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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 | .\" |
3867aa0a | 37 | .\" $OpenBSD: ssh.1,v 1.200 2005/03/01 10:09:52 djm 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 |
9affc5db | 49 | .Bk -words |
5f4a0c58 | 50 | .Op Fl D Ar port |
bf740959 | 51 | .Op Fl e Ar escape_char |
e591b98a | 52 | .Op Fl F Ar configfile |
5f4a0c58 | 53 | .Op Fl i Ar identity_file |
bf740959 | 54 | .Oo Fl L Xo |
55 | .Sm off | |
3867aa0a | 56 | .Oo Ar bind_address : Oc |
bf740959 | 57 | .Ar port : |
7b2ea3a1 | 58 | .Ar host : |
bf740959 | 59 | .Ar hostport |
60 | .Sm on | |
61 | .Xc | |
62 | .Oc | |
5f4a0c58 | 63 | .Op Fl l Ar login_name |
64 | .Op Fl m Ar mac_spec | |
f8c6db83 | 65 | .Op Fl O Ar ctl_cmd |
5f4a0c58 | 66 | .Op Fl o Ar option |
a4e5acef | 67 | .Bk -words |
5f4a0c58 | 68 | .Op Fl p Ar port |
69 | .Ek | |
bf740959 | 70 | .Oo Fl R Xo |
71 | .Sm off | |
3867aa0a | 72 | .Oo Ar bind_address : Oc |
bf740959 | 73 | .Ar port : |
7b2ea3a1 | 74 | .Ar host : |
bf740959 | 75 | .Ar hostport |
76 | .Sm on | |
77 | .Xc | |
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 |
119 | .Pa $HOME/.rhosts | |
bf740959 | 120 | or |
6f5abc1e | 121 | .Pa $HOME/.shosts |
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 |
130 | .Pa $HOME/.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 , |
1d1ffb87 | 138 | .Pa $HOME/.rhosts , |
bf740959 | 139 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
140 | disabled if security is desired.] | |
141 | .Pp | |
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 |
bf740959 | 154 | .Pa $HOME/.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 |
1d1ffb87 | 175 | .Pa $HOME/.ssh/identity |
5f4a0c58 | 176 | and stores the public key in |
1d1ffb87 | 177 | .Pa $HOME/.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 |
1d1ffb87 | 182 | .Pa $HOME/.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 |
1d1ffb87 | 186 | .Pa $HOME/.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, |
1d1ffb87 | 216 | .Pa $HOME/.ssh/id_dsa |
c0ecc314 | 217 | or |
218 | .Pa $HOME/.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 | |
96a7b0cc | 221 | .Pa $HOME/.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 |
1d1ffb87 | 375 | .Pa $HOME/.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 |
433 | Specify the interface to transmit from on machines with multiple | |
434 | interfaces or aliased addresses. | |
5f4a0c58 | 435 | .It Fl C |
436 | Requests compression of all data (including stdin, stdout, stderr, and | |
437 | data for forwarded X11 and TCP/IP connections). | |
438 | The compression algorithm is the same used by | |
439 | .Xr gzip 1 , | |
440 | and the | |
441 | .Dq level | |
442 | can be controlled by the | |
443 | .Cm CompressionLevel | |
444 | option for protocol version 1. | |
445 | Compression is desirable on modem lines and other | |
446 | slow connections, but will only slow down things on fast networks. | |
447 | The default value can be set on a host-by-host basis in the | |
448 | configuration files; see the | |
449 | .Cm Compression | |
450 | option. | |
3b9baa7b | 451 | .It Fl c Ar cipher_spec |
452 | Selects the cipher specification for encrypting the session. | |
453 | .Pp | |
454 | Protocol version 1 allows specification of a single cipher. | |
455 | The suported values are | |
456 | .Dq 3des , | |
457 | .Dq blowfish | |
458 | and | |
459 | .Dq des . | |
bf740959 | 460 | .Ar 3des |
461 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
3b9baa7b | 462 | It is believed to be secure. |
bf740959 | 463 | .Ar blowfish |
5f4a0c58 | 464 | is a fast block cipher; it appears very secure and is much faster than |
610cd5c6 | 465 | .Ar 3des . |
29999e54 | 466 | .Ar des |
467 | is only supported in the | |
468 | .Nm | |
469 | client for interoperability with legacy protocol 1 implementations | |
470 | that do not support the | |
471 | .Ar 3des | |
a4e5acef | 472 | cipher. |
473 | Its use is strongly discouraged due to cryptographic weaknesses. | |
3b9baa7b | 474 | The default is |
475 | .Dq 3des . | |
476 | .Pp | |
477 | For protocol version 2 | |
478 | .Ar cipher_spec | |
479 | is a comma-separated list of ciphers | |
480 | listed in order of preference. | |
481 | The supported ciphers are | |
482 | .Dq 3des-cbc , | |
483 | .Dq aes128-cbc , | |
484 | .Dq aes192-cbc , | |
485 | .Dq aes256-cbc , | |
486 | .Dq aes128-ctr , | |
487 | .Dq aes192-ctr , | |
488 | .Dq aes256-ctr , | |
489 | .Dq arcfour , | |
490 | .Dq blowfish-cbc , | |
491 | and | |
492 | .Dq cast128-cbc . | |
493 | The default is | |
494 | .Bd -literal | |
495 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour, | |
496 | aes192-cbc,aes256-cbc'' | |
497 | .Ed | |
5f4a0c58 | 498 | .It Fl D Ar port |
499 | Specifies a local | |
500 | .Dq dynamic | |
501 | application-level port forwarding. | |
502 | This works by allocating a socket to listen to | |
503 | .Ar port | |
504 | on the local side, and whenever a connection is made to this port, the | |
505 | connection is forwarded over the secure channel, and the application | |
506 | protocol is then used to determine where to connect to from the | |
507 | remote machine. | |
508 | Currently the SOCKS4 and SOCKS5 protocols are supported, and | |
509 | .Nm | |
510 | will act as a SOCKS server. | |
511 | Only root can forward privileged ports. | |
512 | Dynamic port forwardings can also be specified in the configuration file. | |
513 | .It Fl e Ar ch | ^ch | none | |
bf740959 | 514 | Sets the escape character for sessions with a pty (default: |
515 | .Ql ~ ) . | |
610cd5c6 | 516 | The escape character is only recognized at the beginning of a line. |
517 | The escape character followed by a dot | |
bf740959 | 518 | .Pq Ql \&. |
5f4a0c58 | 519 | closes the connection; |
520 | followed by control-Z suspends the connection; | |
521 | and followed by itself sends the escape character once. | |
610cd5c6 | 522 | Setting the character to |
bf740959 | 523 | .Dq none |
524 | disables any escapes and makes the session fully transparent. | |
5f4a0c58 | 525 | .It Fl F Ar configfile |
526 | Specifies an alternative per-user configuration file. | |
527 | If a configuration file is given on the command line, | |
528 | the system-wide configuration file | |
529 | .Pq Pa /etc/ssh/ssh_config | |
530 | will be ignored. | |
531 | The default for the per-user configuration file is | |
532 | .Pa $HOME/.ssh/config . | |
bf740959 | 533 | .It Fl f |
534 | Requests | |
535 | .Nm | |
610cd5c6 | 536 | to go to background just before command execution. |
537 | This is useful if | |
bf740959 | 538 | .Nm |
539 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 540 | wants it in the background. |
f54651ce | 541 | This implies |
bf740959 | 542 | .Fl n . |
543 | The recommended way to start X11 programs at a remote site is with | |
544 | something like | |
545 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 546 | .It Fl g |
547 | Allows remote hosts to connect to local forwarded ports. | |
5f4a0c58 | 548 | .It Fl I Ar smartcard_device |
549 | Specifies which smartcard device to use. | |
550 | The argument is the device | |
551 | .Nm | |
552 | should use to communicate with a smartcard used for storing the user's | |
553 | private RSA key. | |
bf740959 | 554 | .It Fl i Ar identity_file |
cf5a07a8 | 555 | Selects a file from which the identity (private key) for |
fa08c86b | 556 | RSA or DSA authentication is read. |
cf5a07a8 | 557 | The default is |
1d1ffb87 | 558 | .Pa $HOME/.ssh/identity |
cf5a07a8 | 559 | for protocol version 1, and |
560 | .Pa $HOME/.ssh/id_rsa | |
561 | and | |
562 | .Pa $HOME/.ssh/id_dsa | |
563 | for protocol version 2. | |
610cd5c6 | 564 | Identity files may also be specified on |
565 | a per-host basis in the configuration file. | |
566 | It is possible to have multiple | |
bf740959 | 567 | .Fl i |
568 | options (and multiple identities specified in | |
569 | configuration files). | |
bf740959 | 570 | .It Fl k |
f7926e97 | 571 | Disables forwarding (delegation) of GSSAPI credentials to the server. |
5f4a0c58 | 572 | .It Fl L Xo |
573 | .Sm off | |
3867aa0a | 574 | .Oo Ar bind_address : Oc |
5f4a0c58 | 575 | .Ar port : host : hostport |
576 | .Sm on | |
577 | .Xc | |
578 | Specifies that the given port on the local (client) host is to be | |
