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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 | .\" |
a22aff1f | 37 | .\" $OpenBSD: ssh.1,v 1.64 2000/10/16 21:46:31 markus Exp $ |
bf740959 | 38 | .Dd September 25, 1999 |
39 | .Dt SSH 1 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm ssh | |
43 | .Nd OpenSSH secure shell client (remote login program) | |
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 | |
71276795 | 51 | .Op Fl afgknqtvxACNPTX246 |
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 | |
56 | .Op Fl o Ar option | |
57 | .Op Fl p Ar port | |
58 | .Oo Fl L Xo | |
59 | .Sm off | |
bf740959 | 60 | .Ar port : |
7b2ea3a1 | 61 | .Ar host : |
bf740959 | 62 | .Ar hostport |
63 | .Sm on | |
64 | .Xc | |
65 | .Oc | |
66 | .Oo Fl R Xo | |
67 | .Sm off | |
bf740959 | 68 | .Ar port : |
7b2ea3a1 | 69 | .Ar host : |
bf740959 | 70 | .Ar hostport |
71 | .Sm on | |
72 | .Xc | |
73 | .Oc | |
74 | .Op Ar hostname | user@hostname | |
75 | .Op Ar command | |
f54651ce | 76 | .Sh DESCRIPTION |
bf740959 | 77 | .Nm |
78 | (Secure Shell) is a program for logging into a remote machine and for | |
610cd5c6 | 79 | executing commands on a remote machine. |
80 | It is intended to replace | |
bf740959 | 81 | rlogin and rsh, and provide secure encrypted communications between |
610cd5c6 | 82 | two untrusted hosts over an insecure network. |
83 | X11 connections and | |
bf740959 | 84 | arbitrary TCP/IP ports can also be forwarded over the secure channel. |
85 | .Pp | |
86 | .Nm | |
f54651ce | 87 | connects and logs into the specified |
bf740959 | 88 | .Ar hostname . |
89 | The user must prove | |
1d1ffb87 | 90 | his/her identity to the remote machine using one of several methods |
91 | depending on the protocol version used: | |
92 | .Pp | |
93 | .Ss SSH protocol version 1 | |
bf740959 | 94 | .Pp |
95 | First, if the machine the user logs in from is listed in | |
96 | .Pa /etc/hosts.equiv | |
97 | or | |
5f4fdfae | 98 | .Pa /etc/shosts.equiv |
bf740959 | 99 | on the remote machine, and the user names are |
100 | the same on both sides, the user is immediately permitted to log in. | |
f54651ce | 101 | Second, if |
bf740959 | 102 | .Pa \&.rhosts |
103 | or | |
104 | .Pa \&.shosts | |
105 | exists in the user's home directory on the | |
106 | remote machine and contains a line containing the name of the client | |
107 | machine and the name of the user on that machine, the user is | |
610cd5c6 | 108 | permitted to log in. |
109 | This form of authentication alone is normally not | |
bf740959 | 110 | allowed by the server because it is not secure. |
111 | .Pp | |
112 | The second (and primary) authentication method is the | |
113 | .Pa rhosts | |
114 | or | |
115 | .Pa hosts.equiv | |
610cd5c6 | 116 | method combined with RSA-based host authentication. |
117 | It means that if the login would be permitted by | |
1d1ffb87 | 118 | .Pa $HOME/.rhosts , |
119 | .Pa $HOME/.shosts , | |
bf740959 | 120 | .Pa /etc/hosts.equiv , |
121 | or | |
5f4fdfae | 122 | .Pa /etc/shosts.equiv , |
bf740959 | 123 | and if additionally the server can verify the client's |
f54651ce | 124 | host key (see |
5f4fdfae | 125 | .Pa /etc/ssh_known_hosts |
5bbb5681 | 126 | and |
127 | .Pa $HOME/.ssh/known_hosts | |
bf740959 | 128 | in the |
129 | .Sx FILES | |
610cd5c6 | 130 | section), only then login is permitted. |
131 | This authentication method closes security holes due to IP | |
132 | spoofing, DNS spoofing and routing spoofing. | |
133 | [Note to the administrator: | |
bf740959 | 134 | .Pa /etc/hosts.equiv , |
1d1ffb87 | 135 | .Pa $HOME/.rhosts , |
bf740959 | 136 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
137 | disabled if security is desired.] | |
138 | .Pp | |
f54651ce | 139 | As a third authentication method, |
bf740959 | 140 | .Nm |
141 | supports RSA based authentication. | |
142 | The scheme is based on public-key cryptography: there are cryptosystems | |
143 | where encryption and decryption are done using separate keys, and it | |
144 | is not possible to derive the decryption key from the encryption key. | |
610cd5c6 | 145 | RSA is one such system. |
f54651ce | 146 | The idea is that each user creates a public/private |
610cd5c6 | 147 | key pair for authentication purposes. |
148 | The server knows the public key, and only the user knows the private key. | |
f54651ce | 149 | The file |
bf740959 | 150 | .Pa $HOME/.ssh/authorized_keys |
151 | lists the public keys that are permitted for logging | |
610cd5c6 | 152 | in. |
153 | When the user logs in, the | |
bf740959 | 154 | .Nm |
155 | program tells the server which key pair it would like to use for | |
610cd5c6 | 156 | authentication. |
157 | The server checks if this key is permitted, and if | |
bf740959 | 158 | so, sends the user (actually the |
159 | .Nm | |
160 | program running on behalf of the user) a challenge, a random number, | |
610cd5c6 | 161 | encrypted by the user's public key. |
162 | The challenge can only be | |
163 | decrypted using the proper private key. | |
164 | The user's client then decrypts the | |
bf740959 | 165 | challenge using the private key, proving that he/she knows the private |
166 | key but without disclosing it to the server. | |
167 | .Pp | |
168 | .Nm | |
610cd5c6 | 169 | implements the RSA authentication protocol automatically. |
170 | The user creates his/her RSA key pair by running | |
bf740959 | 171 | .Xr ssh-keygen 1 . |
f54651ce | 172 | This stores the private key in |
1d1ffb87 | 173 | .Pa $HOME/.ssh/identity |
bf740959 | 174 | and the public key in |
1d1ffb87 | 175 | .Pa $HOME/.ssh/identity.pub |
610cd5c6 | 176 | in the user's home directory. |
177 | The user should then copy the | |
bf740959 | 178 | .Pa identity.pub |
f54651ce | 179 | to |
1d1ffb87 | 180 | .Pa $HOME/.ssh/authorized_keys |
f54651ce | 181 | in his/her home directory on the remote machine (the |
bf740959 | 182 | .Pa authorized_keys |
f54651ce | 183 | file corresponds to the conventional |
1d1ffb87 | 184 | .Pa $HOME/.rhosts |
bf740959 | 185 | file, and has one key |
610cd5c6 | 186 | per line, though the lines can be very long). |
187 | After this, the user can log in without giving the password. | |
188 | RSA authentication is much | |
bf740959 | 189 | more secure than rhosts authentication. |
190 | .Pp | |
191 | The most convenient way to use RSA authentication may be with an | |
610cd5c6 | 192 | authentication agent. |
193 | See | |
bf740959 | 194 | .Xr ssh-agent 1 |
195 | for more information. | |
196 | .Pp | |
f54651ce | 197 | If other authentication methods fail, |
bf740959 | 198 | .Nm |
610cd5c6 | 199 | prompts the user for a password. |
200 | The password is sent to the remote | |
