Debugging.md

Debugging

Cacti users sometimes complain about NaN's in their graphs. Unfortunately, there are several reasons for this result. The following is a step-by-step procedure recommended for debugging.

Check Cacti Log File

Your cacti log file should be located at <path_cacti>/log/cacti.log. If it is not, see Settings, Paths. Check for this kind of error:

SPINE: Host[...] DS[....] WARNING: SNMP timeout detected [500 ms], ignoring host '........'

For "reasonable" timeouts, this may be related to a snmpbulkwalk issue. To change this, see Settings, Poller and lower the value for The Maximum SNMP OIDs Per SNMP Get Request. Start at a value of 2 and increase it again, if the poller starts working. (1 or less disables snmpbulkwalk) Some agent's don't have the horsepower to deliver that many OIDs at a time. Therefore, we can reduce the number for those older/under-powered devices.

Check Basic Data Gathering

For scripts, run them as cactiuser from CLI to check basic functionality. E.g. for a Perl script named your-perl-script.pl with parameters "p1 p2" under *nix this would look like:

su - cactiuser
/full/path/to/perl your-perl-script.pl p1 p2
... (check output)

For SNMP, snmpget the exact OID you're asking for, using same community string and SNMP version as defined within cacti. For an OID of .1.3.6.1.4.something, community string of very-secret and version 2 for target host target-host this would look like

snmpget -c very-secret -v 2c target-host .1.3.6.1.4.something
.... (check output)

Check Cacti's poller

First make sure that crontab always shows poller.php. This program will either call cmd.php, the PHP based poller or spine, the fast alternative, written in C. Define the poller you're using at Settings, Poller. Spine has to be implemented separately, it does not come with cacti by default.

Now, clear ./log/cacti.log (or rename it to get a fresh start)

Then, change Settings, Poller Logging Level to DEBUG for one polling cycle. You may rename this log as well to avoid more stuff added to it with subsequent polling cycles.

Now, find the host/data source in question. The Host[<id>] is given numerically, the <id> being a specific number for that host. Find this <id> from the Devices menu when editing the host: The URL contains a string like

id=<id>

Check, whether the output is as expected. If not, check your script (e.g. /full/path/to/perl). If OK, proceed to next step

This procedure may be replaced by running the poller manually for the failing host only. To do so, you need the <id>, again. If you're using cmd.php, set the DEBUG logging level as defined above and run

php -q cmd.php <id> <id>

If you're using spine, you may override logging level when calling the poller:

./spine --verbosity=5 <id> <id>

All output is printed to STDOUT in both cases. This procedure allows for repeated tests without waiting for the next polling interval. And there's no need to manually search for the failing host between hundreds of lines of output.

Check MySQL updating

In most cases, this step can be skipped. You may want to return to this step if the next one fails (e.g. no rrdtool update to be found)

From debug log, find the MySQL update statement for that host concerning table poller_output. On very rare occasions, this will fail. Copy that SQL statement and paste it to a MySQL session started from CLI. This may as well be done from some tool like phpMyAdmin. Check the SQL return code.

Check RRDfile updating

Down in the same log, you should find some

rrdtool update <filename> --template ...

You should find exactly one update statement for each file.

RRDfiles should be created by the poller. If it does not create them, it will not fill them either. If it does check your Poller Cache from Utilities and search for your target. Does the query show up here?

Check RRDfile ownership

If RRDfiles were created e.g. with root ownership, a poller running as cactiuser will not be able to update those files

cd /var/www/html/cacti/rra
ls -l localhost*
-rw-r--r--  1 root      root      463824 May 31 12:40 localhost_load_1min_5.rrd
-rw-r--r--  1 cactiuser cactiuser 155584 Jun  1 17:10 localhost_mem_buffers_3.rrd
-rw-r--r--  1 cactiuser cactiuser 155584 Jun  1 17:10 localhost_mem_swap_4.rrd
-rw-r--r--  1 cactiuser cactiuser 155584 Jun  1 17:10 localhost_proc_7.rrd
-rw-r--r--  1 cactiuser cactiuser 155584 Jun  1 17:10 localhost_users_6.rrd

Run the following command to cure this problem

chown cactiuser:cactiuser *.rrd

Check RRDfile numbers

You're perhaps wondering about this step, if the former was OK. But due to data sources MINIMUM and MAXIMUM definitions, it is possible, that valid updates for RRDfiles are suppressed, because MINIMUM was not reached or MAXIMUM was exceeded.

Assuming, you've got some valid rrdtool update in step 3, perform a

rrdtool fetch <RRDfile> AVERAGE

and look at the last 10-20 lines. If you find NaN's there, perform

rrdtool info <RRDfile>

and check the ds[...].min and ds[...].max entries, e.g.

ds[loss].min = 0.0000000000e+00
ds[loss].max = 1.0000000000e+02

In this example, MINIMUM = 0 and MAXIMUM = 100. For a ds.[...].type=GAUGE verify, that e.g. the number returned by the script does not exceed ds[...].MAX (same holds for MINIMUM, respectively).

If you run into this, not only should you update the data source definition within the Data Template, but also perform a:

rrdtool tune <RRDfile> --maximum <ds-name>:<new ds maximum>

for all existing RRDfiles belonging to that Data Template.

At this step, it is wise to check step and heartbeat of the RRDfile as well. For standard 300 seconds polling intervals (step=300), it is wise to set minimal_heartbeat to 600 seconds. If a single update is missing and the next one occurs in less than 600 seconds from the last one, RRDtool will interpolate the missing update. Thus, gaps are "filled" automatically by interpolation. Be aware of the fact, that this is no "real" data! Again, this must be done in the Data Template itself and by using rrdtool tune for all existing RRDfiles of this type.

Check rrdtool graph statement

Last resort would be to check, that the correct data sources are used. Go to Graph Management and select your Graph. Enable DEBUG Mode to find the whole rrdtool graph statement. You should notice the DEF statements. They specify the RRDfile and data source to be used. You may check, that all of them are as wanted.

Duplicate Poller Entries

If you installed Cacti from a package (RPM, DEB, etc.), the package may have created both a cron entry in /etc/cron.d/cacti and enabled the cactid systemd service. Running two pollers simultaneously causes data corruption.

Check for duplicate entries:

systemctl status cactid
cat /etc/cron.d/cacti
cat /etc/crontab
crontab -l -u cactiuser 2>/dev/null
crontab -l -u root 2>/dev/null

The recommended approach is to use the cactid systemd service and remove any cron-based poller entries:

systemctl enable --now cactid
# Then remove or comment out any poller.php line in /etc/cron.d/cacti

If you need to keep cron-based polling, disable the service and leave a single cron entry:

*/5 * * * *  cactiuser  /usr/bin/php -q /var/www/html/cacti/poller.php > /dev/null 2>&1

Replace cactiuser with the user your web server runs as (e.g. www-data on Debian/Ubuntu, apache on RHEL-compatible systems).

Not NaN, but 0 (zero) values

Pay attention to custom scripts. External commands called from there must be in the $PATH of the cactiuser running the poller. Use /full/path/to/external/command to avoid ambiguity.

User "criggie" reported an issue with running smartctl. It was complaining "you are not root" so a quick chmod +s on the script fixed that problem.

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