What you will learn
- List and filter processes
- Send signals to control processes
- Read process state
New to this? Start here
The basics, in plain English
When you run any program, the computer creates a live, running copy of it. That running copy is called a process. This lesson is about seeing what is running and telling those programs to stop, restart, or reload.
- Program
- A file on disk that contains instructions, sitting still until you run it.
- Process
- A program that is actually running right now, using memory and the CPU.
- PID
- A "process ID" is a unique number the system gives each running process so you can refer to it.
- Signal
- A short message you send to a process, such as "please stop" or "reload your settings".
- kill
- A command that sends a signal to a process. Despite the name, it can just ask politely, not only force-quit.
- ps / top
- Commands that show you the list of processes currently running, like a Task Manager.
01
Process model
A process is a running program with a PID. ps and top show what is running; pstree shows the parent/child tree.
02
Signals
kill sends signals, not just death. SIGTERM (15) asks nicely, SIGKILL (9) forces it, SIGHUP (1) often reloads config.
Try it yourself
bash
$ps aux | grep nginx↳List running processes and filter for nginx to find its PID.$kill -TERM 4821↳Politely ask process 4821 to shut down (graceful stop).$kill -HUP $(pgrep nginx)↳Send a reload signal so nginx re-reads its config without restarting.$top -o %MEM↳Watch live processes sorted by memory usage.↳ lines explain what each command does — only the commands get copied
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