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.0 | |
parent | 4ee72c71e31226c81743439fe1ed2b521b5ddb7e (diff) | |
parent | 3e2e0ac10674d77618c4c7339e18b83ced247492 (diff) |
Import OpenSSH 4.6p1.
Diffstat (limited to 'sshd.0')
-rw-r--r-- | sshd.0 | 544 |
1 files changed, 544 insertions, 0 deletions
@@ -0,0 +1,544 @@ | |||
1 | SSHD(8) OpenBSD System Manager's Manual SSHD(8) | ||
2 | |||
3 | NAME | ||
4 | sshd - OpenSSH SSH daemon | ||
5 | |||
6 | SYNOPSIS | ||
7 | sshd [-46Ddeiqt] [-b bits] [-f config_file] [-g login_grace_time] | ||
8 | [-h host_key_file] [-k key_gen_time] [-o option] [-p port] [-u len] | ||
9 | |||
10 | DESCRIPTION | ||
11 | sshd (OpenSSH Daemon) is the daemon program for ssh(1). Together these | ||
12 | programs replace rlogin and rsh, and provide secure encrypted communica- | ||
13 | tions between two untrusted hosts over an insecure network. | ||
14 | |||
15 | sshd listens for connections from clients. It is normally started at | ||
16 | boot from /etc/rc. It forks a new daemon for each incoming connection. | ||
17 | The forked daemons handle key exchange, encryption, authentication, com- | ||
18 | mand execution, and data exchange. | ||
19 | |||
20 | sshd can be configured using command-line options or a configuration file | ||
21 | (by default sshd_config(5)); command-line options override values speci- | ||
22 | fied in the configuration file. sshd rereads its configuration file when | ||
23 | it receives a hangup signal, SIGHUP, by executing itself with the name | ||
24 | and options it was started with, e.g. /usr/sbin/sshd. | ||
25 | |||
26 | The options are as follows: | ||
27 | |||
28 | -4 Forces sshd to use IPv4 addresses only. | ||
29 | |||
30 | -6 Forces sshd to use IPv6 addresses only. | ||
31 | |||
32 | -b bits | ||
33 | Specifies the number of bits in the ephemeral protocol version 1 | ||
34 | server key (default 768). | ||
35 | |||
36 | -D When this option is specified, sshd will not detach and does not | ||
37 | become a daemon. This allows easy monitoring of sshd. | ||
38 | |||
39 | -d Debug mode. The server sends verbose debug output to the system | ||
40 | log, and does not put itself in the background. The server also | ||
41 | will not fork and will only process one connection. This option | ||
42 | is only intended for debugging for the server. Multiple -d op- | ||
43 | tions increase the debugging level. Maximum is 3. | ||
44 | |||
45 | -e When this option is specified, sshd will send the output to the | ||
46 | standard error instead of the system log. | ||
47 | |||
48 | -f configuration_file | ||
49 | Specifies the name of the configuration file. The default is | ||
50 | /etc/ssh/sshd_config. sshd refuses to start if there is no con- | ||
51 | figuration file. | ||
52 | |||
53 | -g login_grace_time | ||
54 | Gives the grace time for clients to authenticate themselves (de- | ||
55 | fault 120 seconds). If the client fails to authenticate the user | ||
56 | within this many seconds, the server disconnects and exits. A | ||
57 | value of zero indicates no limit. | ||
58 | |||
59 | -h host_key_file | ||
60 | Specifies a file from which a host key is read. This option must | ||
61 | be given if sshd is not run as root (as the normal host key files | ||
62 | are normally not readable by anyone but root). The default is | ||
63 | /etc/ssh/ssh_host_key for protocol version 1, and | ||
64 | /etc/ssh/ssh_host_rsa_key and /etc/ssh/ssh_host_dsa_key for pro- | ||
65 | tocol version 2. It is possible to have multiple host key files | ||
66 | for the different protocol versions and host key algorithms. | ||
67 | |||
68 | -i Specifies that sshd is being run from inetd(8). sshd is normally | ||
69 | not run from inetd because it needs to generate the server key | ||
70 | before it can respond to the client, and this may take tens of | ||
71 | seconds. Clients would have to wait too long if the key was re- | ||
72 | generated every time. However, with small key sizes (e.g. 512) | ||
73 | using sshd from inetd may be feasible. | ||
74 | |||
75 | -k key_gen_time | ||
76 | Specifies how often the ephemeral protocol version 1 server key | ||
77 | is regenerated (default 3600 seconds, or one hour). The motiva- | ||
78 | tion for regenerating the key fairly often is that the key is not | ||
