knot-resolver won't start

  I've tried everything.  What's wrong?
    

This was the status when I first installed it onto Ubuntu-18.04 on Jan 1, 2021. Things may have changed since then.

There are two ways to get your error messages:

    systemctl status system-kresd.slice

    -- or --

    systemctl status kresd@N where N is the number of the instance you started

    The second method give more instance specific information. 
      

When I installed knot-resolver I used Ubuntu's package manager apt to install the dot-deb. Having mucked about with debs I learned that each one contains a file system overlay that starts at / and contains all the bits it wants to install already in their appropriate place: "/etc/my-stuff.conf", "/usr/local/bin/my-program", etc. knot-resolver requires a cache directory. It's not in the .deb and it's not created on startup. Create it yourself and you should be ready to go.

    mkdir /var/cache/knot-resolver
    chown knot-resolver:knot-resolver /var/cache/knot-resolver
    systemctl start kresd@1
      

One more possible gotcha comes if the resolver is listening on lo. Both knotd or knot-resolver can listen on lo, but not at the same time. It's one or the other.