auto
  #   €l–дY>”кn-jy@µq—оХ1hЯБ„O6Аї ?ч     Frequently Asked Questions

Table of Contents

  o 1. chrony compared to other programs
      ? 1.1. How does chrony compare to ntpd?
  o 2. Configuration issues
      ? 2.1. What is the minimum recommended configuration for an NTP client?
      ? 2.2. How do I make an NTP server from an NTP client?
      ? 2.3. I have several computers on a LAN. Should be all clients of an
        external server?
      ? 2.4. Must I specify servers by IP address if DNS is not available on
        chronyd start?
      ? 2.5. How can I make chronyd more secure?
      ? 2.6. How can I improve the accuracy of the system clock with NTP
        sources?
      ? 2.7. Does chronyd have an ntpdate mode?
      ? 2.8. Can chronyd be configured to control the clock like ntpd?
      ? 2.9. What happened to the commandkey and generatecommandkey directives?
  o 3. Computer is not synchronising
      ? 3.1. Behind a firewall?
      ? 3.2. Are NTP servers specified with the offline option?
      ? 3.3. Is chronyd allowed to step the system clock?
      ? 3.4. Using a Windows NTP server?
      ? 3.5. Using a PPS reference clock?
  o 4. Issues with chronyc
      ? 4.1. I keep getting the error 506 Cannot talk to daemon
      ? 4.2. I keep getting the error 501 Not authorised
      ? 4.3. Why does chronyc tracking always print an IPv4 address as
        reference ID?
      ? 4.4. Is the chronyc / chronyd protocol documented anywhere?
  o 5. Real-time clock issues
      ? 5.1. What is the real-time clock (RTC)?
      ? 5.2. I want to use chronyd's RTC support. Must I disable hwclock?
      ? 5.3. I just keep getting the 513 RTC driver not running message
      ? 5.4. I get Could not open /dev/rtc, Device or resource busy in my
        syslog file
      ? 5.5. What if my computer does not have an RTC or backup battery?
  o 6. NTP-specific issues
      ? 6.1. Can chronyd be driven from broadcast/multicast NTP servers?
      ? 6.2. Can chronyd transmit broadcast NTP packets?
      ? 6.3. Can chronyd keep the system clock a fixed offset away from real
        time?
      ? 6.4. What happens if the network connection is dropped without using
        chronyc's offline command first?
  o 7. Operating systems
      ? 7.1. Does chrony support Windows?
      ? 7.2. Are there any plans to support Windows?

1. chrony compared to other programs

1.1. How does chrony compare to ntpd?

chronyd was designed to work well in a wide range of conditions and it can
usually synchronise the system clock faster and with better time accuracy. It
doesn't implement some of the less useful NTP modes like broadcast client or
multicast server/client.

If your computer is connected to the Internet only for few minutes at a time,
the network connection is often congested, you turn your computer off or
suspend it frequently, the clock is not very stable (e.g. there are rapid
changes in the temperature or it's a virtual machine), or you want to use NTP
on an isolated network with no hardware reference clocks in sight, chrony will
probably work much better for you.

For a more detailed comparison of features and performance, see the comparison
page on the chrony website.

2. Configuration issues

2.1. What is the minimum recommended configuration for an NTP client?

First, the client needs to know which NTP servers it should ask for the current
time. They are specified by the server or pool directive. The pool directive
can be used for names that resolve to multiple addresses. For good reliability
the client should have at least three servers. The iburst option speeds up the
initial synchronisation.

To stabilise the initial synchronisation on the next start, the estimated drift
of the system clock is saved to a file specified by the driftfile directive.

If the system clock can be far from the true time after boot for any reason,
chronyd should be allowed to correct it quickly by stepping instead of slewing,
which would take a very long time. The makestep directive does that.

In order to keep the real-time clock (RTC) close to the