]>
Commit | Line | Data |
---|---|---|
bf740959 | 1 | .\" -*- nroff -*- |
2 | .\" | |
bf740959 | 3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
bf740959 | 4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
5 | .\" All rights reserved | |
6 | .\" | |
bcbf86ec | 7 | .\" As far as I am concerned, the code I have written for this software |
8 | .\" can be used freely for any purpose. Any derived versions of this | |
9 | .\" software must be clearly marked as such, and if the derived work is | |
10 | .\" incompatible with the protocol description in the RFC file, it must be | |
11 | .\" called by a name other than "ssh" or "Secure Shell". | |
12 | .\" | |
f3c7c613 | 13 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. |
14 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. | |
15 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. | |
bcbf86ec | 16 | .\" |
17 | .\" Redistribution and use in source and binary forms, with or without | |
18 | .\" modification, are permitted provided that the following conditions | |
19 | .\" are met: | |
20 | .\" 1. Redistributions of source code must retain the above copyright | |
21 | .\" notice, this list of conditions and the following disclaimer. | |
22 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
23 | .\" notice, this list of conditions and the following disclaimer in the | |
24 | .\" documentation and/or other materials provided with the distribution. | |
bf740959 | 25 | .\" |
bcbf86ec | 26 | .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
27 | .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES | |
28 | .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |
29 | .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, | |
30 | .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT | |
31 | .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
32 | .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
33 | .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
34 | .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF | |
35 | .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
bf740959 | 36 | .\" |
54bf768d | 37 | .\" $OpenBSD: sshd.8,v 1.141 2001/08/16 20:14:57 stevesk Exp $ |
bf740959 | 38 | .Dd September 25, 1999 |
39 | .Dt SSHD 8 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm sshd | |
da89cf4d | 43 | .Nd OpenSSH SSH daemon |
bf740959 | 44 | .Sh SYNOPSIS |
45 | .Nm sshd | |
ff14faf1 | 46 | .Op Fl deiqD46 |
bf740959 | 47 | .Op Fl b Ar bits |
48 | .Op Fl f Ar config_file | |
49 | .Op Fl g Ar login_grace_time | |
50 | .Op Fl h Ar host_key_file | |
51 | .Op Fl k Ar key_gen_time | |
52 | .Op Fl p Ar port | |
c345cf9d | 53 | .Op Fl u Ar len |
5260325f | 54 | .Op Fl V Ar client_protocol_id |
f54651ce | 55 | .Sh DESCRIPTION |
bf740959 | 56 | .Nm |
2c86906e | 57 | (SSH Daemon) is the daemon program for |
bf740959 | 58 | .Xr ssh 1 . |
3189621b | 59 | Together these programs replace rlogin and rsh, and |
bf740959 | 60 | provide secure encrypted communications between two untrusted hosts |
4fe2af09 | 61 | over an insecure network. |
62 | The programs are intended to be as easy to | |
bf740959 | 63 | install and use as possible. |
64 | .Pp | |
65 | .Nm | |
4fe2af09 | 66 | is the daemon that listens for connections from clients. |
f54651ce | 67 | It is normally started at boot from |
bf740959 | 68 | .Pa /etc/rc . |
69 | It forks a new | |
4fe2af09 | 70 | daemon for each incoming connection. |
71 | The forked daemons handle | |
bf740959 | 72 | key exchange, encryption, authentication, command execution, |
73 | and data exchange. | |
1d1ffb87 | 74 | This implementation of |
75 | .Nm | |
76 | supports both SSH protocol version 1 and 2 simultaneously. | |
bf740959 | 77 | .Nm |
4fe2af09 | 78 | works as follows. |
1d1ffb87 | 79 | .Pp |
80 | .Ss SSH protocol version 1 | |
81 | .Pp | |
4fe2af09 | 82 | Each host has a host-specific RSA key |
83 | (normally 1024 bits) used to identify the host. | |
84 | Additionally, when | |
bf740959 | 85 | the daemon starts, it generates a server RSA key (normally 768 bits). |
86 | This key is normally regenerated every hour if it has been used, and | |
87 | is never stored on disk. | |
88 | .Pp | |
3189621b | 89 | Whenever a client connects the daemon responds with its public |
90 | host and server keys. | |
4fe2af09 | 91 | The client compares the |
1d1ffb87 | 92 | RSA host key against its own database to verify that it has not changed. |
4fe2af09 | 93 | The client then generates a 256 bit random number. |
94 | It encrypts this | |
bf740959 | 95 | random number using both the host key and the server key, and sends |
4fe2af09 | 96 | the encrypted number to the server. |
3189621b | 97 | Both sides then use this |
bf740959 | 98 | random number as a session key which is used to encrypt all further |
4fe2af09 | 99 | communications in the session. |
100 | The rest of the session is encrypted | |
3189621b | 101 | using a conventional cipher, currently Blowfish or 3DES, with 3DES |
7368a6c8 | 102 | being used by default. |
4fe2af09 | 103 | The client selects the encryption algorithm |
bf740959 | 104 | to use from those offered by the server. |
105 | .Pp | |
4fe2af09 | 106 | Next, the server and the client enter an authentication dialog. |
107 | The client tries to authenticate itself using | |
bf740959 | 108 | .Pa .rhosts |
109 | authentication, | |
110 | .Pa .rhosts | |
111 | authentication combined with RSA host | |
112 | authentication, RSA challenge-response authentication, or password | |
113 | based authentication. | |
114 | .Pp | |
115 | Rhosts authentication is normally disabled | |
116 | because it is fundamentally insecure, but can be enabled in the server | |
4fe2af09 | 117 | configuration file if desired. |
118 | System security is not improved unless | |
bf740959 | 119 | .Xr rshd 8 , |
120 | .Xr rlogind 8 , | |
121 | .Xr rexecd 8 , | |
122 | and | |
123 | .Xr rexd 8 | |
124 | are disabled (thus completely disabling | |
125 | .Xr rlogin 1 | |
126 | and | |
127 | .Xr rsh 1 | |
3189621b | 128 | into the machine). |
bf740959 | 129 | .Pp |
1d1ffb87 | 130 | .Ss SSH protocol version 2 |
131 | .Pp | |
c345cf9d | 132 | Version 2 works similarly: |
7f19f8bb | 133 | Each host has a host-specific key (RSA or DSA) used to identify the host. |
1d1ffb87 | 134 | However, when the daemon starts, it does not generate a server key. |
135 | Forward security is provided through a Diffie-Hellman key agreement. | |
136 | This key agreement results in a shared session key. | |
da89cf4d | 137 | .Pp |
51c251f0 | 138 | The rest of the session is encrypted using a symmetric cipher, currently |
da89cf4d | 139 | 128 bit AES, Blowfish, 3DES, CAST128, Arcfour, 192 bit AES, or 256 bit AES. |
1d1ffb87 | 140 | The client selects the encryption algorithm |
141 | to use from those offered by the server. | |
142 | Additionally, session integrity is provided | |
d0c832f3 | 143 | through a cryptographic message authentication code |
1d1ffb87 | 144 | (hmac-sha1 or hmac-md5). |
145 | .Pp | |
146 | Protocol version 2 provides a public key based | |
da89cf4d | 147 | user (PubkeyAuthentication) or |
148 | client host (HostbasedAuthentication) authentication method, | |
149 | conventional password authentication and challenge response based methods. | |
