The program used to display memory information is free. It displays usage information of both RAM and swap. Running it at the terminal will produce the following output;
$ free
total used free shared buffers cached
Mem: 2571088 1605784 965304 0 48316 589324
-/+ buffers/cache: 968144 1602944
Swap: 4393768 0 4393768
By default the program outputs display in kilobyte’s unit. To have it in Megabyte, simply add -m to the parameter when running the program;
$ free -m
total used free shared buffers cached
Mem: 2510 1568 942 0 47 575
-/+ buffers/cache: 945 1565
Swap: 4290 0 4290