So, while at first glance, this system appears to be running short of memory, it's actually just making good use of memory that's currently not needed for anything else. And don't forget that you should like disk caching because it makes the system run much faster. In other words, this shows how much memory is being used (think 'borrowed') for disk caching. This line shows how much of the physical memory is used by the buffer cache. This is probably the trickiest part of understanding free's output. This system has 4 GB of swap, twice the size of the physical memory - following a common rule of thumb for setting up swap space.īetween the Mem: and Swap: lines, we see a line labeled -/+ buffers/cache. If we look at the Swap: line in the output, we see that the swap space appears to be unused. Just looking at these numbers, we see that this system has roughly 2 GB of RAM and that nearly 95% of it is used. The -m option displays the information in terms of megabytes rather than kilobytes (the default). The second, labeled Mem: displays information on how physical memory is being used. The first line of the free command's output contains the column headings. Swap is some portion of space on your hard drive that is used as if it is an extension of your physical memory. Physical memory is the random access storage provided by the RAM modules plugged into your motherboard.

The free command will tell you about used and unused memory and about swap space. The first that probably comes to mind is free. Let's look at some basic commands that report on memory usage.

Memory monitoring in linux