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28 .\" @(#)telnetd.8 8.4 (Berkeley) 6/1/94
29 .\" $FreeBSD: src/crypto/telnet/telnetd/telnetd.8,v 1.5.2.6 2002/04/13 10:59:09 markm Exp $
40 .Nm /usr/libexec/telnetd
50 .Op Fl debug Op Ar port
54 command is a server which supports the
58 virtual terminal protocol.
60 is normally invoked by the internet server (see
62 for requests to connect to the
64 port as indicated by the
70 option may be used to start up
72 manually, instead of through
74 If started up this way,
76 may be specified to run
84 command accepts the following options:
85 .Bl -tag -width indent
87 This option may be used for specifying what mode should
88 be used for authentication.
89 Note that this option is only useful if
91 has been compiled with support for the
94 There are several valid values for
98 Turn on authentication debugging code.
100 Only allow connections when the remote user
101 can provide valid authentication information
102 to identify the remote user,
103 and is allowed access to the specified account
104 without providing a password.
106 Only allow connections when the remote user
107 can provide valid authentication information
108 to identify the remote user.
111 command will provide any additional user verification
112 needed if the remote user is not allowed automatic
113 access to the specified account.
115 Only allow connections that supply some authentication information.
116 This option is currently not supported
117 by any of the existing authentication mechanisms,
118 and is thus the same as specifying
122 This is the default state.
123 Authentication information is not required.
124 If no or insufficient authentication information
125 is provided, then the
127 program will provide the necessary user
130 Disable the authentication code.
131 All user verification will happen through the
136 .\"Specify bftp server mode.
139 .\"causes login to start a
141 .\"session rather than the user's normal shell.
142 .\"In bftp daemon mode normal logins are not supported, and it must be used
143 .\"on a port other than the normal
146 .It Fl D Ar debugmode
147 This option may be used for debugging purposes.
150 to print out debugging information
151 to the connection, allowing the user to see what
154 There are several possible values for
156 .Bl -tag -width exercise
158 Print information about the negotiation of
164 information, plus some additional information
165 about what processing is going on.
167 Display the data stream received by
170 Display data written to the pty.
172 Has not been implemented yet.
175 Enable debugging on each socket created by
184 has been compiled with support for data encryption, then the
186 option may be used to enable encryption debugging code.
188 Disable the printing of host-specific information before
189 login has been completed.
191 This option is only useful if
193 has been compiled with both linemode and kludge linemode
197 option is specified, then if the remote client does not
202 will operate in character at a time mode.
203 It will still support kludge linemode, but will only
204 go into kludge linemode if the remote client requests
206 (This is done by the client sending
207 .Dv DONT SUPPRESS-GO-AHEAD
212 option is most useful when there are remote clients
213 that do not support kludge linemode, but pass the heuristic
214 (if they respond with
218 for kludge linemode support.
221 Try to force clients to use line-at-a-time mode.
224 option is not supported, it will go
225 into kludge linemode.
234 keep-alive mechanism to probe connections that
235 have been idle for some period of time to determine
236 if the client is still there, so that idle connections
237 from machines that have crashed or can no longer
238 be reached may be cleaned up.
239 .It Fl p Ar loginprog
242 command to run to complete the login.
243 The alternate command must
244 understand the same command arguments as the standard login.
247 This option is used to specify the size of the field
250 structure that holds the remote host name.
251 If the resolved host name is longer than
253 the dotted decimal value will be used instead.
254 This allows hosts with very long host names that
255 overflow this field to still be uniquely identified.
258 indicates that only dotted decimal addresses
259 should be put into the
265 to refuse connections from addresses that
266 cannot be mapped back into a symbolic name
271 This option is only valid if
273 has been built with support for the authentication option.
274 It disables the use of
277 can be used to temporarily disable
278 a specific authentication type without having to recompile
283 operates by allocating a pseudo-terminal device (see
285 for a client, then creating a login process which has
286 the slave side of the pseudo-terminal as
292 manipulates the master side of the pseudo-terminal,
295 protocol and passing characters
296 between the remote client and the login process.
300 session is started up,
304 options to the client side indicating
305 a willingness to do the
308 options, which are described in more detail below:
309 .Bd -literal -offset indent
317 WILL SUPPRESS GO AHEAD
326 The pseudo-terminal allocated to the client is configured
336 has support for enabling locally the following
339 .Bl -tag -width "DO AUTHENTICATION"
347 will be sent to the client to indicate the
348 current state of terminal echoing.
349 When terminal echo is not desired, a
351 is sent to indicate that
353 will take care of echoing any data that needs to be
354 echoed to the terminal, and then nothing is echoed.
355 When terminal echo is desired, a
357 is sent to indicate that
359 will not be doing any terminal echoing, so the
360 client should do any terminal echoing that is needed.
362 Indicate that the client is willing to send a
363 8 bits of data, rather than the normal 7 bits
364 of the Network Virtual Terminal.
366 Indicate that it will not be sending
370 Indicate a willingness to send the client, upon
371 request, of the current status of all
374 .It "WILL TIMING-MARK"
377 command is received, it is always responded
379 .Dv WILL TIMING-MARK .
385 is sent in response, and the
387 session is shut down.
391 is compiled with support for data encryption, and
392 indicates a willingness to decrypt
397 has support for enabling remotely the following
400 .Bl -tag -width "DO AUTHENTICATION"
402 Sent to indicate that
404 is willing to receive an 8 bit data stream.
406 Requests that the client handle flow control
409 This is not really supported, but is sent to identify a
412 client, which will improperly respond with
418 will be sent in response.
419 .It "DO TERMINAL-TYPE"
420 Indicate a desire to be able to request the
421 name of the type of terminal that is attached
422 to the client side of the connection.
424 Indicate that it does not need to receive
426 the go ahead command.
428 Requests that the client inform the server when
429 the window (display) size changes.
430 .It "DO TERMINAL-SPEED"
431 Indicate a desire to be able to request information
432 about the speed of the serial line to which
433 the client is attached.
435 Indicate a desire to be able to request the name
436 of the X Window System display that is associated with
439 Indicate a desire to be able to request environment
440 variable information, as described in RFC 1572.
442 Indicate a desire to be able to request environment
443 variable information, as described in RFC 1408.
447 is compiled with support for linemode, and
448 requests that the client do line by line processing.
452 is compiled with support for both linemode and
453 kludge linemode, and the client responded with
455 If the client responds with
457 the it is assumed that the client supports
461 option can be used to disable this.
462 .It "DO AUTHENTICATION"
465 is compiled with support for authentication, and
466 indicates a willingness to receive authentication
467 information for automatic login.
471 is compiled with support for data encryption, and
472 indicates a willingness to decrypt
485 and use that information (if present) to determine
486 what to display before the login: prompt.
487 You can also use a System V style
491 capability, which will override
493 The information specified in either
497 will be displayed to both console and remote logins.
500 .Bl -tag -width ".Pa /etc/services" -compact
505 .\".It Pa /usr/ucb/bftp
515 .Bl -tag -compact -width ".Cm RFC 1572"
518 PROTOCOL SPECIFICATION
520 TELNET OPTION SPECIFICATIONS
522 TELNET BINARY TRANSMISSION
526 TELNET SUPPRESS GO AHEAD OPTION
530 TELNET TIMING MARK OPTION
532 TELNET EXTENDED OPTIONS - LIST OPTION
534 TELNET END OF RECORD OPTION
536 Telnet Window Size Option
538 Telnet Terminal Speed Option
540 Telnet Terminal-Type Option
542 Telnet X Display Location Option
544 Requirements for Internet Hosts -- Application and Support
546 Telnet Linemode Option
548 Telnet Remote Flow Control Option
550 Telnet Authentication Option
552 Telnet Authentication: Kerberos Version 4
554 Telnet Authentication: SPX
556 Telnet Environment Option Interoperability Issues
558 Telnet Environment Option
561 IPv6 support was added by WIDE/KAME project.
565 commands are only partially implemented.
567 Because of bugs in the original
571 performs some dubious protocol exchanges to try to discover if the remote
572 client is, in fact, a
577 has no common interpretation except between similar operating systems
580 The terminal type name received from the remote client is converted to