[Fedora-livecd-list] Help: How to enable rootfs in rw mode?

[Joey Boggs]

On 07/19/2010 11:11 PM, Lee Eric wrote:
> Hi all,
>
> I make a LiveCD by my self(not using livecd-tools) which is based on
> Fedora 12. And I download an official LiveCD from Fedora website for
> study. What I found is the root filesystem of LiveCD is in rw mode. I
> noticed that there's an image named osmin.img in LiveOS folder of
> Fedora LiveCD ISO image. It seems a LVM snapshot, for further
> information I found there's a sentence in Wikipedia says: "Some
> Linux-based Live CD systems also use snapshots to simulate read-write
> access on a read-only compact disc.". So what I feel confused is how
> to make it available in a LiveCD.
>
> Here are steps how do I make my own LiveCD.
>
> 1. Create a folder in /tmp called LiveOS.
> 2. Using yum to create a small base system in LiveOS folder.
> 3. Modify /etc/sysconfig/readonly-root. READONLY=no, TEMPORARY_STATE=yes
> 4. Add some folders in /etc/rwtab like /etc, /home, /root.
> 5. Make a squashfs image by using mksquashfs and rename the image as ext3fs.img.
> 6. Create a folder in /tmp called iso.
> 7. Using isolinux as boot loader for the image and copy necessary
> files including initramfs and vmlinuz in /tmp/iso/isolinux.
> 8. Copy the ext3fs.img to /tmp/iso/LiveOS folder.
> 9. Burning the ISO image.
>
> After these steps the ISO image boots up okay by using qemu. And
> /root, /home, /etc are in rw mode, services start okay. But when I
> wanna restart or stop the system, it shows
>
> umount: /etc: device is busy.
> /etc:
> init: rc0 main process (935) killed by KILL signal
>
> Then system hangs.
>
> So my question is what I shall I do for this LiveCD then can make the
> root fs in rw mode like official Fedora LiveCD? Do I need to use LVM
> snapshot as Wiki said "Some Linux-based Live CD systems also use
> snapshots to simulate read-write access on a read-only compact disc."?
> If yes, could anyone tell me how to achieve that? I really appreciate
> that.
>
> Thanks,
>
> Regards,
>
> Eric
>
> P.S. Please do not just reply "Using livecd-tools them make yourself
> easier", I ask questions here for study. Thanks.
> --
> livecd mailing list
> livecd at lists.fedoraproject.org
> https://admin.fedoraproject.org/mailman/listinfo/livecd
>    

The /etc  hang is due to it attempting to be unmounted.

For ovirt-node we've used the following to work around it in the %post 
of kickstart. There's also a few other readonly-root items in there you 
may be interested in.

http://git.fedorahosted.org/git/?p=ovirt/node.git;a=blob;f=recipe/common-post.ks;h=c6ef496a1d0bfc86adde7d3a402f2116320c6c81;hb=66af4c5cf33419ab26a11a5760939cc38b78cac6

# prevent node from hanging on reboot due to /etc mounts
patch -d /etc/init.d/ -p0<<\EOF
--- halt.orig	2009-12-05 00:44:29.000000000 +0000
+++ halt	2010-03-24 18:12:36.000000000 +0000
@@ -138,7 +138,7 @@
      $"Unmounting pipe file systems (retry): " \
      -f

-LANG=C __umount_loop '$2 ~ /^\/$|^\/proc|^\/dev/{next}
+LANG=C __umount_loop '$2 ~ /^\/$|^\/proc|^\/etc|^\/dev/{next}
  	$3 == "tmpfs" || $3 == "proc" {print $2 ; next}
  	/(loopfs|autofs|nfs|cifs|smbfs|ncpfs|sysfs|^none|^\/dev\/ram|^\/dev\/root$)/ {next}
  	{print $2}' /proc/mounts \
EOF


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