Backup to FTP fails in active mode if Plesk firewall uses default settings: unable to list directory: Curl error: (28) Timeout was reached

Symptoms

• Backup to FTP fails in active mode if Plesk firewall uses default settings:

  PLESK_ERROR: Error: Unable to access to the storage:
  Transport error: unable to list directory: Curl error: (28) Timeout was reached: Last FTP request: LIST -a Last FTP response: 200 Type set to A Make sure you have entered the correct storage settings.
  You can check them independently with the command: curl -v -P - -u ftpuser ftp://203.0.113.2

  OR

  PLESK_ERROR: Error: Unable to access to the storage:
  Transport error: unable to list directory: Curl error: (28) Timeout was reached: Last FTP request: LIST -a Last FTP response: 200 Switching to ASCII mode Make sure you have entered the correct storage settings.
  You can check them independently with the command: curl -v -P - -u ftpuser ftp://203.0.113.2

•  "Use passive mode" option in Backup Manager > FTP Storage Settings is disabled;

•  There are the following records in /var/log/plesk/PMM/pmmcli.log file:

  CONFIG_TEXT: [2018-11-07 10:43:52.201|5514] INFO: Subprocess raised ExecuteException: Subprocess <subprocess[5517] '/usr/local/psa/admin/bin/pmm-ras --get-ftp-dump-list --lightweight-mode --dump-storage=ftps://ftp-username@203.0.113.2 --session-path=/var/log/plesk/PMM'> was finished with exit code 126
  == STDOUT ====================
  Transport error: unable to list directory: Curl error: (28) Timeout was reached: Last FTP request: LIST -a Last FTP response: 200 Type set to A
  == STDERR ====================
  
  [2018-11-07 10:43:52.202|5514] DEBUG: <pmmcli.GetDumpsListAction object at 0x1407a50>: response
  [2018-11-07 10:43:52.207|5514] INFO: Outgoing packet:
  <?xml version="1.0" ?><response>
  <errcode>126</errcode>
  <errmsg>Unable to get ftp dumps list: FTP network error</errmsg>
  <data>
  <dump-list skipped-files-count="">
  </dump-list>
  </data>
  </response>

•  Ftp backup is created with the following warning:

  PLESK_ERROR: Harness not finished running at /usr/local/psa/PMM/agents/shared/Storage/ArchiveStorage.pm line 196

Cause

This is an internal issue with ID #PPPM-6170 , which is planned to be fixed in future product updates.

Resolution

As a workaround, use passive mode for FTP connection: Tools and Settings > Backup Manager > FTP Storage Settings