]>
Commit | Line | Data |
---|---|---|
bf740959 | 1 | .\" -*- nroff -*- |
2 | .\" | |
bf740959 | 3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
bf740959 | 4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
5 | .\" All rights reserved | |
6 | .\" | |
bcbf86ec | 7 | .\" As far as I am concerned, the code I have written for this software |
8 | .\" can be used freely for any purpose. Any derived versions of this | |
9 | .\" software must be clearly marked as such, and if the derived work is | |
10 | .\" incompatible with the protocol description in the RFC file, it must be | |
11 | .\" called by a name other than "ssh" or "Secure Shell". | |
12 | .\" | |
f3c7c613 | 13 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. |
14 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. | |
15 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. | |
bcbf86ec | 16 | .\" |
17 | .\" Redistribution and use in source and binary forms, with or without | |
18 | .\" modification, are permitted provided that the following conditions | |
19 | .\" are met: | |
20 | .\" 1. Redistributions of source code must retain the above copyright | |
21 | .\" notice, this list of conditions and the following disclaimer. | |
22 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
23 | .\" notice, this list of conditions and the following disclaimer in the | |
24 | .\" documentation and/or other materials provided with the distribution. | |
bf740959 | 25 | .\" |
bcbf86ec | 26 | .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
27 | .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES | |
28 | .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |
29 | .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, | |
30 | .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT | |
31 | .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
32 | .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
33 | .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
34 | .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF | |
35 | .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
bf740959 | 36 | .\" |
d20f3c9e | 37 | .\" $OpenBSD: ssh.1,v 1.215 2005/12/06 22:38:27 reyk 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 |
d20f3c9e | 80 | .Op Fl w Ar tunnel : tunnel |
5f4a0c58 | 81 | .Oo Ar user Ns @ Oc Ns Ar hostname |
bf740959 | 82 | .Op Ar command |
f54651ce | 83 | .Sh DESCRIPTION |
bf740959 | 84 | .Nm |
2c86906e | 85 | (SSH client) is a program for logging into a remote machine and for |
610cd5c6 | 86 | executing commands on a remote machine. |
5f4a0c58 | 87 | It is intended to replace rlogin and rsh, |
88 | and provide secure encrypted communications between | |
610cd5c6 | 89 | two untrusted hosts over an insecure network. |
5f4a0c58 | 90 | X11 connections and arbitrary TCP/IP ports |
91 | can also be forwarded over the secure channel. | |
bf740959 | 92 | .Pp |
93 | .Nm | |
f54651ce | 94 | connects and logs into the specified |
5f4a0c58 | 95 | .Ar hostname |
96 | (with optional | |
97 | .Ar user | |
98 | name). | |
bf740959 | 99 | The user must prove |
1d1ffb87 | 100 | his/her identity to the remote machine using one of several methods |
5f4a0c58 | 101 | depending on the protocol version used. |
1d1ffb87 | 102 | .Pp |
5f4a0c58 | 103 | If |
104 | .Ar command | |
105 | is specified, | |
106 | .Ar command | |
107 | is executed on the remote host instead of a login shell. | |
1d1ffb87 | 108 | .Ss SSH protocol version 1 |
6f5abc1e | 109 | The first authentication method is the |
110 | .Em rhosts | |
111 | or | |
112 | .Em hosts.equiv | |
113 | method combined with RSA-based host authentication. | |
114 | If the machine the user logs in from is listed in | |
bf740959 | 115 | .Pa /etc/hosts.equiv |
116 | or | |
5f4fdfae | 117 | .Pa /etc/shosts.equiv |
bf740959 | 118 | on the remote machine, and the user names are |
6f5abc1e | 119 | the same on both sides, or if the files |
140e3e97 | 120 | .Pa ~/.rhosts |
bf740959 | 121 | or |
140e3e97 | 122 | .Pa ~/.shosts |
6f5abc1e | 123 | exist in the user's home directory on the |
124 | remote machine and contain a line containing the name of the client | |
bf740959 | 125 | machine and the name of the user on that machine, the user is |
6f5abc1e | 126 | considered for log in. |
127 | Additionally, if the server can verify the client's | |
f54651ce | 128 | host key (see |
2a8a6488 | 129 | .Pa /etc/ssh/ssh_known_hosts |
5bbb5681 | 130 | and |
140e3e97 | 131 | .Pa ~/.ssh/known_hosts |
bf740959 | 132 | in the |
133 | .Sx FILES | |
5f4a0c58 | 134 | section), only then is login permitted. |
610cd5c6 | 135 | This authentication method closes security holes due to IP |
136 | spoofing, DNS spoofing and routing spoofing. | |
137 | [Note to the administrator: | |
bf740959 | 138 | .Pa /etc/hosts.equiv , |
140e3e97 | 139 | .Pa ~/.rhosts , |
bf740959 | 140 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
141 | disabled if security is desired.] | |
142 | .Pp | |
6f5abc1e | 143 | As a second authentication method, |
bf740959 | 144 | .Nm |
145 | supports RSA based authentication. | |
146 | The scheme is based on public-key cryptography: there are cryptosystems | |
147 | where encryption and decryption are done using separate keys, and it | |
148 | is not possible to derive the decryption key from the encryption key. | |
610cd5c6 | 149 | RSA is one such system. |
f54651ce | 150 | The idea is that each user creates a public/private |
610cd5c6 | 151 | key pair for authentication purposes. |
152 | The server knows the public key, and only the user knows the private key. | |
5f4a0c58 | 153 | .Pp |
f54651ce | 154 | The file |
140e3e97 | 155 | .Pa ~/.ssh/authorized_keys |
5f4a0c58 | 156 | lists the public keys that are permitted for logging in. |
610cd5c6 | 157 | When the user logs in, the |
bf740959 | 158 | .Nm |
159 | program tells the server which key pair it would like to use for | |
610cd5c6 | 160 | authentication. |
5f4a0c58 | 161 | The server checks if this key is permitted, and if so, |
162 | sends the user (actually the | |
bf740959 | 163 | .Nm |
164 | program running on behalf of the user) a challenge, a random number, | |
610cd5c6 | 165 | encrypted by the user's public key. |
5f4a0c58 | 166 | The challenge can only be decrypted using the proper private key. |
167 | The user's client then decrypts the challenge using the private key, | |
168 | proving that he/she knows the private key | |
169 | but without disclosing it to the server. | |
