Nagios, Nagstamon & Naemon

These three make up the monitoring stack I actually operated day to day, different tools, but one connected skill, so they get one page instead of three thin ones.

Nagios is the classic: host/service checks, plugins, and a monitoring core that's been around long enough to be genuinely battle-tested. Nagstamon sits on top of it as a desktop status aggregator; a permanent, glanceable view of what's red, so I notice a problem without needing to keep a browser tab open (even though I still do, because it's a neverending project). Naemon is the more advanced piece: a modern, actively developed fork of the same lineage, with better performance and configuration ergonomics, and it's what I migrated to during my apprenticeship, which was actually my finals project.

Most of what feeds them isn't off-the-shelf either. During my IBM apprenticeship at AMETRAS I wrote the scripts that actually gather the data (disk space, processor load, VPN status, and more, scoped by my supervisor) and format it the way Nagios and Naemon expect, then implemented the whole pipeline myself. See Monitoring & Alerting for how that came together.