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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 | .\" |
d7cf99ff | 37 | .\" $OpenBSD: ssh.1,v 1.213 2005/11/30 11:18:27 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 |
5f4a0c58 | 80 | .Oo Ar user Ns @ Oc Ns Ar hostname |
bf740959 | 81 | .Op Ar command |
f54651ce | 82 | .Sh DESCRIPTION |
bf740959 | 83 | .Nm |
2c86906e | 84 | (SSH client) is a program for logging into a remote machine and for |
610cd5c6 | 85 | executing commands on a remote machine. |
5f4a0c58 | 86 | It is intended to replace rlogin and rsh, |
87 | and provide secure encrypted communications between | |
610cd5c6 | 88 | two untrusted hosts over an insecure network. |
5f4a0c58 | 89 | X11 connections and arbitrary TCP/IP ports |
90 | can also be forwarded over the secure channel. | |
bf740959 | 91 | .Pp |
92 | .Nm | |
f54651ce | 93 | connects and logs into the specified |
5f4a0c58 | 94 | .Ar hostname |
95 | (with optional | |
96 | .Ar user | |
97 | name). | |
bf740959 | 98 | The user must prove |
1d1ffb87 | 99 | his/her identity to the remote machine using one of several methods |
5f4a0c58 | 100 | depending on the protocol version used. |
1d1ffb87 | 101 | .Pp |
5f4a0c58 | 102 | If |
103 | .Ar command | |
104 | is specified, | |
105 | .Ar command | |
106 | is executed on the remote host instead of a login shell. | |
1d1ffb87 | 107 | .Ss SSH protocol version 1 |
6f5abc1e | 108 | The first authentication method is the |
109 | .Em rhosts | |
110 | or | |
111 | .Em hosts.equiv | |
112 | method combined with RSA-based host authentication. | |
113 | If the machine the user logs in from is listed in | |
bf740959 | 114 | .Pa /etc/hosts.equiv |
115 | or | |
5f4fdfae | 116 | .Pa /etc/shosts.equiv |
bf740959 | 117 | on the remote machine, and the user names are |
6f5abc1e | 118 | the same on both sides, or if the files |
140e3e97 | 119 | .Pa ~/.rhosts |
bf740959 | 120 | or |
140e3e97 | 121 | .Pa ~/.shosts |
6f5abc1e | 122 | exist in the user's home directory on the |
123 | remote machine and contain a line containing the name of the client | |
bf740959 | 124 | machine and the name of the user on that machine, the user is |
6f5abc1e | 125 | considered for log in. |
126 | Additionally, if the server can verify the client's | |
f54651ce | 127 | host key (see |
2a8a6488 | 128 | .Pa /etc/ssh/ssh_known_hosts |
5bbb5681 | 129 | and |
140e3e97 | 130 | .Pa ~/.ssh/known_hosts |
bf740959 | 131 | in the |
132 | .Sx FILES | |
5f4a0c58 | 133 | section), only then is login permitted. |
610cd5c6 | 134 | This authentication method closes security holes due to IP |
135 | spoofing, DNS spoofing and routing spoofing. | |
136 | [Note to the administrator: | |
bf740959 | 137 | .Pa /etc/hosts.equiv , |
140e3e97 | 138 | .Pa ~/.rhosts , |
bf740959 | 139 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
140 | disabled if security is desired.] | |
141 | .Pp | |
6f5abc1e | 142 | As a second authentication method, |
bf740959 | 143 | .Nm |
144 | supports RSA based authentication. | |
145 | The scheme is based on public-key cryptography: there are cryptosystems | |
146 | where encryption and decryption are done using separate keys, and it | |
147 | is not possible to derive the decryption key from the encryption key. | |
610cd5c6 | 148 | RSA is one such system. |
f54651ce | 149 | The idea is that each user creates a public/private |
610cd5c6 | 150 | key pair for authentication purposes. |
151 | The server knows the public key, and only the user knows the private key. | |
5f4a0c58 | 152 | .Pp |
f54651ce | 153 | The file |
140e3e97 | 154 | .Pa ~/.ssh/authorized_keys |
5f4a0c58 | 155 | lists the public keys that are permitted for logging in. |
610cd5c6 | 156 | When the user logs in, the |
bf740959 | 157 | .Nm |
158 | program tells the server which key pair it would like to use for | |
610cd5c6 | 159 | authentication. |
5f4a0c58 | 160 | The server checks if this key is permitted, and if so, |
161 | sends the user (actually the | |
bf740959 | 162 | .Nm |
163 | program running on behalf of the user) a challenge, a random number, | |
610cd5c6 | 164 | encrypted by the user's public key. |
5f4a0c58 | 165 | The challenge can only be decrypted using the proper private key. |
166 | The user's client then decrypts the challenge using the private key, | |
167 | proving that he/she knows the private key | |
168 | but without disclosing it to the server. | |
bf740959 | 169 | .Pp |
170 | .Nm | |
610cd5c6 | 171 | implements the RSA authentication protocol automatically. |
172 | The user creates his/her RSA key pair by running | |
bf740959 | 173 | .Xr ssh-keygen 1 . |
f54651ce | 174 | This stores the private key in |
140e3e97 | 175 | .Pa ~/.ssh/identity |
5f4a0c58 | 176 | and stores the public key in |
140e3e97 | 177 | .Pa ~/.ssh/identity.pub |
610cd5c6 | 178 | in the user's home directory. |
179 | The user should then copy the | |
bf740959 | 180 | .Pa identity.pub |
f54651ce | 181 | to |
140e3e97 | 182 | .Pa ~/.ssh/authorized_keys |
f54651ce | 183 | in his/her home directory on the remote machine (the |
bf740959 | 184 | .Pa authorized_keys |
f54651ce | 185 | file corresponds to the conventional |
140e3e97 | 186 | .Pa ~/.rhosts |
bf740959 | 187 | file, and has one key |
610cd5c6 | 188 | per line, though the lines can be very long). |
189 | After this, the user can log in without giving the password. | |
bf740959 | 190 | .Pp |
191 | The most convenient way to use RSA authentication may be with an | |
610cd5c6 | 192 | authentication agent. |
193 | See | |
bf740959 | 194 | .Xr ssh-agent 1 |
195 | for more information. | |
196 | .Pp | |
f54651ce | 197 | If other authentication methods fail, |
bf740959 | 198 | .Nm |
610cd5c6 | 199 | prompts the user for a password. |
200 | The password is sent to the remote | |
bf740959 | 201 | host for checking; however, since all communications are encrypted, |
202 | the password cannot be seen by someone listening on the network. | |
1d1ffb87 | 203 | .Ss SSH protocol version 2 |
5f4a0c58 | 204 | When a user connects using protocol version 2, |
16210ef7 | 205 | similar authentication methods are available. |
da89cf4d | 206 | Using the default values for |
207 | .Cm PreferredAuthentications , | |