bf740959 | 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 |
140e3e97 | 176 | .Pa ~/.ssh/identity |
5f4a0c58 | 177 | and stores the public key in |
140e3e97 | 178 | .Pa ~/.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 |
140e3e97 | 183 | .Pa ~/.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 |
140e3e97 | 187 | .Pa ~/.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. | |
bf740959 | 191 | .Pp |
192 | The most convenient way to use RSA authentication may be with an | |
610cd5c6 | 193 | authentication agent. |
194 | See | |
bf740959 | 195 | .Xr ssh-agent 1 |
196 | for more information. | |
197 | .Pp | |
f54651ce | 198 | If other authentication methods fail, |
bf740959 | 199 | .Nm |
610cd5c6 | 200 | prompts the user for a password. |
201 | The password is sent to the remote | |
bf740959 | 202 | host for checking; however, since all communications are encrypted, |
203 | the password cannot be seen by someone listening on the network. | |
1d1ffb87 | 204 | .Ss SSH protocol version 2 |
5f4a0c58 | 205 | When a user connects using protocol version 2, |
16210ef7 | 206 | similar authentication methods are available. |
da89cf4d | 207 | Using the default values for |
208 | .Cm PreferredAuthentications , | |
29c440a0 | 209 | the client will try to authenticate first using the hostbased method; |
5f4a0c58 | 210 | if this method fails, public key authentication is attempted, |
211 | and finally if this method fails, keyboard-interactive and | |
29c440a0 | 212 | password authentication are tried. |
1d1ffb87 | 213 | .Pp |
214 | The public key method is similar to RSA authentication described | |
da89cf4d | 215 | in the previous section and allows the RSA or DSA algorithm to be used: |
c0ecc314 | 216 | The client uses his private key, |
140e3e97 | 217 | .Pa ~/.ssh/id_dsa |
c0ecc314 | 218 | or |
140e3e97 | 219 | .Pa ~/.ssh/id_rsa , |
1d1ffb87 | 220 | to sign the session identifier and sends the result to the server. |
221 | The server checks whether the matching public key is listed in | |
140e3e97 | 222 | .Pa ~/.ssh/authorized_keys |
1d1ffb87 | 223 | and grants access if both the key is found and the signature is correct. |
224 | The session identifier is derived from a shared Diffie-Hellman value | |
225 | and is only known to the client and the server. | |
226 | .Pp | |
5f4a0c58 | 227 | If public key authentication fails or is not available, a password |
228 | can be sent encrypted to the remote host to prove the user's identity. | |
da89cf4d | 229 | .Pp |
230 | Additionally, | |
231 | .Nm | |
232 | supports hostbased or challenge response authentication. | |
1d1ffb87 | 233 | .Pp |
234 | Protocol 2 provides additional mechanisms for confidentiality | |
3b9baa7b | 235 | (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour) |
236 | and integrity (hmac-md5, hmac-sha1, hmac-ripemd160). | |
1d1ffb87 | 237 | Note that protocol 1 lacks a strong mechanism for ensuring the |
238 | integrity of the connection. | |
1d1ffb87 | 239 | .Ss Login session and remote execution |
bf740959 | 240 | When the user's identity has been accepted by the server, the server |
241 | either executes the given command, or logs into the machine and gives | |
610cd5c6 | 242 | the user a normal shell on the remote machine. |
243 | All communication with | |
bf740959 | 244 | the remote command or shell will be automatically encrypted. |
245 | .Pp | |
246 | If a pseudo-terminal has been allocated (normal login session), the | |
df841692 | 247 | user may use the escape characters noted below. |
bf740959 | 248 | .Pp |
5f4a0c58 | 249 | If no pseudo-tty has been allocated, |
250 | the session is transparent and can be used to reliably transfer binary data. | |
610cd5c6 | 251 | On most systems, setting the escape character to |
bf740959 | 252 | .Dq none |
253 | will also make the session transparent even if a tty is used. | |
254 | .Pp | |
ce9c0b75 | 255 | The session terminates when the command or shell on the remote |
e91c60f2 | 256 | machine exits and all X11 and TCP/IP connections have been closed. |
5f4a0c58 | 257 | The exit status of the remote program is returned as the exit status of |
bf740959 | 258 | .Nm ssh . |
df841692 | 259 | .Ss Escape Characters |
5f4a0c58 | 260 | When a pseudo-terminal has been requested, |
261 | .Nm | |
262 | supports a number of functions through the use of an escape character. | |
df841692 | 263 | .Pp |
264 | A single tilde character can be sent as | |
265 | .Ic ~~ | |
5bef3c35 | 266 | or by following the tilde by a character other than those described below. |
df841692 | 267 | The escape character must always follow a newline to be interpreted as |
268 | special. | |
269 | The escape character can be changed in configuration files using the | |
270 | .Cm EscapeChar | |
3730bb22 | 271 | configuration directive or on the command line by the |
df841692 | 272 | .Fl e |
273 | option. | |
274 | .Pp | |
275 | The supported escapes (assuming the default | |
276 | .Ql ~ ) | |
277 | are: | |
278 | .Bl -tag -width Ds | |
279 | .It Cm ~. | |
5f4a0c58 | 280 | Disconnect. |
df841692 | 281 | .It Cm ~^Z |
5f4a0c58 | 282 | Background |
283 | .Nm ssh . | |
df841692 | 284 | .It Cm ~# |
5f4a0c58 | 285 | List forwarded connections. |
df841692 | 286 | .It Cm ~& |
5f4a0c58 | 287 | Background |
288 | .Nm | |
289 | at logout when waiting for forwarded connection / X11 sessions to terminate. | |
df841692 | 290 | .It Cm ~? |
5f4a0c58 | 291 | Display a list of escape characters. |
16a79097 | 292 | .It Cm ~B |
5f4a0c58 | 293 | Send a BREAK to the remote system |
294 | (only useful for SSH protocol version 2 and if the peer supports it). | |
c53c54c2 | 295 | .It Cm ~C |
d740ec16 | 296 | Open command line. |
297 | Currently this allows the addition of port forwardings using the | |
c53c54c2 | 298 | .Fl L |
299 | and | |
300 | .Fl R | |
d740ec16 | 301 | options (see below). |
790029d9 | 302 | It also allows the cancellation of existing remote port-forwardings |
d740ec16 | 303 | using |
304 | .Fl KR Ar hostport . | |
d20f3c9e | 305 | The |
306 | .Ic ! Ar command | |
307 | allows the user to execute a local command if the | |
308 | .Ic PermitLocalCommand | |
309 | option is enabled in | |
310 | .Xr ssh_config 5 . | |
7069a5e2 | 311 | Basic help is available, using the |
312 | .Fl h | |
d740ec16 | 313 | option. |
df841692 | 314 | .It Cm ~R |
5f4a0c58 | 315 | Request rekeying of the connection |
316 | (only useful for SSH protocol version 2 and if the peer supports it). | |
