Vmstat

vmstat^[1] (virtual memory statistics) is a command that displays information about operating system memory, processes, interrupts, paging and I/O block. vmstat command is available at least in FreeBSD, Linux or Solaris and it is included in procps package in Debian and Ubuntu.

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

vmstat --help

Usage:
 vmstat [options] [delay [count]]

Options:
 -a, --active           active/inactive memory
 -f, --forks            number of forks since boot
 -m, --slabs            slabinfo
 -n, --one-header       do not redisplay header
 -s, --stats            event counter statistics
 -d, --disk             disk statistics
 -D, --disk-sum         summarize disk statistics
 -p, --partition <dev>  partition specific statistics
 -S, --unit <char>      define display unit
 -w, --wide             wide output
 -t, --timestamp        show timestamp

 -h, --help     display this help and exit
 -V, --version  output version information and exit