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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 | .\" | |
13 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. | |
14 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. | |
15 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. | |
16 | .\" | |
17 | .\" Redistribution and use in source and binary forms, with or without | |
18 | .\" modification, are permitted provided that the following conditions | |
19 | .\" are met: | |
20 | .\" 1. Redistributions of source code must retain the above copyright | |
21 | .\" notice, this list of conditions and the following disclaimer. | |
22 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
23 | .\" notice, this list of conditions and the following disclaimer in the | |
24 | .\" documentation and/or other materials provided with the distribution. | |
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 | .\" |
59c97189 | 37 | .\" $OpenBSD: sshd.8,v 1.82 2001/01/18 16:20:22 markus Exp $ |
bf740959 | 38 | .Dd September 25, 1999 |
39 | .Dt SSHD 8 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm sshd | |
43 | .Nd secure shell daemon | |
44 | .Sh SYNOPSIS | |
45 | .Nm sshd | |
8abcdba4 | 46 | .Op Fl diqDQ46 |
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, | |
177 | .Dv SIGHUP . | |
178 | .Pp | |
bf740959 | 179 | The options are as follows: |
180 | .Bl -tag -width Ds | |
181 | .It Fl b Ar bits | |
182 | Specifies the number of bits in the server key (default 768). | |
183 | .Pp | |
184 | .It Fl d | |
4fe2af09 | 185 | Debug mode. |
186 | The server sends verbose debug output to the system | |
187 | log, and does not put itself in the background. | |
188 | The server also will not fork and will only process one connection. | |
189 | This option is only intended for debugging for the server. | |
94ec8c6b | 190 | Multiple -d options increases the debugging level. |
191 | Maximum is 3. | |
bf740959 | 192 | .It Fl f Ar configuration_file |
4fe2af09 | 193 | Specifies the name of the configuration file. |
194 | The default is | |
5f4fdfae | 195 | .Pa /etc/sshd_config . |
bf740959 | 196 | .Nm |
197 | refuses to start if there is no configuration file. | |
198 | .It Fl g Ar login_grace_time | |
199 | Gives the grace time for clients to authenticate themselves (default | |
ee5e6612 | 200 | 600 seconds). |
4fe2af09 | 201 | If the client fails to authenticate the user within |
202 | this many seconds, the server disconnects and exits. | |
203 | A value of zero indicates no limit. | |
bf740959 | 204 | .It Fl h Ar host_key_file |
8abcdba4 | 205 | Specifies the file from which the host key is read (default |
5f4fdfae | 206 | .Pa /etc/ssh_host_key ) . |
bf740959 | 207 | This option must be given if |
208 | .Nm | |
209 | is not run as root (as the normal | |
210 | host file is normally not readable by anyone but root). | |
8abcdba4 | 211 | It is possible to have multiple host key files for |
212 | the different protocol versions. | |
bf740959 | 213 | .It Fl i |
214 | Specifies that | |
215 | .Nm | |
f54651ce | 216 | is being run from inetd. |
bf740959 | 217 | .Nm |
218 | is normally not run | |
219 | from inetd because it needs to generate the server key before it can | |
4fe2af09 | 220 | respond to the client, and this may take tens of seconds. |
221 | Clients would have to wait too long if the key was regenerated every time. | |
610cd5c6 | 222 | However, with small key sizes (e.g., 512) using |
bf740959 | 223 | .Nm |
224 | from inetd may | |
225 | be feasible. | |
226 | .It Fl k Ar key_gen_time | |
227 | Specifies how often the server key is regenerated (default 3600 | |
4fe2af09 | 228 | seconds, or one hour). |
229 | The motivation for regenerating the key fairly | |
bf740959 | 230 | often is that the key is not stored anywhere, and after about an hour, |
231 | it becomes impossible to recover the key for decrypting intercepted | |
232 | communications even if the machine is cracked into or physically | |
4fe2af09 | 233 | seized. |
234 | A value of zero indicates that the key will never be regenerated. | |
bf740959 | 235 | .It Fl p Ar port |
236 | Specifies the port on which the server listens for connections | |
237 | (default 22). | |
238 | .It Fl q | |
4fe2af09 | 239 | Quiet mode. |
240 | Nothing is sent to the system log. | |
241 | Normally the beginning, | |
bf740959 | 242 | authentication, and termination of each connection is logged. |
c345cf9d | 243 | .It Fl u Ar len |
244 | This option is used to specify the size of the field | |
245 | in the | |
246 | .Li utmp | |
247 | structure that holds the remote host name. | |
248 | If the resolved host name is longer than | |
249 | .Ar len , | |
250 | the dotted decimal value will be used instead. | |
251 | This allows hosts with very long host names that | |
252 | overflow this field to still be uniquely identified. | |
253 | Specifying | |
254 | .Fl u0 | |
255 | indicates that only dotted decimal addresses | |
256 | should be put into the | |
257 | .Pa utmp | |
258 | file. | |
8abcdba4 | 259 | .It Fl D |
260 | When this option is specified | |
261 | .Nm | |
262 | will not detach and does not become a daemon. | |
263 | This allows easy monitoring of | |
264 | .Nm sshd . | |
bf740959 | 265 | .It Fl Q |
266 | Do not print an error message if RSA support is missing. | |
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 | |
303 | This keyword can be followed by a number 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 |
324 | This keyword can be followed by a number 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 | |
fa08c86b | 397 | if this file is group/world-accessible. |
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. | |
089fbbd2 | 506 | .It Cm MaxStartups |
507 | Specifies the maximum number of concurrent unauthenticated connections to the | |
508 | .Nm | |
509 | daemon. | |
510 | Additional connections will be dropped until authentication succeeds or the | |
511 | .Cm LoginGraceTime | |
512 | expires for a connection. | |
513 | The default is 10. | |
c345cf9d | 514 | .Pp |
515 | Alternatively, random early drop can be enabled by specifying | |
516 | the three colon separated values | |
517 | .Dq start:rate:full | |
94ec8c6b | 518 | (e.g., "10:30:60"). |
c345cf9d | 519 | .Nm |
520 | will refuse connection attempts with a probabillity of | |
521 | .Dq rate/100 | |
522 | (30%) | |
523 | if there are currently | |
524 | .Dq start | |
525 | (10) | |
526 | unauthenticated connections. | |
527 | The probabillity increases linearly and all connection attempts | |
528 | are refused if the number of unauthenticated connections reaches | |
529 | .Dq full | |
530 | (60). | |
bf740959 | 531 | .It Cm PasswordAuthentication |
532 | Specifies whether password authentication is allowed. | |
533 | The default is | |
534 | .Dq yes . | |
c345cf9d | 535 | Note that this option applies to both protocol versions 1 and 2. |
bf740959 | 536 | .It Cm PermitEmptyPasswords |
537 | When password authentication is allowed, it specifies whether the | |
4fe2af09 | 538 | server allows login to accounts with empty password strings. |
539 | The default is | |
c8d54615 | 540 | .Dq no . |
bf740959 | 541 | .It Cm PermitRootLogin |
542 | Specifies whether the root can log in using | |
543 | .Xr ssh 1 . | |
544 | The argument must be | |
545 | .Dq yes , | |
546 | .Dq without-password | |
547 | or | |
548 | .Dq no . | |
549 | The default is | |
550 | .Dq yes . | |
551 | If this options is set to | |
552 | .Dq without-password | |
553 | only password authentication is disabled for root. | |
554 | .Pp | |
555 | Root login with RSA authentication when the | |
556 | .Ar command | |
557 | option has been | |
558 | specified will be allowed regardless of the value of this setting | |
559 | (which may be useful for taking remote backups even if root login is | |
560 | normally not allowed). | |
0fbe8c74 | 561 | .It Cm PidFile |
562 | Specifies the file that contains the process identifier of the | |
563 | .Nm | |
564 | daemon. | |
565 | The default is | |
566 | .Pa /var/run/sshd.pid . | |
bf740959 | 567 | .It Cm Port |
568 | Specifies the port number that | |
569 | .Nm | |
4fe2af09 | 570 | listens on. |
571 | The default is 22. | |
48e671d5 | 572 | Multiple options of this type are permitted. |
bf740959 | 573 | .It Cm PrintMotd |
574 | Specifies whether | |
575 | .Nm | |
f54651ce | 576 | should print |
bf740959 | 577 | .Pa /etc/motd |
4fe2af09 | 578 | when a user logs in interactively. |
579 | (On some systems it is also printed by the shell, | |
bf740959 | 580 | .Pa /etc/profile , |
4fe2af09 | 581 | or equivalent.) |
582 | The default is | |
bf740959 | 583 | .Dq yes . |
f54651ce | 584 | .It Cm Protocol |
585 | Specifies the protocol versions | |
586 | .Nm | |
587 | should support. | |
588 | The possible values are | |
589 | .Dq 1 | |
590 | and | |
591 | .Dq 2 . | |
592 | Multiple versions must be comma-separated. | |
593 | The default is | |
594 | .Dq 1 . | |
bf740959 | 595 | .It Cm RandomSeed |
4fe2af09 | 596 | Obsolete. |
597 | Random number generation uses other techniques. | |
bf740959 | 598 | .It Cm RhostsAuthentication |
599 | Specifies whether authentication using rhosts or /etc/hosts.equiv | |
4fe2af09 | 600 | files is sufficient. |
601 | Normally, this method should not be permitted because it is insecure. | |
bf740959 | 602 | .Cm RhostsRSAAuthentication |
603 | should be used | |
604 | instead, because it performs RSA-based host authentication in addition | |
605 | to normal rhosts or /etc/hosts.equiv authentication. | |
606 | The default is | |
607 | .Dq no . | |
608 | .It Cm RhostsRSAAuthentication | |
609 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
4fe2af09 | 610 | with successful RSA host authentication is allowed. |
611 | The default is | |
c8d54615 | 612 | .Dq no . |
bf740959 | 613 | .It Cm RSAAuthentication |
4fe2af09 | 614 | Specifies whether pure RSA authentication is allowed. |
615 | The default is | |
bf740959 | 616 | .Dq yes . |
1d1ffb87 | 617 | Note that this option applies to protocol version 1 only. |
bf740959 | 618 | .It Cm ServerKeyBits |
4fe2af09 | 619 | Defines the number of bits in the server key. |
620 | The minimum value is 512, and the default is 768. | |
bf740959 | 621 | .It Cm SkeyAuthentication |
622 | Specifies whether | |
f54651ce | 623 | .Xr skey 1 |
4fe2af09 | 624 | authentication is allowed. |
625 | The default is | |
bf740959 | 626 | .Dq yes . |
627 | Note that s/key authentication is enabled only if | |
628 | .Cm PasswordAuthentication | |
629 | is allowed, too. | |
630 | .It Cm StrictModes | |
631 | Specifies whether | |
632 | .Nm | |
633 | should check file modes and ownership of the | |
4fe2af09 | 634 | user's files and home directory before accepting login. |
635 | This is normally desirable because novices sometimes accidentally leave their | |
636 | directory or files world-writable. | |
637 | The default is | |
bf740959 | 638 | .Dq yes . |
38c295d6 | 639 | .It Cm Subsystem |
94ec8c6b | 640 | Configures an external subsystem (e.g., file transfer daemon). |
641 | Arguments should be a subsystem name and a command to execute upon subsystem | |
642 | request. | |
b5e300c2 | 643 | The command |
644 | .Xr sftp-server 8 | |
645 | implements the | |
646 | .Dq sftp | |
647 | file transfer subsystem. | |
38c295d6 | 648 | By default no subsystems are defined. |
649 | Note that this option applies to protocol version 2 only. | |
bf740959 | 650 | .It Cm SyslogFacility |
651 | Gives the facility code that is used when logging messages from | |
652 | .Nm sshd . | |
653 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, | |
4fe2af09 | 654 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
655 | The default is AUTH. | |
bf740959 | 656 | .It Cm UseLogin |
657 | Specifies whether | |
658 | .Xr login 1 | |
fa649821 | 659 | is used for interactive login sessions. |
660 | Note that | |
661 | .Xr login 1 | |
c345cf9d | 662 | is never used for remote command execution. |
4fe2af09 | 663 | The default is |
bf740959 | 664 | .Dq no . |
bf740959 | 665 | .It Cm X11DisplayOffset |
666 | Specifies the first display number available for | |
667 | .Nm sshd Ns 's | |
4fe2af09 | 668 | X11 forwarding. |
669 | This prevents | |
bf740959 | 670 | .Nm |
671 | from interfering with real X11 servers. | |
c8d54615 | 672 | The default is 10. |
7b2ea3a1 | 673 | .It Cm X11Forwarding |
