I'm using Slackware 10 (kernel 2.4.26), and the amount of free RAM is getting lower and lower, constantly, in a steps of just a few kilobytes, but I installed the system with only basic services, as I need it just for very busy web server...

You may see a screenshot of a top utility after 16 minutes at i.vizio.biz/linux-top-2.gif, and after 2hr52min at this address: i.vizio.biz/linux-top-2.gif

The CPU is Intel Pentium 1 MMX 200 Mhz, RAM is SDRAM 256 MB...

Is it normal behaviour (I believe it is maybe a disk cache?), or is it an error?

Please help,
Marko

You could try looking at the process subdirectories under /proc. In each of these, there is a file called "status". In that file there are records that show the VM (I think I'd grep for "Name:", "VmSize:", and "VmRSS:") usage, etc. for that process. You could try writing a script to read all the "status" files in each of those subdirectories, grepping for these records, and stashing the results in a temp file, wait a while and run it again. Then compare the results to see which process's memory utilization is growing. That's a pretty simplfied description but that might help you out. But I wonder if what you might be seeing is growth in the I/O buffers. What does "free" show over time?

It is likely normal behavior.

On my system when I type "free -m" it says I have 123 total, 121 used and 1 free. The line below w/ "-/+ buffers/cache:" says I have 68 used of that. If you look at "free" over time you will see that the buffers/cache number grows over time. There is nothing wrong w/ this. If another program needs memory then the buffer/cache get moved out of the way.

Does this help?

Linux is writen to use memory if it is there. This is probably normal behavior. You will probably not "run out of memory" because Linux will reclaim memory when it is needed.