pc2006 crashed and rebooted itself.
Investigation is needed:
09:30 < icinga-wm> PROBLEM - mysqld processes on pc2006 is CRITICAL: PROCS CRITICAL: 0 processes with command name mysqld
root@pc2006:~# uptime 09:37:55 up 10 min, 1 user, load average: 0.00, 0.03, 0.03