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bf740959 | 1 | .\" -*- nroff -*- |
2 | .\" | |
bf740959 | 3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
bf740959 | 4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
5 | .\" All rights reserved | |
6 | .\" | |
bcbf86ec | 7 | .\" As far as I am concerned, the code I have written for this software |
8 | .\" can be used freely for any purpose. Any derived versions of this | |
9 | .\" software must be clearly marked as such, and if the derived work is | |
10 | .\" incompatible with the protocol description in the RFC file, it must be | |
11 | .\" called by a name other than "ssh" or "Secure Shell". | |
12 | .\" | |
f3c7c613 | 13 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. |
14 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. | |
15 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. | |
bcbf86ec | 16 | .\" |
17 | .\" Redistribution and use in source and binary forms, with or without | |
18 | .\" modification, are permitted provided that the following conditions | |
19 | .\" are met: | |
20 | .\" 1. Redistributions of source code must retain the above copyright | |
21 | .\" notice, this list of conditions and the following disclaimer. | |
22 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
23 | .\" notice, this list of conditions and the following disclaimer in the | |
24 | .\" documentation and/or other materials provided with the distribution. | |
bf740959 | 25 | .\" |
bcbf86ec | 26 | .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
27 | .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES | |
28 | .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |
29 | .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, | |
30 | .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT | |
31 | .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
32 | .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
33 | .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
34 | .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF | |
35 | .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
bf740959 | 36 | .\" |
da89cf4d | 37 | .\" $OpenBSD: ssh.1,v 1.107 2001/04/22 23:58:36 markus Exp $ |
bf740959 | 38 | .Dd September 25, 1999 |
39 | .Dt SSH 1 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm ssh | |
2c86906e | 43 | .Nd OpenSSH SSH client (remote login program) |
bf740959 | 44 | .Sh SYNOPSIS |
45 | .Nm ssh | |
46 | .Op Fl l Ar login_name | |
47 | .Op Ar hostname | user@hostname | |
48 | .Op Ar command | |
49 | .Pp | |
50 | .Nm ssh | |
9afadca8 | 51 | .Op Fl afgknqstvxACNPTX1246 |
d0c832f3 | 52 | .Op Fl c Ar cipher_spec |
bf740959 | 53 | .Op Fl e Ar escape_char |
54 | .Op Fl i Ar identity_file | |
55 | .Op Fl l Ar login_name | |
b2552997 | 56 | .Op Fl m Ar mac_spec |
bf740959 | 57 | .Op Fl o Ar option |
58 | .Op Fl p Ar port | |
59 | .Oo Fl L Xo | |
60 | .Sm off | |
bf740959 | 61 | .Ar port : |
7b2ea3a1 | 62 | .Ar host : |
bf740959 | 63 | .Ar hostport |
64 | .Sm on | |
65 | .Xc | |
66 | .Oc | |
67 | .Oo Fl R Xo | |
68 | .Sm off | |
bf740959 | 69 | .Ar port : |
7b2ea3a1 | 70 | .Ar host : |
bf740959 | 71 | .Ar hostport |
72 | .Sm on | |
73 | .Xc | |
74 | .Oc | |
75 | .Op Ar hostname | user@hostname | |
76 | .Op Ar command | |
f54651ce | 77 | .Sh DESCRIPTION |
bf740959 | 78 | .Nm |
2c86906e | 79 | (SSH client) is a program for logging into a remote machine and for |
610cd5c6 | 80 | executing commands on a remote machine. |
81 | It is intended to replace | |
bf740959 | 82 | rlogin and rsh, and provide secure encrypted communications between |
610cd5c6 | 83 | two untrusted hosts over an insecure network. |
84 | X11 connections and | |
bf740959 | 85 | arbitrary TCP/IP ports can also be forwarded over the secure channel. |
86 | .Pp | |
87 | .Nm | |
f54651ce | 88 | connects and logs into the specified |
bf740959 | 89 | .Ar hostname . |
90 | The user must prove | |
1d1ffb87 | 91 | his/her identity to the remote machine using one of several methods |
92 | depending on the protocol version used: | |
93 | .Pp | |
94 | .Ss SSH protocol version 1 | |
bf740959 | 95 | .Pp |
96 | First, if the machine the user logs in from is listed in | |
97 | .Pa /etc/hosts.equiv | |
98 | or | |
5f4fdfae | 99 | .Pa /etc/shosts.equiv |
bf740959 | 100 | on the remote machine, and the user names are |
101 | the same on both sides, the user is immediately permitted to log in. | |
f54651ce | 102 | Second, if |
bf740959 | 103 | .Pa \&.rhosts |
104 | or | |
105 | .Pa \&.shosts | |
106 | exists in the user's home directory on the | |
107 | remote machine and contains a line containing the name of the client | |
108 | machine and the name of the user on that machine, the user is | |
610cd5c6 | 109 | permitted to log in. |
110 | This form of authentication alone is normally not | |
bf740959 | 111 | allowed by the server because it is not secure. |
112 | .Pp | |
da89cf4d | 113 | The second authentication method is the |
bf740959 | 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 | |
da89cf4d | 208 | different authentication methods are available. |
209 | Using the default values for | |
210 | .Cm PreferredAuthentications , | |
211 | the client will try to authenticate first using the public key method; | |
212 | if this method fails password authentication is attempted, | |
213 | and finally if this method fails keyboard-interactive authentication | |
214 | is attempted. | |
215 | If this method fails password authentication is | |
216 | tried. | |
1d1ffb87 | 217 | .Pp |
218 | The public key method is similar to RSA authentication described | |
da89cf4d | 219 | in the previous section and allows the RSA or DSA algorithm to be used: |
c0ecc314 | 220 | The client uses his private key, |
1d1ffb87 | 221 | .Pa $HOME/.ssh/id_dsa |
c0ecc314 | 222 | or |
223 | .Pa $HOME/.ssh/id_rsa , | |
1d1ffb87 | 224 | to sign the session identifier and sends the result to the server. |
225 | The server checks whether the matching public key is listed in | |
226 | .Pa $HOME/.ssh/authorized_keys2 | |
227 | and grants access if both the key is found and the signature is correct. | |
228 | The session identifier is derived from a shared Diffie-Hellman value | |
229 | and is only known to the client and the server. | |
230 | .Pp | |
231 | If public key authentication fails or is not available a password | |
232 | can be sent encrypted to the remote host for proving the user's identity. | |
da89cf4d | 233 | .Pp |
234 | Additionally, | |
235 | .Nm | |
236 | supports hostbased or challenge response authentication. | |
1d1ffb87 | 237 | .Pp |
238 | Protocol 2 provides additional mechanisms for confidentiality | |
d0c832f3 | 239 | (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour) |
f2ba0775 | 240 | and integrity (hmac-md5, hmac-sha1). |
1d1ffb87 | 241 | Note that protocol 1 lacks a strong mechanism for ensuring the |
242 | integrity of the connection. | |
243 | .Pp | |
244 | .Ss Login session and remote execution | |
245 | .Pp | |
bf740959 | 246 | When the user's identity has been accepted by the server, the server |
