Where is shared memory allocated in Linux?

Accessing shared memory objects via the filesystem On Linux, shared memory objects are created in a (tmpfs(5)) virtual filesystem, normally mounted under /dev/shm. Since kernel 2.6. 19, Linux supports the use of access control lists (ACLs) to control the permissions of objects in the virtual filesystem.

Where is shared memory stored?

When a shared memory region is setup, the same physical memory location is addressed by the multiple processes. However the virtual addresses can be different though. Each process uses the virtual address it received only in its own context. Both the virtual addresses refer to the same physical memory.