NagMonThe Alerts tab
Alerts in NagMon come from your server's event history — the same state-change events Nagios records in its own log and shows in the web UI's history views. When a host goes Down or a service moves between OK, Warning, and Critical, that transition appears in the Alerts tab on the next refresh.
- Filtering — show all alerts, or narrow by type to focus on, say, host events only.
- Sorting — order by time (what happened most recently), severity (worst first), or host (group related events together). Like the other tabs, your sort choice is remembered.
Alert details
Each alert entry records what changed, when, and to what state — essentially a timestamped line of your infrastructure's story. Tap an alert to navigate to the affected host or service, where you'll find its current state, full plugin output, and the actions to acknowledge or schedule downtime.
Reading a burst of alerts is a skill worth developing: one host-Down alert followed by a wave of service Criticals on the same host usually means one problem, not ten. Sorting by host makes those patterns obvious.
Outages
The outages view answers a different question than Alerts. Alerts are history: everything that changed state recently, good and bad. Outages are current impact: hosts that are down or unreachable right now in a way that blocks monitoring or connectivity to other parts of your network — for example, a down switch that takes an entire rack of hosts to Unreachable with it.
When the outages view shows an entry, start there. Fixing the blocking host typically clears a whole cluster of red at once. The distinction between Down and Unreachable — and why Nagios models network topology with parent hosts — is covered in Nagios Host and Service States Explained.