When a server uses memory more than available RAM, the system will shut down the virtual machine. Then, it is only possible to boot from outside (VPS control panel, e.g. vePortal or SolusVM). However, it should be possible to plan a reboot before possible shut down.
What is the best practical method to check the used memory, and reboot the system upon reaching e.g. 90% of the allowed RAM? Is there a common program or script to do so? I am using Debian/Ubuntu.