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3c0ef626 | 1 | .\" -*- nroff -*- |
2 | .\" | |
3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> | |
4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland | |
5 | .\" All rights reserved | |
6 | .\" | |
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 | .\" | |
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. | |
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. | |
25 | .\" | |
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. | |
36 | .\" | |
08822d99 | 37 | .\" $OpenBSD: sshd.8,v 1.215 2006/02/01 09:11:41 jmc Exp $ |
3c0ef626 | 38 | .Dd September 25, 1999 |
39 | .Dt SSHD 8 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm sshd | |
43 | .Nd OpenSSH SSH daemon | |
44 | .Sh SYNOPSIS | |
45 | .Nm sshd | |
bfe49944 | 46 | .Bk -words |
540d72c3 | 47 | .Op Fl 46Ddeiqt |
3c0ef626 | 48 | .Op Fl b Ar bits |
49 | .Op Fl f Ar config_file | |
50 | .Op Fl g Ar login_grace_time | |
51 | .Op Fl h Ar host_key_file | |
52 | .Op Fl k Ar key_gen_time | |
e9702f7d | 53 | .Op Fl o Ar option |
3c0ef626 | 54 | .Op Fl p Ar port |
55 | .Op Fl u Ar len | |
bfe49944 | 56 | .Ek |
3c0ef626 | 57 | .Sh DESCRIPTION |
58 | .Nm | |
08822d99 | 59 | (OpenSSH Daemon) is the daemon program for |
3c0ef626 | 60 | .Xr ssh 1 . |
61 | Together these programs replace rlogin and rsh, and | |
62 | provide secure encrypted communications between two untrusted hosts | |
63 | over an insecure network. | |
3c0ef626 | 64 | .Pp |
65 | .Nm | |
08822d99 | 66 | listens for connections from clients. |
3c0ef626 | 67 | It is normally started at boot from |
68 | .Pa /etc/rc . | |
69 | It forks a new | |
70 | daemon for each incoming connection. | |
71 | The forked daemons handle | |
72 | key exchange, encryption, authentication, command execution, | |
73 | and data exchange. | |
3c0ef626 | 74 | .Pp |
75 | .Nm | |
540d72c3 | 76 | can be configured using command-line options or a configuration file |
77 | (by default | |
08822d99 | 78 | .Xr sshd_config 5 ) ; |
79 | command-line options override values specified in the | |
3c0ef626 | 80 | configuration file. |
3c0ef626 | 81 | .Nm |
82 | rereads its configuration file when it receives a hangup signal, | |
83 | .Dv SIGHUP , | |
7e82606e | 84 | by executing itself with the name and options it was started with, e.g., |
3c0ef626 | 85 | .Pa /usr/sbin/sshd . |
86 | .Pp | |
87 | The options are as follows: | |
88 | .Bl -tag -width Ds | |
540d72c3 | 89 | .It Fl 4 |
90 | Forces | |
91 | .Nm | |
92 | to use IPv4 addresses only. | |
93 | .It Fl 6 | |
94 | Forces | |
95 | .Nm | |
96 | to use IPv6 addresses only. | |
3c0ef626 | 97 | .It Fl b Ar bits |
98 | Specifies the number of bits in the ephemeral protocol version 1 | |
99 | server key (default 768). | |
540d72c3 | 100 | .It Fl D |
101 | When this option is specified, | |
102 | .Nm | |
103 | will not detach and does not become a daemon. | |
104 | This allows easy monitoring of | |
105 | .Nm sshd . | |
3c0ef626 | 106 | .It Fl d |
107 | Debug mode. | |
108 | The server sends verbose debug output to the system | |
109 | log, and does not put itself in the background. | |
110 | The server also will not fork and will only process one connection. | |
111 | This option is only intended for debugging for the server. | |
bfe49944 | 112 | Multiple |
113 | .Fl d | |
114 | options increase the debugging level. | |
3c0ef626 | 115 | Maximum is 3. |
116 | .It Fl e | |
117 | When this option is specified, | |
118 | .Nm | |
119 | will send the output to the standard error instead of the system log. | |
120 | .It Fl f Ar configuration_file | |
121 | Specifies the name of the configuration file. | |
122 | The default is | |
e9702f7d | 123 | .Pa /etc/ssh/sshd_config . |
3c0ef626 | 124 | .Nm |
125 | refuses to start if there is no configuration file. | |
126 | .It Fl g Ar login_grace_time | |
127 | Gives the grace time for clients to authenticate themselves (default | |
d03f4262 | 128 | 120 seconds). |
3c0ef626 | 129 | If the client fails to authenticate the user within |
130 | this many seconds, the server disconnects and exits. | |
131 | A value of zero indicates no limit. | |
132 | .It Fl h Ar host_key_file | |
e9702f7d | 133 | Specifies a file from which a host key is read. |
3c0ef626 | 134 | This option must be given if |
135 | .Nm | |
136 | is not run as root (as the normal | |
e9702f7d | 137 | host key files are normally not readable by anyone but root). |
138 | The default is | |
139 | .Pa /etc/ssh/ssh_host_key | |
140 | for protocol version 1, and | |
141 | .Pa /etc/ssh/ssh_host_rsa_key | |
142 | and | |
