LinuxCNC M8

M8 is a LinuxCNC M-code that turns flood coolant on. It does so by controlling the iocontrol.0.coolant-flood HAL pin, which must be connected in HAL before the command affects a physical output. M9 turns both mist (M7) and flood (M8) coolant off.

Source checked3/3 values · 2026-10-26

Specification

1 source

Language	gcode
Code	M8
Group	Coolant Control
Syntax	M8
Dialect	LinuxCNC

Study notes

M8 controls the iocontrol.0.coolant-flood pin.
M7 controls the iocontrol.0.coolant-mist pin.
M9 turns both M7 and M8 off.
One or both coolant control pins must be connected in HAL before M7 or M8 will control an output; M7 and M8 can be used to turn on any output via G-code.
It is OK to use M7, M8 or M9 regardless of the current coolant state.
M2/M30 program end turns coolant off like M9.
M70 saves mist (M7) and flood (M8) status as part of modal state.