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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 | .\" |
985bb789 | 37 | .\" $OpenBSD: ssh.1,v 1.216 2005/12/07 10:52:13 jmc 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 | |
0e19494c | 46 | .Op Fl 1246AaCfgkMNnqsTtVvXxY |
3435f5a6 | 47 | .Op Fl b Ar bind_address |
d0c832f3 | 48 | .Op Fl c Ar cipher_spec |
5ddc5eb4 | 49 | .Oo Fl D\ \& |
50 | .Sm off | |
51 | .Oo Ar bind_address : Oc | |
52 | .Ar port | |
53 | .Sm on | |
54 | .Oc | |
bf740959 | 55 | .Op Fl e Ar escape_char |
e591b98a | 56 | .Op Fl F Ar configfile |
37c406a8 | 57 | .Bk -words |
5f4a0c58 | 58 | .Op Fl i Ar identity_file |
37c406a8 | 59 | .Ek |
6c7e3b94 | 60 | .Oo Fl L\ \& |
bf740959 | 61 | .Sm off |
3867aa0a | 62 | .Oo Ar bind_address : Oc |
6c7e3b94 | 63 | .Ar port : host : hostport |
bf740959 | 64 | .Sm on |
bf740959 | 65 | .Oc |
37c406a8 | 66 | .Bk -words |
5f4a0c58 | 67 | .Op Fl l Ar login_name |
37c406a8 | 68 | .Ek |
5f4a0c58 | 69 | .Op Fl m Ar mac_spec |
f8c6db83 | 70 | .Op Fl O Ar ctl_cmd |
5f4a0c58 | 71 | .Op Fl o Ar option |
5f4a0c58 | 72 | .Op Fl p Ar port |
6c7e3b94 | 73 | .Oo Fl R\ \& |
bf740959 | 74 | .Sm off |
3867aa0a | 75 | .Oo Ar bind_address : Oc |
6c7e3b94 | 76 | .Ar port : host : hostport |
bf740959 | 77 | .Sm on |
bf740959 | 78 | .Oc |
f8c6db83 | 79 | .Op Fl S Ar ctl_path |
985bb789 | 80 | .Bk -words |
81 | .Op Fl w Ar tunnel : Ns Ar tunnel | |
5f4a0c58 | 82 | .Oo Ar user Ns @ Oc Ns Ar hostname |
bf740959 | 83 | .Op Ar command |
985bb789 | 84 | .Ek |
f54651ce | 85 | .Sh DESCRIPTION |
bf740959 | 86 | .Nm |
2c86906e | 87 | (SSH client) is a program for logging into a remote machine and for |
610cd5c6 | 88 | executing commands on a remote machine. |
5f4a0c58 | 89 | It is intended to replace rlogin and rsh, |
90 | and provide secure encrypted communications between | |
610cd5c6 | 91 | two untrusted hosts over an insecure network. |
5f4a0c58 | 92 | X11 connections and arbitrary TCP/IP ports |
93 | can also be forwarded over the secure channel. | |
bf740959 | 94 | .Pp |
95 | .Nm | |
f54651ce | 96 | connects and logs into the specified |
5f4a0c58 | 97 | .Ar hostname |
98 | (with optional | |
99 | .Ar user | |
100 | name). | |
bf740959 | 101 | The user must prove |
1d1ffb87 | 102 | his/her identity to the remote machine using one of several methods |
5f4a0c58 | 103 | depending on the protocol version used. |
1d1ffb87 | 104 | .Pp |
5f4a0c58 | 105 | If |
106 | .Ar command | |
107 | is specified, | |
108 | .Ar command | |
109 | is executed on the remote host instead of a login shell. | |
1d1ffb87 | 110 | .Ss SSH protocol version 1 |
6f5abc1e | 111 | The first authentication method is the |
112 | .Em rhosts | |
113 | or | |
114 | .Em hosts.equiv | |
115 | method combined with RSA-based host authentication. | |
116 | If the machine the user logs in from is listed in | |
bf740959 | 117 | .Pa /etc/hosts.equiv |
118 | or | |
5f4fdfae | 119 | .Pa /etc/shosts.equiv |
bf740959 | 120 | on the remote machine, and the user names are |
6f5abc1e | 121 | the same on both sides, or if the files |
140e3e97 | 122 | .Pa ~/.rhosts |
bf740959 | 123 | or |
140e3e97 | 124 | .Pa ~/.shosts |
6f5abc1e | 125 | exist in the user's home directory on the |
126 | remote machine and contain a line containing the name of the client | |
bf740959 | 127 | machine and the name of the user on that machine, the user is |
6f5abc1e | 128 | considered for log in. |
129 | Additionally, if the server can verify the client's | |
f54651ce | 130 | host key (see |
2a8a6488 | 131 | .Pa /etc/ssh/ssh_known_hosts |
5bbb5681 | 132 | and |
140e3e97 | 133 | .Pa ~/.ssh/known_hosts |
bf740959 | 134 | in the |
135 | .Sx FILES | |
5f4a0c58 | 136 | section), only then is login permitted. |
610cd5c6 | 137 | This authentication method closes security holes due to IP |
138 | spoofing, DNS spoofing and routing spoofing. | |
139 | [Note to the administrator: | |
bf740959 | 140 | .Pa /etc/hosts.equiv , |
140e3e97 | 141 | .Pa ~/.rhosts , |
bf740959 | 142 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
143 | disabled if security is desired.] | |
144 | .Pp | |
6f5abc1e | 145 | As a second authentication method, |
bf740959 | 146 | .Nm |
147 | supports RSA based authentication. | |
148 | The scheme is based on public-key cryptography: there are cryptosystems | |
149 | where encryption and decryption are done using separate keys, and it | |
150 | is not possible to derive the decryption key from the encryption key. | |
610cd5c6 | 151 | RSA is one such system. |
f54651ce | 152 | The idea is that each user creates a public/private |
610cd5c6 | 153 | key pair for authentication purposes. |
154 | The server knows the public key, and only the user knows the private key. | |
5f4a0c58 | 155 | .Pp |
f54651ce | 156 | The file |
140e3e97 | 157 | .Pa ~/.ssh/authorized_keys |
5f4a0c58 | 158 | lists the public keys that are permitted for logging in. |
610cd5c6 | 159 | When the user logs in, the |
bf740959 | 160 | .Nm |
161 | program tells the server which key pair it would like to use for | |
610cd5c6 | 162 | authentication. |
5f4a0c58 | 163 | The server checks if this key is permitted, and if so, |
164 | sends the user (actually the | |
bf740959 | 165 | .Nm |
166 | program running on behalf of the user) a challenge, a random number, | |
610cd5c6 | 167 | encrypted by the user's public key. |
5f4a0c58 | 168 | The challenge can only be decrypted using the proper private key. |
169 | The user's client then decrypts the challenge using the private key, | |
170 | proving that he/she knows the private key | |
171 | but without disclosing it to the server. | |
bf740959 | 172 | .Pp |
173 | .Nm | |
610cd5c6 | 174 | implements the RSA authentication protocol automatically. |
175 | The user creates his/her RSA key pair by running | |
bf740959 | 176 | .Xr ssh-keygen 1 . |
f54651ce | 177 | This stores the private key in |
140e3e97 | 178 | .Pa ~/.ssh/identity |
5f4a0c58 | 179 | and stores the public key in |
140e3e97 | 180 | .Pa ~/.ssh/identity.pub |
610cd5c6 | 181 | in the user's home directory. |
182 | The user should then copy the | |
bf740959 | 183 | .Pa identity.pub |
f54651ce | 184 | to |
140e3e97 | 185 | .Pa ~/.ssh/authorized_keys |
f54651ce | 186 | in his/her home directory on the remote machine (the |
bf740959 | 187 | .Pa authorized_keys |
f54651ce | 188 | file corresponds to the conventional |
