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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 | .\" |
e591b98a | 37 | .\" $OpenBSD: ssh.1,v 1.132 2001/08/28 15:39:48 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 | |
c78e5800 | 47 | .Ar hostname | user@hostname |
bf740959 | 48 | .Op Ar command |
49 | .Pp | |
50 | .Nm ssh | |
9afadca8 | 51 | .Op Fl afgknqstvxACNPTX1246 |
3435f5a6 | 52 | .Op Fl b Ar bind_address |
d0c832f3 | 53 | .Op Fl c Ar cipher_spec |
bf740959 | 54 | .Op Fl e Ar escape_char |
55 | .Op Fl i Ar identity_file | |
56 | .Op Fl l Ar login_name | |
b2552997 | 57 | .Op Fl m Ar mac_spec |
bf740959 | 58 | .Op Fl o Ar option |
59 | .Op Fl p Ar port | |
e591b98a | 60 | .Op Fl F Ar configfile |
bf740959 | 61 | .Oo Fl L Xo |
62 | .Sm off | |
bf740959 | 63 | .Ar port : |
7b2ea3a1 | 64 | .Ar host : |
bf740959 | 65 | .Ar hostport |
66 | .Sm on | |
67 | .Xc | |
68 | .Oc | |
69 | .Oo Fl R Xo | |
70 | .Sm off | |
bf740959 | 71 | .Ar port : |
7b2ea3a1 | 72 | .Ar host : |
bf740959 | 73 | .Ar hostport |
74 | .Sm on | |
75 | .Xc | |
76 | .Oc | |
c78e5800 | 77 | .Ar hostname | user@hostname |
bf740959 | 78 | .Op Ar command |
f54651ce | 79 | .Sh DESCRIPTION |
bf740959 | 80 | .Nm |
2c86906e | 81 | (SSH client) is a program for logging into a remote machine and for |
610cd5c6 | 82 | executing commands on a remote machine. |
83 | It is intended to replace | |
bf740959 | 84 | rlogin and rsh, and provide secure encrypted communications between |
610cd5c6 | 85 | two untrusted hosts over an insecure network. |
86 | X11 connections and | |
bf740959 | 87 | arbitrary TCP/IP ports can also be forwarded over the secure channel. |
88 | .Pp | |
89 | .Nm | |
f54651ce | 90 | connects and logs into the specified |
bf740959 | 91 | .Ar hostname . |
92 | The user must prove | |
1d1ffb87 | 93 | his/her identity to the remote machine using one of several methods |
94 | depending on the protocol version used: | |
95 | .Pp | |
96 | .Ss SSH protocol version 1 | |
bf740959 | 97 | .Pp |
98 | First, if the machine the user logs in from is listed in | |
99 | .Pa /etc/hosts.equiv | |
100 | or | |
5f4fdfae | 101 | .Pa /etc/shosts.equiv |
bf740959 | 102 | on the remote machine, and the user names are |
103 | the same on both sides, the user is immediately permitted to log in. | |
f54651ce | 104 | Second, if |
bf740959 | 105 | .Pa \&.rhosts |
106 | or | |
107 | .Pa \&.shosts | |
108 | exists in the user's home directory on the | |
109 | remote machine and contains a line containing the name of the client | |
110 | machine and the name of the user on that machine, the user is | |
610cd5c6 | 111 | permitted to log in. |
112 | This form of authentication alone is normally not | |
bf740959 | 113 | allowed by the server because it is not secure. |
114 | .Pp | |
da89cf4d | 115 | The second authentication method is the |
bf740959 | 116 | .Pa rhosts |
117 | or | |
118 | .Pa hosts.equiv | |
610cd5c6 | 119 | method combined with RSA-based host authentication. |
120 | It means that if the login would be permitted by | |
1d1ffb87 | 121 | .Pa $HOME/.rhosts , |
122 | .Pa $HOME/.shosts , | |
bf740959 | 123 | .Pa /etc/hosts.equiv , |
124 | or | |
5f4fdfae | 125 | .Pa /etc/shosts.equiv , |
bf740959 | 126 | and if additionally the server can verify the client's |
f54651ce | 127 | host key (see |
5f4fdfae | 128 | .Pa /etc/ssh_known_hosts |
5bbb5681 | 129 | and |
130 | .Pa $HOME/.ssh/known_hosts | |
bf740959 | 131 | in the |
132 | .Sx FILES | |
610cd5c6 | 133 | section), only then login is permitted. |
134 | This authentication method closes security holes due to IP | |
135 | spoofing, DNS spoofing and routing spoofing. | |
136 | [Note to the administrator: | |
bf740959 | 137 | .Pa /etc/hosts.equiv , |
1d1ffb87 | 138 | .Pa $HOME/.rhosts , |
bf740959 | 139 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
140 | disabled if security is desired.] | |
141 | .Pp | |
f54651ce | 142 | As a third authentication method, |
bf740959 | 143 | .Nm |
144 | supports RSA based authentication. | |
145 | The scheme is based on public-key cryptography: there are cryptosystems | |
146 | where encryption and decryption are done using separate keys, and it | |
147 | is not possible to derive the decryption key from the encryption key. | |
610cd5c6 | 148 | RSA is one such system. |
f54651ce | 149 | The idea is that each user creates a public/private |
610cd5c6 | 150 | key pair for authentication purposes. |
151 | The server knows the public key, and only the user knows the private key. | |
f54651ce | 152 | The file |
bf740959 | 153 | .Pa $HOME/.ssh/authorized_keys |
154 | lists the public keys that are permitted for logging | |
610cd5c6 | 155 | in. |
156 | When the user logs in, the | |
bf740959 | 157 | .Nm |
158 | program tells the server which key pair it would like to use for | |
610cd5c6 | 159 | authentication. |
160 | The server checks if this key is permitted, and if | |
bf740959 | 161 | so, sends the user (actually the |
162 | .Nm | |
163 | program running on behalf of the user) a challenge, a random number, | |
610cd5c6 | 164 | encrypted by the user's public key. |
165 | The challenge can only be | |
166 | decrypted using the proper private key. | |
167 | The user's client then decrypts the | |
bf740959 | 168 | challenge using the private key, proving that he/she knows the private |
169 | key but without disclosing it to the server. | |
170 | .Pp | |
171 | .Nm | |
610cd5c6 | 172 | implements the RSA authentication protocol automatically. |
173 | The user creates his/her RSA key pair by running | |
bf740959 | 174 | .Xr ssh-keygen 1 . |
f54651ce | 175 | This stores the private key in |
1d1ffb87 | 176 | .Pa $HOME/.ssh/identity |
bf740959 | 177 | and the public key in |
1d1ffb87 | 178 | .Pa $HOME/.ssh/identity.pub |
610cd5c6 | 179 | in the user's home directory. |
180 | The user should then copy the | |
bf740959 | 181 | .Pa identity.pub |
f54651ce | 182 | to |
1d1ffb87 | 183 | .Pa $HOME/.ssh/authorized_keys |
f54651ce | 184 | in his/her home directory on the remote machine (the |
bf740959 | 185 | .Pa authorized_keys |
f54651ce | 186 | file corresponds to the conventional |
1d1ffb87 | 187 | .Pa $HOME/.rhosts |
bf740959 | 188 | file, and has one key |
610cd5c6 | 189 | per line, though the lines can be very long). |
190 | After this, the user can log in without giving the password. | |
191 | RSA authentication is much | |
bf740959 | 192 | more secure than rhosts authentication. |
193 | .Pp | |
194 | The most convenient way to use RSA authentication may be with an | |
610cd5c6 | 195 | authentication agent. |
196 | See | |
bf740959 | 197 | .Xr ssh-agent 1 |
198 | for more information. | |
199 | .Pp | |
f54651ce | 200 | If other authentication methods fail, |
bf740959 | 201 | .Nm |
610cd5c6 | 202 | prompts the user for a password. |
203 | The password is sent to the remote | |
bf740959 | 204 | host for checking; however, since all communications are encrypted, |
205 | the password cannot be seen by someone listening on the network. | |
206 | .Pp | |
1d1ffb87 | 207 | .Ss SSH protocol version 2 |
208 | .Pp | |
209 | When a user connects using the protocol version 2 | |