1d1ffb87 | 150 | .Pp |
151 | .Ss Command execution and data forwarding | |
152 | .Pp | |
bf740959 | 153 | If the client successfully authenticates itself, a dialog for |
4fe2af09 | 154 | preparing the session is entered. |
155 | At this time the client may request | |
bf740959 | 156 | things like allocating a pseudo-tty, forwarding X11 connections, |
157 | forwarding TCP/IP connections, or forwarding the authentication agent | |
158 | connection over the secure channel. | |
159 | .Pp | |
160 | Finally, the client either requests a shell or execution of a command. | |
4fe2af09 | 161 | The sides then enter session mode. |
162 | In this mode, either side may send | |
bf740959 | 163 | data at any time, and such data is forwarded to/from the shell or |
164 | command on the server side, and the user terminal in the client side. | |
165 | .Pp | |
166 | When the user program terminates and all forwarded X11 and other | |
167 | connections have been closed, the server sends command exit status to | |
168 | the client, and both sides exit. | |
169 | .Pp | |
170 | .Nm | |
171 | can be configured using command-line options or a configuration | |
4fe2af09 | 172 | file. |
173 | Command-line options override values specified in the | |
bf740959 | 174 | configuration file. |
175 | .Pp | |
9d6b7add | 176 | .Nm |
177 | rereads its configuration file when it receives a hangup signal, | |
409edaba | 178 | .Dv SIGHUP , |
a5a2da3b | 179 | by executing itself with the name it was started as, i.e., |
409edaba | 180 | .Pa /usr/sbin/sshd . |
9d6b7add | 181 | .Pp |
bf740959 | 182 | The options are as follows: |
183 | .Bl -tag -width Ds | |
184 | .It Fl b Ar bits | |
da89cf4d | 185 | Specifies the number of bits in the ephemeral protocol version 1 |
186 | server key (default 768). | |
bf740959 | 187 | .It Fl d |
4fe2af09 | 188 | Debug mode. |
189 | The server sends verbose debug output to the system | |
190 | log, and does not put itself in the background. | |
191 | The server also will not fork and will only process one connection. | |
192 | This option is only intended for debugging for the server. | |
da89cf4d | 193 | Multiple -d options increase the debugging level. |
94ec8c6b | 194 | Maximum is 3. |
da89cf4d | 195 | .It Fl e |
196 | When this option is specified, | |
197 | .Nm | |
198 | will send the output to the standard error instead of the system log. | |
bf740959 | 199 | .It Fl f Ar configuration_file |
4fe2af09 | 200 | Specifies the name of the configuration file. |
201 | The default is | |
5f4fdfae | 202 | .Pa /etc/sshd_config . |
bf740959 | 203 | .Nm |
204 | refuses to start if there is no configuration file. | |
205 | .It Fl g Ar login_grace_time | |
206 | Gives the grace time for clients to authenticate themselves (default | |
ee5e6612 | 207 | 600 seconds). |
4fe2af09 | 208 | If the client fails to authenticate the user within |
209 | this many seconds, the server disconnects and exits. | |
210 | A value of zero indicates no limit. | |
bf740959 | 211 | .It Fl h Ar host_key_file |
8abcdba4 | 212 | Specifies the file from which the host key is read (default |
5f4fdfae | 213 | .Pa /etc/ssh_host_key ) . |
bf740959 | 214 | This option must be given if |
215 | .Nm | |
216 | is not run as root (as the normal | |
217 | host file is normally not readable by anyone but root). | |
8abcdba4 | 218 | It is possible to have multiple host key files for |
da89cf4d | 219 | the different protocol versions and host key algorithms. |
bf740959 | 220 | .It Fl i |
221 | Specifies that | |
222 | .Nm | |
f54651ce | 223 | is being run from inetd. |
bf740959 | 224 | .Nm |
225 | is normally not run | |
226 | from inetd because it needs to generate the server key before it can | |
4fe2af09 | 227 | respond to the client, and this may take tens of seconds. |
228 | Clients would have to wait too long if the key was regenerated every time. | |
610cd5c6 | 229 | However, with small key sizes (e.g., 512) using |
bf740959 | 230 | .Nm |
231 | from inetd may | |
232 | be feasible. | |
233 | .It Fl k Ar key_gen_time | |
da89cf4d | 234 | Specifies how often the ephemeral protocol version 1 server key is |
235 | regenerated (default 3600 seconds, or one hour). | |
4fe2af09 | 236 | The motivation for regenerating the key fairly |
bf740959 | 237 | often is that the key is not stored anywhere, and after about an hour, |
238 | it becomes impossible to recover the key for decrypting intercepted | |
239 | communications even if the machine is cracked into or physically | |
4fe2af09 | 240 | seized. |
241 | A value of zero indicates that the key will never be regenerated. | |
bf740959 | 242 | .It Fl p Ar port |
243 | Specifies the port on which the server listens for connections | |
244 | (default 22). | |
245 | .It Fl q | |
4fe2af09 | 246 | Quiet mode. |
247 | Nothing is sent to the system log. | |
248 | Normally the beginning, | |
bf740959 | 249 | authentication, and termination of each connection is logged. |
f87f09aa | 250 | .It Fl t |
251 | Test mode. | |
252 | Only check the validity of the configuration file and sanity of the keys. | |
253 | This is useful for updating | |
254 | .Nm | |
255 | reliably as configuration options may change. | |
c345cf9d | 256 | .It Fl u Ar len |
257 | This option is used to specify the size of the field | |
258 | in the | |
259 | .Li utmp | |
260 | structure that holds the remote host name. | |
261 | If the resolved host name is longer than | |
262 | .Ar len , | |
263 | the dotted decimal value will be used instead. | |
264 | This allows hosts with very long host names that | |
265 | overflow this field to still be uniquely identified. | |
266 | Specifying | |
267 | .Fl u0 | |
268 | indicates that only dotted decimal addresses | |
269 | should be put into the | |
270 | .Pa utmp | |
271 | file. | |
8abcdba4 | 272 | .It Fl D |
273 | When this option is specified | |
274 | .Nm | |
275 | will not detach and does not become a daemon. | |
276 | This allows easy monitoring of | |
277 | .Nm sshd . | |
48e671d5 | 278 | .It Fl 4 |
279 | Forces | |
280 | .Nm | |
281 | to use IPv4 addresses only. | |
282 | .It Fl 6 | |
283 | Forces | |
284 | .Nm | |
285 | to use IPv6 addresses only. | |
bf740959 | 286 | .El |
287 | .Sh CONFIGURATION FILE | |
288 | .Nm | |
f54651ce | 289 | reads configuration data from |
5f4fdfae | 290 | .Pa /etc/sshd_config |
bf740959 | 291 | (or the file specified with |
292 | .Fl f | |
4fe2af09 | 293 | on the command line). |
54bf768d | 294 | The file contains keyword-argument pairs, one per line. |
4fe2af09 | 295 | Lines starting with |
bf740959 | 296 | .Ql # |
297 | and empty lines are interpreted as comments. | |
298 | .Pp | |
54bf768d | 299 | The possible |
300 | keywords and their meanings are as follows (note that | |
301 | keywords are case-insensitive and arguments are case-sensitive): | |
bf740959 | 302 | .Bl -tag -width Ds |
303 | .It Cm AFSTokenPassing | |
4fe2af09 | 304 | Specifies whether an AFS token may be forwarded to the server. |
305 | Default is | |
bf740959 | 306 | .Dq yes . |
307 | .It Cm AllowGroups | |
76896b4e | 308 | This keyword can be followed by a list of group names, separated |
4fe2af09 | 309 | by spaces. |
310 | If specified, login is allowed only for users whose primary | |
