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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. | |
94ec8c6b | 189 | Multiple -d options increases the debugging level. |
190 | Maximum is 3. | |
bf740959 | 191 | .It Fl f Ar configuration_file |
4fe2af09 | 192 | Specifies the name of the configuration file. |
193 | The default is | |
5f4fdfae | 194 | .Pa /etc/sshd_config . |
bf740959 | 195 | .Nm |
196 | refuses to start if there is no configuration file. | |
197 | .It Fl g Ar login_grace_time | |
198 | Gives the grace time for clients to authenticate themselves (default | |
4fe2af09 | 199 | 300 seconds). |
200 | If the client fails to authenticate the user within | |
201 | this many seconds, the server disconnects and exits. | |
202 | A value of zero indicates no limit. | |
bf740959 | 203 | .It Fl h Ar host_key_file |
1d1ffb87 | 204 | Specifies the file from which the RSA host key is read (default |
5f4fdfae | 205 | .Pa /etc/ssh_host_key ) . |
bf740959 | 206 | This option must be given if |
207 | .Nm | |
208 | is not run as root (as the normal | |
209 | host file is normally not readable by anyone but root). | |
210 | .It Fl i | |
211 | Specifies that | |
212 | .Nm | |
f54651ce | 213 | is being run from inetd. |
bf740959 | 214 | .Nm |
215 | is normally not run | |
216 | from inetd because it needs to generate the server key before it can | |
4fe2af09 | 217 | respond to the client, and this may take tens of seconds. |
218 | Clients would have to wait too long if the key was regenerated every time. | |
610cd5c6 | 219 | However, with small key sizes (e.g., 512) using |
bf740959 | 220 | .Nm |
221 | from inetd may | |
222 | be feasible. | |
223 | .It Fl k Ar key_gen_time | |
224 | Specifies how often the server key is regenerated (default 3600 | |
4fe2af09 | 225 | seconds, or one hour). |
226 | The motivation for regenerating the key fairly | |
bf740959 | 227 | often is that the key is not stored anywhere, and after about an hour, |
228 | it becomes impossible to recover the key for decrypting intercepted | |
229 | communications even if the machine is cracked into or physically | |
4fe2af09 | 230 | seized. |
231 | A value of zero indicates that the key will never be regenerated. | |
bf740959 | 232 | .It Fl p Ar port |
233 | Specifies the port on which the server listens for connections | |
234 | (default 22). | |
235 | .It Fl q | |
4fe2af09 | 236 | Quiet mode. |
237 | Nothing is sent to the system log. | |
238 | Normally the beginning, | |
bf740959 | 239 | authentication, and termination of each connection is logged. |
c345cf9d | 240 | .It Fl u Ar len |
241 | This option is used to specify the size of the field | |
242 | in the | |
243 | .Li utmp | |
244 | structure that holds the remote host name. | |
245 | If the resolved host name is longer than | |
246 | .Ar len , | |
247 | the dotted decimal value will be used instead. | |
248 | This allows hosts with very long host names that | |
249 | overflow this field to still be uniquely identified. | |
250 | Specifying | |
251 | .Fl u0 | |
252 | indicates that only dotted decimal addresses | |
253 | should be put into the | |
254 | .Pa utmp | |
255 | file. | |
bf740959 | 256 | .It Fl Q |
257 | Do not print an error message if RSA support is missing. | |
5260325f | 258 | .It Fl V Ar client_protocol_id |
94ec8c6b | 259 | SSH-2 compatibility mode. |
3189621b | 260 | When this option is specified |
5260325f | 261 | .Nm |
3189621b | 262 | assumes the client has sent the supplied version string |
5260325f | 263 | and skips the |
264 | Protocol Version Identification Exchange. | |
94ec8c6b | 265 | This option is not intended to be called directly. |
48e671d5 | 266 | .It Fl 4 |
267 | Forces | |
268 | .Nm | |
269 | to use IPv4 addresses only. | |
270 | .It Fl 6 | |
271 | Forces | |
272 | .Nm | |
273 | to use IPv6 addresses only. | |
bf740959 | 274 | .El |
275 | .Sh CONFIGURATION FILE | |
276 | .Nm | |
f54651ce | 277 | reads configuration data from |
5f4fdfae | 278 | .Pa /etc/sshd_config |
bf740959 | 279 | (or the file specified with |
280 | .Fl f | |
4fe2af09 | 281 | on the command line). |
282 | The file contains keyword-value pairs, one per line. | |
283 | Lines starting with | |
bf740959 | 284 | .Ql # |
285 | and empty lines are interpreted as comments. | |
286 | .Pp | |
287 | The following keywords are possible. | |
288 | .Bl -tag -width Ds | |
289 | .It Cm AFSTokenPassing | |
4fe2af09 | 290 | Specifies whether an AFS token may be forwarded to the server. |
291 | Default is | |
bf740959 | 292 | .Dq yes . |
293 | .It Cm AllowGroups | |
294 | This keyword can be followed by a number of group names, separated | |
4fe2af09 | 295 | by spaces. |
296 | If specified, login is allowed only for users whose primary | |
bf740959 | 297 | group matches one of the patterns. |
298 | .Ql \&* | |
299 | and | |
300 | .Ql ? | |
301 | can be used as | |
4fe2af09 | 302 | wildcards in the patterns. |
