Linux: vmstat

vmstat

Provides real-time reports on CPU consumption, CPU dispatcher run queue, RAM page in, scan rate, RAM page outs. Example:
#vmstat 2 5

procs memory swap io system cpu
r b swpd free buff cache si so bi bo in cs us sy id wa
0 0 11160 327148 35036 3446588 0 1 1 0 0 0 0 0 0 1

Procs
r: The number of runnable processes waiting for access to the CPU.
b: The number of processes in uninterruptible sleep.

Memory
swpd: the amount of virtual memory used.
free: the amount of idle memory.
buff: the amount of memory used as buffers.
cache: the amount of memory used as cache.
inact: the amount of inactive memory. (-a option)
active: the amount of active memory. (-a option)

Swap
si: Amount of memory swapped in from disk (/s).
so: Amount of memory swapped to disk (/s).

IO
bi: Blocks received from a block device (blocks/s).
bo: Blocks sent to a block device (blocks/s).

System
in: The number of interrupts per second, including the clock.
cs: The number of context switches per second.

CPU
These are percentages of total CPU time.
us: The percentage of the time the CPU ran user-level code (non-kernel. (user time, including nice time)
sy: Time spent running kernel code. (system time)
id: The percentage of the time the CPU was idle. Prior to Linux 2.5.41, this includes IO-wait time.
wa: Time spent waiting for IO. Prior to Linux 2.5.41, shown as zero.