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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 | .\" | |
13 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. | |
14 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. | |
15 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. | |
16 | .\" | |
17 | .\" Redistribution and use in source and binary forms, with or without | |
18 | .\" modification, are permitted provided that the following conditions | |
19 | .\" are met: | |
20 | .\" 1. Redistributions of source code must retain the above copyright | |
21 | .\" notice, this list of conditions and the following disclaimer. | |
22 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
23 | .\" notice, this list of conditions and the following disclaimer in the | |
24 | .\" documentation and/or other materials provided with the distribution. | |
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 | .\" |
37 | .Dd September 25, 1999 | |
38 | .Dt SSH 1 | |
39 | .Os | |
40 | .Sh NAME | |
41 | .Nm ssh | |
42 | .Nd OpenSSH secure shell client (remote login program) | |
43 | .Sh SYNOPSIS | |
44 | .Nm ssh | |
45 | .Op Fl l Ar login_name | |
46 | .Op Ar hostname | user@hostname | |
47 | .Op Ar command | |
48 | .Pp | |
49 | .Nm ssh | |
71276795 | 50 | .Op Fl afgknqtvxACNPTX246 |
d0c832f3 | 51 | .Op Fl c Ar cipher_spec |
bf740959 | 52 | .Op Fl e Ar escape_char |
53 | .Op Fl i Ar identity_file | |
54 | .Op Fl l Ar login_name | |
55 | .Op Fl o Ar option | |
56 | .Op Fl p Ar port | |
57 | .Oo Fl L Xo | |
58 | .Sm off | |
bf740959 | 59 | .Ar port : |
7b2ea3a1 | 60 | .Ar host : |
bf740959 | 61 | .Ar hostport |
62 | .Sm on | |
63 | .Xc | |
64 | .Oc | |
65 | .Oo Fl R Xo | |
66 | .Sm off | |
bf740959 | 67 | .Ar port : |
7b2ea3a1 | 68 | .Ar host : |
bf740959 | 69 | .Ar hostport |
70 | .Sm on | |
71 | .Xc | |
72 | .Oc | |
73 | .Op Ar hostname | user@hostname | |
74 | .Op Ar command | |
f54651ce | 75 | .Sh DESCRIPTION |
bf740959 | 76 | .Nm |
77 | (Secure Shell) is a program for logging into a remote machine and for | |
610cd5c6 | 78 | executing commands on a remote machine. |
79 | It is intended to replace | |
bf740959 | 80 | rlogin and rsh, and provide secure encrypted communications between |
610cd5c6 | 81 | two untrusted hosts over an insecure network. |
82 | X11 connections and | |
bf740959 | 83 | arbitrary TCP/IP ports can also be forwarded over the secure channel. |
84 | .Pp | |
85 | .Nm | |
f54651ce | 86 | connects and logs into the specified |
bf740959 | 87 | .Ar hostname . |
88 | The user must prove | |
1d1ffb87 | 89 | his/her identity to the remote machine using one of several methods |
90 | depending on the protocol version used: | |
91 | .Pp | |
92 | .Ss SSH protocol version 1 | |
bf740959 | 93 | .Pp |
94 | First, if the machine the user logs in from is listed in | |
95 | .Pa /etc/hosts.equiv | |
96 | or | |
5f4fdfae | 97 | .Pa /etc/shosts.equiv |
bf740959 | 98 | on the remote machine, and the user names are |
99 | the same on both sides, the user is immediately permitted to log in. | |
f54651ce | 100 | Second, if |
bf740959 | 101 | .Pa \&.rhosts |
102 | or | |
103 | .Pa \&.shosts | |
104 | exists in the user's home directory on the | |
105 | remote machine and contains a line containing the name of the client | |
106 | machine and the name of the user on that machine, the user is | |
610cd5c6 | 107 | permitted to log in. |
108 | This form of authentication alone is normally not | |
bf740959 | 109 | allowed by the server because it is not secure. |
110 | .Pp | |
111 | The second (and primary) authentication method is the | |
112 | .Pa rhosts | |
113 | or | |
114 | .Pa hosts.equiv | |
610cd5c6 | 115 | method combined with RSA-based host authentication. |
116 | It means that if the login would be permitted by | |
1d1ffb87 | 117 | .Pa $HOME/.rhosts , |
118 | .Pa $HOME/.shosts , | |
bf740959 | 119 | .Pa /etc/hosts.equiv , |
120 | or | |
5f4fdfae | 121 | .Pa /etc/shosts.equiv , |
bf740959 | 122 | and if additionally the server can verify the client's |
f54651ce | 123 | host key (see |
5f4fdfae | 124 | .Pa /etc/ssh_known_hosts |
5bbb5681 | 125 | and |
126 | .Pa $HOME/.ssh/known_hosts | |
bf740959 | 127 | in the |
128 | .Sx FILES | |
610cd5c6 | 129 | section), only then login is permitted. |
130 | This authentication method closes security holes due to IP | |
131 | spoofing, DNS spoofing and routing spoofing. | |
132 | [Note to the administrator: | |
bf740959 | 133 | .Pa /etc/hosts.equiv , |
1d1ffb87 | 134 | .Pa $HOME/.rhosts , |
bf740959 | 135 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
136 | disabled if security is desired.] | |
137 | .Pp | |
f54651ce | 138 | As a third authentication method, |
bf740959 | 139 | .Nm |
140 | supports RSA based authentication. | |
141 | The scheme is based on public-key cryptography: there are cryptosystems | |
142 | where encryption and decryption are done using separate keys, and it | |
143 | is not possible to derive the decryption key from the encryption key. | |
610cd5c6 | 144 | RSA is one such system. |
f54651ce | 145 | The idea is that each user creates a public/private |
610cd5c6 | 146 | key pair for authentication purposes. |
147 | The server knows the public key, and only the user knows the private key. | |
f54651ce | 148 | The file |
bf740959 | 149 | .Pa $HOME/.ssh/authorized_keys |
150 | lists the public keys that are permitted for logging | |
610cd5c6 | 151 | in. |
152 | When the user logs in, the | |
bf740959 | 153 | .Nm |
154 | program tells the server which key pair it would like to use for | |
610cd5c6 | 155 | authentication. |
156 | The server checks if this key is permitted, and if | |
bf740959 | 157 | so, sends the user (actually the |
158 | .Nm | |
159 | program running on behalf of the user) a challenge, a random number, | |
610cd5c6 | 160 | encrypted by the user's public key. |
161 | The challenge can only be | |
162 | decrypted using the proper private key. | |
163 | The user's client then decrypts the | |
bf740959 | 164 | challenge using the private key, proving that he/she knows the private |
165 | key but without disclosing it to the server. | |
166 | .Pp | |
167 | .Nm | |
610cd5c6 | 168 | implements the RSA authentication protocol automatically. |
169 | The user creates his/her RSA key pair by running | |
bf740959 | 170 | .Xr ssh-keygen 1 . |
f54651ce | 171 | This stores the private key in |
1d1ffb87 | 172 | .Pa $HOME/.ssh/identity |
bf740959 | 173 | and the public key in |
1d1ffb87 | 174 | .Pa $HOME/.ssh/identity.pub |
610cd5c6 | 175 | in the user's home directory. |
176 | The user should then copy the | |
bf740959 | 177 | .Pa identity.pub |
f54651ce | 178 | to |
1d1ffb87 | 179 | .Pa $HOME/.ssh/authorized_keys |
f54651ce | 180 | in his/her home directory on the remote machine (the |
bf740959 | 181 | .Pa authorized_keys |
f54651ce | 182 | file corresponds to the conventional |
1d1ffb87 | 183 | .Pa $HOME/.rhosts |
bf740959 | 184 | file, and has one key |
610cd5c6 | 185 | per line, though the lines can be very long). |
186 | After this, the user can log in without giving the password. | |
187 | RSA authentication is much | |
bf740959 | 188 | more secure than rhosts authentication. |
189 | .Pp | |
190 | The most convenient way to use RSA authentication may be with an | |
610cd5c6 | 191 | authentication agent. |
192 | See | |
bf740959 | 193 | .Xr ssh-agent 1 |
194 | for more information. | |
195 | .Pp | |
f54651ce | 196 | If other authentication methods fail, |
bf740959 | 197 | .Nm |
610cd5c6 | 198 | prompts the user for a password. |
199 | The password is sent to the remote | |
bf740959 | 200 | host for checking; however, since all communications are encrypted, |
201 | the password cannot be seen by someone listening on the network. | |
202 | .Pp | |
1d1ffb87 | 203 | .Ss SSH protocol version 2 |
204 | .Pp | |
205 | When a user connects using the protocol version 2 | |
206 | different authentication methods are available: | |
207 | At first, the client attempts to authenticate using the public key method. | |
208 | If this method fails password authentication is tried. | |
209 | .Pp | |
210 | The public key method is similar to RSA authentication described | |
211 | in the previous section except that the DSA algorithm is used | |
212 | instead of the patented RSA algorithm. | |
213 | The client uses his private DSA key | |
214 | .Pa $HOME/.ssh/id_dsa | |
215 | to sign the session identifier and sends the result to the server. | |
216 | The server checks whether the matching public key is listed in | |
217 | .Pa $HOME/.ssh/authorized_keys2 | |
218 | and grants access if both the key is found and the signature is correct. | |
219 | The session identifier is derived from a shared Diffie-Hellman value | |
220 | and is only known to the client and the server. | |
221 | .Pp | |
222 | If public key authentication fails or is not available a password | |
223 | can be sent encrypted to the remote host for proving the user's identity. | |
224 | This protocol 2 implementation does not yet support Kerberos or | |
225 | S/Key authentication. | |
226 | .Pp | |
227 | Protocol 2 provides additional mechanisms for confidentiality | |
d0c832f3 | 228 | (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour) |
1d1ffb87 | 229 | and integrity (hmac-sha1, hmac-md5). |
230 | Note that protocol 1 lacks a strong mechanism for ensuring the | |
231 | integrity of the connection. | |
232 | .Pp | |
233 | .Ss Login session and remote execution | |
234 | .Pp | |
bf740959 | 235 | When the user's identity has been accepted by the server, the server |
236 | either executes the given command, or logs into the machine and gives | |
610cd5c6 | 237 | the user a normal shell on the remote machine. |
238 | All communication with | |
bf740959 | 239 | the remote command or shell will be automatically encrypted. |
240 | .Pp | |
241 | If a pseudo-terminal has been allocated (normal login session), the | |
242 | user can disconnect with | |
243 | .Ic ~. , | |
244 | and suspend | |
245 | .Nm | |
246 | with | |
247 | .Ic ~^Z . | |
248 | All forwarded connections can be listed with | |
f54651ce | 249 | .Ic ~# |
bf740959 | 250 | and if |
251 | the session blocks waiting for forwarded X11 or TCP/IP | |
252 | connections to terminate, it can be backgrounded with | |
253 | .Ic ~& | |
254 | (this should not be used while the user shell is active, as it can cause the | |
610cd5c6 | 255 | shell to hang). |
256 | All available escapes can be listed with | |
bf740959 | 257 | .Ic ~? . |
258 | .Pp | |
259 | A single tilde character can be sent as | |
260 | .Ic ~~ | |
261 | (or by following the tilde by a character other than those described above). | |
262 | The escape character must always follow a newline to be interpreted as | |
610cd5c6 | 263 | special. |
264 | The escape character can be changed in configuration files | |
265 | or on the command line. | |
bf740959 | 266 | .Pp |
267 | If no pseudo tty has been allocated, the | |
268 | session is transparent and can be used to reliably transfer binary | |
610cd5c6 | 269 | data. |
270 | On most systems, setting the escape character to | |
bf740959 | 271 | .Dq none |
272 | will also make the session transparent even if a tty is used. | |
273 | .Pp | |
274 | The session terminates when the command or shell in on the remote | |
275 | machine exists and all X11 and TCP/IP connections have been closed. | |
276 | The exit status of the remote program is returned as the exit status | |
277 | of | |
278 | .Nm ssh . | |
279 | .Pp | |
1d1ffb87 | 280 | .Ss X11 and TCP forwarding |
281 | .Pp | |
bf740959 | 282 | If the user is using X11 (the |
283 | .Ev DISPLAY | |
284 | environment variable is set), the connection to the X11 display is | |
285 | automatically forwarded to the remote side in such a way that any X11 | |
286 | programs started from the shell (or command) will go through the | |
287 | encrypted channel, and the connection to the real X server will be made | |
610cd5c6 | 288 | from the local machine. |
289 | The user should not manually set | |
bf740959 | 290 | .Ev DISPLAY . |
291 | Forwarding of X11 connections can be | |
292 | configured on the command line or in configuration files. | |
293 | .Pp | |
294 | The | |
f54651ce | 295 | .Ev DISPLAY |
bf740959 | 296 | value set by |
297 | .Nm | |
298 | will point to the server machine, but with a display number greater | |
610cd5c6 | 299 | than zero. |
300 | This is normal, and happens because | |
bf740959 | 301 | .Nm |
302 | creates a | |
303 | .Dq proxy | |
304 | X server on the server machine for forwarding the | |
305 | connections over the encrypted channel. | |
306 | .Pp | |
307 | .Nm | |
308 | will also automatically set up Xauthority data on the server machine. | |
309 | For this purpose, it will generate a random authorization cookie, | |
310 | store it in Xauthority on the server, and verify that any forwarded | |
311 | connections carry this cookie and replace it by the real cookie when | |
610cd5c6 | 312 | the connection is opened. |
313 | The real authentication cookie is never | |
bf740959 | 314 | sent to the server machine (and no cookies are sent in the plain). |
315 | .Pp | |
316 | If the user is using an authentication agent, the connection to the agent | |
317 | is automatically forwarded to the remote side unless disabled on | |
318 | command line or in a configuration file. | |
319 | .Pp | |
320 | Forwarding of arbitrary TCP/IP connections over the secure channel can | |
610cd5c6 | 321 | be specified either on command line or in a configuration file. |
