kovidgoyal/kitty · error

Failed to write to SHM file with error: %w

Error message

Failed to write to SHM file with error: %w

What it means

After creating the SHM file, RunSSHAskpass writes the JSON request with shm.WriteWithSize at offset 1 (offset 0 is the ready flag). If that write fails (mapping too small, mmap error, I/O error), this fatal error is returned.

Source

Thrown at kittens/ssh/askpass.go:139

	q := map[string]any{
		"message":     msg,
		"type":        q_type,
		"is_password": !is_fingerprint_check,
	}
	data, err := json.Marshal(q)
	if err != nil {
		return fatal(err)
	}
	data_shm, err := shm.CreateTemp("askpass-*", uint64(len(data)+32))
	if err != nil {
		return fatal(fmt.Errorf("Failed to create SHM file with error: %w", err))
	}
	defer data_shm.Close()
	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

View on GitHub (pinned to 6d5d0c4406)

Solutions

1. Verify /dev/shm is a real tmpfs
2. Check dmesg for mmap/SHM errors
3. Retry; if persistent, report with the wrapped error details

if err := shm.WriteWithSize(f, data, 1); err != nil { /* log, close, unlink, abort askpass */ }

When it happens

Trigger: SHM file created with insufficient size for the payload, or mmap write failure on the shared memory region.

Common situations: Odd filesystem backing for /dev/shm that does not support the mmap semantics, or a truncated CreateTemp size due to integer issues.

Related errors

• Failed to create SHM file with error: %w
• Failed to flush SHM file with error: %w
• Failed to read from 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/dc65625b9f4a736e. Report an issue: GitHub.