Show only "Free" software in Ubuntu Software Center

In other words, "How to prevent paid software from being listed in Ubuntu Software Center"

Follow three simple steps as root:

1. In the file

/usr/share/software-center/softwarecenter/db/update.py

somewhere near line 480 find the following lines and add the highlighted line:

        doc = self.make_doc(cache)
        if not doc:
            LOG.debug("%r.index_app_info: returned invalid doc %r, ignoring.",
                      self.__class__.__name__, doc)
            return
        name = doc.get_data()

        if doc.get_value(XapianValues.PRICE) not in (""): return
        if name in seen:
            LOG.debug("%r.index_app_info: duplicated name %r (%r)",
                      self.__class__.__name__, name, self.desktopf)
        LOG.debug("%r.index_app_info: indexing %r",
                  self.__class__.__name__, name)
        seen.add(name)
  

2. In the file 

/usr/share/software-center/softwarecenter/backend/channel_impl/aptchannels.py

find the following lines and commentize the highlighted lines:

        if partner_channel is not None:
            channels.append(partner_channel)
        #if get_distro().PURCHASE_APP_URL:
        #    channels.append(for_purchase_channel)
        if new_apps_channel is not None:
            channels.append(new_apps_channel) 

3. Issue the command:

# update-software-center

4. Also disable "multiverse" from "Software and Updates" settings panel.