shmget(2) - NetBSD Manual Pages

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SHMGET(2)                 NetBSD Programmer's Manual                 SHMGET(2)


NAME

     shmget - get shared memory area identifier


SYNOPSIS

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

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


DESCRIPTION

     shmget() returns the shared memory identifier associated with the key
     key.

     A shared memory segment is created if either key is equal to IPC_PRIVATE,
     or key does not have a shared memory segment identifier associated with
     it, and the IPC_CREAT bit is set in shmflg.

     If a new shared memory segment is created, the data structure associated
     with it (the shmid_ds structure, see shmctl(2))  is initialized as fol-
     lows:

     +   shm_perm.cuid and shm_perm.uid are set to the effective uid of the
         calling process.

     +   shm_perm.gid and shm_perm.cgid are set to the effective gid of the
         calling process.

     +   shm_perm.mode is set to the lower 9 bits of shmflg.

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

     +   shm_ctime is set to the current time.

     +   shm_segsz is set to the value of size.


RETURN VALUES

     Upon successful completion a positive shared memory segment identifier is
     returned.  Otherwise, -1 is returned and the global variable errno is set
     to indicate the error.


ERRORS

     [EACESS]      A shared memory segment is already associated with key and
                   the caller has no permission to access it.

     [EEXIST]      Both IPC_CREAT and IPC_EXCL are set in shmflg, and a shared
                   memory segment is already associated with key.

     [ENOSPC]      A new shared memory identifier could not be created because
                   the system limit for the number of shared memory identi-
                   fiers has been reached.

     [ENOENT]      IPC_CREAT is not set in shmflg and no shared memory segment
                   associated with key was found.

     [ENOMEM]      There is not enough memory left to created a shared memory
                   segment of the requested size.


SEE ALSO

     mmap(2),  shmat(2),  shmctl(2)

NetBSD                          August 17, 1995                              1