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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 | .\" |
e961a8f9 | 37 | .\" $OpenBSD: ssh.1,v 1.103 2001/04/17 10:53:26 markus 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 | |
46 | .Op Fl l Ar login_name | |
47 | .Op Ar hostname | user@hostname | |
48 | .Op Ar command | |
49 | .Pp | |
50 | .Nm ssh | |
9afadca8 | 51 | .Op Fl afgknqstvxACNPTX1246 |
d0c832f3 | 52 | .Op Fl c Ar cipher_spec |
bf740959 | 53 | .Op Fl e Ar escape_char |
54 | .Op Fl i Ar identity_file | |
55 | .Op Fl l Ar login_name | |
b2552997 | 56 | .Op Fl m Ar mac_spec |
bf740959 | 57 | .Op Fl o Ar option |
58 | .Op Fl p Ar port | |
59 | .Oo Fl L Xo | |
60 | .Sm off | |
bf740959 | 61 | .Ar port : |
7b2ea3a1 | 62 | .Ar host : |
bf740959 | 63 | .Ar hostport |
64 | .Sm on | |
65 | .Xc | |
66 | .Oc | |
67 | .Oo Fl R Xo | |
68 | .Sm off | |
bf740959 | 69 | .Ar port : |
7b2ea3a1 | 70 | .Ar host : |
bf740959 | 71 | .Ar hostport |
72 | .Sm on | |
73 | .Xc | |
74 | .Oc | |
75 | .Op Ar hostname | user@hostname | |
76 | .Op Ar command | |
f54651ce | 77 | .Sh DESCRIPTION |
bf740959 | 78 | .Nm |
2c86906e | 79 | (SSH client) is a program for logging into a remote machine and for |
610cd5c6 | 80 | executing commands on a remote machine. |
81 | It is intended to replace | |
bf740959 | 82 | rlogin and rsh, and provide secure encrypted communications between |
610cd5c6 | 83 | two untrusted hosts over an insecure network. |
84 | X11 connections and | |
bf740959 | 85 | arbitrary TCP/IP ports can also be forwarded over the secure channel. |
86 | .Pp | |
87 | .Nm | |
f54651ce | 88 | connects and logs into the specified |
bf740959 | 89 | .Ar hostname . |
90 | The user must prove | |
1d1ffb87 | 91 | his/her identity to the remote machine using one of several methods |
92 | depending on the protocol version used: | |
93 | .Pp | |
94 | .Ss SSH protocol version 1 | |
bf740959 | 95 | .Pp |
96 | First, if the machine the user logs in from is listed in | |
97 | .Pa /etc/hosts.equiv | |
98 | or | |
5f4fdfae | 99 | .Pa /etc/shosts.equiv |
bf740959 | 100 | on the remote machine, and the user names are |
101 | the same on both sides, the user is immediately permitted to log in. | |
f54651ce | 102 | Second, if |
bf740959 | 103 | .Pa \&.rhosts |
104 | or | |
105 | .Pa \&.shosts | |
106 | exists in the user's home directory on the | |
107 | remote machine and contains a line containing the name of the client | |
108 | machine and the name of the user on that machine, the user is | |
610cd5c6 | 109 | permitted to log in. |
110 | This form of authentication alone is normally not | |
bf740959 | 111 | allowed by the server because it is not secure. |
112 | .Pp | |
113 | The second (and primary) authentication method is the | |
114 | .Pa rhosts | |
115 | or | |
116 | .Pa hosts.equiv | |
610cd5c6 | 117 | method combined with RSA-based host authentication. |
118 | It means that if the login would be permitted by | |
1d1ffb87 | 119 | .Pa $HOME/.rhosts , |
120 | .Pa $HOME/.shosts , | |
bf740959 | 121 | .Pa /etc/hosts.equiv , |
122 | or | |
5f4fdfae | 123 | .Pa /etc/shosts.equiv , |
bf740959 | 124 | and if additionally the server can verify the client's |
f54651ce | 125 | host key (see |
5f4fdfae | 126 | .Pa /etc/ssh_known_hosts |
5bbb5681 | 127 | and |
128 | .Pa $HOME/.ssh/known_hosts | |
bf740959 | 129 | in the |
130 | .Sx FILES | |
610cd5c6 | 131 | section), only then login is permitted. |
132 | This authentication method closes security holes due to IP | |
133 | spoofing, DNS spoofing and routing spoofing. | |
134 | [Note to the administrator: | |
bf740959 | 135 | .Pa /etc/hosts.equiv , |
1d1ffb87 | 136 | .Pa $HOME/.rhosts , |
bf740959 | 137 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
138 | disabled if security is desired.] | |
139 | .Pp | |
f54651ce | 140 | As a third authentication method, |
bf740959 | 141 | .Nm |
142 | supports RSA based authentication. | |
143 | The scheme is based on public-key cryptography: there are cryptosystems | |
144 | where encryption and decryption are done using separate keys, and it | |
145 | is not possible to derive the decryption key from the encryption key. | |
610cd5c6 | 146 | RSA is one such system. |
f54651ce | 147 | The idea is that each user creates a public/private |
610cd5c6 | 148 | key pair for authentication purposes. |
149 | The server knows the public key, and only the user knows the private key. | |
f54651ce | 150 | The file |
bf740959 | 151 | .Pa $HOME/.ssh/authorized_keys |
152 | lists the public keys that are permitted for logging | |
610cd5c6 | 153 | in. |
154 | When the user logs in, the | |
bf740959 | 155 | .Nm |
156 | program tells the server which key pair it would like to use for | |
610cd5c6 | 157 | authentication. |
158 | The server checks if this key is permitted, and if | |
bf740959 | 159 | so, sends the user (actually the |
160 | .Nm | |
161 | program running on behalf of the user) a challenge, a random number, | |
610cd5c6 | 162 | encrypted by the user's public key. |
163 | The challenge can only be | |
164 | decrypted using the proper private key. | |
165 | The user's client then decrypts the | |
bf740959 | 166 | challenge using the private key, proving that he/she knows the private |
167 | key but without disclosing it to the server. | |
168 | .Pp | |
169 | .Nm | |
610cd5c6 | 170 | implements the RSA authentication protocol automatically. |
171 | The user creates his/her RSA key pair by running | |
bf740959 | 172 | .Xr ssh-keygen 1 . |
f54651ce | 173 | This stores the private key in |
1d1ffb87 | 174 | .Pa $HOME/.ssh/identity |
bf740959 | 175 | and the public key in |
1d1ffb87 | 176 | .Pa $HOME/.ssh/identity.pub |
610cd5c6 | 177 | in the user's home directory. |
178 | The user should then copy the | |
bf740959 | 179 | .Pa identity.pub |
f54651ce | 180 | to |
1d1ffb87 | 181 | .Pa $HOME/.ssh/authorized_keys |
f54651ce | 182 | in his/her home directory on the remote machine (the |
bf740959 | 183 | .Pa authorized_keys |
f54651ce | 184 | file corresponds to the conventional |
1d1ffb87 | 185 | .Pa $HOME/.rhosts |
bf740959 | 186 | file, and has one key |
610cd5c6 | 187 | per line, though the lines can be very long). |
188 | After this, the user can log in without giving the password. | |
189 | RSA authentication is much | |
bf740959 | 190 | more secure than rhosts authentication. |
191 | .Pp | |
192 | The most convenient way to use RSA authentication may be with an | |
610cd5c6 | 193 | authentication agent. |
194 | See | |
bf740959 | 195 | .Xr ssh-agent 1 |
196 | for more information. | |
197 | .Pp | |
f54651ce | 198 | If other authentication methods fail, |
bf740959 | 199 | .Nm |
610cd5c6 | 200 | prompts the user for a password. |
201 | The password is sent to the remote | |
bf740959 | 202 | host for checking; however, since all communications are encrypted, |
203 | the password cannot be seen by someone listening on the network. | |
204 | .Pp | |
1d1ffb87 | 205 | .Ss SSH protocol version 2 |
206 | .Pp | |
207 | When a user connects using the protocol version 2 | |
208 | different authentication methods are available: | |
209 | At first, the client attempts to authenticate using the public key method. | |
210 | If this method fails password authentication is tried. | |
211 | .Pp | |
212 | The public key method is similar to RSA authentication described | |
fa08c86b | 213 | in the previous section except that the DSA or RSA algorithm is used |
214 | instead. | |
c0ecc314 | 215 | The client uses his private key, |
1d1ffb87 | 216 | .Pa $HOME/.ssh/id_dsa |
c0ecc314 | 217 | or |
218 | .Pa $HOME/.ssh/id_rsa , | |
1d1ffb87 | 219 | to sign the session identifier and sends the result to the server. |
220 | The server checks whether the matching public key is listed in | |
221 | .Pa $HOME/.ssh/authorized_keys2 | |
222 | and grants access if both the key is found and the signature is correct. | |
223 | The session identifier is derived from a shared Diffie-Hellman value | |
224 | and is only known to the client and the server. | |
225 | .Pp | |
226 | If public key authentication fails or is not available a password | |
227 | can be sent encrypted to the remote host for proving the user's identity. | |
228 | This protocol 2 implementation does not yet support Kerberos or | |
229 | S/Key authentication. | |
230 | .Pp | |
231 | Protocol 2 provides additional mechanisms for confidentiality | |
d0c832f3 | 232 | (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour) |
f2ba0775 | 233 | and integrity (hmac-md5, hmac-sha1). |
1d1ffb87 | 234 | Note that protocol 1 lacks a strong mechanism for ensuring the |
235 | integrity of the connection. | |
236 | .Pp | |
237 | .Ss Login session and remote execution | |
238 | .Pp | |
bf740959 | 239 | When the user's identity has been accepted by the server, the server |
240 | either executes the given command, or logs into the machine and gives | |
610cd5c6 | 241 | the user a normal shell on the remote machine. |
242 | All communication with | |
bf740959 | 243 | the remote command or shell will be automatically encrypted. |
244 | .Pp | |
245 | If a pseudo-terminal has been allocated (normal login session), the | |
246 | user can disconnect with | |
247 | .Ic ~. , | |
248 | and suspend | |
249 | .Nm | |
250 | with | |
251 | .Ic ~^Z . | |
252 | All forwarded connections can be listed with | |
f54651ce | 253 | .Ic ~# |
bf740959 | 254 | and if |
255 | the session blocks waiting for forwarded X11 or TCP/IP | |
256 | connections to terminate, it can be backgrounded with | |
257 | .Ic ~& | |
258 | (this should not be used while the user shell is active, as it can cause the | |
610cd5c6 | 259 | shell to hang). |
260 | All available escapes can be listed with | |
bf740959 | 261 | .Ic ~? . |
262 | .Pp | |
263 | A single tilde character can be sent as | |
264 | .Ic ~~ | |
265 | (or by following the tilde by a character other than those described above). | |
266 | The escape character must always follow a newline to be interpreted as | |
610cd5c6 | 267 | special. |
268 | The escape character can be changed in configuration files | |
269 | or on the command line. | |
bf740959 | 270 | .Pp |
271 | If no pseudo tty has been allocated, the | |
272 | session is transparent and can be used to reliably transfer binary | |
610cd5c6 | 273 | data. |
274 | On most systems, setting the escape character to | |
bf740959 | 275 | .Dq none |
276 | will also make the session transparent even if a tty is used. | |
277 | .Pp | |
ce9c0b75 | 278 | The session terminates when the command or shell on the remote |
e91c60f2 | 279 | machine exits and all X11 and TCP/IP connections have been closed. |
bf740959 | 280 | The exit status of the remote program is returned as the exit status |
281 | of | |
282 | .Nm ssh . | |
283 | .Pp | |
1d1ffb87 | 284 | .Ss X11 and TCP forwarding |
285 | .Pp | |
bf740959 | 286 | If the user is using X11 (the |
287 | .Ev DISPLAY | |
288 | environment variable is set), the connection to the X11 display is | |
289 | automatically forwarded to the remote side in such a way that any X11 | |
290 | programs started from the shell (or command) will go through the | |
291 | encrypted channel, and the connection to the real X server will be made | |
610cd5c6 | 292 | from the local machine. |
293 | The user should not manually set | |
bf740959 | 294 | .Ev DISPLAY . |
295 | Forwarding of X11 connections can be | |
296 | configured on the command line or in configuration files. | |
297 | .Pp | |
298 | The | |
f54651ce | 299 | .Ev DISPLAY |
bf740959 | 300 | value set by |
301 | .Nm | |
302 | will point to the server machine, but with a display number greater | |
610cd5c6 | 303 | than zero. |
304 | This is normal, and happens because | |
bf740959 | 305 | .Nm |
306 | creates a | |
307 | .Dq proxy | |
308 | X server on the server machine for forwarding the | |
309 | connections over the encrypted channel. | |
310 | .Pp | |
311 | .Nm | |
312 | will also automatically set up Xauthority data on the server machine. | |
313 | For this purpose, it will generate a random authorization cookie, | |
314 | store it in Xauthority on the server, and verify that any forwarded | |
315 | connections carry this cookie and replace it by the real cookie when | |
610cd5c6 | 316 | the connection is opened. |
317 | The real authentication cookie is never | |
bf740959 | 318 | sent to the server machine (and no cookies are sent in the plain). |
319 | .Pp | |
320 | If the user is using an authentication agent, the connection to the agent | |
321 | is automatically forwarded to the remote side unless disabled on | |
322 | command line or in a configuration file. | |
323 | .Pp | |
324 | Forwarding of arbitrary TCP/IP connections over the secure channel can | |
610cd5c6 | 325 | be specified either on command line or in a configuration file. |
326 | One possible application of TCP/IP forwarding is a secure connection to an | |
e91c60f2 | 327 | electronic purse; another is going through firewalls. |
bf740959 | 328 | .Pp |
1d1ffb87 | 329 | .Ss Server authentication |
330 | .Pp | |
bf740959 | 331 | .Nm |
1d1ffb87 | 332 | automatically maintains and checks a database containing |
610cd5c6 | 333 | identifications for all hosts it has ever been used with. |
1d1ffb87 | 334 | RSA host keys are stored in |
335 | .Pa $HOME/.ssh/known_hosts | |
336 | and | |
fa08c86b | 337 | host keys used in the protocol version 2 are stored in |
1d1ffb87 | 338 | .Pa $HOME/.ssh/known_hosts2 |
610cd5c6 | 339 | in the user's home directory. |
1d1ffb87 | 340 | Additionally, the files |
5f4fdfae | 341 | .Pa /etc/ssh_known_hosts |
1d1ffb87 | 342 | and |
343 | .Pa /etc/ssh_known_hosts2 | |
344 | are automatically checked for known hosts. | |
610cd5c6 | 345 | Any new hosts are automatically added to the user's file. |
346 | If a host's identification | |
bf740959 | 347 | ever changes, |
348 | .Nm | |
349 | warns about this and disables password authentication to prevent a | |
610cd5c6 | 350 | trojan horse from getting the user's password. |
351 | Another purpose of | |
bf740959 | 352 | this mechanism is to prevent man-in-the-middle attacks which could |
610cd5c6 | 353 | otherwise be used to circumvent the encryption. |
354 | The | |
