`vmstat` - Report virtual memory statistics

vmstat [options] [delay [count]]

Options you will use

delay: seconds between updates. Without it, one line of averages since boot is printed.
count: number of updates. With a delay and no count, runs until interrupted.
-w, --wide: wide output
-S, --unit: k K m M for the memory columns

$ vmstat 1 5

five samples, one second apart - ignore the first line, it is the since-boot average

Procs: r = runnable (running or waiting for a CPU), b = in uninterruptible sleep (D state).
Memory (KiB): swpd used swap, free idle memory, buff buffers, cache page cache. Swap: si/so KiB/s swapped in/out - sustained non-zero so means memory pressure.
IO: bi/bo blocks/s received from/sent to block devices. System: in interrupts/s, cs context switches/s.
CPU (% of total time): us user, sy system, id idle, wa waiting for block I/O, st stolen from a VM, gu guest.

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