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telnetd(8)
NAME
telnetd - The DARPA telnet protocol server
SYNOPSIS
telnetd [-debug [port]] [-D modifier ...]
FLAGS
-debug [port]
Starts telnetd manually, rather than through inetd, on alternate
TCP port number port (if specified).
-D modifier ...
Prints out debugging information. modifiers are:
options Prints information about negotiation of telnet options
report Same as options with additional processing information
netdata Displays the data stream received by telnetd
ptydata Displays data written to the pty
exercise Not yet implemented
DESCRIPTION
The telnetd daemon is a server that supports the DARPA (Defense Advanced
Research Projects Agency) 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 indicated by the /etc/services
file (see services(4)). The -debug flag may be used, to start up telnetd
manually. If started up this way, port may be specified to run telnetd on
an alternate TCP port number.
The -D options may be used for debugging purposes. This allows telnetd to
print out debugging information to the connection, allowing the user to see
what telnetd is doing.
The telnetd daemon operates by allocating a pseudoterminal device (see
pty(7)) for a client, then creating a login process that has the slave side
of the pseudoterminal 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 process. The
pseudoterminal allocated to the client is configured to operate in cooked
mode, and with XTABS and CRMOD enabled (see tty(7)).
The telnetd daemon is willing to do: echo, binary, suppress go ahead, and
timing mark. telnetd is willing to have the remote client do: line mode,
binary, terminal type, terminal speed, window size, toggle flow control,
environment, X display location, and suppress go ahead.
The telnetd daemon never sends telnet go ahead commands.
Note that binary mode has no common interpretation except between similar
operating systems (Unix compatible systems in this case).
Note also that the terminal type name received from the remote client is
converted to lowercase.
The telnet command uses the default Type-of-Service value recommended by
RFC1060, which is as follows:
telnet
Low delay
You can configure this value by specifying it in the /etc/iptos file. For
more information, see iptos(4).
By default, the telnetd daemon starts the login dialog using the login
string specified in the message field of the /etc/gettydefs file. If you
want to use a customized banner, create an /etc/issue.net or /etc/issue
file. The telnetd daemon reads the file that exists and writes its contents
over a new telnet connection prior to starting the login dialog. If both
files exist, only the /etc/issue.net file is used.
CAUTIONS
Some telnet commands are only partially implemented.
Because of bugs in the original 4.2BSD telnet(1), telnetd performs some
dubious protocol exchanges to try to discover if the remote client is, in
fact, a 4.2BSD telnet(1).
FILES
/usr/sbin/telnetd
Specifies the command path.
/etc/issue.net
Specifies the path name for the network issue identification
file.
/etc/issue
Specifies the path name for the issue identification file.
RELATED INFORMATION
Commands: telnet(1).
Files: iptos(4), issue(4), issue.net(4).
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