Cannot use FTPS in Backup Manager: An unknown option was passed in to libcurl

Symptoms

• Plesk Onyx 17.8 Update #1 or #2 is installed on the server:

  # plesk -v
  Product version: Plesk Onyx 17.8.11 Update #1
  
  

  An error is displayed on attempt to configure FTPS in Plesk > Tools & Settings > Backup Manager > Remote Storage Settings > FTP:

  PLESK_ERROR: Error: Unable to access the storage: Transport error: unable to list directory: Curl error: (48) An unknown option was passed in to libcurl: Last FTP request: Last FTP response:
  Make sure you have entered the correct storage settings. You can check them independently with the command:
  curl -v --ftp-pasv --ssl -k -u ftp-user 'ftp://example.com//backups//'

• The command in the error works correctly on the server

• Following warnings are displayed in Plesk > Tools & Settings > Backup Manager if FTP storage was already configured:

  PLESK_WARN: Warning: Unable to display the list of backups from FTP storage Unable to get ftp dumps list: FTP network error. Check the FTP storage settings.

  PLESK_WARN: Warning: Unable to access the storage: Transport error: unable to list directory: Curl error: (48) An unknown option was passed in to libcurl: Last FTP request: Last FTP response:
  Make sure you have entered the correct storage settings. You can check them independently with the command:
  curl -v --ftp-pasv --ssl -k -u ftp-user 'ftp://example.com//backups//'

  OR
  Following error is displayed instead of Backup Manager:

  PLESK_ERROR: Error: FTP network error

• Similar lines can be found in the /var/log/plesk/panel.log:

  CONFIG_TEXT: ERR [panel] Failed to get dump 'backup_1803100000.tar': Error code: 126: FTP network error
  ERR [panel] FTP network error

• If scheduled backups are stored on the remote FTP storage, following error can be found in the /usr/local/psa/PMM/logs/backup-<date>/backup.log:

  CONFIG_TEXT: INFO: TransportError[babecafe-3a5d-4578-dada-b2d6b441e241]: Transport error: unable to check file existence: Curl error: (48) An unknown option was passed in to libcurl: Last FTP request: Last FTP response: [common/plesk-utils/PMM/repository-transport/transport.cpp:1196]
  virtual bool plesk::tRepositoryFtp::IsExist(const string&)
  INFO: pmm-ras finished. Exit code: 126

• Following error is also sent to the administrator's mail address if the scheduled backups are configured:

  PLESK_INFO: FTP network error
  Unable to access the storage: Transport error: unable to list directory: Curl error: (48) An unknown option was passed in to libcurl: Last FTP request: Last FTP response:
  Make sure you have entered the correct storage settings. You can check them independently with the command:
  curl -v --ftp-pasv --ssl -k -u ftp-user 'ftp://example.com//backups//'

• FTPS is enabled in the remote configuration:

  # plesk db -Ne 'SELECT value FROM BackupsSettings WHERE param = "backup_ftp_settinguse_ftps"'
  true

Cause

Plesk bug with ID #PPPM-8125, that will be fixed in upcoming updates.

Resolution

As a workaround, disable FTPS directly in the remote FTP configuration:

1. Log into Plesk
2. Navigate to Plesk > Tools & Settings > Backup Manager > Remote Storage Settings > FTP
3. Disable Use FTPS and apply changes

Note: If FTP network error is displayed instead of the Backups Manager, use the following article to access it: Cannot access Backup Manager: 504 Gateway Timeout