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bf740959 | 1 | .\" -*- nroff -*- |
2 | .\" | |
bf740959 | 3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
bf740959 | 4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
5 | .\" All rights reserved | |
6 | .\" | |
bcbf86ec | 7 | .\" As far as I am concerned, the code I have written for this software |
8 | .\" can be used freely for any purpose. Any derived versions of this | |
9 | .\" software must be clearly marked as such, and if the derived work is | |
10 | .\" incompatible with the protocol description in the RFC file, it must be | |
11 | .\" called by a name other than "ssh" or "Secure Shell". | |
12 | .\" | |
f3c7c613 | 13 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. |
14 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. | |
15 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. | |
bcbf86ec | 16 | .\" |
17 | .\" Redistribution and use in source and binary forms, with or without | |
18 | .\" modification, are permitted provided that the following conditions | |
19 | .\" are met: | |
20 | .\" 1. Redistributions of source code must retain the above copyright | |
21 | .\" notice, this list of conditions and the following disclaimer. | |
22 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
23 | .\" notice, this list of conditions and the following disclaimer in the | |
24 | .\" documentation and/or other materials provided with the distribution. | |
bf740959 | 25 | .\" |
bcbf86ec | 26 | .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
27 | .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES | |
28 | .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |
29 | .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, | |
30 | .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT | |
31 | .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
32 | .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
33 | .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
34 | .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF | |
35 | .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
bf740959 | 36 | .\" |
6e9944b8 | 37 | .\" $OpenBSD: sshd.8,v 1.110 2001/04/08 16:01:36 stevesk Exp $ |
bf740959 | 38 | .Dd September 25, 1999 |
39 | .Dt SSHD 8 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm sshd | |
2c86906e | 43 | .Nd OpenSSH ssh daemon |
bf740959 | 44 | .Sh SYNOPSIS |
45 | .Nm sshd | |
ab60252b | 46 | .Op Fl diqD46 |
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: |
1d1ffb87 | 133 | Each host has a host-specific DSA key used to identify the host. |
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. | |
51c251f0 | 137 | The rest of the session is encrypted using a symmetric cipher, currently |
138 | Blowfish, 3DES, CAST128, Arcfour, 128 bit AES, or 256 bit AES. | |
1d1ffb87 | 139 | The client selects the encryption algorithm |
140 | to use from those offered by the server. | |
141 | Additionally, session integrity is provided | |
d0c832f3 | 142 | through a cryptographic message authentication code |
1d1ffb87 | 143 | (hmac-sha1 or hmac-md5). |
144 | .Pp | |
145 | Protocol version 2 provides a public key based | |
fa08c86b | 146 | user authentication method (PubkeyAuthentication) |
1d1ffb87 | 147 | and conventional password authentication. |
148 | .Pp | |
149 | .Ss Command execution and data forwarding | |
150 | .Pp | |
bf740959 | 151 | If the client successfully authenticates itself, a dialog for |
4fe2af09 | 152 | preparing the session is entered. |
153 | At this time the client may request | |
bf740959 | 154 | things like allocating a pseudo-tty, forwarding X11 connections, |
155 | forwarding TCP/IP connections, or forwarding the authentication agent | |
156 | connection over the secure channel. | |
157 | .Pp | |
158 | Finally, the client either requests a shell or execution of a command. | |
4fe2af09 | 159 | The sides then enter session mode. |
160 | In this mode, either side may send | |
bf740959 | 161 | data at any time, and such data is forwarded to/from the shell or |
162 | command on the server side, and the user terminal in the client side. | |
163 | .Pp | |
164 | When the user program terminates and all forwarded X11 and other | |
165 | connections have been closed, the server sends command exit status to | |
166 | the client, and both sides exit. | |
167 | .Pp | |
168 | .Nm | |
169 | can be configured using command-line options or a configuration | |
4fe2af09 | 170 | file. |
171 | Command-line options override values specified in the | |
bf740959 | 172 | configuration file. |
173 | .Pp | |
9d6b7add | 174 | .Nm |
175 | rereads its configuration file when it receives a hangup signal, | |
409edaba | 176 | .Dv SIGHUP , |
177 | by executing itself with the name it was started as, ie. | |
178 | .Pa /usr/sbin/sshd . | |
9d6b7add | 179 | .Pp |
bf740959 | 180 | The options are as follows: |
181 | .Bl -tag -width Ds | |
182 | .It Fl b Ar bits | |
183 | Specifies the number of bits in the server key (default 768). | |
184 | .Pp | |
185 | .It Fl d | |
4fe2af09 | 186 | Debug mode. |
187 | The server sends verbose debug output to the system | |
188 | log, and does not put itself in the background. | |
189 | The server also will not fork and will only process one connection. | |
190 | This option is only intended for debugging for the server. | |
94ec8c6b | 191 | Multiple -d options increases the debugging level. |
192 | Maximum is 3. | |
bf740959 | 193 | .It Fl f Ar configuration_file |
4fe2af09 | 194 | Specifies the name of the configuration file. |
195 | The default is | |
5f4fdfae | 196 | .Pa /etc/sshd_config . |
bf740959 | 197 | .Nm |
198 | refuses to start if there is no configuration file. | |
199 | .It Fl g Ar login_grace_time | |
200 | Gives the grace time for clients to authenticate themselves (default | |
ee5e6612 | 201 | 600 seconds). |
4fe2af09 | 202 | If the client fails to authenticate the user within |
203 | this many seconds, the server disconnects and exits. | |
