Linux – top command indicates a different cpu usage than sar command

cpu-usagelinuxsartop

In my CentOS server, when I check the resources with sar command, user cpu usage is around %15 while in top command the sole 'java' process uses like %99 of cpu. sometimes it's even goes further than %100!
who's lying here?

Best Answer

Neither -- they're just giving a different idea of CPU usage.

Top's idea of CPU is "per-core" -- that is, "this program is using 100% of one core". A multithreaded program can, therefore, be using, say, "400% CPU" -- which makes the eyes water a little sometimes.

On the other hand, sar sees it as as a percentage of total CPU -- so on a 4 core system, one fully utilised CPU core will show as "25% CPU", and the 400%-using program will show as 100%.

There's also the issue of instantaneous vs long-term averages, but I'm going to assume that you've accounted for that.

Related Solutions

Tomcat – Java eats %100 cpu up

There is obviously a thread that is hanging.

kill -3 processid

Will show a list of the running threads in the java-app. Collect these and send it back to the dev.

CentOS – High CPU Usage at a particular time in the night

This is when the cron.daily scripts run... By default, it runs daily just after 4:00am.

From /etc/crontabs

SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/

# run-parts
01 * * * * root run-parts /etc/cron.hourly
02 4 * * * root run-parts /etc/cron.daily <-- THIS ONE!!
22 4 * * 0 root run-parts /etc/cron.weekly
42 4 1 * * root run-parts /etc/cron.monthly

And in /etc/cron.daily.

The culprit is probably your mlocate.cron, which runs updatedb and can be quite intensive on some systems:

#!/bin/sh
nodevs=$(< /proc/filesystems awk '$1 == "nodev" { print $2 }')
renice +19 -p $$ >/dev/null 2>&1
/usr/bin/updatedb -f "$nodevs"

Best Answer

Related Solutions

Tomcat – Java eats %100 cpu up

CentOS – High CPU Usage at a particular time in the night

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