How to install Ubuntu 14.04.1 LTS 64-bit on a MacBook Pro Retina 15" Mid 2014 (11,3)

• Ubuntu 14.04 Desktop 64-bit ISO (default, non-Mac version)
  http://www.ubuntu.com/download/desktop
• UNetbootin
  http://unetbootin.sourceforge.net/
• Broadcom 802.11 Linux STA wireless driver source dependencies
  http://packages.ubuntu.com/trusty/all/dkms/download
  http://packages.ubuntu.com/trusty/amd64/bcmwl-kernel-source/download

• this installation process aims to have Ubuntu and Mac OS on dual boot mode

• no need to repair GRUB after installation, the MacBook Pro 11,2 and 11,3 are now able to recognize multi-boot CD images, so there is not need to use the Mac version of the Ubuntu installation image (the USB disk with the will work just fine in native EFI mode)

• the first boot won't have network access because you'll need to install the Broadcom wireless driver in order to be able to use the wireless adapter (either use an Ethernet USB adapter or copy the dkms and bcmwl-kernel-source packages to another USB disk)

• install UNetbootin and create your bootable Ubuntu installation disk (set Diskimage as the Ubuntu ISO image and Drive: as your USB drive)

• with your USB drive plugged in, boot your Mac and hold the option key
• select the EFI USB drive as the boot device
• choose Try Ubuntu (Live mode)
• click Install Ubuntu to start the installation and install Ubuntu Alongside with Mac OS
• when the installation finishes, DO NOT restart

• open a terminal (CTRL + ALT + T)

$ sudo nano /etc/default/grub