I would put in a LiveCD to have those tasks performed, or boot from a different distribution if you have more than one Linux installed on your computer. That way you're always sure that your / isn't mounted (unless you've mounted it manually, of course).
I suspect you were unable to umount / because you were effectively using while doing the maintenance job. After all, even in single-user mode, some part of the system needs to be up and running.
Last edited by jay73; 03-09-2007 at 04:30 AM.