assistant-qt4: cannot connect to X server

Usage: assistant [Options] -collectionFile file Uses the specified collection file instead of the default one -showUrl url Shows the document with the url. -enableRemoteControl Enables Assistant to be remotely controlled. -show widget Shows the specified dockwidget which can be "contents", "index", "bookmarks" or "search". -activate widget Activates the specified dockwidget which can be "contents", "index", "bookmarks" or "search". -hide widget Hides the specified dockwidget which can be "contents", "index" "bookmarks" or "search". -register helpFile Registers the specified help file (.qch) in the given collection file. -unregister helpFile Unregisters the specified help file (.qch) from the give collection file. -setCurrentFilter filter Set the filter as the active filter. -remove-search-index Removes the full text search index. -rebuild-search-index Re-builds the full text search index (potentially slow). -quiet Does not display any error or status message. -help Displays this help.