bf740959 | 201 | host for checking; however, since all communications are encrypted, |
202 | the password cannot be seen by someone listening on the network. | |
203 | .Pp | |
1d1ffb87 | 204 | .Ss SSH protocol version 2 |
205 | .Pp | |
206 | When a user connects using the protocol version 2 | |
207 | different authentication methods are available: | |
208 | At first, the client attempts to authenticate using the public key method. | |
209 | If this method fails password authentication is tried. | |
210 | .Pp | |
211 | The public key method is similar to RSA authentication described | |
212 | in the previous section except that the DSA algorithm is used | |
213 | instead of the patented RSA algorithm. | |
214 | The client uses his private DSA key | |
215 | .Pa $HOME/.ssh/id_dsa | |
216 | to sign the session identifier and sends the result to the server. | |
217 | The server checks whether the matching public key is listed in | |
218 | .Pa $HOME/.ssh/authorized_keys2 | |
219 | and grants access if both the key is found and the signature is correct. | |
220 | The session identifier is derived from a shared Diffie-Hellman value | |
221 | and is only known to the client and the server. | |
222 | .Pp | |
223 | If public key authentication fails or is not available a password | |
224 | can be sent encrypted to the remote host for proving the user's identity. | |
225 | This protocol 2 implementation does not yet support Kerberos or | |
226 | S/Key authentication. | |
227 | .Pp | |
228 | Protocol 2 provides additional mechanisms for confidentiality | |
d0c832f3 | 229 | (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour) |
1d1ffb87 | 230 | and integrity (hmac-sha1, hmac-md5). |
231 | Note that protocol 1 lacks a strong mechanism for ensuring the | |
232 | integrity of the connection. | |
233 | .Pp | |
234 | .Ss Login session and remote execution | |
235 | .Pp | |
bf740959 | 236 | When the user's identity has been accepted by the server, the server |
237 | either executes the given command, or logs into the machine and gives | |
610cd5c6 | 238 | the user a normal shell on the remote machine. |
239 | All communication with | |
bf740959 | 240 | the remote command or shell will be automatically encrypted. |
241 | .Pp | |
242 | If a pseudo-terminal has been allocated (normal login session), the | |
243 | user can disconnect with | |
244 | .Ic ~. , | |
245 | and suspend | |
246 | .Nm | |
247 | with | |
248 | .Ic ~^Z . | |
249 | All forwarded connections can be listed with | |
f54651ce | 250 | .Ic ~# |
bf740959 | 251 | and if |
252 | the session blocks waiting for forwarded X11 or TCP/IP | |
253 | connections to terminate, it can be backgrounded with | |
254 | .Ic ~& | |
255 | (this should not be used while the user shell is active, as it can cause the | |
610cd5c6 | 256 | shell to hang). |
257 | All available escapes can be listed with | |
bf740959 | 258 | .Ic ~? . |
259 | .Pp | |
260 | A single tilde character can be sent as | |
261 | .Ic ~~ | |
262 | (or by following the tilde by a character other than those described above). | |
263 | The escape character must always follow a newline to be interpreted as | |
610cd5c6 | 264 | special. |
265 | The escape character can be changed in configuration files | |
266 | or on the command line. | |
bf740959 | 267 | .Pp |
268 | If no pseudo tty has been allocated, the | |
269 | session is transparent and can be used to reliably transfer binary | |
610cd5c6 | 270 | data. |
271 | On most systems, setting the escape character to | |
bf740959 | 272 | .Dq none |
273 | will also make the session transparent even if a tty is used. | |
274 | .Pp | |
275 | The session terminates when the command or shell in on the remote | |
276 | machine exists and all X11 and TCP/IP connections have been closed. | |
277 | The exit status of the remote program is returned as the exit status | |
278 | of | |
279 | .Nm ssh . | |
280 | .Pp | |
1d1ffb87 | 281 | .Ss X11 and TCP forwarding |
282 | .Pp | |
bf740959 | 283 | If the user is using X11 (the |
284 | .Ev DISPLAY | |
285 | environment variable is set), the connection to the X11 display is | |
286 | automatically forwarded to the remote side in such a way that any X11 | |
287 | programs started from the shell (or command) will go through the | |
288 | encrypted channel, and the connection to the real X server will be made | |
610cd5c6 | 289 | from the local machine. |
290 | The user should not manually set | |
bf740959 | 291 | .Ev DISPLAY . |
292 | Forwarding of X11 connections can be | |
293 | configured on the command line or in configuration files. | |
294 | .Pp | |
295 | The | |
f54651ce | 296 | .Ev DISPLAY |
bf740959 | 297 | value set by |
298 | .Nm | |
299 | will point to the server machine, but with a display number greater | |
610cd5c6 | 300 | than zero. |
301 | This is normal, and happens because | |
bf740959 | 302 | .Nm |
303 | creates a | |
304 | .Dq proxy | |
305 | X server on the server machine for forwarding the | |
306 | connections over the encrypted channel. | |
307 | .Pp | |
308 | .Nm | |
309 | will also automatically set up Xauthority data on the server machine. | |
310 | For this purpose, it will generate a random authorization cookie, | |
311 | store it in Xauthority on the server, and verify that any forwarded | |
312 | connections carry this cookie and replace it by the real cookie when | |
610cd5c6 | 313 | the connection is opened. |
314 | The real authentication cookie is never | |
bf740959 | 315 | sent to the server machine (and no cookies are sent in the plain). |
316 | .Pp | |
317 | If the user is using an authentication agent, the connection to the agent | |
318 | is automatically forwarded to the remote side unless disabled on | |
319 | command line or in a configuration file. | |
320 | .Pp | |
321 | Forwarding of arbitrary TCP/IP connections over the secure channel can | |
610cd5c6 | 322 | be specified either on command line or in a configuration file. |
323 | One possible application of TCP/IP forwarding is a secure connection to an | |
bf740959 | 324 | electronic purse; another is going trough firewalls. |
325 | .Pp | |
1d1ffb87 | 326 | .Ss Server authentication |
327 | .Pp | |
bf740959 | 328 | .Nm |
1d1ffb87 | 329 | automatically maintains and checks a database containing |
610cd5c6 | 330 | identifications for all hosts it has ever been used with. |
1d1ffb87 | 331 | RSA host keys are stored in |
332 | .Pa $HOME/.ssh/known_hosts | |
333 | and | |
334 | DSA host keys are stored in | |
335 | .Pa $HOME/.ssh/known_hosts2 | |
610cd5c6 | 336 | in the user's home directory. |
1d1ffb87 | 337 | Additionally, the files |
5f4fdfae | 338 | .Pa /etc/ssh_known_hosts |
