Makefile

build:
	mpicc -o helloapp helloapp.c -pthread -Wall
run:
        mpirun -np 8 --oversubscribe helloapp
clean:
	rm -f helloapp

Remove -pthread if the app does not use pthread.

Remove -Wall to disable warnings

Update nr of processors (8 in this example)

–oversubscribe - allow more processors than physically available