c6a69271 | 311 | group or supplementary group list matches one of the patterns. |
bf740959 | 312 | .Ql \&* |
313 | and | |
314 | .Ql ? | |
315 | can be used as | |
4fe2af09 | 316 | wildcards in the patterns. |
c345cf9d | 317 | Only group names are valid; a numerical group ID isn't recognized. |
c6a69271 | 318 | By default login is allowed regardless of the group list. |
bf740959 | 319 | .Pp |
33de75a3 | 320 | .It Cm AllowTcpForwarding |
321 | Specifies whether TCP forwarding is permitted. | |
322 | The default is | |
323 | .Dq yes . | |
324 | Note that disabling TCP forwarding does not improve security unless | |
325 | users are also denied shell access, as they can always install their | |
326 | own forwarders. | |
327 | .Pp | |
bf740959 | 328 | .It Cm AllowUsers |
76896b4e | 329 | This keyword can be followed by a list of user names, separated |
4fe2af09 | 330 | by spaces. |
331 | If specified, login is allowed only for users names that | |
bf740959 | 332 | match one of the patterns. |
333 | .Ql \&* | |
334 | and | |
335 | .Ql ? | |
336 | can be used as | |
4fe2af09 | 337 | wildcards in the patterns. |
c345cf9d | 338 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 339 | By default login is allowed regardless of the user name. |
80f8f24f | 340 | If the pattern takes the form USER@HOST then USER and HOST |
341 | are separately checked, allowing you to restrict logins to particular | |
342 | users from particular hosts. | |
bf740959 | 343 | .Pp |
c8445989 | 344 | .It Cm AuthorizedKeysFile |
7f19f8bb | 345 | Specifies the file that contains the public keys that can be used |
346 | for user authentication. | |
c8445989 | 347 | .Cm AuthorizedKeysFile |
348 | may contain tokens of the form %T which are substituted during connection | |
349 | set-up. The following tokens are defined; %% is replaces by a literal '%', | |
350 | %h is replaced by the home directory of the user being authenticated and | |
351 | %u is replaced by the username of that user. | |
352 | After expansion, | |
353 | .Cm AuthorizedKeysFile | |
f740438e | 354 | is taken to be an absolute path or one relative to the user's home |
c8445989 | 355 | directory. |
356 | The default is | |
357 | .Dq .ssh/authorized_keys | |
eea39c02 | 358 | .It Cm Banner |
359 | In some jurisdictions, sending a warning message before authentication | |
360 | may be relevant for getting legal protection. | |
361 | The contents of the specified file are sent to the remote user before | |
362 | authentication is allowed. | |
363 | This option is only available for protocol version 2. | |
364 | .Pp | |
657297ff | 365 | .It Cm ChallengeResponseAuthentication |
248bad82 | 366 | Specifies whether challenge response authentication is allowed. |
367 | All authentication styles from | |
368 | .Xr login.conf 5 | |
369 | are supported. | |
657297ff | 370 | The default is |
371 | .Dq yes . | |
a18395da | 372 | .It Cm Ciphers |
373 | Specifies the ciphers allowed for protocol version 2. | |
374 | Multiple ciphers must be comma-separated. | |
375 | The default is | |
376 | .Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour. | |
3ffc6336 | 377 | .It Cm ClientAliveInterval |
378 | Sets a timeout interval in seconds after which if no data has been received | |
3730bb22 | 379 | from the client, |
3ffc6336 | 380 | .Nm |
381 | will send a message through the encrypted | |
84fc17bf | 382 | channel to request a response from the client. |
383 | The default | |
3ffc6336 | 384 | is 0, indicating that these messages will not be sent to the client. |
84fc17bf | 385 | This option applies to protocol version 2 only. |
3ffc6336 | 386 | .It Cm ClientAliveCountMax |
387 | Sets the number of client alive messages (see above) which may be | |
388 | sent without | |
389 | .Nm | |
390 | receiving any messages back from the client. If this threshold is | |
3730bb22 | 391 | reached while client alive messages are being sent, |
3ffc6336 | 392 | .Nm |
393 | will disconnect the client, terminating the session. It is important | |
3730bb22 | 394 | to note that the use of client alive messages is very different from |
84fc17bf | 395 | .Cm Keepalive |
396 | (below). The client alive messages are sent through the | |
3ffc6336 | 397 | encrypted channel and therefore will not be spoofable. The TCP keepalive |
84fc17bf | 398 | option enabled by |
399 | .Cm Keepalive | |
400 | is spoofable. You want to use the client | |
3ffc6336 | 401 | alive mechanism when you are basing something important on |
402 | clients having an active connection to the server. | |
84fc17bf | 403 | .Pp |
404 | The default value is 3. If you set | |
405 | .Cm ClientAliveInterval | |
3ffc6336 | 406 | (above) to 15, and leave this value at the default, unresponsive ssh clients |
3730bb22 | 407 | will be disconnected after approximately 45 seconds. |
bf740959 | 408 | .It Cm DenyGroups |
409 | This keyword can be followed by a number of group names, separated | |
4fe2af09 | 410 | by spaces. |
c6a69271 | 411 | Users whose primary group or supplementary group list matches |
412 | one of the patterns aren't allowed to log in. | |
bf740959 | 413 | .Ql \&* |
414 | and | |
415 | .Ql ? | |
416 | can be used as | |
4fe2af09 | 417 | wildcards in the patterns. |
c345cf9d | 418 | Only group names are valid; a numerical group ID isn't recognized. |
c6a69271 | 419 | By default login is allowed regardless of the group list. |
bf740959 | 420 | .Pp |
421 | .It Cm DenyUsers | |
422 | This keyword can be followed by a number of user names, separated | |
4fe2af09 | 423 | by spaces. |
424 | Login is disallowed for user names that match one of the patterns. | |
bf740959 | 425 | .Ql \&* |
426 | and | |
427 | .Ql ? | |
4fe2af09 | 428 | can be used as wildcards in the patterns. |
c345cf9d | 429 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 430 | By default login is allowed regardless of the user name. |
1d1ffb87 | 431 | .It Cm GatewayPorts |
432 | Specifies whether remote hosts are allowed to connect to ports | |
433 | forwarded for the client. | |
434 | The argument must be | |
435 | .Dq yes | |
436 | or | |
437 | .Dq no . | |
438 | The default is | |
439 | .Dq no . | |
da89cf4d | 440 | .It Cm HostbasedAuthentication |
441 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
442 | with successful public key client host authentication is allowed | |
443 | (hostbased authentication). | |
444 | This option is similar to | |
445 | .Cm RhostsRSAAuthentication | |
446 | and applies to protocol version 2 only. | |
447 | The default is | |
448 | .Dq no . | |
bf740959 | 449 | .It Cm HostKey |
fa08c86b | 450 | Specifies the file containing the private host keys (default |
1d1ffb87 | 451 | .Pa /etc/ssh_host_key ) |
fa08c86b | 452 | used by SSH protocol versions 1 and 2. |
bf740959 | 453 | Note that |
454 | .Nm | |
42f11eb2 | 455 | will refuse to use a file if it is group/world-accessible. |
fa08c86b | 456 | It is possible to have multiple host key files. |
457 | .Dq rsa1 | |
458 | keys are used for version 1 and | |
459 | .Dq dsa | |
460 | or | |
461 | .Dq rsa | |
462 | are used for version 2 of the SSH protocol. | |
bf740959 | 463 | .It Cm IgnoreRhosts |
c8d54615 | 464 | Specifies that |
465 | .Pa .rhosts | |
f54651ce | 466 | and |
c8d54615 | 467 | .Pa .shosts |
da89cf4d | 468 | files will not be used in |
469 | .Cm RhostsAuthentication , | |
470 | .Cm RhostsRSAAuthentication | |
471 | or | |
472 | .Cm HostbasedAuthentication . | |
473 | .Pp | |
bf740959 | 474 | .Pa /etc/hosts.equiv |
475 | and | |
f54651ce | 476 | .Pa /etc/shosts.equiv |
4fe2af09 | 477 | are still used. |
f54651ce | 478 | The default is |
c8d54615 | 479 | .Dq yes . |
b4748e2f | 480 | .It Cm IgnoreUserKnownHosts |
481 | Specifies whether | |
482 | .Nm | |
483 | should ignore the user's | |
484 | .Pa $HOME/.ssh/known_hosts | |
485 | during | |
da89cf4d | 486 | .Cm RhostsRSAAuthentication |
487 | or | |
488 | .Cm HostbasedAuthentication . | |
b4748e2f | 489 | The default is |
490 | .Dq no . | |
bf740959 | 491 | .It Cm KeepAlive |
492 | Specifies whether the system should send keepalive messages to the | |
4fe2af09 | 493 | other side. |
494 | If they are sent, death of the connection or crash of one | |
495 | of the machines will be properly noticed. | |
496 | However, this means that | |
bf740959 | 497 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 498 | find it annoying. |
d0c832f3 | 499 | On the other hand, if keepalives are not sent, |
bf740959 | 500 | sessions may hang indefinitely on the server, leaving |
501 | .Dq ghost | |
502 | users and consuming server resources. | |
503 | .Pp | |
504 | The default is | |
505 | .Dq yes | |
506 | (to send keepalives), and the server will notice | |
4fe2af09 | 507 | if the network goes down or the client host reboots. |
508 | This avoids infinitely hanging sessions. | |
bf740959 | 509 | .Pp |
510 | To disable keepalives, the value should be set to | |
511 | .Dq no | |
512 | in both the server and the client configuration files. | |
513 | .It Cm KerberosAuthentication | |
4fe2af09 | 514 | Specifies whether Kerberos authentication is allowed. |
515 | This can be in the form of a Kerberos ticket, or if | |
bf740959 | 516 | .Cm PasswordAuthentication |
517 | is yes, the password provided by the user will be validated through | |
94ec8c6b | 518 | the Kerberos KDC. |
519 | To use this option, the server needs a | |
c345cf9d | 520 | Kerberos servtab which allows the verification of the KDC's identity. |
4fe2af09 | 521 | Default is |
bf740959 | 522 | .Dq yes . |
523 | .It Cm KerberosOrLocalPasswd | |
524 | If set then if password authentication through Kerberos fails then | |
525 | the password will be validated via any additional local mechanism | |
526 | such as | |
188adeb2 | 527 | .Pa /etc/passwd . |
4fe2af09 | 528 | Default is |
bf740959 | 529 | .Dq yes . |
530 | .It Cm KerberosTgtPassing | |
531 | Specifies whether a Kerberos TGT may be forwarded to the server. | |
f54651ce | 532 | Default is |
bf740959 | 533 | .Dq no , |
534 | as this only works when the Kerberos KDC is actually an AFS kaserver. | |
535 | .It Cm KerberosTicketCleanup | |
536 | Specifies whether to automatically destroy the user's ticket cache | |
4fe2af09 | 537 | file on logout. |
538 | Default is | |
bf740959 | 539 | .Dq yes . |
540 | .It Cm KeyRegenerationInterval | |
da89cf4d | 541 | In protocol version 1, the ephemeral server key is automatically regenerated |
542 | after this many seconds (if it has been used). | |
4fe2af09 | 543 | The purpose of regeneration is to prevent |
bf740959 | 544 | decrypting captured sessions by later breaking into the machine and |
4fe2af09 | 545 | stealing the keys. |
546 | The key is never stored anywhere. | |
547 | If the value is 0, the key is never regenerated. | |
548 | The default is 3600 (seconds). | |
bf740959 | 549 | .It Cm ListenAddress |
6e9944b8 | 550 | Specifies the local addresses |
da89cf4d | 551 | .Nm |
bf740959 | 552 | should listen on. |
6e9944b8 | 553 | The following forms may be used: |
554 | .Pp | |
555 | .Bl -item -offset indent -compact | |
556 | .It | |
557 | .Cm ListenAddress | |
b8a297f1 | 558 | .Sm off |
559 | .Ar host No | Ar IPv4_addr No | Ar IPv6_addr | |
560 | .Sm on | |
6e9944b8 | 561 | .It |
562 | .Cm ListenAddress | |
b8a297f1 | 563 | .Sm off |
564 | .Ar host No | Ar IPv4_addr No : Ar port | |
565 | .Sm on | |
6e9944b8 | 566 | .It |
567 | .Cm ListenAddress | |
b8a297f1 | 568 | .Sm off |
569 | .Oo | |
570 | .Ar host No | Ar IPv6_addr Oc : Ar port | |
571 | .Sm on | |
6e9944b8 | 572 | .El |
573 | .Pp | |
574 | If | |
b8a297f1 | 575 | .Ar port |
6e9944b8 | 576 | is not specified, |
da89cf4d | 577 | .Nm |
6e9944b8 | 578 | will listen on the address and all prior |
579 | .Cm Port | |
580 | options specified. The default is to listen on all local | |
581 | addresses. Multiple | |
582 | .Cm ListenAddress | |
583 | options are permitted. Additionally, any | |
584 | .Cm Port | |
585 | options must precede this option for non port qualified addresses. | |
bf740959 | 586 | .It Cm LoginGraceTime |
587 | The server disconnects after this time if the user has not | |
4fe2af09 | 588 | successfully logged in. |
589 | If the value is 0, there is no time limit. | |
bf740959 | 590 | The default is 600 (seconds). |
6a17f9c2 | 591 | .It Cm LogLevel |
592 | Gives the verbosity level that is used when logging messages from | |
593 | .Nm sshd . | |
594 | The possible values are: | |
59c97189 | 595 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
596 | The default is INFO. | |
6a17f9c2 | 597 | Logging with level DEBUG violates the privacy of users |
598 | and is not recommended. | |
b2552997 | 599 | .It Cm MACs |
600 | Specifies the available MAC (message authentication code) algorithms. | |
601 | The MAC algorithm is used in protocol version 2 | |
602 | for data integrity protection. | |
603 | Multiple algorithms must be comma-separated. | |
604 | The default is | |
47bf6266 | 605 | .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 . |
089fbbd2 | 606 | .It Cm MaxStartups |
607 | Specifies the maximum number of concurrent unauthenticated connections to the | |
608 | .Nm | |
609 | daemon. | |
610 | Additional connections will be dropped until authentication succeeds or the | |
611 | .Cm LoginGraceTime | |
612 | expires for a connection. | |
613 | The default is 10. | |
c345cf9d | 614 | .Pp |
615 | Alternatively, random early drop can be enabled by specifying | |
616 | the three colon separated values | |
617 | .Dq start:rate:full | |
94ec8c6b | 618 | (e.g., "10:30:60"). |
c345cf9d | 619 | .Nm |
6f37606e | 620 | will refuse connection attempts with a probability of |
c345cf9d | 621 | .Dq rate/100 |
622 | (30%) | |
623 | if there are currently | |
624 | .Dq start | |
625 | (10) | |
626 | unauthenticated connections. | |
6f37606e | 627 | The probability increases linearly and all connection attempts |
c345cf9d | 628 | are refused if the number of unauthenticated connections reaches |
629 | .Dq full | |
630 | (60). | |
10f72868 | 631 | .It Cm PAMAuthenticationViaKbdInt |
632 | Specifies whether PAM challenge response authentication is allowed. This | |
633 | allows the use of most PAM challenge response authentication modules, but | |
634 | it will allow password authentication regardless of whether | |
635 | .Cm PasswordAuthentication | |
636 | is disabled. | |
637 | The default is | |
638 | .Dq no . | |
bf740959 | 639 | .It Cm PasswordAuthentication |
640 | Specifies whether password authentication is allowed. | |
641 | The default is | |
642 | .Dq yes . | |
643 | .It Cm PermitEmptyPasswords | |
