OpenNTPD

OpenNTPD is a lightweight, open-source implementation of the Network Time Protocol (NTP) daemon maintained as part of the OpenBSD project. It provides time synchronization for a system by acting as an NTP client to synchronize with remote time servers and, optionally, as an NTP server for clients on a local network. It is designed to be small, portable, and secure, with a focus on correctness and simplicity rather than feature richness. The codebase is tightly aligned with OpenBSD’s security philosophy, and while it originated with OpenBSD, it has been ported to other Unix-like systems.

OpenNTPD supports the essential NTP functionality required for typical network environments, including querying remote servers to discipline the local clock and, when configured, serving time to other hosts. The project emphasizes reliability and a conservative approach to timekeeping over the inclusion of a broad feature set.

Configuration is performed via a plain text file (commonly /etc/ntpd.conf) where administrators declare upstream servers and configure drift management, access controls, and networking parameters. A drift file is used to store the system’s frequency offset, allowing time to be gradually corrected after restarts or outages, which helps maintain long-term accuracy.

In practice, OpenNTPD is favored in OpenBSD deployments for its predictable behavior and reduced attack surface. It aims to provide dependable time discipline with a simpler, more auditable codebase than some larger NTP stacks. For environments requiring extensive NTP features, other implementations may be used, but OpenNTPD remains a core component of OpenBSD’s networking stack and is available on other platforms as a portable option.