shm_attach() returns an id that can be used to access the System V shared memory with the given key, the first call creates the shared memory segment with memsize and the optional perm-bits perm.
A second call to shm_attach() for the same key will return a different shared memory identifier, but both identifiers access the same underlying shared memory. memsize and perm will be ignored.
The memory size. If not provided, default to the
sysvshm.init_mem in the
php.ini, otherwise 10000
The optional permission bits. Default to 0666.