]>
Commit | Line | Data |
---|---|---|
f5799ae1 | 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 | .\" | |
47686178 | 37 | .\" $OpenBSD: sshd_config.5,v 1.84 2008/03/25 11:58:02 djm Exp $ |
38 | .Dd $Mdocdate: March 27 2008 $ | |
f5799ae1 | 39 | .Dt SSHD_CONFIG 5 |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm sshd_config | |
43 | .Nd OpenSSH SSH daemon configuration file | |
44 | .Sh SYNOPSIS | |
799ae497 | 45 | .Nm /etc/ssh/sshd_config |
f5799ae1 | 46 | .Sh DESCRIPTION |
9108f8d9 | 47 | .Xr sshd 8 |
f5799ae1 | 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. | |
9108f8d9 | 57 | Arguments may optionally be enclosed in double quotes |
58 | .Pq \&" | |
59 | in order to represent arguments containing spaces. | |
f5799ae1 | 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 | |
c9f39d2c | 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 | |
9108f8d9 | 76 | .Ql * |
c9f39d2c | 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. | |
996d5e62 | 87 | .It Cm AddressFamily |
88 | Specifies which address family should be used by | |
9108f8d9 | 89 | .Xr sshd 8 . |
996d5e62 | 90 | Valid arguments are |
91 | .Dq any , | |
92 | .Dq inet | |
9108f8d9 | 93 | (use IPv4 only), or |
996d5e62 | 94 | .Dq inet6 |
95 | (use IPv6 only). | |
96 | The default is | |
97 | .Dq any . | |
f5799ae1 | 98 | .It Cm AllowGroups |
99 | This keyword can be followed by a list of group name patterns, separated | |
100 | by spaces. | |
101 | If specified, login is allowed only for users whose primary | |
102 | group or supplementary group list matches one of the patterns. | |
f5799ae1 | 103 | Only group names are valid; a numerical group ID is not recognized. |
104 | By default, login is allowed for all groups. | |
9108f8d9 | 105 | The allow/deny directives are processed in the following order: |
106 | .Cm DenyUsers , | |
107 | .Cm AllowUsers , | |
108 | .Cm DenyGroups , | |
109 | and finally | |
110 | .Cm AllowGroups . | |
111 | .Pp | |
112 | See | |
113 | .Sx PATTERNS | |
114 | in | |
115 | .Xr ssh_config 5 | |
116 | for more information on patterns. | |
f5799ae1 | 117 | .It Cm AllowTcpForwarding |
118 | Specifies whether TCP forwarding is permitted. | |
119 | The default is | |
120 | .Dq yes . | |
121 | Note that disabling TCP forwarding does not improve security unless | |
122 | users are also denied shell access, as they can always install their | |
123 | own forwarders. | |
f5799ae1 | 124 | .It Cm AllowUsers |
125 | This keyword can be followed by a list of user name patterns, separated | |
126 | by spaces. | |
6a9b3198 | 127 | If specified, login is allowed only for user names that |
f5799ae1 | 128 | match one of the patterns. |
f5799ae1 | 129 | Only user names are valid; a numerical user ID is not recognized. |
130 | By default, login is allowed for all users. | |
131 | If the pattern takes the form USER@HOST then USER and HOST | |
132 | are separately checked, restricting logins to particular | |
133 | users from particular hosts. | |
9108f8d9 | 134 | The allow/deny directives are processed in the following order: |
135 | .Cm DenyUsers , | |
136 | .Cm AllowUsers , | |
137 | .Cm DenyGroups , | |
138 | and finally | |
139 | .Cm AllowGroups . | |
140 | .Pp | |
141 | See | |
142 | .Sx PATTERNS | |
143 | in | |
144 | .Xr ssh_config 5 | |
145 | for more information on patterns. | |
f5799ae1 | 146 | .It Cm AuthorizedKeysFile |
147 | Specifies the file that contains the public keys that can be used | |
148 | for user authentication. | |
149 | .Cm AuthorizedKeysFile | |
150 | may contain tokens of the form %T which are substituted during connection | |
9108f8d9 | 151 | setup. |
0fff78ff | 152 | The following tokens are defined: %% is replaced by a literal '%', |
9108f8d9 | 153 | %h is replaced by the home directory of the user being authenticated, and |
f5799ae1 | 154 | %u is replaced by the username of that user. |
155 | After expansion, | |
156 | .Cm AuthorizedKeysFile | |
157 | is taken to be an absolute path or one relative to the user's home | |
158 | directory. | |
159 | The default is | |
160 | .Dq .ssh/authorized_keys . | |
161 | .It Cm Banner | |
f5799ae1 | 162 | The contents of the specified file are sent to the remote user before |
163 | authentication is allowed. | |
47686178 | 164 | If the argument is |
165 | .Dq none | |
166 | then no banner is displayed. | |
f5799ae1 | 167 | This option is only available for protocol version 2. |
168 | By default, no banner is displayed. | |
f5799ae1 | 169 | .It Cm ChallengeResponseAuthentication |
9108f8d9 | 170 | Specifies whether challenge-response authentication is allowed. |
f5799ae1 | 171 | All authentication styles from |
172 | .Xr login.conf 5 | |
173 | are supported. | |
174 | The default is | |
175 | .Dq yes . | |
47686178 | 176 | .It Cm ChrootDirectory |
177 | Specifies a path to | |
178 | .Xr chroot 2 | |
179 | to after authentication. | |
180 | This path, and all its components, must be root-owned directories that are | |
181 | not writable by any other user or group. | |
182 | .Pp | |
183 | The path may contain the following tokens that are expanded at runtime once | |
184 | the connecting user has been authenticated: %% is replaced by a literal '%', | |
185 | %h is replaced by the home directory of the user being authenticated, and | |
186 | %u is replaced by the username of that user. | |
187 | .Pp | |
188 | The | |
189 | .Cm ChrootDirectory | |
190 | must contain the necessary files and directories to support the | |
191 | users' session. | |
192 | For an interactive session this requires at least a shell, typically | |
193 | .Xr sh 1 , | |
194 | and basic | |
195 | .Pa /dev | |
196 | nodes such as | |
197 | .Xr null 4 , | |
198 | .Xr zero 4 , | |
199 | .Xr stdin 4 , | |
200 | .Xr stdout 4 , | |
201 | .Xr stderr 4 , | |
202 | .Xr arandom 4 | |
203 | and | |
204 | .Xr tty 4 | |
205 | devices. | |
206 | For file transfer sessions using | |
207 | .Dq sftp , | |
208 | no additional configuration of the environment is necessary if the | |
209 | in-process sftp server is used (see | |
210 | .Cm Subsystem | |
211 | for details). | |
212 | .Pp | |
213 | The default is not to | |
214 | .Xr chroot 2 . | |
f5799ae1 | 215 | .It Cm Ciphers |
216 | Specifies the ciphers allowed for protocol version 2. | |
217 | Multiple ciphers must be comma-separated. | |
c9f39d2c | 218 | The supported ciphers are |
219 | .Dq 3des-cbc , | |
220 | .Dq aes128-cbc , | |
221 | .Dq aes192-cbc , | |
222 | .Dq aes256-cbc , | |
223 | .Dq aes128-ctr , | |
224 | .Dq aes192-ctr , | |
225 | .Dq aes256-ctr , | |
665a873d | 226 | .Dq arcfour128 , |
227 | .Dq arcfour256 , | |
c9f39d2c | 228 | .Dq arcfour , |
229 | .Dq blowfish-cbc , | |
230 | and | |
231 | .Dq cast128-cbc . | |
9108f8d9 | 232 | The default is: |
233 | .Bd -literal -offset 3n | |
234 | aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, | |
235 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
236 | aes192-ctr,aes256-ctr | |
f5799ae1 | 237 | .Ed |
f5799ae1 | 238 | .It Cm ClientAliveCountMax |
2c06c99b | 239 | Sets the number of client alive messages (see below) which may be |
f5799ae1 | 240 | sent without |
9108f8d9 | 241 | .Xr sshd 8 |
0fff78ff | 242 | receiving any messages back from the client. |
243 | If this threshold is reached while client alive messages are being sent, | |
9108f8d9 | 244 | sshd will disconnect the client, terminating the session. |
0fff78ff | 245 | It is important to note that the use of client alive messages is very |
246 | different from | |
cdd66111 | 247 | .Cm TCPKeepAlive |
0fff78ff | 248 | (below). |
249 | The client alive messages are sent through the encrypted channel | |
250 | and therefore will not be spoofable. | |
251 | The TCP keepalive option enabled by | |
cdd66111 | 252 | .Cm TCPKeepAlive |
0fff78ff | 253 | is spoofable. |
254 | The client alive mechanism is valuable when the client or | |
f5799ae1 | 255 | server depend on knowing when a connection has become inactive. |
256 | .Pp | |
0fff78ff | 257 | The default value is 3. |
258 | If | |
f5799ae1 | 259 | .Cm ClientAliveInterval |
2c06c99b | 260 | (see below) is set to 15, and |
f5799ae1 | 261 | .Cm ClientAliveCountMax |
9108f8d9 | 262 | is left at the default, unresponsive SSH clients |
f5799ae1 | 263 | will be disconnected after approximately 45 seconds. |
9108f8d9 | 264 | This option applies to protocol version 2 only. |
665a873d | 265 | .It Cm ClientAliveInterval |
266 | Sets a timeout interval in seconds after which if no data has been received | |
267 | from the client, | |
9108f8d9 | 268 | .Xr sshd 8 |
665a873d | 269 | will send a message through the encrypted |
270 | channel to request a response from the client. | |
271 | The default | |
272 | is 0, indicating that these messages will not be sent to the client. | |
273 | This option applies to protocol version 2 only. | |
f5799ae1 | 274 | .It Cm Compression |
665a873d | 275 | Specifies whether compression is allowed, or delayed until |
276 | the user has authenticated successfully. | |
f5799ae1 | 277 | The argument must be |
665a873d | 278 | .Dq yes , |
279 | .Dq delayed , | |
f5799ae1 | 280 | or |
281 | .Dq no . | |
282 | The default is | |
665a873d | 283 | .Dq delayed . |
f5799ae1 | 284 | .It Cm DenyGroups |
285 | This keyword can be followed by a list of group name patterns, separated | |
286 | by spaces. | |
287 | Login is disallowed for users whose primary group or supplementary | |
288 | group list matches one of the patterns. | |
f5799ae1 | 289 | Only group names are valid; a numerical group ID is not recognized. |
