shmget(2)                                               shmget(2)



NAME
     shmget - get shared memory segment

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

     int shmget(key, size, shmflg)
     key_t key;
     int Isize, 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 size bytes are
     created for key if one of the following is true (see
     intro(2)):

          key is equal to IPC_PRIVATE.

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

        Note:  A shared memory segment of size is always
        rounded up to the nearest whole page.


     The key IPC_PRIVATE will create an identifier and associated
     data structure that is unique to the calling process and its
     children.

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

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

          The low-order 9 bits of shm_perm.mode are set equal to
          the low-order 9 bits of shmflg.  shm_segsz is set equal
          to the value of size.

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

          shm_ctime is set equal to the current time.




January 1992                                                    1

shmget(2)                                               shmget(2)



STATUS MESSAGES AND VALUES
     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.

     The shmget command will fail if one or more of the following
     is 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.

     EAGAIN
          The system has temporarily exhausted its available
          memory or swap space.

     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.

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

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

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

     EEXIST
          A shared memory identifier exists for key but ((shmflg
          & IPC_CREAT) && (shmflg & IPC_EXCL)) is ``true''.

SEE ALSO
     intro(2), shmctl(2), shmop(2)








2                                                    January 1992