204 | A value of zero indicates no limit. | |
bf740959 | 205 | .It Fl h Ar host_key_file |
8abcdba4 | 206 | Specifies the file from which the host key is read (default |
5f4fdfae | 207 | .Pa /etc/ssh_host_key ) . |
bf740959 | 208 | This option must be given if |
209 | .Nm | |
210 | is not run as root (as the normal | |
211 | host file is normally not readable by anyone but root). | |
8abcdba4 | 212 | It is possible to have multiple host key files for |
213 | the different protocol versions. | |
bf740959 | 214 | .It Fl i |
215 | Specifies that | |
216 | .Nm | |
f54651ce | 217 | is being run from inetd. |
bf740959 | 218 | .Nm |
219 | is normally not run | |
220 | from inetd because it needs to generate the server key before it can | |
4fe2af09 | 221 | respond to the client, and this may take tens of seconds. |
222 | Clients would have to wait too long if the key was regenerated every time. | |
610cd5c6 | 223 | However, with small key sizes (e.g., 512) using |
bf740959 | 224 | .Nm |
225 | from inetd may | |
226 | be feasible. | |
227 | .It Fl k Ar key_gen_time | |
228 | Specifies how often the server key is regenerated (default 3600 | |
4fe2af09 | 229 | seconds, or one hour). |
230 | The motivation for regenerating the key fairly | |
bf740959 | 231 | often is that the key is not stored anywhere, and after about an hour, |
232 | it becomes impossible to recover the key for decrypting intercepted | |
233 | communications even if the machine is cracked into or physically | |
4fe2af09 | 234 | seized. |
235 | A value of zero indicates that the key will never be regenerated. | |
bf740959 | 236 | .It Fl p Ar port |
237 | Specifies the port on which the server listens for connections | |
238 | (default 22). | |
239 | .It Fl q | |
4fe2af09 | 240 | Quiet mode. |
241 | Nothing is sent to the system log. | |
242 | Normally the beginning, | |
bf740959 | 243 | authentication, and termination of each connection is logged. |
c345cf9d | 244 | .It Fl u Ar len |
245 | This option is used to specify the size of the field | |
246 | in the | |
247 | .Li utmp | |
248 | structure that holds the remote host name. | |
249 | If the resolved host name is longer than | |
250 | .Ar len , | |
251 | the dotted decimal value will be used instead. | |
252 | This allows hosts with very long host names that | |
253 | overflow this field to still be uniquely identified. | |
254 | Specifying | |
255 | .Fl u0 | |
256 | indicates that only dotted decimal addresses | |
257 | should be put into the | |
258 | .Pa utmp | |
259 | file. | |
8abcdba4 | 260 | .It Fl D |
261 | When this option is specified | |
262 | .Nm | |
263 | will not detach and does not become a daemon. | |
264 | This allows easy monitoring of | |
265 | .Nm sshd . | |
5260325f | 266 | .It Fl V Ar client_protocol_id |
94ec8c6b | 267 | SSH-2 compatibility mode. |
3189621b | 268 | When this option is specified |
5260325f | 269 | .Nm |
3189621b | 270 | assumes the client has sent the supplied version string |
5260325f | 271 | and skips the |
272 | Protocol Version Identification Exchange. | |
94ec8c6b | 273 | This option is not intended to be called directly. |
48e671d5 | 274 | .It Fl 4 |
275 | Forces | |
276 | .Nm | |
277 | to use IPv4 addresses only. | |
278 | .It Fl 6 | |
279 | Forces | |
280 | .Nm | |
281 | to use IPv6 addresses only. | |
bf740959 | 282 | .El |
283 | .Sh CONFIGURATION FILE | |
284 | .Nm | |
f54651ce | 285 | reads configuration data from |
5f4fdfae | 286 | .Pa /etc/sshd_config |
bf740959 | 287 | (or the file specified with |
288 | .Fl f | |
4fe2af09 | 289 | on the command line). |
290 | The file contains keyword-value pairs, one per line. | |
291 | Lines starting with | |
bf740959 | 292 | .Ql # |
293 | and empty lines are interpreted as comments. | |
294 | .Pp | |
295 | The following keywords are possible. | |
296 | .Bl -tag -width Ds | |
297 | .It Cm AFSTokenPassing | |
4fe2af09 | 298 | Specifies whether an AFS token may be forwarded to the server. |
299 | Default is | |
bf740959 | 300 | .Dq yes . |
301 | .It Cm AllowGroups | |
76896b4e | 302 | This keyword can be followed by a list of group names, separated |
4fe2af09 | 303 | by spaces. |
304 | If specified, login is allowed only for users whose primary | |
c6a69271 | 305 | group or supplementary group list matches one of the patterns. |
bf740959 | 306 | .Ql \&* |
307 | and | |
308 | .Ql ? | |
309 | can be used as | |
4fe2af09 | 310 | wildcards in the patterns. |
c345cf9d | 311 | Only group names are valid; a numerical group ID isn't recognized. |
c6a69271 | 312 | By default login is allowed regardless of the group list. |
bf740959 | 313 | .Pp |
33de75a3 | 314 | .It Cm AllowTcpForwarding |
315 | Specifies whether TCP forwarding is permitted. | |
316 | The default is | |
317 | .Dq yes . | |
318 | Note that disabling TCP forwarding does not improve security unless | |
319 | users are also denied shell access, as they can always install their | |
320 | own forwarders. | |
321 | .Pp | |
bf740959 | 322 | .It Cm AllowUsers |
76896b4e | 323 | This keyword can be followed by a list of user names, separated |
4fe2af09 | 324 | by spaces. |
325 | If specified, login is allowed only for users names that | |
bf740959 | 326 | match one of the patterns. |
327 | .Ql \&* | |
328 | and | |
329 | .Ql ? | |
330 | can be used as | |
4fe2af09 | 331 | wildcards in the patterns. |
c345cf9d | 332 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 333 | By default login is allowed regardless of the user name. |
bf740959 | 334 | .Pp |
eea39c02 | 335 | .It Cm Banner |
336 | In some jurisdictions, sending a warning message before authentication | |
337 | may be relevant for getting legal protection. | |
338 | The contents of the specified file are sent to the remote user before | |
339 | authentication is allowed. | |
340 | This option is only available for protocol version 2. | |
341 | .Pp | |
657297ff | 342 | .It Cm ChallengeResponseAuthentication |
343 | Specifies whether | |
