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To: linux-kernel@vger.kernel.org
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [Q] pivot_root and initrd
Date: 17 Oct 2001 14:17:59 -0700
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Copyright: Copyright 2001 H. Peter Anvin - All Rights Reserved
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Followup to:  <3BCDCF1D.6030202@usa.net>
By author:    Eric <ebrower@usa.net>
In newsgroup: linux.dev.kernel
> 
> I am mystified that the call to 'exec /sbin/init' works if you are using 
> the standard (you mention "based on RedHat7.1" util-linux") /sbin/init 
> proggie, and that a standard RH7.1 initscripts would not complain when 
> the root filesystem is already mounted r/w.
> 
> I would also guess that you are susceptible to the kernel's change_root 
> call if your /sbin/init terminates.  I'll have to play with the disk a bit.
> 

I modify the initscripts to not try to fsck and remount the root --
its a ramfs (tmpfs in a later version) after all.  If I had been
mounting a filesystem off the harddisk I would either have mounted it
readonly and left the init scripts as-is, or fscked it before
mounting.

I pass the following command line options to the kernel (this is set
up in isolinux.cfg):

        append initrd=initrd.gz root=/dev/ram0 init=/linuxrc single

By specifying root=/dev/ram0 and an explicit init (which I'm calling
/linuxrc but could just as easily have called /sbin/init) I'm telling
the kernel that this is the final root, and effectively turn off most
of the initrd legacy weirdness.

If /sbin/init exits, the kernel panics, just like it would normally do
if init goes away.

	-hpa
-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt	<amsp@zytor.com>
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