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884dc78b | 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 | .\" | |
b5afdff5 | 37 | .\" $OpenBSD: sshd_config.5,v 1.106 2009/04/21 15:13:17 stevesk Exp $ |
38 | .Dd $Mdocdate: April 21 2009 $ | |
884dc78b | 39 | .Dt SSHD_CONFIG 5 |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm sshd_config | |
43 | .Nd OpenSSH SSH daemon configuration file | |
44 | .Sh SYNOPSIS | |
0b90ac93 | 45 | .Nm /etc/ssh/sshd_config |
884dc78b | 46 | .Sh DESCRIPTION |
30460aeb | 47 | .Xr sshd 8 |
884dc78b | 48 | reads configuration data from |
49 | .Pa /etc/ssh/sshd_config | |
50 | (or the file specified with | |
51 | .Fl f | |
52 | on the command line). | |
53 | The file contains keyword-argument pairs, one per line. | |
54 | Lines starting with | |
55 | .Ql # | |
56 | and empty lines are interpreted as comments. | |
30460aeb | 57 | Arguments may optionally be enclosed in double quotes |
58 | .Pq \&" | |
59 | in order to represent arguments containing spaces. | |
884dc78b | 60 | .Pp |
61 | The possible | |
62 | keywords and their meanings are as follows (note that | |
63 | keywords are case-insensitive and arguments are case-sensitive): | |
64 | .Bl -tag -width Ds | |
7e82606e | 65 | .It Cm AcceptEnv |
66 | Specifies what environment variables sent by the client will be copied into | |
67 | the session's | |
68 | .Xr environ 7 . | |
69 | See | |
70 | .Cm SendEnv | |
71 | in | |
72 | .Xr ssh_config 5 | |
73 | for how to configure the client. | |
74 | Note that environment passing is only supported for protocol 2. | |
75 | Variables are specified by name, which may contain the wildcard characters | |
30460aeb | 76 | .Ql * |
7e82606e | 77 | and |
78 | .Ql \&? . | |
79 | Multiple environment variables may be separated by whitespace or spread | |
80 | across multiple | |
81 | .Cm AcceptEnv | |
82 | directives. | |
83 | Be warned that some environment variables could be used to bypass restricted | |
84 | user environments. | |
85 | For this reason, care should be taken in the use of this directive. | |
86 | The default is not to accept any environment variables. | |
dfddba3d | 87 | .It Cm AddressFamily |
88 | Specifies which address family should be used by | |
30460aeb | 89 | .Xr sshd 8 . |
dfddba3d | 90 | Valid arguments are |
91 | .Dq any , | |
92 | .Dq inet | |
30460aeb | 93 | (use IPv4 only), or |
dfddba3d | 94 | .Dq inet6 |
95 | (use IPv6 only). | |
96 | The default is | |
97 | .Dq any . | |
5156b1a1 | 98 | .It Cm AllowAgentForwarding |
99 | Specifies whether | |
100 | .Xr ssh-agent 1 | |
101 | forwarding is permitted. | |
102 | The default is | |
103 | .Dq yes . | |
104 | Note that disabling agent forwarding does not improve security | |
105 | unless users are also denied shell access, as they can always install | |
106 | their own forwarders. | |
884dc78b | 107 | .It Cm AllowGroups |
108 | This keyword can be followed by a list of group name patterns, separated | |
109 | by spaces. | |
110 | If specified, login is allowed only for users whose primary | |
111 | group or supplementary group list matches one of the patterns. | |
884dc78b | 112 | Only group names are valid; a numerical group ID is not recognized. |
113 | By default, login is allowed for all groups. | |
30460aeb | 114 | The allow/deny directives are processed in the following order: |
115 | .Cm DenyUsers , | |
116 | .Cm AllowUsers , | |
117 | .Cm DenyGroups , | |
118 | and finally | |
119 | .Cm AllowGroups . | |
120 | .Pp | |
121 | See | |
122 | .Sx PATTERNS | |
123 | in | |
124 | .Xr ssh_config 5 | |
125 | for more information on patterns. | |
884dc78b | 126 | .It Cm AllowTcpForwarding |
127 | Specifies whether TCP forwarding is permitted. | |
128 | The default is | |
129 | .Dq yes . | |
130 | Note that disabling TCP forwarding does not improve security unless | |
131 | users are also denied shell access, as they can always install their | |
132 | own forwarders. | |
884dc78b | 133 | .It Cm AllowUsers |
134 | This keyword can be followed by a list of user name patterns, separated | |
135 | by spaces. | |
bfe49944 | 136 | If specified, login is allowed only for user names that |
884dc78b | 137 | match one of the patterns. |
884dc78b | 138 | Only user names are valid; a numerical user ID is not recognized. |
139 | By default, login is allowed for all users. | |
140 | If the pattern takes the form USER@HOST then USER and HOST | |
141 | are separately checked, restricting logins to particular | |
142 | users from particular hosts. | |
30460aeb | 143 | The allow/deny directives are processed in the following order: |
144 | .Cm DenyUsers , | |
145 | .Cm AllowUsers , | |
146 | .Cm DenyGroups , | |
147 | and finally | |
148 | .Cm AllowGroups . | |
149 | .Pp | |
150 | See | |
151 | .Sx PATTERNS | |
152 | in | |
153 | .Xr ssh_config 5 | |
154 | for more information on patterns. | |
884dc78b | 155 | .It Cm AuthorizedKeysFile |
156 | Specifies the file that contains the public keys that can be used | |
157 | for user authentication. | |
158 | .Cm AuthorizedKeysFile | |
159 | may contain tokens of the form %T which are substituted during connection | |
30460aeb | 160 | setup. |
7cac2b65 | 161 | The following tokens are defined: %% is replaced by a literal '%', |
30460aeb | 162 | %h is replaced by the home directory of the user being authenticated, and |
884dc78b | 163 | %u is replaced by the username of that user. |
164 | After expansion, | |
165 | .Cm AuthorizedKeysFile | |
166 | is taken to be an absolute path or one relative to the user's home | |
167 | directory. | |
168 | The default is | |
169 | .Dq .ssh/authorized_keys . | |
170 | .It Cm Banner | |
884dc78b | 171 | The contents of the specified file are sent to the remote user before |
172 | authentication is allowed. | |
e74dc197 | 173 | If the argument is |
174 | .Dq none | |
175 | then no banner is displayed. | |
884dc78b | 176 | This option is only available for protocol version 2. |
177 | By default, no banner is displayed. | |
884dc78b | 178 | .It Cm ChallengeResponseAuthentication |
