FTP 150 File Status OK vs 421 Service Not Available
FTP 150 (File Status OK) is a 1xx Positive Preliminary response, while 421 (Service Not Available) is a 4xx Transient Negative response. 150 indicates that the file status is okay and the server is about to open the data connection for the transfer. This is the normal precursor to a file transfer. 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.
Description
The file status is okay and the server is about to open the data connection for the transfer. This is the normal precursor to a file transfer.
Quand vous le voyez
Right before a file download or upload begins, confirming the file is accessible and the data channel is being opened.
Comment résoudre
No fix needed — this means the transfer is about to start. If the transfer stalls after this reply, check firewall rules blocking the data connection.
Description
Service not available, closing control connection. The server is shutting down or has reached its connection limit and cannot serve this request.
Quand vous le voyez
When the FTP server is overloaded, shutting down for maintenance, or has reached its maximum number of concurrent connections.
Comment résoudre
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.
Différences clés
150 is a 1xx Positive Preliminary response, while 421 is a 4xx Transient Negative response.
FTP 150: The file status is okay and the server is about to open the data connection for the transfer. This is the normal precursor to a file transfer.
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 150 when right before a file download or upload begins, confirming the file is accessible and the data channel is being opened.
You encounter 421 when when the FTP server is overloaded, shutting down for maintenance, or has reached its maximum number of concurrent connections.
Quand utiliser lequel
For 150 (File Status OK): No fix needed — this means the transfer is about to start. If the transfer stalls after this reply, check firewall rules blocking the data connection. 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.