Linuxrc runs with PID 7

Linuxrc runs with PID 7

[Paul Powell]

This is a followup question to my previous question
"Why isn't init at PID 1."

Previoulsy I was calling init from within linuxrc. 
Linuxrc was a sash script, so the sash script
supposedly had PID 1.  Now I've removed the script and
have a C program for linuxrc.

I'm still not running at PID 1 but at 7.  The linuxrc
program looks like:

int main(int argc, char* argv[])
{
   printf("PID = %i\n", getpid());
}

When I boot and linuxrc is executed, PID equals 7.

Any ideas as to why this is and how I can run at PID
1?

Thanks,
Paul

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Re: Linuxrc runs with PID 7

[bert hubert]

On Wed, Jan 31, 2001 at 11:23:38AM -0800, Paul Powell wrote:
> This is a followup question to my previous question
> "Why isn't init at PID 1."

Lots of stuff assumes that PID 0 is the idle task, and that PID 1 is init.
For example, the kernel disallows ptraceing of init, based on its pid of 1.

If you are PID 1, make sure that you handle SIGCHLDs etcetera from daemons.
Check the source of init, I suspect it does something which tells the kernel
'I am your init'.

Regards,

bert hubert

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Re: Linuxrc runs with PID 7

[Rogier Wolff]

Paul Powell wrote:
> This is a followup question to my previous question
> "Why isn't init at PID 1."
> 
> Previoulsy I was calling init from within linuxrc. 
> Linuxrc was a sash script, so the sash script
> supposedly had PID 1.  Now I've removed the script and
> have a C program for linuxrc.
> 
> I'm still not running at PID 1 but at 7.  The linuxrc
> program looks like:
> 
> int main(int argc, char* argv[])
> {
>    printf("PID = %i\n", getpid());
> }
> 
> When I boot and linuxrc is executed, PID equals 7.
> 
> Any ideas as to why this is and how I can run at PID
> 1?

Yes, I've noticed this too. 

I concluded that to the kernel there is something magic about
"init=/bin/someprogram":  The program doesn't get PID 1 anymore. 

I used to have a script there fire up X and then exec init inside an
Xterm. I gave up on this after that junk started happening.

Oh, and Init refuses to be useful if it doesn't end up with PID 1. 

			Roger. 

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Re: Linuxrc runs with PID 7

[Russell King]

Firstly, a /linuxrc script can't be PID 1.  Check the bottom of
do_basic_setup in init/main.c:

                pid = kernel_thread(do_linuxrc, "/linuxrc", SIGCHLD);

Since do_basic_setup is already PID 1, /linuxrc won't be.

If you need /linuxrc to be PID 1, don't call it /linuxrc, but /sbin/init,
/etc/init or /bin/init.

--
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html

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