Vmstat

vmstat (virtual memory statistics) is a command that displays information about operating system memory, processes, interrupts, paging and I/O block.

vmstat 1
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0      0 127568  94904 530064    0    0     6    56   23   79  0  0 99  1  0
 0  0      0 127592  94904 530056    0    0     0     0   26   62  0  0 100  0  0
 0  0      0 127592  94904 530056    0    0     0     0   26   61  0  0 100  0  0
 0  0      0 127220  94904 530056    0    0     0   100   43  109  2  0 98  0  0
 0  0      0 127220  94904 530056    0    0     0     0   39   60  0  1 99  0  0