140e3e97 | 189 | .Pa ~/.rhosts |
bf740959 | 190 | file, and has one key |
610cd5c6 | 191 | per line, though the lines can be very long). |
192 | After this, the user can log in without giving the password. | |
bf740959 | 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. | |
1d1ffb87 | 206 | .Ss SSH protocol version 2 |
5f4a0c58 | 207 | When a user connects using protocol version 2, |
16210ef7 | 208 | similar authentication methods are available. |
da89cf4d | 209 | Using the default values for |
210 | .Cm PreferredAuthentications , | |
29c440a0 | 211 | the client will try to authenticate first using the hostbased method; |
5f4a0c58 | 212 | if this method fails, public key authentication is attempted, |
213 | and finally if this method fails, keyboard-interactive and | |
29c440a0 | 214 | password authentication are tried. |
1d1ffb87 | 215 | .Pp |
216 | The public key method is similar to RSA authentication described | |
da89cf4d | 217 | in the previous section and allows the RSA or DSA algorithm to be used: |
c0ecc314 | 218 | The client uses his private key, |
140e3e97 | 219 | .Pa ~/.ssh/id_dsa |
c0ecc314 | 220 | or |
140e3e97 | 221 | .Pa ~/.ssh/id_rsa , |
1d1ffb87 | 222 | to sign the session identifier and sends the result to the server. |
223 | The server checks whether the matching public key is listed in | |
140e3e97 | 224 | .Pa ~/.ssh/authorized_keys |
1d1ffb87 | 225 | and grants access if both the key is found and the signature is correct. |
226 | The session identifier is derived from a shared Diffie-Hellman value | |
227 | and is only known to the client and the server. | |
228 | .Pp | |
5f4a0c58 | 229 | If public key authentication fails or is not available, a password |
230 | can be sent encrypted to the remote host to prove the user's identity. | |
da89cf4d | 231 | .Pp |
232 | Additionally, | |
233 | .Nm | |
234 | supports hostbased or challenge response authentication. | |
1d1ffb87 | 235 | .Pp |
236 | Protocol 2 provides additional mechanisms for confidentiality | |
3b9baa7b | 237 | (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour) |
238 | and integrity (hmac-md5, hmac-sha1, hmac-ripemd160). | |
1d1ffb87 | 239 | Note that protocol 1 lacks a strong mechanism for ensuring the |
240 | integrity of the connection. | |
1d1ffb87 | 241 | .Ss Login session and remote execution |
bf740959 | 242 | When the user's identity has been accepted by the server, the server |
243 | either executes the given command, or logs into the machine and gives | |
610cd5c6 | 244 | the user a normal shell on the remote machine. |
245 | All communication with | |
bf740959 | 246 | the remote command or shell will be automatically encrypted. |
247 | .Pp | |
248 | If a pseudo-terminal has been allocated (normal login session), the | |
df841692 | 249 | user may use the escape characters noted below. |
bf740959 | 250 | .Pp |
5f4a0c58 | 251 | If no pseudo-tty has been allocated, |
252 | the session is transparent and can be used to reliably transfer binary data. | |
610cd5c6 | 253 | On most systems, setting the escape character to |
bf740959 | 254 | .Dq none |
255 | will also make the session transparent even if a tty is used. | |
256 | .Pp | |
ce9c0b75 | 257 | The session terminates when the command or shell on the remote |
e91c60f2 | 258 | machine exits and all X11 and TCP/IP connections have been closed. |
5f4a0c58 | 259 | The exit status of the remote program is returned as the exit status of |
bf740959 | 260 | .Nm ssh . |
df841692 | 261 | .Ss Escape Characters |
5f4a0c58 | 262 | When a pseudo-terminal has been requested, |
263 | .Nm | |
264 | supports a number of functions through the use of an escape character. | |
df841692 | 265 | .Pp |
266 | A single tilde character can be sent as | |
267 | .Ic ~~ | |
5bef3c35 | 268 | or by following the tilde by a character other than those described below. |
df841692 | 269 | The escape character must always follow a newline to be interpreted as |
270 | special. | |
271 | The escape character can be changed in configuration files using the | |
272 | .Cm EscapeChar | |
3730bb22 | 273 | configuration directive or on the command line by the |
df841692 | 274 | .Fl e |
275 | option. | |
276 | .Pp | |
277 | The supported escapes (assuming the default | |
278 | .Ql ~ ) | |
279 | are: | |
280 | .Bl -tag -width Ds | |
281 | .It Cm ~. | |
5f4a0c58 | 282 | Disconnect. |
df841692 | 283 | .It Cm ~^Z |
5f4a0c58 | 284 | Background |
285 | .Nm ssh . | |
df841692 | 286 | .It Cm ~# |
5f4a0c58 | 287 | List forwarded connections. |
df841692 | 288 | .It Cm ~& |
5f4a0c58 | 289 | Background |
290 | .Nm | |
291 | at logout when waiting for forwarded connection / X11 sessions to terminate. | |
df841692 | 292 | .It Cm ~? |
5f4a0c58 | 293 | Display a list of escape characters. |
16a79097 | 294 | .It Cm ~B |
5f4a0c58 | 295 | Send a BREAK to the remote system |
296 | (only useful for SSH protocol version 2 and if the peer supports it). | |
c53c54c2 | 297 | .It Cm ~C |
d740ec16 | 298 | Open command line. |
299 | Currently this allows the addition of port forwardings using the | |
c53c54c2 | 300 | .Fl L |
301 | and | |
302 | .Fl R | |
d740ec16 | 303 | options (see below). |
790029d9 | 304 | It also allows the cancellation of existing remote port-forwardings |
d740ec16 | 305 | using |
306 | .Fl KR Ar hostport . | |
985bb789 | 307 | The |
d20f3c9e | 308 | .Ic ! Ar command |
309 | allows the user to execute a local command if the | |
310 | .Ic PermitLocalCommand | |
311 | option is enabled in | |
312 | .Xr ssh_config 5 . | |
7069a5e2 | 313 | Basic help is available, using the |
314 | .Fl h | |
d740ec16 | 315 | option. |
df841692 | 316 | .It Cm ~R |
5f4a0c58 | 317 | Request rekeying of the connection |
318 | (only useful for SSH protocol version 2 and if the peer supports it). | |
df841692 | 319 | .El |
1d1ffb87 | 320 | .Ss X11 and TCP forwarding |
6efa3d14 | 321 | If the |
322 | .Cm ForwardX11 | |
323 | variable is set to | |
324 | .Dq yes | |
5f4a0c58 | 325 | (or see the description of the |
6efa3d14 | 326 | .Fl X |
327 | and | |
328 | .Fl x | |
329 | options described later) | |
330 | and the user is using X11 (the | |
bf740959 | 331 | .Ev DISPLAY |
332 | environment variable is set), the connection to the X11 display is | |
333 | automatically forwarded to the remote side in such a way that any X11 | |
334 | programs started from the shell (or command) will go through the | |
