This page attempts to list some annoying bugs in Ubuntu distros along with solutions.

1.  popularity_contest – on Ubuntu Mate you constantly receive email like:

etc/cron.daily/apt:
FATAL -> Failed to fork.
/etc/cron.daily/popularity-contest:
/etc/cron.daily/popularity-contest: 18: .: Can’t open /etc/popularity-contest.conf
run-parts: /etc/cron.daily/popularity-contest exited with return code 2

To fix this you need to generate the missing file: /etc/popularity-contest.conf

Here is how: sudo dpkg-reconfigure popularity-contest

This will present you with a screen asking if you want to participate.
Answer “yes or no”. This should generate the missing file above and the nagging email
error should go away.