Kill -9 doesn't kill process in Ubuntu

Question

This process is marked as <defunct> and kill -9 doesn't kill it. What can I do? Why can't this process be killed?

Answer 1

This kind of a process is called a zombie process. Kill command has no effect on zombie processes. Technically, they are dead, and you see them just because they still have an entry in the process table.

To remove zombies from a system, the SIGCHLD signal can be sent to the parent manually, using the kill command. If the parent process still refuses to reap the zombie, the next step would be to remove the parent process. When a process loses its parent, init becomes its new parent. Init periodically executes the wait system call to reap any zombies with init as parent.

Answer 2

Defunct means, that it's a zombie process - it's not really working, it just awaits it's parent process to call wait to receive it's return value.

wait function can be used to read the number of a signal, that killed the zombie process, so it's in fact the correct behavior.

To get rid of zombies you can: - kill the parent process (maybe console, where you typed in your command) - call wait in parent process - ignore SIGCHLD in the parent process, if you never call wait