290 | By default, login is allowed for all groups. | |
9108f8d9 | 291 | The allow/deny directives are processed in the following order: |
292 | .Cm DenyUsers , | |
293 | .Cm AllowUsers , | |
294 | .Cm DenyGroups , | |
295 | and finally | |
296 | .Cm AllowGroups . | |
297 | .Pp | |
298 | See | |
299 | .Sx PATTERNS | |
300 | in | |
301 | .Xr ssh_config 5 | |
302 | for more information on patterns. | |
f5799ae1 | 303 | .It Cm DenyUsers |
304 | This keyword can be followed by a list of user name patterns, separated | |
305 | by spaces. | |
306 | Login is disallowed for user names that match one of the patterns. | |
f5799ae1 | 307 | Only user names are valid; a numerical user ID is not recognized. |
308 | By default, login is allowed for all users. | |
309 | If the pattern takes the form USER@HOST then USER and HOST | |
310 | are separately checked, restricting logins to particular | |
311 | users from particular hosts. | |
9108f8d9 | 312 | The allow/deny directives are processed in the following order: |
313 | .Cm DenyUsers , | |
314 | .Cm AllowUsers , | |
315 | .Cm DenyGroups , | |
316 | and finally | |
317 | .Cm AllowGroups . | |
318 | .Pp | |
319 | See | |
320 | .Sx PATTERNS | |
321 | in | |
322 | .Xr ssh_config 5 | |
323 | for more information on patterns. | |
324 | .It Cm ForceCommand | |
325 | Forces the execution of the command specified by | |
326 | .Cm ForceCommand , | |
47686178 | 327 | ignoring any command supplied by the client and |
328 | .Pa ~/.ssh/rc | |
329 | if present. | |
9108f8d9 | 330 | The command is invoked by using the user's login shell with the -c option. |
331 | This applies to shell, command, or subsystem execution. | |
332 | It is most useful inside a | |
333 | .Cm Match | |
334 | block. | |
335 | The command originally supplied by the client is available in the | |
336 | .Ev SSH_ORIGINAL_COMMAND | |
337 | environment variable. | |
47686178 | 338 | Specifying a command of |
339 | .Dq internal-sftp | |
340 | will force the use of an in-process sftp server that requires no support | |
341 | files when used with | |
342 | .Cm ChrootDirectory . | |
f5799ae1 | 343 | .It Cm GatewayPorts |
344 | Specifies whether remote hosts are allowed to connect to ports | |
345 | forwarded for the client. | |
346 | By default, | |
9108f8d9 | 347 | .Xr sshd 8 |
6a9b3198 | 348 | binds remote port forwardings to the loopback address. |
349 | This prevents other remote hosts from connecting to forwarded ports. | |
f5799ae1 | 350 | .Cm GatewayPorts |
9108f8d9 | 351 | can be used to specify that sshd |
996d5e62 | 352 | should allow remote port forwardings to bind to non-loopback addresses, thus |
353 | allowing other hosts to connect. | |
354 | The argument may be | |
355 | .Dq no | |
356 | to force remote port forwardings to be available to the local host only, | |
f5799ae1 | 357 | .Dq yes |
996d5e62 | 358 | to force remote port forwardings to bind to the wildcard address, or |
359 | .Dq clientspecified | |
360 | to allow the client to select the address to which the forwarding is bound. | |
f5799ae1 | 361 | The default is |
362 | .Dq no . | |
0fff78ff | 363 | .It Cm GSSAPIAuthentication |
364 | Specifies whether user authentication based on GSSAPI is allowed. | |
cdd66111 | 365 | The default is |
0fff78ff | 366 | .Dq no . |
367 | Note that this option applies to protocol version 2 only. | |
368 | .It Cm GSSAPICleanupCredentials | |
369 | Specifies whether to automatically destroy the user's credentials cache | |
370 | on logout. | |
371 | The default is | |
372 | .Dq yes . | |
373 | Note that this option applies to protocol version 2 only. | |
f5799ae1 | 374 | .It Cm HostbasedAuthentication |
375 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
376 | with successful public key client host authentication is allowed | |
9108f8d9 | 377 | (host-based authentication). |
f5799ae1 | 378 | This option is similar to |
379 | .Cm RhostsRSAAuthentication | |
380 | and applies to protocol version 2 only. | |
381 | The default is | |
382 | .Dq no . | |
9108f8d9 | 383 | .It Cm HostbasedUsesNameFromPacketOnly |
384 | Specifies whether or not the server will attempt to perform a reverse | |
385 | name lookup when matching the name in the | |
386 | .Pa ~/.shosts , | |
387 | .Pa ~/.rhosts , | |
388 | and | |
389 | .Pa /etc/hosts.equiv | |
390 | files during | |
391 | .Cm HostbasedAuthentication . | |
392 | A setting of | |
393 | .Dq yes | |
394 | means that | |
395 | .Xr sshd 8 | |
396 | uses the name supplied by the client rather than | |
397 | attempting to resolve the name from the TCP connection itself. | |
398 | The default is | |
399 | .Dq no . | |
f5799ae1 | 400 | .It Cm HostKey |
401 | Specifies a file containing a private host key | |
402 | used by SSH. | |
403 | The default is | |