29c440a0 | 208 | the client will try to authenticate first using the hostbased method; |
5f4a0c58 | 209 | if this method fails, public key authentication is attempted, |
210 | and finally if this method fails, keyboard-interactive and | |
29c440a0 | 211 | password authentication are tried. |
1d1ffb87 | 212 | .Pp |
213 | The public key method is similar to RSA authentication described | |
da89cf4d | 214 | in the previous section and allows the RSA or DSA algorithm to be used: |
c0ecc314 | 215 | The client uses his private key, |
140e3e97 | 216 | .Pa ~/.ssh/id_dsa |
c0ecc314 | 217 | or |
140e3e97 | 218 | .Pa ~/.ssh/id_rsa , |
1d1ffb87 | 219 | to sign the session identifier and sends the result to the server. |
220 | The server checks whether the matching public key is listed in | |
140e3e97 | 221 | .Pa ~/.ssh/authorized_keys |
1d1ffb87 | 222 | and grants access if both the key is found and the signature is correct. |
223 | The session identifier is derived from a shared Diffie-Hellman value | |
224 | and is only known to the client and the server. | |
225 | .Pp | |
5f4a0c58 | 226 | If public key authentication fails or is not available, a password |
227 | can be sent encrypted to the remote host to prove the user's identity. | |
da89cf4d | 228 | .Pp |
229 | Additionally, | |
230 | .Nm | |
231 | supports hostbased or challenge response authentication. | |
1d1ffb87 | 232 | .Pp |
233 | Protocol 2 provides additional mechanisms for confidentiality | |
3b9baa7b | 234 | (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour) |
235 | and integrity (hmac-md5, hmac-sha1, hmac-ripemd160). | |
1d1ffb87 | 236 | Note that protocol 1 lacks a strong mechanism for ensuring the |
237 | integrity of the connection. | |
1d1ffb87 | 238 | .Ss Login session and remote execution |
bf740959 | 239 | When the user's identity has been accepted by the server, the server |
240 | either executes the given command, or logs into the machine and gives | |
610cd5c6 | 241 | the user a normal shell on the remote machine. |
242 | All communication with | |
bf740959 | 243 | the remote command or shell will be automatically encrypted. |
244 | .Pp | |
245 | If a pseudo-terminal has been allocated (normal login session), the | |
df841692 | 246 | user may use the escape characters noted below. |
bf740959 | 247 | .Pp |
5f4a0c58 | 248 | If no pseudo-tty has been allocated, |
249 | the session is transparent and can be used to reliably transfer binary data. | |
610cd5c6 | 250 | On most systems, setting the escape character to |
bf740959 | 251 | .Dq none |
252 | will also make the session transparent even if a tty is used. | |
253 | .Pp | |
ce9c0b75 | 254 | The session terminates when the command or shell on the remote |
e91c60f2 | 255 | machine exits and all X11 and TCP/IP connections have been closed. |
5f4a0c58 | 256 | The exit status of the remote program is returned as the exit status of |
bf740959 | 257 | .Nm ssh . |
df841692 | 258 | .Ss Escape Characters |
5f4a0c58 | 259 | When a pseudo-terminal has been requested, |
260 | .Nm | |
261 | supports a number of functions through the use of an escape character. | |
df841692 | 262 | .Pp |
263 | A single tilde character can be sent as | |
264 | .Ic ~~ | |
5bef3c35 | 265 | or by following the tilde by a character other than those described below. |
df841692 | 266 | The escape character must always follow a newline to be interpreted as |
267 | special. | |
268 | The escape character can be changed in configuration files using the | |
269 | .Cm EscapeChar | |
3730bb22 | 270 | configuration directive or on the command line by the |
df841692 | 271 | .Fl e |
272 | option. | |
273 | .Pp | |
274 | The supported escapes (assuming the default | |
275 | .Ql ~ ) | |
276 | are: | |
277 | .Bl -tag -width Ds | |
278 | .It Cm ~. | |
5f4a0c58 | 279 | Disconnect. |
df841692 | 280 | .It Cm ~^Z |
5f4a0c58 | 281 | Background |
282 | .Nm ssh . | |
df841692 | 283 | .It Cm ~# |
5f4a0c58 | 284 | List forwarded connections. |
df841692 | 285 | .It Cm ~& |
5f4a0c58 | 286 | Background |
287 | .Nm | |
288 | at logout when waiting for forwarded connection / X11 sessions to terminate. | |
df841692 | 289 | .It Cm ~? |
5f4a0c58 | 290 | Display a list of escape characters. |
16a79097 | 291 | .It Cm ~B |
5f4a0c58 | 292 | Send a BREAK to the remote system |
293 | (only useful for SSH protocol version 2 and if the peer supports it). | |
c53c54c2 | 294 | .It Cm ~C |
d740ec16 | 295 | Open command line. |
296 | Currently this allows the addition of port forwardings using the | |
c53c54c2 | 297 | .Fl L |
298 | and | |
299 | .Fl R | |
d740ec16 | 300 | options (see below). |
790029d9 | 301 | It also allows the cancellation of existing remote port-forwardings |
d740ec16 | 302 | using |
303 | .Fl KR Ar hostport . | |
7069a5e2 | 304 | Basic help is available, using the |
305 | .Fl h | |
d740ec16 | 306 | option. |
df841692 | 307 | .It Cm ~R |
5f4a0c58 | 308 | Request rekeying of the connection |
309 | (only useful for SSH protocol version 2 and if the peer supports it). | |
df841692 | 310 | .El |
1d1ffb87 | 311 | .Ss X11 and TCP forwarding |
6efa3d14 | 312 | If the |
313 | .Cm ForwardX11 | |
314 | variable is set to | |
315 | .Dq yes | |
5f4a0c58 | 316 | (or see the description of the |
6efa3d14 | 317 | .Fl X |
318 | and | |
319 | .Fl x | |
320 | options described later) | |
321 | and the user is using X11 (the | |
bf740959 | 322 | .Ev DISPLAY |
323 | environment variable is set), the connection to the X11 display is | |
324 | automatically forwarded to the remote side in such a way that any X11 | |
325 | programs started from the shell (or command) will go through the | |
326 | encrypted channel, and the connection to the real X server will be made | |
610cd5c6 | 327 | from the local machine. |
328 | The user should not manually set | |
bf740959 | 329 | .Ev DISPLAY . |
330 | Forwarding of X11 connections can be | |
331 | configured on the command line or in configuration files. | |
332 | .Pp | |
333 | The | |
f54651ce | 334 | .Ev DISPLAY |
bf740959 | 335 | value set by |
336 | .Nm | |
5f4a0c58 | 337 | will point to the server machine, but with a display number greater than zero. |
610cd5c6 | 338 | This is normal, and happens because |