bf740959 | 355 | .Cm StrictHostKeyChecking |
356 | option (see below) can be used to prevent logins to machines whose | |
357 | host key is not known or has changed. | |
fa08c86b | 358 | .Pp |
359 | The options are as follows: | |
bf740959 | 360 | .Bl -tag -width Ds |
361 | .It Fl a | |
4fe2af09 | 362 | Disables forwarding of the authentication agent connection. |
71276795 | 363 | .It Fl A |
364 | Enables forwarding of the authentication agent connection. | |
365 | This can also be specified on a per-host basis in a configuration file. | |
bf740959 | 366 | .It Fl c Ar blowfish|3des |
f54651ce | 367 | Selects the cipher to use for encrypting the session. |
bf740959 | 368 | .Ar 3des |
610cd5c6 | 369 | is used by default. |
f54651ce | 370 | It is believed to be secure. |
bf740959 | 371 | .Ar 3des |
372 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
373 | It is presumably more secure than the | |
374 | .Ar des | |
a22aff1f | 375 | cipher which is no longer fully supported in |
d0c832f3 | 376 | .Nm ssh . |
bf740959 | 377 | .Ar blowfish |
378 | is a fast block cipher, it appears very secure and is much faster than | |
610cd5c6 | 379 | .Ar 3des . |
9afadca8 | 380 | .It Fl c Ar cipher_spec |
d0c832f3 | 381 | Additionally, for protocol version 2 a comma-separated list of ciphers can |
94ec8c6b | 382 | be specified in order of preference. |
9afadca8 | 383 | See |
384 | .Cm Ciphers | |
385 | for more information. | |
bf740959 | 386 | .It Fl e Ar ch|^ch|none |
387 | Sets the escape character for sessions with a pty (default: | |
388 | .Ql ~ ) . | |
610cd5c6 | 389 | The escape character is only recognized at the beginning of a line. |
390 | The escape character followed by a dot | |
bf740959 | 391 | .Pq Ql \&. |
392 | closes the connection, followed | |
393 | by control-Z suspends the connection, and followed by itself sends the | |
610cd5c6 | 394 | escape character once. |
395 | Setting the character to | |
bf740959 | 396 | .Dq none |
397 | disables any escapes and makes the session fully transparent. | |
398 | .It Fl f | |
399 | Requests | |
400 | .Nm | |
610cd5c6 | 401 | to go to background just before command execution. |
402 | This is useful if | |
bf740959 | 403 | .Nm |
404 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 405 | wants it in the background. |
f54651ce | 406 | This implies |
bf740959 | 407 | .Fl n . |
408 | The recommended way to start X11 programs at a remote site is with | |
409 | something like | |
410 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 411 | .It Fl g |
412 | Allows remote hosts to connect to local forwarded ports. | |
bf740959 | 413 | .It Fl i Ar identity_file |
f54651ce | 414 | Selects the file from which the identity (private key) for |
fa08c86b | 415 | RSA or DSA authentication is read. |
f54651ce | 416 | Default is |
1d1ffb87 | 417 | .Pa $HOME/.ssh/identity |
610cd5c6 | 418 | in the user's home directory. |
419 | Identity files may also be specified on | |
420 | a per-host basis in the configuration file. | |
421 | It is possible to have multiple | |
bf740959 | 422 | .Fl i |
423 | options (and multiple identities specified in | |
424 | configuration files). | |
bf740959 | 425 | .It Fl k |
4fe2af09 | 426 | Disables forwarding of Kerberos tickets and AFS tokens. |
427 | This may also be specified on a per-host basis in the configuration file. | |
bf740959 | 428 | .It Fl l Ar login_name |
610cd5c6 | 429 | Specifies the user to log in as on the remote machine. |
430 | This also may be specified on a per-host basis in the configuration file. | |
b2552997 | 431 | .It Fl m Ar mac_spec |
432 | Additionally, for protocol version 2 a comma-separated list of MAC | |
433 | (message authentication code) algorithms can | |
434 | be specified in order of preference. | |
435 | See the | |
436 | .Cm MACs | |
437 | keyword for more information. | |
bf740959 | 438 | .It Fl n |
439 | Redirects stdin from | |
440 | .Pa /dev/null | |
441 | (actually, prevents reading from stdin). | |
442 | This must be used when | |
443 | .Nm | |
610cd5c6 | 444 | is run in the background. |
445 | A common trick is to use this to run X11 programs on a remote machine. | |
446 | For example, | |
bf740959 | 447 | .Ic ssh -n shadows.cs.hut.fi emacs & |
448 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
449 | connection will be automatically forwarded over an encrypted channel. | |
450 | The | |
451 | .Nm | |
452 | program will be put in the background. | |
453 | (This does not work if | |
454 | .Nm | |
455 | needs to ask for a password or passphrase; see also the | |
456 | .Fl f | |
457 | option.) | |
0e73cc53 | 458 | .It Fl N |
459 | Do not execute a remote command. | |
0b6fbf03 | 460 | This is useful if you just want to forward ports |
0e73cc53 | 461 | (protocol version 2 only). |
bf740959 | 462 | .It Fl o Ar option |
463 | Can be used to give options in the format used in the config file. | |
464 | This is useful for specifying options for which there is no separate | |
610cd5c6 | 465 | command-line flag. |
466 | The option has the same format as a line in the configuration file. | |
bf740959 | 467 | .It Fl p Ar port |
610cd5c6 | 468 | Port to connect to on the remote host. |
469 | This can be specified on a | |
bf740959 | 470 | per-host basis in the configuration file. |
471 | .It Fl P | |
472 | Use a non-privileged port for outgoing connections. | |
473 | This can be used if your firewall does | |
474 | not permit connections from privileged ports. | |
95f1eccc | 475 | Note that this option turns off |
bf740959 | 476 | .Cm RhostsAuthentication |
477 | and | |
6ffc9c88 | 478 | .Cm RhostsRSAAuthentication |
479 | for older servers. | |
bf740959 | 480 | .It Fl q |
610cd5c6 | 481 | Quiet mode. |
482 | Causes all warning and diagnostic messages to be suppressed. | |
483 | Only fatal errors are displayed. | |
ae810de7 | 484 | .It Fl s |
485 | May be used to request invocation of a subsystem on the remote system. Subsystems are a feature of the SSH2 protocol which facilitate the use | |
486 | of SSH as a secure transport for other application (eg. sftp). The | |
487 | subsystem is specified as the remote command. | |
bf740959 | 488 | .It Fl t |
610cd5c6 | 489 | Force pseudo-tty allocation. |
4fe2af09 | 490 | This can be used to execute arbitrary |
610cd5c6 | 491 | screen-based programs on a remote machine, which can be very useful, |
492 | e.g., when implementing menu services. | |
8abcdba4 | 493 | Multiple |
494 | .Fl t | |
495 | options force tty allocation, even if | |
496 | .Nm | |
497 | has no local tty. | |
0e73cc53 | 498 | .It Fl T |
0b6fbf03 | 499 | Disable pseudo-tty allocation. |
bf740959 | 500 | .It Fl v |
610cd5c6 | 501 | Verbose mode. |
502 | Causes | |
bf740959 | 503 | .Nm |
610cd5c6 | 504 | to print debugging messages about its progress. |
505 | This is helpful in | |
bf740959 | 506 | debugging connection, authentication, and configuration problems. |
8abcdba4 | 507 | Multiple |
508 | .Fl v | |
509 | options increases the verbosity. | |
94ec8c6b | 510 | Maximum is 3. |
bf740959 | 511 | .It Fl x |
610cd5c6 | 512 | Disables X11 forwarding. |
