FTP 110 Restart Marker Reply vs 421 Service Not Available
FTP 110 (Restart Marker Reply) is a 1xx Positive Preliminary response, while 421 (Service Not Available) is a 4xx Transient Negative response. 110 indicates that the server is sending a restart marker reply. The text is exact and not left to interpretation. This marker is used to indicate the point at which a file transfer should be restarted. 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 server is sending a restart marker reply. The text is exact and not left to interpretation. This marker is used to indicate the point at which a file transfer should be restarted.
何时出现
During a resumed file transfer when the server confirms the restart position in the data stream.
如何修复
No fix needed — this is a normal response during transfer recovery. If restarts keep failing, verify the marker format matches what your client expects.
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
110 is a 1xx Positive Preliminary response, while 421 is a 4xx Transient Negative response.
FTP 110: The server is sending a restart marker reply. The text is exact and not left to interpretation. This marker is used to indicate the point at which a file transfer should be restarted.
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 110 when during a resumed file transfer when the server confirms the restart position in the data stream.
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 110 (Restart Marker Reply): No fix needed — this is a normal response during transfer recovery. If restarts keep failing, verify the marker format matches what your client expects. 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.