1d1ffb87 | 339 | and |
340 | .Pa /etc/ssh_known_hosts2 | |
341 | are automatically checked for known hosts. | |
610cd5c6 | 342 | Any new hosts are automatically added to the user's file. |
343 | If a host's identification | |
bf740959 | 344 | ever changes, |
345 | .Nm | |
346 | warns about this and disables password authentication to prevent a | |
610cd5c6 | 347 | trojan horse from getting the user's password. |
348 | Another purpose of | |
bf740959 | 349 | this mechanism is to prevent man-in-the-middle attacks which could |
610cd5c6 | 350 | otherwise be used to circumvent the encryption. |
351 | The | |
bf740959 | 352 | .Cm StrictHostKeyChecking |
353 | option (see below) can be used to prevent logins to machines whose | |
354 | host key is not known or has changed. | |
355 | .Sh OPTIONS | |
356 | .Bl -tag -width Ds | |
357 | .It Fl a | |
4fe2af09 | 358 | Disables forwarding of the authentication agent connection. |
71276795 | 359 | .It Fl A |
360 | Enables forwarding of the authentication agent connection. | |
361 | This can also be specified on a per-host basis in a configuration file. | |
bf740959 | 362 | .It Fl c Ar blowfish|3des |
f54651ce | 363 | Selects the cipher to use for encrypting the session. |
bf740959 | 364 | .Ar 3des |
610cd5c6 | 365 | is used by default. |
f54651ce | 366 | It is believed to be secure. |
bf740959 | 367 | .Ar 3des |
368 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
369 | It is presumably more secure than the | |
370 | .Ar des | |
a22aff1f | 371 | cipher which is no longer fully supported in |
d0c832f3 | 372 | .Nm ssh . |
bf740959 | 373 | .Ar blowfish |
374 | is a fast block cipher, it appears very secure and is much faster than | |
610cd5c6 | 375 | .Ar 3des . |
d0c832f3 | 376 | .It Fl c Ar "3des-cbc,blowfish-cbc,arcfour,cast128-cbc" |
377 | Additionally, for protocol version 2 a comma-separated list of ciphers can | |
94ec8c6b | 378 | be specified in order of preference. |
379 | Protocol version 2 supports 3DES, Blowfish, and CAST128 in CBC mode | |
380 | and Arcfour. | |
bf740959 | 381 | .It Fl e Ar ch|^ch|none |
382 | Sets the escape character for sessions with a pty (default: | |
383 | .Ql ~ ) . | |
610cd5c6 | 384 | The escape character is only recognized at the beginning of a line. |
385 | The escape character followed by a dot | |
bf740959 | 386 | .Pq Ql \&. |
387 | closes the connection, followed | |
388 | by control-Z suspends the connection, and followed by itself sends the | |
610cd5c6 | 389 | escape character once. |
390 | Setting the character to | |
bf740959 | 391 | .Dq none |
392 | disables any escapes and makes the session fully transparent. | |
393 | .It Fl f | |
394 | Requests | |
395 | .Nm | |
610cd5c6 | 396 | to go to background just before command execution. |
397 | This is useful if | |
bf740959 | 398 | .Nm |
399 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 400 | wants it in the background. |
f54651ce | 401 | This implies |
bf740959 | 402 | .Fl n . |
403 | The recommended way to start X11 programs at a remote site is with | |
404 | something like | |
405 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 406 | .It Fl g |
407 | Allows remote hosts to connect to local forwarded ports. | |
bf740959 | 408 | .It Fl i Ar identity_file |
f54651ce | 409 | Selects the file from which the identity (private key) for |
610cd5c6 | 410 | RSA authentication is read. |
f54651ce | 411 | Default is |
1d1ffb87 | 412 | .Pa $HOME/.ssh/identity |
610cd5c6 | 413 | in the user's home directory. |
414 | Identity files may also be specified on | |
415 | a per-host basis in the configuration file. | |
416 | It is possible to have multiple | |
bf740959 | 417 | .Fl i |
418 | options (and multiple identities specified in | |
419 | configuration files). | |
bf740959 | 420 | .It Fl k |
4fe2af09 | 421 | Disables forwarding of Kerberos tickets and AFS tokens. |
422 | This may also be specified on a per-host basis in the configuration file. | |
bf740959 | 423 | .It Fl l Ar login_name |
610cd5c6 | 424 | Specifies the user to log in as on the remote machine. |
425 | This also may be specified on a per-host basis in the configuration file. | |
bf740959 | 426 | .It Fl n |
427 | Redirects stdin from | |
428 | .Pa /dev/null | |
429 | (actually, prevents reading from stdin). | |
430 | This must be used when | |
431 | .Nm | |
610cd5c6 | 432 | is run in the background. |
433 | A common trick is to use this to run X11 programs on a remote machine. | |
434 | For example, | |
bf740959 | 435 | .Ic ssh -n shadows.cs.hut.fi emacs & |
436 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
437 | connection will be automatically forwarded over an encrypted channel. | |
438 | The | |
439 | .Nm | |
440 | program will be put in the background. | |
441 | (This does not work if | |
442 | .Nm | |
443 | needs to ask for a password or passphrase; see also the | |
444 | .Fl f | |
445 | option.) | |
0e73cc53 | 446 | .It Fl N |
447 | Do not execute a remote command. | |
448 | This is usefull if you just want to forward ports | |
449 | (protocol version 2 only). | |
bf740959 | 450 | .It Fl o Ar option |
451 | Can be used to give options in the format used in the config file. | |
452 | This is useful for specifying options for which there is no separate | |
610cd5c6 | 453 | command-line flag. |
454 | The option has the same format as a line in the configuration file. | |
bf740959 | 455 | .It Fl p Ar port |
610cd5c6 | 456 | Port to connect to on the remote host. |
457 | This can be specified on a | |
bf740959 | 458 | per-host basis in the configuration file. |
459 | .It Fl P | |
460 | Use a non-privileged port for outgoing connections. | |
461 | This can be used if your firewall does | |
462 | not permit connections from privileged ports. | |
95f1eccc | 463 | Note that this option turns off |
bf740959 | 464 | .Cm RhostsAuthentication |
465 | and | |
466 | .Cm RhostsRSAAuthentication . | |
467 | .It Fl q | |
610cd5c6 | 468 | Quiet mode. |
469 | Causes all warning and diagnostic messages to be suppressed. | |
470 | Only fatal errors are displayed. | |
bf740959 | 471 | .It Fl t |
610cd5c6 | 472 | Force pseudo-tty allocation. |
4fe2af09 | 473 | This can be used to execute arbitrary |
610cd5c6 | 474 | screen-based programs on a remote machine, which can be very useful, |
475 | e.g., when implementing menu services. | |
0e73cc53 | 476 | .It Fl T |
477 | Disable pseudo-tty allocation (protocol version 2 only). | |
bf740959 | 478 | .It Fl v |
610cd5c6 | 479 | Verbose mode. |
480 | Causes | |
bf740959 | 481 | .Nm |
610cd5c6 | 482 | to print debugging messages about its progress. |
483 | This is helpful in | |
