So I just started a new job and one of my tasks is to move our hosting to a new cheaper server, i'm trying to spec out the new server but I'm a little unsure on the amount of memory I will actually need.

Our current server has 4 gigs of RAM and when I use the top command to check out what's running it shows that 3 of the 4 gig is being used, but the system processes only show tasks using very small amounts of memory, the highest used is at 0.7.

first of all, is using 3 out of 4 gigs of RAM usual for a server that hosts less than 20 sites (most of which are fairly small scale) if not where has all my memory gone?

Some Server Info: OS: CentOS 5.5 RAM: 4gig CPU: Quad Core Intel Xeon (2GHz per core)


Ah, it's a classic question. See http://www.linuxatemyram.com/ for an answer.

  • thanks, I just did some googleing and found out what was going, cheers guys – iamthewit Aug 18 '10 at 10:04
  • accepted duplicate, jealousy == downvote – James L Aug 18 '10 at 10:07

Read http://www.linuxatemyram.com/ which will explain true memory usage to you.


It's gone into cache and buffers. Use free, and check the second line.

  • total used free shared buffers cached Mem: 4194480 3290524 903956 0 205332 2656604 -/+ buffers/cache: 428588 3765892 Swap: 6258680 8 6258672 thats what I get out. so I do actually have over 3 gig free then? which should mean I can go for a lower spec with the new webserver? – iamthewit Aug 18 '10 at 9:54
  • Your system uses approx. 420M of your memory. The rest are caches and buffers which will be freed if an application needs more memory. Just answer yourself a question: Is unused RAM really useful? – joschi Aug 18 '10 at 10:00
  • yeah, it makes sense when you say it like that, thanks – iamthewit Aug 18 '10 at 10:05

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