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588df31a | 1 | .\" -*- nroff -*- |
2 | .\" | |
3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> | |
4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland | |
5 | .\" All rights reserved | |
6 | .\" | |
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. | |
25 | .\" | |
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. | |
36 | .\" | |
94ad46d1 | 37 | .\" $OpenBSD: sshd_config.5,v 1.5 2002/07/09 17:46:25 stevesk Exp $ |
588df31a | 38 | .Dd September 25, 1999 |
39 | .Dt SSHD_CONFIG 5 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm sshd_config | |
43 | .Nd OpenSSH SSH daemon configuration file | |
44 | .Sh SYNOPSIS | |
45 | .Bl -tag -width Ds -compact | |
46 | .It Pa /etc/ssh/sshd_config | |
47 | .El | |
48 | .Sh DESCRIPTION | |
49 | .Nm sshd | |
50 | reads configuration data from | |
51 | .Pa /etc/ssh/sshd_config | |
52 | (or the file specified with | |
53 | .Fl f | |
54 | on the command line). | |
55 | The file contains keyword-argument pairs, one per line. | |
56 | Lines starting with | |
57 | .Ql # | |
58 | and empty lines are interpreted as comments. | |
59 | .Pp | |
60 | The possible | |
61 | keywords and their meanings are as follows (note that | |
62 | keywords are case-insensitive and arguments are case-sensitive): | |
63 | .Bl -tag -width Ds | |
64 | .It Cm AFSTokenPassing | |
65 | Specifies whether an AFS token may be forwarded to the server. | |
66 | Default is | |
67 | .Dq no . | |
68 | .It Cm AllowGroups | |
69 | This keyword can be followed by a list of group name patterns, separated | |
70 | by spaces. | |
71 | If specified, login is allowed only for users whose primary | |
72 | group or supplementary group list matches one of the patterns. | |
73 | .Ql \&* | |
74 | and | |
75 | .Ql ? | |
76 | can be used as | |
77 | wildcards in the patterns. | |
78 | Only group names are valid; a numerical group ID is not recognized. | |
79 | By default, login is allowed for all groups. | |
80 | .Pp | |
81 | .It Cm AllowTcpForwarding | |
82 | Specifies whether TCP forwarding is permitted. | |
83 | The default is | |
84 | .Dq yes . | |
85 | Note that disabling TCP forwarding does not improve security unless | |
86 | users are also denied shell access, as they can always install their | |
87 | own forwarders. | |
88 | .Pp | |
89 | .It Cm AllowUsers | |
90 | This keyword can be followed by a list of user name patterns, separated | |
91 | by spaces. | |
92 | If specified, login is allowed only for users names that | |
93 | match one of the patterns. | |
94 | .Ql \&* | |
95 | and | |
96 | .Ql ? | |
97 | can be used as | |
98 | wildcards in the patterns. | |
99 | Only user names are valid; a numerical user ID is not recognized. | |
100 | By default, login is allowed for all users. | |
101 | If the pattern takes the form USER@HOST then USER and HOST | |
102 | are separately checked, restricting logins to particular | |
103 | users from particular hosts. | |
104 | .Pp | |
105 | .It Cm AuthorizedKeysFile | |
106 | Specifies the file that contains the public keys that can be used | |
107 | for user authentication. | |
108 | .Cm AuthorizedKeysFile | |
109 | may contain tokens of the form %T which are substituted during connection | |
110 | set-up. The following tokens are defined: %% is replaced by a literal '%', | |
111 | %h is replaced by the home directory of the user being authenticated and | |
112 | %u is replaced by the username of that user. | |
113 | After expansion, | |
114 | .Cm AuthorizedKeysFile | |
115 | is taken to be an absolute path or one relative to the user's home | |
116 | directory. | |
117 | The default is | |
118 | .Dq .ssh/authorized_keys . | |
119 | .It Cm Banner | |
120 | In some jurisdictions, sending a warning message before authentication | |
