What causes "error writing to stdout: %v" in kubernetes/kops?

Check the receiving end of the pipe did not exit early (avoid piping into commands that close early, or use `set -o pipefail` carefully)

kubernetes/kops · error

error writing to stdout: %v

Error message

error writing to stdout: %v

What it means

After successfully marshaling the dump to YAML, the command writes the bytes to the out writer (stdout). This error means that write failed. It is an I/O error, not a data error — the dump data itself was fine.

Source

Thrown at cmd/kops/toolbox_dump.go:305

			if err != nil {
				return fmt.Errorf("error creating pod log dumper: %w", err)
			}
			if err := logDumper.DumpLogs(ctx); err != nil {
				klog.Warningf("error dumping pod logs: %v", err)
			}
		}
	}

	if cloudResources != nil {
		switch options.Output {
		case OutputYaml:
			b, err := kops.ToRawYaml(cloudResources)
			if err != nil {
				return fmt.Errorf("error marshaling yaml: %v", err)
			}
			_, err = out.Write(b)
			if err != nil {
				return fmt.Errorf("error writing to stdout: %v", err)
			}
			return nil

		case OutputJSON:
			b, err := json.MarshalIndent(cloudResources, "", "  ")
			if err != nil {
				return fmt.Errorf("error marshaling json: %v", err)
			}
			_, err = out.Write(b)
			if err != nil {
				return fmt.Errorf("error writing to stdout: %v", err)
			}
			return nil

		default:
			return fmt.Errorf("unsupported output format: %q", options.Output)
		}
	}

View on GitHub (pinned to 4c8573c808)

Solutions

Check the receiving end of the pipe did not exit early (avoid piping into commands that close early, or use `set -o pipefail` carefully)
Verify disk space if redirecting to a file
Rerun and write to a file: kops toolbox dump -o yaml > dump.yaml

Defensive patterns

Strategy: try-catch

Validate before calling

// Pre-check stdout is writable
if f, ok := out.(*os.File); ok {
	if _, err := f.Stat(); err != nil {
		return fmt.Errorf("stdout unavailable: %w", err)
	}
}

Try / catch

_, err = out.Write(b)
if err != nil {
	var se *os.SyscallError
	if errors.As(err, &se) && errors.Is(se.Err, syscall.EPIPE) {
		// downstream consumer closed the pipe; not fatal for the data
	}
	return fmt.Errorf("error writing to stdout: %v", err)
}

Prevention

Avoid piping kops output into commands that exit early (use full output or a file)
Redirect to a file when disk space is uncertain after checking `df`
Use `cmd1 | cmd2 || true` carefully in scripts consuming dumps

When it happens

Trigger: Running `kops toolbox dump -o yaml` when the process stdout is closed, the pipe consumer exited (e.g. `| head` closed the pipe), or the output device returned an error (ENOSPC, EPIPE, bad fd).

Common situations: Piping into `head` or a grep that exits early; writing to a full disk via redirection; running in an environment with a broken/closed stdout.

Related errors

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/a6e4616b556de805. Report an issue: GitHub.