FTP Error 221: Service Closing Control Connection
FTP reply code 221 is sent by the server after the client issues a QUIT command, confirming the session is ending and the control connection will be closed. This is the normal, graceful end of an FTP session. After 221, the TCP connection on port 21 is terminated. If the server sends 221 without the client sending QUIT, it may be enforcing an idle timeout or shutting down. Any active data transfers should be completed before QUIT is issued — sending QUIT during an active transfer may result in incomplete files.
Status
221 Service Closing Control ConnectionExample
220 ftp.example.com FTP server ready
USER alice
331 Password required
PASS ****
230 User alice logged in
QUIT
221 GoodbyeHow to Troubleshoot
Confirm QUIT was sent intentionally
If the connection closed unexpectedly, check your FTP client logs to see if QUIT was sent. If not, the server may have timed out the connection due to inactivity.
Send NOOP to prevent idle timeouts
If your FTP client is idle for long periods, send NOOP commands periodically to keep the connection alive. Most FTP clients have a keep-alive setting that does this automatically.
Complete transfers before disconnecting
Ensure all data transfers are complete (you have received 226) before sending QUIT. Disconnecting during an active transfer may corrupt the file.
Common Causes
Normal session termination after QUIT
highThe client sent QUIT after completing all file transfers and the server acknowledged with 221. This is the expected end of every FTP session. The client should close its end of the TCP connection after receiving this response.
Server closing idle connection
mediumFTP servers enforce idle timeouts (typically 60-300 seconds). If the client does not send any commands within the timeout period, the server sends 221 and disconnects. This is normal behavior to free up server resources.
Server shutting down
lowDuring a graceful server shutdown, the FTP daemon sends 221 to all connected clients before stopping. This allows clients to cleanly close their connections.
Related Error Codes
Service Ready for New User
The FTP server is ready and accepting connections. This is the greeting banner sent upon connection.
Closing Data Connection, Transfer Complete
The file transfer completed successfully and the data connection is being closed.
Service Not Available, Closing Control Connection
The FTP server is unavailable and is closing the connection. The client should retry later.
References
| Specification | Section |
|---|---|
| RFC 959 | RFC 959 §4.2 |
Frequently Asked Questions
This reference was compiled from official RFCs, protocol specifications, and hands-on troubleshooting experience. AI tools were used primarily for formatting and organizing the content on the page.