143 | .Pa /etc/ssh/ssh_host_dsa_key | |
144 | for protocol version 2. | |
3c0ef626 | 145 | It is possible to have multiple host key files for |
146 | the different protocol versions and host key algorithms. | |
147 | .It Fl i | |
148 | Specifies that | |
149 | .Nm | |
bfe49944 | 150 | is being run from |
151 | .Xr inetd 8 . | |
3c0ef626 | 152 | .Nm |
153 | is normally not run | |
154 | from inetd because it needs to generate the server key before it can | |
155 | respond to the client, and this may take tens of seconds. | |
156 | Clients would have to wait too long if the key was regenerated every time. | |
157 | However, with small key sizes (e.g., 512) using | |
158 | .Nm | |
159 | from inetd may | |
160 | be feasible. | |
161 | .It Fl k Ar key_gen_time | |
162 | Specifies how often the ephemeral protocol version 1 server key is | |
163 | regenerated (default 3600 seconds, or one hour). | |
164 | The motivation for regenerating the key fairly | |
540d72c3 | 165 | often is that the key is not stored anywhere, and after about an hour |
3c0ef626 | 166 | it becomes impossible to recover the key for decrypting intercepted |
167 | communications even if the machine is cracked into or physically | |
168 | seized. | |
169 | A value of zero indicates that the key will never be regenerated. | |
e9702f7d | 170 | .It Fl o Ar option |
171 | Can be used to give options in the format used in the configuration file. | |
172 | This is useful for specifying options for which there is no separate | |
173 | command-line flag. | |
540d72c3 | 174 | For full details of the options, and their values, see |
175 | .Xr sshd_config 5 . | |
3c0ef626 | 176 | .It Fl p Ar port |
177 | Specifies the port on which the server listens for connections | |
178 | (default 22). | |
e9702f7d | 179 | Multiple port options are permitted. |
08822d99 | 180 | Ports specified in the configuration file with the |
181 | .Cm Port | |
182 | option are ignored when a command-line port is specified. | |
183 | Ports specified using the | |
184 | .Cm ListenAddress | |
185 | option override command-line ports. | |
3c0ef626 | 186 | .It Fl q |
187 | Quiet mode. | |
188 | Nothing is sent to the system log. | |
189 | Normally the beginning, | |
190 | authentication, and termination of each connection is logged. | |
191 | .It Fl t | |
192 | Test mode. | |
193 | Only check the validity of the configuration file and sanity of the keys. | |
e9702f7d | 194 | This is useful for updating |
3c0ef626 | 195 | .Nm |
196 | reliably as configuration options may change. | |
197 | .It Fl u Ar len | |
198 | This option is used to specify the size of the field | |
199 | in the | |
200 | .Li utmp | |
201 | structure that holds the remote host name. | |
202 | If the resolved host name is longer than | |
203 | .Ar len , | |
204 | the dotted decimal value will be used instead. | |
205 | This allows hosts with very long host names that | |
206 | overflow this field to still be uniquely identified. | |
207 | Specifying | |
208 | .Fl u0 | |
209 | indicates that only dotted decimal addresses | |
210 | should be put into the | |
211 | .Pa utmp | |
212 | file. | |
213 | .Fl u0 | |
bfe49944 | 214 | may also be used to prevent |
3c0ef626 | 215 | .Nm |
216 | from making DNS requests unless the authentication | |
217 | mechanism or configuration requires it. | |
218 | Authentication mechanisms that may require DNS include | |
3c0ef626 | 219 | .Cm RhostsRSAAuthentication , |
08822d99 | 220 | .Cm HostbasedAuthentication , |
3c0ef626 | 221 | and using a |
222 | .Cm from="pattern-list" | |
223 | option in a key file. | |
e9702f7d | 224 | Configuration options that require DNS include using a |
225 | USER@HOST pattern in | |
226 | .Cm AllowUsers | |
227 | or | |
228 | .Cm DenyUsers . | |
3c0ef626 | 229 | .El |
08822d99 | 230 | .Sh AUTHENTICATION |
231 | The OpenSSH SSH daemon supports SSH protocols 1 and 2. | |
232 | Both protocols are supported by default, | |
233 | though this can be changed via the | |
234 | .Cm Protocol | |
235 | option in | |
44a053a3 | 236 | .Xr sshd_config 5 . |
08822d99 | 237 | Protocol 2 supports both RSA and DSA keys; |
238 | protocol 1 only supports RSA keys. | |
239 | For both protocols, | |
240 | each host has a host-specific key, | |
241 | normally 2048 bits, | |
242 | used to identify the host. | |
243 | .Pp | |
244 | Forward security for protocol 1 is provided through | |
245 | an additional server key, | |
246 | normally 768 bits, | |
247 | generated when the server starts. | |
248 | This key is normally regenerated every hour if it has been used, and | |
249 | is never stored on disk. | |
