Explain what signals in the Unix operating system are and how they are used for inter-process communication.

In Unix systems, signals are a mechanism for asynchronous notification of processes about events. A signal is a short message sent to a process by the kernel or another process to inform it about an event.

Examples of signals:

• SIGINT — interrupt (usually Ctrl+C)
• SIGTERM — request to terminate the process
• SIGKILL — immediate termination of the process
• SIGSTOP — pause the process

Signals are used for:

• Process management (termination, suspension, resumption)
• Error handling (for example, division by zero triggers SIGFPE)
• Inter-process communication (for example, one process can send a signal to another for synchronization)

A process can set a signal handler to perform specific actions upon receiving a signal, or ignore the signal (if permitted).

Example of using a signal in shell:

kill -SIGTERM <pid>  # Send termination signal to the process with ID pid

Thus, signals are a simple and effective way to interact with and manage processes in Unix.