SHMGET(2)                                               SHMGET(2)



     NAME
          shmget - get shared memory segment identifier

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

          int shmget (key, size, shmflg)
          keyt key;
          int size, 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 low-order 9 bits of shmperm.mode are set equal to
               the low-order 9 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 will fail 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.



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     SHMGET(2)                                               SHMGET(2)



          [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 & 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
                         ((shmflg & IPCCREAT) and (shmflg& IPCEXCL))
                         is ``true''.

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

     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.

     ORIGIN
          AT&T V.3




















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