da89cf4d | 210 | different authentication methods are available. |
211 | Using the default values for | |
212 | .Cm PreferredAuthentications , | |
29c440a0 | 213 | the client will try to authenticate first using the hostbased method; |
214 | if this method fails public key authentication is attempted, | |
215 | and finally if this method fails keyboard-interactive and | |
216 | password authentication are 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 | |
96a7b0cc | 226 | .Pa $HOME/.ssh/authorized_keys |
1d1ffb87 | 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 | |
3730bb22 | 271 | through the use of an escape character. |
df841692 | 272 | .Pp |
273 | A single tilde character can be sent as | |
274 | .Ic ~~ | |
5bef3c35 | 275 | or by following the tilde by a character other than those described below. |
df841692 | 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 | |
3730bb22 | 280 | configuration directive or on the command line by the |
df841692 | 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 | |
6efa3d14 | 306 | If the |
307 | .Cm ForwardX11 | |
308 | variable is set to | |
309 | .Dq yes | |
310 | (or, see the description of the | |
311 | .Fl X | |
312 | and | |
313 | .Fl x | |
314 | options described later) | |
315 | and the user is using X11 (the | |
bf740959 | 316 | .Ev DISPLAY |
317 | environment variable is set), the connection to the X11 display is | |
318 | automatically forwarded to the remote side in such a way that any X11 | |
319 | programs started from the shell (or command) will go through the | |
320 | encrypted channel, and the connection to the real X server will be made | |
610cd5c6 | 321 | from the local machine. |
322 | The user should not manually set | |
bf740959 | 323 | .Ev DISPLAY . |
324 | Forwarding of X11 connections can be | |
325 | configured on the command line or in configuration files. | |
326 | .Pp | |
327 | The | |
f54651ce | 328 | .Ev DISPLAY |
bf740959 | 329 | value set by |
330 | .Nm | |
331 | will point to the server machine, but with a display number greater | |
610cd5c6 | 332 | than zero. |
333 | This is normal, and happens because | |
bf740959 | 334 | .Nm |
335 | creates a | |
336 | .Dq proxy | |
337 | X server on the server machine for forwarding the | |
338 | connections over the encrypted channel. | |
339 | .Pp | |
340 | .Nm | |
341 | will also automatically set up Xauthority data on the server machine. | |
342 | For this purpose, it will generate a random authorization cookie, | |
343 | store it in Xauthority on the server, and verify that any forwarded | |
344 | connections carry this cookie and replace it by the real cookie when | |
610cd5c6 | 345 | the connection is opened. |
346 | The real authentication cookie is never | |
bf740959 | 347 | sent to the server machine (and no cookies are sent in the plain). |
348 | .Pp | |
349 | If the user is using an authentication agent, the connection to the agent | |
350 | is automatically forwarded to the remote side unless disabled on | |
491f5f7b | 351 | the command line or in a configuration file. |
bf740959 | 352 | .Pp |
353 | Forwarding of arbitrary TCP/IP connections over the secure channel can | |
491f5f7b | 354 | be specified either on the command line or in a configuration file. |
610cd5c6 | 355 | One possible application of TCP/IP forwarding is a secure connection to an |
e91c60f2 | 356 | electronic purse; another is going through firewalls. |
bf740959 | 357 | .Pp |
1d1ffb87 | 358 | .Ss Server authentication |
359 | .Pp | |
bf740959 | 360 | .Nm |
1d1ffb87 | 361 | automatically maintains and checks a database containing |
610cd5c6 | 362 | identifications for all hosts it has ever been used with. |
f49bc4f7 | 363 | Host keys are stored in |
1d1ffb87 | 364 | .Pa $HOME/.ssh/known_hosts |
610cd5c6 | 365 | in the user's home directory. |
f49bc4f7 | 366 | Additionally, the file |
5f4fdfae | 367 | .Pa /etc/ssh_known_hosts |
f49bc4f7 | 368 | is automatically checked for known hosts. |
610cd5c6 | 369 | Any new hosts are automatically added to the user's file. |
370 | If a host's identification | |
bf740959 | 371 | ever changes, |
372 | .Nm | |
373 | warns about this and disables password authentication to prevent a | |
610cd5c6 | 374 | trojan horse from getting the user's password. |
375 | Another purpose of | |
bf740959 | 376 | this mechanism is to prevent man-in-the-middle attacks which could |
610cd5c6 | 377 | otherwise be used to circumvent the encryption. |
378 | The | |
bf740959 | 379 | .Cm StrictHostKeyChecking |
380 | option (see below) can be used to prevent logins to machines whose | |
381 | host key is not known or has changed. | |
fa08c86b | 382 | .Pp |
383 | The options are as follows: | |
bf740959 | 384 | .Bl -tag -width Ds |
385 | .It Fl a | |
4fe2af09 | 386 | Disables forwarding of the authentication agent connection. |
71276795 | 387 | .It Fl A |
388 | Enables forwarding of the authentication agent connection. | |
389 | This can also be specified on a per-host basis in a configuration file. | |
3435f5a6 | 390 | .It Fl b Ar bind_address |
391 | Specify the interface to transmit from on machines with multiple | |
392 | interfaces or aliased addresses. | |
29999e54 | 393 | .It Fl c Ar blowfish|3des|des |
f54651ce | 394 | Selects the cipher to use for encrypting the session. |
bf740959 | 395 | .Ar 3des |
610cd5c6 | 396 | is used by default. |
f54651ce | 397 | It is believed to be secure. |
bf740959 | 398 | .Ar 3des |
399 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
bf740959 | 400 | .Ar blowfish |
401 | is a fast block cipher, it appears very secure and is much faster than | |
610cd5c6 | 402 | .Ar 3des . |
29999e54 | 403 | .Ar des |
404 | is only supported in the | |
405 | .Nm | |
406 | client for interoperability with legacy protocol 1 implementations | |
407 | that do not support the | |
408 | .Ar 3des | |
409 | cipher. Its use is strongly discouraged due to cryptographic | |
410 | weaknesses. | |
9afadca8 | 411 | .It Fl c Ar cipher_spec |
d0c832f3 | 412 | Additionally, for protocol version 2 a comma-separated list of ciphers can |
94ec8c6b | 413 | be specified in order of preference. |
9afadca8 | 414 | See |
415 | .Cm Ciphers | |
416 | for more information. | |
bf740959 | 417 | .It Fl e Ar ch|^ch|none |
418 | Sets the escape character for sessions with a pty (default: | |
419 | .Ql ~ ) . | |
610cd5c6 | 420 | The escape character is only recognized at the beginning of a line. |
421 | The escape character followed by a dot | |
bf740959 | 422 | .Pq Ql \&. |
423 | closes the connection, followed | |
424 | by control-Z suspends the connection, and followed by itself sends the | |
610cd5c6 | 425 | escape character once. |
426 | Setting the character to | |
bf740959 | 427 | .Dq none |
428 | disables any escapes and makes the session fully transparent. | |
429 | .It Fl f | |
430 | Requests | |
431 | .Nm | |
610cd5c6 | 432 | to go to background just before command execution. |
433 | This is useful if | |
bf740959 | 434 | .Nm |
435 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 436 | wants it in the background. |
f54651ce | 437 | This implies |
