how to calculate memory available if needed on a linux system?

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http://www.linuxquestions.org – I have set swappiness to 0: # sysctl vm.swappiness vm.swappiness = 0 According to various sources, this should mean that applications have priority over file chaches, and swap should only be used when the applications themselves need more memory than is physically available. So I naively took the value free provides in the '-/+ buffers/cache' line as 'free' as the amount of memory to be available on the server. Unfortunately this is not even close to true: On a server with 20GB RAM, memory utilization by this measure never reached 50%, yet the system swaps. (HowTos)