If your Linux PC feels slow or the fan suddenly spins up, something is using your CPU or RAM. You don’t need to guess — two built-in tools show you exactly what’s running and how much it’s using, live.
Start with top
- Open a terminal.
- Type top and press Enter.
- You’ll see a live list of processes, sorted by CPU use, updating every few seconds.
- Press q to quit when you’re done.
Look at the %CPU and %MEM columns. The program at the top of the list is usually the one making your PC work hardest.
Try htop for an easier view
- In the terminal, type htop and press Enter.
- If it’s not installed, add it with sudo apt install htop, then run it again.
- Use the arrow keys to scroll, and press F9 only if you really want to close a stuck program.
htop adds color bars at the top for CPU and memory, so you can see at a glance whether you’re running out of RAM or a core is maxed out.
What to do with what you find
- One app near 100% CPU: it’s likely stuck or working hard — close it normally first.
- Memory almost full: close browser tabs or apps you’re not using and watch the bar drop.
- Nothing looks high: your slowdown is probably not CPU or RAM — check disk space next.
Thirty seconds in top or htop tells you whether to close something, wait, or look elsewhere. No guessing.
