Linux Process Management: Kill, Nice, and Strace

A Linux system is just a kernel juggling thousands of processes. Knowing how to manipulate them is key to system stability.

Viewing Processes

top is classic, but htop is better. It gives a visual representation of CPU cores and memory.

• PID: Process ID.
• USER: Owner.
• RES: Resident Memory (Physical RAM used).
• S: State (Running, Sleeping, Zombie).

The Kill Signals

kill doesn't just kill. It sends signals.

• kill -15 (SIGTERM): "Please stop." The application catches this and cleans up (saves files, closes sockets). Use this first.
• kill -9 (SIGKILL): "Die immediately." The kernel rips the process out of memory. No cleanup. Use only if frozen.
• kill -1 (SIGHUP): "Hang up." Often used to tell services to reload configuration without restarting.

Niceness (CPU Priority)

Nice values range from -20 (Highest Priority) to +19 (Lowest). Default is 0.

• nice -n 10 tar -czf backup.tar.gz /home: Run backup with low priority so it doesn't slow down the website.
• renice -n -5 -p 1234: Give PID 1234 more CPU attention (needs root).

Strace: The Ultimate Debugger

When a process is running but stuck, strace reveals what it's whispering to the kernel.

strace -p 1234

You might see: open("/missing/config.json", O_RDONLY) = -1 ENOENT

Aha! It's crashing because a config file is missing. strace makes you look like a wizard.