bf740959 | 484 | debugging connection, authentication, and configuration problems. |
485 | The verbose mode is also used to display | |
486 | .Xr skey 1 | |
487 | challenges, if the user entered "s/key" as password. | |
94ec8c6b | 488 | Multiple -v options increases the verbosity. |
489 | Maximum is 3. | |
bf740959 | 490 | .It Fl x |
610cd5c6 | 491 | Disables X11 forwarding. |
bf740959 | 492 | .It Fl X |
493 | Enables X11 forwarding. | |
71276795 | 494 | This can also be specified on a per-host basis in a configuration file. |
bf740959 | 495 | .It Fl C |
496 | Requests compression of all data (including stdin, stdout, stderr, and | |
610cd5c6 | 497 | data for forwarded X11 and TCP/IP connections). |
498 | The compression algorithm is the same used by | |
7b2ea3a1 | 499 | .Xr gzip 1 , |
500 | and the | |
bf740959 | 501 | .Dq level |
502 | can be controlled by the | |
503 | .Cm CompressionLevel | |
610cd5c6 | 504 | option (see below). |
505 | Compression is desirable on modem lines and other | |
bf740959 | 506 | slow connections, but will only slow down things on fast networks. |
507 | The default value can be set on a host-by-host basis in the | |
508 | configuration files; see the | |
509 | .Cm Compress | |
510 | option below. | |
511 | .It Fl L Ar port:host:hostport | |
512 | Specifies that the given port on the local (client) host is to be | |
610cd5c6 | 513 | forwarded to the given host and port on the remote side. |
514 | This works by allocating a socket to listen to | |
bf740959 | 515 | .Ar port |
516 | on the local side, and whenever a connection is made to this port, the | |
517 | connection is forwarded over the secure channel, and a connection is | |
518 | made to | |
48e671d5 | 519 | .Ar host |
520 | port | |
521 | .Ar hostport | |
610cd5c6 | 522 | from the remote machine. |
523 | Port forwardings can also be specified in the configuration file. | |
524 | Only root can forward privileged ports. | |
48e671d5 | 525 | IPv6 addresses can be specified with an alternative syntax: |
526 | .Ar port/host/hostport | |
bf740959 | 527 | .It Fl R Ar port:host:hostport |
528 | Specifies that the given port on the remote (server) host is to be | |
610cd5c6 | 529 | forwarded to the given host and port on the local side. |
530 | This works by allocating a socket to listen to | |
bf740959 | 531 | .Ar port |
532 | on the remote side, and whenever a connection is made to this port, the | |
533 | connection is forwarded over the secure channel, and a connection is | |
534 | made to | |
48e671d5 | 535 | .Ar host |
536 | port | |
537 | .Ar hostport | |
610cd5c6 | 538 | from the local machine. |
539 | Port forwardings can also be specified in the configuration file. | |
540 | Privileged ports can be forwarded only when | |
bf740959 | 541 | logging in as root on the remote machine. |
6ae2364d | 542 | .It Fl 2 |
543 | Forces | |
544 | .Nm | |
1d1ffb87 | 545 | to try protocol version 2 only. |
48e671d5 | 546 | .It Fl 4 |
547 | Forces | |
548 | .Nm | |
549 | to use IPv4 addresses only. | |
550 | .It Fl 6 | |
551 | Forces | |
552 | .Nm | |
553 | to use IPv6 addresses only. | |
bf740959 | 554 | .El |
555 | .Sh CONFIGURATION FILES | |
556 | .Nm | |
557 | obtains configuration data from the following sources (in this order): | |
558 | command line options, user's configuration file | |
559 | .Pq Pa $HOME/.ssh/config , | |
560 | and system-wide configuration file | |
5f4fdfae | 561 | .Pq Pa /etc/ssh_config . |
bf740959 | 562 | For each parameter, the first obtained value |
610cd5c6 | 563 | will be used. |
564 | The configuration files contain sections bracketed by | |
565 | .Dq Host | |
566 | specifications, and that section is only applied for hosts that | |
567 | match one of the patterns given in the specification. | |
568 | The matched host name is the one given on the command line. | |
bf740959 | 569 | .Pp |
570 | Since the first obtained value for each parameter is used, more | |
571 | host-specific declarations should be given near the beginning of the | |
572 | file, and general defaults at the end. | |
573 | .Pp | |
574 | The configuration file has the following format: | |
575 | .Pp | |
576 | Empty lines and lines starting with | |
577 | .Ql # | |
578 | are comments. | |
579 | .Pp | |
580 | Otherwise a line is of the format | |
581 | .Dq keyword arguments . | |
582 | The possible | |
583 | keywords and their meanings are as follows (note that the | |
584 | configuration files are case-sensitive): | |
585 | .Bl -tag -width Ds | |
586 | .It Cm Host | |
587 | Restricts the following declarations (up to the next | |
588 | .Cm Host | |
589 | keyword) to be only for those hosts that match one of the patterns | |
590 | given after the keyword. | |
591 | .Ql \&* | |
592 | and | |
593 | .Ql ? | |
594 | can be used as wildcards in the | |
610cd5c6 | 595 | patterns. |
596 | A single | |
bf740959 | 597 | .Ql \&* |
598 | as a pattern can be used to provide global | |
610cd5c6 | 599 | defaults for all hosts. |
600 | The host is the | |
bf740959 | 601 | .Ar hostname |
602 | argument given on the command line (i.e., the name is not converted to | |
603 | a canonicalized host name before matching). | |
604 | .It Cm AFSTokenPassing | |
4fe2af09 | 605 | Specifies whether to pass AFS tokens to remote host. |
606 | The argument to this keyword must be | |
bf740959 | 607 | .Dq yes |
608 | or | |
609 | .Dq no . | |
610 | .It Cm BatchMode | |
611 | If set to | |
612 | .Dq yes , | |
610cd5c6 | 613 | passphrase/password querying will be disabled. |
614 | This option is useful in scripts and other batch jobs where you have no | |
615 | user to supply the password. | |
616 | The argument must be | |
bf740959 | 617 | .Dq yes |
618 | or | |
619 | .Dq no . | |
7b2ea3a1 | 620 | .It Cm CheckHostIP |
621 | If this flag is set to | |
622 | .Dq yes , | |
623 | ssh will additionally check the host ip address in the | |
624 | .Pa known_hosts | |
4fe2af09 | 625 | file. |
626 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
7b2ea3a1 | 627 | If the option is set to |
628 | .Dq no , | |
629 | the check will not be executed. | |
bf740959 | 630 | .It Cm Cipher |
33de75a3 | 631 | Specifies the cipher to use for encrypting the session |
a22aff1f | 632 | in protocol version 1. |
610cd5c6 | 633 | Currently, |
a22aff1f | 634 | .Dq blowfish |
bf740959 | 635 | and |
636 | .Dq 3des | |
610cd5c6 | 637 | are supported. |
638 | The default is | |
bf740959 | 639 | .Dq 3des . |
f54651ce | 640 | .It Cm Ciphers |
641 | Specifies the ciphers allowed for protocol version 2 | |
642 | in order of preference. | |
643 | Multiple ciphers must be comma-separated. | |
644 | The default is | |
33de75a3 | 645 | .Dq 3des-cbc,blowfish-cbc,cast128-cbc,arcfour . |
