Net-SNMP Tutorial -- 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, lets 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.