interprocess communication (IPC) 进程间通信

signals, which are used to indicate that an event has occurred;

pipes (familiar to shell users as the | operator) andFIFOs, which can be used to transfer data between processes;
sockets, which can be used to transfer data from one process to another, either
on the same host computer or on different hosts connected by a network;
file locking, which allows a process to lock regions of a file in order to prevent
other processes from reading or updating the file contents;
message queues, which are used to exchange messages (packets of data) between processes;
semaphores, which are used to synchronize the actions of processes; and

shared memory, which allows two or more processes to share a piece of memory.When one process changes the contents of the shared memory, all of the other processes can immediately see the changes.

the support of real-time applications:  These include 

asynchronous I/O, 

shared memory,

memory-mapped files,

memory locking, 

realtime clocks and timers,

alternative scheduling policies, 

realtime signals, 

message queues, 

and semaphores.