What is the differece between snmp, snmpd and snmptrapd?

Solution 1:

A basic understanding of the SNMP protocol is really broader than what can be squeezed into this answer (and I'm probably not familiar enough to do a competent job) but in brief

• snmp contains tools to talk to SNMP "agents".
• snmpd contains a server which you can install on a device to implement such an "agent". It listens for SNMP client connections and delivers responses to requests for status reports.
• snmptrapd is a server for listening to and reacting to a particular kind of messages from agents.

A device which supports SNMP can tell you when something happens via a trap message. It can also provide statistics about its operation which you can request when you need them.

So in an example scenario, you might install snmpd on a machine to report its disk usage, CPU, etc when you need these numbers, and in addition, perhaps configure it to generate a trap and send it to a central location when the disk utilization crosses a particular threshold. The central server connects periodically to collect statistics, and in addition, is prepared to receive a trap at any time.

http://www.net-snmp.org contains a better and more comprehensive overview of the protocol and the components in this package.