How to Kill a Running Linux Process

The kill command in Linux is used to terminate processes by sending specific signals. By default, it sends the SIGTERM signal (signal 15), which gracefully stops a process. However, other signals, like SIGKILL (9), can forcefully terminate a process when necessary.

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Terminate a Process by PID

kill 1234  

Sends the default SIGTERM signal to gracefully terminate process 1234.

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Forcefully Kill a Process

kill -9 1234  

• -9 sends the SIGKILL signal, which forcefully terminates the process.

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Reload a Process (e.g., Web Server)

kill -1 1234  

• -1 sends the SIGHUP signal, often used to reload configurations (e.g., Nginx, Apache).

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Stop a Process Temporarily

kill -19 1234  

• -19 sends the SIGSTOP signal, pausing the process.

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Resume a Stopped Process

kill -18 1234  

• -18 sends the SIGCONT signal, resuming a paused process.

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List All Available Signals

kill -l  

Displays a list of all signals (e.g., SIGTERM, SIGKILL, SIGHUP).

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Kill a Process by Name

pkill firefox  

Terminates all processes named firefox.

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Kill Processes by User

pkill -u username  

Terminates all processes owned by username.

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Kill Processes Matching a Pattern

pkill -f "python script.py"  

• -f: Matches the full command line (e.g., kills python script.py).

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Send a Custom Signal

kill -SIGUSR1 1234  

Sends the SIGUSR1 signal, often used for custom process handling.

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Kill All Processes in a Process Group

kill -- -12345  

• -- -12345: Sends the signal to all processes in the process group 12345.

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Kill Background Jobs

kill %1  

Terminates the background job with ID 1 (use jobs to list background jobs).

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Gracefully Stop Multiple Processes

kill 1234 5678 91011  

Sends SIGTERM to processes 1234, 5678, and 91011.

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Verify if a Process Was Killed

kill -0 1234  

• -0 checks if the process exists without sending a signal.
• Returns 0 if the process exists, 1 if it doesn’t.

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Kill All Processes Except the Current Shell

kill -9 -1  

• -1: Sends SIGKILL to all processes except the current shell.
• Warning: Use with caution—this can crash the system.

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Key Notes:

• Signals: Use kill -l to list all signals. Common ones include:
• SIGTERM (15): Graceful termination.
• SIGKILL (9): Forceful termination.
• SIGHUP (1): Reload configurations.
• Permissions: Only the root user or process owner can kill processes.
• Alternatives: Use pkill or killall to target processes by name.