telnetd - internet TELNET protocol server
/usr/etc/telnetd [ -h ] [ -n ]
telnetd is a server which supports the Internet standard TELNET virtual
terminal protocol. telnetd is invoked by the Internet super-server (see
inetd(1M)), normally for requests to connect to the TELNET port as
indicated by the /etc/services file (see services(4)). The -h option
suppresses the host information banner before the login prompt. The -n
option suppresses transport-level keep-alive messages. The use of keepalive
messages allows sessions to be timed out if the client crashes or
telnetd operates by allocating a pseudo-terminal device (see pty(7)) 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 protocol 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 characters, 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 created login
telnetd is willing to do: echo, binary, suppress go ahead, and timing
mark. telnetd is willing to have the remote client do: binary, terminal
type, terminal speed, window size, toggle flow control, environment, X
display location, and suppress go ahead. Attempts to set environment
variables understood by rld(1) are ignored and logged. Currently, these
are LD_LIBRARY_PATH and any variable name starting with _RLD.
Some TELNET commands are only partially implemented.
Because of bugs in the original 4.2 BSD telnet(1C), telnetd performs some
dubious protocol exchanges to try to discover if the remote client is, in
fact, a 4.2 BSD telnet(1C).
Binary mode has no common interpretation except between similar operating
systems (UNIX in this case).
The terminal type name received from the remote client is converted to
telnetd never sends TELNET go ahead commands.
PPPPaaaaggggeeee 2222 [ Back ]