The last new year holidays was more than a month ago. it was a good chance to make a major version upgrade on my PC. I upgraded my laptop PC from Debian 8 (Jessie) to Debian 9 (stretch). During the upgrade, I did encountered several times, but no serious trouble. I started to enjoy the lightdm login console showing up with the Debian 9 new theme. But when I booted it without AC power supply, the boot sequence ended in strange way. The lightdm did not show up. Instead, a black screen remains with many error messages. I searched for a hint in the log files in /var/log directory, and found that the root file system was mounted in read-only mode. With this hit, I search for any hints around the world and found a similar problem in the bug database in http://bugs.debian.org/ It seemed to imply that laptop-mode-tools package was involved. In order to test whether the laptop-mode-tools is involved in my case, I installed tlp package which conflicted with laptop-mode-tools. With tlp instead of