c345cf9d | 303 | Only group names are valid; a numerical group ID isn't recognized. |
4fe2af09 | 304 | By default login is allowed regardless of the primary group. |
bf740959 | 305 | .Pp |
306 | .It Cm AllowUsers | |
307 | This keyword can be followed by a number of user names, separated | |
4fe2af09 | 308 | by spaces. |
309 | If specified, login is allowed only for users names that | |
bf740959 | 310 | match one of the patterns. |
311 | .Ql \&* | |
312 | and | |
313 | .Ql ? | |
314 | can be used as | |
4fe2af09 | 315 | wildcards in the patterns. |
c345cf9d | 316 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 317 | By default login is allowed regardless of the user name. |
bf740959 | 318 | .Pp |
f54651ce | 319 | .It Cm Ciphers |
320 | Specifies the ciphers allowed for protocol version 2. | |
321 | Multiple ciphers must be comma-separated. | |
322 | The default is | |
d0c832f3 | 323 | .Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc . |
bf740959 | 324 | .It Cm CheckMail |
325 | Specifies whether | |
326 | .Nm | |
327 | should check for new mail for interactive logins. | |
328 | The default is | |
329 | .Dq no . | |
330 | .It Cm DenyGroups | |
331 | This keyword can be followed by a number of group names, separated | |
4fe2af09 | 332 | by spaces. |
333 | Users whose primary group matches one of the patterns | |
bf740959 | 334 | aren't allowed to log in. |
335 | .Ql \&* | |
336 | and | |
337 | .Ql ? | |
338 | can be used as | |
4fe2af09 | 339 | wildcards in the patterns. |
c345cf9d | 340 | Only group names are valid; a numerical group ID isn't recognized. |
4fe2af09 | 341 | By default login is allowed regardless of the primary group. |
bf740959 | 342 | .Pp |
343 | .It Cm DenyUsers | |
344 | This keyword can be followed by a number of user names, separated | |
4fe2af09 | 345 | by spaces. |
346 | Login is disallowed for user names that match one of the patterns. | |
bf740959 | 347 | .Ql \&* |
348 | and | |
349 | .Ql ? | |
4fe2af09 | 350 | can be used as wildcards in the patterns. |
c345cf9d | 351 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 352 | By default login is allowed regardless of the user name. |
1d1ffb87 | 353 | .It Cm DSAAuthentication |
354 | Specifies whether DSA authentication is allowed. | |
355 | The default is | |
356 | .Dq yes . | |
357 | Note that this option applies to protocol version 2 only. | |
358 | .It Cm GatewayPorts | |
359 | Specifies whether remote hosts are allowed to connect to ports | |
360 | forwarded for the client. | |
361 | The argument must be | |
362 | .Dq yes | |
363 | or | |
364 | .Dq no . | |
365 | The default is | |
366 | .Dq no . | |
c345cf9d | 367 | .It Cm HostDSAKey |
1d1ffb87 | 368 | Specifies the file containing the private DSA host key (default |
369 | .Pa /etc/ssh_host_dsa_key ) | |
370 | used by SSH protocol 2.0. | |
371 | Note that | |
372 | .Nm | |
d0c832f3 | 373 | disables protocol 2.0 if this file is group/world-accessible. |
bf740959 | 374 | .It Cm HostKey |
1d1ffb87 | 375 | Specifies the file containing the private RSA host key (default |
376 | .Pa /etc/ssh_host_key ) | |
377 | used by SSH protocols 1.3 and 1.5. | |
bf740959 | 378 | Note that |
379 | .Nm | |
d0c832f3 | 380 | disables protocols 1.3 and 1.5 if this file is group/world-accessible. |
bf740959 | 381 | .It Cm IgnoreRhosts |
c8d54615 | 382 | Specifies that |
383 | .Pa .rhosts | |
f54651ce | 384 | and |
c8d54615 | 385 | .Pa .shosts |
386 | files will not be used in authentication. | |
bf740959 | 387 | .Pa /etc/hosts.equiv |
388 | and | |
f54651ce | 389 | .Pa /etc/shosts.equiv |
4fe2af09 | 390 | are still used. |
f54651ce | 391 | The default is |
c8d54615 | 392 | .Dq yes . |
b4748e2f | 393 | .It Cm IgnoreUserKnownHosts |
394 | Specifies whether | |
395 | .Nm | |
396 | should ignore the user's | |
397 | .Pa $HOME/.ssh/known_hosts | |
398 | during | |
399 | .Cm RhostsRSAAuthentication . | |
400 | The default is | |
401 | .Dq no . | |
bf740959 | 402 | .It Cm KeepAlive |
403 | Specifies whether the system should send keepalive messages to the | |
4fe2af09 | 404 | other side. |
405 | If they are sent, death of the connection or crash of one | |
406 | of the machines will be properly noticed. | |
407 | However, this means that | |
bf740959 | 408 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 409 | find it annoying. |
d0c832f3 | 410 | On the other hand, if keepalives are not sent, |
bf740959 | 411 | sessions may hang indefinitely on the server, leaving |
412 | .Dq ghost | |
413 | users and consuming server resources. | |
414 | .Pp | |
415 | The default is | |
416 | .Dq yes | |
417 | (to send keepalives), and the server will notice | |
4fe2af09 | 418 | if the network goes down or the client host reboots. |
419 | This avoids infinitely hanging sessions. | |
bf740959 | 420 | .Pp |
421 | To disable keepalives, the value should be set to | |
422 | .Dq no | |
