When should the SIGKILL signal be used?

The SIGKILL (signal 9) should be used in the following cases:

• The process does not respond to other signals: When normal termination signals (SIGTERM, SIGQUIT) are ignored by the process, and it does not terminate.
• The process is in a hung, unresponsive state: If the process consumes excessive resources or blocks the system, and other termination methods are ineffective.
• Urgent resource release is required: For example, when a process holds a lock that prevents other critical components from functioning, and immediate release is necessary.
• In automatic shutdown scripts after timeout: Often in deployment or monitoring scenarios, if the process does not terminate correctly within a set time, SIGKILL is used as the last resort to stop it.

Important points:

• SIGKILL cannot be caught or ignored by the process.
• Using SIGKILL does not allow the process to clean up resources (close files, free memory), which can lead to undesirable side effects or data corruption.
• Always prefer SIGTERM or SIGQUIT as more "gentle" and controlled ways to terminate. SIGKILL is an extreme measure.