250 | Whenever a client connects, the daemon responds with its public | |
251 | host and server keys. | |
252 | The client compares the | |
253 | RSA host key against its own database to verify that it has not changed. | |
254 | The client then generates a 256-bit random number. | |
255 | It encrypts this | |
256 | random number using both the host key and the server key, and sends | |
257 | the encrypted number to the server. | |
258 | Both sides then use this | |
259 | random number as a session key which is used to encrypt all further | |
260 | communications in the session. | |
261 | The rest of the session is encrypted | |
262 | using a conventional cipher, currently Blowfish or 3DES, with 3DES | |
263 | being used by default. | |
264 | The client selects the encryption algorithm | |
265 | to use from those offered by the server. | |
266 | .Pp | |
267 | For protocol 2, | |
268 | forward security is provided through a Diffie-Hellman key agreement. | |
269 | This key agreement results in a shared session key. | |
270 | The rest of the session is encrypted using a symmetric cipher, currently | |
271 | 128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES. | |
272 | The client selects the encryption algorithm | |
273 | to use from those offered by the server. | |
274 | Additionally, session integrity is provided | |
275 | through a cryptographic message authentication code | |
276 | (hmac-sha1 or hmac-md5). | |
277 | .Pp | |
278 | Finally, the server and the client enter an authentication dialog. | |
279 | The client tries to authenticate itself using | |
280 | host-based authentication, | |
281 | public key authentication, | |
282 | challenge-response authentication, | |
283 | or password authentication. | |
284 | .Pp | |
285 | Regardless of the authentication type, the account is checked to | |
286 | ensure that it is accessible. An account is not accessible if it is | |
287 | locked, listed in | |
288 | .Cm DenyUsers | |
289 | or its group is listed in | |
290 | .Cm DenyGroups | |
291 | \&. The definition of a locked account is system dependant. Some platforms | |
292 | have their own account database (eg AIX) and some modify the passwd field ( | |
293 | .Ql \&*LK\&* | |
294 | on Solaris and UnixWare, | |
295 | .Ql \&* | |
296 | on HP-UX, containing | |
297 | .Ql Nologin | |
298 | on Tru64, | |
299 | a leading | |
300 | .Ql \&*LOCKED\&* | |
301 | on FreeBSD and a leading | |
302 | .Ql \&!! | |
303 | on Linux). If there is a requirement to disable password authentication | |
304 | for the account while allowing still public-key, then the passwd field | |
305 | should be set to something other than these values (eg | |
306 | .Ql NP | |
307 | or | |
308 | .Ql \&*NP\&* | |
309 | ). | |
310 | .Pp | |
311 | System security is not improved unless | |
312 | .Nm rshd , | |
313 | .Nm rlogind , | |
314 | and | |
315 | .Nm rexecd | |
316 | are disabled (thus completely disabling | |
317 | .Xr rlogin | |
318 | and | |
319 | .Xr rsh | |
320 | into the machine). | |
321 | .Sh COMMAND EXECUTION AND DATA FORWARDING | |
322 | If the client successfully authenticates itself, a dialog for | |
323 | preparing the session is entered. | |
324 | At this time the client may request | |
325 | things like allocating a pseudo-tty, forwarding X11 connections, | |
326 | forwarding TCP connections, or forwarding the authentication agent | |
327 | connection over the secure channel. | |
328 | .Pp | |
329 | Finally, the client either requests a shell or execution of a command. | |
330 | The sides then enter session mode. | |
331 | In this mode, either side may send | |
332 | data at any time, and such data is forwarded to/from the shell or | |
333 | command on the server side, and the user terminal in the client side. | |
334 | .Pp | |
335 | When the user program terminates and all forwarded X11 and other | |
336 | connections have been closed, the server sends command exit status to | |
337 | the client, and both sides exit. | |
3c0ef626 | 338 | .Sh LOGIN PROCESS |
339 | When a user successfully logs in, | |
340 | .Nm | |
341 | does the following: | |
342 | .Bl -enum -offset indent | |
343 | .It | |
344 | If the login is on a tty, and no command has been specified, | |
345 | prints last login time and | |
346 | .Pa /etc/motd | |
347 | (unless prevented in the configuration file or by | |
2ce0bfe4 | 348 | .Pa ~/.hushlogin ; |
3c0ef626 | 349 | see the |
350 | .Sx FILES | |
351 | section). | |
352 | .It | |
353 | If the login is on a tty, records login time. | |
354 | .It | |
355 | Checks | |
356 | .Pa /etc/nologin ; | |
357 | if it exists, prints contents and quits | |
