The kill, kill -9, and pkill commands send signals to processes but differ in behavior and use cases. 1. kill (default SIGTERM) politely terminates a process gracefully by PID, allowing cleanup. 2. kill -9 (SIGKILL) forcefully stops a process immediately without cleanup, risking data corruption, and should be used only if kill fails. 3. pkill sends signals by process name or attributes like user or session, offering flexibility without needing the PID upfront, also defaulting to SIGTERM and supporting -9 for forceful termination.
When you're dealing with processes in Linux or Unix-like systems, you’ll often come across commands like kill, kill -9, and pkill. They all send signals to running processes, but they’re not exactly the same. Here’s how they differ and when you should use each one.
What does kill actually do?
The kill command sends a signal to a process. By default, it sends SIGTERM (signal 15), which tells the process to terminate gracefully. That means the program gets a chance to clean up resources, close files, or save state before exiting.
- This is the polite way to stop a process.
- You need to know the process ID (PID) to use it.
Example:
kill 1234
This tells the process with PID 1234 to shut down nicely.
If the process doesn’t respond to SIGTERM, that’s when you might consider stronger options.
Why use kill -9?
kill -9 sends SIGKILL, which immediately stops the process without giving it a chance to react. It’s like pulling the plug — no cleanup happens, and it can leave behind temporary files or locked resources.
- Use this only if
killdoesn’t work. - Be cautious, especially with important system services.
Example:
kill -9 1234
?? Tip: If you kill a process that was writing to a file or database, you might end up with corrupted data. Always try a regular
killfirst.
How is pkill different?
While kill works with PIDs, pkill lets you send signals by process name or other attributes. That makes it more flexible and easier to use when you don’t have the exact PID handy.
- Can match processes by name, user, or even terminal session.
- Also sends SIGTERM by default.
Example:
pkill firefox
This sends SIGTERM to all processes named "firefox".
You can also get more specific:
- Kill processes owned by a particular user:
pkill -u username
- Match partial names with
-f:pkill -f "python script.py"
Just like with kill, you can force quit using -9:
pkill -9 firefox
When to use which?
Here’s a quick guide to help you choose:
- ? Start with
kill PID— gives the process a chance to exit cleanly. - ? If that doesn’t work, try
kill -9 PID— forceful but risky. - ? Use
pkill name— convenient when you don’t know the PID. - ??? Combine with options (
-u,-f) for more precise targeting.
Basically, they all do similar things but in slightly different ways. Knowing when to use each one helps avoid unnecessary problems.
The above is the detailed content of What is the difference between kill, kill -9, and pkill?. For more information, please follow other related articles on the PHP Chinese website!
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