79 | stored anywhere, and after about an hour it becomes impossible to | ||
80 | recover the key for decrypting intercepted communications even if | ||
81 | the machine is cracked into or physically seized. A value of ze- | ||
82 | ro indicates that the key will never be regenerated. | ||
83 | |||
84 | -o option | ||
85 | Can be used to give options in the format used in the configura- | ||
86 | tion file. This is useful for specifying options for which there | ||
87 | is no separate command-line flag. For full details of the op- | ||
88 | tions, and their values, see sshd_config(5). | ||
89 | |||
90 | -p port | ||
91 | Specifies the port on which the server listens for connections | ||
92 | (default 22). Multiple port options are permitted. Ports speci- | ||
93 | fied in the configuration file with the Port option are ignored | ||
94 | when a command-line port is specified. Ports specified using the | ||
95 | ListenAddress option override command-line ports. | ||
96 | |||
97 | -q Quiet mode. Nothing is sent to the system log. Normally the be- | ||
98 | ginning, authentication, and termination of each connection is | ||
99 | logged. | ||
100 | |||
101 | -t Test mode. Only check the validity of the configuration file and | ||
102 | sanity of the keys. This is useful for updating sshd reliably as | ||
103 | configuration options may change. | ||
104 | |||
105 | -u len This option is used to specify the size of the field in the utmp | ||
106 | structure that holds the remote host name. If the resolved host | ||
107 | name is longer than len, the dotted decimal value will be used | ||
108 | instead. This allows hosts with very long host names that over- | ||
109 | flow this field to still be uniquely identified. Specifying -u0 | ||
110 | indicates that only dotted decimal addresses should be put into | ||
111 | the utmp file. -u0 may also be used to prevent sshd from making | ||
112 | DNS requests unless the authentication mechanism or configuration | ||
113 | requires it. Authentication mechanisms that may require DNS in- | ||
114 | clude RhostsRSAAuthentication, HostbasedAuthentication, and using | ||
115 | a from="pattern-list" option in a key file. Configuration op- | ||
116 | tions that require DNS include using a USER@HOST pattern in | ||
117 | AllowUsers or DenyUsers. | ||
118 | |||
119 | AUTHENTICATION | ||
120 | The OpenSSH SSH daemon supports SSH protocols 1 and 2. Both protocols | ||
121 | are supported by default, though this can be changed via the Protocol op- | ||
122 | tion in sshd_config(5). Protocol 2 supports both RSA and DSA keys; pro- | ||
123 | tocol 1 only supports RSA keys. For both protocols, each host has a | ||
124 | host-specific key, normally 2048 bits, used to identify the host. | ||
125 | |||
126 | Forward security for protocol 1 is provided through an additional server | ||
127 | key, normally 768 bits, generated when the server starts. This key is | ||
128 | normally regenerated every hour if it has been used, and is never stored | ||
129 | on disk. Whenever a client connects, the daemon responds with its public | ||
130 | host and server keys. The client compares the RSA host key against its | ||
131 | own database to verify that it has not changed. The client then gener- | ||
132 | ates a 256-bit random number. It encrypts this random number using both | ||
133 | the host key and the server key, and sends the encrypted number to the | ||
134 | server. Both sides then use this random number as a session key which is | ||
135 | used to encrypt all further communications in the session. The rest of | ||
136 | the session is encrypted using a conventional cipher, currently Blowfish | ||
137 | or 3DES, with 3DES being used by default. The client selects the encryp- | ||
138 | tion algorithm to use from those offered by the server. | ||
139 | |||
140 | For protocol 2, forward security is provided through a Diffie-Hellman key | ||
141 | agreement. This key agreement results in a shared session key. The rest | ||
142 | of the session is encrypted using a symmetric cipher, currently 128-bit | ||
143 | AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES. The | ||
144 | client selects the encryption algorithm to use from those offered by the | ||
