BFD (Brute Force Detection) on Linux

BFD (Brute Force Detection) is a script that runs on your linux server and checks log files for authentication errors. When it sees recurring authentication failures from a certain IP address it will instruct APF (Advanced Policy Firewall) to block the IP address.

It’s simple to configure, just make sure you have APF running before you continue. Let’s download it:

[root@VPS1 ~]# wget

Now extract it:

[root@VPS1 ~]# tar -xzvf bfd-current.tar.gz 

Open the folder:

[root@VPS1 ~]# cd bfd-1.5/

Now we can install it:

[root@VPS1 bfd-1.5]# ./ 

After installation we can edit the BFD configuration file:

[root@VPS1 bfd-1.5]# vim /usr/local/bfd/conf.bfd

Make sure you enable e-mail notifications:


And configure your e-mail address:


It’s also a good idea to configure BFD to ignore your own IP address so you don’t lock yourself out. Just add your IP address to the following file:

[root@VPS1 bfd]# vim /usr/local/bfd/ignore.hosts

If you want to run BFD you can do this using the following command:

[root@VPS1 bfd]# bfd -s

It will also run automatically thanks to a cronjob:

[root@VPS1 bfd]# vim /etc/cron.d/bfd

*/3 * * * * root /usr/local/sbin/bfd -q

By default each 3 minutes it will run the script and check your log files. When BFD finds anything it will instruct APF to block the IP address and you’ll receive an e-mail that looks like this:

The following is a summary event for exceeded login failures on VPS1.RMCSHOSTING.NL:

EXECUTED COMMAND: /etc/apf/apf -d {bfd.proftpd}


Apr 19 02:13:30 VPS1 proftpd[15133]: ([]) - USER no such user found from [] to
Apr 19 02:41:30 VPS1 proftpd[17222]: ([]) - USER no such user found from [] to
Apr 19 03:10:32 VPS1 proftpd[19741]: ([]) - USER no such user found from [] to

As you can see it has discovered a number of failed authentications for proftp. It instructed APF to block the IP address.

That’s all there is to it. I hope this helps you to protect your linux server(s)! If you have any questions or suggestions please leave a comment.

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Forum Replies

  1. can i use bfd in plesk control panel
    and if apf is Necessary to To work bfd

  2. Hi Rash,

    BFD will work fine in combination with Plesk (I use it on Plesk machines) but it won’t show up in the control panel. APF is required because BFD sends instructions to APF to block the IP address.

    Best Regards,


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