Linuxcnc mesa backlash

Sir,
please tell how add backlash in the ini file for both (Right, Left) directions of y axis .
i  ask because the mostly cnc machine doesn't have equal amount of backlash in both directions of each axis  

I'm not sure you can have different amounts of backlash in the same axis.

Backlash is caused by space between screw and nut / gears / belt and pulley. The space results in a deadzone where when the motor direction reverses there is a time when the motor is rotating without the axis actually moving. Then the motor has rotated far enough and the space / deadzone has been taken up and the axis moves.

You could also be dealing with stick slip