From IPC to TCP and UDP sockets

Linux applications communicate with each other either directly or over a network. But the difference between direct communication and networked communication, from an application programmer's point of view, is not always that big. Let's look at the various communication methods that Linux supports and how SELinux aligns with them.

Using shared memory

The method that is the least network-like is the use of shared memory. Applications can share certain parts of the memory with each other and use those shared segments to communicate between two (or more) processes. To govern access to the shared memory, application programmers can use mutual exclusions (mutexes) or semaphores. A semaphore is an integer that is atomically incremented or decremented (ensuring that two applications do not overwrite each other's values without knowing about the value change), whereas a mutex can be interpreted as a special kind of semaphore that only takes the values...