FTP 421 Service Not Available vs 530 Not Logged In
FTP 421 and 530 both prevent the client from performing operations, but for different reasons. A 421 means the FTP service itself is unavailable (shutting down, too many connections), while a 530 means the user has not logged in or the login credentials were rejected.
Descrição
Service not available, closing control connection. The server is shutting down or has reached its connection limit and cannot serve this request.
Quando você o vê
When the FTP server is overloaded, shutting down for maintenance, or has reached its maximum number of concurrent connections.
Como corrigir
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.
Descrição
Not logged in. The user is not authenticated and must log in before the requested command can be executed.
Quando você o vê
When you try to access files or run commands before authenticating, or after providing incorrect login credentials.
Como corrigir
Send USER and PASS commands with valid credentials. If login fails repeatedly, verify the username, password, and check if the account is locked.
Diferenças principais
421 is a service-level issue — the server is closing the connection because it cannot serve any client right now.
530 is an authentication issue — the user has not successfully logged in with USER/PASS commands.
421 typically closes the control connection immediately after being sent.
530 keeps the connection open so the user can retry with correct credentials.
421 may be caused by server maintenance, connection limits, or idle timeouts; 530 is always about authentication.
Quando usar qual
Return 421 when the FTP server is shutting down, has reached its maximum connection limit, or the idle timeout has expired and the connection must be closed. Return 530 when a client tries to perform file operations without logging in first, or when the USER/PASS authentication fails. The client should retry login with correct credentials for 530, or reconnect later for 421.