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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 | .\" |
ae810de7 | 37 | .\" $OpenBSD: ssh.1,v 1.80 2001/01/29 12:36:10 djm 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 | |
ae810de7 | 51 | .Op Fl afgknqstvxACNPTX246 |
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 | |
fa08c86b | 212 | in the previous section except that the DSA or RSA algorithm is used |
213 | instead. | |
214 | The client uses his private key | |
1d1ffb87 | 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 | |
ce9c0b75 | 275 | The session terminates when the command or shell on the remote |
bf740959 | 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 | |
fa08c86b | 334 | host keys used in the protocol version 2 are stored in |
1d1ffb87 | 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. | |
fa08c86b | 355 | .Pp |
356 | The options are as follows: | |
bf740959 | 357 | .Bl -tag -width Ds |
358 | .It Fl a | |
4fe2af09 | 359 | Disables forwarding of the authentication agent connection. |
71276795 | 360 | .It Fl A |
361 | Enables forwarding of the authentication agent connection. | |
362 | This can also be specified on a per-host basis in a configuration file. | |
bf740959 | 363 | .It Fl c Ar blowfish|3des |
f54651ce | 364 | Selects the cipher to use for encrypting the session. |
bf740959 | 365 | .Ar 3des |
610cd5c6 | 366 | is used by default. |
f54651ce | 367 | It is believed to be secure. |
bf740959 | 368 | .Ar 3des |
369 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
370 | It is presumably more secure than the | |
371 | .Ar des | |
a22aff1f | 372 | cipher which is no longer fully supported in |
d0c832f3 | 373 | .Nm ssh . |
bf740959 | 374 | .Ar blowfish |
375 | is a fast block cipher, it appears very secure and is much faster than | |
610cd5c6 | 376 | .Ar 3des . |
d0c832f3 | 377 | .It Fl c Ar "3des-cbc,blowfish-cbc,arcfour,cast128-cbc" |
378 | Additionally, for protocol version 2 a comma-separated list of ciphers can | |
94ec8c6b | 379 | be specified in order of preference. |
380 | Protocol version 2 supports 3DES, Blowfish, and CAST128 in CBC mode | |
381 | and Arcfour. | |
bf740959 | 382 | .It Fl e Ar ch|^ch|none |
383 | Sets the escape character for sessions with a pty (default: | |
384 | .Ql ~ ) . | |
610cd5c6 | 385 | The escape character is only recognized at the beginning of a line. |
386 | The escape character followed by a dot | |
bf740959 | 387 | .Pq Ql \&. |
388 | closes the connection, followed | |
389 | by control-Z suspends the connection, and followed by itself sends the | |
610cd5c6 | 390 | escape character once. |
391 | Setting the character to | |
bf740959 | 392 | .Dq none |
393 | disables any escapes and makes the session fully transparent. | |
394 | .It Fl f | |
395 | Requests | |
396 | .Nm | |
610cd5c6 | 397 | to go to background just before command execution. |
398 | This is useful if | |
bf740959 | 399 | .Nm |
400 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 401 | wants it in the background. |
f54651ce | 402 | This implies |
bf740959 | 403 | .Fl n . |
404 | The recommended way to start X11 programs at a remote site is with | |
405 | something like | |
406 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 407 | .It Fl g |
408 | Allows remote hosts to connect to local forwarded ports. | |
bf740959 | 409 | .It Fl i Ar identity_file |
f54651ce | 410 | Selects the file from which the identity (private key) for |
fa08c86b | 411 | RSA or DSA authentication is read. |
f54651ce | 412 | Default is |
1d1ffb87 | 413 | .Pa $HOME/.ssh/identity |
610cd5c6 | 414 | in the user's home directory. |
415 | Identity files may also be specified on | |
416 | a per-host basis in the configuration file. | |
417 | It is possible to have multiple | |
bf740959 | 418 | .Fl i |
419 | options (and multiple identities specified in | |
420 | configuration files). | |
bf740959 | 421 | .It Fl k |
4fe2af09 | 422 | Disables forwarding of Kerberos tickets and AFS tokens. |
423 | This may also be specified on a per-host basis in the configuration file. | |
bf740959 | 424 | .It Fl l Ar login_name |
610cd5c6 | 425 | Specifies the user to log in as on the remote machine. |
426 | This also may be specified on a per-host basis in the configuration file. | |
bf740959 | 427 | .It Fl n |
428 | Redirects stdin from | |
429 | .Pa /dev/null | |
430 | (actually, prevents reading from stdin). | |
431 | This must be used when | |
432 | .Nm | |
610cd5c6 | 433 | is run in the background. |
434 | A common trick is to use this to run X11 programs on a remote machine. | |
435 | For example, | |
bf740959 | 436 | .Ic ssh -n shadows.cs.hut.fi emacs & |
437 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
438 | connection will be automatically forwarded over an encrypted channel. | |
439 | The | |
440 | .Nm | |
441 | program will be put in the background. | |
442 | (This does not work if | |
443 | .Nm | |
444 | needs to ask for a password or passphrase; see also the | |
445 | .Fl f | |
446 | option.) | |
0e73cc53 | 447 | .It Fl N |