bf740959 | 438 | .Fl n . |
439 | The recommended way to start X11 programs at a remote site is with | |
440 | something like | |
441 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 442 | .It Fl g |
443 | Allows remote hosts to connect to local forwarded ports. | |
bf740959 | 444 | .It Fl i Ar identity_file |
f54651ce | 445 | Selects the file from which the identity (private key) for |
fa08c86b | 446 | RSA or DSA authentication is read. |
f54651ce | 447 | Default is |
1d1ffb87 | 448 | .Pa $HOME/.ssh/identity |
610cd5c6 | 449 | in the user's home directory. |
450 | Identity files may also be specified on | |
451 | a per-host basis in the configuration file. | |
452 | It is possible to have multiple | |
bf740959 | 453 | .Fl i |
454 | options (and multiple identities specified in | |
455 | configuration files). | |
eea098a3 | 456 | .It Fl I Ar smartcard_device |
457 | Specifies which smartcard device to use. The argument is | |
458 | the device | |
459 | .Nm | |
460 | should use to communicate with a smartcard used for storing the user's | |
461 | private RSA key. | |
bf740959 | 462 | .It Fl k |
4fe2af09 | 463 | Disables forwarding of Kerberos tickets and AFS tokens. |
464 | This may also be specified on a per-host basis in the configuration file. | |
bf740959 | 465 | .It Fl l Ar login_name |
610cd5c6 | 466 | Specifies the user to log in as on the remote machine. |
467 | This also may be specified on a per-host basis in the configuration file. | |
b2552997 | 468 | .It Fl m Ar mac_spec |
469 | Additionally, for protocol version 2 a comma-separated list of MAC | |
470 | (message authentication code) algorithms can | |
471 | be specified in order of preference. | |
472 | See the | |
473 | .Cm MACs | |
474 | keyword for more information. | |
bf740959 | 475 | .It Fl n |
476 | Redirects stdin from | |
477 | .Pa /dev/null | |
478 | (actually, prevents reading from stdin). | |
479 | This must be used when | |
480 | .Nm | |
610cd5c6 | 481 | is run in the background. |
482 | A common trick is to use this to run X11 programs on a remote machine. | |
483 | For example, | |
bf740959 | 484 | .Ic ssh -n shadows.cs.hut.fi emacs & |
485 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
486 | connection will be automatically forwarded over an encrypted channel. | |
487 | The | |
488 | .Nm | |
489 | program will be put in the background. | |
490 | (This does not work if | |
491 | .Nm | |
492 | needs to ask for a password or passphrase; see also the | |
493 | .Fl f | |
494 | option.) | |
0e73cc53 | 495 | .It Fl N |
496 | Do not execute a remote command. | |
0b6fbf03 | 497 | This is useful if you just want to forward ports |
0e73cc53 | 498 | (protocol version 2 only). |
bf740959 | 499 | .It Fl o Ar option |
38539909 | 500 | Can be used to give options in the format used in the configuration file. |
bf740959 | 501 | This is useful for specifying options for which there is no separate |
610cd5c6 | 502 | command-line flag. |
bf740959 | 503 | .It Fl p Ar port |
610cd5c6 | 504 | Port to connect to on the remote host. |
505 | This can be specified on a | |
bf740959 | 506 | per-host basis in the configuration file. |
507 | .It Fl P | |
508 | Use a non-privileged port for outgoing connections. | |
509 | This can be used if your firewall does | |
510 | not permit connections from privileged ports. | |
95f1eccc | 511 | Note that this option turns off |
bf740959 | 512 | .Cm RhostsAuthentication |
513 | and | |
6ffc9c88 | 514 | .Cm RhostsRSAAuthentication |
515 | for older servers. | |
bf740959 | 516 | .It Fl q |
610cd5c6 | 517 | Quiet mode. |
518 | Causes all warning and diagnostic messages to be suppressed. | |
519 | Only fatal errors are displayed. | |
ae810de7 | 520 | .It Fl s |
3730bb22 | 521 | 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 |
522 | of SSH as a secure transport for other applications (eg. sftp). The | |
ae810de7 | 523 | subsystem is specified as the remote command. |
bf740959 | 524 | .It Fl t |
610cd5c6 | 525 | Force pseudo-tty allocation. |
4fe2af09 | 526 | This can be used to execute arbitrary |
610cd5c6 | 527 | screen-based programs on a remote machine, which can be very useful, |
528 | e.g., when implementing menu services. | |
8abcdba4 | 529 | Multiple |
530 | .Fl t | |
531 | options force tty allocation, even if | |
532 | .Nm | |
533 | has no local tty. | |
0e73cc53 | 534 | .It Fl T |
0b6fbf03 | 535 | Disable pseudo-tty allocation. |
bf740959 | 536 | .It Fl v |
610cd5c6 | 537 | Verbose mode. |
538 | Causes | |
bf740959 | 539 | .Nm |
610cd5c6 | 540 | to print debugging messages about its progress. |
541 | This is helpful in | |
bf740959 | 542 | debugging connection, authentication, and configuration problems. |
8abcdba4 | 543 | Multiple |
544 | .Fl v | |
545 | options increases the verbosity. | |
94ec8c6b | 546 | Maximum is 3. |
bf740959 | 547 | .It Fl x |
610cd5c6 | 548 | Disables X11 forwarding. |
bf740959 | 549 | .It Fl X |
550 | Enables X11 forwarding. | |
71276795 | 551 | This can also be specified on a per-host basis in a configuration file. |
bf740959 | 552 | .It Fl C |
553 | Requests compression of all data (including stdin, stdout, stderr, and | |
610cd5c6 | 554 | data for forwarded X11 and TCP/IP connections). |
555 | The compression algorithm is the same used by | |
7b2ea3a1 | 556 | .Xr gzip 1 , |
557 | and the | |
bf740959 | 558 | .Dq level |
559 | can be controlled by the | |
560 | .Cm CompressionLevel | |
610cd5c6 | 561 | option (see below). |
562 | Compression is desirable on modem lines and other | |
bf740959 | 563 | slow connections, but will only slow down things on fast networks. |
564 | The default value can be set on a host-by-host basis in the | |
565 | configuration files; see the | |
0aea6c59 | 566 | .Cm Compression |
bf740959 | 567 | option below. |
e591b98a | 568 | .It Fl F Ar configfile |
569 | Specifies an alternative per-user configuration file. | |
570 | If a configuration file is given on the command line, | |
571 | the system-wide configuration file | |
572 | .Pq Pa /etc/ssh_config | |
573 | will be ignored. | |
574 | The default for the per-user configuration file is | |
575 | .Pa $HOME/.ssh/config . | |
bf740959 | 576 | .It Fl L Ar port:host:hostport |
577 | Specifies that the given port on the local (client) host is to be | |
610cd5c6 | 578 | forwarded to the given host and port on the remote side. |
579 | This works by allocating a socket to listen to | |
bf740959 | 580 | .Ar port |
581 | on the local side, and whenever a connection is made to this port, the | |
582 | connection is forwarded over the secure channel, and a connection is | |
583 | made to | |
48e671d5 | 584 | .Ar host |
585 | port | |
586 | .Ar hostport | |
610cd5c6 | 587 | from the remote machine. |
588 | Port forwardings can also be specified in the configuration file. | |
589 | Only root can forward privileged ports. | |
48e671d5 | 590 | IPv6 addresses can be specified with an alternative syntax: |
591 | .Ar port/host/hostport | |
bf740959 | 592 | .It Fl R Ar port:host:hostport |
593 | Specifies that the given port on the remote (server) host is to be | |
610cd5c6 | 594 | forwarded to the given host and port on the local side. |
595 | This works by allocating a socket to listen to | |
bf740959 | 596 | .Ar port |
597 | on the remote side, and whenever a connection is made to this port, the | |
598 | connection is forwarded over the secure channel, and a connection is | |
599 | made to | |
48e671d5 | 600 | .Ar host |
601 | port | |
602 | .Ar hostport | |
610cd5c6 | 603 | from the local machine. |
604 | Port forwardings can also be specified in the configuration file. | |
605 | Privileged ports can be forwarded only when | |
bf740959 | 606 | logging in as root on the remote machine. |
da89cf4d | 607 | IPv6 addresses can be specified with an alternative syntax: |
608 | .Ar port/host/hostport | |
9afadca8 | 609 | .It Fl 1 |
610 | Forces | |
611 | .Nm | |
612 | to try protocol version 1 only. | |
6ae2364d | 613 | .It Fl 2 |
614 | Forces | |
615 | .Nm | |
1d1ffb87 | 616 | to try protocol version 2 only. |
48e671d5 | 617 | .It Fl 4 |
618 | Forces | |
619 | .Nm | |
620 | to use IPv4 addresses only. | |
621 | .It Fl 6 | |
622 | Forces | |
623 | .Nm | |
624 | to use IPv6 addresses only. | |
bf740959 | 625 | .El |
626 | .Sh CONFIGURATION FILES | |
627 | .Nm | |
38539909 | 628 | obtains configuration data from the following sources in |
629 | the following order: | |
bf740959 | 630 | command line options, user's configuration file |
631 | .Pq Pa $HOME/.ssh/config , | |
632 | and system-wide configuration file | |
5f4fdfae | 633 | .Pq Pa /etc/ssh_config . |
bf740959 | 634 | For each parameter, the first obtained value |
610cd5c6 | 635 | will be used. |
636 | The configuration files contain sections bracketed by | |
637 | .Dq Host | |
638 | specifications, and that section is only applied for hosts that | |
639 | match one of the patterns given in the specification. | |
640 | The matched host name is the one given on the command line. | |
bf740959 | 641 | .Pp |
642 | Since the first obtained value for each parameter is used, more | |
643 | host-specific declarations should be given near the beginning of the | |
644 | file, and general defaults at the end. | |
645 | .Pp | |
646 | The configuration file has the following format: | |
647 | .Pp | |
648 | Empty lines and lines starting with | |
649 | .Ql # | |
650 | are comments. | |
651 | .Pp | |
652 | Otherwise a line is of the format | |
653 | .Dq keyword arguments . | |
38539909 | 654 | Configuration options may be separated by whitespace or |
655 | optional whitespace and exactly one | |
656 | .Ql = ; | |
657 | the latter format is useful to avoid the need to quote whitespace | |
658 | when specifying configuration options using the | |
659 | .Nm ssh , | |
660 | .Nm scp | |
661 | and | |
662 | .Nm sftp | |
663 | .Fl o | |
664 | option. | |
665 | .Pp | |
bf740959 | 666 | The possible |
54bf768d | 667 | keywords and their meanings are as follows (note that |
668 | keywords are case-insensitive and arguments are case-sensitive): | |
bf740959 | 669 | .Bl -tag -width Ds |
670 | .It Cm Host | |
671 | Restricts the following declarations (up to the next | |
672 | .Cm Host | |
673 | keyword) to be only for those hosts that match one of the patterns | |
674 | given after the keyword. | |
675 | .Ql \&* | |
676 | and | |
677 | .Ql ? | |
678 | can be used as wildcards in the | |
610cd5c6 | 679 | patterns. |
680 | A single | |
bf740959 | 681 | .Ql \&* |
682 | as a pattern can be used to provide global | |
610cd5c6 | 683 | defaults for all hosts. |
684 | The host is the | |
bf740959 | 685 | .Ar hostname |
686 | argument given on the command line (i.e., the name is not converted to | |
687 | a canonicalized host name before matching). | |
688 | .It Cm AFSTokenPassing | |
4fe2af09 | 689 | Specifies whether to pass AFS tokens to remote host. |
690 | The argument to this keyword must be | |
bf740959 | 691 | .Dq yes |
692 | or | |
693 | .Dq no . | |
da89cf4d | 694 | This option applies to protocol version 1 only. |
bf740959 | 695 | .It Cm BatchMode |
696 | If set to | |
697 | .Dq yes , | |
610cd5c6 | 698 | passphrase/password querying will be disabled. |
699 | This option is useful in scripts and other batch jobs where you have no | |
700 | user to supply the password. | |
701 | The argument must be | |
bf740959 | 702 | .Dq yes |
703 | or | |
704 | .Dq no . | |
01ce749f | 705 | The default is |
706 | .Dq no . | |
3435f5a6 | 707 | .It Cm BindAddress |
708 | Specify the interface to transmit from on machines with multiple | |
709 | interfaces or aliased addresses. | |
710 | Note that this option does not work if | |
711 | .Cm UsePrivilegedPort | |
712 | is set to | |
713 | .Dq yes . | |
7b2ea3a1 | 714 | .It Cm CheckHostIP |
715 | If this flag is set to | |
716 | .Dq yes , | |
01ce749f | 717 | ssh will additionally check the host IP address in the |
7b2ea3a1 | 718 | .Pa known_hosts |
4fe2af09 | 719 | file. |
720 | This allows ssh to detect if a host key changed due to DNS spoofing. | |
7b2ea3a1 | 721 | If the option is set to |
722 | .Dq no , | |
723 | the check will not be executed. | |
01ce749f | 724 | The default is |
725 | .Dq yes . | |
bf740959 | 726 | .It Cm Cipher |
33de75a3 | 727 | Specifies the cipher to use for encrypting the session |
a22aff1f | 728 | in protocol version 1. |
610cd5c6 | 729 | Currently, |
29999e54 | 730 | .Dq blowfish , |
731 | .Dq 3des , | |
bf740959 | 732 | and |
29999e54 | 733 | .Dq des |
610cd5c6 | 734 | are supported. |
29999e54 | 735 | .Ar des |
736 | is only supported in the | |
737 | .Nm | |
738 | client for interoperability with legacy protocol 1 implementations | |
739 | that do not support the | |
740 | .Ar 3des | |
741 | cipher. Its use is strongly discouraged due to cryptographic | |
742 | weaknesses. | |
610cd5c6 | 743 | The default is |
bf740959 | 744 | .Dq 3des . |
f54651ce | 745 | .It Cm Ciphers |
746 | Specifies the ciphers allowed for protocol version 2 | |
747 | in order of preference. | |
748 | Multiple ciphers must be comma-separated. | |
749 | The default is | |
9afadca8 | 750 | .Pp |
751 | .Bd -literal | |
f2ba0775 | 752 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour, |
da89cf4d | 753 | aes192-cbc,aes256-cbc'' |
9afadca8 | 754 | .Ed |
bf740959 | 755 | .It Cm Compression |
610cd5c6 | 756 | Specifies whether to use compression. |
757 | The argument must be | |
bf740959 | 758 | .Dq yes |
759 | or | |
760 | .Dq no . | |
01ce749f | 761 | The default is |
762 | .Dq no . | |
bf740959 | 763 | .It Cm CompressionLevel |
01ce749f | 764 | Specifies the compression level to use if compression is enabled. |
610cd5c6 | 765 | The argument must be an integer from 1 (fast) to 9 (slow, best). |
766 | The default level is 6, which is good for most applications. | |
767 | The meaning of the values is the same as in | |
7b2ea3a1 | 768 | .Xr gzip 1 . |
da89cf4d | 769 | Note that this option applies to protocol version 1 only. |
bf740959 | 770 | .It Cm ConnectionAttempts |
771 | Specifies the number of tries (one per second) to make before falling | |
610cd5c6 | 772 | back to rsh or exiting. |
773 | The argument must be an integer. | |
774 | This may be useful in scripts if the connection sometimes fails. | |
