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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 | .\" |
f5429434 | 37 | .\" $OpenBSD: sshd.8,v 1.102 2001/03/04 12:54:04 stevesk Exp $ |
bf740959 | 38 | .Dd September 25, 1999 |
39 | .Dt SSHD 8 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm sshd | |
dcb971e1 | 43 | .Nd OpenSSH secure shell 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 |
f54651ce | 57 | (Secure Shell 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. | |
137 | The rest of the session is encrypted | |
138 | using a symmetric cipher, currently | |
139 | Blowfish, 3DES or CAST128 in CBC mode or Arcfour. | |
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 | |
fa08c86b | 147 | user authentication method (PubkeyAuthentication) |
1d1ffb87 | 148 | and conventional password authentication. |
149 | .Pp | |
150 | .Ss Command execution and data forwarding | |
151 | .Pp | |
bf740959 | 152 | If the client successfully authenticates itself, a dialog for |
4fe2af09 | 153 | preparing the session is entered. |
154 | At this time the client may request | |
bf740959 | 155 | things like allocating a pseudo-tty, forwarding X11 connections, |
156 | forwarding TCP/IP connections, or forwarding the authentication agent | |
157 | connection over the secure channel. | |
158 | .Pp | |
159 | Finally, the client either requests a shell or execution of a command. | |
4fe2af09 | 160 | The sides then enter session mode. |
161 | In this mode, either side may send | |
bf740959 | 162 | data at any time, and such data is forwarded to/from the shell or |
163 | command on the server side, and the user terminal in the client side. | |
164 | .Pp | |
165 | When the user program terminates and all forwarded X11 and other | |
166 | connections have been closed, the server sends command exit status to | |
167 | the client, and both sides exit. | |
168 | .Pp | |
169 | .Nm | |
170 | can be configured using command-line options or a configuration | |
4fe2af09 | 171 | file. |
172 | Command-line options override values specified in the | |
bf740959 | 173 | configuration file. |
174 | .Pp | |
9d6b7add | 175 | .Nm |
176 | rereads its configuration file when it receives a hangup signal, | |
409edaba | 177 | .Dv SIGHUP , |
178 | by executing itself with the name it was started as, ie. | |
179 | .Pa /usr/sbin/sshd . | |
9d6b7add | 180 | .Pp |
bf740959 | 181 | The options are as follows: |
182 | .Bl -tag -width Ds | |
183 | .It Fl b Ar bits | |
184 | Specifies the number of bits in the server key (default 768). | |
185 | .Pp | |
186 | .It Fl d | |
4fe2af09 | 187 | Debug mode. |
188 | The server sends verbose debug output to the system | |
189 | log, and does not put itself in the background. | |
190 | The server also will not fork and will only process one connection. | |
191 | This option is only intended for debugging for the server. | |
94ec8c6b | 192 | Multiple -d options increases the debugging level. |
193 | Maximum is 3. | |
bf740959 | 194 | .It Fl f Ar configuration_file |
4fe2af09 | 195 | Specifies the name of the configuration file. |
196 | The default is | |
5f4fdfae | 197 | .Pa /etc/sshd_config . |
bf740959 | 198 | .Nm |
199 | refuses to start if there is no configuration file. | |
200 | .It Fl g Ar login_grace_time | |
201 | Gives the grace time for clients to authenticate themselves (default | |
ee5e6612 | 202 | 600 seconds). |
4fe2af09 | 203 | If the client fails to authenticate the user within |
204 | this many seconds, the server disconnects and exits. | |
205 | A value of zero indicates no limit. | |
bf740959 | 206 | .It Fl h Ar host_key_file |
8abcdba4 | 207 | Specifies the file from which the host key is read (default |
5f4fdfae | 208 | .Pa /etc/ssh_host_key ) . |
bf740959 | 209 | This option must be given if |
210 | .Nm | |
211 | is not run as root (as the normal | |
212 | host file is normally not readable by anyone but root). | |
8abcdba4 | 213 | It is possible to have multiple host key files for |
214 | the different protocol versions. | |
bf740959 | 215 | .It Fl i |
216 | Specifies that | |
217 | .Nm | |
f54651ce | 218 | is being run from inetd. |
bf740959 | 219 | .Nm |
220 | is normally not run | |
221 | from inetd because it needs to generate the server key before it can | |
4fe2af09 | 222 | respond to the client, and this may take tens of seconds. |
223 | Clients would have to wait too long if the key was regenerated every time. | |
610cd5c6 | 224 | However, with small key sizes (e.g., 512) using |
bf740959 | 225 | .Nm |
226 | from inetd may | |
227 | be feasible. | |
228 | .It Fl k Ar key_gen_time | |
229 | Specifies how often the server key is regenerated (default 3600 | |
4fe2af09 | 230 | seconds, or one hour). |
231 | The motivation for regenerating the key fairly | |
bf740959 | 232 | often is that the key is not stored anywhere, and after about an hour, |
233 | it becomes impossible to recover the key for decrypting intercepted | |
234 | communications even if the machine is cracked into or physically | |
4fe2af09 | 235 | seized. |
236 | A value of zero indicates that the key will never be regenerated. | |
bf740959 | 237 | .It Fl p Ar port |
238 | Specifies the port on which the server listens for connections | |
239 | (default 22). | |
240 | .It Fl q | |
4fe2af09 | 241 | Quiet mode. |
242 | Nothing is sent to the system log. | |
243 | Normally the beginning, | |
bf740959 | 244 | authentication, and termination of each connection is logged. |
c345cf9d | 245 | .It Fl u Ar len |
246 | This option is used to specify the size of the field | |