448 | Do not execute a remote command. | |
0b6fbf03 | 449 | This is useful if you just want to forward ports |
0e73cc53 | 450 | (protocol version 2 only). |
bf740959 | 451 | .It Fl o Ar option |
452 | Can be used to give options in the format used in the config file. | |
453 | This is useful for specifying options for which there is no separate | |
610cd5c6 | 454 | command-line flag. |
455 | The option has the same format as a line in the configuration file. | |
bf740959 | 456 | .It Fl p Ar port |
610cd5c6 | 457 | Port to connect to on the remote host. |
458 | This can be specified on a | |
bf740959 | 459 | per-host basis in the configuration file. |
460 | .It Fl P | |
461 | Use a non-privileged port for outgoing connections. | |
462 | This can be used if your firewall does | |
463 | not permit connections from privileged ports. | |
95f1eccc | 464 | Note that this option turns off |
bf740959 | 465 | .Cm RhostsAuthentication |
466 | and | |
6ffc9c88 | 467 | .Cm RhostsRSAAuthentication |
468 | for older servers. | |
bf740959 | 469 | .It Fl q |
610cd5c6 | 470 | Quiet mode. |
471 | Causes all warning and diagnostic messages to be suppressed. | |
472 | Only fatal errors are displayed. | |
ae810de7 | 473 | .It Fl s |
474 | 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 | |
475 | of SSH as a secure transport for other application (eg. sftp). The | |
476 | subsystem is specified as the remote command. | |
bf740959 | 477 | .It Fl t |
610cd5c6 | 478 | Force pseudo-tty allocation. |
4fe2af09 | 479 | This can be used to execute arbitrary |
610cd5c6 | 480 | screen-based programs on a remote machine, which can be very useful, |
481 | e.g., when implementing menu services. | |
8abcdba4 | 482 | Multiple |
483 | .Fl t | |
484 | options force tty allocation, even if | |
485 | .Nm | |
486 | has no local tty. | |
0e73cc53 | 487 | .It Fl T |
0b6fbf03 | 488 | Disable pseudo-tty allocation. |
bf740959 | 489 | .It Fl v |
610cd5c6 | 490 | Verbose mode. |
491 | Causes | |
bf740959 | 492 | .Nm |
610cd5c6 | 493 | to print debugging messages about its progress. |
494 | This is helpful in | |
bf740959 | 495 | debugging connection, authentication, and configuration problems. |
8abcdba4 | 496 | Multiple |
497 | .Fl v | |
498 | options increases the verbosity. | |
94ec8c6b | 499 | Maximum is 3. |
bf740959 | 500 | .It Fl x |
610cd5c6 | 501 | Disables X11 forwarding. |
bf740959 | 502 | .It Fl X |
503 | Enables X11 forwarding. | |
71276795 | 504 | This can also be specified on a per-host basis in a configuration file. |
bf740959 | 505 | .It Fl C |
506 | Requests compression of all data (including stdin, stdout, stderr, and | |
610cd5c6 | 507 | data for forwarded X11 and TCP/IP connections). |
508 | The compression algorithm is the same used by | |
7b2ea3a1 | 509 | .Xr gzip 1 , |
510 | and the | |
bf740959 | 511 | .Dq level |
512 | can be controlled by the | |
513 | .Cm CompressionLevel | |
610cd5c6 | 514 | option (see below). |
515 | Compression is desirable on modem lines and other | |
bf740959 | 516 | slow connections, but will only slow down things on fast networks. |
517 | The default value can be set on a host-by-host basis in the | |
518 | configuration files; see the | |
519 | .Cm Compress | |
520 | option below. | |
521 | .It Fl L Ar port:host:hostport | |
522 | Specifies that the given port on the local (client) host is to be | |
610cd5c6 | 523 | forwarded to the given host and port on the remote side. |
524 | This works by allocating a socket to listen to | |
bf740959 | 525 | .Ar port |
526 | on the local side, and whenever a connection is made to this port, the | |
527 | connection is forwarded over the secure channel, and a connection is | |
528 | made to | |
48e671d5 | 529 | .Ar host |
530 | port | |
531 | .Ar hostport | |
610cd5c6 | 532 | from the remote machine. |
533 | Port forwardings can also be specified in the configuration file. | |
534 | Only root can forward privileged ports. | |
48e671d5 | 535 | IPv6 addresses can be specified with an alternative syntax: |
536 | .Ar port/host/hostport | |
bf740959 | 537 | .It Fl R Ar port:host:hostport |
538 | Specifies that the given port on the remote (server) host is to be | |
610cd5c6 | 539 | forwarded to the given host and port on the local side. |
540 | This works by allocating a socket to listen to | |
bf740959 | 541 | .Ar port |
542 | on the remote side, and whenever a connection is made to this port, the | |
543 | connection is forwarded over the secure channel, and a connection is | |
544 | made to | |
48e671d5 | 545 | .Ar host |
546 | port | |
547 | .Ar hostport | |
610cd5c6 | 548 | from the local machine. |
549 | Port forwardings can also be specified in the configuration file. | |
550 | Privileged ports can be forwarded only when | |
bf740959 | 551 | logging in as root on the remote machine. |
6ae2364d | 552 | .It Fl 2 |
553 | Forces | |
554 | .Nm | |
1d1ffb87 | 555 | to try protocol version 2 only. |
48e671d5 | 556 | .It Fl 4 |
557 | Forces | |
558 | .Nm | |
559 | to use IPv4 addresses only. | |
560 | .It Fl 6 | |