121 | may be relevant for getting legal protection. | |
122 | The contents of the specified file are sent to the remote user before | |
123 | authentication is allowed. | |
124 | This option is only available for protocol version 2. | |
125 | By default, no banner is displayed. | |
126 | .Pp | |
127 | .It Cm ChallengeResponseAuthentication | |
128 | Specifies whether challenge response authentication is allowed. | |
129 | All authentication styles from | |
130 | .Xr login.conf 5 | |
131 | are supported. | |
132 | The default is | |
133 | .Dq yes . | |
134 | .It Cm Ciphers | |
135 | Specifies the ciphers allowed for protocol version 2. | |
136 | Multiple ciphers must be comma-separated. | |
137 | The default is | |
138 | .Pp | |
139 | .Bd -literal | |
140 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour, | |
141 | aes192-cbc,aes256-cbc'' | |
142 | .Ed | |
143 | .It Cm ClientAliveInterval | |
144 | Sets a timeout interval in seconds after which if no data has been received | |
145 | from the client, | |
146 | .Nm sshd | |
147 | will send a message through the encrypted | |
148 | channel to request a response from the client. | |
149 | The default | |
150 | is 0, indicating that these messages will not be sent to the client. | |
151 | This option applies to protocol version 2 only. | |
152 | .It Cm ClientAliveCountMax | |
153 | Sets the number of client alive messages (see above) which may be | |
154 | sent without | |
155 | .Nm sshd | |
156 | receiving any messages back from the client. If this threshold is | |
157 | reached while client alive messages are being sent, | |
158 | .Nm sshd | |
159 | will disconnect the client, terminating the session. It is important | |
160 | to note that the use of client alive messages is very different from | |
161 | .Cm KeepAlive | |
162 | (below). The client alive messages are sent through the | |
163 | encrypted channel and therefore will not be spoofable. The TCP keepalive | |
164 | option enabled by | |
165 | .Cm KeepAlive | |
166 | is spoofable. The client alive mechanism is valuable when the client or | |
167 | server depend on knowing when a connection has become inactive. | |
168 | .Pp | |
169 | The default value is 3. If | |
170 | .Cm ClientAliveInterval | |
171 | (above) is set to 15, and | |
172 | .Cm ClientAliveCountMax | |
173 | is left at the default, unresponsive ssh clients | |
174 | will be disconnected after approximately 45 seconds. | |
175 | .It Cm Compression | |
176 | Specifies whether compression is allowed. | |
177 | The argument must be | |
178 | .Dq yes | |
179 | or | |
180 | .Dq no . | |
181 | The default is | |
182 | .Dq yes . | |
183 | .It Cm DenyGroups | |
184 | This keyword can be followed by a list of group name patterns, separated | |
185 | by spaces. | |
186 | Login is disallowed for users whose primary group or supplementary | |
187 | group list matches one of the patterns. | |
188 | .Ql \&* | |
189 | and | |
190 | .Ql ? | |
191 | can be used as | |
192 | wildcards in the patterns. | |
193 | Only group names are valid; a numerical group ID is not recognized. | |
194 | By default, login is allowed for all groups. | |
195 | .Pp | |
196 | .It Cm DenyUsers | |
197 | This keyword can be followed by a list of user name patterns, separated | |
198 | by spaces. | |
199 | Login is disallowed for user names that match one of the patterns. | |
200 | .Ql \&* | |
201 | and | |
202 | .Ql ? | |
203 | can be used as wildcards in the patterns. | |
204 | Only user names are valid; a numerical user ID is not recognized. | |
205 | By default, login is allowed for all users. | |
206 | If the pattern takes the form USER@HOST then USER and HOST | |
207 | are separately checked, restricting logins to particular | |
