r: The number of processes waiting for run time.
等待运行的进程数
b: The number of processes in uninterruptible sleep.
处在非中断睡眠状态的进程数
swpd: the amount of virtual memory used.
已使用的虚拟内存大小
free: the amount of idle memory.
空闲的物理内存的大小
buff: the amount of memory used as buffers.
用来做buffer（缓存，主要用于块设备缓存）的内存数，单位：KB
cache: the amount of memory used as cache.
用来做cache（缓存，主要用于缓存文件）的内存，单位：KB
si: Amount of memory swapped in from disk (/s).
从磁盘交换到内存的交换页数量，单位：KB/秒。
so: Amount of memory swapped to disk (/s).
从内存交换到磁盘的交换页数量，单位：KB/秒
bi: Blocks received from a block device (blocks/s).
每秒从块设备接收到的块数，单位：块/秒 也就是读块设备。
bo: Blocks sent to a block device (blocks/s).
每秒发送到块设备的块数，单位：块/秒 也就是写块设备。
in: The number of interrupts per second, including the clock.
每秒的中断数，包括时钟中断
cs: The number of context switches per second.
每秒上下文切换次数
us: Time spent running non-kernel code. (user time, including nice time)
用户进程执行时间百分比(user time)
sy: Time spent running kernel code. (system time)
内核系统进程执行时间百分比(system time)
id: Time spent idle.
空闲时间百分比
wa: Time spent waiting for IO
IO等待时间百分比