After installing Ubuntu 12.04 on my dual boot machine with Mac OS X and Ubuntu I no longer see rEFIt when I start the computer. Mac OS X is listed in the Grub menu but I can't start it from there. So how do I reinstall rEFIt from Ubuntu? The documentation only explains how to install rEFIt from OS X.
I fixed the problem by starting OS X from the installation DVD and setting the startup disk (in the Utilities menu) to the Mac OS X partition. After a restart I reinstalled rEFIt from OS X (two restarts are required to make rEFIt show up).