Use and troubleshoot FTP
Troubleshoot common FTP failures
Classify failures by control, authentication, data, TLS, or filesystem layer before changing settings.
8 minute lesson
No greeting suggests DNS, routing, port, or service trouble. 530 points to authentication or account policy. Login followed by a hanging listing points to the data connection.
A TLS certificate error is not repaired by disabling validation. Fix the hostname, certificate chain, clock, or server configuration.
550 commonly means the requested file action is unavailable: inspect the remote path, working directory, permissions, quotas, and server logs. Preserve the exact numeric reply in your diagnosis.
Work from the outside inward:
- Resolve the hostname and reach the configured TCP port.
- Read the
220greeting. - Complete TLS and validate identity when required.
- Authenticate and reach
230. - Confirm
PWD, transfer type, and features. - Negotiate a data endpoint.
- Open the data connection.
- Observe
150, bytes, and final226.
A 425 points at step 6 or 7. A 426 means the data connection started and then failed. A 550 after RETR points at path or authorization, while a 552 during upload can point at storage allocation.
Compare client and server clocks for certificate and timestamp confusion. Compare the control peer, passive advertised address, and firewall logs for NAT problems. Keep FTPS data-channel TLS errors separate from ordinary TCP failures.
Do not disable certificate validation, open every firewall port, or grant broad filesystem permissions as diagnostic shortcuts. Those changes hide the first failing layer and create a security problem.
Take one real verbose trace and write a one-sentence diagnosis naming the first failed layer, exact reply, and next narrow test.
Lesson completed