shmget(2)                                                         shmget(2)

NAME
     shmget - get shared memory segment identifier

SYNOPSIS
     #include <sys/shm.h>

     int shmget(keyt key, sizet 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 are created for key if one of
     the following applies:

     -  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, respec-
        tively, 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.

ERRORS
     The following error code descriptions are function-specific. You will
     find a general description in introprm2(2) or in errno(5).

     shmget() fails if one or more of the following apply:

     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 per-
               mission 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)                                                         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 systemwide would be exceeded.

     ENOMEM    A shared memory identifier and associated shared memory seg-
               ment 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.

RESULT
     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.

     In the future there may be modifications to the interfaces for inter-
     process communication. You should design your applications so that in
     modules using shmget() this function can easily be replaced by others.

SEE ALSO
     shmctl(2), shmop(2), stdipc(3C), shm(5).

























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