4fe2af09 | 674 | Specifies whether X11 forwarding is permitted. |
675 | The default is | |
c8d54615 | 676 | .Dq no . |
7b2ea3a1 | 677 | Note that disabling X11 forwarding does not improve security in any |
678 | way, as users can always install their own forwarders. | |
fa649821 | 679 | .It Cm XAuthLocation |
680 | Specifies the location of the | |
681 | .Xr xauth 1 | |
682 | program. | |
683 | The default is | |
684 | .Pa /usr/X11R6/bin/xauth . | |
bf740959 | 685 | .El |
686 | .Sh LOGIN PROCESS | |
687 | When a user successfully logs in, | |
688 | .Nm | |
689 | does the following: | |
690 | .Bl -enum -offset indent | |
691 | .It | |
692 | If the login is on a tty, and no command has been specified, | |
f54651ce | 693 | prints last login time and |
bf740959 | 694 | .Pa /etc/motd |
695 | (unless prevented in the configuration file or by | |
696 | .Pa $HOME/.hushlogin ; | |
697 | see the | |
f54651ce | 698 | .Sx FILES |
bf740959 | 699 | section). |
700 | .It | |
701 | If the login is on a tty, records login time. | |
702 | .It | |
703 | Checks | |
704 | .Pa /etc/nologin ; | |
705 | if it exists, prints contents and quits | |
706 | (unless root). | |
707 | .It | |
708 | Changes to run with normal user privileges. | |
709 | .It | |
710 | Sets up basic environment. | |
711 | .It | |
712 | Reads | |
713 | .Pa $HOME/.ssh/environment | |
714 | if it exists. | |
715 | .It | |
716 | Changes to user's home directory. | |
717 | .It | |
718 | If | |
719 | .Pa $HOME/.ssh/rc | |
720 | exists, runs it; else if | |
5f4fdfae | 721 | .Pa /etc/sshrc |
bf740959 | 722 | exists, runs |
4fe2af09 | 723 | it; otherwise runs xauth. |
724 | The | |
bf740959 | 725 | .Dq rc |
726 | files are given the X11 | |
727 | authentication protocol and cookie in standard input. | |
728 | .It | |
729 | Runs user's shell or command. | |
730 | .El | |
731 | .Sh AUTHORIZED_KEYS FILE FORMAT | |
f54651ce | 732 | The |
bf740959 | 733 | .Pa $HOME/.ssh/authorized_keys |
734 | file lists the RSA keys that are | |
1d1ffb87 | 735 | permitted for RSA authentication in SSH protocols 1.3 and 1.5 |
d0c832f3 | 736 | Similarly, the |
1d1ffb87 | 737 | .Pa $HOME/.ssh/authorized_keys2 |
8abcdba4 | 738 | file lists the DSA and RSA keys that are |
739 | permitted for public key authentication (PubkeyAuthentication) | |
740 | in SSH protocol 2.0. | |
741 | .Pp | |
4fe2af09 | 742 | Each line of the file contains one |
bf740959 | 743 | key (empty lines and lines starting with a |
744 | .Ql # | |
745 | are ignored as | |
4fe2af09 | 746 | comments). |
8abcdba4 | 747 | Each RSA public key consists of the following fields, separated by |
4fe2af09 | 748 | spaces: options, bits, exponent, modulus, comment. |
8abcdba4 | 749 | Each protocol version 2 public key consists of: |
750 | options, keytype, base64 encoded key, comment. | |
751 | The options fields | |
752 | are optional; its presence is determined by whether the line starts | |
bf740959 | 753 | with a number or not (the option field never starts with a number). |
8abcdba4 | 754 | The bits, exponent, modulus and comment fields give the RSA key for |
755 | protocol version 1; the | |
bf740959 | 756 | comment field is not used for anything (but may be convenient for the |
757 | user to identify the key). | |
8abcdba4 | 758 | For protocol version 2 the keytype is |
759 | .Dq ssh-dss | |
760 | or | |
761 | .Dq ssh-rsa . | |
bf740959 | 762 | .Pp |
763 | Note that lines in this file are usually several hundred bytes long | |
4fe2af09 | 764 | (because of the size of the RSA key modulus). |
765 | You don't want to type them in; instead, copy the | |
bf740959 | 766 | .Pa identity.pub |
8abcdba4 | 767 | or the |
768 | .Pa id_dsa.pub | |
bf740959 | 769 | file and edit it. |
770 | .Pp | |
c345cf9d | 771 | The options (if present) consist of comma-separated option |
4fe2af09 | 772 | specifications. |
773 | No spaces are permitted, except within double quotes. | |
bf740959 | 774 | The following option specifications are supported: |
775 | .Bl -tag -width Ds | |
776 | .It Cm from="pattern-list" | |
777 | Specifies that in addition to RSA authentication, the canonical name | |