561 | Forces | |
562 | .Nm | |
563 | to use IPv6 addresses only. | |
bf740959 | 564 | .El |
fa08c86b | 565 | .Pp |
566 | If | |
567 | .Nm | |
568 | is not invoked with one of the standard program names | |
569 | .Pf ( Dq ssh , | |
570 | .Dq slogin , | |
571 | .Dq rsh , | |
572 | .Dq rlogin , | |
573 | or | |
574 | .Dq remsh ) , | |
575 | it uses this name as its | |
576 | .Ar hostname | |
577 | argument. | |
578 | This is consistent with traditional | |
579 | .Xr rsh 1 | |
580 | behavior. | |
bf740959 | 581 | .Sh CONFIGURATION FILES |
582 | .Nm | |
583 | obtains configuration data from the following sources (in this order): | |
584 | command line options, user's configuration file | |
585 | .Pq Pa $HOME/.ssh/config , | |
586 | and system-wide configuration file | |
5f4fdfae | 587 | .Pq Pa /etc/ssh_config . |
bf740959 | 588 | For each parameter, the first obtained value |
610cd5c6 | 589 | will be used. |
590 | The configuration files contain sections bracketed by | |
591 | .Dq Host | |
592 | specifications, and that section is only applied for hosts that | |
593 | match one of the patterns given in the specification. | |
594 | The matched host name is the one given on the command line. | |
bf740959 | 595 | .Pp |
596 | Since the first obtained value for each parameter is used, more | |
597 | host-specific declarations should be given near the beginning of the | |
598 | file, and general defaults at the end. | |
599 | .Pp | |
600 | The configuration file has the following format: | |
601 | .Pp | |
602 | Empty lines and lines starting with | |
603 | .Ql # | |
604 | are comments. | |
605 | .Pp | |
606 | Otherwise a line is of the format | |
607 | .Dq keyword arguments . | |
608 | The possible | |
609 | keywords and their meanings are as follows (note that the | |
610 | configuration files are case-sensitive): | |
611 | .Bl -tag -width Ds | |
612 | .It Cm Host | |
613 | Restricts the following declarations (up to the next | |
614 | .Cm Host | |
615 | keyword) to be only for those hosts that match one of the patterns | |
616 | given after the keyword. | |
617 | .Ql \&* | |
618 | and | |
619 | .Ql ? | |
620 | can be used as wildcards in the | |
610cd5c6 | 621 | patterns. |
622 | A single | |
bf740959 | 623 | .Ql \&* |
624 | as a pattern can be used to provide global | |
610cd5c6 | 625 | defaults for all hosts. |
626 | The host is the | |
bf740959 | 627 | .Ar hostname |
628 | argument given on the command line (i.e., the name is not converted to | |
629 | a canonicalized host name before matching). | |
630 | .It Cm AFSTokenPassing | |
4fe2af09 | 631 | Specifies whether to pass AFS tokens to remote host. |
632 | The argument to this keyword must be | |
bf740959 | 633 | .Dq yes |
634 | or | |
635 | .Dq no . | |
636 | .It Cm BatchMode | |
637 | If set to | |
638 | .Dq yes , | |
610cd5c6 | 639 | passphrase/password querying will be disabled. |
640 | This option is useful in scripts and other batch jobs where you have no | |
641 | user to supply the password. | |
642 | The argument must be | |
bf740959 | 643 | .Dq yes |
644 | or | |
645 | .Dq no . | |
7b2ea3a1 | 646 | .It Cm CheckHostIP |
647 | If this flag is set to | |
648 | .Dq yes , | |
649 | ssh will additionally check the host ip address in the | |
650 | .Pa known_hosts | |
4fe2af09 | 651 | file. |
652 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
7b2ea3a1 | 653 | If the option is set to |
654 | .Dq no , | |
655 | the check will not be executed. | |
bf740959 | 656 | .It Cm Cipher |
33de75a3 | 657 | Specifies the cipher to use for encrypting the session |
a22aff1f | 658 | in protocol version 1. |
610cd5c6 | 659 | Currently, |
a22aff1f | 660 | .Dq blowfish |
bf740959 | 661 | and |
662 | .Dq 3des | |
610cd5c6 | 663 | are supported. |
664 | The default is | |
bf740959 | 665 | .Dq 3des . |
f54651ce | 666 | .It Cm Ciphers |
667 | Specifies the ciphers allowed for protocol version 2 | |
668 | in order of preference. | |
669 | Multiple ciphers must be comma-separated. | |
670 | The default is | |
9616313f | 671 | .Dq 3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes128-cbc . |
bf740959 | 672 | .It Cm Compression |
610cd5c6 | 673 | Specifies whether to use compression. |
674 | The argument must be | |
bf740959 | 675 | .Dq yes |
676 | or | |
677 | .Dq no . | |
678 | .It Cm CompressionLevel | |
610cd5c6 | 679 | Specifies the compression level to use if compression is enable. |
680 | The argument must be an integer from 1 (fast) to 9 (slow, best). | |
681 | The default level is 6, which is good for most applications. | |
682 | The meaning of the values is the same as in | |
7b2ea3a1 | 683 | .Xr gzip 1 . |
bf740959 | 684 | .It Cm ConnectionAttempts |
685 | Specifies the number of tries (one per second) to make before falling | |
610cd5c6 | 686 | back to rsh or exiting. |
687 | The argument must be an integer. | |
688 | This may be useful in scripts if the connection sometimes fails. | |
fa08c86b | 689 | .It Cm PubkeyAuthentication |
690 | Specifies whether to try public key authentication. | |
1d1ffb87 | 691 | The argument to this keyword must be |