579 | forwarded to the given host and port on the remote side. | |
580 | This works by allocating a socket to listen to | |
581 | .Ar port | |
3867aa0a | 582 | on the local side, optionally bound to the specified |
583 | .Ar bind_address . | |
584 | Whenever a connection is made to this port, the | |
5f4a0c58 | 585 | connection is forwarded over the secure channel, and a connection is |
586 | made to | |
587 | .Ar host | |
588 | port | |
589 | .Ar hostport | |
590 | from the remote machine. | |
591 | Port forwardings can also be specified in the configuration file. | |
5f4a0c58 | 592 | IPv6 addresses can be specified with an alternative syntax: |
593 | .Sm off | |
594 | .Xo | |
3867aa0a | 595 | .Oo Ar bind_address / Oc |
5f4a0c58 | 596 | .Ar port No / Ar host No / |
3867aa0a | 597 | .Ar hostport |
5f4a0c58 | 598 | .Xc |
599 | .Sm on | |
3867aa0a | 600 | or by enclosing the address in square brackets. |
601 | Only the superuser can forward privileged ports. | |
602 | By default, the local port is bound in accordance with the | |
603 | .Cm GatewayPorts | |
604 | setting. | |
605 | However, an explicit | |
606 | .Ar bind_address | |
607 | may be used to bind the connection to a specific address. | |
608 | The | |
609 | .Ar bind_address | |
610 | of | |
611 | .Dq localhost | |
612 | indicates that the listening port be bound for local use only, while an | |
613 | empty address or | |
614 | .Dq * | |
615 | indicates that the port should be available from all interfaces. | |
bf740959 | 616 | .It Fl l Ar login_name |
610cd5c6 | 617 | Specifies the user to log in as on the remote machine. |
618 | This also may be specified on a per-host basis in the configuration file. | |
5e96b616 | 619 | .It Fl M |
620 | Places the | |
621 | .Nm | |
622 | client into | |
623 | .Dq master | |
624 | mode for connection sharing. | |
625 | Refer to the description of | |
626 | .Cm ControlMaster | |
627 | in | |
628 | .Xr ssh_config 5 | |
629 | for details. | |
9affc5db | 630 | .It Fl m Ar mac_spec |
631 | Additionally, for protocol version 2 a comma-separated list of MAC | |
632 | (message authentication code) algorithms can | |
633 | be specified in order of preference. | |
634 | See the | |
635 | .Cm MACs | |
636 | keyword for more information. | |
5f4a0c58 | 637 | .It Fl N |
638 | Do not execute a remote command. | |
639 | This is useful for just forwarding ports | |
640 | (protocol version 2 only). | |
bf740959 | 641 | .It Fl n |
642 | Redirects stdin from | |
643 | .Pa /dev/null | |
644 | (actually, prevents reading from stdin). | |
645 | This must be used when | |
646 | .Nm | |
610cd5c6 | 647 | is run in the background. |
648 | A common trick is to use this to run X11 programs on a remote machine. | |
649 | For example, | |
bf740959 | 650 | .Ic ssh -n shadows.cs.hut.fi emacs & |
651 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
652 | connection will be automatically forwarded over an encrypted channel. | |
653 | The | |
654 | .Nm | |
655 | program will be put in the background. | |
656 | (This does not work if | |
657 | .Nm | |
658 | needs to ask for a password or passphrase; see also the | |
659 | .Fl f | |
660 | option.) | |
cf848a5e | 661 | .It Fl O Ar ctl_cmd |
662 | Control an active connection multiplexing master process. | |
663 | When the | |
664 | .Fl O | |
665 | option is specified, the | |
666 | .Ar ctl_cmd | |
667 | argument is interpreted and passed to the master process. | |
668 | Valid commands are: | |
669 | .Dq check | |
670 | (check that the master process is running) and | |
671 | .Dq exit | |
672 | (request the master to exit). | |
bf740959 | 673 | .It Fl o Ar option |
38539909 | 674 | Can be used to give options in the format used in the configuration file. |
bf740959 | 675 | This is useful for specifying options for which there is no separate |
610cd5c6 | 676 | command-line flag. |
5f4a0c58 | 677 | For full details of the options listed below, and their possible values, see |
678 | .Xr ssh_config 5 . | |
679 | .Pp | |
680 | .Bl -tag -width Ds -offset indent -compact | |
681 | .It AddressFamily | |
682 | .It BatchMode | |
683 | .It BindAddress | |
684 | .It ChallengeResponseAuthentication | |