423 | in both the server and the client configuration files. | |
424 | .It Cm KerberosAuthentication | |
4fe2af09 | 425 | Specifies whether Kerberos authentication is allowed. |
426 | This can be in the form of a Kerberos ticket, or if | |
bf740959 | 427 | .Cm PasswordAuthentication |
428 | is yes, the password provided by the user will be validated through | |
94ec8c6b | 429 | the Kerberos KDC. |
430 | To use this option, the server needs a | |
c345cf9d | 431 | Kerberos servtab which allows the verification of the KDC's identity. |
4fe2af09 | 432 | Default is |
bf740959 | 433 | .Dq yes . |
434 | .It Cm KerberosOrLocalPasswd | |
435 | If set then if password authentication through Kerberos fails then | |
436 | the password will be validated via any additional local mechanism | |
437 | such as | |
188adeb2 | 438 | .Pa /etc/passwd . |
4fe2af09 | 439 | Default is |
bf740959 | 440 | .Dq yes . |
441 | .It Cm KerberosTgtPassing | |
442 | Specifies whether a Kerberos TGT may be forwarded to the server. | |
f54651ce | 443 | Default is |
bf740959 | 444 | .Dq no , |
445 | as this only works when the Kerberos KDC is actually an AFS kaserver. | |
446 | .It Cm KerberosTicketCleanup | |
447 | Specifies whether to automatically destroy the user's ticket cache | |
4fe2af09 | 448 | file on logout. |
449 | Default is | |
bf740959 | 450 | .Dq yes . |
451 | .It Cm KeyRegenerationInterval | |
452 | The server key is automatically regenerated after this many seconds | |
4fe2af09 | 453 | (if it has been used). |
454 | The purpose of regeneration is to prevent | |
bf740959 | 455 | decrypting captured sessions by later breaking into the machine and |
4fe2af09 | 456 | stealing the keys. |
457 | The key is never stored anywhere. | |
458 | If the value is 0, the key is never regenerated. | |
459 | The default is 3600 (seconds). | |
bf740959 | 460 | .It Cm ListenAddress |
461 | Specifies what local address | |
462 | .Nm | |
463 | should listen on. | |
464 | The default is to listen to all local addresses. | |
48e671d5 | 465 | Multiple options of this type are permitted. |
466 | Additionally, the | |
467 | .Cm Ports | |
468 | options must precede this option. | |
bf740959 | 469 | .It Cm LoginGraceTime |
470 | The server disconnects after this time if the user has not | |
4fe2af09 | 471 | successfully logged in. |
472 | If the value is 0, there is no time limit. | |
bf740959 | 473 | The default is 600 (seconds). |
6a17f9c2 | 474 | .It Cm LogLevel |
475 | Gives the verbosity level that is used when logging messages from | |
476 | .Nm sshd . | |
477 | The possible values are: | |
5260325f | 478 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
6a17f9c2 | 479 | The default is INFO. |
480 | Logging with level DEBUG violates the privacy of users | |
481 | and is not recommended. | |
089fbbd2 | 482 | .It Cm MaxStartups |
483 | Specifies the maximum number of concurrent unauthenticated connections to the | |
484 | .Nm | |
485 | daemon. | |
486 | Additional connections will be dropped until authentication succeeds or the | |
487 | .Cm LoginGraceTime | |
488 | expires for a connection. | |
489 | The default is 10. | |
c345cf9d | 490 | .Pp |
491 | Alternatively, random early drop can be enabled by specifying | |
492 | the three colon separated values | |
493 | .Dq start:rate:full | |
94ec8c6b | 494 | (e.g., "10:30:60"). |
c345cf9d | 495 | .Nm |
496 | will refuse connection attempts with a probabillity of | |
497 | .Dq rate/100 | |
498 | (30%) | |
499 | if there are currently | |
500 | .Dq start | |
501 | (10) | |
502 | unauthenticated connections. | |
503 | The probabillity increases linearly and all connection attempts | |
504 | are refused if the number of unauthenticated connections reaches | |
505 | .Dq full | |
506 | (60). | |
bf740959 | 507 | .It Cm PasswordAuthentication |
508 | Specifies whether password authentication is allowed. | |
509 | The default is | |
510 | .Dq yes . | |
c345cf9d | 511 | Note that this option applies to both protocol versions 1 and 2. |
bf740959 | 512 | .It Cm PermitEmptyPasswords |
513 | When password authentication is allowed, it specifies whether the | |
4fe2af09 | 514 | server allows login to accounts with empty password strings. |
515 | The default is | |
c8d54615 | 516 | .Dq no . |
bf740959 | 517 | .It Cm PermitRootLogin |
518 | Specifies whether the root can log in using | |
519 | .Xr ssh 1 . | |
520 | The argument must be | |
521 | .Dq yes , | |
522 | .Dq without-password | |
523 | or | |
524 | .Dq no . | |
525 | The default is | |
526 | .Dq yes . | |
527 | If this options is set to | |
528 | .Dq without-password | |
529 | only password authentication is disabled for root. | |
530 | .Pp | |
531 | Root login with RSA authentication when the | |
532 | .Ar command | |
533 | option has been | |
534 | specified will be allowed regardless of the value of this setting | |
535 | (which may be useful for taking remote backups even if root login is | |
