SHMGET(2-SVR3)      RISC/os Reference Manual       SHMGET(2-SVR3)



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 pro-
          cess.

          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.

ERRORS
     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



                        Printed 11/19/92                   Page 1

SHMGET(2-SVR3)      RISC/os Reference Manual       SHMGET(2-SVR3)



                              [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.

     [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.  This can hap-
                              pen if kernel working storage is
                              exhausted, or if creating the seg-
                              ment would cause the system-imposed
                              limit on the aggregate size of all
                              shared memory segments (the recon-
                              figurable kernel variable
                              shminfo.shmall) to be exceeded.

     [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.







 Page 2                 Printed 11/19/92