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1 .\" Copyright (c) 1983 Regents of the University of California.
2 .\" All rights reserved. The Berkeley software License Agreement
3 .\" specifies the terms and conditions for redistribution.
4 .\"
5 .\" @(#)telnet.1c 6.5 (Berkeley) 5/10/86
6 .\"
7 .TH TELNET 1 "May 10, 1986"
8 .UC 5
9 .SH NAME
10 telnet \- user interface to the \s-1TELNET\s0 protocol
11 .SH SYNOPSIS
12 telnet [
13 .I host
14 [
15 .I port
16 ] ]
17 .SH DESCRIPTION
18 .I Telnet
19 is used to communicate with another host using the
20 .B TELNET
21 protocol.
22 If
23 .I telnet
24 is invoked without arguments, it enters command mode,
25 indicated by its prompt (\*(lqtelnet>\*(rq).
26 In this mode, it accepts and executes the commands listed below.
27 If it is invoked with arguments, it performs an
28 .B open
29 command (see below) with those arguments.
30 .PP
31 Once a connection has been opened,
32 .I telnet
33 enters an input mode.
34 The input mode entered will be either \*(lqcharacter at a time\*(rq
35 or \*(lqline by line\*(rq
36 depending on what the remote system supports.
37 .PP
38 In \*(lqcharacter at a time\*(rq mode, most
39 text typed is immediately sent to the remote host for processing.
40 .PP
41 In \*(lqline by line\*(rq mode, all text is echoed locally,
42 and (normally) only completed lines are sent to the remote host.
43 The \*(lqlocal echo character\*(rq (initially \*(lq^E\*(rq) may be used
44 to turn off and on the local echo
45 (this would mostly be used to enter passwords
46 without the password being echoed).
47 .PP
48 In either mode, if the
49 .I localchars
50 toggle is TRUE (the default in line mode; see below),
51 the user's
52 .IR quit ,
53 .IR intr ,
54 and
55 .I flush
56 characters are trapped locally, and sent as
57 .B TELNET
58 protocol sequences to the remote side.
59 There are options (see
60 .B toggle
61 .I autoflush
62 and
63 .B toggle
64 .I autosynch
65 below)
66 which cause this action to flush subsequent output to the terminal
67 (until the remote host acknowledges the
68 .B TELNET
69 sequence) and flush previous terminal input
70 (in the case of
71 .I quit
72 and
73 .IR intr ).
74 .PP
75 While connected to a remote host,
76 .I telnet
77 command mode may be entered by typing the
78 .I telnet
79 \*(lqescape character\*(rq (initially \*(lq^]\*(rq).
80 When in command mode, the normal terminal editing conventions are available.
81 .PP
82 .B COMMANDS
83 .PP
84 The following commands are available.
85 Only enough of each command to uniquely identify it need be typed
86 (this is also true for arguments to the
87 .BR mode ,
88 .BR set ,
89 .BR toggle ,
90 and
91 .B display
92 commands).
93 .PP
94 .TP
95 .B open \fIhost\fP \fR[\fP \fIport\fP \fR]\fP
96 .br
97 Open a connection to the named host.
98 If no port number
99 is specified,
100 .I telnet
101 will attempt to contact a
102 .B TELNET
103 server at the default port.
104 The host specification may be either a host name (see
105 .IR hosts (5))
106 or an Internet address specified in the \*(lqdot notation\*(rq (see
107 .IR inet (3N)).
108 .TP
109 .B close
110 .br
111 Close a
112 .B TELNET
113 session and return to command mode.
114 .TP
115 .B quit
116 .br
117 Close any open
118 .B TELNET
119 session and exit
120 .IR telnet .
121 An end of file (in command mode) will also close a session and exit.
122 .TP
123 .B z
124 .br
125 Suspend
126 .IR telnet .
127 This command only works when the user is using the
128 .IR csh (1).
129 .TP
130 .B mode \fItype\fP
131 .br
132 .I Type
133 is either
134 .I line
135 (for \*(lqline by line\*(rq mode)
136 or
137 .I character
138 (for \*(lqcharacter at a time\*(rq mode).
139 The remote host is asked for permission to go into the requested mode.
140 If the remote host is capable of entering that mode, the requested
141 mode will be entered.
142 .TP
143 .B status
144 .br
145 Show the current status of
146 .IR telnet .
147 This includes the peer one is connected to, as well
148 as the current mode.
149 .TP
150 .B display \fR[\fP \fIargument...\fP \fR]\fP
151 .br
152 Displays all, or some, of the
153 .B set
154 and
155 .B toggle
156 values (see below).
157 .TP
158 .B ? \fR[\fP \fIcommand\fP \fR]\fP
159 .br
160 Get help. With no arguments,
161 .I telnet
162 prints a help summary.
163 If a command is specified,
164 .I telnet
165 will print the help information for just that command.
