]>
Commit | Line | Data |
---|---|---|
bf740959 | 1 | .\" -*- nroff -*- |
2 | .\" | |
bf740959 | 3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
bf740959 | 4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
5 | .\" All rights reserved | |
6 | .\" | |
bcbf86ec | 7 | .\" As far as I am concerned, the code I have written for this software |
8 | .\" can be used freely for any purpose. Any derived versions of this | |
9 | .\" software must be clearly marked as such, and if the derived work is | |
10 | .\" incompatible with the protocol description in the RFC file, it must be | |
11 | .\" called by a name other than "ssh" or "Secure Shell". | |
12 | .\" | |
f3c7c613 | 13 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. |
14 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. | |
15 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. | |
bcbf86ec | 16 | .\" |
17 | .\" Redistribution and use in source and binary forms, with or without | |
18 | .\" modification, are permitted provided that the following conditions | |
19 | .\" are met: | |
20 | .\" 1. Redistributions of source code must retain the above copyright | |
21 | .\" notice, this list of conditions and the following disclaimer. | |
22 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
23 | .\" notice, this list of conditions and the following disclaimer in the | |
24 | .\" documentation and/or other materials provided with the distribution. | |
bf740959 | 25 | .\" |
bcbf86ec | 26 | .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
27 | .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES | |
28 | .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |
29 | .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, | |
30 | .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT | |
31 | .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
32 | .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
33 | .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
34 | .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF | |
35 | .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
bf740959 | 36 | .\" |
df841692 | 37 | .\" $OpenBSD: ssh.1,v 1.104 2001/04/20 07:17:51 djm Exp $ |
bf740959 | 38 | .Dd September 25, 1999 |
39 | .Dt SSH 1 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm ssh | |
2c86906e | 43 | .Nd OpenSSH SSH client (remote login program) |
bf740959 | 44 | .Sh SYNOPSIS |
45 | .Nm ssh | |
46 | .Op Fl l Ar login_name | |
47 | .Op Ar hostname | user@hostname | |
48 | .Op Ar command | |
49 | .Pp | |
50 | .Nm ssh | |
9afadca8 | 51 | .Op Fl afgknqstvxACNPTX1246 |
d0c832f3 | 52 | .Op Fl c Ar cipher_spec |
bf740959 | 53 | .Op Fl e Ar escape_char |
54 | .Op Fl i Ar identity_file | |
55 | .Op Fl l Ar login_name | |
b2552997 | 56 | .Op Fl m Ar mac_spec |
bf740959 | 57 | .Op Fl o Ar option |
58 | .Op Fl p Ar port | |
59 | .Oo Fl L Xo | |
60 | .Sm off | |
bf740959 | 61 | .Ar port : |
7b2ea3a1 | 62 | .Ar host : |
bf740959 | 63 | .Ar hostport |
64 | .Sm on | |
65 | .Xc | |
66 | .Oc | |
67 | .Oo Fl R Xo | |
68 | .Sm off | |
bf740959 | 69 | .Ar port : |
7b2ea3a1 | 70 | .Ar host : |
bf740959 | 71 | .Ar hostport |
72 | .Sm on | |
73 | .Xc | |
74 | .Oc | |
75 | .Op Ar hostname | user@hostname | |
76 | .Op Ar command | |
f54651ce | 77 | .Sh DESCRIPTION |
bf740959 | 78 | .Nm |
2c86906e | 79 | (SSH client) is a program for logging into a remote machine and for |
610cd5c6 | 80 | executing commands on a remote machine. |
81 | It is intended to replace | |
bf740959 | 82 | rlogin and rsh, and provide secure encrypted communications between |
610cd5c6 | 83 | two untrusted hosts over an insecure network. |
84 | X11 connections and | |
bf740959 | 85 | arbitrary TCP/IP ports can also be forwarded over the secure channel. |
86 | .Pp | |
87 | .Nm | |
f54651ce | 88 | connects and logs into the specified |
bf740959 | 89 | .Ar hostname . |
90 | The user must prove | |
1d1ffb87 | 91 | his/her identity to the remote machine using one of several methods |
92 | depending on the protocol version used: | |
93 | .Pp | |
94 | .Ss SSH protocol version 1 | |
bf740959 | 95 | .Pp |
96 | First, if the machine the user logs in from is listed in | |
97 | .Pa /etc/hosts.equiv | |
98 | or | |
5f4fdfae | 99 | .Pa /etc/shosts.equiv |
bf740959 | 100 | on the remote machine, and the user names are |
101 | the same on both sides, the user is immediately permitted to log in. | |
f54651ce | 102 | Second, if |
bf740959 | 103 | .Pa \&.rhosts |
104 | or | |
105 | .Pa \&.shosts | |
106 | exists in the user's home directory on the | |
107 | remote machine and contains a line containing the name of the client | |
108 | machine and the name of the user on that machine, the user is | |
610cd5c6 | 109 | permitted to log in. |
110 | This form of authentication alone is normally not | |
bf740959 | 111 | allowed by the server because it is not secure. |
112 | .Pp | |
113 | The second (and primary) authentication method is the | |
114 | .Pa rhosts | |
115 | or | |
116 | .Pa hosts.equiv | |
610cd5c6 | 117 | method combined with RSA-based host authentication. |
118 | It means that if the login would be permitted by | |
1d1ffb87 | 119 | .Pa $HOME/.rhosts , |
120 | .Pa $HOME/.shosts , | |
bf740959 | 121 | .Pa /etc/hosts.equiv , |
122 | or | |
5f4fdfae | 123 | .Pa /etc/shosts.equiv , |
bf740959 | 124 | and if additionally the server can verify the client's |
f54651ce | 125 | host key (see |
5f4fdfae | 126 | .Pa /etc/ssh_known_hosts |
5bbb5681 | 127 | and |
128 | .Pa $HOME/.ssh/known_hosts | |
bf740959 | 129 | in the |
130 | .Sx FILES | |
610cd5c6 | 131 | section), only then login is permitted. |
132 | This authentication method closes security holes due to IP | |
133 | spoofing, DNS spoofing and routing spoofing. | |
134 | [Note to the administrator: | |
bf740959 | 135 | .Pa /etc/hosts.equiv , |
1d1ffb87 | 136 | .Pa $HOME/.rhosts , |
bf740959 | 137 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
138 | disabled if security is desired.] | |
139 | .Pp | |
f54651ce | 140 | As a third authentication method, |
bf740959 | 141 | .Nm |
142 | supports RSA based authentication. | |
143 | The scheme is based on public-key cryptography: there are cryptosystems | |
144 | where encryption and decryption are done using separate keys, and it | |
145 | is not possible to derive the decryption key from the encryption key. | |
610cd5c6 | 146 | RSA is one such system. |
f54651ce | 147 | The idea is that each user creates a public/private |
610cd5c6 | 148 | key pair for authentication purposes. |
149 | The server knows the public key, and only the user knows the private key. | |
f54651ce | 150 | The file |
bf740959 | 151 | .Pa $HOME/.ssh/authorized_keys |
152 | lists the public keys that are permitted for logging | |
610cd5c6 | 153 | in. |
154 | When the user logs in, the | |
bf740959 | 155 | .Nm |
156 | program tells the server which key pair it would like to use for | |
610cd5c6 | 157 | authentication. |
158 | The server checks if this key is permitted, and if | |
bf740959 | 159 | so, sends the user (actually the |
160 | .Nm | |
161 | program running on behalf of the user) a challenge, a random number, | |
610cd5c6 | 162 | encrypted by the user's public key. |
163 | The challenge can only be | |
164 | decrypted using the proper private key. | |
165 | The user's client then decrypts the | |
bf740959 | 166 | challenge using the private key, proving that he/she knows the private |