335 | encrypted channel, and the connection to the real X server will be made | |
610cd5c6 | 336 | from the local machine. |
337 | The user should not manually set | |
bf740959 | 338 | .Ev DISPLAY . |
339 | Forwarding of X11 connections can be | |
340 | configured on the command line or in configuration files. | |
341 | .Pp | |
342 | The | |
f54651ce | 343 | .Ev DISPLAY |
bf740959 | 344 | value set by |
345 | .Nm | |
5f4a0c58 | 346 | will point to the server machine, but with a display number greater than zero. |
610cd5c6 | 347 | This is normal, and happens because |
bf740959 | 348 | .Nm |
349 | creates a | |
350 | .Dq proxy | |
351 | X server on the server machine for forwarding the | |
352 | connections over the encrypted channel. | |
353 | .Pp | |
354 | .Nm | |
355 | will also automatically set up Xauthority data on the server machine. | |
356 | For this purpose, it will generate a random authorization cookie, | |
357 | store it in Xauthority on the server, and verify that any forwarded | |
358 | connections carry this cookie and replace it by the real cookie when | |
610cd5c6 | 359 | the connection is opened. |
360 | The real authentication cookie is never | |
bf740959 | 361 | sent to the server machine (and no cookies are sent in the plain). |
362 | .Pp | |
24794905 | 363 | If the |
364 | .Cm ForwardAgent | |
365 | variable is set to | |
366 | .Dq yes | |
5f4a0c58 | 367 | (or see the description of the |
24794905 | 368 | .Fl A |
369 | and | |
370 | .Fl a | |
a4e5acef | 371 | options described later) and |
24794905 | 372 | the user is using an authentication agent, the connection to the agent |
373 | is automatically forwarded to the remote side. | |
bf740959 | 374 | .Pp |
375 | Forwarding of arbitrary TCP/IP connections over the secure channel can | |
491f5f7b | 376 | be specified either on the command line or in a configuration file. |
610cd5c6 | 377 | One possible application of TCP/IP forwarding is a secure connection to an |
e91c60f2 | 378 | electronic purse; another is going through firewalls. |
1d1ffb87 | 379 | .Ss Server authentication |
bf740959 | 380 | .Nm |
1d1ffb87 | 381 | automatically maintains and checks a database containing |
610cd5c6 | 382 | identifications for all hosts it has ever been used with. |
f49bc4f7 | 383 | Host keys are stored in |
140e3e97 | 384 | .Pa ~/.ssh/known_hosts |
610cd5c6 | 385 | in the user's home directory. |
f49bc4f7 | 386 | Additionally, the file |
2a8a6488 | 387 | .Pa /etc/ssh/ssh_known_hosts |
f49bc4f7 | 388 | is automatically checked for known hosts. |
610cd5c6 | 389 | Any new hosts are automatically added to the user's file. |
5f4a0c58 | 390 | If a host's identification ever changes, |
bf740959 | 391 | .Nm |
392 | warns about this and disables password authentication to prevent a | |
610cd5c6 | 393 | trojan horse from getting the user's password. |
5f4a0c58 | 394 | Another purpose of this mechanism is to prevent man-in-the-middle attacks |
395 | which could otherwise be used to circumvent the encryption. | |
610cd5c6 | 396 | The |
bf740959 | 397 | .Cm StrictHostKeyChecking |
588df31a | 398 | option can be used to prevent logins to machines whose |
bf740959 | 399 | host key is not known or has changed. |
fa08c86b | 400 | .Pp |
3a858356 | 401 | .Nm |
402 | can be configured to verify host identification using fingerprint resource | |
403 | records (SSHFP) published in DNS. | |
404 | The | |
405 | .Cm VerifyHostKeyDNS | |
406 | option can be used to control how DNS lookups are performed. | |
407 | SSHFP resource records can be generated using | |
408 | .Xr ssh-keygen 1 . | |
409 | .Pp | |
fa08c86b | 410 | The options are as follows: |
bf740959 | 411 | .Bl -tag -width Ds |
5f4a0c58 | 412 | .It Fl 1 |
413 | Forces | |
414 | .Nm | |
415 | to try protocol version 1 only. | |
416 | .It Fl 2 | |
417 | Forces | |
418 | .Nm | |
419 | to try protocol version 2 only. | |
420 | .It Fl 4 | |
421 | Forces | |
422 | .Nm | |
423 | to use IPv4 addresses only. | |
424 | .It Fl 6 | |
425 | Forces | |
426 | .Nm | |
427 | to use IPv6 addresses only. | |
71276795 | 428 | .It Fl A |
429 | Enables forwarding of the authentication agent connection. | |
430 | This can also be specified on a per-host basis in a configuration file. | |
07d688d5 | 431 | .Pp |
a4e5acef | 432 | Agent forwarding should be enabled with caution. |
433 | Users with the ability to bypass file permissions on the remote host | |
434 | (for the agent's Unix-domain socket) | |
435 | can access the local agent through the forwarded connection. | |
436 | An attacker cannot obtain key material from the agent, | |
07d688d5 | 437 | however they can perform operations on the keys that enable them to |
438 | authenticate using the identities loaded into the agent. | |
5f4a0c58 | 439 | .It Fl a |
440 | Disables forwarding of the authentication agent connection. | |
3435f5a6 | 441 | .It Fl b Ar bind_address |
143f17e8 | 442 | Use |
443 | .Ar bind_address | |
444 | on the local machine as the source address | |
445 | of the connection. | |
446 | Only useful on systems with more than one address. | |
5f4a0c58 | 447 | .It Fl C |
448 | Requests compression of all data (including stdin, stdout, stderr, and | |
449 | data for forwarded X11 and TCP/IP connections). | |
450 | The compression algorithm is the same used by | |
451 | .Xr gzip 1 , | |
452 | and the | |
453 | .Dq level | |
454 | can be controlled by the | |
455 | .Cm CompressionLevel | |
456 | option for protocol version 1. | |
457 | Compression is desirable on modem lines and other | |
458 | slow connections, but will only slow down things on fast networks. | |
459 | The default value can be set on a host-by-host basis in the | |
460 | configuration files; see the | |
461 | .Cm Compression | |
462 | option. | |
3b9baa7b | 463 | .It Fl c Ar cipher_spec |
464 | Selects the cipher specification for encrypting the session. | |
465 | .Pp | |
466 | Protocol version 1 allows specification of a single cipher. | |
2915e42b | 467 | The supported values are |
3b9baa7b | 468 | .Dq 3des , |
469 | .Dq blowfish | |
470 | and | |
471 | .Dq des . | |
bf740959 | 472 | .Ar 3des |
473 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
3b9baa7b | 474 | It is believed to be secure. |
bf740959 | 475 | .Ar blowfish |
5f4a0c58 | 476 | is a fast block cipher; it appears very secure and is much faster than |
610cd5c6 | 477 | .Ar 3des . |
