An interrupted download is not automatically safe to resume. SFTP resumption assumes the existing local prefix belongs to the same remote file. If someone replaced the server export while your connection was down, appending the new remainder can produce a mixed, unusable result.

Establish what the partial file represents

Record the server, remote path, export version and local destination from the interrupted transfer. Ask the file owner whether the source remained unchanged. A filename such as latest-export.zip is weak evidence because its contents may be replaced without renaming it.

Prefer a dated, immutable export for a long transfer. If you cannot establish that the existing partial file matches the current source, retain it separately if useful and start a new download to a new local filename. Do not sacrifice a known complete copy to save a little transfer time.

Inside an authorised SFTP session, pwd shows the remote working directory and lpwd shows the local one. Use those checks before selecting paths. The lcd command changes the local destination directory; it does not move you around the server.

Resume a confirmed pair

OpenSSH documents reget remote-path local-path as a resumed download, equivalent to get with its -a option. Use the exact confirmed paths rather than a wildcard that might match several exports. Quote filenames containing spaces as required by the SFTP interface.

The manual explicitly warns that a different partial prefix can corrupt the result. A successful progress indicator does not verify that precondition, and matching file sizes alone cannot establish matching contents.

After transfer, compare the completed file with a checksum supplied for the stable source through the agreed channel. Open or validate the delivered artifact using its normal application, such as checking that the expected archive contents are present.

Keep the transfer note until the recipient accepts the file. If validation fails, preserve the details and obtain a fresh stable source instead of resuming the same uncertain pair repeatedly. Completion means the intended export is intact locally, not merely that the connection reached the end of a file.

Sources: Ubuntu documentation.