docker/cli · error

cowardly refusing to save to a terminal. Use the -o flag or

Error message

cowardly refusing to save to a terminal. Use the -o flag or redirect

What it means

runExport refuses to write the raw tar archive produced by `docker export` to stdout when stdout is an interactive terminal and no -o/--output file was given. Dumping binary tar data to a TTY would garble the terminal, so the CLI 'cowardly refuses' (a nod to GNU tar's phrasing) unless output is redirected or a file is specified.

Source

Thrown at cli/command/container/export.go:52

		Annotations: map[string]string{
			"aliases": "docker container export, docker export",
		},
		ValidArgsFunction:     completion.ContainerNames(dockerCLI, true),
		DisableFlagsInUseLine: true,
	}

	flags := cmd.Flags()

	flags.StringVarP(&opts.output, "output", "o", "", "Write to a file, instead of STDOUT")

	return cmd
}

func runExport(ctx context.Context, dockerCLI command.Cli, opts exportOptions) error {
	var output io.Writer
	if opts.output == "" {
		if dockerCLI.Out().IsTerminal() {
			return errors.New("cowardly refusing to save to a terminal. Use the -o flag or redirect")
		}
		output = dockerCLI.Out()
	} else {
		writer, err := atomicwriter.New(opts.output, 0o600)
		if err != nil {
			return fmt.Errorf("failed to export container: %w", err)
		}
		defer writer.Close()
		output = writer
	}

	responseBody, err := dockerCLI.Client().ContainerExport(ctx, opts.container, client.ContainerExportOptions{})
	if err != nil {
		return err
	}
	defer responseBody.Close()

	_, err = io.Copy(output, responseBody)

View on GitHub (pinned to e9452d6e78)

Solutions

1. Write to a file with the flag: `docker export -o container.tar mycontainer`.
2. Redirect stdout: `docker export mycontainer > container.tar`.
3. Pipe it onward: `docker export mycontainer | gzip > container.tar.gz`.

Example fix

# before
docker export mycontainer
# after
docker export -o mycontainer.tar mycontainer

When it happens

Trigger: `docker export mycontainer` run in an interactive shell with stdout attached to a TTY and without `-o` and without piping/redirecting the output.

Common situations: First-time use of docker export interactively to 'see' the result; forgetting the redirect in an interactive session that works fine in scripts (where stdout is not a TTY); same pattern exists for docker save.

Related errors

• cowardly refusing to export to a terminal, specify a file pa
• cowardly refusing to save to a terminal. Use the -o flag or
• failed to parse hook template
• unexpected hook response type:
• plugin candidate path cannot be empty

AI-assisted analysis of docker/cli@e9452d6e78 (2026-08-01). Data as JSON: /data/errors/72fd0e6678261c20.json. Report an issue: GitHub.