df841692 | 317 | .El |
1d1ffb87 | 318 | .Ss X11 and TCP forwarding |
6efa3d14 | 319 | If the |
320 | .Cm ForwardX11 | |
321 | variable is set to | |
322 | .Dq yes | |
5f4a0c58 | 323 | (or see the description of the |
6efa3d14 | 324 | .Fl X |
325 | and | |
326 | .Fl x | |
327 | options described later) | |
328 | and the user is using X11 (the | |
bf740959 | 329 | .Ev DISPLAY |
330 | environment variable is set), the connection to the X11 display is | |
331 | automatically forwarded to the remote side in such a way that any X11 | |
332 | programs started from the shell (or command) will go through the | |
333 | encrypted channel, and the connection to the real X server will be made | |
610cd5c6 | 334 | from the local machine. |
335 | The user should not manually set | |
bf740959 | 336 | .Ev DISPLAY . |
337 | Forwarding of X11 connections can be | |
338 | configured on the command line or in configuration files. | |
339 | .Pp | |
340 | The | |
f54651ce | 341 | .Ev DISPLAY |
bf740959 | 342 | value set by |
343 | .Nm | |
5f4a0c58 | 344 | will point to the server machine, but with a display number greater than zero. |
610cd5c6 | 345 | This is normal, and happens because |
bf740959 | 346 | .Nm |
347 | creates a | |
348 | .Dq proxy | |
349 | X server on the server machine for forwarding the | |
350 | connections over the encrypted channel. | |
351 | .Pp | |
352 | .Nm | |
353 | will also automatically set up Xauthority data on the server machine. | |
354 | For this purpose, it will generate a random authorization cookie, | |
355 | store it in Xauthority on the server, and verify that any forwarded | |
356 | connections carry this cookie and replace it by the real cookie when | |
610cd5c6 | 357 | the connection is opened. |
358 | The real authentication cookie is never | |
bf740959 | 359 | sent to the server machine (and no cookies are sent in the plain). |
360 | .Pp | |
24794905 | 361 | If the |
362 | .Cm ForwardAgent | |
363 | variable is set to | |
364 | .Dq yes | |
5f4a0c58 | 365 | (or see the description of the |
24794905 | 366 | .Fl A |
367 | and | |
368 | .Fl a | |
a4e5acef | 369 | options described later) and |
24794905 | 370 | the user is using an authentication agent, the connection to the agent |
371 | is automatically forwarded to the remote side. | |
bf740959 | 372 | .Pp |
373 | Forwarding of arbitrary TCP/IP connections over the secure channel can | |
491f5f7b | 374 | be specified either on the command line or in a configuration file. |
610cd5c6 | 375 | One possible application of TCP/IP forwarding is a secure connection to an |
e91c60f2 | 376 | electronic purse; another is going through firewalls. |
1d1ffb87 | 377 | .Ss Server authentication |
bf740959 | 378 | .Nm |
1d1ffb87 | 379 | automatically maintains and checks a database containing |
610cd5c6 | 380 | identifications for all hosts it has ever been used with. |
f49bc4f7 | 381 | Host keys are stored in |
140e3e97 | 382 | .Pa ~/.ssh/known_hosts |
610cd5c6 | 383 | in the user's home directory. |
f49bc4f7 | 384 | Additionally, the file |
2a8a6488 | 385 | .Pa /etc/ssh/ssh_known_hosts |
f49bc4f7 | 386 | is automatically checked for known hosts. |
610cd5c6 | 387 | Any new hosts are automatically added to the user's file. |
5f4a0c58 | 388 | If a host's identification ever changes, |
bf740959 | 389 | .Nm |
390 | warns about this and disables password authentication to prevent a | |
610cd5c6 | 391 | trojan horse from getting the user's password. |
5f4a0c58 | 392 | Another purpose of this mechanism is to prevent man-in-the-middle attacks |
393 | which could otherwise be used to circumvent the encryption. | |
610cd5c6 | 394 | The |
bf740959 | 395 | .Cm StrictHostKeyChecking |
588df31a | 396 | option can be used to prevent logins to machines whose |
bf740959 | 397 | host key is not known or has changed. |
fa08c86b | 398 | .Pp |
3a858356 | 399 | .Nm |
400 | can be configured to verify host identification using fingerprint resource | |
401 | records (SSHFP) published in DNS. | |
402 | The | |
403 | .Cm VerifyHostKeyDNS | |
404 | option can be used to control how DNS lookups are performed. | |
405 | SSHFP resource records can be generated using | |
406 | .Xr ssh-keygen 1 . | |
407 | .Pp | |
fa08c86b | 408 | The options are as follows: |
bf740959 | 409 | .Bl -tag -width Ds |
5f4a0c58 | 410 | .It Fl 1 |
411 | Forces | |
412 | .Nm | |
413 | to try protocol version 1 only. | |
414 | .It Fl 2 | |
415 | Forces | |
416 | .Nm | |
417 | to try protocol version 2 only. | |
418 | .It Fl 4 | |
419 | Forces | |
420 | .Nm | |
421 | to use IPv4 addresses only. | |
422 | .It Fl 6 | |
423 | Forces | |
424 | .Nm | |
425 | to use IPv6 addresses only. | |
71276795 | 426 | .It Fl A |
427 | Enables forwarding of the authentication agent connection. | |
428 | This can also be specified on a per-host basis in a configuration file. | |
07d688d5 | 429 | .Pp |
a4e5acef | 430 | Agent forwarding should be enabled with caution. |
431 | Users with the ability to bypass file permissions on the remote host | |
432 | (for the agent's Unix-domain socket) | |
433 | can access the local agent through the forwarded connection. | |
434 | An attacker cannot obtain key material from the agent, | |
07d688d5 | 435 | however they can perform operations on the keys that enable them to |
436 | authenticate using the identities loaded into the agent. | |
5f4a0c58 | 437 | .It Fl a |
438 | Disables forwarding of the authentication agent connection. | |
3435f5a6 | 439 | .It Fl b Ar bind_address |
143f17e8 | 440 | Use |
441 | .Ar bind_address | |
442 | on the local machine as the source address | |
443 | of the connection. | |
444 | Only useful on systems with more than one address. | |
5f4a0c58 | 445 | .It Fl C |
446 | Requests compression of all data (including stdin, stdout, stderr, and | |
447 | data for forwarded X11 and TCP/IP connections). | |
448 | The compression algorithm is the same used by | |
449 | .Xr gzip 1 , | |
450 | and the | |
451 | .Dq level | |
452 | can be controlled by the | |
453 | .Cm CompressionLevel | |
454 | option for protocol version 1. | |
455 | Compression is desirable on modem lines and other | |
456 | slow connections, but will only slow down things on fast networks. | |
457 | The default value can be set on a host-by-host basis in the | |
458 | configuration files; see the | |
459 | .Cm Compression | |
460 | option. | |
3b9baa7b | 461 | .It Fl c Ar cipher_spec |
462 | Selects the cipher specification for encrypting the session. | |