208 | users from particular hosts. | |
209 | .It Cm GatewayPorts | |
210 | Specifies whether remote hosts are allowed to connect to ports | |
211 | forwarded for the client. | |
212 | By default, | |
213 | .Nm sshd | |
214 | binds remote port forwardings to the loopback address. This | |
215 | prevents other remote hosts from connecting to forwarded ports. | |
216 | .Cm GatewayPorts | |
217 | can be used to specify that | |
218 | .Nm sshd | |
219 | should bind remote port forwardings to the wildcard address, | |
220 | thus allowing remote hosts to connect to forwarded ports. | |
221 | The argument must be | |
222 | .Dq yes | |
223 | or | |
224 | .Dq no . | |
225 | The default is | |
226 | .Dq no . | |
227 | .It Cm HostbasedAuthentication | |
228 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
229 | with successful public key client host authentication is allowed | |
230 | (hostbased authentication). | |
231 | This option is similar to | |
232 | .Cm RhostsRSAAuthentication | |
233 | and applies to protocol version 2 only. | |
234 | The default is | |
235 | .Dq no . | |
236 | .It Cm HostKey | |
237 | Specifies a file containing a private host key | |
238 | used by SSH. | |
239 | The default is | |
240 | .Pa /etc/ssh/ssh_host_key | |
241 | for protocol version 1, and | |
242 | .Pa /etc/ssh/ssh_host_rsa_key | |
243 | and | |
244 | .Pa /etc/ssh/ssh_host_dsa_key | |
245 | for protocol version 2. | |
246 | Note that | |
247 | .Nm sshd | |
248 | will refuse to use a file if it is group/world-accessible. | |
249 | It is possible to have multiple host key files. | |
250 | .Dq rsa1 | |
251 | keys are used for version 1 and | |
252 | .Dq dsa | |
253 | or | |
254 | .Dq rsa | |
255 | are used for version 2 of the SSH protocol. | |
256 | .It Cm IgnoreRhosts | |
257 | Specifies that | |
258 | .Pa .rhosts | |
259 | and | |
260 | .Pa .shosts | |
261 | files will not be used in | |
262 | .Cm RhostsAuthentication , | |
263 | .Cm RhostsRSAAuthentication | |
264 | or | |
265 | .Cm HostbasedAuthentication . | |
266 | .Pp | |
267 | .Pa /etc/hosts.equiv | |
268 | and | |
269 | .Pa /etc/shosts.equiv | |
270 | are still used. | |
271 | The default is | |
272 | .Dq yes . | |
273 | .It Cm IgnoreUserKnownHosts | |
274 | Specifies whether | |
275 | .Nm sshd | |
276 | should ignore the user's | |
277 | .Pa $HOME/.ssh/known_hosts | |
278 | during | |
279 | .Cm RhostsRSAAuthentication | |
280 | or | |
281 | .Cm HostbasedAuthentication . | |
282 | The default is | |
283 | .Dq no . | |
284 | .It Cm KeepAlive | |
285 | Specifies whether the system should send TCP keepalive messages to the | |
286 | other side. | |
287 | If they are sent, death of the connection or crash of one | |
288 | of the machines will be properly noticed. | |
289 | However, this means that | |
290 | connections will die if the route is down temporarily, and some people | |
291 | find it annoying. | |
292 | On the other hand, if keepalives are not sent, | |
293 | sessions may hang indefinitely on the server, leaving | |
294 | .Dq ghost | |
295 | users and consuming server resources. | |
296 | .Pp | |
297 | The default is | |
298 | .Dq yes | |
299 | (to send keepalives), and the server will notice | |
300 | if the network goes down or the client host crashes. | |
301 | This avoids infinitely hanging sessions. | |
302 | .Pp | |
303 | To disable keepalives, the value should be set to | |
304 | .Dq no . | |
305 | .It Cm KerberosAuthentication | |
306 | Specifies whether Kerberos authentication is allowed. | |
307 | This can be in the form of a Kerberos ticket, or if | |
588df31a | 308 | .Cm PasswordAuthentication |
309 | is yes, the password provided by the user will be validated through | |
310 | the Kerberos KDC. | |
311 | To use this option, the server needs a | |
