I'm running into the same issue. Tried Kernel 4.4-rc5, would also not boot without acpi=off and nomodeset.
After booting with those two parameters, the GUI is very sluggish, animations take on the order of seconds. Also lost mouse and keyboard (wireless) functionality when upgrading - possibly unrelated. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1525615 Title: Ubuntu not booting on iMac 5K with ACPI enabled Status in linux package in Ubuntu: Incomplete Bug description: With a 27in 5k ( new as of two weeks ago) I'm unable to boot the kernel without parameter "acpi=off:", it also needs "nomodeset" into order to get a working system. The applies to both the live installer and a system installed on disk. With out the parameters I just get a blank screen. It gives a blank screen event if the "quiet" is removed from the kernel parameters. The system has a 250G SSD. I'm using the Kubutu live installer for Wily off a USB stick. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1525615/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