344 | challenge response | |
345 | authentication is allowed. | |
346 | Currently there is only support for | |
347 | .Xr skey 1 | |
348 | authentication. | |
349 | The default is | |
350 | .Dq yes . | |
f54651ce | 351 | .It Cm Ciphers |
352 | Specifies the ciphers allowed for protocol version 2. | |
353 | Multiple ciphers must be comma-separated. | |
354 | The default is | |
7a6c39a3 | 355 | .Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour. |
bf740959 | 356 | .It Cm CheckMail |
357 | Specifies whether | |
358 | .Nm | |
359 | should check for new mail for interactive logins. | |
360 | The default is | |
361 | .Dq no . | |
362 | .It Cm DenyGroups | |
363 | This keyword can be followed by a number of group names, separated | |
4fe2af09 | 364 | by spaces. |
c6a69271 | 365 | Users whose primary group or supplementary group list matches |
366 | one of the patterns aren't allowed to log in. | |
bf740959 | 367 | .Ql \&* |
368 | and | |
369 | .Ql ? | |
370 | can be used as | |
4fe2af09 | 371 | wildcards in the patterns. |
c345cf9d | 372 | Only group names are valid; a numerical group ID isn't recognized. |
c6a69271 | 373 | By default login is allowed regardless of the group list. |
bf740959 | 374 | .Pp |
375 | .It Cm DenyUsers | |
376 | This keyword can be followed by a number of user names, separated | |
4fe2af09 | 377 | by spaces. |
378 | Login is disallowed for user names that match one of the patterns. | |
bf740959 | 379 | .Ql \&* |
380 | and | |
381 | .Ql ? | |
4fe2af09 | 382 | can be used as wildcards in the patterns. |
c345cf9d | 383 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 384 | By default login is allowed regardless of the user name. |
1d1ffb87 | 385 | .It Cm GatewayPorts |
386 | Specifies whether remote hosts are allowed to connect to ports | |
387 | forwarded for the client. | |
388 | The argument must be | |
389 | .Dq yes | |
390 | or | |
391 | .Dq no . | |
392 | The default is | |
393 | .Dq no . | |
bf740959 | 394 | .It Cm HostKey |
fa08c86b | 395 | Specifies the file containing the private host keys (default |
1d1ffb87 | 396 | .Pa /etc/ssh_host_key ) |
fa08c86b | 397 | used by SSH protocol versions 1 and 2. |
bf740959 | 398 | Note that |
399 | .Nm | |
42f11eb2 | 400 | will refuse to use a file if it is group/world-accessible. |
fa08c86b | 401 | It is possible to have multiple host key files. |
402 | .Dq rsa1 | |
403 | keys are used for version 1 and | |
404 | .Dq dsa | |
405 | or | |
406 | .Dq rsa | |
407 | are used for version 2 of the SSH protocol. | |
bf740959 | 408 | .It Cm IgnoreRhosts |
c8d54615 | 409 | Specifies that |
410 | .Pa .rhosts | |
f54651ce | 411 | and |
c8d54615 | 412 | .Pa .shosts |
413 | files will not be used in authentication. | |
bf740959 | 414 | .Pa /etc/hosts.equiv |
415 | and | |
f54651ce | 416 | .Pa /etc/shosts.equiv |
4fe2af09 | 417 | are still used. |
f54651ce | 418 | The default is |
c8d54615 | 419 | .Dq yes . |
b4748e2f | 420 | .It Cm IgnoreUserKnownHosts |
421 | Specifies whether | |
422 | .Nm | |
423 | should ignore the user's | |
424 | .Pa $HOME/.ssh/known_hosts | |
425 | during | |
426 | .Cm RhostsRSAAuthentication . | |
427 | The default is | |
428 | .Dq no . | |
bf740959 | 429 | .It Cm KeepAlive |
430 | Specifies whether the system should send keepalive messages to the | |
4fe2af09 | 431 | other side. |
432 | If they are sent, death of the connection or crash of one | |
433 | of the machines will be properly noticed. | |
434 | However, this means that | |
bf740959 | 435 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 436 | find it annoying. |
d0c832f3 | 437 | On the other hand, if keepalives are not sent, |
bf740959 | 438 | sessions may hang indefinitely on the server, leaving |
439 | .Dq ghost | |
440 | users and consuming server resources. | |
441 | .Pp | |
442 | The default is | |
443 | .Dq yes | |
444 | (to send keepalives), and the server will notice | |
4fe2af09 | 445 | if the network goes down or the client host reboots. |
446 | This avoids infinitely hanging sessions. | |
bf740959 | 447 | .Pp |
448 | To disable keepalives, the value should be set to | |
449 | .Dq no | |
450 | in both the server and the client configuration files. | |
451 | .It Cm KerberosAuthentication | |
4fe2af09 | 452 | Specifies whether Kerberos authentication is allowed. |
453 | This can be in the form of a Kerberos ticket, or if | |
bf740959 | 454 | .Cm PasswordAuthentication |
455 | is yes, the password provided by the user will be validated through | |
94ec8c6b | 456 | the Kerberos KDC. |
457 | To use this option, the server needs a | |
c345cf9d | 458 | Kerberos servtab which allows the verification of the KDC's identity. |
4fe2af09 | 459 | Default is |
bf740959 | 460 | .Dq yes . |
461 | .It Cm KerberosOrLocalPasswd | |
462 | If set then if password authentication through Kerberos fails then | |
463 | the password will be validated via any additional local mechanism | |
464 | such as | |
188adeb2 | 465 | .Pa /etc/passwd . |
4fe2af09 | 466 | Default is |
bf740959 | 467 | .Dq yes . |
468 | .It Cm KerberosTgtPassing | |
469 | Specifies whether a Kerberos TGT may be forwarded to the server. | |
f54651ce | 470 | Default is |
bf740959 | 471 | .Dq no , |
472 | as this only works when the Kerberos KDC is actually an AFS kaserver. | |
473 | .It Cm KerberosTicketCleanup | |
474 | Specifies whether to automatically destroy the user's ticket cache | |
4fe2af09 | 475 | file on logout. |
476 | Default is | |
bf740959 | 477 | .Dq yes . |
478 | .It Cm KeyRegenerationInterval | |
479 | The server key is automatically regenerated after this many seconds | |
4fe2af09 | 480 | (if it has been used). |
481 | The purpose of regeneration is to prevent | |
bf740959 | 482 | decrypting captured sessions by later breaking into the machine and |
4fe2af09 | 483 | stealing the keys. |
484 | The key is never stored anywhere. | |
485 | If the value is 0, the key is never regenerated. | |
486 | The default is 3600 (seconds). | |
bf740959 | 487 | .It Cm ListenAddress |