bf740959 | 339 | .Nm |
340 | creates a | |
341 | .Dq proxy | |
342 | X server on the server machine for forwarding the | |
343 | connections over the encrypted channel. | |
344 | .Pp | |
345 | .Nm | |
346 | will also automatically set up Xauthority data on the server machine. | |
347 | For this purpose, it will generate a random authorization cookie, | |
348 | store it in Xauthority on the server, and verify that any forwarded | |
349 | connections carry this cookie and replace it by the real cookie when | |
610cd5c6 | 350 | the connection is opened. |
351 | The real authentication cookie is never | |
bf740959 | 352 | sent to the server machine (and no cookies are sent in the plain). |
353 | .Pp | |
24794905 | 354 | If the |
355 | .Cm ForwardAgent | |
356 | variable is set to | |
357 | .Dq yes | |
5f4a0c58 | 358 | (or see the description of the |
24794905 | 359 | .Fl A |
360 | and | |
361 | .Fl a | |
a4e5acef | 362 | options described later) and |
24794905 | 363 | the user is using an authentication agent, the connection to the agent |
364 | is automatically forwarded to the remote side. | |
bf740959 | 365 | .Pp |
366 | Forwarding of arbitrary TCP/IP connections over the secure channel can | |
491f5f7b | 367 | be specified either on the command line or in a configuration file. |
610cd5c6 | 368 | One possible application of TCP/IP forwarding is a secure connection to an |
e91c60f2 | 369 | electronic purse; another is going through firewalls. |
1d1ffb87 | 370 | .Ss Server authentication |
bf740959 | 371 | .Nm |
1d1ffb87 | 372 | automatically maintains and checks a database containing |
610cd5c6 | 373 | identifications for all hosts it has ever been used with. |
f49bc4f7 | 374 | Host keys are stored in |
140e3e97 | 375 | .Pa ~/.ssh/known_hosts |
610cd5c6 | 376 | in the user's home directory. |
f49bc4f7 | 377 | Additionally, the file |
2a8a6488 | 378 | .Pa /etc/ssh/ssh_known_hosts |
f49bc4f7 | 379 | is automatically checked for known hosts. |
610cd5c6 | 380 | Any new hosts are automatically added to the user's file. |
5f4a0c58 | 381 | If a host's identification ever changes, |
bf740959 | 382 | .Nm |
383 | warns about this and disables password authentication to prevent a | |
610cd5c6 | 384 | trojan horse from getting the user's password. |
5f4a0c58 | 385 | Another purpose of this mechanism is to prevent man-in-the-middle attacks |
386 | which could otherwise be used to circumvent the encryption. | |
610cd5c6 | 387 | The |
bf740959 | 388 | .Cm StrictHostKeyChecking |
588df31a | 389 | option can be used to prevent logins to machines whose |
bf740959 | 390 | host key is not known or has changed. |
fa08c86b | 391 | .Pp |
3a858356 | 392 | .Nm |
393 | can be configured to verify host identification using fingerprint resource | |
394 | records (SSHFP) published in DNS. | |
395 | The | |
396 | .Cm VerifyHostKeyDNS | |
397 | option can be used to control how DNS lookups are performed. | |
398 | SSHFP resource records can be generated using | |
399 | .Xr ssh-keygen 1 . | |
400 | .Pp | |
fa08c86b | 401 | The options are as follows: |
bf740959 | 402 | .Bl -tag -width Ds |
5f4a0c58 | 403 | .It Fl 1 |
404 | Forces | |
405 | .Nm | |
406 | to try protocol version 1 only. | |
407 | .It Fl 2 | |
408 | Forces | |
409 | .Nm | |
410 | to try protocol version 2 only. | |
411 | .It Fl 4 | |
412 | Forces | |
413 | .Nm | |
414 | to use IPv4 addresses only. | |
415 | .It Fl 6 | |
416 | Forces | |
417 | .Nm | |
418 | to use IPv6 addresses only. | |
71276795 | 419 | .It Fl A |
420 | Enables forwarding of the authentication agent connection. | |
421 | This can also be specified on a per-host basis in a configuration file. | |
07d688d5 | 422 | .Pp |
a4e5acef | 423 | Agent forwarding should be enabled with caution. |
424 | Users with the ability to bypass file permissions on the remote host | |
425 | (for the agent's Unix-domain socket) | |
426 | can access the local agent through the forwarded connection. | |
427 | An attacker cannot obtain key material from the agent, | |
07d688d5 | 428 | however they can perform operations on the keys that enable them to |
429 | authenticate using the identities loaded into the agent. | |
5f4a0c58 | 430 | .It Fl a |
431 | Disables forwarding of the authentication agent connection. | |
3435f5a6 | 432 | .It Fl b Ar bind_address |
143f17e8 | 433 | Use |
434 | .Ar bind_address | |
435 | on the local machine as the source address | |
436 | of the connection. | |
437 | Only useful on systems with more than one address. | |
5f4a0c58 | 438 | .It Fl C |
439 | Requests compression of all data (including stdin, stdout, stderr, and | |
440 | data for forwarded X11 and TCP/IP connections). | |
441 | The compression algorithm is the same used by | |
442 | .Xr gzip 1 , | |
443 | and the | |
444 | .Dq level | |
445 | can be controlled by the | |
446 | .Cm CompressionLevel | |
447 | option for protocol version 1. | |
448 | Compression is desirable on modem lines and other | |
449 | slow connections, but will only slow down things on fast networks. | |
450 | The default value can be set on a host-by-host basis in the | |
451 | configuration files; see the | |
452 | .Cm Compression | |
453 | option. | |
3b9baa7b | 454 | .It Fl c Ar cipher_spec |
455 | Selects the cipher specification for encrypting the session. | |
456 | .Pp | |
457 | Protocol version 1 allows specification of a single cipher. | |
2915e42b | 458 | The supported values are |
3b9baa7b | 459 | .Dq 3des , |
460 | .Dq blowfish | |
461 | and | |
462 | .Dq des . | |
bf740959 | 463 | .Ar 3des |
464 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
3b9baa7b | 465 | It is believed to be secure. |
bf740959 | 466 | .Ar blowfish |
5f4a0c58 | 467 | is a fast block cipher; it appears very secure and is much faster than |
610cd5c6 | 468 | .Ar 3des . |
29999e54 | 469 | .Ar des |
470 | is only supported in the | |
471 | .Nm | |
472 | client for interoperability with legacy protocol 1 implementations | |
473 | that do not support the | |
474 | .Ar 3des | |
a4e5acef | 475 | cipher. |
476 | Its use is strongly discouraged due to cryptographic weaknesses. | |
3b9baa7b | 477 | The default is |
478 | .Dq 3des . | |
479 | .Pp | |
480 | For protocol version 2 | |
481 | .Ar cipher_spec | |
