Basic UNIX process
In C, use
fork() to fork the program into two process (i.e. copy the whole stack, heap, memory, etc.), one is parent and the other is child.
fork() will return the pid of the child.
fork() will return 0.
wait until the process with a specific pid ends
run an external program other than c
index 0: file type index 1-3: owner index 4-6: group index 7-9: other
read write execute (rwx)