Setting up mrtg to monitor dedicated server bandwidth usage. A simple howto for all for RedHat/CentOS!
Working in the Technology industry, I hear alot of people asking about how to monitor their bandwidth accurately. Most people (specially sharedhosters, gameserver admins, etc.) will use their control panels to monitor their bandwidth and this often leads to inaccurate results. In this article we will go over setting a basic mrtg bandwidth graph that can be monitored from a webpage on your server to help you keep track of your bandwidth usage. I have written the below howto as a guide to your installation on a RedHat ES 5.x or CentOS 5.x system. The link http://www.cyberciti.biz/nixcraft/linux/docs/uniqlinuxfeatures/mrtg/ was used as a guide regarding the snmpd.conf so if you have any doubts please check it out.
The best way to watch your own bandwidth is with iptables or snmp however in this article we are covering snmp only – If you want to have a better technical understanding of snmp you can read more about snmp protocal here: http://en.wikipedia.org/wiki/Simple_Network_Management_Protocol
Let’s get started
My server enviornment: cat /etc/redhat-release
Red Hat Enterprise Linux Server release 5.3 (Tikanga)
Our goals: Setup snmp and mrtg and have it monitor the bandwidth in 5 minute intervals with it publishing to a webpage.
Setting up snmp:
First we have to get snmp and its utlities installed. To do this we will use yum
yum -y install net-snmp-utils net-snmp
Now we will make sure that snmpd starts at boot time:
chkconfig –add snmpd
chkconfig snmpd on
We can then verify that it is properly setup by issuing this command:
# chkconfig –list | grep snmpd
snmpd 0:off 1:off 2:on 3:on 4:on 5:on 6:off
Start the snmpd daemon up:
/etc/init.d/snmpd start or service snmpd start
Make sure it is up and listening:
# netstat -anp | grep snmpd | grep LISTEN
tcp 0 0 127.0.0.1:199 0.0.0.0:* LISTEN 24465/snmpd
Configuring snmpd.conf:
the snmpd.conf is found /etc/snmp/snmpd.conf – there is a million options here but we will only modify what is necessary to get this working 
We will go section by section:
first find this area and adjust it accordingly with your network address information – make sure and leave localhost as is – for the network part, add your networks cidr notation (you can get this from your dedicated server provider if you are not sure) :
####
# First, map the community name “public” into a “security name”
# sec.name source community
#com2sec notConfigUser default public
com2sec local localhost public
com2sec mynetwork 10.0.0.200/30 public
####
Next, find this area and adjust it exactly as shown below:
####
# Second, map the security name into a group name:
# groupName securityModel securityName
group MyRWGroup v1 local
group MyRWGroup v2c local
group MyRWGroup usm local
group MyROGroup v1 mynetwork
group MyROGroup v2c mynetwork
group MyROGroup usm mynetwork
####
Then, move on the to next section and it configure it exactly as shown below:
# Make at least snmpwalk -v 1 localhost -c public system fast again.
# name incl/excl subtree mask(optional)
#view systemview included .1.3.6.1.2.1.1
#view systemview included .1.3.6.1.2.1.25.1.1
view all included .1
Now modify this section exactly as shown below:
####
# Finally, grant the group read-only access to the systemview view.
# group context sec.model sec.level prefix read write notif
#access notConfigGroup “” any noauth exact systemview none none
access MyROGroup “” any noauth exact all none none
access MyRWGroup “” any noauth exact all all none
Find this section and modify it as you would like:
###############################################################################
# System contact information
#
# It is also possible to set the sysContact and sysLocation system
# variables through the snmpd.conf file:
syslocation www.elitepowerhost.com
syscontact Dustin Larmeir <dustin@larmer.com>
There is a great article on how to configure this that served as a point of reference for me that can be found here: http://www.cyberciti.biz/nixcraft/linux/docs/uniqlinuxfeatures/mrtg/mrtg_config_step_3.php
Now we need to restart the snmpd daemon:
/etc/init.d/snmpd restart or service snmpd restart
And now we need to test it:
# snmpwalk -v 1 -c public localhost IP-MIB::ipAdEntIfIndex
IP-MIB::ipAdEntIfIndex.10.8.118.194 = INTEGER: 2
When executing the snmpwalk command this should show all of your network addresses – if this returns them that means snmp is monitoring correctly. Now how the 10.x.x.x address was returned.
Installing mrtg
Use yum to install the mrtg package
yum -y install mrtg
Assuming your htdocs directory is in /var/www/html – you would create a location to place the mrtg graphs:
mkdir -p /var/www/html/mymrtg/
Now you will setup the config for mrtg:
cfgmaker –global ‘WorkDir: /var/www/html/mymrtg’ –output /etc/mrtg/mymrtg.cfg public@my.fqdn.com
Note, it is best to your FQDN but you can use localhost as well. The FQDN is much cleaner though.
Making the mrtg index file:
indexmaker –output=/var/www/html/mymrtg/index.html /etc/mrtg/mymrtg.cfg
Making sure all the images files are where they should be:
cp -av /var/www/html/mrtg/*.png /var/www/html/mymrtg/
Testing it out:
env LANG=C /usr/bin/mrtg /etc/mrtg/mymrtg.cfg
now browse to your vhost.com/mrtg and you should now see your graphs!
Setting the graphs up as a cron job:
run crontab -e
and put this in the file:
*/5 * * * * env LANG=C mrtg /etc/mrtg/mymrtg1.cfg –logging /var/log/graphing.log
This will generate your graphs every 5 minutes and log it for you.
This should be all you need to monitor your own bandwidth graphs, there are many different options you can modify with this system so researching into it further would be worth your time! Ill write a howto on Debian soon.
