htpdate

htpdate [options] host...

htpdate synchronizes the local system time using HTTP headers from web servers. It extracts the Date header from HTTP responses, providing time synchronization without dedicated NTP ports.
This is useful in restricted network environments where:
- NTP (port 123) is blocked by firewalls
- Only HTTP/HTTPS traffic is allowed
- Time synchronization is needed but NTP servers are inaccessible
htpdate can query multiple servers and average the results for better accuracy. It supports both one-time synchronization and daemon mode for continuous adjustment.

-q

Query only; don't set time

Set time immediately (step)

Adjust for systematic drift

Adjust time gradually (slew)

Run as daemon

Use syslog for logging

Turn off sanity time check

Run as specified user

Create PID file

Less accurate than NTP (HTTP timestamps have one-second resolution). Depends on web servers having accurate time. Network latency affects accuracy. HTTPS requires additional processing that may affect precision.

htpdate was created by Eddy Vervest as an alternative to NTP for environments where NTP traffic is restricted. It leverages the ubiquity of HTTP access to provide basic time synchronization.

ntpd(8), chrony(8), systemd-timesyncd(8), date(1)