Setting up SNMP

Systems tested; Ubuntu Hardy

install packages

apt-get install snmp snmpd

I'm not sure why there are two config files but there are and we have to edit both. The first file configures the daemon itself

vi /etc/default/snmpd

Ensure these two lines exist

SNMPDRUN=yes
SNMPDOPTS='-Lsd -Lf /dev/null -u snmp -I -smux -p /var/run/snmpd.pid 127.0.0.1'

Change the localhost address on the 2nd line to the address of the interface you will listen on (remove it completely to listen on all interfaces)
The second file contains the snmp details such as access rights & community names

vi /etc/snmp/snmpd.conf

Find this section;

#       sec.name  source          community
com2sec paranoid  default         public
#com2sec readonly  default         public
#com2sec readwrite default         private

and change it to;

#       sec.name  source          community
#com2sec paranoid  default         public
com2sec readonly  default         public
#com2sec readwrite default         private

NOTE: Using the default community "public" is not recommended for security reasons. You should change it to a custom community name. It is left as default for simplicities sake. To change it just comment out all lines and add a new one. For example;

#       sec.name  source          community
#com2sec paranoid  default         public
#com2sec readonly  default         public
#com2sec readwrite default         private
com2sec readonly  default         MyCommunity

Checking your configuration from the local host

snmpwalk -Os -c public -v 1 localhost system

This should return a bunch of lines relating to various parts of your system. You can execute the same command from another host (snmp package is required), changing "localhost" to the name of the system.

Sources:
http://www.debuntu.org/how-to-monitor-your-servers-with-snmp-and-cacti