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Time Sync

Disco can synchronize the system clock from GPS time broadcasters on the network. This is useful in airgapped environments where NTP is unavailable. The daemon listens for TIME_ANNOUNCE messages on the same UDP port as discovery (5354).

Prerequisites

At least one node on the network must run disco-gps-broadcaster or an equivalent (Arduino, ESP32). See GPS Broadcaster.

Configure

In /etc/disco/config.yaml:

time_sync:
  enabled: true
  min_sources: 2
  max_source_spread: 100ms
  max_stale_age: 30s
  max_dispersion: 1.0
  step_threshold: 128ms
  slew_threshold: 500us
  poll_interval: 60s
  require_signed: true
  allow_step_backward: false

Key tuning parameters:

  • min_sources: how many independent GPS broadcasters must agree before the daemon adjusts the clock. Set to 1 if you only have one GPS source.
  • step_threshold: offsets above this value cause an immediate clock step; offsets below it are slewed gradually.
  • allow_step_backward: keep false unless your environment has a reason to allow it. Stepping the clock backward can break log timestamps and certificate validity checks.

Restart the daemon

sudo systemctl restart disco-daemon

Check sync status

disco time

Synced: YES
Sources: 2
Offset: +0.000023 seconds
Last sync: 2026-06-13T10:30:00Z

If Synced: NO, the daemon has not received enough agreeing TIME_ANNOUNCE messages yet. Check that GPS broadcasters are running and reachable on the same broadcast domain.

Force a sync

disco timeset

The daemon applies an adjustment immediately using current sources, rather than waiting for the next poll_interval.

Signed time messages

Set require_signed: true to reject unsigned TIME_ANNOUNCE messages. This requires that the GPS broadcaster is configured to sign its messages with a key that is in the daemon's trusted peers list. See Enable Security for key setup.