BoundaryML/baml · error

failed syncing destination

Error message

failed syncing destination %s: %w

What it means

copyFile calls destination.Sync() after copying to flush data to stable storage; if Sync fails the error is wrapped as "failed syncing destination". This guarantees the downloaded native library is durably on disk before use.

Solutions

1. Check and free disk space, then retry the download
2. Test whether the target filesystem supports fsync (try writing a file manually); relocate the cache to a standard local filesystem
3. Check dmesg/system logs for underlying I/O errors on the disk
4. Clear the destination file and re-run

// fsync only works on regular local filesystems; check mount
if isNetworkMount(filepath.Dir(dst)) {
    return fmt.Errorf("do not place library cache on network filesystem")
}

if err := baml.DownloadLibrary(dst); err != nil {
    if strings.Contains(err.Error(), "failed syncing") {
        // verify disk health and space; relocate cache to local fs and retry
        os.Remove(dst)
        return relocateAndRetry(dst)
    }
    return err
}

When it happens

Trigger: destination.Sync() returns non-nil after a successful io.Copy — typically fsync failing due to disk full, I/O errors, or unsupported-on-filesystem operations.

Common situations: Nearly-full disks on CI runners; exotic filesystems (some overlay/FUSE/network mounts) where fsync fails; failing hardware.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

• failed close destination
• failed copying from to
• decodeCheckedValue: valueChecked is nil
• decodeLiteralValue: valueLiteral is nil
• decodeRawObjectImpl is not set. Please call…

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/6b4f305d78791790. Report an issue: GitHub.

Appendix: source

Thrown at engine/language_client_go/baml_go/lib_common.go:660

	destination, err := os.Create(dst)
	if err != nil {
		return fmt.Errorf("failed create destination %s: %w", dst, err)
	}
	defer func() {
		cerr := destination.Close()
		if err == nil && cerr != nil {
			err = fmt.Errorf("failed close destination %s: %w", dst, cerr)
		}
	}()

	_, err = io.Copy(destination, source)
	if err != nil {
		return fmt.Errorf("failed copying from %s to %s: %w", src, dst, err)
	}

	err = destination.Sync()
	if err != nil {
		return fmt.Errorf("failed syncing destination %s: %w", dst, err)
	}

	logger.Debug("File copied successfully", "source", src, "destination", dst)
	return nil
}

func isSupportedPlatform() bool {
	osOk := runtime.GOOS == "darwin" || runtime.GOOS == "linux" || runtime.GOOS == "windows"
	archOk := runtime.GOARCH == "amd64" || runtime.GOARCH == "arm64"
	return osOk && archOk
}

func initSlog() {
	logLevel := slog.LevelInfo

	envLevel := os.Getenv("BAML_LOG")
	switch strings.ToUpper(envLevel) {
	case "TRACE":

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