358 | (unless root). | |
359 | .It | |
360 | Changes to run with normal user privileges. | |
361 | .It | |
362 | Sets up basic environment. | |
363 | .It | |
540d72c3 | 364 | Reads the file |
2ce0bfe4 | 365 | .Pa ~/.ssh/environment , |
540d72c3 | 366 | if it exists, and users are allowed to change their environment. |
d03f4262 | 367 | See the |
368 | .Cm PermitUserEnvironment | |
369 | option in | |
370 | .Xr sshd_config 5 . | |
3c0ef626 | 371 | .It |
372 | Changes to user's home directory. | |
373 | .It | |
374 | If | |
2ce0bfe4 | 375 | .Pa ~/.ssh/rc |
3c0ef626 | 376 | exists, runs it; else if |
e9702f7d | 377 | .Pa /etc/ssh/sshrc |
3c0ef626 | 378 | exists, runs |
379 | it; otherwise runs xauth. | |
380 | The | |
381 | .Dq rc | |
382 | files are given the X11 | |
383 | authentication protocol and cookie in standard input. | |
384 | .It | |
385 | Runs user's shell or command. | |
386 | .El | |
387 | .Sh AUTHORIZED_KEYS FILE FORMAT | |
2ce0bfe4 | 388 | .Pa ~/.ssh/authorized_keys |
3c0ef626 | 389 | is the default file that lists the public keys that are |
390 | permitted for RSA authentication in protocol version 1 | |
391 | and for public key authentication (PubkeyAuthentication) | |
392 | in protocol version 2. | |
393 | .Cm AuthorizedKeysFile | |
394 | may be used to specify an alternative file. | |
395 | .Pp | |
396 | Each line of the file contains one | |
397 | key (empty lines and lines starting with a | |
398 | .Ql # | |
399 | are ignored as | |
400 | comments). | |
401 | Each RSA public key consists of the following fields, separated by | |
402 | spaces: options, bits, exponent, modulus, comment. | |
403 | Each protocol version 2 public key consists of: | |
404 | options, keytype, base64 encoded key, comment. | |
d03f4262 | 405 | The options field |
406 | is optional; its presence is determined by whether the line starts | |
407 | with a number or not (the options field never starts with a number). | |
3c0ef626 | 408 | The bits, exponent, modulus and comment fields give the RSA key for |
409 | protocol version 1; the | |
410 | comment field is not used for anything (but may be convenient for the | |
411 | user to identify the key). | |
412 | For protocol version 2 the keytype is | |
413 | .Dq ssh-dss | |
414 | or | |
415 | .Dq ssh-rsa . | |
416 | .Pp | |
417 | Note that lines in this file are usually several hundred bytes long | |
dfddba3d | 418 | (because of the size of the public key encoding) up to a limit of |
419 | 8 kilobytes, which permits DSA keys up to 8 kilobits and RSA | |
420 | keys up to 16 kilobits. | |
3c0ef626 | 421 | You don't want to type them in; instead, copy the |
422 | .Pa identity.pub , | |
423 | .Pa id_dsa.pub | |
424 | or the | |
425 | .Pa id_rsa.pub | |
426 | file and edit it. | |
427 | .Pp | |
350391c5 | 428 | .Nm |
429 | enforces a minimum RSA key modulus size for protocol 1 | |
430 | and protocol 2 keys of 768 bits. | |
431 | .Pp | |
3c0ef626 | 432 | The options (if present) consist of comma-separated option |
433 | specifications. | |
434 | No spaces are permitted, except within double quotes. | |
435 | The following option specifications are supported (note | |
436 | that option keywords are case-insensitive): | |
437 | .Bl -tag -width Ds | |
438 | .It Cm from="pattern-list" | |
d03f4262 | 439 | Specifies that in addition to public key authentication, the canonical name |
3c0ef626 | 440 | of the remote host must be present in the comma-separated list of |
441 | patterns | |
7cac2b65 | 442 | .Pf ( Ql \&* |
3c0ef626 | 443 | and |
7cac2b65 | 444 | .Ql \&? |
3c0ef626 | 445 | serve as wildcards). |
446 | The list may also contain | |
447 | patterns negated by prefixing them with | |
7cac2b65 | 448 | .Ql \&! ; |
3c0ef626 | 449 | if the canonical host name matches a negated pattern, the key is not accepted. |
450 | The purpose | |
d03f4262 | 451 | of this option is to optionally increase security: public key authentication |
3c0ef626 | 452 | by itself does not trust the network or name servers or anything (but |
453 | the key); however, if somebody somehow steals the key, the key | |
454 | permits an intruder to log in from anywhere in the world. | |
455 | This additional option makes using a stolen key more difficult (name | |
456 | servers and/or routers would have to be compromised in addition to | |
457 | just the key). | |
458 | .It Cm command="command" | |
459 | Specifies that the command is executed whenever this key is used for | |
460 | authentication. | |
461 | The command supplied by the user (if any) is ignored. | |
462 | The command is run on a pty if the client requests a pty; | |
