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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 | .\" | |
13 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. | |
14 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. | |
15 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. | |
16 | .\" | |
17 | .\" Redistribution and use in source and binary forms, with or without | |
18 | .\" modification, are permitted provided that the following conditions | |
19 | .\" are met: | |
20 | .\" 1. Redistributions of source code must retain the above copyright | |
21 | .\" notice, this list of conditions and the following disclaimer. | |
22 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
23 | .\" notice, this list of conditions and the following disclaimer in the | |
24 | .\" documentation and/or other materials provided with the distribution. | |
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 | .\" |
e91c60f2 | 37 | .\" $OpenBSD: sshd.8,v 1.96 2001/02/22 21:57:27 markus Exp $ |
bf740959 | 38 | .Dd September 25, 1999 |
39 | .Dt SSHD 8 | |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm sshd | |
dcb971e1 | 43 | .Nd OpenSSH secure shell 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 |
f54651ce | 57 | (Secure Shell 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. | |
137 | The rest of the session is encrypted | |
138 | using a symmetric cipher, currently | |
139 | Blowfish, 3DES or CAST128 in CBC mode or Arcfour. | |
140 | The client selects the encryption algorithm | |
141 | to use from those offered by the server. | |
142 | Additionally, session integrity is provided | |
d0c832f3 | 143 | through a cryptographic message authentication code |
1d1ffb87 | 144 | (hmac-sha1 or hmac-md5). |
145 | .Pp | |
146 | Protocol version 2 provides a public key based | |
fa08c86b | 147 | user authentication method (PubkeyAuthentication) |
1d1ffb87 | 148 | and conventional password authentication. |
149 | .Pp | |
150 | .Ss Command execution and data forwarding | |
151 | .Pp | |
bf740959 | 152 | If the client successfully authenticates itself, a dialog for |
4fe2af09 | 153 | preparing the session is entered. |
154 | At this time the client may request | |
bf740959 | 155 | things like allocating a pseudo-tty, forwarding X11 connections, |
156 | forwarding TCP/IP connections, or forwarding the authentication agent | |
157 | connection over the secure channel. | |
158 | .Pp | |
159 | Finally, the client either requests a shell or execution of a command. | |
4fe2af09 | 160 | The sides then enter session mode. |
161 | In this mode, either side may send | |
bf740959 | 162 | data at any time, and such data is forwarded to/from the shell or |
163 | command on the server side, and the user terminal in the client side. | |
164 | .Pp | |
165 | When the user program terminates and all forwarded X11 and other | |
166 | connections have been closed, the server sends command exit status to | |
167 | the client, and both sides exit. | |
168 | .Pp | |
169 | .Nm | |
170 | can be configured using command-line options or a configuration | |
4fe2af09 | 171 | file. |
172 | Command-line options override values specified in the | |
bf740959 | 173 | configuration file. |
174 | .Pp | |
9d6b7add | 175 | .Nm |
176 | rereads its configuration file when it receives a hangup signal, | |
177 | .Dv SIGHUP . | |
178 | .Pp | |
bf740959 | 179 | The options are as follows: |
180 | .Bl -tag -width Ds | |
181 | .It Fl b Ar bits | |
182 | Specifies the number of bits in the server key (default 768). | |
183 | .Pp | |
184 | .It Fl d | |
4fe2af09 | 185 | Debug mode. |
186 | The server sends verbose debug output to the system | |
187 | log, and does not put itself in the background. | |
188 | The server also will not fork and will only process one connection. | |
189 | This option is only intended for debugging for the server. | |
94ec8c6b | 190 | Multiple -d options increases the debugging level. |
191 | Maximum is 3. | |
bf740959 | 192 | .It Fl f Ar configuration_file |
4fe2af09 | 193 | Specifies the name of the configuration file. |
194 | The default is | |
5f4fdfae | 195 | .Pa /etc/sshd_config . |
bf740959 | 196 | .Nm |
197 | refuses to start if there is no configuration file. | |
198 | .It Fl g Ar login_grace_time | |
199 | Gives the grace time for clients to authenticate themselves (default | |
ee5e6612 | 200 | 600 seconds). |
4fe2af09 | 201 | If the client fails to authenticate the user within |
202 | this many seconds, the server disconnects and exits. | |
203 | A value of zero indicates no limit. | |
bf740959 | 204 | .It Fl h Ar host_key_file |
8abcdba4 | 205 | Specifies the file from which the host key is read (default |
5f4fdfae | 206 | .Pa /etc/ssh_host_key ) . |
bf740959 | 207 | This option must be given if |
208 | .Nm | |
209 | is not run as root (as the normal | |
210 | host file is normally not readable by anyone but root). | |
8abcdba4 | 211 | It is possible to have multiple host key files for |
212 | the different protocol versions. | |
bf740959 | 213 | .It Fl i |
214 | Specifies that | |
215 | .Nm | |
f54651ce | 216 | is being run from inetd. |
bf740959 | 217 | .Nm |
218 | is normally not run | |
219 | from inetd because it needs to generate the server key before it can | |
4fe2af09 | 220 | respond to the client, and this may take tens of seconds. |
221 | Clients would have to wait too long if the key was regenerated every time. | |
610cd5c6 | 222 | However, with small key sizes (e.g., 512) using |
bf740959 | 223 | .Nm |
224 | from inetd may | |
225 | be feasible. | |
226 | .It Fl k Ar key_gen_time | |
227 | Specifies how often the server key is regenerated (default 3600 | |