692 | .Dq yes | |
693 | or | |
694 | .Dq no . | |
1d1ffb87 | 695 | Note that this option applies to protocol version 2 only. |
bf740959 | 696 | .It Cm EscapeChar |
697 | Sets the escape character (default: | |
698 | .Ql ~ ) . | |
699 | The escape character can also | |
610cd5c6 | 700 | be set on the command line. |
701 | The argument should be a single character, | |
bf740959 | 702 | .Ql ^ |
703 | followed by a letter, or | |
704 | .Dq none | |
705 | to disable the escape | |
706 | character entirely (making the connection transparent for binary | |
707 | data). | |
f54651ce | 708 | .It Cm FallBackToRsh |
bf740959 | 709 | Specifies that if connecting via |
710 | .Nm | |
711 | fails due to a connection refused error (there is no | |
712 | .Xr sshd 8 | |
f54651ce | 713 | listening on the remote host), |
bf740959 | 714 | .Xr rsh 1 |
715 | should automatically be used instead (after a suitable warning about | |
610cd5c6 | 716 | the session being unencrypted). |
717 | The argument must be | |
bf740959 | 718 | .Dq yes |
719 | or | |
720 | .Dq no . | |
721 | .It Cm ForwardAgent | |
722 | Specifies whether the connection to the authentication agent (if any) | |
610cd5c6 | 723 | will be forwarded to the remote machine. |
724 | The argument must be | |
bf740959 | 725 | .Dq yes |
726 | or | |
727 | .Dq no . | |
71276795 | 728 | The default is |
729 | .Dq no . | |
bf740959 | 730 | .It Cm ForwardX11 |
731 | Specifies whether X11 connections will be automatically redirected | |
f54651ce | 732 | over the secure channel and |
bf740959 | 733 | .Ev DISPLAY |
610cd5c6 | 734 | set. |
f54651ce | 735 | The argument must be |
bf740959 | 736 | .Dq yes |
737 | or | |
738 | .Dq no . | |
c8d54615 | 739 | The default is |
740 | .Dq no . | |
bf740959 | 741 | .It Cm GatewayPorts |
742 | Specifies whether remote hosts are allowed to connect to local | |
743 | forwarded ports. | |
744 | The argument must be | |
745 | .Dq yes | |
746 | or | |
747 | .Dq no . | |
748 | The default is | |
749 | .Dq no . | |
750 | .It Cm GlobalKnownHostsFile | |
f54651ce | 751 | Specifies a file to use instead of |
5f4fdfae | 752 | .Pa /etc/ssh_known_hosts . |
8abcdba4 | 753 | .It Cm HostKeyAlias |
754 | Specifies an alias that should be used instead of the | |
755 | real host name when looking up or saving the host key | |
756 | the kown_hosts files. | |
757 | This option is useful for tunneling ssh connection | |
758 | or if you have multiple servers running on a single host. | |
bf740959 | 759 | .It Cm HostName |
610cd5c6 | 760 | Specifies the real host name to log into. |
761 | This can be used to specify nicknames or abbreviations for hosts. | |
762 | Default is the name given on the command line. | |
763 | Numeric IP addresses are also permitted (both on the command line and in | |
bf740959 | 764 | .Cm HostName |
765 | specifications). | |
766 | .It Cm IdentityFile | |
767 | Specifies the file from which the user's RSA authentication identity | |
768 | is read (default | |
1d1ffb87 | 769 | .Pa $HOME/.ssh/identity |
bf740959 | 770 | in the user's home directory). |
771 | Additionally, any identities represented by the authentication agent | |
610cd5c6 | 772 | will be used for authentication. |
773 | The file name may use the tilde | |
774 | syntax to refer to a user's home directory. | |
775 | It is possible to have | |
bf740959 | 776 | multiple identity files specified in configuration files; all these |
777 | identities will be tried in sequence. | |
778 | .It Cm KeepAlive | |
779 | Specifies whether the system should send keepalive messages to the | |
610cd5c6 | 780 | other side. |
781 | If they are sent, death of the connection or crash of one | |
782 | of the machines will be properly noticed. | |
783 | However, this means that | |
bf740959 | 784 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 785 | find it annoying. |
bf740959 | 786 | .Pp |
787 | The default is | |
788 | .Dq yes | |
789 | (to send keepalives), and the client will notice | |
610cd5c6 | 790 | if the network goes down or the remote host dies. |
791 | This is important in scripts, and many users want it too. | |
bf740959 | 792 | .Pp |
793 | To disable keepalives, the value should be set to | |
794 | .Dq no | |
795 | in both the server and the client configuration files. | |
796 | .It Cm KerberosAuthentication | |
4fe2af09 | 797 | Specifies whether Kerberos authentication will be used. |
798 | The argument to this keyword must be | |
bf740959 | 799 | .Dq yes |
800 | or | |
801 | .Dq no . | |
802 | .It Cm KerberosTgtPassing | |
4fe2af09 | 803 | Specifies whether a Kerberos TGT will be forwarded to the server. |
804 | This will only work if the Kerberos server is actually an AFS kaserver. | |
805 | The argument to this keyword must be | |
bf740959 | 806 | .Dq yes |
807 | or | |
808 | .Dq no . | |
809 | .It Cm LocalForward | |
810 | Specifies that a TCP/IP port on the local machine be forwarded over | |
610cd5c6 | 811 | the secure channel to given host:port from the remote machine. |
