Comment 3 for bug 1634871

I am sure this is duplicate to:

  https://bugs.launchpad.net/ubuntu/+source/apt-btrfs-snapshot/+bug/1454306

, whereas the only problem is (as Jay Carlson (nop-nop) wrote on 2017-09-20 in here) that the path has changed.

Due to inexpressible nonsense, the 'fix' is not available, even in the fourth point-release.

Solution is simple; create a symbolic link:

sudo ln -s /bin/btrfs /sbin/btrfs

Hope, it helps