GoogleContainerTools/skaffold · error

writing build output to file: %w

Error message

writing build output to file: %w

What it means

In `skaffold build` (cmd/skaffold/app/cmd/build.go:89), when --build-output is set, the rendered build results are written to the specified file via os.WriteFile with mode 0644. If writing the file fails, this error wraps the OS error.

Source

Thrown at cmd/skaffold/app/cmd/build.go:89

	return withRunner(ctx, out, func(r runner.Runner, configs []util.VersionedConfig) error {
		bRes, err := r.Build(ctx, buildOut, targetArtifacts(opts, configs))

		if quietFlag || buildOutputFlag != "" {
			cmdOut := flags.BuildOutput{Builds: bRes}
			var buildOutput bytes.Buffer
			if err := buildFormatFlag.Template().Execute(&buildOutput, cmdOut); err != nil {
				return fmt.Errorf("executing template: %w", err)
			}

			if quietFlag {
				if _, err := out.Write(buildOutput.Bytes()); err != nil {
					return fmt.Errorf("writing build output: %w", err)
				}
			}

			if buildOutputFlag != "" {
				if err := os.WriteFile(buildOutputFlag, buildOutput.Bytes(), 0644); err != nil {
					return fmt.Errorf("writing build output to file: %w", err)
				}
			}
		}

		return err
	})
}

func targetArtifacts(opts config.SkaffoldOptions, configs []util.VersionedConfig) []*latest.Artifact {
	var targetArtifacts []*latest.Artifact
	for _, cfg := range configs {
		for _, artifact := range cfg.(*latest.SkaffoldConfig).Build.Artifacts {
			if opts.IsTargetImage(artifact) {
				targetArtifacts = append(targetArtifacts, artifact)
			}
		}
	}
	return targetArtifacts

View on GitHub (pinned to a1189de023)

Solutions

1. Create the parent directory of the --build-output path before running (mkdir -p)
2. Fix permissions on the target file/directory so the running user can write (chmod/chown)
3. Point --build-output at a file path, not an existing directory
4. Check available disk space and that the filesystem is not mounted read-only

Example fix

// before
// skaffold build --build-output out/build.json   # out/ does not exist
// after
// mkdir -p out && skaffold build --build-output out/build.json

// Pre-flight the --build-output target before running
outPath := "out/build.json"
if dir := filepath.Dir(outPath); dir != "." {
    if err := os.MkdirAll(dir, 0o755); err != nil {
        return err
    }
}
if fi, err := os.Stat(outPath); err == nil && fi.IsDir() {
    return fmt.Errorf("--build-output target is a directory: %s", outPath)
}

if err := sh.Run("skaffold", "build", "--build-output", outPath); err != nil {
    if strings.Contains(err.Error(), "writing build output to file") {
        log.Fatalf("cannot write %s: create parent dir and check permissions", outPath)
    }
    return err
}

When it happens

Trigger: Running `skaffold build --build-output <path>` where the path is unwritable: parent directory does not exist, permission denied on the target or directory, target path is a directory, or disk is full.

Common situations: CI script pointing --build-output at a directory that was never created; read-only filesystem or volume in the CI container; file owned by another user; path is an existing directory rather than a file.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

• executing template: %w
• writing build output: %w
• writing k8s manifest to file: %w
• writing config to file: %w
• image %q context %q: %w

AI-assisted analysis of GoogleContainerTools/skaffold@a1189de023 (2026-09-05). Data as JSON: /api/errors/081d5eadbfda4c74. Report an issue: GitHub.