Process

Definition

A process is the operating system’s unit of running and accounting: an executing workload with an identity (PID), its own virtual address space, permissions, and kernel-managed resources.

Process vs program

• A program is “code in motion”: the running instance in the abstract.
• A process is the OS object that represents that running instance and enforces boundaries around it.

This distinction is practical: you can inspect and control processes (limits, signals, priority), even when you don’t control the source code.

What a process typically includes

• virtual address space (memory mappings, stack/heap)
• one or more threads of execution (implementation detail, but common)
• open file descriptors (files, sockets, pipes)
• environment variables, working directory
• permissions/identity (user/group, capabilities)

Why processes enable isolation

Processes are the main way the OS enforces isolation: separate address spaces and controlled access to kernel-managed resources reduce the blast radius of bugs.

Lifecycle-related terms

When reasoning about a running system, it helps to be able to describe how a process begins and ends:

• process lifecycle
• process start
• signal
• exit code
• graceful shutdown vs forced shutdown
• crash