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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 | .\" |
37 | .Dd September 25, 1999 | |
38 | .Dt SSHD 8 | |
39 | .Os | |
40 | .Sh NAME | |
41 | .Nm sshd | |
42 | .Nd secure shell daemon | |
43 | .Sh SYNOPSIS | |
44 | .Nm sshd | |
48e671d5 | 45 | .Op Fl diqQ46 |
bf740959 | 46 | .Op Fl b Ar bits |
47 | .Op Fl f Ar config_file | |
48 | .Op Fl g Ar login_grace_time | |
49 | .Op Fl h Ar host_key_file | |
50 | .Op Fl k Ar key_gen_time | |
51 | .Op Fl p Ar port | |
c345cf9d | 52 | .Op Fl u Ar len |
5260325f | 53 | .Op Fl V Ar client_protocol_id |
f54651ce | 54 | .Sh DESCRIPTION |
bf740959 | 55 | .Nm |
f54651ce | 56 | (Secure Shell Daemon) is the daemon program for |
bf740959 | 57 | .Xr ssh 1 . |
3189621b | 58 | Together these programs replace rlogin and rsh, and |
bf740959 | 59 | provide secure encrypted communications between two untrusted hosts |
4fe2af09 | 60 | over an insecure network. |
61 | The programs are intended to be as easy to | |
bf740959 | 62 | install and use as possible. |
63 | .Pp | |
64 | .Nm | |
4fe2af09 | 65 | is the daemon that listens for connections from clients. |
f54651ce | 66 | It is normally started at boot from |
bf740959 | 67 | .Pa /etc/rc . |
68 | It forks a new | |
4fe2af09 | 69 | daemon for each incoming connection. |
70 | The forked daemons handle | |
bf740959 | 71 | key exchange, encryption, authentication, command execution, |
72 | and data exchange. | |
1d1ffb87 | 73 | This implementation of |
74 | .Nm | |
75 | supports both SSH protocol version 1 and 2 simultaneously. | |
bf740959 | 76 | .Nm |
4fe2af09 | 77 | works as follows. |
1d1ffb87 | 78 | .Pp |
79 | .Ss SSH protocol version 1 | |
80 | .Pp | |
4fe2af09 | 81 | Each host has a host-specific RSA key |
82 | (normally 1024 bits) used to identify the host. | |
83 | Additionally, when | |
bf740959 | 84 | the daemon starts, it generates a server RSA key (normally 768 bits). |
85 | This key is normally regenerated every hour if it has been used, and | |
86 | is never stored on disk. | |
87 | .Pp | |
3189621b | 88 | Whenever a client connects the daemon responds with its public |
89 | host and server keys. | |
4fe2af09 | 90 | The client compares the |
1d1ffb87 | 91 | RSA host key against its own database to verify that it has not changed. |
4fe2af09 | 92 | The client then generates a 256 bit random number. |
93 | It encrypts this | |
bf740959 | 94 | random number using both the host key and the server key, and sends |
4fe2af09 | 95 | the encrypted number to the server. |
3189621b | 96 | Both sides then use this |
bf740959 | 97 | random number as a session key which is used to encrypt all further |
4fe2af09 | 98 | communications in the session. |
99 | The rest of the session is encrypted | |
3189621b | 100 | using a conventional cipher, currently Blowfish or 3DES, with 3DES |
7368a6c8 | 101 | being used by default. |
4fe2af09 | 102 | The client selects the encryption algorithm |
bf740959 | 103 | to use from those offered by the server. |
104 | .Pp | |
4fe2af09 | 105 | Next, the server and the client enter an authentication dialog. |
106 | The client tries to authenticate itself using | |
bf740959 | 107 | .Pa .rhosts |
108 | authentication, | |
109 | .Pa .rhosts | |
110 | authentication combined with RSA host | |
111 | authentication, RSA challenge-response authentication, or password | |
112 | based authentication. | |
113 | .Pp | |
114 | Rhosts authentication is normally disabled | |
115 | because it is fundamentally insecure, but can be enabled in the server | |
4fe2af09 | 116 | configuration file if desired. |
117 | System security is not improved unless | |
bf740959 | 118 | .Xr rshd 8 , |
119 | .Xr rlogind 8 , | |
120 | .Xr rexecd 8 , | |
121 | and | |
122 | .Xr rexd 8 | |
123 | are disabled (thus completely disabling | |
124 | .Xr rlogin 1 | |
125 | and | |
126 | .Xr rsh 1 | |
3189621b | 127 | into the machine). |
bf740959 | 128 | .Pp |
1d1ffb87 | 129 | .Ss SSH protocol version 2 |
130 | .Pp | |
c345cf9d | 131 | Version 2 works similarly: |
1d1ffb87 | 132 | Each host has a host-specific DSA key used to identify the host. |
133 | However, when the daemon starts, it does not generate a server key. | |
134 | Forward security is provided through a Diffie-Hellman key agreement. | |
135 | This key agreement results in a shared session key. | |
136 | The rest of the session is encrypted | |
137 | using a symmetric cipher, currently | |
138 | Blowfish, 3DES or CAST128 in CBC mode or Arcfour. | |
139 | The client selects the encryption algorithm | |
140 | to use from those offered by the server. | |
141 | Additionally, session integrity is provided | |
d0c832f3 | 142 | through a cryptographic message authentication code |
1d1ffb87 | 143 | (hmac-sha1 or hmac-md5). |
144 | .Pp | |
145 | Protocol version 2 provides a public key based | |
146 | user authentication method (DSAAuthentication) | |
147 | and conventional password authentication. | |
148 | .Pp | |
149 | .Ss Command execution and data forwarding | |
150 | .Pp | |
bf740959 | 151 | If the client successfully authenticates itself, a dialog for |
4fe2af09 | 152 | preparing the session is entered. |
153 | At this time the client may request | |
bf740959 | 154 | things like allocating a pseudo-tty, forwarding X11 connections, |
155 | forwarding TCP/IP connections, or forwarding the authentication agent | |
156 | connection over the secure channel. | |
157 | .Pp | |
158 | Finally, the client either requests a shell or execution of a command. | |
4fe2af09 | 159 | The sides then enter session mode. |
160 | In this mode, either side may send | |
bf740959 | 161 | data at any time, and such data is forwarded to/from the shell or |
162 | command on the server side, and the user terminal in the client side. | |
163 | .Pp | |
164 | When the user program terminates and all forwarded X11 and other | |
165 | connections have been closed, the server sends command exit status to | |
166 | the client, and both sides exit. | |
167 | .Pp | |
168 | .Nm | |
169 | can be configured using command-line options or a configuration | |
4fe2af09 | 170 | file. |
171 | Command-line options override values specified in the | |
bf740959 | 172 | configuration file. |
173 | .Pp | |
9d6b7add | 174 | .Nm |
175 | rereads its configuration file when it receives a hangup signal, | |
176 | .Dv SIGHUP . | |
177 | .Pp | |
bf740959 | 178 | The options are as follows: |
179 | .Bl -tag -width Ds | |
180 | .It Fl b Ar bits | |
181 | Specifies the number of bits in the server key (default 768). | |
182 | .Pp | |
183 | .It Fl d | |
4fe2af09 | 184 | Debug mode. |
185 | The server sends verbose debug output to the system | |
186 | log, and does not put itself in the background. | |
187 | The server also will not fork and will only process one connection. | |
188 | This option is only intended for debugging for the server. | |
bcbf86ec | 189 | Multiple -d options increases the debugging level. Maximum is 3. |
bf740959 | 190 | .It Fl f Ar configuration_file |
4fe2af09 | 191 | Specifies the name of the configuration file. |
192 | The default is | |
5f4fdfae | 193 | .Pa /etc/sshd_config . |
bf740959 | 194 | .Nm |
195 | refuses to start if there is no configuration file. | |
196 | .It Fl g Ar login_grace_time | |
197 | Gives the grace time for clients to authenticate themselves (default | |
4fe2af09 | 198 | 300 seconds). |
199 | If the client fails to authenticate the user within | |
200 | this many seconds, the server disconnects and exits. | |
201 | A value of zero indicates no limit. | |
bf740959 | 202 | .It Fl h Ar host_key_file |
1d1ffb87 | 203 | Specifies the file from which the RSA host key is read (default |
5f4fdfae | 204 | .Pa /etc/ssh_host_key ) . |
bf740959 | 205 | This option must be given if |
206 | .Nm | |
207 | is not run as root (as the normal | |
208 | host file is normally not readable by anyone but root). | |
209 | .It Fl i | |
210 | Specifies that | |
211 | .Nm | |
f54651ce | 212 | is being run from inetd. |
bf740959 | 213 | .Nm |
214 | is normally not run | |
215 | from inetd because it needs to generate the server key before it can | |
4fe2af09 | 216 | respond to the client, and this may take tens of seconds. |
217 | Clients would have to wait too long if the key was regenerated every time. | |
610cd5c6 | 218 | However, with small key sizes (e.g., 512) using |
bf740959 | 219 | .Nm |
220 | from inetd may | |
221 | be feasible. | |
222 | .It Fl k Ar key_gen_time | |
223 | Specifies how often the server key is regenerated (default 3600 | |
4fe2af09 | 224 | seconds, or one hour). |
225 | The motivation for regenerating the key fairly | |
bf740959 | 226 | often is that the key is not stored anywhere, and after about an hour, |
227 | it becomes impossible to recover the key for decrypting intercepted | |
228 | communications even if the machine is cracked into or physically | |
4fe2af09 | 229 | seized. |
230 | A value of zero indicates that the key will never be regenerated. | |
bf740959 | 231 | .It Fl p Ar port |
232 | Specifies the port on which the server listens for connections | |
233 | (default 22). | |
234 | .It Fl q | |
4fe2af09 | 235 | Quiet mode. |
236 | Nothing is sent to the system log. | |
237 | Normally the beginning, | |
bf740959 | 238 | authentication, and termination of each connection is logged. |
c345cf9d | 239 | .It Fl u Ar len |
240 | This option is used to specify the size of the field | |
241 | in the | |
242 | .Li utmp | |
243 | structure that holds the remote host name. | |
244 | If the resolved host name is longer than | |
245 | .Ar len , | |
246 | the dotted decimal value will be used instead. | |
247 | This allows hosts with very long host names that | |
248 | overflow this field to still be uniquely identified. | |
249 | Specifying | |
250 | .Fl u0 | |
251 | indicates that only dotted decimal addresses | |
252 | should be put into the | |
253 | .Pa utmp | |
254 | file. | |
bf740959 | 255 | .It Fl Q |
256 | Do not print an error message if RSA support is missing. | |
5260325f | 257 | .It Fl V Ar client_protocol_id |
258 | SSH2 compatibility mode. | |
3189621b | 259 | When this option is specified |
5260325f | 260 | .Nm |
3189621b | 261 | assumes the client has sent the supplied version string |
5260325f | 262 | and skips the |
263 | Protocol Version Identification Exchange. | |
48e671d5 | 264 | .It Fl 4 |
265 | Forces | |
266 | .Nm | |
267 | to use IPv4 addresses only. | |
268 | .It Fl 6 | |
269 | Forces | |
270 | .Nm | |
271 | to use IPv6 addresses only. | |
bf740959 | 272 | .El |
273 | .Sh CONFIGURATION FILE | |
274 | .Nm | |
f54651ce | 275 | reads configuration data from |
5f4fdfae | 276 | .Pa /etc/sshd_config |
bf740959 | 277 | (or the file specified with |
278 | .Fl f | |
4fe2af09 | 279 | on the command line). |
280 | The file contains keyword-value pairs, one per line. | |
281 | Lines starting with | |
bf740959 | 282 | .Ql # |
283 | and empty lines are interpreted as comments. | |
284 | .Pp | |
285 | The following keywords are possible. | |
286 | .Bl -tag -width Ds | |
287 | .It Cm AFSTokenPassing | |
4fe2af09 | 288 | Specifies whether an AFS token may be forwarded to the server. |
289 | Default is | |
bf740959 | 290 | .Dq yes . |
291 | .It Cm AllowGroups | |
292 | This keyword can be followed by a number of group names, separated | |
4fe2af09 | 293 | by spaces. |
294 | If specified, login is allowed only for users whose primary | |
bf740959 | 295 | group matches one of the patterns. |
296 | .Ql \&* | |
297 | and | |
298 | .Ql ? | |
299 | can be used as | |
4fe2af09 | 300 | wildcards in the patterns. |
c345cf9d | 301 | Only group names are valid; a numerical group ID isn't recognized. |
4fe2af09 | 302 | By default login is allowed regardless of the primary group. |
bf740959 | 303 | .Pp |
304 | .It Cm AllowUsers | |
305 | This keyword can be followed by a number of user names, separated | |
4fe2af09 | 306 | by spaces. |
307 | If specified, login is allowed only for users names that | |
bf740959 | 308 | match one of the patterns. |
309 | .Ql \&* | |
310 | and | |
311 | .Ql ? | |
312 | can be used as | |
4fe2af09 | 313 | wildcards in the patterns. |
c345cf9d | 314 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 315 | By default login is allowed regardless of the user name. |
bf740959 | 316 | .Pp |
f54651ce | 317 | .It Cm Ciphers |
318 | Specifies the ciphers allowed for protocol version 2. | |
319 | Multiple ciphers must be comma-separated. | |
320 | The default is | |
d0c832f3 | 321 | .Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc . |
bf740959 | 322 | .It Cm CheckMail |
323 | Specifies whether | |
324 | .Nm | |
325 | should check for new mail for interactive logins. | |
326 | The default is | |
327 | .Dq no . | |
328 | .It Cm DenyGroups | |
329 | This keyword can be followed by a number of group names, separated | |
4fe2af09 | 330 | by spaces. |
331 | Users whose primary group matches one of the patterns | |
bf740959 | 332 | aren't allowed to log in. |
333 | .Ql \&* | |
334 | and | |
335 | .Ql ? | |
336 | can be used as | |
4fe2af09 | 337 | wildcards in the patterns. |
c345cf9d | 338 | Only group names are valid; a numerical group ID isn't recognized. |
4fe2af09 | 339 | By default login is allowed regardless of the primary group. |
bf740959 | 340 | .Pp |
341 | .It Cm DenyUsers | |
342 | This keyword can be followed by a number of user names, separated | |
4fe2af09 | 343 | by spaces. |
344 | Login is disallowed for user names that match one of the patterns. | |
bf740959 | 345 | .Ql \&* |
346 | and | |
347 | .Ql ? | |
4fe2af09 | 348 | can be used as wildcards in the patterns. |
c345cf9d | 349 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 350 | By default login is allowed regardless of the user name. |
1d1ffb87 | 351 | .It Cm DSAAuthentication |
352 | Specifies whether DSA authentication is allowed. | |
353 | The default is | |
354 | .Dq yes . | |
355 | Note that this option applies to protocol version 2 only. | |
356 | .It Cm GatewayPorts | |
357 | Specifies whether remote hosts are allowed to connect to ports | |
358 | forwarded for the client. | |
359 | The argument must be | |
360 | .Dq yes | |
361 | or | |
362 | .Dq no . | |
363 | The default is | |
364 | .Dq no . | |
c345cf9d | 365 | .It Cm HostDSAKey |
1d1ffb87 | 366 | Specifies the file containing the private DSA host key (default |
367 | .Pa /etc/ssh_host_dsa_key ) | |
368 | used by SSH protocol 2.0. | |
369 | Note that | |
370 | .Nm | |
d0c832f3 | 371 | disables protocol 2.0 if this file is group/world-accessible. |
bf740959 | 372 | .It Cm HostKey |
1d1ffb87 | 373 | Specifies the file containing the private RSA host key (default |
374 | .Pa /etc/ssh_host_key ) | |
375 | used by SSH protocols 1.3 and 1.5. | |
bf740959 | 376 | Note that |
377 | .Nm | |
d0c832f3 | 378 | disables protocols 1.3 and 1.5 if this file is group/world-accessible. |
bf740959 | 379 | .It Cm IgnoreRhosts |
c8d54615 | 380 | Specifies that |
381 | .Pa .rhosts | |
f54651ce | 382 | and |
c8d54615 | 383 | .Pa .shosts |
384 | files will not be used in authentication. | |
bf740959 | 385 | .Pa /etc/hosts.equiv |
386 | and | |
f54651ce | 387 | .Pa /etc/shosts.equiv |
4fe2af09 | 388 | are still used. |
f54651ce | 389 | The default is |
c8d54615 | 390 | .Dq yes . |
b4748e2f | 391 | .It Cm IgnoreUserKnownHosts |
392 | Specifies whether | |
393 | .Nm | |
394 | should ignore the user's | |
395 | .Pa $HOME/.ssh/known_hosts | |
396 | during | |
397 | .Cm RhostsRSAAuthentication . | |
398 | The default is | |
399 | .Dq no . | |
bf740959 | 400 | .It Cm KeepAlive |
401 | Specifies whether the system should send keepalive messages to the | |
4fe2af09 | 402 | other side. |
403 | If they are sent, death of the connection or crash of one | |
404 | of the machines will be properly noticed. | |
405 | However, this means that | |
bf740959 | 406 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 407 | find it annoying. |
d0c832f3 | 408 | On the other hand, if keepalives are not sent, |
bf740959 | 409 | sessions may hang indefinitely on the server, leaving |
410 | .Dq ghost | |
411 | users and consuming server resources. | |
412 | .Pp | |
413 | The default is | |
414 | .Dq yes | |
415 | (to send keepalives), and the server will notice | |
4fe2af09 | 416 | if the network goes down or the client host reboots. |
417 | This avoids infinitely hanging sessions. | |
bf740959 | 418 | .Pp |
419 | To disable keepalives, the value should be set to | |
420 | .Dq no | |
421 | in both the server and the client configuration files. | |
422 | .It Cm KerberosAuthentication | |
4fe2af09 | 423 | Specifies whether Kerberos authentication is allowed. |
424 | This can be in the form of a Kerberos ticket, or if | |
bf740959 | 425 | .Cm PasswordAuthentication |
426 | is yes, the password provided by the user will be validated through | |
c345cf9d | 427 | the Kerberos KDC. To use this option, the server needs a |
428 | Kerberos servtab which allows the verification of the KDC's identity. | |
4fe2af09 | 429 | Default is |
bf740959 | 430 | .Dq yes . |
431 | .It Cm KerberosOrLocalPasswd | |
432 | If set then if password authentication through Kerberos fails then | |
433 | the password will be validated via any additional local mechanism | |
