I have been affected by an ext4 unmountable problem.
The suggested solution is to run
e2fsck in a live CD. Ubuntu can't be used because it periodically tries to mount the partition (/dev/sda3 in my case) preventing e2fsck from running. In other words, in order to recover Ubuntu, I want to try using a non-Ubuntu Live CD.
Other people have had success with Slax. But it doesn't work on MacBook.
What live CDs will work on my MacBook?