diff options
author | Colin Watson <cjwatson@debian.org> | 2003-09-17 01:19:29 +0000 |
---|---|---|
committer | Colin Watson <cjwatson@debian.org> | 2003-09-17 01:19:29 +0000 |
commit | 9221adce6959801664fd4a340c19e6b69107ad0b (patch) | |
tree | e8b7b5706043a4eb66e0e41aad2a7986cbedeb0f /sshd.0 | |
parent | ade1cee573c0897cd08987dc14e23a555898cd12 (diff) | |
parent | 22f9b945efa61bba12a4778b889df07cf851838a (diff) |
Import OpenSSH 3.7.1p1.
Diffstat (limited to 'sshd.0')
-rw-r--r-- | sshd.0 | 556 |
1 files changed, 556 insertions, 0 deletions
@@ -0,0 +1,556 @@ | |||
1 | SSHD(8) OpenBSD System Manager's Manual SSHD(8) | ||
2 | |||
3 | NAME | ||
4 | sshd - OpenSSH SSH daemon | ||
5 | |||
6 | SYNOPSIS | ||
7 | sshd [-deiqtD46] [-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 (SSH Daemon) is the daemon program for ssh(1). Together these pro- | ||
12 | grams replace rlogin and rsh, and provide secure encrypted communications | ||
13 | between two untrusted hosts over an insecure network. The programs are | ||
14 | intended to be as easy to install and use as possible. | ||
15 | |||
16 | sshd is the daemon that listens for connections from clients. It is nor- | ||
17 | mally started at boot from /etc/rc. It forks a new daemon for each in- | ||
18 | coming connection. The forked daemons handle key exchange, encryption, | ||
19 | authentication, command execution, and data exchange. This implementa- | ||
20 | tion of sshd supports both SSH protocol version 1 and 2 simultaneously. | ||
21 | sshd works as follows: | ||
22 | |||
23 | SSH protocol version 1 | ||
24 | |||
25 | Each host has a host-specific RSA key (normally 1024 bits) used to iden- | ||
26 | tify the host. Additionally, when the daemon starts, it generates a | ||
27 | server RSA key (normally 768 bits). This key is normally regenerated ev- | ||
28 | ery hour if it has been used, and is never stored on disk. | ||
29 | |||
30 | Whenever a client connects, the daemon responds with its public host and | ||
31 | server keys. The client compares the RSA host key against its own | ||
32 | database to verify that it has not changed. The client then generates a | ||
33 | 256 bit random number. It encrypts this random number using both the | ||
34 | host key and the server key, and sends the encrypted number to the serv- | ||
35 | er. Both sides then use this random number as a session key which is | ||
36 | used to encrypt all further communications in the session. The rest of | ||
37 | the session is encrypted using a conventional cipher, currently Blowfish | ||
38 | or 3DES, with 3DES being used by default. The client selects the encryp- | ||
39 | tion algorithm to use from those offered by the server. | ||
40 | |||
41 | Next, the server and the client enter an authentication dialog. The | ||
42 | client tries to authenticate itself using .rhosts authentication, .rhosts | ||
43 | authentication combined with RSA host authentication, RSA challenge-re- | ||
44 | sponse authentication, or password based authentication. | ||
45 | |||
46 | Regardless of the authentication type, the account is checked to ensure | ||
47 | that it is accessible. An account is not accessible if it is locked, | ||
48 | listed in DenyUsers or its group is listed in DenyGroups . The defini- | ||
49 | tion of a locked account is system dependant. Some platforms have their | ||
50 | own account database (eg AIX) and some modify the passwd field ( `*LK*' | ||
51 | on Solaris, `*' on HP-UX, containing `Nologin' on Tru64 and a leading | ||
52 | `!!' on Linux). If there is a requirement to disable password authenti- | ||
53 | cation for the account while allowing still public-key, then the passwd | ||
54 | field should be set to something other than these values (eg `NP' or | ||
55 | `*NP*' ). | ||
56 | |||
57 | Rhosts authentication is normally disabled because it is fundamentally | ||
58 | insecure, but can be enabled in the server configuration file if desired. | ||
59 | System security is not improved unless rshd, rlogind, and rexecd are dis- | ||
60 | abled (thus completely disabling rlogin and rsh into the machine). | ||
61 | |||
62 | SSH protocol version 2 | ||
63 | |||
64 | Version 2 works similarly: Each host has a host-specific key (RSA or DSA) | ||
65 | used to identify the host. However, when the daemon starts, it does not | ||
66 | generate a server key. Forward security is provided through a Diffie- | ||
