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NAME

     shmat, shmdt - attach or detach shared memory

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <machine/param.h>
     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/shm.h>

     void *
     shmat(int shmid, const void *addr, int flag);

     int
     shmdt(const void *addr);

DESCRIPTION

     The shmat() system call attaches the shared memory segment identified by
     shmid to the calling process’s 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 process’s address space.

RETURN VALUES

     Upon success, shmat() returns the address where the segment is attached;
     otherwise, -1 is returned and errno is set to indicate the error.

     The shmdt() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS

     The shmat() system call will fail if:

     [EINVAL]           No shared memory segment was found corresponding to
                        shmid.

     [EINVAL]           The addr argument was not an acceptable address.

     The shmdt() system call will fail if:

     [EINVAL]           The addr argument does not point to a shared memory
                        segment.

SEE ALSO

     shmctl(2), shmget(2)