diff options
author | Colin Watson <cjwatson@debian.org> | 2007-06-12 11:03:36 +0000 |
---|---|---|
committer | Colin Watson <cjwatson@debian.org> | 2007-06-12 11:03:36 +0000 |
commit | 086ea76990b1e6287c24b6db74adffd4605eb3b0 (patch) | |
tree | 4650093038f9f66b02823fb07f49d6a4becd1667 /sshd_config.0 | |
parent | 4ee72c71e31226c81743439fe1ed2b521b5ddb7e (diff) | |
parent | 3e2e0ac10674d77618c4c7339e18b83ced247492 (diff) |
Import OpenSSH 4.6p1.
Diffstat (limited to 'sshd_config.0')
-rw-r--r-- | sshd_config.0 | 573 |
1 files changed, 573 insertions, 0 deletions
diff --git a/sshd_config.0 b/sshd_config.0 new file mode 100644 index 000000000..c9a09a4ff --- /dev/null +++ b/sshd_config.0 | |||
@@ -0,0 +1,573 @@ | |||
1 | SSHD_CONFIG(5) OpenBSD Programmer's Manual SSHD_CONFIG(5) | ||
2 | |||
3 | NAME | ||
4 | sshd_config - OpenSSH SSH daemon configuration file | ||
5 | |||
6 | SYNOPSIS | ||
7 | /etc/ssh/sshd_config | ||
8 | |||
9 | DESCRIPTION | ||
10 | sshd(8) reads configuration data from /etc/ssh/sshd_config (or the file | ||
11 | specified with -f on the command line). The file contains keyword-argu- | ||
12 | ment pairs, one per line. Lines starting with `#' and empty lines are | ||
13 | interpreted as comments. Arguments may optionally be enclosed in double | ||
14 | quotes (") in order to represent arguments containing spaces. | ||
15 | |||
16 | The possible keywords and their meanings are as follows (note that key- | ||
17 | words are case-insensitive and arguments are case-sensitive): | ||
18 | |||
19 | AcceptEnv | ||
20 | Specifies what environment variables sent by the client will be | ||
21 | copied into the session's environ(7). See SendEnv in | ||
22 | ssh_config(5) for how to configure the client. Note that envi- | ||
23 | ronment passing is only supported for protocol 2. Variables are | ||
24 | specified by name, which may contain the wildcard characters `*' | ||
25 | and `?'. Multiple environment variables may be separated by | ||
26 | whitespace or spread across multiple AcceptEnv directives. Be | ||
27 | warned that some environment variables could be used to bypass | ||
28 | restricted user environments. For this reason, care should be | ||
29 | taken in the use of this directive. The default is not to accept | ||
30 | any environment variables. | ||
31 | |||
32 | AddressFamily | ||
33 | Specifies which address family should be used by sshd(8). Valid | ||
34 | arguments are ``any'', ``inet'' (use IPv4 only), or ``inet6'' | ||
35 | (use IPv6 only). The default is ``any''. | ||
36 | |||
37 | AllowGroups | ||
38 | This keyword can be followed by a list of group name patterns, | ||
39 | separated by spaces. If specified, login is allowed only for | ||
40 | users whose primary group or supplementary group list matches one | ||
41 | of the patterns. Only group names are valid; a numerical group | ||
42 | ID is not recognized. By default, login is allowed for all | ||
43 | groups. The allow/deny directives are processed in the following | ||
44 | order: DenyUsers, AllowUsers, DenyGroups, and finally | ||
45 | AllowGroups. | ||
46 | |||
47 | See PATTERNS in ssh_config(5) for more information on patterns. | ||
48 | |||
49 | AllowTcpForwarding | ||
50 | Specifies whether TCP forwarding is permitted. The default is | ||
51 | ``yes''. Note that disabling TCP forwarding does not improve se- | ||
52 | curity unless users are also denied shell access, as they can al- | ||
53 | ways install their own forwarders. | ||
54 | |||
55 | AllowUsers | ||
56 | This keyword can be followed by a list of user name patterns, | ||
57 | separated by spaces. If specified, login is allowed only for us- | ||
58 | er names that match one of the patterns. Only user names are | ||
59 | valid; a numerical user ID is not recognized. By default, login | ||
