OT, determining real amount of free RAM

[Gregory Nowak]

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Hi all,

I've been wondering this for a while, and figured I'd ask here. How
does one determine the amount of free RAM on a gnu/linux system? If I
run "free -m" on one of my machines right after boot, I get something
like:

total       used       free     shared    buffers     cached
Mem:          2957       2933         24          0         78
1590
- -/+ buffers/cache:       1263       1694
Swap:          925          0        925

Here's what I'm getting at. First, I know what runs on this box, and
this machine starts up with a limited amount of programs running, and
pretty much stays like that as long as it remains powered up (running
ps confirms this). What this machine starts with should take up about
1480 megs of RAM according to my calculations. Ok, let's add 100 megs
extra for the system itself, and to make sure I've really accounted
for what runs on this box. That would come out to about 1580 megs of
RAM used, let's round up to 1600. I have also confirmed that if I
physically pull a gig of RAM out, the machine will still run
everything without heavy use of swap.

Second, if the machine stays up for 24 hours or longer, the amount of
free RAM doesn't change much, but a few megs of swap is used. I assume
this is for processes which haven't been used in a while. So, why am I
seeing something around 20 megs free, instead of something around a
gig? To put it another way, if I wanted to run this machine with a
minimum amount of RAM how would I figure out how much I really need?
Thanks in advance.

Greg


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