I think this seems related to bug 397617 in Launchpad and subsequently the upstream bug at https://bugs.freedesktop.org/show_bug.cgi?id=20963 . Chris, can you comment if any of the workarounds noted work for you:
1) https://bugs.edge.launchpad.net/xserver-xorg-video- intel/+bug/397617/comments/2 or 2) Try booting with "acpi_backlight=vendor". This can be done by doing the following. Press 'Escape' key at the 3 second pause by Grub bootloader. Then press 'e' (edit) on the buggy kernel entry, followed by 'e' again on the kernel line. Add "acpi_backlight=vendor" (without quotes) to the end of the line and press 'b' to boot. ** Bug watch added: freedesktop.org Bugzilla #20963 https://bugs.freedesktop.org/show_bug.cgi?id=20963 -- Unable to adjust brightness (KMS bug) https://bugs.launchpad.net/bugs/388216 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