247 | in the | |
248 | .Li utmp | |
249 | structure that holds the remote host name. | |
250 | If the resolved host name is longer than | |
251 | .Ar len , | |
252 | the dotted decimal value will be used instead. | |
253 | This allows hosts with very long host names that | |
254 | overflow this field to still be uniquely identified. | |
255 | Specifying | |
256 | .Fl u0 | |
257 | indicates that only dotted decimal addresses | |
258 | should be put into the | |
259 | .Pa utmp | |
260 | file. | |
8abcdba4 | 261 | .It Fl D |
262 | When this option is specified | |
263 | .Nm | |
264 | will not detach and does not become a daemon. | |
265 | This allows easy monitoring of | |
266 | .Nm sshd . | |
5260325f | 267 | .It Fl V Ar client_protocol_id |
94ec8c6b | 268 | SSH-2 compatibility mode. |
3189621b | 269 | When this option is specified |
5260325f | 270 | .Nm |
3189621b | 271 | assumes the client has sent the supplied version string |
5260325f | 272 | and skips the |
273 | Protocol Version Identification Exchange. | |
94ec8c6b | 274 | This option is not intended to be called directly. |
48e671d5 | 275 | .It Fl 4 |
276 | Forces | |
277 | .Nm | |
278 | to use IPv4 addresses only. | |
279 | .It Fl 6 | |
280 | Forces | |
281 | .Nm | |
282 | to use IPv6 addresses only. | |
bf740959 | 283 | .El |
284 | .Sh CONFIGURATION FILE | |
285 | .Nm | |
f54651ce | 286 | reads configuration data from |
5f4fdfae | 287 | .Pa /etc/sshd_config |
bf740959 | 288 | (or the file specified with |
289 | .Fl f | |
4fe2af09 | 290 | on the command line). |
291 | The file contains keyword-value pairs, one per line. | |
292 | Lines starting with | |
bf740959 | 293 | .Ql # |
294 | and empty lines are interpreted as comments. | |
295 | .Pp | |
296 | The following keywords are possible. | |
297 | .Bl -tag -width Ds | |
298 | .It Cm AFSTokenPassing | |
4fe2af09 | 299 | Specifies whether an AFS token may be forwarded to the server. |
300 | Default is | |
bf740959 | 301 | .Dq yes . |
302 | .It Cm AllowGroups | |
76896b4e | 303 | This keyword can be followed by a list of group names, separated |
4fe2af09 | 304 | by spaces. |
305 | If specified, login is allowed only for users whose primary | |
c6a69271 | 306 | group or supplementary group list matches one of the patterns. |
bf740959 | 307 | .Ql \&* |
308 | and | |
309 | .Ql ? | |
310 | can be used as | |
4fe2af09 | 311 | wildcards in the patterns. |
c345cf9d | 312 | Only group names are valid; a numerical group ID isn't recognized. |
c6a69271 | 313 | By default login is allowed regardless of the group list. |
bf740959 | 314 | .Pp |
33de75a3 | 315 | .It Cm AllowTcpForwarding |
316 | Specifies whether TCP forwarding is permitted. | |
317 | The default is | |
318 | .Dq yes . | |
319 | Note that disabling TCP forwarding does not improve security unless | |
320 | users are also denied shell access, as they can always install their | |
321 | own forwarders. | |
322 | .Pp | |
bf740959 | 323 | .It Cm AllowUsers |
76896b4e | 324 | This keyword can be followed by a list of user names, separated |
4fe2af09 | 325 | by spaces. |
326 | If specified, login is allowed only for users names that | |
bf740959 | 327 | match one of the patterns. |
328 | .Ql \&* | |
329 | and | |
330 | .Ql ? | |
331 | can be used as | |
4fe2af09 | 332 | wildcards in the patterns. |
c345cf9d | 333 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 334 | By default login is allowed regardless of the user name. |
bf740959 | 335 | .Pp |
eea39c02 | 336 | .It Cm Banner |
337 | In some jurisdictions, sending a warning message before authentication | |
338 | may be relevant for getting legal protection. | |
339 | The contents of the specified file are sent to the remote user before | |
340 | authentication is allowed. | |
341 | This option is only available for protocol version 2. | |
342 | .Pp | |
f54651ce | 343 | .It Cm Ciphers |
344 | Specifies the ciphers allowed for protocol version 2. | |
345 | Multiple ciphers must be comma-separated. | |
346 | The default is | |
9616313f | 347 | .Dq 3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes128-cbc . |
bf740959 | 348 | .It Cm CheckMail |
349 | Specifies whether | |
350 | .Nm | |
351 | should check for new mail for interactive logins. | |
352 | The default is | |
353 | .Dq no . | |
354 | .It Cm DenyGroups | |
355 | This keyword can be followed by a number of group names, separated | |
4fe2af09 | 356 | by spaces. |
c6a69271 | 357 | Users whose primary group or supplementary group list matches |
358 | one of the patterns aren't allowed to log in. | |
bf740959 | 359 | .Ql \&* |
360 | and | |
361 | .Ql ? | |
362 | can be used as | |
4fe2af09 | 363 | wildcards in the patterns. |
c345cf9d | 364 | Only group names are valid; a numerical group ID isn't recognized. |
c6a69271 | 365 | By default login is allowed regardless of the group list. |
bf740959 | 366 | .Pp |
367 | .It Cm DenyUsers | |
368 | This keyword can be followed by a number of user names, separated | |
4fe2af09 | 369 | by spaces. |
370 | Login is disallowed for user names that match one of the patterns. | |
bf740959 | 371 | .Ql \&* |
372 | and | |
373 | .Ql ? | |
4fe2af09 | 374 | can be used as wildcards in the patterns. |
c345cf9d | 375 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 376 | By default login is allowed regardless of the user name. |
fa08c86b | 377 | .It Cm PubkeyAuthentication |
378 | Specifies whether public key authentication is allowed. | |
1d1ffb87 | 379 | The default is |
380 | .Dq yes . | |