322 | One possible application of TCP/IP forwarding is a secure connection to an | |
bf740959 | 323 | electronic purse; another is going trough firewalls. |
324 | .Pp | |
1d1ffb87 | 325 | .Ss Server authentication |
326 | .Pp | |
bf740959 | 327 | .Nm |
1d1ffb87 | 328 | automatically maintains and checks a database containing |
610cd5c6 | 329 | identifications for all hosts it has ever been used with. |
1d1ffb87 | 330 | RSA host keys are stored in |
331 | .Pa $HOME/.ssh/known_hosts | |
332 | and | |
333 | DSA host keys are stored in | |
334 | .Pa $HOME/.ssh/known_hosts2 | |
610cd5c6 | 335 | in the user's home directory. |
1d1ffb87 | 336 | Additionally, the files |
5f4fdfae | 337 | .Pa /etc/ssh_known_hosts |
1d1ffb87 | 338 | and |
339 | .Pa /etc/ssh_known_hosts2 | |
340 | are automatically checked for known hosts. | |
610cd5c6 | 341 | Any new hosts are automatically added to the user's file. |
342 | If a host's identification | |
bf740959 | 343 | ever changes, |
344 | .Nm | |
345 | warns about this and disables password authentication to prevent a | |
610cd5c6 | 346 | trojan horse from getting the user's password. |
347 | Another purpose of | |
bf740959 | 348 | this mechanism is to prevent man-in-the-middle attacks which could |
610cd5c6 | 349 | otherwise be used to circumvent the encryption. |
350 | The | |
bf740959 | 351 | .Cm StrictHostKeyChecking |
352 | option (see below) can be used to prevent logins to machines whose | |
353 | host key is not known or has changed. | |
354 | .Sh OPTIONS | |
355 | .Bl -tag -width Ds | |
356 | .It Fl a | |
4fe2af09 | 357 | Disables forwarding of the authentication agent connection. |
71276795 | 358 | .It Fl A |
359 | Enables forwarding of the authentication agent connection. | |
360 | This can also be specified on a per-host basis in a configuration file. | |
bf740959 | 361 | .It Fl c Ar blowfish|3des |
f54651ce | 362 | Selects the cipher to use for encrypting the session. |
bf740959 | 363 | .Ar 3des |
610cd5c6 | 364 | is used by default. |
f54651ce | 365 | It is believed to be secure. |
bf740959 | 366 | .Ar 3des |
367 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
368 | It is presumably more secure than the | |
369 | .Ar des | |
d0c832f3 | 370 | cipher which is no longer supported in |
371 | .Nm ssh . | |
bf740959 | 372 | .Ar blowfish |
373 | is a fast block cipher, it appears very secure and is much faster than | |
610cd5c6 | 374 | .Ar 3des . |
d0c832f3 | 375 | .It Fl c Ar "3des-cbc,blowfish-cbc,arcfour,cast128-cbc" |
376 | Additionally, for protocol version 2 a comma-separated list of ciphers can | |
94ec8c6b | 377 | be specified in order of preference. |
378 | Protocol version 2 supports 3DES, Blowfish, and CAST128 in CBC mode | |
379 | and Arcfour. | |
bf740959 | 380 | .It Fl e Ar ch|^ch|none |
381 | Sets the escape character for sessions with a pty (default: | |
382 | .Ql ~ ) . | |
610cd5c6 | 383 | The escape character is only recognized at the beginning of a line. |
384 | The escape character followed by a dot | |
bf740959 | 385 | .Pq Ql \&. |
386 | closes the connection, followed | |
387 | by control-Z suspends the connection, and followed by itself sends the | |
610cd5c6 | 388 | escape character once. |
389 | Setting the character to | |
bf740959 | 390 | .Dq none |
391 | disables any escapes and makes the session fully transparent. | |
392 | .It Fl f | |
393 | Requests | |
394 | .Nm | |
610cd5c6 | 395 | to go to background just before command execution. |
396 | This is useful if | |
bf740959 | 397 | .Nm |
398 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 399 | wants it in the background. |
f54651ce | 400 | This implies |
bf740959 | 401 | .Fl n . |
402 | The recommended way to start X11 programs at a remote site is with | |
403 | something like | |
404 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 405 | .It Fl g |
406 | Allows remote hosts to connect to local forwarded ports. | |
bf740959 | 407 | .It Fl i Ar identity_file |
f54651ce | 408 | Selects the file from which the identity (private key) for |
610cd5c6 | 409 | RSA authentication is read. |
f54651ce | 410 | Default is |
1d1ffb87 | 411 | .Pa $HOME/.ssh/identity |
610cd5c6 | 412 | in the user's home directory. |
413 | Identity files may also be specified on | |
414 | a per-host basis in the configuration file. | |
415 | It is possible to have multiple | |
bf740959 | 416 | .Fl i |
417 | options (and multiple identities specified in | |
418 | configuration files). | |
bf740959 | 419 | .It Fl k |
4fe2af09 | 420 | Disables forwarding of Kerberos tickets and AFS tokens. |
421 | This may also be specified on a per-host basis in the configuration file. | |
bf740959 | 422 | .It Fl l Ar login_name |
610cd5c6 | 423 | Specifies the user to log in as on the remote machine. |
424 | This also may be specified on a per-host basis in the configuration file. | |
bf740959 | 425 | .It Fl n |
426 | Redirects stdin from | |
427 | .Pa /dev/null | |
428 | (actually, prevents reading from stdin). | |
429 | This must be used when | |
430 | .Nm | |
610cd5c6 | 431 | is run in the background. |
432 | A common trick is to use this to run X11 programs on a remote machine. | |
433 | For example, | |
bf740959 | 434 | .Ic ssh -n shadows.cs.hut.fi emacs & |
435 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
436 | connection will be automatically forwarded over an encrypted channel. | |
437 | The | |
438 | .Nm | |
439 | program will be put in the background. | |
440 | (This does not work if | |
441 | .Nm | |
442 | needs to ask for a password or passphrase; see also the | |
443 | .Fl f | |
444 | option.) | |
0e73cc53 | 445 | .It Fl N |
446 | Do not execute a remote command. | |
447 | This is usefull if you just want to forward ports | |
448 | (protocol version 2 only). | |
bf740959 | 449 | .It Fl o Ar option |
450 | Can be used to give options in the format used in the config file. | |
451 | This is useful for specifying options for which there is no separate | |
610cd5c6 | 452 | command-line flag. |
453 | The option has the same format as a line in the configuration file. | |
bf740959 | 454 | .It Fl p Ar port |
610cd5c6 | 455 | Port to connect to on the remote host. |
456 | This can be specified on a | |
bf740959 | 457 | per-host basis in the configuration file. |
458 | .It Fl P | |
459 | Use a non-privileged port for outgoing connections. | |
460 | This can be used if your firewall does | |
461 | not permit connections from privileged ports. | |
95f1eccc | 462 | Note that this option turns off |
bf740959 | 463 | .Cm RhostsAuthentication |
464 | and | |
465 | .Cm RhostsRSAAuthentication . | |
466 | .It Fl q | |
610cd5c6 | 467 | Quiet mode. |
468 | Causes all warning and diagnostic messages to be suppressed. | |
469 | Only fatal errors are displayed. | |
bf740959 | 470 | .It Fl t |
610cd5c6 | 471 | Force pseudo-tty allocation. |
4fe2af09 | 472 | This can be used to execute arbitrary |
610cd5c6 | 473 | screen-based programs on a remote machine, which can be very useful, |
474 | e.g., when implementing menu services. | |
0e73cc53 | 475 | .It Fl T |
476 | Disable pseudo-tty allocation (protocol version 2 only). | |
bf740959 | 477 | .It Fl v |
610cd5c6 | 478 | Verbose mode. |
479 | Causes | |
bf740959 | 480 | .Nm |
610cd5c6 | 481 | to print debugging messages about its progress. |
482 | This is helpful in | |
bf740959 | 483 | debugging connection, authentication, and configuration problems. |
484 | The verbose mode is also used to display | |
485 | .Xr skey 1 | |
486 | challenges, if the user entered "s/key" as password. | |
94ec8c6b | 487 | Multiple -v options increases the verbosity. |
488 | Maximum is 3. | |
bf740959 | 489 | .It Fl x |
610cd5c6 | 490 | Disables X11 forwarding. |
bf740959 | 491 | .It Fl X |
492 | Enables X11 forwarding. | |
71276795 | 493 | This can also be specified on a per-host basis in a configuration file. |
bf740959 | 494 | .It Fl C |
495 | Requests compression of all data (including stdin, stdout, stderr, and | |
610cd5c6 | 496 | data for forwarded X11 and TCP/IP connections). |
497 | The compression algorithm is the same used by | |
7b2ea3a1 | 498 | .Xr gzip 1 , |
499 | and the | |
bf740959 | 500 | .Dq level |
501 | can be controlled by the | |
502 | .Cm CompressionLevel | |
610cd5c6 | 503 | option (see below). |
504 | Compression is desirable on modem lines and other | |
bf740959 | 505 | slow connections, but will only slow down things on fast networks. |
506 | The default value can be set on a host-by-host basis in the | |
507 | configuration files; see the | |
508 | .Cm Compress | |
509 | option below. | |
510 | .It Fl L Ar port:host:hostport | |
511 | Specifies that the given port on the local (client) host is to be | |
610cd5c6 | 512 | forwarded to the given host and port on the remote side. |
513 | This works by allocating a socket to listen to | |
bf740959 | 514 | .Ar port |
515 | on the local side, and whenever a connection is made to this port, the | |
516 | connection is forwarded over the secure channel, and a connection is | |
517 | made to | |
48e671d5 | 518 | .Ar host |
519 | port | |
520 | .Ar hostport | |
610cd5c6 | 521 | from the remote machine. |
522 | Port forwardings can also be specified in the configuration file. | |
523 | Only root can forward privileged ports. | |
48e671d5 | 524 | IPv6 addresses can be specified with an alternative syntax: |
525 | .Ar port/host/hostport | |
bf740959 | 526 | .It Fl R Ar port:host:hostport |
527 | Specifies that the given port on the remote (server) host is to be | |
610cd5c6 | 528 | forwarded to the given host and port on the local side. |
529 | This works by allocating a socket to listen to | |
bf740959 | 530 | .Ar port |
531 | on the remote side, and whenever a connection is made to this port, the | |
532 | connection is forwarded over the secure channel, and a connection is | |
533 | made to | |
48e671d5 | 534 | .Ar host |
535 | port | |
536 | .Ar hostport | |
610cd5c6 | 537 | from the local machine. |
538 | Port forwardings can also be specified in the configuration file. | |
539 | Privileged ports can be forwarded only when | |
bf740959 | 540 | logging in as root on the remote machine. |
6ae2364d | 541 | .It Fl 2 |
542 | Forces | |
543 | .Nm | |
1d1ffb87 | 544 | to try protocol version 2 only. |
48e671d5 | 545 | .It Fl 4 |
546 | Forces | |
547 | .Nm | |
548 | to use IPv4 addresses only. | |
549 | .It Fl 6 | |
550 | Forces | |
551 | .Nm | |
552 | to use IPv6 addresses only. | |
bf740959 | 553 | .El |
554 | .Sh CONFIGURATION FILES | |
555 | .Nm | |
556 | obtains configuration data from the following sources (in this order): | |
557 | command line options, user's configuration file | |
558 | .Pq Pa $HOME/.ssh/config , | |
559 | and system-wide configuration file | |
5f4fdfae | 560 | .Pq Pa /etc/ssh_config . |
bf740959 | 561 | For each parameter, the first obtained value |
610cd5c6 | 562 | will be used. |
563 | The configuration files contain sections bracketed by | |
564 | .Dq Host | |
565 | specifications, and that section is only applied for hosts that | |
566 | match one of the patterns given in the specification. | |
567 | The matched host name is the one given on the command line. | |
bf740959 | 568 | .Pp |
569 | Since the first obtained value for each parameter is used, more | |
570 | host-specific declarations should be given near the beginning of the | |
571 | file, and general defaults at the end. | |
572 | .Pp | |
573 | The configuration file has the following format: | |
574 | .Pp | |
575 | Empty lines and lines starting with | |
576 | .Ql # | |
577 | are comments. | |
578 | .Pp | |
579 | Otherwise a line is of the format | |
580 | .Dq keyword arguments . | |
581 | The possible | |
582 | keywords and their meanings are as follows (note that the | |
583 | configuration files are case-sensitive): | |
584 | .Bl -tag -width Ds | |
585 | .It Cm Host | |
586 | Restricts the following declarations (up to the next | |
587 | .Cm Host | |
588 | keyword) to be only for those hosts that match one of the patterns | |
589 | given after the keyword. | |
590 | .Ql \&* | |
591 | and | |
592 | .Ql ? | |
593 | can be used as wildcards in the | |
610cd5c6 | 594 | patterns. |
595 | A single | |
bf740959 | 596 | .Ql \&* |
597 | as a pattern can be used to provide global | |
610cd5c6 | 598 | defaults for all hosts. |
599 | The host is the | |
bf740959 | 600 | .Ar hostname |
601 | argument given on the command line (i.e., the name is not converted to | |
602 | a canonicalized host name before matching). | |
603 | .It Cm AFSTokenPassing | |
4fe2af09 | 604 | Specifies whether to pass AFS tokens to remote host. |
605 | The argument to this keyword must be | |
bf740959 | 606 | .Dq yes |
607 | or | |
608 | .Dq no . | |
609 | .It Cm BatchMode | |
610 | If set to | |
611 | .Dq yes , | |
610cd5c6 | 612 | passphrase/password querying will be disabled. |
613 | This option is useful in scripts and other batch jobs where you have no | |
614 | user to supply the password. | |
615 | The argument must be | |
bf740959 | 616 | .Dq yes |
617 | or | |
618 | .Dq no . | |
7b2ea3a1 | 619 | .It Cm CheckHostIP |
620 | If this flag is set to | |
621 | .Dq yes , | |
622 | ssh will additionally check the host ip address in the | |
623 | .Pa known_hosts | |
4fe2af09 | 624 | file. |
625 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
7b2ea3a1 | 626 | If the option is set to |
627 | .Dq no , | |
628 | the check will not be executed. | |
bf740959 | 629 | .It Cm Cipher |
610cd5c6 | 630 | Specifies the cipher to use for encrypting the session. |
631 | Currently, | |