685 | .It CheckHostIP | |
686 | .It Cipher | |
687 | .It Ciphers | |
688 | .It ClearAllForwardings | |
689 | .It Compression | |
690 | .It CompressionLevel | |
691 | .It ConnectionAttempts | |
20b267fb | 692 | .It ConnectTimeout |
5e96b616 | 693 | .It ControlMaster |
694 | .It ControlPath | |
5f4a0c58 | 695 | .It DynamicForward |
5f4a0c58 | 696 | .It EscapeChar |
697 | .It ForwardAgent | |
698 | .It ForwardX11 | |
d73a67d7 | 699 | .It ForwardX11Trusted |
5f4a0c58 | 700 | .It GatewayPorts |
701 | .It GlobalKnownHostsFile | |
702 | .It GSSAPIAuthentication | |
703 | .It GSSAPIDelegateCredentials | |
704 | .It Host | |
705 | .It HostbasedAuthentication | |
706 | .It HostKeyAlgorithms | |
707 | .It HostKeyAlias | |
708 | .It HostName | |
709 | .It IdentityFile | |
3a065ed0 | 710 | .It IdentitiesOnly |
396070f8 | 711 | .It KbdInteractiveDevices |
5f4a0c58 | 712 | .It LocalForward |
713 | .It LogLevel | |
714 | .It MACs | |
715 | .It NoHostAuthenticationForLocalhost | |
716 | .It NumberOfPasswordPrompts | |
717 | .It PasswordAuthentication | |
718 | .It Port | |
719 | .It PreferredAuthentications | |
720 | .It Protocol | |
721 | .It ProxyCommand | |
722 | .It PubkeyAuthentication | |
723 | .It RemoteForward | |
724 | .It RhostsRSAAuthentication | |
725 | .It RSAAuthentication | |
8e99a198 | 726 | .It SendEnv |
5d8d32a3 | 727 | .It ServerAliveInterval |
728 | .It ServerAliveCountMax | |
5f4a0c58 | 729 | .It SmartcardDevice |
730 | .It StrictHostKeyChecking | |
fd573618 | 731 | .It TCPKeepAlive |
5f4a0c58 | 732 | .It UsePrivilegedPort |
733 | .It User | |
734 | .It UserKnownHostsFile | |
735 | .It VerifyHostKeyDNS | |
736 | .It XAuthLocation | |
737 | .El | |
bf740959 | 738 | .It Fl p Ar port |
610cd5c6 | 739 | Port to connect to on the remote host. |
740 | This can be specified on a | |
bf740959 | 741 | per-host basis in the configuration file. |
bf740959 | 742 | .It Fl q |
610cd5c6 | 743 | Quiet mode. |
744 | Causes all warning and diagnostic messages to be suppressed. | |
5f4a0c58 | 745 | .It Fl R Xo |
746 | .Sm off | |
3867aa0a | 747 | .Oo Ar bind_address : Oc |
5f4a0c58 | 748 | .Ar port : host : hostport |
749 | .Sm on | |
750 | .Xc | |
751 | Specifies that the given port on the remote (server) host is to be | |
752 | forwarded to the given host and port on the local side. | |
753 | This works by allocating a socket to listen to | |
754 | .Ar port | |
755 | on the remote side, and whenever a connection is made to this port, the | |
756 | connection is forwarded over the secure channel, and a connection is | |
757 | made to | |
758 | .Ar host | |
759 | port | |
760 | .Ar hostport | |
761 | from the local machine. | |
3867aa0a | 762 | .Pp |
5f4a0c58 | 763 | Port forwardings can also be specified in the configuration file. |
764 | Privileged ports can be forwarded only when | |
765 | logging in as root on the remote machine. | |
3867aa0a | 766 | IPv6 addresses can be specified by enclosing the address in square braces or |
767 | using an alternative syntax: | |
5f4a0c58 | 768 | .Xo |
3867aa0a | 769 | .Sm off |
770 | .Oo Ar bind_address / Oc | |
771 | .Ar host/port/hostport | |
5f4a0c58 | 772 | .Sm on |
3867aa0a | 773 | .Xc . |
774 | .Pp | |
775 | By default, the listening socket on the server will be bound to the loopback | |
776 | interface only. | |
777 | This may be overriden by specifying a | |
778 | .Ar bind_address . | |
779 | An empty | |
780 | .Ar bind_address , | |
781 | or the address | |
782 | .Ql * | |
783 | indicates that the remote socket should listen on all interfaces. | |
784 | Specifying a remote | |
785 | .Ar bind_address | |
786 | will only succeed if the server's | |
787 | .Cm GatewayPorts | |
788 | option is enabled (see | |
789 | .Xr sshd_config 5 ). | |
f8c6db83 | 790 | .It Fl S Ar ctl_path |
9affc5db | 791 | Specifies the location of a control socket for connection sharing. |
5e96b616 | 792 | Refer to the description of |
0e19494c | 793 | .Cm ControlPath |
794 | and | |
5e96b616 | 795 | .Cm ControlMaster |
796 | in | |
797 | .Xr ssh_config 5 | |
798 | for details. | |
ae810de7 | 799 | .It Fl s |
3cbc677d | 800 | May be used to request invocation of a subsystem on the remote system. |
801 | Subsystems are a feature of the SSH2 protocol which facilitate the use | |
5f4a0c58 | 802 | of SSH as a secure transport for other applications (eg.\& |
803 | .Xr sftp 1 ) . | |
3cbc677d | 804 | The subsystem is specified as the remote command. |
5f4a0c58 | 805 | .It Fl T |
806 | Disable pseudo-tty allocation. | |
bf740959 | 807 | .It Fl t |
610cd5c6 | 808 | Force pseudo-tty allocation. |
4fe2af09 | 809 | This can be used to execute arbitrary |
610cd5c6 | 810 | screen-based programs on a remote machine, which can be very useful, |
811 | e.g., when implementing menu services. | |
8abcdba4 | 812 | Multiple |
813 | .Fl t | |
814 | options force tty allocation, even if | |
815 | .Nm | |
816 | has no local tty. | |
5f4a0c58 | 817 | .It Fl V |
818 | Display the version number and exit. | |
bf740959 | 819 | .It Fl v |
610cd5c6 | 820 | Verbose mode. |
821 | Causes | |
bf740959 | 822 | .Nm |
610cd5c6 | 823 | to print debugging messages about its progress. |
824 | This is helpful in | |
bf740959 | 825 | debugging connection, authentication, and configuration problems. |
8abcdba4 | 826 | Multiple |
827 | .Fl v | |
c825cd79 | 828 | options increase the verbosity. |
829 | The maximum is 3. | |
bf740959 | 830 | .It Fl X |
831 | Enables X11 forwarding. | |
71276795 | 832 | This can also be specified on a per-host basis in a configuration file. |
07d688d5 | 833 | .Pp |
a4e5acef | 834 | X11 forwarding should be enabled with caution. |
835 | Users with the ability to bypass file permissions on the remote host | |
836 | (for the user's X authorization database) | |
837 | can access the local X11 display through the forwarded connection. | |
838 | An attacker may then be able to perform activities such as keystroke monitoring. | |
5f4a0c58 | 839 | .It Fl x |
840 | Disables X11 forwarding. | |
d73a67d7 | 841 | .It Fl Y |
842 | Enables trusted X11 forwarding. | |
bf740959 | 843 | .El |
844 | .Sh CONFIGURATION FILES | |
845 | .Nm | |
588df31a | 846 | may additionally obtain configuration data from |
847 | a per-user configuration file and a system-wide configuration file. | |
848 | The file format and configuration options are described in | |
849 | .Xr ssh_config 5 . | |
bf740959 | 850 | .Sh ENVIRONMENT |
851 | .Nm | |
852 | will normally set the following environment variables: | |
5f4a0c58 | 853 | .Bl -tag -width LOGNAME |
bf740959 | 854 | .It Ev DISPLAY |
855 | The | |
856 | .Ev DISPLAY | |
610cd5c6 | 857 | variable indicates the location of the X11 server. |
f54651ce | 858 | It is automatically set by |
bf740959 | 859 | .Nm |
860 | to point to a value of the form | |
861 | .Dq hostname:n | |
862 | where hostname indicates | |
5f4a0c58 | 863 | the host where the shell runs, and n is an integer \*(Ge 1. |
610cd5c6 | 864 | .Nm |
865 | uses this special value to forward X11 connections over the secure | |
866 | channel. | |
da89cf4d | 867 | The user should normally not set |
868 | .Ev DISPLAY | |
869 | explicitly, as that | |
bf740959 | 870 | will render the X11 connection insecure (and will require the user to |
871 | manually copy any required authorization cookies). | |
872 | .It Ev HOME | |
873 | Set to the path of the user's home directory. | |
874 | .It Ev LOGNAME | |
875 | Synonym for | |
876 | .Ev USER ; | |
877 | set for compatibility with systems that use this variable. | |
878 | .It Ev MAIL | |
ae897d7c | 879 | Set to the path of the user's mailbox. |
610cd5c6 | 880 | .It Ev PATH |
bf740959 | 881 | Set to the default |
882 | .Ev PATH , | |
883 | as specified when compiling | |
884 | .Nm ssh . | |
3474b2b4 | 885 | .It Ev SSH_ASKPASS |
886 | If | |
887 | .Nm | |
888 | needs a passphrase, it will read the passphrase from the current | |
889 | terminal if it was run from a terminal. | |
890 | If | |
891 | .Nm | |
892 | does not have a terminal associated with it but | |
893 | .Ev DISPLAY | |
894 | and | |
895 | .Ev SSH_ASKPASS | |
896 | are set, it will execute the program specified by | |
897 | .Ev SSH_ASKPASS | |
898 | and open an X11 window to read the passphrase. | |
899 | This is particularly useful when calling | |
900 | .Nm | |
901 | from a | |
