coredns/coredns · error

cache min TTL can not be negative: %d

Error message

cache min TTL can not be negative: %d

What it means

When the cache plugin's directive specifies a minimum positive-response TTL (`cache <zones> <pttl> <minpttl>`), the min TTL must not be negative. Unlike the main TTL, zero IS allowed for the min TTL (meaning no floor); only negative values trigger this error in cacheParse.

Source

Thrown at plugin/cache/setup.go:100

				ca.pcap = pcap
				if len(args) > 1 {
					pttl, err := strconv.Atoi(args[1])
					if err != nil {
						return nil, err
					}
					// Reserve 0 (and smaller for future things)
					if pttl <= 0 {
						return nil, fmt.Errorf("cache TTL can not be zero or negative: %d", pttl)
					}
					ca.pttl = time.Duration(pttl) * time.Second
					if len(args) > 2 {
						minpttl, err := strconv.Atoi(args[2])
						if err != nil {
							return nil, err
						}
						// Reserve < 0
						if minpttl < 0 {
							return nil, fmt.Errorf("cache min TTL can not be negative: %d", minpttl)
						}
						ca.minpttl = time.Duration(minpttl) * time.Second
					}
				}
			case Denial:
				args := c.RemainingArgs()
				if len(args) == 0 {
					return nil, c.ArgErr()
				}
				ncap, err := strconv.Atoi(args[0])
				if err != nil {
					return nil, err
				}
				ca.ncap = ncap
				if len(args) > 1 {
					nttl, err := strconv.Atoi(args[1])
					if err != nil {
						return nil, err

View on GitHub (pinned to 558c9757a9)

Solutions

1. Change the min positive TTL to 0 or a positive integer, e.g. `cache example.org 30 5`.
2. Drop the third argument if no floor is needed; the min TTL then defaults to 0.
3. Check whether minpttl <= pttl constraints make sense for your intent (min TTL should typically be <= the max TTL).

Example fix

// before (Corefile)
cache example.org 30 -5

// after
cache example.org 30 5

const minPttl = 5; if (!Number.isInteger(minPttl) || minPttl < 0) { throw new Error(`cache min success TTL must be >= 0, got ${minPttl}`); }

When it happens

Trigger: Corefile like `cache example.org 30 -5` where args[2] of the success clause parses to a negative integer and is assigned to ca.minpttl.

Common situations: Sign typos in generated configs, misplacing a hyphen from another directive, or misunderstanding that min TTL floor must be 0 or positive.

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

• cache TTL can not be zero or negative: %d
• invalid negative response TTL for serve_stale
• serve_stale response TTL must be a whole number of seconds
• serve_stale response TTL exceeds the DNS TTL range
• prefetch amount should be positive: %d

AI-assisted analysis of coredns/coredns@558c9757a9 (2026-09-06). Data as JSON: /api/errors/f0e731bcbe056f3b. Report an issue: GitHub.