bf740959 | 513 | .It Fl X |
514 | Enables X11 forwarding. | |
71276795 | 515 | This can also be specified on a per-host basis in a configuration file. |
bf740959 | 516 | .It Fl C |
517 | Requests compression of all data (including stdin, stdout, stderr, and | |
610cd5c6 | 518 | data for forwarded X11 and TCP/IP connections). |
519 | The compression algorithm is the same used by | |
7b2ea3a1 | 520 | .Xr gzip 1 , |
521 | and the | |
bf740959 | 522 | .Dq level |
523 | can be controlled by the | |
524 | .Cm CompressionLevel | |
610cd5c6 | 525 | option (see below). |
526 | Compression is desirable on modem lines and other | |
bf740959 | 527 | slow connections, but will only slow down things on fast networks. |
528 | The default value can be set on a host-by-host basis in the | |
529 | configuration files; see the | |
530 | .Cm Compress | |
531 | option below. | |
532 | .It Fl L Ar port:host:hostport | |
533 | Specifies that the given port on the local (client) host is to be | |
610cd5c6 | 534 | forwarded to the given host and port on the remote side. |
535 | This works by allocating a socket to listen to | |
bf740959 | 536 | .Ar port |
537 | on the local side, and whenever a connection is made to this port, the | |
538 | connection is forwarded over the secure channel, and a connection is | |
539 | made to | |
48e671d5 | 540 | .Ar host |
541 | port | |
542 | .Ar hostport | |
610cd5c6 | 543 | from the remote machine. |
544 | Port forwardings can also be specified in the configuration file. | |
545 | Only root can forward privileged ports. | |
48e671d5 | 546 | IPv6 addresses can be specified with an alternative syntax: |
547 | .Ar port/host/hostport | |
bf740959 | 548 | .It Fl R Ar port:host:hostport |
549 | Specifies that the given port on the remote (server) host is to be | |
610cd5c6 | 550 | forwarded to the given host and port on the local side. |
551 | This works by allocating a socket to listen to | |
bf740959 | 552 | .Ar port |
553 | on the remote side, and whenever a connection is made to this port, the | |
554 | connection is forwarded over the secure channel, and a connection is | |
555 | made to | |
48e671d5 | 556 | .Ar host |
557 | port | |
558 | .Ar hostport | |
610cd5c6 | 559 | from the local machine. |
560 | Port forwardings can also be specified in the configuration file. | |
561 | Privileged ports can be forwarded only when | |
bf740959 | 562 | logging in as root on the remote machine. |
9afadca8 | 563 | .It Fl 1 |
564 | Forces | |
565 | .Nm | |
566 | to try protocol version 1 only. | |
6ae2364d | 567 | .It Fl 2 |
568 | Forces | |
569 | .Nm | |
1d1ffb87 | 570 | to try protocol version 2 only. |
48e671d5 | 571 | .It Fl 4 |
572 | Forces | |
573 | .Nm | |
574 | to use IPv4 addresses only. | |
575 | .It Fl 6 | |
576 | Forces | |
577 | .Nm | |
578 | to use IPv6 addresses only. | |
bf740959 | 579 | .El |
580 | .Sh CONFIGURATION FILES | |
581 | .Nm | |
582 | obtains configuration data from the following sources (in this order): | |
583 | command line options, user's configuration file | |
584 | .Pq Pa $HOME/.ssh/config , | |
585 | and system-wide configuration file | |
5f4fdfae | 586 | .Pq Pa /etc/ssh_config . |
bf740959 | 587 | For each parameter, the first obtained value |
610cd5c6 | 588 | will be used. |
589 | The configuration files contain sections bracketed by | |
590 | .Dq Host | |
591 | specifications, and that section is only applied for hosts that | |
592 | match one of the patterns given in the specification. | |
593 | The matched host name is the one given on the command line. | |
bf740959 | 594 | .Pp |
595 | Since the first obtained value for each parameter is used, more | |
596 | host-specific declarations should be given near the beginning of the | |
597 | file, and general defaults at the end. | |
598 | .Pp | |
599 | The configuration file has the following format: | |
600 | .Pp | |
601 | Empty lines and lines starting with | |
602 | .Ql # | |
603 | are comments. | |
604 | .Pp | |
605 | Otherwise a line is of the format | |
606 | .Dq keyword arguments . | |
607 | The possible | |
608 | keywords and their meanings are as follows (note that the | |
609 | configuration files are case-sensitive): | |
610 | .Bl -tag -width Ds | |
611 | .It Cm Host | |
612 | Restricts the following declarations (up to the next | |
613 | .Cm Host | |
614 | keyword) to be only for those hosts that match one of the patterns | |
615 | given after the keyword. | |
616 | .Ql \&* | |
617 | and | |
618 | .Ql ? | |
619 | can be used as wildcards in the | |
610cd5c6 | 620 | patterns. |
621 | A single | |
bf740959 | 622 | .Ql \&* |
623 | as a pattern can be used to provide global | |
610cd5c6 | 624 | defaults for all hosts. |
625 | The host is the | |
bf740959 | 626 | .Ar hostname |
627 | argument given on the command line (i.e., the name is not converted to | |
628 | a canonicalized host name before matching). | |
629 | .It Cm AFSTokenPassing | |
4fe2af09 | 630 | Specifies whether to pass AFS tokens to remote host. |
631 | The argument to this keyword must be | |
bf740959 | 632 | .Dq yes |
633 | or | |
634 | .Dq no . | |
635 | .It Cm BatchMode | |
636 | If set to | |
637 | .Dq yes , | |
610cd5c6 | 638 | passphrase/password querying will be disabled. |
639 | This option is useful in scripts and other batch jobs where you have no | |
640 | user to supply the password. | |
641 | The argument must be | |
bf740959 | 642 | .Dq yes |
643 | or | |
644 | .Dq no . | |
01ce749f | 645 | The default is |
646 | .Dq no . | |
7b2ea3a1 | 647 | .It Cm CheckHostIP |
648 | If this flag is set to | |
649 | .Dq yes , | |
01ce749f | 650 | ssh will additionally check the host IP address in the |
7b2ea3a1 | 651 | .Pa known_hosts |
4fe2af09 | 652 | file. |
653 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
7b2ea3a1 | 654 | If the option is set to |
655 | .Dq no , | |
656 | the check will not be executed. | |
01ce749f | 657 | The default is |
658 | .Dq yes . | |
bf740959 | 659 | .It Cm Cipher |
33de75a3 | 660 | Specifies the cipher to use for encrypting the session |
a22aff1f | 661 | in protocol version 1. |
610cd5c6 | 662 | Currently, |
a22aff1f | 663 | .Dq blowfish |
bf740959 | 664 | and |
665 | .Dq 3des | |
610cd5c6 | 666 | are supported. |
667 | The default is | |
bf740959 | 668 | .Dq 3des . |
f54651ce | 669 | .It Cm Ciphers |
670 | Specifies the ciphers allowed for protocol version 2 | |
671 | in order of preference. | |
672 | Multiple ciphers must be comma-separated. | |
673 | The default is | |
9afadca8 | 674 | .Pp |
675 | .Bd -literal | |
f2ba0775 | 676 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour, |
9afadca8 | 677 | aes192-cbc,aes256-cbc,rijndael128-cbc,rijndael192-cbc, |
678 | rijndael256-cbc,rijndael-cbc@lysator.liu.se'' | |
679 | .Ed | |
bf740959 | 680 | .It Cm Compression |
610cd5c6 | 681 | Specifies whether to use compression. |
682 | The argument must be | |
bf740959 | 683 | .Dq yes |
684 | or | |
685 | .Dq no . | |
01ce749f | 686 | The default is |
687 | .Dq no . | |
bf740959 | 688 | .It Cm CompressionLevel |
01ce749f | 689 | Specifies the compression level to use if compression is enabled. |
610cd5c6 | 690 | The argument must be an integer from 1 (fast) to 9 (slow, best). |
691 | The default level is 6, which is good for most applications. | |
692 | The meaning of the values is the same as in | |
7b2ea3a1 | 693 | .Xr gzip 1 . |
bf740959 | 694 | .It Cm ConnectionAttempts |
695 | Specifies the number of tries (one per second) to make before falling | |
610cd5c6 | 696 | back to rsh or exiting. |
697 | The argument must be an integer. | |
698 | This may be useful in scripts if the connection sometimes fails. | |
01ce749f | 699 | The default is 4. |
fa08c86b | 700 | .It Cm PubkeyAuthentication |
701 | Specifies whether to try public key authentication. | |
1d1ffb87 | 702 | The argument to this keyword must be |
703 | .Dq yes | |
704 | or | |
705 | .Dq no . | |
01ce749f | 706 | The default is |
707 | .Dq yes . | |
1d1ffb87 | 708 | Note that this option applies to protocol version 2 only. |
bf740959 | 709 | .It Cm EscapeChar |
710 | Sets the escape character (default: | |
711 | .Ql ~ ) . | |
712 | The escape character can also | |
610cd5c6 | 713 | be set on the command line. |
714 | The argument should be a single character, | |
bf740959 | 715 | .Ql ^ |
716 | followed by a letter, or | |
717 | .Dq none | |
718 | to disable the escape | |
719 | character entirely (making the connection transparent for binary | |
720 | data). | |
f54651ce | 721 | .It Cm FallBackToRsh |
bf740959 | 722 | Specifies that if connecting via |
723 | .Nm | |
724 | fails due to a connection refused error (there is no | |
725 | .Xr sshd 8 | |
f54651ce | 726 | listening on the remote host), |
bf740959 | 727 | .Xr rsh 1 |
728 | should automatically be used instead (after a suitable warning about | |
610cd5c6 | 729 | the session being unencrypted). |
730 | The argument must be | |
bf740959 | 731 | .Dq yes |
732 | or | |
733 | .Dq no . | |
01ce749f | 734 | The default is |
735 | .Dq no . | |
bf740959 | 736 | .It Cm ForwardAgent |
737 | Specifies whether the connection to the authentication agent (if any) | |
610cd5c6 | 738 | will be forwarded to the remote machine. |
739 | The argument must be | |
bf740959 | 740 | .Dq yes |
741 | or | |
742 | .Dq no . | |
71276795 | 743 | The default is |
744 | .Dq no . | |
bf740959 | 745 | .It Cm ForwardX11 |
746 | Specifies whether X11 connections will be automatically redirected | |
f54651ce | 747 | over the secure channel and |
bf740959 | 748 | .Ev DISPLAY |
610cd5c6 | 749 | set. |
f54651ce | 750 | The argument must be |
bf740959 | 751 | .Dq yes |
752 | or | |
753 | .Dq no . | |
c8d54615 | 754 | The default is |
755 | .Dq no . | |
bf740959 | 756 | .It Cm GatewayPorts |
757 | Specifies whether remote hosts are allowed to connect to local | |
758 | forwarded ports. | |
759 | The argument must be | |
760 | .Dq yes | |
761 | or | |
762 | .Dq no . | |
763 | The default is | |
764 | .Dq no . | |
765 | .It Cm GlobalKnownHostsFile | |
a5df12e9 | 766 | Specifies a file to use for the protocol version 1 global |
767 | host key database instead of | |
5f4fdfae | 768 | .Pa /etc/ssh_known_hosts . |
a5df12e9 | 769 | .It Cm GlobalKnownHostsFile2 |
770 | Specifies a file to use for the protocol version 2 global | |
771 | host key database instead of | |
772 | .Pa /etc/ssh_known_hosts2 . | |
8abcdba4 | 773 | .It Cm HostKeyAlias |
774 | Specifies an alias that should be used instead of the | |
775 | real host name when looking up or saving the host key | |
61e96248 | 776 | in the known_hosts files. |
777 | This option is useful for tunneling ssh connections | |
8abcdba4 | 778 | or if you have multiple servers running on a single host. |
e961a8f9 | 779 | .It Cm HostKeyAlgorithms |
780 | Specfies the protocol version 2 host key algorithms | |
781 | that the client wants to use in order of preference. | |
782 | The default for this option is: | |
783 | .Dq ssh-rsa,ssh-dss | |
bf740959 | 784 | .It Cm HostName |
610cd5c6 | 785 | Specifies the real host name to log into. |
786 | This can be used to specify nicknames or abbreviations for hosts. | |
787 | Default is the name given on the command line. | |
788 | Numeric IP addresses are also permitted (both on the command line and in | |
bf740959 | 789 | .Cm HostName |
790 | specifications). | |
791 | .It Cm IdentityFile | |
792 | Specifies the file from which the user's RSA authentication identity | |
793 | is read (default | |
1d1ffb87 | 794 | .Pa $HOME/.ssh/identity |
bf740959 | 795 | in the user's home directory). |
796 | Additionally, any identities represented by the authentication agent | |
610cd5c6 | 797 | will be used for authentication. |
798 | The file name may use the tilde | |
799 | syntax to refer to a user's home directory. | |
800 | It is possible to have | |
bf740959 | 801 | multiple identity files specified in configuration files; all these |
802 | identities will be tried in sequence. | |
803 | .It Cm KeepAlive | |
804 | Specifies whether the system should send keepalive messages to the | |
610cd5c6 | 805 | other side. |
806 | If they are sent, death of the connection or crash of one | |
807 | of the machines will be properly noticed. | |
808 | However, this means that | |
bf740959 | 809 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 810 | find it annoying. |
bf740959 | 811 | .Pp |
812 | The default is | |
813 | .Dq yes | |
814 | (to send keepalives), and the client will notice | |
610cd5c6 | 815 | if the network goes down or the remote host dies. |
816 | This is important in scripts, and many users want it too. | |
bf740959 | 817 | .Pp |
818 | To disable keepalives, the value should be set to | |
819 | .Dq no | |
820 | in both the server and the client configuration files. | |
821 | .It Cm KerberosAuthentication | |
4fe2af09 | 822 | Specifies whether Kerberos authentication will be used. |
823 | The argument to this keyword must be | |
bf740959 | 824 | .Dq yes |
825 | or | |
826 | .Dq no . | |
827 | .It Cm KerberosTgtPassing | |
4fe2af09 | 828 | Specifies whether a Kerberos TGT will be forwarded to the server. |
829 | This will only work if the Kerberos server is actually an AFS kaserver. | |
830 | The argument to this keyword must be | |
bf740959 | 831 | .Dq yes |
832 | or | |
833 | .Dq no . | |
834 | .It Cm LocalForward | |
835 | Specifies that a TCP/IP port on the local machine be forwarded over | |
610cd5c6 | 836 | the secure channel to given host:port from the remote machine. |
837 | The first argument must be a port number, and the second must be | |
838 | host:port. | |
839 | Multiple forwardings may be specified, and additional | |
840 | forwardings can be given on the command line. | |
841 | Only the superuser can forward privileged ports. | |
6a17f9c2 | 842 | .It Cm LogLevel |
843 | Gives the verbosity level that is used when logging messages from | |
844 | .Nm ssh . | |
845 | The possible values are: | |
59c97189 | 846 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
847 | The default is INFO. | |
b2552997 | 848 | .It Cm MACs |
849 | Specifies the MAC (message authentication code) algorithms | |
850 | in order of preference. | |
