How to free up RAM

[malaire]

I have 1 GB of RAM and still not enough. After 2 hours of using Knoppix, I launch the performance viewer and I see that I have only a few MB of memory left. Does anyone know a command that frees up some RAM?
I use knoppix to learn Linux commands. Usually I make an apt-get update, launch Gaim and XMMS.

I think you need to learn a bit about how Linux uses memory.

When applications won't be needing all the memory, Linux likes to use that unneeded memory for e.g. by caching files read from the harddrive, so that next time those files are used they can be read from the cache. But if an application needs more memory, Linux will immediately remove some files from the cache and give that memory to the application.

So before thinking about freeing some memory, you need to check if some of the memory is being used for caching files. If yes, then you don't need any command to free memory, because the memory used for caching will be freed automatically when needed.

Now start a console and run a command free which will tell how much memory is being used at the moment:

knoppix@0[knoppix]$ free
             total       used       free     shared    buffers     cached
Mem:        287504     283632       3872          0       6916      75964
-/+ buffers/cache:     200752      86752
Swap:      2028740      10884    2017856

In this example, Linux is using 283632 kB (99%) of the memory. But 6916 kB + 75964 kB (29%) is used by "buffers" and "cached", and that memory is available to applications whenever they need it.

So even through I have "only" 3872 kB (1%) free memory, in practise the amount available to applications is 86752 kB (30%).

Usually, when you want to know how much "free memory" there is in Linux, you'll want to ignore the memory used by buffers and file-cache like I have done in this example.