778 | of the remote host must be present in the comma-separated list of | |
4fe2af09 | 779 | patterns |
780 | .Pf ( Ql * | |
781 | and | |
782 | .Ql ? | |
783 | serve as wildcards). | |
784 | The list may also contain | |
785 | patterns negated by prefixing them with | |
786 | .Ql ! ; | |
787 | if the canonical host name matches a negated pattern, the key is not accepted. | |
788 | The purpose | |
bf740959 | 789 | of this option is to optionally increase security: RSA authentication |
790 | by itself does not trust the network or name servers or anything (but | |
791 | the key); however, if somebody somehow steals the key, the key | |
4fe2af09 | 792 | permits an intruder to log in from anywhere in the world. |
793 | This additional option makes using a stolen key more difficult (name | |
bf740959 | 794 | servers and/or routers would have to be compromised in addition to |
795 | just the key). | |
796 | .It Cm command="command" | |
797 | Specifies that the command is executed whenever this key is used for | |
4fe2af09 | 798 | authentication. |
799 | The command supplied by the user (if any) is ignored. | |
bf740959 | 800 | The command is run on a pty if the connection requests a pty; |
4fe2af09 | 801 | otherwise it is run without a tty. |
802 | A quote may be included in the command by quoting it with a backslash. | |
803 | This option might be useful | |
804 | to restrict certain RSA keys to perform just a specific operation. | |
805 | An example might be a key that permits remote backups but nothing else. | |
d0c832f3 | 806 | Note that the client may specify TCP/IP and/or X11 |
807 | forwarding unless they are explicitly prohibited. | |
bf740959 | 808 | .It Cm environment="NAME=value" |
809 | Specifies that the string is to be added to the environment when | |
4fe2af09 | 810 | logging in using this key. |
811 | Environment variables set this way | |
812 | override other default environment values. | |
813 | Multiple options of this type are permitted. | |
bf740959 | 814 | .It Cm no-port-forwarding |
815 | Forbids TCP/IP forwarding when this key is used for authentication. | |
4fe2af09 | 816 | Any port forward requests by the client will return an error. |
817 | This might be used, e.g., in connection with the | |
bf740959 | 818 | .Cm command |
819 | option. | |
820 | .It Cm no-X11-forwarding | |
821 | Forbids X11 forwarding when this key is used for authentication. | |
822 | Any X11 forward requests by the client will return an error. | |
823 | .It Cm no-agent-forwarding | |
824 | Forbids authentication agent forwarding when this key is used for | |
825 | authentication. | |
826 | .It Cm no-pty | |
827 | Prevents tty allocation (a request to allocate a pty will fail). | |
828 | .El | |
829 | .Ss Examples | |
830 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar | |
831 | .Pp | |
832 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula | |
833 | .Pp | |
834 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi | |
835 | .Sh SSH_KNOWN_HOSTS FILE FORMAT | |
f54651ce | 836 | The |
1d1ffb87 | 837 | .Pa /etc/ssh_known_hosts , |
838 | .Pa /etc/ssh_known_hosts2 , | |
839 | .Pa $HOME/.ssh/known_hosts , | |
f54651ce | 840 | and |
1d1ffb87 | 841 | .Pa $HOME/.ssh/known_hosts2 |
4fe2af09 | 842 | files contain host public keys for all known hosts. |
843 | The global file should | |
844 | be prepared by the administrator (optional), and the per-user file is | |
c345cf9d | 845 | maintained automatically: whenever the user connects from an unknown host |
4fe2af09 | 846 | its key is added to the per-user file. |
bf740959 | 847 | .Pp |
848 | Each line in these files contains the following fields: hostnames, | |
4fe2af09 | 849 | bits, exponent, modulus, comment. |
850 | The fields are separated by spaces. | |
bf740959 | 851 | .Pp |
852 | Hostnames is a comma-separated list of patterns ('*' and '?' act as | |
853 | wildcards); each pattern in turn is matched against the canonical host | |
854 | name (when authenticating a client) or against the user-supplied | |
4fe2af09 | 855 | name (when authenticating a server). |
856 | A pattern may also be preceded by | |