536 | normally not allowed). | |
0fbe8c74 | 537 | .It Cm PidFile |
538 | Specifies the file that contains the process identifier of the | |
539 | .Nm | |
540 | daemon. | |
541 | The default is | |
542 | .Pa /var/run/sshd.pid . | |
bf740959 | 543 | .It Cm Port |
544 | Specifies the port number that | |
545 | .Nm | |
4fe2af09 | 546 | listens on. |
547 | The default is 22. | |
48e671d5 | 548 | Multiple options of this type are permitted. |
bf740959 | 549 | .It Cm PrintMotd |
550 | Specifies whether | |
551 | .Nm | |
f54651ce | 552 | should print |
bf740959 | 553 | .Pa /etc/motd |
4fe2af09 | 554 | when a user logs in interactively. |
555 | (On some systems it is also printed by the shell, | |
bf740959 | 556 | .Pa /etc/profile , |
4fe2af09 | 557 | or equivalent.) |
558 | The default is | |
bf740959 | 559 | .Dq yes . |
f54651ce | 560 | .It Cm Protocol |
561 | Specifies the protocol versions | |
562 | .Nm | |
563 | should support. | |
564 | The possible values are | |
565 | .Dq 1 | |
566 | and | |
567 | .Dq 2 . | |
568 | Multiple versions must be comma-separated. | |
569 | The default is | |
570 | .Dq 1 . | |
bf740959 | 571 | .It Cm RandomSeed |
4fe2af09 | 572 | Obsolete. |
573 | Random number generation uses other techniques. | |
bf740959 | 574 | .It Cm RhostsAuthentication |
575 | Specifies whether authentication using rhosts or /etc/hosts.equiv | |
4fe2af09 | 576 | files is sufficient. |
577 | Normally, this method should not be permitted because it is insecure. | |
bf740959 | 578 | .Cm RhostsRSAAuthentication |
579 | should be used | |
580 | instead, because it performs RSA-based host authentication in addition | |
581 | to normal rhosts or /etc/hosts.equiv authentication. | |
582 | The default is | |
583 | .Dq no . | |
584 | .It Cm RhostsRSAAuthentication | |
585 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
4fe2af09 | 586 | with successful RSA host authentication is allowed. |
587 | The default is | |
c8d54615 | 588 | .Dq no . |
bf740959 | 589 | .It Cm RSAAuthentication |
4fe2af09 | 590 | Specifies whether pure RSA authentication is allowed. |
591 | The default is | |
bf740959 | 592 | .Dq yes . |
1d1ffb87 | 593 | Note that this option applies to protocol version 1 only. |
bf740959 | 594 | .It Cm ServerKeyBits |
4fe2af09 | 595 | Defines the number of bits in the server key. |
596 | The minimum value is 512, and the default is 768. | |
bf740959 | 597 | .It Cm SkeyAuthentication |
598 | Specifies whether | |
f54651ce | 599 | .Xr skey 1 |
4fe2af09 | 600 | authentication is allowed. |
601 | The default is | |
bf740959 | 602 | .Dq yes . |
603 | Note that s/key authentication is enabled only if | |
604 | .Cm PasswordAuthentication | |
605 | is allowed, too. | |
606 | .It Cm StrictModes | |
607 | Specifies whether | |
608 | .Nm | |
609 | should check file modes and ownership of the | |
4fe2af09 | 610 | user's files and home directory before accepting login. |
611 | This is normally desirable because novices sometimes accidentally leave their | |
612 | directory or files world-writable. | |
613 | The default is | |
bf740959 | 614 | .Dq yes . |
38c295d6 | 615 | .It Cm Subsystem |
94ec8c6b | 616 | Configures an external subsystem (e.g., file transfer daemon). |
617 | Arguments should be a subsystem name and a command to execute upon subsystem | |
618 | request. | |
b5e300c2 | 619 | The command |
620 | .Xr sftp-server 8 | |
621 | implements the | |
622 | .Dq sftp | |
623 | file transfer subsystem. | |
38c295d6 | 624 | By default no subsystems are defined. |
625 | Note that this option applies to protocol version 2 only. | |
bf740959 | 626 | .It Cm SyslogFacility |
627 | Gives the facility code that is used when logging messages from | |
628 | .Nm sshd . | |
629 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, | |
4fe2af09 | 630 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
631 | The default is AUTH. | |
bf740959 | 632 | .It Cm UseLogin |
633 | Specifies whether | |
634 | .Xr login 1 | |
fa649821 | 635 | is used for interactive login sessions. |
636 | Note that | |
637 | .Xr login 1 | |
c345cf9d | 638 | is never used for remote command execution. |
4fe2af09 | 639 | The default is |
bf740959 | 640 | .Dq no . |
bf740959 | 641 | .It Cm X11DisplayOffset |
642 | Specifies the first display number available for | |
643 | .Nm sshd Ns 's | |
4fe2af09 | 644 | X11 forwarding. |
645 | This prevents | |
bf740959 | 646 | .Nm |
647 | from interfering with real X11 servers. | |
c8d54615 | 648 | The default is 10. |
7b2ea3a1 | 649 | .It Cm X11Forwarding |
4fe2af09 | 650 | Specifies whether X11 forwarding is permitted. |
651 | The default is | |
c8d54615 | 652 | .Dq no . |
7b2ea3a1 | 653 | Note that disabling X11 forwarding does not improve security in any |
654 | way, as users can always install their own forwarders. | |
fa649821 | 655 | .It Cm XAuthLocation |
656 | Specifies the location of the | |
657 | .Xr xauth 1 | |