404 | .Pa /etc/ssh/ssh_host_key | |
405 | for protocol version 1, and | |
406 | .Pa /etc/ssh/ssh_host_rsa_key | |
407 | and | |
408 | .Pa /etc/ssh/ssh_host_dsa_key | |
409 | for protocol version 2. | |
410 | Note that | |
9108f8d9 | 411 | .Xr sshd 8 |
f5799ae1 | 412 | will refuse to use a file if it is group/world-accessible. |
413 | It is possible to have multiple host key files. | |
414 | .Dq rsa1 | |
415 | keys are used for version 1 and | |
416 | .Dq dsa | |
417 | or | |
418 | .Dq rsa | |
419 | are used for version 2 of the SSH protocol. | |
420 | .It Cm IgnoreRhosts | |
421 | Specifies that | |
422 | .Pa .rhosts | |
423 | and | |
424 | .Pa .shosts | |
425 | files will not be used in | |
f5799ae1 | 426 | .Cm RhostsRSAAuthentication |
427 | or | |
428 | .Cm HostbasedAuthentication . | |
429 | .Pp | |
430 | .Pa /etc/hosts.equiv | |
431 | and | |
432 | .Pa /etc/shosts.equiv | |
433 | are still used. | |
434 | The default is | |
435 | .Dq yes . | |
436 | .It Cm IgnoreUserKnownHosts | |
437 | Specifies whether | |
9108f8d9 | 438 | .Xr sshd 8 |
f5799ae1 | 439 | should ignore the user's |
665a873d | 440 | .Pa ~/.ssh/known_hosts |
f5799ae1 | 441 | during |
442 | .Cm RhostsRSAAuthentication | |
443 | or | |
444 | .Cm HostbasedAuthentication . | |
445 | The default is | |
446 | .Dq no . | |
f5799ae1 | 447 | .It Cm KerberosAuthentication |
0fff78ff | 448 | Specifies whether the password provided by the user for |
f5799ae1 | 449 | .Cm PasswordAuthentication |
0fff78ff | 450 | will be validated through the Kerberos KDC. |
f5799ae1 | 451 | To use this option, the server needs a |
452 | Kerberos servtab which allows the verification of the KDC's identity. | |
9108f8d9 | 453 | The default is |
f5799ae1 | 454 | .Dq no . |
99be0775 | 455 | .It Cm KerberosGetAFSToken |
2c06c99b | 456 | If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire |
99be0775 | 457 | an AFS token before accessing the user's home directory. |
9108f8d9 | 458 | The default is |
99be0775 | 459 | .Dq no . |
f5799ae1 | 460 | .It Cm KerberosOrLocalPasswd |
9108f8d9 | 461 | If password authentication through Kerberos fails then |
f5799ae1 | 462 | the password will be validated via any additional local mechanism |
463 | such as | |
464 | .Pa /etc/passwd . | |
9108f8d9 | 465 | The default is |
f5799ae1 | 466 | .Dq yes . |
f5799ae1 | 467 | .It Cm KerberosTicketCleanup |
468 | Specifies whether to automatically destroy the user's ticket cache | |
469 | file on logout. | |
9108f8d9 | 470 | The default is |
f5799ae1 | 471 | .Dq yes . |
472 | .It Cm KeyRegenerationInterval | |
473 | In protocol version 1, the ephemeral server key is automatically regenerated | |
474 | after this many seconds (if it has been used). | |
475 | The purpose of regeneration is to prevent | |
476 | decrypting captured sessions by later breaking into the machine and | |
477 | stealing the keys. | |
478 | The key is never stored anywhere. | |
479 | If the value is 0, the key is never regenerated. | |
480 | The default is 3600 (seconds). | |
481 | .It Cm ListenAddress | |
482 | Specifies the local addresses | |
9108f8d9 | 483 | .Xr sshd 8 |
f5799ae1 | 484 | should listen on. |
485 | The following forms may be used: | |
486 | .Pp | |
487 | .Bl -item -offset indent -compact | |
488 | .It | |
489 | .Cm ListenAddress | |
490 | .Sm off | |
491 | .Ar host No | Ar IPv4_addr No | Ar IPv6_addr | |
492 | .Sm on | |
493 | .It | |
494 | .Cm ListenAddress | |
495 | .Sm off | |
496 | .Ar host No | Ar IPv4_addr No : Ar port | |
497 | .Sm on | |
498 | .It | |
499 | .Cm ListenAddress | |
500 | .Sm off | |
501 | .Oo | |
502 | .Ar host No | Ar IPv6_addr Oc : Ar port | |
503 | .Sm on | |
504 | .El | |
505 | .Pp | |
506 | If | |
507 | .Ar port | |
508 | is not specified, | |
9108f8d9 | 509 | sshd will listen on the address and all prior |
f5799ae1 | 510 | .Cm Port |
0fff78ff | 511 | options specified. |
512 | The default is to listen on all local addresses. | |
6a9b3198 | 513 | Multiple |
f5799ae1 | 514 | .Cm ListenAddress |
0fff78ff | 515 | options are permitted. |
516 | Additionally, any | |
f5799ae1 | 517 | .Cm Port |
9108f8d9 | 518 | options must precede this option for non-port qualified addresses. |
f5799ae1 | 519 | .It Cm LoginGraceTime |
520 | The server disconnects after this time if the user has not | |
521 | successfully logged in. | |
522 | If the value is 0, there is no time limit. | |
41b2f314 | 523 | The default is 120 seconds. |
f5799ae1 | 524 | .It Cm LogLevel |
525 | Gives the verbosity level that is used when logging messages from | |
9108f8d9 | 526 | .Xr sshd 8 . |
f5799ae1 | 527 | The possible values are: |
9108f8d9 | 528 | QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. |
6a9b3198 | 529 | The default is INFO. |
530 | DEBUG and DEBUG1 are equivalent. | |
531 | DEBUG2 and DEBUG3 each specify higher levels of debugging output. | |
532 | Logging with a DEBUG level violates the privacy of users and is not recommended. | |
f5799ae1 | 533 | .It Cm MACs |
534 | Specifies the available MAC (message authentication code) algorithms. | |
535 | The MAC algorithm is used in protocol version 2 | |
536 | for data integrity protection. | |
537 | Multiple algorithms must be comma-separated. | |
9108f8d9 | 538 | The default is: |
d4487008 | 539 | .Bd -literal -offset indent |
540 | hmac-md5,hmac-sha1,umac-64@openssh.com, | |
541 | hmac-ripemd160,hmac-sha1-96,hmac-md5-96 | |
542 | .Ed | |
9108f8d9 | 543 | .It Cm Match |
544 | Introduces a conditional block. | |
545 | If all of the criteria on the | |
546 | .Cm Match | |
547 | line are satisfied, the keywords on the following lines override those | |
548 | set in the global section of the config file, until either another | |
549 | .Cm Match | |
550 | line or the end of the file. | |
551 | The arguments to | |
552 | .Cm Match | |
553 | are one or more criteria-pattern pairs. | |
554 | The available criteria are | |
555 | .Cm User , | |
556 | .Cm Group , | |
557 | .Cm Host , | |
558 | and | |
559 | .Cm Address . | |
560 | Only a subset of keywords may be used on the lines following a | |
561 | .Cm Match | |
562 | keyword. | |
563 | Available keywords are | |
564 | .Cm AllowTcpForwarding , | |
799ae497 | 565 | .Cm Banner , |
9108f8d9 | 566 | .Cm ForceCommand , |
567 | .Cm GatewayPorts , | |
799ae497 | 568 | .Cm GSSApiAuthentication , |
569 | .Cm KbdInteractiveAuthentication , | |
570 | .Cm KerberosAuthentication , | |
571 | .Cm PasswordAuthentication , | |
9108f8d9 | 572 | .Cm PermitOpen , |
47686178 | 573 | .Cm PermitRootLogin , |
799ae497 | 574 | .Cm RhostsRSAAuthentication , |
575 | .Cm RSAAuthentication , | |
9108f8d9 | 576 | .Cm X11DisplayOffset , |
577 | .Cm X11Forwarding , | |
578 | and | |
579 | .Cm X11UseLocalHost . | |
c9f39d2c | 580 | .It Cm MaxAuthTries |
581 | Specifies the maximum number of authentication attempts permitted per | |
582 | connection. | |
583 | Once the number of failures reaches half this value, | |
584 | additional failures are logged. | |
585 | The default is 6. | |
f5799ae1 | 586 | .It Cm MaxStartups |
587 | Specifies the maximum number of concurrent unauthenticated connections to the | |
9108f8d9 | 588 | SSH daemon. |
f5799ae1 | 589 | Additional connections will be dropped until authentication succeeds or the |
590 | .Cm LoginGraceTime | |
591 | expires for a connection. | |
592 | The default is 10. | |
593 | .Pp | |
594 | Alternatively, random early drop can be enabled by specifying | |
595 | the three colon separated values | |
596 | .Dq start:rate:full | |
9108f8d9 | 597 | (e.g. "10:30:60"). |
598 | .Xr sshd 8 | |
f5799ae1 | 599 | will refuse connection attempts with a probability of |
600 | .Dq rate/100 | |
601 | (30%) | |
602 | if there are currently | |
603 | .Dq start | |
604 | (10) | |
605 | unauthenticated connections. | |
606 | The probability increases linearly and all connection attempts | |
607 | are refused if the number of unauthenticated connections reaches | |
608 | .Dq full | |
609 | (60). | |
610 | .It Cm PasswordAuthentication | |
611 | Specifies whether password authentication is allowed. | |
612 | The default is | |
613 | .Dq yes . | |
614 | .It Cm PermitEmptyPasswords | |
615 | When password authentication is allowed, it specifies whether the | |
616 | server allows login to accounts with empty password strings. | |
617 | The default is | |
618 | .Dq no . | |
9108f8d9 | 619 | .It Cm PermitOpen |
620 | Specifies the destinations to which TCP port forwarding is permitted. | |
621 | The forwarding specification must be one of the following forms: | |
622 | .Pp | |
623 | .Bl -item -offset indent -compact | |
624 | .It | |
625 | .Cm PermitOpen | |
626 | .Sm off | |
627 | .Ar host : port | |
628 | .Sm on | |
629 | .It | |
630 | .Cm PermitOpen | |
631 | .Sm off | |
632 | .Ar IPv4_addr : port | |
633 | .Sm on | |
634 | .It | |
635 | .Cm PermitOpen | |
636 | .Sm off | |
637 | .Ar \&[ IPv6_addr \&] : port | |
638 | .Sm on | |
639 | .El | |
640 | .Pp | |
641 | Multiple forwards may be specified by separating them with whitespace. | |
642 | An argument of | |
643 | .Dq any | |
644 | can be used to remove all restrictions and permit any forwarding requests. | |
645 | By default all port forwarding requests are permitted. | |
f5799ae1 | 646 | .It Cm PermitRootLogin |
996d5e62 | 647 | Specifies whether root can log in using |
f5799ae1 | 648 | .Xr ssh 1 . |
649 | The argument must be | |
650 | .Dq yes , | |
651 | .Dq without-password , | |
9108f8d9 | 652 | .Dq forced-commands-only , |
f5799ae1 | 653 | or |
654 | .Dq no . | |
655 | The default is | |
656 | .Dq yes . | |
