SHM_R
shmid = shmget(2, LENGTH, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
*shmid = shmget(2, size, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
shmid = shmget(IPC_PRIVATE, getpagesize(), SHM_R | SHM_W);