434 | such as | |
188adeb2 | 435 | .Pa /etc/passwd . |
4fe2af09 | 436 | Default is |
bf740959 | 437 | .Dq yes . |
438 | .It Cm KerberosTgtPassing | |
439 | Specifies whether a Kerberos TGT may be forwarded to the server. | |
f54651ce | 440 | Default is |
bf740959 | 441 | .Dq no , |
442 | as this only works when the Kerberos KDC is actually an AFS kaserver. | |
443 | .It Cm KerberosTicketCleanup | |
444 | Specifies whether to automatically destroy the user's ticket cache | |
4fe2af09 | 445 | file on logout. |
446 | Default is | |
bf740959 | 447 | .Dq yes . |
448 | .It Cm KeyRegenerationInterval | |
449 | The server key is automatically regenerated after this many seconds | |
4fe2af09 | 450 | (if it has been used). |
451 | The purpose of regeneration is to prevent | |
bf740959 | 452 | decrypting captured sessions by later breaking into the machine and |
4fe2af09 | 453 | stealing the keys. |
454 | The key is never stored anywhere. | |
455 | If the value is 0, the key is never regenerated. | |
456 | The default is 3600 (seconds). | |
bf740959 | 457 | .It Cm ListenAddress |
458 | Specifies what local address | |
459 | .Nm | |
460 | should listen on. | |
461 | The default is to listen to all local addresses. | |
48e671d5 | 462 | Multiple options of this type are permitted. |
463 | Additionally, the | |
464 | .Cm Ports | |
465 | options must precede this option. | |
bf740959 | 466 | .It Cm LoginGraceTime |
467 | The server disconnects after this time if the user has not | |
4fe2af09 | 468 | successfully logged in. |
469 | If the value is 0, there is no time limit. | |
bf740959 | 470 | The default is 600 (seconds). |
6a17f9c2 | 471 | .It Cm LogLevel |
472 | Gives the verbosity level that is used when logging messages from | |
473 | .Nm sshd . | |
474 | The possible values are: | |
5260325f | 475 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
6a17f9c2 | 476 | The default is INFO. |
477 | Logging with level DEBUG violates the privacy of users | |
478 | and is not recommended. | |
089fbbd2 | 479 | .It Cm MaxStartups |
480 | Specifies the maximum number of concurrent unauthenticated connections to the | |
481 | .Nm | |
482 | daemon. | |
483 | Additional connections will be dropped until authentication succeeds or the | |
484 | .Cm LoginGraceTime | |
485 | expires for a connection. | |
486 | The default is 10. | |
c345cf9d | 487 | .Pp |
488 | Alternatively, random early drop can be enabled by specifying | |
489 | the three colon separated values | |
490 | .Dq start:rate:full | |
491 | (e.g. "10:30:60"). | |
492 | .Nm | |
493 | will refuse connection attempts with a probabillity of | |
494 | .Dq rate/100 | |
495 | (30%) | |
496 | if there are currently | |
497 | .Dq start | |
498 | (10) | |
499 | unauthenticated connections. | |
500 | The probabillity increases linearly and all connection attempts | |
501 | are refused if the number of unauthenticated connections reaches | |
502 | .Dq full | |
503 | (60). | |
bf740959 | 504 | .It Cm PasswordAuthentication |
505 | Specifies whether password authentication is allowed. | |
506 | The default is | |
507 | .Dq yes . | |
c345cf9d | 508 | Note that this option applies to both protocol versions 1 and 2. |
bf740959 | 509 | .It Cm PermitEmptyPasswords |
510 | When password authentication is allowed, it specifies whether the | |
4fe2af09 | 511 | server allows login to accounts with empty password strings. |
512 | The default is | |
c8d54615 | 513 | .Dq no . |
bf740959 | 514 | .It Cm PermitRootLogin |
515 | Specifies whether the root can log in using | |
516 | .Xr ssh 1 . | |
517 | The argument must be | |
518 | .Dq yes , | |
519 | .Dq without-password | |
520 | or | |
521 | .Dq no . | |
522 | The default is | |
523 | .Dq yes . | |
524 | If this options is set to | |
525 | .Dq without-password | |
526 | only password authentication is disabled for root. | |
527 | .Pp | |
528 | Root login with RSA authentication when the | |
529 | .Ar command | |
530 | option has been | |
531 | specified will be allowed regardless of the value of this setting | |
532 | (which may be useful for taking remote backups even if root login is | |
533 | normally not allowed). | |
0fbe8c74 | 534 | .It Cm PidFile |
535 | Specifies the file that contains the process identifier of the | |
536 | .Nm | |
537 | daemon. | |
538 | The default is | |
539 | .Pa /var/run/sshd.pid . | |
bf740959 | 540 | .It Cm Port |
541 | Specifies the port number that | |
542 | .Nm | |
4fe2af09 | 543 | listens on. |
544 | The default is 22. | |
48e671d5 | 545 | Multiple options of this type are permitted. |
bf740959 | 546 | .It Cm PrintMotd |
547 | Specifies whether | |
548 | .Nm | |
f54651ce | 549 | should print |
bf740959 | 550 | .Pa /etc/motd |
4fe2af09 | 551 | when a user logs in interactively. |
552 | (On some systems it is also printed by the shell, | |
bf740959 | 553 | .Pa /etc/profile , |
4fe2af09 | 554 | or equivalent.) |
555 | The default is | |
bf740959 | 556 | .Dq yes . |
f54651ce | 557 | .It Cm Protocol |
558 | Specifies the protocol versions | |
559 | .Nm | |
560 | should support. | |
561 | The possible values are | |
562 | .Dq 1 | |
563 | and | |
564 | .Dq 2 . | |
565 | Multiple versions must be comma-separated. | |
566 | The default is | |
567 | .Dq 1 . | |
bf740959 | 568 | .It Cm RandomSeed |
4fe2af09 | 569 | Obsolete. |
570 | Random number generation uses other techniques. | |
bf740959 | 571 | .It Cm RhostsAuthentication |
572 | Specifies whether authentication using rhosts or /etc/hosts.equiv | |
4fe2af09 | 573 | files is sufficient. |
574 | Normally, this method should not be permitted because it is insecure. | |
bf740959 | 575 | .Cm RhostsRSAAuthentication |
576 | should be used | |
