Upgrading to NDO 3 after having been downgraded in newer versions of Nagios XI

Issue:

You had your NDO3 downgraded to NDO2DB in previous versions of Nagios XI 5.7.x and now want to upgrade to the latest version of NDO3 to take advantage of the performance improvements.

Solution:

Execute the following commands on your server:

systemctl stop nagios
cd /tmp
rm -rf /tmp/nagiosxi
wget http://assets.nagios.com/downloads/nagiosxi/xi-latest.tar.gz
tar zxf xi-latest.tar.gz
cd /tmp/nagiosxi/subcomponents/ndo
./install

Then edit your /usr/local/nagios/etc/nagios.cfg and make sure this line is commented out:
#broker_module=/usr/local/nagios/bin/ndomod.o config_file=/usr/local/nagios/etc/ndomod.cfg
Make sure this line is uncommented:
broker_module=/usr/local/nagios/bin/ndo.so /usr/local/nagios/etc/ndo.cfg

Then start the nagios service:

systemctl start nagios