FTP 450 File Action Not Taken vs 550 File Unavailable
FTP 450 and 550 both indicate a file operation failed, but they differ in whether the error is recoverable. A 450 is a transient failure (the file is locked, the server is busy), while a 550 is a permanent failure (the file does not exist or the user lacks permission).
説明
Requested file action not taken. The file is unavailable due to being busy, locked by another process, or temporarily inaccessible.
このコードが表示される場合
When you try to access a file that is locked by another user or process, or when the server temporarily cannot process the file.
修正方法
Wait and retry the operation — the file may be locked by another transfer. If persistent, check server-side file locks and permissions.
説明
Requested action not taken. File unavailable — the file does not exist, the path is wrong, or you do not have permission to access it.
このコードが表示される場合
When you try to download, delete, or navigate to a file or directory that does not exist or is restricted by server permissions.
修正方法
Verify the file path and name are correct (FTP paths are case-sensitive on most servers). Check your user permissions with the server administrator.
主な違い
450 is transient (4xx) — the file exists but the action cannot be performed right now (locked, busy, in use).
550 is permanent (5xx) — the file does not exist, the path is wrong, or the user has no permission.
450 should be retried after a delay; 550 requires the user to fix the path, filename, or permissions.
450 can occur when another process has a lock on the file; 550 occurs when the file simply is not there.
550 is the most common FTP error — it usually means a typo in the path or insufficient directory permissions.
使い分け方
Return 450 when a file operation cannot proceed temporarily — the file is locked by another transfer, the server is at capacity, or a temporary I/O error occurred. Return 550 when the file definitively cannot be accessed — it does not exist, the directory is wrong, or the user's permissions do not allow the operation.