What do the [..] mean in 'ps' and how do you create a process like it?

Question

When running ps, you get something like:

root         2  0.0  0.0      0     0 ?        S<   00:00   0:00 [kthreadd]
root         3  0.0  0.0      0     0 ?        S<   00:00   0:00 [ksoftirqd/0]
root         4  0.0  0.0      0     0 ?        S<   00:00   0:00 [events/0]

All the daemon processes generally have the [..] brackets around them.

What do they mean (if anything)? How do you create a process that appears like this?

The reason I ask is we create a system daemon from the rcS (the programme uses fork to create the daemon), but ps entry looks like:

root       207  0.0  0.2   1516   200 ?        S    00:00   0:00 /root/testdaemo

So we were wondering if it is important to have the [..] brackets and how processes get them in the first place.

Thanks.

http://unix.stackexchange.com/questions/22121/what-do-the-brackets-around-processes-mean — Ciro Santilli OurBigBook.com, Sep 16 '16 at 13:06

score 19 · Accepted Answer · answered Aug 16 '11 at 12:43

19

Square brackets are used for processes that do not have an associated command line (mostly kernel threads and some system services).

If I recall correctly, you might be able to achieve the same effect for your process by setting argv[0] to the empty string.

answered Aug 16 '11 at 12:43

Frédéric Hamidi

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`mostly` - what can make an exception? – n611x007 Nov 24 '13 at 21:30
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What does the trailing /0 mean? – RyanN Feb 21 '14 at 21:25
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@RyanN, it means that kernel thread is running on the first CPU. – Frédéric Hamidi Feb 21 '14 at 21:39

score 7 · Answer 2 · answered Aug 16 '11 at 15:46

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Yes, they are kernel threads, created by kernel subsystems. They are created using kthread_create() or kernel_thread() functions in kernel.

answered Aug 16 '11 at 15:46

score 2 · Answer 3 · answered Aug 16 '11 at 12:44

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Your example doesn't even show the [...], so I'm not 100% sure what you're talking about. However it IS possible to modify the argv arguments of any program (in Linux). The arguments are reflected in the output of ps.

answered Aug 16 '11 at 12:44

Chris Eberle

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`[...]` was meant as a placeholder. I was referring to the `[kthreadd]` <- the `[]` that encapsulate the name. – Aug 16 '11 at 12:47
ah I see. Then yes I believe those are kernel processes. – Chris Eberle Aug 16 '11 at 12:48

What do the [..] mean in 'ps' and how do you create a process like it?

3 Answers3