Just a quick note: if you’re trying to run something that queries a specific MIB like:
snmpwalk -v1 -c public ${host} system
and you get an error like:
Unknown Object Identifier (Sub-id not found: (top) -> system)
This is because MIBs are not “free”, so Ubuntu disables them by default.
To get them back, install the MIBS using
# apt-get install snmp-mibs-downloader
Then go comment out the mibs : line in /etc/snmp/snmp.conf (it’s line 4 as of this post). Now run your query again and things should be better.