644 | When password authentication is allowed, it specifies whether the | |
4fe2af09 | 645 | server allows login to accounts with empty password strings. |
646 | The default is | |
c8d54615 | 647 | .Dq no . |
bf740959 | 648 | .It Cm PermitRootLogin |
46f23b8d | 649 | Specifies whether root can login using |
bf740959 | 650 | .Xr ssh 1 . |
651 | The argument must be | |
652 | .Dq yes , | |
15853e93 | 653 | .Dq without-password , |
654 | .Dq forced-commands-only | |
bf740959 | 655 | or |
656 | .Dq no . | |
657 | The default is | |
658 | .Dq yes . | |
15853e93 | 659 | .Pp |
660 | If this option is set to | |
bf740959 | 661 | .Dq without-password |
15853e93 | 662 | password authentication is disabled for root. |
bf740959 | 663 | .Pp |
15853e93 | 664 | If this option is set to |
665 | .Dq forced-commands-only | |
666 | root login with public key authentication will be allowed, | |
667 | but only if the | |
bf740959 | 668 | .Ar command |
15853e93 | 669 | option has been specified |
bf740959 | 670 | (which may be useful for taking remote backups even if root login is |
15853e93 | 671 | normally not allowed). All other authentication methods are disabled |
672 | for root. | |
46f23b8d | 673 | .Pp |
674 | If this option is set to | |
675 | .Dq no | |
676 | root is not allowed to login. | |
0fbe8c74 | 677 | .It Cm PidFile |
678 | Specifies the file that contains the process identifier of the | |
679 | .Nm | |
680 | daemon. | |
681 | The default is | |
682 | .Pa /var/run/sshd.pid . | |
bf740959 | 683 | .It Cm Port |
684 | Specifies the port number that | |
685 | .Nm | |
4fe2af09 | 686 | listens on. |
687 | The default is 22. | |
48e671d5 | 688 | Multiple options of this type are permitted. |
da89cf4d | 689 | See also |
690 | .Cm ListenAddress . | |
4f4648f9 | 691 | .It Cm PrintLastLog |
692 | Specifies whether | |
693 | .Nm | |
694 | should print the date and time when the user last logged in. | |
695 | The default is | |
696 | .Dq yes . | |
bf740959 | 697 | .It Cm PrintMotd |
698 | Specifies whether | |
699 | .Nm | |
f54651ce | 700 | should print |
bf740959 | 701 | .Pa /etc/motd |
4fe2af09 | 702 | when a user logs in interactively. |
703 | (On some systems it is also printed by the shell, | |
bf740959 | 704 | .Pa /etc/profile , |
4fe2af09 | 705 | or equivalent.) |
706 | The default is | |
bf740959 | 707 | .Dq yes . |
f54651ce | 708 | .It Cm Protocol |
709 | Specifies the protocol versions | |
710 | .Nm | |
711 | should support. | |
712 | The possible values are | |
713 | .Dq 1 | |
714 | and | |
715 | .Dq 2 . | |
716 | Multiple versions must be comma-separated. | |
717 | The default is | |
6023325e | 718 | .Dq 2,1 . |
657297ff | 719 | .It Cm PubkeyAuthentication |
720 | Specifies whether public key authentication is allowed. | |
721 | The default is | |
722 | .Dq yes . | |
723 | Note that this option applies to protocol version 2 only. | |
61e96248 | 724 | .It Cm ReverseMappingCheck |
725 | Specifies whether | |
726 | .Nm | |
727 | should try to verify the remote host name and check that | |
728 | the resolved host name for the remote IP address maps back to the | |
729 | very same IP address. | |
730 | The default is | |
731 | .Dq no . | |
bf740959 | 732 | .It Cm RhostsAuthentication |
733 | Specifies whether authentication using rhosts or /etc/hosts.equiv | |
4fe2af09 | 734 | files is sufficient. |
735 | Normally, this method should not be permitted because it is insecure. | |
bf740959 | 736 | .Cm RhostsRSAAuthentication |
737 | should be used | |
738 | instead, because it performs RSA-based host authentication in addition | |
739 | to normal rhosts or /etc/hosts.equiv authentication. | |
740 | The default is | |
741 | .Dq no . | |
da89cf4d | 742 | This option applies to protocol version 1 only. |
bf740959 | 743 | .It Cm RhostsRSAAuthentication |
744 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
4fe2af09 | 745 | with successful RSA host authentication is allowed. |
746 | The default is | |
c8d54615 | 747 | .Dq no . |
da89cf4d | 748 | This option applies to protocol version 1 only. |
bf740959 | 749 | .It Cm RSAAuthentication |
4fe2af09 | 750 | Specifies whether pure RSA authentication is allowed. |
751 | The default is | |
bf740959 | 752 | .Dq yes . |
da89cf4d | 753 | This option applies to protocol version 1 only. |
bf740959 | 754 | .It Cm ServerKeyBits |
da89cf4d | 755 | Defines the number of bits in the ephemeral protocol version 1 server key. |
4fe2af09 | 756 | The minimum value is 512, and the default is 768. |
bf740959 | 757 | .It Cm StrictModes |
758 | Specifies whether | |
759 | .Nm | |
760 | should check file modes and ownership of the | |
4fe2af09 | 761 | user's files and home directory before accepting login. |
762 | This is normally desirable because novices sometimes accidentally leave their | |
763 | directory or files world-writable. | |
764 | The default is | |
bf740959 | 765 | .Dq yes . |
38c295d6 | 766 | .It Cm Subsystem |
94ec8c6b | 767 | Configures an external subsystem (e.g., file transfer daemon). |
768 | Arguments should be a subsystem name and a command to execute upon subsystem | |
769 | request. | |
b5e300c2 | 770 | The command |
771 | .Xr sftp-server 8 | |
772 | implements the | |
773 | .Dq sftp | |
774 | file transfer subsystem. | |
38c295d6 | 775 | By default no subsystems are defined. |
776 | Note that this option applies to protocol version 2 only. | |
bf740959 | 777 | .It Cm SyslogFacility |
778 | Gives the facility code that is used when logging messages from | |
779 | .Nm sshd . | |
780 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, | |
4fe2af09 | 781 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
782 | The default is AUTH. | |
bf740959 | 783 | .It Cm UseLogin |
784 | Specifies whether | |
785 | .Xr login 1 | |
fa649821 | 786 | is used for interactive login sessions. |
ff027d84 | 787 | The default is |
788 | .Dq no . | |
fa649821 | 789 | Note that |
790 | .Xr login 1 | |
c345cf9d | 791 | is never used for remote command execution. |
3730bb22 | 792 | Note also, that if this is enabled, |
793 | .Cm X11Forwarding | |
ff027d84 | 794 | will be disabled because |
795 | .Xr login 1 | |
796 | does not know how to handle | |
3730bb22 | 797 | .Xr xauth 1 |
ff027d84 | 798 | cookies. |
bf740959 | 799 | .It Cm X11DisplayOffset |
800 | Specifies the first display number available for | |
801 | .Nm sshd Ns 's | |
4fe2af09 | 802 | X11 forwarding. |
803 | This prevents | |
bf740959 | 804 | .Nm |
805 | from interfering with real X11 servers. | |
c8d54615 | 806 | The default is 10. |
7b2ea3a1 | 807 | .It Cm X11Forwarding |
4fe2af09 | 808 | Specifies whether X11 forwarding is permitted. |
809 | The default is | |
c8d54615 | 810 | .Dq no . |
7b2ea3a1 | 811 | Note that disabling X11 forwarding does not improve security in any |
812 | way, as users can always install their own forwarders. | |
3730bb22 | 813 | X11 forwarding is automatically disabled if |
814 | .Cm UseLogin | |
815 | is enabled. | |
fa649821 | 816 | .It Cm XAuthLocation |
817 | Specifies the location of the | |
818 | .Xr xauth 1 | |
819 | program. | |
820 | The default is | |
821 | .Pa /usr/X11R6/bin/xauth . | |
bf740959 | 822 | .El |
e2b1fb42 | 823 | .Ss Time Formats |
824 | .Pp | |
825 | .Nm | |
826 | command-line arguments and configuration file options that specify time | |
827 | may be expressed using a sequence of the form: | |
828 | .Sm off | |
829 | .Ar time Oo Ar qualifier Oc , | |
830 | .Sm on | |
831 | where | |
832 | .Ar time | |
833 | is a positive integer value and | |
834 | .Ar qualifier | |
835 | is one of the following: | |
836 | .Pp | |
837 | .Bl -tag -width Ds -compact -offset indent | |
838 | .It Cm <none> | |
839 | seconds | |
840 | .It Cm s | Cm S | |
841 | seconds | |
842 | .It Cm m | Cm M | |
843 | minutes | |
844 | .It Cm h | Cm H | |
845 | hours | |
846 | .It Cm d | Cm D | |
847 | days | |
848 | .It Cm w | Cm W | |
849 | weeks | |
850 | .El | |
851 | .Pp | |
852 | Each member of the sequence is added together to calculate | |
853 | the total time value. | |
854 | .Pp | |
855 | Time format examples: | |
856 | .Pp | |
857 | .Bl -tag -width Ds -compact -offset indent | |
858 | .It 600 | |
859 | 600 seconds (10 minutes) | |
860 | .It 10m | |
861 | 10 minutes | |
862 | .It 1h30m | |
863 | 1 hour 30 minutes (90 minutes) | |
864 | .El | |
bf740959 | 865 | .Sh LOGIN PROCESS |
866 | When a user successfully logs in, | |
867 | .Nm | |
868 | does the following: | |
869 | .Bl -enum -offset indent | |
870 | .It | |
871 | If the login is on a tty, and no command has been specified, | |
f54651ce | 872 | prints last login time and |
bf740959 | 873 | .Pa /etc/motd |
874 | (unless prevented in the configuration file or by | |
875 | .Pa $HOME/.hushlogin ; | |
876 | see the | |
f54651ce | 877 | .Sx FILES |
bf740959 | 878 | section). |
879 | .It | |
880 | If the login is on a tty, records login time. | |
881 | .It | |
882 | Checks | |
883 | .Pa /etc/nologin ; | |
884 | if it exists, prints contents and quits | |
885 | (unless root). | |
886 | .It | |
887 | Changes to run with normal user privileges. | |
888 | .It | |
889 | Sets up basic environment. | |
890 | .It | |
891 | Reads | |
892 | .Pa $HOME/.ssh/environment | |
893 | if it exists. | |
894 | .It | |
895 | Changes to user's home directory. | |
896 | .It | |
897 | If | |
898 | .Pa $HOME/.ssh/rc | |
899 | exists, runs it; else if | |
5f4fdfae | 900 | .Pa /etc/sshrc |
bf740959 | 901 | exists, runs |
4fe2af09 | 902 | it; otherwise runs xauth. |
903 | The | |
bf740959 | 904 | .Dq rc |
905 | files are given the X11 | |
906 | authentication protocol and cookie in standard input. | |
907 | .It | |
908 | Runs user's shell or command. | |
909 | .El | |
910 | .Sh AUTHORIZED_KEYS FILE FORMAT | |
bf740959 | 911 | .Pa $HOME/.ssh/authorized_keys |
96a7b0cc | 912 | is the default file that lists the public keys that are |
913 | permitted for RSA authentication in protocol version 1 | |
914 | and for public key authentication (PubkeyAuthentication) | |
da89cf4d | 915 | in protocol version 2. |
96a7b0cc | 916 | .Cm AuthorizedKeysFile |
c8445989 | 917 | may be used to specify an alternative file. |
8abcdba4 | 918 | .Pp |
4fe2af09 | 919 | Each line of the file contains one |
bf740959 | 920 | key (empty lines and lines starting with a |
921 | .Ql # | |
922 | are ignored as | |
4fe2af09 | 923 | comments). |
8abcdba4 | 924 | Each RSA public key consists of the following fields, separated by |
4fe2af09 | 925 | spaces: options, bits, exponent, modulus, comment. |
8abcdba4 | 926 | Each protocol version 2 public key consists of: |
927 | options, keytype, base64 encoded key, comment. | |
928 | The options fields | |
929 | are optional; its presence is determined by whether the line starts | |
bf740959 | 930 | with a number or not (the option field never starts with a number). |
8abcdba4 | 931 | The bits, exponent, modulus and comment fields give the RSA key for |
932 | protocol version 1; the | |
bf740959 | 933 | comment field is not used for anything (but may be convenient for the |
934 | user to identify the key). | |
8abcdba4 | 935 | For protocol version 2 the keytype is |
936 | .Dq ssh-dss | |
937 | or | |
938 | .Dq ssh-rsa . | |
bf740959 | 939 | .Pp |
940 | Note that lines in this file are usually several hundred bytes long | |
4fe2af09 | 941 | (because of the size of the RSA key modulus). |
942 | You don't want to type them in; instead, copy the | |
c0ecc314 | 943 | .Pa identity.pub , |
8abcdba4 | 944 | .Pa id_dsa.pub |
c0ecc314 | 945 | or the |
946 | .Pa id_rsa.pub | |
bf740959 | 947 | file and edit it. |
948 | .Pp | |
c345cf9d | 949 | The options (if present) consist of comma-separated option |
4fe2af09 | 950 | specifications. |
951 | No spaces are permitted, except within double quotes. | |
54bf768d | 952 | The following option specifications are supported (note |
953 | that option keywords are case-insensitive): | |
bf740959 | 954 | .Bl -tag -width Ds |
955 | .It Cm from="pattern-list" | |
956 | Specifies that in addition to RSA authentication, the canonical name | |
957 | of the remote host must be present in the comma-separated list of | |
4fe2af09 | 958 | patterns |
959 | .Pf ( Ql * | |
960 | and | |
961 | .Ql ? | |
962 | serve as wildcards). | |
963 | The list may also contain | |
964 | patterns negated by prefixing them with | |
965 | .Ql ! ; | |
966 | if the canonical host name matches a negated pattern, the key is not accepted. | |
967 | The purpose | |
bf740959 | 968 | of this option is to optionally increase security: RSA authentication |
969 | by itself does not trust the network or name servers or anything (but | |
970 | the key); however, if somebody somehow steals the key, the key | |
4fe2af09 | 971 | permits an intruder to log in from anywhere in the world. |
972 | This additional option makes using a stolen key more difficult (name | |
bf740959 | 973 | servers and/or routers would have to be compromised in addition to |
974 | just the key). | |
975 | .It Cm command="command" | |
976 | Specifies that the command is executed whenever this key is used for | |
4fe2af09 | 977 | authentication. |
978 | The command supplied by the user (if any) is ignored. | |
bf740959 | 979 | The command is run on a pty if the connection requests a pty; |
4fe2af09 | 980 | otherwise it is run without a tty. |
61e96248 | 981 | Note that if you want a 8-bit clean channel, |
982 | you must not request a pty or should specify | |
983 | .Cm no-pty . | |
4fe2af09 | 984 | A quote may be included in the command by quoting it with a backslash. |
985 | This option might be useful | |
986 | to restrict certain RSA keys to perform just a specific operation. | |
987 | An example might be a key that permits remote backups but nothing else. | |
d0c832f3 | 988 | Note that the client may specify TCP/IP and/or X11 |
989 | forwarding unless they are explicitly prohibited. | |
bf740959 | 990 | .It Cm environment="NAME=value" |
991 | Specifies that the string is to be added to the environment when | |
4fe2af09 | 992 | logging in using this key. |
993 | Environment variables set this way | |
994 | override other default environment values. | |
995 | Multiple options of this type are permitted. | |
bf740959 | 996 | .It Cm no-port-forwarding |
997 | Forbids TCP/IP forwarding when this key is used for authentication. | |
4fe2af09 | 998 | Any port forward requests by the client will return an error. |
999 | This might be used, e.g., in connection with the | |
bf740959 | 1000 | .Cm command |
1001 | option. | |