247 | either executes the given command, or logs into the machine and gives | |
610cd5c6 | 248 | the user a normal shell on the remote machine. |
249 | All communication with | |
bf740959 | 250 | the remote command or shell will be automatically encrypted. |
251 | .Pp | |
252 | If a pseudo-terminal has been allocated (normal login session), the | |
df841692 | 253 | user may use the escape characters noted below. |
bf740959 | 254 | .Pp |
255 | If no pseudo tty has been allocated, the | |
256 | session is transparent and can be used to reliably transfer binary | |
610cd5c6 | 257 | data. |
258 | On most systems, setting the escape character to | |
bf740959 | 259 | .Dq none |
260 | will also make the session transparent even if a tty is used. | |
261 | .Pp | |
ce9c0b75 | 262 | The session terminates when the command or shell on the remote |
e91c60f2 | 263 | machine exits and all X11 and TCP/IP connections have been closed. |
bf740959 | 264 | The exit status of the remote program is returned as the exit status |
265 | of | |
266 | .Nm ssh . | |
267 | .Pp | |
df841692 | 268 | .Ss Escape Characters |
269 | .Pp | |
270 | When a pseudo terminal has been requested, ssh supports a number of functions | |
67b964a1 | 271 | through the use of an escape character. |
df841692 | 272 | .Pp |
273 | A single tilde character can be sent as | |
274 | .Ic ~~ | |
275 | (or by following the tilde by a character other than those described above). | |
276 | The escape character must always follow a newline to be interpreted as | |
277 | special. | |
278 | The escape character can be changed in configuration files using the | |
279 | .Cm EscapeChar | |
280 | configuration directive or on the command line by the | |
281 | .Fl e | |
282 | option. | |
283 | .Pp | |
284 | The supported escapes (assuming the default | |
285 | .Ql ~ ) | |
286 | are: | |
287 | .Bl -tag -width Ds | |
288 | .It Cm ~. | |
289 | Disconnect | |
290 | .It Cm ~^Z | |
291 | Background ssh | |
292 | .It Cm ~# | |
293 | List forwarded connections | |
294 | .It Cm ~& | |
295 | Background ssh at logout when waiting for forwarded connection / X11 sessions | |
da89cf4d | 296 | to terminate (protocol version 1 only) |
df841692 | 297 | .It Cm ~? |
298 | Display a list of escape characters | |
299 | .It Cm ~R | |
67b964a1 | 300 | Request rekeying of the connection (only useful for SSH protocol version 2 |
301 | and if the peer supports it) | |
df841692 | 302 | .El |
303 | .Pp | |
1d1ffb87 | 304 | .Ss X11 and TCP forwarding |
305 | .Pp | |
bf740959 | 306 | If the user is using X11 (the |
307 | .Ev DISPLAY | |
308 | environment variable is set), the connection to the X11 display is | |
309 | automatically forwarded to the remote side in such a way that any X11 | |
310 | programs started from the shell (or command) will go through the | |
311 | encrypted channel, and the connection to the real X server will be made | |
610cd5c6 | 312 | from the local machine. |
313 | The user should not manually set | |
bf740959 | 314 | .Ev DISPLAY . |
315 | Forwarding of X11 connections can be | |
316 | configured on the command line or in configuration files. | |
317 | .Pp | |
318 | The | |
f54651ce | 319 | .Ev DISPLAY |
bf740959 | 320 | value set by |
321 | .Nm | |
322 | will point to the server machine, but with a display number greater | |
610cd5c6 | 323 | than zero. |
324 | This is normal, and happens because | |
bf740959 | 325 | .Nm |
326 | creates a | |
327 | .Dq proxy | |
328 | X server on the server machine for forwarding the | |
329 | connections over the encrypted channel. | |
330 | .Pp | |
331 | .Nm | |
332 | will also automatically set up Xauthority data on the server machine. | |
333 | For this purpose, it will generate a random authorization cookie, | |
334 | store it in Xauthority on the server, and verify that any forwarded | |
335 | connections carry this cookie and replace it by the real cookie when | |
610cd5c6 | 336 | the connection is opened. |
337 | The real authentication cookie is never | |
bf740959 | 338 | sent to the server machine (and no cookies are sent in the plain). |
339 | .Pp | |
340 | If the user is using an authentication agent, the connection to the agent | |
341 | is automatically forwarded to the remote side unless disabled on | |
342 | command line or in a configuration file. | |
343 | .Pp | |
344 | Forwarding of arbitrary TCP/IP connections over the secure channel can | |
610cd5c6 | 345 | be specified either on command line or in a configuration file. |
346 | One possible application of TCP/IP forwarding is a secure connection to an | |
e91c60f2 | 347 | electronic purse; another is going through firewalls. |
bf740959 | 348 | .Pp |
1d1ffb87 | 349 | .Ss Server authentication |
350 | .Pp | |
bf740959 | 351 | .Nm |
1d1ffb87 | 352 | automatically maintains and checks a database containing |
610cd5c6 | 353 | identifications for all hosts it has ever been used with. |
1d1ffb87 | 354 | RSA host keys are stored in |
355 | .Pa $HOME/.ssh/known_hosts | |
356 | and | |
fa08c86b | 357 | host keys used in the protocol version 2 are stored in |
1d1ffb87 | 358 | .Pa $HOME/.ssh/known_hosts2 |
610cd5c6 | 359 | in the user's home directory. |
1d1ffb87 | 360 | Additionally, the files |
5f4fdfae | 361 | .Pa /etc/ssh_known_hosts |
1d1ffb87 | 362 | and |
363 | .Pa /etc/ssh_known_hosts2 | |
364 | are automatically checked for known hosts. | |
610cd5c6 | 365 | Any new hosts are automatically added to the user's file. |
366 | If a host's identification | |
bf740959 | 367 | ever changes, |
368 | .Nm | |
369 | warns about this and disables password authentication to prevent a | |
610cd5c6 | 370 | trojan horse from getting the user's password. |
371 | Another purpose of | |
bf740959 | 372 | this mechanism is to prevent man-in-the-middle attacks which could |
610cd5c6 | 373 | otherwise be used to circumvent the encryption. |
374 | The | |
bf740959 | 375 | .Cm StrictHostKeyChecking |
376 | option (see below) can be used to prevent logins to machines whose | |
377 | host key is not known or has changed. | |
fa08c86b | 378 | .Pp |
379 | The options are as follows: | |
bf740959 | 380 | .Bl -tag -width Ds |
381 | .It Fl a | |
4fe2af09 | 382 | Disables forwarding of the authentication agent connection. |
71276795 | 383 | .It Fl A |
384 | Enables forwarding of the authentication agent connection. | |
385 | This can also be specified on a per-host basis in a configuration file. | |
bf740959 | 386 | .It Fl c Ar blowfish|3des |
f54651ce | 387 | Selects the cipher to use for encrypting the session. |
bf740959 | 388 | .Ar 3des |
610cd5c6 | 389 | is used by default. |
f54651ce | 390 | It is believed to be secure. |
bf740959 | 391 | .Ar 3des |
392 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
393 | It is presumably more secure than the | |
394 | .Ar des | |
a22aff1f | 395 | cipher which is no longer fully supported in |
d0c832f3 | 396 | .Nm ssh . |
bf740959 | 397 | .Ar blowfish |
398 | is a fast block cipher, it appears very secure and is much faster than | |
610cd5c6 | 399 | .Ar 3des . |
