services.graylog.rootPasswordSha2

You MUST specify a hash password for the root user (which you only need to initially set up the system and in case you lose connectivity to your authentication backend) This password cannot be changed using the API or via the web interface. If you need to change it, modify it here. Create one by using for example: echo -n yourpassword | shasum -a 256 and use the resulting hash value as string for the option.