b5afdff5 | 179 | Specifies whether challenge-response authentication is allowed (e.g. via |
180 | PAM or though authentication styles supported in | |
181 | .Xr login.conf 5 ) | |
884dc78b | 182 | The default is |
183 | .Dq yes . | |
e74dc197 | 184 | .It Cm ChrootDirectory |
185 | Specifies a path to | |
186 | .Xr chroot 2 | |
187 | to after authentication. | |
188 | This path, and all its components, must be root-owned directories that are | |
189 | not writable by any other user or group. | |
b5afdff5 | 190 | After the chroot, |
191 | .Xr sshd 8 | |
192 | changes the working directory to the user's home directory. | |
e74dc197 | 193 | .Pp |
194 | The path may contain the following tokens that are expanded at runtime once | |
195 | the connecting user has been authenticated: %% is replaced by a literal '%', | |
196 | %h is replaced by the home directory of the user being authenticated, and | |
197 | %u is replaced by the username of that user. | |
198 | .Pp | |
199 | The | |
200 | .Cm ChrootDirectory | |
201 | must contain the necessary files and directories to support the | |
b5afdff5 | 202 | user's session. |
e74dc197 | 203 | For an interactive session this requires at least a shell, typically |
204 | .Xr sh 1 , | |
205 | and basic | |
206 | .Pa /dev | |
207 | nodes such as | |
208 | .Xr null 4 , | |
209 | .Xr zero 4 , | |
210 | .Xr stdin 4 , | |
211 | .Xr stdout 4 , | |
212 | .Xr stderr 4 , | |
213 | .Xr arandom 4 | |
214 | and | |
215 | .Xr tty 4 | |
216 | devices. | |
217 | For file transfer sessions using | |
218 | .Dq sftp , | |
219 | no additional configuration of the environment is necessary if the | |
b5afdff5 | 220 | in-process sftp server is used, |
221 | though sessions which use logging do require | |
222 | .Pa /dev/log | |
223 | inside the chroot directory (see | |
224 | .Xr sftp-server 8 | |
e74dc197 | 225 | for details). |
226 | .Pp | |
227 | The default is not to | |
228 | .Xr chroot 2 . | |
884dc78b | 229 | .It Cm Ciphers |
230 | Specifies the ciphers allowed for protocol version 2. | |
231 | Multiple ciphers must be comma-separated. | |
7e82606e | 232 | The supported ciphers are |
233 | .Dq 3des-cbc , | |
234 | .Dq aes128-cbc , | |
235 | .Dq aes192-cbc , | |
236 | .Dq aes256-cbc , | |
237 | .Dq aes128-ctr , | |
238 | .Dq aes192-ctr , | |
239 | .Dq aes256-ctr , | |
2ce0bfe4 | 240 | .Dq arcfour128 , |
241 | .Dq arcfour256 , | |
7e82606e | 242 | .Dq arcfour , |
243 | .Dq blowfish-cbc , | |
244 | and | |
245 | .Dq cast128-cbc . | |
30460aeb | 246 | The default is: |
247 | .Bd -literal -offset 3n | |
5262cbfb | 248 | aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128, |
249 | aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc, | |
250 | aes256-cbc,arcfour | |
884dc78b | 251 | .Ed |
884dc78b | 252 | .It Cm ClientAliveCountMax |
08822d99 | 253 | Sets the number of client alive messages (see below) which may be |
884dc78b | 254 | sent without |
30460aeb | 255 | .Xr sshd 8 |
7cac2b65 | 256 | receiving any messages back from the client. |
257 | If this threshold is reached while client alive messages are being sent, | |
30460aeb | 258 | sshd will disconnect the client, terminating the session. |
7cac2b65 | 259 | It is important to note that the use of client alive messages is very |
260 | different from | |
540d72c3 | 261 | .Cm TCPKeepAlive |
7cac2b65 | 262 | (below). |
263 | The client alive messages are sent through the encrypted channel | |
264 | and therefore will not be spoofable. | |
265 | The TCP keepalive option enabled by | |
540d72c3 | 266 | .Cm TCPKeepAlive |
7cac2b65 | 267 | is spoofable. |
268 | The client alive mechanism is valuable when the client or | |
884dc78b | 269 | server depend on knowing when a connection has become inactive. |
270 | .Pp | |
7cac2b65 | 271 | The default value is 3. |
272 | If | |
884dc78b | 273 | .Cm ClientAliveInterval |
08822d99 | 274 | (see below) is set to 15, and |
884dc78b | 275 | .Cm ClientAliveCountMax |
30460aeb | 276 | is left at the default, unresponsive SSH clients |
884dc78b | 277 | will be disconnected after approximately 45 seconds. |
30460aeb | 278 | This option applies to protocol version 2 only. |
2ce0bfe4 | 279 | .It Cm ClientAliveInterval |
280 | Sets a timeout interval in seconds after which if no data has been received | |
281 | from the client, | |
30460aeb | 282 | .Xr sshd 8 |
2ce0bfe4 | 283 | will send a message through the encrypted |
284 | channel to request a response from the client. | |
285 | The default | |
286 | is 0, indicating that these messages will not be sent to the client. | |
287 | This option applies to protocol version 2 only. | |
884dc78b | 288 | .It Cm Compression |
2ce0bfe4 | 289 | Specifies whether compression is allowed, or delayed until |
290 | the user has authenticated successfully. | |
884dc78b | 291 | The argument must be |
2ce0bfe4 | 292 | .Dq yes , |
293 | .Dq delayed , | |
884dc78b | 294 | or |
295 | .Dq no . | |
296 | The default is | |
2ce0bfe4 | 297 | .Dq delayed . |
884dc78b | 298 | .It Cm DenyGroups |
299 | This keyword can be followed by a list of group name patterns, separated | |
300 | by spaces. | |
301 | Login is disallowed for users whose primary group or supplementary | |
302 | group list matches one of the patterns. | |
884dc78b | 303 | Only group names are valid; a numerical group ID is not recognized. |
304 | By default, login is allowed for all groups. | |
30460aeb | 305 | The allow/deny directives are processed in the following order: |
306 | .Cm DenyUsers , | |
307 | .Cm AllowUsers , | |
308 | .Cm DenyGroups , | |
309 | and finally | |
310 | .Cm AllowGroups . | |
311 | .Pp | |
312 | See | |
313 | .Sx PATTERNS | |
314 | in | |
315 | .Xr ssh_config 5 | |
316 | for more information on patterns. | |
884dc78b | 317 | .It Cm DenyUsers |
318 | This keyword can be followed by a list of user name patterns, separated | |
319 | by spaces. | |
320 | Login is disallowed for user names that match one of the patterns. | |
884dc78b | 321 | Only user names are valid; a numerical user ID is not recognized. |