9afadca8 | 400 | .It Fl c Ar cipher_spec |
d0c832f3 | 401 | Additionally, for protocol version 2 a comma-separated list of ciphers can |
94ec8c6b | 402 | be specified in order of preference. |
9afadca8 | 403 | See |
404 | .Cm Ciphers | |
405 | for more information. | |
bf740959 | 406 | .It Fl e Ar ch|^ch|none |
407 | Sets the escape character for sessions with a pty (default: | |
408 | .Ql ~ ) . | |
610cd5c6 | 409 | The escape character is only recognized at the beginning of a line. |
410 | The escape character followed by a dot | |
bf740959 | 411 | .Pq Ql \&. |
412 | closes the connection, followed | |
413 | by control-Z suspends the connection, and followed by itself sends the | |
610cd5c6 | 414 | escape character once. |
415 | Setting the character to | |
bf740959 | 416 | .Dq none |
417 | disables any escapes and makes the session fully transparent. | |
418 | .It Fl f | |
419 | Requests | |
420 | .Nm | |
610cd5c6 | 421 | to go to background just before command execution. |
422 | This is useful if | |
bf740959 | 423 | .Nm |
424 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 425 | wants it in the background. |
f54651ce | 426 | This implies |
bf740959 | 427 | .Fl n . |
428 | The recommended way to start X11 programs at a remote site is with | |
429 | something like | |
430 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 431 | .It Fl g |
432 | Allows remote hosts to connect to local forwarded ports. | |
bf740959 | 433 | .It Fl i Ar identity_file |
f54651ce | 434 | Selects the file from which the identity (private key) for |
fa08c86b | 435 | RSA or DSA authentication is read. |
f54651ce | 436 | Default is |
1d1ffb87 | 437 | .Pa $HOME/.ssh/identity |
610cd5c6 | 438 | in the user's home directory. |
439 | Identity files may also be specified on | |
440 | a per-host basis in the configuration file. | |
441 | It is possible to have multiple | |
bf740959 | 442 | .Fl i |
443 | options (and multiple identities specified in | |
444 | configuration files). | |
bf740959 | 445 | .It Fl k |
4fe2af09 | 446 | Disables forwarding of Kerberos tickets and AFS tokens. |
447 | This may also be specified on a per-host basis in the configuration file. | |
bf740959 | 448 | .It Fl l Ar login_name |
610cd5c6 | 449 | Specifies the user to log in as on the remote machine. |
450 | This also may be specified on a per-host basis in the configuration file. | |
b2552997 | 451 | .It Fl m Ar mac_spec |
452 | Additionally, for protocol version 2 a comma-separated list of MAC | |
453 | (message authentication code) algorithms can | |
454 | be specified in order of preference. | |
455 | See the | |
456 | .Cm MACs | |
457 | keyword for more information. | |
bf740959 | 458 | .It Fl n |
459 | Redirects stdin from | |
460 | .Pa /dev/null | |
461 | (actually, prevents reading from stdin). | |
462 | This must be used when | |
463 | .Nm | |
610cd5c6 | 464 | is run in the background. |
465 | A common trick is to use this to run X11 programs on a remote machine. | |
466 | For example, | |
bf740959 | 467 | .Ic ssh -n shadows.cs.hut.fi emacs & |
468 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
469 | connection will be automatically forwarded over an encrypted channel. | |
470 | The | |
471 | .Nm | |
472 | program will be put in the background. | |
473 | (This does not work if | |
474 | .Nm | |
475 | needs to ask for a password or passphrase; see also the | |
476 | .Fl f | |
477 | option.) | |
0e73cc53 | 478 | .It Fl N |
479 | Do not execute a remote command. | |
0b6fbf03 | 480 | This is useful if you just want to forward ports |
0e73cc53 | 481 | (protocol version 2 only). |
bf740959 | 482 | .It Fl o Ar option |
483 | Can be used to give options in the format used in the config file. | |
484 | This is useful for specifying options for which there is no separate | |
610cd5c6 | 485 | command-line flag. |
486 | The option has the same format as a line in the configuration file. | |
bf740959 | 487 | .It Fl p Ar port |
610cd5c6 | 488 | Port to connect to on the remote host. |
489 | This can be specified on a | |
bf740959 | 490 | per-host basis in the configuration file. |
491 | .It Fl P | |
492 | Use a non-privileged port for outgoing connections. | |
493 | This can be used if your firewall does | |
494 | not permit connections from privileged ports. | |
95f1eccc | 495 | Note that this option turns off |
bf740959 | 496 | .Cm RhostsAuthentication |
497 | and | |
6ffc9c88 | 498 | .Cm RhostsRSAAuthentication |
499 | for older servers. | |
bf740959 | 500 | .It Fl q |
610cd5c6 | 501 | Quiet mode. |
502 | Causes all warning and diagnostic messages to be suppressed. | |
503 | Only fatal errors are displayed. | |
ae810de7 | 504 | .It Fl s |
505 | 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 | |
506 | of SSH as a secure transport for other application (eg. sftp). The | |
507 | subsystem is specified as the remote command. | |
bf740959 | 508 | .It Fl t |
610cd5c6 | 509 | Force pseudo-tty allocation. |
4fe2af09 | 510 | This can be used to execute arbitrary |
610cd5c6 | 511 | screen-based programs on a remote machine, which can be very useful, |
512 | e.g., when implementing menu services. | |
8abcdba4 | 513 | Multiple |
514 | .Fl t | |
515 | options force tty allocation, even if | |
516 | .Nm | |
517 | has no local tty. | |
0e73cc53 | 518 | .It Fl T |
0b6fbf03 | 519 | Disable pseudo-tty allocation. |
bf740959 | 520 | .It Fl v |
610cd5c6 | 521 | Verbose mode. |
522 | Causes | |
bf740959 | 523 | .Nm |
610cd5c6 | 524 | to print debugging messages about its progress. |
525 | This is helpful in | |
bf740959 | 526 | debugging connection, authentication, and configuration problems. |
8abcdba4 | 527 | Multiple |
528 | .Fl v | |
529 | options increases the verbosity. | |
94ec8c6b | 530 | Maximum is 3. |
bf740959 | 531 | .It Fl x |
610cd5c6 | 532 | Disables X11 forwarding. |
bf740959 | 533 | .It Fl X |
534 | Enables X11 forwarding. | |
71276795 | 535 | This can also be specified on a per-host basis in a configuration file. |
bf740959 | 536 | .It Fl C |
537 | Requests compression of all data (including stdin, stdout, stderr, and | |
610cd5c6 | 538 | data for forwarded X11 and TCP/IP connections). |
539 | The compression algorithm is the same used by | |
7b2ea3a1 | 540 | .Xr gzip 1 , |
541 | and the | |
bf740959 | 542 | .Dq level |
543 | can be controlled by the | |
544 | .Cm CompressionLevel | |
610cd5c6 | 545 | option (see below). |
546 | Compression is desirable on modem lines and other | |
bf740959 | 547 | slow connections, but will only slow down things on fast networks. |
548 | The default value can be set on a host-by-host basis in the | |
549 | configuration files; see the | |
550 | .Cm Compress | |
551 | option below. | |
552 | .It Fl L Ar port:host:hostport | |
553 | Specifies that the given port on the local (client) host is to be | |
610cd5c6 | 554 | forwarded to the given host and port on the remote side. |
555 | This works by allocating a socket to listen to | |
bf740959 | 556 | .Ar port |
557 | on the local side, and whenever a connection is made to this port, the | |
