telnet(1) UNIX System V(TCP/IP) telnet(1)
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 notation
[see inet(7)].
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telnet(1) UNIX System V(TCP/IP) telnet(1)
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.
ao Sends the TELNET AO (Abort Output) sequence, which flushes
all output from the remote system to the user's terminal.
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telnet(1) UNIX System V(TCP/IP) telnet(1)
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.
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.
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telnet(1) UNIX System V(TCP/IP) telnet(1)
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 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.
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telnet(1) UNIX System V(TCP/IP) telnet(1)
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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