322 | By default, login is allowed for all users. | |
323 | If the pattern takes the form USER@HOST then USER and HOST | |
324 | are separately checked, restricting logins to particular | |
325 | users from particular hosts. | |
30460aeb | 326 | The allow/deny directives are processed in the following order: |
327 | .Cm DenyUsers , | |
328 | .Cm AllowUsers , | |
329 | .Cm DenyGroups , | |
330 | and finally | |
331 | .Cm AllowGroups . | |
332 | .Pp | |
333 | See | |
334 | .Sx PATTERNS | |
335 | in | |
336 | .Xr ssh_config 5 | |
337 | for more information on patterns. | |
99a78107 | 338 | .It Cm DisableUsageStats |
339 | This keyword can be followed by one of the keywords "true", "enabled", "yes", | |
340 | "on" or "1" to disable reporting of usage metrics. Or it can be set to "false", | |
341 | "disabled", "no", "off", "0" to enable reporting of usage metrics, which is the | |
342 | default. Setting the | |
343 | .Cm GLOBUS_USAGE_OPTOUT | |
344 | environment variable to "1" will also disable the reporting of usage metrics. | |
345 | Disabling reporting of usage metrics will cause the | |
346 | .Cm UsageStatsTargets | |
347 | setting to be ignored. | |
30460aeb | 348 | .It Cm ForceCommand |
349 | Forces the execution of the command specified by | |
350 | .Cm ForceCommand , | |
e74dc197 | 351 | ignoring any command supplied by the client and |
352 | .Pa ~/.ssh/rc | |
353 | if present. | |
30460aeb | 354 | The command is invoked by using the user's login shell with the -c option. |
355 | This applies to shell, command, or subsystem execution. | |
356 | It is most useful inside a | |
357 | .Cm Match | |
358 | block. | |
359 | The command originally supplied by the client is available in the | |
360 | .Ev SSH_ORIGINAL_COMMAND | |
361 | environment variable. | |
e74dc197 | 362 | Specifying a command of |
363 | .Dq internal-sftp | |
364 | will force the use of an in-process sftp server that requires no support | |
365 | files when used with | |
366 | .Cm ChrootDirectory . | |
884dc78b | 367 | .It Cm GatewayPorts |
368 | Specifies whether remote hosts are allowed to connect to ports | |
369 | forwarded for the client. | |
370 | By default, | |
30460aeb | 371 | .Xr sshd 8 |
bfe49944 | 372 | binds remote port forwardings to the loopback address. |
373 | This prevents other remote hosts from connecting to forwarded ports. | |
884dc78b | 374 | .Cm GatewayPorts |
30460aeb | 375 | can be used to specify that sshd |
dfddba3d | 376 | should allow remote port forwardings to bind to non-loopback addresses, thus |
377 | allowing other hosts to connect. | |
378 | The argument may be | |
379 | .Dq no | |
380 | to force remote port forwardings to be available to the local host only, | |
884dc78b | 381 | .Dq yes |
dfddba3d | 382 | to force remote port forwardings to bind to the wildcard address, or |
383 | .Dq clientspecified | |
384 | to allow the client to select the address to which the forwarding is bound. | |
884dc78b | 385 | The default is |
386 | .Dq no . | |
7cac2b65 | 387 | .It Cm GSSAPIAuthentication |
388 | Specifies whether user authentication based on GSSAPI is allowed. | |
540d72c3 | 389 | The default is |
c5448518 | 390 | .Dq yes . |
7cac2b65 | 391 | Note that this option applies to protocol version 2 only. |
05ed7e1e | 392 | .It Cm GSSAPIDelegateCredentials |
393 | Specifies whether delegated credentials are stored in the user's environment. | |
394 | The default is | |
395 | .Dq yes . | |
c5448518 | 396 | .It Cm GSSAPIKeyExchange |
fe4ad273 | 397 | Specifies whether key exchange based on GSSAPI is allowed. GSSAPI key exchange |
398 | doesn't rely on ssh keys to verify host identity. | |
44a053a3 | 399 | The default is |
400 | .Dq yes . | |
c5448518 | 401 | Note that this option applies to protocol version 2 only. |
fe4ad273 | 402 | .It Cm GSSAPICleanupCredentials |
403 | Specifies whether to automatically destroy the user's credentials cache | |
404 | on logout. | |
44a053a3 | 405 | The default is |
406 | .Dq yes . | |
c5448518 | 407 | Note that this option applies to protocol version 2 only. |
c7931c9a | 408 | .It Cm GSSAPICredentialsPath |
409 | If specified, the delegated GSSAPI credential is stored in the | |
410 | given path, overwriting any existing credentials. | |
411 | Paths can be specified with syntax similar to the AuthorizedKeysFile | |
412 | option (i.e., accepting %h and %u tokens). | |
413 | When using this option, | |
414 | setting 'GssapiCleanupCredentials no' is recommended, | |
415 | so logging out of one session | |
416 | doesn't remove the credentials in use by another session of | |
417 | the same user. | |
418 | Currently only implemented for the GSI mechanism. | |
419 | .It Cm GSIAllowLimitedProxy | |
420 | Specifies whether to accept limited proxy credentials for | |
421 | authentication. | |
422 | The default is | |
423 | .Dq no . | |
f713db99 | 424 | .It Cm GSSAPIStrictAcceptorCheck |
425 | Determines whether to be strict about the identity of the GSSAPI acceptor | |
426 | a client authenticates against. If | |
427 | .Dq yes | |
428 | then the client must authenticate against the | |
429 | .Pa host | |
430 | service on the current hostname. If | |
431 | .Dq no | |
432 | then the client may authenticate against any service key stored in the | |
433 | machine's default store. This facility is provided to assist with operation | |
434 | on multi homed machines. | |
435 | The default is | |
436 | .Dq yes . | |
437 | Note that this option applies only to protocol version 2 GSSAPI connections, | |
438 | and setting it to | |
439 | .Dq no | |
440 | may only work with recent Kerberos GSSAPI libraries. | |
f97edba6 | 441 | .It Cm GSSAPIStoreCredentialsOnRekey |
442 | Controls whether the user's GSSAPI credentials should be updated following a | |
443 | successful connection rekeying. This option can be used to accepted renewed | |
444 | or updated credentials from a compatible client. The default is | |
826a9049 | 445 | .Dq no . |
c5448518 | 446 | .It Cm HostbasedAuthentication |
447 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