658 | program. | |
659 | The default is | |
660 | .Pa /usr/X11R6/bin/xauth . | |
bf740959 | 661 | .El |
662 | .Sh LOGIN PROCESS | |
663 | When a user successfully logs in, | |
664 | .Nm | |
665 | does the following: | |
666 | .Bl -enum -offset indent | |
667 | .It | |
668 | If the login is on a tty, and no command has been specified, | |
f54651ce | 669 | prints last login time and |
bf740959 | 670 | .Pa /etc/motd |
671 | (unless prevented in the configuration file or by | |
672 | .Pa $HOME/.hushlogin ; | |
673 | see the | |
f54651ce | 674 | .Sx FILES |
bf740959 | 675 | section). |
676 | .It | |
677 | If the login is on a tty, records login time. | |
678 | .It | |
679 | Checks | |
680 | .Pa /etc/nologin ; | |
681 | if it exists, prints contents and quits | |
682 | (unless root). | |
683 | .It | |
684 | Changes to run with normal user privileges. | |
685 | .It | |
686 | Sets up basic environment. | |
687 | .It | |
688 | Reads | |
689 | .Pa $HOME/.ssh/environment | |
690 | if it exists. | |
691 | .It | |
692 | Changes to user's home directory. | |
693 | .It | |
694 | If | |
695 | .Pa $HOME/.ssh/rc | |
696 | exists, runs it; else if | |
5f4fdfae | 697 | .Pa /etc/sshrc |
bf740959 | 698 | exists, runs |
4fe2af09 | 699 | it; otherwise runs xauth. |
700 | The | |
bf740959 | 701 | .Dq rc |
702 | files are given the X11 | |
703 | authentication protocol and cookie in standard input. | |
704 | .It | |
705 | Runs user's shell or command. | |
706 | .El | |
707 | .Sh AUTHORIZED_KEYS FILE FORMAT | |
f54651ce | 708 | The |
bf740959 | 709 | .Pa $HOME/.ssh/authorized_keys |
710 | file lists the RSA keys that are | |
1d1ffb87 | 711 | permitted for RSA authentication in SSH protocols 1.3 and 1.5 |
d0c832f3 | 712 | Similarly, the |
1d1ffb87 | 713 | .Pa $HOME/.ssh/authorized_keys2 |
714 | file lists the DSA keys that are | |
715 | permitted for DSA authentication in SSH protocol 2.0. | |
4fe2af09 | 716 | Each line of the file contains one |
bf740959 | 717 | key (empty lines and lines starting with a |
718 | .Ql # | |
719 | are ignored as | |
4fe2af09 | 720 | comments). |
721 | Each line consists of the following fields, separated by | |
722 | spaces: options, bits, exponent, modulus, comment. | |
723 | The options field | |
bf740959 | 724 | is optional; its presence is determined by whether the line starts |
725 | with a number or not (the option field never starts with a number). | |
726 | The bits, exponent, modulus and comment fields give the RSA key; the | |
727 | comment field is not used for anything (but may be convenient for the | |
728 | user to identify the key). | |
729 | .Pp | |
730 | Note that lines in this file are usually several hundred bytes long | |
4fe2af09 | 731 | (because of the size of the RSA key modulus). |
732 | You don't want to type them in; instead, copy the | |
bf740959 | 733 | .Pa identity.pub |
734 | file and edit it. | |
735 | .Pp | |
c345cf9d | 736 | The options (if present) consist of comma-separated option |
4fe2af09 | 737 | specifications. |
738 | No spaces are permitted, except within double quotes. | |
bf740959 | 739 | The following option specifications are supported: |
740 | .Bl -tag -width Ds | |
741 | .It Cm from="pattern-list" | |
742 | Specifies that in addition to RSA authentication, the canonical name | |
743 | of the remote host must be present in the comma-separated list of | |
4fe2af09 | 744 | patterns |
745 | .Pf ( Ql * | |
746 | and | |
747 | .Ql ? | |
748 | serve as wildcards). | |
749 | The list may also contain | |
750 | patterns negated by prefixing them with | |
751 | .Ql ! ; | |
752 | if the canonical host name matches a negated pattern, the key is not accepted. | |
753 | The purpose | |
bf740959 | 754 | of this option is to optionally increase security: RSA authentication |
755 | by itself does not trust the network or name servers or anything (but | |
756 | the key); however, if somebody somehow steals the key, the key | |
4fe2af09 | 757 | permits an intruder to log in from anywhere in the world. |
758 | This additional option makes using a stolen key more difficult (name | |
bf740959 | 759 | servers and/or routers would have to be compromised in addition to |
760 | just the key). | |
761 | .It Cm command="command" | |
762 | Specifies that the command is executed whenever this key is used for | |
4fe2af09 | 763 | authentication. |
764 | The command supplied by the user (if any) is ignored. | |
bf740959 | 765 | The command is run on a pty if the connection requests a pty; |
4fe2af09 | 766 | otherwise it is run without a tty. |
767 | A quote may be included in the command by quoting it with a backslash. | |
768 | This option might be useful | |
769 | to restrict certain RSA keys to perform just a specific operation. | |
770 | An example might be a key that permits remote backups but nothing else. | |
d0c832f3 | 771 | Note that the client may specify TCP/IP and/or X11 |
