memory usage doesn't add up [duplicate]

Question

Possible Duplicate:
How do I get the actual used memory including RAM disks?

If I add up all the memory usage I get from top -b -n 1 or htop or ps aux, I get a number that is a few GB under what I get with free. The kernel could account for some of that memory, but not up to a few GB, could it ?

Answer 1

Check the output of free -m. It will look similar to this:

             total       used       free     shared    buffers     cached
Mem:          7459       1483       5975          0         63        730
-/+ buffers/cache:        689       6769
Swap:         9536          0       9536

With different numbers probably. The first line ("Mem:") gives you the overall consumption, including cache and buffers (to speed up things, Linux uses free RAM to cache things like e.g. file system info -- see the "cache" column in my example. If the RAM occupied by this cache is needed elsewhere, that cache will shrink to free it). So look at the second line ("-/+ buffers/cache:"), which gives you the amount of memory really used by applications (plus kernel etc. of course). This should usually rawly match your calculation.