bf740959 | 857 | .Ql ! |
858 | to indicate negation: if the host name matches a negated | |
859 | pattern, it is not accepted (by that line) even if it matched another | |
860 | pattern on the line. | |
861 | .Pp | |
1d1ffb87 | 862 | Bits, exponent, and modulus are taken directly from the RSA host key; they |
bf740959 | 863 | can be obtained, e.g., from |
5f4fdfae | 864 | .Pa /etc/ssh_host_key.pub . |
bf740959 | 865 | The optional comment field continues to the end of the line, and is not used. |
866 | .Pp | |
867 | Lines starting with | |
868 | .Ql # | |
869 | and empty lines are ignored as comments. | |
870 | .Pp | |
871 | When performing host authentication, authentication is accepted if any | |
4fe2af09 | 872 | matching line has the proper key. |
873 | It is thus permissible (but not | |
bf740959 | 874 | recommended) to have several lines or different host keys for the same |
4fe2af09 | 875 | names. |
876 | This will inevitably happen when short forms of host names | |
877 | from different domains are put in the file. | |
878 | It is possible | |
bf740959 | 879 | that the files contain conflicting information; authentication is |
880 | accepted if valid information can be found from either file. | |
881 | .Pp | |
882 | Note that the lines in these files are typically hundreds of characters | |
883 | long, and you definitely don't want to type in the host keys by hand. | |
884 | Rather, generate them by a script | |
f54651ce | 885 | or by taking |
5f4fdfae | 886 | .Pa /etc/ssh_host_key.pub |
bf740959 | 887 | and adding the host names at the front. |
888 | .Ss Examples | |
889 | closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi | |
890 | .Sh FILES | |
891 | .Bl -tag -width Ds | |
5f4fdfae | 892 | .It Pa /etc/sshd_config |
bf740959 | 893 | Contains configuration data for |
894 | .Nm sshd . | |
895 | This file should be writable by root only, but it is recommended | |
896 | (though not necessary) that it be world-readable. | |
5f4fdfae | 897 | .It Pa /etc/ssh_host_key |
bf740959 | 898 | Contains the private part of the host key. |
899 | This file should only be owned by root, readable only by root, and not | |
900 | accessible to others. | |
901 | Note that | |
902 | .Nm | |
903 | does not start if this file is group/world-accessible. | |
5f4fdfae | 904 | .It Pa /etc/ssh_host_key.pub |
bf740959 | 905 | Contains the public part of the host key. |
906 | This file should be world-readable but writable only by | |
4fe2af09 | 907 | root. |
908 | Its contents should match the private part. | |
909 | This file is not | |
bf740959 | 910 | really used for anything; it is only provided for the convenience of |
911 | the user so its contents can be copied to known hosts files. | |
912 | These two files are created using | |
913 | .Xr ssh-keygen 1 . | |
c523303b | 914 | .It Pa /etc/primes |
915 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". | |
5f4fdfae | 916 | .It Pa /var/run/sshd.pid |
bf740959 | 917 | Contains the process ID of the |
918 | .Nm | |
919 | listening for connections (if there are several daemons running | |
920 | concurrently for different ports, this contains the pid of the one | |
4fe2af09 | 921 | started last). |
c345cf9d | 922 | The content of this file is not sensitive; it can be world-readable. |
bf740959 | 923 | .It Pa $HOME/.ssh/authorized_keys |
924 | Lists the RSA keys that can be used to log into the user's account. | |
925 | This file must be readable by root (which may on some machines imply | |
926 | it being world-readable if the user's home directory resides on an NFS | |
4fe2af09 | 927 | volume). |
928 | It is recommended that it not be accessible by others. | |
929 | The format of this file is described above. | |
1d1ffb87 | 930 | Users will place the contents of their |
931 | .Pa identity.pub | |
932 | files into this file, as described in | |
933 | .Xr ssh-keygen 1 . | |
934 | .It Pa $HOME/.ssh/authorized_keys2 | |
935 | Lists the DSA keys that can be used to log into the user's account. | |
936 | This file must be readable by root (which may on some machines imply | |