812 | The first argument must be a port number, and the second must be | |
813 | host:port. | |
814 | Multiple forwardings may be specified, and additional | |
815 | forwardings can be given on the command line. | |
816 | Only the superuser can forward privileged ports. | |
6a17f9c2 | 817 | .It Cm LogLevel |
818 | Gives the verbosity level that is used when logging messages from | |
819 | .Nm ssh . | |
820 | The possible values are: | |
59c97189 | 821 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
822 | The default is INFO. | |
bf740959 | 823 | .It Cm NumberOfPasswordPrompts |
4fe2af09 | 824 | Specifies the number of password prompts before giving up. |
825 | The argument to this keyword must be an integer. | |
826 | Default is 3. | |
7b2ea3a1 | 827 | .It Cm PasswordAuthentication |
610cd5c6 | 828 | Specifies whether to use password authentication. |
829 | The argument to this keyword must be | |
7b2ea3a1 | 830 | .Dq yes |
831 | or | |
832 | .Dq no . | |
1d1ffb87 | 833 | Note that this option applies to both protocol version 1 and 2. |
bf740959 | 834 | .It Cm Port |
610cd5c6 | 835 | Specifies the port number to connect on the remote host. |
836 | Default is 22. | |
f54651ce | 837 | .It Cm Protocol |
838 | Specifies the protocol versions | |
839 | .Nm | |
840 | should support in order of preference. | |
841 | The possible values are | |
842 | .Dq 1 | |
843 | and | |
844 | .Dq 2 . | |
845 | Multiple versions must be comma-separated. | |
846 | The default is | |
1d1ffb87 | 847 | .Dq 1,2 . |
848 | This means that | |
849 | .Nm | |
850 | tries version 1 and falls back to version 2 | |
d0c832f3 | 851 | if version 1 is not available. |
bf740959 | 852 | .It Cm ProxyCommand |
610cd5c6 | 853 | Specifies the command to use to connect to the server. |
854 | The command | |
855 | string extends to the end of the line, and is executed with | |
856 | .Pa /bin/sh . | |
857 | In the command string, | |
858 | .Ql %h | |
859 | will be substituted by the host name to | |
860 | connect and | |
861 | .Ql %p | |
862 | by the port. | |
863 | The command can be basically anything, | |
864 | and should read from its standard input and write to its standard output. | |
865 | It should eventually connect an | |
bf740959 | 866 | .Xr sshd 8 |
867 | server running on some machine, or execute | |
868 | .Ic sshd -i | |
610cd5c6 | 869 | somewhere. |
870 | Host key management will be done using the | |
bf740959 | 871 | HostName of the host being connected (defaulting to the name typed by |
872 | the user). | |
57112b5a | 873 | Note that |
874 | .Cm CheckHostIP | |
875 | is not available for connects with a proxy command. | |
bf740959 | 876 | .Pp |
877 | .It Cm RemoteForward | |
878 | Specifies that a TCP/IP port on the remote machine be forwarded over | |
610cd5c6 | 879 | the secure channel to given host:port from the local machine. |
880 | The first argument must be a port number, and the second must be | |
881 | host:port. | |
882 | Multiple forwardings may be specified, and additional | |
883 | forwardings can be given on the command line. | |
884 | Only the superuser can forward privileged ports. | |
bf740959 | 885 | .It Cm RhostsAuthentication |
610cd5c6 | 886 | Specifies whether to try rhosts based authentication. |
887 | Note that this | |
bf740959 | 888 | declaration only affects the client side and has no effect whatsoever |
610cd5c6 | 889 | on security. |
890 | Disabling rhosts authentication may reduce | |
bf740959 | 891 | authentication time on slow connections when rhosts authentication is |
610cd5c6 | 892 | not used. |
893 | Most servers do not permit RhostsAuthentication because it | |
894 | is not secure (see RhostsRSAAuthentication). | |
895 | The argument to this keyword must be | |
bf740959 | 896 | .Dq yes |
897 | or | |
898 | .Dq no . | |
899 | .It Cm RhostsRSAAuthentication | |
900 | Specifies whether to try rhosts based authentication with RSA host | |
610cd5c6 | 901 | authentication. |
902 | This is the primary authentication method for most sites. | |
903 | The argument must be | |
bf740959 | 904 | .Dq yes |
905 | or | |
906 | .Dq no . | |
907 | .It Cm RSAAuthentication | |
610cd5c6 | 908 | Specifies whether to try RSA authentication. |
909 | The argument to this keyword must be | |
bf740959 | 910 | .Dq yes |
911 | or | |
912 | .Dq no . | |
913 | RSA authentication will only be | |
914 | attempted if the identity file exists, or an authentication agent is | |
915 | running. | |
1d1ffb87 | 916 | Note that this option applies to protocol version 1 only. |
5260325f | 917 | .It Cm SkeyAuthentication |
918 | Specifies whether to use | |
919 | .Xr skey 1 | |
610cd5c6 | 920 | authentication. |
921 | The argument to this keyword must be | |
5260325f | 922 | .Dq yes |
923 | or | |
924 | .Dq no . | |
925 | The default is | |
926 | .Dq no . | |
bf740959 | 927 | .It Cm StrictHostKeyChecking |
928 | If this flag is set to | |
f54651ce | 929 | .Dq yes , |
bf740959 | 930 | .Nm |
a877488a | 931 | will never automatically add host keys to the |
bf740959 | 932 | .Pa $HOME/.ssh/known_hosts |
1d1ffb87 | 933 | and |