657 | .Pp | |
658 | If this option is set to | |
9108f8d9 | 659 | .Dq without-password , |
996d5e62 | 660 | password authentication is disabled for root. |
f5799ae1 | 661 | .Pp |
662 | If this option is set to | |
9108f8d9 | 663 | .Dq forced-commands-only , |
f5799ae1 | 664 | root login with public key authentication will be allowed, |
665 | but only if the | |
666 | .Ar command | |
667 | option has been specified | |
668 | (which may be useful for taking remote backups even if root login is | |
0fff78ff | 669 | normally not allowed). |
670 | All other authentication methods are disabled for root. | |
f5799ae1 | 671 | .Pp |
672 | If this option is set to | |
9108f8d9 | 673 | .Dq no , |
996d5e62 | 674 | root is not allowed to log in. |
2c06c99b | 675 | .It Cm PermitTunnel |
676 | Specifies whether | |
677 | .Xr tun 4 | |
678 | device forwarding is allowed. | |
679 | The argument must be | |
680 | .Dq yes , | |
9108f8d9 | 681 | .Dq point-to-point |
682 | (layer 3), | |
2c06c99b | 683 | .Dq ethernet |
9108f8d9 | 684 | (layer 2), or |
2c06c99b | 685 | .Dq no . |
9108f8d9 | 686 | Specifying |
687 | .Dq yes | |
688 | permits both | |
689 | .Dq point-to-point | |
690 | and | |
691 | .Dq ethernet . | |
2c06c99b | 692 | The default is |
693 | .Dq no . | |
41b2f314 | 694 | .It Cm PermitUserEnvironment |
695 | Specifies whether | |
696 | .Pa ~/.ssh/environment | |
697 | and | |
698 | .Cm environment= | |
699 | options in | |
700 | .Pa ~/.ssh/authorized_keys | |
701 | are processed by | |
9108f8d9 | 702 | .Xr sshd 8 . |
41b2f314 | 703 | The default is |
704 | .Dq no . | |
705 | Enabling environment processing may enable users to bypass access | |
706 | restrictions in some configurations using mechanisms such as | |
707 | .Ev LD_PRELOAD . | |
f5799ae1 | 708 | .It Cm PidFile |
680cee3b | 709 | Specifies the file that contains the process ID of the |
9108f8d9 | 710 | SSH daemon. |
f5799ae1 | 711 | The default is |
712 | .Pa /var/run/sshd.pid . | |
713 | .It Cm Port | |
714 | Specifies the port number that | |
9108f8d9 | 715 | .Xr sshd 8 |
f5799ae1 | 716 | listens on. |
717 | The default is 22. | |
718 | Multiple options of this type are permitted. | |
719 | See also | |
720 | .Cm ListenAddress . | |
721 | .It Cm PrintLastLog | |
722 | Specifies whether | |
9108f8d9 | 723 | .Xr sshd 8 |
996d5e62 | 724 | should print the date and time of the last user login when a user logs |
725 | in interactively. | |
f5799ae1 | 726 | The default is |
727 | .Dq yes . | |
728 | .It Cm PrintMotd | |
729 | Specifies whether | |
9108f8d9 | 730 | .Xr sshd 8 |
f5799ae1 | 731 | should print |
732 | .Pa /etc/motd | |
733 | when a user logs in interactively. | |
734 | (On some systems it is also printed by the shell, | |
735 | .Pa /etc/profile , | |
736 | or equivalent.) | |
737 | The default is | |
738 | .Dq yes . | |
739 | .It Cm Protocol | |
740 | Specifies the protocol versions | |
9108f8d9 | 741 | .Xr sshd 8 |
41b2f314 | 742 | supports. |
f5799ae1 | 743 | The possible values are |
9108f8d9 | 744 | .Sq 1 |
f5799ae1 | 745 | and |
9108f8d9 | 746 | .Sq 2 . |
f5799ae1 | 747 | Multiple versions must be comma-separated. |
748 | The default is | |
749 | .Dq 2,1 . | |
41b2f314 | 750 | Note that the order of the protocol list does not indicate preference, |
751 | because the client selects among multiple protocol versions offered | |
752 | by the server. | |
753 | Specifying | |
754 | .Dq 2,1 | |
755 | is identical to | |
756 | .Dq 1,2 . | |
f5799ae1 | 757 | .It Cm PubkeyAuthentication |
758 | Specifies whether public key authentication is allowed. | |
759 | The default is | |
760 | .Dq yes . | |
761 | Note that this option applies to protocol version 2 only. | |
f5799ae1 | 762 | .It Cm RhostsRSAAuthentication |
763 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
764 | with successful RSA host authentication is allowed. | |
765 | The default is | |
766 | .Dq no . | |
767 | This option applies to protocol version 1 only. | |
768 | .It Cm RSAAuthentication | |
769 | Specifies whether pure RSA authentication is allowed. | |
770 | The default is | |
771 | .Dq yes . | |
772 | This option applies to protocol version 1 only. | |
773 | .It Cm ServerKeyBits | |
774 | Defines the number of bits in the ephemeral protocol version 1 server key. | |
775 | The minimum value is 512, and the default is 768. | |
776 | .It Cm StrictModes | |
777 | Specifies whether | |
9108f8d9 | 778 | .Xr sshd 8 |
f5799ae1 | 779 | should check file modes and ownership of the |
780 | user's files and home directory before accepting login. | |
781 | This is normally desirable because novices sometimes accidentally leave their | |
782 | directory or files world-writable. | |
783 | The default is | |
784 | .Dq yes . | |
785 | .It Cm Subsystem | |