29999e54 | 478 | .Ar des |
479 | is only supported in the | |
480 | .Nm | |
481 | client for interoperability with legacy protocol 1 implementations | |
482 | that do not support the | |
483 | .Ar 3des | |
a4e5acef | 484 | cipher. |
485 | Its use is strongly discouraged due to cryptographic weaknesses. | |
3b9baa7b | 486 | The default is |
487 | .Dq 3des . | |
488 | .Pp | |
489 | For protocol version 2 | |
490 | .Ar cipher_spec | |
491 | is a comma-separated list of ciphers | |
492 | listed in order of preference. | |
493 | The supported ciphers are | |
494 | .Dq 3des-cbc , | |
495 | .Dq aes128-cbc , | |
496 | .Dq aes192-cbc , | |
497 | .Dq aes256-cbc , | |
498 | .Dq aes128-ctr , | |
499 | .Dq aes192-ctr , | |
500 | .Dq aes256-ctr , | |
74a66cc8 | 501 | .Dq arcfour128 , |
502 | .Dq arcfour256 , | |
3b9baa7b | 503 | .Dq arcfour , |
504 | .Dq blowfish-cbc , | |
505 | and | |
506 | .Dq cast128-cbc . | |
507 | The default is | |
508 | .Bd -literal | |
74a66cc8 | 509 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, |
510 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
511 | aes192-ctr,aes256-ctr'' | |
3b9baa7b | 512 | .Ed |
5ddc5eb4 | 513 | .It Fl D Xo |
514 | .Sm off | |
515 | .Oo Ar bind_address : Oc | |
516 | .Ar port | |
517 | .Sm on | |
518 | .Xc | |
5f4a0c58 | 519 | Specifies a local |
520 | .Dq dynamic | |
521 | application-level port forwarding. | |
522 | This works by allocating a socket to listen to | |
523 | .Ar port | |
5ddc5eb4 | 524 | on the local side, optionally bound to the specified |
525 | .Ar bind_address . | |
526 | Whenever a connection is made to this port, the | |
5f4a0c58 | 527 | connection is forwarded over the secure channel, and the application |
528 | protocol is then used to determine where to connect to from the | |
529 | remote machine. | |
530 | Currently the SOCKS4 and SOCKS5 protocols are supported, and | |
531 | .Nm | |
532 | will act as a SOCKS server. | |
533 | Only root can forward privileged ports. | |
534 | Dynamic port forwardings can also be specified in the configuration file. | |
5ddc5eb4 | 535 | .Pp |
536 | IPv6 addresses can be specified with an alternative syntax: | |
537 | .Sm off | |
538 | .Xo | |
539 | .Op Ar bind_address No / | |
540 | .Ar port | |
541 | .Xc | |
542 | .Sm on | |
543 | or by enclosing the address in square brackets. | |
544 | Only the superuser can forward privileged ports. | |
545 | By default, the local port is bound in accordance with the | |
546 | .Cm GatewayPorts | |
547 | setting. | |
548 | However, an explicit | |
549 | .Ar bind_address | |
550 | may be used to bind the connection to a specific address. | |
551 | The | |
552 | .Ar bind_address | |
553 | of | |
554 | .Dq localhost | |
555 | indicates that the listening port be bound for local use only, while an | |
556 | empty address or | |
557 | .Sq * | |
558 | indicates that the port should be available from all interfaces. | |
5f4a0c58 | 559 | .It Fl e Ar ch | ^ch | none |
bf740959 | 560 | Sets the escape character for sessions with a pty (default: |
561 | .Ql ~ ) . | |
610cd5c6 | 562 | The escape character is only recognized at the beginning of a line. |
563 | The escape character followed by a dot | |
bf740959 | 564 | .Pq Ql \&. |
5f4a0c58 | 565 | closes the connection; |
566 | followed by control-Z suspends the connection; | |
567 | and followed by itself sends the escape character once. | |
610cd5c6 | 568 | Setting the character to |
bf740959 | 569 | .Dq none |
570 | disables any escapes and makes the session fully transparent. | |
5f4a0c58 | 571 | .It Fl F Ar configfile |
572 | Specifies an alternative per-user configuration file. | |
573 | If a configuration file is given on the command line, | |
574 | the system-wide configuration file | |
575 | .Pq Pa /etc/ssh/ssh_config | |
576 | will be ignored. | |
577 | The default for the per-user configuration file is | |
140e3e97 | 578 | .Pa ~/.ssh/config . |
bf740959 | 579 | .It Fl f |
580 | Requests | |
581 | .Nm | |
610cd5c6 | 582 | to go to background just before command execution. |
583 | This is useful if | |
bf740959 | 584 | .Nm |
585 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 586 | wants it in the background. |
f54651ce | 587 | This implies |
bf740959 | 588 | .Fl n . |
589 | The recommended way to start X11 programs at a remote site is with | |
590 | something like | |
591 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 592 | .It Fl g |
593 | Allows remote hosts to connect to local forwarded ports. | |
5f4a0c58 | 594 | .It Fl I Ar smartcard_device |
595 | Specifies which smartcard device to use. | |
596 | The argument is the device | |
597 | .Nm | |
598 | should use to communicate with a smartcard used for storing the user's | |
599 | private RSA key. | |
bf740959 | 600 | .It Fl i Ar identity_file |
cf5a07a8 | 601 | Selects a file from which the identity (private key) for |
fa08c86b | 602 | RSA or DSA authentication is read. |
cf5a07a8 | 603 | The default is |
140e3e97 | 604 | .Pa ~/.ssh/identity |
cf5a07a8 | 605 | for protocol version 1, and |
140e3e97 | 606 | .Pa ~/.ssh/id_rsa |
cf5a07a8 | 607 | and |
140e3e97 | 608 | .Pa ~/.ssh/id_dsa |
cf5a07a8 | 609 | for protocol version 2. |
610cd5c6 | 610 | Identity files may also be specified on |
611 | a per-host basis in the configuration file. | |
612 | It is possible to have multiple | |
bf740959 | 613 | .Fl i |
614 | options (and multiple identities specified in | |
615 | configuration files). | |
bf740959 | 616 | .It Fl k |
f7926e97 | 617 | Disables forwarding (delegation) of GSSAPI credentials to the server. |
5f4a0c58 | 618 | .It Fl L Xo |
619 | .Sm off | |
3867aa0a | 620 | .Oo Ar bind_address : Oc |
5f4a0c58 | 621 | .Ar port : host : hostport |
622 | .Sm on | |
623 | .Xc | |
624 | Specifies that the given port on the local (client) host is to be | |
625 | forwarded to the given host and port on the remote side. | |
626 | This works by allocating a socket to listen to | |
627 | .Ar port | |
3867aa0a | 628 | on the local side, optionally bound to the specified |
629 | .Ar bind_address . | |
630 | Whenever a connection is made to this port, the | |
5f4a0c58 | 631 | connection is forwarded over the secure channel, and a connection is |
632 | made to | |
633 | .Ar host | |
634 | port | |
635 | .Ar hostport | |
636 | from the remote machine. | |
637 | Port forwardings can also be specified in the configuration file. | |