167 | key but without disclosing it to the server. | |
168 | .Pp | |
169 | .Nm | |
610cd5c6 | 170 | implements the RSA authentication protocol automatically. |
171 | The user creates his/her RSA key pair by running | |
bf740959 | 172 | .Xr ssh-keygen 1 . |
f54651ce | 173 | This stores the private key in |
1d1ffb87 | 174 | .Pa $HOME/.ssh/identity |
bf740959 | 175 | and the public key in |
1d1ffb87 | 176 | .Pa $HOME/.ssh/identity.pub |
610cd5c6 | 177 | in the user's home directory. |
178 | The user should then copy the | |
bf740959 | 179 | .Pa identity.pub |
f54651ce | 180 | to |
1d1ffb87 | 181 | .Pa $HOME/.ssh/authorized_keys |
f54651ce | 182 | in his/her home directory on the remote machine (the |
bf740959 | 183 | .Pa authorized_keys |
f54651ce | 184 | file corresponds to the conventional |
1d1ffb87 | 185 | .Pa $HOME/.rhosts |
bf740959 | 186 | file, and has one key |
610cd5c6 | 187 | per line, though the lines can be very long). |
188 | After this, the user can log in without giving the password. | |
189 | RSA authentication is much | |
bf740959 | 190 | more secure than rhosts authentication. |
191 | .Pp | |
192 | The most convenient way to use RSA authentication may be with an | |
610cd5c6 | 193 | authentication agent. |
194 | See | |
bf740959 | 195 | .Xr ssh-agent 1 |
196 | for more information. | |
197 | .Pp | |
f54651ce | 198 | If other authentication methods fail, |
bf740959 | 199 | .Nm |
610cd5c6 | 200 | prompts the user for a password. |
201 | The password is sent to the remote | |
bf740959 | 202 | host for checking; however, since all communications are encrypted, |
203 | the password cannot be seen by someone listening on the network. | |
204 | .Pp | |
1d1ffb87 | 205 | .Ss SSH protocol version 2 |
206 | .Pp | |
207 | When a user connects using the protocol version 2 | |
208 | different authentication methods are available: | |
209 | At first, the client attempts to authenticate using the public key method. | |
210 | If this method fails password authentication is tried. | |
211 | .Pp | |
212 | The public key method is similar to RSA authentication described | |
fa08c86b | 213 | in the previous section except that the DSA or RSA algorithm is used |
214 | instead. | |
c0ecc314 | 215 | The client uses his private key, |
1d1ffb87 | 216 | .Pa $HOME/.ssh/id_dsa |
c0ecc314 | 217 | or |
218 | .Pa $HOME/.ssh/id_rsa , | |
1d1ffb87 | 219 | to sign the session identifier and sends the result to the server. |
220 | The server checks whether the matching public key is listed in | |
221 | .Pa $HOME/.ssh/authorized_keys2 | |
222 | and grants access if both the key is found and the signature is correct. | |
223 | The session identifier is derived from a shared Diffie-Hellman value | |
224 | and is only known to the client and the server. | |
225 | .Pp | |
226 | If public key authentication fails or is not available a password | |
227 | can be sent encrypted to the remote host for proving the user's identity. | |
228 | This protocol 2 implementation does not yet support Kerberos or | |
229 | S/Key authentication. | |
230 | .Pp | |
231 | Protocol 2 provides additional mechanisms for confidentiality | |
d0c832f3 | 232 | (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour) |
f2ba0775 | 233 | and integrity (hmac-md5, hmac-sha1). |
1d1ffb87 | 234 | Note that protocol 1 lacks a strong mechanism for ensuring the |
235 | integrity of the connection. | |
236 | .Pp | |
237 | .Ss Login session and remote execution | |
238 | .Pp | |
bf740959 | 239 | When the user's identity has been accepted by the server, the server |
240 | either executes the given command, or logs into the machine and gives | |
610cd5c6 | 241 | the user a normal shell on the remote machine. |
242 | All communication with | |
bf740959 | 243 | the remote command or shell will be automatically encrypted. |
244 | .Pp | |
245 | If a pseudo-terminal has been allocated (normal login session), the | |
df841692 | 246 | user may use the escape characters noted below. |
bf740959 | 247 | .Pp |
248 | If no pseudo tty has been allocated, the | |
249 | session is transparent and can be used to reliably transfer binary | |
610cd5c6 | 250 | data. |
251 | On most systems, setting the escape character to | |
bf740959 | 252 | .Dq none |
253 | will also make the session transparent even if a tty is used. | |
254 | .Pp | |
ce9c0b75 | 255 | The session terminates when the command or shell on the remote |
e91c60f2 | 256 | machine exits and all X11 and TCP/IP connections have been closed. |
bf740959 | 257 | The exit status of the remote program is returned as the exit status |
258 | of | |
259 | .Nm ssh . | |
260 | .Pp | |
df841692 | 261 | .Ss Escape Characters |
262 | .Pp | |
263 | When a pseudo terminal has been requested, ssh supports a number of functions | |
264 | through the use of an escape charater. | |
265 | .Pp | |
266 | A single tilde character can be sent as | |
267 | .Ic ~~ | |
268 | (or by following the tilde by a character other than those described above). | |
269 | The escape character must always follow a newline to be interpreted as | |
270 | special. | |
271 | The escape character can be changed in configuration files using the | |
272 | .Cm EscapeChar | |
273 | configuration directive or on the command line by the | |
274 | .Fl e | |
275 | option. | |
276 | .Pp | |
277 | The supported escapes (assuming the default | |
278 | .Ql ~ ) | |
279 | are: | |
280 | .Bl -tag -width Ds | |
281 | .It Cm ~. | |
282 | Disconnect | |
283 | .It Cm ~^Z | |
284 | Background ssh | |
285 | .It Cm ~# | |
286 | List forwarded connections | |
287 | .It Cm ~& | |
288 | Background ssh at logout when waiting for forwarded connection / X11 sessions | |
289 | to terminate (this does not currently work for SSH protocol version 2) | |
290 | .It Cm ~? | |
291 | Display a list of escape characters | |
292 | .It Cm ~R | |
293 | Request rekeying of connection (only useful for SSH protocol version 2 and if | |
294 | the peer supports it) | |
295 | .El | |
296 | .Pp | |
1d1ffb87 | 297 | .Ss X11 and TCP forwarding |
298 | .Pp | |
bf740959 | 299 | If the user is using X11 (the |
300 | .Ev DISPLAY | |
301 | environment variable is set), the connection to the X11 display is | |
302 | automatically forwarded to the remote side in such a way that any X11 | |
303 | programs started from the shell (or command) will go through the | |
304 | encrypted channel, and the connection to the real X server will be made | |
610cd5c6 | 305 | from the local machine. |
306 | The user should not manually set | |
bf740959 | 307 | .Ev DISPLAY . |
308 | Forwarding of X11 connections can be | |
309 | configured on the command line or in configuration files. | |
310 | .Pp | |
311 | The | |
f54651ce | 312 | .Ev DISPLAY |
bf740959 | 313 | value set by |
314 | .Nm | |
315 | will point to the server machine, but with a display number greater | |
610cd5c6 | 316 | than zero. |
317 | This is normal, and happens because | |
bf740959 | 318 | .Nm |
319 | creates a | |
320 | .Dq proxy | |
321 | X server on the server machine for forwarding the | |
322 | connections over the encrypted channel. | |
323 | .Pp | |
324 | .Nm | |
325 | will also automatically set up Xauthority data on the server machine. | |
326 | For this purpose, it will generate a random authorization cookie, | |
327 | store it in Xauthority on the server, and verify that any forwarded | |
328 | connections carry this cookie and replace it by the real cookie when | |
