telnetd - The DARPA telnet protocol server
telnetd [-debug [port]] [-D modifier ...]
Starts telnetd manually, rather than through inetd, on alternate TCP port number port (if specified). Prints out debugging information. modifiers are: Prints information about negotiation of telnet options Same as options with additional processing information Displays the data stream received by telnetd Displays data written to the pty Not yet implemented
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: 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 an /etc/issue.net file present, telnetd reads the file and writes its contents over a new telnet connection prior to starting the login dialog. If an /etc/issue file is present, but not a /etc/issue.net file, telnetd reads that file and writes its contents over a new telnet connection instead.
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).
Specifies the command path. Specifies the path name for the network issue identification file. Specifies the path name for the issue identification file.
Files: iptos(4), issue(4), issue.net(4). delim off