Scroll down to the configuration XML discussion, it shows:
<context-param>
<description>Full path to the configuration file where OpenGrok can read its configuration</description>
<param-name>CONFIGURATION</param-name>
<param-value>/opengrok/etc/configuration.xml</param-value>
</context-param>
The <param-value> is incorrect, it should be: /var/opengrok/etc/configuration.xml
See: https://github.com/oracle/opengrok/wiki/How-to-setup-OpenGrok
Scroll down to the configuration XML discussion, it shows:
The
<param-value>
is incorrect, it should be:/var/opengrok/etc/configuration.xml