588 lines
11 KiB
Groff
588 lines
11 KiB
Groff
.\" Copyright (c) 1983 Regents of the University of California.
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.\" All rights reserved. The Berkeley software License Agreement
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.\" specifies the terms and conditions for redistribution.
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.\"
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.\" @(#)telnet.1c 6.5 (Berkeley) 5/10/86
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.\"
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.TH TELNET 1 "May 10, 1986"
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.UC 5
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.SH NAME
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telnet \- user interface to the \s-1TELNET\s0 protocol
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.SH SYNOPSIS
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telnet [
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.I host
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[
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.I port
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] ]
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.SH DESCRIPTION
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.I Telnet
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is used to communicate with another host using the
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.B TELNET
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protocol.
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If
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.I telnet
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is invoked without arguments, it enters command mode,
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indicated by its prompt (\*(lqtelnet>\*(rq).
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In this mode, it accepts and executes the commands listed below.
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If it is invoked with arguments, it performs an
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.B open
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command (see below) with those arguments.
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.PP
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Once a connection has been opened,
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.I telnet
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enters an input mode.
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The input mode entered will be either \*(lqcharacter at a time\*(rq
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or \*(lqline by line\*(rq
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depending on what the remote system supports.
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.PP
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In \*(lqcharacter at a time\*(rq mode, most
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text typed is immediately sent to the remote host for processing.
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.PP
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In \*(lqline by line\*(rq mode, all text is echoed locally,
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and (normally) only completed lines are sent to the remote host.
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The \*(lqlocal echo character\*(rq (initially \*(lq^E\*(rq) may be used
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to turn off and on the local echo
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(this would mostly be used to enter passwords
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without the password being echoed).
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.PP
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In either mode, if the
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.I localchars
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toggle is TRUE (the default in line mode; see below),
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the user's
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.IR quit ,
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.IR intr ,
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and
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.I flush
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characters are trapped locally, and sent as
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.B TELNET
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protocol sequences to the remote side.
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There are options (see
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.B toggle
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.I autoflush
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and
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.B toggle
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.I autosynch
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below)
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which cause this action to flush subsequent output to the terminal
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(until the remote host acknowledges the
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.B TELNET
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sequence) and flush previous terminal input
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(in the case of
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.I quit
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and
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.IR intr ).
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.PP
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While connected to a remote host,
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.I telnet
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command mode may be entered by typing the
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.I telnet
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\*(lqescape character\*(rq (initially \*(lq^]\*(rq).
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When in command mode, the normal terminal editing conventions are available.
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.PP
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.B COMMANDS
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.PP
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The following commands are available.
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Only enough of each command to uniquely identify it need be typed
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(this is also true for arguments to the
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.BR mode ,
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.BR set ,
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.BR toggle ,
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and
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.B display
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commands).
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.PP
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.TP
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.B open \fIhost\fP \fR[\fP \fIport\fP \fR]\fP
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.br
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Open a connection to the named host.
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If no port number
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is specified,
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.I telnet
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will attempt to contact a
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.B TELNET
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server at the default port.
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The host specification may be either a host name (see
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.IR hosts (5))
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or an Internet address specified in the \*(lqdot notation\*(rq (see
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.IR inet (3N)).
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.TP
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.B close
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.br
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Close a
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.B TELNET
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session and return to command mode.
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.TP
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.B quit
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.br
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Close any open
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.B TELNET
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session and exit
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.IR telnet .
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An end of file (in command mode) will also close a session and exit.
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.TP
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.B z
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.br
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Suspend
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.IR telnet .
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This command only works when the user is using the
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.IR csh (1).
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.TP
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.B mode \fItype\fP
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.br
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.I Type
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is either
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.I line
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(for \*(lqline by line\*(rq mode)
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or
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.I character
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(for \*(lqcharacter at a time\*(rq mode).
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The remote host is asked for permission to go into the requested mode.
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If the remote host is capable of entering that mode, the requested
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mode will be entered.
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.TP
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.B status
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.br
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Show the current status of
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.IR telnet .
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This includes the peer one is connected to, as well
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as the current mode.
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.TP
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.B display \fR[\fP \fIargument...\fP \fR]\fP
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.br
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Displays all, or some, of the
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.B set
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and
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.B toggle
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values (see below).
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.TP
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.B ? \fR[\fP \fIcommand\fP \fR]\fP
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.br
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Get help. With no arguments,
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.I telnet
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prints a help summary.
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If a command is specified,
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.I telnet
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will print the help information for just that command.