482 | is a comma-separated list of ciphers | |
483 | listed in order of preference. | |
484 | The supported ciphers are | |
485 | .Dq 3des-cbc , | |
486 | .Dq aes128-cbc , | |
487 | .Dq aes192-cbc , | |
488 | .Dq aes256-cbc , | |
489 | .Dq aes128-ctr , | |
490 | .Dq aes192-ctr , | |
491 | .Dq aes256-ctr , | |
74a66cc8 | 492 | .Dq arcfour128 , |
493 | .Dq arcfour256 , | |
3b9baa7b | 494 | .Dq arcfour , |
495 | .Dq blowfish-cbc , | |
496 | and | |
497 | .Dq cast128-cbc . | |
498 | The default is | |
499 | .Bd -literal | |
74a66cc8 | 500 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, |
501 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
502 | aes192-ctr,aes256-ctr'' | |
3b9baa7b | 503 | .Ed |
5ddc5eb4 | 504 | .It Fl D Xo |
505 | .Sm off | |
506 | .Oo Ar bind_address : Oc | |
507 | .Ar port | |
508 | .Sm on | |
509 | .Xc | |
5f4a0c58 | 510 | Specifies a local |
511 | .Dq dynamic | |
512 | application-level port forwarding. | |
513 | This works by allocating a socket to listen to | |
514 | .Ar port | |
5ddc5eb4 | 515 | on the local side, optionally bound to the specified |
516 | .Ar bind_address . | |
517 | Whenever a connection is made to this port, the | |
5f4a0c58 | 518 | connection is forwarded over the secure channel, and the application |
519 | protocol is then used to determine where to connect to from the | |
520 | remote machine. | |
521 | Currently the SOCKS4 and SOCKS5 protocols are supported, and | |
522 | .Nm | |
523 | will act as a SOCKS server. | |
524 | Only root can forward privileged ports. | |
525 | Dynamic port forwardings can also be specified in the configuration file. | |
5ddc5eb4 | 526 | .Pp |
527 | IPv6 addresses can be specified with an alternative syntax: | |
528 | .Sm off | |
529 | .Xo | |
530 | .Op Ar bind_address No / | |
531 | .Ar port | |
532 | .Xc | |
533 | .Sm on | |
534 | or by enclosing the address in square brackets. | |
535 | Only the superuser can forward privileged ports. | |
536 | By default, the local port is bound in accordance with the | |
537 | .Cm GatewayPorts | |
538 | setting. | |
539 | However, an explicit | |
540 | .Ar bind_address | |
541 | may be used to bind the connection to a specific address. | |
542 | The | |
543 | .Ar bind_address | |
544 | of | |
545 | .Dq localhost | |
546 | indicates that the listening port be bound for local use only, while an | |
547 | empty address or | |
548 | .Sq * | |
549 | indicates that the port should be available from all interfaces. | |
5f4a0c58 | 550 | .It Fl e Ar ch | ^ch | none |
bf740959 | 551 | Sets the escape character for sessions with a pty (default: |
552 | .Ql ~ ) . | |
610cd5c6 | 553 | The escape character is only recognized at the beginning of a line. |
554 | The escape character followed by a dot | |
bf740959 | 555 | .Pq Ql \&. |
5f4a0c58 | 556 | closes the connection; |
557 | followed by control-Z suspends the connection; | |
558 | and followed by itself sends the escape character once. | |
610cd5c6 | 559 | Setting the character to |
bf740959 | 560 | .Dq none |
561 | disables any escapes and makes the session fully transparent. | |
5f4a0c58 | 562 | .It Fl F Ar configfile |
563 | Specifies an alternative per-user configuration file. | |
564 | If a configuration file is given on the command line, | |
565 | the system-wide configuration file | |
566 | .Pq Pa /etc/ssh/ssh_config | |
567 | will be ignored. | |
568 | The default for the per-user configuration file is | |
140e3e97 | 569 | .Pa ~/.ssh/config . |
bf740959 | 570 | .It Fl f |
571 | Requests | |
572 | .Nm | |
610cd5c6 | 573 | to go to background just before command execution. |
574 | This is useful if | |
bf740959 | 575 | .Nm |
576 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 577 | wants it in the background. |
f54651ce | 578 | This implies |
bf740959 | 579 | .Fl n . |
580 | The recommended way to start X11 programs at a remote site is with | |
581 | something like | |
582 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 583 | .It Fl g |
584 | Allows remote hosts to connect to local forwarded ports. | |
5f4a0c58 | 585 | .It Fl I Ar smartcard_device |
586 | Specifies which smartcard device to use. | |
587 | The argument is the device | |
588 | .Nm | |
589 | should use to communicate with a smartcard used for storing the user's | |
590 | private RSA key. | |
bf740959 | 591 | .It Fl i Ar identity_file |
cf5a07a8 | 592 | Selects a file from which the identity (private key) for |
fa08c86b | 593 | RSA or DSA authentication is read. |
cf5a07a8 | 594 | The default is |
140e3e97 | 595 | .Pa ~/.ssh/identity |
cf5a07a8 | 596 | for protocol version 1, and |
140e3e97 | 597 | .Pa ~/.ssh/id_rsa |
cf5a07a8 | 598 | and |
140e3e97 | 599 | .Pa ~/.ssh/id_dsa |
cf5a07a8 | 600 | for protocol version 2. |
610cd5c6 | 601 | Identity files may also be specified on |
602 | a per-host basis in the configuration file. | |
603 | It is possible to have multiple | |
bf740959 | 604 | .Fl i |
605 | options (and multiple identities specified in | |
606 | configuration files). | |
bf740959 | 607 | .It Fl k |
f7926e97 | 608 | Disables forwarding (delegation) of GSSAPI credentials to the server. |
5f4a0c58 | 609 | .It Fl L Xo |
610 | .Sm off | |
3867aa0a | 611 | .Oo Ar bind_address : Oc |
5f4a0c58 | 612 | .Ar port : host : hostport |
613 | .Sm on | |
614 | .Xc | |
615 | Specifies that the given port on the local (client) host is to be | |
616 | forwarded to the given host and port on the remote side. | |
617 | This works by allocating a socket to listen to | |
618 | .Ar port | |
3867aa0a | 619 | on the local side, optionally bound to the specified |
620 | .Ar bind_address . | |
621 | Whenever a connection is made to this port, the | |
5f4a0c58 | 622 | connection is forwarded over the secure channel, and a connection is |
623 | made to | |
624 | .Ar host | |
625 | port | |
626 | .Ar hostport | |
627 | from the remote machine. | |
628 | Port forwardings can also be specified in the configuration file. | |
5f4a0c58 | 629 | IPv6 addresses can be specified with an alternative syntax: |
630 | .Sm off | |
631 | .Xo | |
6d7a9e8f | 632 | .Op Ar bind_address No / |
5f4a0c58 | 633 | .Ar port No / Ar host No / |
3867aa0a | 634 | .Ar hostport |
5f4a0c58 | 635 | .Xc |
