Where all my memory went on my Linux box ?

1. Check the Used memory with free command:

[admin@BIZ-UPGRADE-NN1 ~]# free -g
             total       used       free     shared    buffers     cached
Mem:            44         17         26          0          0          8
-/+ buffers/cache:          8         35
Swap:           20          0         19



2.  Check the Top 20 Processes consuming memory: 

ps -eo pmem,pcpu,vsize,pid,cmd | sort -k 1 -nr | head -20  => Sort by Resident  memory


& ps -eo pmem,pcpu,vsize,pid,cmd | sort -k 3 -nr | head -20  => Sort by Virtual memory