shmget(2) shmget(2) NAME shmget - get shared memory segment SYNOPSIS #include <sys/shm.h> int shmget(key_t key, size_t 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 size size bytes (see glossary(9)) are created for key if one of the following is true: o key is equal to IPC_PRIVATE. This call creates a new identifier, subject to available resources. The identifier will never be returned by another call to shmget() until it has been released by a call to shmctl(). The identifier should be used among the calling process and its descendents; however, it is not a requirement. The resource can be accessed by any process having the proper permissions. o key does not already have a shared memory identifier associated with it, and (shmflg & IPC_CREAT) is ``true''. Upon creation, the data structure associated with the new shared memory identifier is initialized as follows: o 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. o shm_perm.cuid, 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. o shm_lpid, shm_nattch, shm_atime, and shm_dtime are set equal to 0. o shm_ctime is set equal to the current time. EXAMPLES The following call to shmget() returns a unique shmid for the newly created shared memory segment of 4096 bytes: int myshmid; myshmid = shmget (IPC_PRIVATE, 4096, 0600); Hewlett-Packard Company - 1 - HP-UX Release 10.20: July 1996 shmget(2) shmget(2) RETURN VALUE 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. ERRORS shmget() fails if any of the following conditions are encountered: [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 glossary(9)) 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 & 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 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 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 ipcrm(1), ipcs(1), shmctl(2), shmop(2), stdipc(3C). STANDARDS CONFORMANCE shmget(): SVID2, SVID3, XPG2, XPG3, XPG4 Hewlett-Packard Company - 2 - HP-UX Release 10.20: July 1996