Fail2ban does not ban

It took me a while to make fail2ban running correctly. The issue roots in a well-known bug. A quick fix:
# locate the 'backend' setting (set to 'auto' by default):
grep -b5 -i gamin /etc/fail2ban/jail.conf

# replace its value with 'polling':
perl -i -pe 's/^(backend\s*=).*/$1 polling/' /etc/fail2ban/jail.conf 

# restart the daemon:
/etc/init.d/fail2ban restart