4fe2af09 | 228 | seconds, or one hour). |
229 | The motivation for regenerating the key fairly | |
bf740959 | 230 | often is that the key is not stored anywhere, and after about an hour, |
231 | it becomes impossible to recover the key for decrypting intercepted | |
232 | communications even if the machine is cracked into or physically | |
4fe2af09 | 233 | seized. |
234 | A value of zero indicates that the key will never be regenerated. | |
bf740959 | 235 | .It Fl p Ar port |
236 | Specifies the port on which the server listens for connections | |
237 | (default 22). | |
238 | .It Fl q | |
4fe2af09 | 239 | Quiet mode. |
240 | Nothing is sent to the system log. | |
241 | Normally the beginning, | |
bf740959 | 242 | authentication, and termination of each connection is logged. |
c345cf9d | 243 | .It Fl u Ar len |
244 | This option is used to specify the size of the field | |
245 | in the | |
246 | .Li utmp | |
247 | structure that holds the remote host name. | |
248 | If the resolved host name is longer than | |
249 | .Ar len , | |
250 | the dotted decimal value will be used instead. | |
251 | This allows hosts with very long host names that | |
252 | overflow this field to still be uniquely identified. | |
253 | Specifying | |
254 | .Fl u0 | |
255 | indicates that only dotted decimal addresses | |
256 | should be put into the | |
257 | .Pa utmp | |
258 | file. | |
8abcdba4 | 259 | .It Fl D |
260 | When this option is specified | |
261 | .Nm | |
262 | will not detach and does not become a daemon. | |
263 | This allows easy monitoring of | |
264 | .Nm sshd . | |
5260325f | 265 | .It Fl V Ar client_protocol_id |
94ec8c6b | 266 | SSH-2 compatibility mode. |
3189621b | 267 | When this option is specified |
5260325f | 268 | .Nm |
3189621b | 269 | assumes the client has sent the supplied version string |
5260325f | 270 | and skips the |
271 | Protocol Version Identification Exchange. | |
94ec8c6b | 272 | This option is not intended to be called directly. |
48e671d5 | 273 | .It Fl 4 |
274 | Forces | |
275 | .Nm | |
276 | to use IPv4 addresses only. | |
277 | .It Fl 6 | |
278 | Forces | |
279 | .Nm | |
280 | to use IPv6 addresses only. | |
bf740959 | 281 | .El |
282 | .Sh CONFIGURATION FILE | |
283 | .Nm | |
f54651ce | 284 | reads configuration data from |
5f4fdfae | 285 | .Pa /etc/sshd_config |
bf740959 | 286 | (or the file specified with |
287 | .Fl f | |
4fe2af09 | 288 | on the command line). |
289 | The file contains keyword-value pairs, one per line. | |
290 | Lines starting with | |
bf740959 | 291 | .Ql # |
292 | and empty lines are interpreted as comments. | |
293 | .Pp | |
294 | The following keywords are possible. | |
295 | .Bl -tag -width Ds | |
296 | .It Cm AFSTokenPassing | |
4fe2af09 | 297 | Specifies whether an AFS token may be forwarded to the server. |
298 | Default is | |
bf740959 | 299 | .Dq yes . |
300 | .It Cm AllowGroups | |
76896b4e | 301 | This keyword can be followed by a list of group names, separated |
4fe2af09 | 302 | by spaces. |
303 | If specified, login is allowed only for users whose primary | |
c6a69271 | 304 | group or supplementary group list matches one of the patterns. |
bf740959 | 305 | .Ql \&* |
306 | and | |
307 | .Ql ? | |
308 | can be used as | |
4fe2af09 | 309 | wildcards in the patterns. |
c345cf9d | 310 | Only group names are valid; a numerical group ID isn't recognized. |
c6a69271 | 311 | By default login is allowed regardless of the group list. |
bf740959 | 312 | .Pp |
33de75a3 | 313 | .It Cm AllowTcpForwarding |
314 | Specifies whether TCP forwarding is permitted. | |
315 | The default is | |
316 | .Dq yes . | |
317 | Note that disabling TCP forwarding does not improve security unless | |
318 | users are also denied shell access, as they can always install their | |
319 | own forwarders. | |
320 | .Pp | |
bf740959 | 321 | .It Cm AllowUsers |
76896b4e | 322 | This keyword can be followed by a list of user names, separated |
4fe2af09 | 323 | by spaces. |
324 | If specified, login is allowed only for users names that | |
bf740959 | 325 | match one of the patterns. |
326 | .Ql \&* | |
327 | and | |
328 | .Ql ? | |
329 | can be used as | |
4fe2af09 | 330 | wildcards in the patterns. |
c345cf9d | 331 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 332 | By default login is allowed regardless of the user name. |
bf740959 | 333 | .Pp |
eea39c02 | 334 | .It Cm Banner |
335 | In some jurisdictions, sending a warning message before authentication | |
336 | may be relevant for getting legal protection. | |
337 | The contents of the specified file are sent to the remote user before | |
338 | authentication is allowed. | |
339 | This option is only available for protocol version 2. | |
340 | .Pp | |
f54651ce | 341 | .It Cm Ciphers |
342 | Specifies the ciphers allowed for protocol version 2. | |
343 | Multiple ciphers must be comma-separated. | |
344 | The default is | |
9616313f | 345 | .Dq 3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes128-cbc . |
bf740959 | 346 | .It Cm CheckMail |
347 | Specifies whether | |
348 | .Nm | |
349 | should check for new mail for interactive logins. | |
350 | The default is | |
351 | .Dq no . | |
352 | .It Cm DenyGroups | |
353 | This keyword can be followed by a number of group names, separated | |
4fe2af09 | 354 | by spaces. |
c6a69271 | 355 | Users whose primary group or supplementary group list matches |
356 | one of the patterns aren't allowed to log in. | |
bf740959 | 357 | .Ql \&* |
358 | and | |
359 | .Ql ? | |
360 | can be used as | |
4fe2af09 | 361 | wildcards in the patterns. |
c345cf9d | 362 | Only group names are valid; a numerical group ID isn't recognized. |
c6a69271 | 363 | By default login is allowed regardless of the group list. |
bf740959 | 364 | .Pp |
365 | .It Cm DenyUsers | |
366 | This keyword can be followed by a number of user names, separated | |
4fe2af09 | 367 | by spaces. |
368 | Login is disallowed for user names that match one of the patterns. | |
bf740959 | 369 | .Ql \&* |
370 | and | |
371 | .Ql ? | |
4fe2af09 | 372 | can be used as wildcards in the patterns. |
c345cf9d | 373 | Only user names are valid; a numerical user ID isn't recognized. |
4fe2af09 | 374 | By default login is allowed regardless of the user name. |
fa08c86b | 375 | .It Cm PubkeyAuthentication |
376 | Specifies whether public key authentication is allowed. | |
1d1ffb87 | 377 | The default is |
378 | .Dq yes . | |
379 | Note that this option applies to protocol version 2 only. | |
380 | .It Cm GatewayPorts | |
381 | Specifies whether remote hosts are allowed to connect to ports | |
382 | forwarded for the client. | |
383 | The argument must be | |
384 | .Dq yes | |
385 | or | |
386 | .Dq no . | |
387 | The default is | |
388 | .Dq no . | |
bf740959 | 389 | .It Cm HostKey |
fa08c86b | 390 | Specifies the file containing the private host keys (default |
1d1ffb87 | 391 | .Pa /etc/ssh_host_key ) |
fa08c86b | 392 | used by SSH protocol versions 1 and 2. |
bf740959 | 393 | Note that |
394 | .Nm | |
42f11eb2 | 395 | will refuse to use a file if it is group/world-accessible. |
fa08c86b | 396 | It is possible to have multiple host key files. |
397 | .Dq rsa1 | |
398 | keys are used for version 1 and | |
399 | .Dq dsa | |
400 | or | |
401 | .Dq rsa | |
402 | are used for version 2 of the SSH protocol. | |
bf740959 | 403 | .It Cm IgnoreRhosts |
c8d54615 | 404 | Specifies that |
405 | .Pa .rhosts | |
f54651ce | 406 | and |
c8d54615 | 407 | .Pa .shosts |
408 | files will not be used in authentication. | |
bf740959 | 409 | .Pa /etc/hosts.equiv |
410 | and | |
f54651ce | 411 | .Pa /etc/shosts.equiv |
4fe2af09 | 412 | are still used. |
f54651ce | 413 | The default is |
c8d54615 | 414 | .Dq yes . |
b4748e2f | 415 | .It Cm IgnoreUserKnownHosts |
416 | Specifies whether | |
417 | .Nm | |
418 | should ignore the user's | |
419 | .Pa $HOME/.ssh/known_hosts | |
420 | during | |
421 | .Cm RhostsRSAAuthentication . | |
422 | The default is | |
423 | .Dq no . | |
bf740959 | 424 | .It Cm KeepAlive |
425 | Specifies whether the system should send keepalive messages to the | |
4fe2af09 | 426 | other side. |
427 | If they are sent, death of the connection or crash of one | |
428 | of the machines will be properly noticed. | |
429 | However, this means that | |
bf740959 | 430 | connections will die if the route is down temporarily, and some people |
4fe2af09 | 431 | find it annoying. |
d0c832f3 | 432 | On the other hand, if keepalives are not sent, |
bf740959 | 433 | sessions may hang indefinitely on the server, leaving |
434 | .Dq ghost | |
435 | users and consuming server resources. | |
436 | .Pp | |
437 | The default is | |
438 | .Dq yes | |
439 | (to send keepalives), and the server will notice | |
4fe2af09 | 440 | if the network goes down or the client host reboots. |
441 | This avoids infinitely hanging sessions. | |
bf740959 | 442 | .Pp |
443 | To disable keepalives, the value should be set to | |
444 | .Dq no | |
445 | in both the server and the client configuration files. | |
446 | .It Cm KerberosAuthentication | |
4fe2af09 | 447 | Specifies whether Kerberos authentication is allowed. |
448 | This can be in the form of a Kerberos ticket, or if | |
bf740959 | 449 | .Cm PasswordAuthentication |
450 | is yes, the password provided by the user will be validated through | |
94ec8c6b | 451 | the Kerberos KDC. |
452 | To use this option, the server needs a | |
c345cf9d | 453 | Kerberos servtab which allows the verification of the KDC's identity. |
4fe2af09 | 454 | Default is |
bf740959 | 455 | .Dq yes . |
456 | .It Cm KerberosOrLocalPasswd | |
457 | If set then if password authentication through Kerberos fails then | |
458 | the password will be validated via any additional local mechanism | |
459 | such as | |
188adeb2 | 460 | .Pa /etc/passwd . |
4fe2af09 | 461 | Default is |
bf740959 | 462 | .Dq yes . |
463 | .It Cm KerberosTgtPassing | |
464 | Specifies whether a Kerberos TGT may be forwarded to the server. | |
f54651ce | 465 | Default is |
bf740959 | 466 | .Dq no , |
467 | as this only works when the Kerberos KDC is actually an AFS kaserver. | |
468 | .It Cm KerberosTicketCleanup | |
469 | Specifies whether to automatically destroy the user's ticket cache | |
4fe2af09 | 470 | file on logout. |
471 | Default is | |
bf740959 | 472 | .Dq yes . |
473 | .It Cm KeyRegenerationInterval | |
474 | The server key is automatically regenerated after this many seconds | |
4fe2af09 | 475 | (if it has been used). |
476 | The purpose of regeneration is to prevent | |
bf740959 | 477 | decrypting captured sessions by later breaking into the machine and |
4fe2af09 | 478 | stealing the keys. |
479 | The key is never stored anywhere. | |
480 | If the value is 0, the key is never regenerated. | |
481 | The default is 3600 (seconds). | |
bf740959 | 482 | .It Cm ListenAddress |
483 | Specifies what local address | |
484 | .Nm | |
485 | should listen on. | |
486 | The default is to listen to all local addresses. | |
48e671d5 | 487 | Multiple options of this type are permitted. |
488 | Additionally, the | |
489 | .Cm Ports | |
490 | options must precede this option. | |
bf740959 | 491 | .It Cm LoginGraceTime |
492 | The server disconnects after this time if the user has not | |
4fe2af09 | 493 | successfully logged in. |
494 | If the value is 0, there is no time limit. | |
bf740959 | 495 | The default is 600 (seconds). |
6a17f9c2 | 496 | .It Cm LogLevel |
497 | Gives the verbosity level that is used when logging messages from | |
498 | .Nm sshd . | |
499 | The possible values are: | |
59c97189 | 500 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
501 | The default is INFO. | |
6a17f9c2 | 502 | Logging with level DEBUG violates the privacy of users |
503 | and is not recommended. | |
b2552997 | 504 | .It Cm MACs |
505 | Specifies the available MAC (message authentication code) algorithms. | |
506 | The MAC algorithm is used in protocol version 2 | |
507 | for data integrity protection. | |
508 | Multiple algorithms must be comma-separated. | |
509 | The default is | |
510 | .Pp | |
511 | .Bd -literal | |
512 | ``hmac-sha1,hmac-md5,hmac-ripemd160,hmac-ripemd160@openssh.com, | |
513 | hmac-sha1-96,hmac-md5-96'' | |
514 | .Ed | |
089fbbd2 | 515 | .It Cm MaxStartups |
516 | Specifies the maximum number of concurrent unauthenticated connections to the | |
517 | .Nm | |
518 | daemon. | |
519 | Additional connections will be dropped until authentication succeeds or the | |
520 | .Cm LoginGraceTime | |
521 | expires for a connection. | |
522 | The default is 10. | |
c345cf9d | 523 | .Pp |
524 | Alternatively, random early drop can be enabled by specifying | |
525 | the three colon separated values | |
526 | .Dq start:rate:full | |
94ec8c6b | 527 | (e.g., "10:30:60"). |
c345cf9d | 528 | .Nm |
6f37606e | 529 | will refuse connection attempts with a probability of |
c345cf9d | 530 | .Dq rate/100 |
531 | (30%) | |
532 | if there are currently | |
533 | .Dq start | |
534 | (10) | |
535 | unauthenticated connections. | |
6f37606e | 536 | The probability increases linearly and all connection attempts |
c345cf9d | 537 | are refused if the number of unauthenticated connections reaches |
538 | .Dq full | |
539 | (60). | |
bf740959 | 540 | .It Cm PasswordAuthentication |
541 | Specifies whether password authentication is allowed. | |
542 | The default is | |
543 | .Dq yes . | |
c345cf9d | 544 | Note that this option applies to both protocol versions 1 and 2. |
bf740959 | 545 | .It Cm PermitEmptyPasswords |
546 | When password authentication is allowed, it specifies whether the | |
4fe2af09 | 547 | server allows login to accounts with empty password strings. |
548 | The default is | |
c8d54615 | 549 | .Dq no . |
bf740959 | 550 | .It Cm PermitRootLogin |
551 | Specifies whether the root can log in using | |
552 | .Xr ssh 1 . | |
553 | The argument must be | |
554 | .Dq yes , | |
15853e93 | 555 | .Dq without-password , |
556 | .Dq forced-commands-only | |
bf740959 | 557 | or |
558 | .Dq no . | |
559 | The default is | |
560 | .Dq yes . | |
15853e93 | 561 | .Pp |
562 | If this option is set to | |
bf740959 | 563 | .Dq without-password |
15853e93 | 564 | password authentication is disabled for root. |
bf740959 | 565 | .Pp |
15853e93 | 566 | If this option is set to |
567 | .Dq forced-commands-only | |
568 | root login with public key authentication will be allowed, | |
569 | but only if the | |
bf740959 | 570 | .Ar command |
15853e93 | 571 | option has been specified |
bf740959 | 572 | (which may be useful for taking remote backups even if root login is |
15853e93 | 573 | normally not allowed). All other authentication methods are disabled |
574 | for root. | |
0fbe8c74 | 575 | .It Cm PidFile |
576 | Specifies the file that contains the process identifier of the | |
577 | .Nm | |
578 | daemon. | |
579 | The default is | |
580 | .Pa /var/run/sshd.pid . | |
bf740959 | 581 | .It Cm Port |
582 | Specifies the port number that | |
583 | .Nm | |
4fe2af09 | 584 | listens on. |
585 | The default is 22. | |
48e671d5 | 586 | Multiple options of this type are permitted. |
bf740959 | 587 | .It Cm PrintMotd |
588 | Specifies whether | |
589 | .Nm | |
f54651ce | 590 | should print |
bf740959 | 591 | .Pa /etc/motd |
4fe2af09 | 592 | when a user logs in interactively. |
593 | (On some systems it is also printed by the shell, | |
bf740959 | 594 | .Pa /etc/profile , |
4fe2af09 | 595 | or equivalent.) |
596 | The default is | |
bf740959 | 597 | .Dq yes . |
f54651ce | 598 | .It Cm Protocol |
599 | Specifies the protocol versions | |
600 | .Nm | |
601 | should support. | |
602 | The possible values are | |
603 | .Dq 1 | |
604 | and | |
605 | .Dq 2 . | |
606 | Multiple versions must be comma-separated. | |
607 | The default is | |
608 | .Dq 1 . | |
bf740959 | 609 | .It Cm RandomSeed |
4fe2af09 | 610 | Obsolete. |
611 | Random number generation uses other techniques. | |
61e96248 | 612 | .It Cm ReverseMappingCheck |
613 | Specifies whether | |
614 | .Nm | |
615 | should try to verify the remote host name and check that | |
616 | the resolved host name for the remote IP address maps back to the | |
617 | very same IP address. | |
618 | The default is | |
619 | .Dq no . | |
bf740959 | 620 | .It Cm RhostsAuthentication |
621 | Specifies whether authentication using rhosts or /etc/hosts.equiv | |
4fe2af09 | 622 | files is sufficient. |
623 | Normally, this method should not be permitted because it is insecure. | |
bf740959 | 624 | .Cm RhostsRSAAuthentication |
625 | should be used | |
626 | instead, because it performs RSA-based host authentication in addition | |
627 | to normal rhosts or /etc/hosts.equiv authentication. | |
628 | The default is | |
629 | .Dq no . | |
630 | .It Cm RhostsRSAAuthentication | |
631 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
4fe2af09 | 632 | with successful RSA host authentication is allowed. |
633 | The default is | |
c8d54615 | 634 | .Dq no . |
bf740959 | 635 | .It Cm RSAAuthentication |
4fe2af09 | 636 | Specifies whether pure RSA authentication is allowed. |
637 | The default is | |
bf740959 | 638 | .Dq yes . |
1d1ffb87 | 639 | Note that this option applies to protocol version 1 only. |
bf740959 | 640 | .It Cm ServerKeyBits |
4fe2af09 | 641 | Defines the number of bits in the server key. |
642 | The minimum value is 512, and the default is 768. | |
61e96248 | 643 | .It Cm ChallengeResponseAuthentication |
bf740959 | 644 | Specifies whether |
61e96248 | 645 | challenge reponse |
4fe2af09 | 646 | authentication is allowed. |
78c8106e | 647 | Currently there is support for |
61e96248 | 648 | .Xr skey 1 |
78c8106e | 649 | and PAM authentication. |
4fe2af09 | 650 | The default is |
bf740959 | 651 | .Dq yes . |
78c8106e | 652 | Note that enabling ChallengeResponseAuthentication for PAM bypasses |
653 | OpenSSH's password checking code, thus rendering options such as | |
654 | .Cm PasswordAuthentication | |
655 | and | |
656 | .Cm PermitEmptyPasswords | |
657 | ineffective. | |
bf740959 | 658 | .It Cm StrictModes |
659 | Specifies whether | |
660 | .Nm | |
661 | should check file modes and ownership of the | |
4fe2af09 | 662 | user's files and home directory before accepting login. |
663 | This is normally desirable because novices sometimes accidentally leave their | |
664 | directory or files world-writable. | |
665 | The default is | |
bf740959 | 666 | .Dq yes . |
38c295d6 | 667 | .It Cm Subsystem |
94ec8c6b | 668 | Configures an external subsystem (e.g., file transfer daemon). |
669 | Arguments should be a subsystem name and a command to execute upon subsystem | |
670 | request. | |
b5e300c2 | 671 | The command |
672 | .Xr sftp-server 8 | |
673 | implements the | |
674 | .Dq sftp | |
675 | file transfer subsystem. | |
38c295d6 | 676 | By default no subsystems are defined. |
677 | Note that this option applies to protocol version 2 only. | |
bf740959 | 678 | .It Cm SyslogFacility |
679 | Gives the facility code that is used when logging messages from | |
680 | .Nm sshd . | |
681 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, | |
4fe2af09 | 682 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
683 | The default is AUTH. | |
bf740959 | 684 | .It Cm UseLogin |
685 | Specifies whether | |
686 | .Xr login 1 | |
fa649821 | 687 | is used for interactive login sessions. |
688 | Note that | |
689 | .Xr login 1 | |
c345cf9d | 690 | is never used for remote command execution. |
4fe2af09 | 691 | The default is |
bf740959 | 692 | .Dq no . |
bf740959 | 693 | .It Cm X11DisplayOffset |
694 | Specifies the first display number available for | |
695 | .Nm sshd Ns 's | |
4fe2af09 | 696 | X11 forwarding. |
697 | This prevents | |
bf740959 | 698 | .Nm |
699 | from interfering with real X11 servers. | |
c8d54615 | 700 | The default is 10. |
7b2ea3a1 | 701 | .It Cm X11Forwarding |
4fe2af09 | 702 | Specifies whether X11 forwarding is permitted. |
703 | The default is | |
c8d54615 | 704 | .Dq no . |
7b2ea3a1 | 705 | Note that disabling X11 forwarding does not improve security in any |
706 | way, as users can always install their own forwarders. | |
fa649821 | 707 | .It Cm XAuthLocation |
708 | Specifies the location of the | |
709 | .Xr xauth 1 | |
710 | program. | |
711 | The default is | |
712 | .Pa /usr/X11R6/bin/xauth . | |
bf740959 | 713 | .El |
714 | .Sh LOGIN PROCESS | |
715 | When a user successfully logs in, | |
716 | .Nm | |
717 | does the following: | |
718 | .Bl -enum -offset indent | |
719 | .It | |
720 | If the login is on a tty, and no command has been specified, | |
f54651ce | 721 | prints last login time and |
bf740959 | 722 | .Pa /etc/motd |
723 | (unless prevented in the configuration file or by | |
724 | .Pa $HOME/.hushlogin ; | |
725 | see the | |
f54651ce | 726 | .Sx FILES |
bf740959 | 727 | section). |
728 | .It | |
729 | If the login is on a tty, records login time. | |
730 | .It | |
731 | Checks | |
732 | .Pa /etc/nologin ; | |
733 | if it exists, prints contents and quits | |
734 | (unless root). | |
735 | .It | |
736 | Changes to run with normal user privileges. | |
737 | .It | |
738 | Sets up basic environment. | |
739 | .It | |
740 | Reads | |
741 | .Pa $HOME/.ssh/environment | |
742 | if it exists. | |
743 | .It | |
744 | Changes to user's home directory. | |
745 | .It | |
746 | If | |
747 | .Pa $HOME/.ssh/rc | |
748 | exists, runs it; else if | |
5f4fdfae | 749 | .Pa /etc/sshrc |
bf740959 | 750 | exists, runs |
4fe2af09 | 751 | it; otherwise runs xauth. |
752 | The | |
bf740959 | 753 | .Dq rc |
754 | files are given the X11 | |
755 | authentication protocol and cookie in standard input. | |
756 | .It | |
757 | Runs user's shell or command. | |
758 | .El | |
759 | .Sh AUTHORIZED_KEYS FILE FORMAT | |
f54651ce | 760 | The |
bf740959 | 761 | .Pa $HOME/.ssh/authorized_keys |
762 | file lists the RSA keys that are | |
1d1ffb87 | 763 | permitted for RSA authentication in SSH protocols 1.3 and 1.5 |
d0c832f3 | 764 | Similarly, the |
1d1ffb87 | 765 | .Pa $HOME/.ssh/authorized_keys2 |
8abcdba4 | 766 | file lists the DSA and RSA keys that are |
767 | permitted for public key authentication (PubkeyAuthentication) | |
768 | in SSH protocol 2.0. | |
769 | .Pp | |
4fe2af09 | 770 | Each line of the file contains one |
bf740959 | 771 | key (empty lines and lines starting with a |
772 | .Ql # | |
773 | are ignored as | |
4fe2af09 | 774 | comments). |
8abcdba4 | 775 | Each RSA public key consists of the following fields, separated by |
4fe2af09 | 776 | spaces: options, bits, exponent, modulus, comment. |
8abcdba4 | 777 | Each protocol version 2 public key consists of: |
778 | options, keytype, base64 encoded key, comment. | |
779 | The options fields | |
780 | are optional; its presence is determined by whether the line starts | |
bf740959 | 781 | with a number or not (the option field never starts with a number). |
8abcdba4 | 782 | The bits, exponent, modulus and comment fields give the RSA key for |
783 | protocol version 1; the | |
bf740959 | 784 | comment field is not used for anything (but may be convenient for the |
785 | user to identify the key). | |
8abcdba4 | 786 | For protocol version 2 the keytype is |
787 | .Dq ssh-dss | |
788 | or | |
789 | .Dq ssh-rsa . | |
bf740959 | 790 | .Pp |
791 | Note that lines in this file are usually several hundred bytes long | |
4fe2af09 | 792 | (because of the size of the RSA key modulus). |
793 | You don't want to type them in; instead, copy the | |
bf740959 | 794 | .Pa identity.pub |
8abcdba4 | 795 | or the |
796 | .Pa id_dsa.pub | |
bf740959 | 797 | file and edit it. |
798 | .Pp | |
c345cf9d | 799 | The options (if present) consist of comma-separated option |
4fe2af09 | 800 | specifications. |
801 | No spaces are permitted, except within double quotes. | |
bf740959 | 802 | The following option specifications are supported: |
803 | .Bl -tag -width Ds | |
804 | .It Cm from="pattern-list" | |
805 | Specifies that in addition to RSA authentication, the canonical name | |
806 | of the remote host must be present in the comma-separated list of | |
4fe2af09 | 807 | patterns |
808 | .Pf ( Ql * | |
809 | and | |
810 | .Ql ? | |
811 | serve as wildcards). | |
812 | The list may also contain | |
813 | patterns negated by prefixing them with | |
814 | .Ql ! ; | |
815 | if the canonical host name matches a negated pattern, the key is not accepted. | |
816 | The purpose | |
bf740959 | 817 | of this option is to optionally increase security: RSA authentication |
818 | by itself does not trust the network or name servers or anything (but | |
819 | the key); however, if somebody somehow steals the key, the key | |
4fe2af09 | 820 | permits an intruder to log in from anywhere in the world. |
821 | This additional option makes using a stolen key more difficult (name | |
bf740959 | 822 | servers and/or routers would have to be compromised in addition to |
823 | just the key). | |
824 | .It Cm command="command" | |
825 | Specifies that the command is executed whenever this key is used for | |
4fe2af09 | 826 | authentication. |
827 | The command supplied by the user (if any) is ignored. | |
bf740959 | 828 | The command is run on a pty if the connection requests a pty; |
4fe2af09 | 829 | otherwise it is run without a tty. |
61e96248 | 830 | Note that if you want a 8-bit clean channel, |
831 | you must not request a pty or should specify | |
832 | .Cm no-pty . | |
4fe2af09 | 833 | A quote may be included in the command by quoting it with a backslash. |
834 | This option might be useful | |
835 | to restrict certain RSA keys to perform just a specific operation. | |
836 | An example might be a key that permits remote backups but nothing else. | |
d0c832f3 | 837 | Note that the client may specify TCP/IP and/or X11 |
838 | forwarding unless they are explicitly prohibited. | |
bf740959 | 839 | .It Cm environment="NAME=value" |
840 | Specifies that the string is to be added to the environment when | |
4fe2af09 | 841 | logging in using this key. |
842 | Environment variables set this way | |
843 | override other default environment values. | |
844 | Multiple options of this type are permitted. | |
bf740959 | 845 | .It Cm no-port-forwarding |
846 | Forbids TCP/IP forwarding when this key is used for authentication. | |
4fe2af09 | 847 | Any port forward requests by the client will return an error. |
848 | This might be used, e.g., in connection with the | |
bf740959 | 849 | .Cm command |
850 | option. | |
851 | .It Cm no-X11-forwarding | |
852 | Forbids X11 forwarding when this key is used for authentication. | |
853 | Any X11 forward requests by the client will return an error. | |
854 | .It Cm no-agent-forwarding | |
855 | Forbids authentication agent forwarding when this key is used for | |
856 | authentication. | |
857 | .It Cm no-pty | |
858 | Prevents tty allocation (a request to allocate a pty will fail). | |
859 | .El | |
860 | .Ss Examples | |
861 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar | |
862 | .Pp | |
863 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula | |
864 | .Pp | |
865 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi | |
866 | .Sh SSH_KNOWN_HOSTS FILE FORMAT | |
f54651ce | 867 | The |
1d1ffb87 | 868 | .Pa /etc/ssh_known_hosts , |
869 | .Pa /etc/ssh_known_hosts2 , | |
870 | .Pa $HOME/.ssh/known_hosts , | |
f54651ce | 871 | and |
1d1ffb87 | 872 | .Pa $HOME/.ssh/known_hosts2 |
4fe2af09 | 873 | files contain host public keys for all known hosts. |
874 | The global file should | |
875 | be prepared by the administrator (optional), and the per-user file is | |
c345cf9d | 876 | maintained automatically: whenever the user connects from an unknown host |
4fe2af09 | 877 | its key is added to the per-user file. |
bf740959 | 878 | .Pp |
879 | Each line in these files contains the following fields: hostnames, | |
4fe2af09 | 880 | bits, exponent, modulus, comment. |
881 | The fields are separated by spaces. | |
bf740959 | 882 | .Pp |
883 | Hostnames is a comma-separated list of patterns ('*' and '?' act as | |
884 | wildcards); each pattern in turn is matched against the canonical host | |
885 | name (when authenticating a client) or against the user-supplied | |
4fe2af09 | 886 | name (when authenticating a server). |
887 | A pattern may also be preceded by | |
bf740959 | 888 | .Ql ! |
889 | to indicate negation: if the host name matches a negated | |
890 | pattern, it is not accepted (by that line) even if it matched another | |
891 | pattern on the line. | |
892 | .Pp | |
1d1ffb87 | 893 | Bits, exponent, and modulus are taken directly from the RSA host key; they |
bf740959 | 894 | can be obtained, e.g., from |
5f4fdfae | 895 | .Pa /etc/ssh_host_key.pub . |
bf740959 | 896 | The optional comment field continues to the end of the line, and is not used. |
897 | .Pp | |
898 | Lines starting with | |
899 | .Ql # | |
900 | and empty lines are ignored as comments. | |
901 | .Pp | |
902 | When performing host authentication, authentication is accepted if any | |
4fe2af09 | 903 | matching line has the proper key. |
904 | It is thus permissible (but not | |
bf740959 | 905 | recommended) to have several lines or different host keys for the same |
4fe2af09 | 906 | names. |
907 | This will inevitably happen when short forms of host names | |
908 | from different domains are put in the file. | |
909 | It is possible | |
bf740959 | 910 | that the files contain conflicting information; authentication is |
911 | accepted if valid information can be found from either file. | |
912 | .Pp | |
913 | Note that the lines in these files are typically hundreds of characters | |
914 | long, and you definitely don't want to type in the host keys by hand. | |
915 | Rather, generate them by a script | |
f54651ce | 916 | or by taking |
5f4fdfae | 917 | .Pa /etc/ssh_host_key.pub |
bf740959 | 918 | and adding the host names at the front. |
919 | .Ss Examples | |
920 | closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi | |
921 | .Sh FILES | |
922 | .Bl -tag -width Ds | |
5f4fdfae | 923 | .It Pa /etc/sshd_config |
bf740959 | 924 | Contains configuration data for |
925 | .Nm sshd . | |
926 | This file should be writable by root only, but it is recommended | |
927 | (though not necessary) that it be world-readable. | |
5f4fdfae | 928 | .It Pa /etc/ssh_host_key |
bf740959 | 929 | Contains the private part of the host key. |
930 | This file should only be owned by root, readable only by root, and not | |
931 | accessible to others. | |
932 | Note that | |
933 | .Nm | |
934 | does not start if this file is group/world-accessible. | |
5f4fdfae | 935 | .It Pa /etc/ssh_host_key.pub |
bf740959 | 936 | Contains the public part of the host key. |
937 | This file should be world-readable but writable only by | |
4fe2af09 | 938 | root. |
939 | Its contents should match the private part. | |
940 | This file is not | |
bf740959 | 941 | really used for anything; it is only provided for the convenience of |
942 | the user so its contents can be copied to known hosts files. | |
943 | These two files are created using | |
944 | .Xr ssh-keygen 1 . | |
c523303b | 945 | .It Pa /etc/primes |
946 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". | |
5f4fdfae | 947 | .It Pa /var/run/sshd.pid |
bf740959 | 948 | Contains the process ID of the |
949 | .Nm | |
950 | listening for connections (if there are several daemons running | |
951 | concurrently for different ports, this contains the pid of the one | |
4fe2af09 | 952 | started last). |
c345cf9d | 953 | The content of this file is not sensitive; it can be world-readable. |
bf740959 | 954 | .It Pa $HOME/.ssh/authorized_keys |
955 | Lists the RSA keys that can be used to log into the user's account. | |
956 | This file must be readable by root (which may on some machines imply | |
957 | it being world-readable if the user's home directory resides on an NFS | |
4fe2af09 | 958 | volume). |
959 | It is recommended that it not be accessible by others. | |
960 | The format of this file is described above. | |
1d1ffb87 | 961 | Users will place the contents of their |
962 | .Pa identity.pub | |
963 | files into this file, as described in | |
964 | .Xr ssh-keygen 1 . | |
965 | .It Pa $HOME/.ssh/authorized_keys2 | |
966 | Lists the DSA keys that can be used to log into the user's account. | |
967 | This file must be readable by root (which may on some machines imply | |
968 | it being world-readable if the user's home directory resides on an NFS | |
969 | volume). | |
970 | It is recommended that it not be accessible by others. | |
971 | The format of this file is described above. | |
972 | Users will place the contents of their | |
973 | .Pa id_dsa.pub | |
974 | files into this file, as described in | |
975 | .Xr ssh-keygen 1 . | |
5f4fdfae | 976 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
6a17f9c2 | 977 | These files are consulted when using rhosts with RSA host |
4fe2af09 | 978 | authentication to check the public key of the host. |
979 | The key must be listed in one of these files to be accepted. | |
5bbb5681 | 980 | The client uses the same files |
e91c60f2 | 981 | to verify that it is connecting to the correct remote host. |
4fe2af09 | 982 | These files should be writable only by root/the owner. |
5f4fdfae | 983 | .Pa /etc/ssh_known_hosts |
bf740959 | 984 | should be world-readable, and |
985 | .Pa $HOME/.ssh/known_hosts | |
986 | can but need not be world-readable. | |
987 | .It Pa /etc/nologin | |
f54651ce | 988 | If this file exists, |
bf740959 | 989 | .Nm |
4fe2af09 | 990 | refuses to let anyone except root log in. |
991 | The contents of the file | |
bf740959 | 992 | are displayed to anyone trying to log in, and non-root connections are |
4fe2af09 | 993 | refused. |
994 | The file should be world-readable. | |
bf740959 | 995 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
996 | If compiled with | |
997 | .Sy LIBWRAP | |
998 | support, tcp-wrappers access controls may be defined here as described in | |
999 | .Xr hosts_access 5 . | |
1000 | .It Pa $HOME/.rhosts | |
1001 | This file contains host-username pairs, separated by a space, one per | |
4fe2af09 | 1002 | line. |
1003 | The given user on the corresponding host is permitted to log in | |
1004 | without password. | |
1005 | The same file is used by rlogind and rshd. | |
bf740959 | 1006 | The file must |
1007 | be writable only by the user; it is recommended that it not be | |
1008 | accessible by others. | |
1009 | .Pp | |
4fe2af09 | 1010 | If is also possible to use netgroups in the file. |
1011 | Either host or user | |
bf740959 | 1012 | name may be of the form +@groupname to specify all hosts or all users |
1013 | in the group. | |
1014 | .It Pa $HOME/.shosts | |
1015 | For ssh, | |
1016 | this file is exactly the same as for | |
1017 | .Pa .rhosts . | |
1018 | However, this file is | |
1019 | not used by rlogin and rshd, so using this permits access using SSH only. | |
c345cf9d | 1020 | .It Pa /etc/hosts.equiv |
bf740959 | 1021 | This file is used during |
1022 | .Pa .rhosts | |
4fe2af09 | 1023 | authentication. |
1024 | In the simplest form, this file contains host names, one per line. | |
1025 | Users on | |
bf740959 | 1026 | those hosts are permitted to log in without a password, provided they |
4fe2af09 | 1027 | have the same user name on both machines. |
1028 | The host name may also be | |
bf740959 | 1029 | followed by a user name; such users are permitted to log in as |
1030 | .Em any | |
4fe2af09 | 1031 | user on this machine (except root). |
1032 | Additionally, the syntax | |
bf740959 | 1033 | .Dq +@group |
4fe2af09 | 1034 | can be used to specify netgroups. |
1035 | Negated entries start with | |
bf740959 | 1036 | .Ql \&- . |
1037 | .Pp | |
1038 | If the client host/user is successfully matched in this file, login is | |
1039 | automatically permitted provided the client and server user names are the | |
4fe2af09 | 1040 | same. |
1041 | Additionally, successful RSA host authentication is normally required. | |
1042 | This file must be writable only by root; it is recommended | |
bf740959 | 1043 | that it be world-readable. |
1044 | .Pp | |
1045 | .Sy "Warning: It is almost never a good idea to use user names in" | |
1046 | .Pa hosts.equiv . | |
1047 | Beware that it really means that the named user(s) can log in as | |
1048 | .Em anybody , | |
1049 | which includes bin, daemon, adm, and other accounts that own critical | |
4fe2af09 | 1050 | binaries and directories. |
1051 | Using a user name practically grants the user root access. | |
1052 | The only valid use for user names that I can think | |
bf740959 | 1053 | of is in negative entries. |
1054 | .Pp | |
1055 | Note that this warning also applies to rsh/rlogin. | |
5f4fdfae | 1056 | .It Pa /etc/shosts.equiv |
bf740959 | 1057 | This is processed exactly as |
1058 | .Pa /etc/hosts.equiv . | |
1059 | However, this file may be useful in environments that want to run both | |
1060 | rsh/rlogin and ssh. | |
1061 | .It Pa $HOME/.ssh/environment | |
4fe2af09 | 1062 | This file is read into the environment at login (if it exists). |
1063 | It can only contain empty lines, comment lines (that start with | |
bf740959 | 1064 | .Ql # ) , |
4fe2af09 | 1065 | and assignment lines of the form name=value. |
1066 | The file should be writable | |
bf740959 | 1067 | only by the user; it need not be readable by anyone else. |
1068 | .It Pa $HOME/.ssh/rc | |
1069 | If this file exists, it is run with /bin/sh after reading the | |
4fe2af09 | 1070 | environment files but before starting the user's shell or command. |
1071 | If X11 spoofing is in use, this will receive the "proto cookie" pair in | |
bf740959 | 1072 | standard input (and |
1073 | .Ev DISPLAY | |
4fe2af09 | 1074 | in environment). |
1075 | This must call | |
bf740959 | 1076 | .Xr xauth 1 |
1077 | in that case. | |
1078 | .Pp | |
1079 | The primary purpose of this file is to run any initialization routines | |
1080 | which may be needed before the user's home directory becomes | |
1081 | accessible; AFS is a particular example of such an environment. | |
1082 | .Pp | |
1083 | This file will probably contain some initialization code followed by | |
1084 | something similar to: "if read proto cookie; then echo add $DISPLAY | |
1085 | $proto $cookie | xauth -q -; fi". | |
1086 | .Pp | |
1087 | If this file does not exist, | |
5f4fdfae | 1088 | .Pa /etc/sshrc |
bf740959 | 1089 | is run, and if that |
1090 | does not exist either, xauth is used to store the cookie. | |
1091 | .Pp | |
1092 | This file should be writable only by the user, and need not be | |
1093 | readable by anyone else. | |
5f4fdfae | 1094 | .It Pa /etc/sshrc |
bf740959 | 1095 | Like |
1096 | .Pa $HOME/.ssh/rc . | |
1097 | This can be used to specify | |
4fe2af09 | 1098 | machine-specific login-time initializations globally. |
1099 | This file should be writable only by root, and should be world-readable. | |
089fbbd2 | 1100 | .El |
fa08c86b | 1101 | .Sh AUTHORS |
7f5c4295 | 1102 | OpenSSH is a derivative of the original and free |
1103 | ssh 1.2.12 release by Tatu Ylonen. | |
1104 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
1105 | Theo de Raadt and Dug Song | |
1106 | removed many bugs, re-added newer features and | |
1107 | created OpenSSH. | |
1108 | Markus Friedl contributed the support for SSH | |
1109 | protocol versions 1.5 and 2.0. | |
bf740959 | 1110 | .Sh SEE ALSO |
bf740959 | 1111 | .Xr scp 1 , |
61e96248 | 1112 | .Xr sftp 1 , |
b5e300c2 | 1113 | .Xr sftp-server 8 , |
bf740959 | 1114 | .Xr ssh 1 , |
1115 | .Xr ssh-add 1 , | |
1116 | .Xr ssh-agent 1 , | |
1117 | .Xr ssh-keygen 1 , | |
7368a6c8 | 1118 | .Xr rlogin 1 , |
1119 | .Xr rsh 1 |