I run a Debian Linux server (with Apache 2 and MySQL) on a virtual private server with 256 MB memory. (I also use swapspace package.)
The system hanged.
The memory graph (provided by the hoster) showed that the used memory felt to almost zero (around 3 MB).
The CPU usage hit 100% at the same time.
I've rebooted the system and it works again.
What has happened?