ps aux | awk '{sum1 +=$4}; END {print sum1}'

/usr/local/bin/mysqltuner.pl

ps -ylC httpd | awk '{x += $8;y += 1} END {print "Apache Memory Usage (MB): "x/1024; print "Average Proccess Size (MB): "x/((y-1)*1024)}'

http://diywpblog.com/how-to-work-out-max-clients-for-your-vps-or-dedicated-server-running-apache/comment-page-1/#comment-2393