Attachment and Detachment

• To make the shared memory segment available, a process must use shmat, (SHared Memory ATtach).
  • Pass the shared memory segment identifier SHMID returned by shmget.
  • The second argument is a pointer that specifies where in your process's address space you want to map the shared memory; if you specify NULL, Linux will choose an available address.
  • The third argument is a flag, which can include the following:
    • SHM_RND indicates that the address specified for the second parameter should be rounded down to a multiple of the page size.
    • SHM_RDONLY indicates that the segment will be only read, not written.
• If the call succeeds, it returns the address of the attached shared segment. Children created by calls to fork inherit attached shared segments; they can detach the shared memory segments, if desired.