5f4a0c58 | 638 | IPv6 addresses can be specified with an alternative syntax: |
639 | .Sm off | |
640 | .Xo | |
6d7a9e8f | 641 | .Op Ar bind_address No / |
5f4a0c58 | 642 | .Ar port No / Ar host No / |
3867aa0a | 643 | .Ar hostport |
5f4a0c58 | 644 | .Xc |
645 | .Sm on | |
3867aa0a | 646 | or by enclosing the address in square brackets. |
647 | Only the superuser can forward privileged ports. | |
648 | By default, the local port is bound in accordance with the | |
649 | .Cm GatewayPorts | |
650 | setting. | |
651 | However, an explicit | |
652 | .Ar bind_address | |
653 | may be used to bind the connection to a specific address. | |
654 | The | |
655 | .Ar bind_address | |
656 | of | |
657 | .Dq localhost | |
6c7e3b94 | 658 | indicates that the listening port be bound for local use only, while an |
659 | empty address or | |
660 | .Sq * | |
3867aa0a | 661 | indicates that the port should be available from all interfaces. |
bf740959 | 662 | .It Fl l Ar login_name |
610cd5c6 | 663 | Specifies the user to log in as on the remote machine. |
664 | This also may be specified on a per-host basis in the configuration file. | |
5e96b616 | 665 | .It Fl M |
666 | Places the | |
667 | .Nm | |
668 | client into | |
669 | .Dq master | |
670 | mode for connection sharing. | |
671 | Refer to the description of | |
672 | .Cm ControlMaster | |
673 | in | |
674 | .Xr ssh_config 5 | |
675 | for details. | |
9affc5db | 676 | .It Fl m Ar mac_spec |
677 | Additionally, for protocol version 2 a comma-separated list of MAC | |
678 | (message authentication code) algorithms can | |
679 | be specified in order of preference. | |
680 | See the | |
681 | .Cm MACs | |
682 | keyword for more information. | |
5f4a0c58 | 683 | .It Fl N |
684 | Do not execute a remote command. | |
685 | This is useful for just forwarding ports | |
686 | (protocol version 2 only). | |
bf740959 | 687 | .It Fl n |
688 | Redirects stdin from | |
689 | .Pa /dev/null | |
690 | (actually, prevents reading from stdin). | |
691 | This must be used when | |
692 | .Nm | |
610cd5c6 | 693 | is run in the background. |
694 | A common trick is to use this to run X11 programs on a remote machine. | |
695 | For example, | |
bf740959 | 696 | .Ic ssh -n shadows.cs.hut.fi emacs & |
697 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
698 | connection will be automatically forwarded over an encrypted channel. | |
699 | The | |
700 | .Nm | |
701 | program will be put in the background. | |
702 | (This does not work if | |
703 | .Nm | |
704 | needs to ask for a password or passphrase; see also the | |
705 | .Fl f | |
706 | option.) | |
cf848a5e | 707 | .It Fl O Ar ctl_cmd |
708 | Control an active connection multiplexing master process. | |
709 | When the | |
710 | .Fl O | |
711 | option is specified, the | |
712 | .Ar ctl_cmd | |
713 | argument is interpreted and passed to the master process. | |
714 | Valid commands are: | |
715 | .Dq check | |
716 | (check that the master process is running) and | |
717 | .Dq exit | |
718 | (request the master to exit). | |
bf740959 | 719 | .It Fl o Ar option |
38539909 | 720 | Can be used to give options in the format used in the configuration file. |
bf740959 | 721 | This is useful for specifying options for which there is no separate |
610cd5c6 | 722 | command-line flag. |
5f4a0c58 | 723 | For full details of the options listed below, and their possible values, see |
724 | .Xr ssh_config 5 . | |
725 | .Pp | |
726 | .Bl -tag -width Ds -offset indent -compact | |
727 | .It AddressFamily | |
728 | .It BatchMode | |
729 | .It BindAddress | |
730 | .It ChallengeResponseAuthentication | |
731 | .It CheckHostIP | |
732 | .It Cipher | |
733 | .It Ciphers | |
734 | .It ClearAllForwardings | |
735 | .It Compression | |
736 | .It CompressionLevel | |
737 | .It ConnectionAttempts | |
20b267fb | 738 | .It ConnectTimeout |
5e96b616 | 739 | .It ControlMaster |
740 | .It ControlPath | |
5f4a0c58 | 741 | .It DynamicForward |
5f4a0c58 | 742 | .It EscapeChar |
743 | .It ForwardAgent | |
744 | .It ForwardX11 | |
d73a67d7 | 745 | .It ForwardX11Trusted |
5f4a0c58 | 746 | .It GatewayPorts |
747 | .It GlobalKnownHostsFile | |
748 | .It GSSAPIAuthentication | |
749 | .It GSSAPIDelegateCredentials | |
5c63c2ab | 750 | .It HashKnownHosts |
5f4a0c58 | 751 | .It Host |
752 | .It HostbasedAuthentication | |
753 | .It HostKeyAlgorithms | |
754 | .It HostKeyAlias | |
755 | .It HostName | |
756 | .It IdentityFile | |
3a065ed0 | 757 | .It IdentitiesOnly |
396070f8 | 758 | .It KbdInteractiveDevices |
d20f3c9e | 759 | .It LocalCommand |
5f4a0c58 | 760 | .It LocalForward |
761 | .It LogLevel | |
762 | .It MACs | |
763 | .It NoHostAuthenticationForLocalhost | |
764 | .It NumberOfPasswordPrompts | |
765 | .It PasswordAuthentication | |
d20f3c9e | 766 | .It PermitLocalCommand |
5f4a0c58 | 767 | .It Port |
768 | .It PreferredAuthentications | |
769 | .It Protocol | |
770 | .It ProxyCommand | |
771 | .It PubkeyAuthentication | |
772 | .It RemoteForward | |
773 | .It RhostsRSAAuthentication | |
774 | .It RSAAuthentication | |
8e99a198 | 775 | .It SendEnv |
5d8d32a3 | 776 | .It ServerAliveInterval |
777 | .It ServerAliveCountMax | |
5f4a0c58 | 778 | .It SmartcardDevice |
779 | .It StrictHostKeyChecking | |
fd573618 | 780 | .It TCPKeepAlive |
d20f3c9e | 781 | .It Tunnel |
782 | .It TunnelDevice | |
5f4a0c58 | 783 | .It UsePrivilegedPort |
784 | .It User | |
785 | .It UserKnownHostsFile | |
786 | .It VerifyHostKeyDNS | |
787 | .It XAuthLocation | |
788 | .El | |
bf740959 | 789 | .It Fl p Ar port |
610cd5c6 | 790 | Port to connect to on the remote host. |
791 | This can be specified on a | |
bf740959 | 792 | per-host basis in the configuration file. |
bf740959 | 793 | .It Fl q |
610cd5c6 | 794 | Quiet mode. |
795 | Causes all warning and diagnostic messages to be suppressed. | |
5f4a0c58 | 796 | .It Fl R Xo |
797 | .Sm off | |
3867aa0a | 798 | .Oo Ar bind_address : Oc |
5f4a0c58 | 799 | .Ar port : host : hostport |
800 | .Sm on | |
801 | .Xc | |
802 | Specifies that the given port on the remote (server) host is to be | |
803 | forwarded to the given host and port on the local side. | |
804 | This works by allocating a socket to listen to | |
805 | .Ar port | |
806 | on the remote side, and whenever a connection is made to this port, the | |
807 | connection is forwarded over the secure channel, and a connection is | |
808 | made to | |
809 | .Ar host | |
810 | port | |
811 | .Ar hostport | |
812 | from the local machine. | |
3867aa0a | 813 | .Pp |
5f4a0c58 | 814 | Port forwardings can also be specified in the configuration file. |
815 | Privileged ports can be forwarded only when | |
816 | logging in as root on the remote machine. | |
3867aa0a | 817 | IPv6 addresses can be specified by enclosing the address in square braces or |
818 | using an alternative syntax: | |
3867aa0a | 819 | .Sm off |
6c7e3b94 | 820 | .Xo |
6d7a9e8f | 821 | .Op Ar bind_address No / |
6c7e3b94 | 822 | .Ar host No / Ar port No / |
823 | .Ar hostport | |
3867aa0a | 824 | .Xc . |
6c7e3b94 | 825 | .Sm on |
3867aa0a | 826 | .Pp |
827 | By default, the listening socket on the server will be bound to the loopback | |
828 | interface only. | |
829 | This may be overriden by specifying a | |
830 | .Ar bind_address . | |
6c7e3b94 | 831 | An empty |
832 | .Ar bind_address , | |
3867aa0a | 833 | or the address |
6c7e3b94 | 834 | .Ql * , |
3867aa0a | 835 | indicates that the remote socket should listen on all interfaces. |
836 | Specifying a remote | |
837 | .Ar bind_address | |
6c7e3b94 | 838 | will only succeed if the server's |
839 | .Cm GatewayPorts | |
3867aa0a | 840 | option is enabled (see |
6c7e3b94 | 841 | .Xr sshd_config 5 ) . |
f8c6db83 | 842 | .It Fl S Ar ctl_path |
9affc5db | 843 | Specifies the location of a control socket for connection sharing. |
5e96b616 | 844 | Refer to the description of |
0e19494c | 845 | .Cm ControlPath |
846 | and | |
5e96b616 | 847 | .Cm ControlMaster |
848 | in | |
849 | .Xr ssh_config 5 | |
850 | for details. | |
ae810de7 | 851 | .It Fl s |
3cbc677d | 852 | May be used to request invocation of a subsystem on the remote system. |
853 | Subsystems are a feature of the SSH2 protocol which facilitate the use | |
5f4a0c58 | 854 | of SSH as a secure transport for other applications (eg.\& |
855 | .Xr sftp 1 ) . | |
3cbc677d | 856 | The subsystem is specified as the remote command. |
5f4a0c58 | 857 | .It Fl T |
858 | Disable pseudo-tty allocation. | |
bf740959 | 859 | .It Fl t |
610cd5c6 | 860 | Force pseudo-tty allocation. |
4fe2af09 | 861 | This can be used to execute arbitrary |
610cd5c6 | 862 | screen-based programs on a remote machine, which can be very useful, |
863 | e.g., when implementing menu services. | |
8abcdba4 | 864 | Multiple |
865 | .Fl t | |
866 | options force tty allocation, even if | |
867 | .Nm | |
868 | has no local tty. | |
5f4a0c58 | 869 | .It Fl V |
870 | Display the version number and exit. | |
bf740959 | 871 | .It Fl v |
610cd5c6 | 872 | Verbose mode. |
873 | Causes | |
bf740959 | 874 | .Nm |
610cd5c6 | 875 | to print debugging messages about its progress. |
876 | This is helpful in | |
bf740959 | 877 | debugging connection, authentication, and configuration problems. |
8abcdba4 | 878 | Multiple |
879 | .Fl v | |
c825cd79 | 880 | options increase the verbosity. |
881 | The maximum is 3. | |
985bb789 | 882 | .It Fl w Ar tunnel : Ns Ar tunnel |
d20f3c9e | 883 | Requests a |
884 | .Xr tun 4 | |
885 | device on the client and server like the | |
886 | .Cm Tunnel | |
887 | directive in | |
888 | .Xr ssh_config 5 . | |
bf740959 | 889 | .It Fl X |
890 | Enables X11 forwarding. | |
71276795 | 891 | This can also be specified on a per-host basis in a configuration file. |
07d688d5 | 892 | .Pp |
a4e5acef | 893 | X11 forwarding should be enabled with caution. |
894 | Users with the ability to bypass file permissions on the remote host | |
895 | (for the user's X authorization database) | |
896 | can access the local X11 display through the forwarded connection. | |
897 | An attacker may then be able to perform activities such as keystroke monitoring. | |
82966fe8 | 898 | .Pp |
4469b0cf | 899 | For this reason, X11 forwarding is subjected to X11 SECURITY extension |
82966fe8 | 900 | restrictions by default. |
901 | Please refer to the | |
902 | .Nm | |
903 | .Fl Y | |
904 | option and the | |
905 | .Cm ForwardX11Trusted | |
906 | directive in | |
907 | .Xr ssh_config 5 | |
908 | for more information. | |
5f4a0c58 | 909 | .It Fl x |
910 | Disables X11 forwarding. | |
d73a67d7 | 911 | .It Fl Y |
912 | Enables trusted X11 forwarding. | |
82966fe8 | 913 | Trusted X11 forwardings are not subjected to the X11 SECURITY extension |
914 | controls. | |
bf740959 | 915 | .El |
916 | .Sh CONFIGURATION FILES | |
917 | .Nm | |
588df31a | 918 | may additionally obtain configuration data from |
919 | a per-user configuration file and a system-wide configuration file. | |
920 | The file format and configuration options are described in | |
921 | .Xr ssh_config 5 . | |
bf740959 | 922 | .Sh ENVIRONMENT |
923 | .Nm | |
924 | will normally set the following environment variables: | |
5f4a0c58 | 925 | .Bl -tag -width LOGNAME |
bf740959 | 926 | .It Ev DISPLAY |
927 | The | |
928 | .Ev DISPLAY | |
610cd5c6 | 929 | variable indicates the location of the X11 server. |
f54651ce | 930 | It is automatically set by |
bf740959 | 931 | .Nm |
932 | to point to a value of the form | |
933 | .Dq hostname:n | |
934 | where hostname indicates | |
5f4a0c58 | 935 | the host where the shell runs, and n is an integer \*(Ge 1. |
610cd5c6 | 936 | .Nm |
937 | uses this special value to forward X11 connections over the secure | |
938 | channel. | |
da89cf4d | 939 | The user should normally not set |
940 | .Ev DISPLAY | |
941 | explicitly, as that | |
bf740959 | 942 | will render the X11 connection insecure (and will require the user to |
943 | manually copy any required authorization cookies). | |
944 | .It Ev HOME | |
945 | Set to the path of the user's home directory. | |
946 | .It Ev LOGNAME | |
947 | Synonym for | |
948 | .Ev USER ; | |
949 | set for compatibility with systems that use this variable. | |
950 | .It Ev MAIL | |
ae897d7c | 951 | Set to the path of the user's mailbox. |
610cd5c6 | 952 | .It Ev PATH |
bf740959 | 953 | Set to the default |
954 | .Ev PATH , | |
955 | as specified when compiling | |
956 | .Nm ssh . | |
3474b2b4 | 957 | .It Ev SSH_ASKPASS |
958 | If | |
959 | .Nm | |
960 | needs a passphrase, it will read the passphrase from the current | |
961 | terminal if it was run from a terminal. | |
962 | If | |
963 | .Nm | |
964 | does not have a terminal associated with it but | |
965 | .Ev DISPLAY | |
966 | and | |
967 | .Ev SSH_ASKPASS | |
968 | are set, it will execute the program specified by | |
