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NAME

     shmat, shmdt — attach or detach shared memory

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #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)