How to Send SIGKILL in htop

The htop command-line utility provides an interactive way to manage system processes in Linux, including the ability to terminate unresponsive applications. While pressing the [F9] or [K] key defaults to sending a SIGTERM (Signal 15) to gracefully shut down a process, users often need to escalate to a SIGKILL (Signal 9) when a process becomes completely frozen. This article provides a quick, step-by-step guide on how to navigate the htop interface to select and send a forceful SIGKILL signal to any running process.

Step-by-Step Guide to Sending SIGKILL

To forcefully terminate a process using htop, follow these steps:

1. Open htop: Launch the utility by typing htop in your terminal and pressing [Enter].
2. Locate the Target Process: Use the [Up Arrow] and [Down Arrow] keys to scroll through the process list, or press [F3] to search for the process by its name or PID. Highlight the desired process.
3. Open the Signal Menu: Press the [F9] key (or [K] on some configurations) to bring up the “Kill” menu on the left side of the screen.
4. Select SIGKILL: By default, the menu will highlight 15 SIGTERM. Use the arrow keys to scroll up or down the list until you highlight 9 SIGKILL.
5. Send the Signal: Press [Enter] to confirm and send the SIGKILL signal to the highlighted process.

Understanding SIGTERM vs. SIGKILL

When managing processes in Linux, it is important to understand the difference between these two destructive signals:

• SIGTERM (Signal 15): This is the default termination signal. It requests the process to stop running, allowing it to save its current state, release allocated resources, and close open files safely.
• SIGKILL (Signal 9): This signal cannot be caught, blocked, or ignored by the target process. The Linux kernel immediately terminates the process, which is highly effective for frozen applications but carries a risk of data corruption or leaving temporary files behind.