Process Management

When you write code in VS Code, it's just a "File." But the moment you type node app.js or python script.py, that code springs to life and becomes a Process.

A Process is a living, breathing program that has its own ID (PID), consumes memory (RAM), and uses the CPU to perform tasks.

How to See What's Running

In DevOps, the first thing you do when a server feels "slow" is look at the process list.

1. The top Command (The Live Dashboard)

Type top in your terminal to see a real-time list of every process. It’s like the "Task Manager" on Windows.

• PID: The unique "Social Security Number" for the process.
• %CPU: How hard the process is making the brain work.
• %MEM: How much space it's taking up in short-term memory.

2. The ps Command (The Snapshot)

If you want a quick list of all processes without the live updates, use:

• ps aux: Shows every process running for every user on the system.
• ps aux | grep node: A "Pro" trick to find only your Node.js processes.

How to Stop a Process

Sometimes an app "hangs" or gets stuck in an infinite loop. When that happens, you have to use the kill command.

The "Levels" of Killing

Not all "kills" are the same. You send a Signal to the process:

• SIGTERM (15): The "Polite" kill. It tells the app, "Please save your work and close down." (kill PID)
• SIGKILL (9): The "Angry" kill. It forces the app to stop immediately. Use this as a last resort. (kill -9 PID)

Foreground vs. Background

At CodeHarborHub, you don't want to keep your terminal window open just to keep a script running.

1. Foreground: The process takes over your terminal. You can't type anything else until it's done.
2. Background: You add an & at the end of your command (e.g., python script.py &). The script runs "behind the scenes," and you can keep using your terminal.

The Life-Saver: systemd

In a professional environment, we don't manually start and stop apps. We use systemd. It is a manager that:

• Starts your app automatically when the server turns on.
• Restarts your app if it crashes.
• Keeps logs of everything your app prints.

Common Systemd Commands:

• sudo systemctl start nginx: Start the web server.
• sudo systemctl status nginx: See if the server is healthy.
• sudo systemctl restart nginx: Apply new settings by restarting.

Summary Checklist

• I understand that a Process is a running instance of a program.
• I can identify a process by its PID.
• I know how to use top and ps aux to monitor the server.
• I understand when to use kill vs kill -9.
• I know that systemd is used for "Production" level management.

Why this matters for DevOps

Imagine you are hosting CodeHarborHub and the site goes down.

1. You SSH into the server.
2. You run top and see that a "Log Collector" script is using 100% CPU.
3. You kill that process.
4. The site is back up. You just saved the day!