ce773142 | 775 | The default is 1. |
bf740959 | 776 | .It Cm EscapeChar |
777 | Sets the escape character (default: | |
778 | .Ql ~ ) . | |
779 | The escape character can also | |
610cd5c6 | 780 | be set on the command line. |
781 | The argument should be a single character, | |
bf740959 | 782 | .Ql ^ |
783 | followed by a letter, or | |
784 | .Dq none | |
785 | to disable the escape | |
786 | character entirely (making the connection transparent for binary | |
787 | data). | |
f54651ce | 788 | .It Cm FallBackToRsh |
bf740959 | 789 | Specifies that if connecting via |
790 | .Nm | |
791 | fails due to a connection refused error (there is no | |
792 | .Xr sshd 8 | |
f54651ce | 793 | listening on the remote host), |
bf740959 | 794 | .Xr rsh 1 |
795 | should automatically be used instead (after a suitable warning about | |
610cd5c6 | 796 | the session being unencrypted). |
797 | The argument must be | |
bf740959 | 798 | .Dq yes |
799 | or | |
800 | .Dq no . | |
01ce749f | 801 | The default is |
802 | .Dq no . | |
bf740959 | 803 | .It Cm ForwardAgent |
804 | Specifies whether the connection to the authentication agent (if any) | |
610cd5c6 | 805 | will be forwarded to the remote machine. |
806 | The argument must be | |
bf740959 | 807 | .Dq yes |
808 | or | |
809 | .Dq no . | |
71276795 | 810 | The default is |
811 | .Dq no . | |
bf740959 | 812 | .It Cm ForwardX11 |
813 | Specifies whether X11 connections will be automatically redirected | |
f54651ce | 814 | over the secure channel and |
bf740959 | 815 | .Ev DISPLAY |
610cd5c6 | 816 | set. |
f54651ce | 817 | The argument must be |
bf740959 | 818 | .Dq yes |
819 | or | |
820 | .Dq no . | |
c8d54615 | 821 | The default is |
822 | .Dq no . | |
bf740959 | 823 | .It Cm GatewayPorts |
824 | Specifies whether remote hosts are allowed to connect to local | |
825 | forwarded ports. | |
826 | The argument must be | |
827 | .Dq yes | |
828 | or | |
829 | .Dq no . | |
830 | The default is | |
831 | .Dq no . | |
832 | .It Cm GlobalKnownHostsFile | |
f49bc4f7 | 833 | Specifies a file to use for the global |
a5df12e9 | 834 | host key database instead of |
5f4fdfae | 835 | .Pa /etc/ssh_known_hosts . |
da89cf4d | 836 | .It Cm HostbasedAuthentication |
837 | Specifies whether to try rhosts based authentication with public key | |
838 | authentication. | |
839 | The argument must be | |
840 | .Dq yes | |
841 | or | |
842 | .Dq no . | |
843 | The default is | |
3398dda9 | 844 | .Dq no . |
da89cf4d | 845 | This option applies to protocol version 2 only and |
846 | is similar to | |
847 | .Cm RhostsRSAAuthentication . | |
e961a8f9 | 848 | .It Cm HostKeyAlgorithms |
98143cfc | 849 | Specifies the protocol version 2 host key algorithms |
e961a8f9 | 850 | that the client wants to use in order of preference. |
851 | The default for this option is: | |
852 | .Dq ssh-rsa,ssh-dss | |
da89cf4d | 853 | .It Cm HostKeyAlias |
854 | Specifies an alias that should be used instead of the | |
855 | real host name when looking up or saving the host key | |
856 | in the host key database files. | |
857 | This option is useful for tunneling ssh connections | |
858 | or if you have multiple servers running on a single host. | |
bf740959 | 859 | .It Cm HostName |
610cd5c6 | 860 | Specifies the real host name to log into. |
861 | This can be used to specify nicknames or abbreviations for hosts. | |
862 | Default is the name given on the command line. | |
863 | Numeric IP addresses are also permitted (both on the command line and in | |
bf740959 | 864 | .Cm HostName |
865 | specifications). | |
866 | .It Cm IdentityFile | |
da89cf4d | 867 | Specifies the file from which the user's RSA or DSA authentication identity |
bf740959 | 868 | is read (default |
1d1ffb87 | 869 | .Pa $HOME/.ssh/identity |
bf740959 | 870 | in the user's home directory). |
871 | Additionally, any identities represented by the authentication agent | |
610cd5c6 | 872 | will be used for authentication. |
873 | The file name may use the tilde | |
874 | syntax to refer to a user's home directory. | |
875 | It is possible to have | |
bf740959 | 876 | multiple identity files specified in configuration files; all these |
877 | identities will be tried in sequence. | |
878 | .It Cm KeepAlive | |
879 | Specifies whether the system should send keepalive messages to the | |
610cd5c6 | 880 | other side. |
881 | If they are sent, death of the connection or crash of one | |
882 | of the machines will be properly noticed. | |
883 | However, this means that | |
bf740959 | 884 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 885 | find it annoying. |
bf740959 | 886 | .Pp |
887 | The default is | |
888 | .Dq yes | |
889 | (to send keepalives), and the client will notice | |
610cd5c6 | 890 | if the network goes down or the remote host dies. |
891 | This is important in scripts, and many users want it too. | |
bf740959 | 892 | .Pp |
893 | To disable keepalives, the value should be set to | |
894 | .Dq no | |
895 | in both the server and the client configuration files. | |
896 | .It Cm KerberosAuthentication | |
4fe2af09 | 897 | Specifies whether Kerberos authentication will be used. |
898 | The argument to this keyword must be | |
bf740959 | 899 | .Dq yes |
900 | or | |
901 | .Dq no . | |
902 | .It Cm KerberosTgtPassing | |
4fe2af09 | 903 | Specifies whether a Kerberos TGT will be forwarded to the server. |
904 | This will only work if the Kerberos server is actually an AFS kaserver. | |
905 | The argument to this keyword must be | |
bf740959 | 906 | .Dq yes |
907 | or | |
908 | .Dq no . | |
909 | .It Cm LocalForward | |
910 | Specifies that a TCP/IP port on the local machine be forwarded over | |
610cd5c6 | 911 | the secure channel to given host:port from the remote machine. |
912 | The first argument must be a port number, and the second must be | |
913 | host:port. | |
914 | Multiple forwardings may be specified, and additional | |
915 | forwardings can be given on the command line. | |
916 | Only the superuser can forward privileged ports. | |
6a17f9c2 | 917 | .It Cm LogLevel |
918 | Gives the verbosity level that is used when logging messages from | |
919 | .Nm ssh . | |
920 | The possible values are: | |
59c97189 | 921 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
922 | The default is INFO. | |
b2552997 | 923 | .It Cm MACs |
3730bb22 | 924 | Specifies the MAC (message authentication code) algorithms |
b2552997 | 925 | in order of preference. |
926 | The MAC algorithm is used in protocol version 2 | |
927 | for data integrity protection. | |
928 | Multiple algorithms must be comma-separated. | |
929 | The default is | |
47bf6266 | 930 | .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 . |
bf740959 | 931 | .It Cm NumberOfPasswordPrompts |
4fe2af09 | 932 | Specifies the number of password prompts before giving up. |
933 | The argument to this keyword must be an integer. | |
934 | Default is 3. | |
7b2ea3a1 | 935 | .It Cm PasswordAuthentication |
610cd5c6 | 936 | Specifies whether to use password authentication. |
937 | The argument to this keyword must be | |
7b2ea3a1 | 938 | .Dq yes |
939 | or | |
940 | .Dq no . | |
01ce749f | 941 | The default is |
942 | .Dq yes . | |
bf740959 | 943 | .It Cm Port |
610cd5c6 | 944 | Specifies the port number to connect on the remote host. |
945 | Default is 22. | |
babd91d4 | 946 | .It Cm PreferredAuthentications |
3730bb22 | 947 | Specifies the order in which the client should try protocol 2 |
948 | authentication methods. This allows a client to prefer one method (e.g. | |
babd91d4 | 949 | .Cm keyboard-interactive ) |
950 | over another method (e.g. | |
951 | .Cm password ) | |
952 | The default for this option is: | |
29c440a0 | 953 | .Dq hostbased,publickey,keyboard-interactive,password |
f54651ce | 954 | .It Cm Protocol |
955 | Specifies the protocol versions | |
956 | .Nm | |
957 | should support in order of preference. | |
958 | The possible values are | |
959 | .Dq 1 | |
960 | and | |
961 | .Dq 2 . | |
962 | Multiple versions must be comma-separated. | |
963 | The default is | |
b4a19d21 | 964 | .Dq 2,1 . |
1d1ffb87 | 965 | This means that |
966 | .Nm | |
b4a19d21 | 967 | tries version 2 and falls back to version 1 |
968 | if version 2 is not available. | |
bf740959 | 969 | .It Cm ProxyCommand |
610cd5c6 | 970 | Specifies the command to use to connect to the server. |
971 | The command | |
972 | string extends to the end of the line, and is executed with | |
973 | .Pa /bin/sh . | |
974 | In the command string, | |
975 | .Ql %h | |
976 | will be substituted by the host name to | |
977 | connect and | |
978 | .Ql %p | |
979 | by the port. | |
980 | The command can be basically anything, | |
981 | and should read from its standard input and write to its standard output. | |
982 | It should eventually connect an | |
bf740959 | 983 | .Xr sshd 8 |
984 | server running on some machine, or execute | |
985 | .Ic sshd -i | |
610cd5c6 | 986 | somewhere. |
987 | Host key management will be done using the | |
bf740959 | 988 | HostName of the host being connected (defaulting to the name typed by |
989 | the user). | |
57112b5a | 990 | Note that |
991 | .Cm CheckHostIP | |
992 | is not available for connects with a proxy command. | |
bf740959 | 993 | .Pp |
da89cf4d | 994 | .It Cm PubkeyAuthentication |
995 | Specifies whether to try public key authentication. | |
996 | The argument to this keyword must be | |
997 | .Dq yes | |
998 | or | |
999 | .Dq no . | |
1000 | The default is | |
1001 | .Dq yes . | |
1002 | This option applies to protocol version 2 only. | |
bf740959 | 1003 | .It Cm RemoteForward |
1004 | Specifies that a TCP/IP port on the remote machine be forwarded over | |
610cd5c6 | 1005 | the secure channel to given host:port from the local machine. |
1006 | The first argument must be a port number, and the second must be | |
1007 | host:port. | |
1008 | Multiple forwardings may be specified, and additional | |
1009 | forwardings can be given on the command line. | |
1010 | Only the superuser can forward privileged ports. | |
bf740959 | 1011 | .It Cm RhostsAuthentication |
610cd5c6 | 1012 | Specifies whether to try rhosts based authentication. |
1013 | Note that this | |
bf740959 | 1014 | declaration only affects the client side and has no effect whatsoever |
610cd5c6 | 1015 | on security. |
1016 | Disabling rhosts authentication may reduce | |
bf740959 | 1017 | authentication time on slow connections when rhosts authentication is |
610cd5c6 | 1018 | not used. |
1019 | Most servers do not permit RhostsAuthentication because it | |
3730bb22 | 1020 | is not secure (see |
a5a2da3b | 1021 | .Cm RhostsRSAAuthentication ) . |
610cd5c6 | 1022 | The argument to this keyword must be |
bf740959 | 1023 | .Dq yes |
1024 | or | |
1025 | .Dq no . | |
01ce749f | 1026 | The default is |
1027 | .Dq yes . | |
da89cf4d | 1028 | This option applies to protocol version 1 only. |
bf740959 | 1029 | .It Cm RhostsRSAAuthentication |
1030 | Specifies whether to try rhosts based authentication with RSA host | |
610cd5c6 | 1031 | authentication. |
610cd5c6 | 1032 | The argument must be |
bf740959 | 1033 | .Dq yes |
1034 | or | |
1035 | .Dq no . | |
01ce749f | 1036 | The default is |
1037 | .Dq yes . | |
da89cf4d | 1038 | This option applies to protocol version 1 only. |
bf740959 | 1039 | .It Cm RSAAuthentication |
610cd5c6 | 1040 | Specifies whether to try RSA authentication. |
1041 | The argument to this keyword must be | |
bf740959 | 1042 | .Dq yes |
1043 | or | |
1044 | .Dq no . | |
1045 | RSA authentication will only be | |
1046 | attempted if the identity file exists, or an authentication agent is | |
1047 | running. | |
01ce749f | 1048 | The default is |
1049 | .Dq yes . | |
1d1ffb87 | 1050 | Note that this option applies to protocol version 1 only. |
61e96248 | 1051 | .It Cm ChallengeResponseAuthentication |
1052 | Specifies whether to use challenge response authentication. | |
610cd5c6 | 1053 | The argument to this keyword must be |
5260325f | 1054 | .Dq yes |
1055 | or | |
1056 | .Dq no . | |
1057 | The default is | |
10a2cbef | 1058 | .Dq yes . |
eea098a3 | 1059 | .It Cm SmartcardDevice |
1060 | Specifies which smartcard device to use. The argument to this keyword is | |
1061 | the device | |
1062 | .Nm | |
1063 | should use to communicate with a smartcard used for storing the user's | |
1064 | private RSA key. By default, no device is specified and smartcard support | |
1065 | is not activated. | |
bf740959 | 1066 | .It Cm StrictHostKeyChecking |
1067 | If this flag is set to | |
f54651ce | 1068 | .Dq yes , |
bf740959 | 1069 | .Nm |
a877488a | 1070 | will never automatically add host keys to the |
bf740959 | 1071 | .Pa $HOME/.ssh/known_hosts |
f49bc4f7 | 1072 | file, and refuses to connect to hosts whose host key has changed. |
610cd5c6 | 1073 | This provides maximum protection against trojan horse attacks. |
1074 | However, it can be somewhat annoying if you don't have good | |
5f4fdfae | 1075 | .Pa /etc/ssh_known_hosts |
bf740959 | 1076 | files installed and frequently |
a877488a | 1077 | connect to new hosts. |
1078 | This option forces the user to manually | |
1079 | add all new hosts. | |
1080 | If this flag is set to | |
1081 | .Dq no , | |
1082 | .Nm | |
1083 | will automatically add new host keys to the | |
1084 | user known hosts files. | |
1085 | If this flag is set to | |
1086 | .Dq ask , | |
1087 | new host keys | |
1088 | will be added to the user known host files only after the user | |
1089 | has confirmed that is what they really want to do, and | |
1090 | .Nm | |
1091 | will refuse to connect to hosts whose host key has changed. | |
610cd5c6 | 1092 | The host keys of |
a877488a | 1093 | known hosts will be verified automatically in all cases. |
610cd5c6 | 1094 | The argument must be |
a877488a | 1095 | .Dq yes , |
1096 | .Dq no | |
bf740959 | 1097 | or |
a877488a | 1098 | .Dq ask . |
1099 | The default is | |
1100 | .Dq ask . | |
bf740959 | 1101 | .It Cm UsePrivilegedPort |
1102 | Specifies whether to use a privileged port for outgoing connections. | |
1103 | The argument must be | |
1104 | .Dq yes | |
1105 | or | |
1106 | .Dq no . | |
1107 | The default is | |
d5ebca2b | 1108 | .Dq no . |
da89cf4d | 1109 | Note that you need to set this option to |
1110 | .Dq yes | |
