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Systems & Data Center · Foundational

Process ID (PID)

A unique number the Linux kernel assigns to each running process.

Definition

PIDs identify processes for monitoring and signaling. PID 1 is the init system (systemd), and each process also has a parent PID (PPID). Process details appear under /proc/<PID>.

Example

pgrep -a sshd prints the PIDs and command lines of SSH daemon processes.

Exam tip

PID 1 is systemd on modern Linux; killing it would crash the system.

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