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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 | .\" |
cf848a5e | 37 | .\" $OpenBSD: ssh.1,v 1.199 2004/11/07 17:42:36 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 |
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 | |
bf740959 | 56 | .Ar port : |
7b2ea3a1 | 57 | .Ar host : |
bf740959 | 58 | .Ar hostport |
59 | .Sm on | |
60 | .Xc | |
61 | .Oc | |
a4e5acef | 62 | .Ek |
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 | |
bf740959 | 72 | .Ar port : |
7b2ea3a1 | 73 | .Ar host : |
bf740959 | 74 | .Ar hostport |
75 | .Sm on | |
76 | .Xc | |
77 | .Oc | |
f8c6db83 | 78 | .Op Fl S Ar ctl_path |
5f4a0c58 | 79 | .Oo Ar user Ns @ Oc Ns Ar hostname |
bf740959 | 80 | .Op Ar command |
f54651ce | 81 | .Sh DESCRIPTION |
bf740959 | 82 | .Nm |
2c86906e | 83 | (SSH client) is a program for logging into a remote machine and for |
610cd5c6 | 84 | executing commands on a remote machine. |
5f4a0c58 | 85 | It is intended to replace rlogin and rsh, |
86 | and provide secure encrypted communications between | |
610cd5c6 | 87 | two untrusted hosts over an insecure network. |
5f4a0c58 | 88 | X11 connections and arbitrary TCP/IP ports |
89 | can also be forwarded over the secure channel. | |
bf740959 | 90 | .Pp |
91 | .Nm | |
f54651ce | 92 | connects and logs into the specified |
5f4a0c58 | 93 | .Ar hostname |
94 | (with optional | |
95 | .Ar user | |
96 | name). | |
bf740959 | 97 | The user must prove |
1d1ffb87 | 98 | his/her identity to the remote machine using one of several methods |
5f4a0c58 | 99 | depending on the protocol version used. |
1d1ffb87 | 100 | .Pp |
5f4a0c58 | 101 | If |
102 | .Ar command | |
103 | is specified, | |
104 | .Ar command | |
105 | is executed on the remote host instead of a login shell. | |
1d1ffb87 | 106 | .Ss SSH protocol version 1 |
6f5abc1e | 107 | The first authentication method is the |
108 | .Em rhosts | |
109 | or | |
110 | .Em hosts.equiv | |
111 | method combined with RSA-based host authentication. | |
112 | If the machine the user logs in from is listed in | |
bf740959 | 113 | .Pa /etc/hosts.equiv |
114 | or | |
5f4fdfae | 115 | .Pa /etc/shosts.equiv |
bf740959 | 116 | on the remote machine, and the user names are |
6f5abc1e | 117 | the same on both sides, or if the files |
118 | .Pa $HOME/.rhosts | |
bf740959 | 119 | or |
6f5abc1e | 120 | .Pa $HOME/.shosts |
121 | exist in the user's home directory on the | |
122 | remote machine and contain a line containing the name of the client | |
bf740959 | 123 | machine and the name of the user on that machine, the user is |
6f5abc1e | 124 | considered for log in. |
125 | Additionally, if the server can verify the client's | |
f54651ce | 126 | host key (see |
2a8a6488 | 127 | .Pa /etc/ssh/ssh_known_hosts |
5bbb5681 | 128 | and |
129 | .Pa $HOME/.ssh/known_hosts | |
bf740959 | 130 | in the |
131 | .Sx FILES | |
5f4a0c58 | 132 | section), only then is login permitted. |
610cd5c6 | 133 | This authentication method closes security holes due to IP |
134 | spoofing, DNS spoofing and routing spoofing. | |
135 | [Note to the administrator: | |
bf740959 | 136 | .Pa /etc/hosts.equiv , |
1d1ffb87 | 137 | .Pa $HOME/.rhosts , |
bf740959 | 138 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
139 | disabled if security is desired.] | |
140 | .Pp | |
6f5abc1e | 141 | As a second authentication method, |
bf740959 | 142 | .Nm |
143 | supports RSA based authentication. | |
144 | The scheme is based on public-key cryptography: there are cryptosystems | |
145 | where encryption and decryption are done using separate keys, and it | |
146 | is not possible to derive the decryption key from the encryption key. | |
610cd5c6 | 147 | RSA is one such system. |
f54651ce | 148 | The idea is that each user creates a public/private |
610cd5c6 | 149 | key pair for authentication purposes. |
150 | The server knows the public key, and only the user knows the private key. | |
5f4a0c58 | 151 | .Pp |
f54651ce | 152 | The file |
bf740959 | 153 | .Pa $HOME/.ssh/authorized_keys |
5f4a0c58 | 154 | lists the public keys that are permitted for logging in. |
610cd5c6 | 155 | When the user logs in, the |
bf740959 | 156 | .Nm |
157 | program tells the server which key pair it would like to use for | |
610cd5c6 | 158 | authentication. |
5f4a0c58 | 159 | The server checks if this key is permitted, and if so, |
160 | sends the user (actually the | |
bf740959 | 161 | .Nm |
162 | program running on behalf of the user) a challenge, a random number, | |
610cd5c6 | 163 | encrypted by the user's public key. |
5f4a0c58 | 164 | The challenge can only be decrypted using the proper private key. |
165 | The user's client then decrypts the challenge using the private key, | |
166 | proving that he/she knows the private key | |
167 | but without disclosing it to the server. | |
bf740959 | 168 | .Pp |
169 | .Nm | |
610cd5c6 | 170 | implements the RSA authentication protocol automatically. |
171 | The user creates his/her RSA key pair by running | |
bf740959 | 172 | .Xr ssh-keygen 1 . |
f54651ce | 173 | This stores the private key in |
1d1ffb87 | 174 | .Pa $HOME/.ssh/identity |
5f4a0c58 | 175 | and stores the public key in |
1d1ffb87 | 176 | .Pa $HOME/.ssh/identity.pub |
610cd5c6 | 177 | in the user's home directory. |
178 | The user should then copy the | |
bf740959 | 179 | .Pa identity.pub |
f54651ce | 180 | to |
1d1ffb87 | 181 | .Pa $HOME/.ssh/authorized_keys |
f54651ce | 182 | in his/her home directory on the remote machine (the |
bf740959 | 183 | .Pa authorized_keys |
f54651ce | 184 | file corresponds to the conventional |
1d1ffb87 | 185 | .Pa $HOME/.rhosts |
bf740959 | 186 | file, and has one key |
610cd5c6 | 187 | per line, though the lines can be very long). |
188 | After this, the user can log in without giving the password. | |
bf740959 | 189 | .Pp |