772 | forwarding unless they are explicitly prohibited. | |
bf740959 | 773 | .It Cm environment="NAME=value" |
774 | Specifies that the string is to be added to the environment when | |
4fe2af09 | 775 | logging in using this key. |
776 | Environment variables set this way | |
777 | override other default environment values. | |
778 | Multiple options of this type are permitted. | |
bf740959 | 779 | .It Cm no-port-forwarding |
780 | Forbids TCP/IP forwarding when this key is used for authentication. | |
4fe2af09 | 781 | Any port forward requests by the client will return an error. |
782 | This might be used, e.g., in connection with the | |
bf740959 | 783 | .Cm command |
784 | option. | |
785 | .It Cm no-X11-forwarding | |
786 | Forbids X11 forwarding when this key is used for authentication. | |
787 | Any X11 forward requests by the client will return an error. | |
788 | .It Cm no-agent-forwarding | |
789 | Forbids authentication agent forwarding when this key is used for | |
790 | authentication. | |
791 | .It Cm no-pty | |
792 | Prevents tty allocation (a request to allocate a pty will fail). | |
793 | .El | |
794 | .Ss Examples | |
795 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar | |
796 | .Pp | |
797 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula | |
798 | .Pp | |
799 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi | |
800 | .Sh SSH_KNOWN_HOSTS FILE FORMAT | |
f54651ce | 801 | The |
1d1ffb87 | 802 | .Pa /etc/ssh_known_hosts , |
803 | .Pa /etc/ssh_known_hosts2 , | |
804 | .Pa $HOME/.ssh/known_hosts , | |
f54651ce | 805 | and |
1d1ffb87 | 806 | .Pa $HOME/.ssh/known_hosts2 |
4fe2af09 | 807 | files contain host public keys for all known hosts. |
808 | The global file should | |
809 | be prepared by the administrator (optional), and the per-user file is | |
c345cf9d | 810 | maintained automatically: whenever the user connects from an unknown host |
4fe2af09 | 811 | its key is added to the per-user file. |
bf740959 | 812 | .Pp |
813 | Each line in these files contains the following fields: hostnames, | |
4fe2af09 | 814 | bits, exponent, modulus, comment. |
815 | The fields are separated by spaces. | |
bf740959 | 816 | .Pp |
817 | Hostnames is a comma-separated list of patterns ('*' and '?' act as | |
818 | wildcards); each pattern in turn is matched against the canonical host | |
819 | name (when authenticating a client) or against the user-supplied | |
4fe2af09 | 820 | name (when authenticating a server). |
821 | A pattern may also be preceded by | |
bf740959 | 822 | .Ql ! |
823 | to indicate negation: if the host name matches a negated | |
824 | pattern, it is not accepted (by that line) even if it matched another | |
825 | pattern on the line. | |
826 | .Pp | |
1d1ffb87 | 827 | Bits, exponent, and modulus are taken directly from the RSA host key; they |
bf740959 | 828 | can be obtained, e.g., from |
5f4fdfae | 829 | .Pa /etc/ssh_host_key.pub . |
bf740959 | 830 | The optional comment field continues to the end of the line, and is not used. |
831 | .Pp | |
832 | Lines starting with | |
833 | .Ql # | |
834 | and empty lines are ignored as comments. | |
835 | .Pp | |
836 | When performing host authentication, authentication is accepted if any | |
4fe2af09 | 837 | matching line has the proper key. |
838 | It is thus permissible (but not | |
bf740959 | 839 | recommended) to have several lines or different host keys for the same |
4fe2af09 | 840 | names. |
841 | This will inevitably happen when short forms of host names | |
842 | from different domains are put in the file. | |
843 | It is possible | |
bf740959 | 844 | that the files contain conflicting information; authentication is |
845 | accepted if valid information can be found from either file. | |
846 | .Pp | |
847 | Note that the lines in these files are typically hundreds of characters | |
848 | long, and you definitely don't want to type in the host keys by hand. | |
849 | Rather, generate them by a script | |
f54651ce | 850 | or by taking |
5f4fdfae | 851 | .Pa /etc/ssh_host_key.pub |
bf740959 | 852 | and adding the host names at the front. |
853 | .Ss Examples | |
854 | closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi | |
855 | .Sh FILES | |
856 | .Bl -tag -width Ds | |
5f4fdfae | 857 | .It Pa /etc/sshd_config |
bf740959 | 858 | Contains configuration data for |
859 | .Nm sshd . | |
860 | This file should be writable by root only, but it is recommended | |
861 | (though not necessary) that it be world-readable. | |
5f4fdfae | 862 | .It Pa /etc/ssh_host_key |
bf740959 | 863 | Contains the private part of the host key. |
864 | This file should only be owned by root, readable only by root, and not | |
865 | accessible to others. | |
866 | Note that | |
867 | .Nm | |
868 | does not start if this file is group/world-accessible. | |
5f4fdfae | 869 | .It Pa /etc/ssh_host_key.pub |
bf740959 | 870 | Contains the public part of the host key. |
