shmget(2) - NetBSD Manual Pages

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SHMGET(2)                 NetBSD System Calls Manual                 SHMGET(2)

shmget -- get shared memory segment
Standard C Library (libc, -lc)
#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 both the IPC_CREAT bit and the IPC_EXCL bit are set in shmflg, and key has a shared memory seg- ment identifier associated with it already, the operation will fail. 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. [EINVAL] No shared memory segment is to be created, and a shared memory segment exists for key, but the size of the segment associated with it is less than size, which is non-zero. A shared memory segment is to be created, and size is less than the system imposed minimum, or greater than the system imposed maximum (refer to the kern.ipc val- ues in sysctl(7)). [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 create a shared memory segment of the requested size. [ENOSPC] A new shared memory identifier could not be created because the system limit for the number of shared mem- ory identifiers has been reached.
ipcrm(1), ipcs(1), mmap(2), shmat(2), shmctl(2), ftok(3), sysctl(7)
The shmget system call conforms to X/Open System Interfaces and Headers Issue 5 (``XSH5'').
Shared memory segments appeared in the first release of AT&T System V UNIX. NetBSD 9.3 October 27, 2008 NetBSD 9.3
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