9108f8d9 | 786 | Configures an external subsystem (e.g. file transfer daemon). |
787 | Arguments should be a subsystem name and a command (with optional arguments) | |
788 | to execute upon subsystem request. | |
47686178 | 789 | .Pp |
f5799ae1 | 790 | The command |
791 | .Xr sftp-server 8 | |
792 | implements the | |
793 | .Dq sftp | |
794 | file transfer subsystem. | |
47686178 | 795 | .Pp |
796 | Alternately the name | |
797 | .Dq internal-sftp | |
798 | implements an in-process | |
799 | .Dq sftp | |
800 | server. | |
801 | This may simplify configurations using | |
802 | .Cm ChrootDirectory | |
803 | to force a different filesystem root on clients. | |
804 | .Pp | |
f5799ae1 | 805 | By default no subsystems are defined. |
806 | Note that this option applies to protocol version 2 only. | |
807 | .It Cm SyslogFacility | |
808 | Gives the facility code that is used when logging messages from | |
9108f8d9 | 809 | .Xr sshd 8 . |
f5799ae1 | 810 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, |
811 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. | |
812 | The default is AUTH. | |
cdd66111 | 813 | .It Cm TCPKeepAlive |
814 | Specifies whether the system should send TCP keepalive messages to the | |
815 | other side. | |
816 | If they are sent, death of the connection or crash of one | |
817 | of the machines will be properly noticed. | |
818 | However, this means that | |
819 | connections will die if the route is down temporarily, and some people | |
820 | find it annoying. | |
821 | On the other hand, if TCP keepalives are not sent, | |
822 | sessions may hang indefinitely on the server, leaving | |
823 | .Dq ghost | |
824 | users and consuming server resources. | |
825 | .Pp | |
826 | The default is | |
827 | .Dq yes | |
828 | (to send TCP keepalive messages), and the server will notice | |
829 | if the network goes down or the client host crashes. | |
830 | This avoids infinitely hanging sessions. | |
831 | .Pp | |
832 | To disable TCP keepalive messages, the value should be set to | |
833 | .Dq no . | |
0fff78ff | 834 | .It Cm UseDNS |
835 | Specifies whether | |
9108f8d9 | 836 | .Xr sshd 8 |
dec6d9fe | 837 | should look up the remote host name and check that |
0fff78ff | 838 | the resolved host name for the remote IP address maps back to the |
839 | very same IP address. | |
840 | The default is | |
841 | .Dq yes . | |
f5799ae1 | 842 | .It Cm UseLogin |
843 | Specifies whether | |
844 | .Xr login 1 | |
845 | is used for interactive login sessions. | |
846 | The default is | |
847 | .Dq no . | |
848 | Note that | |
849 | .Xr login 1 | |
850 | is never used for remote command execution. | |
851 | Note also, that if this is enabled, | |
852 | .Cm X11Forwarding | |
853 | will be disabled because | |
854 | .Xr login 1 | |
855 | does not know how to handle | |
856 | .Xr xauth 1 | |
6a9b3198 | 857 | cookies. |
858 | If | |
f5799ae1 | 859 | .Cm UsePrivilegeSeparation |
860 | is specified, it will be disabled after authentication. | |
0fff78ff | 861 | .It Cm UsePAM |
c9f39d2c | 862 | Enables the Pluggable Authentication Module interface. |
863 | If set to | |
864 | .Dq yes | |
865 | this will enable PAM authentication using | |
866 | .Cm ChallengeResponseAuthentication | |
9108f8d9 | 867 | and |
868 | .Cm PasswordAuthentication | |
869 | in addition to PAM account and session module processing for all | |
870 | authentication types. | |
c9f39d2c | 871 | .Pp |
872 | Because PAM challenge-response authentication usually serves an equivalent | |
873 | role to password authentication, you should disable either | |
874 | .Cm PasswordAuthentication | |
875 | or | |
876 | .Cm ChallengeResponseAuthentication. | |
877 | .Pp | |
878 | If | |
879 | .Cm UsePAM | |
880 | is enabled, you will not be able to run | |
881 | .Xr sshd 8 | |
882 | as a non-root user. | |
883 | The default is | |
cdd66111 | 884 | .Dq no . |
f5799ae1 | 885 | .It Cm UsePrivilegeSeparation |
886 | Specifies whether | |
9108f8d9 | 887 | .Xr sshd 8 |
f5799ae1 | 888 | separates privileges by creating an unprivileged child process |
6a9b3198 | 889 | to deal with incoming network traffic. |
890 | After successful authentication, another process will be created that has | |
891 | the privilege of the authenticated user. | |
892 | The goal of privilege separation is to prevent privilege | |
f5799ae1 | 893 | escalation by containing any corruption within the unprivileged processes. |
894 | The default is | |
895 | .Dq yes . | |
f5799ae1 | 896 | .It Cm X11DisplayOffset |
897 | Specifies the first display number available for | |
9108f8d9 | 898 | .Xr sshd 8 Ns 's |
f5799ae1 | 899 | X11 forwarding. |
9108f8d9 | 900 | This prevents sshd from interfering with real X11 servers. |
f5799ae1 | 901 | The default is 10. |
902 | .It Cm X11Forwarding | |
