How to identify a thread is a kernel thread or not through `bash`?

Question

How to identify a thread is a kernel thread or not through bash?

I found that you could identify the kernel thread by ps: if the thread name is enclosed in [], it's a kernel thread. But i do not think it is a good solution.

I would be thankful for any hint on this question.

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– Cyrus, Commented May 21, 2020 at 13:29

Marco Bonelli · Accepted Answer · 2020-05-21 22:32:55Z

4

You can determine whether a particular task is a kthread or not by looking at /proc/<PID>/stat. More presicesely, according to man 5 proc the 9th field of this virtual file contains the kernel flags for the process. In case of a kthread, the flags will have PF_KTHREAD set.

Here's an example of a Bash script that takes a PID as argument and checks if it's a kthread or not:

#!/bin/bash

read -a stats < /proc/$1/stat
flags=${stats[8]}

if (( ($flags & 0x00200000) == 0x00200000 )); then
    echo 'KTHREAD'
else
    echo 'NOT KTHREAD'
fi

This isn't really simpler than just doing ps u -p <PID> and checking for [], but it's a pure Bash solution nonetheless.

There are also some more "tricks" which can be used to identify a kernel thread, it's easy to modify the above script to use one of the methods highlighted in this post.

edited May 21, 2020 at 22:32

answered May 21, 2020 at 17:55

Marco Bonelli

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