The source code control system you use must be specified in your POM file in an scm entry similar to the one shown here:
<scm> <connection> scm:svn:http://svn.apache.org/repos/asf/maven/components/trunk </connection> <developerConnection> scm:svn:https://svn.apache.org/repos/asf/maven/components/trunk </developerConnection> <url>http://svn.apache.org/viewcvs.cgi/maven/components/trunk</url> </scm>
To determine what to enter for your connection URL (the " <connection> " tag) go to the link http://maven.apache.org/scm/scms-overview.html for a list of supported SCMs and click on your source code control system to see the appropriate syntax for your particular software.
In general the format for an SCM URL is: scm:<scm_provider><delimiter><provider_specific_part>
In the example above, the scm_provider is "svn" (Subversion). The delimiter is a colon. And the rest of the line is the "provider_specific_part".
It is important to prepare the release just before performing the release. The reason these processes have been separated into two steps is to allow the user to confirm that everything has been set correctly before the actual release. If between the prepare and performing of the release there is a change to the SCM tree, an error will occur causing the prepare process to restart.