610cd5c6 | 329 | the connection is opened. |
330 | The real authentication cookie is never | |
bf740959 | 331 | sent to the server machine (and no cookies are sent in the plain). |
332 | .Pp | |
333 | If the user is using an authentication agent, the connection to the agent | |
334 | is automatically forwarded to the remote side unless disabled on | |
335 | command line or in a configuration file. | |
336 | .Pp | |
337 | Forwarding of arbitrary TCP/IP connections over the secure channel can | |
610cd5c6 | 338 | be specified either on command line or in a configuration file. |
339 | One possible application of TCP/IP forwarding is a secure connection to an | |
e91c60f2 | 340 | electronic purse; another is going through firewalls. |
bf740959 | 341 | .Pp |
1d1ffb87 | 342 | .Ss Server authentication |
343 | .Pp | |
bf740959 | 344 | .Nm |
1d1ffb87 | 345 | automatically maintains and checks a database containing |
610cd5c6 | 346 | identifications for all hosts it has ever been used with. |
1d1ffb87 | 347 | RSA host keys are stored in |
348 | .Pa $HOME/.ssh/known_hosts | |
349 | and | |
fa08c86b | 350 | host keys used in the protocol version 2 are stored in |
1d1ffb87 | 351 | .Pa $HOME/.ssh/known_hosts2 |
610cd5c6 | 352 | in the user's home directory. |
1d1ffb87 | 353 | Additionally, the files |
5f4fdfae | 354 | .Pa /etc/ssh_known_hosts |
1d1ffb87 | 355 | and |
356 | .Pa /etc/ssh_known_hosts2 | |
357 | are automatically checked for known hosts. | |
610cd5c6 | 358 | Any new hosts are automatically added to the user's file. |
359 | If a host's identification | |
bf740959 | 360 | ever changes, |
361 | .Nm | |
362 | warns about this and disables password authentication to prevent a | |
610cd5c6 | 363 | trojan horse from getting the user's password. |
364 | Another purpose of | |
bf740959 | 365 | this mechanism is to prevent man-in-the-middle attacks which could |
610cd5c6 | 366 | otherwise be used to circumvent the encryption. |
367 | The | |
bf740959 | 368 | .Cm StrictHostKeyChecking |
369 | option (see below) can be used to prevent logins to machines whose | |
370 | host key is not known or has changed. | |
fa08c86b | 371 | .Pp |
372 | The options are as follows: | |
bf740959 | 373 | .Bl -tag -width Ds |
374 | .It Fl a | |
4fe2af09 | 375 | Disables forwarding of the authentication agent connection. |
71276795 | 376 | .It Fl A |
377 | Enables forwarding of the authentication agent connection. | |
378 | This can also be specified on a per-host basis in a configuration file. | |
bf740959 | 379 | .It Fl c Ar blowfish|3des |
f54651ce | 380 | Selects the cipher to use for encrypting the session. |
bf740959 | 381 | .Ar 3des |
610cd5c6 | 382 | is used by default. |
f54651ce | 383 | It is believed to be secure. |
bf740959 | 384 | .Ar 3des |
385 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
386 | It is presumably more secure than the | |
387 | .Ar des | |
a22aff1f | 388 | cipher which is no longer fully supported in |
d0c832f3 | 389 | .Nm ssh . |
bf740959 | 390 | .Ar blowfish |
391 | is a fast block cipher, it appears very secure and is much faster than | |
610cd5c6 | 392 | .Ar 3des . |
9afadca8 | 393 | .It Fl c Ar cipher_spec |
d0c832f3 | 394 | Additionally, for protocol version 2 a comma-separated list of ciphers can |
94ec8c6b | 395 | be specified in order of preference. |
9afadca8 | 396 | See |
397 | .Cm Ciphers | |
398 | for more information. | |
bf740959 | 399 | .It Fl e Ar ch|^ch|none |
400 | Sets the escape character for sessions with a pty (default: | |
401 | .Ql ~ ) . | |
610cd5c6 | 402 | The escape character is only recognized at the beginning of a line. |
403 | The escape character followed by a dot | |
bf740959 | 404 | .Pq Ql \&. |
405 | closes the connection, followed | |
406 | by control-Z suspends the connection, and followed by itself sends the | |
610cd5c6 | 407 | escape character once. |
408 | Setting the character to | |
bf740959 | 409 | .Dq none |
410 | disables any escapes and makes the session fully transparent. | |
411 | .It Fl f | |
412 | Requests | |
413 | .Nm | |
610cd5c6 | 414 | to go to background just before command execution. |
415 | This is useful if | |
bf740959 | 416 | .Nm |
417 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 418 | wants it in the background. |
f54651ce | 419 | This implies |
bf740959 | 420 | .Fl n . |
421 | The recommended way to start X11 programs at a remote site is with | |
422 | something like | |
423 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 424 | .It Fl g |
425 | Allows remote hosts to connect to local forwarded ports. | |
bf740959 | 426 | .It Fl i Ar identity_file |
f54651ce | 427 | Selects the file from which the identity (private key) for |
fa08c86b | 428 | RSA or DSA authentication is read. |
f54651ce | 429 | Default is |
1d1ffb87 | 430 | .Pa $HOME/.ssh/identity |
610cd5c6 | 431 | in the user's home directory. |
432 | Identity files may also be specified on | |
433 | a per-host basis in the configuration file. | |
434 | It is possible to have multiple | |
bf740959 | 435 | .Fl i |
436 | options (and multiple identities specified in | |
437 | configuration files). | |
bf740959 | 438 | .It Fl k |
4fe2af09 | 439 | Disables forwarding of Kerberos tickets and AFS tokens. |
440 | This may also be specified on a per-host basis in the configuration file. | |
bf740959 | 441 | .It Fl l Ar login_name |
610cd5c6 | 442 | Specifies the user to log in as on the remote machine. |
443 | This also may be specified on a per-host basis in the configuration file. | |
b2552997 | 444 | .It Fl m Ar mac_spec |
445 | Additionally, for protocol version 2 a comma-separated list of MAC | |
446 | (message authentication code) algorithms can | |
447 | be specified in order of preference. | |
448 | See the | |
449 | .Cm MACs | |
450 | keyword for more information. | |
bf740959 | 451 | .It Fl n |
452 | Redirects stdin from | |
453 | .Pa /dev/null | |
454 | (actually, prevents reading from stdin). | |
455 | This must be used when | |
456 | .Nm | |
610cd5c6 | 457 | is run in the background. |
458 | A common trick is to use this to run X11 programs on a remote machine. | |
459 | For example, | |
bf740959 | 460 | .Ic ssh -n shadows.cs.hut.fi emacs & |
461 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
462 | connection will be automatically forwarded over an encrypted channel. | |
463 | The | |
464 | .Nm | |
465 | program will be put in the background. | |
466 | (This does not work if | |
467 | .Nm | |
468 | needs to ask for a password or passphrase; see also the | |
469 | .Fl f | |
470 | option.) | |
0e73cc53 | 471 | .It Fl N |
472 | Do not execute a remote command. | |
0b6fbf03 | 473 | This is useful if you just want to forward ports |
0e73cc53 | 474 | (protocol version 2 only). |
bf740959 | 475 | .It Fl o Ar option |
476 | Can be used to give options in the format used in the config file. | |
477 | This is useful for specifying options for which there is no separate | |
610cd5c6 | 478 | command-line flag. |
479 | The option has the same format as a line in the configuration file. | |
bf740959 | 480 | .It Fl p Ar port |
610cd5c6 | 481 | Port to connect to on the remote host. |
482 | This can be specified on a | |
bf740959 | 483 | per-host basis in the configuration file. |
484 | .It Fl P | |
485 | Use a non-privileged port for outgoing connections. | |
486 | This can be used if your firewall does | |