1111 | if you want to use | |
bf740959 | 1112 | .Cm RhostsAuthentication |
1113 | and | |
6ffc9c88 | 1114 | .Cm RhostsRSAAuthentication |
da89cf4d | 1115 | with older servers. |
7b2ea3a1 | 1116 | .It Cm User |
610cd5c6 | 1117 | Specifies the user to log in as. |
1118 | This can be useful if you have a different user name on different machines. | |
1119 | This saves the trouble of | |
7b2ea3a1 | 1120 | having to remember to give the user name on the command line. |
1121 | .It Cm UserKnownHostsFile | |
f49bc4f7 | 1122 | Specifies a file to use for the user |
a5df12e9 | 1123 | host key database instead of |
7b2ea3a1 | 1124 | .Pa $HOME/.ssh/known_hosts . |
bf740959 | 1125 | .It Cm UseRsh |
610cd5c6 | 1126 | Specifies that rlogin/rsh should be used for this host. |
1127 | It is possible that the host does not at all support the | |
bf740959 | 1128 | .Nm |
610cd5c6 | 1129 | protocol. |
1130 | This causes | |
bf740959 | 1131 | .Nm |
610cd5c6 | 1132 | to immediately execute |
bf740959 | 1133 | .Xr rsh 1 . |
1134 | All other options (except | |
1135 | .Cm HostName ) | |
610cd5c6 | 1136 | are ignored if this has been specified. |
1137 | The argument must be | |
bf740959 | 1138 | .Dq yes |
1139 | or | |
1140 | .Dq no . | |
fa649821 | 1141 | .It Cm XAuthLocation |
1142 | Specifies the location of the | |
1143 | .Xr xauth 1 | |
1144 | program. | |
1145 | The default is | |
1146 | .Pa /usr/X11R6/bin/xauth . | |
b5e300c2 | 1147 | .El |
bf740959 | 1148 | .Sh ENVIRONMENT |
1149 | .Nm | |
1150 | will normally set the following environment variables: | |
1151 | .Bl -tag -width Ds | |
1152 | .It Ev DISPLAY | |
1153 | The | |
1154 | .Ev DISPLAY | |
610cd5c6 | 1155 | variable indicates the location of the X11 server. |
f54651ce | 1156 | It is automatically set by |
bf740959 | 1157 | .Nm |
1158 | to point to a value of the form | |
1159 | .Dq hostname:n | |
1160 | where hostname indicates | |
610cd5c6 | 1161 | the host where the shell runs, and n is an integer >= 1. |
1162 | .Nm | |
1163 | uses this special value to forward X11 connections over the secure | |
1164 | channel. | |
da89cf4d | 1165 | The user should normally not set |
1166 | .Ev DISPLAY | |
1167 | explicitly, as that | |
bf740959 | 1168 | will render the X11 connection insecure (and will require the user to |
1169 | manually copy any required authorization cookies). | |
1170 | .It Ev HOME | |
1171 | Set to the path of the user's home directory. | |
1172 | .It Ev LOGNAME | |
1173 | Synonym for | |
1174 | .Ev USER ; | |
1175 | set for compatibility with systems that use this variable. | |
1176 | .It Ev MAIL | |
ae897d7c | 1177 | Set to the path of the user's mailbox. |
610cd5c6 | 1178 | .It Ev PATH |
bf740959 | 1179 | Set to the default |
1180 | .Ev PATH , | |
1181 | as specified when compiling | |
1182 | .Nm ssh . | |
3474b2b4 | 1183 | .It Ev SSH_ASKPASS |
1184 | If | |
1185 | .Nm | |
1186 | needs a passphrase, it will read the passphrase from the current | |
1187 | terminal if it was run from a terminal. | |
1188 | If | |
1189 | .Nm | |
1190 | does not have a terminal associated with it but | |
1191 | .Ev DISPLAY | |
1192 | and | |
1193 | .Ev SSH_ASKPASS | |
1194 | are set, it will execute the program specified by | |
1195 | .Ev SSH_ASKPASS | |
1196 | and open an X11 window to read the passphrase. | |
1197 | This is particularly useful when calling | |
1198 | .Nm | |
1199 | from a | |
1200 | .Pa .Xsession | |
1201 | or related script. | |
1202 | (Note that on some machines it | |
1203 | may be necessary to redirect the input from | |
1204 | .Pa /dev/null | |
1205 | to make this work.) | |
bf740959 | 1206 | .It Ev SSH_AUTH_SOCK |
ae897d7c | 1207 | Identifies the path of a unix-domain socket used to communicate with the |
bf740959 | 1208 | agent. |
1209 | .It Ev SSH_CLIENT | |
610cd5c6 | 1210 | Identifies the client end of the connection. |
1211 | The variable contains | |
bf740959 | 1212 | three space-separated values: client ip-address, client port number, |
1213 | and server port number. | |
8abcdba4 | 1214 | .It Ev SSH_ORIGINAL_COMMAND |
1215 | The variable contains the original command line if a forced command | |
1216 | is executed. | |
1217 | It can be used to extract the original arguments. | |
bf740959 | 1218 | .It Ev SSH_TTY |
1219 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 1220 | with the current shell or command. |
1221 | If the current session has no tty, | |
bf740959 | 1222 | this variable is not set. |
1223 | .It Ev TZ | |
1224 | The timezone variable is set to indicate the present timezone if it | |
c345cf9d | 1225 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 1226 | on to new connections). |
1227 | .It Ev USER | |
1228 | Set to the name of the user logging in. | |
1229 | .El | |
1230 | .Pp | |
f54651ce | 1231 | Additionally, |
bf740959 | 1232 | .Nm |
f54651ce | 1233 | reads |
1234 | .Pa $HOME/.ssh/environment , | |
bf740959 | 1235 | and adds lines of the format |
1236 | .Dq VARNAME=value | |
1237 | to the environment. | |
1238 | .Sh FILES | |
c8d54615 | 1239 | .Bl -tag -width Ds |
f49bc4f7 | 1240 | .It Pa $HOME/.ssh/known_hosts |
ae897d7c | 1241 | Records host keys for all hosts the user has logged into that are not |
bf740959 | 1242 | in |
f49bc4f7 | 1243 | .Pa /etc/ssh_known_hosts . |
bf740959 | 1244 | See |
1245 | .Xr sshd 8 . | |
c0ecc314 | 1246 | .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa |
1247 | Contains the authentication identity of the user. | |
1248 | They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. | |
1d1ffb87 | 1249 | These files |
1250 | contain sensitive data and should be readable by the user but not | |
bf740959 | 1251 | accessible by others (read/write/execute). |
1252 | Note that | |
1253 | .Nm | |
1d1ffb87 | 1254 | ignores a private key file if it is accessible by others. |
bf740959 | 1255 | It is possible to specify a passphrase when |
1256 | generating the key; the passphrase will be used to encrypt the | |
1257 | sensitive part of this file using 3DES. | |
c0ecc314 | 1258 | .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub |
bf740959 | 1259 | Contains the public key for authentication (public part of the |
610cd5c6 | 1260 | identity file in human-readable form). |
1d1ffb87 | 1261 | The contents of the |
1262 | .Pa $HOME/.ssh/identity.pub | |
1263 | file should be added to | |
bf740959 | 1264 | .Pa $HOME/.ssh/authorized_keys |
1265 | on all machines | |
c0ecc314 | 1266 | where you wish to log in using protocol version 1 RSA authentication. |
1d1ffb87 | 1267 | The contents of the |
1268 | .Pa $HOME/.ssh/id_dsa.pub | |
c0ecc314 | 1269 | and |
1270 | .Pa $HOME/.ssh/id_rsa.pub | |
1d1ffb87 | 1271 | file should be added to |
96a7b0cc | 1272 | .Pa $HOME/.ssh/authorized_keys |
1d1ffb87 | 1273 | on all machines |
c0ecc314 | 1274 | where you wish to log in using protocol version 2 DSA/RSA authentication. |
1d1ffb87 | 1275 | These files are not |
610cd5c6 | 1276 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 1277 | These files are |
c44559d2 | 1278 | never used automatically and are not necessary; they are only provided for |
bf740959 | 1279 | the convenience of the user. |
