Message-ID: <3BCDCF1D.6030202@usa.net>
Date: Wed, 17 Oct 2001 11:34:05 -0700
From: Eric <ebrower@usa.net>
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To: linux-kernel@vger.kernel.org
Subject: Re: [Q] pivot_root and initrd
In-Reply-To: <p05100300b7f2b3b94b17@[10.128.7.49]>
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 >>
 >> Works great.  I use it in my SuperRescue CD for example; you can
 >> there check out a complete, working example.
 >>
 >>   ftp://ftp.kernel.org/pub/dist/superresuce/
 >>
 >>     -hpa


hpa,

Thanks for the example.  The documentation for pivot_root must be just 
plain lousy--  I thought I'd go "by the book" with the following 
admonitions from the manpage:

   1) cd to new_root prior to calling pivot_root
   2) call pivot_root with relative new_root (.) and put_old
   3) call 'chroot' immediately after pivot and redirect stdin/out

You are simply doing the following, I assume with success:

   [ ... ]
   # Switch roots and run init
   cd /ram
   pivot_root /ram /ram/initrd
   exec /sbin/init "$@"

whereas I am doing something like the following:

   [ ... ]
   mount -o ro $ROOTDEV $NEWROOT
   cd $NEWROOT
   pivot_root . $OLDROOT

   # export for visibility to exec'ed shell
   export INITARGS="$@"
   export OLDROOT

   exec chroot . sh -c 'umount $OLDROOT; exec -a init.new /sbin/init
     $INITARGS' <dev/console >dev/console 2>&1

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.

E

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