937 | it being world-readable if the user's home directory resides on an NFS | |
938 | volume). | |
939 | It is recommended that it not be accessible by others. | |
940 | The format of this file is described above. | |
941 | Users will place the contents of their | |
942 | .Pa id_dsa.pub | |
943 | files into this file, as described in | |
944 | .Xr ssh-keygen 1 . | |
5f4fdfae | 945 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
6a17f9c2 | 946 | These files are consulted when using rhosts with RSA host |
4fe2af09 | 947 | authentication to check the public key of the host. |
948 | The key must be listed in one of these files to be accepted. | |
5bbb5681 | 949 | The client uses the same files |
c345cf9d | 950 | to verify that the remote host is the one it intended to connect. |
4fe2af09 | 951 | These files should be writable only by root/the owner. |
5f4fdfae | 952 | .Pa /etc/ssh_known_hosts |
bf740959 | 953 | should be world-readable, and |
954 | .Pa $HOME/.ssh/known_hosts | |
955 | can but need not be world-readable. | |
956 | .It Pa /etc/nologin | |
f54651ce | 957 | If this file exists, |
bf740959 | 958 | .Nm |
4fe2af09 | 959 | refuses to let anyone except root log in. |
960 | The contents of the file | |
bf740959 | 961 | are displayed to anyone trying to log in, and non-root connections are |
4fe2af09 | 962 | refused. |
963 | The file should be world-readable. | |
bf740959 | 964 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
965 | If compiled with | |
966 | .Sy LIBWRAP | |
967 | support, tcp-wrappers access controls may be defined here as described in | |
968 | .Xr hosts_access 5 . | |
969 | .It Pa $HOME/.rhosts | |
970 | This file contains host-username pairs, separated by a space, one per | |
4fe2af09 | 971 | line. |
972 | The given user on the corresponding host is permitted to log in | |
973 | without password. | |
974 | The same file is used by rlogind and rshd. | |
bf740959 | 975 | The file must |
976 | be writable only by the user; it is recommended that it not be | |
977 | accessible by others. | |
978 | .Pp | |
4fe2af09 | 979 | If is also possible to use netgroups in the file. |
980 | Either host or user | |
bf740959 | 981 | name may be of the form +@groupname to specify all hosts or all users |
982 | in the group. | |
983 | .It Pa $HOME/.shosts | |
984 | For ssh, | |
985 | this file is exactly the same as for | |
986 | .Pa .rhosts . | |
987 | However, this file is | |
988 | not used by rlogin and rshd, so using this permits access using SSH only. | |
c345cf9d | 989 | .It Pa /etc/hosts.equiv |
bf740959 | 990 | This file is used during |
991 | .Pa .rhosts | |
4fe2af09 | 992 | authentication. |
993 | In the simplest form, this file contains host names, one per line. | |
994 | Users on | |
bf740959 | 995 | those hosts are permitted to log in without a password, provided they |
4fe2af09 | 996 | have the same user name on both machines. |
997 | The host name may also be | |
bf740959 | 998 | followed by a user name; such users are permitted to log in as |
999 | .Em any | |
4fe2af09 | 1000 | user on this machine (except root). |
1001 | Additionally, the syntax | |
bf740959 | 1002 | .Dq +@group |
4fe2af09 | 1003 | can be used to specify netgroups. |
1004 | Negated entries start with | |
bf740959 | 1005 | .Ql \&- . |
1006 | .Pp | |
1007 | If the client host/user is successfully matched in this file, login is | |
1008 | automatically permitted provided the client and server user names are the | |
4fe2af09 | 1009 | same. |
1010 | Additionally, successful RSA host authentication is normally required. | |
1011 | This file must be writable only by root; it is recommended | |
bf740959 | 1012 | that it be world-readable. |
1013 | .Pp | |
1014 | .Sy "Warning: It is almost never a good idea to use user names in" | |
1015 | .Pa hosts.equiv . | |
1016 | Beware that it really means that the named user(s) can log in as | |
1017 | .Em anybody , | |
1018 | which includes bin, daemon, adm, and other accounts that own critical | |
4fe2af09 | 1019 | binaries and directories. |
1020 | Using a user name practically grants the user root access. | |
1021 | The only valid use for user names that I can think | |