190 | The most convenient way to use RSA authentication may be with an | |
610cd5c6 | 191 | authentication agent. |
192 | See | |
bf740959 | 193 | .Xr ssh-agent 1 |
194 | for more information. | |
195 | .Pp | |
f54651ce | 196 | If other authentication methods fail, |
bf740959 | 197 | .Nm |
610cd5c6 | 198 | prompts the user for a password. |
199 | The password is sent to the remote | |
bf740959 | 200 | host for checking; however, since all communications are encrypted, |
201 | the password cannot be seen by someone listening on the network. | |
1d1ffb87 | 202 | .Ss SSH protocol version 2 |
5f4a0c58 | 203 | When a user connects using protocol version 2, |
16210ef7 | 204 | similar authentication methods are available. |
da89cf4d | 205 | Using the default values for |
206 | .Cm PreferredAuthentications , | |
29c440a0 | 207 | the client will try to authenticate first using the hostbased method; |
5f4a0c58 | 208 | if this method fails, public key authentication is attempted, |
209 | and finally if this method fails, keyboard-interactive and | |
29c440a0 | 210 | password authentication are tried. |
1d1ffb87 | 211 | .Pp |
212 | The public key method is similar to RSA authentication described | |
da89cf4d | 213 | in the previous section and allows the RSA or DSA algorithm to be used: |
c0ecc314 | 214 | The client uses his private key, |
1d1ffb87 | 215 | .Pa $HOME/.ssh/id_dsa |
c0ecc314 | 216 | or |
217 | .Pa $HOME/.ssh/id_rsa , | |
1d1ffb87 | 218 | to sign the session identifier and sends the result to the server. |
219 | The server checks whether the matching public key is listed in | |
96a7b0cc | 220 | .Pa $HOME/.ssh/authorized_keys |
1d1ffb87 | 221 | and grants access if both the key is found and the signature is correct. |
222 | The session identifier is derived from a shared Diffie-Hellman value | |
223 | and is only known to the client and the server. | |
224 | .Pp | |
5f4a0c58 | 225 | If public key authentication fails or is not available, a password |
226 | can be sent encrypted to the remote host to prove the user's identity. | |
da89cf4d | 227 | .Pp |
228 | Additionally, | |
229 | .Nm | |
230 | supports hostbased or challenge response authentication. | |
1d1ffb87 | 231 | .Pp |
232 | Protocol 2 provides additional mechanisms for confidentiality | |
3b9baa7b | 233 | (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour) |
234 | and integrity (hmac-md5, hmac-sha1, hmac-ripemd160). | |
1d1ffb87 | 235 | Note that protocol 1 lacks a strong mechanism for ensuring the |
236 | integrity of the connection. | |
1d1ffb87 | 237 | .Ss Login session and remote execution |
bf740959 | 238 | When the user's identity has been accepted by the server, the server |
239 | either executes the given command, or logs into the machine and gives | |
610cd5c6 | 240 | the user a normal shell on the remote machine. |
241 | All communication with | |
bf740959 | 242 | the remote command or shell will be automatically encrypted. |
243 | .Pp | |
244 | If a pseudo-terminal has been allocated (normal login session), the | |
df841692 | 245 | user may use the escape characters noted below. |
bf740959 | 246 | .Pp |
5f4a0c58 | 247 | If no pseudo-tty has been allocated, |
248 | the session is transparent and can be used to reliably transfer binary data. | |
610cd5c6 | 249 | On most systems, setting the escape character to |
bf740959 | 250 | .Dq none |
251 | will also make the session transparent even if a tty is used. | |
252 | .Pp | |
ce9c0b75 | 253 | The session terminates when the command or shell on the remote |
e91c60f2 | 254 | machine exits and all X11 and TCP/IP connections have been closed. |
5f4a0c58 | 255 | The exit status of the remote program is returned as the exit status of |
bf740959 | 256 | .Nm ssh . |
df841692 | 257 | .Ss Escape Characters |
5f4a0c58 | 258 | When a pseudo-terminal has been requested, |
259 | .Nm | |
260 | supports a number of functions through the use of an escape character. | |
df841692 | 261 | .Pp |
262 | A single tilde character can be sent as | |
263 | .Ic ~~ | |
5bef3c35 | 264 | or by following the tilde by a character other than those described below. |
df841692 | 265 | The escape character must always follow a newline to be interpreted as |
266 | special. | |
267 | The escape character can be changed in configuration files using the | |
268 | .Cm EscapeChar | |
3730bb22 | 269 | configuration directive or on the command line by the |
df841692 | 270 | .Fl e |
271 | option. | |
272 | .Pp | |
273 | The supported escapes (assuming the default | |
274 | .Ql ~ ) | |
275 | are: | |
276 | .Bl -tag -width Ds | |
277 | .It Cm ~. | |
5f4a0c58 | 278 | Disconnect. |
df841692 | 279 | .It Cm ~^Z |
5f4a0c58 | 280 | Background |
281 | .Nm ssh . | |
df841692 | 282 | .It Cm ~# |
5f4a0c58 | 283 | List forwarded connections. |
df841692 | 284 | .It Cm ~& |
5f4a0c58 | 285 | Background |
286 | .Nm | |
287 | at logout when waiting for forwarded connection / X11 sessions to terminate. | |
df841692 | 288 | .It Cm ~? |
5f4a0c58 | 289 | Display a list of escape characters. |
16a79097 | 290 | .It Cm ~B |
5f4a0c58 | 291 | Send a BREAK to the remote system |
292 | (only useful for SSH protocol version 2 and if the peer supports it). | |
c53c54c2 | 293 | .It Cm ~C |
d740ec16 | 294 | Open command line. |
295 | Currently this allows the addition of port forwardings using the | |
c53c54c2 | 296 | .Fl L |
297 | and | |
298 | .Fl R | |
d740ec16 | 299 | options (see below). |
790029d9 | 300 | It also allows the cancellation of existing remote port-forwardings |
d740ec16 | 301 | using |
302 | .Fl KR Ar hostport . | |
7069a5e2 | 303 | Basic help is available, using the |
304 | .Fl h | |
d740ec16 | 305 | option. |
df841692 | 306 | .It Cm ~R |
5f4a0c58 | 307 | Request rekeying of the connection |
308 | (only useful for SSH protocol version 2 and if the peer supports it). | |