577 | instead, because it performs RSA-based host authentication in addition | |
578 | to normal rhosts or /etc/hosts.equiv authentication. | |
579 | The default is | |
580 | .Dq no . | |
581 | .It Cm RhostsRSAAuthentication | |
582 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
4fe2af09 | 583 | with successful RSA host authentication is allowed. |
584 | The default is | |
c8d54615 | 585 | .Dq no . |
bf740959 | 586 | .It Cm RSAAuthentication |
4fe2af09 | 587 | Specifies whether pure RSA authentication is allowed. |
588 | The default is | |
bf740959 | 589 | .Dq yes . |
1d1ffb87 | 590 | Note that this option applies to protocol version 1 only. |
bf740959 | 591 | .It Cm ServerKeyBits |
4fe2af09 | 592 | Defines the number of bits in the server key. |
593 | The minimum value is 512, and the default is 768. | |
bf740959 | 594 | .It Cm SkeyAuthentication |
595 | Specifies whether | |
f54651ce | 596 | .Xr skey 1 |
4fe2af09 | 597 | authentication is allowed. |
598 | The default is | |
bf740959 | 599 | .Dq yes . |
600 | Note that s/key authentication is enabled only if | |
601 | .Cm PasswordAuthentication | |
602 | is allowed, too. | |
603 | .It Cm StrictModes | |
604 | Specifies whether | |
605 | .Nm | |
606 | should check file modes and ownership of the | |
4fe2af09 | 607 | user's files and home directory before accepting login. |
608 | This is normally desirable because novices sometimes accidentally leave their | |
609 | directory or files world-writable. | |
610 | The default is | |
bf740959 | 611 | .Dq yes . |
38c295d6 | 612 | .It Cm Subsystem |
613 | Configures an external subsystem (e.g. file transfer daemon). | |
614 | Arguments should be a subsystem name and a command to execute upon subsystem request. | |
b5e300c2 | 615 | The command |
616 | .Xr sftp-server 8 | |
617 | implements the | |
618 | .Dq sftp | |
619 | file transfer subsystem. | |
38c295d6 | 620 | By default no subsystems are defined. |
621 | Note that this option applies to protocol version 2 only. | |
bf740959 | 622 | .It Cm SyslogFacility |
623 | Gives the facility code that is used when logging messages from | |
624 | .Nm sshd . | |
625 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, | |
4fe2af09 | 626 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
627 | The default is AUTH. | |
bf740959 | 628 | .It Cm UseLogin |
629 | Specifies whether | |
630 | .Xr login 1 | |
fa649821 | 631 | is used for interactive login sessions. |
632 | Note that | |
633 | .Xr login 1 | |
c345cf9d | 634 | is never used for remote command execution. |
4fe2af09 | 635 | The default is |
bf740959 | 636 | .Dq no . |
bf740959 | 637 | .It Cm X11DisplayOffset |
638 | Specifies the first display number available for | |
639 | .Nm sshd Ns 's | |
4fe2af09 | 640 | X11 forwarding. |
641 | This prevents | |
bf740959 | 642 | .Nm |
643 | from interfering with real X11 servers. | |
c8d54615 | 644 | The default is 10. |
7b2ea3a1 | 645 | .It Cm X11Forwarding |
4fe2af09 | 646 | Specifies whether X11 forwarding is permitted. |
647 | The default is | |
c8d54615 | 648 | .Dq no . |
7b2ea3a1 | 649 | Note that disabling X11 forwarding does not improve security in any |
650 | way, as users can always install their own forwarders. | |
fa649821 | 651 | .It Cm XAuthLocation |
652 | Specifies the location of the | |
653 | .Xr xauth 1 | |
654 | program. | |
655 | The default is | |
656 | .Pa /usr/X11R6/bin/xauth . | |
bf740959 | 657 | .El |
658 | .Sh LOGIN PROCESS | |
659 | When a user successfully logs in, | |
660 | .Nm | |
661 | does the following: | |
662 | .Bl -enum -offset indent | |
663 | .It | |
664 | If the login is on a tty, and no command has been specified, | |
f54651ce | 665 | prints last login time and |
bf740959 | 666 | .Pa /etc/motd |
667 | (unless prevented in the configuration file or by | |
668 | .Pa $HOME/.hushlogin ; | |
669 | see the | |
f54651ce | 670 | .Sx FILES |
bf740959 | 671 | section). |
672 | .It | |
673 | If the login is on a tty, records login time. | |
674 | .It | |
675 | Checks | |
676 | .Pa /etc/nologin ; | |
677 | if it exists, prints contents and quits | |
678 | (unless root). | |
679 | .It | |
680 | Changes to run with normal user privileges. | |
681 | .It | |
682 | Sets up basic environment. | |
683 | .It | |
684 | Reads | |
685 | .Pa $HOME/.ssh/environment | |
686 | if it exists. | |
687 | .It | |
688 | Changes to user's home directory. | |
689 | .It | |
690 | If | |
691 | .Pa $HOME/.ssh/rc | |
692 | exists, runs it; else if | |
5f4fdfae | 693 | .Pa /etc/sshrc |
bf740959 | 694 | exists, runs |
4fe2af09 | 695 | it; otherwise runs xauth. |
696 | The | |
bf740959 | 697 | .Dq rc |
698 | files are given the X11 | |
699 | authentication protocol and cookie in standard input. | |
700 | .It | |
701 | Runs user's shell or command. | |
702 | .El | |
703 | .Sh AUTHORIZED_KEYS FILE FORMAT | |
f54651ce | 704 | The |
bf740959 | 705 | .Pa $HOME/.ssh/authorized_keys |
706 | file lists the RSA keys that are | |
1d1ffb87 | 707 | permitted for RSA authentication in SSH protocols 1.3 and 1.5 |
d0c832f3 | 708 | Similarly, the |
1d1ffb87 | 709 | .Pa $HOME/.ssh/authorized_keys2 |
710 | file lists the DSA keys that are | |
711 | permitted for DSA authentication in SSH protocol 2.0. | |
4fe2af09 | 712 | Each line of the file contains one |
bf740959 | 713 | key (empty lines and lines starting with a |
714 | .Ql # | |
715 | are ignored as | |
4fe2af09 | 716 | comments). |
717 | Each line consists of the following fields, separated by | |
718 | spaces: options, bits, exponent, modulus, comment. | |
719 | The options field | |
bf740959 | 720 | is optional; its presence is determined by whether the line starts |
721 | with a number or not (the option field never starts with a number). | |
