admin is an alias for org.apache.nutch.tools.WebDBAdminTool
The WebDBAdminTool is for Nutch administrators who need special access to the webdb. It allows for finer editing of the stored values.
Usage: bin/nutch org.apache.nutch.tools.WebDBAdminTool (-local | -ndfs <namenode:port>) db [-create] [-textdump dumpPrefix] [-scoredump] [-top k]