FTP 200 Command OK vs 421 Service Not Available
FTP 200 (Command OK) is a 2xx Positive Completion response, while 421 (Service Not Available) is a 4xx Transient Negative response. 200 indicates that the command has been successfully executed. This is a general acknowledgment that the command was understood and carried out. In contrast, 421 means that service not available, closing control connection. The server is shutting down or has reached its connection limit and cannot serve this request.
描述
The command has been successfully executed. This is a general acknowledgment that the command was understood and carried out.
何时出现
After issuing any command that completes successfully, such as TYPE, MODE, or NOOP.
如何修复
No fix needed — the command succeeded. This is the standard positive response for commands that don't return data.
描述
Service not available, closing control connection. The server is shutting down or has reached its connection limit and cannot serve this request.
何时出现
When the FTP server is overloaded, shutting down for maintenance, or has reached its maximum number of concurrent connections.
如何修复
Wait a few minutes and try reconnecting. If persistent, check if the server has a connection limit and whether your IP is being rate-limited.
主要区别
200 is a 2xx Positive Completion response, while 421 is a 4xx Transient Negative response.
FTP 200: The command has been successfully executed. This is a general acknowledgment that the command was understood and carried out.
FTP 421: Service not available, closing control connection. The server is shutting down or has reached its connection limit and cannot serve this request.
You encounter 200 when after issuing any command that completes successfully, such as TYPE, MODE, or NOOP.
You encounter 421 when when the FTP server is overloaded, shutting down for maintenance, or has reached its maximum number of concurrent connections.
何时使用哪个
For 200 (Command OK): No fix needed — the command succeeded. This is the standard positive response for commands that don't return data. For 421 (Service Not Available): Wait a few minutes and try reconnecting. If persistent, check if the server has a connection limit and whether your IP is being rate-limited.