[CentOS] SNMP V3 libraries not found, SNMPV3 disabled.

Dear all,

I have installed mrtg via yum on centos 7, and using cron job to load mrtg
every 5 mins. Everything work fine but just snmp v3 graph no show up. I try
to load the command LAND=C /usr/bin/mrtg /etc/mrtg/metg.cfg it will show an
error "SNMP V3 libraries not found, SNMPV3 disabled.". so, i installed all
the net-snmp but still showing the error. I can't find any suggestion on
google. can anyone have the same problem ?

Thanks

Alex