caeffafb | 902 | .Pa .xsession |
3474b2b4 | 903 | or related script. |
904 | (Note that on some machines it | |
905 | may be necessary to redirect the input from | |
906 | .Pa /dev/null | |
907 | to make this work.) | |
bf740959 | 908 | .It Ev SSH_AUTH_SOCK |
ae897d7c | 909 | Identifies the path of a unix-domain socket used to communicate with the |
bf740959 | 910 | agent. |
da0561eb | 911 | .It Ev SSH_CONNECTION |
912 | Identifies the client and server ends of the connection. | |
610cd5c6 | 913 | The variable contains |
da0561eb | 914 | four space-separated values: client ip-address, client port number, |
915 | server ip-address and server port number. | |
8abcdba4 | 916 | .It Ev SSH_ORIGINAL_COMMAND |
917 | The variable contains the original command line if a forced command | |
918 | is executed. | |
919 | It can be used to extract the original arguments. | |
bf740959 | 920 | .It Ev SSH_TTY |
921 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 922 | with the current shell or command. |
923 | If the current session has no tty, | |
bf740959 | 924 | this variable is not set. |
925 | .It Ev TZ | |
926 | The timezone variable is set to indicate the present timezone if it | |
c345cf9d | 927 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 928 | on to new connections). |
929 | .It Ev USER | |
930 | Set to the name of the user logging in. | |
931 | .El | |
932 | .Pp | |
f54651ce | 933 | Additionally, |
bf740959 | 934 | .Nm |
f54651ce | 935 | reads |
936 | .Pa $HOME/.ssh/environment , | |
bf740959 | 937 | and adds lines of the format |
938 | .Dq VARNAME=value | |
6a342527 | 939 | to the environment if the file exists and if users are allowed to |
940 | change their environment. | |
5f4a0c58 | 941 | For more information, see the |
6a342527 | 942 | .Cm PermitUserEnvironment |
35453849 | 943 | option in |
6a342527 | 944 | .Xr sshd_config 5 . |
bf740959 | 945 | .Sh FILES |
c8d54615 | 946 | .Bl -tag -width Ds |
f49bc4f7 | 947 | .It Pa $HOME/.ssh/known_hosts |
ae897d7c | 948 | Records host keys for all hosts the user has logged into that are not |
bf740959 | 949 | in |
2a8a6488 | 950 | .Pa /etc/ssh/ssh_known_hosts . |
bf740959 | 951 | See |
952 | .Xr sshd 8 . | |
c0ecc314 | 953 | .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa |
954 | Contains the authentication identity of the user. | |
955 | They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. | |
1d1ffb87 | 956 | These files |
957 | contain sensitive data and should be readable by the user but not | |
bf740959 | 958 | accessible by others (read/write/execute). |
959 | Note that | |
960 | .Nm | |
1d1ffb87 | 961 | ignores a private key file if it is accessible by others. |
bf740959 | 962 | It is possible to specify a passphrase when |
963 | generating the key; the passphrase will be used to encrypt the | |
964 | sensitive part of this file using 3DES. | |
c0ecc314 | 965 | .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub |
bf740959 | 966 | Contains the public key for authentication (public part of the |
610cd5c6 | 967 | identity file in human-readable form). |
1d1ffb87 | 968 | The contents of the |
969 | .Pa $HOME/.ssh/identity.pub | |
5f4a0c58 | 970 | file should be added to the file |
bf740959 | 971 | .Pa $HOME/.ssh/authorized_keys |
972 | on all machines | |
91789042 | 973 | where the user wishes to log in using protocol version 1 RSA authentication. |
1d1ffb87 | 974 | The contents of the |
975 | .Pa $HOME/.ssh/id_dsa.pub | |
c0ecc314 | 976 | and |
977 | .Pa $HOME/.ssh/id_rsa.pub | |
1d1ffb87 | 978 | file should be added to |
96a7b0cc | 979 | .Pa $HOME/.ssh/authorized_keys |
1d1ffb87 | 980 | on all machines |
91789042 | 981 | where the user wishes to log in using protocol version 2 DSA/RSA authentication. |
1d1ffb87 | 982 | These files are not |
610cd5c6 | 983 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 984 | These files are |
c44559d2 | 985 | never used automatically and are not necessary; they are only provided for |
bf740959 | 986 | the convenience of the user. |
987 | .It Pa $HOME/.ssh/config | |
610cd5c6 | 988 | This is the per-user configuration file. |
