Introduction
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
/lib64/libexpat.so.1
/lib64/libexpat.so.1.6.0
/lib64/libstdc++.so.6
/lib64/libstdc++.so.6.0.18
/usr/sbin/thin_dump
/usr/sbin/thin_check
/usr/sbin/thin_restore
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.
Dusty