kovidgoyal/kitty · error

Failed to open image data output file: %s with error: %w

Error message

Failed to open image data output file: %s with error: %w

What it means

In the shared-memory transmission path, icat tried to os.Open the frame's on-disk file (frame.filename) before copying it into an shm segment, and the open failed.

Source

Thrown at kittens/icat/transmit.go:91

	} else {
		gc.SetAction(graphics.GRT_action_frame)
		gc.SetGap(int32(frame.delay_ms))
		gc.SetCompositionMode(utils.IfElse(frame.replace, graphics.Overwrite, graphics.AlphaBlend))
		if frame.compose_onto > 0 {
			gc.SetOverlaidFrame(uint64(frame.compose_onto))
		}
		gc.SetLeftEdge(uint64(frame.left)).SetTopEdge(uint64(frame.top))
	}
	return gc
}

func transmit_shm(imgd *image_data, frame_num int, frame *image_frame) (err error) {
	var mmap shm.MMap
	var data_size int64
	if frame.in_memory_bytes == nil {
		f, err := os.Open(frame.filename)
		if err != nil {
			return fmt.Errorf("Failed to open image data output file: %s with error: %w", frame.filename, err)
		}
		defer f.Close()
		if data_size, err = f.Seek(0, io.SeekEnd); err != nil {
			return fmt.Errorf("Failed to seek in image data output file: %s with error: %w", frame.filename, err)
		}
		if _, err = f.Seek(0, io.SeekStart); err != nil {
			return fmt.Errorf("Failed to seek in image data output file: %s with error: %w", frame.filename, err)
		}
		if mmap, err = shm.CreateTemp("icat-*", uint64(data_size)); err != nil {
			return fmt.Errorf("Failed to create a SHM file for transmission: %w", err)
		}
		if _, err = io.ReadFull(f, mmap.Slice()); err != nil {
			mmap.Close()
			mmap.Unlink()
			return fmt.Errorf("Failed to read data from image output data file: %w", err)
		}
	} else {
		data_size = int64(len(frame.in_memory_bytes))

View on GitHub (pinned to 6d5d0c4406)

Solutions

1. Check that the intermediate file still exists and is readable when transmission starts
2. Avoid aggressive temp-dir cleaners (systemd-tmpfiles, TMPDIR cleaner daemons) for icat runs
3. Retry the icat invocation; transient races usually clear

if _, err := os.Stat(frameFile); err != nil { /* regenerate frame before transmit */ }

if err != nil && strings.Contains(err.Error(), "Failed to open image data output file") { /* regenerate and retry once */ }

When it happens

Trigger: Frame data was written to a temp file that has been deleted or is unreadable (permissions, ENOENT) by the time transmit_shm runs.

Common situations: Temp cleanup races on busy systems; file removed by concurrent process; permission mismatch when running under different users; disk-backed tempdir issues.

Related errors

• Failed to seek in image data output file: %s with error: %w
• Failed to read data from image output data file: %w
• Failed to create a SHM file for transmission: %w
• Failed to convert image data output file: %s to absolute pat
• Failed to write image data to temp file for transmission: %w

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/c189500444dd85e5. Report an issue: GitHub.