PID
also: Process ID, Process identifier
PID (Process ID) is a unique numerical identifier assigned by the kernel to every running process on a Linux system, used to manage, track, and control processes.
Each process running on a Linux system receives a unique positive integer called a Process ID (PID) when it starts. The kernel uses PIDs to manage process resources, scheduling, and lifecycle. PIDs are allocated sequentially and recycled after reaching a maximum value (typically 32,768 or higher on modern systems).
You can view running processes and their PIDs using commands like ps, top, or pgrep. For example, ps aux displays all processes with their PIDs in the first column, and pgrep bash returns the PID of bash processes.
PIDs are essential for process control—you can send signals to a specific process using its PID with the kill command (e.g., kill 1234), or monitor its resource usage. The init system always has PID 1 and is the parent of all other processes.