From Second Life Wiki
There is a small grid named 'uma' in the linden network that can be used for testing. We will keep that grid in sync with the source releases regardless of the state of the primary 'agni' grid.
- Uma grid is reported not to be accessible
There are two common ways to connect to the test grid. The easiest way is to turn on "UseDebugLogin" in your client options. On subsequent runs, the viewer will include a drop-down grid list on the login screen.
The other way is to specify the options on the command line. This is useful if you want to make a shortcut or a script that always logs into the alternate grid. To do this, launch the viewer with the following options:
-loginuri https://login.uma.lindenlab.com/cgi-bin/login.cgi -user userserver.uma.lindenlab.com
See Client parameters for information about additional paramaters and for information about activating the parameters in XCode and Visual Studio.