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SHMGET(2)                   BSD System Calls Manual                  SHMGET(2)

NAME
     shmget -- get shared memory area identifier

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

     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]           A shared memory segment is already associated with key
                        and its size is less than the requested size.

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

     [ENOENT]           IPC_CREAT was 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.

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

BSD                            November 15, 2014                           BSD