bf740959 | 632 | .Dq blowfish , |
633 | and | |
634 | .Dq 3des | |
610cd5c6 | 635 | are supported. |
636 | The default is | |
bf740959 | 637 | .Dq 3des . |
f54651ce | 638 | .It Cm Ciphers |
639 | Specifies the ciphers allowed for protocol version 2 | |
640 | in order of preference. | |
641 | Multiple ciphers must be comma-separated. | |
642 | The default is | |
d0c832f3 | 643 | .Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc . |
bf740959 | 644 | .It Cm Compression |
610cd5c6 | 645 | Specifies whether to use compression. |
646 | The argument must be | |
bf740959 | 647 | .Dq yes |
648 | or | |
649 | .Dq no . | |
650 | .It Cm CompressionLevel | |
610cd5c6 | 651 | Specifies the compression level to use if compression is enable. |
652 | The argument must be an integer from 1 (fast) to 9 (slow, best). | |
653 | The default level is 6, which is good for most applications. | |
654 | The meaning of the values is the same as in | |
7b2ea3a1 | 655 | .Xr gzip 1 . |
bf740959 | 656 | .It Cm ConnectionAttempts |
657 | Specifies the number of tries (one per second) to make before falling | |
610cd5c6 | 658 | back to rsh or exiting. |
659 | The argument must be an integer. | |
660 | This may be useful in scripts if the connection sometimes fails. | |
1d1ffb87 | 661 | .It Cm DSAAuthentication |
662 | Specifies whether to try DSA authentication. | |
663 | The argument to this keyword must be | |
664 | .Dq yes | |
665 | or | |
666 | .Dq no . | |
667 | DSA authentication will only be | |
668 | attempted if a DSA identity file exists. | |
669 | Note that this option applies to protocol version 2 only. | |
bf740959 | 670 | .It Cm EscapeChar |
671 | Sets the escape character (default: | |
672 | .Ql ~ ) . | |
673 | The escape character can also | |
610cd5c6 | 674 | be set on the command line. |
675 | The argument should be a single character, | |
bf740959 | 676 | .Ql ^ |
677 | followed by a letter, or | |
678 | .Dq none | |
679 | to disable the escape | |
680 | character entirely (making the connection transparent for binary | |
681 | data). | |
f54651ce | 682 | .It Cm FallBackToRsh |
bf740959 | 683 | Specifies that if connecting via |
684 | .Nm | |
685 | fails due to a connection refused error (there is no | |
686 | .Xr sshd 8 | |
f54651ce | 687 | listening on the remote host), |
bf740959 | 688 | .Xr rsh 1 |
689 | should automatically be used instead (after a suitable warning about | |
610cd5c6 | 690 | the session being unencrypted). |
691 | The argument must be | |
bf740959 | 692 | .Dq yes |
693 | or | |
694 | .Dq no . | |
695 | .It Cm ForwardAgent | |
696 | Specifies whether the connection to the authentication agent (if any) | |
610cd5c6 | 697 | will be forwarded to the remote machine. |
698 | The argument must be | |
bf740959 | 699 | .Dq yes |
700 | or | |
701 | .Dq no . | |
71276795 | 702 | The default is |
703 | .Dq no . | |
bf740959 | 704 | .It Cm ForwardX11 |
705 | Specifies whether X11 connections will be automatically redirected | |
f54651ce | 706 | over the secure channel and |
bf740959 | 707 | .Ev DISPLAY |
610cd5c6 | 708 | set. |
f54651ce | 709 | The argument must be |
bf740959 | 710 | .Dq yes |
711 | or | |
712 | .Dq no . | |
c8d54615 | 713 | The default is |
714 | .Dq no . | |
bf740959 | 715 | .It Cm GatewayPorts |
716 | Specifies whether remote hosts are allowed to connect to local | |
717 | forwarded ports. | |
718 | The argument must be | |
719 | .Dq yes | |
720 | or | |
721 | .Dq no . | |
722 | The default is | |
723 | .Dq no . | |
724 | .It Cm GlobalKnownHostsFile | |
f54651ce | 725 | Specifies a file to use instead of |
5f4fdfae | 726 | .Pa /etc/ssh_known_hosts . |
bf740959 | 727 | .It Cm HostName |
610cd5c6 | 728 | Specifies the real host name to log into. |
729 | This can be used to specify nicknames or abbreviations for hosts. | |
730 | Default is the name given on the command line. | |
731 | Numeric IP addresses are also permitted (both on the command line and in | |
bf740959 | 732 | .Cm HostName |
733 | specifications). | |
734 | .It Cm IdentityFile | |
735 | Specifies the file from which the user's RSA authentication identity | |
736 | is read (default | |
1d1ffb87 | 737 | .Pa $HOME/.ssh/identity |
bf740959 | 738 | in the user's home directory). |
739 | Additionally, any identities represented by the authentication agent | |
610cd5c6 | 740 | will be used for authentication. |
741 | The file name may use the tilde | |
742 | syntax to refer to a user's home directory. | |
743 | It is possible to have | |
bf740959 | 744 | multiple identity files specified in configuration files; all these |
745 | identities will be tried in sequence. | |
1d1ffb87 | 746 | .It Cm IdentityFile2 |
747 | Specifies the file from which the user's DSA authentication identity | |
748 | is read (default | |
749 | .Pa $HOME/.ssh/id_dsa | |
750 | in the user's home directory). | |
751 | The file name may use the tilde | |
752 | syntax to refer to a user's home directory. | |
753 | It is possible to have | |
754 | multiple identity files specified in configuration files; all these | |
755 | identities will be tried in sequence. | |
bf740959 | 756 | .It Cm KeepAlive |
757 | Specifies whether the system should send keepalive messages to the | |
610cd5c6 | 758 | other side. |
759 | If they are sent, death of the connection or crash of one | |
760 | of the machines will be properly noticed. | |
761 | However, this means that | |
bf740959 | 762 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 763 | find it annoying. |
bf740959 | 764 | .Pp |
765 | The default is | |
766 | .Dq yes | |
767 | (to send keepalives), and the client will notice | |
610cd5c6 | 768 | if the network goes down or the remote host dies. |
769 | This is important in scripts, and many users want it too. | |
bf740959 | 770 | .Pp |
771 | To disable keepalives, the value should be set to | |
772 | .Dq no | |
773 | in both the server and the client configuration files. | |
774 | .It Cm KerberosAuthentication | |
4fe2af09 | 775 | Specifies whether Kerberos authentication will be used. |
776 | The argument to this keyword must be | |
bf740959 | 777 | .Dq yes |
778 | or | |
779 | .Dq no . | |
780 | .It Cm KerberosTgtPassing | |
4fe2af09 | 781 | Specifies whether a Kerberos TGT will be forwarded to the server. |
782 | This will only work if the Kerberos server is actually an AFS kaserver. | |
783 | The argument to this keyword must be | |
bf740959 | 784 | .Dq yes |
785 | or | |
786 | .Dq no . | |
787 | .It Cm LocalForward | |
788 | Specifies that a TCP/IP port on the local machine be forwarded over | |
610cd5c6 | 789 | the secure channel to given host:port from the remote machine. |
790 | The first argument must be a port number, and the second must be | |
791 | host:port. | |
792 | Multiple forwardings may be specified, and additional | |