463 | .Pp | |
464 | Protocol version 1 allows specification of a single cipher. | |
2915e42b | 465 | The supported values are |
3b9baa7b | 466 | .Dq 3des , |
467 | .Dq blowfish | |
468 | and | |
469 | .Dq des . | |
bf740959 | 470 | .Ar 3des |
471 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
3b9baa7b | 472 | It is believed to be secure. |
bf740959 | 473 | .Ar blowfish |
5f4a0c58 | 474 | is a fast block cipher; it appears very secure and is much faster than |
610cd5c6 | 475 | .Ar 3des . |
29999e54 | 476 | .Ar des |
477 | is only supported in the | |
478 | .Nm | |
479 | client for interoperability with legacy protocol 1 implementations | |
480 | that do not support the | |
481 | .Ar 3des | |
a4e5acef | 482 | cipher. |
483 | Its use is strongly discouraged due to cryptographic weaknesses. | |
3b9baa7b | 484 | The default is |
485 | .Dq 3des . | |
486 | .Pp | |
487 | For protocol version 2 | |
488 | .Ar cipher_spec | |
489 | is a comma-separated list of ciphers | |
490 | listed in order of preference. | |
491 | The supported ciphers are | |
492 | .Dq 3des-cbc , | |
493 | .Dq aes128-cbc , | |
494 | .Dq aes192-cbc , | |
495 | .Dq aes256-cbc , | |
496 | .Dq aes128-ctr , | |
497 | .Dq aes192-ctr , | |
498 | .Dq aes256-ctr , | |
74a66cc8 | 499 | .Dq arcfour128 , |
500 | .Dq arcfour256 , | |
3b9baa7b | 501 | .Dq arcfour , |
502 | .Dq blowfish-cbc , | |
503 | and | |
504 | .Dq cast128-cbc . | |
505 | The default is | |
506 | .Bd -literal | |
74a66cc8 | 507 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, |
508 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
509 | aes192-ctr,aes256-ctr'' | |
3b9baa7b | 510 | .Ed |
5ddc5eb4 | 511 | .It Fl D Xo |
512 | .Sm off | |
513 | .Oo Ar bind_address : Oc | |
514 | .Ar port | |
515 | .Sm on | |
516 | .Xc | |
5f4a0c58 | 517 | Specifies a local |
518 | .Dq dynamic | |
519 | application-level port forwarding. | |
520 | This works by allocating a socket to listen to | |
521 | .Ar port | |
5ddc5eb4 | 522 | on the local side, optionally bound to the specified |
523 | .Ar bind_address . | |
524 | Whenever a connection is made to this port, the | |
5f4a0c58 | 525 | connection is forwarded over the secure channel, and the application |
526 | protocol is then used to determine where to connect to from the | |
527 | remote machine. | |
528 | Currently the SOCKS4 and SOCKS5 protocols are supported, and | |
529 | .Nm | |
530 | will act as a SOCKS server. | |
531 | Only root can forward privileged ports. | |
532 | Dynamic port forwardings can also be specified in the configuration file. | |
5ddc5eb4 | 533 | .Pp |
534 | IPv6 addresses can be specified with an alternative syntax: | |
535 | .Sm off | |
536 | .Xo | |
537 | .Op Ar bind_address No / | |
538 | .Ar port | |
539 | .Xc | |
540 | .Sm on | |
541 | or by enclosing the address in square brackets. | |
542 | Only the superuser can forward privileged ports. | |
543 | By default, the local port is bound in accordance with the | |
544 | .Cm GatewayPorts | |
545 | setting. | |
546 | However, an explicit | |
547 | .Ar bind_address | |
548 | may be used to bind the connection to a specific address. | |
549 | The | |
550 | .Ar bind_address | |
551 | of | |
552 | .Dq localhost | |
553 | indicates that the listening port be bound for local use only, while an | |
554 | empty address or | |
555 | .Sq * | |
556 | indicates that the port should be available from all interfaces. | |
5f4a0c58 | 557 | .It Fl e Ar ch | ^ch | none |
bf740959 | 558 | Sets the escape character for sessions with a pty (default: |
559 | .Ql ~ ) . | |
610cd5c6 | 560 | The escape character is only recognized at the beginning of a line. |
561 | The escape character followed by a dot | |
bf740959 | 562 | .Pq Ql \&. |
5f4a0c58 | 563 | closes the connection; |
564 | followed by control-Z suspends the connection; | |
565 | and followed by itself sends the escape character once. | |
610cd5c6 | 566 | Setting the character to |
bf740959 | 567 | .Dq none |
568 | disables any escapes and makes the session fully transparent. | |
5f4a0c58 | 569 | .It Fl F Ar configfile |
570 | Specifies an alternative per-user configuration file. | |
571 | If a configuration file is given on the command line, | |
572 | the system-wide configuration file | |
573 | .Pq Pa /etc/ssh/ssh_config | |
574 | will be ignored. | |
575 | The default for the per-user configuration file is | |
140e3e97 | 576 | .Pa ~/.ssh/config . |
bf740959 | 577 | .It Fl f |
578 | Requests | |
579 | .Nm | |
610cd5c6 | 580 | to go to background just before command execution. |
581 | This is useful if | |
bf740959 | 582 | .Nm |
583 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 584 | wants it in the background. |
f54651ce | 585 | This implies |
bf740959 | 586 | .Fl n . |
587 | The recommended way to start X11 programs at a remote site is with | |
588 | something like | |
589 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 590 | .It Fl g |
591 | Allows remote hosts to connect to local forwarded ports. | |
5f4a0c58 | 592 | .It Fl I Ar smartcard_device |
593 | Specifies which smartcard device to use. | |
594 | The argument is the device | |
595 | .Nm | |
596 | should use to communicate with a smartcard used for storing the user's | |
597 | private RSA key. | |
bf740959 | 598 | .It Fl i Ar identity_file |
cf5a07a8 | 599 | Selects a file from which the identity (private key) for |
fa08c86b | 600 | RSA or DSA authentication is read. |
cf5a07a8 | 601 | The default is |
140e3e97 | 602 | .Pa ~/.ssh/identity |
cf5a07a8 | 603 | for protocol version 1, and |
140e3e97 | 604 | .Pa ~/.ssh/id_rsa |
cf5a07a8 | 605 | and |
140e3e97 | 606 | .Pa ~/.ssh/id_dsa |
cf5a07a8 | 607 | for protocol version 2. |
610cd5c6 | 608 | Identity files may also be specified on |
609 | a per-host basis in the configuration file. | |
610 | It is possible to have multiple | |
bf740959 | 611 | .Fl i |
612 | options (and multiple identities specified in | |
613 | configuration files). | |
bf740959 | 614 | .It Fl k |
f7926e97 | 615 | Disables forwarding (delegation) of GSSAPI credentials to the server. |
5f4a0c58 | 616 | .It Fl L Xo |
617 | .Sm off | |
3867aa0a | 618 | .Oo Ar bind_address : Oc |
5f4a0c58 | 619 | .Ar port : host : hostport |
620 | .Sm on | |
621 | .Xc | |
622 | Specifies that the given port on the local (client) host is to be | |
623 | forwarded to the given host and port on the remote side. | |
624 | This works by allocating a socket to listen to | |
625 | .Ar port | |
