or with 255 | |
1214 | if an error occurred. | |
bf740959 | 1215 | .Sh SEE ALSO |
5f4a0c58 | 1216 | .Xr gzip 1 , |
bf740959 | 1217 | .Xr rsh 1 , |
1218 | .Xr scp 1 , | |
61e96248 | 1219 | .Xr sftp 1 , |
bf740959 | 1220 | .Xr ssh-add 1 , |
1221 | .Xr ssh-agent 1 , | |
1222 | .Xr ssh-keygen 1 , | |
1223 | .Xr telnet 1 , | |
5f4a0c58 | 1224 | .Xr hosts.equiv 5 , |
1ae02182 | 1225 | .Xr ssh_config 5 , |
b2843ec6 | 1226 | .Xr ssh-keysign 8 , |
9afadca8 | 1227 | .Xr sshd 8 |
2cad6cef | 1228 | .Rs |
1229 | .%A T. Ylonen | |
1230 | .%A T. Kivinen | |
1231 | .%A M. Saarinen | |
1232 | .%A T. Rinne | |
1233 | .%A S. Lehtinen | |
1234 | .%T "SSH Protocol Architecture" | |
17f5e68a | 1235 | .%N draft-ietf-secsh-architecture-12.txt |
1236 | .%D January 2002 | |
2cad6cef | 1237 | .%O work in progress material |
1238 | .Re | |
be193d89 | 1239 | .Sh AUTHORS |
1240 | OpenSSH is a derivative of the original and free | |
1241 | ssh 1.2.12 release by Tatu Ylonen. | |
1242 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1243 | Theo de Raadt and Dug Song | |
1244 | removed many bugs, re-added newer features and | |
1245 | created OpenSSH. | |
1246 | Markus Friedl contributed the support for SSH | |
1247 | protocol versions 1.5 and 2.0. |