TUT:snmpset
Contents
snmpset
The snmpset command is used to actually modify information on the remote host. For each variable you want to set, you need to specify the OID to update, the data type and the value you want to set it to.
The valid datatypes can be found at the end of the snmpset help output:
% snmpset -h |& tail -4
type - one of i, u, t, a, o, s, x, d, n
i: INTEGER, u: unsigned INTEGER, t: TIMETICKS, a: IPADDRESS
o: OBJID, s: STRING, x: HEX STRING, d: DECIMAL STRING
U: unsigned int64, I: signed int64, F: float, D: double
So, let's check, set, and check again the value of a variable using snmpget and snmpset:
% snmpget -v 2c -c demopublic test.net-snmp.org ucdDemoPublicString.0 enterprises.ucdavis.ucdDemoMIB.ucdDemoMIBObjects.ucdDemoPublic.ucdDemoPublicString.0 = "hi there"
% snmpset -v 2c -c demopublic test.net-snmp.org ucdDemoPublicString.0 s "hello world" enterprises.ucdavis.ucdDemoMIB.ucdDemoMIBObjects.ucdDemoPublic.ucdDemoPublicString.0 = "hello world"
% snmpget -v 2c -c demopublic test.net-snmp.org ucdDemoPublicString.0 enterprises.ucdavis.ucdDemoMIB.ucdDemoMIBObjects.ucdDemoPublic.ucdDemoPublicString.0 = "hello world"
As you can see, we successfully changed the value of the ucdDemoPublicString.0 object.
Note that if you don't have write permission to the object, the errors will differ greatly between SNMPv1 and SNMPv2c:
% snmpset -v 1 -c badcommunity test.net-snmp.org ucdDemoPublicString.0 s "hello" Error in packet. Reason: (noSuchName) There is no such variable name in this MIB. This name doesn't exist: ucdDemoPublicString.0
% snmpset -v 2c -c badcommunity test.net-snmp.org ucdDemoPublicString.0 s "hello" Error in packet. Reason: notWritable
SNMPv1 did not have nearly as descriptive error codes, which SNMPv2c fixed. It's a good reason to use SNMPv2c in preference to SNMPv1. Even better is to use SNMPv3 which has a much better security system and also uses the better error reporting. We'll talk extensively about SNMPv3 later.
Tutorial Sections
About the SNMP Protocol
These tutorial links talk about SNMP generically and how the protocol itself works. They are good introductory reading material and the concepts are important to understand before diving into the later tutorials about Net-SNMP itself.
- How SNMP Works: About the protocol itself (GETs, GETNEXTs, etc)
- What data is in SNMP: All about SNMP Management Information Bases (MIBs)
- Securing SNMP: How to use the SNMP protocol securely
Net-SNMP Command Line Applications
These tutorial pages discuss the command line tools provided in the Net-SNMP suite of tools. Nearly all the example commands in these tutorials works if you try it yourself, as they're all examples that talk to our online Net-SNMP test agent. Given them a shot!
- snmptranslate: learning about the MIB tree.
- snmpget: retrieving data from a host.
- snmpgetnext: retrieving unknown indexed data.
- snmpwalk: retrieving lots of data at once!
- snmptable: displaying a table.
- snmpset: peforming write operations.
- snmpbulkget: communicates with a network entity using SNMP GETBULK request
- snmpbulkwalk: retrieve a sub-tree of management values using SNMP GETBULK requests.
- snmptrap: Sending and receiving traps, and acting upon them.
- Traps/informs with SNMPv3/USM: Sending and receiving SNMPv3/USM TRAPs and INFORMs
- Sending Traps/Informs via AgentX: Sending notifications from the command line through snmpd
- Common command line options:
- Writing mib2c config files
Application Configuration
All of our applications support configuration to allow you to customize how they behave.
Net-SNMP Daemons
Net-SNMP comes with two long-running daemons: a SNMP agent (snmpd) for responding to management requests and a notification receiver (snmptrapd) for receiving SNMP notifications.
- SNMP Agent (snmpd) Configuration
- SNMP Notification Receiver (snmptrapd)
- Agent Monitoring
Coding Tutorials
Net-SNMP comes with a highly flexible and extensible API. The API allows you to create your own commands, add extensions to the agent to support your own MIBs and perform specialized processing of notifications.
- Client / Manager Coding Tutorials
- Agent Coding Tutorials
- The Agent Architecture page might be worth reading before or after the agent coding tutorials, and describes how the Agent Helpers work under the hood.
- Writing a mib module to serve information described by an SNMP MIB, and how to compile it into the net-snmp snmpd agent.
- Writing a Dynamically Loadable Object that can be loaded into the SNMP agent.
- Writing a Subagent that can be run to attach to the snmpd master agent.
- Writing a perl plugin to extend the agent using the NetSNMP::agent module.
- Writing shell scripts to extend the agent
- Using mib2c to help write an agent code template for you
- Header files and autoconf
Debugging SNMP Applications and Agents
All our tools and applications have extensive debugging output. These tutorials talk about how the debugging system works and how you can add your own debugging statements to you code:
- Debugging output printed using the -D command line option
- Using -Ddump to display packet breakdowns
- Debugging using GDB
Operating System Specific Tutorials
- Building With Visual Studio 2005 Express
- Building Net-SNMP 64-bit with Visual C++ 2010 Express
- Net-Snmp on Ubuntu
- Net-SNMP and lm-sensors on Ubuntu 10.04
- Net-SNMP for windows:
