The shmat system call attaches the shared memory segment identified by shmid to the calling processs address space. The address where the segment is attached is determined as follows:
- If addr is 0, the segment is attached at an address selected by the kernel.
- If addr is nonzero and SHM_RND is not specified in flag, the segment is attached the specified address.
- If addr is specified and SHM_RND is specified, addr is rounded down to the nearest multiple of SHMLBA.
The shmdt system call detaches the shared memory segment at the address specified by addr from the calling processs address space.
Upon success, shmat returns the address where the segment is attached; otherwise, -1 is returned and errno is set to indicate the error.
.Rv -std shmdt
The shmat system call will fail if: