Unable to activate or remove Fail2ban in Plesk: error reading information on service fail2ban: No such file or directory

Symptoms

• Modifying fail2ban settings in Tools & Settings > IP Address Banning (Fail2Ban) fails with an error:

  PLESK_ERROR: ERROR:f2bmng:No section: 'Definition'

  ---

  PLESK_ERROR: Error: f2bmng failed: error reading information on service fail2ban: No such file or directory
  ERROR:f2bmng:Command '['/sbin/chkconfig', '--add', 'fail2ban']' returned non-zero exit status 1

  ---

  PLESK_ERROR: Error: Unable to save the settings: f2bmng failed: Service fail2ban doesn't exist
  
  Usage: register_service {--enable service [options] | --disable service | --list | --full-list}
  Enables or disables the specified service.
  
  --enable enable the specified service
  --disable disable the specified service
  --list show list of services
  --full-list show list of services with status
  
  enable options:
  --with-resource-controller register the service in Plesk Resource Controller
  --no-watchdog don't monitor by watchdog
  ERROR:main:Command '['/usr/local/psa/admin/sbin/register_service', '--enable', 'fail2ban']' returned non-zero exit status 1.

• On Red Hat -based operating system (RHEL, CentOS, CloudLinux) fail2ban cannot be completely removed from Tools & Settings > Updates and Upgrades:

  PLESK_INFO: Error in PREUN scriptlet in rpm package 1:fail2ban-0.9.6-centos7.17122713.noarch
  Exception: Scriptlet or other non-fatal errors occurred during transaction.
  Erasing: plesk-fail2ban-configurator [1/2]
  Failed to stop fail2ban.service: Unit fail2ban.service not loaded.
  Failed to execute operation: No such file or directory
  error: %preun(fail2ban-1:0.9.6-centos7.17122713.noarch) scriptlet failed, exit status 1

  ---

  PLESK_INFO: Error in PREUN scriptlet in rpm package fail2ban
  fail2ban-0.8.13-14052018.noarch was supposed to be removed but is not!
  Exception: Scriptlet or other non-fatal errors occurred during transaction.
  Erasing: plesk-fail2ban-configurator [1/2]
  fail2ban: unrecognized service
  error reading information on service fail2ban: No such file or directory
  error: %preun(fail2ban-0.8.13-14052018.noarch) scriptlet failed, exit status 1

Cause

Corrupted Fail2ban installation.

Resolution

1. Connect to the server via SSH;

2. Create a backup of Fail2ban configuration and log:

   # mkdir /fail2ban_backup && mv /etc/fail2ban /fail2ban_backup && mv /var/log/fail2ban.log /fail2ban_backup

3. Remove fail2ban-related packages:

   • For Red Hat -based operating systems (RHEL, CentOS, CloudLinux):

     # rpm -e --nopreun fail2ban
     # rpm -e --nopreun plesk-fail2ban-configurator

   • For Debian-based operating systems (Debian, Ubuntu):

     # plesk installer --select-release-current --remove-component fail2ban

4. Install fail2ban back using Plesk installer:

   # plesk installer --select-release-current --install-component fail2ban