871 | This file should be world-readable but writable only by | |
4fe2af09 | 872 | root. |
873 | Its contents should match the private part. | |
874 | This file is not | |
bf740959 | 875 | really used for anything; it is only provided for the convenience of |
876 | the user so its contents can be copied to known hosts files. | |
877 | These two files are created using | |
878 | .Xr ssh-keygen 1 . | |
5f4fdfae | 879 | .It Pa /var/run/sshd.pid |
bf740959 | 880 | Contains the process ID of the |
881 | .Nm | |
882 | listening for connections (if there are several daemons running | |
883 | concurrently for different ports, this contains the pid of the one | |
4fe2af09 | 884 | started last). |
c345cf9d | 885 | The content of this file is not sensitive; it can be world-readable. |
bf740959 | 886 | .It Pa $HOME/.ssh/authorized_keys |
887 | Lists the RSA keys that can be used to log into the user's account. | |
888 | This file must be readable by root (which may on some machines imply | |
889 | it being world-readable if the user's home directory resides on an NFS | |
4fe2af09 | 890 | volume). |
891 | It is recommended that it not be accessible by others. | |
892 | The format of this file is described above. | |
1d1ffb87 | 893 | Users will place the contents of their |
894 | .Pa identity.pub | |
895 | files into this file, as described in | |
896 | .Xr ssh-keygen 1 . | |
897 | .It Pa $HOME/.ssh/authorized_keys2 | |
898 | Lists the DSA keys that can be used to log into the user's account. | |
899 | This file must be readable by root (which may on some machines imply | |
900 | it being world-readable if the user's home directory resides on an NFS | |
901 | volume). | |
902 | It is recommended that it not be accessible by others. | |
903 | The format of this file is described above. | |
904 | Users will place the contents of their | |
905 | .Pa id_dsa.pub | |
906 | files into this file, as described in | |
907 | .Xr ssh-keygen 1 . | |
5f4fdfae | 908 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
6a17f9c2 | 909 | These files are consulted when using rhosts with RSA host |
4fe2af09 | 910 | authentication to check the public key of the host. |
911 | The key must be listed in one of these files to be accepted. | |
5bbb5681 | 912 | The client uses the same files |
c345cf9d | 913 | to verify that the remote host is the one it intended to connect. |
4fe2af09 | 914 | These files should be writable only by root/the owner. |
5f4fdfae | 915 | .Pa /etc/ssh_known_hosts |
bf740959 | 916 | should be world-readable, and |
917 | .Pa $HOME/.ssh/known_hosts | |
918 | can but need not be world-readable. | |
919 | .It Pa /etc/nologin | |
f54651ce | 920 | If this file exists, |
bf740959 | 921 | .Nm |
4fe2af09 | 922 | refuses to let anyone except root log in. |
923 | The contents of the file | |
bf740959 | 924 | are displayed to anyone trying to log in, and non-root connections are |
4fe2af09 | 925 | refused. |
926 | The file should be world-readable. | |
bf740959 | 927 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
928 | If compiled with | |
929 | .Sy LIBWRAP | |
930 | support, tcp-wrappers access controls may be defined here as described in | |
931 | .Xr hosts_access 5 . | |
932 | .It Pa $HOME/.rhosts | |
933 | This file contains host-username pairs, separated by a space, one per | |
4fe2af09 | 934 | line. |
935 | The given user on the corresponding host is permitted to log in | |
936 | without password. | |
937 | The same file is used by rlogind and rshd. | |
bf740959 | 938 | The file must |
939 | be writable only by the user; it is recommended that it not be | |
940 | accessible by others. | |
941 | .Pp | |
4fe2af09 | 942 | If is also possible to use netgroups in the file. |
943 | Either host or user | |
bf740959 | 944 | name may be of the form +@groupname to specify all hosts or all users |
945 | in the group. | |
946 | .It Pa $HOME/.shosts | |
947 | For ssh, | |
948 | this file is exactly the same as for | |
949 | .Pa .rhosts . | |
950 | However, this file is | |
951 | not used by rlogin and rshd, so using this permits access using SSH only. | |
c345cf9d | 952 | .It Pa /etc/hosts.equiv |
bf740959 | 953 | This file is used during |
954 | .Pa .rhosts | |
4fe2af09 | 955 | authentication. |
956 | In the simplest form, this file contains host names, one per line. | |
957 | Users on | |
bf740959 | 958 | those hosts are permitted to log in without a password, provided they |
4fe2af09 | 959 | have the same user name on both machines. |
960 | The host name may also be | |
bf740959 | 961 | followed by a user name; such users are permitted to log in as |
962 | .Em any | |
4fe2af09 | 963 | user on this machine (except root). |
964 | Additionally, the syntax | |
bf740959 | 965 | .Dq +@group |
4fe2af09 | 966 | can be used to specify netgroups. |
967 | Negated entries start with | |
bf740959 | 968 | .Ql \&- . |
969 | .Pp | |
