clockdiff - Linux


clockdiff measures the performance characteristics of the system clock by calculating its drift per second from an external reference source, typically a GPS receiver. This information is valuable for applications requiring precise timing, such as financial trading, scientific research, and network time synchronization.


clockdiff [options] <ntp server> <duration>


  • -h, –help: Display help information and exit.
  • -V, –version: Display version information and exit.
  • -d, –debug: Enable debug logging.
  • -f, –frequency: Calculate the clock frequency in Hz.
  • -s, –start: Start measuring at a specific time in seconds past epoch.
  • -p, –pps: Use the PPS signal as the reference source.
  • -c, –counts: Print the number of reference counts used for drift calculation.


Measure clock drift for 10 seconds using an NTP server:

clockdiff 10

Display clock frequency in Hz:

clockdiff -f 300

Start measuring after 10 seconds past epoch:

clockdiff -s 10 10

Common Issues

  • NTP server unreachable: Ensure the NTP server is accessible and responds to requests.
  • PPS signal not available: Not all systems have a PPS signal. Use the -s option to avoid this dependency.
  • Drift calculation is inaccurate: Increase the duration or use a more reliable reference source.


Use with crontab: Automate periodic clockdrift measurements by adding commands to crontab, such as:

0 0 * * * clockdiff -s 10 300

Combine with other tools: Use clockdiff to provide accurate timing information for other applications, such as htop:

htop --check-frequency $(clockdiff -f 60) -d

Related Commands

  • ntpdate: Synchronize the system clock with an NTP server.
  • hwclock: Manage the hardware clock.
  • timedatectl: Display and control system time settings.