When managing a Linux system, it is crucial to know how to monitor resource usage and control running programs. In Linux, a running instance of a program is called a process.

Viewing Active Processes: ps

The ps (process status) command takes a snapshot of currently running processes.

• To see processes running in your current terminal session:

  ps

• To see a detailed list of all processes running on the system by all users:

  ps aux

This command outputs the Process ID (PID), user, CPU usage, memory usage, and the command that started the process.

Real-Time Monitoring: top and htop

While ps provides a static snapshot, top provides a dynamic, real-time view of system processes.

top

By default, top sorts processes by CPU usage, allowing you to quickly identify resource hogs. Press q to exit top.

An even better alternative is htop, which provides a colorful, interactive interface where you can scroll horizontally and vertically. It usually needs to be installed via your package manager (e.g., sudo apt install htop).

Managing Processes: kill

If a process is unresponsive or consuming too many resources, you may need to terminate it. You do this by sending a signal to the process using the kill command along with the Process ID (PID).

1. First, find the PID using ps or top.
2. Then, use the kill command:

   kill 1234

   (Replace 1234 with the actual PID). This sends a standard termination signal (SIGTERM), asking the process to shut down gracefully.

If the process refuses to terminate, you can force it to stop by sending a SIGKILL signal using the -9 flag:

kill -9 1234

Use kill -9 as a last resort, as it doesn’t allow the program to clean up temporary files or save data before closing.

Understanding these tools gives you complete control over the applications running on your system.