67 | Hellman key agreement. This key agreement results in a shared session | ||
68 | key. | ||
69 | |||
70 | The rest of the session is encrypted using a symmetric cipher, currently | ||
71 | 128 bit AES, Blowfish, 3DES, CAST128, Arcfour, 192 bit AES, or 256 bit | ||
72 | AES. The client selects the encryption algorithm to use from those of- | ||
73 | fered by the server. Additionally, session integrity is provided through | ||
74 | a cryptographic message authentication code (hmac-sha1 or hmac-md5). | ||
75 | |||
76 | Protocol version 2 provides a public key based user (PubkeyAuthentica- | ||
77 | tion) or client host (HostbasedAuthentication) authentication method, | ||
78 | conventional password authentication and challenge response based meth- | ||
79 | ods. | ||
80 | |||
81 | Command execution and data forwarding | ||
82 | |||
83 | If the client successfully authenticates itself, a dialog for preparing | ||
84 | the session is entered. At this time the client may request things like | ||
85 | allocating a pseudo-tty, forwarding X11 connections, forwarding TCP/IP | ||
86 | connections, or forwarding the authentication agent connection over the | ||
87 | secure channel. | ||
88 | |||
89 | Finally, the client either requests a shell or execution of a command. | ||
90 | The sides then enter session mode. In this mode, either side may send | ||
91 | data at any time, and such data is forwarded to/from the shell or command | ||
92 | on the server side, and the user terminal in the client side. | ||
93 | |||
94 | When the user program terminates and all forwarded X11 and other connec- | ||
95 | tions have been closed, the server sends command exit status to the | ||
96 | client, and both sides exit. | ||
97 | |||
98 | sshd can be configured using command-line options or a configuration | ||
99 | file. Command-line options override values specified in the configura- | ||
100 | tion file. | ||
101 | |||
102 | sshd rereads its configuration file when it receives a hangup signal, | ||
103 | SIGHUP, by executing itself with the name it was started as, i.e., | ||
104 | /usr/sbin/sshd. | ||
105 | |||
106 | The options are as follows: | ||
107 | |||
108 | -b bits | ||
109 | Specifies the number of bits in the ephemeral protocol version 1 | ||
110 | server key (default 768). | ||
111 | |||
112 | -d Debug mode. The server sends verbose debug output to the system | ||
113 | log, and does not put itself in the background. The server also | ||
114 | will not fork and will only process one connection. This option | ||
115 | is only intended for debugging for the server. Multiple -d op- | ||
116 | tions increase the debugging level. Maximum is 3. | ||
117 | |||
118 | -e When this option is specified, sshd will send the output to the | ||
119 | standard error instead of the system log. | ||
120 | |||
121 | -f configuration_file | ||
122 | Specifies the name of the configuration file. The default is | ||
123 | /etc/ssh/sshd_config. sshd refuses to start if there is no con- | ||
124 | figuration file. | ||
125 | |||
126 | -g login_grace_time | ||
127 | Gives the grace time for clients to authenticate themselves (de- | ||
128 | fault 120 seconds). If the client fails to authenticate the user | ||
129 | within this many seconds, the server disconnects and exits. A | ||
130 | value of zero indicates no limit. | ||
131 | |||
132 | -h host_key_file | ||
133 | Specifies a file from which a host key is read. This option must | ||
134 | be given if sshd is not run as root (as the normal host key files | ||
135 | are normally not readable by anyone but root). The default is | ||
136 | /etc/ssh/ssh_host_key for protocol version 1, and | ||
137 | /etc/ssh/ssh_host_rsa_key and /etc/ssh/ssh_host_dsa_key for pro- | ||
138 | tocol version 2. It is possible to have multiple host key files | ||
139 | for the different protocol versions and host key algorithms. | ||
140 | |||
141 | -i Specifies that sshd is being run from inetd(8). sshd is normally | ||
142 | not run from inetd because it needs to generate the server key | ||
143 | before it can respond to the client, and this may take tens of | ||
144 | seconds. Clients would have to wait too long if the key was re- | ||
145 | generated every time. However, with small key sizes (e.g., 512) | ||
146 | using sshd from inetd may be feasible. | ||
147 | |||
148 | -k key_gen_time | ||
