The Virtual Appliance introduces several restrictions in terms of permissions on the files in the web application server. These prevent the option of creating the logout page as it once was done in pre 14.0 versions.
How can I configure the logout.jsp page for Identity Manager in Virtual Appliance?
Virtual Appliance 14.0 and up
1) Place a file named logoff.html under this location:
(* These are the same - the first is a symbolic link to the second)
2) Then refer to it as: /iam/im/app/imcss/logoff.html in the management console property setting for the logout page per the original documentation.