This article explains how to configure SNMP for use with Nagios on a CentOS server. It’s assumed you already have Nagios installed but not necessarily configure to use SNMP to monitor a host. We use “Disk Space” monitoring in this article.
For this article, i’ve used the following versions:
1. Nagios Version 3.5.0
2. CentOS 6.2
Configure SNMP
Install SNMP:
yum install net-snmp*
Change the “community name” from “public” to something more secure. Edit the file “/etc/snmp/snmpd.conf” using this example as a guide:
com2sec mynetwork 127.0.0.1 public com2sec mynetwork 192.168.0.0/24 public com2sec mynetwork nagios.agix.com.au public group MyROGroup v1 mynetwork group MyROGroup v2c mynetwork view all included .1 access MyROGroup "" any noauth exact all none none syslocation Unknown (edit /etc/snmp/snmpd.conf) syscontact Root <root@localhost> (configure /etc/snmp/snmp.local.conf) disk / 1000000 pass .1.3.6.1.4.1.4413.4.1 /usr/bin/ucd5820stat rwuser agixmon
Restart SNMP:
service snmpd restart
Test if from the localhost (the server running SNMP):
snmpwalk -v2c -c myComNameSecret localhost:161
You should get plenty of information out of it. Make sure to allow UDP port “161” through your firewall/router to this SNMP server.
Configure Nagios
Add the following to your “/usr/local/nagios/etc/objects/services.cfg” file:
define service{
use generic-service
hostgroup_name group_disk_space
service_description checkDiskSpace
is_volatile 0
check_period 24x7
max_check_attempts 3
normal_check_interval 60
retry_check_interval 1
notification_interval 240
notification_period 24x7
notification_options c,r
check_command check_hd
}
And now list the computers that need to be monitored (“MYSERVER1” and “MYSERVER2” in this example). This is in the same file as above:
define hostgroup{
hostgroup_name group_disk_space
alias group_disk_space
members MYSERVER1, MYSERVER2
#hostgroup_members hostgroups
notes group_disk_space
notes_url url
action_url url
}
Now edit your “/usr/local/nagios/etc/objects/commands.cfg” and add the following. Note that you should change the “public” community name to be the same as used earlier – assuming you changed it earlier:
define command{
command_name check_hd
command_line $USER1$/check_hd $HOSTADDRESS$ public 90 95 /home
}
You will need to add the following script contents into the file “/usr/local/nagios/libexec/check_hd”:
#!/usr/bin/perl
# Dont use the embedded apache perl....
# Author : Peter
# Date : Apr 11 2006
# check_hd IP COMMUNITY warnlevel criticallevel disc
use POSIX;
sub print_usage
{
print "
############################## check_hd ###############################
# Version : 1.0
# Date : Apr 11 2006
# Author : Peter Stimpel
# Modified : By AGIX July 03 2013
# Thanks to Benjamin Jakubowski for the idea to walk through snmp
# Help : http://www.peters-webcorner.de/nagios/
# Licence : GPL - http://www.fsf.org/licenses/gpl.txt
#######################################################################n";
print "check_hd IP COMMUNITY warnlevel criticallevel discn";
print"ncheck_hd -v for version infon";
}
$PROGNAME = "check_hd";
if (@ARGV[0] eq "-v") {
print_usage();
exit 0;
}
if ( @ARGV[0] eq "" || @ARGV[1] eq "" || @ARGV[2] eq "" || @ARGV[3] eq "" || @ARGV[4] eq "")
{
print_usage();
exit 0;
}
$IP=@ARGV[0];
$COMMUNITY=@ARGV[1];
$Service=@ARGV[2];
$LW=@ARGV[4];
$resultat =`/usr/bin/snmpwalk -v 2c -c $COMMUNITY $IP hrStorageDescr | grep -m 1 $LW`;
$fullsize1=0;
$usedsize1=0;
$freespace=0;
if ( $resultat ) {
$resstring= $resultat;
if ($resultat = ~/hrStorageDescr./) {
$tsid = substr($resstring,35,2);
$resultat2 =`/usr/bin/snmpwalk -v 2c -c $COMMUNITY $IP hrStorageAllocationUnits.$tsid`;
$resstring2 = $resultat2;
if ($resultat2 = ~/hrStorageAllocationUnits.$tsid/) {
#@unit = substr($resstring2,58,5);
@unit=split(/:/,$resstring2);
@unit1=split(/ /,$unit[3]);
$unit1=$unit1[1];
$resultat3 =`/usr/bin/snmpwalk -v 2c -c $COMMUNITY $IP hrStorageSize.$tsid`;
$resstring3 = $resultat3;
if ($resultat3 = ~/hrStorageSize.$tsid/) {
@ta=split(/INTEGER/,$resstring3);
chomp($ta[1]);
$size1=substr($ta[1],1);
$fullsize1 = $fullsize1 + $size1;
$fullsize1 = $fullsize1 * $unit1;
}
$resultat4 =`/usr/bin/snmpwalk -v 2c -c $COMMUNITY $IP hrStorageUsed.$tsid`;
$resstring4 = $resultat4;
if ($resultat4 = ~/hrStorageUsed.$tsid/) {
@tb=split(/INTEGER/,$resstring4);
chomp($tb[1]);
$size1=substr($tb[1],1);
$usedsize1 = $usedsize1 + $size1;
$usedsize1 = $usedsize1 * $unit1;
}
if ($usedsize1 > 0 && $fullsize1 > 0) {
$freespace=$fullsize1 - $usedsize1;
$freespace=$freespace / 1024 / 1024 / 1024;
$percfilled=$usedsize1 * 100 / $fullsize1;
if ($percfilled > @ARGV[3]) {
print "critical: $LW in use " . ceil($percfilled) .
"% and " . ceil($freespace) . "GB free w-$ARGV[2]% c-$ARGV[3]%n";
exit 2;
}
if ($percfilled > @ARGV[2]) {
print "warning: $LW in use " . ceil($percfilled) .
"% and " . ceil($freespace) . "GB free w-$ARGV[2]% c-$ARGV[3]%n";
exit 1;
}
print "OK: $LW in use " . ceil($percfilled) .
"% and " . ceil($freespace) . "GB free w-$ARGV[2]% c-$ARGV[3]%n";
exit 0;
}
}
}
print "Critical : Response unknownn";
exit 2;
}
else
{
print "Critical : no responsen";
exit 2;
}
Set the permissions and ownership of the above script:
chmod 755 /usr/local/nagios/libexec/check_hd chown nagios.root /usr/local/nagios/libexec/check_hd
Restart Nagios:
service nagios restart