793 | forwardings can be given on the command line. | |
794 | Only the superuser can forward privileged ports. | |
6a17f9c2 | 795 | .It Cm LogLevel |
796 | Gives the verbosity level that is used when logging messages from | |
797 | .Nm ssh . | |
798 | The possible values are: | |
22fa590f | 799 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
6a17f9c2 | 800 | The default is INFO. |
bf740959 | 801 | .It Cm NumberOfPasswordPrompts |
4fe2af09 | 802 | Specifies the number of password prompts before giving up. |
803 | The argument to this keyword must be an integer. | |
804 | Default is 3. | |
7b2ea3a1 | 805 | .It Cm PasswordAuthentication |
610cd5c6 | 806 | Specifies whether to use password authentication. |
807 | The argument to this keyword must be | |
7b2ea3a1 | 808 | .Dq yes |
809 | or | |
810 | .Dq no . | |
1d1ffb87 | 811 | Note that this option applies to both protocol version 1 and 2. |
bf740959 | 812 | .It Cm Port |
610cd5c6 | 813 | Specifies the port number to connect on the remote host. |
814 | Default is 22. | |
f54651ce | 815 | .It Cm Protocol |
816 | Specifies the protocol versions | |
817 | .Nm | |
818 | should support in order of preference. | |
819 | The possible values are | |
820 | .Dq 1 | |
821 | and | |
822 | .Dq 2 . | |
823 | Multiple versions must be comma-separated. | |
824 | The default is | |
1d1ffb87 | 825 | .Dq 1,2 . |
826 | This means that | |
827 | .Nm | |
828 | tries version 1 and falls back to version 2 | |
d0c832f3 | 829 | if version 1 is not available. |
bf740959 | 830 | .It Cm ProxyCommand |
610cd5c6 | 831 | Specifies the command to use to connect to the server. |
832 | The command | |
833 | string extends to the end of the line, and is executed with | |
834 | .Pa /bin/sh . | |
835 | In the command string, | |
836 | .Ql %h | |
837 | will be substituted by the host name to | |
838 | connect and | |
839 | .Ql %p | |
840 | by the port. | |
841 | The command can be basically anything, | |
842 | and should read from its standard input and write to its standard output. | |
843 | It should eventually connect an | |
bf740959 | 844 | .Xr sshd 8 |
845 | server running on some machine, or execute | |
846 | .Ic sshd -i | |
610cd5c6 | 847 | somewhere. |
848 | Host key management will be done using the | |
bf740959 | 849 | HostName of the host being connected (defaulting to the name typed by |
850 | the user). | |
57112b5a | 851 | Note that |
852 | .Cm CheckHostIP | |
853 | is not available for connects with a proxy command. | |
bf740959 | 854 | .Pp |
855 | .It Cm RemoteForward | |
856 | Specifies that a TCP/IP port on the remote machine be forwarded over | |
610cd5c6 | 857 | the secure channel to given host:port from the local machine. |
858 | The first argument must be a port number, and the second must be | |
859 | host:port. | |
860 | Multiple forwardings may be specified, and additional | |
861 | forwardings can be given on the command line. | |
862 | Only the superuser can forward privileged ports. | |
bf740959 | 863 | .It Cm RhostsAuthentication |
610cd5c6 | 864 | Specifies whether to try rhosts based authentication. |
865 | Note that this | |
bf740959 | 866 | declaration only affects the client side and has no effect whatsoever |
610cd5c6 | 867 | on security. |
868 | Disabling rhosts authentication may reduce | |
bf740959 | 869 | authentication time on slow connections when rhosts authentication is |
610cd5c6 | 870 | not used. |
871 | Most servers do not permit RhostsAuthentication because it | |
872 | is not secure (see RhostsRSAAuthentication). | |
873 | The argument to this keyword must be | |
bf740959 | 874 | .Dq yes |
875 | or | |
876 | .Dq no . | |
877 | .It Cm RhostsRSAAuthentication | |
878 | Specifies whether to try rhosts based authentication with RSA host | |
610cd5c6 | 879 | authentication. |
880 | This is the primary authentication method for most sites. | |
881 | The argument must be | |
bf740959 | 882 | .Dq yes |
883 | or | |
884 | .Dq no . | |
885 | .It Cm RSAAuthentication | |
610cd5c6 | 886 | Specifies whether to try RSA authentication. |
887 | The argument to this keyword must be | |
bf740959 | 888 | .Dq yes |
889 | or | |
890 | .Dq no . | |
891 | RSA authentication will only be | |
892 | attempted if the identity file exists, or an authentication agent is | |
893 | running. | |
1d1ffb87 | 894 | Note that this option applies to protocol version 1 only. |
5260325f | 895 | .It Cm SkeyAuthentication |
896 | Specifies whether to use | |
897 | .Xr skey 1 | |
610cd5c6 | 898 | authentication. |
899 | The argument to this keyword must be | |
5260325f | 900 | .Dq yes |
901 | or | |
902 | .Dq no . | |
903 | The default is | |
904 | .Dq no . | |
bf740959 | 905 | .It Cm StrictHostKeyChecking |
906 | If this flag is set to | |
f54651ce | 907 | .Dq yes , |
bf740959 | 908 | .Nm |
909 | ssh will never automatically add host keys to the | |
910 | .Pa $HOME/.ssh/known_hosts | |
1d1ffb87 | 911 | and |
912 | .Pa $HOME/.ssh/known_hosts2 | |
913 | files, and refuses to connect hosts whose host key has changed. | |
610cd5c6 | 914 | This provides maximum protection against trojan horse attacks. |
915 | However, it can be somewhat annoying if you don't have good | |
5f4fdfae | 916 | .Pa /etc/ssh_known_hosts |
1d1ffb87 | 917 | and |
918 | .Pa /etc/ssh_known_hosts2 | |
bf740959 | 919 | files installed and frequently |
610cd5c6 | 920 | connect new hosts. |
921 | Basically this option forces the user to manually | |
922 | add any new hosts. | |
923 | Normally this option is disabled, and new hosts | |
924 | will automatically be added to the known host files. | |
925 | The host keys of | |
926 | known hosts will be verified automatically in either case. | |
927 | The argument must be | |
bf740959 | 928 | .Dq yes |
929 | or | |
930 | .Dq no . | |
bf740959 | 931 | .It Cm UsePrivilegedPort |
932 | Specifies whether to use a privileged port for outgoing connections. | |
933 | The argument must be | |
934 | .Dq yes | |
935 | or | |
936 | .Dq no . | |
937 | The default is | |
938 | .Dq yes . | |
939 | Note that setting this option to | |
940 | .Dq no | |
95f1eccc | 941 | turns off |
bf740959 | 942 | .Cm RhostsAuthentication |
943 | and | |
944 | .Cm RhostsRSAAuthentication . | |
7b2ea3a1 | 945 | .It Cm User |
610cd5c6 | 946 | Specifies the user to log in as. |
947 | This can be useful if you have a different user name on different machines. | |
948 | This saves the trouble of | |
7b2ea3a1 | 949 | having to remember to give the user name on the command line. |
950 | .It Cm UserKnownHostsFile | |
951 | Specifies a file to use instead of | |
952 | .Pa $HOME/.ssh/known_hosts . | |
bf740959 | 953 | .It Cm UseRsh |
610cd5c6 | 954 | Specifies that rlogin/rsh should be used for this host. |
955 | It is possible that the host does not at all support the | |
