I'm a Mint user. I was trying to solve a problem, which is that when I suspend my PC I can't resume. I found on stack exchange Ubuntu an answer saying to use "ukuu" in order to upgrade the kernel. This was supposed to solve the problem. However, after I installed ukuu, I ran "ukuu --install-latest" and I rebooted my PC, I got the error "error: /boot/vmlinuz-5.0.9-050009-generic has invalid signature. error: you need to load the kernel first".