Observium - Graphs shows no data (nan) or empty graphs - sysadmin

Question

I have problem with Observium.
On CentOS 7 I installed Observium. On this server i also have DirectAdmin and Wordpress.
When I login to webpanel Observium, Graphs shows no data (nan).
Graphs no data
<?php
## Check http://www.observium.org/docs/config_options/ for documentation of possible settings
## It's recommended that settings are edited in the web interface at /settings/ on your observium installation.
## Authentication and Database settings must be hardcoded here because they need to work before you can reach the web-based configuration interface
// Database config --- This MUST be configured
$config['db_extension'] = 'mysqli';
$config['db_host'] = 'localhost';
$config['db_user'] = 'root';
$config['db_pass'] = '[MyPassword]';
$config['db_name'] = 'observium';
$config['ping'] = "/usr/sbin/ping";
$config['fping'] = "/usr/sbin/fping";
// Base directory
#$config['install_dir'] = "/opt/observium";
// Default community list to use when adding/discovering
$config['snmp']['community'] = array("public");
// Authentication Model
$config['auth_mechanism'] = "mysql"; // default, other options: ldap, http-auth, please see documentation for config help
// Enable alerter
// $config['poller-wrapper']['alerter'] = TRUE;
//$config['web_show_disabled'] = FALSE; // Show or not disabled devices on major pages.
// Set up a default alerter (email to a single address)
//$config['email']['default'] = "user#your-domain";
//$config['email']['from'] = "Observium <observium#your-domain>";
//$config['email']['default_only'] = TRUE;
$config['enable_syslog'] = 1; // Enable Syslog
// End config.php
I do not see any error when I manually execute:
cd /opt/observium && ./discovery.php -h all && ./poller.php -h all
My /etc/cron.d/observium file
33 */6 * * * root cd /opt/observium/ && ./discovery.php -h all >> /dev/null 2>&1
*/15 * * * * root cd /opt/observium/ && ./discovery.php -h new >> /dev/null 2>&1
*/15 * * * * root cd /opt/observium/ && ./poller.php -h all >> /dev/null 2>&1

Answer 1

you used incorrect polling time (15 mins). Correct polling time is 5min. Use cron entries as described in official install guide CentOS Cron:
# Run a complete discovery of all devices once every 6 hours
33 */6 * * * root /opt/observium/discovery.php -h all >> /dev/null 2>&1
# Run automated discovery of newly added devices every 5 minutes
*/5 * * * * root /opt/observium/discovery.php -h new >> /dev/null 2>&1
# Run multithreaded poller wrapper every 5 minutes
*/5 * * * * root /opt/observium/poller-wrapper.py >> /dev/null 2>&1

Answer 2

It might be problem with installation as it was in my case. Observium has bug here Observium bugreport with explonation "install it again exactly according to the manual". Good page to use for installation information is this observium installation guide.
Problem in my case was that I had a observium folder with all scripts in Documents folder and symlink for html subfolder to /opt/observium/html. I fixed that by making symling of whole observium folder to /opt/observium/ which is set according to observium manual DocumentRoot in
/etc/apache2/sites-available/000-default.conf:
<VirtualHost *:80>
ServerAdmin webmaster#localhost
DocumentRoot /opt/observium/html
<FilesMatch \.php$>
SetHandler application/x-httpd-php
</FilesMatch>
<Directory />
Options FollowSymLinks
AllowOverride None
</Directory>
<Directory /opt/observium/html/>
DirectoryIndex index.php
Options Indexes FollowSymLinks MultiViews
AllowOverride All
Require all granted
</Directory>
ErrorLog ${APACHE_LOG_DIR}/error.log
LogLevel warn
CustomLog ${APACHE_LOG_DIR}/access.log combined
ServerSignature On
</VirtualHost>