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 the transfer is interrupted, by user or because of dropped connection, partial file (with .filepart extensions) remains in the target folder. Once you attempt to transfer the same file again, WinSCP looks for the partial file. If it finds any, 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, automatic resuming of file transfer is supported only for files larger then a given threshold. By default the threshold is 100 kB. This can be configured on Resume 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.

When you attempt to transfer file that already exists in target directory and target file is smaller then source file, the overwrite confirmation dialog offers either Resume button directly or Append button (when appending is supported). After pressing an Append button another prompt will be displayed offering you either to append source file or to resume transfer.

If you select to resume transfer, the part of source file equal to size of the target file will be skipped and only the remaining part will be transferred.

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.

It is on user responsibility that he/she resumes transfer with the same version of source file as the transfer was interrupted. Otherwise you will end with target file consisting partly of previous version and partly of current version of the source file. For automatic resume, if the partial file is bigger than the source file, WinSCP will display error and disallow resume.

If the target file already 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 protocol, when connection is broken, WinSCP can automatically reconnect and resume the transfer2. This can be configured on Resume tab of Preferences dialog.