Hello, How to rollback a fixpak (Version 9 on Linux)?

Install an earlier fixpak over it. You may need to restore all databases from the backups taken just before the upgrade (you still have them, of course?)

I'm getting ready to install a new fixpak. Do I need to download an earlier fixpak again and take an offline backup?

Please take a look at the following link for information about uninstalling a fixpak:
DB2 Database for Linux, UNIX, and Windows


You need to execute "installfixpack -f level" from an earlier fixpak image. Nothing should happen to your databases so backup is not really required.