3867aa0a | 626 | on the local side, optionally bound to the specified |
627 | .Ar bind_address . | |
628 | Whenever a connection is made to this port, the | |
5f4a0c58 | 629 | connection is forwarded over the secure channel, and a connection is |
630 | made to | |
631 | .Ar host | |
632 | port | |
633 | .Ar hostport | |
634 | from the remote machine. | |
635 | Port forwardings can also be specified in the configuration file. | |
5f4a0c58 | 636 | IPv6 addresses can be specified with an alternative syntax: |
637 | .Sm off | |
638 | .Xo | |
6d7a9e8f | 639 | .Op Ar bind_address No / |
5f4a0c58 | 640 | .Ar port No / Ar host No / |
3867aa0a | 641 | .Ar hostport |
5f4a0c58 | 642 | .Xc |
643 | .Sm on | |
3867aa0a | 644 | or by enclosing the address in square brackets. |
645 | Only the superuser can forward privileged ports. | |
646 | By default, the local port is bound in accordance with the | |
647 | .Cm GatewayPorts | |
648 | setting. | |
649 | However, an explicit | |
650 | .Ar bind_address | |
651 | may be used to bind the connection to a specific address. | |
652 | The | |
653 | .Ar bind_address | |
654 | of | |
655 | .Dq localhost | |
6c7e3b94 | 656 | indicates that the listening port be bound for local use only, while an |
657 | empty address or | |
658 | .Sq * | |
3867aa0a | 659 | indicates that the port should be available from all interfaces. |
bf740959 | 660 | .It Fl l Ar login_name |
610cd5c6 | 661 | Specifies the user to log in as on the remote machine. |
662 | This also may be specified on a per-host basis in the configuration file. | |
5e96b616 | 663 | .It Fl M |
664 | Places the | |
665 | .Nm | |
666 | client into | |
667 | .Dq master | |
668 | mode for connection sharing. | |
669 | Refer to the description of | |
670 | .Cm ControlMaster | |
671 | in | |
672 | .Xr ssh_config 5 | |
673 | for details. | |
9affc5db | 674 | .It Fl m Ar mac_spec |
675 | Additionally, for protocol version 2 a comma-separated list of MAC | |
676 | (message authentication code) algorithms can | |
677 | be specified in order of preference. | |
678 | See the | |
679 | .Cm MACs | |
680 | keyword for more information. | |
5f4a0c58 | 681 | .It Fl N |
682 | Do not execute a remote command. | |
683 | This is useful for just forwarding ports | |
684 | (protocol version 2 only). | |
bf740959 | 685 | .It Fl n |
686 | Redirects stdin from | |
687 | .Pa /dev/null | |
688 | (actually, prevents reading from stdin). | |
689 | This must be used when | |
690 | .Nm | |
610cd5c6 | 691 | is run in the background. |
692 | A common trick is to use this to run X11 programs on a remote machine. | |
693 | For example, | |
bf740959 | 694 | .Ic ssh -n shadows.cs.hut.fi emacs & |
695 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
696 | connection will be automatically forwarded over an encrypted channel. | |
697 | The | |
698 | .Nm | |
699 | program will be put in the background. | |
700 | (This does not work if | |
701 | .Nm | |
702 | needs to ask for a password or passphrase; see also the | |
703 | .Fl f | |
704 | option.) | |
cf848a5e | 705 | .It Fl O Ar ctl_cmd |
706 | Control an active connection multiplexing master process. | |
707 | When the | |
708 | .Fl O | |
709 | option is specified, the | |
710 | .Ar ctl_cmd | |
711 | argument is interpreted and passed to the master process. | |
712 | Valid commands are: | |
713 | .Dq check | |
714 | (check that the master process is running) and | |
715 | .Dq exit | |
716 | (request the master to exit). | |
bf740959 | 717 | .It Fl o Ar option |
38539909 | 718 | Can be used to give options in the format used in the configuration file. |
bf740959 | 719 | This is useful for specifying options for which there is no separate |
610cd5c6 | 720 | command-line flag. |
5f4a0c58 | 721 | For full details of the options listed below, and their possible values, see |
722 | .Xr ssh_config 5 . | |
723 | .Pp | |
724 | .Bl -tag -width Ds -offset indent -compact | |
725 | .It AddressFamily | |
726 | .It BatchMode | |
727 | .It BindAddress | |
728 | .It ChallengeResponseAuthentication | |
729 | .It CheckHostIP | |
730 | .It Cipher | |
731 | .It Ciphers | |
732 | .It ClearAllForwardings | |
733 | .It Compression | |
734 | .It CompressionLevel | |
735 | .It ConnectionAttempts | |
20b267fb | 736 | .It ConnectTimeout |
5e96b616 | 737 | .It ControlMaster |
738 | .It ControlPath | |
5f4a0c58 | 739 | .It DynamicForward |
5f4a0c58 | 740 | .It EscapeChar |
741 | .It ForwardAgent | |
742 | .It ForwardX11 | |
d73a67d7 | 743 | .It ForwardX11Trusted |
5f4a0c58 | 744 | .It GatewayPorts |
745 | .It GlobalKnownHostsFile | |
746 | .It GSSAPIAuthentication | |
747 | .It GSSAPIDelegateCredentials | |
5c63c2ab | 748 | .It HashKnownHosts |
5f4a0c58 | 749 | .It Host |
750 | .It HostbasedAuthentication | |
751 | .It HostKeyAlgorithms | |
752 | .It HostKeyAlias | |
753 | .It HostName | |
754 | .It IdentityFile | |
3a065ed0 | 755 | .It IdentitiesOnly |
396070f8 | 756 | .It KbdInteractiveDevices |
d20f3c9e | 757 | .It LocalCommand |
5f4a0c58 | 758 | .It LocalForward |
759 | .It LogLevel | |
760 | .It MACs | |
761 | .It NoHostAuthenticationForLocalhost | |
762 | .It NumberOfPasswordPrompts | |
763 | .It PasswordAuthentication | |
d20f3c9e | 764 | .It PermitLocalCommand |
5f4a0c58 | 765 | .It Port |
766 | .It PreferredAuthentications | |
767 | .It Protocol | |
768 | .It ProxyCommand | |
769 | .It PubkeyAuthentication | |
770 | .It RemoteForward | |
771 | .It RhostsRSAAuthentication | |
772 | .It RSAAuthentication | |
8e99a198 | 773 | .It SendEnv |
5d8d32a3 | 774 | .It ServerAliveInterval |
775 | .It ServerAliveCountMax | |
5f4a0c58 | 776 | .It SmartcardDevice |
777 | .It StrictHostKeyChecking | |
fd573618 | 778 | .It TCPKeepAlive |
d20f3c9e | 779 | .It Tunnel |
780 | .It TunnelDevice | |
5f4a0c58 | 781 | .It UsePrivilegedPort |
782 | .It User | |
783 | .It UserKnownHostsFile | |
784 | .It VerifyHostKeyDNS | |
785 | .It XAuthLocation | |
786 | .El | |
bf740959 | 787 | .It Fl p Ar port |
610cd5c6 | 788 | Port to connect to on the remote host. |
789 | This can be specified on a | |
bf740959 | 790 | per-host basis in the configuration file. |
bf740959 | 791 | .It Fl q |
610cd5c6 | 792 | Quiet mode. |
793 | Causes all warning and diagnostic messages to be suppressed. | |
5f4a0c58 | 794 | .It Fl R Xo |
795 | .Sm off | |
3867aa0a | 796 | .Oo Ar bind_address : Oc |
5f4a0c58 | 797 | .Ar port : host : hostport |
798 | .Sm on | |
799 | .Xc | |
800 | Specifies that the given port on the remote (server) host is to be | |
801 | forwarded to the given host and port on the local side. | |
802 | This works by allocating a socket to listen to | |
803 | .Ar port | |
804 | on the remote side, and whenever a connection is made to this port, the | |
805 | connection is forwarded over the secure channel, and a connection is | |
806 | made to | |
807 | .Ar host | |
808 | port | |
809 | .Ar hostport | |
810 | from the local machine. | |
3867aa0a | 811 | .Pp |
5f4a0c58 | 812 | Port forwardings can also be specified in the configuration file. |
813 | Privileged ports can be forwarded only when | |
814 | logging in as root on the remote machine. | |
3867aa0a | 815 | IPv6 addresses can be specified by enclosing the address in square braces or |
816 | using an alternative syntax: | |
3867aa0a | 817 | .Sm off |
6c7e3b94 | 818 | .Xo |
6d7a9e8f | 819 | .Op Ar bind_address No / |
6c7e3b94 | 820 | .Ar host No / Ar port No / |
821 | .Ar hostport | |
3867aa0a | 822 | .Xc . |
6c7e3b94 | 823 | .Sm on |
3867aa0a | 824 | .Pp |
825 | By default, the listening socket on the server will be bound to the loopback | |
826 | interface only. | |
827 | This may be overriden by specifying a | |
828 | .Ar bind_address . | |
6c7e3b94 | 829 | An empty |
830 | .Ar bind_address , | |
3867aa0a | 831 | or the address |
6c7e3b94 | 832 | .Ql * , |
3867aa0a | 833 | indicates that the remote socket should listen on all interfaces. |
834 | Specifying a remote | |
835 | .Ar bind_address | |
6c7e3b94 | 836 | will only succeed if the server's |
837 | .Cm GatewayPorts | |
3867aa0a | 838 | option is enabled (see |
6c7e3b94 | 839 | .Xr sshd_config 5 ) . |
f8c6db83 | 840 | .It Fl S Ar ctl_path |
9affc5db | 841 | Specifies the location of a control socket for connection sharing. |
5e96b616 | 842 | Refer to the description of |
0e19494c | 843 | .Cm ControlPath |
844 | and | |
5e96b616 | 845 | .Cm ControlMaster |
846 | in | |
847 | .Xr ssh_config 5 | |
848 | for details. | |
ae810de7 | 849 | .It Fl s |
3cbc677d | 850 | May be used to request invocation of a subsystem on the remote system. |
851 | Subsystems are a feature of the SSH2 protocol which facilitate the use | |
5f4a0c58 | 852 | of SSH as a secure transport for other applications (eg.\& |
853 | .Xr sftp 1 ) . | |
3cbc677d | 854 | The subsystem is specified as the remote command. |
5f4a0c58 | 855 | .It Fl T |
856 | Disable pseudo-tty allocation. | |
bf740959 | 857 | .It Fl t |
610cd5c6 | 858 | Force pseudo-tty allocation. |
4fe2af09 | 859 | This can be used to execute arbitrary |
610cd5c6 | 860 | screen-based programs on a remote machine, which can be very useful, |
861 | e.g., when implementing menu services. | |
8abcdba4 | 862 | Multiple |
863 | .Fl t | |
864 | options force tty allocation, even if | |
865 | .Nm | |
866 | has no local tty. | |
5f4a0c58 | 867 | .It Fl V |
868 | Display the version number and exit. | |
bf740959 | 869 | .It Fl v |
610cd5c6 | 870 | Verbose mode. |
871 | Causes | |
bf740959 | 872 | .Nm |
610cd5c6 | 873 | to print debugging messages about its progress. |
874 | This is helpful in | |
bf740959 | 875 | debugging connection, authentication, and configuration problems. |
8abcdba4 | 876 | Multiple |
877 | .Fl v | |
c825cd79 | 878 | options increase the verbosity. |
879 | The maximum is 3. | |
d20f3c9e | 880 | .It Fl w |
881 | Requests a | |
882 | .Xr tun 4 | |
883 | device on the client and server like the | |
884 | .Cm Tunnel | |
885 | directive in | |
886 | .Xr ssh_config 5 . | |
bf740959 | 887 | .It Fl X |
888 | Enables X11 forwarding. | |
71276795 | 889 | This can also be specified on a per-host basis in a configuration file. |
07d688d5 | 890 | .Pp |
a4e5acef | 891 | X11 forwarding should be enabled with caution. |
892 | Users with the ability to bypass file permissions on the remote host | |
893 | (for the user's X authorization database) | |
894 | can access the local X11 display through the forwarded connection. | |
895 | An attacker may then be able to perform activities such as keystroke monitoring. | |
82966fe8 | 896 | .Pp |
4469b0cf | 897 | For this reason, X11 forwarding is subjected to X11 SECURITY extension |
82966fe8 | 898 | restrictions by default. |
899 | Please refer to the | |
900 | .Nm | |
901 | .Fl Y | |
902 | option and the | |
903 | .Cm ForwardX11Trusted | |
904 | directive in | |
905 | .Xr ssh_config 5 | |
906 | for more information. | |
5f4a0c58 | 907 | .It Fl x |
908 | Disables X11 forwarding. | |
d73a67d7 | 909 | .It Fl Y |
910 | Enables trusted X11 forwarding. | |
82966fe8 | 911 | Trusted X11 forwardings are not subjected to the X11 SECURITY extension |
912 | controls. | |
bf740959 | 913 | .El |
914 | .Sh CONFIGURATION FILES | |
915 | .Nm | |
588df31a | 916 | may additionally obtain configuration data from |
917 | a per-user configuration file and a system-wide configuration file. | |
918 | The file format and configuration options are described in | |
919 | .Xr ssh_config 5 . | |
bf740959 | 920 | .Sh ENVIRONMENT |
921 | .Nm | |
922 | will normally set the following environment variables: | |
5f4a0c58 | 923 | .Bl -tag -width LOGNAME |
bf740959 | 924 | .It Ev DISPLAY |
925 | The | |
926 | .Ev DISPLAY | |
610cd5c6 | 927 | variable indicates the location of the X11 server. |
f54651ce | 928 | It is automatically set by |
bf740959 | 929 | .Nm |
930 | to point to a value of the form | |
931 | .Dq hostname:n | |
932 | where hostname indicates | |
5f4a0c58 | 933 | the host where the shell runs, and n is an integer \*(Ge 1. |
610cd5c6 | 934 | .Nm |
935 | uses this special value to forward X11 connections over the secure | |
936 | channel. | |
da89cf4d | 937 | The user should normally not set |
938 | .Ev DISPLAY | |
939 | explicitly, as that | |
bf740959 | 940 | will render the X11 connection insecure (and will require the user to |
941 | manually copy any required authorization cookies). | |
942 | .It Ev HOME | |
943 | Set to the path of the user's home directory. | |
944 | .It Ev LOGNAME | |
945 | Synonym for | |
946 | .Ev USER ; | |
947 | set for compatibility with systems that use this variable. | |
948 | .It Ev MAIL | |
ae897d7c | 949 | Set to the path of the user's mailbox. |
610cd5c6 | 950 | .It Ev PATH |
bf740959 | 951 | Set to the default |
952 | .Ev PATH , | |
953 | as specified when compiling | |
954 | .Nm ssh . | |
3474b2b4 | 955 | .It Ev SSH_ASKPASS |
956 | If | |
957 | .Nm | |
958 | needs a passphrase, it will read the passphrase from the current | |
959 | terminal if it was run from a terminal. | |
960 | If | |
961 | .Nm | |
962 | does not have a terminal associated with it but | |
963 | .Ev DISPLAY | |
964 | and | |
965 | .Ev SSH_ASKPASS | |
966 | are set, it will execute the program specified by | |
967 | .Ev SSH_ASKPASS | |
968 | and open an X11 window to read the passphrase. | |
969 | This is particularly useful when calling | |
970 | .Nm | |
971 | from a | |
caeffafb | 972 | .Pa .xsession |
3474b2b4 | 973 | or related script. |
974 | (Note that on some machines it | |
975 | may be necessary to redirect the input from | |
976 | .Pa /dev/null | |
977 | to make this work.) | |
bf740959 | 978 | .It Ev SSH_AUTH_SOCK |
ae897d7c | 979 | Identifies the path of a unix-domain socket used to communicate with the |
bf740959 | 980 | agent. |
da0561eb | 981 | .It Ev SSH_CONNECTION |
982 | Identifies the client and server ends of the connection. | |
610cd5c6 | 983 | The variable contains |
da0561eb | 984 | four space-separated values: client ip-address, client port number, |
985 | server ip-address and server port number. | |
8abcdba4 | 986 | .It Ev SSH_ORIGINAL_COMMAND |
987 | The variable contains the original command line if a forced command | |
988 | is executed. | |
989 | It can be used to extract the original arguments. | |
bf740959 | 990 | .It Ev SSH_TTY |
991 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 992 | with the current shell or command. |
993 | If the current session has no tty, | |
bf740959 | 994 | this variable is not set. |
995 | .It Ev TZ | |
04ac3e62 | 996 | This variable is set to indicate the present time zone if it |
c345cf9d | 997 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 998 | on to new connections). |
999 | .It Ev USER | |
1000 | Set to the name of the user logging in. | |
1001 | .El | |
1002 | .Pp | |
f54651ce | 1003 | Additionally, |
bf740959 | 1004 | .Nm |
f54651ce | 1005 | reads |
140e3e97 | 1006 | .Pa ~/.ssh/environment , |
bf740959 | 1007 | and adds lines of the format |
1008 | .Dq VARNAME=value | |
6a342527 | 1009 | to the environment if the file exists and if users are allowed to |
1010 | change their environment. | |
5f4a0c58 | 1011 | For more information, see the |
6a342527 | 1012 | .Cm PermitUserEnvironment |
35453849 | 1013 | option in |
6a342527 | 1014 | .Xr sshd_config 5 . |
bf740959 | 1015 | .Sh FILES |
c8d54615 | 1016 | .Bl -tag -width Ds |
140e3e97 | 1017 | .It Pa ~/.ssh/known_hosts |
ae897d7c | 1018 | Records host keys for all hosts the user has logged into that are not |
bf740959 | 1019 | in |
2a8a6488 | 1020 | .Pa /etc/ssh/ssh_known_hosts . |
bf740959 | 1021 | See |
1022 | .Xr sshd 8 . | |
140e3e97 | 1023 | .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa |
c0ecc314 | 1024 | Contains the authentication identity of the user. |
1025 | They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. | |
1d1ffb87 | 1026 | These files |
1027 | contain sensitive data and should be readable by the user but not | |
bf740959 | 1028 | accessible by others (read/write/execute). |
1029 | Note that | |
1030 | .Nm | |
1d1ffb87 | 1031 | ignores a private key file if it is accessible by others. |
bf740959 | 1032 | It is possible to specify a passphrase when |
1033 | generating the key; the passphrase will be used to encrypt the | |
1034 | sensitive part of this file using 3DES. | |
140e3e97 | 1035 | .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub |
bf740959 | 1036 | Contains the public key for authentication (public part of the |
610cd5c6 | 1037 | identity file in human-readable form). |
1d1ffb87 | 1038 | The contents of the |
140e3e97 | 1039 | .Pa ~/.ssh/identity.pub |
5f4a0c58 | 1040 | file should be added to the file |
140e3e97 | 1041 | .Pa ~/.ssh/authorized_keys |
bf740959 | 1042 | on all machines |
91789042 | 1043 | where the user wishes to log in using protocol version 1 RSA authentication. |
1d1ffb87 | 1044 | The contents of the |
140e3e97 | 1045 | .Pa ~/.ssh/id_dsa.pub |
c0ecc314 | 1046 | and |
140e3e97 | 1047 | .Pa ~/.ssh/id_rsa.pub |
1d1ffb87 | 1048 | file should be added to |
140e3e97 | 1049 | .Pa ~/.ssh/authorized_keys |
1d1ffb87 | 1050 | on all machines |
91789042 | 1051 | where the user wishes to log in using protocol version 2 DSA/RSA authentication. |
1d1ffb87 | 1052 | These files are not |
610cd5c6 | 1053 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 1054 | These files are |
c44559d2 | 1055 | never used automatically and are not necessary; they are only provided for |
bf740959 | 1056 | the convenience of the user. |
140e3e97 | 1057 | .It Pa ~/.ssh/config |
610cd5c6 | 1058 | This is the per-user configuration file. |
588df31a | 1059 | The file format and configuration options are described in |
1060 | .Xr ssh_config 5 . | |
e1520719 | 1061 | Because of the potential for abuse, this file must have strict permissions: |
1062 | read/write for the user, and not accessible by others. | |
140e3e97 | 1063 | .It Pa ~/.ssh/authorized_keys |
96a7b0cc | 1064 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. |
610cd5c6 | 1065 | The format of this file is described in the |
bf740959 | 1066 | .Xr sshd 8 |
610cd5c6 | 1067 | manual page. |
5f4a0c58 | 1068 | In the simplest form the format is the same as the |
1069 | .Pa .pub | |
f49bc4f7 | 1070 | identity files. |
1d1ffb87 | 1071 | This file is not highly sensitive, but the recommended |
1072 | permissions are read/write for the user, and not accessible by others. | |
2a8a6488 | 1073 | .It Pa /etc/ssh/ssh_known_hosts |
610cd5c6 | 1074 | Systemwide list of known host keys. |
f49bc4f7 | 1075 | This file should be prepared by the |
bf740959 | 1076 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1077 | organization. |
1078 | This file should be world-readable. | |
1079 | This file contains | |
bf740959 | 1080 | public keys, one per line, in the following format (fields separated |
f49bc4f7 | 1081 | by spaces): system name, public key and optional comment field. |
610cd5c6 | 1082 | When different names are used |
bf740959 | 1083 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1084 | commas. |
5f4a0c58 | 1085 | The format is described in the |
bf740959 | 1086 | .Xr sshd 8 |
1087 | manual page. | |
1088 | .Pp | |
1089 | The canonical system name (as returned by name servers) is used by | |
1090 | .Xr sshd 8 | |
1091 | to verify the client host when logging in; other names are needed because | |
1092 | .Nm | |
1093 | does not convert the user-supplied name to a canonical name before | |
1094 | checking the key, because someone with access to the name servers | |