60 | is allowed for all users. If the pattern takes the form US- | ||
61 | ER@HOST then USER and HOST are separately checked, restricting | ||
62 | logins to particular users from particular hosts. The allow/deny | ||
63 | directives are processed in the following order: DenyUsers, | ||
64 | AllowUsers, DenyGroups, and finally AllowGroups. | ||
65 | |||
66 | See PATTERNS in ssh_config(5) for more information on patterns. | ||
67 | |||
68 | AuthorizedKeysFile | ||
69 | Specifies the file that contains the public keys that can be used | ||
70 | for user authentication. AuthorizedKeysFile may contain tokens | ||
71 | of the form %T which are substituted during connection setup. | ||
72 | The following tokens are defined: %% is replaced by a literal | ||
73 | '%', %h is replaced by the home directory of the user being au- | ||
74 | thenticated, and %u is replaced by the username of that user. | ||
75 | After expansion, AuthorizedKeysFile is taken to be an absolute | ||
76 | path or one relative to the user's home directory. The default | ||
77 | is ``.ssh/authorized_keys''. | ||
78 | |||
79 | Banner In some jurisdictions, sending a warning message before authenti- | ||
80 | cation may be relevant for getting legal protection. The con- | ||
81 | tents of the specified file are sent to the remote user before | ||
82 | authentication is allowed. This option is only available for | ||
83 | protocol version 2. By default, no banner is displayed. | ||
84 | |||
85 | ChallengeResponseAuthentication | ||
86 | Specifies whether challenge-response authentication is allowed. | ||
87 | All authentication styles from login.conf(5) are supported. The | ||
88 | default is ``yes''. | ||
89 | |||
90 | Ciphers | ||
91 | Specifies the ciphers allowed for protocol version 2. Multiple | ||
92 | ciphers must be comma-separated. The supported ciphers are | ||
93 | ``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'', ``aes256-cbc'', | ||
94 | ``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'', ``arcfour128'', | ||
95 | ``arcfour256'', ``arcfour'', ``blowfish-cbc'', and | ||
96 | ``cast128-cbc''. The default is: | ||
97 | |||
98 | aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, | ||
99 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | ||
100 | aes192-ctr,aes256-ctr | ||
101 | |||
102 | ClientAliveCountMax | ||
103 | Sets the number of client alive messages (see below) which may be | ||
104 | sent without sshd(8) receiving any messages back from the client. | ||
105 | If this threshold is reached while client alive messages are be- | ||
106 | ing sent, sshd will disconnect the client, terminating the ses- | ||
107 | sion. It is important to note that the use of client alive mes- | ||
108 | sages is very different from TCPKeepAlive (below). The client | ||
109 | alive messages are sent through the encrypted channel and there- | ||
110 | fore will not be spoofable. The TCP keepalive option enabled by | ||
111 | TCPKeepAlive is spoofable. The client alive mechanism is valu- | ||
112 | able when the client or server depend on knowing when a connec- | ||
113 | tion has become inactive. | ||
114 | |||
115 | The default value is 3. If ClientAliveInterval (see below) is | ||
116 | set to 15, and ClientAliveCountMax is left at the default, unre- | ||
117 | sponsive SSH clients will be disconnected after approximately 45 | ||
118 | seconds. This option applies to protocol version 2 only. | ||
119 | |||
120 | ClientAliveInterval | ||
121 | Sets a timeout interval in seconds after which if no data has | ||
122 | been received from the client, sshd(8) will send a message | ||
123 | through the encrypted channel to request a response from the | ||
124 | client. The default is 0, indicating that these messages will | ||
125 | not be sent to the client. This option applies to protocol ver- | ||
126 | sion 2 only. | ||