487 | not permit connections from privileged ports. | |
95f1eccc | 488 | Note that this option turns off |
bf740959 | 489 | .Cm RhostsAuthentication |
490 | and | |
6ffc9c88 | 491 | .Cm RhostsRSAAuthentication |
492 | for older servers. | |
bf740959 | 493 | .It Fl q |
610cd5c6 | 494 | Quiet mode. |
495 | Causes all warning and diagnostic messages to be suppressed. | |
496 | Only fatal errors are displayed. | |
ae810de7 | 497 | .It Fl s |
498 | May be used to request invocation of a subsystem on the remote system. Subsystems are a feature of the SSH2 protocol which facilitate the use | |
499 | of SSH as a secure transport for other application (eg. sftp). The | |
500 | subsystem is specified as the remote command. | |
bf740959 | 501 | .It Fl t |
610cd5c6 | 502 | Force pseudo-tty allocation. |
4fe2af09 | 503 | This can be used to execute arbitrary |
610cd5c6 | 504 | screen-based programs on a remote machine, which can be very useful, |
505 | e.g., when implementing menu services. | |
8abcdba4 | 506 | Multiple |
507 | .Fl t | |
508 | options force tty allocation, even if | |
509 | .Nm | |
510 | has no local tty. | |
0e73cc53 | 511 | .It Fl T |
0b6fbf03 | 512 | Disable pseudo-tty allocation. |
bf740959 | 513 | .It Fl v |
610cd5c6 | 514 | Verbose mode. |
515 | Causes | |
bf740959 | 516 | .Nm |
610cd5c6 | 517 | to print debugging messages about its progress. |
518 | This is helpful in | |
bf740959 | 519 | debugging connection, authentication, and configuration problems. |
8abcdba4 | 520 | Multiple |
521 | .Fl v | |
522 | options increases the verbosity. | |
94ec8c6b | 523 | Maximum is 3. |
bf740959 | 524 | .It Fl x |
610cd5c6 | 525 | Disables X11 forwarding. |
bf740959 | 526 | .It Fl X |
527 | Enables X11 forwarding. | |
71276795 | 528 | This can also be specified on a per-host basis in a configuration file. |
bf740959 | 529 | .It Fl C |
530 | Requests compression of all data (including stdin, stdout, stderr, and | |
610cd5c6 | 531 | data for forwarded X11 and TCP/IP connections). |
532 | The compression algorithm is the same used by | |
7b2ea3a1 | 533 | .Xr gzip 1 , |
534 | and the | |
bf740959 | 535 | .Dq level |
536 | can be controlled by the | |
537 | .Cm CompressionLevel | |
610cd5c6 | 538 | option (see below). |
539 | Compression is desirable on modem lines and other | |
bf740959 | 540 | slow connections, but will only slow down things on fast networks. |
541 | The default value can be set on a host-by-host basis in the | |
542 | configuration files; see the | |
543 | .Cm Compress | |
544 | option below. | |
545 | .It Fl L Ar port:host:hostport | |
546 | Specifies that the given port on the local (client) host is to be | |
610cd5c6 | 547 | forwarded to the given host and port on the remote side. |
548 | This works by allocating a socket to listen to | |
bf740959 | 549 | .Ar port |
550 | on the local side, and whenever a connection is made to this port, the | |
551 | connection is forwarded over the secure channel, and a connection is | |
552 | made to | |
48e671d5 | 553 | .Ar host |
554 | port | |
555 | .Ar hostport | |
610cd5c6 | 556 | from the remote machine. |
557 | Port forwardings can also be specified in the configuration file. | |
558 | Only root can forward privileged ports. | |
48e671d5 | 559 | IPv6 addresses can be specified with an alternative syntax: |
560 | .Ar port/host/hostport | |
bf740959 | 561 | .It Fl R Ar port:host:hostport |
562 | Specifies that the given port on the remote (server) host is to be | |
610cd5c6 | 563 | forwarded to the given host and port on the local side. |
564 | This works by allocating a socket to listen to | |
bf740959 | 565 | .Ar port |
566 | on the remote side, and whenever a connection is made to this port, the | |
567 | connection is forwarded over the secure channel, and a connection is | |
568 | made to | |
48e671d5 | 569 | .Ar host |
570 | port | |
571 | .Ar hostport | |
610cd5c6 | 572 | from the local machine. |
573 | Port forwardings can also be specified in the configuration file. | |
574 | Privileged ports can be forwarded only when | |
bf740959 | 575 | logging in as root on the remote machine. |
9afadca8 | 576 | .It Fl 1 |
577 | Forces | |
578 | .Nm | |
579 | to try protocol version 1 only. | |
6ae2364d | 580 | .It Fl 2 |
581 | Forces | |
582 | .Nm | |
1d1ffb87 | 583 | to try protocol version 2 only. |
48e671d5 | 584 | .It Fl 4 |
585 | Forces | |
586 | .Nm | |
587 | to use IPv4 addresses only. | |
588 | .It Fl 6 | |
589 | Forces | |
590 | .Nm | |
591 | to use IPv6 addresses only. | |
bf740959 | 592 | .El |
593 | .Sh CONFIGURATION FILES | |
594 | .Nm | |
595 | obtains configuration data from the following sources (in this order): | |
596 | command line options, user's configuration file | |
597 | .Pq Pa $HOME/.ssh/config , | |
598 | and system-wide configuration file | |
5f4fdfae | 599 | .Pq Pa /etc/ssh_config . |
bf740959 | 600 | For each parameter, the first obtained value |
610cd5c6 | 601 | will be used. |
602 | The configuration files contain sections bracketed by | |
603 | .Dq Host | |
604 | specifications, and that section is only applied for hosts that | |
605 | match one of the patterns given in the specification. | |
606 | The matched host name is the one given on the command line. | |
bf740959 | 607 | .Pp |
608 | Since the first obtained value for each parameter is used, more | |
609 | host-specific declarations should be given near the beginning of the | |
610 | file, and general defaults at the end. | |
611 | .Pp | |
612 | The configuration file has the following format: | |
613 | .Pp | |
614 | Empty lines and lines starting with | |
615 | .Ql # | |
616 | are comments. | |
617 | .Pp | |
618 | Otherwise a line is of the format | |
619 | .Dq keyword arguments . | |
620 | The possible | |
621 | keywords and their meanings are as follows (note that the | |
622 | configuration files are case-sensitive): | |
623 | .Bl -tag -width Ds | |
624 | .It Cm Host | |
625 | Restricts the following declarations (up to the next | |
626 | .Cm Host | |
627 | keyword) to be only for those hosts that match one of the patterns | |
628 | given after the keyword. | |
629 | .Ql \&* | |
630 | and | |
631 | .Ql ? | |
632 | can be used as wildcards in the | |
610cd5c6 | 633 | patterns. |
634 | A single | |
bf740959 | 635 | .Ql \&* |
636 | as a pattern can be used to provide global | |
610cd5c6 | 637 | defaults for all hosts. |
638 | The host is the | |
bf740959 | 639 | .Ar hostname |
640 | argument given on the command line (i.e., the name is not converted to | |
641 | a canonicalized host name before matching). | |
642 | .It Cm AFSTokenPassing | |
4fe2af09 | 643 | Specifies whether to pass AFS tokens to remote host. |
644 | The argument to this keyword must be | |
bf740959 | 645 | .Dq yes |
646 | or | |
647 | .Dq no . | |
648 | .It Cm BatchMode | |
649 | If set to | |
650 | .Dq yes , | |
610cd5c6 | 651 | passphrase/password querying will be disabled. |
652 | This option is useful in scripts and other batch jobs where you have no | |
653 | user to supply the password. | |
654 | The argument must be | |
bf740959 | 655 | .Dq yes |
656 | or | |
657 | .Dq no . | |
01ce749f | 658 | The default is |
659 | .Dq no . | |
7b2ea3a1 | 660 | .It Cm CheckHostIP |
661 | If this flag is set to | |
662 | .Dq yes , | |
01ce749f | 663 | ssh will additionally check the host IP address in the |
7b2ea3a1 | 664 | .Pa known_hosts |
4fe2af09 | 665 | file. |
666 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
