The attached dpkg log shows that grub was successfully installed on your system in EFI mode. But your bug report claims that your system is not booted in EFI mode, and shows that you are booted into an upstream 'lowlatency' kernel version, not the 4.4.0 kernel that was installed as part of the Xubuntu installation; and that this lowlatency kernel was present on your disk at the time that the install was done, which means you did not reformat the partition that was mounted at /boot as part of the install; and your /boot/efi is also reported to be empty.
This is not an actionable bug report given the currently available information. You will need to explain precisely what steps you took that led you to this situation in order for us to determine if there is a bug in Ubuntu. ** Changed in: shim-signed (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1738525 Title: package shim-signed 1.32~16.04.1+0.9+1474479173.6c180c6-1ubuntu1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/shim-signed/+bug/1738525/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs