File Transfer Resume

WinSCP supports resuming file transfers with SFTP and FTP protocols. SCP and WebDAV protocols do not allow it. With S3 protocol, transfer can be resumed only immediately by reconnecting a lost session, not later.

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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 command or an Append command (when appending is supported), in the drop down menu of the No button. 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.

With SFTP and FTP protocols, when connection is broken, WinSCP can automatically reconnect and resume the transfer.1 This can be configured on Endurance page of Preferences dialog.