taiclockd

## Name

taiclockd — announce the system's clock through TAICLOCK

## Synopsis

`taiclockd`

## Description

taiclockd announces the local UNIX clock through the TAICLOCK protocol. It accepts TAICLOCK requests from hosts around the Internet, and responds with the system's current time.

Normally taiclockd is run via a server program such as udp-socket-listen to listen for TAICLOCK queries from hosts around the Internet. It understands the `LISTEN_PID` and `LISTEN_FDS` environment variable convention for having an already-listening socket passed to it by such a program, and uses the last open file descriptor in the list that refers to a UDP/IPv6 socket. If no such open file descriptor is provided it falls back to opening its own UDP/IPv6 socket, bound to port 4014 of the IP address given by the value of the `IP` environment variable.

taiclockd is capable of handling both IPv4 and IPv6 requests on combined-stack systems.

Do not run `taiclockd` if your system is tuned by `xntpd`. See Daniel J. Bernstein's UTC, TAI, and UNIX time paper for further discussion.

## Security

taiclockd does not need to run as root.

## History

taiclockd was originally part of Daniel J. Bernstein's clockspeed toolset in 1998. It was converted to IPv6 in 2025 with the original IPv4-only tool renamed to taiclock4d(1).

## Author

Original code and documentation by Daniel J. Bernstein. Documentation modernizations by Jonathan de Boyne Pollard.