127 | |||
128 | Compression | ||
129 | Specifies whether compression is allowed, or delayed until the | ||
130 | user has authenticated successfully. The argument must be | ||
131 | ``yes'', ``delayed'', or ``no''. The default is ``delayed''. | ||
132 | |||
133 | DenyGroups | ||
134 | This keyword can be followed by a list of group name patterns, | ||
135 | separated by spaces. Login is disallowed for users whose primary | ||
136 | group or supplementary group list matches one of the patterns. | ||
137 | Only group names are valid; a numerical group ID is not recog- | ||
138 | nized. By default, login is allowed for all groups. The al- | ||
139 | low/deny directives are processed in the following order: | ||
140 | DenyUsers, AllowUsers, DenyGroups, and finally AllowGroups. | ||
141 | |||
142 | See PATTERNS in ssh_config(5) for more information on patterns. | ||
143 | |||
144 | DenyUsers | ||
145 | This keyword can be followed by a list of user name patterns, | ||
146 | separated by spaces. Login is disallowed for user names that | ||
147 | match one of the patterns. Only user names are valid; a numeri- | ||
148 | cal user ID is not recognized. By default, login is allowed for | ||
149 | all users. If the pattern takes the form USER@HOST then USER and | ||
150 | HOST are separately checked, restricting logins to particular | ||
151 | users from particular hosts. The allow/deny directives are pro- | ||
152 | cessed in the following order: DenyUsers, AllowUsers, DenyGroups, | ||
153 | and finally AllowGroups. | ||
154 | |||
155 | See PATTERNS in ssh_config(5) for more information on patterns. | ||
156 | |||
157 | ForceCommand | ||
158 | Forces the execution of the command specified by ForceCommand, | ||
159 | ignoring any command supplied by the client. The command is in- | ||
160 | voked by using the user's login shell with the -c option. This | ||
161 | applies to shell, command, or subsystem execution. It is most | ||
162 | useful inside a Match block. The command originally supplied by | ||
163 | the client is available in the SSH_ORIGINAL_COMMAND environment | ||
164 | variable. | ||
165 | |||
166 | GatewayPorts | ||
167 | Specifies whether remote hosts are allowed to connect to ports | ||
168 | forwarded for the client. By default, sshd(8) binds remote port | ||
169 | forwardings to the loopback address. This prevents other remote | ||
170 | hosts from connecting to forwarded ports. GatewayPorts can be | ||
171 | used to specify that sshd should allow remote port forwardings to | ||
172 | bind to non-loopback addresses, thus allowing other hosts to con- | ||
173 | nect. The argument may be ``no'' to force remote port forward- | ||
174 | ings to be available to the local host only, ``yes'' to force re- | ||
175 | mote port forwardings to bind to the wildcard address, or | ||
176 | ``clientspecified'' to allow the client to select the address to | ||
177 | which the forwarding is bound. The default is ``no''. | ||
178 | |||
179 | GSSAPIAuthentication | ||
180 | Specifies whether user authentication based on GSSAPI is allowed. | ||
181 | The default is ``no''. Note that this option applies to protocol | ||
182 | version 2 only. | ||
183 | |||
184 | GSSAPICleanupCredentials | ||
185 | Specifies whether to automatically destroy the user's credentials | ||
186 | cache on logout. The default is ``yes''. Note that this option | ||
187 | applies to protocol version 2 only. | ||
188 | |||
189 | HostbasedAuthentication | ||
190 | Specifies whether rhosts or /etc/hosts.equiv authentication to- | ||
191 | gether with successful public key client host authentication is | ||
192 | allowed (host-based authentication). This option is similar to | ||
193 | RhostsRSAAuthentication and applies to protocol version 2 only. | ||
194 | The default is ``no''. | ||
195 | |||
