hashicorp/nomad · warning

failed to resize tty: %v

Error message

failed to resize tty: %v

What it means

handleStdin processes stdin frames from the client; when a frame carries a TtySize it resizes the pty via setTTYSize. On failure it pushes this wrapped error onto errCh, which runTTY/runNoTTY surface to the caller. The process keeps running but the terminal resize did not apply.

Source

Thrown at drivers/shared/executor/exec_utils.go:199

			errCh <- err
			return
		}

		if m.Stdin != nil {
			if len(m.Stdin.Data) != 0 {
				_, err := stdin.Write(m.Stdin.Data)
				if err != nil {
					errCh <- err
					return
				}
			}
			if m.Stdin.Close {
				stdin.Close()
			}
		} else if m.TtySize != nil {
			err := setTTYSize(stdin, m.TtySize.Height, m.TtySize.Width)
			if err != nil {
				errCh <- fmt.Errorf("failed to resize tty: %v", err)
				return
			}
		}
	}
}

func handleStdout(logger hclog.Logger, reader io.Reader, wg *sync.WaitGroup, send func(*drivers.ExecTaskStreamingResponseMsg) error, errCh chan<- error) {
	defer wg.Done()

	buf := make([]byte, 4096)
	for {
		n, err := reader.Read(buf)
		// always send output first if we read something
		if n > 0 {
			if err := send(&drivers.ExecTaskStreamingResponseMsg{
				Stdout: &dproto.ExecTaskStreamingIOOperation{
					Data: buf[:n],
				},

View on GitHub (pinned to 482b49bf1a)

Solutions

1. Verify the task was started with tty=true if interactive resize is expected
2. Ignore/retry: the resize error is often transient after process exit; restart the exec session
3. Check /dev/pts availability in the execution environment
4. Update the client so resize frames are only sent for TTY sessions

Example fix

// before
// nomad alloc exec -task web /bin/sh  # task started without tty
// after
// ensure driver task config has tty = true, or omit TtySize frames for non-tty tasks

func canResize(taskTTY bool) error {
  if !taskTTY { return errors.New("resize frame requested for non-tty task") }
  if _, err := os.Stat("/dev/pts"); err != nil { return err }
  return nil
}

if err := attachExecSession(); err != nil {
  if strings.Contains(err.Error(), "failed to resize tty") {
    // transient: pty may have closed; retry once, then drop resize handling
    time.Sleep(100 * time.Millisecond)
    return retryAttach()
  }
  return err
}

When it happens

Trigger: Client sends a stdin message with TtySize set (terminal window resize in exec/alloc UI or `nomad alloc exec` with tty) and setTTYSize fails — most often because stdin is not actually a pty (TIOCSWINSZ ioctl fails ENOTTY) or the pty was already closed.

Common situations: Attaching to a non-TTY task that receives resize frames, pty closed after process exit while a resize frame is in flight, running inside environments without pty support (CI, restricted containers), Windows terminal clients negotiating sizes on non-pty sessions.

Related errors

• failed to start command: %v
• failed to get pty: %v
• attempted to resize a non-tty session
• not a terminal
• stdin is not supported

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/09932c096e56ce35. Report an issue: GitHub.