can you install Linux on an external hard drive on a Macbook?
 

From some Googling, I've found that you can use Bootcamp to install Linux on a Macbook. However, I have a Macbook air and do not have sufficient disk space. I was wondering if I could install it on an external drive, and boot it from the Macbook? I think that the problem is the bootloader. But, if I still use Bootcamp to install Ubuntu, it would set up the bootloader, and then I would just install to an external?

At one point the internal harddrive on my laptop (no mac - sorry) failed.
I plugged in a USB hard drive and was able to install and run linux from that external harddrive without any problems (though slower of course).

The same should be possible on a Mac!

Plug in a hard disk, run a linux live distribution, and see if it sees the usb drive. Even if the mac can not boot form a USB harddrive, a small boot partition on the main disk should be able to see and boot the rest of the system from a external hard drive.