while Preparing for RHCE and RHCT exam certification one should know how to check memory utilization in redhat enterprise Linux. one useful command is free , you can get memory usage in megabytes and gigabytes :
[root@ldev ~]# free -m
total used free shared buffers cached
Mem: 992 975 16 0 137 628
-/+ buffers/cache: 210 781
Swap: 2047 0 2047
