file: /proc/sys/kernel/auto_msgmni
variable: kernel.auto_msgmni
Official reference

This variable has no effect and may be removed in future kernel releases. Reading it always returns 0. Up to Linux 3.17, it enabled/disabled automatic recomputing of msgmni upon memory add/remove or upon ipc namespace creation/removal. Echoing “1” into this file enabled msgmni automatic recomputing. Echoing “0” turned it off. auto_msgmni default value was 1.