File Transfer Resume

WinSCP supports resuming file transfers with SFTP and FTP protocols. SCP protocol does not allow it.

When transferring file with SFTP protocol1, it is first transferred into a temporary file with .filepart extension. Only after the transfer is completed the extension is removed.

If your transfer is interrupted, a partial file (with .filepart extensions) remains in the target folder. After you try to transfer the file a second time, WinSCP looks for the partial file. If it finds a partial file, it offers you chance to resume the transfer (the confirmation can be disabled).

Note that partial files can be distinguished in file panel by special “torn sheet” overlay icon.

For performance reasons, WinSCP only supports automatic file transfer resumption for files larger than a given threshold. By default, the threshold is 100 KiB. This can be configured on Endurance tab of Preferences dialog. Also automatic resuming of text mode transfers is not supported.

There’s an alternative manual method to resume transfer, which can be used with FTP protocol.

If you attempt to transfer a file already in the target directory and the target file is smaller then the source file, the overwrite confirmation dialog displays a Resume button or an Append button (when appending is supported). After you click Append, WinSCP opens another prompt that lets you append source file or resume your transfer.

If you resume the transfer, WinSCP will skip a part of the source file equal to the target file’s size. The program will only transfer the remainder.

Note that you must have overwrite confirmations enabled to use the method.

The method is also useful for resuming transfers initiated by other clients and also to update log files. Manual resuming of text mode transfers with SFTP-4 and newer is not supported.

If you want to resume your transfer, you must use the same source file version as the interrupted transfer. If you do not, your target file will include the source file’s previous version and its current version. For automatic resume, if the partial file is bigger than the source file, WinSCP will display error and disallow resume.

If the target file exists and it is not write-able, but the target directory is, the file will may be transferred anyway with automatic resume. The error overwriting the file will occur only after the transfer finishes. It is because the file is first transferred into temporary file.

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With SFTP protocol, when connection is broken, WinSCP can automatically reconnect and resume the transfer2. This can be configured on Endurance tab of Preferences dialog.