6e9944b8 | 488 | Specifies the local addresses |
bf740959 | 489 | .Nm |
490 | should listen on. | |
6e9944b8 | 491 | The following forms may be used: |
492 | .Pp | |
493 | .Bl -item -offset indent -compact | |
494 | .It | |
495 | .Cm ListenAddress | |
496 | host|IPv4_addr|IPv6_addr | |
497 | .It | |
498 | .Cm ListenAddress | |
499 | host|IPv4_addr:port | |
500 | .It | |
501 | .Cm ListenAddress | |
502 | [host|IPv6_addr]:port | |
503 | .El | |
504 | .Pp | |
505 | If | |
506 | .Dq :port | |
507 | is not specified, | |
508 | .Nm | |
509 | will listen on the address and all prior | |
510 | .Cm Port | |
511 | options specified. The default is to listen on all local | |
512 | addresses. Multiple | |
513 | .Cm ListenAddress | |
514 | options are permitted. Additionally, any | |
515 | .Cm Port | |
516 | options must precede this option for non port qualified addresses. | |
bf740959 | 517 | .It Cm LoginGraceTime |
518 | The server disconnects after this time if the user has not | |
4fe2af09 | 519 | successfully logged in. |
520 | If the value is 0, there is no time limit. | |
bf740959 | 521 | The default is 600 (seconds). |
6a17f9c2 | 522 | .It Cm LogLevel |
523 | Gives the verbosity level that is used when logging messages from | |
524 | .Nm sshd . | |
525 | The possible values are: | |
59c97189 | 526 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
527 | The default is INFO. | |
6a17f9c2 | 528 | Logging with level DEBUG violates the privacy of users |
529 | and is not recommended. | |
b2552997 | 530 | .It Cm MACs |
531 | Specifies the available MAC (message authentication code) algorithms. | |
532 | The MAC algorithm is used in protocol version 2 | |
533 | for data integrity protection. | |
534 | Multiple algorithms must be comma-separated. | |
535 | The default is | |
536 | .Pp | |
537 | .Bd -literal | |
7a6c39a3 | 538 | ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com, |
b2552997 | 539 | hmac-sha1-96,hmac-md5-96'' |
540 | .Ed | |
089fbbd2 | 541 | .It Cm MaxStartups |
542 | Specifies the maximum number of concurrent unauthenticated connections to the | |
543 | .Nm | |
544 | daemon. | |
545 | Additional connections will be dropped until authentication succeeds or the | |
546 | .Cm LoginGraceTime | |
547 | expires for a connection. | |
548 | The default is 10. | |
c345cf9d | 549 | .Pp |
550 | Alternatively, random early drop can be enabled by specifying | |
551 | the three colon separated values | |
552 | .Dq start:rate:full | |
94ec8c6b | 553 | (e.g., "10:30:60"). |
c345cf9d | 554 | .Nm |
6f37606e | 555 | will refuse connection attempts with a probability of |
c345cf9d | 556 | .Dq rate/100 |
557 | (30%) | |
558 | if there are currently | |
559 | .Dq start | |
560 | (10) | |
561 | unauthenticated connections. | |
6f37606e | 562 | The probability increases linearly and all connection attempts |
c345cf9d | 563 | are refused if the number of unauthenticated connections reaches |
564 | .Dq full | |
565 | (60). | |
bf740959 | 566 | .It Cm PasswordAuthentication |
567 | Specifies whether password authentication is allowed. | |
568 | The default is | |
569 | .Dq yes . | |
c345cf9d | 570 | Note that this option applies to both protocol versions 1 and 2. |
bf740959 | 571 | .It Cm PermitEmptyPasswords |
572 | When password authentication is allowed, it specifies whether the | |
4fe2af09 | 573 | server allows login to accounts with empty password strings. |
574 | The default is | |
c8d54615 | 575 | .Dq no . |
bf740959 | 576 | .It Cm PermitRootLogin |
46f23b8d | 577 | Specifies whether root can login using |
bf740959 | 578 | .Xr ssh 1 . |
579 | The argument must be | |
580 | .Dq yes , | |
15853e93 | 581 | .Dq without-password , |
582 | .Dq forced-commands-only | |
bf740959 | 583 | or |
584 | .Dq no . | |
585 | The default is | |
586 | .Dq yes . | |
15853e93 | 587 | .Pp |
588 | If this option is set to | |
bf740959 | 589 | .Dq without-password |
15853e93 | 590 | password authentication is disabled for root. |
bf740959 | 591 | .Pp |
15853e93 | 592 | If this option is set to |
593 | .Dq forced-commands-only | |
594 | root login with public key authentication will be allowed, | |
595 | but only if the | |
bf740959 | 596 | .Ar command |
15853e93 | 597 | option has been specified |
bf740959 | 598 | (which may be useful for taking remote backups even if root login is |
15853e93 | 599 | normally not allowed). All other authentication methods are disabled |
600 | for root. | |
46f23b8d | 601 | .Pp |
602 | If this option is set to | |
603 | .Dq no | |
604 | root is not allowed to login. | |
0fbe8c74 | 605 | .It Cm PidFile |
606 | Specifies the file that contains the process identifier of the | |
607 | .Nm | |
608 | daemon. | |
609 | The default is | |
610 | .Pa /var/run/sshd.pid . | |
bf740959 | 611 | .It Cm Port |
612 | Specifies the port number that | |
613 | .Nm | |
4fe2af09 | 614 | listens on. |
615 | The default is 22. | |
48e671d5 | 616 | Multiple options of this type are permitted. |
4f4648f9 | 617 | .It Cm PrintLastLog |
618 | Specifies whether | |
619 | .Nm | |
620 | should print the date and time when the user last logged in. | |
621 | The default is | |
622 | .Dq yes . | |
bf740959 | 623 | .It Cm PrintMotd |
624 | Specifies whether | |
625 | .Nm | |
f54651ce | 626 | should print |
bf740959 | 627 | .Pa /etc/motd |
4fe2af09 | 628 | when a user logs in interactively. |
629 | (On some systems it is also printed by the shell, | |
bf740959 | 630 | .Pa /etc/profile , |
4fe2af09 | 631 | or equivalent.) |
632 | The default is | |
bf740959 | 633 | .Dq yes . |
f54651ce | 634 | .It Cm Protocol |
635 | Specifies the protocol versions | |
636 | .Nm | |
637 | should support. | |
638 | The possible values are | |
639 | .Dq 1 | |
640 | and | |
641 | .Dq 2 . | |
642 | Multiple versions must be comma-separated. | |
643 | The default is | |
644 | .Dq 1 . | |
657297ff | 645 | .It Cm PubkeyAuthentication |
646 | Specifies whether public key authentication is allowed. | |
