How to unblock all IPs banned by fail2ban on a Digital Ocean Ubuntu 16.04 droplet

1. find the location of the fail2ban database file:

sudo fail2ban-client get dbfile  

 Current database file is:
`- /var/lib/fail2ban/fail2ban.sqlite3

2. stop the fail2ban service:

sudo service fail2ban stop

3. delete the fail2ban database file:

sudo rm /var/lib/fail2ban/fail2ban.sqlite3

4. start the fail2ban service:

sudo service fail2ban start

5. check the list of all packet filter rules in the Linux kernel:

sudo iptables -L