The previous article on installing MRTG with IOSTAT adapted monitoring-tool commands for use with MRTG. This differs from the usual approach of using SNMP to send status information to MRTG. This article covers SNMP with MRTG, a more widely used method than MRTG with IOSTAT. Let’s get started. First edit snmp.conf to enable the services that expose system information, as shown below:

#vi /etc/snmp/snmpd.conf
com2sec local     127.0.0.1/32    public
com2sec local     10.10.10.0/24   public
group MyROGroup v1         local
group MyROGroup v2c        local
group MyROGroup usm        local
view all    included  .1                               80
access MyROGroup ""      any       noauth    exact  all    none   none
syslocation (MyLocation)
syscontact ([email protected])

Next configure Apache specifically for MRTG by editing: #vi /etc/httpd/conf/httpd.conf and adding the following:

DocumentRoot "/var/www/html/mrtg"

Use the command below to create a configuration file for monitoring network traffic:

/usr/bin/cfgmaker  \
--output=/etc/mrtg/traffic.cfg \
--ifdesc=ip \
--ifref=descr \
--global "WorkDir: /var/www/html/mrtg/traffic" \
--global "Options[_]: bits,growright" \
public@localhost

Next create the CPU monitoring configuration. Run #vi /etc/mrtg/cpu.cfg and add the settings below:

WorkDir: /var/www/html/mrtg/cpu
LoadMIBs: /usr/share/snmp/mibs/UCD-SNMP-MIB.txt
Target[localhost.cpu]:ssCpuRawUser.0&ssCpuRawUser.0:[email protected] + ssCpuRawSystem.0&ssCpuRawSystem.0:[email protected] + ssCpuRawNice.0&ssCpuRawNice.0:[email protected]
RouterUptime[localhost.cpu]: [email protected]
MaxBytes[localhost.cpu]: 100
Title[localhost.cpu]: CPU Load
PageTop[localhost.cpu]: Active CPU Load %
Unscaled[localhost.cpu]: ymwd
ShortLegend[localhost.cpu]: %
YLegend[localhost.cpu]: CPU Utilization
Legend1[localhost.cpu]: Active CPU in % (Load)
Legend2[localhost.cpu]:
Legend3[localhost.cpu]:
Legend4[localhost.cpu]:
LegendI[localhost.cpu]:  Active
LegendO[localhost.cpu]:
Options[localhost.cpu]: growright,nopercent

Next configure CPU temperature monitoring by creating a file with #vi /etc/mrtg/cpu-temp.cfg and adding the following: MRTG can monitor CPU temperature only if the machine has a temperature sensor.

LoadMIBs: /usr/share/snmp/mibs/LM-SENSORS-MIB.txt
Target[localhost.cpu-temp]: .1.3.6.1.4.1.2021.13.16.2.1.3.1&.1.3.6.1.4.1.2021.13.16.2.1.3.1:public@localhost
PageTop[localhost.cpu-temp]: CPU Temperature
WorkDir: /var/www/html/mrtg/temp
Options[localhost.cpu-temp]: nopercent,growright,gauge,noinfo,pngdate,nobanner
Factor[localhost.cpu-temp]: 0.001
PNGTitle[localhost.cpu-temp]: CPU Temperature
Title[localhost.cpu-temp]: CPU Temperature
kMG[localhost.cpu-temp]: C
MaxBytes[localhost.cpu-temp]: 100000
YLegend[localhost.cpu-temp]: Temperature (c)
ShortLegend[localhost.cpu-temp]: C
LegendI[localhost.cpu-temp]: CPU Temperature:
LegendO[localhost.cpu-temp]:
Legend1[localhost.cpu-temp]: CPU Temperature
Legend2[localhost.cpu-temp]:
#Unscaled[localhost.cpu-temp]: ymwd
#WithPeak[localhost.cpu-temp]: ymwd
XSize[localhost.cpu-temp]: 360
YSize[localhost.cpu-temp]: 75
#YTics[localhost.cpu-temp]: 10
Colours[localhost.cpu-temp]: DKBLUE#61A0DF,DKBLUE#0000DD,DARKGREEN#006600,VIOLET#FF00FF

Next monitor memory and swap by adding /etc/mrtg/mem.cfg and /etc/mrtg/swap.cfg as shown below: #vi /etc/mrtg/mem.cfg