df841692 | 309 | .El |
1d1ffb87 | 310 | .Ss X11 and TCP forwarding |
6efa3d14 | 311 | If the |
312 | .Cm ForwardX11 | |
313 | variable is set to | |
314 | .Dq yes | |
5f4a0c58 | 315 | (or see the description of the |
6efa3d14 | 316 | .Fl X |
317 | and | |
318 | .Fl x | |
319 | options described later) | |
320 | and the user is using X11 (the | |
bf740959 | 321 | .Ev DISPLAY |
322 | environment variable is set), the connection to the X11 display is | |
323 | automatically forwarded to the remote side in such a way that any X11 | |
324 | programs started from the shell (or command) will go through the | |
325 | encrypted channel, and the connection to the real X server will be made | |
610cd5c6 | 326 | from the local machine. |
327 | The user should not manually set | |
bf740959 | 328 | .Ev DISPLAY . |
329 | Forwarding of X11 connections can be | |
330 | configured on the command line or in configuration files. | |
331 | .Pp | |
332 | The | |
f54651ce | 333 | .Ev DISPLAY |
bf740959 | 334 | value set by |
335 | .Nm | |
5f4a0c58 | 336 | will point to the server machine, but with a display number greater than zero. |
610cd5c6 | 337 | This is normal, and happens because |
bf740959 | 338 | .Nm |
339 | creates a | |
340 | .Dq proxy | |
341 | X server on the server machine for forwarding the | |
342 | connections over the encrypted channel. | |
343 | .Pp | |
344 | .Nm | |
345 | will also automatically set up Xauthority data on the server machine. | |
346 | For this purpose, it will generate a random authorization cookie, | |
347 | store it in Xauthority on the server, and verify that any forwarded | |
348 | connections carry this cookie and replace it by the real cookie when | |
610cd5c6 | 349 | the connection is opened. |
350 | The real authentication cookie is never | |
bf740959 | 351 | sent to the server machine (and no cookies are sent in the plain). |
352 | .Pp | |
24794905 | 353 | If the |
354 | .Cm ForwardAgent | |
355 | variable is set to | |
356 | .Dq yes | |
5f4a0c58 | 357 | (or see the description of the |
24794905 | 358 | .Fl A |
359 | and | |
360 | .Fl a | |
a4e5acef | 361 | options described later) and |
24794905 | 362 | the user is using an authentication agent, the connection to the agent |
363 | is automatically forwarded to the remote side. | |
bf740959 | 364 | .Pp |
365 | Forwarding of arbitrary TCP/IP connections over the secure channel can | |
491f5f7b | 366 | be specified either on the command line or in a configuration file. |
610cd5c6 | 367 | One possible application of TCP/IP forwarding is a secure connection to an |
e91c60f2 | 368 | electronic purse; another is going through firewalls. |
1d1ffb87 | 369 | .Ss Server authentication |
bf740959 | 370 | .Nm |
1d1ffb87 | 371 | automatically maintains and checks a database containing |
610cd5c6 | 372 | identifications for all hosts it has ever been used with. |
f49bc4f7 | 373 | Host keys are stored in |
1d1ffb87 | 374 | .Pa $HOME/.ssh/known_hosts |
610cd5c6 | 375 | in the user's home directory. |
f49bc4f7 | 376 | Additionally, the file |
2a8a6488 | 377 | .Pa /etc/ssh/ssh_known_hosts |
f49bc4f7 | 378 | is automatically checked for known hosts. |
610cd5c6 | 379 | Any new hosts are automatically added to the user's file. |
5f4a0c58 | 380 | If a host's identification ever changes, |
bf740959 | 381 | .Nm |
382 | warns about this and disables password authentication to prevent a | |
610cd5c6 | 383 | trojan horse from getting the user's password. |
5f4a0c58 | 384 | Another purpose of this mechanism is to prevent man-in-the-middle attacks |
385 | which could otherwise be used to circumvent the encryption. | |
610cd5c6 | 386 | The |
bf740959 | 387 | .Cm StrictHostKeyChecking |
588df31a | 388 | option can be used to prevent logins to machines whose |
bf740959 | 389 | host key is not known or has changed. |
fa08c86b | 390 | .Pp |
3a858356 | 391 | .Nm |
392 | can be configured to verify host identification using fingerprint resource | |
393 | records (SSHFP) published in DNS. | |
394 | The | |
395 | .Cm VerifyHostKeyDNS | |
396 | option can be used to control how DNS lookups are performed. | |
397 | SSHFP resource records can be generated using | |
398 | .Xr ssh-keygen 1 . | |
399 | .Pp | |
fa08c86b | 400 | The options are as follows: |
bf740959 | 401 | .Bl -tag -width Ds |
5f4a0c58 | 402 | .It Fl 1 |
403 | Forces | |
404 | .Nm | |
405 | to try protocol version 1 only. | |
406 | .It Fl 2 | |
407 | Forces | |
408 | .Nm | |
409 | to try protocol version 2 only. | |
410 | .It Fl 4 | |
411 | Forces | |
412 | .Nm | |
413 | to use IPv4 addresses only. | |
414 | .It Fl 6 | |
415 | Forces | |
416 | .Nm | |
417 | to use IPv6 addresses only. | |
71276795 | 418 | .It Fl A |
419 | Enables forwarding of the authentication agent connection. | |
420 | This can also be specified on a per-host basis in a configuration file. | |
07d688d5 | 421 | .Pp |
a4e5acef | 422 | Agent forwarding should be enabled with caution. |
423 | Users with the ability to bypass file permissions on the remote host | |
424 | (for the agent's Unix-domain socket) | |
425 | can access the local agent through the forwarded connection. | |
426 | An attacker cannot obtain key material from the agent, | |
07d688d5 | 427 | however they can perform operations on the keys that enable them to |
428 | authenticate using the identities loaded into the agent. | |
5f4a0c58 | 429 | .It Fl a |
430 | Disables forwarding of the authentication agent connection. | |
3435f5a6 | 431 | .It Fl b Ar bind_address |
432 | Specify the interface to transmit from on machines with multiple | |
433 | interfaces or aliased addresses. | |
5f4a0c58 | 434 | .It Fl C |
435 | Requests compression of all data (including stdin, stdout, stderr, and | |
436 | data for forwarded X11 and TCP/IP connections). | |
437 | The compression algorithm is the same used by | |