bf740959 | 646 | .It Cm Compression |
610cd5c6 | 647 | Specifies whether to use compression. |
648 | The argument must be | |
bf740959 | 649 | .Dq yes |
650 | or | |
651 | .Dq no . | |
652 | .It Cm CompressionLevel | |
610cd5c6 | 653 | Specifies the compression level to use if compression is enable. |
654 | The argument must be an integer from 1 (fast) to 9 (slow, best). | |
655 | The default level is 6, which is good for most applications. | |
656 | The meaning of the values is the same as in | |
7b2ea3a1 | 657 | .Xr gzip 1 . |
bf740959 | 658 | .It Cm ConnectionAttempts |
659 | Specifies the number of tries (one per second) to make before falling | |
610cd5c6 | 660 | back to rsh or exiting. |
661 | The argument must be an integer. | |
662 | This may be useful in scripts if the connection sometimes fails. | |
1d1ffb87 | 663 | .It Cm DSAAuthentication |
664 | Specifies whether to try DSA authentication. | |
665 | The argument to this keyword must be | |
666 | .Dq yes | |
667 | or | |
668 | .Dq no . | |
669 | DSA authentication will only be | |
670 | attempted if a DSA identity file exists. | |
671 | Note that this option applies to protocol version 2 only. | |
bf740959 | 672 | .It Cm EscapeChar |
673 | Sets the escape character (default: | |
674 | .Ql ~ ) . | |
675 | The escape character can also | |
610cd5c6 | 676 | be set on the command line. |
677 | The argument should be a single character, | |
bf740959 | 678 | .Ql ^ |
679 | followed by a letter, or | |
680 | .Dq none | |
681 | to disable the escape | |
682 | character entirely (making the connection transparent for binary | |
683 | data). | |
f54651ce | 684 | .It Cm FallBackToRsh |
bf740959 | 685 | Specifies that if connecting via |
686 | .Nm | |
687 | fails due to a connection refused error (there is no | |
688 | .Xr sshd 8 | |
f54651ce | 689 | listening on the remote host), |
bf740959 | 690 | .Xr rsh 1 |
691 | should automatically be used instead (after a suitable warning about | |
610cd5c6 | 692 | the session being unencrypted). |
693 | The argument must be | |
bf740959 | 694 | .Dq yes |
695 | or | |
696 | .Dq no . | |
697 | .It Cm ForwardAgent | |
698 | Specifies whether the connection to the authentication agent (if any) | |
610cd5c6 | 699 | will be forwarded to the remote machine. |
700 | The argument must be | |
bf740959 | 701 | .Dq yes |
702 | or | |
703 | .Dq no . | |
71276795 | 704 | The default is |
705 | .Dq no . | |
bf740959 | 706 | .It Cm ForwardX11 |
707 | Specifies whether X11 connections will be automatically redirected | |
f54651ce | 708 | over the secure channel and |
bf740959 | 709 | .Ev DISPLAY |
610cd5c6 | 710 | set. |
f54651ce | 711 | The argument must be |
bf740959 | 712 | .Dq yes |
713 | or | |
714 | .Dq no . | |
c8d54615 | 715 | The default is |
716 | .Dq no . | |
bf740959 | 717 | .It Cm GatewayPorts |
718 | Specifies whether remote hosts are allowed to connect to local | |
719 | forwarded ports. | |
720 | The argument must be | |
721 | .Dq yes | |
722 | or | |
723 | .Dq no . | |
724 | The default is | |
725 | .Dq no . | |
726 | .It Cm GlobalKnownHostsFile | |
f54651ce | 727 | Specifies a file to use instead of |
5f4fdfae | 728 | .Pa /etc/ssh_known_hosts . |
bf740959 | 729 | .It Cm HostName |
610cd5c6 | 730 | Specifies the real host name to log into. |
731 | This can be used to specify nicknames or abbreviations for hosts. | |
732 | Default is the name given on the command line. | |
733 | Numeric IP addresses are also permitted (both on the command line and in | |
bf740959 | 734 | .Cm HostName |
735 | specifications). | |
736 | .It Cm IdentityFile | |
737 | Specifies the file from which the user's RSA authentication identity | |
738 | is read (default | |
1d1ffb87 | 739 | .Pa $HOME/.ssh/identity |
bf740959 | 740 | in the user's home directory). |
741 | Additionally, any identities represented by the authentication agent | |
610cd5c6 | 742 | will be used for authentication. |
743 | The file name may use the tilde | |
744 | syntax to refer to a user's home directory. | |
745 | It is possible to have | |
bf740959 | 746 | multiple identity files specified in configuration files; all these |
747 | identities will be tried in sequence. | |
1d1ffb87 | 748 | .It Cm IdentityFile2 |
749 | Specifies the file from which the user's DSA authentication identity | |
750 | is read (default | |
751 | .Pa $HOME/.ssh/id_dsa | |
752 | in the user's home directory). | |
753 | The file name may use the tilde | |
754 | syntax to refer to a user's home directory. | |
755 | It is possible to have | |
756 | multiple identity files specified in configuration files; all these | |
757 | identities will be tried in sequence. | |
bf740959 | 758 | .It Cm KeepAlive |
759 | Specifies whether the system should send keepalive messages to the | |
610cd5c6 | 760 | other side. |
761 | If they are sent, death of the connection or crash of one | |
762 | of the machines will be properly noticed. | |
763 | However, this means that | |
bf740959 | 764 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 765 | find it annoying. |
bf740959 | 766 | .Pp |
767 | The default is | |
768 | .Dq yes | |
769 | (to send keepalives), and the client will notice | |
610cd5c6 | 770 | if the network goes down or the remote host dies. |
771 | This is important in scripts, and many users want it too. | |
bf740959 | 772 | .Pp |
773 | To disable keepalives, the value should be set to | |
774 | .Dq no | |
775 | in both the server and the client configuration files. | |
776 | .It Cm KerberosAuthentication | |
4fe2af09 | 777 | Specifies whether Kerberos authentication will be used. |
778 | The argument to this keyword must be | |
bf740959 | 779 | .Dq yes |
780 | or | |
781 | .Dq no . | |
782 | .It Cm KerberosTgtPassing | |
4fe2af09 | 783 | Specifies whether a Kerberos TGT will be forwarded to the server. |
784 | This will only work if the Kerberos server is actually an AFS kaserver. | |
785 | The argument to this keyword must be | |
bf740959 | 786 | .Dq yes |
787 | or | |
788 | .Dq no . | |
789 | .It Cm LocalForward | |
790 | Specifies that a TCP/IP port on the local machine be forwarded over | |
610cd5c6 | 791 | the secure channel to given host:port from the remote machine. |
792 | The first argument must be a port number, and the second must be | |
793 | host:port. | |
794 | Multiple forwardings may be specified, and additional | |
795 | forwardings can be given on the command line. | |
796 | Only the superuser can forward privileged ports. | |
6a17f9c2 | 797 | .It Cm LogLevel |
798 | Gives the verbosity level that is used when logging messages from | |
799 | .Nm ssh . | |
800 | The possible values are: | |
