Making a Bootable USB Ubuntu 15.10 Wily on Mac El Capitan
The Mac Tutorial Shows You Step-by-step How-to Create a Bootable Ubuntu 15.10 Live USB Stick on Mac OS X 10.11 El Capitan.
UNetbootin allows you to create bootable Live USB drives for Ubuntu, Fedora, and other distributions without burning a CD.

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Launch DiskUtility
In Applications >> Utilities -
Format USB Key as FAT-DOS
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Download & Install UNetbootin Bootable USB Creator:
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Launch UNetbootin
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Browse for the Ubuntu 15.10 Wily ISO
Then Select the USB Key (Take care to be Sure of Your Choice…)
To List all Devices on Terminal:diskutil list
Confirm for Burning with OK.
When the process is Successfully Achieved You will dispose of an Ubuntu 15.10 Wily Live USB Key!