149 | Specifies how often the ephemeral protocol version 1 server key | ||
150 | is regenerated (default 3600 seconds, or one hour). The motiva- | ||
151 | tion for regenerating the key fairly often is that the key is not | ||
152 | stored anywhere, and after about an hour, it becomes impossible | ||
153 | to recover the key for decrypting intercepted communications even | ||
154 | if the machine is cracked into or physically seized. A value of | ||
155 | zero indicates that the key will never be regenerated. | ||
156 | |||
157 | -o option | ||
158 | Can be used to give options in the format used in the configura- | ||
159 | tion file. This is useful for specifying options for which there | ||
160 | is no separate command-line flag. | ||
161 | |||
162 | -p port | ||
163 | Specifies the port on which the server listens for connections | ||
164 | (default 22). Multiple port options are permitted. Ports speci- | ||
165 | fied in the configuration file are ignored when a command-line | ||
166 | port is specified. | ||
167 | |||
168 | -q Quiet mode. Nothing is sent to the system log. Normally the be- | ||
169 | ginning, authentication, and termination of each connection is | ||
170 | logged. | ||
171 | |||
172 | -t Test mode. Only check the validity of the configuration file and | ||
173 | sanity of the keys. This is useful for updating sshd reliably as | ||
174 | configuration options may change. | ||
175 | |||
176 | -u len This option is used to specify the size of the field in the utmp | ||
177 | structure that holds the remote host name. If the resolved host | ||
178 | name is longer than len, the dotted decimal value will be used | ||
179 | instead. This allows hosts with very long host names that over- | ||
180 | flow this field to still be uniquely identified. Specifying -u0 | ||
181 | indicates that only dotted decimal addresses should be put into | ||
182 | the utmp file. -u0 may also be used to prevent sshd from making | ||
183 | DNS requests unless the authentication mechanism or configuration | ||
184 | requires it. Authentication mechanisms that may require DNS in- | ||
185 | clude RhostsRSAAuthentication, HostbasedAuthentication and using | ||
186 | a from="pattern-list" option in a key file. Configuration op- | ||
187 | tions that require DNS include using a USER@HOST pattern in | ||
188 | AllowUsers or DenyUsers. | ||
189 | |||
190 | -D When this option is specified sshd will not detach and does not | ||
191 | become a daemon. This allows easy monitoring of sshd. | ||
192 | |||
193 | -4 Forces sshd to use IPv4 addresses only. | ||
194 | |||
195 | -6 Forces sshd to use IPv6 addresses only. | ||
196 | |||
197 | CONFIGURATION FILE | ||
198 | sshd reads configuration data from /etc/ssh/sshd_config (or the file | ||
199 | specified with -f on the command line). The file format and configura- | ||
200 | tion options are described in sshd_config(5). | ||
201 | |||
202 | LOGIN PROCESS | ||
203 | When a user successfully logs in, sshd does the following: | ||
204 | |||
205 | 1. If the login is on a tty, and no command has been specified, | ||
206 | prints last login time and /etc/motd (unless prevented in the | ||
207 | configuration file or by $HOME/.hushlogin; see the FILES sec- | ||
208 | tion). | ||
209 | |||
210 | 2. If the login is on a tty, records login time. | ||
211 | |||
212 | 3. Checks /etc/nologin; if it exists, prints contents and quits | ||
213 | (unless root). | ||
214 | |||
215 | 4. Changes to run with normal user privileges. | ||
216 | |||
217 | 5. Sets up basic environment. | ||
218 | |||
219 | 6. Reads $HOME/.ssh/environment if it exists and users are al- | ||
220 | lowed to change their environment. See the | ||
221 | PermitUserEnvironment option in sshd_config(5). | ||
222 | |||
223 | 7. Changes to user's home directory. | ||
224 | |||
225 | 8. If $HOME/.ssh/rc exists, runs it; else if /etc/ssh/sshrc ex- | ||
226 | ists, runs it; otherwise runs xauth. The ``rc'' files are | ||
227 | given the X11 authentication protocol and cookie in standard | ||
228 | input. | ||
229 | |||
230 | 9. Runs user's shell or command. | ||
231 | |||
232 | AUTHORIZED_KEYS FILE FORMAT | ||
233 | $HOME/.ssh/authorized_keys is the default file that lists the public keys | ||
234 | that are permitted for RSA authentication in protocol version 1 and for | ||
235 | public key authentication (PubkeyAuthentication) in protocol version 2. | ||
236 | AuthorizedKeysFile may be used to specify an alternative file. | ||
237 | |||
238 | Each line of the file contains one key (empty lines and lines starting | ||
239 | with a `#' are ignored as comments). Each RSA public key consists of the | ||
240 | following fields, separated by spaces: options, bits, exponent, modulus, | ||
241 | comment. Each protocol version 2 public key consists of: options, key- | ||
242 | type, base64 encoded key, comment. The options field is optional; its | ||
243 | presence is determined by whether the line starts with a number or not | ||
244 | (the options field never starts with a number). The bits, exponent, mod- | ||
245 | ulus and comment fields give the RSA key for protocol version 1; the com- | ||
246 | ment field is not used for anything (but may be convenient for the user | ||
247 | to identify the key). For protocol version 2 the keytype is ``ssh-dss'' | ||
248 | or ``ssh-rsa''. | ||
249 | |||
250 | Note that lines in this file are usually several hundred bytes long (be- | ||
251 | cause of the size of the public key encoding). You don't want to type | ||
252 | them in; instead, copy the identity.pub, id_dsa.pub or the id_rsa.pub | ||
253 | file and edit it. | ||
254 | |||
255 | sshd enforces a minimum RSA key modulus size for protocol 1 and protocol | ||
256 | 2 keys of 768 bits. | ||
257 | |||
258 | The options (if present) consist of comma-separated option specifica- | ||
259 | tions. No spaces are permitted, except within double quotes. The fol- | ||
260 | lowing option specifications are supported (note that option keywords are | ||
261 | case-insensitive): | ||
262 | |||
263 | from="pattern-list" | ||
264 | Specifies that in addition to public key authentication, the | ||
265 | canonical name of the remote host must be present in the comma- | ||
266 | separated list of patterns (`*' and `?' serve as wildcards). The | ||
267 | list may also contain patterns negated by prefixing them with | ||
268 | `!'; if the canonical host name matches a negated pattern, the | ||
269 | key is not accepted. The purpose of this option is to optionally | ||
270 | increase security: public key authentication by itself does not | ||
271 | trust the network or name servers or anything (but the key); how- | ||
272 | ever, if somebody somehow steals the key, the key permits an in- | ||
273 | truder to log in from anywhere in the world. This additional op- | ||
274 | tion makes using a stolen key more difficult (name servers and/or | ||
275 | routers would have to be compromised in addition to just the | ||
276 | key). | ||
277 | |||
278 | command="command" | ||
279 | Specifies that the command is executed whenever this key is used | ||
280 | for authentication. The command supplied by the user (if any) is | ||
281 | ignored. The command is run on a pty if the client requests a | ||
282 | pty; otherwise it is run without a tty. If an 8-bit clean chan- | ||
283 | nel is required, one must not request a pty or should specify no- | ||
284 | pty. A quote may be included in the command by quoting it with a | ||
285 | backslash. This option might be useful to restrict certain pub- | ||
286 | lic keys to perform just a specific operation. An example might | ||
287 | be a key that permits remote backups but nothing else. Note that | ||
288 | the client may specify TCP/IP and/or X11 forwarding unless they | ||
289 | are explicitly prohibited. Note that this option applies to | ||
290 | shell, command or subsystem execution. | ||
291 | |||
292 | environment="NAME=value" | ||
293 | Specifies that the string is to be added to the environment when | ||
294 | logging in using this key. Environment variables set this way | ||
295 | override other default environment values. Multiple options of | ||
296 | this type are permitted. Environment processing is disabled by | ||
297 | default and is controlled via the PermitUserEnvironment option. | ||
298 | This option is automatically disabled if UseLogin is enabled. | ||
299 | |||
300 | no-port-forwarding | ||
301 | Forbids TCP/IP forwarding when this key is used for authentica- | ||
302 | tion. Any port forward requests by the client will return an er- | ||
303 | ror. This might be used, e.g., in connection with the command | ||
304 | option. | ||
305 | |||
306 | no-X11-forwarding | ||
307 | Forbids X11 forwarding when this key is used for authentication. | ||
308 | Any X11 forward requests by the client will return an error. | ||
309 | |||
310 | no-agent-forwarding | ||
311 | Forbids authentication agent forwarding when this key is used for | ||
312 | authentication. | ||
313 | |||
314 | no-pty Prevents tty allocation (a request to allocate a pty will fail). | ||
315 | |||
316 | permitopen="host:port" | ||
317 | Limit local ``ssh -L'' port forwarding such that it may only con- | ||
318 | nect to the specified host and port. IPv6 addresses can be spec- | ||
319 | ified with an alternative syntax: host/port. Multiple permitopen | ||
320 | options may be applied separated by commas. No pattern matching | ||
321 | is performed on the specified hostnames, they must be literal do- | ||
322 | mains or addresses. | ||
323 | |||
324 | Examples | ||
325 | 1024 33 12121...312314325 ylo@foo.bar | ||
326 | |||
327 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23...2334 ylo@niksula | ||
328 | |||
329 | command="dump /home",no-pty,no-port-forwarding 1024 33 23...2323 back- | ||
330 | up.hut.fi | ||
331 | |||
332 | permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23...2323 | ||
333 | |||
334 | SSH_KNOWN_HOSTS FILE FORMAT | ||
335 | The /etc/ssh/ssh_known_hosts and $HOME/.ssh/known_hosts files contain | ||
336 | host public keys for all known hosts. The global file should be prepared | ||
337 | by the administrator (optional), and the per-user file is maintained au- | ||
338 | tomatically: whenever the user connects from an unknown host its key is | ||
339 | added to the per-user file. | ||
340 | |||
341 | Each line in these files contains the following fields: hostnames, bits, | ||
342 | exponent, modulus, comment. The fields are separated by spaces. | ||
343 | |||
344 | Hostnames is a comma-separated list of patterns (`*' and `?' act as wild- | ||
345 | cards); each pattern in turn is matched against the canonical host name | ||
346 | (when authenticating a client) or against the user-supplied name (when | ||
347 | authenticating a server). A pattern may also be preceded by `!' to indi- | ||
348 | cate negation: if the host name matches a negated pattern, it is not ac- | ||
349 | cepted (by that line) even if it matched another pattern on the line. | ||
350 | |||
351 | Bits, exponent, and modulus are taken directly from the RSA host key; | ||
352 | they can be obtained, e.g., from /etc/ssh/ssh_host_key.pub. The optional | ||
353 | comment field continues to the end of the line, and is not used. | ||
354 | |||
355 | Lines starting with `#' and empty lines are ignored as comments. | ||
356 | |||
357 | When performing host authentication, authentication is accepted if any | ||
358 | matching line has the proper key. It is thus permissible (but not recom- | ||
359 | mended) to have several lines or different host keys for the same names. | ||
360 | This will inevitably happen when short forms of host names from different | ||
361 | domains are put in the file. It is possible that the files contain con- | ||
362 | flicting information; authentication is accepted if valid information can | ||
363 | be found from either file. | ||
364 | |||
365 | Note that the lines in these files are typically hundreds of characters | ||
366 | long, and you definitely don't want to type in the host keys by hand. | ||
367 | Rather, generate them by a script or by taking /etc/ssh/ssh_host_key.pub | ||
368 | and adding the host names at the front. | ||
369 | |||
370 | Examples | ||
371 | |||
372 | closenet,...,130.233.208.41 1024 37 159...93 closenet.hut.fi | ||
373 | cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....= | ||
374 | |||
375 | FILES | ||
376 | /etc/ssh/sshd_config | ||
377 | Contains configuration data for sshd. The file format and con- | ||
378 | figuration options are described in sshd_config(5). | ||
379 | |||
380 | /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, | ||
381 | /etc/ssh/ssh_host_rsa_key | ||
382 | These three files contain the private parts of the host keys. | ||
383 | These files should only be owned by root, readable only by root, | ||
384 | and not accessible to others. Note that sshd does not start if | ||
385 | this file is group/world-accessible. | ||
386 | |||
387 | /etc/ssh/ssh_host_key.pub, /etc/ssh/ssh_host_dsa_key.pub, | ||
388 | /etc/ssh/ssh_host_rsa_key.pub | ||
389 | These three files contain the public parts of the host keys. | ||
390 | These files should be world-readable but writable only by root. | ||
391 | Their contents should match the respective private parts. These | ||
392 | files are not really used for anything; they are provided for the | ||
393 | convenience of the user so their contents can be copied to known | ||
394 | hosts files. These files are created using ssh-keygen(1). | ||
395 | |||
396 | /etc/moduli | ||
397 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group | ||
398 | Exchange". The file format is described in moduli(5). | ||
399 | |||
400 | /var/empty | ||
401 | chroot(2) directory used by sshd during privilege separation in | ||
402 | the pre-authentication phase. The directory should not contain | ||
403 | any files and must be owned by root and not group or world- | ||
404 | writable. | ||
405 | |||
406 | /var/run/sshd.pid | ||
407 | Contains the process ID of the sshd listening for connections (if | ||
408 | there are several daemons running concurrently for different | ||
409 | ports, this contains the process ID of the one started last). | ||
410 | The content of this file is not sensitive; it can be world-read- | ||
411 | able. | ||
412 | |||
413 | $HOME/.ssh/authorized_keys | ||
414 | Lists the public keys (RSA or DSA) that can be used to log into | ||
415 | the user's account. This file must be readable by root (which | ||
416 | may on some machines imply it being world-readable if the user's | ||
417 | home directory resides on an NFS volume). It is recommended that | ||
418 | it not be accessible by others. The format of this file is de- | ||
419 | scribed above. Users will place the contents of their | ||
420 | identity.pub, id_dsa.pub and/or id_rsa.pub files into this file, | ||
421 | as described in ssh-keygen(1). | ||
422 | |||
423 | /etc/ssh/ssh_known_hosts and $HOME/.ssh/known_hosts | ||
424 | These files are consulted when using rhosts with RSA host authen- | ||
425 | tication or protocol version 2 hostbased authentication to check | ||
426 | the public key of the host. The key must be listed in one of | ||
427 | these files to be accepted. The client uses the same files to | ||
428 | verify that it is connecting to the correct remote host. These | ||
429 | files should be writable only by root/the owner. | ||
430 | /etc/ssh/ssh_known_hosts should be world-readable, and | ||
431 | $HOME/.ssh/known_hosts can, but need not be, world-readable. | ||
432 | |||
433 | /etc/nologin | ||
434 | If this file exists, sshd refuses to let anyone except root log | ||
435 | in. The contents of the file are displayed to anyone trying to | ||
436 | log in, and non-root connections are refused. The file should be | ||
437 | world-readable. | ||
438 | |||
439 | /etc/hosts.allow, /etc/hosts.deny | ||
440 | Access controls that should be enforced by tcp-wrappers are de- | ||
441 | fined here. Further details are described in hosts_access(5). | ||
442 | |||
443 | $HOME/.rhosts | ||
444 | This file contains host-username pairs, separated by a space, one | ||
445 | per line. The given user on the corresponding host is permitted | ||
446 | to log in without a password. The same file is used by rlogind | ||
447 | and rshd. The file must be writable only by the user; it is rec- | ||
448 | ommended that it not be accessible by others. | ||
449 | |||
450 | If is also possible to use netgroups in the file. Either host or | ||
451 | user name may be of the form +@groupname to specify all hosts or | ||
452 | all users in the group. | ||
453 | |||
454 | $HOME/.shosts | ||
455 | For ssh, this file is exactly the same as for .rhosts. However, | ||
456 | this file is not used by rlogin and rshd, so using this permits | ||
457 | access using SSH only. | ||
458 | |||
459 | /etc/hosts.equiv | ||
460 | This file is used during .rhosts authentication. In the simplest | ||
461 | form, this file contains host names, one per line. Users on | ||
462 | those hosts are permitted to log in without a password, provided | ||
463 | they have the same user name on both machines. The host name may | ||
464 | also be followed by a user name; such users are permitted to log | ||
465 | in as any user on this machine (except root). Additionally, the | ||
466 | syntax ``+@group'' can be used to specify netgroups. Negated en- | ||
467 | tries start with `-'. | ||
468 | |||
469 | If the client host/user is successfully matched in this file, lo- | ||
470 | gin is automatically permitted provided the client and server us- | ||
471 | er names are the same. Additionally, successful RSA host authen- | ||
472 | tication is normally required. This file must be writable only | ||
473 | by root; it is recommended that it be world-readable. | ||
474 | |||
475 | Warning: It is almost never a good idea to use user names in | ||
476 | hosts.equiv. Beware that it really means that the named user(s) | ||
477 | can log in as anybody, which includes bin, daemon, adm, and other | ||
478 | accounts that own critical binaries and directories. Using a us- | ||
479 | er name practically grants the user root access. The only valid | ||
480 | use for user names that I can think of is in negative entries. | ||
481 | |||
482 | Note that this warning also applies to rsh/rlogin. | ||
483 | |||
484 | /etc/shosts.equiv | ||
485 | This is processed exactly as /etc/hosts.equiv. However, this | ||
486 | file may be useful in environments that want to run both | ||
487 | rsh/rlogin and ssh. | ||
488 | |||
489 | $HOME/.ssh/environment | ||
490 | This file is read into the environment at login (if it exists). | ||
491 | It can only contain empty lines, comment lines (that start with | ||
492 | `#'), and assignment lines of the form name=value. The file | ||
493 | should be writable only by the user; it need not be readable by | ||
494 | anyone else. Environment processing is disabled by default and | ||
495 | is controlled via the PermitUserEnvironment option. | ||
496 | |||
497 | $HOME/.ssh/rc | ||
498 | If this file exists, it is run with /bin/sh after reading the en- | ||
499 | vironment files but before starting the user's shell or command. | ||
500 | It must not produce any output on stdout; stderr must be used in- | ||
501 | stead. If X11 forwarding is in use, it will receive the "proto | ||
502 | cookie" pair in its standard input (and DISPLAY in its environ- | ||
503 | ment). The script must call xauth(1) because sshd will not run | ||
504 | xauth automatically to add X11 cookies. | ||
505 | |||
506 | The primary purpose of this file is to run any initialization | ||
507 | routines which may be needed before the user's home directory be- | ||
508 | comes accessible; AFS is a particular example of such an environ- | ||
509 | ment. | ||
510 | |||
511 | This file will probably contain some initialization code followed | ||
512 | by something similar to: | ||
513 | |||
514 | if read proto cookie && [ -n "$DISPLAY" ]; then | ||
515 | if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then | ||
516 | # X11UseLocalhost=yes | ||
517 | echo add unix:`echo $DISPLAY | | ||
518 | cut -c11-` $proto $cookie | ||
519 | else | ||
520 | # X11UseLocalhost=no | ||
521 | echo add $DISPLAY $proto $cookie | ||
522 | fi | xauth -q - | ||
523 | fi | ||
524 | |||
525 | If this file does not exist, /etc/ssh/sshrc is run, and if that | ||
526 | does not exist either, xauth is used to add the cookie. | ||
527 | |||
528 | This file should be writable only by the user, and need not be | ||
529 | readable by anyone else. | ||
530 | |||
531 | /etc/ssh/sshrc | ||
532 | Like $HOME/.ssh/rc. This can be used to specify machine-specific | ||
533 | login-time initializations globally. This file should be | ||
534 | writable only by root, and should be world-readable. | ||
535 | |||
536 | SEE ALSO | ||
537 | scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), | ||
538 | login.conf(5), moduli(5), sshd_config(5), sftp-server(8) | ||
539 | |||
540 | T. Ylonen, T. Kivinen, M. Saarinen, T. Rinne, and S. Lehtinen, SSH | ||
541 | Protocol Architecture, draft-ietf-secsh-architecture-12.txt, January | ||
542 | 2002, work in progress material. | ||
543 | |||
544 | M. Friedl, N. Provos, and W. A. Simpson, Diffie-Hellman Group Exchange | ||
545 | for the SSH Transport Layer Protocol, draft-ietf-secsh-dh-group- | ||
546 | exchange-02.txt, January 2002, work in progress material. | ||
547 | |||
548 | AUTHORS | ||
549 | OpenSSH is a derivative of the original and free ssh 1.2.12 release by | ||
550 | Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo | ||
551 | de Raadt and Dug Song removed many bugs, re-added newer features and | ||
552 | created OpenSSH. Markus Friedl contributed the support for SSH protocol | ||
553 | versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support | ||
554 | for privilege separation. | ||
555 | |||
556 | OpenBSD 3.4 September 25, 1999 9 | ||