NTP time server for closed networks
Runs an NTP server on a Mac so the devices on an isolated or air-gapped network sync to one clock. No internet connection required.
Download for macOSVersion 1.7.0 · macOS 13 or later · Universal · Automatic updates
Free for students, teachers and non-pro users. Paid work needs a license: see Pricing.
SiChronize Connect ↓ sets each client Mac or Windows PC to use this server.
Features
Runs offline
Set the time manually or use the Mac's clock. The server keeps time on a monotonic clock.
Standard port 123
Serves NTP on port 123 despite the macOS port-123 restriction. Clients need no special setup.
Optional upstream sync
Syncs from a primary and a secondary upstream source when one is reachable, with automatic failover.
Per-interface binding
Serves time only on the network interfaces you select.
Client list
Shows each client's address, whether it is direct or relayed, its last request and its request count.
Source checks
Monitors jitter, offset and stability for each upstream source, and rejects any time before 2026.
SiChronize Connect 1.8.0 — client setup
A one-time setup utility for each client Mac or Windows PC. It finds the server on the network and sets the computer to sync time at boot and every 30 minutes. If the client starts before the server, it keeps retrying for the first few minutes.
Connect finds the server by name when Advertise on network is on in SiChronize Server (the default). Across subnets or VLANs, enter the server's IP address in Connect.
All versions
Every version stays here after a newer one comes out.
-
1.7.0