Few things in life makes me unhappy than a unoptimal or broken system. When my machine does not work at its best I start to suffer itches and bad mood.
Like many other nerds, I can't avoid to update my laptop operating system with the latest developments. No exceptions with Kubuntu 18.04, where I innocently thought it will fix some nasty bugs of 17.10 I was enduring, notably, a very slow desktop login. I took the radical approach, let's format the root partition and install from scratch.
All backups done, machine reinstalled and bingo! now I can't get a second user session, without disconnecting the first. To put in perspective, what is an operating system, especially linux, that can't get more than one user session active at the time?
As usual, Google here, Google there, countless web pages of irrelevant content... and nothing. Greping the syslog, and the culprit was sddm, the login service of Kubuntu. On Github, a report on the issue, but no further indication that the bug will be fixed someday.
Then a hint on the bug report, and it was related to the dual hybrid graphics architecture of the laptop. In my case, I have an Intel and a Radeon dual graphic laptop. The suggestion was to disable the Radeon chip and work only with the Intel, which is no big deal for me. I was happy to finally fix it.
Too easy huh? Not at all. The laptop began to warm too much, even with no CPU load. It was uncomfortable even to rest the hand on the keyboard.
Another set of Google searches and a page in Ubuntu on hybrid graphics. Joining the two solutions, I enabled back the radeon driver, and enabled the switch to let the kernel manage the second graphic chip, so sddm know about it, even if I don't use it.
Second session working, and laptop in normal temperature.