SHMGET(2) BSD Programmer's Manual SHMGET(2)
shmget - get shared memory area identifier
#include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> int shmget(key_t key, size_t size, int shmflg);
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.
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.
[EACCES] 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 identif- iers has been reached. [ENOENT] IPC_CREAT was not set in shmflg and no shared memory seg- ment associated with key was found. [ENOMEM] There is not enough memory left to create a shared memory segment of the requested size.
ipcrm(1), ipcs(1), mmap(2), shmat(2), shmctl(2), ftok(3) MirOS BSD #10-current August 17, 1995 1
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