shmget(2)                        UNIX System V                        shmget(2)


NAME
      shmget - get shared memory segment identifier

SYNOPSIS
      #include <sys/types.h>
      #include <sys/ipc.h>
      #include <sys/shm.h>

      int shmget(keyt key, int size, int shmflg);

DESCRIPTION
      shmget returns the shared memory identifier associated with key.

      A shared memory identifier and associated data structure and shared
      memory segment of at least size bytes [see intro(2)] are created for key
      if one of the following are true:

            key is equal to IPCPRIVATE.

            key does not already have a shared memory identifier associated
            with it, and (shmflg&IPCCREAT) is true.

      Upon creation, the data structure associated with the new shared memory
      identifier is initialized as follows:

            shmperm.cuid, shmperm.uid, shmperm.cgid, and shmperm.gid are
            set equal to the effective user ID and effective group ID,
            respectively, of the calling process.

            The access permission bits of shmperm.mode are set equal to the
            access permission bits of shmflg.  shmsegsz is set equal to the
            value of size.

            shmlpid, shmnattch shmatime, and shmdtime are set equal to 0.

            shmctime is set equal to the current time.

      shmget fails if one or more of the following are true:

      EINVAL         size is less than the system-imposed minimum or greater
                     than the system-imposed maximum.

      EACCES         A shared memory identifier exists for key but operation
                     permission [see intro(2)] as specified by the low-order 9
                     bits of shmflg would not be granted.

      EINVAL         A shared memory identifier exists for key but the size of
                     the segment associated with it is less than size and size
                     is not equal to zero.





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shmget(2)                        UNIX System V                        shmget(2)


      ENOENT         A shared memory identifier does not exist for key and
                     (shmflg&IPCCREAT) is false.

      ENOSPC         A shared memory identifier is to be created but the
                     system-imposed limit on the maximum number of allowed
                     shared memory identifiers system wide would be exceeded.

      ENOMEM         A shared memory identifier and associated shared memory
                     segment are to be created but the amount of available
                     memory is not sufficient to fill the request.

      EEXIST         A shared memory identifier exists for key but both
                     (shmflg&IPCCREAT) and (shmflg&IPCEXCL) are true.

SEE ALSO
      intro(2), shmctl(2), shmop(2), stdipc(3C).

DIAGNOSTICS
      Upon successful completion, a non-negative integer, namely a shared
      memory identifier is returned.  Otherwise, a value of -1 is returned and
      errno is set to indicate the error.

NOTES
      The user must explicitly remove shared memory segments after the last
      reference to them has been removed.





























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