463 | otherwise it is run without a tty. | |
bfe49944 | 464 | If an 8-bit clean channel is required, |
3c0ef626 | 465 | one must not request a pty or should specify |
466 | .Cm no-pty . | |
467 | A quote may be included in the command by quoting it with a backslash. | |
468 | This option might be useful | |
d03f4262 | 469 | to restrict certain public keys to perform just a specific operation. |
3c0ef626 | 470 | An example might be a key that permits remote backups but nothing else. |
08822d99 | 471 | Note that the client may specify TCP and/or X11 |
3c0ef626 | 472 | forwarding unless they are explicitly prohibited. |
473 | Note that this option applies to shell, command or subsystem execution. | |
474 | .It Cm environment="NAME=value" | |
475 | Specifies that the string is to be added to the environment when | |
476 | logging in using this key. | |
477 | Environment variables set this way | |
478 | override other default environment values. | |
479 | Multiple options of this type are permitted. | |
d03f4262 | 480 | Environment processing is disabled by default and is |
481 | controlled via the | |
482 | .Cm PermitUserEnvironment | |
483 | option. | |
3c0ef626 | 484 | This option is automatically disabled if |
485 | .Cm UseLogin | |
486 | is enabled. | |
487 | .It Cm no-port-forwarding | |
08822d99 | 488 | Forbids TCP forwarding when this key is used for authentication. |
3c0ef626 | 489 | Any port forward requests by the client will return an error. |
490 | This might be used, e.g., in connection with the | |
491 | .Cm command | |
492 | option. | |
493 | .It Cm no-X11-forwarding | |
494 | Forbids X11 forwarding when this key is used for authentication. | |
495 | Any X11 forward requests by the client will return an error. | |
496 | .It Cm no-agent-forwarding | |
497 | Forbids authentication agent forwarding when this key is used for | |
498 | authentication. | |
499 | .It Cm no-pty | |
500 | Prevents tty allocation (a request to allocate a pty will fail). | |
501 | .It Cm permitopen="host:port" | |
502 | Limit local | |
503 | .Li ``ssh -L'' | |
504 | port forwarding such that it may only connect to the specified host and | |
505 | port. | |
506 | IPv6 addresses can be specified with an alternative syntax: | |
540d72c3 | 507 | .Ar host Ns / Ns Ar port . |
3c0ef626 | 508 | Multiple |
509 | .Cm permitopen | |
7cac2b65 | 510 | options may be applied separated by commas. |
511 | No pattern matching is performed on the specified hostnames, | |
512 | they must be literal domains or addresses. | |
08822d99 | 513 | .It Cm tunnel="n" |
514 | Force a | |
515 | .Xr tun 4 | |
516 | device on the server. | |
517 | Without this option, the next available device will be used if | |
518 | the client requests a tunnel. | |
3c0ef626 | 519 | .El |
520 | .Ss Examples | |
540d72c3 | 521 | 1024 33 12121...312314325 ylo@foo.bar |
3c0ef626 | 522 | .Pp |
540d72c3 | 523 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23...2334 ylo@niksula |
3c0ef626 | 524 | .Pp |
540d72c3 | 525 | command="dump /home",no-pty,no-port-forwarding 1024 33 23...2323 backup.hut.fi |
3c0ef626 | 526 | .Pp |
540d72c3 | 527 | permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23...2323 |
08822d99 | 528 | .Pp |
529 | tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...== reyk@openbsd.org | |
3c0ef626 | 530 | .Sh SSH_KNOWN_HOSTS FILE FORMAT |
531 | The | |
bfe49944 | 532 | .Pa /etc/ssh/ssh_known_hosts |
3c0ef626 | 533 | and |
2ce0bfe4 | 534 | .Pa ~/.ssh/known_hosts |
3c0ef626 | 535 | files contain host public keys for all known hosts. |
536 | The global file should | |
537 | be prepared by the administrator (optional), and the per-user file is | |
538 | maintained automatically: whenever the user connects from an unknown host | |
539 | its key is added to the per-user file. | |
540 | .Pp | |
541 | Each line in these files contains the following fields: hostnames, | |
542 | bits, exponent, modulus, comment. | |
543 | The fields are separated by spaces. | |
544 | .Pp | |
7cac2b65 | 545 | Hostnames is a comma-separated list of patterns |
546 | .Pf ( Ql \&* | |
547 | and | |
548 | .Ql \&? | |
549 | act as | |
3c0ef626 | 550 | wildcards); each pattern in turn is matched against the canonical host |
551 | name (when authenticating a client) or against the user-supplied | |
552 | name (when authenticating a server). | |
553 | A pattern may also be preceded by | |
7cac2b65 | 554 | .Ql \&! |
3c0ef626 | 555 | to indicate negation: if the host name matches a negated |
556 | pattern, it is not accepted (by that line) even if it matched another | |
557 | pattern on the line. | |
