Re: Keep initrd tasks running?

[linux-os (Dick Johnson)]

On Tue, 18 Oct 2005, John Richard Moser wrote:

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>
> I have no idea who's the best to ask for this.
>
> I want to start a task in an initrd and have it stay running after init
> is started.  Pretty much:
>
>
> - kernel boot
> - initrd loaded
> - linuxrc executes
> - /bin/mydaemon runs
> - mount rootfs
> - pivot_root
> - exec /sbin/init (PID=1; linuxrc and sh is replaced)
> - mydaemon keeps running, reparented under init, uninterrupted
>
>
> What's the feasibility of this without the system balking and vomiting
> chunks everywhere?  I'm pretty sure 'exec /sbin/init' from linuxrc
> (PID=1) will replace the process image of sh (linuxrc) with init,
> keeping PID=1; but I'm worried this may terminate children too.  Haven't
> tried.
>
> (this actually has a useful application)

Note that the 'init' of linuxrc (/sbin/nash or /sbin/sash) also
has a PID of 1. It gets replaced with /sbin/init or whatever you
use for an emergency shell.

You can load a kernel thread from a driver that gets installed
by initrd. This would allow you to have processes running with
PIDs greater than 1 before the final init gets started. The
present kernel starts quite a few threads up to PID=8 right
now.

Once 'init' gets started, you are going to have either new 'inits'
exec(ed) with PID 1 or children with PIDs greater than 1.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.13.4 on an i686 machine (5589.55 BogoMips).
Warning : 98.36% of all statistics are fiction.
.

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