Documented as: -b duration.pitch | belltype Set the bell duration in milliseconds and pitch in hertz. If a belltype argument is specified, it may be one of normal which sets sound parameters back to normal values, off which disables the bell entirely, or visual which sets the bell to visual mode, i.e., flashes the screen instead. If belltype is preceded by the word quiet., the bell will not be rung when the ringing process is in the background vty. The visual bell, when chosen, applies to all vtys; other bell types can be set individually for each vty. in vt(4) mode kbdcontrol -b has no effect (and does not produce an error).