>sudo apt-get install icedtea-7-plugin
in Centos linux, your command should be:
>yum install icedtea-web
If you get a security warning which asking about running the application, simply sign that you accept the risk and press the "run" button.
If you get a message stating that you need to approve the plug-in, right click the mouse while on the applet area and then choose to run this plug-in. In the subsequent pop-up window approve this selection by checking the message "I accept the risk and want to run this app" and press "Run". You may update your Java version to avoid future warnings.
You may get a direct warning that you java version is out of date. You can update it by pressing "Update", however if you want to delay the updating process and continue, you may chose the "Later" option.
If you get a security message stating that the applet is not trustable and cannot be run, you may tell Java to trust this site: In Windows you should search for the Java control page. This panel may be found at the start menu ("Configuring Java"), from the programs menu in the system Control Panel, or by typing "java" in the command prompt in Windows operation systems. In the Java Control Panel, choose the "Security" tab in the upper part. Press the "Edit Site List..." button and add "http://anm.csb.pitt.edu" to the list of locations. Press OK. Now restart your browser and you should be able to open Jmol applets in the new ANM web server.