7b2ea3a1 | 667 | If the option is set to |
668 | .Dq no , | |
669 | the check will not be executed. | |
01ce749f | 670 | The default is |
671 | .Dq yes . | |
bf740959 | 672 | .It Cm Cipher |
33de75a3 | 673 | Specifies the cipher to use for encrypting the session |
a22aff1f | 674 | in protocol version 1. |
610cd5c6 | 675 | Currently, |
a22aff1f | 676 | .Dq blowfish |
bf740959 | 677 | and |
678 | .Dq 3des | |
610cd5c6 | 679 | are supported. |
680 | The default is | |
bf740959 | 681 | .Dq 3des . |
f54651ce | 682 | .It Cm Ciphers |
683 | Specifies the ciphers allowed for protocol version 2 | |
684 | in order of preference. | |
685 | Multiple ciphers must be comma-separated. | |
686 | The default is | |
9afadca8 | 687 | .Pp |
688 | .Bd -literal | |
f2ba0775 | 689 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour, |
9afadca8 | 690 | aes192-cbc,aes256-cbc,rijndael128-cbc,rijndael192-cbc, |
691 | rijndael256-cbc,rijndael-cbc@lysator.liu.se'' | |
692 | .Ed | |
bf740959 | 693 | .It Cm Compression |
610cd5c6 | 694 | Specifies whether to use compression. |
695 | The argument must be | |
bf740959 | 696 | .Dq yes |
697 | or | |
698 | .Dq no . | |
01ce749f | 699 | The default is |
700 | .Dq no . | |
bf740959 | 701 | .It Cm CompressionLevel |
01ce749f | 702 | Specifies the compression level to use if compression is enabled. |
610cd5c6 | 703 | The argument must be an integer from 1 (fast) to 9 (slow, best). |
704 | The default level is 6, which is good for most applications. | |
705 | The meaning of the values is the same as in | |
7b2ea3a1 | 706 | .Xr gzip 1 . |
bf740959 | 707 | .It Cm ConnectionAttempts |
708 | Specifies the number of tries (one per second) to make before falling | |
610cd5c6 | 709 | back to rsh or exiting. |
710 | The argument must be an integer. | |
711 | This may be useful in scripts if the connection sometimes fails. | |
01ce749f | 712 | The default is 4. |
fa08c86b | 713 | .It Cm PubkeyAuthentication |
714 | Specifies whether to try public key authentication. | |
1d1ffb87 | 715 | The argument to this keyword must be |
716 | .Dq yes | |
717 | or | |
718 | .Dq no . | |
01ce749f | 719 | The default is |
720 | .Dq yes . | |
1d1ffb87 | 721 | Note that this option applies to protocol version 2 only. |
bf740959 | 722 | .It Cm EscapeChar |
723 | Sets the escape character (default: | |
724 | .Ql ~ ) . | |
725 | The escape character can also | |
610cd5c6 | 726 | be set on the command line. |
727 | The argument should be a single character, | |
bf740959 | 728 | .Ql ^ |
729 | followed by a letter, or | |
730 | .Dq none | |
731 | to disable the escape | |
732 | character entirely (making the connection transparent for binary | |
733 | data). | |
f54651ce | 734 | .It Cm FallBackToRsh |
bf740959 | 735 | Specifies that if connecting via |
736 | .Nm | |
737 | fails due to a connection refused error (there is no | |
738 | .Xr sshd 8 | |
f54651ce | 739 | listening on the remote host), |
bf740959 | 740 | .Xr rsh 1 |
741 | should automatically be used instead (after a suitable warning about | |
610cd5c6 | 742 | the session being unencrypted). |
743 | The argument must be | |
bf740959 | 744 | .Dq yes |
745 | or | |
746 | .Dq no . | |
01ce749f | 747 | The default is |
748 | .Dq no . | |
bf740959 | 749 | .It Cm ForwardAgent |
750 | Specifies whether the connection to the authentication agent (if any) | |
610cd5c6 | 751 | will be forwarded to the remote machine. |
752 | The argument must be | |
bf740959 | 753 | .Dq yes |
754 | or | |
755 | .Dq no . | |
71276795 | 756 | The default is |
757 | .Dq no . | |
bf740959 | 758 | .It Cm ForwardX11 |
759 | Specifies whether X11 connections will be automatically redirected | |
f54651ce | 760 | over the secure channel and |
bf740959 | 761 | .Ev DISPLAY |
610cd5c6 | 762 | set. |
f54651ce | 763 | The argument must be |
bf740959 | 764 | .Dq yes |
765 | or | |
766 | .Dq no . | |
c8d54615 | 767 | The default is |
768 | .Dq no . | |
bf740959 | 769 | .It Cm GatewayPorts |
770 | Specifies whether remote hosts are allowed to connect to local | |
771 | forwarded ports. | |
772 | The argument must be | |
773 | .Dq yes | |
774 | or | |
775 | .Dq no . | |
776 | The default is | |
777 | .Dq no . | |
778 | .It Cm GlobalKnownHostsFile | |
a5df12e9 | 779 | Specifies a file to use for the protocol version 1 global |
780 | host key database instead of | |
5f4fdfae | 781 | .Pa /etc/ssh_known_hosts . |
a5df12e9 | 782 | .It Cm GlobalKnownHostsFile2 |
783 | Specifies a file to use for the protocol version 2 global | |
784 | host key database instead of | |
785 | .Pa /etc/ssh_known_hosts2 . | |
8abcdba4 | 786 | .It Cm HostKeyAlias |
787 | Specifies an alias that should be used instead of the | |
788 | real host name when looking up or saving the host key | |
61e96248 | 789 | in the known_hosts files. |
790 | This option is useful for tunneling ssh connections | |
8abcdba4 | 791 | or if you have multiple servers running on a single host. |
e961a8f9 | 792 | .It Cm HostKeyAlgorithms |
793 | Specfies the protocol version 2 host key algorithms | |
794 | that the client wants to use in order of preference. | |
795 | The default for this option is: | |
796 | .Dq ssh-rsa,ssh-dss | |
bf740959 | 797 | .It Cm HostName |
610cd5c6 | 798 | Specifies the real host name to log into. |
799 | This can be used to specify nicknames or abbreviations for hosts. | |
800 | Default is the name given on the command line. | |
801 | Numeric IP addresses are also permitted (both on the command line and in | |
bf740959 | 802 | .Cm HostName |
803 | specifications). | |
804 | .It Cm IdentityFile | |
805 | Specifies the file from which the user's RSA authentication identity | |
806 | is read (default | |
1d1ffb87 | 807 | .Pa $HOME/.ssh/identity |
bf740959 | 808 | in the user's home directory). |
809 | Additionally, any identities represented by the authentication agent | |
610cd5c6 | 810 | will be used for authentication. |
811 | The file name may use the tilde | |
812 | syntax to refer to a user's home directory. | |
813 | It is possible to have | |
bf740959 | 814 | multiple identity files specified in configuration files; all these |
815 | identities will be tried in sequence. | |
816 | .It Cm KeepAlive | |
817 | Specifies whether the system should send keepalive messages to the | |
610cd5c6 | 818 | other side. |
819 | If they are sent, death of the connection or crash of one | |
820 | of the machines will be properly noticed. | |
821 | However, this means that | |
bf740959 | 822 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 823 | find it annoying. |
bf740959 | 824 | .Pp |
825 | The default is | |
826 | .Dq yes | |
827 | (to send keepalives), and the client will notice | |
610cd5c6 | 828 | if the network goes down or the remote host dies. |
829 | This is important in scripts, and many users want it too. | |
bf740959 | 830 | .Pp |
831 | To disable keepalives, the value should be set to | |
832 | .Dq no | |
833 | in both the server and the client configuration files. | |
834 | .It Cm KerberosAuthentication | |
4fe2af09 | 835 | Specifies whether Kerberos authentication will be used. |
836 | The argument to this keyword must be | |
bf740959 | 837 | .Dq yes |
838 | or | |
839 | .Dq no . | |
840 | .It Cm KerberosTgtPassing | |
4fe2af09 | 841 | Specifies whether a Kerberos TGT will be forwarded to the server. |
842 | This will only work if the Kerberos server is actually an AFS kaserver. | |