196 | HostbasedUsesNameFromPacketOnly | ||
197 | Specifies whether or not the server will attempt to perform a re- | ||
198 | verse name lookup when matching the name in the ~/.shosts, | ||
199 | ~/.rhosts, and /etc/hosts.equiv files during | ||
200 | HostbasedAuthentication. A setting of ``yes'' means that sshd(8) | ||
201 | uses the name supplied by the client rather than attempting to | ||
202 | resolve the name from the TCP connection itself. The default is | ||
203 | ``no''. | ||
204 | |||
205 | HostKey | ||
206 | Specifies a file containing a private host key used by SSH. The | ||
207 | default is /etc/ssh/ssh_host_key for protocol version 1, and | ||
208 | /etc/ssh/ssh_host_rsa_key and /etc/ssh/ssh_host_dsa_key for pro- | ||
209 | tocol version 2. Note that sshd(8) will refuse to use a file if | ||
210 | it is group/world-accessible. It is possible to have multiple | ||
211 | host key files. ``rsa1'' keys are used for version 1 and ``dsa'' | ||
212 | or ``rsa'' are used for version 2 of the SSH protocol. | ||
213 | |||
214 | IgnoreRhosts | ||
215 | Specifies that .rhosts and .shosts files will not be used in | ||
216 | RhostsRSAAuthentication or HostbasedAuthentication. | ||
217 | |||
218 | /etc/hosts.equiv and /etc/shosts.equiv are still used. The de- | ||
219 | fault is ``yes''. | ||
220 | |||
221 | IgnoreUserKnownHosts | ||
222 | Specifies whether sshd(8) should ignore the user's | ||
223 | ~/.ssh/known_hosts during RhostsRSAAuthentication or | ||
224 | HostbasedAuthentication. The default is ``no''. | ||
225 | |||
226 | KerberosAuthentication | ||
227 | Specifies whether the password provided by the user for | ||
228 | PasswordAuthentication will be validated through the Kerberos | ||
229 | KDC. To use this option, the server needs a Kerberos servtab | ||
230 | which allows the verification of the KDC's identity. The default | ||
231 | is ``no''. | ||
232 | |||
233 | KerberosGetAFSToken | ||
234 | If AFS is active and the user has a Kerberos 5 TGT, attempt to | ||
235 | acquire an AFS token before accessing the user's home directory. | ||
236 | The default is ``no''. | ||
237 | |||
238 | KerberosOrLocalPasswd | ||
239 | If password authentication through Kerberos fails then the pass- | ||
240 | word will be validated via any additional local mechanism such as | ||
241 | /etc/passwd. The default is ``yes''. | ||
242 | |||
243 | KerberosTicketCleanup | ||
244 | Specifies whether to automatically destroy the user's ticket | ||
245 | cache file on logout. The default is ``yes''. | ||
246 | |||
247 | KeyRegenerationInterval | ||
248 | In protocol version 1, the ephemeral server key is automatically | ||
249 | regenerated after this many seconds (if it has been used). The | ||
250 | purpose of regeneration is to prevent decrypting captured ses- | ||
251 | sions by later breaking into the machine and stealing the keys. | ||
252 | The key is never stored anywhere. If the value is 0, the key is | ||
253 | never regenerated. The default is 3600 (seconds). | ||
254 | |||
255 | ListenAddress | ||
256 | Specifies the local addresses sshd(8) should listen on. The fol- | ||
257 | lowing forms may be used: | ||
258 | |||
259 | ListenAddress host|IPv4_addr|IPv6_addr | ||
260 | ListenAddress host|IPv4_addr:port | ||
261 | ListenAddress [host|IPv6_addr]:port | ||
262 | |||
263 | If port is not specified, sshd will listen on the address and all | ||
264 | prior Port options specified. The default is to listen on all | ||
265 | local addresses. Multiple ListenAddress options are permitted. | ||
266 | Additionally, any Port options must precede this option for non- | ||
267 | port qualified addresses. | ||
268 | |||
269 | LoginGraceTime | ||
270 | The server disconnects after this time if the user has not suc- | ||
271 | cessfully logged in. If the value is 0, there is no time limit. | ||
