FTP error codes are three-digit replies your server sends back for every command — the first digit tells you the most important thing: codes starting with 4 are usually temporary and worth retrying, codes starting with 5 mean the server flatly rejected the request and retrying won’t help until something changes. Below are the codes people actually run into, grouped by what they’re about, with the most likely cause and fix for each.
How to read an FTP error code
You don’t need to memorize all of them — the first digit alone tells you how to react:
- 4xx (transient): the server understood the request but couldn’t complete it right now — a busy file, a dropped data connection, a temporary permissions hiccup. Often clears up on its own or with a small config change (like switching to passive mode).
- 5xx (permanent): the server understood the request and rejected it outright — wrong password, no permission, file doesn’t exist, quota exceeded. Retrying the exact same thing won’t help; something has to change first.
Connection and login codes
| Code | What it means | Most likely fix |
|---|---|---|
| 421 | Service not available, server is closing the connection — often a timeout, too many connections, or the server shutting down for maintenance. | Wait and retry. If it happens repeatedly, ask your host whether there’s a connection limit you’re hitting. |
| 425 | Can’t open the data connection — the control channel is fine, but the separate connection FTP uses to actually move data failed. | Almost always an active/passive mode or firewall mismatch. See FTP Active vs Passive Mode. |
| 426 | Connection closed, transfer aborted partway through. | Usually a dropped network connection. Retry the transfer; if it keeps happening on large files, check for an unstable connection or an overly aggressive firewall timeout. |
| 530 | Not logged in — wrong username or password, or the account doesn’t have access from your current IP. | Double-check credentials with your host. If you’re certain they’re correct, ask whether your IP needs to be allow-listed. |
File and storage codes
| Code | What it means | Most likely fix |
|---|---|---|
| 450 | Requested file action not taken — the file is unavailable right now, often because it’s locked or in use. | Retry after a moment. If it’s consistent, check whether another process has the file open. |
| 452 | Requested action not taken — insufficient storage space on the server. | Free up space on the server or check your hosting plan’s storage quota. |
| 550 | Requested action not taken, file unavailable — by far the most common one, usually meaning the file/directory doesn’t exist, or you don’t have permission. | Confirm the path is correct and check the file or directory’s permissions on the server. |
| 552 | Requested file action aborted — exceeded storage allocation for the current directory or account. | Same as 452: this is a quota problem, not a connection problem. |
| 553 | Requested action not taken, file name not allowed — the filename itself is invalid for the server’s filesystem (bad characters, reserved names). | Rename the file to remove special characters and try again. |
Command codes (less common, but confusing when they show up)
| Code | What it means | Most likely fix |
|---|---|---|
| 500 / 501 | Syntax error — the command itself, or its parameters, wasn’t recognized by the server. | Usually a client/server compatibility quirk rather than something you typed. Update your FTP client and try again. |
| 502 | Command not implemented — the server doesn’t support that command at all. | Nothing to fix on your end; the server (or the protocol mode you’re using) just doesn’t offer that feature. |
| 503 | Bad sequence of commands — your client sent commands in an order the server didn’t expect. | Almost always a client bug rather than a user error. Worth reporting if it’s reproducible. |
Still stuck?
If your transfers are failing or files aren’t deleting without a clear error code attached, that’s usually a different kind of problem — see What to Do if Files Are Not Transferred or Deleted for permission, passive-mode, and queue-specific causes that don’t always surface as a numbered code.
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