rmiregistry is bundled with jdk by default and is located in <jdk_directory>/bin. You can start this from the command line itself by following the same procedure to set PATH variable for jdk installation.
The rmiregistry command starts a remote object registry on the specified port on the current host.
Its syntax is,
If port is omitted the port number 1099 is used by default.
A remote object registry is a bootstrap naming service that is used by RMI servers on the same host to bind remote objects to names. Clients on local and remote hosts can then look up remote objects and make remote method invocations.
Usually this is started in the background as,