How to Kill a Process on Linux

So, you want to kill a process on Linux? No worries, let’s break it down. There are a few commands you can use for this, like kill, killall, pkill, and even xkill for GUI processes.

First, to kill a process, you’ll need to find its process ID (PID). You can use commands like ps, top, or pgrep to locate it. For example, running ps aux | grep process_name will help you find the PID of a specific process. Once you have the PID, you can use the kill command to send a signal to the process. The default signal is SIGTERM (15), which tries to close the process gracefully. If that doesn’t work, you can use SIGKILL (9), which forces the process to quit immediately. I’d recommend trying SIGTERM first and then moving to SIGKILL if needed.

Alternatively, if you don’t want to mess with finding a PID, killall is a great option because it lets you use the process name directly instead of the PID. Similarly, pkill can be used to match patterns, so you can kill multiple instances of a process at once. After sending the kill signal, you might want to check if the process is still running. You can do that by using ps or pgrep again to verify.

A few things to watch out for: If you don’t have permission to kill a process, you might need to run the command with sudo. Also, be aware of zombie processes that might not die easily. And always double-check the PID to avoid accidentally killing the wrong process. If you’re using a desktop environment, you can also kill processes with GUI tools like System Monitor, which is a bit more visual if you’re not into the command line.

Here’s a step-by-step guide to use commands like kill, pkill, or killall to terminate it by PID (Process ID) or name :-

1. Find the Process ID (PID)

Using ps or pgrep

ps aux | grep "process_name"   # Search by name/pattern

Example:

ps aux | grep "firefox"        # Find Firefox's PID

Using pgrep

pgrep -f "process_name"        # Returns the PID directly

Using top or htop

• Run top or htop, navigate to the process, and note the PID.

2. Terminate the Process

Kill by PID

kill [signal] PID              # Graceful termination (default: SIGTERM)
kill -9 PID                    # Forceful termination (SIGKILL)

Example:

kill 1234                      # Ask process 1234 to exit gracefully
kill -9 1234                   # Force-kill process 1234

Kill by Name

pkill "process_name"           # Send SIGTERM to all matching processes
pkill -9 "process_name"        # Force-kill by name
killall "process_name"         # Kill all instances of a process

Example:

pkill firefox                  # Terminate all Firefox processes
killall -9 chrome              # Force-kill all Chrome instances

3. Verify the Process is Killed

ps aux | grep "process_name"   # Check if the PID is gone
pgrep "process_name"           # Returns nothing if terminated

Key Signals

Advanced Methods

Kill Processes by Port

sudo lsof -i :8080            # Find PID using port 8080
kill -9 $(lsof -t -i:8080)    # Terminate process on port 8080

Kill User-Owned Processes

pkill -u username             # Terminate all processes by a user

Kill GUI Applications

Use xkill (if running a desktop environment):

xkill                        # Click a window to force-close it

Troubleshooting

• Permission Denied: Use sudo if the process is owned by another user:

  sudo kill -9 PID

• Zombie Processes: These can’t be killed (already dead). Reboot to clear them.
• Process Respawns: Some processes auto-restart (e.g., system services). Use:

  systemctl stop service_name   # For systemd services

Example Workflow

1. Find the PID of a frozen app:

   pgrep -f "chromium"
   # Output: 5678

2. Terminate it gracefully:

   kill 5678

3. If it persists, force-kill:

   kill -9 5678

4. Verify:

   ps -p 5678                # No output means success

Important Notes

• Use SIGKILL (-9) sparingly—it doesn’t allow cleanup and can corrupt data.
• Prefer SIGTERM first to let the process exit properly.
• Avoid killing critical system processes (e.g., systemd, sshd).

Summary Table

That’s all.