438 | .Xr gzip 1 , | |
439 | and the | |
440 | .Dq level | |
441 | can be controlled by the | |
442 | .Cm CompressionLevel | |
443 | option for protocol version 1. | |
444 | Compression is desirable on modem lines and other | |
445 | slow connections, but will only slow down things on fast networks. | |
446 | The default value can be set on a host-by-host basis in the | |
447 | configuration files; see the | |
448 | .Cm Compression | |
449 | option. | |
3b9baa7b | 450 | .It Fl c Ar cipher_spec |
451 | Selects the cipher specification for encrypting the session. | |
452 | .Pp | |
453 | Protocol version 1 allows specification of a single cipher. | |
454 | The suported values are | |
455 | .Dq 3des , | |
456 | .Dq blowfish | |
457 | and | |
458 | .Dq des . | |
bf740959 | 459 | .Ar 3des |
460 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. | |
3b9baa7b | 461 | It is believed to be secure. |
bf740959 | 462 | .Ar blowfish |
5f4a0c58 | 463 | is a fast block cipher; it appears very secure and is much faster than |
610cd5c6 | 464 | .Ar 3des . |
29999e54 | 465 | .Ar des |
466 | is only supported in the | |
467 | .Nm | |
468 | client for interoperability with legacy protocol 1 implementations | |
469 | that do not support the | |
470 | .Ar 3des | |
a4e5acef | 471 | cipher. |
472 | Its use is strongly discouraged due to cryptographic weaknesses. | |
3b9baa7b | 473 | The default is |
474 | .Dq 3des . | |
475 | .Pp | |
476 | For protocol version 2 | |
477 | .Ar cipher_spec | |
478 | is a comma-separated list of ciphers | |
479 | listed in order of preference. | |
480 | The supported ciphers are | |
481 | .Dq 3des-cbc , | |
482 | .Dq aes128-cbc , | |
483 | .Dq aes192-cbc , | |
484 | .Dq aes256-cbc , | |
485 | .Dq aes128-ctr , | |
486 | .Dq aes192-ctr , | |
487 | .Dq aes256-ctr , | |
488 | .Dq arcfour , | |
489 | .Dq blowfish-cbc , | |
490 | and | |
491 | .Dq cast128-cbc . | |
492 | The default is | |
493 | .Bd -literal | |
494 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour, | |
495 | aes192-cbc,aes256-cbc'' | |
496 | .Ed | |
5f4a0c58 | 497 | .It Fl D Ar port |
498 | Specifies a local | |
499 | .Dq dynamic | |
500 | application-level port forwarding. | |
501 | This works by allocating a socket to listen to | |
502 | .Ar port | |
503 | on the local side, and whenever a connection is made to this port, the | |
504 | connection is forwarded over the secure channel, and the application | |
505 | protocol is then used to determine where to connect to from the | |
506 | remote machine. | |
507 | Currently the SOCKS4 and SOCKS5 protocols are supported, and | |
508 | .Nm | |
509 | will act as a SOCKS server. | |
510 | Only root can forward privileged ports. | |
511 | Dynamic port forwardings can also be specified in the configuration file. | |
512 | .It Fl e Ar ch | ^ch | none | |
bf740959 | 513 | Sets the escape character for sessions with a pty (default: |
514 | .Ql ~ ) . | |
610cd5c6 | 515 | The escape character is only recognized at the beginning of a line. |
516 | The escape character followed by a dot | |
bf740959 | 517 | .Pq Ql \&. |
5f4a0c58 | 518 | closes the connection; |
519 | followed by control-Z suspends the connection; | |
520 | and followed by itself sends the escape character once. | |
610cd5c6 | 521 | Setting the character to |
bf740959 | 522 | .Dq none |
523 | disables any escapes and makes the session fully transparent. | |
5f4a0c58 | 524 | .It Fl F Ar configfile |
525 | Specifies an alternative per-user configuration file. | |
526 | If a configuration file is given on the command line, | |
527 | the system-wide configuration file | |
528 | .Pq Pa /etc/ssh/ssh_config | |
529 | will be ignored. | |
530 | The default for the per-user configuration file is | |
531 | .Pa $HOME/.ssh/config . | |
bf740959 | 532 | .It Fl f |
533 | Requests | |
534 | .Nm | |
610cd5c6 | 535 | to go to background just before command execution. |
536 | This is useful if | |
bf740959 | 537 | .Nm |
538 | is going to ask for passwords or passphrases, but the user | |
610cd5c6 | 539 | wants it in the background. |
f54651ce | 540 | This implies |
bf740959 | 541 | .Fl n . |
542 | The recommended way to start X11 programs at a remote site is with | |
543 | something like | |
544 | .Ic ssh -f host xterm . | |
7b2ea3a1 | 545 | .It Fl g |
546 | Allows remote hosts to connect to local forwarded ports. | |
5f4a0c58 | 547 | .It Fl I Ar smartcard_device |
548 | Specifies which smartcard device to use. | |
549 | The argument is the device | |
550 | .Nm | |
551 | should use to communicate with a smartcard used for storing the user's | |
552 | private RSA key. | |
bf740959 | 553 | .It Fl i Ar identity_file |
cf5a07a8 | 554 | Selects a file from which the identity (private key) for |
fa08c86b | 555 | RSA or DSA authentication is read. |
cf5a07a8 | 556 | The default is |
1d1ffb87 | 557 | .Pa $HOME/.ssh/identity |
cf5a07a8 | 558 | for protocol version 1, and |
559 | .Pa $HOME/.ssh/id_rsa | |
560 | and | |
561 | .Pa $HOME/.ssh/id_dsa | |
562 | for protocol version 2. | |
610cd5c6 | 563 | Identity files may also be specified on |
564 | a per-host basis in the configuration file. | |
565 | It is possible to have multiple | |
bf740959 | 566 | .Fl i |
567 | options (and multiple identities specified in | |
568 | configuration files). | |
bf740959 | 569 | .It Fl k |
f7926e97 | 570 | Disables forwarding (delegation) of GSSAPI credentials to the server. |
5f4a0c58 | 571 | .It Fl L Xo |
572 | .Sm off | |
573 | .Ar port : host : hostport | |
574 | .Sm on | |
575 | .Xc | |
576 | Specifies that the given port on the local (client) host is to be | |
577 | forwarded to the given host and port on the remote side. | |
578 | This works by allocating a socket to listen to | |
579 | .Ar port | |
580 | on the local side, and whenever a connection is made to this port, the | |
