grafana/k6 · error

unknown file prefix `%s` for file `%s`

Error message

unknown file prefix `%s` for file `%s`

What it means

ReadArchive encountered a tar entry whose path inside the archive starts with a directory prefix that is neither a known filesystem ('https', 'file') nor a legacy 'files'/'scripts' directory. The archive is malformed or produced by an incompatible k6 version — the entry's prefix cannot be mapped to any filesystem.

Source

Thrown at lib/archive.go:181

		case "files", "scripts": // old archives
			// in old archives (pre 0.25.0) names without "_" at the beginning were  https, the ones with "_" are local files
			pfx = "https"
			if len(name) >= 2 && name[0:2] == "/_" {
				pfx = "file"
				name = name[2:]
			}
			fallthrough
		case "https", "file":
			fileSystem := arc.getFs(pfx)
			name = filepath.FromSlash(name)
			if err = fsext.WriteFile(fileSystem, name, data, fs.FileMode(hdr.Mode)); err != nil { //nolint:gosec
				return nil, err
			}
			if err = fileSystem.Chtimes(name, hdr.AccessTime, hdr.ModTime); err != nil {
				return nil, err
			}
		default:
			return nil, fmt.Errorf("unknown file prefix `%s` for file `%s`", pfx, normPath)
		}
	}
	scheme, pathOnFs := getURLPathOnFs(arc.FilenameURL)
	var err error
	pathOnFs, err = url.PathUnescape(pathOnFs)
	if err != nil {
		return nil, err
	}
	err = fsext.WriteFile(arc.getFs(scheme), pathOnFs, arc.Data, 0o644) // TODO fix the mode ?
	if err != nil {
		return nil, err
	}

	return arc, nil
}

func normalizeAndAnonymizeURL(u *url.URL) {
	if u.Scheme == "file" {

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Regenerate the archive with a compatible k6 version (k6 archive script.js)
2. Verify the .tar archive was not manually repacked or corrupted

When it happens

Trigger: Thrown at lib/archive.go:181 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/b2da1c749ac4a75a. Report an issue: GitHub.