apt dist-upgrade but it only upgraded a few packages, and I got this:
Processing triggers for initramfs-tools (0.122ubuntu8) ...
update-initramfs: Generating /boot/initrd.img-4.4.0-134-generic
UUID e809c3b8-af61-438f-8521-6af7e4963fbc doesn't exist in /dev/disk/by-uuid
Warning: root device /dev/disk/by-uuid/e809c3b8-af61-438f-8521-6af7e4963fbc does not exist
Press Ctrl-C to abort build, or Enter to continue
W: plymouth: The plugin label.so is missing, the selected theme might not work as expected.
W: plymouth: You might want to install the plymouth-themes and plymouth-label package to fix this.
run-parts: /etc/initramfs/post-update.d//flash-kernel exited with return code 1
dpkg: error processing package initramfs-tools (--configure):
subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
E: Sub-process /usr/bin/dpkg returned an error code (1)
Any chance you could explain me how to upgrade to 18.04?