[NTLUG:Discuss] True memory usage

[Chris Cox]

Robert Thompson wrote:
> Hello,
> 
> 	I am trying to figure out the best way to get the 'true' memory usage
> for a machine. When I do a free I think I'm supposed to look at the
> 'used' section under the -/+ buffers/cache line:
> 
> $ free
>              total       used       free     shared    buffers
> cached
> Mem:        904832     895972       8860          0      18060
> 565936
> -/+ buffers/cache:     311976     592856
> Swap:       755044        164     754880
> 
> 	So the above means I am using 311M of memory?
> 
> 	When I attempt to add up the memory from doing a ps aux and adding the
> RSS (resident set size) I get something different (larger than total
> memory):

It can be complicated.  Do you need a VERY exact number?  I would think
the value in free would work fine (or /proc/meminfo).  ps can be
misleading since threaded applications will show up multiple times with
the same RSS (or even SZ) size.  There can be other things shared as
well.