Graylog 5 has its own Java

[rogermartensson]

For Ubuntu-installs:

This module modifies /etc/default/java and inserts the environment variable JAVA to point to /usr/bin/java.

As of version 5 Java is included and this variable should not be set unless needed.

The workaround for this until it's fixed is to either install supported version of java och create a link to for /usr/bin/java to /usr/share/graylog-server/jvm/bin/java.