netbirdio/netbird · warning

duration must not be negative

Error message

duration must not be negative

What it means

buildCaptureRequest reads the --duration/-d flag and refuses a negative value: a non-zero negative duration would be meaningless for the capture (the daemon stops the stream after the elapsed duration). It is a pure client-side flag validation, raised before the gRPC stream is opened.

Source

Thrown at client/cmd/capture.go:123

}

func buildCaptureRequest(cmd *cobra.Command, args []string) (*proto.StartCaptureRequest, error) {
	req := &proto.StartCaptureRequest{}

	if len(args) > 0 {
		expr := strings.Join(args, " ")
		if _, err := capture.ParseFilter(expr); err != nil {
			return nil, fmt.Errorf("invalid filter: %w", err)
		}
		req.FilterExpr = expr
	}

	if snap, _ := cmd.Flags().GetUint32("snap-len"); snap > 0 {
		req.SnapLen = snap
	}
	if d, _ := cmd.Flags().GetDuration("duration"); d != 0 {
		if d < 0 {
			return nil, fmt.Errorf("duration must not be negative")
		}
		req.Duration = durationpb.New(d)
	}
	req.Verbose, _ = cmd.Flags().GetBool("verbose")
	req.Ascii, _ = cmd.Flags().GetBool("ascii")

	outPath, _ := cmd.Flags().GetString("output")
	forcePcap, _ := cmd.Flags().GetBool("pcap")
	req.TextOutput = !forcePcap && outPath == ""

	return req, nil
}

func streamCapture(ctx context.Context, cmd *cobra.Command, stream proto.DaemonService_StartCaptureClient, out io.Writer) error {
	for {
		pkt, err := stream.Recv()
		if err != nil {
			if ctx.Err() != nil {

View on GitHub (pinned to 93e97f4bf1)

Solutions

1. Pass a positive duration (netbird debug capture -d 30s) or omit the flag to run until Ctrl+C
2. If the value is computed, clamp it: use the value only when > 0, e.g. netbird debug capture -d "${remaining}s" after checking remaining>0
3. Double-check for a stray leading dash introduced by flag style: --duration=-5s is parsed as the value -5s, which this check catches

Example fix

# before: computed value may be negative
netbird debug capture -d $((END-NOW))s

# after: guard in the caller or clamp
remaining=$((END-NOW)); [ "$remaining" -lt 1 ] && remaining=1
netbird debug capture -d ${remaining}s

// In scripts, clamp before invoking:
d=${CALC_SECONDS:-0}
if [ "$d" -gt 0 ] 2>/dev/null; then DUR="${d}s"; else DUR=""; fi
netbird debug capture -d "$DUR" # empty resets to default 0

When it happens

Trigger: Passing an explicitly negative duration: netbird debug capture --duration=-30s or -d -1m; a shell alias or script computing the duration from a subtraction that went negative (END-START where END < START, producing e.g. -45s). Note d != 0 gates the check, so zero means 'until interrupted' and is allowed.

Common situations: Automation scripts that compute a countdown and pass it through without clamping; typo of the minus sign; reusing a timeout budget variable that has already been spent.

Related errors

• invalid filter: %w
• invalid duration format: %v
• invalid anonymize level %q: use %q or %q
• --expiration must be a positive duration (e.g., 720h, 365d,
• cannot specify both --all flag and state name

AI-assisted analysis of netbirdio/netbird@93e97f4bf1 (2026-08-16). Data as JSON: /api/errors/98d05617ceb85d83. Report an issue: GitHub.