When you have an SNMP polling service running like Cacti, you can poll your Ubuntu machine's easily in a few steps.

1. install snmpd (snmp deamon)
sudo apt-get install snmpd

2. now edit the settings file
sudo vim /etc/snmp/snmpd.conf

3. comment out when the SNMP polling server is not running on the local host:
#agentAddress udp:

4. add listen on all interfaces for both IPv4 and IPv6 UDP 161
agentAddress udp:161,udp6:[::1]:161

5 option 1. scroll further down and add above "rocommunity secret" (your polling community string "secret" and your polling server ip address i.e.; Cacti):
rocommunity secret

5 option 2. or with FQDN
rocommunity ForgeMe123 cacti.example.com

6. Save the config and restart services:
sudo service snmpd restart