722 | The bits, exponent, modulus and comment fields give the RSA key; the | |
723 | comment field is not used for anything (but may be convenient for the | |
724 | user to identify the key). | |
725 | .Pp | |
726 | Note that lines in this file are usually several hundred bytes long | |
4fe2af09 | 727 | (because of the size of the RSA key modulus). |
728 | You don't want to type them in; instead, copy the | |
bf740959 | 729 | .Pa identity.pub |
730 | file and edit it. | |
731 | .Pp | |
c345cf9d | 732 | The options (if present) consist of comma-separated option |
4fe2af09 | 733 | specifications. |
734 | No spaces are permitted, except within double quotes. | |
bf740959 | 735 | The following option specifications are supported: |
736 | .Bl -tag -width Ds | |
737 | .It Cm from="pattern-list" | |
738 | Specifies that in addition to RSA authentication, the canonical name | |
739 | of the remote host must be present in the comma-separated list of | |
4fe2af09 | 740 | patterns |
741 | .Pf ( Ql * | |
742 | and | |
743 | .Ql ? | |
744 | serve as wildcards). | |
745 | The list may also contain | |
746 | patterns negated by prefixing them with | |
747 | .Ql ! ; | |
748 | if the canonical host name matches a negated pattern, the key is not accepted. | |
749 | The purpose | |
bf740959 | 750 | of this option is to optionally increase security: RSA authentication |
751 | by itself does not trust the network or name servers or anything (but | |
752 | the key); however, if somebody somehow steals the key, the key | |
4fe2af09 | 753 | permits an intruder to log in from anywhere in the world. |
754 | This additional option makes using a stolen key more difficult (name | |
bf740959 | 755 | servers and/or routers would have to be compromised in addition to |
756 | just the key). | |
757 | .It Cm command="command" | |
758 | Specifies that the command is executed whenever this key is used for | |
4fe2af09 | 759 | authentication. |
760 | The command supplied by the user (if any) is ignored. | |
bf740959 | 761 | The command is run on a pty if the connection requests a pty; |
4fe2af09 | 762 | otherwise it is run without a tty. |
763 | A quote may be included in the command by quoting it with a backslash. | |
764 | This option might be useful | |
765 | to restrict certain RSA keys to perform just a specific operation. | |
766 | An example might be a key that permits remote backups but nothing else. | |
d0c832f3 | 767 | Note that the client may specify TCP/IP and/or X11 |
768 | forwarding unless they are explicitly prohibited. | |
bf740959 | 769 | .It Cm environment="NAME=value" |
770 | Specifies that the string is to be added to the environment when | |
4fe2af09 | 771 | logging in using this key. |
772 | Environment variables set this way | |
773 | override other default environment values. | |
774 | Multiple options of this type are permitted. | |
bf740959 | 775 | .It Cm no-port-forwarding |
776 | Forbids TCP/IP forwarding when this key is used for authentication. | |
4fe2af09 | 777 | Any port forward requests by the client will return an error. |
778 | This might be used, e.g., in connection with the | |
bf740959 | 779 | .Cm command |
780 | option. | |
781 | .It Cm no-X11-forwarding | |
782 | Forbids X11 forwarding when this key is used for authentication. | |
783 | Any X11 forward requests by the client will return an error. | |
784 | .It Cm no-agent-forwarding | |
785 | Forbids authentication agent forwarding when this key is used for | |
786 | authentication. | |
787 | .It Cm no-pty | |
788 | Prevents tty allocation (a request to allocate a pty will fail). | |
789 | .El | |
790 | .Ss Examples | |
791 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar | |
792 | .Pp | |
793 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula | |
794 | .Pp | |
795 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi | |
796 | .Sh SSH_KNOWN_HOSTS FILE FORMAT | |
f54651ce | 797 | The |
1d1ffb87 | 798 | .Pa /etc/ssh_known_hosts , |
799 | .Pa /etc/ssh_known_hosts2 , | |
800 | .Pa $HOME/.ssh/known_hosts , | |
f54651ce | 801 | and |
1d1ffb87 | 802 | .Pa $HOME/.ssh/known_hosts2 |
4fe2af09 | 803 | files contain host public keys for all known hosts. |
804 | The global file should | |
805 | be prepared by the administrator (optional), and the per-user file is | |
c345cf9d | 806 | maintained automatically: whenever the user connects from an unknown host |
4fe2af09 | 807 | its key is added to the per-user file. |
bf740959 | 808 | .Pp |
809 | Each line in these files contains the following fields: hostnames, | |
4fe2af09 | 810 | bits, exponent, modulus, comment. |
811 | The fields are separated by spaces. | |
bf740959 | 812 | .Pp |
813 | Hostnames is a comma-separated list of patterns ('*' and '?' act as | |
814 | wildcards); each pattern in turn is matched against the canonical host | |
815 | name (when authenticating a client) or against the user-supplied | |
4fe2af09 | 816 | name (when authenticating a server). |
817 | A pattern may also be preceded by | |
bf740959 | 818 | .Ql ! |
819 | to indicate negation: if the host name matches a negated | |
820 | pattern, it is not accepted (by that line) even if it matched another | |
821 | pattern on the line. | |
822 | .Pp | |
1d1ffb87 | 823 | Bits, exponent, and modulus are taken directly from the RSA host key; they |
bf740959 | 824 | can be obtained, e.g., from |
5f4fdfae | 825 | .Pa /etc/ssh_host_key.pub . |
bf740959 | 826 | The optional comment field continues to the end of the line, and is not used. |
827 | .Pp | |
828 | Lines starting with | |
829 | .Ql # | |
830 | and empty lines are ignored as comments. | |
831 | .Pp | |
832 | When performing host authentication, authentication is accepted if any | |
4fe2af09 | 833 | matching line has the proper key. |
