During the initial startup screen, press ESC, F1, F2, F8, or F10.Press the Power button on your computer.Start by plugging the thumb drive into a USB port. Otherwise, the computer will load from the hard drive as standard. If you're booting from USB media, you must change the BIOS boot order so the USB device is listed first. The boot order tells the machine which devices to search for the software needed to launch the computer and the priority of each device in that search.

That's because the BIOS settings include the machine's boot sequence when starting up. If it fails, try again-sometimes the system doesn't unmount the volume in time and the process will be unable to complete.Starting your PC using USB rescue media is not difficult, although it first requires an adjustment in the BIOS (Basic Input Output System). Give it a name and choose MS-DOS (FAT) under Format and GUID Partition Map under Scheme.Select your USB device in the menu on the left, then click Erase.Insert your USB drive into your Mac and launch Disk Utility (under Applications > Utilities, or search for it using Spotlight with Cmd + Space).

Warning: Everything on your drive will be erased when you do this! Others don't have any strict requirements, but formatting to FAT beforehand is a good idea regardless. Generally speaking, anything above 4GB will do the job. Some Linux variants may require larger volumes, so pay attention to the requirements when downloading. When you're looking to create a bootable Linux USB drive on a Mac, the first step is to make sure you've got the right USB drive for the job, and that it's formatted correctly to avoid any problems.

How to make a ubuntu bootable usb mac