telnetd(1M)

NAME

telnetd − TELNET protocol server

SYNOPSIS

/etc/telnetd [-b [bannerfile]]

DESCRIPTION

telnetd is a server that supports the DARPA standard TELNET virtual terminal protocol. The Internet daemon (inetd) executes telnetd when it receives a service request at the port listed in the services data base for telnet using the tcp protocol (see inetd(1M) and services(4)).

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 client and 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, and to receive terminal type 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 pseudo-terminal allocated to the client is configured as a normal terminal is for login, with the exception of echoing characters (see tty(7)).

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 , and suppress go ahead .

To start telnetd from the Internet daemon, the configuration file /etc/inetd.conf must contain an entry as follows:

telnet stream tcp nowait root /etc/telnetd telnetd

To override the standard telnetd login banner, specify a file containing a custom banner with the −b bannerfile option. For example, to use /etc/issue as the login banner, have inetd start telnetd with the following line in /etc/inetd.conf:

telnet stream tcp nowait root /etc/telnetd telnetd -b/etc/issue

If bannerfile is not specified, telnetd does not print a login banner.

DIAGNOSTICS

If any error is encountered by telnetd in establishing the connection, an error message is returned through the connection after which the connection is closed and the server exits. Any errors generated by the login process or its descendents are passed through as ordinary data.

All ptys on remote host in use
The server was unable to obtain a pseudo-terminal for use with the login process. Either all pseudo-terminals were in use or the pty driver has not been properly set up (see pty(7)).

Next step: Check the pty configuration of the host where telnetd is executing.

fork: No more processes
telnetd was unable to fork a process to handle the incoming connection.

Next step: Wait a period of time and try again. If this message persists, the server’s host may have runaway processes that are using all the entries in the process table.

/bin/login: ...
The login program could not be started via exec() for the reason indicated (see exec(2).

WARNINGS

The terminal type name received from the remote client is converted to lowercase.

telnetd never sends TELNET go ahead commands.

AUTHOR

telnetd was developed by the University of California, Berkeley.

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