ufw is outputting an error because it can’t load the necessary kernel modules to run a firewall. You need to install the currently-running kernel’s modules on your droplet which is done by running sudo apt-get install linux-image-$(uname -r).

Because you’re trying to use a 15.04 kernel on a 14.04 system, that command won’t work because the kernel package does not exist in 14.04’s repositories.

Generally, you should be fine running the latest kernel that is available in 14.04’s repositories as it is an “LTS” (long-term support) release, which means that it will keep receiving security updates until April, 2019.

I would like to move to 15.04 so I can run kernel updates via apt-get. What is the easiest way to do this on DigitalOcean? Not being able to update at terminal is a huge pain. Thanks for any tips.