834 | It is thus permissible (but not | |
bf740959 | 835 | recommended) to have several lines or different host keys for the same |
4fe2af09 | 836 | names. |
837 | This will inevitably happen when short forms of host names | |
838 | from different domains are put in the file. | |
839 | It is possible | |
bf740959 | 840 | that the files contain conflicting information; authentication is |
841 | accepted if valid information can be found from either file. | |
842 | .Pp | |
843 | Note that the lines in these files are typically hundreds of characters | |
844 | long, and you definitely don't want to type in the host keys by hand. | |
845 | Rather, generate them by a script | |
f54651ce | 846 | or by taking |
5f4fdfae | 847 | .Pa /etc/ssh_host_key.pub |
bf740959 | 848 | and adding the host names at the front. |
849 | .Ss Examples | |
850 | closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi | |
851 | .Sh FILES | |
852 | .Bl -tag -width Ds | |
5f4fdfae | 853 | .It Pa /etc/sshd_config |
bf740959 | 854 | Contains configuration data for |
855 | .Nm sshd . | |
856 | This file should be writable by root only, but it is recommended | |
857 | (though not necessary) that it be world-readable. | |
5f4fdfae | 858 | .It Pa /etc/ssh_host_key |
bf740959 | 859 | Contains the private part of the host key. |
860 | This file should only be owned by root, readable only by root, and not | |
861 | accessible to others. | |
862 | Note that | |
863 | .Nm | |
864 | does not start if this file is group/world-accessible. | |
5f4fdfae | 865 | .It Pa /etc/ssh_host_key.pub |
bf740959 | 866 | Contains the public part of the host key. |
867 | This file should be world-readable but writable only by | |
4fe2af09 | 868 | root. |
869 | Its contents should match the private part. | |
870 | This file is not | |
bf740959 | 871 | really used for anything; it is only provided for the convenience of |
872 | the user so its contents can be copied to known hosts files. | |
873 | These two files are created using | |
874 | .Xr ssh-keygen 1 . | |
5f4fdfae | 875 | .It Pa /var/run/sshd.pid |
bf740959 | 876 | Contains the process ID of the |
877 | .Nm | |
878 | listening for connections (if there are several daemons running | |
879 | concurrently for different ports, this contains the pid of the one | |
4fe2af09 | 880 | started last). |
c345cf9d | 881 | The content of this file is not sensitive; it can be world-readable. |
bf740959 | 882 | .It Pa $HOME/.ssh/authorized_keys |
883 | Lists the RSA keys that can be used to log into the user's account. | |
884 | This file must be readable by root (which may on some machines imply | |
885 | it being world-readable if the user's home directory resides on an NFS | |
4fe2af09 | 886 | volume). |
887 | It is recommended that it not be accessible by others. | |
888 | The format of this file is described above. | |
1d1ffb87 | 889 | Users will place the contents of their |
890 | .Pa identity.pub | |
891 | files into this file, as described in | |
892 | .Xr ssh-keygen 1 . | |
893 | .It Pa $HOME/.ssh/authorized_keys2 | |
894 | Lists the DSA keys that can be used to log into the user's account. | |
895 | This file must be readable by root (which may on some machines imply | |
896 | it being world-readable if the user's home directory resides on an NFS | |
897 | volume). | |
898 | It is recommended that it not be accessible by others. | |
899 | The format of this file is described above. | |
900 | Users will place the contents of their | |
901 | .Pa id_dsa.pub | |
902 | files into this file, as described in | |
903 | .Xr ssh-keygen 1 . | |
5f4fdfae | 904 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
6a17f9c2 | 905 | These files are consulted when using rhosts with RSA host |
4fe2af09 | 906 | authentication to check the public key of the host. |
907 | The key must be listed in one of these files to be accepted. | |
5bbb5681 | 908 | The client uses the same files |
c345cf9d | 909 | to verify that the remote host is the one it intended to connect. |
4fe2af09 | 910 | These files should be writable only by root/the owner. |
5f4fdfae | 911 | .Pa /etc/ssh_known_hosts |
bf740959 | 912 | should be world-readable, and |
913 | .Pa $HOME/.ssh/known_hosts | |
914 | can but need not be world-readable. | |
915 | .It Pa /etc/nologin | |
f54651ce | 916 | If this file exists, |
bf740959 | 917 | .Nm |
4fe2af09 | 918 | refuses to let anyone except root log in. |
919 | The contents of the file | |
bf740959 | 920 | are displayed to anyone trying to log in, and non-root connections are |
4fe2af09 | 921 | refused. |
922 | The file should be world-readable. | |
bf740959 | 923 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
924 | If compiled with | |
925 | .Sy LIBWRAP | |
926 | support, tcp-wrappers access controls may be defined here as described in | |
927 | .Xr hosts_access 5 . | |
928 | .It Pa $HOME/.rhosts | |
929 | This file contains host-username pairs, separated by a space, one per | |
4fe2af09 | 930 | line. |
931 | The given user on the corresponding host is permitted to log in | |
932 | without password. | |
933 | The same file is used by rlogind and rshd. | |
bf740959 | 934 | The file must |
935 | be writable only by the user; it is recommended that it not be | |
936 | accessible by others. | |
937 | .Pp | |
4fe2af09 | 938 | If is also possible to use netgroups in the file. |
939 | Either host or user | |
bf740959 | 940 | name may be of the form +@groupname to specify all hosts or all users |
941 | in the group. | |
942 | .It Pa $HOME/.shosts | |
943 | For ssh, | |
944 | this file is exactly the same as for | |
945 | .Pa .rhosts . | |
946 | However, this file is | |
947 | not used by rlogin and rshd, so using this permits access using SSH only. | |
