To connect to the ftp server, the Internet centos cannot be connected through the ftp command. The ftp command under the Local cmd can be connected to the client.

Linux on the Internet cannot be connected to ftp_connect of php through ftp commands. I tried three machines and can ping them. However, the system remains in the waiting state during the initial connection, not to mention logging on to the ftp server. However, the local windows Server can be connected through the ftp commands in the client or cmd... linux on the Internet cannot be connected to ftp_connect of php through ftp commands. I tried three machines and can ping them. However, the system remains in the waiting state during the initial connection, not to mention logging on to the ftp server.
However, you can connect to and log on to the local windows server by using ftp commands on the client or cmd.
The firewall of the ftp server has been disabled. The default ftp port is 21.

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Linux on the Internet cannot be connected to ftp_connect of php through ftp commands. I tried three machines and can ping them. However, the system remains in the waiting state during the initial connection, not to mention logging on to the ftp server.
However, you can connect to and log on to the local windows server by using ftp commands on the client or cmd.
The firewall of the ftp server has been disabled. The default ftp port is 21.

Telnet to check whether your interface is open to the public network.
According to your statement, your port 21 cannot be accessed under the public network.