Fedup 19 to 20 with a Thin LVM Configuration


I have been running my home desktop on thin logical volumes for a while now. I have enjoyed the flexibility of this setup and I like taking a snapshot before making any big changes to my setup. Recently I decided to update to Fedora 20 from Fedora 19 and I hit some trouble along the way because the Fedora 20 initramfs (images/pxeboot/upgrade.img) that is used by fedup for the upgrade does not have support for thin logical volumes. After running fedup and rebooting you end up with a message to the screen that looks something like this:

[  OK  ] Started Show Plymouth Boot Screen.
[  OK  ] Reached target Paths.
[  OK  ] Reached target Basic System.
[  191.023332] dracut-initqueue[363]: Warning: Could not boot.
[  191.028263] dracut-initqueue[363]: Warning: /dev/mapper/vg_root-thin_root does not exist
[  191.029689] dracut-initqueue[363]: Warning: /dev/vg_root/thin_root does not exist
         Starting Dracut Emergency Shell...
Warning: /dev/mapper/vg_root-thin_root does not exist
Warning: /dev/vg_root/thin_root does not exist

Generating "/run/initramfs/rdsosreport.txt"

Entering emergency mode. Exit the shell to continue.

Working Around the Issue

First off run install and run fedup :

[root@localhost ~]# yum update -y fedup fedora-release &>/dev/null
[root@localhost ~]# fedup --network 20                 &>/dev/null 

After running fedup usually you would be able to reboot and go directly into the upgrade process. For us we need to add a few helper utilities (thin_dump, thin_check, thin_restore) to the initramfs so that thin LVs will work. This can be done by appending more files in a cpio archive to the end of the initramfs that was downloaded by fedup. I learned about this technique by peeking at the initramfs_append_files() function within fedup’s boot.py. Note also that I had to append a few libraries that are required by the utilities into the initramfs as well.

[root@localhost ~]# cpio -co >> /boot/initramfs-fedup.img << EOF
4334 blocks
[root@localhost ~]#

And thats it.. You are now able to reboot into the upgrade environment and watch the upgrade. If you’d like to watch a (rather lengthy) screencast of the entire process then you can download the screencast.log and the screencast.timing files and follow the instructions here.