/usr/lib/jvm/java-7-openjdk-amd64/bin/rmiregistry is in openjdk-7-jre-headless 7u51-2.4.6-1ubuntu4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/jvm/java-7-openjdk-amd64/bin/../jre/bin/rmiregistry