272 | The default is 120 seconds. | ||
273 | |||
274 | LogLevel | ||
275 | Gives the verbosity level that is used when logging messages from | ||
276 | sshd(8). The possible values are: QUIET, FATAL, ERROR, INFO, | ||
277 | VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. | ||
278 | DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify | ||
279 | higher levels of debugging output. Logging with a DEBUG level | ||
280 | violates the privacy of users and is not recommended. | ||
281 | |||
282 | MACs Specifies the available MAC (message authentication code) algo- | ||
283 | rithms. The MAC algorithm is used in protocol version 2 for data | ||
284 | integrity protection. Multiple algorithms must be comma-separat- | ||
285 | ed. The default is: ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac- | ||
286 | sha1-96,hmac-md5-96''. | ||
287 | |||
288 | Match Introduces a conditional block. If all of the criteria on the | ||
289 | Match line are satisfied, the keywords on the following lines | ||
290 | override those set in the global section of the config file, un- | ||
291 | til either another Match line or the end of the file. The argu- | ||
292 | ments to Match are one or more criteria-pattern pairs. The | ||
293 | available criteria are User, Group, Host, and Address. Only a | ||
294 | subset of keywords may be used on the lines following a Match | ||
295 | keyword. Available keywords are AllowTcpForwarding, Banner, | ||
296 | ForceCommand, GatewayPorts, GSSApiAuthentication, | ||
297 | KbdInteractiveAuthentication, KerberosAuthentication, | ||
298 | PasswordAuthentication, PermitOpen, RhostsRSAAuthentication, | ||
299 | RSAAuthentication, X11DisplayOffset, X11Forwarding, and | ||
300 | X11UseLocalHost. | ||
301 | |||
302 | MaxAuthTries | ||
303 | Specifies the maximum number of authentication attempts permitted | ||
304 | per connection. Once the number of failures reaches half this | ||
305 | value, additional failures are logged. The default is 6. | ||
306 | |||
307 | MaxStartups | ||
308 | Specifies the maximum number of concurrent unauthenticated con- | ||
309 | nections to the SSH daemon. Additional connections will be | ||
310 | dropped until authentication succeeds or the LoginGraceTime ex- | ||
311 | pires for a connection. The default is 10. | ||
312 | |||
313 | Alternatively, random early drop can be enabled by specifying the | ||
314 | three colon separated values ``start:rate:full'' (e.g. | ||
315 | "10:30:60"). sshd(8) will refuse connection attempts with a | ||
316 | probability of ``rate/100'' (30%) if there are currently | ||
317 | ``start'' (10) unauthenticated connections. The probability in- | ||
318 | creases linearly and all connection attempts are refused if the | ||
319 | number of unauthenticated connections reaches ``full'' (60). | ||
320 | |||
321 | PasswordAuthentication | ||
322 | Specifies whether password authentication is allowed. The de- | ||
323 | fault is ``yes''. | ||
324 | |||
325 | PermitEmptyPasswords | ||
326 | When password authentication is allowed, it specifies whether the | ||
327 | server allows login to accounts with empty password strings. The | ||
328 | default is ``no''. | ||
329 | |||
330 | PermitOpen | ||
331 | Specifies the destinations to which TCP port forwarding is per- | ||
332 | mitted. The forwarding specification must be one of the follow- | ||
333 | ing forms: | ||
334 | |||
335 | PermitOpen host:port | ||
336 | PermitOpen IPv4_addr:port | ||
337 | PermitOpen [IPv6_addr]:port | ||
338 | |||
339 | Multiple forwards may be specified by separating them with | ||
340 | whitespace. An argument of ``any'' can be used to remove all re- | ||
341 | strictions and permit any forwarding requests. By default all | ||
342 | port forwarding requests are permitted. | ||
343 | |||
344 | PermitRootLogin | ||
