Device showing as delayed polling for a while instead of offline


I’ve noticed in the last week or so, some devices are taking a long time to alert as offline.
For example, we powered off a device this morning and I’m unable to snmpwalk or ping the device (confirming it is offline), however it simply sits in the “Poller” section in Validate.php for a while (about 30 minutes) advising that polling took longer than 5 minutes.

Our down alert rule has no delays on alerting.

We use the new LibreNMS ‘dispatcher’ Service in a cluster (managed by Redis, the 3 dispatcher pollers are in the same group, the example device is in this poller group)

$ ./validate.php

Component Version
LibreNMS 1.60-18-g19a82e150
DB Schema 2020_02_05_224042_device_inserted_null (158)
PHP 7.2.24-0ubuntu0.18.04.2
MySQL 10.1.44-MariaDB-0ubuntu0.18.04.1
RRDTool 1.7.0


[OK] Composer Version: 1.9.3
[OK] Dependencies up-to-date.
[OK] Database connection successful
[OK] Database schema correct
[WARN] Some devices have not been polled in the last 5 minutes. You may have performance issues.
Check your poll log and see: