TERMHANGUP, Terminal has disconnected

Run Time Error: This indicates that the terminal serving as the PRINCIPAL device has disconnected. By default, GT.M ignores terminal "hang-ups," which can allow the terminal to reconnect at a later time to a process that does not need the terminal to continue work. You can enable recognition of Principal device disconnects with USE $PRINCIPAL:HUPENABLE or by starting the process with the gtm_hupenable set to 1, TRUE or YES, or disable them with USE $PRINCIPAL:NOHUPENABLE.

Action: When a process receives this error it must avoid any further READs from, or WRITEs to, $PRINCIPAL, typically by shutting down in a wholesome fashion. Failure to do so causes GT.M to terminate the process with a NOPRINCIO message to the operator log.