Comprendre les processus : `ps`, `top`, `htop`

Welcome! In this lesson, we'll explore how to view and monitor programs running on your Linux system. These running programs are called processes.

Understanding processes is crucial for system administration, troubleshooting, and managing resource usage.

The simplest way to see active processes is with the ps command. It gives you a snapshot of current processes.

By default, ps shows processes owned by your user in the current terminal session.

To see all processes on the system, including those owned by other users and system processes, we use options like aux or -ef.

• a: Show processes for all users.
• u: Display user/owner.
• x: Show processes without a controlling terminal.

The -ef option is a common alternative on some systems, providing similar comprehensive output.

When you run ps aux, you'll see several columns:

• USER: The owner of the process.
• PID: The unique Process ID.
• %CPU: CPU usage percentage.
• %MEM: Memory usage percentage.
• CMD: The command that started the process.

These details help you identify what's running and by whom.

Every process has a unique PID (Process ID). It's like a social security number for a process.

Many processes are started by other processes. The process that starts another is called its parent process. The child process will have a PPID (Parent Process ID) that matches the parent's PID.

This creates a process tree, showing how processes are related.

While ps gives a snapshot, top provides a dynamic, real-time view of your system's processes.

It continuously updates, showing CPU and memory usage, uptime, and a list of processes sorted by CPU usage (by default).

This is great for spotting processes consuming a lot of resources.

top is interactive! Here are some basic keys:

• Press q to quit.
• Press M to sort processes by memory usage.
• Press P to sort processes by CPU usage (default).
• Press k to "kill" a process (you'll need the PID).

Remember to be careful when using k!

htop is an improved, interactive process viewer that's often preferred over top due to its user-friendliness.

It offers a more colorful and intuitive interface, making it easier to see CPU and memory usage visually.

You might need to install it first (e.g., sudo apt install htop on Debian/Ubuntu).

htop provides several advantages:

• Visual Bars: Clear graphs for CPU, memory, and swap.
• Scrolling: Easily scroll horizontally and vertically.
• Mouse Support: Click to sort columns or select processes.
• Easy Filtering/Searching: Quickly find specific processes.
• Tree View: See process hierarchy clearly.

It's a powerful tool for monitoring system health.

You've learned about ps, top, and htop. Let's see if you can distinguish their primary uses.

Great job! You now understand how to monitor processes on Linux.

• ps: Gives a static snapshot of processes. Use ps aux or ps -ef for comprehensive lists.
• top: Provides a real-time, interactive view of processes, sorted by resource usage.
• htop: An enhanced, more user-friendly version of top with visual bars, mouse support, and easier navigation.

These tools are essential for any Linux user!