636 | .Sm on | |
3867aa0a | 637 | or by enclosing the address in square brackets. |
638 | Only the superuser can forward privileged ports. | |
639 | By default, the local port is bound in accordance with the | |
640 | .Cm GatewayPorts | |
641 | setting. | |
642 | However, an explicit | |
643 | .Ar bind_address | |
644 | may be used to bind the connection to a specific address. | |
645 | The | |
646 | .Ar bind_address | |
647 | of | |
648 | .Dq localhost | |
6c7e3b94 | 649 | indicates that the listening port be bound for local use only, while an |
650 | empty address or | |
651 | .Sq * | |
3867aa0a | 652 | indicates that the port should be available from all interfaces. |
bf740959 | 653 | .It Fl l Ar login_name |
610cd5c6 | 654 | Specifies the user to log in as on the remote machine. |
655 | This also may be specified on a per-host basis in the configuration file. | |
5e96b616 | 656 | .It Fl M |
657 | Places the | |
658 | .Nm | |
659 | client into | |
660 | .Dq master | |
661 | mode for connection sharing. | |
662 | Refer to the description of | |
663 | .Cm ControlMaster | |
664 | in | |
665 | .Xr ssh_config 5 | |
666 | for details. | |
9affc5db | 667 | .It Fl m Ar mac_spec |
668 | Additionally, for protocol version 2 a comma-separated list of MAC | |
669 | (message authentication code) algorithms can | |
670 | be specified in order of preference. | |
671 | See the | |
672 | .Cm MACs | |
673 | keyword for more information. | |
5f4a0c58 | 674 | .It Fl N |
675 | Do not execute a remote command. | |
676 | This is useful for just forwarding ports | |
677 | (protocol version 2 only). | |
bf740959 | 678 | .It Fl n |
679 | Redirects stdin from | |
680 | .Pa /dev/null | |
681 | (actually, prevents reading from stdin). | |
682 | This must be used when | |
683 | .Nm | |
610cd5c6 | 684 | is run in the background. |
685 | A common trick is to use this to run X11 programs on a remote machine. | |
686 | For example, | |
bf740959 | 687 | .Ic ssh -n shadows.cs.hut.fi emacs & |
688 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
689 | connection will be automatically forwarded over an encrypted channel. | |
690 | The | |
691 | .Nm | |
692 | program will be put in the background. | |
693 | (This does not work if | |
694 | .Nm | |
695 | needs to ask for a password or passphrase; see also the | |
696 | .Fl f | |
697 | option.) | |
cf848a5e | 698 | .It Fl O Ar ctl_cmd |
699 | Control an active connection multiplexing master process. | |
700 | When the | |
701 | .Fl O | |
702 | option is specified, the | |
703 | .Ar ctl_cmd | |
704 | argument is interpreted and passed to the master process. | |
705 | Valid commands are: | |
706 | .Dq check | |
707 | (check that the master process is running) and | |
708 | .Dq exit | |
709 | (request the master to exit). | |
bf740959 | 710 | .It Fl o Ar option |
38539909 | 711 | Can be used to give options in the format used in the configuration file. |
bf740959 | 712 | This is useful for specifying options for which there is no separate |
610cd5c6 | 713 | command-line flag. |
5f4a0c58 | 714 | For full details of the options listed below, and their possible values, see |
715 | .Xr ssh_config 5 . | |
716 | .Pp | |
717 | .Bl -tag -width Ds -offset indent -compact | |
718 | .It AddressFamily | |
719 | .It BatchMode | |
720 | .It BindAddress | |
721 | .It ChallengeResponseAuthentication | |
722 | .It CheckHostIP | |
723 | .It Cipher | |
724 | .It Ciphers | |
725 | .It ClearAllForwardings | |
726 | .It Compression | |
727 | .It CompressionLevel | |
728 | .It ConnectionAttempts | |
20b267fb | 729 | .It ConnectTimeout |
5e96b616 | 730 | .It ControlMaster |
731 | .It ControlPath | |
5f4a0c58 | 732 | .It DynamicForward |
5f4a0c58 | 733 | .It EscapeChar |
734 | .It ForwardAgent | |
735 | .It ForwardX11 | |
d73a67d7 | 736 | .It ForwardX11Trusted |
5f4a0c58 | 737 | .It GatewayPorts |
738 | .It GlobalKnownHostsFile | |
739 | .It GSSAPIAuthentication | |
740 | .It GSSAPIDelegateCredentials | |
5c63c2ab | 741 | .It HashKnownHosts |
5f4a0c58 | 742 | .It Host |
743 | .It HostbasedAuthentication | |
744 | .It HostKeyAlgorithms | |
745 | .It HostKeyAlias | |
746 | .It HostName | |
747 | .It IdentityFile | |
3a065ed0 | 748 | .It IdentitiesOnly |
396070f8 | 749 | .It KbdInteractiveDevices |
5f4a0c58 | 750 | .It LocalForward |
751 | .It LogLevel | |
752 | .It MACs | |
753 | .It NoHostAuthenticationForLocalhost | |
754 | .It NumberOfPasswordPrompts | |
755 | .It PasswordAuthentication | |
756 | .It Port | |
757 | .It PreferredAuthentications | |
758 | .It Protocol | |
759 | .It ProxyCommand | |
760 | .It PubkeyAuthentication | |
761 | .It RemoteForward | |
762 | .It RhostsRSAAuthentication | |
763 | .It RSAAuthentication | |
8e99a198 | 764 | .It SendEnv |
5d8d32a3 | 765 | .It ServerAliveInterval |
766 | .It ServerAliveCountMax | |
5f4a0c58 | 767 | .It SmartcardDevice |
768 | .It StrictHostKeyChecking | |
fd573618 | 769 | .It TCPKeepAlive |
5f4a0c58 | 770 | .It UsePrivilegedPort |
771 | .It User | |
772 | .It UserKnownHostsFile | |
773 | .It VerifyHostKeyDNS | |
774 | .It XAuthLocation | |
775 | .El | |
bf740959 | 776 | .It Fl p Ar port |
610cd5c6 | 777 | Port to connect to on the remote host. |
778 | This can be specified on a | |
bf740959 | 779 | per-host basis in the configuration file. |
bf740959 | 780 | .It Fl q |
610cd5c6 | 781 | Quiet mode. |
782 | Causes all warning and diagnostic messages to be suppressed. | |
5f4a0c58 | 783 | .It Fl R Xo |
784 | .Sm off | |
3867aa0a | 785 | .Oo Ar bind_address : Oc |
5f4a0c58 | 786 | .Ar port : host : hostport |
787 | .Sm on | |
788 | .Xc | |
789 | Specifies that the given port on the remote (server) host is to be | |
790 | forwarded to the given host and port on the local side. | |
791 | This works by allocating a socket to listen to | |
792 | .Ar port | |
793 | on the remote side, and whenever a connection is made to this port, the | |
794 | connection is forwarded over the secure channel, and a connection is | |
795 | made to | |
796 | .Ar host | |
797 | port | |
798 | .Ar hostport | |
799 | from the local machine. | |
3867aa0a | 800 | .Pp |
5f4a0c58 | 801 | Port forwardings can also be specified in the configuration file. |
802 | Privileged ports can be forwarded only when | |
