Processes and Services

Every running program in Linux is a process. Understanding how to view, manage, and control processes — as well as how to work with system services — is essential for system administration and troubleshooting.

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What is a Process?

A process is an instance of a running program. Each process has:

Attribute	Description
PID	Process ID — unique numeric identifier
PPID	Parent Process ID — the process that started this one
UID	User ID — who owns the process
State	Running, sleeping, stopped, zombie, etc.
Nice value	Process priority (-20 highest to 19 lowest)
Memory	Resident and virtual memory usage
CPU	CPU time consumed

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Viewing Processes

ps — Process Status