381 | Note that this option applies to protocol version 2 only. | |
382 | .It Cm GatewayPorts | |
383 | Specifies whether remote hosts are allowed to connect to ports | |
384 | forwarded for the client. | |
385 | The argument must be | |
386 | .Dq yes | |
387 | or | |
388 | .Dq no . | |
389 | The default is | |
390 | .Dq no . | |
bf740959 | 391 | .It Cm HostKey |
fa08c86b | 392 | Specifies the file containing the private host keys (default |
1d1ffb87 | 393 | .Pa /etc/ssh_host_key ) |
fa08c86b | 394 | used by SSH protocol versions 1 and 2. |
bf740959 | 395 | Note that |
396 | .Nm | |
42f11eb2 | 397 | will refuse to use a file if it is group/world-accessible. |
fa08c86b | 398 | It is possible to have multiple host key files. |
399 | .Dq rsa1 | |
400 | keys are used for version 1 and | |
401 | .Dq dsa | |
402 | or | |
403 | .Dq rsa | |
404 | are used for version 2 of the SSH protocol. | |
bf740959 | 405 | .It Cm IgnoreRhosts |
c8d54615 | 406 | Specifies that |
407 | .Pa .rhosts | |
f54651ce | 408 | and |
c8d54615 | 409 | .Pa .shosts |
410 | files will not be used in authentication. | |
bf740959 | 411 | .Pa /etc/hosts.equiv |
412 | and | |
f54651ce | 413 | .Pa /etc/shosts.equiv |
4fe2af09 | 414 | are still used. |
f54651ce | 415 | The default is |
c8d54615 | 416 | .Dq yes . |
b4748e2f | 417 | .It Cm IgnoreUserKnownHosts |
418 | Specifies whether | |
419 | .Nm | |
420 | should ignore the user's | |
421 | .Pa $HOME/.ssh/known_hosts | |
422 | during | |
423 | .Cm RhostsRSAAuthentication . | |
424 | The default is | |
425 | .Dq no . | |
bf740959 | 426 | .It Cm KeepAlive |
427 | Specifies whether the system should send keepalive messages to the | |
4fe2af09 | 428 | other side. |
429 | If they are sent, death of the connection or crash of one | |
430 | of the machines will be properly noticed. | |
431 | However, this means that | |
bf740959 | 432 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 433 | find it annoying. |
d0c832f3 | 434 | On the other hand, if keepalives are not sent, |
bf740959 | 435 | sessions may hang indefinitely on the server, leaving |
436 | .Dq ghost | |
437 | users and consuming server resources. | |
438 | .Pp | |
439 | The default is | |
440 | .Dq yes | |
441 | (to send keepalives), and the server will notice | |
4fe2af09 | 442 | if the network goes down or the client host reboots. |
443 | This avoids infinitely hanging sessions. | |
bf740959 | 444 | .Pp |
445 | To disable keepalives, the value should be set to | |
446 | .Dq no | |
447 | in both the server and the client configuration files. | |
448 | .It Cm KerberosAuthentication | |
4fe2af09 | 449 | Specifies whether Kerberos authentication is allowed. |
450 | This can be in the form of a Kerberos ticket, or if | |
bf740959 | 451 | .Cm PasswordAuthentication |
452 | is yes, the password provided by the user will be validated through | |
94ec8c6b | 453 | the Kerberos KDC. |
454 | To use this option, the server needs a | |
c345cf9d | 455 | Kerberos servtab which allows the verification of the KDC's identity. |
4fe2af09 | 456 | Default is |
bf740959 | 457 | .Dq yes . |
458 | .It Cm KerberosOrLocalPasswd | |
459 | If set then if password authentication through Kerberos fails then | |
460 | the password will be validated via any additional local mechanism | |
461 | such as | |
188adeb2 | 462 | .Pa /etc/passwd . |
4fe2af09 | 463 | Default is |
bf740959 | 464 | .Dq yes . |
465 | .It Cm KerberosTgtPassing | |
466 | Specifies whether a Kerberos TGT may be forwarded to the server. | |
f54651ce | 467 | Default is |
bf740959 | 468 | .Dq no , |
469 | as this only works when the Kerberos KDC is actually an AFS kaserver. | |
470 | .It Cm KerberosTicketCleanup | |
471 | Specifies whether to automatically destroy the user's ticket cache | |
4fe2af09 | 472 | file on logout. |
473 | Default is | |
bf740959 | 474 | .Dq yes . |
475 | .It Cm KeyRegenerationInterval | |
476 | The server key is automatically regenerated after this many seconds | |
4fe2af09 | 477 | (if it has been used). |
478 | The purpose of regeneration is to prevent | |
bf740959 | 479 | decrypting captured sessions by later breaking into the machine and |
4fe2af09 | 480 | stealing the keys. |
481 | The key is never stored anywhere. | |
482 | If the value is 0, the key is never regenerated. | |
483 | The default is 3600 (seconds). | |
bf740959 | 484 | .It Cm ListenAddress |
485 | Specifies what local address | |
486 | .Nm | |
487 | should listen on. | |
488 | The default is to listen to all local addresses. | |
48e671d5 | 489 | Multiple options of this type are permitted. |
490 | Additionally, the | |
491 | .Cm Ports | |
492 | options must precede this option. | |
bf740959 | 493 | .It Cm LoginGraceTime |
494 | The server disconnects after this time if the user has not | |
4fe2af09 | 495 | successfully logged in. |
496 | If the value is 0, there is no time limit. | |
bf740959 | 497 | The default is 600 (seconds). |
6a17f9c2 | 498 | .It Cm LogLevel |
499 | Gives the verbosity level that is used when logging messages from | |
500 | .Nm sshd . | |
501 | The possible values are: | |
59c97189 | 502 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
503 | The default is INFO. | |
6a17f9c2 | 504 | Logging with level DEBUG violates the privacy of users |
505 | and is not recommended. | |
b2552997 | 506 | .It Cm MACs |
507 | Specifies the available MAC (message authentication code) algorithms. | |
508 | The MAC algorithm is used in protocol version 2 | |
509 | for data integrity protection. | |
510 | Multiple algorithms must be comma-separated. | |
511 | The default is | |