843 | The argument to this keyword must be | |
bf740959 | 844 | .Dq yes |
845 | or | |
846 | .Dq no . | |
847 | .It Cm LocalForward | |
848 | Specifies that a TCP/IP port on the local machine be forwarded over | |
610cd5c6 | 849 | the secure channel to given host:port from the remote machine. |
850 | The first argument must be a port number, and the second must be | |
851 | host:port. | |
852 | Multiple forwardings may be specified, and additional | |
853 | forwardings can be given on the command line. | |
854 | Only the superuser can forward privileged ports. | |
6a17f9c2 | 855 | .It Cm LogLevel |
856 | Gives the verbosity level that is used when logging messages from | |
857 | .Nm ssh . | |
858 | The possible values are: | |
59c97189 | 859 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
860 | The default is INFO. | |
b2552997 | 861 | .It Cm MACs |
862 | Specifies the MAC (message authentication code) algorithms | |
863 | in order of preference. | |
864 | The MAC algorithm is used in protocol version 2 | |
865 | for data integrity protection. | |
866 | Multiple algorithms must be comma-separated. | |
867 | The default is | |
868 | .Pp | |
869 | .Bd -literal | |
f2ba0775 | 870 | ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com, |
b2552997 | 871 | hmac-sha1-96,hmac-md5-96'' |
872 | .Ed | |
bf740959 | 873 | .It Cm NumberOfPasswordPrompts |
4fe2af09 | 874 | Specifies the number of password prompts before giving up. |
875 | The argument to this keyword must be an integer. | |
876 | Default is 3. | |
7b2ea3a1 | 877 | .It Cm PasswordAuthentication |
610cd5c6 | 878 | Specifies whether to use password authentication. |
879 | The argument to this keyword must be | |
7b2ea3a1 | 880 | .Dq yes |
881 | or | |
882 | .Dq no . | |
01ce749f | 883 | The default is |
884 | .Dq yes . | |
1d1ffb87 | 885 | Note that this option applies to both protocol version 1 and 2. |
bf740959 | 886 | .It Cm Port |
610cd5c6 | 887 | Specifies the port number to connect on the remote host. |
888 | Default is 22. | |
babd91d4 | 889 | .It Cm PreferredAuthentications |
890 | Specifies the order in which the client should try protocol 2 | |
891 | authentication methods. This allows a client to prefer one method (e.g. | |
892 | .Cm keyboard-interactive ) | |
893 | over another method (e.g. | |
894 | .Cm password ) | |
895 | The default for this option is: | |
896 | .Dq publickey, password, keyboard-interactive | |
f54651ce | 897 | .It Cm Protocol |
898 | Specifies the protocol versions | |
899 | .Nm | |
900 | should support in order of preference. | |
901 | The possible values are | |
902 | .Dq 1 | |
903 | and | |
904 | .Dq 2 . | |
905 | Multiple versions must be comma-separated. | |
906 | The default is | |
b4a19d21 | 907 | .Dq 2,1 . |
1d1ffb87 | 908 | This means that |
909 | .Nm | |
b4a19d21 | 910 | tries version 2 and falls back to version 1 |
911 | if version 2 is not available. | |
bf740959 | 912 | .It Cm ProxyCommand |
610cd5c6 | 913 | Specifies the command to use to connect to the server. |
914 | The command | |
915 | string extends to the end of the line, and is executed with | |
916 | .Pa /bin/sh . | |
917 | In the command string, | |
918 | .Ql %h | |
919 | will be substituted by the host name to | |
920 | connect and | |
921 | .Ql %p | |
922 | by the port. | |
923 | The command can be basically anything, | |
924 | and should read from its standard input and write to its standard output. | |
925 | It should eventually connect an | |
bf740959 | 926 | .Xr sshd 8 |
927 | server running on some machine, or execute | |
928 | .Ic sshd -i | |
610cd5c6 | 929 | somewhere. |
930 | Host key management will be done using the | |
bf740959 | 931 | HostName of the host being connected (defaulting to the name typed by |
932 | the user). | |
57112b5a | 933 | Note that |
934 | .Cm CheckHostIP | |
935 | is not available for connects with a proxy command. | |
bf740959 | 936 | .Pp |
937 | .It Cm RemoteForward | |
938 | Specifies that a TCP/IP port on the remote machine be forwarded over | |
610cd5c6 | 939 | the secure channel to given host:port from the local machine. |
940 | The first argument must be a port number, and the second must be | |
941 | host:port. | |
942 | Multiple forwardings may be specified, and additional | |
943 | forwardings can be given on the command line. | |
944 | Only the superuser can forward privileged ports. | |
bf740959 | 945 | .It Cm RhostsAuthentication |
610cd5c6 | 946 | Specifies whether to try rhosts based authentication. |
947 | Note that this | |
bf740959 | 948 | declaration only affects the client side and has no effect whatsoever |
610cd5c6 | 949 | on security. |
950 | Disabling rhosts authentication may reduce | |
bf740959 | 951 | authentication time on slow connections when rhosts authentication is |
610cd5c6 | 952 | not used. |
953 | Most servers do not permit RhostsAuthentication because it | |
954 | is not secure (see RhostsRSAAuthentication). | |
955 | The argument to this keyword must be | |
bf740959 | 956 | .Dq yes |
957 | or | |
958 | .Dq no . | |
01ce749f | 959 | The default is |
960 | .Dq yes . | |
bf740959 | 961 | .It Cm RhostsRSAAuthentication |
962 | Specifies whether to try rhosts based authentication with RSA host | |
610cd5c6 | 963 | authentication. |
610cd5c6 | 964 | The argument must be |
bf740959 | 965 | .Dq yes |
966 | or | |
967 | .Dq no . | |
01ce749f | 968 | The default is |
969 | .Dq yes . | |
bf740959 | 970 | .It Cm RSAAuthentication |
610cd5c6 | 971 | Specifies whether to try RSA authentication. |
972 | The argument to this keyword must be | |
bf740959 | 973 | .Dq yes |
974 | or | |
975 | .Dq no . | |
976 | RSA authentication will only be | |
977 | attempted if the identity file exists, or an authentication agent is | |
978 | running. | |
01ce749f | 979 | The default is |
980 | .Dq yes . | |
1d1ffb87 | 981 | Note that this option applies to protocol version 1 only. |
61e96248 | 982 | .It Cm ChallengeResponseAuthentication |
983 | Specifies whether to use challenge response authentication. | |
984 | Currently there is only support for | |
5260325f | 985 | .Xr skey 1 |
610cd5c6 | 986 | authentication. |
987 | The argument to this keyword must be | |
5260325f | 988 | .Dq yes |
989 | or | |
990 | .Dq no . | |
991 | The default is | |
992 | .Dq no . | |
bf740959 | 993 | .It Cm StrictHostKeyChecking |
994 | If this flag is set to | |
f54651ce | 995 | .Dq yes , |
bf740959 | 996 | .Nm |
a877488a | 997 | will never automatically add host keys to the |
bf740959 | 998 | .Pa $HOME/.ssh/known_hosts |
1d1ffb87 | 999 | and |
1000 | .Pa $HOME/.ssh/known_hosts2 | |
a877488a | 1001 | files, and refuses to connect to hosts whose host key has changed. |
610cd5c6 | 1002 | This provides maximum protection against trojan horse attacks. |
1003 | However, it can be somewhat annoying if you don't have good | |
5f4fdfae | 1004 | .Pa /etc/ssh_known_hosts |
1d1ffb87 | 1005 | and |
1006 | .Pa /etc/ssh_known_hosts2 | |
bf740959 | 1007 | files installed and frequently |
a877488a | 1008 | connect to new hosts. |
1009 | This option forces the user to manually | |
1010 | add all new hosts. | |
1011 | If this flag is set to | |
1012 | .Dq no , | |
1013 | .Nm | |
1014 | will automatically add new host keys to the | |
1015 | user known hosts files. | |
1016 | If this flag is set to | |
1017 | .Dq ask , | |
1018 | new host keys | |
1019 | will be added to the user known host files only after the user | |
