It turns out that it is possible to merge down the persistent overlay into the base image, if you have access to another OS installation and sufficient disk space.
- Another OS installation is optional. (See LiveOS image/overlay#Merge overlay into new image.)
- Thanks for demonstrating this technique. --FGrose 01:21, 20 August 2012 (EDT)
- Really. I'd be nervous running that on a loaded system, but I've got to try it now! --Agilmore (talk) 22:11, 2 October 2012 (UTC)
I like that result better than just having to increase the overlay size without bounds.
Tested and working on a Fedora 17 x86_64 Live image installed via livecd-iso-to-disk to a USB stick, all commands as root. You will need disk space sufficient for the uncompressed size of the root filesystem, 4 GB in the case of Fedora 17. I assume only one image and one user on the machine.
Step 1: Get access to read-write base image, note that I got loop2 and loop3 here, YMMV.
mkdir squashfs mount -o loop /run/media/*/LIVE/LiveOS/squashfs.img squashfs/ cp squashfs/LiveOS/ext3fs.img .
Step 2: Set up loopback and device mapper devices for persistent overlay, base device mapper and snapshot.
losetup -f ext3fs.img losetup -f /run/media/*/LIVE/LiveOS/overlay-* echo 0 $(blockdev --getsize /dev/loop2) linear /dev/loop2 0 |dmsetup create orig echo 0 $(blockdev --getsize /dev/mapper/orig) snapshot /dev/mapper/orig /dev/loop3 p 8 | dmsetup create top
Step 3: Stop the snapshot device and merge the snapshot with the base
dmsetup suspend top echo 0 $(blockdev --getsize /dev/loop2) snapshot-merge /dev/loop2 /dev/loop3 p 8 | dmsetup create mergeomatic && dmsetup status mergeomatic
Step 4: Wait for merge to complete. When the status report on mergeomatic reports allocated blocks equal to the metadata blocks, the merge is finished.
Step 5: Remove the merge target.
dmsetup remove mergeomatic
Step 6: Set the top device to no snapshot, and inspect the filesystem for results, if desired.
echo 0 $(blockdev --getsize /dev/loop2) linear /dev/loop2 0 | dmsetup load top dmsetup resume top mkdir root mount /dev/mapper/top root cd root chroot .
Step 7: Clean up.
cd .. umount root dmsetup remove top dmsetup remove orig losetup -d /dev/loop2 losetup -d /dev/loop3 umount squashfs/
Step 8: Copy the root filesystem image back into the squashfs image, you may need -noappend
mkdir LiveOS mv ext3fs.img LiveOS rm /run/media/*/LIVE/LiveOS/squashfs.img mksquashfs LiveOS /run/media/*/LIVE/LiveOS/squashfs.img -keep-as-directory