512 | .Pp | |
513 | .Bd -literal | |
514 | ``hmac-sha1,hmac-md5,hmac-ripemd160,hmac-ripemd160@openssh.com, | |
515 | hmac-sha1-96,hmac-md5-96'' | |
516 | .Ed | |
089fbbd2 | 517 | .It Cm MaxStartups |
518 | Specifies the maximum number of concurrent unauthenticated connections to the | |
519 | .Nm | |
520 | daemon. | |
521 | Additional connections will be dropped until authentication succeeds or the | |
522 | .Cm LoginGraceTime | |
523 | expires for a connection. | |
524 | The default is 10. | |
c345cf9d | 525 | .Pp |
526 | Alternatively, random early drop can be enabled by specifying | |
527 | the three colon separated values | |
528 | .Dq start:rate:full | |
94ec8c6b | 529 | (e.g., "10:30:60"). |
c345cf9d | 530 | .Nm |
6f37606e | 531 | will refuse connection attempts with a probability of |
c345cf9d | 532 | .Dq rate/100 |
533 | (30%) | |
534 | if there are currently | |
535 | .Dq start | |
536 | (10) | |
537 | unauthenticated connections. | |
6f37606e | 538 | The probability increases linearly and all connection attempts |
c345cf9d | 539 | are refused if the number of unauthenticated connections reaches |
540 | .Dq full | |
541 | (60). | |
bf740959 | 542 | .It Cm PasswordAuthentication |
543 | Specifies whether password authentication is allowed. | |
544 | The default is | |
545 | .Dq yes . | |
c345cf9d | 546 | Note that this option applies to both protocol versions 1 and 2. |
bf740959 | 547 | .It Cm PermitEmptyPasswords |
548 | When password authentication is allowed, it specifies whether the | |
4fe2af09 | 549 | server allows login to accounts with empty password strings. |
550 | The default is | |
c8d54615 | 551 | .Dq no . |
bf740959 | 552 | .It Cm PermitRootLogin |
46f23b8d | 553 | Specifies whether root can login using |
bf740959 | 554 | .Xr ssh 1 . |
555 | The argument must be | |
556 | .Dq yes , | |
15853e93 | 557 | .Dq without-password , |
558 | .Dq forced-commands-only | |
bf740959 | 559 | or |
560 | .Dq no . | |
561 | The default is | |
562 | .Dq yes . | |
15853e93 | 563 | .Pp |
564 | If this option is set to | |
bf740959 | 565 | .Dq without-password |
15853e93 | 566 | password authentication is disabled for root. |
bf740959 | 567 | .Pp |
15853e93 | 568 | If this option is set to |
569 | .Dq forced-commands-only | |
570 | root login with public key authentication will be allowed, | |
571 | but only if the | |
bf740959 | 572 | .Ar command |
15853e93 | 573 | option has been specified |
bf740959 | 574 | (which may be useful for taking remote backups even if root login is |
15853e93 | 575 | normally not allowed). All other authentication methods are disabled |
576 | for root. | |
46f23b8d | 577 | .Pp |
578 | If this option is set to | |
579 | .Dq no | |
580 | root is not allowed to login. | |
0fbe8c74 | 581 | .It Cm PidFile |
582 | Specifies the file that contains the process identifier of the | |
583 | .Nm | |
584 | daemon. | |
585 | The default is | |
586 | .Pa /var/run/sshd.pid . | |
bf740959 | 587 | .It Cm Port |
588 | Specifies the port number that | |
589 | .Nm | |
4fe2af09 | 590 | listens on. |
591 | The default is 22. | |
48e671d5 | 592 | Multiple options of this type are permitted. |
bf740959 | 593 | .It Cm PrintMotd |
594 | Specifies whether | |
595 | .Nm | |
f54651ce | 596 | should print |
bf740959 | 597 | .Pa /etc/motd |
4fe2af09 | 598 | when a user logs in interactively. |
599 | (On some systems it is also printed by the shell, | |
bf740959 | 600 | .Pa /etc/profile , |
4fe2af09 | 601 | or equivalent.) |
602 | The default is | |
bf740959 | 603 | .Dq yes . |
f54651ce | 604 | .It Cm Protocol |
605 | Specifies the protocol versions | |
606 | .Nm | |
607 | should support. | |
608 | The possible values are | |
609 | .Dq 1 | |
610 | and | |
611 | .Dq 2 . | |
612 | Multiple versions must be comma-separated. | |
613 | The default is | |
614 | .Dq 1 . | |
61e96248 | 615 | .It Cm ReverseMappingCheck |
616 | Specifies whether | |
617 | .Nm | |
618 | should try to verify the remote host name and check that | |
619 | the resolved host name for the remote IP address maps back to the | |
620 | very same IP address. | |
621 | The default is | |
622 | .Dq no . | |
bf740959 | 623 | .It Cm RhostsAuthentication |
624 | Specifies whether authentication using rhosts or /etc/hosts.equiv | |
4fe2af09 | 625 | files is sufficient. |
626 | Normally, this method should not be permitted because it is insecure. | |
bf740959 | 627 | .Cm RhostsRSAAuthentication |
628 | should be used | |
629 | instead, because it performs RSA-based host authentication in addition | |
630 | to normal rhosts or /etc/hosts.equiv authentication. | |
631 | The default is | |
632 | .Dq no . | |
633 | .It Cm RhostsRSAAuthentication | |
634 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
4fe2af09 | 635 | with successful RSA host authentication is allowed. |
636 | The default is | |
c8d54615 | 637 | .Dq no . |
bf740959 | 638 | .It Cm RSAAuthentication |
4fe2af09 | 639 | Specifies whether pure RSA authentication is allowed. |
640 | The default is | |
bf740959 | 641 | .Dq yes . |
1d1ffb87 | 642 | Note that this option applies to protocol version 1 only. |
bf740959 | 643 | .It Cm ServerKeyBits |
4fe2af09 | 644 | Defines the number of bits in the server key. |
645 | The minimum value is 512, and the default is 768. | |
61e96248 | 646 | .It Cm ChallengeResponseAuthentication |
bf740959 | 647 | Specifies whether |
f5429434 | 648 | challenge response |
4fe2af09 | 649 | authentication is allowed. |
78c8106e | 650 | Currently there is support for |
61e96248 | 651 | .Xr skey 1 |
