Linux Memory Usage : (actual physical memory)

Linux 'ps aux ' list on mem usage is vague.
       {{ Read this FIRST }} if you want to get an idea of memory usage.

[root@fts-vm-prod ~]# cat /proc/meminfo | head
MemTotal:       65979160 kB
MemFree:          998616 kB
Buffers:          144104 kB
Cached:         63197468 kB
SwapCached:            0 kB

    mem Free = MemFree+Buffers+Cached+SwapCached.
                ( you got 63 Gig free out of 66Gig - approx )

[root@fts-vm-prod ~]# cat /proc/meminfo | head

MemTotal:       65979160 kB   ç 65979160 / 1024  = 64432 MB

MemFree:          998616 kB   ç WRONG.  ( Add buffers and Cached to it.)

Buffers:          144104 kB

Cached:         63197468 kB   ç 63197468 / 1024 = 61716 MB  FREE

SwapCached:            0 kB

    mem Free = MemFree+Buffers+Cached+SwapCached.

                ( you got 63 Gig free out of 66Gig - approx )

RSS lists shared libraries.

Physical_Dirty size inside each process at /proc/<procid>smaps file is right one (close to reality).
So, sum these dudes.

memusage.sh  (lifted from blogs )

#!/bin/sh
for i in /proc/[0-9]*; do
  grep -q 'Private_Dirty' $i/smaps;
  if [ $? -ne 0 ]; then
    continue;
  fi;
  echo -n "${i}: ";
  awk '/Private_Dirty/ {print $2,$3}' $i/smaps |
   sed 's/ tB/*1024 gB/;s/ gB/*1024 mB/;s/ mB/*1024 kB/;s/ kB/*1024/;1!s/^/+/;' |
   tr -d '\n' |
   sed 's/$/\n/' |
   bc |
   tr -d '\n';
  echo;
done |
 sort -n -k 2

./memusage.sh  | awk ' { print $2  } ' |xargs | sed -e 's/\ /+/g' | bc