1020 | has confirmed that is what they really want to do, and | |
1021 | .Nm | |
1022 | will refuse to connect to hosts whose host key has changed. | |
610cd5c6 | 1023 | The host keys of |
a877488a | 1024 | known hosts will be verified automatically in all cases. |
610cd5c6 | 1025 | The argument must be |
a877488a | 1026 | .Dq yes , |
1027 | .Dq no | |
bf740959 | 1028 | or |
a877488a | 1029 | .Dq ask . |
1030 | The default is | |
1031 | .Dq ask . | |
bf740959 | 1032 | .It Cm UsePrivilegedPort |
1033 | Specifies whether to use a privileged port for outgoing connections. | |
1034 | The argument must be | |
1035 | .Dq yes | |
1036 | or | |
1037 | .Dq no . | |
1038 | The default is | |
d5ebca2b | 1039 | .Dq no . |
bf740959 | 1040 | Note that setting this option to |
1041 | .Dq no | |
95f1eccc | 1042 | turns off |
bf740959 | 1043 | .Cm RhostsAuthentication |
1044 | and | |
6ffc9c88 | 1045 | .Cm RhostsRSAAuthentication |
1046 | for older servers. | |
7b2ea3a1 | 1047 | .It Cm User |
610cd5c6 | 1048 | Specifies the user to log in as. |
1049 | This can be useful if you have a different user name on different machines. | |
1050 | This saves the trouble of | |
7b2ea3a1 | 1051 | having to remember to give the user name on the command line. |
1052 | .It Cm UserKnownHostsFile | |
a5df12e9 | 1053 | Specifies a file to use for the protocol version 1 user |
1054 | host key database instead of | |
7b2ea3a1 | 1055 | .Pa $HOME/.ssh/known_hosts . |
a5df12e9 | 1056 | .It Cm UserKnownHostsFile2 |
1057 | Specifies a file to use for the protocol version 2 user | |
1058 | host key database instead of | |
1059 | .Pa $HOME/.ssh/known_hosts2 . | |
bf740959 | 1060 | .It Cm UseRsh |
610cd5c6 | 1061 | Specifies that rlogin/rsh should be used for this host. |
1062 | It is possible that the host does not at all support the | |
bf740959 | 1063 | .Nm |
610cd5c6 | 1064 | protocol. |
1065 | This causes | |
bf740959 | 1066 | .Nm |
610cd5c6 | 1067 | to immediately execute |
bf740959 | 1068 | .Xr rsh 1 . |
1069 | All other options (except | |
1070 | .Cm HostName ) | |
610cd5c6 | 1071 | are ignored if this has been specified. |
1072 | The argument must be | |
bf740959 | 1073 | .Dq yes |
1074 | or | |
1075 | .Dq no . | |
fa649821 | 1076 | .It Cm XAuthLocation |
1077 | Specifies the location of the | |
1078 | .Xr xauth 1 | |
1079 | program. | |
1080 | The default is | |
1081 | .Pa /usr/X11R6/bin/xauth . | |
b5e300c2 | 1082 | .El |
bf740959 | 1083 | .Sh ENVIRONMENT |
1084 | .Nm | |
1085 | will normally set the following environment variables: | |
1086 | .Bl -tag -width Ds | |
1087 | .It Ev DISPLAY | |
1088 | The | |
1089 | .Ev DISPLAY | |
610cd5c6 | 1090 | variable indicates the location of the X11 server. |
f54651ce | 1091 | It is automatically set by |
bf740959 | 1092 | .Nm |
1093 | to point to a value of the form | |
1094 | .Dq hostname:n | |
1095 | where hostname indicates | |
610cd5c6 | 1096 | the host where the shell runs, and n is an integer >= 1. |
1097 | .Nm | |
1098 | uses this special value to forward X11 connections over the secure | |
1099 | channel. | |
1100 | The user should normally not set DISPLAY explicitly, as that | |
bf740959 | 1101 | will render the X11 connection insecure (and will require the user to |
1102 | manually copy any required authorization cookies). | |
1103 | .It Ev HOME | |
1104 | Set to the path of the user's home directory. | |
1105 | .It Ev LOGNAME | |
1106 | Synonym for | |
1107 | .Ev USER ; | |
1108 | set for compatibility with systems that use this variable. | |
1109 | .It Ev MAIL | |
1110 | Set to point the user's mailbox. | |
610cd5c6 | 1111 | .It Ev PATH |
bf740959 | 1112 | Set to the default |
1113 | .Ev PATH , | |
1114 | as specified when compiling | |
1115 | .Nm ssh . | |
1116 | .It Ev SSH_AUTH_SOCK | |
1117 | indicates the path of a unix-domain socket used to communicate with the | |
1118 | agent. | |
1119 | .It Ev SSH_CLIENT | |
610cd5c6 | 1120 | Identifies the client end of the connection. |
1121 | The variable contains | |
bf740959 | 1122 | three space-separated values: client ip-address, client port number, |
1123 | and server port number. | |
8abcdba4 | 1124 | .It Ev SSH_ORIGINAL_COMMAND |
1125 | The variable contains the original command line if a forced command | |
1126 | is executed. | |
1127 | It can be used to extract the original arguments. | |
bf740959 | 1128 | .It Ev SSH_TTY |
1129 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 1130 | with the current shell or command. |
1131 | If the current session has no tty, | |
bf740959 | 1132 | this variable is not set. |
1133 | .It Ev TZ | |
1134 | The timezone variable is set to indicate the present timezone if it | |
c345cf9d | 1135 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 1136 | on to new connections). |
1137 | .It Ev USER | |
1138 | Set to the name of the user logging in. | |
1139 | .El | |
1140 | .Pp | |
f54651ce | 1141 | Additionally, |
bf740959 | 1142 | .Nm |
f54651ce | 1143 | reads |
1144 | .Pa $HOME/.ssh/environment , | |
bf740959 | 1145 | and adds lines of the format |
1146 | .Dq VARNAME=value | |
1147 | to the environment. | |
1148 | .Sh FILES | |
c8d54615 | 1149 | .Bl -tag -width Ds |
a5df12e9 | 1150 | .It Pa $HOME/.ssh/known_hosts, $HOME/.ssh/known_hosts2 |
bf740959 | 1151 | Records host keys for all hosts the user has logged into (that are not |
1152 | in | |
a5df12e9 | 1153 | .Pa /etc/ssh_known_hosts |
1154 | for protocol version 1 or | |
1155 | .Pa /etc/ssh_known_hosts2 | |
1156 | for protocol version 2). | |
bf740959 | 1157 | See |
1158 | .Xr sshd 8 . | |
c0ecc314 | 1159 | .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa |
1160 | Contains the authentication identity of the user. | |
1161 | They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. | |
1d1ffb87 | 1162 | These files |
1163 | contain sensitive data and should be readable by the user but not | |
bf740959 | 1164 | accessible by others (read/write/execute). |
1165 | Note that | |
1166 | .Nm | |
1d1ffb87 | 1167 | ignores a private key file if it is accessible by others. |
bf740959 | 1168 | It is possible to specify a passphrase when |
1169 | generating the key; the passphrase will be used to encrypt the | |
1170 | sensitive part of this file using 3DES. | |
c0ecc314 | 1171 | .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub |
bf740959 | 1172 | Contains the public key for authentication (public part of the |
610cd5c6 | 1173 | identity file in human-readable form). |
1d1ffb87 | 1174 | The contents of the |
1175 | .Pa $HOME/.ssh/identity.pub | |
1176 | file should be added to | |
bf740959 | 1177 | .Pa $HOME/.ssh/authorized_keys |
1178 | on all machines | |
c0ecc314 | 1179 | where you wish to log in using protocol version 1 RSA authentication. |
1d1ffb87 | 1180 | The contents of the |
1181 | .Pa $HOME/.ssh/id_dsa.pub | |
c0ecc314 | 1182 | and |
1183 | .Pa $HOME/.ssh/id_rsa.pub | |
1d1ffb87 | 1184 | file should be added to |
1185 | .Pa $HOME/.ssh/authorized_keys2 | |
1186 | on all machines | |
c0ecc314 | 1187 | where you wish to log in using protocol version 2 DSA/RSA authentication. |
1d1ffb87 | 1188 | These files are not |
610cd5c6 | 1189 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 1190 | These files are |
c44559d2 | 1191 | never used automatically and are not necessary; they are only provided for |
bf740959 | 1192 | the convenience of the user. |
1193 | .It Pa $HOME/.ssh/config | |
610cd5c6 | 1194 | This is the per-user configuration file. |