78c8106e | 652 | and PAM authentication. |
4fe2af09 | 653 | The default is |
bf740959 | 654 | .Dq yes . |
78c8106e | 655 | Note that enabling ChallengeResponseAuthentication for PAM bypasses |
656 | OpenSSH's password checking code, thus rendering options such as | |
657 | .Cm PasswordAuthentication | |
658 | and | |
659 | .Cm PermitEmptyPasswords | |
660 | ineffective. | |
bf740959 | 661 | .It Cm StrictModes |
662 | Specifies whether | |
663 | .Nm | |
664 | should check file modes and ownership of the | |
4fe2af09 | 665 | user's files and home directory before accepting login. |
666 | This is normally desirable because novices sometimes accidentally leave their | |
667 | directory or files world-writable. | |
668 | The default is | |
bf740959 | 669 | .Dq yes . |
38c295d6 | 670 | .It Cm Subsystem |
94ec8c6b | 671 | Configures an external subsystem (e.g., file transfer daemon). |
672 | Arguments should be a subsystem name and a command to execute upon subsystem | |
673 | request. | |
b5e300c2 | 674 | The command |
675 | .Xr sftp-server 8 | |
676 | implements the | |
677 | .Dq sftp | |
678 | file transfer subsystem. | |
38c295d6 | 679 | By default no subsystems are defined. |
680 | Note that this option applies to protocol version 2 only. | |
bf740959 | 681 | .It Cm SyslogFacility |
682 | Gives the facility code that is used when logging messages from | |
683 | .Nm sshd . | |
684 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, | |
4fe2af09 | 685 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
686 | The default is AUTH. | |
bf740959 | 687 | .It Cm UseLogin |
688 | Specifies whether | |
689 | .Xr login 1 | |
fa649821 | 690 | is used for interactive login sessions. |
691 | Note that | |
692 | .Xr login 1 | |
c345cf9d | 693 | is never used for remote command execution. |
4fe2af09 | 694 | The default is |
bf740959 | 695 | .Dq no . |
bf740959 | 696 | .It Cm X11DisplayOffset |
697 | Specifies the first display number available for | |
698 | .Nm sshd Ns 's | |
4fe2af09 | 699 | X11 forwarding. |
700 | This prevents | |
bf740959 | 701 | .Nm |
702 | from interfering with real X11 servers. | |
c8d54615 | 703 | The default is 10. |
7b2ea3a1 | 704 | .It Cm X11Forwarding |
4fe2af09 | 705 | Specifies whether X11 forwarding is permitted. |
706 | The default is | |
c8d54615 | 707 | .Dq no . |
7b2ea3a1 | 708 | Note that disabling X11 forwarding does not improve security in any |
709 | way, as users can always install their own forwarders. | |
fa649821 | 710 | .It Cm XAuthLocation |
711 | Specifies the location of the | |
712 | .Xr xauth 1 | |
713 | program. | |
714 | The default is | |
715 | .Pa /usr/X11R6/bin/xauth . | |
bf740959 | 716 | .El |
717 | .Sh LOGIN PROCESS | |
718 | When a user successfully logs in, | |
719 | .Nm | |
720 | does the following: | |
721 | .Bl -enum -offset indent | |
722 | .It | |
723 | If the login is on a tty, and no command has been specified, | |
f54651ce | 724 | prints last login time and |
bf740959 | 725 | .Pa /etc/motd |
726 | (unless prevented in the configuration file or by | |
727 | .Pa $HOME/.hushlogin ; | |
728 | see the | |
f54651ce | 729 | .Sx FILES |
bf740959 | 730 | section). |
731 | .It | |
732 | If the login is on a tty, records login time. | |
733 | .It | |
734 | Checks | |
735 | .Pa /etc/nologin ; | |
736 | if it exists, prints contents and quits | |
737 | (unless root). | |
738 | .It | |
739 | Changes to run with normal user privileges. | |
740 | .It | |
741 | Sets up basic environment. | |
742 | .It | |
743 | Reads | |
744 | .Pa $HOME/.ssh/environment | |
745 | if it exists. | |
746 | .It | |
747 | Changes to user's home directory. | |
748 | .It | |
749 | If | |
750 | .Pa $HOME/.ssh/rc | |
751 | exists, runs it; else if | |
5f4fdfae | 752 | .Pa /etc/sshrc |
bf740959 | 753 | exists, runs |
4fe2af09 | 754 | it; otherwise runs xauth. |
755 | The | |
bf740959 | 756 | .Dq rc |
757 | files are given the X11 | |
758 | authentication protocol and cookie in standard input. | |
759 | .It | |
760 | Runs user's shell or command. | |
761 | .El | |
762 | .Sh AUTHORIZED_KEYS FILE FORMAT | |
f54651ce | 763 | The |
bf740959 | 764 | .Pa $HOME/.ssh/authorized_keys |
765 | file lists the RSA keys that are | |
1d1ffb87 | 766 | permitted for RSA authentication in SSH protocols 1.3 and 1.5 |
d0c832f3 | 767 | Similarly, the |
1d1ffb87 | 768 | .Pa $HOME/.ssh/authorized_keys2 |
8abcdba4 | 769 | file lists the DSA and RSA keys that are |
770 | permitted for public key authentication (PubkeyAuthentication) | |
771 | in SSH protocol 2.0. | |
772 | .Pp | |
4fe2af09 | 773 | Each line of the file contains one |
bf740959 | 774 | key (empty lines and lines starting with a |
775 | .Ql # | |
776 | are ignored as | |
4fe2af09 | 777 | comments). |
8abcdba4 | 778 | Each RSA public key consists of the following fields, separated by |
4fe2af09 | 779 | spaces: options, bits, exponent, modulus, comment. |
8abcdba4 | 780 | Each protocol version 2 public key consists of: |
781 | options, keytype, base64 encoded key, comment. | |
782 | The options fields | |
783 | are optional; its presence is determined by whether the line starts | |
bf740959 | 784 | with a number or not (the option field never starts with a number). |
8abcdba4 | 785 | The bits, exponent, modulus and comment fields give the RSA key for |
786 | protocol version 1; the | |
bf740959 | 787 | comment field is not used for anything (but may be convenient for the |
788 | user to identify the key). | |
8abcdba4 | 789 | For protocol version 2 the keytype is |
790 | .Dq ssh-dss | |