647 | The default is | |
648 | .Dq yes . | |
649 | Note that this option applies to protocol version 2 only. | |
61e96248 | 650 | .It Cm ReverseMappingCheck |
651 | Specifies whether | |
652 | .Nm | |
653 | should try to verify the remote host name and check that | |
654 | the resolved host name for the remote IP address maps back to the | |
655 | very same IP address. | |
656 | The default is | |
657 | .Dq no . | |
bf740959 | 658 | .It Cm RhostsAuthentication |
659 | Specifies whether authentication using rhosts or /etc/hosts.equiv | |
4fe2af09 | 660 | files is sufficient. |
661 | Normally, this method should not be permitted because it is insecure. | |
bf740959 | 662 | .Cm RhostsRSAAuthentication |
663 | should be used | |
664 | instead, because it performs RSA-based host authentication in addition | |
665 | to normal rhosts or /etc/hosts.equiv authentication. | |
666 | The default is | |
667 | .Dq no . | |
668 | .It Cm RhostsRSAAuthentication | |
669 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
4fe2af09 | 670 | with successful RSA host authentication is allowed. |
671 | The default is | |
c8d54615 | 672 | .Dq no . |
bf740959 | 673 | .It Cm RSAAuthentication |
4fe2af09 | 674 | Specifies whether pure RSA authentication is allowed. |
675 | The default is | |
bf740959 | 676 | .Dq yes . |
1d1ffb87 | 677 | Note that this option applies to protocol version 1 only. |
bf740959 | 678 | .It Cm ServerKeyBits |
4fe2af09 | 679 | Defines the number of bits in the server key. |
680 | The minimum value is 512, and the default is 768. | |
bf740959 | 681 | .It Cm StrictModes |
682 | Specifies whether | |
683 | .Nm | |
684 | should check file modes and ownership of the | |
4fe2af09 | 685 | user's files and home directory before accepting login. |
686 | This is normally desirable because novices sometimes accidentally leave their | |
687 | directory or files world-writable. | |
688 | The default is | |
bf740959 | 689 | .Dq yes . |
38c295d6 | 690 | .It Cm Subsystem |
94ec8c6b | 691 | Configures an external subsystem (e.g., file transfer daemon). |
692 | Arguments should be a subsystem name and a command to execute upon subsystem | |
693 | request. | |
b5e300c2 | 694 | The command |
695 | .Xr sftp-server 8 | |
696 | implements the | |
697 | .Dq sftp | |
698 | file transfer subsystem. | |
38c295d6 | 699 | By default no subsystems are defined. |
700 | Note that this option applies to protocol version 2 only. | |
bf740959 | 701 | .It Cm SyslogFacility |
702 | Gives the facility code that is used when logging messages from | |
703 | .Nm sshd . | |
704 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, | |
4fe2af09 | 705 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
706 | The default is AUTH. | |
bf740959 | 707 | .It Cm UseLogin |
708 | Specifies whether | |
709 | .Xr login 1 | |
fa649821 | 710 | is used for interactive login sessions. |
711 | Note that | |
712 | .Xr login 1 | |
c345cf9d | 713 | is never used for remote command execution. |
4fe2af09 | 714 | The default is |
bf740959 | 715 | .Dq no . |
bf740959 | 716 | .It Cm X11DisplayOffset |
717 | Specifies the first display number available for | |
718 | .Nm sshd Ns 's | |
4fe2af09 | 719 | X11 forwarding. |
720 | This prevents | |
bf740959 | 721 | .Nm |
722 | from interfering with real X11 servers. | |
c8d54615 | 723 | The default is 10. |
7b2ea3a1 | 724 | .It Cm X11Forwarding |
4fe2af09 | 725 | Specifies whether X11 forwarding is permitted. |
726 | The default is | |
c8d54615 | 727 | .Dq no . |
7b2ea3a1 | 728 | Note that disabling X11 forwarding does not improve security in any |
729 | way, as users can always install their own forwarders. | |
fa649821 | 730 | .It Cm XAuthLocation |
731 | Specifies the location of the | |
732 | .Xr xauth 1 | |
733 | program. | |
734 | The default is | |
735 | .Pa /usr/X11R6/bin/xauth . | |
bf740959 | 736 | .El |
737 | .Sh LOGIN PROCESS | |
738 | When a user successfully logs in, | |
739 | .Nm | |
740 | does the following: | |
741 | .Bl -enum -offset indent | |
742 | .It | |
743 | If the login is on a tty, and no command has been specified, | |
f54651ce | 744 | prints last login time and |
bf740959 | 745 | .Pa /etc/motd |
746 | (unless prevented in the configuration file or by | |
747 | .Pa $HOME/.hushlogin ; | |
748 | see the | |
f54651ce | 749 | .Sx FILES |
bf740959 | 750 | section). |
751 | .It | |
752 | If the login is on a tty, records login time. | |
753 | .It | |
754 | Checks | |
755 | .Pa /etc/nologin ; | |
756 | if it exists, prints contents and quits | |
757 | (unless root). | |
758 | .It | |
759 | Changes to run with normal user privileges. | |
760 | .It | |
761 | Sets up basic environment. | |
762 | .It | |
763 | Reads | |
764 | .Pa $HOME/.ssh/environment | |
765 | if it exists. | |
766 | .It | |
767 | Changes to user's home directory. | |
768 | .It | |
769 | If | |
770 | .Pa $HOME/.ssh/rc | |
771 | exists, runs it; else if | |
5f4fdfae | 772 | .Pa /etc/sshrc |
bf740959 | 773 | exists, runs |
4fe2af09 | 774 | it; otherwise runs xauth. |
775 | The | |
bf740959 | 776 | .Dq rc |
777 | files are given the X11 | |
778 | authentication protocol and cookie in standard input. | |
779 | .It | |
780 | Runs user's shell or command. | |
781 | .El | |
782 | .Sh AUTHORIZED_KEYS FILE FORMAT | |
f54651ce | 783 | The |
bf740959 | 784 | .Pa $HOME/.ssh/authorized_keys |
785 | file lists the RSA keys that are | |
1d1ffb87 | 786 | permitted for RSA authentication in SSH protocols 1.3 and 1.5 |
d0c832f3 | 787 | Similarly, the |
1d1ffb87 | 788 | .Pa $HOME/.ssh/authorized_keys2 |
8abcdba4 | 789 | file lists the DSA and RSA keys that are |
790 | permitted for public key authentication (PubkeyAuthentication) | |
791 | in SSH protocol 2.0. | |
792 | .Pp | |
4fe2af09 | 793 | Each line of the file contains one |
bf740959 | 794 | key (empty lines and lines starting with a |
795 | .Ql # | |
796 | are ignored as | |
4fe2af09 | 797 | comments). |
8abcdba4 | 798 | Each RSA public key consists of the following fields, separated by |
