I have an Amazon EC2 instance which has given me a tiny '/' partition and a large '/mnt' partition. As such, I have moved my mysql data-dir over to the /mnt partition. However I am now having issues with the /tmp folder running out of space on my massive join queries and am trying to also move /tmp to /mnt/tmp. I tried to do this with a symlink but that results in the mysql service being unable to start.

Please advise on how to move the storage of /tmp over to /mnt (/dev/xvdb)