Comment 8 for bug 1579454

It looks like you are trying to replace the OS on an existing partition and the permissions are messed up somehow. Can you mount the partition and provide the output of ls -al /mnt/etc/default? You should be able to mount it with:

sudo -s
mount -t ext4 /dev/sda1 /mnt

Assuming the partition in question is number 1, otherwise you will need to change the number.