table of contents
|SHMGET(2)||System Calls Manual||SHMGET(2)|
NAME¶shmget — obtain a shared memory identifier
LIBRARY¶Standard C Library (libc, -lc)
#include <sys/shm.h> int
shmget(key_t key, size_t size, int flag);
DESCRIPTION¶Based on the values of key and flag, shmget() returns the identifier of a newly created or previously existing shared memory segment. The key is analogous to a filename: it provides a handle that names an IPC object. There are three ways to specify a key:
- IPC_PRIVATE may be specified, in which case a new IPC object will be created.
- An integer constant may be specified. If no IPC object corresponding to key is specified and the IPC_CREAT bit is set in flag, a new one will be created.
- The ftok(3) may be used to generate a key from a pathname.
- Read access for user.
- Write access for user.
- Read access for group.
- Write access for group.
- Read access for other.
- Write access for other.
RETURN VALUES¶Upon successful completion, shmget() returns the positive integer identifier of a shared memory segment. Otherwise, -1 is returned and errno set to indicate the error.
ERRORS¶The shmget() system call will fail if:
- Size specified is greater than the size of the previously existing segment. Size specified is less than the system imposed minimum, or greater than the system imposed maximum.
- No shared memory segment was found matching key, and IPC_CREAT was not specified.
- The kernel was unable to allocate enough memory to satisfy the request.
- IPC_CREAT and IPC_EXCL were specified, and a shared memory segment corresponding to key already exists.
SEE ALSO¶shmat(2), shmctl(2), shmdt(2), ftok(3)
|July 3, 1995||Debian|