Here are the steps on how to repair Mac hard drive using the Mac disk repair tool. This will launch the Startup manager which will show all the available bootable devices connected to the machine.
In case you want to use the Ubuntu Live USB stick on a MAC, insert the USB stick and restart (or power on) your Mac while holding the Option key. Instead, click on Eject and remove the USB device.It is typically removable, rewritable and much smaller than an optical disc. A USB flash drive is a data storage device that includes flash memory with an integrated USB interface.