166 .TP
167 .B send \fIarguments\fP
168 .br
169 Sends one or more special character sequences to the remote host.
170 The following are the arguments which may be specified
171 (more than one argument may be specified at a time):
172 .RS
173 .TP
174 .I escape
175 .br
176 Sends the current
177 .I telnet
178 escape character (initially \*(lq^]\*(rq).
179 .TP
180 .I synch
181 .br
182 Sends the
183 .B TELNET SYNCH
184 sequence.
185 This sequence causes the remote system to discard all previously typed
186 (but not yet read) input.
187 This sequence is sent as TCP urgent
188 data (and may not work if the remote system is a 4.2 BSD system -- if
189 it doesn't work, a lower case \*(lqr\*(rq may be echoed on the terminal).
190 .TP
191 .I brk
192 .br
193 Sends the
194 .B TELNET BRK
195 (Break) sequence, which may have significance to the remote
196 system.
197 .TP
198 .I ip
199 .br
200 Sends the
201 .B TELNET IP
202 (Interrupt Process) sequence, which should cause the remote
203 system to abort the currently running process.
204 .TP
205 .I ao
206 .br
207 Sends the
208 .B TELNET AO
209 (Abort Output) sequence, which should cause the remote system to flush
210 all output
211 .B from
212 the remote system
213 .B to
214 the user's terminal.
215 .TP
216 .I ayt
217 .br
218 Sends the
219 .B TELNET AYT
220 (Are You There)
221 sequence, to which the remote system may or may not choose to respond.
222 .TP
223 .I ec
224 .br
225 Sends the
226 .B TELNET EC
227 (Erase Character)
228 sequence, which should cause the remote system to erase the last character
229 entered.
230 .TP
231 .I el
232 .br
233 Sends the
234 .B TELNET EL
235 (Erase Line)
236 sequence, which should cause the remote system to erase the line currently
237 being entered.
238 .TP
239 .I ga
240 .br
241 Sends the
242 .B TELNET GA
243 (Go Ahead)
244 sequence, which likely has no significance to the remote system.
245 .TP
246 .I nop
247 .br
248 Sends the
249 .B TELNET NOP
250 (No OPeration)
251 sequence.
252 .TP
253 .I ?
254 .br
255 Prints out help information for the
256 .B send
257 command.
258 .RE
259 .TP
260 .B set \fIargument value\fP
261 .br
262 Set any one of a number of
263 .I telnet
264 variables to a specific value.
265 The special value \*(lqoff\*(rq turns off the function associated with
266 the variable.
267 The values of variables may be interrogated with the
268 .B display
269 command.
270 The variables which may be specified are:
271 .RS
272 .TP
273 .I echo
274 .br
275 This is the value (initially \*(lq^E\*(rq) which, when in
276 \*(lqline by line\*(rq mode, toggles between doing local echoing
277 of entered characters (for normal processing), and suppressing
278 echoing of entered characters (for entering, say, a password).
279 .TP
280 .I escape
281 .br
282 This is the
283 .I telnet
284 escape character (initially \*(lq^[\*(rq) which causes entry
285 into
286 .I telnet
287 command mode (when connected to a remote system).
288 .TP
289 .I interrupt
290 .br
291 If
292 .I telnet
293 is in
294 .I localchars
295 mode (see
296 .B toggle
297 .I localchars
298 below)
299 and the
300 .I interrupt
301 character is typed, a
302 .B TELNET IP
303 sequence (see
304 .B send
305 .I ip
306 above)
307 is sent to the remote host.
308 The initial value for the interrupt character is taken to be
309 the terminal's
310 .B intr
311 character.
312 .TP
313 .I quit
314 .br
315 If
316 .I telnet
317 is in
318 .I localchars
319 mode (see
320 .B toggle
321 .I localchars
322 below)
323 and the
324 .I quit
325 character is typed, a
326 .B TELNET BRK
327 sequence (see
328 .B send
329 .I brk
330 above)
331 is sent to the remote host.
332 The initial value for the quit character is taken to be
333 the terminal's
334 .B quit
335 character.
336 .TP
337 .I flushoutput
338 .br
339 If
340 .I telnet
341 is in
342 .I localchars
343 mode (see
344 .B toggle
345 .I localchars
346 below)
347 and the
348 .I flushoutput
349 character is typed, a
350 .B TELNET AO
351 sequence (see
352 .B send
353 .I ao
354 above)
355 is sent to the remote host.
356 The initial value for the flush character is taken to be
357 the terminal's
358 .B flush
359 character.
360 .TP
361 .I erase
362 .br
363 If
364 .I telnet
365 is in
366 .I localchars
367 mode (see
368 .B toggle
369 .I localchars
370 below),
371 .B and
372 if
373 .I telnet
374 is operating in \*(lqcharacter at a time\*(rq mode, then when this
375 character is typed, a
376 .B TELNET EC
377 sequence (see
378 .B send
379 .I ec
380 above)
381 is sent to the remote system.
382 The initial value for the erase character is taken to be
383 the terminal's
384 .B erase
385 character.
386 .TP
387 .I kill
388 .br
389 If
390 .I telnet
391 is in
392 .I localchars
393 mode (see
394 .B toggle
395 .I localchars
396 below),
397 .B and
398 if
399 .I telnet
400 is operating in \*(lqcharacter at a time\*(rq mode, then when this
401 character is typed, a
402 .B TELNET EL
403 sequence (see
404 .B send
405 .I el
406 above)
407 is sent to the remote system.
408 The initial value for the kill character is taken to be
409 the terminal's
410 .B kill
411 character.
412 .TP
413 .I eof
414 .br
415 If
416 .I telnet
417 is operating in \*(lqline by line\*(rq mode, entering this character
418 as the first character on a line will cause this character to be
419 sent to the remote system.
420 The initial value of the eof character is taken to be the terminal's
421 .B eof
422 character.
423 .RE
424 .TP
425 .B toggle \fIarguments...\fP
426 .br
427 Toggle (between
428 TRUE
429 and
430 FALSE)
431 various flags that control how
432 .I telnet
433 responds to events.
434 More than one argument may be specified.
435 The state of these flags may be interrogated with the
436 .B display
437 command.
438 Valid arguments are:
439 .RS
440 .TP
441 .I localchars
442 .br
443 If this is
444 TRUE,
445 then the
446 .IR flush ,
447 .IR interrupt ,
448 .IR quit ,
449 .IR erase ,
450 and
451 .I kill
452 characters (see
453 .B set
454 above) are recognized locally, and transformed into (hopefully) appropriate
455 .B TELNET
456 control sequences
457 (respectively
458 .IR ao ,
459 .IR ip ,
460 .IR brk ,
461 .IR ec ,
462 and
463 .IR el ;
464 see
465 .B send
466 above).
467 The initial value for this toggle is TRUE in \*(lqline by line\*(rq mode,
468 and FALSE in \*(lqcharacter at a time\*(rq mode.
469 .TP
470 .I autoflush
471 .br
472 If
473 .I autoflush
474 and
475 .I localchars
476 are both
477 TRUE,
478 then when the
479 .IR ao ,
480 .IR intr ,
481 or
482 .I quit
483 characters are recognized (and transformed into
484 .B TELNET
485 sequences; see
486 .B set
487 above for details),
488 .I telnet
489 refuses to display any data on the user's terminal
490 until the remote system acknowledges (via a
491 .B TELNET
492 .I Timing Mark
493 option)
494 that it has processed those
495 .B TELNET
496 sequences.
497 The initial value for this toggle is TRUE if the terminal user had not
498 done an "stty noflsh", otherwise FALSE (see
499 .IR stty(1)).
500 .TP
501 .I autosynch
502 If
503 .I autosynch
504 and
505 .I localchars
506 are both
507 TRUE,
508 then when either the
509 .I intr
510 or
511 .I quit
512 characters is typed (see
513 .B set
514 above for descriptions of the
515 .I intr
516 and
517 .I quit
518 characters), the resulting
519 .B TELNET
520 sequence sent is followed by the
521 .B TELNET SYNCH
522 sequence.
523 This procedure
524 .B should
525 cause the remote system to begin throwing away all previously
526 typed input until both of the
527 .B TELNET
528 sequences have been read and acted upon.
529 The initial value of this toggle is FALSE.
530 .TP
531 .I crmod
532 .br
533 Toggle carriage return mode.
534 When this mode is enabled, most carriage return characters received from
535 the remote host will be mapped into a carriage return followed by
536 a line feed.
537 This mode does not affect those characters typed by the user, only
538 those received from the remote host.
539 This mode is not very useful unless the remote host
540 only sends carriage return, but never line feed.
541 The initial value for this toggle is FALSE.
542 .TP
543 .I debug
544 .br
545 Toggles socket level debugging (useful only to the
546 .IR super user ).
547 The initial value for this toggle is FALSE.
548 .TP
549 .I options
550 .br
551 Toggles the display of some internal
552 .I telnet
553 protocol processing (having to do with
554 .B TELNET
555 options).
556 The initial value for this toggle is FALSE.
557 .TP
558 .I netdata
559 .br
560 Toggles the display of all network data (in hexadecimal format).
561 The initial value for this toggle is FALSE.
562 .TP
563 .I ?
564 .br
565 Displays the legal
566 .B toggle
567 commands.
568 .RE
569 .SH BUGS
570 .PP
571 There is no adequate way for dealing with flow control.
572 .PP
573 On some remote systems, echo has to be turned off manually when in
574 \*(lqline by line\*(rq mode.
575 .PP
576 There is enough settable state to justify a
577 .RI . telnetrc
578 file.
579 .PP
580 No capability for a
581 .RI . telnetrc
582 file is provided.
583 .PP
584 In \*(lqline by line\*(rq mode, the terminal's
585 .I eof
586 character is only recognized (and sent to the remote system)
587 when it is the first character on a line.