UnionFS in initrd

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UnionFS in initrd

Dennis Muhlestein-2
I've played around with UnionFS a bit.  I like the idea for a COW file
system.

Anyhow, I have an initrd file that I'd like to use to set up the unionfs
root.

Here is the linuxrc file:

== SNIP:linuxrc ==
# unionfs module inserted previously

# these directories already exist in the initrd image
BASE=/mnt/basefs
UNION=/mnt/union
CHANGES=/mnt/userfs

echo "Mount base filesystem.."
mount -t ext3 /dev/sda1 $BASE
echo "Mount user filesystem.."
mount -t ext3 /dev/sda2 $CHANGES

echo "Mount root UnionFS.."
mount -t unionfs -o dirs=$CHANGES=rw:$BASE=ro none $UNION

cd $UNION
mkdir -p initrd
pivot_root . initrd
exec chroot . sbin/init 3 < /dev/console > /dev/console 2>&1
== END ==

So now my issue is:

init: timeout opening/writing control channel /dev/initctl
(After which kernel panic )

If I exec chroot . /bin/bash instead of sbin/init...  I get a shell in
the current unionfs root. (As expected)

Any thoughts on the sbin/init problem?  I'm using a gentoo base file system

-Dennis

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Re: UnionFS in initrd

Charles Duffy-6
Dennis wrote:
> I've played around with UnionFS a bit.  I like the idea for a COW file
> system.

It doesn't work properly right now for a root FS running a completely
unmodified distribution; there are some bad interactions with procfs
(/proc/<pid>/exe ends up pointing at the particular UnionFS branch
rather than at the UnionFS filesystem itself, which confuses a number of
distributions' tools for checking daemon status), and the unionfs patch
I've been using to override this issue via changing /proc's symlink
resolution is a bit crashy (though there are newer proposed patches I
haven't been able to test with yet). See my posts on
gmane.comp.file-systems.unionfs.general and the surrounding threads.


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