1002 | .It Cm no-X11-forwarding | |
1003 | Forbids X11 forwarding when this key is used for authentication. | |
1004 | Any X11 forward requests by the client will return an error. | |
1005 | .It Cm no-agent-forwarding | |
1006 | Forbids authentication agent forwarding when this key is used for | |
1007 | authentication. | |
1008 | .It Cm no-pty | |
1009 | Prevents tty allocation (a request to allocate a pty will fail). | |
dc504afd | 1010 | .It Cm permitopen="host:port" |
3730bb22 | 1011 | Limit local |
dc504afd | 1012 | .Li ``ssh -L'' |
b2ae83b8 | 1013 | port forwarding such that it may only connect to the specified host and |
3730bb22 | 1014 | port. Multiple |
dc504afd | 1015 | .Cm permitopen |
3730bb22 | 1016 | options may be applied separated by commas. No pattern matching is |
1017 | performed on the specified hostnames, they must be literal domains or | |
dc504afd | 1018 | addresses. |
bf740959 | 1019 | .El |
1020 | .Ss Examples | |
1021 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar | |
1022 | .Pp | |
1023 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula | |
1024 | .Pp | |
1025 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi | |
dc504afd | 1026 | .Pp |
1027 | permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323 | |
bf740959 | 1028 | .Sh SSH_KNOWN_HOSTS FILE FORMAT |
f54651ce | 1029 | The |
1d1ffb87 | 1030 | .Pa /etc/ssh_known_hosts , |
f54651ce | 1031 | and |
f49bc4f7 | 1032 | .Pa $HOME/.ssh/known_hosts |
4fe2af09 | 1033 | files contain host public keys for all known hosts. |
1034 | The global file should | |
1035 | be prepared by the administrator (optional), and the per-user file is | |
c345cf9d | 1036 | maintained automatically: whenever the user connects from an unknown host |
4fe2af09 | 1037 | its key is added to the per-user file. |
bf740959 | 1038 | .Pp |
1039 | Each line in these files contains the following fields: hostnames, | |
4fe2af09 | 1040 | bits, exponent, modulus, comment. |
1041 | The fields are separated by spaces. | |
bf740959 | 1042 | .Pp |
1043 | Hostnames is a comma-separated list of patterns ('*' and '?' act as | |
1044 | wildcards); each pattern in turn is matched against the canonical host | |
1045 | name (when authenticating a client) or against the user-supplied | |
4fe2af09 | 1046 | name (when authenticating a server). |
1047 | A pattern may also be preceded by | |
bf740959 | 1048 | .Ql ! |
1049 | to indicate negation: if the host name matches a negated | |
1050 | pattern, it is not accepted (by that line) even if it matched another | |
1051 | pattern on the line. | |
1052 | .Pp | |
1d1ffb87 | 1053 | Bits, exponent, and modulus are taken directly from the RSA host key; they |
bf740959 | 1054 | can be obtained, e.g., from |
5f4fdfae | 1055 | .Pa /etc/ssh_host_key.pub . |
bf740959 | 1056 | The optional comment field continues to the end of the line, and is not used. |
1057 | .Pp | |
1058 | Lines starting with | |
1059 | .Ql # | |
1060 | and empty lines are ignored as comments. | |
1061 | .Pp | |
1062 | When performing host authentication, authentication is accepted if any | |
4fe2af09 | 1063 | matching line has the proper key. |
1064 | It is thus permissible (but not | |
bf740959 | 1065 | recommended) to have several lines or different host keys for the same |
4fe2af09 | 1066 | names. |
1067 | This will inevitably happen when short forms of host names | |
1068 | from different domains are put in the file. | |
1069 | It is possible | |
bf740959 | 1070 | that the files contain conflicting information; authentication is |
1071 | accepted if valid information can be found from either file. | |
1072 | .Pp | |
1073 | Note that the lines in these files are typically hundreds of characters | |
1074 | long, and you definitely don't want to type in the host keys by hand. | |
1075 | Rather, generate them by a script | |
f54651ce | 1076 | or by taking |
5f4fdfae | 1077 | .Pa /etc/ssh_host_key.pub |
bf740959 | 1078 | and adding the host names at the front. |
1079 | .Ss Examples | |
da89cf4d | 1080 | .Bd -literal |
1081 | closenet,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi | |
1082 | cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....= | |
1083 | .Ed | |
bf740959 | 1084 | .Sh FILES |
1085 | .Bl -tag -width Ds | |
5f4fdfae | 1086 | .It Pa /etc/sshd_config |
bf740959 | 1087 | Contains configuration data for |
1088 | .Nm sshd . | |
1089 | This file should be writable by root only, but it is recommended | |
1090 | (though not necessary) that it be world-readable. | |
b8dc87d3 | 1091 | .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key |
da89cf4d | 1092 | These three files contain the private parts of the host keys. |
b8dc87d3 | 1093 | These files should only be owned by root, readable only by root, and not |
bf740959 | 1094 | accessible to others. |
1095 | Note that | |
1096 | .Nm | |
1097 | does not start if this file is group/world-accessible. | |
b8dc87d3 | 1098 | .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub |
da89cf4d | 1099 | These three files contain the public parts of the host keys. |
b8dc87d3 | 1100 | These files should be world-readable but writable only by |
4fe2af09 | 1101 | root. |
b8dc87d3 | 1102 | Their contents should match the respective private parts. |
1103 | These files are not | |
1104 | really used for anything; they are provided for the convenience of | |
1105 | the user so their contents can be copied to known hosts files. | |
1106 | These files are created using | |
bf740959 | 1107 | .Xr ssh-keygen 1 . |
e2432638 | 1108 | .It Pa /etc/moduli |
c523303b | 1109 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". |
5f4fdfae | 1110 | .It Pa /var/run/sshd.pid |
bf740959 | 1111 | Contains the process ID of the |
1112 | .Nm | |
1113 | listening for connections (if there are several daemons running | |
1114 | concurrently for different ports, this contains the pid of the one | |
4fe2af09 | 1115 | started last). |
c345cf9d | 1116 | The content of this file is not sensitive; it can be world-readable. |
bf740959 | 1117 | .It Pa $HOME/.ssh/authorized_keys |
da89cf4d | 1118 | Lists the public keys (RSA or DSA) that can be used to log into the user's account. |
1d1ffb87 | 1119 | This file must be readable by root (which may on some machines imply |
1120 | it being world-readable if the user's home directory resides on an NFS | |
1121 | volume). | |
1122 | It is recommended that it not be accessible by others. | |
1123 | The format of this file is described above. | |
1124 | Users will place the contents of their | |
96a7b0cc | 1125 | .Pa identity.pub , |
1d1ffb87 | 1126 | .Pa id_dsa.pub |
c0ecc314 | 1127 | and/or |
1128 | .Pa id_rsa.pub | |
1d1ffb87 | 1129 | files into this file, as described in |
1130 | .Xr ssh-keygen 1 . | |
5f4fdfae | 1131 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
6a17f9c2 | 1132 | These files are consulted when using rhosts with RSA host |
f49bc4f7 | 1133 | authentication or protocol version 2 hostbased authentication |
1134 | to check the public key of the host. | |
4fe2af09 | 1135 | The key must be listed in one of these files to be accepted. |
5bbb5681 | 1136 | The client uses the same files |
e91c60f2 | 1137 | to verify that it is connecting to the correct remote host. |
