For 18.04 the Chapter on cgroups (Chapter 21 in the PDF) needs to either be deleted or rewritten. See also: https://launchpad.net/ubuntu/+source/cgmanager/+publishinghistory https://bugs.launchpad.net/ubuntu/+source/upstart/+bug/1649310 …

Ubuntu VPS Hosting via Chapter 21 – Control groups – delete or rewrite.