What causes "failed to convert %s: %v" in vitessio/vitess?

Fix the my.cnf entry to contain a plain integer (e.g. port = 3306).

failed to convert %s: %v

Error message

failed to convert %s: %v

What it means

lookupInt fetches a my.cnf key via lookupWithDefault then strconv.Atoi's the string; if the value is present but not a valid integer, this error wraps the key name and Atoi error. It means the my.cnf holds a non-numeric value where an integer was expected.

Source

Thrown at go/vt/mysqlctl/mycnf.go:150

func (cnf *Mycnf) lookupWithDefault(key, defaultVal string) (string, error) {
	val := cnf.lookup(key)
	if val == "" {
		if defaultVal == "" {
			return "", fmt.Errorf("value for key '%v' not set and no default value set", key)
		}
		return defaultVal, nil
	}
	return val, nil
}

func (cnf *Mycnf) lookupInt(key string) (int, error) {
	val, err := cnf.lookupWithDefault(key, "")
	if err != nil {
		return 0, err
	}
	ival, err := strconv.Atoi(val)
	if err != nil {
		return 0, fmt.Errorf("failed to convert %s: %v", key, err)
	}
	return ival, nil
}

func normKey(bkey []byte) string {
	// FIXME(msolomon) People are careless about hyphen vs underscore - we should normalize.
	// But you have to normalize to hyphen, or mysqld_safe can fail.
	return string(bytes.ReplaceAll(bytes.TrimSpace(bkey), []byte("_"), []byte("-")))
}

// ReadMycnf will read an existing my.cnf from disk, and update the passed in Mycnf object
// with values from the my.cnf on disk.
func ReadMycnf(mycnf *Mycnf, waitTime time.Duration) (*Mycnf, error) {
	f, err := os.Open(mycnf.Path)
	if waitTime != 0 {
		timer := time.NewTimer(waitTime)
		for err != nil {
			select {

View on GitHub (pinned to 01a25a7d17)

Solutions

Fix the my.cnf entry to contain a plain integer (e.g. port = 3306).
Remove quotes, units, inline comments, or whitespace from the value.
Check provisioning scripts/template rendering for unexpanded variables.

Example fix

// before
port = "3306" ; primary port
// after
port = 3306

Defensive patterns

Strategy: validation

Validate before calling

for _, line := range strings.Split(string(data), "\n") {
	if k, v, ok := parseCnfLine(line); ok && k == "port" {
		if _, err := strconv.Atoi(strings.TrimSpace(v)); err != nil {
			return fmt.Errorf("mycnf port not numeric: %q", v)
		}
	}
}

Try / catch

val, err := mycnf.lookupInt("port")
if err != nil {
	return fmt.Errorf("bad my.cnf integer: %w", err)
}

Prevention

Keep my.cnf free of inline comments, quotes, and units on numeric options
Verify template rendering substitutes all variables
Add a config linter step in provisioning that Atoi-checks numeric fields

When it happens

Trigger: ReadMycnf calling lookupInt (e.g. for 'port') when the config value contains non-numeric characters, units ('3306M'), quotes, comments, or stray whitespace.

Common situations: Hand-edited my.cnf with values like port = 3306; # comment on same line; variables like port = ${PORT} left unexpanded; corruption from a provisioning tool.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/b1195ed74f60495d. Report an issue: GitHub.