4fe2af09 | 799 | spaces: options, bits, exponent, modulus, comment. |
8abcdba4 | 800 | Each protocol version 2 public key consists of: |
801 | options, keytype, base64 encoded key, comment. | |
802 | The options fields | |
803 | are optional; its presence is determined by whether the line starts | |
bf740959 | 804 | with a number or not (the option field never starts with a number). |
8abcdba4 | 805 | The bits, exponent, modulus and comment fields give the RSA key for |
806 | protocol version 1; the | |
bf740959 | 807 | comment field is not used for anything (but may be convenient for the |
808 | user to identify the key). | |
8abcdba4 | 809 | For protocol version 2 the keytype is |
810 | .Dq ssh-dss | |
811 | or | |
812 | .Dq ssh-rsa . | |
bf740959 | 813 | .Pp |
814 | Note that lines in this file are usually several hundred bytes long | |
4fe2af09 | 815 | (because of the size of the RSA key modulus). |
816 | You don't want to type them in; instead, copy the | |
bf740959 | 817 | .Pa identity.pub |
8abcdba4 | 818 | or the |
819 | .Pa id_dsa.pub | |
bf740959 | 820 | file and edit it. |
821 | .Pp | |
c345cf9d | 822 | The options (if present) consist of comma-separated option |
4fe2af09 | 823 | specifications. |
824 | No spaces are permitted, except within double quotes. | |
bf740959 | 825 | The following option specifications are supported: |
826 | .Bl -tag -width Ds | |
827 | .It Cm from="pattern-list" | |
828 | Specifies that in addition to RSA authentication, the canonical name | |
829 | of the remote host must be present in the comma-separated list of | |
4fe2af09 | 830 | patterns |
831 | .Pf ( Ql * | |
832 | and | |
833 | .Ql ? | |
834 | serve as wildcards). | |
835 | The list may also contain | |
836 | patterns negated by prefixing them with | |
837 | .Ql ! ; | |
838 | if the canonical host name matches a negated pattern, the key is not accepted. | |
839 | The purpose | |
bf740959 | 840 | of this option is to optionally increase security: RSA authentication |
841 | by itself does not trust the network or name servers or anything (but | |
842 | the key); however, if somebody somehow steals the key, the key | |
4fe2af09 | 843 | permits an intruder to log in from anywhere in the world. |
844 | This additional option makes using a stolen key more difficult (name | |
bf740959 | 845 | servers and/or routers would have to be compromised in addition to |
846 | just the key). | |
847 | .It Cm command="command" | |
848 | Specifies that the command is executed whenever this key is used for | |
4fe2af09 | 849 | authentication. |
850 | The command supplied by the user (if any) is ignored. | |
bf740959 | 851 | The command is run on a pty if the connection requests a pty; |
4fe2af09 | 852 | otherwise it is run without a tty. |
61e96248 | 853 | Note that if you want a 8-bit clean channel, |
854 | you must not request a pty or should specify | |
855 | .Cm no-pty . | |
4fe2af09 | 856 | A quote may be included in the command by quoting it with a backslash. |
857 | This option might be useful | |
858 | to restrict certain RSA keys to perform just a specific operation. | |
859 | An example might be a key that permits remote backups but nothing else. | |
d0c832f3 | 860 | Note that the client may specify TCP/IP and/or X11 |
861 | forwarding unless they are explicitly prohibited. | |
bf740959 | 862 | .It Cm environment="NAME=value" |
863 | Specifies that the string is to be added to the environment when | |
4fe2af09 | 864 | logging in using this key. |
865 | Environment variables set this way | |
866 | override other default environment values. | |
867 | Multiple options of this type are permitted. | |
bf740959 | 868 | .It Cm no-port-forwarding |
869 | Forbids TCP/IP forwarding when this key is used for authentication. | |
4fe2af09 | 870 | Any port forward requests by the client will return an error. |
871 | This might be used, e.g., in connection with the | |
bf740959 | 872 | .Cm command |
873 | option. | |
874 | .It Cm no-X11-forwarding | |
875 | Forbids X11 forwarding when this key is used for authentication. | |
876 | Any X11 forward requests by the client will return an error. | |
877 | .It Cm no-agent-forwarding | |
878 | Forbids authentication agent forwarding when this key is used for | |
879 | authentication. | |
880 | .It Cm no-pty | |
881 | Prevents tty allocation (a request to allocate a pty will fail). | |
dc504afd | 882 | .It Cm permitopen="host:port" |
883 | Limit local | |
884 | .Li ``ssh -L'' | |
885 | port-forwading such that it may only connect to the specified host and | |
886 | port. Multiple | |
887 | .Cm permitopen | |
888 | options may be applied seperated by commas. No pattern matching is | |
889 | performed on the specified hostnames, they must be literal domains or | |
890 | addresses. | |
bf740959 | 891 | .El |
892 | .Ss Examples | |
893 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar | |
894 | .Pp | |
895 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula | |
896 | .Pp | |
897 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi | |
dc504afd | 898 | .Pp |
899 | permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323 | |
bf740959 | 900 | .Sh SSH_KNOWN_HOSTS FILE FORMAT |
f54651ce | 901 | The |
1d1ffb87 | 902 | .Pa /etc/ssh_known_hosts , |
903 | .Pa /etc/ssh_known_hosts2 , | |
904 | .Pa $HOME/.ssh/known_hosts , | |
f54651ce | 905 | and |
1d1ffb87 | 906 | .Pa $HOME/.ssh/known_hosts2 |
4fe2af09 | 907 | files contain host public keys for all known hosts. |
908 | The global file should | |
909 | be prepared by the administrator (optional), and the per-user file is | |
c345cf9d | 910 | maintained automatically: whenever the user connects from an unknown host |
4fe2af09 | 911 | its key is added to the per-user file. |
bf740959 | 912 | .Pp |
913 | Each line in these files contains the following fields: hostnames, | |
4fe2af09 | 914 | bits, exponent, modulus, comment. |
915 | The fields are separated by spaces. | |
bf740959 | 916 | .Pp |
