In cacti 0.8.6g (and perhaps f), using redhat (I've seen enterprise, RH9, Fedora 3 and 4 mentioned) there's a problem getting the list of interfaces to be detected, which allows you to graph traffic. 

The typical problems involve the following errors: 
"No SNMP data returned" (from verbose query in the devices detail) 
No data returned while running snmpwalk -v 1 -c public localhost .1.3.6.1.2.1.2.2.1.1 
General problems getting Interface - Traffic graphs to work 

The problem resides in the permissions for SNMP version 1 users in the /etc/snmp/snmpd.conf file 

You need to change the following limits: 
view systemview included .1.3.6.1.2.1.1 
view systemview included .1.3.6.1.2.1.25.1.1 

to: 
view systemview included .1.3.6.1.2.1 
view systemview included .1.3.6.1.2.1.25.1.1 

This reduces the limits to the pubic group's access using smtpwalk and allows cacti to get the list of interfaces.

实在不行 ，试试用这句启动snmpd

snmpd -Le -C -c /etc/snmp/snmpd.conf