FTP 220 Service Ready vs 421 Service Not Available
FTP 220 (Service Ready) is a 2xx Positive Completion response, while 421 (Service Not Available) is a 4xx Transient Negative response. 220 indicates that service ready for new user. This is the greeting message sent by the FTP server when a client first connects. 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.
คำอธิบาย
Service ready for new user. This is the greeting message sent by the FTP server when a client first connects.
เมื่อคุณพบเห็น
Immediately upon connecting to an FTP server. This is the welcome banner confirming the server is accepting connections.
วิธีแก้ไข
No fix needed — the server is ready. Proceed with USER and PASS commands to authenticate.
คำอธิบาย
Service not available, closing control connection. The server is shutting down or has reached its connection limit and cannot serve this request.
เมื่อคุณพบเห็น
When the FTP server is overloaded, shutting down for maintenance, or has reached its maximum number of concurrent connections.
วิธีแก้ไข
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.
ความแตกต่างหลัก
220 is a 2xx Positive Completion response, while 421 is a 4xx Transient Negative response.
FTP 220: Service ready for new user. This is the greeting message sent by the FTP server when a client first connects.
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 220 when immediately upon connecting to an FTP server. This is the welcome banner confirming the server is accepting connections.
You encounter 421 when when the FTP server is overloaded, shutting down for maintenance, or has reached its maximum number of concurrent connections.
ควรใช้อันไหนเมื่อไร
For 220 (Service Ready): No fix needed — the server is ready. Proceed with USER and PASS commands to authenticate. 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.