Top Command
Interpreting Free To see how much memory you are currently using, run free -m. It will provide output like:
total used free shared buffers cached
Mem: 90 85 4 0 3 34
-/+ buffers/cache: 46 43
Swap: 9 0 9
The top row 'used' (85) value will almost always nearly match the top row mem value (90). Since Linux likes to use any spare memory to cache disk blocks (34).
The key used figure to look at is the buffers/cache row used value (46). This is how much space your applications are currently using. For best performance, this number should be less than your total (90) memory. To prevent out of memory errors, it needs to be less than the total memory (90) and swap space (9).
If you wish to quickly see how much memory is free look at the buffers/cache row free value (43). This is the total memory (90)- the actual used (46). (90 - 46 = 44, not 43, this will just be a rounding issue)
