After a while, my personal PC-server hanged up on temperature logging. Next morning, SSH tried to connect but got stuck at verifying SSH RSA. Trying to access owncloud, whole thing crashed completely. Even the physical monitor, attached to PC directly, was dead. Only hard reboot left.
sudo apt-get install htop lnav
and, if applicable,
dmesg | grep "..."
Thank b4d later (buy him a beer)
And yeah, it seems that Owncloud Cron services (in my case, via system cron) made cpu stuck at 100% for all the time. Hm.