803 | logging in as root on the remote machine. | |
3867aa0a | 804 | IPv6 addresses can be specified by enclosing the address in square braces or |
805 | using an alternative syntax: | |
3867aa0a | 806 | .Sm off |
6c7e3b94 | 807 | .Xo |
6d7a9e8f | 808 | .Op Ar bind_address No / |
6c7e3b94 | 809 | .Ar host No / Ar port No / |
810 | .Ar hostport | |
3867aa0a | 811 | .Xc . |
6c7e3b94 | 812 | .Sm on |
3867aa0a | 813 | .Pp |
814 | By default, the listening socket on the server will be bound to the loopback | |
815 | interface only. | |
816 | This may be overriden by specifying a | |
817 | .Ar bind_address . | |
6c7e3b94 | 818 | An empty |
819 | .Ar bind_address , | |
3867aa0a | 820 | or the address |
6c7e3b94 | 821 | .Ql * , |
3867aa0a | 822 | indicates that the remote socket should listen on all interfaces. |
823 | Specifying a remote | |
824 | .Ar bind_address | |
6c7e3b94 | 825 | will only succeed if the server's |
826 | .Cm GatewayPorts | |
3867aa0a | 827 | option is enabled (see |
6c7e3b94 | 828 | .Xr sshd_config 5 ) . |
f8c6db83 | 829 | .It Fl S Ar ctl_path |
9affc5db | 830 | Specifies the location of a control socket for connection sharing. |
5e96b616 | 831 | Refer to the description of |
0e19494c | 832 | .Cm ControlPath |
833 | and | |
5e96b616 | 834 | .Cm ControlMaster |
835 | in | |
836 | .Xr ssh_config 5 | |
837 | for details. | |
ae810de7 | 838 | .It Fl s |
3cbc677d | 839 | May be used to request invocation of a subsystem on the remote system. |
840 | Subsystems are a feature of the SSH2 protocol which facilitate the use | |
5f4a0c58 | 841 | of SSH as a secure transport for other applications (eg.\& |
842 | .Xr sftp 1 ) . | |
3cbc677d | 843 | The subsystem is specified as the remote command. |
5f4a0c58 | 844 | .It Fl T |
845 | Disable pseudo-tty allocation. | |
bf740959 | 846 | .It Fl t |
610cd5c6 | 847 | Force pseudo-tty allocation. |
4fe2af09 | 848 | This can be used to execute arbitrary |
610cd5c6 | 849 | screen-based programs on a remote machine, which can be very useful, |
850 | e.g., when implementing menu services. | |
8abcdba4 | 851 | Multiple |
852 | .Fl t | |
853 | options force tty allocation, even if | |
854 | .Nm | |
855 | has no local tty. | |
5f4a0c58 | 856 | .It Fl V |
857 | Display the version number and exit. | |
bf740959 | 858 | .It Fl v |
610cd5c6 | 859 | Verbose mode. |
860 | Causes | |
bf740959 | 861 | .Nm |
610cd5c6 | 862 | to print debugging messages about its progress. |
863 | This is helpful in | |
bf740959 | 864 | debugging connection, authentication, and configuration problems. |
8abcdba4 | 865 | Multiple |
866 | .Fl v | |
c825cd79 | 867 | options increase the verbosity. |
868 | The maximum is 3. | |
bf740959 | 869 | .It Fl X |
870 | Enables X11 forwarding. | |
71276795 | 871 | This can also be specified on a per-host basis in a configuration file. |
07d688d5 | 872 | .Pp |
a4e5acef | 873 | X11 forwarding should be enabled with caution. |
874 | Users with the ability to bypass file permissions on the remote host | |
875 | (for the user's X authorization database) | |
876 | can access the local X11 display through the forwarded connection. | |
877 | An attacker may then be able to perform activities such as keystroke monitoring. | |
82966fe8 | 878 | .Pp |
4469b0cf | 879 | For this reason, X11 forwarding is subjected to X11 SECURITY extension |
82966fe8 | 880 | restrictions by default. |
881 | Please refer to the | |
882 | .Nm | |
883 | .Fl Y | |
884 | option and the | |
885 | .Cm ForwardX11Trusted | |
886 | directive in | |
887 | .Xr ssh_config 5 | |
888 | for more information. | |
5f4a0c58 | 889 | .It Fl x |
890 | Disables X11 forwarding. | |
d73a67d7 | 891 | .It Fl Y |
892 | Enables trusted X11 forwarding. | |
82966fe8 | 893 | Trusted X11 forwardings are not subjected to the X11 SECURITY extension |
894 | controls. | |
bf740959 | 895 | .El |
896 | .Sh CONFIGURATION FILES | |
897 | .Nm | |
588df31a | 898 | may additionally obtain configuration data from |
899 | a per-user configuration file and a system-wide configuration file. | |
900 | The file format and configuration options are described in | |
901 | .Xr ssh_config 5 . | |
bf740959 | 902 | .Sh ENVIRONMENT |
903 | .Nm | |
904 | will normally set the following environment variables: | |
5f4a0c58 | 905 | .Bl -tag -width LOGNAME |
bf740959 | 906 | .It Ev DISPLAY |
907 | The | |
908 | .Ev DISPLAY | |
610cd5c6 | 909 | variable indicates the location of the X11 server. |
f54651ce | 910 | It is automatically set by |
bf740959 | 911 | .Nm |
912 | to point to a value of the form | |
913 | .Dq hostname:n | |
914 | where hostname indicates | |
5f4a0c58 | 915 | the host where the shell runs, and n is an integer \*(Ge 1. |
610cd5c6 | 916 | .Nm |
917 | uses this special value to forward X11 connections over the secure | |
918 | channel. | |
da89cf4d | 919 | The user should normally not set |
920 | .Ev DISPLAY | |
921 | explicitly, as that | |
bf740959 | 922 | will render the X11 connection insecure (and will require the user to |
923 | manually copy any required authorization cookies). | |
924 | .It Ev HOME | |
925 | Set to the path of the user's home directory. | |
926 | .It Ev LOGNAME | |
927 | Synonym for | |
928 | .Ev USER ; | |
929 | set for compatibility with systems that use this variable. | |
930 | .It Ev MAIL | |
ae897d7c | 931 | Set to the path of the user's mailbox. |
610cd5c6 | 932 | .It Ev PATH |
bf740959 | 933 | Set to the default |
934 | .Ev PATH , | |
935 | as specified when compiling | |
936 | .Nm ssh . | |
3474b2b4 | 937 | .It Ev SSH_ASKPASS |
938 | If | |
939 | .Nm | |
940 | needs a passphrase, it will read the passphrase from the current | |
941 | terminal if it was run from a terminal. | |
942 | If | |
943 | .Nm | |
944 | does not have a terminal associated with it but | |
945 | .Ev DISPLAY | |
946 | and | |
947 | .Ev SSH_ASKPASS | |
948 | are set, it will execute the program specified by | |
949 | .Ev SSH_ASKPASS | |
950 | and open an X11 window to read the passphrase. | |
951 | This is particularly useful when calling | |
952 | .Nm | |
953 | from a | |
caeffafb | 954 | .Pa .xsession |
3474b2b4 | 955 | or related script. |
956 | (Note that on some machines it | |
957 | may be necessary to redirect the input from | |
