FTP connection is randomly dropped during file transfer on Plesk for Linux server with SELinux

Symptoms

• FTP connection is randomly dropped during file transfer on Plesk server.
• Errors in FileZilla client log:

  8000 3 Command: PORT 127,0,0,1,243,14
  8000 3 Response: 500 Illegal PORT command

• Following entries can be found in
/var/log/secure:

  proftpd: pam_env(proftpd:setcred): Unable to open config file: /etc/security/pam_env.conf: Permission Denied
  proftpd: pam_systemd(proftpd:session): Failed to connect to system bus: Permission Denied

Cause

SELinux prohibits using passive ports for FTP connection.

Resolution

1. Connect to the server using SSH.

2. Configure SELinux to allow passive ports during FTP connection:

   # setsebool -P ftpd_use_passive_mode 1