581 | connection is forwarded over the secure channel, and a connection is | |
582 | made to | |
583 | .Ar host | |
584 | port | |
585 | .Ar hostport | |
586 | from the remote machine. | |
587 | Port forwardings can also be specified in the configuration file. | |
588 | Only root can forward privileged ports. | |
589 | IPv6 addresses can be specified with an alternative syntax: | |
590 | .Sm off | |
591 | .Xo | |
592 | .Ar port No / Ar host No / | |
593 | .Ar hostport . | |
594 | .Xc | |
595 | .Sm on | |
bf740959 | 596 | .It Fl l Ar login_name |
610cd5c6 | 597 | Specifies the user to log in as on the remote machine. |
598 | This also may be specified on a per-host basis in the configuration file. | |
5e96b616 | 599 | .It Fl M |
600 | Places the | |
601 | .Nm | |
602 | client into | |
603 | .Dq master | |
604 | mode for connection sharing. | |
605 | Refer to the description of | |
606 | .Cm ControlMaster | |
607 | in | |
608 | .Xr ssh_config 5 | |
609 | for details. | |
9affc5db | 610 | .It Fl m Ar mac_spec |
611 | Additionally, for protocol version 2 a comma-separated list of MAC | |
612 | (message authentication code) algorithms can | |
613 | be specified in order of preference. | |
614 | See the | |
615 | .Cm MACs | |
616 | keyword for more information. | |
5f4a0c58 | 617 | .It Fl N |
618 | Do not execute a remote command. | |
619 | This is useful for just forwarding ports | |
620 | (protocol version 2 only). | |
bf740959 | 621 | .It Fl n |
622 | Redirects stdin from | |
623 | .Pa /dev/null | |
624 | (actually, prevents reading from stdin). | |
625 | This must be used when | |
626 | .Nm | |
610cd5c6 | 627 | is run in the background. |
628 | A common trick is to use this to run X11 programs on a remote machine. | |
629 | For example, | |
bf740959 | 630 | .Ic ssh -n shadows.cs.hut.fi emacs & |
631 | will start an emacs on shadows.cs.hut.fi, and the X11 | |
632 | connection will be automatically forwarded over an encrypted channel. | |
633 | The | |
634 | .Nm | |
635 | program will be put in the background. | |
636 | (This does not work if | |
637 | .Nm | |
638 | needs to ask for a password or passphrase; see also the | |
639 | .Fl f | |
640 | option.) | |
cf848a5e | 641 | .It Fl O Ar ctl_cmd |
642 | Control an active connection multiplexing master process. | |
643 | When the | |
644 | .Fl O | |
645 | option is specified, the | |
646 | .Ar ctl_cmd | |
647 | argument is interpreted and passed to the master process. | |
648 | Valid commands are: | |
649 | .Dq check | |
650 | (check that the master process is running) and | |
651 | .Dq exit | |
652 | (request the master to exit). | |
bf740959 | 653 | .It Fl o Ar option |
38539909 | 654 | Can be used to give options in the format used in the configuration file. |
bf740959 | 655 | This is useful for specifying options for which there is no separate |
610cd5c6 | 656 | command-line flag. |
5f4a0c58 | 657 | For full details of the options listed below, and their possible values, see |
658 | .Xr ssh_config 5 . | |
659 | .Pp | |
660 | .Bl -tag -width Ds -offset indent -compact | |
661 | .It AddressFamily | |
662 | .It BatchMode | |
663 | .It BindAddress | |
664 | .It ChallengeResponseAuthentication | |
665 | .It CheckHostIP | |
666 | .It Cipher | |
667 | .It Ciphers | |
668 | .It ClearAllForwardings | |
669 | .It Compression | |
670 | .It CompressionLevel | |
671 | .It ConnectionAttempts | |
20b267fb | 672 | .It ConnectTimeout |
5e96b616 | 673 | .It ControlMaster |
674 | .It ControlPath | |
5f4a0c58 | 675 | .It DynamicForward |
5f4a0c58 | 676 | .It EscapeChar |
677 | .It ForwardAgent | |
678 | .It ForwardX11 | |
d73a67d7 | 679 | .It ForwardX11Trusted |
5f4a0c58 | 680 | .It GatewayPorts |
681 | .It GlobalKnownHostsFile | |
682 | .It GSSAPIAuthentication | |
683 | .It GSSAPIDelegateCredentials | |
684 | .It Host | |
685 | .It HostbasedAuthentication | |
686 | .It HostKeyAlgorithms | |
687 | .It HostKeyAlias | |
688 | .It HostName | |
689 | .It IdentityFile | |
3a065ed0 | 690 | .It IdentitiesOnly |
396070f8 | 691 | .It KbdInteractiveDevices |
5f4a0c58 | 692 | .It LocalForward |
693 | .It LogLevel | |
694 | .It MACs | |
695 | .It NoHostAuthenticationForLocalhost | |
696 | .It NumberOfPasswordPrompts | |
697 | .It PasswordAuthentication | |
698 | .It Port | |
699 | .It PreferredAuthentications | |
700 | .It Protocol | |
701 | .It ProxyCommand | |
702 | .It PubkeyAuthentication | |
703 | .It RemoteForward | |
704 | .It RhostsRSAAuthentication | |
705 | .It RSAAuthentication | |
8e99a198 | 706 | .It SendEnv |
5d8d32a3 | 707 | .It ServerAliveInterval |
708 | .It ServerAliveCountMax | |
5f4a0c58 | 709 | .It SmartcardDevice |
710 | .It StrictHostKeyChecking | |
fd573618 | 711 | .It TCPKeepAlive |
5f4a0c58 | 712 | .It UsePrivilegedPort |
713 | .It User | |
714 | .It UserKnownHostsFile | |
715 | .It VerifyHostKeyDNS | |
716 | .It XAuthLocation | |
717 | .El | |
bf740959 | 718 | .It Fl p Ar port |
610cd5c6 | 719 | Port to connect to on the remote host. |
720 | This can be specified on a | |
bf740959 | 721 | per-host basis in the configuration file. |
bf740959 | 722 | .It Fl q |
610cd5c6 | 723 | Quiet mode. |
724 | Causes all warning and diagnostic messages to be suppressed. | |
5f4a0c58 | 725 | .It Fl R Xo |
726 | .Sm off | |
727 | .Ar port : host : hostport | |
728 | .Sm on | |
729 | .Xc | |
730 | Specifies that the given port on the remote (server) host is to be | |
731 | forwarded to the given host and port on the local side. | |
732 | This works by allocating a socket to listen to | |
733 | .Ar port | |
734 | on the remote side, and whenever a connection is made to this port, the | |
735 | connection is forwarded over the secure channel, and a connection is | |
736 | made to | |
737 | .Ar host | |
738 | port | |
739 | .Ar hostport | |
740 | from the local machine. | |
741 | Port forwardings can also be specified in the configuration file. | |
742 | Privileged ports can be forwarded only when | |
743 | logging in as root on the remote machine. | |
744 | IPv6 addresses can be specified with an alternative syntax: | |
745 | .Sm off | |
746 | .Xo | |
747 | .Ar port No / Ar host No / | |
748 | .Ar hostport . | |
749 | .Xc | |
750 | .Sm on | |
f8c6db83 | 751 | .It Fl S Ar ctl_path |
9affc5db | 752 | Specifies the location of a control socket for connection sharing. |
5e96b616 | 753 | Refer to the description of |
0e19494c | 754 | .Cm ControlPath |
755 | and | |
5e96b616 | 756 | .Cm ControlMaster |
757 | in | |
758 | .Xr ssh_config 5 | |
759 | for details. | |
ae810de7 | 760 | .It Fl s |
3cbc677d | 761 | May be used to request invocation of a subsystem on the remote system. |
762 | Subsystems are a feature of the SSH2 protocol which facilitate the use | |
5f4a0c58 | 763 | of SSH as a secure transport for other applications (eg.\& |
764 | .Xr sftp 1 ) . | |
3cbc677d | 765 | The subsystem is specified as the remote command. |
5f4a0c58 | 766 | .It Fl T |
767 | Disable pseudo-tty allocation. | |
bf740959 | 768 | .It Fl t |
610cd5c6 | 769 | Force pseudo-tty allocation. |
4fe2af09 | 770 | This can be used to execute arbitrary |
610cd5c6 | 771 | screen-based programs on a remote machine, which can be very useful, |
772 | e.g., when implementing menu services. | |
8abcdba4 | 773 | Multiple |
774 | .Fl t | |
775 | options force tty allocation, even if | |
776 | .Nm | |
777 | has no local tty. | |
5f4a0c58 | 778 | .It Fl V |
779 | Display the version number and exit. | |
bf740959 | 780 | .It Fl v |
610cd5c6 | 781 | Verbose mode. |
782 | Causes | |
bf740959 | 783 | .Nm |
610cd5c6 | 784 | to print debugging messages about its progress. |
785 | This is helpful in | |
bf740959 | 786 | debugging connection, authentication, and configuration problems. |
8abcdba4 | 787 | Multiple |
788 | .Fl v | |
c825cd79 | 789 | options increase the verbosity. |
790 | The maximum is 3. | |
bf740959 | 791 | .It Fl X |
792 | Enables X11 forwarding. | |
71276795 | 793 | This can also be specified on a per-host basis in a configuration file. |
07d688d5 | 794 | .Pp |
a4e5acef | 795 | X11 forwarding should be enabled with caution. |
796 | Users with the ability to bypass file permissions on the remote host | |
797 | (for the user's X authorization database) | |
798 | can access the local X11 display through the forwarded connection. | |
799 | An attacker may then be able to perform activities such as keystroke monitoring. | |
5f4a0c58 | 800 | .It Fl x |
801 | Disables X11 forwarding. | |
d73a67d7 | 802 | .It Fl Y |
803 | Enables trusted X11 forwarding. | |
bf740959 | 804 | .El |
805 | .Sh CONFIGURATION FILES | |
806 | .Nm | |
588df31a | 807 | may additionally obtain configuration data from |
808 | a per-user configuration file and a system-wide configuration file. | |
809 | The file format and configuration options are described in | |
810 | .Xr ssh_config 5 . | |
bf740959 | 811 | .Sh ENVIRONMENT |
812 | .Nm | |
813 | will normally set the following environment variables: | |
5f4a0c58 | 814 | .Bl -tag -width LOGNAME |
bf740959 | 815 | .It Ev DISPLAY |
816 | The | |
817 | .Ev DISPLAY | |
610cd5c6 | 818 | variable indicates the location of the X11 server. |
f54651ce | 819 | It is automatically set by |
bf740959 | 820 | .Nm |
821 | to point to a value of the form | |
822 | .Dq hostname:n | |
823 | where hostname indicates | |
5f4a0c58 | 824 | the host where the shell runs, and n is an integer \*(Ge 1. |
610cd5c6 | 825 | .Nm |
826 | uses this special value to forward X11 connections over the secure | |
827 | channel. | |
da89cf4d | 828 | The user should normally not set |
829 | .Ev DISPLAY | |
830 | explicitly, as that | |
bf740959 | 831 | will render the X11 connection insecure (and will require the user to |
832 | manually copy any required authorization cookies). | |
833 | .It Ev HOME | |
834 | Set to the path of the user's home directory. | |
835 | .It Ev LOGNAME | |
836 | Synonym for | |
837 | .Ev USER ; | |
838 | set for compatibility with systems that use this variable. | |
839 | .It Ev MAIL | |
ae897d7c | 840 | Set to the path of the user's mailbox. |
610cd5c6 | 841 | .It Ev PATH |
bf740959 | 842 | Set to the default |
843 | .Ev PATH , | |
844 | as specified when compiling | |
845 | .Nm ssh . | |
3474b2b4 | 846 | .It Ev SSH_ASKPASS |
847 | If | |
848 | .Nm | |
849 | needs a passphrase, it will read the passphrase from the current | |
850 | terminal if it was run from a terminal. | |
851 | If | |
852 | .Nm | |
853 | does not have a terminal associated with it but | |
854 | .Ev DISPLAY | |
855 | and | |
856 | .Ev SSH_ASKPASS | |
857 | are set, it will execute the program specified by | |
858 | .Ev SSH_ASKPASS | |
859 | and open an X11 window to read the passphrase. | |
860 | This is particularly useful when calling | |
861 | .Nm | |
862 | from a | |
caeffafb | 863 | .Pa .xsession |
3474b2b4 | 864 | or related script. |
865 | (Note that on some machines it | |
866 | may be necessary to redirect the input from | |
867 | .Pa /dev/null | |
868 | to make this work.) | |
bf740959 | 869 | .It Ev SSH_AUTH_SOCK |
ae897d7c | 870 | Identifies the path of a unix-domain socket used to communicate with the |
bf740959 | 871 | agent. |
da0561eb | 872 | .It Ev SSH_CONNECTION |
873 | Identifies the client and server ends of the connection. | |
610cd5c6 | 874 | The variable contains |
da0561eb | 875 | four space-separated values: client ip-address, client port number, |
876 | server ip-address and server port number. | |
8abcdba4 | 877 | .It Ev SSH_ORIGINAL_COMMAND |
878 | The variable contains the original command line if a forced command | |
879 | is executed. | |
880 | It can be used to extract the original arguments. | |
bf740959 | 881 | .It Ev SSH_TTY |
