I upgraded to Ubuntu Bionic on our server but it asks me to upgrade to Xenial?

Welcome to Ubuntu 18.04 LTS (GNU/Linux 4.15.0-15-generic x86_64)

 * Meltdown, Spectre and Ubuntu: What are the attack vectors,
   how the fixes work, and everything else you need to know
   - https://ubu.one/u2Know

 * Canonical Livepatch is enabled.
   - All available patches applied.

0 packages can be updated.
0 updates are security updates.


You have packages from the Hardware Enablement Stack (HWE) installed that
are going out of support on 2016-08-04.

To upgrade to a supported (or longer-supported) configuration:

* Upgrade from Ubuntu 14.04 LTS to Ubuntu 16.04 LTS by running:
sudo do-release-upgrade 

OR

* Switch to the current security-supported stack by running:
sudo apt-get install linux-generic-lts-xenial

Besides, it always says, I should reboot, I have rebooted many times.

Solution 1:

This happens because you most likely have leftover packages from previous Ubuntu versions.

You can run hwe-support-status --show-all-unsupported as root to figure out which packages are causing it, then run apt --purge remove on each package to get rid of them.

Afterwards the error goes away.

Solution 2:

My install was from an Ubuntu 14 Server iso, upgraded via CLI over time to 16 then 18. If yours is a similar pattern, then check out the instructions on LTSEnablementStack which made the message go away for me.

Depending on which release you're on (here's the instructions for 18.xx):

sudo apt-get install --install-recommends linux-generic-hwe-18.xx

After upgrading, I now see this after logging in.

Your Hardware Enablement Stack (HWE) is supported until April 2023.