558 | .Pp | |
dfddba3d | 559 | Alternately, hostnames may be stored in a hashed form which hides host names |
560 | and addresses should the file's contents be disclosed. | |
561 | Hashed hostnames start with a | |
562 | .Ql | | |
563 | character. | |
564 | Only one hashed hostname may appear on a single line and none of the above | |
565 | negation or wildcard operators may be applied. | |
566 | .Pp | |
3c0ef626 | 567 | Bits, exponent, and modulus are taken directly from the RSA host key; they |
568 | can be obtained, e.g., from | |
e9702f7d | 569 | .Pa /etc/ssh/ssh_host_key.pub . |
3c0ef626 | 570 | The optional comment field continues to the end of the line, and is not used. |
571 | .Pp | |
572 | Lines starting with | |
573 | .Ql # | |
574 | and empty lines are ignored as comments. | |
575 | .Pp | |
576 | When performing host authentication, authentication is accepted if any | |
577 | matching line has the proper key. | |
578 | It is thus permissible (but not | |
579 | recommended) to have several lines or different host keys for the same | |
580 | names. | |
581 | This will inevitably happen when short forms of host names | |
582 | from different domains are put in the file. | |
583 | It is possible | |
584 | that the files contain conflicting information; authentication is | |
585 | accepted if valid information can be found from either file. | |
586 | .Pp | |
587 | Note that the lines in these files are typically hundreds of characters | |
588 | long, and you definitely don't want to type in the host keys by hand. | |
589 | Rather, generate them by a script | |
590 | or by taking | |
e9702f7d | 591 | .Pa /etc/ssh/ssh_host_key.pub |
3c0ef626 | 592 | and adding the host names at the front. |
593 | .Ss Examples | |
594 | .Bd -literal | |
540d72c3 | 595 | closenet,...,130.233.208.41 1024 37 159...93 closenet.hut.fi |
3c0ef626 | 596 | cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....= |
597 | .Ed | |
dfddba3d | 598 | .Bd -literal |
599 | # A hashed hostname | |
600 | |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa | |
601 | AAAA1234.....= | |
602 | .Ed | |
3c0ef626 | 603 | .Sh FILES |
604 | .Bl -tag -width Ds | |
e9702f7d | 605 | .It Pa /etc/ssh/sshd_config |
3c0ef626 | 606 | Contains configuration data for |
607 | .Nm sshd . | |
44a053a3 | 608 | The file format and configuration options are described in |
609 | .Xr sshd_config 5 . | |
e9702f7d | 610 | .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key |
3c0ef626 | 611 | These three files contain the private parts of the host keys. |
612 | These files should only be owned by root, readable only by root, and not | |
613 | accessible to others. | |
614 | Note that | |
615 | .Nm | |
616 | does not start if this file is group/world-accessible. | |
e9702f7d | 617 | .It Pa /etc/ssh/ssh_host_key.pub, /etc/ssh/ssh_host_dsa_key.pub, /etc/ssh/ssh_host_rsa_key.pub |
3c0ef626 | 618 | These three files contain the public parts of the host keys. |
619 | These files should be world-readable but writable only by | |
620 | root. | |
621 | Their contents should match the respective private parts. | |
622 | These files are not | |
623 | really used for anything; they are provided for the convenience of | |
624 | the user so their contents can be copied to known hosts files. | |
625 | These files are created using | |
626 | .Xr ssh-keygen 1 . | |
627 | .It Pa /etc/moduli | |
628 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". | |
d03f4262 | 629 | The file format is described in |
630 | .Xr moduli 5 . | |
276b07a3 | 631 | .It Pa /var/empty |
632 | .Xr chroot 2 | |
633 | directory used by | |
634 | .Nm | |
635 | during privilege separation in the pre-authentication phase. | |
636 | The directory should not contain any files and must be owned by root | |
637 | and not group or world-writable. | |
3c0ef626 | 638 | .It Pa /var/run/sshd.pid |
639 | Contains the process ID of the | |
640 | .Nm | |
641 | listening for connections (if there are several daemons running | |
276b07a3 | 642 | concurrently for different ports, this contains the process ID of the one |
3c0ef626 | 643 | started last). |
644 | The content of this file is not sensitive; it can be world-readable. | |
2ce0bfe4 | 645 | .It Pa ~/.ssh/authorized_keys |
3c0ef626 | 646 | Lists the public keys (RSA or DSA) that can be used to log into the user's account. |
647 | This file must be readable by root (which may on some machines imply | |
648 | it being world-readable if the user's home directory resides on an NFS | |
649 | volume). | |
650 | It is recommended that it not be accessible by others. | |
651 | The format of this file is described above. | |
652 | Users will place the contents of their | |
653 | .Pa identity.pub , | |
654 | .Pa id_dsa.pub | |
655 | and/or | |
656 | .Pa id_rsa.pub | |
657 | files into this file, as described in | |
658 | .Xr ssh-keygen 1 . | |
2ce0bfe4 | 659 | .It Pa "/etc/ssh/ssh_known_hosts", "~/.ssh/known_hosts" |
3c0ef626 | 660 | These files are consulted when using rhosts with RSA host |
661 | authentication or protocol version 2 hostbased authentication | |
662 | to check the public key of the host. | |
663 | The key must be listed in one of these files to be accepted. | |
664 | The client uses the same files | |
665 | to verify that it is connecting to the correct remote host. | |
666 | These files should be writable only by root/the owner. | |
e9702f7d | 667 | .Pa /etc/ssh/ssh_known_hosts |
3c0ef626 | 668 | should be world-readable, and |
2ce0bfe4 | 669 | .Pa ~/.ssh/known_hosts |
bfe49944 | 670 | can, but need not be, world-readable. |
dfddba3d | 671 | .It Pa /etc/motd |
672 | See | |
673 | .Xr motd 5 . | |
2ce0bfe4 | 674 | .It Pa ~/.hushlogin |
dfddba3d | 675 | This file is used to suppress printing the last login time and |
676 | .Pa /etc/motd , | |
677 | if | |
678 | .Cm PrintLastLog | |
679 | and | |
680 | .Cm PrintMotd , | |
681 | respectively, | |
682 | are enabled. | |
683 | It does not suppress printing of the banner specified by | |
684 | .Cm Banner . | |
3c0ef626 | 685 | .It Pa /etc/nologin |
686 | If this file exists, | |
687 | .Nm | |
688 | refuses to let anyone except root log in. | |
689 | The contents of the file | |
690 | are displayed to anyone trying to log in, and non-root connections are | |
691 | refused. | |
692 | The file should be world-readable. | |
693 | .It Pa /etc/hosts.allow, /etc/hosts.deny | |
694 | Access controls that should be enforced by tcp-wrappers are defined here. | |
695 | Further details are described in | |
696 | .Xr hosts_access 5 . | |
2ce0bfe4 | 697 | .It Pa ~/.rhosts |
dfddba3d | 698 | This file is used during |
699 | .Cm RhostsRSAAuthentication | |
700 | and | |
701 | .Cm HostbasedAuthentication | |
702 | and contains host-username pairs, separated by a space, one per | |
3c0ef626 | 703 | line. |
704 | The given user on the corresponding host is permitted to log in | |
bfe49944 | 705 | without a password. |
3c0ef626 | 706 | The same file is used by rlogind and rshd. |
707 | The file must | |
708 | be writable only by the user; it is recommended that it not be | |
709 | accessible by others. | |
710 | .Pp | |
540d72c3 | 711 | It is also possible to use netgroups in the file. |
3c0ef626 | 712 | Either host or user |
713 | name may be of the form +@groupname to specify all hosts or all users | |
714 | in the group. | |
2ce0bfe4 | 715 | .It Pa ~/.shosts |
3c0ef626 | 716 | For ssh, |
717 | this file is exactly the same as for | |
718 | .Pa .rhosts . | |
719 | However, this file is | |
720 | not used by rlogin and rshd, so using this permits access using SSH only. | |
721 | .It Pa /etc/hosts.equiv | |
722 | This file is used during | |
dfddba3d | 723 | .Cm RhostsRSAAuthentication |
724 | and | |
725 | .Cm HostbasedAuthentication | |
3c0ef626 | 726 | authentication. |
727 | In the simplest form, this file contains host names, one per line. | |
728 | Users on | |
729 | those hosts are permitted to log in without a password, provided they | |
730 | have the same user name on both machines. | |
731 | The host name may also be | |
732 | followed by a user name; such users are permitted to log in as | |
733 | .Em any | |
734 | user on this machine (except root). | |
735 | Additionally, the syntax | |
736 | .Dq +@group | |
737 | can be used to specify netgroups. | |
738 | Negated entries start with | |
739 | .Ql \&- . | |
740 | .Pp | |
741 | If the client host/user is successfully matched in this file, login is | |
742 | automatically permitted provided the client and server user names are the | |
743 | same. | |
dfddba3d | 744 | Additionally, successful client host key authentication is required. |
3c0ef626 | 745 | This file must be writable only by root; it is recommended |
746 | that it be world-readable. | |
747 | .Pp | |
748 | .Sy "Warning: It is almost never a good idea to use user names in" | |
749 | .Pa hosts.equiv . | |
750 | Beware that it really means that the named user(s) can log in as | |
751 | .Em anybody , | |
752 | which includes bin, daemon, adm, and other accounts that own critical | |
753 | binaries and directories. | |
754 | Using a user name practically grants the user root access. | |
755 | The only valid use for user names that I can think | |