558 | connection is forwarded over the secure channel, and a connection is | |
559 | made to | |
48e671d5 | 560 | .Ar host |
561 | port | |
562 | .Ar hostport | |
610cd5c6 | 563 | from the remote machine. |
564 | Port forwardings can also be specified in the configuration file. | |
565 | Only root can forward privileged ports. | |
48e671d5 | 566 | IPv6 addresses can be specified with an alternative syntax: |
567 | .Ar port/host/hostport | |
bf740959 | 568 | .It Fl R Ar port:host:hostport |
569 | Specifies that the given port on the remote (server) host is to be | |
610cd5c6 | 570 | forwarded to the given host and port on the local side. |
571 | This works by allocating a socket to listen to | |
bf740959 | 572 | .Ar port |
573 | on the remote side, and whenever a connection is made to this port, the | |
574 | connection is forwarded over the secure channel, and a connection is | |
575 | made to | |
48e671d5 | 576 | .Ar host |
577 | port | |
578 | .Ar hostport | |
610cd5c6 | 579 | from the local machine. |
580 | Port forwardings can also be specified in the configuration file. | |
581 | Privileged ports can be forwarded only when | |
bf740959 | 582 | logging in as root on the remote machine. |
da89cf4d | 583 | IPv6 addresses can be specified with an alternative syntax: |
584 | .Ar port/host/hostport | |
9afadca8 | 585 | .It Fl 1 |
586 | Forces | |
587 | .Nm | |
588 | to try protocol version 1 only. | |
6ae2364d | 589 | .It Fl 2 |
590 | Forces | |
591 | .Nm | |
1d1ffb87 | 592 | to try protocol version 2 only. |
48e671d5 | 593 | .It Fl 4 |
594 | Forces | |
595 | .Nm | |
596 | to use IPv4 addresses only. | |
597 | .It Fl 6 | |
598 | Forces | |
599 | .Nm | |
600 | to use IPv6 addresses only. | |
bf740959 | 601 | .El |
602 | .Sh CONFIGURATION FILES | |
603 | .Nm | |
604 | obtains configuration data from the following sources (in this order): | |
605 | command line options, user's configuration file | |
606 | .Pq Pa $HOME/.ssh/config , | |
607 | and system-wide configuration file | |
5f4fdfae | 608 | .Pq Pa /etc/ssh_config . |
bf740959 | 609 | For each parameter, the first obtained value |
610cd5c6 | 610 | will be used. |
611 | The configuration files contain sections bracketed by | |
612 | .Dq Host | |
613 | specifications, and that section is only applied for hosts that | |
614 | match one of the patterns given in the specification. | |
615 | The matched host name is the one given on the command line. | |
bf740959 | 616 | .Pp |
617 | Since the first obtained value for each parameter is used, more | |
618 | host-specific declarations should be given near the beginning of the | |
619 | file, and general defaults at the end. | |
620 | .Pp | |
621 | The configuration file has the following format: | |
622 | .Pp | |
623 | Empty lines and lines starting with | |
624 | .Ql # | |
625 | are comments. | |
626 | .Pp | |
627 | Otherwise a line is of the format | |
628 | .Dq keyword arguments . | |
629 | The possible | |
630 | keywords and their meanings are as follows (note that the | |
631 | configuration files are case-sensitive): | |
632 | .Bl -tag -width Ds | |
633 | .It Cm Host | |
634 | Restricts the following declarations (up to the next | |
635 | .Cm Host | |
636 | keyword) to be only for those hosts that match one of the patterns | |
637 | given after the keyword. | |
638 | .Ql \&* | |
639 | and | |
640 | .Ql ? | |
641 | can be used as wildcards in the | |
610cd5c6 | 642 | patterns. |
643 | A single | |
bf740959 | 644 | .Ql \&* |
645 | as a pattern can be used to provide global | |
610cd5c6 | 646 | defaults for all hosts. |
647 | The host is the | |
bf740959 | 648 | .Ar hostname |
649 | argument given on the command line (i.e., the name is not converted to | |
650 | a canonicalized host name before matching). | |
651 | .It Cm AFSTokenPassing | |
4fe2af09 | 652 | Specifies whether to pass AFS tokens to remote host. |
653 | The argument to this keyword must be | |
bf740959 | 654 | .Dq yes |
655 | or | |
656 | .Dq no . | |
da89cf4d | 657 | This option applies to protocol version 1 only. |
bf740959 | 658 | .It Cm BatchMode |
659 | If set to | |
660 | .Dq yes , | |
610cd5c6 | 661 | passphrase/password querying will be disabled. |
662 | This option is useful in scripts and other batch jobs where you have no | |
663 | user to supply the password. | |
664 | The argument must be | |
bf740959 | 665 | .Dq yes |
666 | or | |
667 | .Dq no . | |
01ce749f | 668 | The default is |
669 | .Dq no . | |
7b2ea3a1 | 670 | .It Cm CheckHostIP |
671 | If this flag is set to | |
672 | .Dq yes , | |
01ce749f | 673 | ssh will additionally check the host IP address in the |
7b2ea3a1 | 674 | .Pa known_hosts |
4fe2af09 | 675 | file. |
676 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
7b2ea3a1 | 677 | If the option is set to |
678 | .Dq no , | |
679 | the check will not be executed. | |
01ce749f | 680 | The default is |
681 | .Dq yes . | |
bf740959 | 682 | .It Cm Cipher |
33de75a3 | 683 | Specifies the cipher to use for encrypting the session |
a22aff1f | 684 | in protocol version 1. |
610cd5c6 | 685 | Currently, |
a22aff1f | 686 | .Dq blowfish |
bf740959 | 687 | and |
688 | .Dq 3des | |
610cd5c6 | 689 | are supported. |
690 | The default is | |
bf740959 | 691 | .Dq 3des . |
f54651ce | 692 | .It Cm Ciphers |
693 | Specifies the ciphers allowed for protocol version 2 | |
694 | in order of preference. | |
695 | Multiple ciphers must be comma-separated. | |
696 | The default is | |
9afadca8 | 697 | .Pp |
698 | .Bd -literal | |
f2ba0775 | 699 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour, |
da89cf4d | 700 | aes192-cbc,aes256-cbc'' |
9afadca8 | 701 | .Ed |
bf740959 | 702 | .It Cm Compression |
610cd5c6 | 703 | Specifies whether to use compression. |
704 | The argument must be | |
bf740959 | 705 | .Dq yes |
706 | or | |
707 | .Dq no . | |
01ce749f | 708 | The default is |
709 | .Dq no . | |
bf740959 | 710 | .It Cm CompressionLevel |
01ce749f | 711 | Specifies the compression level to use if compression is enabled. |
610cd5c6 | 712 | The argument must be an integer from 1 (fast) to 9 (slow, best). |
713 | The default level is 6, which is good for most applications. | |
714 | The meaning of the values is the same as in | |
7b2ea3a1 | 715 | .Xr gzip 1 . |
da89cf4d | 716 | Note that this option applies to protocol version 1 only. |
bf740959 | 717 | .It Cm ConnectionAttempts |
718 | Specifies the number of tries (one per second) to make before falling | |
610cd5c6 | 719 | back to rsh or exiting. |
720 | The argument must be an integer. | |
721 | This may be useful in scripts if the connection sometimes fails. | |
01ce749f | 722 | The default is 4. |
bf740959 | 723 | .It Cm EscapeChar |
724 | Sets the escape character (default: | |
725 | .Ql ~ ) . | |
726 | The escape character can also | |
610cd5c6 | 727 | be set on the command line. |
728 | The argument should be a single character, | |
bf740959 | 729 | .Ql ^ |
730 | followed by a letter, or | |
731 | .Dq none | |
732 | to disable the escape | |
733 | character entirely (making the connection transparent for binary | |
