Step one:
Upgrade to Jaunty. You now have a working jaunty install running the ext3 file system.

Step two:
Make a backup of all your (important) data. You can use fwbackups or any other app.

Step three:
Boot from a (jaunty) live-cd and run the following code (in this example the partition to convert is on /dev/sda1) to convert the partition:

sudo bash
tune2fs -O extents,uninit_bg,dir_index /dev/sda1
e2fsck -pf /dev/sda1

Step four:
Mount the partition and change the type of the converted partition in fstab:

sudo bash
mount -t ext4 /dev/sda1 /mnt
nano /mnt/etc/fstab

change “ext3″ to “ext4″ like in the example below:

# /dev/sda1
UUID=XXXXXXXXXXXXXXXXXXXXXXXXXX / ext3 relatime,errors=remount-ro 0 1

change it to:

# /dev/sda1
UUID=XXXXXXXXXXXXXXXXXXXXXXXXXX / ext4 relatime,errors=remount-ro 0 1

and save the changes.

Step five:
This step might be optional but when I upgraded from Intrepid to Jaunty the upgrade process did not install/update the new grub stage. So if you don’t run this you might get an (fatal) error 13 when booting the machine.

sudo bash
mount /dev/sda1 /mnt
grub-install /dev/sda –root-directory=/mnt –recheck

That’s it, after you reboot you you will be running from an ext4 file system.