[CentOS] Find reason for heavy load

John R Pierce pierce at hogranch.com
Wed Dec 30 06:21:03 UTC 2009

Noob Centos Admin wrote:
> However, iostat reports much lower %user and $system compared to top 
> running at the same time so I'm not quite sure if I can rely on its 
> figures.
> ...
> iostat
> Linux 2.6.18-128.1.16.el5xen     12/30/2009
> avg-cpu:  %user   %nice %system %iowait  %steal   %idle
>            3.28    0.20    1.16    2.38    0.01   92.97

iostat, if run with no parameters shows the average since reboot or 
statistics reset.

run `iostat -x 5` to a) show details on all devices, and B) show 5 
second samples.    ignore the first output as thats average.  the 2nd 
and beyond outputs represent 5 second samples.

note, btw, 'load average' isn't CPU usage, its the number of processes 
that are waiting to run.   a load average of 8 means there are 8 
processes waiting to use system resources.  this does include processes 
in iowait, but doesn't include processes that are sleeping on semaphores 
and such, so it can be quite a lot higher than the cpu workload.

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