Ubuntu bootable USB drive does not show up as bootable

You don’t mention which Mac you have, OS Version or anything like that. It’s as if this question belonged on Ubuntu’s forums :)

In any case, I’m assuming you have some Mac computer and want to install or Boot an operating system other than Windows via BootCamp or the native OS X. In your example you need to boot from Ubuntu.

Turns out your Mac uses EFI instead of the archaic BIOS. So you need a little “helper” program in the boot process to tell the EFI to also look elsewhere.

The steps for installing the tools and the process are perfectly described in the Ubuntu Community Wiki.

Before you go there, bear in mind the following things:

• The instructions do not work for new iMacs.
• The instructions are for CD booting (tho you have a link for USB at some point in the document).
• You will need to install rEFIt, I did it on an old Macbook (White) and had zero problems, but the usual warning about “have a backup” applies.

If you want to boot from USB you must reformatted your device in a new partition format specific to Intel-based Macs called GUID Partition Table (GPT).

In a Intel-based systems, like the MacBook Pro, you can boot from external USB drives, if drive is formatted appropriately (GPT) and a compatible version of Mac OS X is installed.(like OS X on USB Drive for MacBook Air)

So you can't boot bootable Ubuntu USB by default with your macbook pro because have different Partition table(at least I can't do that).

But I some where read that you can do this if you install rEFIt (you can continue his toturial here)