vnstat setup guide/tutorial
yum -y install vnstat
chown nobody.nobody -R /var/lib/vnstat/
#replace venet0 below with your desired interface
sudo -u nobody vnstat -u -i venet0
#edit: vi /etc/sysconfig/vnstat
#VNSTAT_OPTIONS="-i venet0"
# only use the sed below if you are using venet0 instead of eth0 or replace accordingly
sed -i 's/eth0/venet0/g' /etc/sysconfig/vnstat
[root@monitor]# yum install vn........