Monitoring memory usage is useful in general getting started with a new distribution, playing with new applications, etc. It is not RPI specific, however important due to relative low memory. While it sounds simple, in fact a bit tricky specially coming from the other world.
Using the 'free' command in terminal it usually shows high memory usage and a newbie start to look for bugs where memory is gone.
Let's see piCore in QEMU (no video RAM, configured for 256M) with few mounted CLI extensions, nothing loaded in RAM:
Looks strange
Also strange, that after boot there was 202M free. What is wrong? Nothing. LINUX is using 'free' RAM for buffers and caching not let it just hanging around unused. However when necessary buffers are freed up and used, when for example you are storing files in the RAM file system.
There are many tools showing more user friendly figures, in current piCore repo I advise
htop. It shows more understandable figures:
You see, only 27M used in conventional terms. A bit strange that green is for used at first.
Interpretation (just press F1 for help:
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