In Unix/Linux process control, which command is commonly used to terminate a running process by sending a signal (for example, SIGTERM or SIGKILL)?

Introduction / Context:
When a program hangs or must be stopped, Unix/Linux provides a signal mechanism to request termination. The standard user-space tool to send signals to processes—whether gentle or forceful—is fundamental for administration and scripting.

Given Data / Assumptions:

• You know the process ID (PID) or can find it with 'ps'/'pgrep'.
• You want to end the process cleanly if possible.
• You have appropriate permissions to signal the process.

Concept / Approach:
Use 'kill PID' to send SIGTERM (15) by default, allowing the process to exit gracefully. If it does not respond, 'kill -9 PID' sends SIGKILL, which the process cannot catch or ignore. Other signals like SIGHUP can request reloads. The 'kill' command is versatile and supports multiple PIDs and process group signaling.

Step-by-Step Solution:

Verification / Alternative check:
Check logs or process status post-signal. For services managed by init/systemd, use service-aware tools (for example, 'systemctl stop') which may call 'kill' under the hood.

Why Other Options Are Wrong:

• shutdown / haltsys: System-level power management, not per-process termination.
• cancel: Not a standard Unix signal-sending command.
• None of the above: Incorrect because 'kill' is correct.

Common Pitfalls:
Overusing '-9' which bypasses cleanup, signaling the wrong PID, or failing to consider service managers that auto-respawn processes.

Final Answer:
kill