Please help. I wanted to install linux so I follow this guide: http://www.ubuntu.com/download/desktop/create-a-usb-stick-on-mac-osx I used my external hard drive to do this but then after I finished everything, when I plugged in my external hard drive I get "The disk you inserted was not readable by this computer" and I cannot see my external hard drive in Finder, but I could see it in the Disk Utility. Does this mean all my data was erased? How do I get my external hard drive back? Thank you.
Well, if you had data already on the drive, it's gone. You could use a data recover, or ship it off somewhere. But, I'll just go into formatting the drive.
A. Sorta. Generally Linux uses a diffrent type of format for drives (ext4, and a couple others) so it could be that it did work, and your Mac just can't read it. B. If it really did get messed up (you can't boot it into it) then :
- Go to Disk Utility.
- Click on your drive.
- Click on the "Erase" tab.
- If you'd like to, enter a name for the drive. Or, just keep it as Untiled if you'd like to try Linux again.
- Select a format type, if you'd like to. Fat works best for cross-device compatibility.
- Click the "Erase" button.
- Get some coffee, or water, depending on the size of your drive.
The instructions from Ubuntu are for creating a bootable USB thumb drive for trying and installing Ubuntu. They aren't really meant for making a persistent running installation - doing an installation is one of the options when booted from the thumb drive. If you followed the very last instruction in the guide you linked and were not given the option to boot from the disk, then either your Mac doesn't support USB boot or you ran into a restriction of the EFI firmware. awesomebing1 is spot-on regarding why your external drive is unreadable and for the steps to reclaim the drive, but if there was data already on it, consider it lost.
"UNetbootin for Mac OS X can be used to automate the process of extracting the Ubuntu ISO file to USB, and making the USB drive bootable. The resulting USB drive, however, can be booted on PCs only. If attempting to make a USB drive that can be booted from a Mac, follow the instructions below." - Ubuntu.com website