Some problems have been identified in VisualVM when running on Linux or Solaris using OpenJDK or JDK 7. Due to a JDK bug in GTK LaF implementation it's not possible to open the Host customizer in VisualVM 1.2 and newer. This affects the 'Add Remote Host' and 'Host Properties' actions which throw a
java.lang.NullPointerException and don't allow to edit and/or add hosts. Details are available in the VisualVM Troubleshooting Guide.
There's an easy workaround to this problem, the VisualVM can be configured to use a different look'n'feel:
visualvm --laf Nimbus or
visualvm --laf Metal. The LaF to be used can be configured permanently in
visualvm/etc/visualvm.conf configuration file. Another possibility is to run the VisualVM using Sun JDK 6.
The problem is now resolved on VisualVM side in development builds and will be available in the next release.