In what ways can processes communicate?

UNIX processes on their own are boring; they are interesting when they communicate. There are many methods of “Inter-process communication”, or IPC. What are all these methods? There are many!:

• Files: open, close, read, write. The sender writes to a file; the receiver reads from it. USP: durability.
• Pipes: pipe, close, read, write. A pipe, created with pipe, is a byte queue. pipe returns file descriptors for both ends. Closing both ends destroys the pipe.
• Signals: sigaction, kill. The sender can send a signal to the receiver. A signal does not have associated data.
• Socket: socket, bind-listen-accept/connect, close, read, write. Sockets link processes over network interfaces. USP: connecting remote processes (not just local ones).
• Message queues: mq_open, mq_timedreceive, mq_timedsend. A message queue is a bit like a pipe, but with a proper concept of messages (a message is a byte array).
• Semaphores: semget, semop. Used to protect common resources used by processes.
• Shared memory: shmget and friends. A single memory location can be read/written by multiple processes. USP: communication via memory, not system calls.

I wrote this because I felt like it. This post is my own, and not associated with my employer.