791 | or | |
792 | .Dq ssh-rsa . | |
bf740959 | 793 | .Pp |
794 | Note that lines in this file are usually several hundred bytes long | |
4fe2af09 | 795 | (because of the size of the RSA key modulus). |
796 | You don't want to type them in; instead, copy the | |
bf740959 | 797 | .Pa identity.pub |
8abcdba4 | 798 | or the |
799 | .Pa id_dsa.pub | |
bf740959 | 800 | file and edit it. |
801 | .Pp | |
c345cf9d | 802 | The options (if present) consist of comma-separated option |
4fe2af09 | 803 | specifications. |
804 | No spaces are permitted, except within double quotes. | |
bf740959 | 805 | The following option specifications are supported: |
806 | .Bl -tag -width Ds | |
807 | .It Cm from="pattern-list" | |
808 | Specifies that in addition to RSA authentication, the canonical name | |
809 | of the remote host must be present in the comma-separated list of | |
4fe2af09 | 810 | patterns |
811 | .Pf ( Ql * | |
812 | and | |
813 | .Ql ? | |
814 | serve as wildcards). | |
815 | The list may also contain | |
816 | patterns negated by prefixing them with | |
817 | .Ql ! ; | |
818 | if the canonical host name matches a negated pattern, the key is not accepted. | |
819 | The purpose | |
bf740959 | 820 | of this option is to optionally increase security: RSA authentication |
821 | by itself does not trust the network or name servers or anything (but | |
822 | the key); however, if somebody somehow steals the key, the key | |
4fe2af09 | 823 | permits an intruder to log in from anywhere in the world. |
824 | This additional option makes using a stolen key more difficult (name | |
bf740959 | 825 | servers and/or routers would have to be compromised in addition to |
826 | just the key). | |
827 | .It Cm command="command" | |
828 | Specifies that the command is executed whenever this key is used for | |
4fe2af09 | 829 | authentication. |
830 | The command supplied by the user (if any) is ignored. | |
bf740959 | 831 | The command is run on a pty if the connection requests a pty; |
4fe2af09 | 832 | otherwise it is run without a tty. |
61e96248 | 833 | Note that if you want a 8-bit clean channel, |
834 | you must not request a pty or should specify | |
835 | .Cm no-pty . | |
4fe2af09 | 836 | A quote may be included in the command by quoting it with a backslash. |
837 | This option might be useful | |
838 | to restrict certain RSA keys to perform just a specific operation. | |
839 | An example might be a key that permits remote backups but nothing else. | |
d0c832f3 | 840 | Note that the client may specify TCP/IP and/or X11 |
841 | forwarding unless they are explicitly prohibited. | |
bf740959 | 842 | .It Cm environment="NAME=value" |
843 | Specifies that the string is to be added to the environment when | |
4fe2af09 | 844 | logging in using this key. |
845 | Environment variables set this way | |
846 | override other default environment values. | |
847 | Multiple options of this type are permitted. | |
bf740959 | 848 | .It Cm no-port-forwarding |
849 | Forbids TCP/IP forwarding when this key is used for authentication. | |
4fe2af09 | 850 | Any port forward requests by the client will return an error. |
851 | This might be used, e.g., in connection with the | |
bf740959 | 852 | .Cm command |
853 | option. | |
854 | .It Cm no-X11-forwarding | |
855 | Forbids X11 forwarding when this key is used for authentication. | |
856 | Any X11 forward requests by the client will return an error. | |
857 | .It Cm no-agent-forwarding | |
858 | Forbids authentication agent forwarding when this key is used for | |
859 | authentication. | |
860 | .It Cm no-pty | |
861 | Prevents tty allocation (a request to allocate a pty will fail). | |
862 | .El | |
863 | .Ss Examples | |
864 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar | |
865 | .Pp | |
866 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula | |
867 | .Pp | |
868 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi | |
869 | .Sh SSH_KNOWN_HOSTS FILE FORMAT | |
f54651ce | 870 | The |
1d1ffb87 | 871 | .Pa /etc/ssh_known_hosts , |
872 | .Pa /etc/ssh_known_hosts2 , | |
873 | .Pa $HOME/.ssh/known_hosts , | |
f54651ce | 874 | and |
1d1ffb87 | 875 | .Pa $HOME/.ssh/known_hosts2 |
4fe2af09 | 876 | files contain host public keys for all known hosts. |
877 | The global file should | |
878 | be prepared by the administrator (optional), and the per-user file is | |
c345cf9d | 879 | maintained automatically: whenever the user connects from an unknown host |
4fe2af09 | 880 | its key is added to the per-user file. |
bf740959 | 881 | .Pp |
882 | Each line in these files contains the following fields: hostnames, | |
4fe2af09 | 883 | bits, exponent, modulus, comment. |
884 | The fields are separated by spaces. | |
bf740959 | 885 | .Pp |
886 | Hostnames is a comma-separated list of patterns ('*' and '?' act as | |
887 | wildcards); each pattern in turn is matched against the canonical host | |
888 | name (when authenticating a client) or against the user-supplied | |
4fe2af09 | 889 | name (when authenticating a server). |
890 | A pattern may also be preceded by | |
bf740959 | 891 | .Ql ! |
892 | to indicate negation: if the host name matches a negated | |
893 | pattern, it is not accepted (by that line) even if it matched another | |
894 | pattern on the line. | |
895 | .Pp | |
1d1ffb87 | 896 | Bits, exponent, and modulus are taken directly from the RSA host key; they |
bf740959 | 897 | can be obtained, e.g., from |
5f4fdfae | 898 | .Pa /etc/ssh_host_key.pub . |
bf740959 | 899 | The optional comment field continues to the end of the line, and is not used. |