917 | Hostnames is a comma-separated list of patterns ('*' and '?' act as | |
918 | wildcards); each pattern in turn is matched against the canonical host | |
919 | name (when authenticating a client) or against the user-supplied | |
4fe2af09 | 920 | name (when authenticating a server). |
921 | A pattern may also be preceded by | |
bf740959 | 922 | .Ql ! |
923 | to indicate negation: if the host name matches a negated | |
924 | pattern, it is not accepted (by that line) even if it matched another | |
925 | pattern on the line. | |
926 | .Pp | |
1d1ffb87 | 927 | Bits, exponent, and modulus are taken directly from the RSA host key; they |
bf740959 | 928 | can be obtained, e.g., from |
5f4fdfae | 929 | .Pa /etc/ssh_host_key.pub . |
bf740959 | 930 | The optional comment field continues to the end of the line, and is not used. |
931 | .Pp | |
932 | Lines starting with | |
933 | .Ql # | |
934 | and empty lines are ignored as comments. | |
935 | .Pp | |
936 | When performing host authentication, authentication is accepted if any | |
4fe2af09 | 937 | matching line has the proper key. |
938 | It is thus permissible (but not | |
bf740959 | 939 | recommended) to have several lines or different host keys for the same |
4fe2af09 | 940 | names. |
941 | This will inevitably happen when short forms of host names | |
942 | from different domains are put in the file. | |
943 | It is possible | |
bf740959 | 944 | that the files contain conflicting information; authentication is |
945 | accepted if valid information can be found from either file. | |
946 | .Pp | |
947 | Note that the lines in these files are typically hundreds of characters | |
948 | long, and you definitely don't want to type in the host keys by hand. | |
949 | Rather, generate them by a script | |
f54651ce | 950 | or by taking |
5f4fdfae | 951 | .Pa /etc/ssh_host_key.pub |
bf740959 | 952 | and adding the host names at the front. |
953 | .Ss Examples | |
954 | closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi | |
955 | .Sh FILES | |
956 | .Bl -tag -width Ds | |
5f4fdfae | 957 | .It Pa /etc/sshd_config |
bf740959 | 958 | Contains configuration data for |
959 | .Nm sshd . | |
960 | This file should be writable by root only, but it is recommended | |
961 | (though not necessary) that it be world-readable. | |
b8dc87d3 | 962 | .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key |
963 | These three files contain the private parts of the | |
964 | (SSH1, SSH2 DSA, and SSH2 RSA) host keys. | |
965 | These files should only be owned by root, readable only by root, and not | |
bf740959 | 966 | accessible to others. |
967 | Note that | |
968 | .Nm | |
969 | does not start if this file is group/world-accessible. | |
b8dc87d3 | 970 | .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub |
672f212f | 971 | These three files contain the public parts of the |
b8dc87d3 | 972 | (SSH1, SSH2 DSA, and SSH2 RSA) host keys. |
973 | These files should be world-readable but writable only by | |
4fe2af09 | 974 | root. |
b8dc87d3 | 975 | Their contents should match the respective private parts. |
976 | These files are not | |
977 | really used for anything; they are provided for the convenience of | |
978 | the user so their contents can be copied to known hosts files. | |
979 | These files are created using | |
bf740959 | 980 | .Xr ssh-keygen 1 . |
c523303b | 981 | .It Pa /etc/primes |
982 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". | |
5f4fdfae | 983 | .It Pa /var/run/sshd.pid |
bf740959 | 984 | Contains the process ID of the |
985 | .Nm | |
986 | listening for connections (if there are several daemons running | |
987 | concurrently for different ports, this contains the pid of the one | |
4fe2af09 | 988 | started last). |
c345cf9d | 989 | The content of this file is not sensitive; it can be world-readable. |
bf740959 | 990 | .It Pa $HOME/.ssh/authorized_keys |
991 | Lists the RSA keys that can be used to log into the user's account. | |
992 | This file must be readable by root (which may on some machines imply | |
993 | it being world-readable if the user's home directory resides on an NFS | |
4fe2af09 | 994 | volume). |
995 | It is recommended that it not be accessible by others. | |
996 | The format of this file is described above. | |
1d1ffb87 | 997 | Users will place the contents of their |
998 | .Pa identity.pub | |
999 | files into this file, as described in | |
1000 | .Xr ssh-keygen 1 . | |
1001 | .It Pa $HOME/.ssh/authorized_keys2 | |
1002 | Lists the DSA keys that can be used to log into the user's account. | |
1003 | This file must be readable by root (which may on some machines imply | |
1004 | it being world-readable if the user's home directory resides on an NFS | |
1005 | volume). | |
1006 | It is recommended that it not be accessible by others. | |
1007 | The format of this file is described above. | |
1008 | Users will place the contents of their | |
1009 | .Pa id_dsa.pub | |
1010 | files into this file, as described in | |
1011 | .Xr ssh-keygen 1 . | |
5f4fdfae | 1012 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
6a17f9c2 | 1013 | These files are consulted when using rhosts with RSA host |
4fe2af09 | 1014 | authentication to check the public key of the host. |
1015 | The key must be listed in one of these files to be accepted. | |
5bbb5681 | 1016 | The client uses the same files |
e91c60f2 | 1017 | to verify that it is connecting to the correct remote host. |
4fe2af09 | 1018 | These files should be writable only by root/the owner. |
5f4fdfae | 1019 | .Pa /etc/ssh_known_hosts |
bf740959 | 1020 | should be world-readable, and |
1021 | .Pa $HOME/.ssh/known_hosts | |
1022 | can but need not be world-readable. | |
1023 | .It Pa /etc/nologin | |
f54651ce | 1024 | If this file exists, |
bf740959 | 1025 | .Nm |
4fe2af09 | 1026 | refuses to let anyone except root log in. |
1027 | The contents of the file | |
bf740959 | 1028 | are displayed to anyone trying to log in, and non-root connections are |
