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I am running virtual box on Debian Lenny. The machine is patched up. Total available memory on the server is 4 gig. The guest operating system is Debian Lenny. It is running postfix mailserver, mysql, and antispam. Guest is typically using 300mb of 600mb allocated. Yesterday, evening, Total host machine memory usage started at around 570mb. Yesterday evening, it was 880mb. Today it is 1gig. Nothing has been done to the server since it was started.

Is this a normal behavior? or should I make configuration changes?

Thanks in advance