Article ID: 125338, created on Apr 30, 2015, last review on Apr 30, 2015

  • Applies to:
  • Plesk 12.0 for Linux
  • Plesk 11.5 for Linux


Unable to connect to FTP server:

# ftp domain.tld 21
550 SSL/TLS required on the control channel
Login failed.
Remote system type is UNIX.
Using binary mode to transfer files.


Allow only secure FTPS connections option is enabled.


Set Allow both secure FTPS and non-secure FTP connections in

Plesk > Tools & Settings > Security Policy.

Search Words

550 SSL/TLS required

550 SSL/TLS required on the control channel


ftp connection fails

Unable to connect to ftp server

FTP connection does not work

Failed to retrieve directory listing

ftp does not work

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