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File broken after upload

Zero-byte files, corrupt jars and worlds after an upload: what went wrong and how to redo it safely.

1 min readUpdated 2026-09-14Diese Anleitung auf Deutsch lesen →

Symptoms

  • A jar shows 0 B or a few KB in the Files tab; the server says Invalid or corrupt jarfile / zip END header not found.
  • An unpacked world is missing level.dat, or region files are tiny.
  • A zip refuses to unarchive.

Causes

  1. The browser upload stopped halfway (tab closed, Wi-Fi hiccup). The file exists but is incomplete.
  2. ASCII transfer mode in an FTP client turned a binary jar into garbage. Set the client to binary.
  3. A download link that returned an HTML page instead of the file (login walls, "click to download" pages). The "jar" is a web page.
  4. Zipped with an extra folder level, so files ended up in world/world/.

Redo it

Delete the broken file, upload again with SFTP for anything large, and compare the size with the original. For links, use a direct download URL (right-click the download button → copy link) or let Kowalski fetch it. It checks that the result is a real file, not HTML.