734 | data). | |
f54651ce | 735 | .It Cm FallBackToRsh |
bf740959 | 736 | Specifies that if connecting via |
737 | .Nm | |
738 | fails due to a connection refused error (there is no | |
739 | .Xr sshd 8 | |
f54651ce | 740 | listening on the remote host), |
bf740959 | 741 | .Xr rsh 1 |
742 | should automatically be used instead (after a suitable warning about | |
610cd5c6 | 743 | the session being unencrypted). |
744 | The argument must be | |
bf740959 | 745 | .Dq yes |
746 | or | |
747 | .Dq no . | |
01ce749f | 748 | The default is |
749 | .Dq no . | |
bf740959 | 750 | .It Cm ForwardAgent |
751 | Specifies whether the connection to the authentication agent (if any) | |
610cd5c6 | 752 | will be forwarded to the remote machine. |
753 | The argument must be | |
bf740959 | 754 | .Dq yes |
755 | or | |
756 | .Dq no . | |
71276795 | 757 | The default is |
758 | .Dq no . | |
bf740959 | 759 | .It Cm ForwardX11 |
760 | Specifies whether X11 connections will be automatically redirected | |
f54651ce | 761 | over the secure channel and |
bf740959 | 762 | .Ev DISPLAY |
610cd5c6 | 763 | set. |
f54651ce | 764 | The argument must be |
bf740959 | 765 | .Dq yes |
766 | or | |
767 | .Dq no . | |
c8d54615 | 768 | The default is |
769 | .Dq no . | |
bf740959 | 770 | .It Cm GatewayPorts |
771 | Specifies whether remote hosts are allowed to connect to local | |
772 | forwarded ports. | |
773 | The argument must be | |
774 | .Dq yes | |
775 | or | |
776 | .Dq no . | |
777 | The default is | |
778 | .Dq no . | |
779 | .It Cm GlobalKnownHostsFile | |
a5df12e9 | 780 | Specifies a file to use for the protocol version 1 global |
781 | host key database instead of | |
5f4fdfae | 782 | .Pa /etc/ssh_known_hosts . |
a5df12e9 | 783 | .It Cm GlobalKnownHostsFile2 |
784 | Specifies a file to use for the protocol version 2 global | |
785 | host key database instead of | |
786 | .Pa /etc/ssh_known_hosts2 . | |
da89cf4d | 787 | .It Cm HostbasedAuthentication |
788 | Specifies whether to try rhosts based authentication with public key | |
789 | authentication. | |
790 | The argument must be | |
791 | .Dq yes | |
792 | or | |
793 | .Dq no . | |
794 | The default is | |
795 | .Dq yes . | |
796 | This option applies to protocol version 2 only and | |
797 | is similar to | |
798 | .Cm RhostsRSAAuthentication . | |
e961a8f9 | 799 | .It Cm HostKeyAlgorithms |
800 | Specfies the protocol version 2 host key algorithms | |
801 | that the client wants to use in order of preference. | |
802 | The default for this option is: | |
803 | .Dq ssh-rsa,ssh-dss | |
da89cf4d | 804 | .It Cm HostKeyAlias |
805 | Specifies an alias that should be used instead of the | |
806 | real host name when looking up or saving the host key | |
807 | in the host key database files. | |
808 | This option is useful for tunneling ssh connections | |
809 | or if you have multiple servers running on a single host. | |
bf740959 | 810 | .It Cm HostName |
610cd5c6 | 811 | Specifies the real host name to log into. |
812 | This can be used to specify nicknames or abbreviations for hosts. | |
813 | Default is the name given on the command line. | |
814 | Numeric IP addresses are also permitted (both on the command line and in | |
bf740959 | 815 | .Cm HostName |
816 | specifications). | |
817 | .It Cm IdentityFile | |
da89cf4d | 818 | Specifies the file from which the user's RSA or DSA authentication identity |
bf740959 | 819 | is read (default |
1d1ffb87 | 820 | .Pa $HOME/.ssh/identity |
bf740959 | 821 | in the user's home directory). |
822 | Additionally, any identities represented by the authentication agent | |
610cd5c6 | 823 | will be used for authentication. |
824 | The file name may use the tilde | |
825 | syntax to refer to a user's home directory. | |
826 | It is possible to have | |
bf740959 | 827 | multiple identity files specified in configuration files; all these |
828 | identities will be tried in sequence. | |
829 | .It Cm KeepAlive | |
830 | Specifies whether the system should send keepalive messages to the | |
610cd5c6 | 831 | other side. |
832 | If they are sent, death of the connection or crash of one | |
833 | of the machines will be properly noticed. | |
834 | However, this means that | |
bf740959 | 835 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 836 | find it annoying. |
bf740959 | 837 | .Pp |
838 | The default is | |
839 | .Dq yes | |
840 | (to send keepalives), and the client will notice | |
610cd5c6 | 841 | if the network goes down or the remote host dies. |
842 | This is important in scripts, and many users want it too. | |
bf740959 | 843 | .Pp |
844 | To disable keepalives, the value should be set to | |
845 | .Dq no | |
846 | in both the server and the client configuration files. | |
847 | .It Cm KerberosAuthentication | |
4fe2af09 | 848 | Specifies whether Kerberos authentication will be used. |
849 | The argument to this keyword must be | |
bf740959 | 850 | .Dq yes |
851 | or | |
852 | .Dq no . | |
853 | .It Cm KerberosTgtPassing | |
4fe2af09 | 854 | Specifies whether a Kerberos TGT will be forwarded to the server. |
855 | This will only work if the Kerberos server is actually an AFS kaserver. | |
856 | The argument to this keyword must be | |
bf740959 | 857 | .Dq yes |
858 | or | |
859 | .Dq no . | |
860 | .It Cm LocalForward | |
861 | Specifies that a TCP/IP port on the local machine be forwarded over | |
610cd5c6 | 862 | the secure channel to given host:port from the remote machine. |
863 | The first argument must be a port number, and the second must be | |
864 | host:port. | |
865 | Multiple forwardings may be specified, and additional | |
866 | forwardings can be given on the command line. | |
867 | Only the superuser can forward privileged ports. | |
6a17f9c2 | 868 | .It Cm LogLevel |
869 | Gives the verbosity level that is used when logging messages from | |
870 | .Nm ssh . | |
871 | The possible values are: | |
59c97189 | 872 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
873 | The default is INFO. | |
b2552997 | 874 | .It Cm MACs |
875 | Specifies the MAC (message authentication code) algorithms | |
876 | in order of preference. | |
877 | The MAC algorithm is used in protocol version 2 | |
878 | for data integrity protection. | |
879 | Multiple algorithms must be comma-separated. | |
880 | The default is | |
881 | .Pp | |
882 | .Bd -literal | |
f2ba0775 | 883 | ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com, |
b2552997 | 884 | hmac-sha1-96,hmac-md5-96'' |
885 | .Ed | |
bf740959 | 886 | .It Cm NumberOfPasswordPrompts |
4fe2af09 | 887 | Specifies the number of password prompts before giving up. |
888 | The argument to this keyword must be an integer. | |
889 | Default is 3. | |
7b2ea3a1 | 890 | .It Cm PasswordAuthentication |
610cd5c6 | 891 | Specifies whether to use password authentication. |
892 | The argument to this keyword must be | |
7b2ea3a1 | 893 | .Dq yes |
894 | or | |
895 | .Dq no . | |
01ce749f | 896 | The default is |
897 | .Dq yes . | |
bf740959 | 898 | .It Cm Port |
610cd5c6 | 899 | Specifies the port number to connect on the remote host. |