4fe2af09 | 1029 | refused. |
1030 | The file should be world-readable. | |
bf740959 | 1031 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
1032 | If compiled with | |
1033 | .Sy LIBWRAP | |
1034 | support, tcp-wrappers access controls may be defined here as described in | |
1035 | .Xr hosts_access 5 . | |
1036 | .It Pa $HOME/.rhosts | |
1037 | This file contains host-username pairs, separated by a space, one per | |
4fe2af09 | 1038 | line. |
1039 | The given user on the corresponding host is permitted to log in | |
1040 | without password. | |
1041 | The same file is used by rlogind and rshd. | |
bf740959 | 1042 | The file must |
1043 | be writable only by the user; it is recommended that it not be | |
1044 | accessible by others. | |
1045 | .Pp | |
4fe2af09 | 1046 | If is also possible to use netgroups in the file. |
1047 | Either host or user | |
bf740959 | 1048 | name may be of the form +@groupname to specify all hosts or all users |
1049 | in the group. | |
1050 | .It Pa $HOME/.shosts | |
1051 | For ssh, | |
1052 | this file is exactly the same as for | |
1053 | .Pa .rhosts . | |
1054 | However, this file is | |
1055 | not used by rlogin and rshd, so using this permits access using SSH only. | |
c345cf9d | 1056 | .It Pa /etc/hosts.equiv |
bf740959 | 1057 | This file is used during |
1058 | .Pa .rhosts | |
4fe2af09 | 1059 | authentication. |
1060 | In the simplest form, this file contains host names, one per line. | |
1061 | Users on | |
bf740959 | 1062 | those hosts are permitted to log in without a password, provided they |
4fe2af09 | 1063 | have the same user name on both machines. |
1064 | The host name may also be | |
bf740959 | 1065 | followed by a user name; such users are permitted to log in as |
1066 | .Em any | |
4fe2af09 | 1067 | user on this machine (except root). |
1068 | Additionally, the syntax | |
bf740959 | 1069 | .Dq +@group |
4fe2af09 | 1070 | can be used to specify netgroups. |
1071 | Negated entries start with | |
bf740959 | 1072 | .Ql \&- . |
1073 | .Pp | |
1074 | If the client host/user is successfully matched in this file, login is | |
1075 | automatically permitted provided the client and server user names are the | |
4fe2af09 | 1076 | same. |
1077 | Additionally, successful RSA host authentication is normally required. | |
1078 | This file must be writable only by root; it is recommended | |
bf740959 | 1079 | that it be world-readable. |
1080 | .Pp | |
1081 | .Sy "Warning: It is almost never a good idea to use user names in" | |
1082 | .Pa hosts.equiv . | |
1083 | Beware that it really means that the named user(s) can log in as | |
1084 | .Em anybody , | |
1085 | which includes bin, daemon, adm, and other accounts that own critical | |
4fe2af09 | 1086 | binaries and directories. |
1087 | Using a user name practically grants the user root access. | |
1088 | The only valid use for user names that I can think | |
bf740959 | 1089 | of is in negative entries. |
1090 | .Pp | |
1091 | Note that this warning also applies to rsh/rlogin. | |
5f4fdfae | 1092 | .It Pa /etc/shosts.equiv |
bf740959 | 1093 | This is processed exactly as |
1094 | .Pa /etc/hosts.equiv . | |
1095 | However, this file may be useful in environments that want to run both | |
1096 | rsh/rlogin and ssh. | |
1097 | .It Pa $HOME/.ssh/environment | |
4fe2af09 | 1098 | This file is read into the environment at login (if it exists). |
1099 | It can only contain empty lines, comment lines (that start with | |
bf740959 | 1100 | .Ql # ) , |
4fe2af09 | 1101 | and assignment lines of the form name=value. |
1102 | The file should be writable | |
bf740959 | 1103 | only by the user; it need not be readable by anyone else. |
1104 | .It Pa $HOME/.ssh/rc | |
1105 | If this file exists, it is run with /bin/sh after reading the | |
4fe2af09 | 1106 | environment files but before starting the user's shell or command. |
1107 | If X11 spoofing is in use, this will receive the "proto cookie" pair in | |
bf740959 | 1108 | standard input (and |
1109 | .Ev DISPLAY | |
4fe2af09 | 1110 | in environment). |
1111 | This must call | |
bf740959 | 1112 | .Xr xauth 1 |
1113 | in that case. | |
1114 | .Pp | |
1115 | The primary purpose of this file is to run any initialization routines | |
1116 | which may be needed before the user's home directory becomes | |
1117 | accessible; AFS is a particular example of such an environment. | |
1118 | .Pp | |
1119 | This file will probably contain some initialization code followed by | |
1120 | something similar to: "if read proto cookie; then echo add $DISPLAY | |
1121 | $proto $cookie | xauth -q -; fi". | |
1122 | .Pp | |
1123 | If this file does not exist, | |
5f4fdfae | 1124 | .Pa /etc/sshrc |
bf740959 | 1125 | is run, and if that |
1126 | does not exist either, xauth is used to store the cookie. | |
1127 | .Pp | |
1128 | This file should be writable only by the user, and need not be | |
1129 | readable by anyone else. | |
5f4fdfae | 1130 | .It Pa /etc/sshrc |
bf740959 | 1131 | Like |
1132 | .Pa $HOME/.ssh/rc . | |
1133 | This can be used to specify | |
4fe2af09 | 1134 | machine-specific login-time initializations globally. |
1135 | This file should be writable only by root, and should be world-readable. | |
089fbbd2 | 1136 | .El |
fa08c86b | 1137 | .Sh AUTHORS |
7f5c4295 | 1138 | OpenSSH is a derivative of the original and free |
1139 | ssh 1.2.12 release by Tatu Ylonen. | |
1140 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1141 | Theo de Raadt and Dug Song | |
1142 | removed many bugs, re-added newer features and | |
1143 | created OpenSSH. | |
1144 | Markus Friedl contributed the support for SSH | |
1145 | protocol versions 1.5 and 2.0. | |
bf740959 | 1146 | .Sh SEE ALSO |
bf740959 | 1147 | .Xr scp 1 , |
61e96248 | 1148 | .Xr sftp 1 , |
b5e300c2 | 1149 | .Xr sftp-server 8 , |
bf740959 | 1150 | .Xr ssh 1 , |
1151 | .Xr ssh-add 1 , | |
1152 | .Xr ssh-agent 1 , | |
1153 | .Xr ssh-keygen 1 , | |
7368a6c8 | 1154 | .Xr rlogin 1 , |
1155 | .Xr rsh 1 |