851 | The MAC algorithm is used in protocol version 2 | |
852 | for data integrity protection. | |
853 | Multiple algorithms must be comma-separated. | |
854 | The default is | |
855 | .Pp | |
856 | .Bd -literal | |
f2ba0775 | 857 | ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com, |
b2552997 | 858 | hmac-sha1-96,hmac-md5-96'' |
859 | .Ed | |
bf740959 | 860 | .It Cm NumberOfPasswordPrompts |
4fe2af09 | 861 | Specifies the number of password prompts before giving up. |
862 | The argument to this keyword must be an integer. | |
863 | Default is 3. | |
7b2ea3a1 | 864 | .It Cm PasswordAuthentication |
610cd5c6 | 865 | Specifies whether to use password authentication. |
866 | The argument to this keyword must be | |
7b2ea3a1 | 867 | .Dq yes |
868 | or | |
869 | .Dq no . | |
01ce749f | 870 | The default is |
871 | .Dq yes . | |
1d1ffb87 | 872 | Note that this option applies to both protocol version 1 and 2. |
bf740959 | 873 | .It Cm Port |
610cd5c6 | 874 | Specifies the port number to connect on the remote host. |
875 | Default is 22. | |
babd91d4 | 876 | .It Cm PreferredAuthentications |
877 | Specifies the order in which the client should try protocol 2 | |
878 | authentication methods. This allows a client to prefer one method (e.g. | |
879 | .Cm keyboard-interactive ) | |
880 | over another method (e.g. | |
881 | .Cm password ) | |
882 | The default for this option is: | |
883 | .Dq publickey, password, keyboard-interactive | |
f54651ce | 884 | .It Cm Protocol |
885 | Specifies the protocol versions | |
886 | .Nm | |
887 | should support in order of preference. | |
888 | The possible values are | |
889 | .Dq 1 | |
890 | and | |
891 | .Dq 2 . | |
892 | Multiple versions must be comma-separated. | |
893 | The default is | |
b4a19d21 | 894 | .Dq 2,1 . |
1d1ffb87 | 895 | This means that |
896 | .Nm | |
b4a19d21 | 897 | tries version 2 and falls back to version 1 |
898 | if version 2 is not available. | |
bf740959 | 899 | .It Cm ProxyCommand |
610cd5c6 | 900 | Specifies the command to use to connect to the server. |
901 | The command | |
902 | string extends to the end of the line, and is executed with | |
903 | .Pa /bin/sh . | |
904 | In the command string, | |
905 | .Ql %h | |
906 | will be substituted by the host name to | |
907 | connect and | |
908 | .Ql %p | |
909 | by the port. | |
910 | The command can be basically anything, | |
911 | and should read from its standard input and write to its standard output. | |
912 | It should eventually connect an | |
bf740959 | 913 | .Xr sshd 8 |
914 | server running on some machine, or execute | |
915 | .Ic sshd -i | |
610cd5c6 | 916 | somewhere. |
917 | Host key management will be done using the | |
bf740959 | 918 | HostName of the host being connected (defaulting to the name typed by |
919 | the user). | |
57112b5a | 920 | Note that |
921 | .Cm CheckHostIP | |
922 | is not available for connects with a proxy command. | |
bf740959 | 923 | .Pp |
924 | .It Cm RemoteForward | |
925 | Specifies that a TCP/IP port on the remote machine be forwarded over | |
610cd5c6 | 926 | the secure channel to given host:port from the local machine. |
927 | The first argument must be a port number, and the second must be | |
928 | host:port. | |
929 | Multiple forwardings may be specified, and additional | |
930 | forwardings can be given on the command line. | |
931 | Only the superuser can forward privileged ports. | |
bf740959 | 932 | .It Cm RhostsAuthentication |
610cd5c6 | 933 | Specifies whether to try rhosts based authentication. |
934 | Note that this | |
bf740959 | 935 | declaration only affects the client side and has no effect whatsoever |
610cd5c6 | 936 | on security. |
937 | Disabling rhosts authentication may reduce | |
bf740959 | 938 | authentication time on slow connections when rhosts authentication is |
610cd5c6 | 939 | not used. |
940 | Most servers do not permit RhostsAuthentication because it | |
941 | is not secure (see RhostsRSAAuthentication). | |
942 | The argument to this keyword must be | |
bf740959 | 943 | .Dq yes |
944 | or | |
945 | .Dq no . | |
01ce749f | 946 | The default is |
947 | .Dq yes . | |
bf740959 | 948 | .It Cm RhostsRSAAuthentication |
949 | Specifies whether to try rhosts based authentication with RSA host | |
610cd5c6 | 950 | authentication. |
610cd5c6 | 951 | The argument must be |
bf740959 | 952 | .Dq yes |
953 | or | |
954 | .Dq no . | |
01ce749f | 955 | The default is |
956 | .Dq yes . | |
bf740959 | 957 | .It Cm RSAAuthentication |
610cd5c6 | 958 | Specifies whether to try RSA authentication. |
959 | The argument to this keyword must be | |
bf740959 | 960 | .Dq yes |
961 | or | |
962 | .Dq no . | |
963 | RSA authentication will only be | |
964 | attempted if the identity file exists, or an authentication agent is | |
965 | running. | |
01ce749f | 966 | The default is |
967 | .Dq yes . | |
1d1ffb87 | 968 | Note that this option applies to protocol version 1 only. |
61e96248 | 969 | .It Cm ChallengeResponseAuthentication |
970 | Specifies whether to use challenge response authentication. | |
971 | Currently there is only support for | |
5260325f | 972 | .Xr skey 1 |
610cd5c6 | 973 | authentication. |
974 | The argument to this keyword must be | |
5260325f | 975 | .Dq yes |
976 | or | |
977 | .Dq no . | |
978 | The default is | |
979 | .Dq no . | |
bf740959 | 980 | .It Cm StrictHostKeyChecking |
981 | If this flag is set to | |
f54651ce | 982 | .Dq yes , |
bf740959 | 983 | .Nm |
a877488a | 984 | will never automatically add host keys to the |
bf740959 | 985 | .Pa $HOME/.ssh/known_hosts |
1d1ffb87 | 986 | and |
987 | .Pa $HOME/.ssh/known_hosts2 | |
a877488a | 988 | files, and refuses to connect to hosts whose host key has changed. |
610cd5c6 | 989 | This provides maximum protection against trojan horse attacks. |
990 | However, it can be somewhat annoying if you don't have good | |
5f4fdfae | 991 | .Pa /etc/ssh_known_hosts |
1d1ffb87 | 992 | and |
993 | .Pa /etc/ssh_known_hosts2 | |
bf740959 | 994 | files installed and frequently |
a877488a | 995 | connect to new hosts. |
996 | This option forces the user to manually | |
997 | add all new hosts. | |
998 | If this flag is set to | |
999 | .Dq no , | |
1000 | .Nm | |
1001 | will automatically add new host keys to the | |
1002 | user known hosts files. | |
1003 | If this flag is set to | |
1004 | .Dq ask , | |
1005 | new host keys | |
1006 | will be added to the user known host files only after the user | |
1007 | has confirmed that is what they really want to do, and | |
1008 | .Nm | |
1009 | will refuse to connect to hosts whose host key has changed. | |
610cd5c6 | 1010 | The host keys of |
a877488a | 1011 | known hosts will be verified automatically in all cases. |
610cd5c6 | 1012 | The argument must be |
a877488a | 1013 | .Dq yes , |
1014 | .Dq no | |
bf740959 | 1015 | or |
a877488a | 1016 | .Dq ask . |
1017 | The default is | |
1018 | .Dq ask . | |
bf740959 | 1019 | .It Cm UsePrivilegedPort |
1020 | Specifies whether to use a privileged port for outgoing connections. | |
1021 | The argument must be | |
1022 | .Dq yes | |
1023 | or | |
1024 | .Dq no . | |