312 | Kerberos servtab which allows the verification of the KDC's identity. | |
313 | Default is | |
314 | .Dq no . | |
315 | .It Cm KerberosOrLocalPasswd | |
316 | If set then if password authentication through Kerberos fails then | |
317 | the password will be validated via any additional local mechanism | |
318 | such as | |
319 | .Pa /etc/passwd . | |
320 | Default is | |
321 | .Dq yes . | |
322 | .It Cm KerberosTgtPassing | |
323 | Specifies whether a Kerberos TGT may be forwarded to the server. | |
324 | Default is | |
325 | .Dq no , | |
326 | as this only works when the Kerberos KDC is actually an AFS kaserver. | |
327 | .It Cm KerberosTicketCleanup | |
328 | Specifies whether to automatically destroy the user's ticket cache | |
329 | file on logout. | |
330 | Default is | |
331 | .Dq yes . | |
332 | .It Cm KeyRegenerationInterval | |
333 | In protocol version 1, the ephemeral server key is automatically regenerated | |
334 | after this many seconds (if it has been used). | |
335 | The purpose of regeneration is to prevent | |
336 | decrypting captured sessions by later breaking into the machine and | |
337 | stealing the keys. | |
338 | The key is never stored anywhere. | |
339 | If the value is 0, the key is never regenerated. | |
340 | The default is 3600 (seconds). | |
341 | .It Cm ListenAddress | |
342 | Specifies the local addresses | |
343 | .Nm sshd | |
344 | should listen on. | |
345 | The following forms may be used: | |
346 | .Pp | |
347 | .Bl -item -offset indent -compact | |
348 | .It | |
349 | .Cm ListenAddress | |
350 | .Sm off | |
351 | .Ar host No | Ar IPv4_addr No | Ar IPv6_addr | |
352 | .Sm on | |
353 | .It | |
354 | .Cm ListenAddress | |
355 | .Sm off | |
356 | .Ar host No | Ar IPv4_addr No : Ar port | |
357 | .Sm on | |
358 | .It | |
359 | .Cm ListenAddress | |
360 | .Sm off | |
361 | .Oo | |
362 | .Ar host No | Ar IPv6_addr Oc : Ar port | |
363 | .Sm on | |
364 | .El | |
365 | .Pp | |
366 | If | |
367 | .Ar port | |
368 | is not specified, | |
369 | .Nm sshd | |
370 | will listen on the address and all prior | |
371 | .Cm Port | |
372 | options specified. The default is to listen on all local | |
373 | addresses. Multiple | |
374 | .Cm ListenAddress | |
375 | options are permitted. Additionally, any | |
376 | .Cm Port | |
377 | options must precede this option for non port qualified addresses. | |
378 | .It Cm LoginGraceTime | |
379 | The server disconnects after this time if the user has not | |
380 | successfully logged in. | |
381 | If the value is 0, there is no time limit. | |
382 | The default is 600 (seconds). | |
383 | .It Cm LogLevel | |
384 | Gives the verbosity level that is used when logging messages from | |
385 | .Nm sshd . | |
386 | The possible values are: | |
387 | QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3. | |
388 | The default is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2 | |
389 | and DEBUG3 each specify higher levels of debugging output. | |
390 | Logging with a DEBUG level violates the privacy of users | |
391 | and is not recommended. | |
392 | .It Cm MACs | |
393 | Specifies the available MAC (message authentication code) algorithms. | |
394 | The MAC algorithm is used in protocol version 2 | |
395 | for data integrity protection. | |
396 | Multiple algorithms must be comma-separated. | |
397 | The default is | |
398 | .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 . | |
399 | .It Cm MaxStartups | |
400 | Specifies the maximum number of concurrent unauthenticated connections to the | |
401 | .Nm sshd | |
402 | daemon. | |
403 | Additional connections will be dropped until authentication succeeds or the | |
404 | .Cm LoginGraceTime | |
405 | expires for a connection. | |
406 | The default is 10. | |
407 | .Pp | |