LoadMIBs: /usr/share/snmp/mibs/HOST-RESOURCES-MIB.txt
Target[localhost.mem]: .1.3.6.1.4.1.2021.4.6.0&.1.3.6.1.4.1.2021.4.6.0:public@localhost
PageTop[localhost.mem]: Free Memory
WorkDir: /var/www/html/mrtg/mem
Options[localhost.mem]: nopercent,growright,gauge,noinfo
Title[localhost.mem]: Free Memory
MaxBytes[localhost.mem]: 1000000
kMG[localhost.mem]: k,M,G,T,P,X
YLegend[localhost.mem]: bytes
ShortLegend[localhost.mem]: bytes
LegendI[localhost.mem]:  Free Memory:
LegendO[localhost.mem]:
Legend1[localhost.mem]: Free memory, not including swap, in bytes

#vi /etc/mrtg/swap.cfg

LoadMIBs: /usr/share/snmp/mibs/UCD-SNMP-MIB.txt
Target[localhost.swap]: memAvailSwap.0&memAvailSwap.0:public@localhost
PageTop[localhost.swap]: Swap Memory
WorkDir: /var/www/html/mrtg/swap
Options[localhost.swap]: nopercent,growright,gauge,noinfo
Title[localhost.swap]: Free Memory
MaxBytes[localhost.swap]: 1000000
kMG[localhost.swap]: k,M,G,T,P,X
YLegend[localhost.swap]: bytes
ShortLegend[localhost.swap]: bytes
LegendI[localhost.swap]:  Free Memory:
LegendO[localhost.swap]:
Legend1[localhost.swap]: Swap memory avail, in bytes

This step adds ping monitoring to MRTG. Put the following settings in /etc/mrtg/ping.cfg: #vi /etc/mrtg/ping.cfg

WorkDir: /var/www/html/mrtg/ping
Title[localhost.ping]: Round Trip Time
PageTop[localhost.ping]: Round Trip Time
Target[localhost.ping]: `/etc/mrtg/ping.sh`
MaxBytes[localhost.ping]: 2000
Options[localhost.ping]: growright,unknaszero,nopercent,gauge
LegendI[localhost.ping]: Pkt loss %
LegendO[localhost.ping]: Avg RTT
YLegend[localhost.ping]: RTT (ms)

The ping configuration alone is not enough. First write the ping script below: vi /etc/mrtg/ping.sh

#!/bin/sh
PING="/bin/ping"
# Google, for example
ADDR="google.com"
DATA=`$PING -c10 -s500 $ADDR -q `
LOSS=`echo $DATA | awk '{print $18 }' | tr -d %`
echo $LOSS
if [ $LOSS = 100 ]; then
    echo 0
else
    echo $DATA | awk -F/ '{print $5 }'
fi

Use chmod to avoid “Permission denied” when MRTG runs:

chmod 755 /etc/mrtg/ping.sh

Start MRTG with the commands below. The graphs will not show data yet.

# env LANG=C /usr/bin/mrtg /etc/mrtg/cpu.cfg
# env LANG=C /usr/bin/mrtg /etc/mrtg/cpu-temp.cfg
# env LANG=C /usr/bin/mrtg /etc/mrtg/mem.cfg
# env LANG=C /usr/bin/mrtg /etc/mrtg/swap.cfg
# env LANG=C /usr/bin/mrtg /etc/mrtg/ping.cfg
# env LANG=C /usr/bin/mrtg /etc/mrtg/traffic.cfg

Next create an index file linking to the monitoring pages by entering the commands below:

/usr/bin/indexmaker --output=/var/www/html/mrtg/index.html \
--title="Power Under Control" \
--sort=name \
--enumerate \
/etc/mrtg/traffic.cfg \
/etc/mrtg/cpu.cfg \
/etc/mrtg/cpu-temp.cfg \
/etc/mrtg/mem.cfg \
/etc/mrtg/swap.cfg \

Finally, schedule it with crontab -e and enter the following:

*/3 * * * * /usr/bin/env LANG=C /usr/bin/mrtg /etc/mrtg/cpu.cfg
*/3 * * * * /usr/bin/env LANG=C /usr/bin/mrtg /etc/mrtg/cpu-temp.cfg
*/3 * * * * /usr/bin/env LANG=C /usr/bin/mrtg /etc/mrtg/mem.cfg
*/3 * * * * /usr/bin/env LANG=C /usr/bin/mrtg /etc/mrtg/swap.cfg
*/3 * * * * /usr/bin/env LANG=C /usr/bin/mrtg /etc/mrtg/ping.cfg
*/3 * * * * /usr/bin/env LANG=C /usr/bin/mrtg /etc/mrtg/cpu.cfg
*/5 * * * * /usr/bin/env LANG=C /usr/bin/mrtg /etc/mrtg/traffic.cfg

After finishing the configuration, wait a while, then visit http://SERVERorIP for your server. How was that? It is not difficult. Linux is easy…