1195 | The format of this file is described above. | |
1196 | This file is used by the | |
bf740959 | 1197 | .Nm |
610cd5c6 | 1198 | client. |
1199 | This file does not usually contain any sensitive information, | |
bf740959 | 1200 | but the recommended permissions are read/write for the user, and not |
1201 | accessible by others. | |
1202 | .It Pa $HOME/.ssh/authorized_keys | |
610cd5c6 | 1203 | Lists the RSA keys that can be used for logging in as this user. |
1204 | The format of this file is described in the | |
bf740959 | 1205 | .Xr sshd 8 |
610cd5c6 | 1206 | manual page. |
1207 | In the simplest form the format is the same as the .pub | |
bf740959 | 1208 | identity files (that is, each line contains the number of bits in |
1209 | modulus, public exponent, modulus, and comment fields, separated by | |
610cd5c6 | 1210 | spaces). |
1211 | This file is not highly sensitive, but the recommended | |
bf740959 | 1212 | permissions are read/write for the user, and not accessible by others. |
1d1ffb87 | 1213 | .It Pa $HOME/.ssh/authorized_keys2 |
fa08c86b | 1214 | Lists the public keys (DSA/RSA) that can be used for logging in as this user. |
1d1ffb87 | 1215 | This file is not highly sensitive, but the recommended |
1216 | permissions are read/write for the user, and not accessible by others. | |
1217 | .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2 | |
610cd5c6 | 1218 | Systemwide list of known host keys. |
1d1ffb87 | 1219 | .Pa /etc/ssh_known_hosts |
1220 | contains RSA and | |
1221 | .Pa /etc/ssh_known_hosts2 | |
fa08c86b | 1222 | contains DSA or RSA keys for protocol version 2. |
1d1ffb87 | 1223 | These files should be prepared by the |
bf740959 | 1224 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1225 | organization. |
1226 | This file should be world-readable. | |
1227 | This file contains | |
bf740959 | 1228 | public keys, one per line, in the following format (fields separated |
1229 | by spaces): system name, number of bits in modulus, public exponent, | |
610cd5c6 | 1230 | modulus, and optional comment field. |
1231 | When different names are used | |
bf740959 | 1232 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1233 | commas. |
1234 | The format is described on the | |
bf740959 | 1235 | .Xr sshd 8 |
1236 | manual page. | |
1237 | .Pp | |
1238 | The canonical system name (as returned by name servers) is used by | |
1239 | .Xr sshd 8 | |
1240 | to verify the client host when logging in; other names are needed because | |
1241 | .Nm | |
1242 | does not convert the user-supplied name to a canonical name before | |
1243 | checking the key, because someone with access to the name servers | |
1244 | would then be able to fool host authentication. | |
5f4fdfae | 1245 | .It Pa /etc/ssh_config |
610cd5c6 | 1246 | Systemwide configuration file. |
1247 | This file provides defaults for those | |
bf740959 | 1248 | values that are not specified in the user's configuration file, and |
610cd5c6 | 1249 | for those users who do not have a configuration file. |
1250 | This file must be world-readable. | |
bf740959 | 1251 | .It Pa $HOME/.rhosts |
1252 | This file is used in | |
1253 | .Pa \&.rhosts | |
1254 | authentication to list the | |
610cd5c6 | 1255 | host/user pairs that are permitted to log in. |
1256 | (Note that this file is | |
bf740959 | 1257 | also used by rlogin and rsh, which makes using this file insecure.) |
1258 | Each line of the file contains a host name (in the canonical form | |
1259 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1260 | separated by a space. |
e91c60f2 | 1261 | On some machines this file may need to be |
bf740959 | 1262 | world-readable if the user's home directory is on a NFS partition, |
1263 | because | |
1264 | .Xr sshd 8 | |
610cd5c6 | 1265 | reads it as root. |
1266 | Additionally, this file must be owned by the user, | |
1267 | and must not have write permissions for anyone else. | |
1268 | The recommended | |
bf740959 | 1269 | permission for most machines is read/write for the user, and not |
1270 | accessible by others. | |
1271 | .Pp | |
1272 | Note that by default | |
1273 | .Xr sshd 8 | |
1274 | will be installed so that it requires successful RSA host | |
610cd5c6 | 1275 | authentication before permitting \s+2.\s0rhosts authentication. |
1276 | If your server machine does not have the client's host key in | |
5f4fdfae | 1277 | .Pa /etc/ssh_known_hosts , |
bf740959 | 1278 | you can store it in |
1279 | .Pa $HOME/.ssh/known_hosts . | |
1280 | The easiest way to do this is to | |
1281 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1282 | will automatically add the host key to |
bf740959 | 1283 | .Pa $HOME/.ssh/known_hosts . |
1284 | .It Pa $HOME/.shosts | |
1285 | This file is used exactly the same way as | |
1286 | .Pa \&.rhosts . | |
1287 | The purpose for | |
1288 | having this file is to be able to use rhosts authentication with | |
1289 | .Nm | |
1290 | without permitting login with | |
1291 | .Xr rlogin 1 | |
1292 | or | |
1293 | .Xr rsh 1 . | |
1294 | .It Pa /etc/hosts.equiv | |
1295 | This file is used during | |
610cd5c6 | 1296 | .Pa \&.rhosts authentication. |
1297 | It contains | |
bf740959 | 1298 | canonical hosts names, one per line (the full format is described on |
1299 | the | |
1300 | .Xr sshd 8 | |
610cd5c6 | 1301 | manual page). |
1302 | If the client host is found in this file, login is | |
bf740959 | 1303 | automatically permitted provided client and server user names are the |
610cd5c6 | 1304 | same. |
1305 | Additionally, successful RSA host authentication is normally | |
1306 | required. | |
1307 | This file should only be writable by root. | |
5f4fdfae | 1308 | .It Pa /etc/shosts.equiv |
f54651ce | 1309 | This file is processed exactly as |
bf740959 | 1310 | .Pa /etc/hosts.equiv . |
1311 | This file may be useful to permit logins using | |
1312 | .Nm | |
1313 | but not using rsh/rlogin. | |
5f4fdfae | 1314 | .It Pa /etc/sshrc |
bf740959 | 1315 | Commands in this file are executed by |
1316 | .Nm | |
1317 | when the user logs in just before the user's shell (or command) is started. | |
1318 | See the | |
1319 | .Xr sshd 8 | |
1320 | manual page for more information. | |
1321 | .It Pa $HOME/.ssh/rc | |
1322 | Commands in this file are executed by | |
1323 | .Nm | |
1324 | when the user logs in just before the user's shell (or command) is | |
1325 | started. | |
f54651ce | 1326 | See the |
bf740959 | 1327 | .Xr sshd 8 |
1328 | manual page for more information. | |
83b7f649 | 1329 | .It Pa $HOME/.ssh/environment |
1330 | Contains additional definitions for environment variables, see section | |
1331 | .Sx ENVIRONMENT | |
1332 | above. | |
b5e300c2 | 1333 | .El |
fa08c86b | 1334 | .Sh AUTHORS |
5fb622e4 | 1335 | OpenSSH is a derivative of the original and free |
1336 | ssh 1.2.12 release by Tatu Ylonen. | |
1337 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1338 | Theo de Raadt and Dug Song | |
1339 | removed many bugs, re-added newer features and | |
1340 | created OpenSSH. | |
1341 | Markus Friedl contributed the support for SSH | |
1342 | protocol versions 1.5 and 2.0. | |
bf740959 | 1343 | .Sh SEE ALSO |
1344 | .Xr rlogin 1 , | |
1345 | .Xr rsh 1 , | |
1346 | .Xr scp 1 , | |
61e96248 | 1347 | .Xr sftp 1 , |
bf740959 | 1348 | .Xr ssh-add 1 , |
1349 | .Xr ssh-agent 1 , | |
1350 | .Xr ssh-keygen 1 , | |
1351 | .Xr telnet 1 , | |
9afadca8 | 1352 | .Xr sshd 8 |