900 | Default is 22. | |
babd91d4 | 901 | .It Cm PreferredAuthentications |
902 | Specifies the order in which the client should try protocol 2 | |
903 | authentication methods. This allows a client to prefer one method (e.g. | |
904 | .Cm keyboard-interactive ) | |
905 | over another method (e.g. | |
906 | .Cm password ) | |
907 | The default for this option is: | |
908 | .Dq publickey, password, keyboard-interactive | |
f54651ce | 909 | .It Cm Protocol |
910 | Specifies the protocol versions | |
911 | .Nm | |
912 | should support in order of preference. | |
913 | The possible values are | |
914 | .Dq 1 | |
915 | and | |
916 | .Dq 2 . | |
917 | Multiple versions must be comma-separated. | |
918 | The default is | |
b4a19d21 | 919 | .Dq 2,1 . |
1d1ffb87 | 920 | This means that |
921 | .Nm | |
b4a19d21 | 922 | tries version 2 and falls back to version 1 |
923 | if version 2 is not available. | |
bf740959 | 924 | .It Cm ProxyCommand |
610cd5c6 | 925 | Specifies the command to use to connect to the server. |
926 | The command | |
927 | string extends to the end of the line, and is executed with | |
928 | .Pa /bin/sh . | |
929 | In the command string, | |
930 | .Ql %h | |
931 | will be substituted by the host name to | |
932 | connect and | |
933 | .Ql %p | |
934 | by the port. | |
935 | The command can be basically anything, | |
936 | and should read from its standard input and write to its standard output. | |
937 | It should eventually connect an | |
bf740959 | 938 | .Xr sshd 8 |
939 | server running on some machine, or execute | |
940 | .Ic sshd -i | |
610cd5c6 | 941 | somewhere. |
942 | Host key management will be done using the | |
bf740959 | 943 | HostName of the host being connected (defaulting to the name typed by |
944 | the user). | |
57112b5a | 945 | Note that |
946 | .Cm CheckHostIP | |
947 | is not available for connects with a proxy command. | |
bf740959 | 948 | .Pp |
da89cf4d | 949 | .It Cm PubkeyAuthentication |
950 | Specifies whether to try public key authentication. | |
951 | The argument to this keyword must be | |
952 | .Dq yes | |
953 | or | |
954 | .Dq no . | |
955 | The default is | |
956 | .Dq yes . | |
957 | This option applies to protocol version 2 only. | |
bf740959 | 958 | .It Cm RemoteForward |
959 | Specifies that a TCP/IP port on the remote machine be forwarded over | |
610cd5c6 | 960 | the secure channel to given host:port from the local machine. |
961 | The first argument must be a port number, and the second must be | |
962 | host:port. | |
963 | Multiple forwardings may be specified, and additional | |
964 | forwardings can be given on the command line. | |
965 | Only the superuser can forward privileged ports. | |
bf740959 | 966 | .It Cm RhostsAuthentication |
610cd5c6 | 967 | Specifies whether to try rhosts based authentication. |
968 | Note that this | |
bf740959 | 969 | declaration only affects the client side and has no effect whatsoever |
610cd5c6 | 970 | on security. |
971 | Disabling rhosts authentication may reduce | |
bf740959 | 972 | authentication time on slow connections when rhosts authentication is |
610cd5c6 | 973 | not used. |
974 | Most servers do not permit RhostsAuthentication because it | |
da89cf4d | 975 | is not secure (see |
976 | .Cm RhostsRSAAuthentication ). | |
610cd5c6 | 977 | The argument to this keyword must be |
bf740959 | 978 | .Dq yes |
979 | or | |
980 | .Dq no . | |
01ce749f | 981 | The default is |
982 | .Dq yes . | |
da89cf4d | 983 | This option applies to protocol version 1 only. |
bf740959 | 984 | .It Cm RhostsRSAAuthentication |
985 | Specifies whether to try rhosts based authentication with RSA host | |
610cd5c6 | 986 | authentication. |
610cd5c6 | 987 | The argument must be |
bf740959 | 988 | .Dq yes |
989 | or | |
990 | .Dq no . | |
01ce749f | 991 | The default is |
992 | .Dq yes . | |
da89cf4d | 993 | This option applies to protocol version 1 only. |
bf740959 | 994 | .It Cm RSAAuthentication |
610cd5c6 | 995 | Specifies whether to try RSA authentication. |
996 | The argument to this keyword must be | |
bf740959 | 997 | .Dq yes |
998 | or | |
999 | .Dq no . | |
1000 | RSA authentication will only be | |
1001 | attempted if the identity file exists, or an authentication agent is | |
1002 | running. | |
01ce749f | 1003 | The default is |
1004 | .Dq yes . | |
1d1ffb87 | 1005 | Note that this option applies to protocol version 1 only. |
61e96248 | 1006 | .It Cm ChallengeResponseAuthentication |
1007 | Specifies whether to use challenge response authentication. | |
1008 | Currently there is only support for | |
5260325f | 1009 | .Xr skey 1 |
610cd5c6 | 1010 | authentication. |
1011 | The argument to this keyword must be | |
5260325f | 1012 | .Dq yes |
1013 | or | |
1014 | .Dq no . | |
1015 | The default is | |
1016 | .Dq no . | |
bf740959 | 1017 | .It Cm StrictHostKeyChecking |
1018 | If this flag is set to | |
f54651ce | 1019 | .Dq yes , |
bf740959 | 1020 | .Nm |
a877488a | 1021 | will never automatically add host keys to the |
bf740959 | 1022 | .Pa $HOME/.ssh/known_hosts |
1d1ffb87 | 1023 | and |
1024 | .Pa $HOME/.ssh/known_hosts2 | |
a877488a | 1025 | files, and refuses to connect to hosts whose host key has changed. |
610cd5c6 | 1026 | This provides maximum protection against trojan horse attacks. |
1027 | However, it can be somewhat annoying if you don't have good | |
5f4fdfae | 1028 | .Pa /etc/ssh_known_hosts |
1d1ffb87 | 1029 | and |
1030 | .Pa /etc/ssh_known_hosts2 | |
bf740959 | 1031 | files installed and frequently |
a877488a | 1032 | connect to new hosts. |
1033 | This option forces the user to manually | |
1034 | add all new hosts. | |
1035 | If this flag is set to | |
1036 | .Dq no , | |
1037 | .Nm | |
1038 | will automatically add new host keys to the | |
1039 | user known hosts files. | |
1040 | If this flag is set to | |
1041 | .Dq ask , | |
1042 | new host keys | |
1043 | will be added to the user known host files only after the user | |
1044 | has confirmed that is what they really want to do, and | |
1045 | .Nm | |
1046 | will refuse to connect to hosts whose host key has changed. | |
610cd5c6 | 1047 | The host keys of |
a877488a | 1048 | known hosts will be verified automatically in all cases. |
610cd5c6 | 1049 | The argument must be |
a877488a | 1050 | .Dq yes , |
1051 | .Dq no | |
bf740959 | 1052 | or |
a877488a | 1053 | .Dq ask . |
1054 | The default is | |
1055 | .Dq ask . | |
bf740959 | 1056 | .It Cm UsePrivilegedPort |
1057 | Specifies whether to use a privileged port for outgoing connections. | |
1058 | The argument must be | |
1059 | .Dq yes | |
1060 | or | |
1061 | .Dq no . | |
1062 | The default is | |
d5ebca2b | 1063 | .Dq no . |
da89cf4d | 1064 | Note that you need to set this option to |
1065 | .Dq yes | |
1066 | if you want to use | |
bf740959 | 1067 | .Cm RhostsAuthentication |
1068 | and | |
6ffc9c88 | 1069 | .Cm RhostsRSAAuthentication |
da89cf4d | 1070 | with older servers. |
7b2ea3a1 | 1071 | .It Cm User |
610cd5c6 | 1072 | Specifies the user to log in as. |
