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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 $
31 .Dd September 10, 2019
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 provided for backward compatibility and has no effect.
251 to refuse connections from addresses that
252 cannot be mapped back into a symbolic name
257 This option is only valid if
259 has been built with support for the authentication option.
260 It disables the use of
263 can be used to temporarily disable
264 a specific authentication type without having to recompile
269 operates by allocating a pseudo-terminal device (see
271 for a client, then creating a login process which has
272 the slave side of the pseudo-terminal as
278 manipulates the master side of the pseudo-terminal,
281 protocol and passing characters
282 between the remote client and the login process.
286 session is started up,
290 options to the client side indicating
291 a willingness to do the
294 options, which are described in more detail below:
295 .Bd -literal -offset indent
303 WILL SUPPRESS GO AHEAD
312 The pseudo-terminal allocated to the client is configured
322 has support for enabling locally the following
325 .Bl -tag -width "DO AUTHENTICATION"
333 will be sent to the client to indicate the
334 current state of terminal echoing.
335 When terminal echo is not desired, a
337 is sent to indicate that
339 will take care of echoing any data that needs to be
340 echoed to the terminal, and then nothing is echoed.
341 When terminal echo is desired, a
343 is sent to indicate that
345 will not be doing any terminal echoing, so the
346 client should do any terminal echoing that is needed.
348 Indicate that the client is willing to send a
349 8 bits of data, rather than the normal 7 bits
350 of the Network Virtual Terminal.
352 Indicate that it will not be sending
356 Indicate a willingness to send the client, upon
357 request, of the current status of all
360 .It "WILL TIMING-MARK"
363 command is received, it is always responded
365 .Dv WILL TIMING-MARK .
371 is sent in response, and the
373 session is shut down.
377 is compiled with support for data encryption, and
378 indicates a willingness to decrypt
383 has support for enabling remotely the following
386 .Bl -tag -width "DO AUTHENTICATION"
388 Sent to indicate that
390 is willing to receive an 8 bit data stream.
392 Requests that the client handle flow control
395 This is not really supported, but is sent to identify a
398 client, which will improperly respond with
404 will be sent in response.
405 .It "DO TERMINAL-TYPE"
406 Indicate a desire to be able to request the
407 name of the type of terminal that is attached
408 to the client side of the connection.
410 Indicate that it does not need to receive
412 the go ahead command.
414 Requests that the client inform the server when
415 the window (display) size changes.
416 .It "DO TERMINAL-SPEED"
417 Indicate a desire to be able to request information
418 about the speed of the serial line to which
419 the client is attached.
421 Indicate a desire to be able to request the name
422 of the X Window System display that is associated with
425 Indicate a desire to be able to request environment
426 variable information, as described in RFC 1572.
428 Indicate a desire to be able to request environment
429 variable information, as described in RFC 1408.
433 is compiled with support for linemode, and
434 requests that the client do line by line processing.
438 is compiled with support for both linemode and
439 kludge linemode, and the client responded with
441 If the client responds with
443 the it is assumed that the client supports
447 option can be used to disable this.
448 .It "DO AUTHENTICATION"
451 is compiled with support for authentication, and
452 indicates a willingness to receive authentication
453 information for automatic login.
457 is compiled with support for data encryption, and
458 indicates a willingness to decrypt
471 and use that information (if present) to determine
472 what to display before the login: prompt.
473 You can also use a System V style
477 capability, which will override
479 The information specified in either
483 will be displayed to both console and remote logins.
486 .Bl -tag -width ".Pa /etc/services" -compact
491 .\".It Pa /usr/ucb/bftp
501 .Bl -tag -compact -width ".Cm RFC 1572"
504 PROTOCOL SPECIFICATION
506 TELNET OPTION SPECIFICATIONS
508 TELNET BINARY TRANSMISSION
512 TELNET SUPPRESS GO AHEAD OPTION
516 TELNET TIMING MARK OPTION
518 TELNET EXTENDED OPTIONS - LIST OPTION
520 TELNET END OF RECORD OPTION
522 Telnet Window Size Option
524 Telnet Terminal Speed Option
526 Telnet Terminal-Type Option
528 Telnet X Display Location Option
530 Requirements for Internet Hosts -- Application and Support
532 Telnet Linemode Option
534 Telnet Remote Flow Control Option
536 Telnet Authentication Option
538 Telnet Authentication: Kerberos Version 4
540 Telnet Authentication: SPX
542 Telnet Environment Option Interoperability Issues
544 Telnet Environment Option
547 IPv6 support was added by WIDE/KAME project.
551 commands are only partially implemented.
553 Because of bugs in the original
557 performs some dubious protocol exchanges to try to discover if the remote
558 client is, in fact, a
563 has no common interpretation except between similar operating systems
566 The terminal type name received from the remote client is converted to