448 | with successful public key client host authentication is allowed | |
30460aeb | 449 | (host-based authentication). |
c5448518 | 450 | This option is similar to |
451 | .Cm RhostsRSAAuthentication | |
452 | and applies to protocol version 2 only. | |
52b36949 | 453 | The default is |
c5448518 | 454 | .Dq no . |
30460aeb | 455 | .It Cm HostbasedUsesNameFromPacketOnly |
456 | Specifies whether or not the server will attempt to perform a reverse | |
457 | name lookup when matching the name in the | |
458 | .Pa ~/.shosts , | |
459 | .Pa ~/.rhosts , | |
460 | and | |
461 | .Pa /etc/hosts.equiv | |
462 | files during | |
463 | .Cm HostbasedAuthentication . | |
464 | A setting of | |
465 | .Dq yes | |
466 | means that | |
467 | .Xr sshd 8 | |
468 | uses the name supplied by the client rather than | |
469 | attempting to resolve the name from the TCP connection itself. | |
470 | The default is | |
471 | .Dq no . | |
884dc78b | 472 | .It Cm HostKey |
473 | Specifies a file containing a private host key | |
474 | used by SSH. | |
475 | The default is | |
476 | .Pa /etc/ssh/ssh_host_key | |
477 | for protocol version 1, and | |
478 | .Pa /etc/ssh/ssh_host_rsa_key | |
479 | and | |
480 | .Pa /etc/ssh/ssh_host_dsa_key | |
481 | for protocol version 2. | |
482 | Note that | |
30460aeb | 483 | .Xr sshd 8 |
884dc78b | 484 | will refuse to use a file if it is group/world-accessible. |
485 | It is possible to have multiple host key files. | |
486 | .Dq rsa1 | |
487 | keys are used for version 1 and | |
488 | .Dq dsa | |
489 | or | |
490 | .Dq rsa | |
491 | are used for version 2 of the SSH protocol. | |
492 | .It Cm IgnoreRhosts | |
493 | Specifies that | |
494 | .Pa .rhosts | |
495 | and | |
496 | .Pa .shosts | |
497 | files will not be used in | |
884dc78b | 498 | .Cm RhostsRSAAuthentication |
499 | or | |
500 | .Cm HostbasedAuthentication . | |
501 | .Pp | |
502 | .Pa /etc/hosts.equiv | |
503 | and | |
504 | .Pa /etc/shosts.equiv | |
505 | are still used. | |
506 | The default is | |
507 | .Dq yes . | |
508 | .It Cm IgnoreUserKnownHosts | |
509 | Specifies whether | |
30460aeb | 510 | .Xr sshd 8 |
884dc78b | 511 | should ignore the user's |
2ce0bfe4 | 512 | .Pa ~/.ssh/known_hosts |
884dc78b | 513 | during |
514 | .Cm RhostsRSAAuthentication | |
515 | or | |
516 | .Cm HostbasedAuthentication . | |
517 | The default is | |
518 | .Dq no . | |
884dc78b | 519 | .It Cm KerberosAuthentication |
7cac2b65 | 520 | Specifies whether the password provided by the user for |
884dc78b | 521 | .Cm PasswordAuthentication |
7cac2b65 | 522 | will be validated through the Kerberos KDC. |
884dc78b | 523 | To use this option, the server needs a |
524 | Kerberos servtab which allows the verification of the KDC's identity. | |
30460aeb | 525 | The default is |
884dc78b | 526 | .Dq no . |
12a403af | 527 | .It Cm KerberosGetAFSToken |
08822d99 | 528 | If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire |
12a403af | 529 | an AFS token before accessing the user's home directory. |
30460aeb | 530 | The default is |
12a403af | 531 | .Dq no . |
884dc78b | 532 | .It Cm KerberosOrLocalPasswd |
30460aeb | 533 | If password authentication through Kerberos fails then |
884dc78b | 534 | the password will be validated via any additional local mechanism |
535 | such as | |
536 | .Pa /etc/passwd . | |
30460aeb | 537 | The default is |
884dc78b | 538 | .Dq yes . |
884dc78b | 539 | .It Cm KerberosTicketCleanup |
540 | Specifies whether to automatically destroy the user's ticket cache | |
541 | file on logout. | |
30460aeb | 542 | The default is |
884dc78b | 543 | .Dq yes . |
544 | .It Cm KeyRegenerationInterval | |
545 | In protocol version 1, the ephemeral server key is automatically regenerated | |
546 | after this many seconds (if it has been used). | |
547 | The purpose of regeneration is to prevent | |
548 | decrypting captured sessions by later breaking into the machine and | |
549 | stealing the keys. | |
550 | The key is never stored anywhere. | |
551 | If the value is 0, the key is never regenerated. | |
552 | The default is 3600 (seconds). | |
553 | .It Cm ListenAddress | |
554 | Specifies the local addresses | |
30460aeb | 555 | .Xr sshd 8 |
884dc78b | 556 | should listen on. |
557 | The following forms may be used: | |
558 | .Pp | |
559 | .Bl -item -offset indent -compact | |
560 | .It | |
561 | .Cm ListenAddress | |
562 | .Sm off | |
563 | .Ar host No | Ar IPv4_addr No | Ar IPv6_addr | |
564 | .Sm on | |
565 | .It | |
566 | .Cm ListenAddress | |
567 | .Sm off | |
568 | .Ar host No | Ar IPv4_addr No : Ar port | |
569 | .Sm on | |
570 | .It | |
571 | .Cm ListenAddress | |
572 | .Sm off | |
573 | .Oo | |
574 | .Ar host No | Ar IPv6_addr Oc : Ar port | |
575 | .Sm on | |
576 | .El | |
577 | .Pp | |
578 | If | |
579 | .Ar port | |
580 | is not specified, | |
30460aeb | 581 | sshd will listen on the address and all prior |
884dc78b | 582 | .Cm Port |
7cac2b65 | 583 | options specified. |
584 | The default is to listen on all local addresses. | |
bfe49944 | 585 | Multiple |
884dc78b | 586 | .Cm ListenAddress |
7cac2b65 | 587 | options are permitted. |
588 | Additionally, any | |
884dc78b | 589 | .Cm Port |
30460aeb | 590 | options must precede this option for non-port qualified addresses. |
884dc78b | 591 | .It Cm LoginGraceTime |
592 | The server disconnects after this time if the user has not | |
593 | successfully logged in. | |
594 | If the value is 0, there is no time limit. | |
d03f4262 | 595 | The default is 120 seconds. |
884dc78b | 596 | .It Cm LogLevel |
597 | Gives the verbosity level that is used when logging messages from | |
30460aeb | 598 | .Xr sshd 8 . |
884dc78b | 599 | The possible values are: |
30460aeb | 600 | QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. |
bfe49944 | 601 | The default is INFO. |
602 | DEBUG and DEBUG1 are equivalent. | |
603 | DEBUG2 and DEBUG3 each specify higher levels of debugging output. | |
604 | Logging with a DEBUG level violates the privacy of users and is not recommended. | |
884dc78b | 605 | .It Cm MACs |
