Restoring rEFIt on Macbook Air

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http://askubuntu.com – My Macbook Air dual boots Mac OS X and Ubuntu Precise. Normally when you turn it on the first thing you see is the rEFIt menu which allows you to select which OS to boot. If you select Ubuntu then Grub will show up next, though Grub cannot boot Mac OS X. Last friday I restarted Ubuntu and it skipped straight to Grub. I've restarted it a few times and it seems that rEFIt will not show up anymore. How can I fix this so I can boot into Mac OS X again? (HowTos)