408 | Alternatively, random early drop can be enabled by specifying | |
409 | the three colon separated values | |
410 | .Dq start:rate:full | |
411 | (e.g., "10:30:60"). | |
412 | .Nm sshd | |
413 | will refuse connection attempts with a probability of | |
414 | .Dq rate/100 | |
415 | (30%) | |
416 | if there are currently | |
417 | .Dq start | |
418 | (10) | |
419 | unauthenticated connections. | |
420 | The probability increases linearly and all connection attempts | |
421 | are refused if the number of unauthenticated connections reaches | |
422 | .Dq full | |
423 | (60). | |
c4186be7 | 424 | .It Cm PAMAuthenticationViaKbdInt |
425 | Specifies whether PAM challenge response authentication is allowed. This | |
426 | allows the use of most PAM challenge response authentication modules, but | |
427 | it will allow password authentication regardless of whether | |
428 | .Cm PasswordAuthentication | |
429 | is enabled. | |
588df31a | 430 | .It Cm PasswordAuthentication |
431 | Specifies whether password authentication is allowed. | |
432 | The default is | |
433 | .Dq yes . | |
434 | .It Cm PermitEmptyPasswords | |
435 | When password authentication is allowed, it specifies whether the | |
436 | server allows login to accounts with empty password strings. | |
437 | The default is | |
438 | .Dq no . | |
439 | .It Cm PermitRootLogin | |
440 | Specifies whether root can login using | |
441 | .Xr ssh 1 . | |
442 | The argument must be | |
443 | .Dq yes , | |
444 | .Dq without-password , | |
445 | .Dq forced-commands-only | |
446 | or | |
447 | .Dq no . | |
448 | The default is | |
449 | .Dq yes . | |
450 | .Pp | |
451 | If this option is set to | |
452 | .Dq without-password | |
453 | password authentication is disabled for root. | |
454 | .Pp | |
455 | If this option is set to | |
456 | .Dq forced-commands-only | |
457 | root login with public key authentication will be allowed, | |
458 | but only if the | |
459 | .Ar command | |
460 | option has been specified | |
461 | (which may be useful for taking remote backups even if root login is | |
462 | normally not allowed). All other authentication methods are disabled | |
463 | for root. | |
464 | .Pp | |
465 | If this option is set to | |
466 | .Dq no | |
467 | root is not allowed to login. | |
468 | .It Cm PidFile | |
baa08b92 | 469 | Specifies the file that contains the process ID of the |
588df31a | 470 | .Nm sshd |
471 | daemon. | |
472 | The default is | |
473 | .Pa /var/run/sshd.pid . | |
474 | .It Cm Port | |
475 | Specifies the port number that | |
476 | .Nm sshd | |
477 | listens on. | |
478 | The default is 22. | |
479 | Multiple options of this type are permitted. | |
480 | See also | |
481 | .Cm ListenAddress . | |
482 | .It Cm PrintLastLog | |
483 | Specifies whether | |
484 | .Nm sshd | |
485 | should print the date and time when the user last logged in. | |
486 | The default is | |
487 | .Dq yes . | |
488 | .It Cm PrintMotd | |
489 | Specifies whether | |
490 | .Nm sshd | |
491 | should print | |
492 | .Pa /etc/motd | |
493 | when a user logs in interactively. | |
494 | (On some systems it is also printed by the shell, | |
495 | .Pa /etc/profile , | |
496 | or equivalent.) | |
497 | The default is | |
498 | .Dq yes . | |
499 | .It Cm Protocol | |
500 | Specifies the protocol versions | |
501 | .Nm sshd | |
94ad46d1 | 502 | supports. |
588df31a | 503 | The possible values are |
504 | .Dq 1 | |
505 | and | |
506 | .Dq 2 . | |
507 | Multiple versions must be comma-separated. | |
508 | The default is | |
509 | .Dq 2,1 . | |
94ad46d1 | 510 | Note that the order of the protocol list does not indicate preference, |
511 | because the client selects among multiple protocol versions offered | |
512 | by the server. | |
513 | Specifying | |
514 | .Dq 2,1 | |