bf740959 | 956 | .Nm |
610cd5c6 | 957 | protocol. |
958 | This causes | |
bf740959 | 959 | .Nm |
610cd5c6 | 960 | to immediately execute |
bf740959 | 961 | .Xr rsh 1 . |
962 | All other options (except | |
963 | .Cm HostName ) | |
610cd5c6 | 964 | are ignored if this has been specified. |
965 | The argument must be | |
bf740959 | 966 | .Dq yes |
967 | or | |
968 | .Dq no . | |
fa649821 | 969 | .It Cm XAuthLocation |
970 | Specifies the location of the | |
971 | .Xr xauth 1 | |
972 | program. | |
973 | The default is | |
974 | .Pa /usr/X11R6/bin/xauth . | |
b5e300c2 | 975 | .El |
bf740959 | 976 | .Sh ENVIRONMENT |
977 | .Nm | |
978 | will normally set the following environment variables: | |
979 | .Bl -tag -width Ds | |
980 | .It Ev DISPLAY | |
981 | The | |
982 | .Ev DISPLAY | |
610cd5c6 | 983 | variable indicates the location of the X11 server. |
f54651ce | 984 | It is automatically set by |
bf740959 | 985 | .Nm |
986 | to point to a value of the form | |
987 | .Dq hostname:n | |
988 | where hostname indicates | |
610cd5c6 | 989 | the host where the shell runs, and n is an integer >= 1. |
990 | .Nm | |
991 | uses this special value to forward X11 connections over the secure | |
992 | channel. | |
993 | The user should normally not set DISPLAY explicitly, as that | |
bf740959 | 994 | will render the X11 connection insecure (and will require the user to |
995 | manually copy any required authorization cookies). | |
996 | .It Ev HOME | |
997 | Set to the path of the user's home directory. | |
998 | .It Ev LOGNAME | |
999 | Synonym for | |
1000 | .Ev USER ; | |
1001 | set for compatibility with systems that use this variable. | |
1002 | .It Ev MAIL | |
1003 | Set to point the user's mailbox. | |
610cd5c6 | 1004 | .It Ev PATH |
bf740959 | 1005 | Set to the default |
1006 | .Ev PATH , | |
1007 | as specified when compiling | |
1008 | .Nm ssh . | |
1009 | .It Ev SSH_AUTH_SOCK | |
1010 | indicates the path of a unix-domain socket used to communicate with the | |
1011 | agent. | |
1012 | .It Ev SSH_CLIENT | |
610cd5c6 | 1013 | Identifies the client end of the connection. |
1014 | The variable contains | |
bf740959 | 1015 | three space-separated values: client ip-address, client port number, |
1016 | and server port number. | |
1017 | .It Ev SSH_TTY | |
1018 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 1019 | with the current shell or command. |
1020 | If the current session has no tty, | |
bf740959 | 1021 | this variable is not set. |
1022 | .It Ev TZ | |
1023 | The timezone variable is set to indicate the present timezone if it | |
c345cf9d | 1024 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 1025 | on to new connections). |
1026 | .It Ev USER | |
1027 | Set to the name of the user logging in. | |
1028 | .El | |
1029 | .Pp | |
f54651ce | 1030 | Additionally, |
bf740959 | 1031 | .Nm |
f54651ce | 1032 | reads |
1033 | .Pa $HOME/.ssh/environment , | |
bf740959 | 1034 | and adds lines of the format |
1035 | .Dq VARNAME=value | |
1036 | to the environment. | |
1037 | .Sh FILES | |
c8d54615 | 1038 | .Bl -tag -width Ds |
bf740959 | 1039 | .It Pa $HOME/.ssh/known_hosts |
1040 | Records host keys for all hosts the user has logged into (that are not | |
1041 | in | |
5f4fdfae | 1042 | .Pa /etc/ssh_known_hosts ) . |
bf740959 | 1043 | See |
1044 | .Xr sshd 8 . | |
1d1ffb87 | 1045 | .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa |
1046 | Contains the RSA and the DSA authentication identity of the user. | |
1047 | These files | |
1048 | contain sensitive data and should be readable by the user but not | |
bf740959 | 1049 | accessible by others (read/write/execute). |
1050 | Note that | |
1051 | .Nm | |
1d1ffb87 | 1052 | ignores a private key file if it is accessible by others. |
bf740959 | 1053 | It is possible to specify a passphrase when |
1054 | generating the key; the passphrase will be used to encrypt the | |
1055 | sensitive part of this file using 3DES. | |
1d1ffb87 | 1056 | .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub |
bf740959 | 1057 | Contains the public key for authentication (public part of the |
610cd5c6 | 1058 | identity file in human-readable form). |
1d1ffb87 | 1059 | The contents of the |
1060 | .Pa $HOME/.ssh/identity.pub | |
1061 | file should be added to | |
bf740959 | 1062 | .Pa $HOME/.ssh/authorized_keys |
1063 | on all machines | |
610cd5c6 | 1064 | where you wish to log in using RSA authentication. |
1d1ffb87 | 1065 | The contents of the |
1066 | .Pa $HOME/.ssh/id_dsa.pub | |
1067 | file should be added to | |
1068 | .Pa $HOME/.ssh/authorized_keys2 | |
1069 | on all machines | |
1070 | where you wish to log in using DSA authentication. | |
1071 | These files are not | |
610cd5c6 | 1072 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 1073 | These files are |
1074 | never used automatically and are not necessary; they is only provided for | |
bf740959 | 1075 | the convenience of the user. |
1076 | .It Pa $HOME/.ssh/config | |
610cd5c6 | 1077 | This is the per-user configuration file. |
1078 | The format of this file is described above. | |
1079 | This file is used by the | |
bf740959 | 1080 | .Nm |
610cd5c6 | 1081 | client. |
1082 | This file does not usually contain any sensitive information, | |
bf740959 | 1083 | but the recommended permissions are read/write for the user, and not |
1084 | accessible by others. | |
1085 | .It Pa $HOME/.ssh/authorized_keys | |
610cd5c6 | 1086 | Lists the RSA keys that can be used for logging in as this user. |
1087 | The format of this file is described in the | |
bf740959 | 1088 | .Xr sshd 8 |
610cd5c6 | 1089 | manual page. |
1090 | In the simplest form the format is the same as the .pub | |
bf740959 | 1091 | identity files (that is, each line contains the number of bits in |
1092 | modulus, public exponent, modulus, and comment fields, separated by | |
610cd5c6 | 1093 | spaces). |
1094 | This file is not highly sensitive, but the recommended | |
bf740959 | 1095 | permissions are read/write for the user, and not accessible by others. |
1d1ffb87 | 1096 | .It Pa $HOME/.ssh/authorized_keys2 |
1097 | Lists the DSA keys that can be used for logging in as this user. | |
1098 | This file is not highly sensitive, but the recommended | |
1099 | permissions are read/write for the user, and not accessible by others. | |
1100 | .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2 | |
610cd5c6 | 1101 | Systemwide list of known host keys. |
1d1ffb87 | 1102 | .Pa /etc/ssh_known_hosts |
1103 | contains RSA and | |
1104 | .Pa /etc/ssh_known_hosts2 | |
1105 | contains DSA keys. | |
1106 | These files should be prepared by the | |
bf740959 | 1107 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1108 | organization. |
1109 | This file should be world-readable. | |