1280 | .It Pa $HOME/.ssh/config | |
610cd5c6 | 1281 | This is the per-user configuration file. |
1282 | The format of this file is described above. | |
1283 | This file is used by the | |
bf740959 | 1284 | .Nm |
610cd5c6 | 1285 | client. |
1286 | This file does not usually contain any sensitive information, | |
bf740959 | 1287 | but the recommended permissions are read/write for the user, and not |
1288 | accessible by others. | |
1289 | .It Pa $HOME/.ssh/authorized_keys | |
96a7b0cc | 1290 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. |
610cd5c6 | 1291 | The format of this file is described in the |
bf740959 | 1292 | .Xr sshd 8 |
610cd5c6 | 1293 | manual page. |
f49bc4f7 | 1294 | In the simplest form the format is the same as the .pub |
1295 | identity files. | |
1d1ffb87 | 1296 | This file is not highly sensitive, but the recommended |
1297 | permissions are read/write for the user, and not accessible by others. | |
f49bc4f7 | 1298 | .It Pa /etc/ssh_known_hosts |
610cd5c6 | 1299 | Systemwide list of known host keys. |
f49bc4f7 | 1300 | This file should be prepared by the |
bf740959 | 1301 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1302 | organization. |
1303 | This file should be world-readable. | |
1304 | This file contains | |
bf740959 | 1305 | public keys, one per line, in the following format (fields separated |
f49bc4f7 | 1306 | by spaces): system name, public key and optional comment field. |
610cd5c6 | 1307 | When different names are used |
bf740959 | 1308 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1309 | commas. |
1310 | The format is described on the | |
bf740959 | 1311 | .Xr sshd 8 |
1312 | manual page. | |
1313 | .Pp | |
1314 | The canonical system name (as returned by name servers) is used by | |
1315 | .Xr sshd 8 | |
1316 | to verify the client host when logging in; other names are needed because | |
1317 | .Nm | |
1318 | does not convert the user-supplied name to a canonical name before | |
1319 | checking the key, because someone with access to the name servers | |
1320 | would then be able to fool host authentication. | |
5f4fdfae | 1321 | .It Pa /etc/ssh_config |
610cd5c6 | 1322 | Systemwide configuration file. |
1323 | This file provides defaults for those | |
bf740959 | 1324 | values that are not specified in the user's configuration file, and |
610cd5c6 | 1325 | for those users who do not have a configuration file. |
1326 | This file must be world-readable. | |
bf740959 | 1327 | .It Pa $HOME/.rhosts |
1328 | This file is used in | |
1329 | .Pa \&.rhosts | |
1330 | authentication to list the | |
610cd5c6 | 1331 | host/user pairs that are permitted to log in. |
1332 | (Note that this file is | |
bf740959 | 1333 | also used by rlogin and rsh, which makes using this file insecure.) |
1334 | Each line of the file contains a host name (in the canonical form | |
1335 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1336 | separated by a space. |
e91c60f2 | 1337 | On some machines this file may need to be |
bf740959 | 1338 | world-readable if the user's home directory is on a NFS partition, |
1339 | because | |
1340 | .Xr sshd 8 | |
610cd5c6 | 1341 | reads it as root. |
1342 | Additionally, this file must be owned by the user, | |
1343 | and must not have write permissions for anyone else. | |
1344 | The recommended | |
bf740959 | 1345 | permission for most machines is read/write for the user, and not |
1346 | accessible by others. | |
1347 | .Pp | |
1348 | Note that by default | |
1349 | .Xr sshd 8 | |
1350 | will be installed so that it requires successful RSA host | |
610cd5c6 | 1351 | authentication before permitting \s+2.\s0rhosts authentication. |
1352 | If your server machine does not have the client's host key in | |
5f4fdfae | 1353 | .Pa /etc/ssh_known_hosts , |
bf740959 | 1354 | you can store it in |
1355 | .Pa $HOME/.ssh/known_hosts . | |
1356 | The easiest way to do this is to | |
1357 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1358 | will automatically add the host key to |
bf740959 | 1359 | .Pa $HOME/.ssh/known_hosts . |
1360 | .It Pa $HOME/.shosts | |
1361 | This file is used exactly the same way as | |
1362 | .Pa \&.rhosts . | |
1363 | The purpose for | |
1364 | having this file is to be able to use rhosts authentication with | |
1365 | .Nm | |
1366 | without permitting login with | |
1367 | .Xr rlogin 1 | |
1368 | or | |
1369 | .Xr rsh 1 . | |
1370 | .It Pa /etc/hosts.equiv | |
1371 | This file is used during | |
610cd5c6 | 1372 | .Pa \&.rhosts authentication. |
1373 | It contains | |
bf740959 | 1374 | canonical hosts names, one per line (the full format is described on |
1375 | the | |
1376 | .Xr sshd 8 | |
610cd5c6 | 1377 | manual page). |
1378 | If the client host is found in this file, login is | |
bf740959 | 1379 | automatically permitted provided client and server user names are the |
610cd5c6 | 1380 | same. |
1381 | Additionally, successful RSA host authentication is normally | |
1382 | required. | |
1383 | This file should only be writable by root. | |
5f4fdfae | 1384 | .It Pa /etc/shosts.equiv |
f54651ce | 1385 | This file is processed exactly as |
bf740959 | 1386 | .Pa /etc/hosts.equiv . |
1387 | This file may be useful to permit logins using | |
1388 | .Nm | |
1389 | but not using rsh/rlogin. | |
5f4fdfae | 1390 | .It Pa /etc/sshrc |
bf740959 | 1391 | Commands in this file are executed by |
1392 | .Nm | |
1393 | when the user logs in just before the user's shell (or command) is started. | |
1394 | See the | |
1395 | .Xr sshd 8 | |
1396 | manual page for more information. | |
1397 | .It Pa $HOME/.ssh/rc | |
1398 | Commands in this file are executed by | |
1399 | .Nm | |
1400 | when the user logs in just before the user's shell (or command) is | |
1401 | started. | |
f54651ce | 1402 | See the |
bf740959 | 1403 | .Xr sshd 8 |
1404 | manual page for more information. | |
83b7f649 | 1405 | .It Pa $HOME/.ssh/environment |
1406 | Contains additional definitions for environment variables, see section | |
1407 | .Sx ENVIRONMENT | |
1408 | above. | |
b5e300c2 | 1409 | .El |
fa08c86b | 1410 | .Sh AUTHORS |
5fb622e4 | 1411 | OpenSSH is a derivative of the original and free |
1412 | ssh 1.2.12 release by Tatu Ylonen. | |
1413 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1414 | Theo de Raadt and Dug Song | |
1415 | removed many bugs, re-added newer features and | |
1416 | created OpenSSH. | |
1417 | Markus Friedl contributed the support for SSH | |
1418 | protocol versions 1.5 and 2.0. | |
bf740959 | 1419 | .Sh SEE ALSO |
1420 | .Xr rlogin 1 , | |
1421 | .Xr rsh 1 , | |
1422 | .Xr scp 1 , | |
61e96248 | 1423 | .Xr sftp 1 , |
bf740959 | 1424 | .Xr ssh-add 1 , |
1425 | .Xr ssh-agent 1 , | |
1426 | .Xr ssh-keygen 1 , | |
1427 | .Xr telnet 1 , | |
9afadca8 | 1428 | .Xr sshd 8 |
2cad6cef | 1429 | .Rs |
1430 | .%A T. Ylonen | |
1431 | .%A T. Kivinen | |
1432 | .%A M. Saarinen | |
1433 | .%A T. Rinne | |
1434 | .%A S. Lehtinen | |
1435 | .%T "SSH Protocol Architecture" | |
1930af48 | 1436 | .%N draft-ietf-secsh-architecture-09.txt |
1437 | .%D July 2001 | |
2cad6cef | 1438 | .%O work in progress material |
1439 | .Re |