Docs The addons agent Sensors

Sensors

Checks run on a schedule. Sensors run continuously, subscribed to the kernel, and report the moment something happens on the box the agent runs on.

New in addons 0.2.0. Linux only. Gated behind agent.enable_sensors, so a config naming a sensor without that fails at startup, like the privileged addons.

Sensor	Watches	Needs
`nftwatch`	The host’s nftables ruleset. Reports the moment it changes. Sends only ruleset hashes and object counts, never the rules.	`CAP_NET_ADMIN`
`network`	Every inbound TCP connection attempt, through a pass-only eBPF program that can observe and never drop, redirect or rewrite. Aggregated by port and redacted remote prefix.	`CAP_BPF`, `CAP_NET_ADMIN`
`authwatch`	SSH and sudo authentication events from the system journal, matched strictly against the distribution’s exact message forms. Usernames and raw messages are never sent; remote addresses are reduced to a /24 or /64.	journal read access
`filewatch`	An explicit set of files and shallow directory roots. inotify is only a wake-up; every event settles into a stat reconciliation, so an atomic editor replace is a confirmed change. Events carry path, type, owner, mode and SHA-256, never contents.	read access
`listeningports`	The kernel’s TCP and UDP listener inventory against an explicit baseline. Undeclared and vanished listeners become events. Exact addresses and PIDs never enter events.	none
`servicewatch`	An explicit list of systemd units: failures, recoveries, restart-loop crossings, unit-file hash changes, and a service whose command became a different binary.	none
`pressure`	Kernel PSI stall triggers for CPU, memory and I/O. One event per crossing, one per recovery.	none

Several run under the stock unit with an empty capability set. The kernel-attached ones take one narrow capability through a local systemd drop-in; the tarball’s README has the exact drop-in for each.

agent:
  enable_sensors: [nftwatch, network]

sensors:
  - id: host-firewall
    sensor: nftwatch
    with: { netns: host, settle: 250ms, reconcile: 5m }
  - id: public-ingress
    sensor: network
    with:
      interfaces: [eth0]
      direction: ingress
      ports: [22, 80, 443]
      window: 60s

The agent’s heartbeat carries sensors, sensor_events and sensor_failures, so a sensor that stops sensing is itself a rule away from paging someone.

Privacy is the design, not a settingEvery sensor is built so that contents, usernames and exact addresses never leave the box. What reaches the tower is that something changed, where, and a hash.