4fe2af09 | 1138 | These files should be writable only by root/the owner. |
5f4fdfae | 1139 | .Pa /etc/ssh_known_hosts |
bf740959 | 1140 | should be world-readable, and |
1141 | .Pa $HOME/.ssh/known_hosts | |
1142 | can but need not be world-readable. | |
1143 | .It Pa /etc/nologin | |
f54651ce | 1144 | If this file exists, |
bf740959 | 1145 | .Nm |
4fe2af09 | 1146 | refuses to let anyone except root log in. |
1147 | The contents of the file | |
bf740959 | 1148 | are displayed to anyone trying to log in, and non-root connections are |
4fe2af09 | 1149 | refused. |
1150 | The file should be world-readable. | |
bf740959 | 1151 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
1152 | If compiled with | |
1153 | .Sy LIBWRAP | |
1154 | support, tcp-wrappers access controls may be defined here as described in | |
1155 | .Xr hosts_access 5 . | |
1156 | .It Pa $HOME/.rhosts | |
1157 | This file contains host-username pairs, separated by a space, one per | |
4fe2af09 | 1158 | line. |
1159 | The given user on the corresponding host is permitted to log in | |
1160 | without password. | |
1161 | The same file is used by rlogind and rshd. | |
bf740959 | 1162 | The file must |
1163 | be writable only by the user; it is recommended that it not be | |
1164 | accessible by others. | |
1165 | .Pp | |
4fe2af09 | 1166 | If is also possible to use netgroups in the file. |
1167 | Either host or user | |
bf740959 | 1168 | name may be of the form +@groupname to specify all hosts or all users |
1169 | in the group. | |
1170 | .It Pa $HOME/.shosts | |
1171 | For ssh, | |
1172 | this file is exactly the same as for | |
1173 | .Pa .rhosts . | |
1174 | However, this file is | |
1175 | not used by rlogin and rshd, so using this permits access using SSH only. | |
c345cf9d | 1176 | .It Pa /etc/hosts.equiv |
bf740959 | 1177 | This file is used during |
1178 | .Pa .rhosts | |
4fe2af09 | 1179 | authentication. |
1180 | In the simplest form, this file contains host names, one per line. | |
1181 | Users on | |
bf740959 | 1182 | those hosts are permitted to log in without a password, provided they |
4fe2af09 | 1183 | have the same user name on both machines. |
1184 | The host name may also be | |
bf740959 | 1185 | followed by a user name; such users are permitted to log in as |
1186 | .Em any | |
4fe2af09 | 1187 | user on this machine (except root). |
1188 | Additionally, the syntax | |
bf740959 | 1189 | .Dq +@group |
4fe2af09 | 1190 | can be used to specify netgroups. |
1191 | Negated entries start with | |
bf740959 | 1192 | .Ql \&- . |
1193 | .Pp | |
1194 | If the client host/user is successfully matched in this file, login is | |
1195 | automatically permitted provided the client and server user names are the | |
4fe2af09 | 1196 | same. |
1197 | Additionally, successful RSA host authentication is normally required. | |
1198 | This file must be writable only by root; it is recommended | |
bf740959 | 1199 | that it be world-readable. |
1200 | .Pp | |
1201 | .Sy "Warning: It is almost never a good idea to use user names in" | |
1202 | .Pa hosts.equiv . | |
1203 | Beware that it really means that the named user(s) can log in as | |
1204 | .Em anybody , | |
1205 | which includes bin, daemon, adm, and other accounts that own critical | |
4fe2af09 | 1206 | binaries and directories. |
1207 | Using a user name practically grants the user root access. | |
1208 | The only valid use for user names that I can think | |
bf740959 | 1209 | of is in negative entries. |
1210 | .Pp | |
1211 | Note that this warning also applies to rsh/rlogin. | |
5f4fdfae | 1212 | .It Pa /etc/shosts.equiv |
bf740959 | 1213 | This is processed exactly as |
1214 | .Pa /etc/hosts.equiv . | |
1215 | However, this file may be useful in environments that want to run both | |
1216 | rsh/rlogin and ssh. | |
1217 | .It Pa $HOME/.ssh/environment | |
4fe2af09 | 1218 | This file is read into the environment at login (if it exists). |
1219 | It can only contain empty lines, comment lines (that start with | |
bf740959 | 1220 | .Ql # ) , |
4fe2af09 | 1221 | and assignment lines of the form name=value. |
1222 | The file should be writable | |
bf740959 | 1223 | only by the user; it need not be readable by anyone else. |
1224 | .It Pa $HOME/.ssh/rc | |
1225 | If this file exists, it is run with /bin/sh after reading the | |
4fe2af09 | 1226 | environment files but before starting the user's shell or command. |
1227 | If X11 spoofing is in use, this will receive the "proto cookie" pair in | |
bf740959 | 1228 | standard input (and |
1229 | .Ev DISPLAY | |
4fe2af09 | 1230 | in environment). |
1231 | This must call | |
bf740959 | 1232 | .Xr xauth 1 |
1233 | in that case. | |
1234 | .Pp | |
1235 | The primary purpose of this file is to run any initialization routines | |
1236 | which may be needed before the user's home directory becomes | |
1237 | accessible; AFS is a particular example of such an environment. | |
1238 | .Pp | |
1239 | This file will probably contain some initialization code followed by | |
da89cf4d | 1240 | something similar to: |
1241 | .Bd -literal | |
1242 | if read proto cookie; then | |
1243 | echo add $DISPLAY $proto $cookie | xauth -q - | |
1244 | fi | |
1245 | .Ed | |
bf740959 | 1246 | .Pp |
1247 | If this file does not exist, | |
5f4fdfae | 1248 | .Pa /etc/sshrc |
bf740959 | 1249 | is run, and if that |
1250 | does not exist either, xauth is used to store the cookie. | |
1251 | .Pp | |
1252 | This file should be writable only by the user, and need not be | |
1253 | readable by anyone else. | |
5f4fdfae | 1254 | .It Pa /etc/sshrc |
bf740959 | 1255 | Like |
1256 | .Pa $HOME/.ssh/rc . | |
1257 | This can be used to specify | |
4fe2af09 | 1258 | machine-specific login-time initializations globally. |
1259 | This file should be writable only by root, and should be world-readable. | |
089fbbd2 | 1260 | .El |
fa08c86b | 1261 | .Sh AUTHORS |
7f5c4295 | 1262 | OpenSSH is a derivative of the original and free |
1263 | ssh 1.2.12 release by Tatu Ylonen. | |
1264 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1265 | Theo de Raadt and Dug Song | |
1266 | removed many bugs, re-added newer features and | |
1267 | created OpenSSH. | |
1268 | Markus Friedl contributed the support for SSH | |
1269 | protocol versions 1.5 and 2.0. | |
bf740959 | 1270 | .Sh SEE ALSO |
bf740959 | 1271 | .Xr scp 1 , |
61e96248 | 1272 | .Xr sftp 1 , |
bf740959 | 1273 | .Xr ssh 1 , |
1274 | .Xr ssh-add 1 , | |
1275 | .Xr ssh-agent 1 , | |
1276 | .Xr ssh-keygen 1 , | |
248bad82 | 1277 | .Xr login.conf 5 , |
1278 | .Xr moduli 5 , | |
a5a2da3b | 1279 | .Xr sftp-server 8 |
2cad6cef | 1280 | .Rs |
1281 | .%A T. Ylonen | |
1282 | .%A T. Kivinen | |
1283 | .%A M. Saarinen | |
1284 | .%A T. Rinne | |
1285 | .%A S. Lehtinen | |
1286 | .%T "SSH Protocol Architecture" | |
1930af48 | 1287 | .%N draft-ietf-secsh-architecture-09.txt |
1288 | .%D July 2001 | |
2cad6cef | 1289 | .%O work in progress material |
1290 | .Re | |
da89cf4d | 1291 | .Rs |
1292 | .%A M. Friedl | |
1293 | .%A N. Provos | |
1294 | .%A W. A. Simpson | |
1295 | .%T "Diffie-Hellman Group Exchange for the SSH Transport Layer Protocol" | |
7d747e89 | 1296 | .%N draft-ietf-secsh-dh-group-exchange-01.txt |
1297 | .%D April 2001 | |
da89cf4d | 1298 | .%O work in progress material |
1299 | .Re |