958 | .Pa /dev/null | |
959 | to make this work.) | |
bf740959 | 960 | .It Ev SSH_AUTH_SOCK |
ae897d7c | 961 | Identifies the path of a unix-domain socket used to communicate with the |
bf740959 | 962 | agent. |
da0561eb | 963 | .It Ev SSH_CONNECTION |
964 | Identifies the client and server ends of the connection. | |
610cd5c6 | 965 | The variable contains |
da0561eb | 966 | four space-separated values: client ip-address, client port number, |
967 | server ip-address and server port number. | |
8abcdba4 | 968 | .It Ev SSH_ORIGINAL_COMMAND |
969 | The variable contains the original command line if a forced command | |
970 | is executed. | |
971 | It can be used to extract the original arguments. | |
bf740959 | 972 | .It Ev SSH_TTY |
973 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 974 | with the current shell or command. |
975 | If the current session has no tty, | |
bf740959 | 976 | this variable is not set. |
977 | .It Ev TZ | |
d7cf99ff | 978 | The time zone variable is set to indicate the present time zone if it |
c345cf9d | 979 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 980 | on to new connections). |
981 | .It Ev USER | |
982 | Set to the name of the user logging in. | |
983 | .El | |
984 | .Pp | |
f54651ce | 985 | Additionally, |
bf740959 | 986 | .Nm |
f54651ce | 987 | reads |
140e3e97 | 988 | .Pa ~/.ssh/environment , |
bf740959 | 989 | and adds lines of the format |
990 | .Dq VARNAME=value | |
6a342527 | 991 | to the environment if the file exists and if users are allowed to |
992 | change their environment. | |
5f4a0c58 | 993 | For more information, see the |
6a342527 | 994 | .Cm PermitUserEnvironment |
35453849 | 995 | option in |
6a342527 | 996 | .Xr sshd_config 5 . |
bf740959 | 997 | .Sh FILES |
c8d54615 | 998 | .Bl -tag -width Ds |
140e3e97 | 999 | .It Pa ~/.ssh/known_hosts |
ae897d7c | 1000 | Records host keys for all hosts the user has logged into that are not |
bf740959 | 1001 | in |
2a8a6488 | 1002 | .Pa /etc/ssh/ssh_known_hosts . |
bf740959 | 1003 | See |
1004 | .Xr sshd 8 . | |
140e3e97 | 1005 | .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa |
c0ecc314 | 1006 | Contains the authentication identity of the user. |
1007 | They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. | |
1d1ffb87 | 1008 | These files |
1009 | contain sensitive data and should be readable by the user but not | |
bf740959 | 1010 | accessible by others (read/write/execute). |
1011 | Note that | |
1012 | .Nm | |
1d1ffb87 | 1013 | ignores a private key file if it is accessible by others. |
bf740959 | 1014 | It is possible to specify a passphrase when |
1015 | generating the key; the passphrase will be used to encrypt the | |
1016 | sensitive part of this file using 3DES. | |
140e3e97 | 1017 | .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub |
bf740959 | 1018 | Contains the public key for authentication (public part of the |
610cd5c6 | 1019 | identity file in human-readable form). |
1d1ffb87 | 1020 | The contents of the |
140e3e97 | 1021 | .Pa ~/.ssh/identity.pub |
5f4a0c58 | 1022 | file should be added to the file |
140e3e97 | 1023 | .Pa ~/.ssh/authorized_keys |
bf740959 | 1024 | on all machines |
91789042 | 1025 | where the user wishes to log in using protocol version 1 RSA authentication. |
1d1ffb87 | 1026 | The contents of the |
140e3e97 | 1027 | .Pa ~/.ssh/id_dsa.pub |
c0ecc314 | 1028 | and |
140e3e97 | 1029 | .Pa ~/.ssh/id_rsa.pub |
1d1ffb87 | 1030 | file should be added to |
140e3e97 | 1031 | .Pa ~/.ssh/authorized_keys |
1d1ffb87 | 1032 | on all machines |
91789042 | 1033 | where the user wishes to log in using protocol version 2 DSA/RSA authentication. |
1d1ffb87 | 1034 | These files are not |
610cd5c6 | 1035 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 1036 | These files are |
c44559d2 | 1037 | never used automatically and are not necessary; they are only provided for |
bf740959 | 1038 | the convenience of the user. |
140e3e97 | 1039 | .It Pa ~/.ssh/config |
610cd5c6 | 1040 | This is the per-user configuration file. |
588df31a | 1041 | The file format and configuration options are described in |
1042 | .Xr ssh_config 5 . | |
e1520719 | 1043 | Because of the potential for abuse, this file must have strict permissions: |
1044 | read/write for the user, and not accessible by others. | |
140e3e97 | 1045 | .It Pa ~/.ssh/authorized_keys |
96a7b0cc | 1046 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. |
610cd5c6 | 1047 | The format of this file is described in the |
bf740959 | 1048 | .Xr sshd 8 |
610cd5c6 | 1049 | manual page. |
5f4a0c58 | 1050 | In the simplest form the format is the same as the |
1051 | .Pa .pub | |
f49bc4f7 | 1052 | identity files. |
1d1ffb87 | 1053 | This file is not highly sensitive, but the recommended |
1054 | permissions are read/write for the user, and not accessible by others. | |
2a8a6488 | 1055 | .It Pa /etc/ssh/ssh_known_hosts |
610cd5c6 | 1056 | Systemwide list of known host keys. |
f49bc4f7 | 1057 | This file should be prepared by the |
bf740959 | 1058 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1059 | organization. |
1060 | This file should be world-readable. | |
1061 | This file contains | |
bf740959 | 1062 | public keys, one per line, in the following format (fields separated |
f49bc4f7 | 1063 | by spaces): system name, public key and optional comment field. |
610cd5c6 | 1064 | When different names are used |
bf740959 | 1065 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1066 | commas. |
5f4a0c58 | 1067 | The format is described in the |
bf740959 | 1068 | .Xr sshd 8 |
1069 | manual page. | |
1070 | .Pp | |
1071 | The canonical system name (as returned by name servers) is used by | |
1072 | .Xr sshd 8 | |
1073 | to verify the client host when logging in; other names are needed because | |
1074 | .Nm | |
1075 | does not convert the user-supplied name to a canonical name before | |
1076 | checking the key, because someone with access to the name servers | |
1077 | would then be able to fool host authentication. | |
2a8a6488 | 1078 | .It Pa /etc/ssh/ssh_config |
610cd5c6 | 1079 | Systemwide configuration file. |
588df31a | 1080 | The file format and configuration options are described in |
