We appear to have a problem with Ubuntu guests running out of memory. We have several on 12.04 (LTS) and one on 13.04 and seem to have the same problem.
It takes around 30 days from restart to running out of memory.
It is likely that the problem lies with the Integration Services, when Ubuntu is run on bare metal (apparently) it can go for years without being rebooted.
Is there a solution?
Should we reboot Linux (Ubuntu) VM's regularly?