756 | of is in negative entries. | |
757 | .Pp | |
758 | Note that this warning also applies to rsh/rlogin. | |
759 | .It Pa /etc/shosts.equiv | |
760 | This is processed exactly as | |
761 | .Pa /etc/hosts.equiv . | |
762 | However, this file may be useful in environments that want to run both | |
763 | rsh/rlogin and ssh. | |
2ce0bfe4 | 764 | .It Pa ~/.ssh/environment |
3c0ef626 | 765 | This file is read into the environment at login (if it exists). |
766 | It can only contain empty lines, comment lines (that start with | |
767 | .Ql # ) , | |
768 | and assignment lines of the form name=value. | |
769 | The file should be writable | |
770 | only by the user; it need not be readable by anyone else. | |
d03f4262 | 771 | Environment processing is disabled by default and is |
772 | controlled via the | |
773 | .Cm PermitUserEnvironment | |
774 | option. | |
2ce0bfe4 | 775 | .It Pa ~/.ssh/rc |
bfe49944 | 776 | If this file exists, it is run with |
777 | .Pa /bin/sh | |
778 | after reading the | |
3c0ef626 | 779 | environment files but before starting the user's shell or command. |
350391c5 | 780 | It must not produce any output on stdout; stderr must be used |
781 | instead. | |
782 | If X11 forwarding is in use, it will receive the "proto cookie" pair in | |
783 | its standard input (and | |
3c0ef626 | 784 | .Ev DISPLAY |
350391c5 | 785 | in its environment). |
786 | The script must call | |
3c0ef626 | 787 | .Xr xauth 1 |
350391c5 | 788 | because |
789 | .Nm | |
790 | will not run xauth automatically to add X11 cookies. | |
3c0ef626 | 791 | .Pp |
792 | The primary purpose of this file is to run any initialization routines | |
793 | which may be needed before the user's home directory becomes | |
794 | accessible; AFS is a particular example of such an environment. | |
795 | .Pp | |
796 | This file will probably contain some initialization code followed by | |
797 | something similar to: | |
798 | .Bd -literal | |
350391c5 | 799 | if read proto cookie && [ -n "$DISPLAY" ]; then |
800 | if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then | |
801 | # X11UseLocalhost=yes | |
d03f4262 | 802 | echo add unix:`echo $DISPLAY | |
350391c5 | 803 | cut -c11-` $proto $cookie |
804 | else | |
805 | # X11UseLocalhost=no | |
d03f4262 | 806 | echo add $DISPLAY $proto $cookie |
807 | fi | xauth -q - | |
350391c5 | 808 | fi |
3c0ef626 | 809 | .Ed |
810 | .Pp | |
811 | If this file does not exist, | |
e9702f7d | 812 | .Pa /etc/ssh/sshrc |
3c0ef626 | 813 | is run, and if that |
350391c5 | 814 | does not exist either, xauth is used to add the cookie. |
3c0ef626 | 815 | .Pp |
816 | This file should be writable only by the user, and need not be | |
817 | readable by anyone else. | |
e9702f7d | 818 | .It Pa /etc/ssh/sshrc |
3c0ef626 | 819 | Like |
2ce0bfe4 | 820 | .Pa ~/.ssh/rc . |
3c0ef626 | 821 | This can be used to specify |
822 | machine-specific login-time initializations globally. | |
823 | This file should be writable only by root, and should be world-readable. | |
824 | .El | |
3c0ef626 | 825 | .Sh SEE ALSO |
826 | .Xr scp 1 , | |
827 | .Xr sftp 1 , | |
828 | .Xr ssh 1 , | |
829 | .Xr ssh-add 1 , | |
830 | .Xr ssh-agent 1 , | |
831 | .Xr ssh-keygen 1 , | |
540d72c3 | 832 | .Xr chroot 2 , |
833 | .Xr hosts_access 5 , | |
3c0ef626 | 834 | .Xr login.conf 5 , |
835 | .Xr moduli 5 , | |
44a053a3 | 836 | .Xr sshd_config 5 , |
540d72c3 | 837 | .Xr inetd 8 , |
3c0ef626 | 838 | .Xr sftp-server 8 |
839 | .Rs | |
840 | .%A T. Ylonen | |
841 | .%A T. Kivinen | |
842 | .%A M. Saarinen | |
843 | .%A T. Rinne | |
844 | .%A S. Lehtinen | |
845 | .%T "SSH Protocol Architecture" | |
350391c5 | 846 | .%N draft-ietf-secsh-architecture-12.txt |
847 | .%D January 2002 | |
3c0ef626 | 848 | .%O work in progress material |
849 | .Re | |
850 | .Rs | |
851 | .%A M. Friedl | |
852 | .%A N. Provos | |
853 | .%A W. A. Simpson | |
854 | .%T "Diffie-Hellman Group Exchange for the SSH Transport Layer Protocol" | |
350391c5 | 855 | .%N draft-ietf-secsh-dh-group-exchange-02.txt |
856 | .%D January 2002 | |
3c0ef626 | 857 | .%O work in progress material |
858 | .Re | |
7cac2b65 | 859 | .Sh AUTHORS |
860 | OpenSSH is a derivative of the original and free | |
861 | ssh 1.2.12 release by Tatu Ylonen. | |
862 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
863 | Theo de Raadt and Dug Song | |
864 | removed many bugs, re-added newer features and | |
865 | created OpenSSH. | |
866 | Markus Friedl contributed the support for SSH | |
867 | protocol versions 1.5 and 2.0. | |
868 | Niels Provos and Markus Friedl contributed support | |
869 | for privilege separation. |