Thefree command displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel.<br /> Display free memory size in MB:

free -m

Displays a line containing the totals memory in MB:

free -t -m

Thevmstat command reports information about processes, memory, paging, block IO, traps, and CPU activity.

vmstat

Thetop command which provides a dynamic real-time view of a running system.

top

PressSHIFT+M to sort on memory utilization.<br /> Pressz to colorize.<br /> Press1 to see multiple CPU's.<br /> Pressq to quit.

For more help type ' _command–help' or 'man _command'

– FredPettis - 02 Jun 2009