[dm-devel] Persistent Overlay COW Full: Flipped the Invalid bit in a hexdump; how do I grow it now?

[Frederick Grose]

On Tue, Jun 3, 2014 at 9:20 AM, Rahul Nabar <rpnabar at gmail.com> wrote:

> I accidentally managed to fill up the persistent COW snapshot overlay
> on my Fedora20 USB & it got flagged Invalid thus rendering the Live
> USB unbootable since the root filesystem couldn't be mounted.
>
> dmsetup status
> live-rw 0 8388608 snapshot Invalid.
>
>  Subsequently I used a 2011 thread(link below) on the dm-devel mailing
> list ( Alasdair Kergon, Frederick Grose etc.) and flipped the invalid
> bit in the overlay file by booting a different system and attaching
> the USB stick to it.
>
> Like so:  echo $'\x01' | dd
> of=/run/media..../liveuser/LIVE.../overlay-LIVE-17F4-055A  bs=1
> count=1 seek=4 conv=notrunc
>
> hexdump of the file verified the flipped 5th byte. Now the LiveUSB
> boots & I can successfully see my data but it's hard to do anything
> more since it gets full almost immediately after I boot.
>
> Is there a way to grow the overlay file? Would this work?
>
>  dd if=/dev/zero of=overlay-LIVE-17F4-055A seek=overlay_size
> count=size_increase
>
> How do I compute the number overlay_size?


​blockdev -q --getsz <overlay/device/path or overlay/file/path>​

or the denominator in the

dmsetup status

for the live-rw snapshot

(Units are 512 byte sectors.)

I suppose size_increase can
> be some large number?
>
> Or are more steps needed to expand the overlay?
>
>
> http://thread.gmane.org/gmane.linux.kernel.device-mapper.devel/14644


​See
​https://fedoraproject.org/wiki/LiveOS_image#Merge_overlay_into_new_image

     --Fred
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