TELNET(TC) UNIX System V
Name
telnet - User interface to the TELNET protocol
Syntax
telnet [ host [ port ] ]
Description
The telnet command is used to communicate 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 with those arguments. (See below.)
Once a connection has been opened, telnet enters an input
mode. 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
the local echo off and on. (This would mostly be used to
enter passwords without the passwords being echoed.)
In either mode, if the localchars toggle is TRUE (the
default in line mode, discussed 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 (toggle autoflush and toggle autosynch described
below) 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.
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 (such as hosts(ADMN)) or an
Internet address specified in the dot notation. (See
inet(SLIB).)
close
Close a TELNET session and return to command mode.
quit
Close any open TELNET session and exit telnet. An
end-of-file (in command mode) will also close a session
and exit.
z
Suspend telnet. On System V systems, this command
provides the user with an escape to a shell running on
the local machine.
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 to which one is connected, as well as the current
mode. In addition, both the local and the remote
TELNET options in effect are shown.
display [ argument... ]
Displays all, or some, of the set and toggle values.
(See below.)
? [ command ]
Get help. With no arguments, telnet prints a help
summary. If a command is specified, telnet will print
the help information for just that command.
send arguments
Sends 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
Sends the current telnet escape character
(initially ^]).
synch
Sends the TELNET SYNCH sequence. This sequence
causes the remote system to discard all previously
typed (but not yet read) input. This sequence is
sent as TCP urgent data. (It may not work if the
remote system is a 4.2 BSD system. If it doesn't
work, a lowercase r may be echoed on the
terminal.)
brk
Sends the TELNET BRK (Break) sequence, which may
have significance to the remote system.
ip
Sends the TELNET IP (Interrupt Process) sequence,
which should cause the remote system to abort the
currently-running process.
ao
Sends the TELNET AO (Abort Output) sequence, which
should cause the remote system to flush 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 should cause the remote system to erase 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
entering, say, a password).
escape
This is the telnet escape character (initially ^[)
which causes entry into telnet command mode (when
connected to a remote system).
interrupt
If telnet is in localchars mode (discussed below) and
the interrupt character is typed, a TELNET IP sequence
(send ip, discussed above) 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 (discussed below) and
the quit character is typed, a TELNET BRK sequence
(send brk, discussed above) 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 (discussed below) and
the flushoutput character is typed, a TELNET AO
sequence (send ao, discussed above) 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 (discussed below), and
if telnet is operating in character-at-a-time mode,
then when this character is typed, a TELNET EC sequence
(send ec, discussed above) 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 (discussed below), and
if telnet is operating in character-at-a-time mode,
then when this character is typed, a TELNET EL sequence
(send el, discussed above) 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 will
cause the character to be sent 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:
localchars
If this is TRUE, then the flush, interrupt, quit,
erase, and kill characters (discussed under set, above)
are recognized locally, and transformed into
(hopefully) appropriate TELNET control sequences
(respectively, ao, ip, brk, ec, and el; see send
above). The initial value for this toggle is TRUE in
line-by-line mode, and FALSE in character-at-a-time
mode.
autoflush
If autoflush and localchars are both TRUE, then when
the ao, intr, or quit character is recognized (and
transformed into TELNET sequences; detailed under set
above), telnet refuses to display any data on the
user's terminal until the remote system acknowledges
(via 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(C).)
autosynch
If autosynch and localchars are both TRUE, then when
either the intr or quit characters (described above) is
typed, the 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 carriage return mode. When this mode is
enabled, most carriage return characters received from
the remote host will be mapped into a carriage 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 carriage return, but
never line feed. The initial value for this toggle is
FALSE.
debug
Toggles socket-level debugging (useful only to the
super user). The initial value for this toggle is
FALSE.
options
Toggles the display of some internal telnet protocol
processing (having to do with TELNET options). The
initial value for this toggle is FALSE.
netdata
Toggles the display of all network data (in hexadecimal
format). The initial value for this toggle is FALSE.
?
Displays the legal toggle commands.
do option
dont option
will option
wont option
These commands allow the user to send the appropriate TELNET
option sequence. If no option is specified, telnet will
prompt for one.
Notes
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 .telnetrc file.
No capability for a .telnetrc file is provided.
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.
(printed 8/17/89) TELNET(TC)