What really is kthreadd (PID=2)?

In chapter 3, page 6 creating processes
, the course states that kthreadd
(PID=2) purpose is to adopt orphaned processes.
I'm running ArchLinux with kernel 5.13 and all the processes with PPID=2 as reported with ps axjf
are reported in square brackets, i assume they are kernel threads?
I also see many processes with PPID=1 (/sbin/init
, that is a symlink to systemd), for example tmux and ssh-agent have PPID=1. I was expecting them to be have kthreadd
as the parent, not init
.
So, when does init
adopt a process and when does kthreadd
adopts?
Is there a documentation/man about kthreadd
somewhere? I could not find it.
Comments
-
If you examine the list you will see all [ ] processes have ppid=2 (kthreadd) while all user space processes may have ppid=1 (systemd/init). kthreadd is actually the internal kernel thread that is used in kernel code with functions like kthread_create() to create these kernel threads or adopt them. Perhaps the wording is not the best, I will investigate. thanks
as far as documentation about kthreadd goes, http://www.tovantran.com/blog/?p=2591 is one simple (but dated) explanation,
0 -
Hi @coop,
Thanks for the explanation and the link.
There's also a similar statement in page 8 (Process States):
If the parent of any process dies, the process is adopted by init (PID = 1) or kthreadd (PID = 2).
Do you think it is possible to amend/update these pages with a clearer explanation about which process adopts orphans?
Is there a place that I can suggest/submit changes?
0
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