1025 | The default is | |
d5ebca2b | 1026 | .Dq no . |
bf740959 | 1027 | Note that setting this option to |
1028 | .Dq no | |
95f1eccc | 1029 | turns off |
bf740959 | 1030 | .Cm RhostsAuthentication |
1031 | and | |
6ffc9c88 | 1032 | .Cm RhostsRSAAuthentication |
1033 | for older servers. | |
7b2ea3a1 | 1034 | .It Cm User |
610cd5c6 | 1035 | Specifies the user to log in as. |
1036 | This can be useful if you have a different user name on different machines. | |
1037 | This saves the trouble of | |
7b2ea3a1 | 1038 | having to remember to give the user name on the command line. |
1039 | .It Cm UserKnownHostsFile | |
a5df12e9 | 1040 | Specifies a file to use for the protocol version 1 user |
1041 | host key database instead of | |
7b2ea3a1 | 1042 | .Pa $HOME/.ssh/known_hosts . |
a5df12e9 | 1043 | .It Cm UserKnownHostsFile2 |
1044 | Specifies a file to use for the protocol version 2 user | |
1045 | host key database instead of | |
1046 | .Pa $HOME/.ssh/known_hosts2 . | |
bf740959 | 1047 | .It Cm UseRsh |
610cd5c6 | 1048 | Specifies that rlogin/rsh should be used for this host. |
1049 | It is possible that the host does not at all support the | |
bf740959 | 1050 | .Nm |
610cd5c6 | 1051 | protocol. |
1052 | This causes | |
bf740959 | 1053 | .Nm |
610cd5c6 | 1054 | to immediately execute |
bf740959 | 1055 | .Xr rsh 1 . |
1056 | All other options (except | |
1057 | .Cm HostName ) | |
610cd5c6 | 1058 | are ignored if this has been specified. |
1059 | The argument must be | |
bf740959 | 1060 | .Dq yes |
1061 | or | |
1062 | .Dq no . | |
fa649821 | 1063 | .It Cm XAuthLocation |
1064 | Specifies the location of the | |
1065 | .Xr xauth 1 | |
1066 | program. | |
1067 | The default is | |
1068 | .Pa /usr/X11R6/bin/xauth . | |
b5e300c2 | 1069 | .El |
bf740959 | 1070 | .Sh ENVIRONMENT |
1071 | .Nm | |
1072 | will normally set the following environment variables: | |
1073 | .Bl -tag -width Ds | |
1074 | .It Ev DISPLAY | |
1075 | The | |
1076 | .Ev DISPLAY | |
610cd5c6 | 1077 | variable indicates the location of the X11 server. |
f54651ce | 1078 | It is automatically set by |
bf740959 | 1079 | .Nm |
1080 | to point to a value of the form | |
1081 | .Dq hostname:n | |
1082 | where hostname indicates | |
610cd5c6 | 1083 | the host where the shell runs, and n is an integer >= 1. |
1084 | .Nm | |
1085 | uses this special value to forward X11 connections over the secure | |
1086 | channel. | |
1087 | The user should normally not set DISPLAY explicitly, as that | |
bf740959 | 1088 | will render the X11 connection insecure (and will require the user to |
1089 | manually copy any required authorization cookies). | |
1090 | .It Ev HOME | |
1091 | Set to the path of the user's home directory. | |
1092 | .It Ev LOGNAME | |
1093 | Synonym for | |
1094 | .Ev USER ; | |
1095 | set for compatibility with systems that use this variable. | |
1096 | .It Ev MAIL | |
1097 | Set to point the user's mailbox. | |
610cd5c6 | 1098 | .It Ev PATH |
bf740959 | 1099 | Set to the default |
1100 | .Ev PATH , | |
1101 | as specified when compiling | |
1102 | .Nm ssh . | |
1103 | .It Ev SSH_AUTH_SOCK | |
1104 | indicates the path of a unix-domain socket used to communicate with the | |
1105 | agent. | |
1106 | .It Ev SSH_CLIENT | |
610cd5c6 | 1107 | Identifies the client end of the connection. |
1108 | The variable contains | |
bf740959 | 1109 | three space-separated values: client ip-address, client port number, |
1110 | and server port number. | |
8abcdba4 | 1111 | .It Ev SSH_ORIGINAL_COMMAND |
1112 | The variable contains the original command line if a forced command | |
1113 | is executed. | |
1114 | It can be used to extract the original arguments. | |
bf740959 | 1115 | .It Ev SSH_TTY |
1116 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 1117 | with the current shell or command. |
1118 | If the current session has no tty, | |
bf740959 | 1119 | this variable is not set. |
1120 | .It Ev TZ | |
1121 | The timezone variable is set to indicate the present timezone if it | |
c345cf9d | 1122 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 1123 | on to new connections). |
1124 | .It Ev USER | |
1125 | Set to the name of the user logging in. | |
1126 | .El | |
1127 | .Pp | |
f54651ce | 1128 | Additionally, |
bf740959 | 1129 | .Nm |
f54651ce | 1130 | reads |
1131 | .Pa $HOME/.ssh/environment , | |
bf740959 | 1132 | and adds lines of the format |
1133 | .Dq VARNAME=value | |
1134 | to the environment. | |
1135 | .Sh FILES | |
c8d54615 | 1136 | .Bl -tag -width Ds |
a5df12e9 | 1137 | .It Pa $HOME/.ssh/known_hosts, $HOME/.ssh/known_hosts2 |
bf740959 | 1138 | Records host keys for all hosts the user has logged into (that are not |
1139 | in | |
a5df12e9 | 1140 | .Pa /etc/ssh_known_hosts |
1141 | for protocol version 1 or | |
1142 | .Pa /etc/ssh_known_hosts2 | |
1143 | for protocol version 2). | |
bf740959 | 1144 | See |
1145 | .Xr sshd 8 . | |
c0ecc314 | 1146 | .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa |
1147 | Contains the authentication identity of the user. | |
1148 | They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. | |
1d1ffb87 | 1149 | These files |
1150 | contain sensitive data and should be readable by the user but not | |
bf740959 | 1151 | accessible by others (read/write/execute). |
1152 | Note that | |
1153 | .Nm | |
1d1ffb87 | 1154 | ignores a private key file if it is accessible by others. |
bf740959 | 1155 | It is possible to specify a passphrase when |
1156 | generating the key; the passphrase will be used to encrypt the | |
1157 | sensitive part of this file using 3DES. | |
c0ecc314 | 1158 | .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub |
bf740959 | 1159 | Contains the public key for authentication (public part of the |
610cd5c6 | 1160 | identity file in human-readable form). |
1d1ffb87 | 1161 | The contents of the |
1162 | .Pa $HOME/.ssh/identity.pub | |
1163 | file should be added to | |
bf740959 | 1164 | .Pa $HOME/.ssh/authorized_keys |
1165 | on all machines | |
c0ecc314 | 1166 | where you wish to log in using protocol version 1 RSA authentication. |
1d1ffb87 | 1167 | The contents of the |
1168 | .Pa $HOME/.ssh/id_dsa.pub | |
c0ecc314 | 1169 | and |
1170 | .Pa $HOME/.ssh/id_rsa.pub | |
1d1ffb87 | 1171 | file should be added to |
1172 | .Pa $HOME/.ssh/authorized_keys2 | |
1173 | on all machines | |
c0ecc314 | 1174 | where you wish to log in using protocol version 2 DSA/RSA authentication. |
1d1ffb87 | 1175 | These files are not |
610cd5c6 | 1176 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 1177 | These files are |
c44559d2 | 1178 | never used automatically and are not necessary; they are only provided for |
bf740959 | 1179 | the convenience of the user. |
1180 | .It Pa $HOME/.ssh/config | |
610cd5c6 | 1181 | This is the per-user configuration file. |
1182 | The format of this file is described above. | |
1183 | This file is used by the | |
bf740959 | 1184 | .Nm |
610cd5c6 | 1185 | client. |
1186 | This file does not usually contain any sensitive information, | |
bf740959 | 1187 | but the recommended permissions are read/write for the user, and not |
