How to Handle Zombie Processes in Ubuntu

Today, when I logged into the console, I found the following output:

TEXT

There are 20 zombie processes

I'm not very familiar with Linux, and when I saw the word zombie, my first thought was a Trojan (I just set up my new server, so where could a Trojan come from? And how could Ubuntu scan for a Trojan on its own, let alone 20 of them?).

After checking, it turns out it wasn't what I had imagined. The definition (from Jianshu) is as follows:

APEU2's definition of a zombie process: In UNIX system terminology, a process that has terminated but whose parent has not yet waited for it is called a zombie. When a parent thread does not use the wait method to get the termination status of its child thread, the child thread becomes a zombie after it terminates.

The dangers of zombie processes When a child thread ends, it sends a SIGCHLD signal to the parent thread. The parent thread enters the wait method to release related resources and close open files, etc. When the parent thread doesn't know that the child thread has ended and doesn't enter the wait method to release resources, a large number of zombie processes will consume a lot of system resources. On the other hand, the process ID of the child process is still occupied. When a large number of zombie processes occur, it may cause the system to be unable to create new processes.

Indeed, it's not something good.

So, we can use the following command to view all zombie processes:

BASH

ps aux | grep Z

From here, I can see that these processes are Chrome processes, which may be related to the Koishi I installed yesterday.

We can solve this using the following command:

BASH

ps -eo pid,ppid,stat,cmd | grep 'Z'  # Find zombie processes and their parent processes

BASH

kill -HUP <PPID>  # Send SIGHUP signal to the parent process, where <PPID> is the parent process ID

Alternatively, you can choose to terminate the parent process:

BASH

kill -9 <PPID>  # Forcefully terminate the parent process