934 | .Pa $HOME/.ssh/known_hosts2 | |
a877488a | 935 | files, and refuses to connect to hosts whose host key has changed. |
610cd5c6 | 936 | This provides maximum protection against trojan horse attacks. |
937 | However, it can be somewhat annoying if you don't have good | |
5f4fdfae | 938 | .Pa /etc/ssh_known_hosts |
1d1ffb87 | 939 | and |
940 | .Pa /etc/ssh_known_hosts2 | |
bf740959 | 941 | files installed and frequently |
a877488a | 942 | connect to new hosts. |
943 | This option forces the user to manually | |
944 | add all new hosts. | |
945 | If this flag is set to | |
946 | .Dq no , | |
947 | .Nm | |
948 | will automatically add new host keys to the | |
949 | user known hosts files. | |
950 | If this flag is set to | |
951 | .Dq ask , | |
952 | new host keys | |
953 | will be added to the user known host files only after the user | |
954 | has confirmed that is what they really want to do, and | |
955 | .Nm | |
956 | will refuse to connect to hosts whose host key has changed. | |
610cd5c6 | 957 | The host keys of |
a877488a | 958 | known hosts will be verified automatically in all cases. |
610cd5c6 | 959 | The argument must be |
a877488a | 960 | .Dq yes , |
961 | .Dq no | |
bf740959 | 962 | or |
a877488a | 963 | .Dq ask . |
964 | The default is | |
965 | .Dq ask . | |
bf740959 | 966 | .It Cm UsePrivilegedPort |
967 | Specifies whether to use a privileged port for outgoing connections. | |
968 | The argument must be | |
969 | .Dq yes | |
970 | or | |
971 | .Dq no . | |
972 | The default is | |
973 | .Dq yes . | |
974 | Note that setting this option to | |
975 | .Dq no | |
95f1eccc | 976 | turns off |
bf740959 | 977 | .Cm RhostsAuthentication |
978 | and | |
6ffc9c88 | 979 | .Cm RhostsRSAAuthentication |
980 | for older servers. | |
7b2ea3a1 | 981 | .It Cm User |
610cd5c6 | 982 | Specifies the user to log in as. |
983 | This can be useful if you have a different user name on different machines. | |
984 | This saves the trouble of | |
7b2ea3a1 | 985 | having to remember to give the user name on the command line. |
986 | .It Cm UserKnownHostsFile | |
987 | Specifies a file to use instead of | |
988 | .Pa $HOME/.ssh/known_hosts . | |
bf740959 | 989 | .It Cm UseRsh |
610cd5c6 | 990 | Specifies that rlogin/rsh should be used for this host. |
991 | It is possible that the host does not at all support the | |
bf740959 | 992 | .Nm |
610cd5c6 | 993 | protocol. |
994 | This causes | |
bf740959 | 995 | .Nm |
610cd5c6 | 996 | to immediately execute |
bf740959 | 997 | .Xr rsh 1 . |
998 | All other options (except | |
999 | .Cm HostName ) | |
610cd5c6 | 1000 | are ignored if this has been specified. |
1001 | The argument must be | |
bf740959 | 1002 | .Dq yes |
1003 | or | |
1004 | .Dq no . | |
fa649821 | 1005 | .It Cm XAuthLocation |
1006 | Specifies the location of the | |
1007 | .Xr xauth 1 | |
1008 | program. | |
1009 | The default is | |
1010 | .Pa /usr/X11R6/bin/xauth . | |
b5e300c2 | 1011 | .El |
bf740959 | 1012 | .Sh ENVIRONMENT |
1013 | .Nm | |
1014 | will normally set the following environment variables: | |
1015 | .Bl -tag -width Ds | |
1016 | .It Ev DISPLAY | |
1017 | The | |
1018 | .Ev DISPLAY | |
610cd5c6 | 1019 | variable indicates the location of the X11 server. |
f54651ce | 1020 | It is automatically set by |
bf740959 | 1021 | .Nm |
1022 | to point to a value of the form | |
1023 | .Dq hostname:n | |
1024 | where hostname indicates | |
610cd5c6 | 1025 | the host where the shell runs, and n is an integer >= 1. |
1026 | .Nm | |
1027 | uses this special value to forward X11 connections over the secure | |
1028 | channel. | |
1029 | The user should normally not set DISPLAY explicitly, as that | |
bf740959 | 1030 | will render the X11 connection insecure (and will require the user to |
1031 | manually copy any required authorization cookies). | |
1032 | .It Ev HOME | |
1033 | Set to the path of the user's home directory. | |
1034 | .It Ev LOGNAME | |
1035 | Synonym for | |
1036 | .Ev USER ; | |
1037 | set for compatibility with systems that use this variable. | |
1038 | .It Ev MAIL | |
1039 | Set to point the user's mailbox. | |
610cd5c6 | 1040 | .It Ev PATH |
bf740959 | 1041 | Set to the default |
1042 | .Ev PATH , | |
1043 | as specified when compiling | |
1044 | .Nm ssh . | |
1045 | .It Ev SSH_AUTH_SOCK | |
1046 | indicates the path of a unix-domain socket used to communicate with the | |
1047 | agent. | |
1048 | .It Ev SSH_CLIENT | |
610cd5c6 | 1049 | Identifies the client end of the connection. |
1050 | The variable contains | |
bf740959 | 1051 | three space-separated values: client ip-address, client port number, |
1052 | and server port number. | |
8abcdba4 | 1053 | .It Ev SSH_ORIGINAL_COMMAND |
1054 | The variable contains the original command line if a forced command | |
1055 | is executed. | |
1056 | It can be used to extract the original arguments. | |
bf740959 | 1057 | .It Ev SSH_TTY |
1058 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 1059 | with the current shell or command. |
1060 | If the current session has no tty, | |
bf740959 | 1061 | this variable is not set. |
1062 | .It Ev TZ | |
1063 | The timezone variable is set to indicate the present timezone if it | |
c345cf9d | 1064 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 1065 | on to new connections). |
1066 | .It Ev USER | |
1067 | Set to the name of the user logging in. | |
1068 | .El | |
1069 | .Pp | |
f54651ce | 1070 | Additionally, |
bf740959 | 1071 | .Nm |
f54651ce | 1072 | reads |
1073 | .Pa $HOME/.ssh/environment , | |
bf740959 | 1074 | and adds lines of the format |
1075 | .Dq VARNAME=value | |
1076 | to the environment. | |
1077 | .Sh FILES | |
c8d54615 | 1078 | .Bl -tag -width Ds |
bf740959 | 1079 | .It Pa $HOME/.ssh/known_hosts |
1080 | Records host keys for all hosts the user has logged into (that are not | |
1081 | in | |
5f4fdfae | 1082 | .Pa /etc/ssh_known_hosts ) . |
bf740959 | 1083 | See |
1084 | .Xr sshd 8 . | |
1d1ffb87 | 1085 | .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa |
1086 | Contains the RSA and the DSA authentication identity of the user. | |
1087 | These files | |
1088 | contain sensitive data and should be readable by the user but not | |
bf740959 | 1089 | accessible by others (read/write/execute). |
1090 | Note that | |
1091 | .Nm | |
1d1ffb87 | 1092 | ignores a private key file if it is accessible by others. |
bf740959 | 1093 | It is possible to specify a passphrase when |
1094 | generating the key; the passphrase will be used to encrypt the | |
1095 | sensitive part of this file using 3DES. | |
1d1ffb87 | 1096 | .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub |
bf740959 | 1097 | Contains the public key for authentication (public part of the |
610cd5c6 | 1098 | identity file in human-readable form). |
1d1ffb87 | 1099 | The contents of the |
1100 | .Pa $HOME/.ssh/identity.pub | |
1101 | file should be added to | |
bf740959 | 1102 | .Pa $HOME/.ssh/authorized_keys |
1103 | on all machines | |
610cd5c6 | 1104 | where you wish to log in using RSA authentication. |
1d1ffb87 | 1105 | The contents of the |
1106 | .Pa $HOME/.ssh/id_dsa.pub | |
1107 | file should be added to | |
1108 | .Pa $HOME/.ssh/authorized_keys2 | |
1109 | on all machines | |
1110 | where you wish to log in using DSA authentication. | |
1111 | These files are not | |
610cd5c6 | 1112 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 1113 | These files are |
1114 | never used automatically and are not necessary; they is only provided for | |
bf740959 | 1115 | the convenience of the user. |
1116 | .It Pa $HOME/.ssh/config | |
610cd5c6 | 1117 | This is the per-user configuration file. |
1118 | The format of this file is described above. | |
1119 | This file is used by the | |
bf740959 | 1120 | .Nm |
610cd5c6 | 1121 | client. |
1122 | This file does not usually contain any sensitive information, | |
bf740959 | 1123 | but the recommended permissions are read/write for the user, and not |
1124 | accessible by others. | |
1125 | .It Pa $HOME/.ssh/authorized_keys | |
610cd5c6 | 1126 | Lists the RSA keys that can be used for logging in as this user. |
1127 | The format of this file is described in the | |
bf740959 | 1128 | .Xr sshd 8 |
610cd5c6 | 1129 | manual page. |
1130 | In the simplest form the format is the same as the .pub | |
bf740959 | 1131 | identity files (that is, each line contains the number of bits in |
1132 | modulus, public exponent, modulus, and comment fields, separated by | |
610cd5c6 | 1133 | spaces). |
1134 | This file is not highly sensitive, but the recommended | |
bf740959 | 1135 | permissions are read/write for the user, and not accessible by others. |
1d1ffb87 | 1136 | .It Pa $HOME/.ssh/authorized_keys2 |
fa08c86b | 1137 | Lists the public keys (DSA/RSA) that can be used for logging in as this user. |
1d1ffb87 | 1138 | This file is not highly sensitive, but the recommended |
1139 | permissions are read/write for the user, and not accessible by others. | |
1140 | .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2 | |
610cd5c6 | 1141 | Systemwide list of known host keys. |
1d1ffb87 | 1142 | .Pa /etc/ssh_known_hosts |
1143 | contains RSA and | |
1144 | .Pa /etc/ssh_known_hosts2 | |
fa08c86b | 1145 | contains DSA or RSA keys for protocol version 2. |
1d1ffb87 | 1146 | These files should be prepared by the |
bf740959 | 1147 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1148 | organization. |
1149 | This file should be world-readable. | |
1150 | This file contains | |
bf740959 | 1151 | public keys, one per line, in the following format (fields separated |
1152 | by spaces): system name, number of bits in modulus, public exponent, | |
610cd5c6 | 1153 | modulus, and optional comment field. |
1154 | When different names are used | |
bf740959 | 1155 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1156 | commas. |
1157 | The format is described on the | |
bf740959 | 1158 | .Xr sshd 8 |
1159 | manual page. | |
1160 | .Pp | |
1161 | The canonical system name (as returned by name servers) is used by | |
1162 | .Xr sshd 8 | |
1163 | to verify the client host when logging in; other names are needed because | |
