TELNETD(8)TELNETD(8)NAMEtelnetd - DARPA TELNET protocol server
SYNOPSIS
/etc/telnetd [-debug [port]] [-l] [-D options] [-D report] [-D exer‐
cise] [-D netdata] [-D ptydata]
DESCRIPTION
Telnetd is a server which supports the DARPA standard TELNET virtual
terminal protocol. Telnetd is invoked by the internet server (see
inetd(8)), normally for requests to connect to the TELNET port as indi‐
cated by the /etc/services file (see services(5)). If the -debug may
be used, to start up telnetd manually, instead of through inetd(8). If
started up this way, port may be specified to run telnetd on an alter‐
nate TCP port number.
The -D option may be used for debugging purposes. This allows telnet
to print out debugging information to the connection, allowing the user
to see what telnetd is doing. There are several modifiers: options
prints information about the negotiation of TELNET options, report
prints the options information, plus some additional information about
what processing is going on, netdata displays the data stream received
by telnetd, ptydata displays data written to the pty, and exercise has
not been implemented yet.
Telnetd operates by allocating a pseudo-terminal device (see pty(4))
for a client, then creating a login process which has the slave side of
the pseudo-terminal as stdin, stdout, and stderr. Telnetd manipulates
the master side of the pseudo-terminal, implementing the TELNET proto‐
col and passing characters between the remote client and the login
process.
When a TELNET session is started up, telnetd sends TELNET options to
the client side indicating a willingness to do remote echo of charac‐
ters, to suppress go ahead, to do remote flow control, and to receive
terminal type information, terminal speed information, and window size
information from the remote client. If the remote client is willing,
the remote terminal type is propagated in the environment of the cre‐
ated login process. The pseudo-terminal allocated to the client is
configured to operate in “cooked” mode, and with XTABS and CRMOD
enabled (see tty(4)).
Telnetd is willing to do: echo, binary, suppress go ahead, and timing
mark. Telnetd is willing to have the remote client do: linemode,
binary, terminal type, terminal speed, window size, toggle flow con‐
trol, environment, X display location, and suppress go ahead.
SEE ALSOtelnet(1)BUGS
Some TELNET commands are only partially implemented.
Because of bugs in the original 4.2 BSD telnet(1), telnetd performs
some dubious protocol exchanges to try to discover if the remote client
is, in fact, a 4.2 BSD telnet(1).
Binary mode has no common interpretation except between similar operat‐
ing systems (Unix in this case).
The terminal type name received from the remote client is converted to
lower case.
Telnetd never sends TELNET go ahead commands.
4.2 Berkeley Distribution June 28, 1990 TELNETD(8)