515 | is identical to | |
516 | .Dq 1,2 . | |
588df31a | 517 | .It Cm PubkeyAuthentication |
518 | Specifies whether public key authentication is allowed. | |
519 | The default is | |
520 | .Dq yes . | |
521 | Note that this option applies to protocol version 2 only. | |
522 | .It Cm RhostsAuthentication | |
523 | Specifies whether authentication using rhosts or /etc/hosts.equiv | |
524 | files is sufficient. | |
525 | Normally, this method should not be permitted because it is insecure. | |
526 | .Cm RhostsRSAAuthentication | |
527 | should be used | |
528 | instead, because it performs RSA-based host authentication in addition | |
529 | to normal rhosts or /etc/hosts.equiv authentication. | |
530 | The default is | |
531 | .Dq no . | |
532 | This option applies to protocol version 1 only. | |
533 | .It Cm RhostsRSAAuthentication | |
534 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
535 | with successful RSA host authentication is allowed. | |
536 | The default is | |
537 | .Dq no . | |
538 | This option applies to protocol version 1 only. | |
539 | .It Cm RSAAuthentication | |
540 | Specifies whether pure RSA authentication is allowed. | |
541 | The default is | |
542 | .Dq yes . | |
543 | This option applies to protocol version 1 only. | |
544 | .It Cm ServerKeyBits | |
545 | Defines the number of bits in the ephemeral protocol version 1 server key. | |
546 | The minimum value is 512, and the default is 768. | |
547 | .It Cm StrictModes | |
548 | Specifies whether | |
549 | .Nm sshd | |
550 | should check file modes and ownership of the | |
551 | user's files and home directory before accepting login. | |
552 | This is normally desirable because novices sometimes accidentally leave their | |
553 | directory or files world-writable. | |
554 | The default is | |
555 | .Dq yes . | |
556 | .It Cm Subsystem | |
557 | Configures an external subsystem (e.g., file transfer daemon). | |
558 | Arguments should be a subsystem name and a command to execute upon subsystem | |
559 | request. | |
560 | The command | |
561 | .Xr sftp-server 8 | |
562 | implements the | |
563 | .Dq sftp | |
564 | file transfer subsystem. | |
565 | By default no subsystems are defined. | |
566 | Note that this option applies to protocol version 2 only. | |
567 | .It Cm SyslogFacility | |
568 | Gives the facility code that is used when logging messages from | |
569 | .Nm sshd . | |
570 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, | |
571 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. | |
572 | The default is AUTH. | |
573 | .It Cm UseLogin | |
574 | Specifies whether | |
575 | .Xr login 1 | |
576 | is used for interactive login sessions. | |
577 | The default is | |
578 | .Dq no . | |
579 | Note that | |
580 | .Xr login 1 | |
581 | is never used for remote command execution. | |
582 | Note also, that if this is enabled, | |
583 | .Cm X11Forwarding | |
584 | will be disabled because | |
585 | .Xr login 1 | |
586 | does not know how to handle | |
587 | .Xr xauth 1 | |
588 | cookies. If | |
589 | .Cm UsePrivilegeSeparation | |
590 | is specified, it will be disabled after authentication. | |
591 | .It Cm UsePrivilegeSeparation | |
592 | Specifies whether | |
593 | .Nm sshd | |
594 | separates privileges by creating an unprivileged child process | |
595 | to deal with incoming network traffic. After successful authentication, | |
596 | another process will be created that has the privilege of the authenticated | |
597 | user. The goal of privilege separation is to prevent privilege | |
598 | escalation by containing any corruption within the unprivileged processes. | |
599 | The default is | |
600 | .Dq yes . | |
601 | .It Cm VerifyReverseMapping | |
602 | Specifies whether | |
603 | .Nm sshd | |