1164 | .Nm | |
1165 | does not convert the user-supplied name to a canonical name before | |
1166 | checking the key, because someone with access to the name servers | |
1167 | would then be able to fool host authentication. | |
5f4fdfae | 1168 | .It Pa /etc/ssh_config |
610cd5c6 | 1169 | Systemwide configuration file. |
1170 | This file provides defaults for those | |
bf740959 | 1171 | values that are not specified in the user's configuration file, and |
610cd5c6 | 1172 | for those users who do not have a configuration file. |
1173 | This file must be world-readable. | |
bf740959 | 1174 | .It Pa $HOME/.rhosts |
1175 | This file is used in | |
1176 | .Pa \&.rhosts | |
1177 | authentication to list the | |
610cd5c6 | 1178 | host/user pairs that are permitted to log in. |
1179 | (Note that this file is | |
bf740959 | 1180 | also used by rlogin and rsh, which makes using this file insecure.) |
1181 | Each line of the file contains a host name (in the canonical form | |
1182 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1183 | separated by a space. |
1184 | One some machines this file may need to be | |
bf740959 | 1185 | world-readable if the user's home directory is on a NFS partition, |
1186 | because | |
1187 | .Xr sshd 8 | |
610cd5c6 | 1188 | reads it as root. |
1189 | Additionally, this file must be owned by the user, | |
1190 | and must not have write permissions for anyone else. | |
1191 | The recommended | |
bf740959 | 1192 | permission for most machines is read/write for the user, and not |
1193 | accessible by others. | |
1194 | .Pp | |
1195 | Note that by default | |
1196 | .Xr sshd 8 | |
1197 | will be installed so that it requires successful RSA host | |
610cd5c6 | 1198 | authentication before permitting \s+2.\s0rhosts authentication. |
1199 | If your server machine does not have the client's host key in | |
5f4fdfae | 1200 | .Pa /etc/ssh_known_hosts , |
bf740959 | 1201 | you can store it in |
1202 | .Pa $HOME/.ssh/known_hosts . | |
1203 | The easiest way to do this is to | |
1204 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1205 | will automatically add the host key to |
bf740959 | 1206 | .Pa $HOME/.ssh/known_hosts . |
1207 | .It Pa $HOME/.shosts | |
1208 | This file is used exactly the same way as | |
1209 | .Pa \&.rhosts . | |
1210 | The purpose for | |
1211 | having this file is to be able to use rhosts authentication with | |
1212 | .Nm | |
1213 | without permitting login with | |
1214 | .Xr rlogin 1 | |
1215 | or | |
1216 | .Xr rsh 1 . | |
1217 | .It Pa /etc/hosts.equiv | |
1218 | This file is used during | |
610cd5c6 | 1219 | .Pa \&.rhosts authentication. |
1220 | It contains | |
bf740959 | 1221 | canonical hosts names, one per line (the full format is described on |
1222 | the | |
1223 | .Xr sshd 8 | |
610cd5c6 | 1224 | manual page). |
1225 | If the client host is found in this file, login is | |
bf740959 | 1226 | automatically permitted provided client and server user names are the |
610cd5c6 | 1227 | same. |
1228 | Additionally, successful RSA host authentication is normally | |
1229 | required. | |
1230 | This file should only be writable by root. | |
5f4fdfae | 1231 | .It Pa /etc/shosts.equiv |
f54651ce | 1232 | This file is processed exactly as |
bf740959 | 1233 | .Pa /etc/hosts.equiv . |
1234 | This file may be useful to permit logins using | |
1235 | .Nm | |
1236 | but not using rsh/rlogin. | |
5f4fdfae | 1237 | .It Pa /etc/sshrc |
bf740959 | 1238 | Commands in this file are executed by |
1239 | .Nm | |
1240 | when the user logs in just before the user's shell (or command) is started. | |
1241 | See the | |
1242 | .Xr sshd 8 | |
1243 | manual page for more information. | |
1244 | .It Pa $HOME/.ssh/rc | |
1245 | Commands in this file are executed by | |
1246 | .Nm | |
1247 | when the user logs in just before the user's shell (or command) is | |
1248 | started. | |
f54651ce | 1249 | See the |
bf740959 | 1250 | .Xr sshd 8 |
1251 | manual page for more information. | |
83b7f649 | 1252 | .It Pa $HOME/.ssh/environment |
1253 | Contains additional definitions for environment variables, see section | |
1254 | .Sx ENVIRONMENT | |
1255 | above. | |
bf740959 | 1256 | .It Pa libcrypto.so.X.1 |
1257 | A version of this library which includes support for the RSA algorithm | |
1258 | is required for proper operation. | |
b5e300c2 | 1259 | .El |
fa08c86b | 1260 | .Sh AUTHORS |
5fb622e4 | 1261 | OpenSSH is a derivative of the original and free |
1262 | ssh 1.2.12 release by Tatu Ylonen. | |
1263 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1264 | Theo de Raadt and Dug Song | |
1265 | removed many bugs, re-added newer features and | |
1266 | created OpenSSH. | |
1267 | Markus Friedl contributed the support for SSH | |
1268 | protocol versions 1.5 and 2.0. | |
bf740959 | 1269 | .Sh SEE ALSO |
1270 | .Xr rlogin 1 , | |
1271 | .Xr rsh 1 , | |
1272 | .Xr scp 1 , | |
1273 | .Xr ssh-add 1 , | |
1274 | .Xr ssh-agent 1 , | |
1275 | .Xr ssh-keygen 1 , | |
1276 | .Xr telnet 1 , | |
1277 | .Xr sshd 8 , | |
0b6fbf03 | 1278 | .Xr ssl 8 |