Say we are using Synaptic Package Manager with our distribution, but the Quick Filter is missing from it. We need to run: apt-get install apt-xapian-index and start Synaptic to check it out. If it still does not appear, we need to close Synaptic and run further: update-apt-xapian-index -vf and wait for it to finish. Starting Synaptic again, we should have Quick Filter available on the toolbar.