telnet(1N) (TCP/IP) telnet(1N)
NAME
telnet - user interface to a remote system using the TELNET protocol
SYNOPSIS
telnet [ host [ port ] ]
DESCRIPTION
telnet communicates with another host using the TELNET protocol. If
telnet is invoked without arguments, it enters command mode,
indicated by its prompt telnet>. In this mode, it accepts and
executes the commands listed below. If it is invoked with arguments,
it performs an open command (see ``Telnet Commands'' below) with
those arguments.
Once a connection has been opened, telnet enters input mode. In this
mode, text typed is sent to the remote host. The input mode entered
will be either character at a time or line by line depending on what
the remote system supports.
In character at a time mode, most text typed is immediately sent to
the remote host for processing.
In line by line mode, all text is echoed locally, and (normally) only
completed lines are sent to the remote host. The local echo
character (initially ^E) may be used to turn off and on the local
echo (this would mostly be used to enter passwords without the
password being echoed).
In either mode, if the localchars toggle is TRUE (the default in line
mode; see below), the user's quit, intr, and flush characters are
trapped locally, and sent as TELNET protocol sequences to the remote
side. There are options (see toggle, autoflush, and toggle,
autosynch) which cause this action to flush subsequent output to the
terminal (until the remote host acknowledges the TELNET sequence) and
flush previous terminal input (in the case of quit and intr).
While connected to a remote host, telnet command mode may be entered
by typing the telnet escape character (initially ^]). When in
command mode, the normal terminal editing conventions are available.
USAGE
Telnet Commands
The following commands are available. Only enough of each command to
uniquely identify it need be typed (this is also true for arguments
to the mode, set, toggle, and display commands).
open host [ port ]
Open a connection to the named host. If no port number is
specified, telnet will attempt to contact a TELNET server at
the default port. The host specification may be either a host
name [see hosts(4)] or an Internet address specified in the dot
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telnet(1N) (TCP/IP) telnet(1N)
notation [see inet(7)].
close Close any open TELNET session and exit telnet. An EOF (in
command mode) will also close a session and exit.
quit Same as close, above.
z Suspend telnet. This command only works when the user is using
a shell that supports job control, such as sh(1).
mode type
type is either line (for line by line mode) or character (for
character at a time mode). The remote host is asked for
permission to go into the requested mode. If the remote host
is capable of entering that mode, the requested mode will be
entered.
status
Show the current status of telnet. This includes the peer one
is connected to, as well as the current mode.
display [ argument... ]
Display all, or some, of the set and toggle values (see toggle,
arguments).
? [ command ]
Get help. With no arguments, telnet print a help summary. If
a command is specified, telnet will print the help information
for just that command.
send arguments
Send one or more special character sequences to the remote
host. The following are the arguments which may be specified
(more than one argument may be specified at a time):
escape
Send the current telnet escape character (initially ^]).
synch Send the TELNET SYNCH sequence. This sequence discards
all previously typed (but not yet read) input on the
remote system. This sequence is sent as TCP urgent data
(and may not work if the remote system is a 4.2 BSD
system - if it does not work, a lower case r may be
echoed on the terminal).
brk Send the TELNET BRK (Break) sequence, which may have
significance to the remote system.
ip Send the TELNET IP (Interrupt Process) sequence, which
aborts the currently running process on the remote
system.
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telnet(1N) (TCP/IP) telnet(1N)
ao Sends the TELNET AO (Abort Output) sequence, which
flushes all output from the remote system to the user's
terminal.
ayt Sends the TELNET AYT (Are You There) sequence, to which
the remote system may or may not choose to respond.
ec Sends the TELNET EC (Erase Character) sequence, which
erases the last character entered.
el Sends the TELNET EL (Erase Line) sequence, which should
cause the remote system to erase the line currently being
entered.
ga Sends the TELNET GA (Go Ahead) sequence, which likely has
no significance to the remote system.
nop Sends the TELNET NOP (No Operation) sequence.
? Prints out help information for the send command.
set argument value
Set any one of a number of telnet variables to a specific
value. The special value off turns off the function associated
with the variable. The values of variables may be interrogated
with the display command. The variables which may be specified
are:
echo This is the value (initially ^E) which, when in line by
line mode, toggles between doing local echoing of entered
characters (for normal processing), and suppressing
echoing of entered characters (for example, entering a
password).
escape
This is the telnet escape character (initially ^]) which
enters telnet command mode (when connected to a remote
system).
interrupt
If telnet is in localchars mode (see toggle localchars)
and the interrupt character is typed, a TELNET IP
sequence (see send and ip) is sent to the remote host.
The initial value for the interrupt character is taken to
be the terminal's intr character.
quit If telnet is in localchars mode (see toggle localchars)
and the quit character is typed, a TELNET BRK sequence
(see send, brk) is sent to the remote host. The initial
value for the quit character is taken to be the
terminal's quit character.
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telnet(1N) (TCP/IP) telnet(1N)
flushoutput
If telnet is in localchars mode (see toggle localchars)
and the flushoutput character is typed, a TELNET AO
sequence (see send, ao) is sent to the remote host. The
initial value for the flush character is taken to be the
terminal's flush character.
erase If telnet is in localchars mode (see toggle localchars),
and if telnet is operating in character at a time mode,
then when this character is typed, a TELNET EC sequence
(see send, ec) is sent to the remote system. The initial
value for the erase character is taken to be the
terminal's erase character.
kill If telnet is in localchars mode (see toggle localchars),
and if telnet is operating in character at a time mode,
then when this character is typed, a TELNET EL sequence
(see send, el) is sent to the remote system. The initial
value for the kill character is taken to be the
terminal's kill character.
eof If telnet is operating in line by line mode, entering
this character as the first character on a line sends
this character to the remote system. The initial value
of the eof character is taken to be the terminal's eof
character.
toggle arguments...
Toggle (between TRUE and FALSE) various flags that control how
telnet responds to events. More than one argument may be
specified. The state of these flags may be interrogated with
the display command. Valid arguments are:
autoflush
If autoflush and localchars are both TRUE, then when the
ao, intr, or quit characters are recognized (and
transformed into TELNET sequences; see set for details),
telnet refuses to display any data on the user's terminal
until the remote system acknowledges (using a TELNET
Timing Mark option) that it has processed those TELNET
sequences. The initial value for this toggle is TRUE if
the terminal user had not done an stty noflsh, otherwise
FALSE [see stty(1)].
autosynch
If autosynch and localchars are both TRUE, then when
either the intr or quit characters are typed (see set for
descriptions of the intr and quit characters), the
resulting TELNET sequence sent is followed by the TELNET
SYNCH sequence. This procedure should cause the remote
system to begin throwing away all previously typed input
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telnet(1N) (TCP/IP) telnet(1N)
until both of the TELNET sequences have been read and
acted upon. The initial value of this toggle is FALSE.
crmod Toggle RETURN mode. When this mode is enabled, most
RETURN characters received from the remote host will be
mapped into a RETURN followed by a line feed. This mode
does not affect those characters typed by the user, only
those received from the remote host. This mode is not
very useful unless the remote host only sends RETURN, but
never LINEFEED. The initial value for this toggle is
FALSE.
debug Toggle socket level debugging (useful only to the super-
user). The initial value for this toggle is FALSE .
localchars
If this is TRUE , then the flush, interrupt, quit, erase,
and kill characters (see set) are recognized locally, and
transformed into appropriate TELNET control sequences
(respectively ao, ip, brk, ec, and el; see send). The
initial value for this toggle is TRUE in line by line
mode, and FALSE in character at a time mode.
netdata
Toggle the display of all network data (in hexadecimal
format). The initial value for this toggle is FALSE.
options
Toggle the display of some internal telnet protocol
processing (having to do with TELNET options). The
initial value for this toggle is FALSE.
? Display the legal toggle commands.
SEE ALSO
rlogin(1), sh(1), stty(1), hosts(4), inet(7).
NOTES
Do not attempt to run layers(1) while using telnet.
There is no adequate way for dealing with flow control.
On some remote systems, echo has to be turned off manually when in
line by line mode.
There is enough settable state to justify a file.
In line by line mode, the terminal's EOF character is only recognized
(and sent to the remote system) when it is the first character on a
line.
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