howto/upgrades.md

@@ -219,9 +219,20 @@ Try to run `apt update` by hand to see if it fixes the issue:
     apt update
     /usr/share/prometheus-node-exporter-collectors/apt_info.py | grep timestamp
 
-If it does, it means a cron job is missing. Normally, unattended
-upgrades should update the package list regularly, check if the
-service timer is properly configured:
+If it does, it means a job is missing or failing. The metrics
+themselves are updated with a systemd unit (currently
+`prometheus-node-exporter-apt.service`, provided by the Debian
+package), so you can see the status of that with:
+
+    systemctl status prometheus-node-exporter-apt.service
+
+If that works correctly (i.e. the metric in
+`/var/lib/prometheus/node-exporter/apt.prom` matches the
+`apt_info.py` output), then the problem is the package lists are not
+being updated.
+
+Normally, unattended upgrades should update the package list
+regularly, check if the service timer is properly configured:
 
     systemctl status apt-daily.timer