604 | should try to verify the remote host name and check that | |
605 | the resolved host name for the remote IP address maps back to the | |
606 | very same IP address. | |
607 | The default is | |
608 | .Dq no . | |
609 | .It Cm X11DisplayOffset | |
610 | Specifies the first display number available for | |
611 | .Nm sshd Ns 's | |
612 | X11 forwarding. | |
613 | This prevents | |
614 | .Nm sshd | |
615 | from interfering with real X11 servers. | |
616 | The default is 10. | |
617 | .It Cm X11Forwarding | |
618 | Specifies whether X11 forwarding is permitted. | |
619 | The default is | |
620 | .Dq no . | |
621 | Note that disabling X11 forwarding does not improve security in any | |
622 | way, as users can always install their own forwarders. | |
623 | X11 forwarding is automatically disabled if | |
624 | .Cm UseLogin | |
625 | is enabled. | |
626 | .It Cm X11UseLocalhost | |
627 | Specifies whether | |
628 | .Nm sshd | |
629 | should bind the X11 forwarding server to the loopback address or to | |
630 | the wildcard address. By default, | |
631 | .Nm sshd | |
632 | binds the forwarding server to the loopback address and sets the | |
633 | hostname part of the | |
634 | .Ev DISPLAY | |
635 | environment variable to | |
636 | .Dq localhost . | |
637 | This prevents remote hosts from connecting to the fake display. | |
638 | However, some older X11 clients may not function with this | |
639 | configuration. | |
640 | .Cm X11UseLocalhost | |
641 | may be set to | |
642 | .Dq no | |
643 | to specify that the forwarding server should be bound to the wildcard | |
644 | address. | |
645 | The argument must be | |
646 | .Dq yes | |
647 | or | |
648 | .Dq no . | |
649 | The default is | |
650 | .Dq yes . | |
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 . | |
657 | .El | |
658 | .Ss Time Formats | |
659 | .Pp | |
660 | .Nm sshd | |
661 | command-line arguments and configuration file options that specify time | |
662 | may be expressed using a sequence of the form: | |
663 | .Sm off | |
664 | .Ar time Oo Ar qualifier Oc , | |
665 | .Sm on | |
666 | where | |
667 | .Ar time | |
668 | is a positive integer value and | |
669 | .Ar qualifier | |
670 | is one of the following: | |
671 | .Pp | |
672 | .Bl -tag -width Ds -compact -offset indent | |
673 | .It Cm <none> | |
674 | seconds | |
675 | .It Cm s | Cm S | |
676 | seconds | |
677 | .It Cm m | Cm M | |
678 | minutes | |
679 | .It Cm h | Cm H | |
680 | hours | |
681 | .It Cm d | Cm D | |
682 | days | |
683 | .It Cm w | Cm W | |
684 | weeks | |
685 | .El | |
686 | .Pp | |
687 | Each member of the sequence is added together to calculate | |
688 | the total time value. | |
689 | .Pp | |
690 | Time format examples: | |
691 | .Pp | |
692 | .Bl -tag -width Ds -compact -offset indent | |
693 | .It 600 | |
694 | 600 seconds (10 minutes) | |
695 | .It 10m | |
696 | 10 minutes | |
697 | .It 1h30m | |
698 | 1 hour 30 minutes (90 minutes) | |
699 | .El | |
700 | .Sh FILES | |
701 | .Bl -tag -width Ds | |
702 | .It Pa /etc/ssh/sshd_config | |
703 | Contains configuration data for | |
704 | .Nm sshd . | |
705 | This file should be writable by root only, but it is recommended | |
706 | (though not necessary) that it be world-readable. | |
707 | .El | |
708 | .Sh AUTHORS | |
709 | OpenSSH is a derivative of the original and free | |
710 | ssh 1.2.12 release by Tatu Ylonen. | |
711 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
712 | Theo de Raadt and Dug Song | |
713 | removed many bugs, re-added newer features and | |
714 | created OpenSSH. | |
715 | Markus Friedl contributed the support for SSH | |
716 | protocol versions 1.5 and 2.0. | |
717 | Niels Provos and Markus Friedl contributed support | |
718 | for privilege separation. | |
719 | .Sh SEE ALSO | |
720 | .Xr sshd 8 |