969 | .Ev SSH_ASKPASS | |
970 | and open an X11 window to read the passphrase. | |
971 | This is particularly useful when calling | |
972 | .Nm | |
973 | from a | |
caeffafb | 974 | .Pa .xsession |
3474b2b4 | 975 | or related script. |
976 | (Note that on some machines it | |
977 | may be necessary to redirect the input from | |
978 | .Pa /dev/null | |
979 | to make this work.) | |
bf740959 | 980 | .It Ev SSH_AUTH_SOCK |
ae897d7c | 981 | Identifies the path of a unix-domain socket used to communicate with the |
bf740959 | 982 | agent. |
da0561eb | 983 | .It Ev SSH_CONNECTION |
984 | Identifies the client and server ends of the connection. | |
610cd5c6 | 985 | The variable contains |
da0561eb | 986 | four space-separated values: client ip-address, client port number, |
987 | server ip-address and server port number. | |
8abcdba4 | 988 | .It Ev SSH_ORIGINAL_COMMAND |
989 | The variable contains the original command line if a forced command | |
990 | is executed. | |
991 | It can be used to extract the original arguments. | |
bf740959 | 992 | .It Ev SSH_TTY |
993 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 994 | with the current shell or command. |
995 | If the current session has no tty, | |
bf740959 | 996 | this variable is not set. |
997 | .It Ev TZ | |
04ac3e62 | 998 | This variable is set to indicate the present time zone if it |
c345cf9d | 999 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 1000 | on to new connections). |
1001 | .It Ev USER | |
1002 | Set to the name of the user logging in. | |
1003 | .El | |
1004 | .Pp | |
f54651ce | 1005 | Additionally, |
bf740959 | 1006 | .Nm |
f54651ce | 1007 | reads |
140e3e97 | 1008 | .Pa ~/.ssh/environment , |
bf740959 | 1009 | and adds lines of the format |
1010 | .Dq VARNAME=value | |
6a342527 | 1011 | to the environment if the file exists and if users are allowed to |
1012 | change their environment. | |
5f4a0c58 | 1013 | For more information, see the |
6a342527 | 1014 | .Cm PermitUserEnvironment |
35453849 | 1015 | option in |
6a342527 | 1016 | .Xr sshd_config 5 . |
bf740959 | 1017 | .Sh FILES |
c8d54615 | 1018 | .Bl -tag -width Ds |
140e3e97 | 1019 | .It Pa ~/.ssh/known_hosts |
ae897d7c | 1020 | Records host keys for all hosts the user has logged into that are not |
bf740959 | 1021 | in |
2a8a6488 | 1022 | .Pa /etc/ssh/ssh_known_hosts . |
bf740959 | 1023 | See |
1024 | .Xr sshd 8 . | |
140e3e97 | 1025 | .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa |
c0ecc314 | 1026 | Contains the authentication identity of the user. |
1027 | They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. | |
1d1ffb87 | 1028 | These files |
1029 | contain sensitive data and should be readable by the user but not | |
bf740959 | 1030 | accessible by others (read/write/execute). |
1031 | Note that | |
1032 | .Nm | |
1d1ffb87 | 1033 | ignores a private key file if it is accessible by others. |
bf740959 | 1034 | It is possible to specify a passphrase when |
1035 | generating the key; the passphrase will be used to encrypt the | |
1036 | sensitive part of this file using 3DES. | |
140e3e97 | 1037 | .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub |
bf740959 | 1038 | Contains the public key for authentication (public part of the |
610cd5c6 | 1039 | identity file in human-readable form). |
1d1ffb87 | 1040 | The contents of the |
140e3e97 | 1041 | .Pa ~/.ssh/identity.pub |
5f4a0c58 | 1042 | file should be added to the file |
140e3e97 | 1043 | .Pa ~/.ssh/authorized_keys |
bf740959 | 1044 | on all machines |
91789042 | 1045 | where the user wishes to log in using protocol version 1 RSA authentication. |
1d1ffb87 | 1046 | The contents of the |
140e3e97 | 1047 | .Pa ~/.ssh/id_dsa.pub |
c0ecc314 | 1048 | and |
140e3e97 | 1049 | .Pa ~/.ssh/id_rsa.pub |
1d1ffb87 | 1050 | file should be added to |
140e3e97 | 1051 | .Pa ~/.ssh/authorized_keys |
1d1ffb87 | 1052 | on all machines |
91789042 | 1053 | where the user wishes to log in using protocol version 2 DSA/RSA authentication. |
1d1ffb87 | 1054 | These files are not |
610cd5c6 | 1055 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 1056 | These files are |
c44559d2 | 1057 | never used automatically and are not necessary; they are only provided for |
bf740959 | 1058 | the convenience of the user. |
140e3e97 | 1059 | .It Pa ~/.ssh/config |
610cd5c6 | 1060 | This is the per-user configuration file. |
588df31a | 1061 | The file format and configuration options are described in |
1062 | .Xr ssh_config 5 . | |
e1520719 | 1063 | Because of the potential for abuse, this file must have strict permissions: |
1064 | read/write for the user, and not accessible by others. | |
140e3e97 | 1065 | .It Pa ~/.ssh/authorized_keys |
96a7b0cc | 1066 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. |
610cd5c6 | 1067 | The format of this file is described in the |
bf740959 | 1068 | .Xr sshd 8 |
610cd5c6 | 1069 | manual page. |
5f4a0c58 | 1070 | In the simplest form the format is the same as the |
1071 | .Pa .pub | |
f49bc4f7 | 1072 | identity files. |
1d1ffb87 | 1073 | This file is not highly sensitive, but the recommended |
1074 | permissions are read/write for the user, and not accessible by others. | |
2a8a6488 | 1075 | .It Pa /etc/ssh/ssh_known_hosts |
610cd5c6 | 1076 | Systemwide list of known host keys. |
f49bc4f7 | 1077 | This file should be prepared by the |
bf740959 | 1078 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1079 | organization. |
1080 | This file should be world-readable. | |
1081 | This file contains | |
bf740959 | 1082 | public keys, one per line, in the following format (fields separated |
f49bc4f7 | 1083 | by spaces): system name, public key and optional comment field. |
610cd5c6 | 1084 | When different names are used |
bf740959 | 1085 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1086 | commas. |
5f4a0c58 | 1087 | The format is described in the |
bf740959 | 1088 | .Xr sshd 8 |
1089 | manual page. | |
1090 | .Pp | |
1091 | The canonical system name (as returned by name servers) is used by | |
1092 | .Xr sshd 8 | |
1093 | to verify the client host when logging in; other names are needed because | |
1094 | .Nm | |
1095 | does not convert the user-supplied name to a canonical name before | |
1096 | checking the key, because someone with access to the name servers | |
1097 | would then be able to fool host authentication. | |