970 | If the client host/user is successfully matched in this file, login is | |
971 | automatically permitted provided the client and server user names are the | |
4fe2af09 | 972 | same. |
973 | Additionally, successful RSA host authentication is normally required. | |
974 | This file must be writable only by root; it is recommended | |
bf740959 | 975 | that it be world-readable. |
976 | .Pp | |
977 | .Sy "Warning: It is almost never a good idea to use user names in" | |
978 | .Pa hosts.equiv . | |
979 | Beware that it really means that the named user(s) can log in as | |
980 | .Em anybody , | |
981 | which includes bin, daemon, adm, and other accounts that own critical | |
4fe2af09 | 982 | binaries and directories. |
983 | Using a user name practically grants the user root access. | |
984 | The only valid use for user names that I can think | |
bf740959 | 985 | of is in negative entries. |
986 | .Pp | |
987 | Note that this warning also applies to rsh/rlogin. | |
5f4fdfae | 988 | .It Pa /etc/shosts.equiv |
bf740959 | 989 | This is processed exactly as |
990 | .Pa /etc/hosts.equiv . | |
991 | However, this file may be useful in environments that want to run both | |
992 | rsh/rlogin and ssh. | |
993 | .It Pa $HOME/.ssh/environment | |
4fe2af09 | 994 | This file is read into the environment at login (if it exists). |
995 | It can only contain empty lines, comment lines (that start with | |
bf740959 | 996 | .Ql # ) , |
4fe2af09 | 997 | and assignment lines of the form name=value. |
998 | The file should be writable | |
bf740959 | 999 | only by the user; it need not be readable by anyone else. |
1000 | .It Pa $HOME/.ssh/rc | |
1001 | If this file exists, it is run with /bin/sh after reading the | |
4fe2af09 | 1002 | environment files but before starting the user's shell or command. |
1003 | If X11 spoofing is in use, this will receive the "proto cookie" pair in | |
bf740959 | 1004 | standard input (and |
1005 | .Ev DISPLAY | |
4fe2af09 | 1006 | in environment). |
1007 | This must call | |
bf740959 | 1008 | .Xr xauth 1 |
1009 | in that case. | |
1010 | .Pp | |
1011 | The primary purpose of this file is to run any initialization routines | |
1012 | which may be needed before the user's home directory becomes | |
1013 | accessible; AFS is a particular example of such an environment. | |
1014 | .Pp | |
1015 | This file will probably contain some initialization code followed by | |
1016 | something similar to: "if read proto cookie; then echo add $DISPLAY | |
1017 | $proto $cookie | xauth -q -; fi". | |
1018 | .Pp | |
1019 | If this file does not exist, | |
5f4fdfae | 1020 | .Pa /etc/sshrc |
bf740959 | 1021 | is run, and if that |
1022 | does not exist either, xauth is used to store the cookie. | |
1023 | .Pp | |
1024 | This file should be writable only by the user, and need not be | |
1025 | readable by anyone else. | |
5f4fdfae | 1026 | .It Pa /etc/sshrc |
bf740959 | 1027 | Like |
1028 | .Pa $HOME/.ssh/rc . | |
1029 | This can be used to specify | |
4fe2af09 | 1030 | machine-specific login-time initializations globally. |
1031 | This file should be writable only by root, and should be world-readable. | |
089fbbd2 | 1032 | .El |
bf740959 | 1033 | .Sh AUTHOR |
bf740959 | 1034 | OpenSSH |
c8d54615 | 1035 | is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen, |
4fe2af09 | 1036 | but with bugs removed and newer features re-added. |
1037 | Rapidly after the | |
c8d54615 | 1038 | 1.2.12 release, newer versions of the original ssh bore successively |
1039 | more restrictive licenses, and thus demand for a free version was born. | |
1d1ffb87 | 1040 | .Pp |
c8d54615 | 1041 | This version of OpenSSH |
bf740959 | 1042 | .Bl -bullet |
1043 | .It | |
bcbf86ec | 1044 | has all components of a restrictive nature (i.e., patents, see |
1045 | .Xr crypto 3 ) | |
bf740959 | 1046 | directly removed from the source code; any licensed or patented components |
1047 | are chosen from | |
1048 | external libraries. | |
1049 | .It | |
1d1ffb87 | 1050 | has been updated to support SSH protocol 1.5 and 2, making it compatible with |
1051 | all other SSH clients and servers. | |
bf740959 | 1052 | .It |
f54651ce | 1053 | contains added support for |
bf740959 | 1054 | .Xr kerberos 8 |
1055 | authentication and ticket passing. | |
1056 | .It | |
1057 | supports one-time password authentication with | |
1058 | .Xr skey 1 . | |
1059 | .El | |
1d1ffb87 | 1060 | .Pp |
1061 | OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl, | |
1062 | Niels Provos, Theo de Raadt, and Dug Song. | |
1063 | .Pp | |
1064 | The support for SSH protocol 2 was written by Markus Friedl. | |
bf740959 | 1065 | .Sh SEE ALSO |
bf740959 | 1066 | .Xr scp 1 , |
b5e300c2 | 1067 | .Xr sftp-server 8 , |
bf740959 | 1068 | .Xr ssh 1 , |
1069 | .Xr ssh-add 1 , | |
1070 | .Xr ssh-agent 1 , | |
1071 | .Xr ssh-keygen 1 , | |
bcbf86ec | 1072 | .Xr crypto 3 , |
7368a6c8 | 1073 | .Xr rlogin 1 , |
1074 | .Xr rsh 1 |