588df31a | 989 | The file format and configuration options are described in |
990 | .Xr ssh_config 5 . | |
e1520719 | 991 | Because of the potential for abuse, this file must have strict permissions: |
992 | read/write for the user, and not accessible by others. | |
bf740959 | 993 | .It Pa $HOME/.ssh/authorized_keys |
96a7b0cc | 994 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. |
610cd5c6 | 995 | The format of this file is described in the |
bf740959 | 996 | .Xr sshd 8 |
610cd5c6 | 997 | manual page. |
5f4a0c58 | 998 | In the simplest form the format is the same as the |
999 | .Pa .pub | |
f49bc4f7 | 1000 | identity files. |
1d1ffb87 | 1001 | This file is not highly sensitive, but the recommended |
1002 | permissions are read/write for the user, and not accessible by others. | |
2a8a6488 | 1003 | .It Pa /etc/ssh/ssh_known_hosts |
610cd5c6 | 1004 | Systemwide list of known host keys. |
f49bc4f7 | 1005 | This file should be prepared by the |
bf740959 | 1006 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 1007 | organization. |
1008 | This file should be world-readable. | |
1009 | This file contains | |
bf740959 | 1010 | public keys, one per line, in the following format (fields separated |
f49bc4f7 | 1011 | by spaces): system name, public key and optional comment field. |
610cd5c6 | 1012 | When different names are used |
bf740959 | 1013 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 1014 | commas. |
5f4a0c58 | 1015 | The format is described in the |
bf740959 | 1016 | .Xr sshd 8 |
1017 | manual page. | |
1018 | .Pp | |
1019 | The canonical system name (as returned by name servers) is used by | |
1020 | .Xr sshd 8 | |
1021 | to verify the client host when logging in; other names are needed because | |
1022 | .Nm | |
1023 | does not convert the user-supplied name to a canonical name before | |
1024 | checking the key, because someone with access to the name servers | |
1025 | would then be able to fool host authentication. | |
2a8a6488 | 1026 | .It Pa /etc/ssh/ssh_config |
610cd5c6 | 1027 | Systemwide configuration file. |
588df31a | 1028 | The file format and configuration options are described in |
1029 | .Xr ssh_config 5 . | |
2a8a6488 | 1030 | .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key |
dd58cb5e | 1031 | These three files contain the private parts of the host keys |
1032 | and are used for | |
1033 | .Cm RhostsRSAAuthentication | |
1034 | and | |
1035 | .Cm HostbasedAuthentication . | |
d83cbdc3 | 1036 | If the protocol version 1 |
1037 | .Cm RhostsRSAAuthentication | |
7203d6bb | 1038 | method is used, |
d83cbdc3 | 1039 | .Nm |
1040 | must be setuid root, since the host key is readable only by root. | |
1041 | For protocol version 2, | |
1042 | .Nm | |
1043 | uses | |
1044 | .Xr ssh-keysign 8 | |
1045 | to access the host keys for | |
1046 | .Cm HostbasedAuthentication . | |
1047 | This eliminates the requirement that | |
1048 | .Nm | |
1049 | be setuid root when that authentication method is used. | |
1050 | By default | |
dd58cb5e | 1051 | .Nm |
d83cbdc3 | 1052 | is not setuid root. |
bf740959 | 1053 | .It Pa $HOME/.rhosts |
1054 | This file is used in | |
6f5abc1e | 1055 | .Cm RhostsRSAAuthentication |
1056 | and | |
1057 | .Cm HostbasedAuthentication | |
bf740959 | 1058 | authentication to list the |
610cd5c6 | 1059 | host/user pairs that are permitted to log in. |
1060 | (Note that this file is | |
bf740959 | 1061 | also used by rlogin and rsh, which makes using this file insecure.) |
1062 | Each line of the file contains a host name (in the canonical form | |
1063 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1064 | separated by a space. |
e91c60f2 | 1065 | On some machines this file may need to be |
bf740959 | 1066 | world-readable if the user's home directory is on a NFS partition, |
1067 | because | |
1068 | .Xr sshd 8 | |
610cd5c6 | 1069 | reads it as root. |
1070 | Additionally, this file must be owned by the user, | |
1071 | and must not have write permissions for anyone else. | |
1072 | The recommended | |
bf740959 | 1073 | permission for most machines is read/write for the user, and not |
1074 | accessible by others. | |
1075 | .Pp | |
6f5abc1e | 1076 | Note that |