903 | Specifies whether X11 forwarding is permitted. | |
41b2f314 | 904 | The argument must be |
905 | .Dq yes | |
906 | or | |
907 | .Dq no . | |
f5799ae1 | 908 | The default is |
909 | .Dq no . | |
41b2f314 | 910 | .Pp |
911 | When X11 forwarding is enabled, there may be additional exposure to | |
912 | the server and to client displays if the | |
9108f8d9 | 913 | .Xr sshd 8 |
41b2f314 | 914 | proxy display is configured to listen on the wildcard address (see |
915 | .Cm X11UseLocalhost | |
9108f8d9 | 916 | below), though this is not the default. |
41b2f314 | 917 | Additionally, the authentication spoofing and authentication data |
918 | verification and substitution occur on the client side. | |
919 | The security risk of using X11 forwarding is that the client's X11 | |
9108f8d9 | 920 | display server may be exposed to attack when the SSH client requests |
41b2f314 | 921 | forwarding (see the warnings for |
922 | .Cm ForwardX11 | |
923 | in | |
0fff78ff | 924 | .Xr ssh_config 5 ) . |
41b2f314 | 925 | A system administrator may have a stance in which they want to |
926 | protect clients that may expose themselves to attack by unwittingly | |
927 | requesting X11 forwarding, which can warrant a | |
928 | .Dq no | |
929 | setting. | |
930 | .Pp | |
931 | Note that disabling X11 forwarding does not prevent users from | |
932 | forwarding X11 traffic, as users can always install their own forwarders. | |
f5799ae1 | 933 | X11 forwarding is automatically disabled if |
934 | .Cm UseLogin | |
935 | is enabled. | |
936 | .It Cm X11UseLocalhost | |
937 | Specifies whether | |
9108f8d9 | 938 | .Xr sshd 8 |
f5799ae1 | 939 | should bind the X11 forwarding server to the loopback address or to |
6a9b3198 | 940 | the wildcard address. |
941 | By default, | |
9108f8d9 | 942 | sshd binds the forwarding server to the loopback address and sets the |
f5799ae1 | 943 | hostname part of the |
944 | .Ev DISPLAY | |
945 | environment variable to | |
946 | .Dq localhost . | |
41b2f314 | 947 | This prevents remote hosts from connecting to the proxy display. |
f5799ae1 | 948 | However, some older X11 clients may not function with this |
949 | configuration. | |
950 | .Cm X11UseLocalhost | |
951 | may be set to | |
952 | .Dq no | |
953 | to specify that the forwarding server should be bound to the wildcard | |
954 | address. | |
955 | The argument must be | |
956 | .Dq yes | |
957 | or | |
958 | .Dq no . | |
959 | The default is | |
960 | .Dq yes . | |
961 | .It Cm XAuthLocation | |
41b2f314 | 962 | Specifies the full pathname of the |
f5799ae1 | 963 | .Xr xauth 1 |
964 | program. | |
965 | The default is | |
966 | .Pa /usr/X11R6/bin/xauth . | |
967 | .El | |
9108f8d9 | 968 | .Sh TIME FORMATS |
969 | .Xr sshd 8 | |
f5799ae1 | 970 | command-line arguments and configuration file options that specify time |
971 | may be expressed using a sequence of the form: | |
972 | .Sm off | |
41b2f314 | 973 | .Ar time Op Ar qualifier , |
f5799ae1 | 974 | .Sm on |
975 | where | |
976 | .Ar time | |
977 | is a positive integer value and | |
978 | .Ar qualifier | |
979 | is one of the following: | |
980 | .Pp | |
981 | .Bl -tag -width Ds -compact -offset indent | |
9108f8d9 | 982 | .It Aq Cm none |
f5799ae1 | 983 | seconds |
984 | .It Cm s | Cm S | |
985 | seconds | |
986 | .It Cm m | Cm M | |
987 | minutes | |
988 | .It Cm h | Cm H | |
989 | hours | |
990 | .It Cm d | Cm D | |
991 | days | |
992 | .It Cm w | Cm W | |
993 | weeks | |
994 | .El | |
995 | .Pp | |
996 | Each member of the sequence is added together to calculate | |
997 | the total time value. | |
998 | .Pp | |
999 | Time format examples: | |
1000 | .Pp | |
1001 | .Bl -tag -width Ds -compact -offset indent | |
1002 | .It 600 | |
1003 | 600 seconds (10 minutes) | |
1004 | .It 10m | |
1005 | 10 minutes | |
1006 | .It 1h30m | |
1007 | 1 hour 30 minutes (90 minutes) | |
1008 | .El | |
1009 | .Sh FILES | |
1010 | .Bl -tag -width Ds | |
1011 | .It Pa /etc/ssh/sshd_config | |
1012 | Contains configuration data for | |
9108f8d9 | 1013 | .Xr sshd 8 . |
f5799ae1 | 1014 | This file should be writable by root only, but it is recommended |
1015 | (though not necessary) that it be world-readable. | |
1016 | .El | |
0fff78ff | 1017 | .Sh SEE ALSO |
1018 | .Xr sshd 8 | |
f5799ae1 | 1019 | .Sh AUTHORS |
1020 | OpenSSH is a derivative of the original and free | |
1021 | ssh 1.2.12 release by Tatu Ylonen. | |
1022 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1023 | Theo de Raadt and Dug Song | |
1024 | removed many bugs, re-added newer features and | |
1025 | created OpenSSH. | |
1026 | Markus Friedl contributed the support for SSH | |
1027 | protocol versions 1.5 and 2.0. | |
1028 | Niels Provos and Markus Friedl contributed support | |
1029 | for privilege separation. |