|SHMGET(2)||System Calls Manual||SHMGET(2)|
LIBRARY¶Standard C Library (libc, -lc)
key, size_t size,
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.
The mode of a newly created IPC object is determined by which are set by ORing these constants into the flag argument:
- Read access for owner.
- Write access for owner.
- Read access for group.
- Write access for group.
- Read access for other.
- Write access for other.
When creating a new shared memory segment, size indicates the desired size of the new segment in bytes. The size of the segment may be rounded up to a multiple convenient to the kernel (i.e., the page size).
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.
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)
|March 4, 2018||Linux 4.19.0-6-amd64|