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bf740959 | 1 | .\" -*- nroff -*- |
2 | .\" | |
bf740959 | 3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
bf740959 | 4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
5 | .\" All rights reserved | |
6 | .\" | |
bcbf86ec | 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 | .\" | |
f3c7c613 | 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. | |
bcbf86ec | 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. | |
bf740959 | 25 | .\" |
bcbf86ec | 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. | |
bf740959 | 36 | .\" |
c0ecc314 | 37 | .\" $OpenBSD: sshd.8,v 1.113 2001/04/10 09:13:22 itojun Exp $ |
bf740959 | 38 | .Dd September 25, 1999 |
39 | .Dt SSHD 8 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm sshd | |
2c86906e | 43 | .Nd OpenSSH ssh daemon |
bf740959 | 44 | .Sh SYNOPSIS |
45 | .Nm sshd | |
ab60252b | 46 | .Op Fl diqD46 |
bf740959 | 47 | .Op Fl b Ar bits |
48 | .Op Fl f Ar config_file | |
49 | .Op Fl g Ar login_grace_time | |
50 | .Op Fl h Ar host_key_file | |
51 | .Op Fl k Ar key_gen_time | |
52 | .Op Fl p Ar port | |
c345cf9d | 53 | .Op Fl u Ar len |
5260325f | 54 | .Op Fl V Ar client_protocol_id |
f54651ce | 55 | .Sh DESCRIPTION |
bf740959 | 56 | .Nm |
2c86906e | 57 | (SSH Daemon) is the daemon program for |
bf740959 | 58 | .Xr ssh 1 . |
3189621b | 59 | Together these programs replace rlogin and rsh, and |
bf740959 | 60 | provide secure encrypted communications between two untrusted hosts |
4fe2af09 | 61 | over an insecure network. |
62 | The programs are intended to be as easy to | |
bf740959 | 63 | install and use as possible. |
64 | .Pp | |
65 | .Nm | |
4fe2af09 | 66 | is the daemon that listens for connections from clients. |
f54651ce | 67 | It is normally started at boot from |
bf740959 | 68 | .Pa /etc/rc . |
69 | It forks a new | |
4fe2af09 | 70 | daemon for each incoming connection. |
71 | The forked daemons handle | |
bf740959 | 72 | key exchange, encryption, authentication, command execution, |
73 | and data exchange. | |
1d1ffb87 | 74 | This implementation of |
75 | .Nm | |
76 | supports both SSH protocol version 1 and 2 simultaneously. | |
bf740959 | 77 | .Nm |
4fe2af09 | 78 | works as follows. |
1d1ffb87 | 79 | .Pp |
80 | .Ss SSH protocol version 1 | |
81 | .Pp | |
4fe2af09 | 82 | Each host has a host-specific RSA key |
83 | (normally 1024 bits) used to identify the host. | |
84 | Additionally, when | |
bf740959 | 85 | the daemon starts, it generates a server RSA key (normally 768 bits). |
86 | This key is normally regenerated every hour if it has been used, and | |
87 | is never stored on disk. | |
88 | .Pp | |
3189621b | 89 | Whenever a client connects the daemon responds with its public |
90 | host and server keys. | |
4fe2af09 | 91 | The client compares the |
1d1ffb87 | 92 | RSA host key against its own database to verify that it has not changed. |
4fe2af09 | 93 | The client then generates a 256 bit random number. |
94 | It encrypts this | |
bf740959 | 95 | random number using both the host key and the server key, and sends |
4fe2af09 | 96 | the encrypted number to the server. |
3189621b | 97 | Both sides then use this |
bf740959 | 98 | random number as a session key which is used to encrypt all further |
4fe2af09 | 99 | communications in the session. |
100 | The rest of the session is encrypted | |
3189621b | 101 | using a conventional cipher, currently Blowfish or 3DES, with 3DES |
7368a6c8 | 102 | being used by default. |
4fe2af09 | 103 | The client selects the encryption algorithm |
bf740959 | 104 | to use from those offered by the server. |
105 | .Pp | |
4fe2af09 | 106 | Next, the server and the client enter an authentication dialog. |
107 | The client tries to authenticate itself using | |
bf740959 | 108 | .Pa .rhosts |
109 | authentication, | |
110 | .Pa .rhosts | |
111 | authentication combined with RSA host | |
112 | authentication, RSA challenge-response authentication, or password | |
113 | based authentication. | |
114 | .Pp | |
115 | Rhosts authentication is normally disabled | |
116 | because it is fundamentally insecure, but can be enabled in the server | |
4fe2af09 | 117 | configuration file if desired. |
118 | System security is not improved unless | |
bf740959 | 119 | .Xr rshd 8 , |
120 | .Xr rlogind 8 , | |
121 | .Xr rexecd 8 , | |
122 | and | |
123 | .Xr rexd 8 | |
124 | are disabled (thus completely disabling | |
125 | .Xr rlogin 1 | |
126 | and | |
127 | .Xr rsh 1 | |
3189621b | 128 | into the machine). |
bf740959 | 129 | .Pp |
1d1ffb87 | 130 | .Ss SSH protocol version 2 |
131 | .Pp | |
c345cf9d | 132 | Version 2 works similarly: |
1d1ffb87 | 133 | Each host has a host-specific DSA key used to identify the host. |
134 | However, when the daemon starts, it does not generate a server key. | |
135 | Forward security is provided through a Diffie-Hellman key agreement. | |
136 | This key agreement results in a shared session key. | |
51c251f0 | 137 | The rest of the session is encrypted using a symmetric cipher, currently |
138 | Blowfish, 3DES, CAST128, Arcfour, 128 bit AES, or 256 bit AES. | |
1d1ffb87 | 139 | The client selects the encryption algorithm |
140 | to use from those offered by the server. | |
141 | Additionally, session integrity is provided | |
d0c832f3 | 142 | through a cryptographic message authentication code |
1d1ffb87 | 143 | (hmac-sha1 or hmac-md5). |
144 | .Pp | |
145 | Protocol version 2 provides a public key based | |
fa08c86b | 146 | user authentication method (PubkeyAuthentication) |
1d1ffb87 | 147 | and conventional password authentication. |
148 | .Pp | |
149 | .Ss Command execution and data forwarding | |
150 | .Pp | |
bf740959 | 151 | If the client successfully authenticates itself, a dialog for |
4fe2af09 | 152 | preparing the session is entered. |
153 | At this time the client may request | |
bf740959 | 154 | things like allocating a pseudo-tty, forwarding X11 connections, |
155 | forwarding TCP/IP connections, or forwarding the authentication agent | |
156 | connection over the secure channel. | |
157 | .Pp | |
158 | Finally, the client either requests a shell or execution of a command. | |
4fe2af09 | 159 | The sides then enter session mode. |
160 | In this mode, either side may send | |
bf740959 | 161 | data at any time, and such data is forwarded to/from the shell or |
162 | command on the server side, and the user terminal in the client side. | |
163 | .Pp | |
164 | When the user program terminates and all forwarded X11 and other | |
165 | connections have been closed, the server sends command exit status to | |
166 | the client, and both sides exit. | |
167 | .Pp | |
168 | .Nm | |
169 | can be configured using command-line options or a configuration | |
4fe2af09 | 170 | file. |
171 | Command-line options override values specified in the | |
bf740959 | 172 | configuration file. |
173 | .Pp | |
9d6b7add | 174 | .Nm |
175 | rereads its configuration file when it receives a hangup signal, | |
409edaba | 176 | .Dv SIGHUP , |
177 | by executing itself with the name it was started as, ie. | |
178 | .Pa /usr/sbin/sshd . | |
9d6b7add | 179 | .Pp |
bf740959 | 180 | The options are as follows: |
181 | .Bl -tag -width Ds | |
182 | .It Fl b Ar bits | |
183 | Specifies the number of bits in the server key (default 768). | |
184 | .Pp | |
185 | .It Fl d | |
4fe2af09 | 186 | Debug mode. |
187 | The server sends verbose debug output to the system | |
188 | log, and does not put itself in the background. | |
189 | The server also will not fork and will only process one connection. | |
190 | This option is only intended for debugging for the server. | |
94ec8c6b | 191 | Multiple -d options increases the debugging level. |
192 | Maximum is 3. | |
bf740959 | 193 | .It Fl f Ar configuration_file |
4fe2af09 | 194 | Specifies the name of the configuration file. |
195 | The default is | |
5f4fdfae | 196 | .Pa /etc/sshd_config . |
bf740959 | 197 | .Nm |
198 | refuses to start if there is no configuration file. | |
199 | .It Fl g Ar login_grace_time | |
200 | Gives the grace time for clients to authenticate themselves (default | |
ee5e6612 | 201 | 600 seconds). |
4fe2af09 | 202 | If the client fails to authenticate the user within |
203 | this many seconds, the server disconnects and exits. | |
204 | A value of zero indicates no limit. | |
bf740959 | 205 | .It Fl h Ar host_key_file |
8abcdba4 | 206 | Specifies the file from which the host key is read (default |
5f4fdfae | 207 | .Pa /etc/ssh_host_key ) . |
bf740959 | 208 | This option must be given if |
209 | .Nm | |
210 | is not run as root (as the normal | |
211 | host file is normally not readable by anyone but root). | |
8abcdba4 | 212 | It is possible to have multiple host key files for |
213 | the different protocol versions. | |
bf740959 | 214 | .It Fl i |
215 | Specifies that | |
216 | .Nm | |
f54651ce | 217 | is being run from inetd. |
bf740959 | 218 | .Nm |
219 | is normally not run | |
220 | from inetd because it needs to generate the server key before it can | |
4fe2af09 | 221 | respond to the client, and this may take tens of seconds. |
222 | Clients would have to wait too long if the key was regenerated every time. | |
610cd5c6 | 223 | However, with small key sizes (e.g., 512) using |
bf740959 | 224 | .Nm |
225 | from inetd may | |
226 | be feasible. | |
227 | .It Fl k Ar key_gen_time | |
228 | Specifies how often the server key is regenerated (default 3600 | |
4fe2af09 | 229 | seconds, or one hour). |
230 | The motivation for regenerating the key fairly | |
bf740959 | 231 | often is that the key is not stored anywhere, and after about an hour, |
232 | it becomes impossible to recover the key for decrypting intercepted | |
233 | communications even if the machine is cracked into or physically | |
4fe2af09 | 234 | seized. |
235 | A value of zero indicates that the key will never be regenerated. | |
bf740959 | 236 | .It Fl p Ar port |
237 | Specifies the port on which the server listens for connections | |
238 | (default 22). | |
239 | .It Fl q | |
4fe2af09 | 240 | Quiet mode. |
241 | Nothing is sent to the system log. | |
242 | Normally the beginning, | |
bf740959 | 243 | authentication, and termination of each connection is logged. |
c345cf9d | 244 | .It Fl u Ar len |
245 | This option is used to specify the size of the field | |
246 | in the | |
247 | .Li utmp | |
248 | structure that holds the remote host name. | |
249 | If the resolved host name is longer than | |
250 | .Ar len , | |
251 | the dotted decimal value will be used instead. | |
252 | This allows hosts with very long host names that | |
253 | overflow this field to still be uniquely identified. | |
254 | Specifying | |
255 | .Fl u0 | |
256 | indicates that only dotted decimal addresses | |
257 | should be put into the | |
258 | .Pa utmp | |
259 | file. | |
8abcdba4 | 260 | .It Fl D |
261 | When this option is specified | |
262 | .Nm | |
263 | will not detach and does not become a daemon. | |
264 | This allows easy monitoring of | |
265 | .Nm sshd . | |
5260325f | 266 | .It Fl V Ar client_protocol_id |
94ec8c6b | 267 | SSH-2 compatibility mode. |
3189621b | 268 | When this option is specified |
5260325f | 269 | .Nm |
3189621b | 270 | assumes the client has sent the supplied version string |
5260325f | 271 | and skips the |
272 | Protocol Version Identification Exchange. | |
94ec8c6b | 273 | This option is not intended to be called directly. |
48e671d5 | 274 | .It Fl 4 |
275 | Forces | |
276 | .Nm | |
277 | to use IPv4 addresses only. | |
278 | .It Fl 6 | |
279 | Forces | |
280 | .Nm | |
281 | to use IPv6 addresses only. | |
bf740959 | 282 | .El |
283 | .Sh CONFIGURATION FILE | |
284 | .Nm | |
f54651ce | 285 | reads configuration data from |
5f4fdfae | 286 | .Pa /etc/sshd_config |
bf740959 | 287 | (or the file specified with |
288 | .Fl f | |
4fe2af09 | 289 | on the command line). |
290 | The file contains keyword-value pairs, one per line. | |
291 | Lines starting with | |
bf740959 | 292 | .Ql # |
293 | and empty lines are interpreted as comments. | |
294 | .Pp | |
295 | The following keywords are possible. | |
296 | .Bl -tag -width Ds | |
297 | .It Cm AFSTokenPassing | |
4fe2af09 | 298 | Specifies whether an AFS token may be forwarded to the server. |
299 | Default is | |
bf740959 | 300 | .Dq yes . |
301 | .It Cm AllowGroups | |
76896b4e | 302 | This keyword can be followed by a list of group names, separated |
4fe2af09 | 303 | by spaces. |
304 | If specified, login is allowed only for users whose primary | |
c6a69271 | 305 | group or supplementary group list matches one of the patterns. |
bf740959 | 306 | .Ql \&* |
307 | and | |
308 | .Ql ? | |
309 | can be used as | |
4fe2af09 | 310 | wildcards in the patterns. |
c345cf9d | 311 | Only group names are valid; a numerical group ID isn't recognized. |
c6a69271 | 312 | By default login is allowed regardless of the group list. |
bf740959 | 313 | .Pp |
33de75a3 | 314 | .It Cm AllowTcpForwarding |
315 | Specifies whether TCP forwarding is permitted. | |
316 | The default is | |
317 | .Dq yes . | |
318 | Note that disabling TCP forwarding does not improve security unless | |
319 | users are also denied shell access, as they can always install their | |
320 | own forwarders. | |
321 | .Pp | |
bf740959 | 322 | .It Cm AllowUsers |
76896b4e | 323 | This keyword can be followed by a list of user names, separated |
4fe2af09 | 324 | by spaces. |
325 | If specified, login is allowed only for users names that | |
bf740959 | 326 | match one of the patterns. |
327 | .Ql \&* | |
328 | and | |
329 | .Ql ? | |
330 | can be used as | |
4fe2af09 | 331 | wildcards in the patterns. |
c345cf9d | 332 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 333 | By default login is allowed regardless of the user name. |
bf740959 | 334 | .Pp |
eea39c02 | 335 | .It Cm Banner |
336 | In some jurisdictions, sending a warning message before authentication | |
337 | may be relevant for getting legal protection. | |
338 | The contents of the specified file are sent to the remote user before | |
339 | authentication is allowed. | |
340 | This option is only available for protocol version 2. | |
341 | .Pp | |
657297ff | 342 | .It Cm ChallengeResponseAuthentication |
343 | Specifies whether | |
344 | challenge response | |
345 | authentication is allowed. | |
346 | Currently there is only support for | |
347 | .Xr skey 1 | |
348 | authentication. | |
349 | The default is | |
350 | .Dq yes . | |
f54651ce | 351 | .It Cm Ciphers |
352 | Specifies the ciphers allowed for protocol version 2. | |
353 | Multiple ciphers must be comma-separated. | |
354 | The default is | |
7a6c39a3 | 355 | .Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour. |
bf740959 | 356 | .It Cm CheckMail |
357 | Specifies whether | |
358 | .Nm | |
359 | should check for new mail for interactive logins. | |
360 | The default is | |
361 | .Dq no . | |
362 | .It Cm DenyGroups | |
363 | This keyword can be followed by a number of group names, separated | |
4fe2af09 | 364 | by spaces. |
c6a69271 | 365 | Users whose primary group or supplementary group list matches |
366 | one of the patterns aren't allowed to log in. | |
bf740959 | 367 | .Ql \&* |
368 | and | |
369 | .Ql ? | |
370 | can be used as | |
4fe2af09 | 371 | wildcards in the patterns. |
c345cf9d | 372 | Only group names are valid; a numerical group ID isn't recognized. |
c6a69271 | 373 | By default login is allowed regardless of the group list. |
bf740959 | 374 | .Pp |
375 | .It Cm DenyUsers | |
376 | This keyword can be followed by a number of user names, separated | |
4fe2af09 | 377 | by spaces. |
378 | Login is disallowed for user names that match one of the patterns. | |
bf740959 | 379 | .Ql \&* |
380 | and | |
381 | .Ql ? | |
4fe2af09 | 382 | can be used as wildcards in the patterns. |
c345cf9d | 383 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 384 | By default login is allowed regardless of the user name. |
1d1ffb87 | 385 | .It Cm GatewayPorts |
386 | Specifies whether remote hosts are allowed to connect to ports | |
387 | forwarded for the client. | |
388 | The argument must be | |
389 | .Dq yes | |
390 | or | |
391 | .Dq no . | |
392 | The default is | |
393 | .Dq no . | |
bf740959 | 394 | .It Cm HostKey |
fa08c86b | 395 | Specifies the file containing the private host keys (default |
1d1ffb87 | 396 | .Pa /etc/ssh_host_key ) |
fa08c86b | 397 | used by SSH protocol versions 1 and 2. |
bf740959 | 398 | Note that |
399 | .Nm | |
42f11eb2 | 400 | will refuse to use a file if it is group/world-accessible. |
fa08c86b | 401 | It is possible to have multiple host key files. |
402 | .Dq rsa1 | |
403 | keys are used for version 1 and | |
404 | .Dq dsa | |
405 | or | |
406 | .Dq rsa | |
407 | are used for version 2 of the SSH protocol. | |
bf740959 | 408 | .It Cm IgnoreRhosts |
c8d54615 | 409 | Specifies that |
410 | .Pa .rhosts | |
f54651ce | 411 | and |
c8d54615 | 412 | .Pa .shosts |
413 | files will not be used in authentication. | |
bf740959 | 414 | .Pa /etc/hosts.equiv |
415 | and | |
f54651ce | 416 | .Pa /etc/shosts.equiv |
4fe2af09 | 417 | are still used. |
f54651ce | 418 | The default is |
c8d54615 | 419 | .Dq yes . |
b4748e2f | 420 | .It Cm IgnoreUserKnownHosts |
421 | Specifies whether | |
422 | .Nm | |
423 | should ignore the user's | |
424 | .Pa $HOME/.ssh/known_hosts | |
425 | during | |
426 | .Cm RhostsRSAAuthentication . | |
427 | The default is | |
428 | .Dq no . | |
bf740959 | 429 | .It Cm KeepAlive |
430 | Specifies whether the system should send keepalive messages to the | |
4fe2af09 | 431 | other side. |
432 | If they are sent, death of the connection or crash of one | |
433 | of the machines will be properly noticed. | |
434 | However, this means that | |
bf740959 | 435 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 436 | find it annoying. |
d0c832f3 | 437 | On the other hand, if keepalives are not sent, |
bf740959 | 438 | sessions may hang indefinitely on the server, leaving |
439 | .Dq ghost | |
440 | users and consuming server resources. | |
441 | .Pp | |
442 | The default is | |
443 | .Dq yes | |
444 | (to send keepalives), and the server will notice | |
4fe2af09 | 445 | if the network goes down or the client host reboots. |
446 | This avoids infinitely hanging sessions. | |
bf740959 | 447 | .Pp |
448 | To disable keepalives, the value should be set to | |
449 | .Dq no | |
450 | in both the server and the client configuration files. | |
451 | .It Cm KerberosAuthentication | |
4fe2af09 | 452 | Specifies whether Kerberos authentication is allowed. |
453 | This can be in the form of a Kerberos ticket, or if | |
bf740959 | 454 | .Cm PasswordAuthentication |
455 | is yes, the password provided by the user will be validated through | |
94ec8c6b | 456 | the Kerberos KDC. |
457 | To use this option, the server needs a | |
c345cf9d | 458 | Kerberos servtab which allows the verification of the KDC's identity. |
4fe2af09 | 459 | Default is |
bf740959 | 460 | .Dq yes . |
461 | .It Cm KerberosOrLocalPasswd | |
462 | If set then if password authentication through Kerberos fails then | |
463 | the password will be validated via any additional local mechanism | |
464 | such as | |
188adeb2 | 465 | .Pa /etc/passwd . |
4fe2af09 | 466 | Default is |
bf740959 | 467 | .Dq yes . |
468 | .It Cm KerberosTgtPassing | |
469 | Specifies whether a Kerberos TGT may be forwarded to the server. | |
f54651ce | 470 | Default is |
bf740959 | 471 | .Dq no , |
472 | as this only works when the Kerberos KDC is actually an AFS kaserver. | |
473 | .It Cm KerberosTicketCleanup | |
474 | Specifies whether to automatically destroy the user's ticket cache | |
4fe2af09 | 475 | file on logout. |
476 | Default is | |
bf740959 | 477 | .Dq yes . |
478 | .It Cm KeyRegenerationInterval | |
479 | The server key is automatically regenerated after this many seconds | |
4fe2af09 | 480 | (if it has been used). |
481 | The purpose of regeneration is to prevent | |
bf740959 | 482 | decrypting captured sessions by later breaking into the machine and |
4fe2af09 | 483 | stealing the keys. |
484 | The key is never stored anywhere. | |
485 | If the value is 0, the key is never regenerated. | |
486 | The default is 3600 (seconds). | |
bf740959 | 487 | .It Cm ListenAddress |
6e9944b8 | 488 | Specifies the local addresses |
b8a297f1 | 489 | .Xr sshd 8 |
bf740959 | 490 | should listen on. |
6e9944b8 | 491 | The following forms may be used: |
492 | .Pp | |
493 | .Bl -item -offset indent -compact | |
494 | .It | |
495 | .Cm ListenAddress | |
b8a297f1 | 496 | .Sm off |
497 | .Ar host No | Ar IPv4_addr No | Ar IPv6_addr | |
498 | .Sm on | |
6e9944b8 | 499 | .It |
500 | .Cm ListenAddress | |
b8a297f1 | 501 | .Sm off |
502 | .Ar host No | Ar IPv4_addr No : Ar port | |
503 | .Sm on | |
6e9944b8 | 504 | .It |
505 | .Cm ListenAddress | |
b8a297f1 | 506 | .Sm off |
507 | .Oo | |
508 | .Ar host No | Ar IPv6_addr Oc : Ar port | |
509 | .Sm on | |
6e9944b8 | 510 | .El |
511 | .Pp | |
512 | If | |
b8a297f1 | 513 | .Ar port |
6e9944b8 | 514 | is not specified, |
b8a297f1 | 515 | .Xr sshd 8 |
6e9944b8 | 516 | will listen on the address and all prior |
517 | .Cm Port | |
518 | options specified. The default is to listen on all local | |
519 | addresses. Multiple | |
520 | .Cm ListenAddress | |
521 | options are permitted. Additionally, any | |
522 | .Cm Port | |
523 | options must precede this option for non port qualified addresses. | |
bf740959 | 524 | .It Cm LoginGraceTime |
525 | The server disconnects after this time if the user has not | |
4fe2af09 | 526 | successfully logged in. |
527 | If the value is 0, there is no time limit. | |
bf740959 | 528 | The default is 600 (seconds). |
6a17f9c2 | 529 | .It Cm LogLevel |
530 | Gives the verbosity level that is used when logging messages from | |
531 | .Nm sshd . | |
532 | The possible values are: | |
59c97189 | 533 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
534 | The default is INFO. | |
6a17f9c2 | 535 | Logging with level DEBUG violates the privacy of users |
536 | and is not recommended. | |
b2552997 | 537 | .It Cm MACs |
538 | Specifies the available MAC (message authentication code) algorithms. | |
539 | The MAC algorithm is used in protocol version 2 | |
540 | for data integrity protection. | |
541 | Multiple algorithms must be comma-separated. | |
542 | The default is | |
543 | .Pp | |
544 | .Bd -literal | |
7a6c39a3 | 545 | ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com, |
b2552997 | 546 | hmac-sha1-96,hmac-md5-96'' |
547 | .Ed | |
089fbbd2 | 548 | .It Cm MaxStartups |
549 | Specifies the maximum number of concurrent unauthenticated connections to the | |
550 | .Nm | |
551 | daemon. | |
552 | Additional connections will be dropped until authentication succeeds or the | |
553 | .Cm LoginGraceTime | |
554 | expires for a connection. | |
555 | The default is 10. | |
c345cf9d | 556 | .Pp |
557 | Alternatively, random early drop can be enabled by specifying | |
558 | the three colon separated values | |
559 | .Dq start:rate:full | |
94ec8c6b | 560 | (e.g., "10:30:60"). |
c345cf9d | 561 | .Nm |
6f37606e | 562 | will refuse connection attempts with a probability of |
c345cf9d | 563 | .Dq rate/100 |
564 | (30%) | |
565 | if there are currently | |
566 | .Dq start | |
567 | (10) | |
568 | unauthenticated connections. | |
6f37606e | 569 | The probability increases linearly and all connection attempts |
c345cf9d | 570 | are refused if the number of unauthenticated connections reaches |
571 | .Dq full | |
572 | (60). | |
bf740959 | 573 | .It Cm PasswordAuthentication |
574 | Specifies whether password authentication is allowed. | |
575 | The default is | |
576 | .Dq yes . | |
c345cf9d | 577 | Note that this option applies to both protocol versions 1 and 2. |
bf740959 | 578 | .It Cm PermitEmptyPasswords |
579 | When password authentication is allowed, it specifies whether the | |
4fe2af09 | 580 | server allows login to accounts with empty password strings. |
581 | The default is | |
c8d54615 | 582 | .Dq no . |
bf740959 | 583 | .It Cm PermitRootLogin |
46f23b8d | 584 | Specifies whether root can login using |
bf740959 | 585 | .Xr ssh 1 . |
586 | The argument must be | |
587 | .Dq yes , | |
15853e93 | 588 | .Dq without-password , |
589 | .Dq forced-commands-only | |
bf740959 | 590 | or |
591 | .Dq no . | |
592 | The default is | |
593 | .Dq yes . | |
15853e93 | 594 | .Pp |
595 | If this option is set to | |
bf740959 | 596 | .Dq without-password |
15853e93 | 597 | password authentication is disabled for root. |
bf740959 | 598 | .Pp |
15853e93 | 599 | If this option is set to |
600 | .Dq forced-commands-only | |
601 | root login with public key authentication will be allowed, | |
602 | but only if the | |
bf740959 | 603 | .Ar command |
15853e93 | 604 | option has been specified |
bf740959 | 605 | (which may be useful for taking remote backups even if root login is |
15853e93 | 606 | normally not allowed). All other authentication methods are disabled |
607 | for root. | |
46f23b8d | 608 | .Pp |
609 | If this option is set to | |
610 | .Dq no | |
611 | root is not allowed to login. | |
0fbe8c74 | 612 | .It Cm PidFile |
613 | Specifies the file that contains the process identifier of the | |
614 | .Nm | |
615 | daemon. | |
616 | The default is | |
617 | .Pa /var/run/sshd.pid . | |
bf740959 | 618 | .It Cm Port |
619 | Specifies the port number that | |
620 | .Nm | |
4fe2af09 | 621 | listens on. |
622 | The default is 22. | |
48e671d5 | 623 | Multiple options of this type are permitted. |
4f4648f9 | 624 | .It Cm PrintLastLog |
625 | Specifies whether | |
626 | .Nm | |
627 | should print the date and time when the user last logged in. | |
628 | The default is | |
629 | .Dq yes . | |
bf740959 | 630 | .It Cm PrintMotd |
631 | Specifies whether | |
632 | .Nm | |
f54651ce | 633 | should print |
bf740959 | 634 | .Pa /etc/motd |
4fe2af09 | 635 | when a user logs in interactively. |
636 | (On some systems it is also printed by the shell, | |
bf740959 | 637 | .Pa /etc/profile , |
4fe2af09 | 638 | or equivalent.) |
639 | The default is | |
bf740959 | 640 | .Dq yes . |
f54651ce | 641 | .It Cm Protocol |
642 | Specifies the protocol versions | |
643 | .Nm | |
644 | should support. | |
645 | The possible values are | |
646 | .Dq 1 | |
647 | and | |
648 | .Dq 2 . | |
649 | Multiple versions must be comma-separated. | |
650 | The default is | |
651 | .Dq 1 . | |
657297ff | 652 | .It Cm PubkeyAuthentication |
653 | Specifies whether public key authentication is allowed. | |
654 | The default is | |
655 | .Dq yes . | |
656 | Note that this option applies to protocol version 2 only. | |
61e96248 | 657 | .It Cm ReverseMappingCheck |
658 | Specifies whether | |
659 | .Nm | |
660 | should try to verify the remote host name and check that | |
661 | the resolved host name for the remote IP address maps back to the | |
662 | very same IP address. | |
663 | The default is | |
664 | .Dq no . | |
bf740959 | 665 | .It Cm RhostsAuthentication |
666 | Specifies whether authentication using rhosts or /etc/hosts.equiv | |
4fe2af09 | 667 | files is sufficient. |
668 | Normally, this method should not be permitted because it is insecure. | |
bf740959 | 669 | .Cm RhostsRSAAuthentication |
670 | should be used | |
671 | instead, because it performs RSA-based host authentication in addition | |
672 | to normal rhosts or /etc/hosts.equiv authentication. | |
673 | The default is | |
674 | .Dq no . | |
675 | .It Cm RhostsRSAAuthentication | |
676 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
4fe2af09 | 677 | with successful RSA host authentication is allowed. |
678 | The default is | |
c8d54615 | 679 | .Dq no . |
bf740959 | 680 | .It Cm RSAAuthentication |
4fe2af09 | 681 | Specifies whether pure RSA authentication is allowed. |
682 | The default is | |
bf740959 | 683 | .Dq yes . |
1d1ffb87 | 684 | Note that this option applies to protocol version 1 only. |
bf740959 | 685 | .It Cm ServerKeyBits |
4fe2af09 | 686 | Defines the number of bits in the server key. |
687 | The minimum value is 512, and the default is 768. | |
bf740959 | 688 | .It Cm StrictModes |
689 | Specifies whether | |
690 | .Nm | |
691 | should check file modes and ownership of the | |
4fe2af09 | 692 | user's files and home directory before accepting login. |
693 | This is normally desirable because novices sometimes accidentally leave their | |
694 | directory or files world-writable. | |
695 | The default is | |
bf740959 | 696 | .Dq yes . |
38c295d6 | 697 | .It Cm Subsystem |
94ec8c6b | 698 | Configures an external subsystem (e.g., file transfer daemon). |
699 | Arguments should be a subsystem name and a command to execute upon subsystem | |
700 | request. | |
b5e300c2 | 701 | The command |
702 | .Xr sftp-server 8 | |
703 | implements the | |
704 | .Dq sftp | |
705 | file transfer subsystem. | |
38c295d6 | 706 | By default no subsystems are defined. |
707 | Note that this option applies to protocol version 2 only. | |
bf740959 | 708 | .It Cm SyslogFacility |
709 | Gives the facility code that is used when logging messages from | |
710 | .Nm sshd . | |
711 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, | |
4fe2af09 | 712 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
713 | The default is AUTH. | |
bf740959 | 714 | .It Cm UseLogin |
715 | Specifies whether | |
716 | .Xr login 1 | |
fa649821 | 717 | is used for interactive login sessions. |
718 | Note that | |
719 | .Xr login 1 | |
c345cf9d | 720 | is never used for remote command execution. |
4fe2af09 | 721 | The default is |
bf740959 | 722 | .Dq no . |
bf740959 | 723 | .It Cm X11DisplayOffset |
724 | Specifies the first display number available for | |
725 | .Nm sshd Ns 's | |
4fe2af09 | 726 | X11 forwarding. |
727 | This prevents | |
bf740959 | 728 | .Nm |
729 | from interfering with real X11 servers. | |
c8d54615 | 730 | The default is 10. |
7b2ea3a1 | 731 | .It Cm X11Forwarding |
4fe2af09 | 732 | Specifies whether X11 forwarding is permitted. |
733 | The default is | |
c8d54615 | 734 | .Dq no . |
7b2ea3a1 | 735 | Note that disabling X11 forwarding does not improve security in any |
736 | way, as users can always install their own forwarders. | |
fa649821 | 737 | .It Cm XAuthLocation |
738 | Specifies the location of the | |
739 | .Xr xauth 1 | |
740 | program. | |
741 | The default is | |
742 | .Pa /usr/X11R6/bin/xauth . | |
bf740959 | 743 | .El |
744 | .Sh LOGIN PROCESS | |
745 | When a user successfully logs in, | |
746 | .Nm | |
747 | does the following: | |
748 | .Bl -enum -offset indent | |
749 | .It | |
750 | If the login is on a tty, and no command has been specified, | |
f54651ce | 751 | prints last login time and |
bf740959 | 752 | .Pa /etc/motd |
753 | (unless prevented in the configuration file or by | |
754 | .Pa $HOME/.hushlogin ; | |
755 | see the | |
f54651ce | 756 | .Sx FILES |
bf740959 | 757 | section). |
758 | .It | |
759 | If the login is on a tty, records login time. | |
760 | .It | |
761 | Checks | |
762 | .Pa /etc/nologin ; | |
763 | if it exists, prints contents and quits | |
764 | (unless root). | |
765 | .It | |
766 | Changes to run with normal user privileges. | |
767 | .It | |
768 | Sets up basic environment. | |
769 | .It | |
770 | Reads | |
771 | .Pa $HOME/.ssh/environment | |
772 | if it exists. | |
773 | .It | |
774 | Changes to user's home directory. | |
775 | .It | |
776 | If | |
777 | .Pa $HOME/.ssh/rc | |
778 | exists, runs it; else if | |
5f4fdfae | 779 | .Pa /etc/sshrc |
bf740959 | 780 | exists, runs |
4fe2af09 | 781 | it; otherwise runs xauth. |
782 | The | |
bf740959 | 783 | .Dq rc |
784 | files are given the X11 | |
785 | authentication protocol and cookie in standard input. | |
786 | .It | |
787 | Runs user's shell or command. | |
788 | .El | |
789 | .Sh AUTHORIZED_KEYS FILE FORMAT | |
f54651ce | 790 | The |
bf740959 | 791 | .Pa $HOME/.ssh/authorized_keys |
792 | file lists the RSA keys that are | |
1d1ffb87 | 793 | permitted for RSA authentication in SSH protocols 1.3 and 1.5 |
d0c832f3 | 794 | Similarly, the |
1d1ffb87 | 795 | .Pa $HOME/.ssh/authorized_keys2 |
8abcdba4 | 796 | file lists the DSA and RSA keys that are |
797 | permitted for public key authentication (PubkeyAuthentication) | |
798 | in SSH protocol 2.0. | |
799 | .Pp | |
4fe2af09 | 800 | Each line of the file contains one |
bf740959 | 801 | key (empty lines and lines starting with a |
802 | .Ql # | |
803 | are ignored as | |
4fe2af09 | 804 | comments). |
8abcdba4 | 805 | Each RSA public key consists of the following fields, separated by |
4fe2af09 | 806 | spaces: options, bits, exponent, modulus, comment. |
8abcdba4 | 807 | Each protocol version 2 public key consists of: |
808 | options, keytype, base64 encoded key, comment. | |
809 | The options fields | |
810 | are optional; its presence is determined by whether the line starts | |
bf740959 | 811 | with a number or not (the option field never starts with a number). |
8abcdba4 | 812 | The bits, exponent, modulus and comment fields give the RSA key for |
813 | protocol version 1; the | |
bf740959 | 814 | comment field is not used for anything (but may be convenient for the |
815 | user to identify the key). | |
8abcdba4 | 816 | For protocol version 2 the keytype is |
817 | .Dq ssh-dss | |
818 | or | |
819 | .Dq ssh-rsa . | |
bf740959 | 820 | .Pp |
821 | Note that lines in this file are usually several hundred bytes long | |
4fe2af09 | 822 | (because of the size of the RSA key modulus). |
823 | You don't want to type them in; instead, copy the | |
c0ecc314 | 824 | .Pa identity.pub , |
8abcdba4 | 825 | .Pa id_dsa.pub |
c0ecc314 | 826 | or the |
827 | .Pa id_rsa.pub | |
bf740959 | 828 | file and edit it. |
829 | .Pp | |
c345cf9d | 830 | The options (if present) consist of comma-separated option |
4fe2af09 | 831 | specifications. |
832 | No spaces are permitted, except within double quotes. | |
bf740959 | 833 | The following option specifications are supported: |
834 | .Bl -tag -width Ds | |
835 | .It Cm from="pattern-list" | |
836 | Specifies that in addition to RSA authentication, the canonical name | |
837 | of the remote host must be present in the comma-separated list of | |
4fe2af09 | 838 | patterns |
839 | .Pf ( Ql * | |
840 | and | |
841 | .Ql ? | |
842 | serve as wildcards). | |
843 | The list may also contain | |
844 | patterns negated by prefixing them with | |
845 | .Ql ! ; | |
846 | if the canonical host name matches a negated pattern, the key is not accepted. | |
847 | The purpose | |
bf740959 | 848 | of this option is to optionally increase security: RSA authentication |
849 | by itself does not trust the network or name servers or anything (but | |
850 | the key); however, if somebody somehow steals the key, the key | |
4fe2af09 | 851 | permits an intruder to log in from anywhere in the world. |
852 | This additional option makes using a stolen key more difficult (name | |
bf740959 | 853 | servers and/or routers would have to be compromised in addition to |
854 | just the key). | |
855 | .It Cm command="command" | |
856 | Specifies that the command is executed whenever this key is used for | |
4fe2af09 | 857 | authentication. |
858 | The command supplied by the user (if any) is ignored. | |
bf740959 | 859 | The command is run on a pty if the connection requests a pty; |
4fe2af09 | 860 | otherwise it is run without a tty. |
61e96248 | 861 | Note that if you want a 8-bit clean channel, |
862 | you must not request a pty or should specify | |
863 | .Cm no-pty . | |
4fe2af09 | 864 | A quote may be included in the command by quoting it with a backslash. |
865 | This option might be useful | |
866 | to restrict certain RSA keys to perform just a specific operation. | |
867 | An example might be a key that permits remote backups but nothing else. | |
d0c832f3 | 868 | Note that the client may specify TCP/IP and/or X11 |
869 | forwarding unless they are explicitly prohibited. | |
bf740959 | 870 | .It Cm environment="NAME=value" |
871 | Specifies that the string is to be added to the environment when | |
4fe2af09 | 872 | logging in using this key. |
873 | Environment variables set this way | |
874 | override other default environment values. | |
875 | Multiple options of this type are permitted. | |
bf740959 | 876 | .It Cm no-port-forwarding |
877 | Forbids TCP/IP forwarding when this key is used for authentication. | |
4fe2af09 | 878 | Any port forward requests by the client will return an error. |
879 | This might be used, e.g., in connection with the | |
bf740959 | 880 | .Cm command |
881 | option. | |
882 | .It Cm no-X11-forwarding | |
883 | Forbids X11 forwarding when this key is used for authentication. | |
884 | Any X11 forward requests by the client will return an error. | |
885 | .It Cm no-agent-forwarding | |
886 | Forbids authentication agent forwarding when this key is used for | |
887 | authentication. | |
888 | .It Cm no-pty | |
889 | Prevents tty allocation (a request to allocate a pty will fail). | |
dc504afd | 890 | .It Cm permitopen="host:port" |
891 | Limit local | |
892 | .Li ``ssh -L'' | |
b2ae83b8 | 893 | port forwarding such that it may only connect to the specified host and |
dc504afd | 894 | port. Multiple |
895 | .Cm permitopen | |
b2ae83b8 | 896 | options may be applied separated by commas. No pattern matching is |
dc504afd | 897 | performed on the specified hostnames, they must be literal domains or |
898 | addresses. | |
bf740959 | 899 | .El |
900 | .Ss Examples | |
901 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar | |
902 | .Pp | |
903 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula | |
904 | .Pp | |
905 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi | |
dc504afd | 906 | .Pp |
907 | permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323 | |
bf740959 | 908 | .Sh SSH_KNOWN_HOSTS FILE FORMAT |
f54651ce | 909 | The |
1d1ffb87 | 910 | .Pa /etc/ssh_known_hosts , |
911 | .Pa /etc/ssh_known_hosts2 , | |
912 | .Pa $HOME/.ssh/known_hosts , | |
f54651ce | 913 | and |
1d1ffb87 | 914 | .Pa $HOME/.ssh/known_hosts2 |
4fe2af09 | 915 | files contain host public keys for all known hosts. |
916 | The global file should | |
917 | be prepared by the administrator (optional), and the per-user file is | |
c345cf9d | 918 | maintained automatically: whenever the user connects from an unknown host |
4fe2af09 | 919 | its key is added to the per-user file. |
bf740959 | 920 | .Pp |
921 | Each line in these files contains the following fields: hostnames, | |
4fe2af09 | 922 | bits, exponent, modulus, comment. |
923 | The fields are separated by spaces. | |
bf740959 | 924 | .Pp |
925 | Hostnames is a comma-separated list of patterns ('*' and '?' act as | |
926 | wildcards); each pattern in turn is matched against the canonical host | |
927 | name (when authenticating a client) or against the user-supplied | |
4fe2af09 | 928 | name (when authenticating a server). |
929 | A pattern may also be preceded by | |
bf740959 | 930 | .Ql ! |
931 | to indicate negation: if the host name matches a negated | |
932 | pattern, it is not accepted (by that line) even if it matched another | |
933 | pattern on the line. | |
934 | .Pp | |
1d1ffb87 | 935 | Bits, exponent, and modulus are taken directly from the RSA host key; they |
bf740959 | 936 | can be obtained, e.g., from |
5f4fdfae | 937 | .Pa /etc/ssh_host_key.pub . |
bf740959 | 938 | The optional comment field continues to the end of the line, and is not used. |
939 | .Pp | |
940 | Lines starting with | |
941 | .Ql # | |
942 | and empty lines are ignored as comments. | |
943 | .Pp | |
944 | When performing host authentication, authentication is accepted if any | |
4fe2af09 | 945 | matching line has the proper key. |
946 | It is thus permissible (but not | |
bf740959 | 947 | recommended) to have several lines or different host keys for the same |
4fe2af09 | 948 | names. |
949 | This will inevitably happen when short forms of host names | |
950 | from different domains are put in the file. | |
951 | It is possible | |
bf740959 | 952 | that the files contain conflicting information; authentication is |
953 | accepted if valid information can be found from either file. | |
954 | .Pp | |
955 | Note that the lines in these files are typically hundreds of characters | |
956 | long, and you definitely don't want to type in the host keys by hand. | |
957 | Rather, generate them by a script | |
f54651ce | 958 | or by taking |
5f4fdfae | 959 | .Pa /etc/ssh_host_key.pub |
bf740959 | 960 | and adding the host names at the front. |
961 | .Ss Examples | |
962 | closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi | |
963 | .Sh FILES | |
964 | .Bl -tag -width Ds | |
5f4fdfae | 965 | .It Pa /etc/sshd_config |
bf740959 | 966 | Contains configuration data for |
967 | .Nm sshd . | |
968 | This file should be writable by root only, but it is recommended | |
969 | (though not necessary) that it be world-readable. | |
b8dc87d3 | 970 | .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key |
971 | These three files contain the private parts of the | |
972 | (SSH1, SSH2 DSA, and SSH2 RSA) host keys. | |
973 | These files should only be owned by root, readable only by root, and not | |
bf740959 | 974 | accessible to others. |
975 | Note that | |
976 | .Nm | |
977 | does not start if this file is group/world-accessible. | |
b8dc87d3 | 978 | .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub |
672f212f | 979 | These three files contain the public parts of the |
b8dc87d3 | 980 | (SSH1, SSH2 DSA, and SSH2 RSA) host keys. |
981 | These files should be world-readable but writable only by | |
4fe2af09 | 982 | root. |
b8dc87d3 | 983 | Their contents should match the respective private parts. |
984 | These files are not | |
985 | really used for anything; they are provided for the convenience of | |
986 | the user so their contents can be copied to known hosts files. | |
987 | These files are created using | |
bf740959 | 988 | .Xr ssh-keygen 1 . |
c523303b | 989 | .It Pa /etc/primes |
990 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". | |
5f4fdfae | 991 | .It Pa /var/run/sshd.pid |
bf740959 | 992 | Contains the process ID of the |
993 | .Nm | |
994 | listening for connections (if there are several daemons running | |
995 | concurrently for different ports, this contains the pid of the one | |
4fe2af09 | 996 | started last). |
c345cf9d | 997 | The content of this file is not sensitive; it can be world-readable. |
bf740959 | 998 | .It Pa $HOME/.ssh/authorized_keys |
999 | Lists the RSA keys that can be used to log into the user's account. | |
1000 | This file must be readable by root (which may on some machines imply | |
1001 | it being world-readable if the user's home directory resides on an NFS | |
4fe2af09 | 1002 | volume). |
1003 | It is recommended that it not be accessible by others. | |
1004 | The format of this file is described above. | |
1d1ffb87 | 1005 | Users will place the contents of their |
1006 | .Pa identity.pub | |
1007 | files into this file, as described in | |
1008 | .Xr ssh-keygen 1 . | |
1009 | .It Pa $HOME/.ssh/authorized_keys2 | |
1010 | Lists the DSA keys that can be used to log into the user's account. | |
1011 | This file must be readable by root (which may on some machines imply | |
1012 | it being world-readable if the user's home directory resides on an NFS | |
1013 | volume). | |
1014 | It is recommended that it not be accessible by others. | |
1015 | The format of this file is described above. | |
1016 | Users will place the contents of their | |
1017 | .Pa id_dsa.pub | |
c0ecc314 | 1018 | and/or |
1019 | .Pa id_rsa.pub | |
1d1ffb87 | 1020 | files into this file, as described in |
1021 | .Xr ssh-keygen 1 . | |
5f4fdfae | 1022 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
6a17f9c2 | 1023 | These files are consulted when using rhosts with RSA host |
4fe2af09 | 1024 | authentication to check the public key of the host. |
1025 | The key must be listed in one of these files to be accepted. | |
5bbb5681 | 1026 | The client uses the same files |
e91c60f2 | 1027 | to verify that it is connecting to the correct remote host. |
4fe2af09 | 1028 | These files should be writable only by root/the owner. |
5f4fdfae | 1029 | .Pa /etc/ssh_known_hosts |
bf740959 | 1030 | should be world-readable, and |
1031 | .Pa $HOME/.ssh/known_hosts | |
1032 | can but need not be world-readable. | |
1033 | .It Pa /etc/nologin | |
f54651ce | 1034 | If this file exists, |
bf740959 | 1035 | .Nm |
4fe2af09 | 1036 | refuses to let anyone except root log in. |
1037 | The contents of the file | |
bf740959 | 1038 | are displayed to anyone trying to log in, and non-root connections are |
4fe2af09 | 1039 | refused. |
1040 | The file should be world-readable. | |
bf740959 | 1041 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
1042 | If compiled with | |
1043 | .Sy LIBWRAP | |
1044 | support, tcp-wrappers access controls may be defined here as described in | |
1045 | .Xr hosts_access 5 . | |
1046 | .It Pa $HOME/.rhosts | |
1047 | This file contains host-username pairs, separated by a space, one per | |
4fe2af09 | 1048 | line. |
1049 | The given user on the corresponding host is permitted to log in | |
1050 | without password. | |
1051 | The same file is used by rlogind and rshd. | |
bf740959 | 1052 | The file must |
1053 | be writable only by the user; it is recommended that it not be | |
1054 | accessible by others. | |
1055 | .Pp | |
4fe2af09 | 1056 | If is also possible to use netgroups in the file. |
1057 | Either host or user | |
bf740959 | 1058 | name may be of the form +@groupname to specify all hosts or all users |
1059 | in the group. | |
1060 | .It Pa $HOME/.shosts | |
1061 | For ssh, | |
1062 | this file is exactly the same as for | |
1063 | .Pa .rhosts . | |
1064 | However, this file is | |
1065 | not used by rlogin and rshd, so using this permits access using SSH only. | |
c345cf9d | 1066 | .It Pa /etc/hosts.equiv |
bf740959 | 1067 | This file is used during |
1068 | .Pa .rhosts | |
4fe2af09 | 1069 | authentication. |
1070 | In the simplest form, this file contains host names, one per line. | |
1071 | Users on | |
bf740959 | 1072 | those hosts are permitted to log in without a password, provided they |
4fe2af09 | 1073 | have the same user name on both machines. |
1074 | The host name may also be | |
bf740959 | 1075 | followed by a user name; such users are permitted to log in as |
1076 | .Em any | |
4fe2af09 | 1077 | user on this machine (except root). |
1078 | Additionally, the syntax | |
bf740959 | 1079 | .Dq +@group |
4fe2af09 | 1080 | can be used to specify netgroups. |
1081 | Negated entries start with | |
bf740959 | 1082 | .Ql \&- . |
1083 | .Pp | |
1084 | If the client host/user is successfully matched in this file, login is | |
1085 | automatically permitted provided the client and server user names are the | |
4fe2af09 | 1086 | same. |
1087 | Additionally, successful RSA host authentication is normally required. | |
1088 | This file must be writable only by root; it is recommended | |
bf740959 | 1089 | that it be world-readable. |
1090 | .Pp | |
1091 | .Sy "Warning: It is almost never a good idea to use user names in" | |
1092 | .Pa hosts.equiv . | |
1093 | Beware that it really means that the named user(s) can log in as | |
1094 | .Em anybody , | |
1095 | which includes bin, daemon, adm, and other accounts that own critical | |
4fe2af09 | 1096 | binaries and directories. |
1097 | Using a user name practically grants the user root access. | |
1098 | The only valid use for user names that I can think | |
bf740959 | 1099 | of is in negative entries. |
1100 | .Pp | |
1101 | Note that this warning also applies to rsh/rlogin. | |
5f4fdfae | 1102 | .It Pa /etc/shosts.equiv |
bf740959 | 1103 | This is processed exactly as |
1104 | .Pa /etc/hosts.equiv . | |
1105 | However, this file may be useful in environments that want to run both | |
1106 | rsh/rlogin and ssh. | |
1107 | .It Pa $HOME/.ssh/environment | |
4fe2af09 | 1108 | This file is read into the environment at login (if it exists). |
1109 | It can only contain empty lines, comment lines (that start with | |
bf740959 | 1110 | .Ql # ) , |
4fe2af09 | 1111 | and assignment lines of the form name=value. |
1112 | The file should be writable | |
bf740959 | 1113 | only by the user; it need not be readable by anyone else. |
1114 | .It Pa $HOME/.ssh/rc | |
1115 | If this file exists, it is run with /bin/sh after reading the | |
4fe2af09 | 1116 | environment files but before starting the user's shell or command. |
1117 | If X11 spoofing is in use, this will receive the "proto cookie" pair in | |
bf740959 | 1118 | standard input (and |
1119 | .Ev DISPLAY | |
4fe2af09 | 1120 | in environment). |
1121 | This must call | |
bf740959 | 1122 | .Xr xauth 1 |
1123 | in that case. | |
1124 | .Pp | |
1125 | The primary purpose of this file is to run any initialization routines | |
1126 | which may be needed before the user's home directory becomes | |
1127 | accessible; AFS is a particular example of such an environment. | |
1128 | .Pp | |
1129 | This file will probably contain some initialization code followed by | |
1130 | something similar to: "if read proto cookie; then echo add $DISPLAY | |
1131 | $proto $cookie | xauth -q -; fi". | |
1132 | .Pp | |
1133 | If this file does not exist, | |
5f4fdfae | 1134 | .Pa /etc/sshrc |
bf740959 | 1135 | is run, and if that |
1136 | does not exist either, xauth is used to store the cookie. | |
1137 | .Pp | |
1138 | This file should be writable only by the user, and need not be | |
1139 | readable by anyone else. | |
5f4fdfae | 1140 | .It Pa /etc/sshrc |
bf740959 | 1141 | Like |
1142 | .Pa $HOME/.ssh/rc . | |
1143 | This can be used to specify | |
4fe2af09 | 1144 | machine-specific login-time initializations globally. |
1145 | This file should be writable only by root, and should be world-readable. | |
089fbbd2 | 1146 | .El |
fa08c86b | 1147 | .Sh AUTHORS |
7f5c4295 | 1148 | OpenSSH is a derivative of the original and free |
1149 | ssh 1.2.12 release by Tatu Ylonen. | |
1150 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1151 | Theo de Raadt and Dug Song | |
1152 | removed many bugs, re-added newer features and | |
1153 | created OpenSSH. | |
1154 | Markus Friedl contributed the support for SSH | |
1155 | protocol versions 1.5 and 2.0. | |
bf740959 | 1156 | .Sh SEE ALSO |
bf740959 | 1157 | .Xr scp 1 , |
61e96248 | 1158 | .Xr sftp 1 , |
b5e300c2 | 1159 | .Xr sftp-server 8 , |
bf740959 | 1160 | .Xr ssh 1 , |
1161 | .Xr ssh-add 1 , | |
1162 | .Xr ssh-agent 1 , | |
1163 | .Xr ssh-keygen 1 , | |
7368a6c8 | 1164 | .Xr rlogin 1 , |
1165 | .Xr rsh 1 |