Sometimes sar can return errors complaining about an invalid system activity file such as:
sar Invalid system activity file: /var/log/sysstat/sa03
It can be resolved by:
rm /var/log/sysstat/sa03 /etc/init.d/sysstat start * Starting the system activity data collector sadc [ OK ]
Now if you rerun sar, you should see the stats output starting to populate:
sar Linux 3.2.0-83-virtual (web01) 04/03/2014 _x86_64_ (8 CPU)