2a8a6488 | 1098 | .It Pa /etc/ssh/ssh_config |
610cd5c6 | 1099 | Systemwide configuration file. |
588df31a | 1100 | The file format and configuration options are described in |
1101 | .Xr ssh_config 5 . | |
2a8a6488 | 1102 | .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key |
dd58cb5e | 1103 | These three files contain the private parts of the host keys |
1104 | and are used for | |
1105 | .Cm RhostsRSAAuthentication | |
1106 | and | |
1107 | .Cm HostbasedAuthentication . | |
d83cbdc3 | 1108 | If the protocol version 1 |
1109 | .Cm RhostsRSAAuthentication | |
7203d6bb | 1110 | method is used, |
d83cbdc3 | 1111 | .Nm |
1112 | must be setuid root, since the host key is readable only by root. | |
1113 | For protocol version 2, | |
1114 | .Nm | |
1115 | uses | |
1116 | .Xr ssh-keysign 8 | |
1117 | to access the host keys for | |
1118 | .Cm HostbasedAuthentication . | |
1119 | This eliminates the requirement that | |
1120 | .Nm | |
1121 | be setuid root when that authentication method is used. | |
1122 | By default | |
dd58cb5e | 1123 | .Nm |
d83cbdc3 | 1124 | is not setuid root. |
140e3e97 | 1125 | .It Pa ~/.rhosts |
bf740959 | 1126 | This file is used in |
6f5abc1e | 1127 | .Cm RhostsRSAAuthentication |
1128 | and | |
1129 | .Cm HostbasedAuthentication | |
bf740959 | 1130 | authentication to list the |
610cd5c6 | 1131 | host/user pairs that are permitted to log in. |
1132 | (Note that this file is | |
bf740959 | 1133 | also used by rlogin and rsh, which makes using this file insecure.) |
1134 | Each line of the file contains a host name (in the canonical form | |
1135 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1136 | separated by a space. |
e91c60f2 | 1137 | On some machines this file may need to be |
bf740959 | 1138 | world-readable if the user's home directory is on a NFS partition, |
1139 | because | |
1140 | .Xr sshd 8 | |
610cd5c6 | 1141 | reads it as root. |
1142 | Additionally, this file must be owned by the user, | |
1143 | and must not have write permissions for anyone else. | |
1144 | The recommended | |
bf740959 | 1145 | permission for most machines is read/write for the user, and not |
1146 | accessible by others. | |
1147 | .Pp | |
6f5abc1e | 1148 | Note that |
bf740959 | 1149 | .Xr sshd 8 |
6f5abc1e | 1150 | allows authentication only in combination with client host key |
1151 | authentication before permitting log in. | |
91789042 | 1152 | If the server machine does not have the client's host key in |
2a8a6488 | 1153 | .Pa /etc/ssh/ssh_known_hosts , |
91789042 | 1154 | it can be stored in |
140e3e97 | 1155 | .Pa ~/.ssh/known_hosts . |
bf740959 | 1156 | The easiest way to do this is to |
1157 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1158 | will automatically add the host key to |
140e3e97 | 1159 | .Pa ~/.ssh/known_hosts . |
1160 | .It Pa ~/.shosts | |
bf740959 | 1161 | This file is used exactly the same way as |
5f4a0c58 | 1162 | .Pa .rhosts . |
bf740959 | 1163 | The purpose for |
6f5abc1e | 1164 | having this file is to be able to use |
1165 | .Cm RhostsRSAAuthentication | |
1166 | and | |
1167 | .Cm HostbasedAuthentication | |
1168 | authentication without permitting login with | |
5f4a0c58 | 1169 | .Xr rlogin |
bf740959 | 1170 | or |
1171 | .Xr rsh 1 . | |
1172 | .It Pa /etc/hosts.equiv | |
1173 | This file is used during | |
6f5abc1e | 1174 | .Cm RhostsRSAAuthentication |
1175 | and | |
1176 | .Cm HostbasedAuthentication | |
be193d89 | 1177 | authentication. |
610cd5c6 | 1178 | It contains |
5f4a0c58 | 1179 | canonical hosts names, one per line (the full format is described in the |
bf740959 | 1180 | .Xr sshd 8 |
610cd5c6 | 1181 | manual page). |
1182 | If the client host is found in this file, login is | |
bf740959 | 1183 | automatically permitted provided client and server user names are the |
610cd5c6 | 1184 | same. |
6f5abc1e | 1185 | Additionally, successful client host key authentication is required. |
610cd5c6 | 1186 | This file should only be writable by root. |
5f4fdfae | 1187 | .It Pa /etc/shosts.equiv |
f54651ce | 1188 | This file is processed exactly as |
bf740959 | 1189 | .Pa /etc/hosts.equiv . |
1190 | This file may be useful to permit logins using | |
1191 | .Nm | |
1192 | but not using rsh/rlogin. | |
2a8a6488 | 1193 | .It Pa /etc/ssh/sshrc |
bf740959 | 1194 | Commands in this file are executed by |
1195 | .Nm | |
1196 | when the user logs in just before the user's shell (or command) is started. | |
1197 | See the | |
1198 | .Xr sshd 8 | |
1199 | manual page for more information. | |
140e3e97 | 1200 | .It Pa ~/.ssh/rc |
bf740959 | 1201 | Commands in this file are executed by |
1202 | .Nm | |
1203 | when the user logs in just before the user's shell (or command) is | |
1204 | started. | |
f54651ce | 1205 | See the |
bf740959 | 1206 | .Xr sshd 8 |
1207 | manual page for more information. | |
140e3e97 | 1208 | .It Pa ~/.ssh/environment |
83b7f649 | 1209 | Contains additional definitions for environment variables, see section |
1210 | .Sx ENVIRONMENT | |
1211 | above. | |
b5e300c2 | 1212 | .El |
16210ef7 | 1213 | .Sh DIAGNOSTICS |
1214 | .Nm | |
1215 | exits with the exit status of the remote command or with 255 | |
1216 | if an error occurred. | |
bf740959 | 1217 | .Sh SEE ALSO |
5f4a0c58 | 1218 | .Xr gzip 1 , |
bf740959 | 1219 | .Xr rsh 1 , |
1220 | .Xr scp 1 , | |
61e96248 | 1221 | .Xr sftp 1 , |
bf740959 | 1222 | .Xr ssh-add 1 , |
1223 | .Xr ssh-agent 1 , | |
1224 | .Xr ssh-keygen 1 , | |
1225 | .Xr telnet 1 , | |
5f4a0c58 | 1226 | .Xr hosts.equiv 5 , |
1ae02182 | 1227 | .Xr ssh_config 5 , |
b2843ec6 | 1228 | .Xr ssh-keysign 8 , |
9afadca8 | 1229 | .Xr sshd 8 |
2cad6cef | 1230 | .Rs |
1231 | .%A T. Ylonen | |
1232 | .%A T. Kivinen | |
1233 | .%A M. Saarinen | |
1234 | .%A T. Rinne | |
1235 | .%A S. Lehtinen | |
1236 | .%T "SSH Protocol Architecture" | |
17f5e68a | 1237 | .%N draft-ietf-secsh-architecture-12.txt |
1238 | .%D January 2002 | |
2cad6cef | 1239 | .%O work in progress material |
1240 | .Re | |
be193d89 | 1241 | .Sh AUTHORS |
1242 | OpenSSH is a derivative of the original and free | |
1243 | ssh 1.2.12 release by Tatu Ylonen. | |
1244 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1245 | Theo de Raadt and Dug Song | |
1246 | removed many bugs, re-added newer features and | |
1247 | created OpenSSH. | |
1248 | Markus Friedl contributed the support for SSH | |
1249 | protocol versions 1.5 and 2.0. |