1073 | This can be useful if you have a different user name on different machines. | |
1074 | This saves the trouble of | |
7b2ea3a1 | 1075 | having to remember to give the user name on the command line. |
1076 | .It Cm UserKnownHostsFile | |
a5df12e9 | 1077 | Specifies a file to use for the protocol version 1 user |
1078 | host key database instead of | |
7b2ea3a1 | 1079 | .Pa $HOME/.ssh/known_hosts . |
a5df12e9 | 1080 | .It Cm UserKnownHostsFile2 |
1081 | Specifies a file to use for the protocol version 2 user | |
1082 | host key database instead of | |
1083 | .Pa $HOME/.ssh/known_hosts2 . | |
bf740959 | 1084 | .It Cm UseRsh |
610cd5c6 | 1085 | Specifies that rlogin/rsh should be used for this host. |
1086 | It is possible that the host does not at all support the | |
bf740959 | 1087 | .Nm |
610cd5c6 | 1088 | protocol. |
1089 | This causes | |
bf740959 | 1090 | .Nm |
610cd5c6 | 1091 | to immediately execute |
bf740959 | 1092 | .Xr rsh 1 . |
1093 | All other options (except | |
1094 | .Cm HostName ) | |
610cd5c6 | 1095 | are ignored if this has been specified. |
1096 | The argument must be | |
bf740959 | 1097 | .Dq yes |
1098 | or | |
1099 | .Dq no . | |
fa649821 | 1100 | .It Cm XAuthLocation |
1101 | Specifies the location of the | |
1102 | .Xr xauth 1 | |
1103 | program. | |
1104 | The default is | |
1105 | .Pa /usr/X11R6/bin/xauth . | |
b5e300c2 | 1106 | .El |
bf740959 | 1107 | .Sh ENVIRONMENT |
1108 | .Nm | |
1109 | will normally set the following environment variables: | |
1110 | .Bl -tag -width Ds | |
1111 | .It Ev DISPLAY | |
1112 | The | |
1113 | .Ev DISPLAY | |
610cd5c6 | 1114 | variable indicates the location of the X11 server. |
f54651ce | 1115 | It is automatically set by |
bf740959 | 1116 | .Nm |
1117 | to point to a value of the form | |
1118 | .Dq hostname:n | |
1119 | where hostname indicates | |
610cd5c6 | 1120 | the host where the shell runs, and n is an integer >= 1. |
1121 | .Nm | |
1122 | uses this special value to forward X11 connections over the secure | |
1123 | channel. | |
da89cf4d | 1124 | The user should normally not set |
1125 | .Ev DISPLAY | |
1126 | explicitly, as that | |
bf740959 | 1127 | will render the X11 connection insecure (and will require the user to |
1128 | manually copy any required authorization cookies). | |
1129 | .It Ev HOME | |
1130 | Set to the path of the user's home directory. | |
1131 | .It Ev LOGNAME | |
1132 | Synonym for | |
1133 | .Ev USER ; | |
1134 | set for compatibility with systems that use this variable. | |
1135 | .It Ev MAIL | |
1136 | Set to point the user's mailbox. | |
610cd5c6 | 1137 | .It Ev PATH |
bf740959 | 1138 | Set to the default |
1139 | .Ev PATH , | |
1140 | as specified when compiling | |
1141 | .Nm ssh . | |
1142 | .It Ev SSH_AUTH_SOCK | |
1143 | indicates the path of a unix-domain socket used to communicate with the | |
1144 | agent. | |
1145 | .It Ev SSH_CLIENT | |
610cd5c6 | 1146 | Identifies the client end of the connection. |
1147 | The variable contains | |
bf740959 | 1148 | three space-separated values: client ip-address, client port number, |
1149 | and server port number. | |
8abcdba4 | 1150 | .It Ev SSH_ORIGINAL_COMMAND |
1151 | The variable contains the original command line if a forced command | |
1152 | is executed. | |
1153 | It can be used to extract the original arguments. | |
bf740959 | 1154 | .It Ev SSH_TTY |
1155 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 1156 | with the current shell or command. |
1157 | If the current session has no tty, | |
bf740959 | 1158 | this variable is not set. |
1159 | .It Ev TZ | |
1160 | The timezone variable is set to indicate the present timezone if it | |
c345cf9d | 1161 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 1162 | on to new connections). |
1163 | .It Ev USER | |
1164 | Set to the name of the user logging in. | |
1165 | .El | |
1166 | .Pp | |
f54651ce | 1167 | Additionally, |
bf740959 | 1168 | .Nm |
f54651ce | 1169 | reads |
1170 | .Pa $HOME/.ssh/environment , | |
bf740959 | 1171 | and adds lines of the format |
1172 | .Dq VARNAME=value | |
1173 | to the environment. | |
1174 | .Sh FILES | |
c8d54615 | 1175 | .Bl -tag -width Ds |
a5df12e9 | 1176 | .It Pa $HOME/.ssh/known_hosts, $HOME/.ssh/known_hosts2 |
bf740959 | 1177 | Records host keys for all hosts the user has logged into (that are not |
1178 | in | |
a5df12e9 | 1179 | .Pa /etc/ssh_known_hosts |
1180 | for protocol version 1 or | |
1181 | .Pa /etc/ssh_known_hosts2 | |
1182 | for protocol version 2). | |
bf740959 | 1183 | See |
1184 | .Xr sshd 8 . | |
c0ecc314 | 1185 | .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa |
1186 | Contains the authentication identity of the user. | |
1187 | They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. | |
1d1ffb87 | 1188 | These files |
1189 | contain sensitive data and should be readable by the user but not | |
bf740959 | 1190 | accessible by others (read/write/execute). |
1191 | Note that | |
1192 | .Nm | |
1d1ffb87 | 1193 | ignores a private key file if it is accessible by others. |
bf740959 | 1194 | It is possible to specify a passphrase when |
1195 | generating the key; the passphrase will be used to encrypt the | |
1196 | sensitive part of this file using 3DES. | |
c0ecc314 | 1197 | .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub |
bf740959 | 1198 | Contains the public key for authentication (public part of the |
610cd5c6 | 1199 | identity file in human-readable form). |
1d1ffb87 | 1200 | The contents of the |
1201 | .Pa $HOME/.ssh/identity.pub | |
1202 | file should be added to | |
bf740959 | 1203 | .Pa $HOME/.ssh/authorized_keys |
1204 | on all machines | |
c0ecc314 | 1205 | where you wish to log in using protocol version 1 RSA authentication. |
1d1ffb87 | 1206 | The contents of the |
1207 | .Pa $HOME/.ssh/id_dsa.pub | |
c0ecc314 | 1208 | and |
1209 | .Pa $HOME/.ssh/id_rsa.pub | |
1d1ffb87 | 1210 | file should be added to |
1211 | .Pa $HOME/.ssh/authorized_keys2 | |
1212 | on all machines | |
c0ecc314 | 1213 | where you wish to log in using protocol version 2 DSA/RSA authentication. |
1d1ffb87 | 1214 | These files are not |
610cd5c6 | 1215 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 1216 | These files are |
c44559d2 | 1217 | never used automatically and are not necessary; they are only provided for |
bf740959 | 1218 | the convenience of the user. |
1219 | .It Pa $HOME/.ssh/config | |
610cd5c6 | 1220 | This is the per-user configuration file. |
1221 | The format of this file is described above. | |
1222 | This file is used by the | |
bf740959 | 1223 | .Nm |
610cd5c6 | 1224 | client. |
1225 | This file does not usually contain any sensitive information, | |
bf740959 | 1226 | but the recommended permissions are read/write for the user, and not |
1227 | accessible by others. | |
1228 | .It Pa $HOME/.ssh/authorized_keys | |
610cd5c6 | 1229 | Lists the RSA keys that can be used for logging in as this user. |
1230 | The format of this file is described in the | |
bf740959 | 1231 | .Xr sshd 8 |
610cd5c6 | 1232 | manual page. |
1233 | In the simplest form the format is the same as the .pub | |