bf740959 | 1022 | of is in negative entries. |
1023 | .Pp | |
1024 | Note that this warning also applies to rsh/rlogin. | |
5f4fdfae | 1025 | .It Pa /etc/shosts.equiv |
bf740959 | 1026 | This is processed exactly as |
1027 | .Pa /etc/hosts.equiv . | |
1028 | However, this file may be useful in environments that want to run both | |
1029 | rsh/rlogin and ssh. | |
1030 | .It Pa $HOME/.ssh/environment | |
4fe2af09 | 1031 | This file is read into the environment at login (if it exists). |
1032 | It can only contain empty lines, comment lines (that start with | |
bf740959 | 1033 | .Ql # ) , |
4fe2af09 | 1034 | and assignment lines of the form name=value. |
1035 | The file should be writable | |
bf740959 | 1036 | only by the user; it need not be readable by anyone else. |
1037 | .It Pa $HOME/.ssh/rc | |
1038 | If this file exists, it is run with /bin/sh after reading the | |
4fe2af09 | 1039 | environment files but before starting the user's shell or command. |
1040 | If X11 spoofing is in use, this will receive the "proto cookie" pair in | |
bf740959 | 1041 | standard input (and |
1042 | .Ev DISPLAY | |
4fe2af09 | 1043 | in environment). |
1044 | This must call | |
bf740959 | 1045 | .Xr xauth 1 |
1046 | in that case. | |
1047 | .Pp | |
1048 | The primary purpose of this file is to run any initialization routines | |
1049 | which may be needed before the user's home directory becomes | |
1050 | accessible; AFS is a particular example of such an environment. | |
1051 | .Pp | |
1052 | This file will probably contain some initialization code followed by | |
1053 | something similar to: "if read proto cookie; then echo add $DISPLAY | |
1054 | $proto $cookie | xauth -q -; fi". | |
1055 | .Pp | |
1056 | If this file does not exist, | |
5f4fdfae | 1057 | .Pa /etc/sshrc |
bf740959 | 1058 | is run, and if that |
1059 | does not exist either, xauth is used to store the cookie. | |
1060 | .Pp | |
1061 | This file should be writable only by the user, and need not be | |
1062 | readable by anyone else. | |
5f4fdfae | 1063 | .It Pa /etc/sshrc |
bf740959 | 1064 | Like |
1065 | .Pa $HOME/.ssh/rc . | |
1066 | This can be used to specify | |
4fe2af09 | 1067 | machine-specific login-time initializations globally. |
1068 | This file should be writable only by root, and should be world-readable. | |
089fbbd2 | 1069 | .El |
fa08c86b | 1070 | .Sh AUTHORS |
bf740959 | 1071 | OpenSSH |
c8d54615 | 1072 | is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen, |
4fe2af09 | 1073 | but with bugs removed and newer features re-added. |
1074 | Rapidly after the | |
c8d54615 | 1075 | 1.2.12 release, newer versions of the original ssh bore successively |
1076 | more restrictive licenses, and thus demand for a free version was born. | |
1d1ffb87 | 1077 | .Pp |
c8d54615 | 1078 | This version of OpenSSH |
bf740959 | 1079 | .Bl -bullet |
1080 | .It | |
bcbf86ec | 1081 | has all components of a restrictive nature (i.e., patents, see |
8abcdba4 | 1082 | .Xr ssl 8 ) |
bf740959 | 1083 | directly removed from the source code; any licensed or patented components |
1084 | are chosen from | |
1085 | external libraries. | |
1086 | .It | |
1d1ffb87 | 1087 | has been updated to support SSH protocol 1.5 and 2, making it compatible with |
1088 | all other SSH clients and servers. | |
bf740959 | 1089 | .It |
f54651ce | 1090 | contains added support for |
bf740959 | 1091 | .Xr kerberos 8 |
1092 | authentication and ticket passing. | |
1093 | .It | |
1094 | supports one-time password authentication with | |
1095 | .Xr skey 1 . | |
1096 | .El | |
1d1ffb87 | 1097 | .Pp |
1098 | OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl, | |
1099 | Niels Provos, Theo de Raadt, and Dug Song. | |
1100 | .Pp | |
1101 | The support for SSH protocol 2 was written by Markus Friedl. | |
bf740959 | 1102 | .Sh SEE ALSO |
bf740959 | 1103 | .Xr scp 1 , |
b5e300c2 | 1104 | .Xr sftp-server 8 , |
bf740959 | 1105 | .Xr ssh 1 , |
1106 | .Xr ssh-add 1 , | |
1107 | .Xr ssh-agent 1 , | |
1108 | .Xr ssh-keygen 1 , | |
8abcdba4 | 1109 | .Xr ssl 8 , |
7368a6c8 | 1110 | .Xr rlogin 1 , |
1111 | .Xr rsh 1 |