1188 | accessible by others. | |
1189 | .It Pa $HOME/.ssh/authorized_keys | |
610cd5c6 | 1190 | Lists the RSA keys that can be used for logging in as this user. |
1191 | The format of this file is described in the | |
bf740959 | 1192 | .Xr sshd 8 |
610cd5c6 | 1193 | manual page. |
1194 | In the simplest form the format is the same as the .pub | |
bf740959 | 1195 | identity files (that is, each line contains the number of bits in |
1196 | modulus, public exponent, modulus, and comment fields, separated by | |
610cd5c6 | 1197 | spaces). |
1198 | This file is not highly sensitive, but the recommended | |
bf740959 | 1199 | permissions are read/write for the user, and not accessible by others. |
1d1ffb87 | 1200 | .It Pa $HOME/.ssh/authorized_keys2 |
fa08c86b | 1201 | Lists the public keys (DSA/RSA) that can be used for logging in as this user. |
1d1ffb87 | 1202 | This file is not highly sensitive, but the recommended |
1203 | permissions are read/write for the user, and not accessible by others. | |
1204 | .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2 | |
610cd5c6 | 1205 | Systemwide list of known host keys. |
1d1ffb87 | 1206 | .Pa /etc/ssh_known_hosts |
1207 | contains RSA and | |
1208 | .Pa /etc/ssh_known_hosts2 | |
fa08c86b | 1209 | contains DSA or RSA keys for protocol version 2. |
1d1ffb87 | 1210 | These files should be prepared by the |
bf740959 | 1211 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1212 | organization. |
1213 | This file should be world-readable. | |
1214 | This file contains | |
bf740959 | 1215 | public keys, one per line, in the following format (fields separated |
1216 | by spaces): system name, number of bits in modulus, public exponent, | |
610cd5c6 | 1217 | modulus, and optional comment field. |
1218 | When different names are used | |
bf740959 | 1219 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1220 | commas. |
1221 | The format is described on the | |
bf740959 | 1222 | .Xr sshd 8 |
1223 | manual page. | |
1224 | .Pp | |
1225 | The canonical system name (as returned by name servers) is used by | |
1226 | .Xr sshd 8 | |
1227 | to verify the client host when logging in; other names are needed because | |
1228 | .Nm | |
1229 | does not convert the user-supplied name to a canonical name before | |
1230 | checking the key, because someone with access to the name servers | |
1231 | would then be able to fool host authentication. | |
5f4fdfae | 1232 | .It Pa /etc/ssh_config |
610cd5c6 | 1233 | Systemwide configuration file. |
1234 | This file provides defaults for those | |
bf740959 | 1235 | values that are not specified in the user's configuration file, and |
610cd5c6 | 1236 | for those users who do not have a configuration file. |
1237 | This file must be world-readable. | |
bf740959 | 1238 | .It Pa $HOME/.rhosts |
1239 | This file is used in | |
1240 | .Pa \&.rhosts | |
1241 | authentication to list the | |
610cd5c6 | 1242 | host/user pairs that are permitted to log in. |
1243 | (Note that this file is | |
bf740959 | 1244 | also used by rlogin and rsh, which makes using this file insecure.) |
1245 | Each line of the file contains a host name (in the canonical form | |
1246 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1247 | separated by a space. |
e91c60f2 | 1248 | On some machines this file may need to be |
bf740959 | 1249 | world-readable if the user's home directory is on a NFS partition, |
1250 | because | |
1251 | .Xr sshd 8 | |
610cd5c6 | 1252 | reads it as root. |
1253 | Additionally, this file must be owned by the user, | |
1254 | and must not have write permissions for anyone else. | |
1255 | The recommended | |
bf740959 | 1256 | permission for most machines is read/write for the user, and not |
1257 | accessible by others. | |
1258 | .Pp | |
1259 | Note that by default | |
1260 | .Xr sshd 8 | |
1261 | will be installed so that it requires successful RSA host | |
610cd5c6 | 1262 | authentication before permitting \s+2.\s0rhosts authentication. |
1263 | If your server machine does not have the client's host key in | |
5f4fdfae | 1264 | .Pa /etc/ssh_known_hosts , |
bf740959 | 1265 | you can store it in |
1266 | .Pa $HOME/.ssh/known_hosts . | |
1267 | The easiest way to do this is to | |
1268 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1269 | will automatically add the host key to |
bf740959 | 1270 | .Pa $HOME/.ssh/known_hosts . |
1271 | .It Pa $HOME/.shosts | |
1272 | This file is used exactly the same way as | |
1273 | .Pa \&.rhosts . | |
1274 | The purpose for | |
1275 | having this file is to be able to use rhosts authentication with | |
1276 | .Nm | |
1277 | without permitting login with | |
1278 | .Xr rlogin 1 | |
1279 | or | |
1280 | .Xr rsh 1 . | |
1281 | .It Pa /etc/hosts.equiv | |
1282 | This file is used during | |
610cd5c6 | 1283 | .Pa \&.rhosts authentication. |
1284 | It contains | |
bf740959 | 1285 | canonical hosts names, one per line (the full format is described on |
1286 | the | |
1287 | .Xr sshd 8 | |
610cd5c6 | 1288 | manual page). |
1289 | If the client host is found in this file, login is | |
bf740959 | 1290 | automatically permitted provided client and server user names are the |
610cd5c6 | 1291 | same. |
1292 | Additionally, successful RSA host authentication is normally | |
1293 | required. | |
1294 | This file should only be writable by root. | |
5f4fdfae | 1295 | .It Pa /etc/shosts.equiv |
f54651ce | 1296 | This file is processed exactly as |
bf740959 | 1297 | .Pa /etc/hosts.equiv . |
1298 | This file may be useful to permit logins using | |
1299 | .Nm | |
1300 | but not using rsh/rlogin. | |
5f4fdfae | 1301 | .It Pa /etc/sshrc |
bf740959 | 1302 | Commands in this file are executed by |
1303 | .Nm | |
1304 | when the user logs in just before the user's shell (or command) is started. | |
1305 | See the | |
1306 | .Xr sshd 8 | |
1307 | manual page for more information. | |
1308 | .It Pa $HOME/.ssh/rc | |
1309 | Commands in this file are executed by | |
1310 | .Nm | |
1311 | when the user logs in just before the user's shell (or command) is | |
1312 | started. | |
f54651ce | 1313 | See the |
bf740959 | 1314 | .Xr sshd 8 |
1315 | manual page for more information. | |
83b7f649 | 1316 | .It Pa $HOME/.ssh/environment |
1317 | Contains additional definitions for environment variables, see section | |
1318 | .Sx ENVIRONMENT | |
1319 | above. | |
b5e300c2 | 1320 | .El |
fa08c86b | 1321 | .Sh AUTHORS |
5fb622e4 | 1322 | OpenSSH is a derivative of the original and free |
1323 | ssh 1.2.12 release by Tatu Ylonen. | |
1324 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1325 | Theo de Raadt and Dug Song | |
1326 | removed many bugs, re-added newer features and | |
1327 | created OpenSSH. | |
1328 | Markus Friedl contributed the support for SSH | |
1329 | protocol versions 1.5 and 2.0. | |
bf740959 | 1330 | .Sh SEE ALSO |
1331 | .Xr rlogin 1 , | |
1332 | .Xr rsh 1 , | |
1333 | .Xr scp 1 , | |
61e96248 | 1334 | .Xr sftp 1 , |
bf740959 | 1335 | .Xr ssh-add 1 , |
1336 | .Xr ssh-agent 1 , | |
1337 | .Xr ssh-keygen 1 , | |
1338 | .Xr telnet 1 , | |
9afadca8 | 1339 | .Xr sshd 8 |