882 | This is set to the name of the tty (path to the device) associated | |
610cd5c6 | 883 | with the current shell or command. |
884 | If the current session has no tty, | |
bf740959 | 885 | this variable is not set. |
886 | .It Ev TZ | |
887 | The timezone variable is set to indicate the present timezone if it | |
c345cf9d | 888 | was set when the daemon was started (i.e., the daemon passes the value |
bf740959 | 889 | on to new connections). |
890 | .It Ev USER | |
891 | Set to the name of the user logging in. | |
892 | .El | |
893 | .Pp | |
f54651ce | 894 | Additionally, |
bf740959 | 895 | .Nm |
f54651ce | 896 | reads |
897 | .Pa $HOME/.ssh/environment , | |
bf740959 | 898 | and adds lines of the format |
899 | .Dq VARNAME=value | |
6a342527 | 900 | to the environment if the file exists and if users are allowed to |
901 | change their environment. | |
5f4a0c58 | 902 | For more information, see the |
6a342527 | 903 | .Cm PermitUserEnvironment |
35453849 | 904 | option in |
6a342527 | 905 | .Xr sshd_config 5 . |
bf740959 | 906 | .Sh FILES |
c8d54615 | 907 | .Bl -tag -width Ds |
f49bc4f7 | 908 | .It Pa $HOME/.ssh/known_hosts |
ae897d7c | 909 | Records host keys for all hosts the user has logged into that are not |
bf740959 | 910 | in |
2a8a6488 | 911 | .Pa /etc/ssh/ssh_known_hosts . |
bf740959 | 912 | See |
913 | .Xr sshd 8 . | |
c0ecc314 | 914 | .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa |
915 | Contains the authentication identity of the user. | |
916 | They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. | |
1d1ffb87 | 917 | These files |
918 | contain sensitive data and should be readable by the user but not | |
bf740959 | 919 | accessible by others (read/write/execute). |
920 | Note that | |
921 | .Nm | |
1d1ffb87 | 922 | ignores a private key file if it is accessible by others. |
bf740959 | 923 | It is possible to specify a passphrase when |
924 | generating the key; the passphrase will be used to encrypt the | |
925 | sensitive part of this file using 3DES. | |
c0ecc314 | 926 | .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub |
bf740959 | 927 | Contains the public key for authentication (public part of the |
610cd5c6 | 928 | identity file in human-readable form). |
1d1ffb87 | 929 | The contents of the |
930 | .Pa $HOME/.ssh/identity.pub | |
5f4a0c58 | 931 | file should be added to the file |
bf740959 | 932 | .Pa $HOME/.ssh/authorized_keys |
933 | on all machines | |
91789042 | 934 | where the user wishes to log in using protocol version 1 RSA authentication. |
1d1ffb87 | 935 | The contents of the |
936 | .Pa $HOME/.ssh/id_dsa.pub | |
c0ecc314 | 937 | and |
938 | .Pa $HOME/.ssh/id_rsa.pub | |
1d1ffb87 | 939 | file should be added to |
96a7b0cc | 940 | .Pa $HOME/.ssh/authorized_keys |
1d1ffb87 | 941 | on all machines |
91789042 | 942 | where the user wishes to log in using protocol version 2 DSA/RSA authentication. |
1d1ffb87 | 943 | These files are not |
610cd5c6 | 944 | sensitive and can (but need not) be readable by anyone. |
1d1ffb87 | 945 | These files are |
c44559d2 | 946 | never used automatically and are not necessary; they are only provided for |
bf740959 | 947 | the convenience of the user. |
948 | .It Pa $HOME/.ssh/config | |
610cd5c6 | 949 | This is the per-user configuration file. |
588df31a | 950 | The file format and configuration options are described in |
951 | .Xr ssh_config 5 . | |
e1520719 | 952 | Because of the potential for abuse, this file must have strict permissions: |
953 | read/write for the user, and not accessible by others. | |
bf740959 | 954 | .It Pa $HOME/.ssh/authorized_keys |
96a7b0cc | 955 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. |
610cd5c6 | 956 | The format of this file is described in the |
bf740959 | 957 | .Xr sshd 8 |
610cd5c6 | 958 | manual page. |
5f4a0c58 | 959 | In the simplest form the format is the same as the |
960 | .Pa .pub | |
f49bc4f7 | 961 | identity files. |
1d1ffb87 | 962 | This file is not highly sensitive, but the recommended |
963 | permissions are read/write for the user, and not accessible by others. | |
2a8a6488 | 964 | .It Pa /etc/ssh/ssh_known_hosts |
610cd5c6 | 965 | Systemwide list of known host keys. |
f49bc4f7 | 966 | This file should be prepared by the |
bf740959 | 967 | system administrator to contain the public host keys of all machines in the |
610cd5c6 | 968 | organization. |
969 | This file should be world-readable. | |
970 | This file contains | |
bf740959 | 971 | public keys, one per line, in the following format (fields separated |
f49bc4f7 | 972 | by spaces): system name, public key and optional comment field. |
610cd5c6 | 973 | When different names are used |
bf740959 | 974 | for the same machine, all such names should be listed, separated by |
610cd5c6 | 975 | commas. |
5f4a0c58 | 976 | The format is described in the |
bf740959 | 977 | .Xr sshd 8 |
978 | manual page. | |
979 | .Pp | |
980 | The canonical system name (as returned by name servers) is used by | |
981 | .Xr sshd 8 | |
982 | to verify the client host when logging in; other names are needed because | |
983 | .Nm | |
984 | does not convert the user-supplied name to a canonical name before | |
985 | checking the key, because someone with access to the name servers | |
986 | would then be able to fool host authentication. | |
2a8a6488 | 987 | .It Pa /etc/ssh/ssh_config |
610cd5c6 | 988 | Systemwide configuration file. |
588df31a | 989 | The file format and configuration options are described in |
990 | .Xr ssh_config 5 . | |
2a8a6488 | 991 | .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key |
dd58cb5e | 992 | These three files contain the private parts of the host keys |
993 | and are used for | |
994 | .Cm RhostsRSAAuthentication | |
995 | and | |
996 | .Cm HostbasedAuthentication . | |
d83cbdc3 | 997 | If the protocol version 1 |
998 | .Cm RhostsRSAAuthentication | |
7203d6bb | 999 | method is used, |
d83cbdc3 | 1000 | .Nm |
1001 | must be setuid root, since the host key is readable only by root. | |
1002 | For protocol version 2, | |
1003 | .Nm | |
1004 | uses | |
1005 | .Xr ssh-keysign 8 | |
1006 | to access the host keys for | |
1007 | .Cm HostbasedAuthentication . | |
1008 | This eliminates the requirement that | |
1009 | .Nm | |
1010 | be setuid root when that authentication method is used. | |
1011 | By default | |
dd58cb5e | 1012 | .Nm |
d83cbdc3 | 1013 | is not setuid root. |
bf740959 | 1014 | .It Pa $HOME/.rhosts |
1015 | This file is used in | |
6f5abc1e | 1016 | .Cm RhostsRSAAuthentication |
1017 | and | |
1018 | .Cm HostbasedAuthentication | |
bf740959 | 1019 | authentication to list the |
610cd5c6 | 1020 | host/user pairs that are permitted to log in. |
1021 | (Note that this file is | |
bf740959 | 1022 | also used by rlogin and rsh, which makes using this file insecure.) |
1023 | Each line of the file contains a host name (in the canonical form | |
1024 | returned by name servers), and then a user name on that host, | |
610cd5c6 | 1025 | separated by a space. |
e91c60f2 | 1026 | On some machines this file may need to be |
bf740959 | 1027 | world-readable if the user's home directory is on a NFS partition, |
1028 | because | |
1029 | .Xr sshd 8 | |
610cd5c6 | 1030 | reads it as root. |
1031 | Additionally, this file must be owned by the user, | |
1032 | and must not have write permissions for anyone else. | |
1033 | The recommended | |
bf740959 | 1034 | permission for most machines is read/write for the user, and not |
1035 | accessible by others. | |
1036 | .Pp | |
6f5abc1e | 1037 | Note that |
bf740959 | 1038 | .Xr sshd 8 |
6f5abc1e | 1039 | allows authentication only in combination with client host key |
1040 | authentication before permitting log in. | |
91789042 | 1041 | If the server machine does not have the client's host key in |
2a8a6488 | 1042 | .Pa /etc/ssh/ssh_known_hosts , |
91789042 | 1043 | it can be stored in |
bf740959 | 1044 | .Pa $HOME/.ssh/known_hosts . |
1045 | The easiest way to do this is to | |
1046 | connect back to the client from the server machine using ssh; this | |
1d1ffb87 | 1047 | will automatically add the host key to |
bf740959 | 1048 | .Pa $HOME/.ssh/known_hosts . |
1049 | .It Pa $HOME/.shosts | |
1050 | This file is used exactly the same way as | |
5f4a0c58 | 1051 | .Pa .rhosts . |
bf740959 | 1052 | The purpose for |
6f5abc1e | 1053 | having this file is to be able to use |
1054 | .Cm RhostsRSAAuthentication | |
1055 | and | |
1056 | .Cm HostbasedAuthentication | |
1057 | authentication without permitting login with | |
5f4a0c58 | 1058 | .Xr rlogin |
bf740959 | 1059 | or |
1060 | .Xr rsh 1 . | |
1061 | .It Pa /etc/hosts.equiv | |
1062 | This file is used during | |
6f5abc1e | 1063 | .Cm RhostsRSAAuthentication |
1064 | and | |
1065 | .Cm HostbasedAuthentication | |
be193d89 | 1066 | authentication. |
610cd5c6 | 1067 | It contains |
5f4a0c58 | 1068 | canonical hosts names, one per line (the full format is described in the |
bf740959 | 1069 | .Xr sshd 8 |
610cd5c6 | 1070 | manual page). |
1071 | If the client host is found in this file, login is | |
bf740959 | 1072 | automatically permitted provided client and server user names are the |
610cd5c6 | 1073 | same. |
6f5abc1e | 1074 | Additionally, successful client host key authentication is required. |
610cd5c6 | 1075 | This file should only be writable by root. |
5f4fdfae | 1076 | .It Pa /etc/shosts.equiv |
f54651ce | 1077 | This file is processed exactly as |
bf740959 | 1078 | .Pa /etc/hosts.equiv . |
1079 | This file may be useful to permit logins using | |
1080 | .Nm | |
1081 | but not using rsh/rlogin. | |
2a8a6488 | 1082 | .It Pa /etc/ssh/sshrc |
bf740959 | 1083 | Commands in this file are executed by |
1084 | .Nm | |
1085 | when the user logs in just before the user's shell (or command) is started. | |
1086 | See the | |
1087 | .Xr sshd 8 | |
1088 | manual page for more information. | |
1089 | .It Pa $HOME/.ssh/rc | |
1090 | Commands in this file are executed by | |
1091 | .Nm | |
1092 | when the user logs in just before the user's shell (or command) is | |
1093 | started. | |
f54651ce | 1094 | See the |
bf740959 | 1095 | .Xr sshd 8 |
1096 | manual page for more information. | |
83b7f649 | 1097 | .It Pa $HOME/.ssh/environment |
1098 | Contains additional definitions for environment variables, see section | |
1099 | .Sx ENVIRONMENT | |
1100 | above. | |
b5e300c2 | 1101 | .El |
16210ef7 | 1102 | .Sh DIAGNOSTICS |
1103 | .Nm | |
1104 | exits with the exit status of the remote command or with 255 | |
1105 | if an error occurred. | |
bf740959 | 1106 | .Sh SEE ALSO |
5f4a0c58 | 1107 | .Xr gzip 1 , |
bf740959 | 1108 | .Xr rsh 1 , |
1109 | .Xr scp 1 , | |
61e96248 | 1110 | .Xr sftp 1 , |
bf740959 | 1111 | .Xr ssh-add 1 , |
1112 | .Xr ssh-agent 1 , | |
1113 | .Xr ssh-keygen 1 , | |
1114 | .Xr telnet 1 , | |
5f4a0c58 | 1115 | .Xr hosts.equiv 5 , |
1ae02182 | 1116 | .Xr ssh_config 5 , |
b2843ec6 | 1117 | .Xr ssh-keysign 8 , |
9afadca8 | 1118 | .Xr sshd 8 |
2cad6cef | 1119 | .Rs |
1120 | .%A T. Ylonen | |
1121 | .%A T. Kivinen | |
1122 | .%A M. Saarinen | |
1123 | .%A T. Rinne | |
1124 | .%A S. Lehtinen | |
1125 | .%T "SSH Protocol Architecture" | |
17f5e68a | 1126 | .%N draft-ietf-secsh-architecture-12.txt |
1127 | .%D January 2002 | |
2cad6cef | 1128 | .%O work in progress material |
1129 | .Re | |
be193d89 | 1130 | .Sh AUTHORS |
1131 | OpenSSH is a derivative of the original and free | |
1132 | ssh 1.2.12 release by Tatu Ylonen. | |
1133 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1134 | Theo de Raadt and Dug Song | |
1135 | removed many bugs, re-added newer features and | |
1136 | created OpenSSH. | |
1137 | Markus Friedl contributed the support for SSH | |
1138 | protocol versions 1.5 and 2.0. |