FAQ:Applications 13

Variables seem to disappear when I try to set them. Why?

This is actually the same as the previous question - it just isn't particularly obvious, particularly when using SNMPv1. A typical example of this effect would be

       $ snmpget -v1 -c public localhost sysLocation.0
       sysLocation.0 = somewhere nearby
       

       $ snmpset -v1 -c public localhost
               sysLocation.0 s "right here"
       Error in packet.
       Reason: (noSuchName) There is no such variable name in this MIB.
       This name doesn't exist: sysLocation.0

Trying the same request using SNMPv2 or above is somewhat more informative:

       $ snmpset -v 2c -c public localhost
               sysLocation.0 s "right here"
       Error in packet.
       Reason: notWritable

The SNMPv1 error 'noSuchName' actually means: "You can't do that to this variable" rather than "this variable doesn't exist".
It may be the case that it doesn't exist at all. It may exist but you don't have access to it (although different administrative credentials might be accepted). Or it may exist, but you simply can't perform that particular operation (e.g. changing it).
Similarly, the SNMPv2 error 'notWritable' means "not writable in this particular case" rather than "not writable under any circumstances".

If you are sure that the object is both defined as writable, and has been implemented as such, then you probably need to look at the agent access control. See the AGENT section for more details.
But see the next entry first.

   FAQ:Applications
   

1. How do I add a MIB?
2. How do I add a MIB to the tools?
3. Why can't I see anything from the agent?
4. Why doesn't the agent respond?
5. I can see the system group, but nothing else. Why?
6. Why can't I see values in the <ENTERPRISE> tree?
7. The agent worked for a while, then stopped responding. Why?
8. Requesting an object fails with "Unknown Object Identifier" Why?
9. Why do I get "noSuchName" when asking for "sysUpTime" (or similar)?
10. Why do I sometimes get "End of MIB" when walking a tree, and sometimes not?
11. How do I use SNMPv3?
12. Why can't I set any variables in the MIB?
13. Variables seem to disappear when I try to set them. Why?
14. Why can't I change sysLocation (or sysContact)?
15. I get an error when trying to set a negative value - why?
16. I get an error when trying to query a string-indexed table value - why?
17. How should I specify string-index table values?
18. How do I send traps and notifications?
19. How do I receive traps and notifications?
20. How do I receive SNNMPv1 traps?
21. Why don't I receive incoming traps?
22. My traphandler script doesn't work when run like this - why not?
23. How can the agent receive traps and notifications?
24. How big can an SNMP request (or reply) be?
25. How can I monitor my systems (disk, memory, etc)?
26. Applications complain about entries in your example 'snmp.conf' file. Why?
27. OK, what should I put in snmp.conf?
28. How do I specify IPv6 addresses in tools command line arguments?