22fa590f | 801 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
6a17f9c2 | 802 | The default is INFO. |
bf740959 | 803 | .It Cm NumberOfPasswordPrompts |
4fe2af09 | 804 | Specifies the number of password prompts before giving up. |
805 | The argument to this keyword must be an integer. | |
806 | Default is 3. | |
7b2ea3a1 | 807 | .It Cm PasswordAuthentication |
610cd5c6 | 808 | Specifies whether to use password authentication. |
809 | The argument to this keyword must be | |
7b2ea3a1 | 810 | .Dq yes |
811 | or | |
812 | .Dq no . | |
1d1ffb87 | 813 | Note that this option applies to both protocol version 1 and 2. |
bf740959 | 814 | .It Cm Port |
610cd5c6 | 815 | Specifies the port number to connect on the remote host. |
816 | Default is 22. | |
f54651ce | 817 | .It Cm Protocol |
818 | Specifies the protocol versions | |
819 | .Nm | |
820 | should support in order of preference. | |
821 | The possible values are | |
822 | .Dq 1 | |
823 | and | |
824 | .Dq 2 . | |
825 | Multiple versions must be comma-separated. | |
826 | The default is | |
1d1ffb87 | 827 | .Dq 1,2 . |
828 | This means that | |
829 | .Nm | |
830 | tries version 1 and falls back to version 2 | |
d0c832f3 | 831 | if version 1 is not available. |
bf740959 | 832 | .It Cm ProxyCommand |
610cd5c6 | 833 | Specifies the command to use to connect to the server. |
834 | The command | |
835 | string extends to the end of the line, and is executed with | |
836 | .Pa /bin/sh . | |
837 | In the command string, | |
838 | .Ql %h | |
839 | will be substituted by the host name to | |
840 | connect and | |
841 | .Ql %p | |
842 | by the port. | |
843 | The command can be basically anything, | |
844 | and should read from its standard input and write to its standard output. | |
845 | It should eventually connect an | |
bf740959 | 846 | .Xr sshd 8 |
847 | server running on some machine, or execute | |
848 | .Ic sshd -i | |
610cd5c6 | 849 | somewhere. |
850 | Host key management will be done using the | |
bf740959 | 851 | HostName of the host being connected (defaulting to the name typed by |
852 | the user). | |
57112b5a | 853 | Note that |
854 | .Cm CheckHostIP | |
855 | is not available for connects with a proxy command. | |
bf740959 | 856 | .Pp |
857 | .It Cm RemoteForward | |
858 | Specifies that a TCP/IP port on the remote machine be forwarded over | |
610cd5c6 | 859 | the secure channel to given host:port from the local machine. |
860 | The first argument must be a port number, and the second must be | |
861 | host:port. | |
862 | Multiple forwardings may be specified, and additional | |
863 | forwardings can be given on the command line. | |
864 | Only the superuser can forward privileged ports. | |
bf740959 | 865 | .It Cm RhostsAuthentication |
610cd5c6 | 866 | Specifies whether to try rhosts based authentication. |
867 | Note that this | |
bf740959 | 868 | declaration only affects the client side and has no effect whatsoever |
610cd5c6 | 869 | on security. |
870 | Disabling rhosts authentication may reduce | |
bf740959 | 871 | authentication time on slow connections when rhosts authentication is |
610cd5c6 | 872 | not used. |
873 | Most servers do not permit RhostsAuthentication because it | |
874 | is not secure (see RhostsRSAAuthentication). | |
875 | The argument to this keyword must be | |
bf740959 | 876 | .Dq yes |
877 | or | |
878 | .Dq no . | |
879 | .It Cm RhostsRSAAuthentication | |
880 | Specifies whether to try rhosts based authentication with RSA host | |
610cd5c6 | 881 | authentication. |
882 | This is the primary authentication method for most sites. | |
883 | The argument must be | |
bf740959 | 884 | .Dq yes |
885 | or | |
886 | .Dq no . | |
887 | .It Cm RSAAuthentication | |
610cd5c6 | 888 | Specifies whether to try RSA authentication. |
889 | The argument to this keyword must be | |
bf740959 | 890 | .Dq yes |
891 | or | |
892 | .Dq no . | |
893 | RSA authentication will only be | |
894 | attempted if the identity file exists, or an authentication agent is | |
895 | running. | |
1d1ffb87 | 896 | Note that this option applies to protocol version 1 only. |
5260325f | 897 | .It Cm SkeyAuthentication |
898 | Specifies whether to use | |
899 | .Xr skey 1 | |
610cd5c6 | 900 | authentication. |
901 | The argument to this keyword must be | |
5260325f | 902 | .Dq yes |
903 | or | |
904 | .Dq no . | |
905 | The default is | |
906 | .Dq no . | |
bf740959 | 907 | .It Cm StrictHostKeyChecking |
908 | If this flag is set to | |
f54651ce | 909 | .Dq yes , |
bf740959 | 910 | .Nm |
911 | ssh will never automatically add host keys to the | |
912 | .Pa $HOME/.ssh/known_hosts | |
1d1ffb87 | 913 | and |
914 | .Pa $HOME/.ssh/known_hosts2 | |
915 | files, and refuses to connect hosts whose host key has changed. | |
610cd5c6 | 916 | This provides maximum protection against trojan horse attacks. |
917 | However, it can be somewhat annoying if you don't have good | |
5f4fdfae | 918 | .Pa /etc/ssh_known_hosts |
1d1ffb87 | 919 | and |
920 | .Pa /etc/ssh_known_hosts2 | |
bf740959 | 921 | files installed and frequently |
610cd5c6 | 922 | connect new hosts. |
923 | Basically this option forces the user to manually | |
924 | add any new hosts. | |
925 | Normally this option is disabled, and new hosts | |
926 | will automatically be added to the known host files. | |
927 | The host keys of | |
928 | known hosts will be verified automatically in either case. | |
929 | The argument must be | |
bf740959 | 930 | .Dq yes |
931 | or | |
932 | .Dq no . | |
bf740959 | 933 | .It Cm UsePrivilegedPort |
934 | Specifies whether to use a privileged port for outgoing connections. | |
935 | The argument must be | |
936 | .Dq yes | |
937 | or | |
938 | .Dq no . | |
939 | The default is | |
940 | .Dq yes . | |
941 | Note that setting this option to | |
942 | .Dq no | |
95f1eccc | 943 | turns off |
bf740959 | 944 | .Cm RhostsAuthentication |
945 | and | |
946 | .Cm RhostsRSAAuthentication . | |
7b2ea3a1 | 947 | .It Cm User |
610cd5c6 | 948 | Specifies the user to log in as. |
949 | This can be useful if you have a different user name on different machines. | |
950 | This saves the trouble of | |
7b2ea3a1 | 951 | having to remember to give the user name on the command line. |
952 | .It Cm UserKnownHostsFile | |
953 | Specifies a file to use instead of | |
954 | .Pa $HOME/.ssh/known_hosts . | |
bf740959 | 955 | .It Cm UseRsh |
610cd5c6 | 956 | Specifies that rlogin/rsh should be used for this host. |
957 | It is possible that the host does not at all support the | |
bf740959 | 958 | .Nm |
610cd5c6 | 959 | protocol. |
960 | This causes | |
bf740959 | 961 | .Nm |
610cd5c6 | 962 | to immediately execute |
bf740959 | 963 | .Xr rsh 1 . |
964 | All other options (except | |
965 | .Cm HostName ) | |
610cd5c6 | 966 | are ignored if this has been specified. |
967 | The argument must be | |
bf740959 | 968 | .Dq yes |
969 | or | |
970 | .Dq no . | |
fa649821 | 971 | .It Cm XAuthLocation |
972 | Specifies the location of the | |
973 | .Xr xauth 1 | |
974 | program. | |
975 | The default is | |
976 | .Pa /usr/X11R6/bin/xauth . | |
b5e300c2 | 977 | .El |
bf740959 | 978 | .Sh ENVIRONMENT |
979 | .Nm | |
980 | will normally set the following environment variables: | |
981 | .Bl -tag -width Ds | |
982 | .It Ev DISPLAY | |
983 | The | |
984 | .Ev DISPLAY | |
610cd5c6 | 985 | variable indicates the location of the X11 server. |
f54651ce | 986 | It is automatically set by |
bf740959 | 987 | .Nm |
988 | to point to a value of the form | |
989 | .Dq hostname:n | |
990 | where hostname indicates | |
610cd5c6 | 991 | the host where the shell runs, and n is an integer >= 1. |
992 | .Nm | |
993 | uses this special value to forward X11 connections over the secure | |
994 | channel. | |
995 | The user should normally not set DISPLAY explicitly, as that | |
bf740959 | 996 | will render the X11 connection insecure (and will require the user to |
997 | manually copy any required authorization cookies). | |
998 | .It Ev HOME | |
999 | Set to the path of the user's home directory. | |
1000 | .It Ev LOGNAME | |
1001 | Synonym for | |
1002 | .Ev USER ; | |
1003 | set for compatibility with systems that use this variable. | |
1004 | .It Ev MAIL | |
1005 | Set to point the user's mailbox. | |
610cd5c6 | 1006 | .It Ev PATH |
bf740959 | 1007 | Set to the default |
1008 | .Ev PATH , | |
1009 | as specified when compiling | |
1010 | .Nm ssh . | |
1011 | .It Ev SSH_AUTH_SOCK | |
1012 | indicates the path of a unix-domain socket used to communicate with the | |
1013 | agent. | |
1014 | .It Ev SSH_CLIENT | |
610cd5c6 | 1015 | Identifies the client end of the connection. |
1016 | The variable contains | |
bf740959 | 1017 | three space-separated values: client ip-address, client port number, |
1018 | and server port number. | |
1019 | .It Ev SSH_TTY | |
1020 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 1021 | with the current shell or command. |
1022 | If the current session has no tty, | |
bf740959 | 1023 | this variable is not set. |
1024 | .It Ev TZ | |
1025 | The timezone variable is set to indicate the present timezone if it | |
c345cf9d | 1026 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 1027 | on to new connections). |
1028 | .It Ev USER | |
1029 | Set to the name of the user logging in. | |
1030 | .El | |
1031 | .Pp | |
f54651ce | 1032 | Additionally, |
bf740959 | 1033 | .Nm |
f54651ce | 1034 | reads |
1035 | .Pa $HOME/.ssh/environment , | |
bf740959 | 1036 | and adds lines of the format |
1037 | .Dq VARNAME=value | |
1038 | to the environment. | |
1039 | .Sh FILES | |
c8d54615 | 1040 | .Bl -tag -width Ds |
bf740959 | 1041 | .It Pa $HOME/.ssh/known_hosts |
1042 | Records host keys for all hosts the user has logged into (that are not | |
1043 | in | |
5f4fdfae | 1044 | .Pa /etc/ssh_known_hosts ) . |
bf740959 | 1045 | See |
1046 | .Xr sshd 8 . | |
1d1ffb87 | 1047 | .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa |
1048 | Contains the RSA and the DSA authentication identity of the user. | |
1049 | These files | |
1050 | contain sensitive data and should be readable by the user but not | |
bf740959 | 1051 | accessible by others (read/write/execute). |
1052 | Note that | |
1053 | .Nm | |
1d1ffb87 | 1054 | ignores a private key file if it is accessible by others. |
bf740959 | 1055 | It is possible to specify a passphrase when |
1056 | generating the key; the passphrase will be used to encrypt the | |
1057 | sensitive part of this file using 3DES. | |
1d1ffb87 | 1058 | .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub |
bf740959 | 1059 | Contains the public key for authentication (public part of the |
610cd5c6 | 1060 | identity file in human-readable form). |
1d1ffb87 | 1061 | The contents of the |
1062 | .Pa $HOME/.ssh/identity.pub | |
1063 | file should be added to | |
bf740959 | 1064 | .Pa $HOME/.ssh/authorized_keys |
1065 | on all machines | |
610cd5c6 | 1066 | where you wish to log in using RSA authentication. |
1d1ffb87 | 1067 | The contents of the |
1068 | .Pa $HOME/.ssh/id_dsa.pub | |
1069 | file should be added to | |
1070 | .Pa $HOME/.ssh/authorized_keys2 | |
1071 | on all machines | |
1072 | where you wish to log in using DSA authentication. | |
1073 | These files are not | |
610cd5c6 | 1074 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 1075 | These files are |
1076 | never used automatically and are not necessary; they is only provided for | |
bf740959 | 1077 | the convenience of the user. |
1078 | .It Pa $HOME/.ssh/config | |
610cd5c6 | 1079 | This is the per-user configuration file. |
1080 | The format of this file is described above. | |
1081 | This file is used by the | |
bf740959 | 1082 | .Nm |
610cd5c6 | 1083 | client. |
1084 | This file does not usually contain any sensitive information, | |
bf740959 | 1085 | but the recommended permissions are read/write for the user, and not |
1086 | accessible by others. | |
1087 | .It Pa $HOME/.ssh/authorized_keys | |
610cd5c6 | 1088 | Lists the RSA keys that can be used for logging in as this user. |
1089 | The format of this file is described in the | |
bf740959 | 1090 | .Xr sshd 8 |
610cd5c6 | 1091 | manual page. |
1092 | In the simplest form the format is the same as the .pub | |
bf740959 | 1093 | identity files (that is, each line contains the number of bits in |
1094 | modulus, public exponent, modulus, and comment fields, separated by | |
610cd5c6 | 1095 | spaces). |
1096 | This file is not highly sensitive, but the recommended | |
bf740959 | 1097 | permissions are read/write for the user, and not accessible by others. |
1d1ffb87 | 1098 | .It Pa $HOME/.ssh/authorized_keys2 |
1099 | Lists the DSA keys that can be used for logging in as this user. | |
1100 | This file is not highly sensitive, but the recommended | |
1101 | permissions are read/write for the user, and not accessible by others. | |
1102 | .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2 | |
610cd5c6 | 1103 | Systemwide list of known host keys. |
1d1ffb87 | 1104 | .Pa /etc/ssh_known_hosts |
1105 | contains RSA and | |
1106 | .Pa /etc/ssh_known_hosts2 | |
1107 | contains DSA keys. | |
1108 | These files should be prepared by the | |
bf740959 | 1109 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1110 | organization. |
1111 | This file should be world-readable. | |
1112 | This file contains | |
bf740959 | 1113 | public keys, one per line, in the following format (fields separated |
