prometheus/node_exporter · error

couldn't get sysctl

Error message

couldn't get sysctl: %w

What it means

The FreeBSD netisr collector reads each configured sysctl OID (via the gosysctl-style m.Value() call) to export netisr queue/processing metrics. Any failure reading a sysctl value is wrapped as 'couldn't get sysctl' and aborts the Update, dropping all node_netisr_* metrics for that scrape.

Solutions

1. Run `sysctl net.isr` (or the specific OID) manually on the host to confirm it exists and is readable.
2. If inside a jail, run node_exporter on the host or grant the jail access to the needed sysctls.
3. Check the FreeBSD version matches what the node_exporter release supports; upgrade the exporter for newer/renamed OIDs.
4. Read the wrapped inner error to see which sysctl name failed.
5. Temporarily disable the collector (--collector.disable-defaults, enable others) if netisr metrics are not required.

// preflight on FreeBSD: verify sysctl OIDs are readable
for _, name := range []string{"net.isr.num_threads", "net.isr.drop"} {
	if _, err := sysctl.Sysctl(name); err != nil {
		return fmt.Errorf("sysctl %s unreadable: %w", name, err)
	}
}

err := collector.Update(ch)
if err != nil && strings.Contains(err.Error(), "couldn't get sysctl") {
	logger.Warn("netisr sysctl unavailable; skipping netisr scrape", "cause", err)
	return nil
}

When it happens

Trigger: m.Value() fails for one of c.sysctls: the OID does not exist on this kernel (netisr disabled or renamed), the sysctl name string is malformed, or reading is denied by permissions/jail restrictions.

Common situations: Running inside a FreeBSD jail where netisr sysctls are hidden; FreeBSD version differences that renamed or removed net.*.netisr OIDs; building with a stale sysctl list after a FreeBSD upgrade; typos in collector-maintained sysctl names.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

• Data Size mismatch
• sysctl(vm.stats.vm.v_page_size) failed
• couldn't get memory
• invalid TCP states data: expected
• could not retrieve CPU times

AI-assisted analysis of prometheus/node_exporter@17ddd77c59 (2026-09-07). Data as JSON: /api/errors/4bb5797a7c691a15. Report an issue: GitHub.

Appendix: source

Thrown at collector/netisr_freebsd.go:92

				valueType:   prometheus.GaugeValue,
			},
			{
				name:        "maxthreads",
				description: "netisr maximum thread count",
				mib:         "net.isr.maxthreads",
				dataType:    bsdSysctlTypeUint32,
				valueType:   prometheus.GaugeValue,
			},
		},
		logger: logger,
	}, nil
}

func (c *netisrCollector) Update(ch chan<- prometheus.Metric) error {
	for _, m := range c.sysctls {
		v, err := m.Value()
		if err != nil {
			return fmt.Errorf("couldn't get sysctl: %w", err)
		}

		ch <- prometheus.MustNewConstMetric(
			prometheus.NewDesc(
				prometheus.BuildFQName(namespace, netisrCollectorSubsystem, m.name),
				m.description,
				nil, nil,
			), m.valueType, v)
	}

	return nil
}

View on GitHub (pinned to 17ddd77c59)