Diag: empty metrics explorer, confirm submission before blaming the query

Diag: metrics explorer empty after install

Symptom (exact): agent installed and running, but Metrics Explorer shows no data for the host, not even system metrics.

Likely causes: (a) agent not submitting (key/site), (b) querying the wrong thing, (c) clock skew.

Confirm:

1. datadog-agent status: forwarder accepting payloads? If 403/connection errors, stop here and run the 403 or proxy runbook. This is not a metrics problem.
2. In the app, Infrastructure, Hosts: is the host listed at all? Not listed means nothing is submitted (cause a). Listed but metrics empty is weirder, keep going.
3. Query system.cpu.user with no tags and a 1-hour window. System metrics are unconditional: if even these are missing, submission is broken.
4. Check the host clock against NTP. Skew breaks TLS to intake.

Fix: fix submission (key/site/proxy), or fix the query (metric name spelling, tag filters, wider window).

Verify: system.cpu.user graphs within two minutes of the fix. Then check your custom metric. Rule: system metrics first, custom second. If system metrics flow and yours does not, the emitter is the problem, not the agent.

The agent getting-started docs: the agent collects 75-100 system metrics every 15-20 seconds with datadog.agent.up OK on connect; the site/key docs cover the ghost-agent failure modes. Verified against live docs 2026-09-26.