当系统响应缓慢时，一般会用top或uptime命令查看系统负载是否过高。 例如输入uptime命令显示如下图,其中23:47:19表示现在的时间,up 260 days,14:39表示系统运行了多久,1 user表示当前登录用户数,最重要的是 load average,有三个数值，分别表示过去1分钟、5分钟、15分钟系统的负载。系统负载的英文解释为:
System load averages is the average number of processes that are either in a runnable or uninterruptable state. A process in a runnable state is either using the CPU or waiting to use the CPU. A
process in uninterruptable state is waiting for some I/O access, eg waiting for disk. The averages are taken over the three time intervals. Load averages are not normalized for the number of
CPUs in a system, so a load average of 1 means a single CPU system is loaded all the time while on a 4 CPU system it means it was idle 75% of the time.
系统负载表示每分钟处于可运行状态(运行态和就绪态)以及不可中断状态(等待io)的进程数目，且没有做归一化处理。