Comment 4 for bug 1762164

Support for Ubuntu 14.4 runs out in the first quarter of 2019. We must update the server to bionic beaver (18.04 LTS). The last time I did update the server, it went absolutely fine with in-place update, however this time it is better to restore from backup after reinstall. This is a lot of work, unfortunately :(

One reason is that in-place update cannot update the kernel version, which is pretty ancient on our machine. [1] seems to indicate that a new install is required to update the server's kernel version.

[1] https://serversupportforum.de/forum/virtuelle-server/60693-starto-vserver-plesk-dist-upgrade-ubuntu-16-04-a.html