606 | Specifies the available MAC (message authentication code) algorithms. | |
607 | The MAC algorithm is used in protocol version 2 | |
608 | for data integrity protection. | |
609 | Multiple algorithms must be comma-separated. | |
30460aeb | 610 | The default is: |
fa0f0f45 | 611 | .Bd -literal -offset indent |
612 | hmac-md5,hmac-sha1,umac-64@openssh.com, | |
613 | hmac-ripemd160,hmac-sha1-96,hmac-md5-96 | |
614 | .Ed | |
30460aeb | 615 | .It Cm Match |
616 | Introduces a conditional block. | |
617 | If all of the criteria on the | |
618 | .Cm Match | |
619 | line are satisfied, the keywords on the following lines override those | |
620 | set in the global section of the config file, until either another | |
621 | .Cm Match | |
622 | line or the end of the file. | |
5156b1a1 | 623 | .Pp |
30460aeb | 624 | The arguments to |
625 | .Cm Match | |
626 | are one or more criteria-pattern pairs. | |
627 | The available criteria are | |
628 | .Cm User , | |
629 | .Cm Group , | |
630 | .Cm Host , | |
631 | and | |
632 | .Cm Address . | |
5156b1a1 | 633 | The match patterns may consist of single entries or comma-separated |
634 | lists and may use the wildcard and negation operators described in the | |
635 | .Sx PATTERNS | |
636 | section of | |
637 | .Xr ssh_config 5 . | |
638 | .Pp | |
639 | The patterns in an | |
640 | .Cm Address | |
641 | criteria may additionally contain addresses to match in CIDR | |
642 | address/masklen format, e.g.\& | |
643 | .Dq 192.0.2.0/24 | |
644 | or | |
645 | .Dq 3ffe:ffff::/32 . | |
646 | Note that the mask length provided must be consistent with the address - | |
647 | it is an error to specify a mask length that is too long for the address | |
648 | or one with bits set in this host portion of the address. | |
649 | For example, | |
650 | .Dq 192.0.2.0/33 | |
651 | and | |
652 | .Dq 192.0.2.0/8 | |
653 | respectively. | |
654 | .Pp | |
30460aeb | 655 | Only a subset of keywords may be used on the lines following a |
656 | .Cm Match | |
657 | keyword. | |
658 | Available keywords are | |
5262cbfb | 659 | .Cm AllowAgentForwarding , |
30460aeb | 660 | .Cm AllowTcpForwarding , |
0b90ac93 | 661 | .Cm Banner , |
5156b1a1 | 662 | .Cm ChrootDirectory , |
30460aeb | 663 | .Cm ForceCommand , |
664 | .Cm GatewayPorts , | |
5156b1a1 | 665 | .Cm GSSAPIAuthentication , |
666 | .Cm HostbasedAuthentication , | |
0b90ac93 | 667 | .Cm KbdInteractiveAuthentication , |
668 | .Cm KerberosAuthentication , | |
5156b1a1 | 669 | .Cm MaxAuthTries , |
670 | .Cm MaxSessions , | |
0b90ac93 | 671 | .Cm PasswordAuthentication , |
5262cbfb | 672 | .Cm PermitEmptyPasswords , |
30460aeb | 673 | .Cm PermitOpen , |
e74dc197 | 674 | .Cm PermitRootLogin , |
0b90ac93 | 675 | .Cm RhostsRSAAuthentication , |
676 | .Cm RSAAuthentication , | |
30460aeb | 677 | .Cm X11DisplayOffset , |
5262cbfb | 678 | .Cm X11Forwarding |
30460aeb | 679 | and |
680 | .Cm X11UseLocalHost . | |
7e82606e | 681 | .It Cm MaxAuthTries |
682 | Specifies the maximum number of authentication attempts permitted per | |
683 | connection. | |
684 | Once the number of failures reaches half this value, | |
685 | additional failures are logged. | |
686 | The default is 6. | |
5156b1a1 | 687 | .It Cm MaxSessions |
688 | Specifies the maximum number of open sessions permitted per network connection. | |
689 | The default is 10. | |
884dc78b | 690 | .It Cm MaxStartups |
691 | Specifies the maximum number of concurrent unauthenticated connections to the | |
30460aeb | 692 | SSH daemon. |
884dc78b | 693 | Additional connections will be dropped until authentication succeeds or the |
694 | .Cm LoginGraceTime | |
695 | expires for a connection. | |
696 | The default is 10. | |
697 | .Pp | |
698 | Alternatively, random early drop can be enabled by specifying | |
699 | the three colon separated values | |
700 | .Dq start:rate:full | |
30460aeb | 701 | (e.g. "10:30:60"). |
702 | .Xr sshd 8 | |
884dc78b | 703 | will refuse connection attempts with a probability of |
704 | .Dq rate/100 | |
705 | (30%) | |
706 | if there are currently | |
707 | .Dq start | |
708 | (10) | |
709 | unauthenticated connections. | |
710 | The probability increases linearly and all connection attempts | |
711 | are refused if the number of unauthenticated connections reaches | |
712 | .Dq full | |
713 | (60). | |
714 | .It Cm PasswordAuthentication | |
715 | Specifies whether password authentication is allowed. | |
716 | The default is | |
717 | .Dq yes . | |
718 | .It Cm PermitEmptyPasswords | |
719 | When password authentication is allowed, it specifies whether the | |
720 | server allows login to accounts with empty password strings. | |
721 | The default is | |
722 | .Dq no . | |
30460aeb | 723 | .It Cm PermitOpen |
724 | Specifies the destinations to which TCP port forwarding is permitted. | |
725 | The forwarding specification must be one of the following forms: | |
726 | .Pp | |
727 | .Bl -item -offset indent -compact | |
728 | .It | |
729 | .Cm PermitOpen | |
730 | .Sm off | |
731 | .Ar host : port | |
732 | .Sm on | |
733 | .It | |
734 | .Cm PermitOpen | |
735 | .Sm off | |
736 | .Ar IPv4_addr : port | |
737 | .Sm on | |
738 | .It | |
739 | .Cm PermitOpen | |
740 | .Sm off | |
741 | .Ar \&[ IPv6_addr \&] : port | |
742 | .Sm on | |
743 | .El | |
744 | .Pp | |
745 | Multiple forwards may be specified by separating them with whitespace. | |
746 | An argument of | |
747 | .Dq any | |
748 | can be used to remove all restrictions and permit any forwarding requests. | |
749 | By default all port forwarding requests are permitted. | |
884dc78b | 750 | .It Cm PermitRootLogin |
dfddba3d | 751 | Specifies whether root can log in using |
884dc78b | 752 | .Xr ssh 1 . |
753 | The argument must be | |
754 | .Dq yes , | |
755 | .Dq without-password , | |
30460aeb | 756 | .Dq forced-commands-only , |
884dc78b | 757 | or |
758 | .Dq no . | |
759 | The default is | |
760 | .Dq yes . | |
761 | .Pp | |
762 | If this option is set to | |
30460aeb | 763 | .Dq without-password , |
dfddba3d | 764 | password authentication is disabled for root. |
884dc78b | 765 | .Pp |