900 | .Pp | |
901 | Lines starting with | |
902 | .Ql # | |
903 | and empty lines are ignored as comments. | |
904 | .Pp | |
905 | When performing host authentication, authentication is accepted if any | |
4fe2af09 | 906 | matching line has the proper key. |
907 | It is thus permissible (but not | |
bf740959 | 908 | recommended) to have several lines or different host keys for the same |
4fe2af09 | 909 | names. |
910 | This will inevitably happen when short forms of host names | |
911 | from different domains are put in the file. | |
912 | It is possible | |
bf740959 | 913 | that the files contain conflicting information; authentication is |
914 | accepted if valid information can be found from either file. | |
915 | .Pp | |
916 | Note that the lines in these files are typically hundreds of characters | |
917 | long, and you definitely don't want to type in the host keys by hand. | |
918 | Rather, generate them by a script | |
f54651ce | 919 | or by taking |
5f4fdfae | 920 | .Pa /etc/ssh_host_key.pub |
bf740959 | 921 | and adding the host names at the front. |
922 | .Ss Examples | |
923 | closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi | |
924 | .Sh FILES | |
925 | .Bl -tag -width Ds | |
5f4fdfae | 926 | .It Pa /etc/sshd_config |
bf740959 | 927 | Contains configuration data for |
928 | .Nm sshd . | |
929 | This file should be writable by root only, but it is recommended | |
930 | (though not necessary) that it be world-readable. | |
b8dc87d3 | 931 | .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key |
932 | These three files contain the private parts of the | |
933 | (SSH1, SSH2 DSA, and SSH2 RSA) host keys. | |
934 | These files should only be owned by root, readable only by root, and not | |
bf740959 | 935 | accessible to others. |
936 | Note that | |
937 | .Nm | |
938 | does not start if this file is group/world-accessible. | |
b8dc87d3 | 939 | .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub |
940 | There three files contain the public parts of the | |
941 | (SSH1, SSH2 DSA, and SSH2 RSA) host keys. | |
942 | These files should be world-readable but writable only by | |
4fe2af09 | 943 | root. |
b8dc87d3 | 944 | Their contents should match the respective private parts. |
945 | These files are not | |
946 | really used for anything; they are provided for the convenience of | |
947 | the user so their contents can be copied to known hosts files. | |
948 | These files are created using | |
bf740959 | 949 | .Xr ssh-keygen 1 . |
c523303b | 950 | .It Pa /etc/primes |
951 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". | |
5f4fdfae | 952 | .It Pa /var/run/sshd.pid |
bf740959 | 953 | Contains the process ID of the |
954 | .Nm | |
955 | listening for connections (if there are several daemons running | |
956 | concurrently for different ports, this contains the pid of the one | |
4fe2af09 | 957 | started last). |
c345cf9d | 958 | The content of this file is not sensitive; it can be world-readable. |
bf740959 | 959 | .It Pa $HOME/.ssh/authorized_keys |
960 | Lists the RSA keys that can be used to log into the user's account. | |
961 | This file must be readable by root (which may on some machines imply | |
962 | it being world-readable if the user's home directory resides on an NFS | |
4fe2af09 | 963 | volume). |
964 | It is recommended that it not be accessible by others. | |
965 | The format of this file is described above. | |
1d1ffb87 | 966 | Users will place the contents of their |
967 | .Pa identity.pub | |
968 | files into this file, as described in | |
969 | .Xr ssh-keygen 1 . | |
970 | .It Pa $HOME/.ssh/authorized_keys2 | |
971 | Lists the DSA keys that can be used to log into the user's account. | |
972 | This file must be readable by root (which may on some machines imply | |
973 | it being world-readable if the user's home directory resides on an NFS | |
974 | volume). | |
975 | It is recommended that it not be accessible by others. | |
976 | The format of this file is described above. | |
977 | Users will place the contents of their | |
978 | .Pa id_dsa.pub | |
979 | files into this file, as described in | |
980 | .Xr ssh-keygen 1 . | |
5f4fdfae | 981 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
6a17f9c2 | 982 | These files are consulted when using rhosts with RSA host |
4fe2af09 | 983 | authentication to check the public key of the host. |
984 | The key must be listed in one of these files to be accepted. | |
5bbb5681 | 985 | The client uses the same files |
e91c60f2 | 986 | to verify that it is connecting to the correct remote host. |
4fe2af09 | 987 | These files should be writable only by root/the owner. |
5f4fdfae | 988 | .Pa /etc/ssh_known_hosts |
bf740959 | 989 | should be world-readable, and |
990 | .Pa $HOME/.ssh/known_hosts | |
991 | can but need not be world-readable. | |
992 | .It Pa /etc/nologin | |
f54651ce | 993 | If this file exists, |
bf740959 | 994 | .Nm |
4fe2af09 | 995 | refuses to let anyone except root log in. |
996 | The contents of the file | |
bf740959 | 997 | are displayed to anyone trying to log in, and non-root connections are |
4fe2af09 | 998 | refused. |
999 | The file should be world-readable. | |
bf740959 | 1000 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
1001 | If compiled with | |
1002 | .Sy LIBWRAP | |
1003 | support, tcp-wrappers access controls may be defined here as described in | |
1004 | .Xr hosts_access 5 . | |
1005 | .It Pa $HOME/.rhosts | |
1006 | This file contains host-username pairs, separated by a space, one per | |
