Mrtg graph not display for some devices

Question

I have MRTG get data from multiple devices, but 4 of them populate graphs on MRTG but other devices show empty graph, Could you please help me how to troubleshot this issue

Answer 1

If the graphs are showing as empty, then this is because MRTG does not have data for the time period you are requesting.

There are several possible reasons for this, so I'll put them in the most likely order.

1. The data is being collected via SNMP, and the community string is incorrect (maybe it was changed?)
2. The data is being collected via SNMP, but an ACL or firewall is preventing data collection
3. The data is being collected, but you have the wrong MaxBytes setting and it is being dropped as too high (this can happen if an interface is upgraded or changed)
4. You have given the wrong hostname or IP address for the device, so MRTG cannot find it (or maybe the DNS has changed)
5. The credentials are correct, but you are trying to graph an interface identifier which no longer exists (sometimes, interfaces are reenumerated if the device changes)
6. The device is actually switched off or unreachable
7. You are collecting data, but you are requesting a historical time period for which you do not have data stored yet
8. You are not running the MRTG data collection periodic task at all (maybe your scheduler has changed or stopped?)
9. The .rrd or .log files, or the directory, are not writeable by the account you are using to run MRTG and so the database cannot be updated. This could be an ownership issue, or permissions, or even a full filesystem.

Try running MRTG interactively, and it should output error messages to tell you where the problem is.