1081 | .Xr ssh_config 5 . | |
2a8a6488 | 1082 | .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key |
dd58cb5e | 1083 | These three files contain the private parts of the host keys |
1084 | and are used for | |
1085 | .Cm RhostsRSAAuthentication | |
1086 | and | |
1087 | .Cm HostbasedAuthentication . | |
d83cbdc3 | 1088 | If the protocol version 1 |
1089 | .Cm RhostsRSAAuthentication | |
7203d6bb | 1090 | method is used, |
d83cbdc3 | 1091 | .Nm |
1092 | must be setuid root, since the host key is readable only by root. | |
1093 | For protocol version 2, | |
1094 | .Nm | |
1095 | uses | |
1096 | .Xr ssh-keysign 8 | |
1097 | to access the host keys for | |
1098 | .Cm HostbasedAuthentication . | |
1099 | This eliminates the requirement that | |
1100 | .Nm | |
1101 | be setuid root when that authentication method is used. | |
1102 | By default | |
dd58cb5e | 1103 | .Nm |
d83cbdc3 | 1104 | is not setuid root. |
140e3e97 | 1105 | .It Pa ~/.rhosts |
bf740959 | 1106 | This file is used in |
6f5abc1e | 1107 | .Cm RhostsRSAAuthentication |
1108 | and | |
1109 | .Cm HostbasedAuthentication | |
bf740959 | 1110 | authentication to list the |
610cd5c6 | 1111 | host/user pairs that are permitted to log in. |
1112 | (Note that this file is | |
bf740959 | 1113 | also used by rlogin and rsh, which makes using this file insecure.) |
1114 | Each line of the file contains a host name (in the canonical form | |
1115 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1116 | separated by a space. |
e91c60f2 | 1117 | On some machines this file may need to be |
bf740959 | 1118 | world-readable if the user's home directory is on a NFS partition, |
1119 | because | |
1120 | .Xr sshd 8 | |
610cd5c6 | 1121 | reads it as root. |
1122 | Additionally, this file must be owned by the user, | |
1123 | and must not have write permissions for anyone else. | |
1124 | The recommended | |
bf740959 | 1125 | permission for most machines is read/write for the user, and not |
1126 | accessible by others. | |
1127 | .Pp | |
6f5abc1e | 1128 | Note that |
bf740959 | 1129 | .Xr sshd 8 |
6f5abc1e | 1130 | allows authentication only in combination with client host key |
1131 | authentication before permitting log in. | |
91789042 | 1132 | If the server machine does not have the client's host key in |
2a8a6488 | 1133 | .Pa /etc/ssh/ssh_known_hosts , |
91789042 | 1134 | it can be stored in |
140e3e97 | 1135 | .Pa ~/.ssh/known_hosts . |
bf740959 | 1136 | The easiest way to do this is to |
1137 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1138 | will automatically add the host key to |
140e3e97 | 1139 | .Pa ~/.ssh/known_hosts . |
1140 | .It Pa ~/.shosts | |
bf740959 | 1141 | This file is used exactly the same way as |
5f4a0c58 | 1142 | .Pa .rhosts . |
bf740959 | 1143 | The purpose for |
6f5abc1e | 1144 | having this file is to be able to use |
1145 | .Cm RhostsRSAAuthentication | |
1146 | and | |
1147 | .Cm HostbasedAuthentication | |
1148 | authentication without permitting login with | |
5f4a0c58 | 1149 | .Xr rlogin |
bf740959 | 1150 | or |
1151 | .Xr rsh 1 . | |
1152 | .It Pa /etc/hosts.equiv | |
1153 | This file is used during | |
6f5abc1e | 1154 | .Cm RhostsRSAAuthentication |
1155 | and | |
1156 | .Cm HostbasedAuthentication | |
be193d89 | 1157 | authentication. |
610cd5c6 | 1158 | It contains |
5f4a0c58 | 1159 | canonical hosts names, one per line (the full format is described in the |
bf740959 | 1160 | .Xr sshd 8 |
610cd5c6 | 1161 | manual page). |
1162 | If the client host is found in this file, login is | |
bf740959 | 1163 | automatically permitted provided client and server user names are the |
610cd5c6 | 1164 | same. |
6f5abc1e | 1165 | Additionally, successful client host key authentication is required. |
610cd5c6 | 1166 | This file should only be writable by root. |
5f4fdfae | 1167 | .It Pa /etc/shosts.equiv |
f54651ce | 1168 | This file is processed exactly as |
bf740959 | 1169 | .Pa /etc/hosts.equiv . |
1170 | This file may be useful to permit logins using | |
1171 | .Nm | |
1172 | but not using rsh/rlogin. | |
2a8a6488 | 1173 | .It Pa /etc/ssh/sshrc |
bf740959 | 1174 | Commands in this file are executed by |
1175 | .Nm | |
1176 | when the user logs in just before the user's shell (or command) is started. | |
1177 | See the | |
1178 | .Xr sshd 8 | |
1179 | manual page for more information. | |
140e3e97 | 1180 | .It Pa ~/.ssh/rc |
bf740959 | 1181 | Commands in this file are executed by |
1182 | .Nm | |
1183 | when the user logs in just before the user's shell (or command) is | |
1184 | started. | |
f54651ce | 1185 | See the |
bf740959 | 1186 | .Xr sshd 8 |
1187 | manual page for more information. | |
140e3e97 | 1188 | .It Pa ~/.ssh/environment |
83b7f649 | 1189 | Contains additional definitions for environment variables, see section |
1190 | .Sx ENVIRONMENT | |
1191 | above. | |
b5e300c2 | 1192 | .El |
16210ef7 | 1193 | .Sh DIAGNOSTICS |
1194 | .Nm | |
1195 | exits with the exit status of the remote command or with 255 | |
1196 | if an error occurred. | |
bf740959 | 1197 | .Sh SEE ALSO |
5f4a0c58 | 1198 | .Xr gzip 1 , |
bf740959 | 1199 | .Xr rsh 1 , |
1200 | .Xr scp 1 , | |
61e96248 | 1201 | .Xr sftp 1 , |
bf740959 | 1202 | .Xr ssh-add 1 , |
1203 | .Xr ssh-agent 1 , | |
1204 | .Xr ssh-keygen 1 , | |
1205 | .Xr telnet 1 , | |
5f4a0c58 | 1206 | .Xr hosts.equiv 5 , |
1ae02182 | 1207 | .Xr ssh_config 5 , |
b2843ec6 | 1208 | .Xr ssh-keysign 8 , |
9afadca8 | 1209 | .Xr sshd 8 |
2cad6cef | 1210 | .Rs |
1211 | .%A T. Ylonen | |
1212 | .%A T. Kivinen | |
1213 | .%A M. Saarinen | |
1214 | .%A T. Rinne | |
1215 | .%A S. Lehtinen | |
1216 | .%T "SSH Protocol Architecture" | |
17f5e68a | 1217 | .%N draft-ietf-secsh-architecture-12.txt |
1218 | .%D January 2002 | |
2cad6cef | 1219 | .%O work in progress material |
1220 | .Re | |
be193d89 | 1221 | .Sh AUTHORS |
1222 | OpenSSH is a derivative of the original and free | |
1223 | ssh 1.2.12 release by Tatu Ylonen. | |
1224 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1225 | Theo de Raadt and Dug Song | |
1226 | removed many bugs, re-added newer features and | |
1227 | created OpenSSH. | |
1228 | Markus Friedl contributed the support for SSH | |
1229 | protocol versions 1.5 and 2.0. |