4fe2af09 | 1007 | line. |
1008 | The given user on the corresponding host is permitted to log in | |
1009 | without password. | |
1010 | The same file is used by rlogind and rshd. | |
bf740959 | 1011 | The file must |
1012 | be writable only by the user; it is recommended that it not be | |
1013 | accessible by others. | |
1014 | .Pp | |
4fe2af09 | 1015 | If is also possible to use netgroups in the file. |
1016 | Either host or user | |
bf740959 | 1017 | name may be of the form +@groupname to specify all hosts or all users |
1018 | in the group. | |
1019 | .It Pa $HOME/.shosts | |
1020 | For ssh, | |
1021 | this file is exactly the same as for | |
1022 | .Pa .rhosts . | |
1023 | However, this file is | |
1024 | not used by rlogin and rshd, so using this permits access using SSH only. | |
c345cf9d | 1025 | .It Pa /etc/hosts.equiv |
bf740959 | 1026 | This file is used during |
1027 | .Pa .rhosts | |
4fe2af09 | 1028 | authentication. |
1029 | In the simplest form, this file contains host names, one per line. | |
1030 | Users on | |
bf740959 | 1031 | those hosts are permitted to log in without a password, provided they |
4fe2af09 | 1032 | have the same user name on both machines. |
1033 | The host name may also be | |
bf740959 | 1034 | followed by a user name; such users are permitted to log in as |
1035 | .Em any | |
4fe2af09 | 1036 | user on this machine (except root). |
1037 | Additionally, the syntax | |
bf740959 | 1038 | .Dq +@group |
4fe2af09 | 1039 | can be used to specify netgroups. |
1040 | Negated entries start with | |
bf740959 | 1041 | .Ql \&- . |
1042 | .Pp | |
1043 | If the client host/user is successfully matched in this file, login is | |
1044 | automatically permitted provided the client and server user names are the | |
4fe2af09 | 1045 | same. |
1046 | Additionally, successful RSA host authentication is normally required. | |
1047 | This file must be writable only by root; it is recommended | |
bf740959 | 1048 | that it be world-readable. |
1049 | .Pp | |
1050 | .Sy "Warning: It is almost never a good idea to use user names in" | |
1051 | .Pa hosts.equiv . | |
1052 | Beware that it really means that the named user(s) can log in as | |
1053 | .Em anybody , | |
1054 | which includes bin, daemon, adm, and other accounts that own critical | |
4fe2af09 | 1055 | binaries and directories. |
1056 | Using a user name practically grants the user root access. | |
1057 | The only valid use for user names that I can think | |
bf740959 | 1058 | of is in negative entries. |
1059 | .Pp | |
1060 | Note that this warning also applies to rsh/rlogin. | |
5f4fdfae | 1061 | .It Pa /etc/shosts.equiv |
bf740959 | 1062 | This is processed exactly as |
1063 | .Pa /etc/hosts.equiv . | |
1064 | However, this file may be useful in environments that want to run both | |
1065 | rsh/rlogin and ssh. | |
1066 | .It Pa $HOME/.ssh/environment | |
4fe2af09 | 1067 | This file is read into the environment at login (if it exists). |
1068 | It can only contain empty lines, comment lines (that start with | |
bf740959 | 1069 | .Ql # ) , |
4fe2af09 | 1070 | and assignment lines of the form name=value. |
1071 | The file should be writable | |
bf740959 | 1072 | only by the user; it need not be readable by anyone else. |
1073 | .It Pa $HOME/.ssh/rc | |
1074 | If this file exists, it is run with /bin/sh after reading the | |
4fe2af09 | 1075 | environment files but before starting the user's shell or command. |
1076 | If X11 spoofing is in use, this will receive the "proto cookie" pair in | |
bf740959 | 1077 | standard input (and |
1078 | .Ev DISPLAY | |
4fe2af09 | 1079 | in environment). |
1080 | This must call | |
bf740959 | 1081 | .Xr xauth 1 |
1082 | in that case. | |
1083 | .Pp | |
1084 | The primary purpose of this file is to run any initialization routines | |
1085 | which may be needed before the user's home directory becomes | |
1086 | accessible; AFS is a particular example of such an environment. | |
1087 | .Pp | |
1088 | This file will probably contain some initialization code followed by | |
1089 | something similar to: "if read proto cookie; then echo add $DISPLAY | |
1090 | $proto $cookie | xauth -q -; fi". | |
1091 | .Pp | |
1092 | If this file does not exist, | |
5f4fdfae | 1093 | .Pa /etc/sshrc |
bf740959 | 1094 | is run, and if that |
1095 | does not exist either, xauth is used to store the cookie. | |
1096 | .Pp | |
1097 | This file should be writable only by the user, and need not be | |
1098 | readable by anyone else. | |
5f4fdfae | 1099 | .It Pa /etc/sshrc |
bf740959 | 1100 | Like |
1101 | .Pa $HOME/.ssh/rc . | |
1102 | This can be used to specify | |
4fe2af09 | 1103 | machine-specific login-time initializations globally. |
1104 | This file should be writable only by root, and should be world-readable. | |
089fbbd2 | 1105 | .El |
fa08c86b | 1106 | .Sh AUTHORS |
7f5c4295 | 1107 | OpenSSH is a derivative of the original and free |
1108 | ssh 1.2.12 release by Tatu Ylonen. | |
1109 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1110 | Theo de Raadt and Dug Song | |
1111 | removed many bugs, re-added newer features and | |
1112 | created OpenSSH. | |
1113 | Markus Friedl contributed the support for SSH | |
1114 | protocol versions 1.5 and 2.0. | |
bf740959 | 1115 | .Sh SEE ALSO |
bf740959 | 1116 | .Xr scp 1 , |
61e96248 | 1117 | .Xr sftp 1 , |
b5e300c2 | 1118 | .Xr sftp-server 8 , |
bf740959 | 1119 | .Xr ssh 1 , |
1120 | .Xr ssh-add 1 , | |
1121 | .Xr ssh-agent 1 , | |
1122 | .Xr ssh-keygen 1 , | |
7368a6c8 | 1123 | .Xr rlogin 1 , |
1124 | .Xr rsh 1 |