Inter-process communication (IPC) is needed in a variety of situations where different processes need to communicate with each other or share resources.

Here are some common scenarios where IPC is necessary:

1. Coordinating activities between different processes: In an operating system, different processes may need to communicate with each other to coordinate their activities, such as when a parent process creates a child process or when a program needs to send output to another program.
2. Sharing resources: IPC is used to enable different processes to share resources such as memory, files, and hardware devices. For example, multiple processes may need to share access to a printer or a network connection.
3. Parallel computing: IPC is used to coordinate the activities of different threads or processes running on multiple processors or cores. This is essential for achieving performance gains in parallel computing applications.
4. Distributed systems: IPC is used to enable different nodes or machines to communicate with each other and share data or resources in a distributed system.

Overall, IPC is necessary in many different computing scenarios, and it plays a crucial role in enabling different processes, nodes, or threads to work together and achieve common goals.

The choice of IPC mechanism depends on the specific requirements of the application, including performance, reliability, and scalability.