SFTP Connection Error – Fixing ‘500 Syntax Error, Command Unrecognized’

ftpsftpUbuntu

I've been trying to connect to an FTP server using sftp. The connection closes with 500 Syntax error, command unrecognized:

...
debug1: ssh_exchange_identification: 220-Welcome To FTP Server

debug1: ssh_exchange_identification: 220-....

debug1: ssh_exchange_identification: 220 ....

debug1: ssh_exchange_identification: 500 Syntax error, command unrecognized

debug1: ssh_exchange_identification: 421 Login time exceeded. Closing control connection.

ssh_exchange_identification: Connection closed by remote host

Screenshot of the complete verbose output

Was wondering what will be the possible error and what the fix would be.

Best Answer

The welcome message is an FTP thing. The same with "500 Syntax error, command unrecognized" – That's an FTP error message. There's nothing like that in the SFTP protocol.

Their server responds with FTP protocol on the SSH/SFTP 22 port. It can also be FTPS vs. SFTP confusion. The FTPS is secure extension of the FTP. While the SFTP is different thing.

You cannot connect to an FTP server using an SFTP client. The FTP and SFTP are two completely different protocols. Use an FTP client, like the common Linux commandline ftp.

As the FTP server listens on a non-standard port (22), you have to do something like:

$ ftp
ftp> open example.com 22

Related Solutions

Firewall – IIS 7.5 FTP “error in the push function”

The chances are good that your firewall supports FTP by watching the control connection (basically what you pasted above) and opening ports dynamically to enable the data connection to be made (where it said: "150 Opening BINARY mode data connection.").

You've encrypted the control connection. The firewall can't see inside to do that.

What you'll want to do is edit the firewall to permit a range of ports (how many depends on the number of clients you'll have) to enter (or leave, if you're permitting "active" PORT commands instead of or in addition to PASV). You will then need to configure the FTP server to only use those ports.

It is hard / annoying, but I've seen it work with at least one secure FTP server

Ftp – vsftpd not responding to LIST

Agree with Luke404. Check that your vsftpd.conf has the following entries configured and your firewall allows the pasv_min & pasv_max port ranges (10000 - 100010 is just an example). Remember to restart the service if changes are made to the conf file.


    pasv_enable=YES
    pasv_min_port=10000
    pasv_max_port=10010
    pasv_address=[Public IP address of your server]

Best Answer

Related Solutions

Firewall – IIS 7.5 FTP “error in the push function”

Ftp – vsftpd not responding to LIST

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