766 | If this option is set to | |
30460aeb | 767 | .Dq forced-commands-only , |
884dc78b | 768 | root login with public key authentication will be allowed, |
769 | but only if the | |
770 | .Ar command | |
771 | option has been specified | |
772 | (which may be useful for taking remote backups even if root login is | |
7cac2b65 | 773 | normally not allowed). |
774 | All other authentication methods are disabled for root. | |
884dc78b | 775 | .Pp |
776 | If this option is set to | |
30460aeb | 777 | .Dq no , |
dfddba3d | 778 | root is not allowed to log in. |
08822d99 | 779 | .It Cm PermitTunnel |
780 | Specifies whether | |
781 | .Xr tun 4 | |
782 | device forwarding is allowed. | |
783 | The argument must be | |
784 | .Dq yes , | |
30460aeb | 785 | .Dq point-to-point |
786 | (layer 3), | |
08822d99 | 787 | .Dq ethernet |
30460aeb | 788 | (layer 2), or |
08822d99 | 789 | .Dq no . |
30460aeb | 790 | Specifying |
791 | .Dq yes | |
792 | permits both | |
793 | .Dq point-to-point | |
794 | and | |
795 | .Dq ethernet . | |
08822d99 | 796 | The default is |
797 | .Dq no . | |
d03f4262 | 798 | .It Cm PermitUserEnvironment |
799 | Specifies whether | |
800 | .Pa ~/.ssh/environment | |
801 | and | |
802 | .Cm environment= | |
803 | options in | |
804 | .Pa ~/.ssh/authorized_keys | |
805 | are processed by | |
30460aeb | 806 | .Xr sshd 8 . |
d03f4262 | 807 | The default is |
808 | .Dq no . | |
809 | Enabling environment processing may enable users to bypass access | |
810 | restrictions in some configurations using mechanisms such as | |
811 | .Ev LD_PRELOAD . | |
884dc78b | 812 | .It Cm PidFile |
276b07a3 | 813 | Specifies the file that contains the process ID of the |
30460aeb | 814 | SSH daemon. |
884dc78b | 815 | The default is |
816 | .Pa /var/run/sshd.pid . | |
817 | .It Cm Port | |
818 | Specifies the port number that | |
30460aeb | 819 | .Xr sshd 8 |
884dc78b | 820 | listens on. |
821 | The default is 22. | |
822 | Multiple options of this type are permitted. | |
823 | See also | |
824 | .Cm ListenAddress . | |
825 | .It Cm PrintLastLog | |
826 | Specifies whether | |
30460aeb | 827 | .Xr sshd 8 |
dfddba3d | 828 | should print the date and time of the last user login when a user logs |
829 | in interactively. | |
884dc78b | 830 | The default is |
831 | .Dq yes . | |
832 | .It Cm PrintMotd | |
833 | Specifies whether | |
30460aeb | 834 | .Xr sshd 8 |
884dc78b | 835 | should print |
836 | .Pa /etc/motd | |
837 | when a user logs in interactively. | |
838 | (On some systems it is also printed by the shell, | |
839 | .Pa /etc/profile , | |
840 | or equivalent.) | |
841 | The default is | |
842 | .Dq yes . | |
843 | .It Cm Protocol | |
844 | Specifies the protocol versions | |
30460aeb | 845 | .Xr sshd 8 |
d03f4262 | 846 | supports. |
884dc78b | 847 | The possible values are |
30460aeb | 848 | .Sq 1 |
884dc78b | 849 | and |
30460aeb | 850 | .Sq 2 . |
884dc78b | 851 | Multiple versions must be comma-separated. |
852 | The default is | |
853 | .Dq 2,1 . | |
d03f4262 | 854 | Note that the order of the protocol list does not indicate preference, |
855 | because the client selects among multiple protocol versions offered | |
856 | by the server. | |
857 | Specifying | |
858 | .Dq 2,1 | |
859 | is identical to | |
860 | .Dq 1,2 . | |
884dc78b | 861 | .It Cm PubkeyAuthentication |
862 | Specifies whether public key authentication is allowed. | |
863 | The default is | |
864 | .Dq yes . | |
865 | Note that this option applies to protocol version 2 only. | |
884dc78b | 866 | .It Cm RhostsRSAAuthentication |
867 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
868 | with successful RSA host authentication is allowed. | |
869 | The default is | |
870 | .Dq no . | |
871 | This option applies to protocol version 1 only. | |
872 | .It Cm RSAAuthentication | |
873 | Specifies whether pure RSA authentication is allowed. | |
874 | The default is | |
875 | .Dq yes . | |
876 | This option applies to protocol version 1 only. | |
877 | .It Cm ServerKeyBits | |
878 | Defines the number of bits in the ephemeral protocol version 1 server key. | |
5156b1a1 | 879 | The minimum value is 512, and the default is 1024. |
884dc78b | 880 | .It Cm StrictModes |
881 | Specifies whether | |
30460aeb | 882 | .Xr sshd 8 |
884dc78b | 883 | should check file modes and ownership of the |
884 | user's files and home directory before accepting login. | |
885 | This is normally desirable because novices sometimes accidentally leave their | |
886 | directory or files world-writable. | |
887 | The default is | |
888 | .Dq yes . | |
889 | .It Cm Subsystem | |
30460aeb | 890 | Configures an external subsystem (e.g. file transfer daemon). |
891 | Arguments should be a subsystem name and a command (with optional arguments) | |
892 | to execute upon subsystem request. | |
e74dc197 | 893 | .Pp |
884dc78b | 894 | The command |
895 | .Xr sftp-server 8 | |
896 | implements the | |
897 | .Dq sftp | |
898 | file transfer subsystem. | |
e74dc197 | 899 | .Pp |
900 | Alternately the name | |
901 | .Dq internal-sftp | |
902 | implements an in-process | |
903 | .Dq sftp | |
904 | server. | |
905 | This may simplify configurations using | |
906 | .Cm ChrootDirectory | |
907 | to force a different filesystem root on clients. | |
908 | .Pp | |
884dc78b | 909 | By default no subsystems are defined. |
910 | Note that this option applies to protocol version 2 only. | |
911 | .It Cm SyslogFacility | |
912 | Gives the facility code that is used when logging messages from | |
30460aeb | 913 | .Xr sshd 8 . |
884dc78b | 914 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, |
915 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. | |
916 | The default is AUTH. | |
540d72c3 | 917 | .It Cm TCPKeepAlive |
918 | Specifies whether the system should send TCP keepalive messages to the | |
919 | other side. | |
920 | If they are sent, death of the connection or crash of one | |
921 | of the machines will be properly noticed. | |
922 | However, this means that | |
923 | connections will die if the route is down temporarily, and some people | |
924 | find it annoying. | |
925 | On the other hand, if TCP keepalives are not sent, | |
926 | sessions may hang indefinitely on the server, leaving | |
927 | .Dq ghost | |
928 | users and consuming server resources. | |
929 | .Pp | |
930 | The default is | |
931 | .Dq yes | |
932 | (to send TCP keepalive messages), and the server will notice | |
933 | if the network goes down or the client host crashes. | |
934 | This avoids infinitely hanging sessions. | |
935 | .Pp | |
936 | To disable TCP keepalive messages, the value should be set to | |
937 | .Dq no . | |
99a78107 | 938 | .It Cm UsageStatsTargets |
939 | This option can be used to specify the target collector hosts to which usage | |
940 | metrics should be reported. This setting will be ignored if | |
941 | .Cm DisableUsageStats | |
942 | is enabled. Multiple targets can be specified separated by comma(s), but no | |
943 | space(s). Each target specification is of the format | |
944 | .Pa host:port[!tags]. | |
945 | Tags control what data elements are reported. The following list specifies | |
946 | the tags for the corresponding data elements. | |
947 | .Pp | |
948 | .Bl -item -offset indent -compact | |
949 | .It | |
950 | .Cm V | |
951 | .Sm off | |
952 | - OpenSSH version, reported by default. | |
953 | .Sm on | |
954 | .It | |
955 | .Cm v | |
956 | .Sm off | |
957 | - SSL version, reported by default. | |
958 | .Sm on | |
959 | .It | |
960 | .Cm M | |
961 | .Sm off | |
962 | - User authentication method used such as "gssapi-keyex", "gssapi-with-mic", etc. Reported by default. | |
963 | .Sm on | |
964 | .It | |
965 | .Cm m | |
966 | .Sm off | |
967 | - User authentication mechanism used such as "GSI", "Kerberos", etc. Reported by default. | |
968 | .Sm on | |
969 | .It | |
970 | .Cm I | |
971 | .Sm off | |
972 | - Client IP address. Not reported by default. | |
973 | .Sm on | |
974 | .It | |
975 | .Cm u | |
976 | .Sm off | |
977 | - User name. Not reported by default. | |
978 | .Sm on | |
979 | .It | |
980 | .Cm U | |
981 | .Sm off | |
982 | - User DN. Not reported by default. | |
983 | .Sm on | |
984 | .Pp | |
985 | In addition to the above selected information, the following data are | |
986 | reported to ALL the specified/default target collectors. There's no way to | |
987 | exclude these from being reported other than by disabling the reporting of | |
988 | usage metrics altogether: | |
989 | .Pp | |
990 | .It | |
991 | .Cm Component code | |
992 | .Sm off | |
993 | - 12 for GSI OpenSSH | |
994 | .Sm on | |
995 | .It | |
996 | .Cm Component Data Format version | |
997 | .Sm off | |
998 | - 0 currently | |
999 | .Sm on | |
1000 | .It | |
1001 | .Cm IP Address | |
1002 | .Sm off | |
1003 | - IP address of reporting server | |
1004 | .Sm on | |
1005 | .It | |
1006 | .Cm Timestamp | |
1007 | .It | |
1008 | .Cm Hostname | |
1009 | .Sm off | |
1010 | - Host name of reporting server | |
1011 | .Sm on | |
1012 | .Pp | |
1013 | If no tags are specified in a host spec, or the special string "default" | |
699b5bd6 | 1014 | is specified, the tags VvMm are assumed. A site could choose to allow a |
99a78107 | 1015 | different set of data to be reported by specifying a different tag set. The |
1016 | last 3 tags I, u and U above are more meant for a local collector that a | |
1017 | site might like to deploy since they could be construed as private information. | |
1018 | The special string "all" denotes all tags. | |
1019 | .El | |
1020 | .Pp | |
1021 | By default, Usage Metrics reporting is sent to | |
1022 | .Dq usage-stats.cilogon.org:4810 . | |
1023 | This can be made explicit by specifying | |
1024 | .Dq default | |
1025 | (all by itself) for the | |
1026 | target specification as in: | |
1027 | .Pp | |
1028 | .Bl -item -offset indent -compact | |
1029 | .It | |
1030 | .Cm UsageStatsTargets | |
1031 | .Sm off | |
1032 | default | |
1033 | .Sm on | |
1034 | .El | |
1035 | .Pp | |
1036 | If | |
1037 | .Cm UsageStatsTargets | |
1038 | is not specified, a comma-separated list of targets | |
1039 | (without any tags specified) if specified in the environment variable | |
1040 | .Cm GLOBUS_USAGE_TARGETS | |
1041 | will be used. | |
1042 | .Pp | |
7cac2b65 | 1043 | .It Cm UseDNS |
1044 | Specifies whether | |
30460aeb | 1045 | .Xr sshd 8 |
8b32eddc | 1046 | should look up the remote host name and check that |
7cac2b65 | 1047 | the resolved host name for the remote IP address maps back to the |
1048 | very same IP address. | |
1049 | The default is | |
1050 | .Dq yes . | |
884dc78b | 1051 | .It Cm UseLogin |
1052 | Specifies whether | |
1053 | .Xr login 1 | |
1054 | is used for interactive login sessions. | |
1055 | The default is | |
1056 | .Dq no . | |
1057 | Note that | |
1058 | .Xr login 1 | |
1059 | is never used for remote command execution. | |
1060 | Note also, that if this is enabled, | |
1061 | .Cm X11Forwarding | |
1062 | will be disabled because | |
1063 | .Xr login 1 | |
1064 | does not know how to handle | |
1065 | .Xr xauth 1 | |
bfe49944 | 1066 | cookies. |
1067 | If | |
884dc78b | 1068 | .Cm UsePrivilegeSeparation |
1069 | is specified, it will be disabled after authentication. | |
7cac2b65 | 1070 | .It Cm UsePAM |
7e82606e | 1071 | Enables the Pluggable Authentication Module interface. |
1072 | If set to | |
1073 | .Dq yes | |
1074 | this will enable PAM authentication using | |
1075 | .Cm ChallengeResponseAuthentication | |
30460aeb | 1076 | and |
1077 | .Cm PasswordAuthentication | |
1078 | in addition to PAM account and session module processing for all | |
1079 | authentication types. | |
7e82606e | 1080 | .Pp |
1081 | Because PAM challenge-response authentication usually serves an equivalent | |
1082 | role to password authentication, you should disable either | |
1083 | .Cm PasswordAuthentication | |
1084 | or | |
1085 | .Cm ChallengeResponseAuthentication. | |
1086 | .Pp | |
1087 | If | |
1088 | .Cm UsePAM | |
1089 | is enabled, you will not be able to run | |
1090 | .Xr sshd 8 | |
1091 | as a non-root user. | |
1092 | The default is | |