145 | server. Additionally, session integrity is provided through a crypto- | ||
146 | graphic message authentication code (hmac-sha1 or hmac-md5). | ||
147 | |||
148 | Finally, the server and the client enter an authentication dialog. The | ||
149 | client tries to authenticate itself using host-based authentication, pub- | ||
150 | lic key authentication, challenge-response authentication, or password | ||
151 | authentication. | ||
152 | |||
153 | Regardless of the authentication type, the account is checked to ensure | ||
154 | that it is accessible. An account is not accessible if it is locked, | ||
155 | listed in DenyUsers or its group is listed in DenyGroups . The defini- | ||
156 | tion of a locked account is system dependant. Some platforms have their | ||
157 | own account database (eg AIX) and some modify the passwd field ( `*LK*' | ||
158 | on Solaris and UnixWare, `*' on HP-UX, containing `Nologin' on Tru64, a | ||
159 | leading `*LOCKED*' on FreeBSD and a leading `!!' on Linux). If there is | ||
160 | a requirement to disable password authentication for the account while | ||
161 | allowing still public-key, then the passwd field should be set to some- | ||
162 | thing other than these values (eg `NP' or `*NP*' ). | ||
163 | |||
164 | If the client successfully authenticates itself, a dialog for preparing | ||
165 | the session is entered. At this time the client may request things like | ||
166 | allocating a pseudo-tty, forwarding X11 connections, forwarding TCP con- | ||
167 | nections, or forwarding the authentication agent connection over the se- | ||
168 | cure channel. | ||
169 | |||
170 | After this, the client either requests a shell or execution of a command. | ||
171 | The sides then enter session mode. In this mode, either side may send | ||
172 | data at any time, and such data is forwarded to/from the shell or command | ||
173 | on the server side, and the user terminal in the client side. | ||
174 | |||
175 | When the user program terminates and all forwarded X11 and other connec- | ||
176 | tions have been closed, the server sends command exit status to the | ||
177 | client, and both sides exit. | ||
178 | |||
179 | LOGIN PROCESS | ||
180 | When a user successfully logs in, sshd does the following: | ||
181 | |||
182 | 1. If the login is on a tty, and no command has been specified, | ||
183 | prints last login time and /etc/motd (unless prevented in the | ||
184 | configuration file or by ~/.hushlogin; see the FILES section). | ||
185 | |||
186 | 2. If the login is on a tty, records login time. | ||
187 | |||
188 | 3. Checks /etc/nologin; if it exists, prints contents and quits | ||
189 | (unless root). | ||
190 | |||
191 | 4. Changes to run with normal user privileges. | ||
192 | |||
193 | 5. Sets up basic environment. | ||
194 | |||
195 | 6. Reads the file ~/.ssh/environment, if it exists, and users are | ||
196 | allowed to change their environment. See the | ||
197 | PermitUserEnvironment option in sshd_config(5). | ||
198 | |||
199 | 7. Changes to user's home directory. | ||
200 | |||
201 | 8. If ~/.ssh/rc exists, runs it; else if /etc/ssh/sshrc exists, | ||
202 | runs it; otherwise runs xauth. The ``rc'' files are given the | ||
203 | X11 authentication protocol and cookie in standard input. See | ||
204 | SSHRC, below. | ||
205 | |||
206 | 9. Runs user's shell or command. | ||
207 | |||
208 | SSHRC | ||
209 | If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment | ||
210 | files but before starting the user's shell or command. It must not pro- | ||
211 | duce any output on stdout; stderr must be used instead. If X11 forward- | ||
212 | ing is in use, it will receive the "proto cookie" pair in its standard | ||
213 | input (and DISPLAY in its environment). The script must call xauth(1) | ||
214 | because sshd will not run xauth automatically to add X11 cookies. | ||
215 | |||
216 | The primary purpose of this file is to run any initialization routines | ||
217 | which may be needed before the user's home directory becomes accessible; | ||
218 | AFS is a particular example of such an environment. | ||
219 | |||
220 | This file will probably contain some initialization code followed by | ||
221 | something similar to: | ||
222 | |||
223 | if read proto cookie && [ -n "$DISPLAY" ]; then | ||
224 | if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then | ||
225 | # X11UseLocalhost=yes | ||
226 | echo add unix:`echo $DISPLAY | | ||
227 | cut -c11-` $proto $cookie | ||
228 | else | ||
229 | # X11UseLocalhost=no | ||
230 | echo add $DISPLAY $proto $cookie | ||
231 | fi | xauth -q - | ||
232 | fi | ||
233 | |||
234 | If this file does not exist, /etc/ssh/sshrc is run, and if that does not | ||
235 | exist either, xauth is used to add the cookie. | ||
236 | |||
237 | AUTHORIZED_KEYS FILE FORMAT | ||
238 | AuthorizedKeysFile specifies the file containing public keys for public | ||
239 | key authentication; if none is specified, the default is | ||
240 | ~/.ssh/authorized_keys. Each line of the file contains one key (empty | ||
241 | lines and lines starting with a `#' are ignored as comments). Protocol 1 | ||
242 | public keys consist of the following space-separated fields: options, | ||
243 | bits, exponent, modulus, comment. Protocol 2 public key consist of: op- | ||
244 | tions, keytype, base64-encoded key, comment. The options field is op- | ||
245 | tional; its presence is determined by whether the line starts with a num- | ||
246 | ber or not (the options field never starts with a number). The bits, ex- | ||
247 | ponent, modulus, and comment fields give the RSA key for protocol version | ||
248 | 1; the comment field is not used for anything (but may be convenient for | ||
249 | the user to identify the key). For protocol version 2 the keytype is | ||
250 | ``ssh-dss'' or ``ssh-rsa''. | ||
251 | |||
252 | Note that lines in this file are usually several hundred bytes long (be- | ||
253 | cause of the size of the public key encoding) up to a limit of 8 kilo- | ||
254 | bytes, which permits DSA keys up to 8 kilobits and RSA keys up to 16 | ||
255 | kilobits. You don't want to type them in; instead, copy the | ||
256 | identity.pub, id_dsa.pub, or the id_rsa.pub file and edit it. | ||
257 | |||
258 | sshd enforces a minimum RSA key modulus size for protocol 1 and protocol | ||
259 | 2 keys of 768 bits. | ||
260 | |||
261 | The options (if present) consist of comma-separated option specifica- | ||
262 | tions. No spaces are permitted, except within double quotes. The fol- | ||
263 | lowing option specifications are supported (note that option keywords are | ||
264 | case-insensitive): | ||
265 | |||
266 | command="command" | ||
267 | Specifies that the command is executed whenever this key is used | ||
268 | for authentication. The command supplied by the user (if any) is | ||
269 | ignored. The command is run on a pty if the client requests a | ||
270 | pty; otherwise it is run without a tty. If an 8-bit clean chan- | ||
271 | nel is required, one must not request a pty or should specify no- | ||
272 | pty. A quote may be included in the command by quoting it with a | ||
273 | backslash. This option might be useful to restrict certain pub- | ||
274 | lic keys to perform just a specific operation. An example might | ||
275 | be a key that permits remote backups but nothing else. Note that | ||
276 | the client may specify TCP and/or X11 forwarding unless they are | ||
277 | explicitly prohibited. The command originally supplied by the | ||
278 | client is available in the SSH_ORIGINAL_COMMAND environment vari- | ||
279 | able. Note that this option applies to shell, command or subsys- | ||
280 | tem execution. | ||
281 | |||
282 | environment="NAME=value" | ||
283 | Specifies that the string is to be added to the environment when | ||
284 | logging in using this key. Environment variables set this way | ||
285 | override other default environment values. Multiple options of | ||
286 | this type are permitted. Environment processing is disabled by | ||
287 | default and is controlled via the PermitUserEnvironment option. | ||
288 | This option is automatically disabled if UseLogin is enabled. | ||
289 | |||
290 | from="pattern-list" | ||
291 | Specifies that in addition to public key authentication, the | ||
292 | canonical name of the remote host must be present in the comma- | ||
293 | separated list of patterns. The purpose of this option is to op- | ||
294 | tionally increase security: public key authentication by itself | ||
295 | does not trust the network or name servers or anything (but the | ||
296 | key); however, if somebody somehow steals the key, the key per- | ||
297 | mits an intruder to log in from anywhere in the world. This ad- | ||
298 | ditional option makes using a stolen key more difficult (name | ||
299 | servers and/or routers would have to be compromised in addition | ||
300 | to just the key). | ||
301 | |||
302 | See PATTERNS in ssh_config(5) for more information on patterns. | ||
303 | |||
304 | no-agent-forwarding | ||
305 | Forbids authentication agent forwarding when this key is used for | ||
306 | authentication. | ||
307 | |||
308 | no-port-forwarding | ||
309 | Forbids TCP forwarding when this key is used for authentication. | ||
310 | Any port forward requests by the client will return an error. | ||
311 | This might be used, e.g. in connection with the command option. | ||
312 | |||
313 | no-pty Prevents tty allocation (a request to allocate a pty will fail). | ||
314 | |||
315 | no-X11-forwarding | ||
316 | Forbids X11 forwarding when this key is used for authentication. | ||
317 | Any X11 forward requests by the client will return an error. | ||
318 | |||
319 | permitopen="host:port" | ||
320 | Limit local ``ssh -L'' port forwarding such that it may only con- | ||
321 | nect to the specified host and port. IPv6 addresses can be spec- | ||
322 | ified with an alternative syntax: host/port. Multiple permitopen | ||
323 | options may be applied separated by commas. No pattern matching | ||
324 | is performed on the specified hostnames, they must be literal do- | ||
325 | mains or addresses. | ||
326 | |||
327 | tunnel="n" | ||
328 | Force a tun(4) device on the server. Without this option, the | ||
329 | next available device will be used if the client requests a tun- | ||
330 | nel. | ||
331 | |||
332 | An example authorized_keys file: | ||
333 | |||
334 | # Comments allowed at start of line | ||
335 | ssh-rsa AAAAB3Nza...LiPk== user@example.net | ||
336 | from="*.sales.example.net,!pc.sales.example.net" ssh-rsa | ||
337 | AAAAB2...19Q== john@example.net | ||
338 | command="dump /home",no-pty,no-port-forwarding ssh-dss | ||
339 | AAAAC3...51R== example.net | ||
340 | permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss | ||
341 | AAAAB5...21S== | ||
342 | tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...== | ||
343 | jane@example.net | ||
344 | |||
345 | SSH_KNOWN_HOSTS FILE FORMAT | ||
346 | The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host | ||
347 | public keys for all known hosts. The global file should be prepared by | ||
348 | the administrator (optional), and the per-user file is maintained auto- | ||
349 | matically: whenever the user connects from an unknown host, its key is | ||
350 | added to the per-user file. | ||
351 | |||
352 | Each line in these files contains the following fields: hostnames, bits, | ||
353 | exponent, modulus, comment. The fields are separated by spaces. | ||
354 | |||
355 | Hostnames is a comma-separated list of patterns (`*' and `?' act as wild- | ||
356 | cards); each pattern in turn is matched against the canonical host name | ||
357 | (when authenticating a client) or against the user-supplied name (when | ||
358 | authenticating a server). A pattern may also be preceded by `!' to indi- | ||
359 | cate negation: if the host name matches a negated pattern, it is not ac- | ||
360 | cepted (by that line) even if it matched another pattern on the line. A | ||
361 | hostname or address may optionally be enclosed within `[' and `]' brack- | ||
362 | ets then followed by `:' and a non-standard port number. | ||
363 | |||
364 | Alternately, hostnames may be stored in a hashed form which hides host | ||
365 | names and addresses should the file's contents be disclosed. Hashed | ||
366 | hostnames start with a `|' character. Only one hashed hostname may ap- | ||
367 | pear on a single line and none of the above negation or wildcard opera- | ||
368 | tors may be applied. | ||
369 | |||
370 | Bits, exponent, and modulus are taken directly from the RSA host key; | ||
371 | they can be obtained, for example, from /etc/ssh/ssh_host_key.pub. The | ||
372 | optional comment field continues to the end of the line, and is not used. | ||
373 | |||
374 | Lines starting with `#' and empty lines are ignored as comments. | ||
375 | |||
376 | When performing host authentication, authentication is accepted if any | ||
377 | matching line has the proper key. It is thus permissible (but not recom- | ||
378 | mended) to have several lines or different host keys for the same names. | ||
379 | This will inevitably happen when short forms of host names from different | ||
380 | domains are put in the file. It is possible that the files contain con- | ||
381 | flicting information; authentication is accepted if valid information can | ||
382 | be found from either file. | ||
383 | |||
384 | Note that the lines in these files are typically hundreds of characters | ||
385 | long, and you definitely don't want to type in the host keys by hand. | ||
386 | Rather, generate them by a script or by taking /etc/ssh/ssh_host_key.pub | ||
387 | and adding the host names at the front. | ||
388 | |||
389 | An example ssh_known_hosts file: | ||
390 | |||
391 | # Comments allowed at start of line | ||
392 | closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net | ||
393 | cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....= | ||
394 | # A hashed hostname | ||
395 | |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa | ||
396 | AAAA1234.....= | ||
397 | |||
398 | FILES | ||
399 | ~/.hushlogin | ||
400 | This file is used to suppress printing the last login time and | ||
401 | /etc/motd, if PrintLastLog and PrintMotd, respectively, are en- | ||
402 | abled. It does not suppress printing of the banner specified by | ||
403 | Banner. | ||
404 | |||
405 | ~/.rhosts | ||
406 | This file is used for host-based authentication (see ssh(1) for | ||
407 | more information). On some machines this file may need to be | ||
408 | world-readable if the user's home directory is on an NFS parti- | ||
409 | tion, because sshd reads it as root. Additionally, this file | ||
410 | must be owned by the user, and must not have write permissions | ||
411 | for anyone else. The recommended permission for most machines is | ||
412 | read/write for the user, and not accessible by others. | ||
413 | |||
414 | ~/.shosts | ||
415 | This file is used in exactly the same way as .rhosts, but allows | ||
416 | host-based authentication without permitting login with | ||
417 | rlogin/rsh. | ||
418 | |||
419 | ~/.ssh/authorized_keys | ||
420 | Lists the public keys (RSA/DSA) that can be used for logging in | ||
421 | as this user. The format of this file is described above. The | ||
422 | content of the file is not highly sensitive, but the recommended | ||
423 | permissions are read/write for the user, and not accessible by | ||
424 | others. | ||
425 | |||
426 | If this file, the ~/.ssh directory, or the user's home directory | ||
427 | are writable by other users, then the file could be modified or | ||
428 | replaced by unauthorized users. In this case, sshd will not al- | ||
429 | low it to be used unless the StrictModes option has been set to | ||
430 | ``no''. The recommended permissions can be set by executing | ||
431 | ``chmod go-w ~/ ~/.ssh ~/.ssh/authorized_keys''. | ||
432 | |||
433 | ~/.ssh/environment | ||
434 | This file is read into the environment at login (if it exists). | ||
435 | It can only contain empty lines, comment lines (that start with | ||
436 | `#'), and assignment lines of the form name=value. The file | ||
437 | should be writable only by the user; it need not be readable by | ||
438 | anyone else. Environment processing is disabled by default and | ||
439 | is controlled via the PermitUserEnvironment option. | ||
440 | |||
441 | ~/.ssh/known_hosts | ||
442 | Contains a list of host keys for all hosts the user has logged | ||
443 | into that are not already in the systemwide list of known host | ||
444 | keys. The format of this file is described above. This file | ||
445 | should be writable only by root/the owner and can, but need not | ||
446 | be, world-readable. | ||
447 | |||
448 | ~/.ssh/rc | ||
449 | Contains initialization routines to be run before the user's home | ||
450 | directory becomes accessible. This file should be writable only | ||
451 | by the user, and need not be readable by anyone else. | ||
452 | |||
453 | /etc/hosts.allow | ||
454 | /etc/hosts.deny | ||
455 | Access controls that should be enforced by tcp-wrappers are de- | ||
456 | fined here. Further details are described in hosts_access(5). | ||
457 | |||
458 | /etc/hosts.equiv | ||
459 | This file is for host-based authentication (see ssh(1)). It | ||
460 | should only be writable by root. | ||
461 | |||
462 | /etc/moduli | ||
463 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group | ||
464 | Exchange". The file format is described in moduli(5). | ||
465 | |||
466 | /etc/motd | ||
467 | See motd(5). | ||
468 | |||
469 | /etc/nologin | ||
470 | If this file exists, sshd refuses to let anyone except root log | ||
471 | in. The contents of the file are displayed to anyone trying to | ||
472 | log in, and non-root connections are refused. The file should be | ||
473 | world-readable. | ||
474 | |||
475 | /etc/shosts.equiv | ||
476 | This file is used in exactly the same way as hosts.equiv, but al- | ||
477 | lows host-based authentication without permitting login with | ||
478 | rlogin/rsh. | ||
479 | |||
480 | /etc/ssh/ssh_known_hosts | ||
481 | Systemwide list of known host keys. This file should be prepared | ||
482 | by the system administrator to contain the public host keys of | ||
483 | all machines in the organization. The format of this file is de- | ||
484 | scribed above. This file should be writable only by root/the | ||
485 | owner and should be world-readable. | ||
486 | |||
487 | /etc/ssh/ssh_host_key | ||
488 | /etc/ssh/ssh_host_dsa_key | ||
489 | /etc/ssh/ssh_host_rsa_key | ||
490 | These three files contain the private parts of the host keys. | ||
491 | These files should only be owned by root, readable only by root, | ||
492 | and not accessible to others. Note that sshd does not start if | ||
493 | these files are group/world-accessible. | ||
494 | |||
495 | /etc/ssh/ssh_host_key.pub | ||
496 | /etc/ssh/ssh_host_dsa_key.pub | ||
497 | /etc/ssh/ssh_host_rsa_key.pub | ||
498 | These three files contain the public parts of the host keys. | ||
499 | These files should be world-readable but writable only by root. | ||
500 | Their contents should match the respective private parts. These | ||
501 | files are not really used for anything; they are provided for the | ||
502 | convenience of the user so their contents can be copied to known | ||
503 | hosts files. These files are created using ssh-keygen(1). | ||
504 | |||
505 | /etc/ssh/sshd_config | ||
506 | Contains configuration data for sshd. The file format and con- | ||
507 | figuration options are described in sshd_config(5). | ||
508 | |||
509 | /etc/ssh/sshrc | ||
510 | Similar to ~/.ssh/rc, it can be used to specify machine-specific | ||
511 | login-time initializations globally. This file should be | ||
512 | writable only by root, and should be world-readable. | ||
513 | |||
514 | /var/empty | ||
515 | chroot(2) directory used by sshd during privilege separation in | ||
516 | the pre-authentication phase. The directory should not contain | ||
517 | any files and must be owned by root and not group or world- | ||
518 | writable. | ||
519 | |||
520 | /var/run/sshd.pid | ||
521 | Contains the process ID of the sshd listening for connections (if | ||
522 | there are several daemons running concurrently for different | ||
523 | ports, this contains the process ID of the one started last). | ||
524 | The content of this file is not sensitive; it can be world-read- | ||
525 | able. | ||
526 | |||
527 | SEE ALSO | ||
528 | scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), | ||
529 | chroot(2), hosts_access(5), login.conf(5), moduli(5), sshd_config(5), | ||
530 | inetd(8), sftp-server(8) | ||
531 | |||
532 | AUTHORS | ||
533 | OpenSSH is a derivative of the original and free ssh 1.2.12 release by | ||
534 | Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo | ||
535 | de Raadt and Dug Song removed many bugs, re-added newer features and cre- | ||
536 | ated OpenSSH. Markus Friedl contributed the support for SSH protocol | ||
537 | versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support | ||
538 | for privilege separation. | ||
539 | |||
540 | CAVEATS | ||
541 | System security is not improved unless rshd, rlogind, and rexecd are dis- | ||
542 | abled (thus completely disabling rlogin and rsh into the machine). | ||
543 | |||
544 | OpenBSD 4.1 September 25, 1999 9 | ||