bf740959 | 1234 | identity files (that is, each line contains the number of bits in |
1235 | modulus, public exponent, modulus, and comment fields, separated by | |
610cd5c6 | 1236 | spaces). |
1237 | This file is not highly sensitive, but the recommended | |
bf740959 | 1238 | permissions are read/write for the user, and not accessible by others. |
1d1ffb87 | 1239 | .It Pa $HOME/.ssh/authorized_keys2 |
da89cf4d | 1240 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. |
1d1ffb87 | 1241 | This file is not highly sensitive, but the recommended |
1242 | permissions are read/write for the user, and not accessible by others. | |
1243 | .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2 | |
610cd5c6 | 1244 | Systemwide list of known host keys. |
1d1ffb87 | 1245 | .Pa /etc/ssh_known_hosts |
1246 | contains RSA and | |
1247 | .Pa /etc/ssh_known_hosts2 | |
da89cf4d | 1248 | contains RSA or DSA keys for protocol version 2. |
1d1ffb87 | 1249 | These files should be prepared by the |
bf740959 | 1250 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1251 | organization. |
1252 | This file should be world-readable. | |
1253 | This file contains | |
bf740959 | 1254 | public keys, one per line, in the following format (fields separated |
1255 | by spaces): system name, number of bits in modulus, public exponent, | |
610cd5c6 | 1256 | modulus, and optional comment field. |
1257 | When different names are used | |
bf740959 | 1258 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1259 | commas. |
1260 | The format is described on the | |
bf740959 | 1261 | .Xr sshd 8 |
1262 | manual page. | |
1263 | .Pp | |
1264 | The canonical system name (as returned by name servers) is used by | |
1265 | .Xr sshd 8 | |
1266 | to verify the client host when logging in; other names are needed because | |
1267 | .Nm | |
1268 | does not convert the user-supplied name to a canonical name before | |
1269 | checking the key, because someone with access to the name servers | |
1270 | would then be able to fool host authentication. | |
5f4fdfae | 1271 | .It Pa /etc/ssh_config |
610cd5c6 | 1272 | Systemwide configuration file. |
1273 | This file provides defaults for those | |
bf740959 | 1274 | values that are not specified in the user's configuration file, and |
610cd5c6 | 1275 | for those users who do not have a configuration file. |
1276 | This file must be world-readable. | |
bf740959 | 1277 | .It Pa $HOME/.rhosts |
1278 | This file is used in | |
1279 | .Pa \&.rhosts | |
1280 | authentication to list the | |
610cd5c6 | 1281 | host/user pairs that are permitted to log in. |
1282 | (Note that this file is | |
bf740959 | 1283 | also used by rlogin and rsh, which makes using this file insecure.) |
1284 | Each line of the file contains a host name (in the canonical form | |
1285 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1286 | separated by a space. |
e91c60f2 | 1287 | On some machines this file may need to be |
bf740959 | 1288 | world-readable if the user's home directory is on a NFS partition, |
1289 | because | |
1290 | .Xr sshd 8 | |
610cd5c6 | 1291 | reads it as root. |
1292 | Additionally, this file must be owned by the user, | |
1293 | and must not have write permissions for anyone else. | |
1294 | The recommended | |
bf740959 | 1295 | permission for most machines is read/write for the user, and not |
1296 | accessible by others. | |
1297 | .Pp | |
1298 | Note that by default | |
1299 | .Xr sshd 8 | |
1300 | will be installed so that it requires successful RSA host | |
610cd5c6 | 1301 | authentication before permitting \s+2.\s0rhosts authentication. |
1302 | If your server machine does not have the client's host key in | |
5f4fdfae | 1303 | .Pa /etc/ssh_known_hosts , |
bf740959 | 1304 | you can store it in |
1305 | .Pa $HOME/.ssh/known_hosts . | |
1306 | The easiest way to do this is to | |
1307 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1308 | will automatically add the host key to |
bf740959 | 1309 | .Pa $HOME/.ssh/known_hosts . |
1310 | .It Pa $HOME/.shosts | |
1311 | This file is used exactly the same way as | |
1312 | .Pa \&.rhosts . | |
1313 | The purpose for | |
1314 | having this file is to be able to use rhosts authentication with | |
1315 | .Nm | |
1316 | without permitting login with | |
1317 | .Xr rlogin 1 | |
1318 | or | |
1319 | .Xr rsh 1 . | |
1320 | .It Pa /etc/hosts.equiv | |
1321 | This file is used during | |
610cd5c6 | 1322 | .Pa \&.rhosts authentication. |
1323 | It contains | |
bf740959 | 1324 | canonical hosts names, one per line (the full format is described on |
1325 | the | |
1326 | .Xr sshd 8 | |
610cd5c6 | 1327 | manual page). |
1328 | If the client host is found in this file, login is | |
bf740959 | 1329 | automatically permitted provided client and server user names are the |
610cd5c6 | 1330 | same. |
1331 | Additionally, successful RSA host authentication is normally | |
1332 | required. | |
1333 | This file should only be writable by root. | |
5f4fdfae | 1334 | .It Pa /etc/shosts.equiv |
f54651ce | 1335 | This file is processed exactly as |
bf740959 | 1336 | .Pa /etc/hosts.equiv . |
1337 | This file may be useful to permit logins using | |
1338 | .Nm | |
1339 | but not using rsh/rlogin. | |
5f4fdfae | 1340 | .It Pa /etc/sshrc |
bf740959 | 1341 | Commands in this file are executed by |
1342 | .Nm | |
1343 | when the user logs in just before the user's shell (or command) is started. | |
1344 | See the | |
1345 | .Xr sshd 8 | |
1346 | manual page for more information. | |
1347 | .It Pa $HOME/.ssh/rc | |
1348 | Commands in this file are executed by | |
1349 | .Nm | |
1350 | when the user logs in just before the user's shell (or command) is | |
1351 | started. | |
f54651ce | 1352 | See the |
bf740959 | 1353 | .Xr sshd 8 |
1354 | manual page for more information. | |
83b7f649 | 1355 | .It Pa $HOME/.ssh/environment |
1356 | Contains additional definitions for environment variables, see section | |
1357 | .Sx ENVIRONMENT | |
1358 | above. | |
b5e300c2 | 1359 | .El |
fa08c86b | 1360 | .Sh AUTHORS |
5fb622e4 | 1361 | OpenSSH is a derivative of the original and free |
1362 | ssh 1.2.12 release by Tatu Ylonen. | |
1363 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1364 | Theo de Raadt and Dug Song | |
1365 | removed many bugs, re-added newer features and | |
1366 | created OpenSSH. | |
1367 | Markus Friedl contributed the support for SSH | |
1368 | protocol versions 1.5 and 2.0. | |
bf740959 | 1369 | .Sh SEE ALSO |
1370 | .Xr rlogin 1 , | |
1371 | .Xr rsh 1 , | |
1372 | .Xr scp 1 , | |
61e96248 | 1373 | .Xr sftp 1 , |
bf740959 | 1374 | .Xr ssh-add 1 , |
1375 | .Xr ssh-agent 1 , | |
1376 | .Xr ssh-keygen 1 , | |
1377 | .Xr telnet 1 , | |
9afadca8 | 1378 | .Xr sshd 8 |
2cad6cef | 1379 | .Rs |
1380 | .%A T. Ylonen | |
1381 | .%A T. Kivinen | |
1382 | .%A M. Saarinen | |
1383 | .%A T. Rinne | |
1384 | .%A S. Lehtinen | |
1385 | .%T "SSH Protocol Architecture" | |
1386 | .%N draft-ietf-secsh-architecture-07.txt | |
1387 | .%D January 2001 | |
1388 | .%O work in progress material | |
1389 | .Re |