slimtoolkit/slim · error

bad output tar

Error message

bad output tar - %s

What it means

After merging the layer maps, OnCommand writes the merged data to a tar file via tarFromMap and then validates the output: the file must exist, be a regular file, and be a readable tar archive. If any check fails, the command aborts with 'bad output tar'. The merge produced an unusable output artifact.

Solutions

1. Check free disk space and write permissions in the output directory, then re-run the merge.
2. Re-pull both source images to rule out corrupted/partial layer data (`docker pull image1 && docker pull image2`).
3. Run with --debug/verbose logging to see the error returned by tarFromMap that is being discarded before the validation.
4. Report a bug: the handler ignores tarFromMap's error (`err :=` discarded), so validation failures mask the root cause.

Example fix

// before
outTarFileName, err := tarFromMap(logger, "", index)
if !fsutil.Exists(outTarFileName) || ... {
    xc.FailOn(fmt.Errorf("bad output tar - %s", outTarFileName))
}
// after
outTarFileName, err := tarFromMap(logger, "", index)
if err != nil {
    xc.FailOn(fmt.Errorf("failed to build output tar: %w", err))
}
if !fsutil.Exists(outTarFileName) || ... {
    xc.FailOn(fmt.Errorf("bad output tar - %s", outTarFileName))
}

df -h . | awk 'NR==2 {exit ($5+0 > 90 ? 1 : 0)}' || { echo "disk nearly full"; exit 1; }
[ -w . ] || { echo "output dir not writable"; exit 1; }

if err := runMerge(args); err != nil && strings.Contains(err.Error(), "bad output tar") {
    // free disk space / re-pull images, then retry once
}

When it happens

Trigger: tarFromMap returns an empty/unset filename (error swallowed — err is not checked) or writes a corrupt/missing file, so fsutil.Exists/IsRegularFile/IsTarFile fails in merge/handler.go:274.

Common situations: Disk full or permission denied in the output directory so the tar write failed silently; source image layers corrupted or partially pulled; filesystem not supporting the temp file; tarFromMap failing internally but its error ignored by the caller.

Related errors

• cannot write file
• failed to calculate relative path
• failed to read file into the tar
• failed to scan files
• not implemented archiving file type

AI-assisted analysis of slimtoolkit/slim@81940d17fa (2026-08-31). Data as JSON: /api/errors/0b4a4e5a80a667cc. Report an issue: GitHub.

Appendix: source

Thrown at pkg/app/master/command/merge/handler.go:274

			//	info.Replaced = append(other.Replaced, other)
			//	index[p] = info
			//	continue
			//}

			other.Dups++
			continue
		}

		info.Replaced = append(other.Replaced, other)
		index[p] = info
	}

	outTarFileName, err := tarFromMap(logger, "", index)

	if !fsutil.Exists(outTarFileName) ||
		!fsutil.IsRegularFile(outTarFileName) ||
		!fsutil.IsTarFile(outTarFileName) {
		xc.FailOn(fmt.Errorf("bad output tar - %s", outTarFileName))
	}

	xc.Out.State("image.data.merge.done")
	xc.Out.State("output.image.generate.start")

	ibo, err := imagebuilder.SimpleBuildOptionsFromImageConfig(outImageConfig)
	xc.FailOn(err)

	ibo.Tags = outputTags

	layerInfo := imagebuilder.LayerDataInfo{
		Type:   imagebuilder.TarSource,
		Source: outTarFileName,
		Params: &imagebuilder.DataParams{
			TargetPath: "/",
		},
	}

View on GitHub (pinned to 81940d17fa)