1110 | This file contains | |
bf740959 | 1111 | public keys, one per line, in the following format (fields separated |
1112 | by spaces): system name, number of bits in modulus, public exponent, | |
610cd5c6 | 1113 | modulus, and optional comment field. |
1114 | When different names are used | |
bf740959 | 1115 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1116 | commas. |
1117 | The format is described on the | |
bf740959 | 1118 | .Xr sshd 8 |
1119 | manual page. | |
1120 | .Pp | |
1121 | The canonical system name (as returned by name servers) is used by | |
1122 | .Xr sshd 8 | |
1123 | to verify the client host when logging in; other names are needed because | |
1124 | .Nm | |
1125 | does not convert the user-supplied name to a canonical name before | |
1126 | checking the key, because someone with access to the name servers | |
1127 | would then be able to fool host authentication. | |
5f4fdfae | 1128 | .It Pa /etc/ssh_config |
610cd5c6 | 1129 | Systemwide configuration file. |
1130 | This file provides defaults for those | |
bf740959 | 1131 | values that are not specified in the user's configuration file, and |
610cd5c6 | 1132 | for those users who do not have a configuration file. |
1133 | This file must be world-readable. | |
bf740959 | 1134 | .It Pa $HOME/.rhosts |
1135 | This file is used in | |
1136 | .Pa \&.rhosts | |
1137 | authentication to list the | |
610cd5c6 | 1138 | host/user pairs that are permitted to log in. |
1139 | (Note that this file is | |
bf740959 | 1140 | also used by rlogin and rsh, which makes using this file insecure.) |
1141 | Each line of the file contains a host name (in the canonical form | |
1142 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1143 | separated by a space. |
1144 | One some machines this file may need to be | |
bf740959 | 1145 | world-readable if the user's home directory is on a NFS partition, |
1146 | because | |
1147 | .Xr sshd 8 | |
610cd5c6 | 1148 | reads it as root. |
1149 | Additionally, this file must be owned by the user, | |
1150 | and must not have write permissions for anyone else. | |
1151 | The recommended | |
bf740959 | 1152 | permission for most machines is read/write for the user, and not |
1153 | accessible by others. | |
1154 | .Pp | |
1155 | Note that by default | |
1156 | .Xr sshd 8 | |
1157 | will be installed so that it requires successful RSA host | |
610cd5c6 | 1158 | authentication before permitting \s+2.\s0rhosts authentication. |
1159 | If your server machine does not have the client's host key in | |
5f4fdfae | 1160 | .Pa /etc/ssh_known_hosts , |
bf740959 | 1161 | you can store it in |
1162 | .Pa $HOME/.ssh/known_hosts . | |
1163 | The easiest way to do this is to | |
1164 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1165 | will automatically add the host key to |
bf740959 | 1166 | .Pa $HOME/.ssh/known_hosts . |
1167 | .It Pa $HOME/.shosts | |
1168 | This file is used exactly the same way as | |
1169 | .Pa \&.rhosts . | |
1170 | The purpose for | |
1171 | having this file is to be able to use rhosts authentication with | |
1172 | .Nm | |
1173 | without permitting login with | |
1174 | .Xr rlogin 1 | |
1175 | or | |
1176 | .Xr rsh 1 . | |
1177 | .It Pa /etc/hosts.equiv | |
1178 | This file is used during | |
610cd5c6 | 1179 | .Pa \&.rhosts authentication. |
1180 | It contains | |
bf740959 | 1181 | canonical hosts names, one per line (the full format is described on |
1182 | the | |
1183 | .Xr sshd 8 | |
610cd5c6 | 1184 | manual page). |
1185 | If the client host is found in this file, login is | |
bf740959 | 1186 | automatically permitted provided client and server user names are the |
610cd5c6 | 1187 | same. |
1188 | Additionally, successful RSA host authentication is normally | |
1189 | required. | |
1190 | This file should only be writable by root. | |
5f4fdfae | 1191 | .It Pa /etc/shosts.equiv |
f54651ce | 1192 | This file is processed exactly as |
bf740959 | 1193 | .Pa /etc/hosts.equiv . |
1194 | This file may be useful to permit logins using | |
1195 | .Nm | |
1196 | but not using rsh/rlogin. | |
5f4fdfae | 1197 | .It Pa /etc/sshrc |
bf740959 | 1198 | Commands in this file are executed by |
1199 | .Nm | |
1200 | when the user logs in just before the user's shell (or command) is started. | |
1201 | See the | |
1202 | .Xr sshd 8 | |
1203 | manual page for more information. | |
1204 | .It Pa $HOME/.ssh/rc | |
1205 | Commands in this file are executed by | |
1206 | .Nm | |
1207 | when the user logs in just before the user's shell (or command) is | |
1208 | started. | |
f54651ce | 1209 | See the |
bf740959 | 1210 | .Xr sshd 8 |
1211 | manual page for more information. | |
83b7f649 | 1212 | .It Pa $HOME/.ssh/environment |
1213 | Contains additional definitions for environment variables, see section | |
1214 | .Sx ENVIRONMENT | |
1215 | above. | |
bf740959 | 1216 | .It Pa libcrypto.so.X.1 |
1217 | A version of this library which includes support for the RSA algorithm | |
1218 | is required for proper operation. | |
b5e300c2 | 1219 | .El |
bf740959 | 1220 | .Sh AUTHOR |
bf740959 | 1221 | OpenSSH |
c8d54615 | 1222 | is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen, |
610cd5c6 | 1223 | but with bugs removed and newer features re-added. |
1224 | Rapidly after the | |
c8d54615 | 1225 | 1.2.12 release, newer versions of the original ssh bore successively |
1226 | more restrictive licenses, and thus demand for a free version was born. | |
1d1ffb87 | 1227 | .Pp |
c8d54615 | 1228 | This version of OpenSSH |
bf740959 | 1229 | .Bl -bullet |
1230 | .It | |
bcbf86ec | 1231 | has all components of a restrictive nature (i.e., patents, see |
1232 | .Xr crypto 3 ) | |
bf740959 | 1233 | directly removed from the source code; any licensed or patented components |
1234 | are chosen from | |
1235 | external libraries. | |
1236 | .It | |
1d1ffb87 | 1237 | has been updated to support SSH protocol 1.5 and 2, making it compatible with |
1238 | all other SSH clients and servers. | |
bf740959 | 1239 | .It |
f54651ce | 1240 | contains added support for |
bf740959 | 1241 | .Xr kerberos 8 |
1242 | authentication and ticket passing. | |
1243 | .It | |
1244 | supports one-time password authentication with | |
1245 | .Xr skey 1 . | |
1246 | .El | |
1247 | .Pp | |
0c16a097 | 1248 | OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl, |
f095fcc7 | 1249 | Niels Provos, Theo de Raadt, and Dug Song. |
1d1ffb87 | 1250 | .Pp |
1251 | The support for SSH protocol 2 was written by Markus Friedl. | |
bf740959 | 1252 | .Sh SEE ALSO |
1253 | .Xr rlogin 1 , | |
1254 | .Xr rsh 1 , | |
1255 | .Xr scp 1 , | |
1256 | .Xr ssh-add 1 , | |
1257 | .Xr ssh-agent 1 , | |
1258 | .Xr ssh-keygen 1 , | |
1259 | .Xr telnet 1 , | |
1260 | .Xr sshd 8 , | |
bcbf86ec | 1261 | .Xr crypto 3 |