540d72c3 | 1093 | .Dq no . |
d037a8b0 | 1094 | .It Cm PermitPAMUserChange |
1095 | If set to | |
1096 | .Dq yes | |
1097 | this will enable PAM authentication to change the name of the user being | |
1098 | authenticated. The default is | |
1099 | .Dq no . | |
884dc78b | 1100 | .It Cm UsePrivilegeSeparation |
1101 | Specifies whether | |
30460aeb | 1102 | .Xr sshd 8 |
884dc78b | 1103 | separates privileges by creating an unprivileged child process |
bfe49944 | 1104 | to deal with incoming network traffic. |
1105 | After successful authentication, another process will be created that has | |
1106 | the privilege of the authenticated user. | |
1107 | The goal of privilege separation is to prevent privilege | |
884dc78b | 1108 | escalation by containing any corruption within the unprivileged processes. |
1109 | The default is | |
1110 | .Dq yes . | |
884dc78b | 1111 | .It Cm X11DisplayOffset |
1112 | Specifies the first display number available for | |
30460aeb | 1113 | .Xr sshd 8 Ns 's |
884dc78b | 1114 | X11 forwarding. |
30460aeb | 1115 | This prevents sshd from interfering with real X11 servers. |
884dc78b | 1116 | The default is 10. |
1117 | .It Cm X11Forwarding | |
1118 | Specifies whether X11 forwarding is permitted. | |
d03f4262 | 1119 | The argument must be |
1120 | .Dq yes | |
1121 | or | |
1122 | .Dq no . | |
884dc78b | 1123 | The default is |
1124 | .Dq no . | |
d03f4262 | 1125 | .Pp |
1126 | When X11 forwarding is enabled, there may be additional exposure to | |
1127 | the server and to client displays if the | |
30460aeb | 1128 | .Xr sshd 8 |
d03f4262 | 1129 | proxy display is configured to listen on the wildcard address (see |
1130 | .Cm X11UseLocalhost | |
30460aeb | 1131 | below), though this is not the default. |
d03f4262 | 1132 | Additionally, the authentication spoofing and authentication data |
1133 | verification and substitution occur on the client side. | |
1134 | The security risk of using X11 forwarding is that the client's X11 | |
30460aeb | 1135 | display server may be exposed to attack when the SSH client requests |
d03f4262 | 1136 | forwarding (see the warnings for |
1137 | .Cm ForwardX11 | |
1138 | in | |
7cac2b65 | 1139 | .Xr ssh_config 5 ) . |
d03f4262 | 1140 | A system administrator may have a stance in which they want to |
1141 | protect clients that may expose themselves to attack by unwittingly | |
1142 | requesting X11 forwarding, which can warrant a | |
1143 | .Dq no | |
1144 | setting. | |
1145 | .Pp | |
1146 | Note that disabling X11 forwarding does not prevent users from | |
1147 | forwarding X11 traffic, as users can always install their own forwarders. | |
884dc78b | 1148 | X11 forwarding is automatically disabled if |
1149 | .Cm UseLogin | |
1150 | is enabled. | |
1151 | .It Cm X11UseLocalhost | |
1152 | Specifies whether | |
30460aeb | 1153 | .Xr sshd 8 |
884dc78b | 1154 | should bind the X11 forwarding server to the loopback address or to |
bfe49944 | 1155 | the wildcard address. |
1156 | By default, | |
30460aeb | 1157 | sshd binds the forwarding server to the loopback address and sets the |
884dc78b | 1158 | hostname part of the |
1159 | .Ev DISPLAY | |
1160 | environment variable to | |
1161 | .Dq localhost . | |
d03f4262 | 1162 | This prevents remote hosts from connecting to the proxy display. |
884dc78b | 1163 | However, some older X11 clients may not function with this |
1164 | configuration. | |
1165 | .Cm X11UseLocalhost | |
1166 | may be set to | |
1167 | .Dq no | |
1168 | to specify that the forwarding server should be bound to the wildcard | |
1169 | address. | |
1170 | The argument must be | |
1171 | .Dq yes | |
1172 | or | |
1173 | .Dq no . | |
1174 | The default is | |
1175 | .Dq yes . | |
1176 | .It Cm XAuthLocation | |
d03f4262 | 1177 | Specifies the full pathname of the |
884dc78b | 1178 | .Xr xauth 1 |
1179 | program. | |
1180 | The default is | |
1181 | .Pa /usr/X11R6/bin/xauth . | |
1182 | .El | |
30460aeb | 1183 | .Sh TIME FORMATS |
1184 | .Xr sshd 8 | |
884dc78b | 1185 | command-line arguments and configuration file options that specify time |
1186 | may be expressed using a sequence of the form: | |
1187 | .Sm off | |
d03f4262 | 1188 | .Ar time Op Ar qualifier , |
884dc78b | 1189 | .Sm on |
1190 | where | |
1191 | .Ar time | |
1192 | is a positive integer value and | |
1193 | .Ar qualifier | |
1194 | is one of the following: | |
1195 | .Pp | |
1196 | .Bl -tag -width Ds -compact -offset indent | |
30460aeb | 1197 | .It Aq Cm none |
884dc78b | 1198 | seconds |
1199 | .It Cm s | Cm S | |
1200 | seconds | |
1201 | .It Cm m | Cm M | |
1202 | minutes | |
1203 | .It Cm h | Cm H | |
1204 | hours | |
1205 | .It Cm d | Cm D | |
1206 | days | |
1207 | .It Cm w | Cm W | |
1208 | weeks | |
1209 | .El | |
1210 | .Pp | |
1211 | Each member of the sequence is added together to calculate | |
1212 | the total time value. | |
1213 | .Pp | |
1214 | Time format examples: | |
1215 | .Pp | |
1216 | .Bl -tag -width Ds -compact -offset indent | |
1217 | .It 600 | |
1218 | 600 seconds (10 minutes) | |
1219 | .It 10m | |
1220 | 10 minutes | |
1221 | .It 1h30m | |
1222 | 1 hour 30 minutes (90 minutes) | |
1223 | .El | |
1224 | .Sh FILES | |
1225 | .Bl -tag -width Ds | |
1226 | .It Pa /etc/ssh/sshd_config | |
1227 | Contains configuration data for | |
30460aeb | 1228 | .Xr sshd 8 . |
884dc78b | 1229 | This file should be writable by root only, but it is recommended |
1230 | (though not necessary) that it be world-readable. | |
1231 | .El | |
7cac2b65 | 1232 | .Sh SEE ALSO |
1233 | .Xr sshd 8 | |
884dc78b | 1234 | .Sh AUTHORS |
1235 | OpenSSH is a derivative of the original and free | |
1236 | ssh 1.2.12 release by Tatu Ylonen. | |
1237 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1238 | Theo de Raadt and Dug Song | |
1239 | removed many bugs, re-added newer features and | |
1240 | created OpenSSH. | |
1241 | Markus Friedl contributed the support for SSH | |
1242 | protocol versions 1.5 and 2.0. | |
1243 | Niels Provos and Markus Friedl contributed support | |
1244 | for privilege separation. |