1095 | would then be able to fool host authentication. | |
2a8a6488 | 1096 | .It Pa /etc/ssh/ssh_config |
610cd5c6 | 1097 | Systemwide configuration file. |
588df31a | 1098 | The file format and configuration options are described in |
1099 | .Xr ssh_config 5 . | |
2a8a6488 | 1100 | .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key |
dd58cb5e | 1101 | These three files contain the private parts of the host keys |
1102 | and are used for | |
1103 | .Cm RhostsRSAAuthentication | |
1104 | and | |
1105 | .Cm HostbasedAuthentication . | |
d83cbdc3 | 1106 | If the protocol version 1 |
1107 | .Cm RhostsRSAAuthentication | |
7203d6bb | 1108 | method is used, |
d83cbdc3 | 1109 | .Nm |
1110 | must be setuid root, since the host key is readable only by root. | |
1111 | For protocol version 2, | |
1112 | .Nm | |
1113 | uses | |
1114 | .Xr ssh-keysign 8 | |
1115 | to access the host keys for | |
1116 | .Cm HostbasedAuthentication . | |
1117 | This eliminates the requirement that | |
1118 | .Nm | |
1119 | be setuid root when that authentication method is used. | |
1120 | By default | |
dd58cb5e | 1121 | .Nm |
d83cbdc3 | 1122 | is not setuid root. |
140e3e97 | 1123 | .It Pa ~/.rhosts |
bf740959 | 1124 | This file is used in |
6f5abc1e | 1125 | .Cm RhostsRSAAuthentication |
1126 | and | |
1127 | .Cm HostbasedAuthentication | |
bf740959 | 1128 | authentication to list the |
610cd5c6 | 1129 | host/user pairs that are permitted to log in. |
1130 | (Note that this file is | |
bf740959 | 1131 | also used by rlogin and rsh, which makes using this file insecure.) |
1132 | Each line of the file contains a host name (in the canonical form | |
1133 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1134 | separated by a space. |
e91c60f2 | 1135 | On some machines this file may need to be |
bf740959 | 1136 | world-readable if the user's home directory is on a NFS partition, |
1137 | because | |
1138 | .Xr sshd 8 | |
610cd5c6 | 1139 | reads it as root. |
1140 | Additionally, this file must be owned by the user, | |
1141 | and must not have write permissions for anyone else. | |
1142 | The recommended | |
bf740959 | 1143 | permission for most machines is read/write for the user, and not |
1144 | accessible by others. | |
1145 | .Pp | |
6f5abc1e | 1146 | Note that |
bf740959 | 1147 | .Xr sshd 8 |
6f5abc1e | 1148 | allows authentication only in combination with client host key |
1149 | authentication before permitting log in. | |
91789042 | 1150 | If the server machine does not have the client's host key in |
2a8a6488 | 1151 | .Pa /etc/ssh/ssh_known_hosts , |
91789042 | 1152 | it can be stored in |
140e3e97 | 1153 | .Pa ~/.ssh/known_hosts . |
bf740959 | 1154 | The easiest way to do this is to |
1155 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1156 | will automatically add the host key to |
140e3e97 | 1157 | .Pa ~/.ssh/known_hosts . |
1158 | .It Pa ~/.shosts | |
bf740959 | 1159 | This file is used exactly the same way as |
5f4a0c58 | 1160 | .Pa .rhosts . |
bf740959 | 1161 | The purpose for |
6f5abc1e | 1162 | having this file is to be able to use |
1163 | .Cm RhostsRSAAuthentication | |
1164 | and | |
1165 | .Cm HostbasedAuthentication | |
1166 | authentication without permitting login with | |
5f4a0c58 | 1167 | .Xr rlogin |
bf740959 | 1168 | or |
1169 | .Xr rsh 1 . | |
1170 | .It Pa /etc/hosts.equiv | |
1171 | This file is used during | |
6f5abc1e | 1172 | .Cm RhostsRSAAuthentication |
1173 | and | |
1174 | .Cm HostbasedAuthentication | |
be193d89 | 1175 | authentication. |
610cd5c6 | 1176 | It contains |
5f4a0c58 | 1177 | canonical hosts names, one per line (the full format is described in the |
bf740959 | 1178 | .Xr sshd 8 |
610cd5c6 | 1179 | manual page). |
1180 | If the client host is found in this file, login is | |
bf740959 | 1181 | automatically permitted provided client and server user names are the |
610cd5c6 | 1182 | same. |
6f5abc1e | 1183 | Additionally, successful client host key authentication is required. |
610cd5c6 | 1184 | This file should only be writable by root. |
5f4fdfae | 1185 | .It Pa /etc/shosts.equiv |
f54651ce | 1186 | This file is processed exactly as |
bf740959 | 1187 | .Pa /etc/hosts.equiv . |
1188 | This file may be useful to permit logins using | |
1189 | .Nm | |
1190 | but not using rsh/rlogin. | |
2a8a6488 | 1191 | .It Pa /etc/ssh/sshrc |
bf740959 | 1192 | Commands in this file are executed by |
1193 | .Nm | |
1194 | when the user logs in just before the user's shell (or command) is started. | |
1195 | See the | |
1196 | .Xr sshd 8 | |
1197 | manual page for more information. | |
140e3e97 | 1198 | .It Pa ~/.ssh/rc |
bf740959 | 1199 | Commands in this file are executed by |
1200 | .Nm | |
1201 | when the user logs in just before the user's shell (or command) is | |
1202 | started. | |
f54651ce | 1203 | See the |
bf740959 | 1204 | .Xr sshd 8 |
1205 | manual page for more information. | |
140e3e97 | 1206 | .It Pa ~/.ssh/environment |
83b7f649 | 1207 | Contains additional definitions for environment variables, see section |
1208 | .Sx ENVIRONMENT | |
1209 | above. | |
b5e300c2 | 1210 | .El |
16210ef7 | 1211 | .Sh DIAGNOSTICS |
1212 | .Nm | |
1213 | exits with the exit status of the remote command or with 255 | |
1214 | if an error occurred. | |
bf740959 | 1215 | .Sh SEE ALSO |
5f4a0c58 | 1216 | .Xr gzip 1 , |
bf740959 | 1217 | .Xr rsh 1 , |
1218 | .Xr scp 1 , | |
61e96248 | 1219 | .Xr sftp 1 , |
bf740959 | 1220 | .Xr ssh-add 1 , |
1221 | .Xr ssh-agent 1 , | |
1222 | .Xr ssh-keygen 1 , | |
1223 | .Xr telnet 1 , | |
5f4a0c58 | 1224 | .Xr hosts.equiv 5 , |
1ae02182 | 1225 | .Xr ssh_config 5 , |
b2843ec6 | 1226 | .Xr ssh-keysign 8 , |
9afadca8 | 1227 | .Xr sshd 8 |
2cad6cef | 1228 | .Rs |
1229 | .%A T. Ylonen | |
1230 | .%A T. Kivinen | |
1231 | .%A M. Saarinen | |
1232 | .%A T. Rinne | |
1233 | .%A S. Lehtinen | |
1234 | .%T "SSH Protocol Architecture" | |
17f5e68a | 1235 | .%N draft-ietf-secsh-architecture-12.txt |
1236 | .%D January 2002 | |
2cad6cef | 1237 | .%O work in progress material |
1238 | .Re | |
be193d89 | 1239 | .Sh AUTHORS |
1240 | OpenSSH is a derivative of the original and free | |
1241 | ssh 1.2.12 release by Tatu Ylonen. | |
1242 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1243 | Theo de Raadt and Dug Song | |
1244 | removed many bugs, re-added newer features and | |
1245 | created OpenSSH. | |
1246 | Markus Friedl contributed the support for SSH | |
1247 | protocol versions 1.5 and 2.0. |