slimtoolkit/slim · error

malformed HEALTHCHECK parameters: %q

Error message

malformed HEALTHCHECK parameters: %q

What it means

Thrown by the Dockerfile reverse-engineering parser when reconstructing a HEALTHCHECK instruction: the instruction body could not be split into the 4 required parameters (start-interval/check timing fields of the healthcheck flags). The parser splits the remainder of the HEALTHCHECK line on spaces with SplitN(..., 4) and requires all 4 parts; anything fewer means the parameters are structurally malformed, so the builder aborts with the offending data quoted.

Source

Thrown at pkg/docker/dockerfile/reverse/reverse.go:804

		}
		// Cleans HEALTHCHECK part and splits the first part further
		parts := strings.SplitN(instParts[0], " ", 2)
		// joins the first part of the string
		instPart1 := strings.Join(parts[1:], " ")
		// removes quotes from the first part of the string
		instPart1 = strings.ReplaceAll(instPart1, "\"", "")

		// cleans it to assign it to the pointer config.Test
		config.Test = strings.Split(instPart1, " ")

		// removes the } from the second part of the string
		instPart2 := strings.Replace(instParts[1], "}", "", -1)
		// removes extra spaces from string
		instPart2 = strings.TrimSpace(instPart2)

		paramParts := strings.SplitN(instPart2, " ", 4)
		if len(paramParts) < 4 {
			return strTest, &config, fmt.Errorf("malformed HEALTHCHECK parameters: %q", data)
		}
		for i, param := range paramParts {
			paramParts[i] = strings.Trim(param, "\"'")
		}

		var err error
		config.Interval, err = time.ParseDuration(paramParts[0])
		if err != nil {
			log.Errorf("[%s] config.Interval err = %v", paramParts[0], err)
		}

		config.Timeout, err = time.ParseDuration(paramParts[1])
		if err != nil {
			log.Errorf("[%s] config.Timeout err = %v", paramParts[1], err)
		}

		config.StartPeriod, err = time.ParseDuration(paramParts[2])
		if err != nil {

View on GitHub (pinned to 81940d17fa)

Solutions

1. Inspect the quoted data in the error and rewrite the HEALTHCHECK entry in image history/config metadata to the 4-parameter quoted form the parser expects.
2. If the source image's HEALTHCHECK is shell-form, drop the HEALTHCHECK metadata or convert it to JSON/exec form before running the reverse builder.
3. If the image is trusted and you only need the rest of the Dockerfile, pre-process the history to remove the malformed HEALTHCHECK instruction.

Example fix

// before (shell form in history)
HEALTHCHECK CMD curl -f http://localhost/ || exit 1
// after (exec/JSON form with all parameters)
HEALTHCHECK ["CMD", "curl", "-f", "http://localhost/"]

// validate HEALTHCHECK history entry before reverse-building
func validHealthcheck(hist string) bool {
	i := strings.Index(hist, "HEALTHCHECK")
	if i < 0 { return true }
	parts := strings.SplitN(strings.TrimSpace(hist[i+len("HEALTHCHECK"):]), " ", 4)
	return len(parts) == 4
}

if _, cfgErr := builder.Run(...); cfgErr != nil && strings.Contains(cfgErr.Error(), "malformed HEALTHCHECK") {
	// fall back: strip HEALTHCHECK from history and retry
}

When it happens

Trigger: Parsing a HEALTHCHECK instruction whose parameter section has fewer than 4 space-separated quoted parameters, e.g. `HEALTHCHECK CMD curl -f http://localhost/ || exit 1` without the surrounding JSON-array form (`HEALTHCHECK ["CMD", "curl", ...]`-style reconstruction) or with parameters collapsed onto fewer tokens, when calling the reverse Dockerfile builder (Run/NewBasicImageBuilder).

Common situations: Reconstructing Dockerfiles from OCI image history where the original HEALTHCHECK used shell form instead of exec/JSON form; hand-edited image history strings; images built by tooling that emitted non-standard HEALTHCHECK metadata.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• expected retries (%s) to be an escape sequence
• got an invalid escape sequence: %s
• when using JSON array syntax, arrays must be comprised of st
• unknown instruction
• only one escape parser directive can be used

AI-assisted analysis of slimtoolkit/slim@81940d17fa (2026-08-31). Data as JSON: /api/errors/71ad31599a5df2ad. Report an issue: GitHub.