3R Monitor

3R Monitor watches your Linux servers and the websites and APIs they run. It emails you when something goes down, and again when it recovers. It is freeware by 3R Soft: free for personal and commercial use, on as many servers as you own or operate.

This documentation covers version 1.1.1.

How it worksCopy Anchor Link

One program, 3rmonitor (a single file written in Go, with no dependencies), has two roles:

  web-1  (agent) ──┐
  web-2  (agent) ──┼──►  master  ──►  alert emails
  db-1   (agent) ──┘     (panel)
                            │
                            └──►  checks websites, APIs, ports, DNS and certificates

The usual setup is master + agent on the first server, so that it monitors itself too, and the agent alone on every other server. Services where you can't install an agent (an external website, a database port, a DNS record) are checked from the master by their address.

What it monitorsCopy Anchor Link

• Servers: CPU (per core), memory, disks, load, bandwidth, processes, listening ports and network interfaces, with live charts and up to 30 days of history; traffic used per day and per month, with an optional monthly quota.
• Services and software: systemd services that failed or are enabled at boot but not running; the version and status of PHP, Apache, Nginx, MySQL / MariaDB, PostgreSQL, Redis, Docker, Supervisor, Node.js and more; Let's Encrypt certificate expiry dates.
• Websites and APIs: HTTP(S) status code, keyword and JSON field checks, TCP ports, Ping, SSL certificates and DNS records.
• Vulnerabilities: the latest published vulnerabilities, matched against the exact software and versions installed on each server. Critical and actively exploited ones are emailed the same day.
• Traffic: which countries and IPs send the most requests to your websites, and who is scanning you. Block or allow an IP, a range or a whole country with one click.
• AI analysis (optional, with your own model): daily and weekly reports, the vulnerabilities that really matter, the likely cause in outage emails, an assistant that answers questions, and an on-call engineer that investigates problems and applies the repairs you allow. Names and IPs are sent to the model as codes.

An outage is declared only after several failed checks in a row, so one slow response doesn't trigger an alert. The panel, the alert emails, the 3rmonitor command and the installer are available in English, Spanish and Chinese.

Where to startCopy Anchor Link

SectionsCopy Anchor Link

Quick referenceCopy Anchor Link