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.TP
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.B send \fIarguments\fP
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.br
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Sends one or more special character sequences to the remote host.
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The following are the arguments which may be specified
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(more than one argument may be specified at a time):
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.RS
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.TP
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.I escape
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.br
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Sends the current
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.I telnet
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escape character (initially \*(lq^]\*(rq).
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.TP
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.I synch
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.br
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Sends the
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.B TELNET SYNCH
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sequence.
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This sequence causes the remote system to discard all previously typed
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(but not yet read) input.
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This sequence is sent as TCP urgent
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data (and may not work if the remote system is a 4.2 BSD system -- if
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it doesn't work, a lower case \*(lqr\*(rq may be echoed on the terminal).
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.TP
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.I brk
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.br
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Sends the
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.B TELNET BRK
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(Break) sequence, which may have significance to the remote
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system.
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.TP
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.I ip
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.br
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Sends the
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.B TELNET IP
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(Interrupt Process) sequence, which should cause the remote
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system to abort the currently running process.
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.TP
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.I ao
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.br
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Sends the
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.B TELNET AO
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(Abort Output) sequence, which should cause the remote system to flush
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all output
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.B from
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the remote system
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.B to
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the user's terminal.
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.TP
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.I ayt
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.br
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Sends the
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.B TELNET AYT
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(Are You There)
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sequence, to which the remote system may or may not choose to respond.
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.TP
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.I ec
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.br
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Sends the
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.B TELNET EC
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(Erase Character)
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sequence, which should cause the remote system to erase the last character
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entered.
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.TP
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.I el
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.br
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Sends the
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.B TELNET EL
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(Erase Line)
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sequence, which should cause the remote system to erase the line currently
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being entered.
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.TP
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.I ga
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.br
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Sends the
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.B TELNET GA
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(Go Ahead)
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sequence, which likely has no significance to the remote system.
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.TP
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.I nop
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.br
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Sends the
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.B TELNET NOP
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(No OPeration)
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sequence.
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.TP
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.I ?
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.br
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Prints out help information for the
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.B send
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command.
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.RE
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.TP
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.B set \fIargument value\fP
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.br
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Set any one of a number of
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.I telnet
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variables to a specific value.
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The special value \*(lqoff\*(rq turns off the function associated with
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the variable.
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The values of variables may be interrogated with the
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.B display
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command.
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The variables which may be specified are:
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.RS
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.TP
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.I echo
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.br
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This is the value (initially \*(lq^E\*(rq) which, when in
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\*(lqline by line\*(rq mode, toggles between doing local echoing
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of entered characters (for normal processing), and suppressing
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echoing of entered characters (for entering, say, a password).
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.TP
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.I escape
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.br
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This is the
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.I telnet
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escape character (initially \*(lq^[\*(rq) which causes entry
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into
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.I telnet
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command mode (when connected to a remote system).
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.TP
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.I interrupt
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.br
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If
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.I telnet
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is in
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.I localchars
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mode (see
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.B toggle
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.I localchars
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below)
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and the
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.I interrupt
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character is typed, a
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.B TELNET IP
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sequence (see
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.B send
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.I ip
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above)
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is sent to the remote host.
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The initial value for the interrupt character is taken to be
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the terminal's
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.B intr
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character.
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.TP
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.I quit
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.br
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If
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.I telnet
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is in
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.I localchars
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mode (see
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.B toggle
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.I localchars
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below)
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and the
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.I quit
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character is typed, a
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.B TELNET BRK
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sequence (see
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.B send
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.I brk
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above)
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is sent to the remote host.
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The initial value for the quit character is taken to be
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the terminal's
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.B quit
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character.
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.TP
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.I flushoutput
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.br
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If
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.I telnet
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is in
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.I localchars
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mode (see
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.B toggle
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.I localchars
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below)
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and the
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.I flushoutput
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character is typed, a
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.B TELNET AO
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sequence (see
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.B send
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.I ao
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above)
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is sent to the remote host.
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The initial value for the flush character is taken to be
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the terminal's
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.B flush
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character.
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.TP
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.I erase
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.br
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If
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.I telnet
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is in
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.I localchars
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mode (see
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.B toggle
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.I localchars
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below),
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.B and
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if
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.I telnet
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is operating in \*(lqcharacter at a time\*(rq mode, then when this
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character is typed, a
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.B TELNET EC
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sequence (see
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.B send
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.I ec
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above)
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is sent to the remote system.
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The initial value for the erase character is taken to be
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the terminal's
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.B erase
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character.
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.TP
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.I kill
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.br
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If
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.I telnet
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is in
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.I localchars
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mode (see
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.B toggle
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.I localchars
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below),
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.B and
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if
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.I telnet
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is operating in \*(lqcharacter at a time\*(rq mode, then when this
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character is typed, a
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.B TELNET EL
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sequence (see
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.B send
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.I el
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above)
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is sent to the remote system.
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The initial value for the kill character is taken to be
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the terminal's
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.B kill
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character.
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.TP
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.I eof
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.br
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If
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.I telnet
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is operating in \*(lqline by line\*(rq mode, entering this character
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as the first character on a line will cause this character to be
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sent to the remote system.
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The initial value of the eof character is taken to be the terminal's
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.B eof
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character.
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.RE
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.TP
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.B toggle \fIarguments...\fP
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.br
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Toggle (between
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TRUE
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and
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FALSE)
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various flags that control how
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.I telnet
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responds to events.
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More than one argument may be specified.
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The state of these flags may be interrogated with the
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.B display
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command.
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Valid arguments are:
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.RS
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.TP
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.I localchars
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.br
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If this is
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TRUE,
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then the
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.IR flush ,
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.IR interrupt ,
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.IR quit ,
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.IR erase ,
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and
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.I kill
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characters (see
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.B set
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above) are recognized locally, and transformed into (hopefully) appropriate
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.B TELNET
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control sequences
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(respectively
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.IR ao ,
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.IR ip ,
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.IR brk ,
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.IR ec ,
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and
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.IR el ;
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see
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.B send
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above).
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The initial value for this toggle is TRUE in \*(lqline by line\*(rq mode,
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and FALSE in \*(lqcharacter at a time\*(rq mode.
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.TP
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.I autoflush
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.br
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If
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.I autoflush
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and
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.I localchars
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are both
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TRUE,
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then when the
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.IR ao ,
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.IR intr ,
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or
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.I quit
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characters are recognized (and transformed into
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.B TELNET
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sequences; see
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.B set
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above for details),
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.I telnet
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refuses to display any data on the user's terminal
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until the remote system acknowledges (via a
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.B TELNET
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.I Timing Mark
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option)
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that it has processed those
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.B TELNET
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sequences.
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The initial value for this toggle is TRUE if the terminal user had not
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done an "stty noflsh", otherwise FALSE (see
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.IR stty(1)).
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.TP
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.I autosynch
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If
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.I autosynch
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and
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.I localchars
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are both
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TRUE,
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then when either the
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.I intr
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or
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.I quit
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characters is typed (see
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.B set
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above for descriptions of the
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.I intr
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and
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.I quit
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characters), the resulting
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.B TELNET
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sequence sent is followed by the
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.B TELNET SYNCH
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sequence.
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This procedure
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.B should
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cause the remote system to begin throwing away all previously
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typed input until both of the
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.B TELNET
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sequences have been read and acted upon.
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The initial value of this toggle is FALSE.
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.TP
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.I crmod
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.br
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Toggle carriage return mode.
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When this mode is enabled, most carriage return characters received from
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the remote host will be mapped into a carriage return followed by
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a line feed.
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This mode does not affect those characters typed by the user, only
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those received from the remote host.
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This mode is not very useful unless the remote host
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only sends carriage return, but never line feed.
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The initial value for this toggle is FALSE.
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.TP
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.I debug
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.br
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Toggles socket level debugging (useful only to the
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.IR super user ).
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The initial value for this toggle is FALSE.
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.TP
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.I options
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.br
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Toggles the display of some internal
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.I telnet
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protocol processing (having to do with
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.B TELNET
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options).
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The initial value for this toggle is FALSE.
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.TP
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.I netdata
|
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.br
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Toggles the display of all network data (in hexadecimal format).
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The initial value for this toggle is FALSE.
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.TP
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.I ?
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.br
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Displays the legal
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.B toggle
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commands.
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.RE
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.SH BUGS
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.PP
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There is no adequate way for dealing with flow control.
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.PP
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On some remote systems, echo has to be turned off manually when in
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\*(lqline by line\*(rq mode.
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.PP
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There is enough settable state to justify a
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.RI . telnetrc
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file.
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.PP
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No capability for a
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.RI . telnetrc
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file is provided.
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.PP
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In \*(lqline by line\*(rq mode, the terminal's
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.I eof
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character is only recognized (and sent to the remote system)
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when it is the first character on a line.
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