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Check the NMIS Dashboard. If the web server is running but you can't access the GUI check your firewall; some Linux distributions do ship with a firewall enabled by default (e.g. RedHat 7) so a quick sudo iptables -n -L is recommended to verify the firewall status.
After authenting authenticating you should see the dashboard in all its glory, likely overlapped by the "Basic Setup" helper panel if this is an NMIS installation from scratch.
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