Tomorrow, Tuesday, 24 November, 2015 at 17:00 UTC, we will be bringing down rika, our sandbox server, to update the operating system. We expect this to take approximately two and a half hours, during which time rika will be updated to Ubuntu 14.04 LTS. If you are running any services (such as a MusicBrainz sandbox) on rika, remember to back up your data (like the MOTD says!), and be aware that you will need to restart these services once the server is available. Thank you for understanding the brief inconvenience as we put shiny new things in place.
UPDATE: Unfortunately, something has gone wrong during the update process. rika is responding to pings, but no services have come up. We will do our best to resolve this quickly, but there is currently no ETA.
MetaBrainz Blog 
It’s taking longer than expected. No new ETA yet. (Just in case someone is actually waiting for one of the sandboxes …)