kovidgoyal/kitty · error

Failed to read from SHM file with error: %w

Error message

Failed to read from SHM file with error: %w

What it means

After the parent sets the ready flag, RunSSHAskpass reads the response back with shm.ReadWithSize. If the size header or payload read fails, this fatal error is returned, meaning the IPC round-trip was corrupted.

Source

Thrown at kittens/ssh/askpass.go:153

	defer func() { _ = data_shm.Unlink() }()

	data_shm.Slice()[0] = 0
	if err = shm.WriteWithSize(data_shm, data, 1); err != nil {
		return fatal(fmt.Errorf("Failed to write to SHM file with error: %w", err))
	}
	if err = data_shm.Flush(); err != nil {
		return fatal(fmt.Errorf("Failed to flush SHM file with error: %w", err))
	}
	trigger_ask(data_shm.Name())
	for {
		time.Sleep(50 * time.Millisecond)
		if data_shm.Slice()[0] == 1 {
			break
		}
	}
	data, err = shm.ReadWithSize(data_shm, 1)
	if err != nil {
		return fatal(fmt.Errorf("Failed to read from SHM file with error: %w", err))
	}
	response := ""
	if is_confirm {
		var ok bool
		err = json.Unmarshal(data, &ok)
		if err != nil {
			return fatal(fmt.Errorf("Failed to parse response data: %#v with error: %w", string(data), err))
		}
		response = "no"
		if ok {
			response = "yes"
		}
	} else {
		err = json.Unmarshal(data, &response)
		if err != nil {
			return fatal(fmt.Errorf("Failed to parse response data: %#v with error: %w", string(data), err))
		}
		if is_fingerprint_check {

View on GitHub (pinned to 6d5d0c4406)

Solutions

1. Ensure kitty and the ssh kitten askpass helper are the same version
2. Avoid killing the UI while an askpass prompt is open
3. Retry the ssh operation; persistent failures suggest protocol mismatch — upgrade kitty

data, err := shm.ReadWithSize(f, 1)
if err != nil { /* treat askpass session as failed, unlink and exit */ }

When it happens

Trigger: Parent process wrote a malformed size prefix, SHM region was resized/truncated, or the parent crashed mid-write leaving inconsistent data.

Common situations: kitty or the askpass UI process being killed while answering, version mismatch between the askpass helper and kitty changing the SHM protocol.

Related errors

• Failed to create SHM file with error: %w
• Failed to write to SHM file with error: %w
• Failed to flush SHM file with error: %w
• Failed to parse response data: %#v with error: %w
• Incorrect owner on pwfile: uid={shm.stats.st_uid} gid={shm.s

AI-assisted analysis of kovidgoyal/kitty@6d5d0c4406 (2026-08-27). Data as JSON: /api/errors/da0d6216bc59d748. Report an issue: GitHub.