hpux 10.20 - telnet (1)
NAME
telnet - user interface to the TELNET protocol
SYNOPSIS
telnet [[options]host [port]]
DESCRIPTION
telnet 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 telnet is invoked with
arguments, it performs an open command (see below) with those
arguments.
Once a connection has been opened, telnet enters an input mode. The
input mode 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) can 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 and intr characters are trapped
locally, and sent as TELNET protocol sequences to the remote side.
There are options (see toggle autoflush and toggle autosynch 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 can be entered
by typing the telnet ``escape character'' (initially ^]). When in
command mode, the normal terminal editing conventions are available.
telnet supports eight-bit characters when communicating with the
server on the remote host. To use eight-bit characters you may need
to reconfigure your terminal or the remote host appropriately (see
stty(1)). Furthermore, you may have to use the binary toggle to
enable an 8-bit data stream between telnet and the remote host. Note
that some remote hosts may not provide the necessary support for
eight-bit characters.
If, at any time, telnet is unable to read from or write to the server
over the connection, the message Connection closed by foreign host. is
printed on standard error. telnet then exits with a value of 1.
telnet supports the TAC User ID (also known as the TAC Access Control
System, or TACACS User ID) option. Enabling the option on a host
server allows the user to telnet into that host without being prompted
for a second login sequence. The TAC User ID option uses the same
security mechanism as rlogin for authorizing acces by remote hosts and
users. The system administrator must enable the (telnetd) option only
on systems which are designated as participating hosts. The system
administrator must also assign to each user of TAC User ID the very
same UID on every system for which he is allowed to use the feature.
(See telnetd(1M) and the System Administration Tasks manual, PN 2355-
90051.)
The following telnet options are available:
-8 Enable cs8 (8 bit transfer) on local tty.
-ec Set the telnet command mode escape character to be ^c
instead of its default value of ^].
-l Disable the TAC User ID option if enabled on the client, to
cause the user to be prompted for login username and
password. Omitting the -l option executes the default
setting.
Commands
The following commands are available in command mode. You need only
type enough of each command to uniquely identify it (this is also true
for arguments to the mode, set, toggle, and display commands).
open host [port]
Open a connection to the named host at the indicated
port. If no port is specified, telnet attempts to
contact a TELNET server at the standard TELNET port.
The hostname can be either the official name or an
alias as understood by gethostbyname() (see
gethostent(3N)), or an Internet address specified in
the dot notation as described in hosts(4). If no
hostname is given, telnet prompts for one.
close Close a TELNET session. If the session was started
from command mode, telnet returns to command mode;
otherwise telnet exits.
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. If telnet is run from a shell that
supports job control, (such as csh(1) or ksh(1)), the z
command suspends the TELNET session and returns the
user to the shell that invoked telnet. The job can
then be resumed with the fg command (see csh(1) or
ksh(1)).
mode mode Change telnet's user input mode to mode, which can be
character (for ``character at a time'' mode) or line
(for ``line by line'' 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 is entered. In character mode, telnet
sends each character to the remote host as it is typed.
In line mode, telnet gathers user input into lines and
transmits each line to the remote host when the user
types carriage return, linefeed, or EOF (normally ^D;
see stty(1)). Note that setting line-mode also sets
local echo. Applications that expect to interpret user
input character by character (such as more, csh, ksh,
and vi) do not work correctly in line mode.
status Show current status of telnet. telnet reports the
current escape character. If telnet is connected, it
reports the host to which it is connected and the
current mode. If telnet is not connected to a remote
host, it reports No connection. Once telnet has been
connected, it reports the local flow control toggle
value.
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 prints the
help information available about that command only.
Help information is limited to a one-line description
of the command.
! [shell_command]
Shell escape. The SHELL environment variable is
checked for the name of a shell to use to execute the
command. If no shell_command is specified, a shell is
started and connected to the user's terminal. If SHELL
is undefined, /usr/bin/sh is used.
send arguments Sends one or more special character sequences to the
remote host. Each argument can have any of the
following values (multiple arguments can be specified
with each send command):
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 (and may not work to
some systems -- if it doesn't work, a
lower case ``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 variable_name 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 can be shown by using the display command.
The following variable_names can be specified:
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, for example, 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 (see toggle
localchars below) and the interrupt character is
typed, a TELNET IP sequence (see send ip 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 (see toggle
localchars below) and the quit character is typed,
a TELNET BRK sequence (see send brk 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 (see toggle
localchars below) and the flushoutput character is
typed, a TELNET AO sequence (see send ao above) is
sent to the remote host. The initial value for
the flush character is ^O.
erase
If telnet is in localchars mode (see toggle
localchars below), and if telnet is operating in
character-at-a-time mode, then when this character
is typed, a TELNET EC sequence (see send ec 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 (see toggle
localchars below), and if telnet is operating in
character-at-a-time mode, then when this character
is typed, a TELNET EL sequence (see send el 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 causes this 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 can be specified. The state of these flags
can be shown by using the display command. Valid
arguments are:
localchars
If TRUE, the flush, interrupt, quit, erase,
and kill characters (see set above) are
recognized locally, and transformed into
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,
whenever the ao, intr, or quit characters are
recognized (and transformed into TELNET
sequences - see set above for details),
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.
autosynch
If autosynch and localchars are both TRUE,
when either the intr or quit character is
typed (see set above 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 discarding
all previously typed input until both of the
TELNET sequences have been read and acted
upon. The initial value of this toggle is
FALSE.
binary
Enable or disable the TELNET BINARY option on
both input and output. This option should be
enabled in order to send and receive 8-bit
characters to and from the TELNET server.
crlf If TRUE, end-of-line sequences are sent as an
ASCII carriage-return and line-feed pair. If
FALSE, end-of-line sequences are sent as an
ASCII carriage-return and NUL character pair.
The initial value for this toggle is FALSE.
crmod
Toggle carriage return mode. When this mode
is enabled, any carriage return characters
received from the remote host are mapped into
a carriage return and a line feed. This mode
does not affect those characters typed by the
user; only those received. This mode is only
required for some hosts that require the
client to do local echoing, but output
``naked'' carriage returns. The initial
value for this toggle is FALSE.
echo Toggle local echo mode or remote echo mode.
In local echo mode, user input is echoed to
the terminal by the local telnet before being
transmitted to the remote host. In remote
echo, any echoing of user input is done by
the remote host. Applications that handle
echoing of user input themselves, such as C
shell, Korn shell, and vi (see csh(1),
ksh(1), and vi(1)), do not work correctly
with local echo.
options
Toggle viewing of TELNET options processing.
When options viewing is enabled, all TELNET
option negotiations are displayed. Options
sent by telnet are displayed as ``SENT'',
while options received from the TELNET server
are displayed as ``RCVD''. 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.
RETURN VALUE
In the event of an error, or if the TELNET connection is closed by the
remote host, telnet returns a value of 1. Otherwise it returns zero
(0).
DIAGNOSTICS
The following diagnostic messages are displayed by telnet:
telnet/tcp: Unknown service
telnet was unable to find the TELNET service entry in the
services(4) database.
hostname: Unknown host
telnet was unable to map the host name to an Internet
address. Your next step should be to contact the system
administrator to check whether there is an entry for the
remote host in the hosts database (see hosts(4)).
?Invalid command
An invalid command was typed in telnet command mode.
system call>: ...
An error occurred in the specified system call. See the
appropriate manual entry for a description of the error.
AUTHOR
telnet was developed by the University of California, Berkeley.
SEE ALSO
csh(1), ksh(1), login(1), rlogin(1), stty(1), telnetd(1M), hosts(4),
services(4), termio(7).