DoubleForkAndExecute fork current process twice and runs syscall.Exec.

WriteToEventfd writes value to an given eventfd it is said from http://man7.org/linux/man-pages/man2/eventfd.2.html A write(2) fails with the error EINVAL if the size of the supplied buffer is less than 8 bytes, or if an attempt is made to write the value 0xffffffffffffffff.