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SHMGET(2)                     System Calls Manual                    SHMGET(2)

NAME
     shmget -- get shared memory segment

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <&lt;sys/shm.h>&gt;

     int
     shmget(key_t key, size_t size, int shmflg);

DESCRIPTION
     shmget() returns the shared memory identifier associated with the key
     key.

     A shared memory segment is created if either key is equal to IPC_PRIVATE,
     or key does not have a shared memory segment identifier associated with
     it, and the IPC_CREAT bit is set in shmflg.  If both the IPC_CREAT bit
     and the IPC_EXCL bit are set in shmflg, and key has a shared memory
     segment identifier associated with it already, the operation will fail.

     If a new shared memory segment is created, the data structure associated
     with it (the shmid_ds structure, see shmctl(2)) is initialized as
     follows:

     o   shm_perm.cuid and shm_perm.uid are set to the effective uid of the
         calling process.

     o   shm_perm.gid and shm_perm.cgid are set to the effective gid of the
         calling process.

     o   shm_perm.mode is set to the lower 9 bits of shmflg.

     o   shm_lpid, shm_nattch, shm_atime, and shm_dtime are set to 0.

     o   shm_ctime is set to the current time.

     o   shm_segsz is set to the value of size.

RETURN VALUES
     Upon successful completion a positive shared memory segment identifier is
     returned.  Otherwise, -1 is returned and the global variable errno is set
     to indicate the error.

ERRORS
     [EACCES]           A shared memory segment is already associated with key
                        and the caller has no permission to access it.

     [EEXIST]           Both IPC_CREAT and IPC_EXCL are set in shmflg, and a
                        shared memory segment is already associated with key.

     [EINVAL]           No shared memory segment is to be created, and a
                        shared memory segment exists for key, but the size of
                        the segment associated with it is less than size,
                        which is non-zero.

                        A shared memory segment is to be created, and size is
                        less than the system imposed minimum, or greater than
                        the system imposed maximum (refer to the kern.ipc
                        values in sysctl(7)).

     [ENOENT]           IPC_CREAT is not set in shmflg and no shared memory
                        segment associated with key was found.

     [ENOMEM]           There is not enough memory left to create a shared
                        memory segment of the requested size.

     [ENOSPC]           A new shared memory identifier could not be created
                        because the system limit for the number of shared
                        memory identifiers has been reached.

SEE ALSO
     ipcrm(1), ipcs(1), mmap(2), shmat(2), shmctl(2), ftok(3), sysctl(7)

STANDARDS
     The shmget system call conforms to X/Open System Interfaces and Headers
     Issue 5 (``XSH5'').

HISTORY
     Shared memory segments appeared in the first release of AT&T System V
     UNIX.

NetBSD 6.1.5                   October 27, 2008                   NetBSD 6.1.5