caddyserver/caddy · error

timeout cannot be less than 0

Error message

timeout cannot be less than 0

What it means

NetWriter.Provision guard on dial_timeout: a negative timeout is invalid (0 means no/default timeout), so the network log writer rejects the config before any connection is attempted; fires during provisioning validation.

Solutions

1. Set dial_timeout to a positive duration like 10s, or remove it to use the default
2. Use 0 (or omit) rather than a negative value to express 'default'

Example fix

// before
{"output": {"output": "net", "address": "udp/h:514", "dial_timeout": "-5s"}}

// after
{"output": {"output": "net", "address": "udp/h:514", "dial_timeout": "10s"}}

if d, err := time.ParseDuration(cfg.DialTimeout); err == nil && d < 0 {
    return fmt.Errorf("dial_timeout must be >= 0")
}

When it happens

Trigger: Setting dial_timeout to a negative value in the net writer config, e.g. {"dial_timeout": "-5s"} or 'dial_timeout -5s' in Caddyfile syntax.

Common situations: Sign typos in duration strings; templates subtracting from a timeout and going below zero; confusing a '0 means default' convention with negative sentinels.

Understand the failure class

• Timeouts: ETIMEDOUT, deadlines, and hung requests — what actually expires when a request times out.

Related errors

• invalid host in address
• multiple ports not supported
• parsing network address
• cannot add operation: maximum
• config missing, unable to create dev logger

AI-assisted analysis of caddyserver/caddy@50e54ee279 (2026-08-15). Data as JSON: /api/errors/76d4377edd3add2f. Report an issue: GitHub.

Appendix: source

Thrown at modules/logging/netwriter.go:77

// Provision sets up the module.
func (nw *NetWriter) Provision(ctx caddy.Context) error {
	repl := caddy.NewReplacer()
	address, err := repl.ReplaceOrErr(nw.Address, true, true)
	if err != nil {
		return fmt.Errorf("invalid host in address: %v", err)
	}

	nw.addr, err = caddy.ParseNetworkAddress(address)
	if err != nil {
		return fmt.Errorf("parsing network address '%s': %v", address, err)
	}

	if nw.addr.PortRangeSize() != 1 {
		return fmt.Errorf("multiple ports not supported")
	}

	if nw.DialTimeout < 0 {
		return fmt.Errorf("timeout cannot be less than 0")
	}

	return nil
}

func (nw NetWriter) String() string {
	return nw.addr.String()
}

// WriterKey returns a unique key representing this nw.
func (nw NetWriter) WriterKey() string {
	return nw.addr.String()
}

// OpenWriter opens a new network connection.
func (nw NetWriter) OpenWriter() (io.WriteCloser, error) {
	reconn := &redialerConn{
		nw:      nw,

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