345 | Specifies whether root can log in using ssh(1). The argument | ||
346 | must be ``yes'', ``without-password'', ``forced-commands-only'', | ||
347 | or ``no''. The default is ``yes''. | ||
348 | |||
349 | If this option is set to ``without-password'', password authenti- | ||
350 | cation is disabled for root. | ||
351 | |||
352 | If this option is set to ``forced-commands-only'', root login | ||
353 | with public key authentication will be allowed, but only if the | ||
354 | command option has been specified (which may be useful for taking | ||
355 | remote backups even if root login is normally not allowed). All | ||
356 | other authentication methods are disabled for root. | ||
357 | |||
358 | If this option is set to ``no'', root is not allowed to log in. | ||
359 | |||
360 | PermitTunnel | ||
361 | Specifies whether tun(4) device forwarding is allowed. The argu- | ||
362 | ment must be ``yes'', ``point-to-point'' (layer 3), ``ethernet'' | ||
363 | (layer 2), or ``no''. Specifying ``yes'' permits both ``point- | ||
364 | to-point'' and ``ethernet''. The default is ``no''. | ||
365 | |||
366 | PermitUserEnvironment | ||
367 | Specifies whether ~/.ssh/environment and environment= options in | ||
368 | ~/.ssh/authorized_keys are processed by sshd(8). The default is | ||
369 | ``no''. Enabling environment processing may enable users to by- | ||
370 | pass access restrictions in some configurations using mechanisms | ||
371 | such as LD_PRELOAD. | ||
372 | |||
373 | PidFile | ||
374 | Specifies the file that contains the process ID of the SSH dae- | ||
375 | mon. The default is /var/run/sshd.pid. | ||
376 | |||
377 | Port Specifies the port number that sshd(8) listens on. The default | ||
378 | is 22. Multiple options of this type are permitted. See also | ||
379 | ListenAddress. | ||
380 | |||
381 | PrintLastLog | ||
382 | Specifies whether sshd(8) should print the date and time of the | ||
383 | last user login when a user logs in interactively. The default | ||
384 | is ``yes''. | ||
385 | |||
386 | PrintMotd | ||
387 | Specifies whether sshd(8) should print /etc/motd when a user logs | ||
388 | in interactively. (On some systems it is also printed by the | ||
389 | shell, /etc/profile, or equivalent.) The default is ``yes''. | ||
390 | |||
391 | Protocol | ||
392 | Specifies the protocol versions sshd(8) supports. The possible | ||
393 | values are `1' and `2'. Multiple versions must be comma-separat- | ||
394 | ed. The default is ``2,1''. Note that the order of the protocol | ||
395 | list does not indicate preference, because the client selects | ||
396 | among multiple protocol versions offered by the server. Specify- | ||
397 | ing ``2,1'' is identical to ``1,2''. | ||
398 | |||
399 | PubkeyAuthentication | ||
400 | Specifies whether public key authentication is allowed. The de- | ||
401 | fault is ``yes''. Note that this option applies to protocol ver- | ||
402 | sion 2 only. | ||
403 | |||
404 | RhostsRSAAuthentication | ||
405 | Specifies whether rhosts or /etc/hosts.equiv authentication to- | ||
406 | gether with successful RSA host authentication is allowed. The | ||
407 | default is ``no''. This option applies to protocol version 1 on- | ||
408 | ly. | ||
409 | |||
410 | RSAAuthentication | ||
411 | Specifies whether pure RSA authentication is allowed. The de- | ||
412 | fault is ``yes''. This option applies to protocol version 1 on- | ||
413 | ly. | ||
414 | |||
415 | ServerKeyBits | ||
416 | Defines the number of bits in the ephemeral protocol version 1 | ||
417 | server key. The minimum value is 512, and the default is 768. | ||
418 | |||
419 | StrictModes | ||
420 | Specifies whether sshd(8) should check file modes and ownership | ||
421 | of the user's files and home directory before accepting login. | ||
422 | This is normally desirable because novices sometimes accidentally | ||
423 | leave their directory or files world-writable. The default is | ||
424 | ``yes''. | ||
425 | |||
426 | Subsystem | ||
427 | Configures an external subsystem (e.g. file transfer daemon). | ||
428 | Arguments should be a subsystem name and a command (with optional | ||
429 | arguments) to execute upon subsystem request. The command | ||
430 | sftp-server(8) implements the ``sftp'' file transfer subsystem. | ||
431 | By default no subsystems are defined. Note that this option ap- | ||
432 | plies to protocol version 2 only. | ||
433 | |||
434 | SyslogFacility | ||
435 | Gives the facility code that is used when logging messages from | ||
436 | sshd(8). The possible values are: DAEMON, USER, AUTH, LOCAL0, | ||
437 | LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The de- | ||
438 | fault is AUTH. | ||
439 | |||
440 | TCPKeepAlive | ||
441 | Specifies whether the system should send TCP keepalive messages | ||
442 | to the other side. If they are sent, death of the connection or | ||
443 | crash of one of the machines will be properly noticed. However, | ||
444 | this means that connections will die if the route is down tem- | ||
445 | porarily, and some people find it annoying. On the other hand, | ||
446 | if TCP keepalives are not sent, sessions may hang indefinitely on | ||
447 | the server, leaving ``ghost'' users and consuming server re- | ||
448 | sources. | ||
449 | |||
450 | The default is ``yes'' (to send TCP keepalive messages), and the | ||
451 | server will notice if the network goes down or the client host | ||
452 | crashes. This avoids infinitely hanging sessions. | ||
453 | |||
454 | To disable TCP keepalive messages, the value should be set to | ||
455 | ``no''. | ||
456 | |||
457 | UseDNS Specifies whether sshd(8) should look up the remote host name and | ||
458 | check that the resolved host name for the remote IP address maps | ||
459 | back to the very same IP address. The default is ``yes''. | ||
460 | |||
461 | UseLogin | ||
462 | Specifies whether login(1) is used for interactive login ses- | ||
463 | sions. The default is ``no''. Note that login(1) is never used | ||
464 | for remote command execution. Note also, that if this is en- | ||
465 | abled, X11Forwarding will be disabled because login(1) does not | ||
466 | know how to handle xauth(1) cookies. If UsePrivilegeSeparation | ||
467 | is specified, it will be disabled after authentication. | ||
468 | |||
469 | UsePAM Enables the Pluggable Authentication Module interface. If set to | ||
470 | ``yes'' this will enable PAM authentication using | ||
471 | ChallengeResponseAuthentication and PasswordAuthentication in ad- | ||
472 | dition to PAM account and session module processing for all au- | ||
473 | thentication types. | ||
474 | |||
475 | Because PAM challenge-response authentication usually serves an | ||
476 | equivalent role to password authentication, you should disable | ||
477 | either PasswordAuthentication or ChallengeResponseAuthentication. | ||
478 | |||
479 | If UsePAM is enabled, you will not be able to run sshd(8) as a | ||
480 | non-root user. The default is ``no''. | ||
481 | |||
482 | UsePrivilegeSeparation | ||
483 | Specifies whether sshd(8) separates privileges by creating an un- | ||
484 | privileged child process to deal with incoming network traffic. | ||
485 | After successful authentication, another process will be created | ||
486 | that has the privilege of the authenticated user. The goal of | ||
487 | privilege separation is to prevent privilege escalation by con- | ||
488 | taining any corruption within the unprivileged processes. The | ||
489 | default is ``yes''. | ||
490 | |||
491 | X11DisplayOffset | ||
492 | Specifies the first display number available for sshd(8)'s X11 | ||
493 | forwarding. This prevents sshd from interfering with real X11 | ||
494 | servers. The default is 10. | ||
495 | |||
496 | X11Forwarding | ||
497 | Specifies whether X11 forwarding is permitted. The argument must | ||
498 | be ``yes'' or ``no''. The default is ``no''. | ||
499 | |||
500 | When X11 forwarding is enabled, there may be additional exposure | ||
501 | to the server and to client displays if the sshd(8) proxy display | ||
502 | is configured to listen on the wildcard address (see | ||
503 | X11UseLocalhost below), though this is not the default. Addi- | ||
504 | tionally, the authentication spoofing and authentication data | ||
505 | verification and substitution occur on the client side. The se- | ||
506 | curity risk of using X11 forwarding is that the client's X11 dis- | ||
507 | play server may be exposed to attack when the SSH client requests | ||
508 | forwarding (see the warnings for ForwardX11 in ssh_config(5)). A | ||
509 | system administrator may have a stance in which they want to pro- | ||
510 | tect clients that may expose themselves to attack by unwittingly | ||
511 | requesting X11 forwarding, which can warrant a ``no'' setting. | ||
512 | |||
513 | Note that disabling X11 forwarding does not prevent users from | ||
514 | forwarding X11 traffic, as users can always install their own | ||
515 | forwarders. X11 forwarding is automatically disabled if UseLogin | ||
516 | is enabled. | ||
517 | |||
518 | X11UseLocalhost | ||
519 | Specifies whether sshd(8) should bind the X11 forwarding server | ||
520 | to the loopback address or to the wildcard address. By default, | ||
521 | sshd binds the forwarding server to the loopback address and sets | ||
522 | the hostname part of the DISPLAY environment variable to | ||
523 | ``localhost''. This prevents remote hosts from connecting to the | ||
524 | proxy display. However, some older X11 clients may not function | ||
525 | with this configuration. X11UseLocalhost may be set to ``no'' to | ||
526 | specify that the forwarding server should be bound to the wild- | ||
527 | card address. The argument must be ``yes'' or ``no''. The de- | ||
528 | fault is ``yes''. | ||
529 | |||
530 | XAuthLocation | ||
531 | Specifies the full pathname of the xauth(1) program. The default | ||
532 | is /usr/X11R6/bin/xauth. | ||
533 | |||
534 | TIME FORMATS | ||
535 | sshd(8) command-line arguments and configuration file options that speci- | ||
536 | fy time may be expressed using a sequence of the form: time[qualifier], | ||
537 | where time is a positive integer value and qualifier is one of the fol- | ||
538 | lowing: | ||
539 | |||
540 | <none> seconds | ||
541 | s | S seconds | ||
542 | m | M minutes | ||
543 | h | H hours | ||
544 | d | D days | ||
545 | w | W weeks | ||
546 | |||
547 | Each member of the sequence is added together to calculate the total time | ||
548 | value. | ||
549 | |||
550 | Time format examples: | ||
551 | |||
552 | 600 600 seconds (10 minutes) | ||
553 | 10m 10 minutes | ||
554 | 1h30m 1 hour 30 minutes (90 minutes) | ||
555 | |||
556 | FILES | ||
557 | /etc/ssh/sshd_config | ||
558 | Contains configuration data for sshd(8). This file should be | ||
559 | writable by root only, but it is recommended (though not neces- | ||
560 | sary) that it be world-readable. | ||
561 | |||
562 | SEE ALSO | ||
563 | sshd(8) | ||
564 | |||
565 | AUTHORS | ||
566 | OpenSSH is a derivative of the original and free ssh 1.2.12 release by | ||
567 | Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo | ||
568 | de Raadt and Dug Song removed many bugs, re-added newer features and cre- | ||
569 | ated OpenSSH. Markus Friedl contributed the support for SSH protocol | ||
570 | versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support | ||
571 | for privilege separation. | ||
572 | |||
573 | OpenBSD 4.1 September 25, 1999 9 | ||