c345cf9d | 948 | .It Pa /etc/hosts.equiv |
bf740959 | 949 | This file is used during |
950 | .Pa .rhosts | |
4fe2af09 | 951 | authentication. |
952 | In the simplest form, this file contains host names, one per line. | |
953 | Users on | |
bf740959 | 954 | those hosts are permitted to log in without a password, provided they |
4fe2af09 | 955 | have the same user name on both machines. |
956 | The host name may also be | |
bf740959 | 957 | followed by a user name; such users are permitted to log in as |
958 | .Em any | |
4fe2af09 | 959 | user on this machine (except root). |
960 | Additionally, the syntax | |
bf740959 | 961 | .Dq +@group |
4fe2af09 | 962 | can be used to specify netgroups. |
963 | Negated entries start with | |
bf740959 | 964 | .Ql \&- . |
965 | .Pp | |
966 | If the client host/user is successfully matched in this file, login is | |
967 | automatically permitted provided the client and server user names are the | |
4fe2af09 | 968 | same. |
969 | Additionally, successful RSA host authentication is normally required. | |
970 | This file must be writable only by root; it is recommended | |
bf740959 | 971 | that it be world-readable. |
972 | .Pp | |
973 | .Sy "Warning: It is almost never a good idea to use user names in" | |
974 | .Pa hosts.equiv . | |
975 | Beware that it really means that the named user(s) can log in as | |
976 | .Em anybody , | |
977 | which includes bin, daemon, adm, and other accounts that own critical | |
4fe2af09 | 978 | binaries and directories. |
979 | Using a user name practically grants the user root access. | |
980 | The only valid use for user names that I can think | |
bf740959 | 981 | of is in negative entries. |
982 | .Pp | |
983 | Note that this warning also applies to rsh/rlogin. | |
5f4fdfae | 984 | .It Pa /etc/shosts.equiv |
bf740959 | 985 | This is processed exactly as |
986 | .Pa /etc/hosts.equiv . | |
987 | However, this file may be useful in environments that want to run both | |
988 | rsh/rlogin and ssh. | |
989 | .It Pa $HOME/.ssh/environment | |
4fe2af09 | 990 | This file is read into the environment at login (if it exists). |
991 | It can only contain empty lines, comment lines (that start with | |
bf740959 | 992 | .Ql # ) , |
4fe2af09 | 993 | and assignment lines of the form name=value. |
994 | The file should be writable | |
bf740959 | 995 | only by the user; it need not be readable by anyone else. |
996 | .It Pa $HOME/.ssh/rc | |
997 | If this file exists, it is run with /bin/sh after reading the | |
4fe2af09 | 998 | environment files but before starting the user's shell or command. |
999 | If X11 spoofing is in use, this will receive the "proto cookie" pair in | |
bf740959 | 1000 | standard input (and |
1001 | .Ev DISPLAY | |
4fe2af09 | 1002 | in environment). |
1003 | This must call | |
bf740959 | 1004 | .Xr xauth 1 |
1005 | in that case. | |
1006 | .Pp | |
1007 | The primary purpose of this file is to run any initialization routines | |
1008 | which may be needed before the user's home directory becomes | |
1009 | accessible; AFS is a particular example of such an environment. | |
1010 | .Pp | |
1011 | This file will probably contain some initialization code followed by | |
1012 | something similar to: "if read proto cookie; then echo add $DISPLAY | |
1013 | $proto $cookie | xauth -q -; fi". | |
1014 | .Pp | |
1015 | If this file does not exist, | |
5f4fdfae | 1016 | .Pa /etc/sshrc |
bf740959 | 1017 | is run, and if that |
1018 | does not exist either, xauth is used to store the cookie. | |
1019 | .Pp | |
1020 | This file should be writable only by the user, and need not be | |
1021 | readable by anyone else. | |
5f4fdfae | 1022 | .It Pa /etc/sshrc |
bf740959 | 1023 | Like |
1024 | .Pa $HOME/.ssh/rc . | |
1025 | This can be used to specify | |
4fe2af09 | 1026 | machine-specific login-time initializations globally. |
1027 | This file should be writable only by root, and should be world-readable. | |
089fbbd2 | 1028 | .El |
bf740959 | 1029 | .Sh AUTHOR |
bf740959 | 1030 | OpenSSH |
c8d54615 | 1031 | is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen, |
4fe2af09 | 1032 | but with bugs removed and newer features re-added. |
1033 | Rapidly after the | |
c8d54615 | 1034 | 1.2.12 release, newer versions of the original ssh bore successively |
1035 | more restrictive licenses, and thus demand for a free version was born. | |
1d1ffb87 | 1036 | .Pp |
c8d54615 | 1037 | This version of OpenSSH |
bf740959 | 1038 | .Bl -bullet |
1039 | .It | |
bcbf86ec | 1040 | has all components of a restrictive nature (i.e., patents, see |
1041 | .Xr crypto 3 ) | |
bf740959 | 1042 | directly removed from the source code; any licensed or patented components |
1043 | are chosen from | |
1044 | external libraries. | |
1045 | .It | |
1d1ffb87 | 1046 | has been updated to support SSH protocol 1.5 and 2, making it compatible with |
1047 | all other SSH clients and servers. | |
bf740959 | 1048 | .It |
f54651ce | 1049 | contains added support for |
bf740959 | 1050 | .Xr kerberos 8 |
1051 | authentication and ticket passing. | |
1052 | .It | |
1053 | supports one-time password authentication with | |
1054 | .Xr skey 1 . | |
1055 | .El | |
1d1ffb87 | 1056 | .Pp |
1057 | OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl, | |
1058 | Niels Provos, Theo de Raadt, and Dug Song. | |
1059 | .Pp | |
1060 | The support for SSH protocol 2 was written by Markus Friedl. | |
bf740959 | 1061 | .Sh SEE ALSO |
bf740959 | 1062 | .Xr scp 1 , |
b5e300c2 | 1063 | .Xr sftp-server 8 , |
bf740959 | 1064 | .Xr ssh 1 , |
1065 | .Xr ssh-add 1 , | |
1066 | .Xr ssh-agent 1 , | |
1067 | .Xr ssh-keygen 1 , | |
bcbf86ec | 1068 | .Xr crypto 3 , |
7368a6c8 | 1069 | .Xr rlogin 1 , |
1070 | .Xr rsh 1 |