process id 0

aggrishabh · 01-12-2011, 11:39 AM

Hi All,

Can someone shed some light on the role of process id 0 in linux. i know this process is for scheduler, but what this process do.

Please correct me if i am wrong.

fbsduser · 01-12-2011, 11:41 AM

IIRC. ID 0 is init.

aaaaatoz · 01-12-2011, 11:21 PM

Quote:

Originally Posted by fbsduser

IIRC. ID 0 is init.

I am confused whether init's PID is 0 or 1 ?

Aquarius_Girl · 01-12-2011, 11:26 PM

Quote:

Originally Posted by aaaaatoz

I am confused whether init's PID is 0 or 1 ?

Also do a man init

Code:

anisha@linux-uitj:~>ps -el
F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
4 S     0     1     0  0  80   0 -  2018 poll_s ?        00:00:00 init
1 S     0     2     0  0  75  -5 -     0 kthrea ?        00:00:00 kthreadd
1 S     0     3     2  0 -40   - -     0 migrat ?        00:00:00 migration/0
1 S     0     4     2  0  75  -5 -     0 ksofti ?        00:00:04 ksoftirqd/0
5 S     0     5     2  0 -40   - -     0 watchd ?        00:00:00 watchdog/0 
1 S     0     9     2  0  75  -5 -     0 worker ?        00:00:00 events/0   
1 S     0    11     2  0  75  -5 -     0 worker ?        00:00:00 khelper    
1 S     0    12     2  0  75  -5 -     0 worker ?        00:00:00 netns      
1 S     0    13     2  0  75  -5 -     0 async_ ?        00:00:00 async/mgr  
1 S     0    14     2  0  75  -5 -     0 worker ?        00:00:00 kintegrityd/0
1 S     0    16     2  0  75  -5 -     0 worker ?        00:00:00 kblockd/0    
...
0 S  1000  6566  5281  0  80   0 -  3472 wait   pts/3    00:00:00 bash
0 R  1000  6587  6566  0  80   0 -  1139 -      pts/3    00:00:00 ps
0 S  1000  9750  5354  0  80   0 - 163619 poll_s pts/0   00:03:51 qtcreator
...
0 S  1000 16742  5281  0  80   0 -  3500 n_tty_ pts/2    00:00:00 bash

divyashree · 01-13-2011, 02:01 AM

Quote:

Originally Posted by aggrishabh

Hi All,

Can someone shed some light on the role of process id 0 in linux. i know this process is for scheduler, but what this process do.

Please correct me if i am wrong.

swapper or sched has process ID 0 and is responsible for paging during kernel initialization.

Aquarius_Girl · 01-13-2011, 02:21 AM

and putting the following keywords in Google will yield more results:

Quote:

Linux scheduler pid

archtoad6 · 01-14-2011, 07:40 AM

My compliments on the way you suggested Google keywords -- nice phrasing, helpful, & polite.

Aquarius_Girl · 01-14-2011, 08:41 AM

Well, thank you, I could have given the OP link too but I wanted him to know how to form appropriate keywords to get the desired results from Google.

resetreset · 01-14-2011, 08:47 AM

Quote:

Originally Posted by divyashree

swapper or sched has process ID 0 and is responsible for paging during kernel initialization.

Can you expound on this a bit?

What do you mean swapper OR sched? And what do you mean "paging during kernel initialization"?

deeh514 · 01-14-2011, 08:52 AM

@Anisha....i think it's time for a link :P

Aquarius_Girl · 01-14-2011, 09:28 AM

Quote:

Originally Posted by deeh514

@Anisha....i think it's time for a link :P

Welcome to LQ!

resetreset · 01-16-2011, 04:52 AM

thanks, but I still don't get what "paging during kernel initialization" is.....

divyashree · 01-17-2011, 01:01 AM

Quote:

Originally Posted by resetreset

thanks, but I still don't get what "paging during kernel initialization" is.....

Do you know what is paging ? Please google for details. Its a beautiful memory mgmt. technique used by the kernel.

Our primary memory is divided into some logical blocks of same size called pages, by the kernel.

swapper or sched is the swapper daemon which swaps processes from primary memory to swap area(virtual memory) whenever needed i.e to free the pages from primary memory. And during kernel initialization, kernel starts the swapper daemon(sched) to do this.

resetreset · 01-19-2011, 01:03 AM

I am extremely well aware what paging is. There is no "paging during kernel initialization" - the x86 *chip* will simply take addresses that are not in RAM, and the kernel has to bring that data off the disk. This whole thing is activated when the chip is put into Protected Mode, it's not the *kernel* which does anything.

syg00 · 01-19-2011, 02:46 AM

Hmmmm.
Swapper has nothing to do with (modern) swap. In fact process swap-out in Linux hasn't existed for years. kswapd manages pages to swap.
The kernel doesn't page, although it does have page table built for it - by "swapper/process 0" I believe. Who knows where the name came from originally.