Difference between user mode and system mode

[kenny chia]

Hi
the sar command reports user mode, system mode, wait IO and idle percentages.
What is the difference between user and system mode?
Does user + system + wait IO + idle = 100% ?
Will a slow disk system increase wait IO?

[Steven E. Protter]

A system will slow if its waiting for I/O.

Attaching a little script that gives you some more performance output in a format you can read more easily.

SEP

[Sridhar Bhaskarla]

Hi,

Yes. user mode is the utilization spent while running user instructions like arthmetic operations. System mode is the utilization spent while running the system calls for ex., open(), close() etc., %wio in sar output is not really the CPU utilization. It's to be accounted as idle except that the processes are waiting on responses from the IO subsystem. Yes. A slow disk subsystem can make this figure high. However, use 'sar -d 2 20' to get a good picture on the disk utilization. A high avserv indicates a slower system.

Glance can give you a very good picture. But you have to purchase it.

-Sri