bf740959 | 1077 | .Xr sshd 8 |
6f5abc1e | 1078 | allows authentication only in combination with client host key |
1079 | authentication before permitting log in. | |
91789042 | 1080 | If the server machine does not have the client's host key in |
2a8a6488 | 1081 | .Pa /etc/ssh/ssh_known_hosts , |
91789042 | 1082 | it can be stored in |
bf740959 | 1083 | .Pa $HOME/.ssh/known_hosts . |
1084 | The easiest way to do this is to | |
1085 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1086 | will automatically add the host key to |
bf740959 | 1087 | .Pa $HOME/.ssh/known_hosts . |
1088 | .It Pa $HOME/.shosts | |
1089 | This file is used exactly the same way as | |
5f4a0c58 | 1090 | .Pa .rhosts . |
bf740959 | 1091 | The purpose for |
6f5abc1e | 1092 | having this file is to be able to use |
1093 | .Cm RhostsRSAAuthentication | |
1094 | and | |
1095 | .Cm HostbasedAuthentication | |
1096 | authentication without permitting login with | |
5f4a0c58 | 1097 | .Xr rlogin |
bf740959 | 1098 | or |
1099 | .Xr rsh 1 . | |
1100 | .It Pa /etc/hosts.equiv | |
1101 | This file is used during | |
6f5abc1e | 1102 | .Cm RhostsRSAAuthentication |
1103 | and | |
1104 | .Cm HostbasedAuthentication | |
be193d89 | 1105 | authentication. |
610cd5c6 | 1106 | It contains |
5f4a0c58 | 1107 | canonical hosts names, one per line (the full format is described in the |
bf740959 | 1108 | .Xr sshd 8 |
610cd5c6 | 1109 | manual page). |
1110 | If the client host is found in this file, login is | |
bf740959 | 1111 | automatically permitted provided client and server user names are the |
610cd5c6 | 1112 | same. |
6f5abc1e | 1113 | Additionally, successful client host key authentication is required. |
610cd5c6 | 1114 | This file should only be writable by root. |
5f4fdfae | 1115 | .It Pa /etc/shosts.equiv |
f54651ce | 1116 | This file is processed exactly as |
bf740959 | 1117 | .Pa /etc/hosts.equiv . |
1118 | This file may be useful to permit logins using | |
1119 | .Nm | |
1120 | but not using rsh/rlogin. | |
2a8a6488 | 1121 | .It Pa /etc/ssh/sshrc |
bf740959 | 1122 | Commands in this file are executed by |
1123 | .Nm | |
1124 | when the user logs in just before the user's shell (or command) is started. | |
1125 | See the | |
1126 | .Xr sshd 8 | |
1127 | manual page for more information. | |
1128 | .It Pa $HOME/.ssh/rc | |
1129 | Commands in this file are executed by | |
1130 | .Nm | |
1131 | when the user logs in just before the user's shell (or command) is | |
1132 | started. | |
f54651ce | 1133 | See the |
bf740959 | 1134 | .Xr sshd 8 |
1135 | manual page for more information. | |
83b7f649 | 1136 | .It Pa $HOME/.ssh/environment |
1137 | Contains additional definitions for environment variables, see section | |
1138 | .Sx ENVIRONMENT | |
1139 | above. | |
b5e300c2 | 1140 | .El |
16210ef7 | 1141 | .Sh DIAGNOSTICS |
1142 | .Nm | |
1143 | exits with the exit status of the remote command or with 255 | |
1144 | if an error occurred. | |
bf740959 | 1145 | .Sh SEE ALSO |
5f4a0c58 | 1146 | .Xr gzip 1 , |
bf740959 | 1147 | .Xr rsh 1 , |
1148 | .Xr scp 1 , | |
61e96248 | 1149 | .Xr sftp 1 , |
bf740959 | 1150 | .Xr ssh-add 1 , |
1151 | .Xr ssh-agent 1 , | |
1152 | .Xr ssh-keygen 1 , | |
1153 | .Xr telnet 1 , | |
5f4a0c58 | 1154 | .Xr hosts.equiv 5 , |
1ae02182 | 1155 | .Xr ssh_config 5 , |
b2843ec6 | 1156 | .Xr ssh-keysign 8 , |
9afadca8 | 1157 | .Xr sshd 8 |
2cad6cef | 1158 | .Rs |
1159 | .%A T. Ylonen | |
1160 | .%A T. Kivinen | |
1161 | .%A M. Saarinen | |
1162 | .%A T. Rinne | |
1163 | .%A S. Lehtinen | |
1164 | .%T "SSH Protocol Architecture" | |
17f5e68a | 1165 | .%N draft-ietf-secsh-architecture-12.txt |
1166 | .%D January 2002 | |
2cad6cef | 1167 | .%O work in progress material |
1168 | .Re | |
be193d89 | 1169 | .Sh AUTHORS |
1170 | OpenSSH is a derivative of the original and free | |
1171 | ssh 1.2.12 release by Tatu Ylonen. | |
1172 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1173 | Theo de Raadt and Dug Song | |
1174 | removed many bugs, re-added newer features and | |
1175 | created OpenSSH. | |
1176 | Markus Friedl contributed the support for SSH | |
1177 | protocol versions 1.5 and 2.0. |