That fact that 4.4.21 does not have the bug indicates this is a Ubuntu specific bug.
We can bisect between -38 and -40 to find the commit that introduced this. Can you first test the latest kernel that is in Xenial -proposed? It can be downloaded from: https://launchpad.net/~canonical-kernel-team/+archive/ubuntu/ppa/+build/10960867 -- 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/1628546 Title: 4.4.0-40-generic no prompts for disk encryption + loops on dots load screen Status in linux package in Ubuntu: In Progress Status in linux source package in Xenial: In Progress Bug description: Since the upgrade to Ubuntu's 16.04.1 Linux kernel 4.4.0-40.60, it is impossible to boot my machine with full root encryption. It will keep loading the purple Ubuntu "dots" loading screen for ages and stay there. There is no issue rebooting back with kernel 4.4.0-38.57. I tried recreating the initramfs to no avail: update-initramfs -d -u -k 4.4.0-40-generic Hardware is a Dell Laptop: XPS13 9350 16GB/i7/512GB SSD. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1628546/+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
