Chapter 14. Frequently Asked Questions

Redhat 8.0

comes with a broken php snmp package. Updating your 'php snmp' and 'net snmp' packages to

their latest versions should fix this problem.

How do I configure

net snmp

so it will work with Cacti?

Run snmpconf  g basic_setup and follow the prompts. Also check that the file being used by snmpd

is the correct config file. For Redhat Linux, snmpconf creates the

/etc/snmpd.conf

, but snmpd uses

/etc/snmpd/snmpd.conf

.

If this doesn't work a very simple config file is:

# contact

syslocation Something

syscontact "root@someone.com"

# auth

rocommunity public

# disk monitoring

disk /

4. Graphs

I just installed Cacti and all of my graphs appear as broken images.

For you to actually get graph images, poller.php must run at least once so it can create .rrd files in Cacti's 'rra/'

directory. Double check that you configured your

/etc/crontab

file to execute poller.php every five minutes.

Also make sure that the user poller.php runs as has permission to create new files in Cacti's 'rra/' directory.

If all of your settings appear correct, try running poller.php manually by cd'ing to Cacti's directory and typing:

shell

>

php poller.php

If you have files in your 'rra/' directory, but your graphs still appear as broken images, you should enable graph

debug mode see exactly why the graphs are not rendering. To do this go into Cacti, select Graph Management

from the menu, select any graph listed, and select Turn On Graph Debug Mode.

My graphs render, but they do not contain any data.

More often than not, this problem's cause is permissions. For instance if you run poller.php manually as root for

testing, any .rrd files that it creates will be owned by root. Now when poller.php runs from cron, it will not be

able to update these .rrd files because they are owned by root. You can double check the owner of your .rrd files

by running the following command in your Cacti directory:

shell

>

ls  al rra/

If only some of your graphs are not updating correctly, double check the Maximum Value field for all data sources

used by these graphs. If the value being fed to the .rrd file exceeds its Maximum Value, RRDTool will insert an

Unknown and you will see no data on the graph.

A lot of my graphs contain long ifAlias names, but they are being truncated to 15 characters.

Cacti does this by default to better control graph title formatting. You can change this limit, by going to Cacti

Settings on the Cacti menu, selecting the Visual tab, and changing the value for Data Queries   Maximum Field

Length.

One of my devices rebooted and now I have a huge spike on my graph!

This occurs because the reboot causes SNMP's counters to reset, which can cause a rather large spike on the

graph when

RRDTool

tries to determine the change between the new small counter value and the large previous

value. One way to combat this issue is to specify realistic maximum values for your data sources.

RRDTool

will

ignore any value that is larger than the maximum value.

If you already have a spike on one or more of your graphs, there is a really useful Perl script

1

that will remove

them for you.

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