1114 | by spaces): system name, number of bits in modulus, public exponent, | |
610cd5c6 | 1115 | modulus, and optional comment field. |
1116 | When different names are used | |
bf740959 | 1117 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1118 | commas. |
1119 | The format is described on the | |
bf740959 | 1120 | .Xr sshd 8 |
1121 | manual page. | |
1122 | .Pp | |
1123 | The canonical system name (as returned by name servers) is used by | |
1124 | .Xr sshd 8 | |
1125 | to verify the client host when logging in; other names are needed because | |
1126 | .Nm | |
1127 | does not convert the user-supplied name to a canonical name before | |
1128 | checking the key, because someone with access to the name servers | |
1129 | would then be able to fool host authentication. | |
5f4fdfae | 1130 | .It Pa /etc/ssh_config |
610cd5c6 | 1131 | Systemwide configuration file. |
1132 | This file provides defaults for those | |
bf740959 | 1133 | values that are not specified in the user's configuration file, and |
610cd5c6 | 1134 | for those users who do not have a configuration file. |
1135 | This file must be world-readable. | |
bf740959 | 1136 | .It Pa $HOME/.rhosts |
1137 | This file is used in | |
1138 | .Pa \&.rhosts | |
1139 | authentication to list the | |
610cd5c6 | 1140 | host/user pairs that are permitted to log in. |
1141 | (Note that this file is | |
bf740959 | 1142 | also used by rlogin and rsh, which makes using this file insecure.) |
1143 | Each line of the file contains a host name (in the canonical form | |
1144 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1145 | separated by a space. |
1146 | One some machines this file may need to be | |
bf740959 | 1147 | world-readable if the user's home directory is on a NFS partition, |
1148 | because | |
1149 | .Xr sshd 8 | |
610cd5c6 | 1150 | reads it as root. |
1151 | Additionally, this file must be owned by the user, | |
1152 | and must not have write permissions for anyone else. | |
1153 | The recommended | |
bf740959 | 1154 | permission for most machines is read/write for the user, and not |
1155 | accessible by others. | |
1156 | .Pp | |
1157 | Note that by default | |
1158 | .Xr sshd 8 | |
1159 | will be installed so that it requires successful RSA host | |
610cd5c6 | 1160 | authentication before permitting \s+2.\s0rhosts authentication. |
1161 | If your server machine does not have the client's host key in | |
5f4fdfae | 1162 | .Pa /etc/ssh_known_hosts , |
bf740959 | 1163 | you can store it in |
1164 | .Pa $HOME/.ssh/known_hosts . | |
1165 | The easiest way to do this is to | |
1166 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1167 | will automatically add the host key to |
bf740959 | 1168 | .Pa $HOME/.ssh/known_hosts . |
1169 | .It Pa $HOME/.shosts | |
1170 | This file is used exactly the same way as | |
1171 | .Pa \&.rhosts . | |
1172 | The purpose for | |
1173 | having this file is to be able to use rhosts authentication with | |
1174 | .Nm | |
1175 | without permitting login with | |
1176 | .Xr rlogin 1 | |
1177 | or | |
1178 | .Xr rsh 1 . | |
1179 | .It Pa /etc/hosts.equiv | |
1180 | This file is used during | |
610cd5c6 | 1181 | .Pa \&.rhosts authentication. |
1182 | It contains | |
bf740959 | 1183 | canonical hosts names, one per line (the full format is described on |
1184 | the | |
1185 | .Xr sshd 8 | |
610cd5c6 | 1186 | manual page). |
1187 | If the client host is found in this file, login is | |
bf740959 | 1188 | automatically permitted provided client and server user names are the |
610cd5c6 | 1189 | same. |
1190 | Additionally, successful RSA host authentication is normally | |
1191 | required. | |
1192 | This file should only be writable by root. | |
5f4fdfae | 1193 | .It Pa /etc/shosts.equiv |
f54651ce | 1194 | This file is processed exactly as |
bf740959 | 1195 | .Pa /etc/hosts.equiv . |
1196 | This file may be useful to permit logins using | |
1197 | .Nm | |
1198 | but not using rsh/rlogin. | |
5f4fdfae | 1199 | .It Pa /etc/sshrc |
bf740959 | 1200 | Commands in this file are executed by |
1201 | .Nm | |
1202 | when the user logs in just before the user's shell (or command) is started. | |
1203 | See the | |
1204 | .Xr sshd 8 | |
1205 | manual page for more information. | |
1206 | .It Pa $HOME/.ssh/rc | |
1207 | Commands in this file are executed by | |
1208 | .Nm | |
1209 | when the user logs in just before the user's shell (or command) is | |
1210 | started. | |
f54651ce | 1211 | See the |
bf740959 | 1212 | .Xr sshd 8 |
1213 | manual page for more information. | |
83b7f649 | 1214 | .It Pa $HOME/.ssh/environment |
1215 | Contains additional definitions for environment variables, see section | |
1216 | .Sx ENVIRONMENT | |
1217 | above. | |
bf740959 | 1218 | .It Pa libcrypto.so.X.1 |
1219 | A version of this library which includes support for the RSA algorithm | |
1220 | is required for proper operation. | |
b5e300c2 | 1221 | .El |
bf740959 | 1222 | .Sh AUTHOR |
bf740959 | 1223 | OpenSSH |
c8d54615 | 1224 | is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen, |
610cd5c6 | 1225 | but with bugs removed and newer features re-added. |
1226 | Rapidly after the | |
c8d54615 | 1227 | 1.2.12 release, newer versions of the original ssh bore successively |
1228 | more restrictive licenses, and thus demand for a free version was born. | |
1d1ffb87 | 1229 | .Pp |
c8d54615 | 1230 | This version of OpenSSH |
bf740959 | 1231 | .Bl -bullet |
1232 | .It | |
bcbf86ec | 1233 | has all components of a restrictive nature (i.e., patents, see |
1234 | .Xr crypto 3 ) | |
bf740959 | 1235 | directly removed from the source code; any licensed or patented components |
1236 | are chosen from | |
1237 | external libraries. | |
1238 | .It | |
1d1ffb87 | 1239 | has been updated to support SSH protocol 1.5 and 2, making it compatible with |
1240 | all other SSH clients and servers. | |
bf740959 | 1241 | .It |
f54651ce | 1242 | contains added support for |
bf740959 | 1243 | .Xr kerberos 8 |
1244 | authentication and ticket passing. | |
1245 | .It | |
1246 | supports one-time password authentication with | |
1247 | .Xr skey 1 . | |
1248 | .El | |
1249 | .Pp | |
0c16a097 | 1250 | OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl, |
f095fcc7 | 1251 | Niels Provos, Theo de Raadt, and Dug Song. |
1d1ffb87 | 1252 | .Pp |
1253 | The support for SSH protocol 2 was written by Markus Friedl. | |
bf740959 | 1254 | .Sh SEE ALSO |
1255 | .Xr rlogin 1 , | |
1256 | .Xr rsh 1 , | |
1257 | .Xr scp 1 , | |
1258 | .Xr ssh-add 1 , | |
1259 | .Xr ssh-agent 1 , | |
1260 | .Xr ssh-keygen 1 , | |
1261 | .Xr telnet 1 , | |
1262 | .Xr sshd 8 , | |
bcbf86ec | 1263 | .Xr crypto 3 |