Ubuntu freezes when attaching external hard drive due to hard drive mount mismatch. Is there a solution to fix it?

Question

Ok I think I understand why my Ubuntu 10.10 freezes when pluggin in an external hard drive through USB.

First of all I have to mention that my Ubuntu is installed on another 160gb external hard drive. During the installation it was mounted as /dev/sdc

/dev/sda = primary laptop hard disk with windows 7 /dev/sdb = 4gb usb flash drive used to install ubuntu 10.10 /dev/sdc = my external hard drive where ubuntu had been installed

After performing a System Update and restarting computer, I've received an error message that ubuntu is unable to mount: /boot, /, /home, /windows partitions.

I immediately googled the problem and seems I wasn't the only one with this issue. I've solved the problem by editing /etc/fstab (I don't remembered the exact filename) during the startup console before ubuntu is loaded. I have changed long UUID strings to /dev/sdb/ for all 5 of my partitions. The reason for /dev/sdb is because that was the actual mount showing by typing sudo blkud (again, please edit this post if I have mispelled some commands, as I don't remember exactly what was it called; it shows you the current mount points for every partition that is connected to the computer).

Now whenever I connect my backup external hard drive while ubuntu is loaded, the system just freezes. If I connect it before ubuntu loads, it gives me that same error message I firs received after doing System Update, because now this backup hard drive is pointing to /dev/sdb and my ubuntu external hard drive is pointing to /dev/sdc, while my /etc/fstab file still says that my ubuntu partitions are on /dev/sdb.

So is there any workaround to that? What should I do?

Answer 1

I would think the original /etc/fstab file created during Ubuntu install should've worked regardless of the changes in the disk drive device name - it uses UUIDs which were invented exactly for this purpose; UUIDs never change and are unique as their name implies.

So I'm not sure if your original problem was caused by the "bad" /etc/fstab file - at least the partitions mounted using UUIDs should've continued to work.

Now, regarding the freezing - once a device is detected, its name doesn't change - i.e. if your linux partitions were on /dev/sdb during boot, plugging in an external drive won't change the linux drive's name to /dev/sdc, instead, the "another" external drive will be mounted as /dev/sdc, so the system should continue to function.

However, if you plug the "another" drive before booting the machine - it presence may affect the order in which the devices are named, so it may become /dev/sdb or /dev/sdc. Using partition UUIDs or labels is a way to make sure those changes do not affect access to filesystems.