Monitoring DHCP server with check_dhcp
by Alpha01
Setting Nagios to monitor my DHCP server using the plugin check_dhcp was a little tricky to setup.
First, the check_dhcp documentation indicates setting setuid on the check_dhcp binary in order to successfully query the dhcp server and receive a valid dhcp offer.
Error
root@monitor libexec]# su - nagios -c '/usr/local/nagios/libexec/check_dhcp -s 192.168.1.2'
Warning: This plugin must be either run as root or setuid root.
To run as root, you can use a tool like sudo.
To set the setuid permissions, use the command:
chmod u+s yourpluginfile
Error: Could not bind socket to interface eth0. Check your privileges...
Fix
chown root.root check_dhcp
chmod u+s check_dhcp
Secondly, since I always have all of my machines block all incoming traffic, I had to open up the UDP Port 68 in order for the Nagios machine to accept the dhcp offer.
iptables -A INPUT -p udp --dport 68 -j ACCEPT
networking nagios iptables