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-<head>
-<title>Frequently asked questions</title>
-<meta name="description" content="Chrony FAQ (frequently asked questions)">
-<meta name="keywords" content="chrony,network time protocol,NTP,RFC 1305,dial-up connection,real time clock,RTC,Linux,FAQ,frequently asked questns">
-<?php
- $root = ".";
- include "$root/styles.php";
-?>
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-<body>
-<?php
- include 'main_banner.php';
- include 'header.php';
-?>
-<?php pretty_h1("Introduction") ?>
-<p>
-This is a set of questions and answers to common problems and issues.
-<p>
-As we receive more emails about the software, we will add new questions
-to this page.
-<hr>
-<p>
-The developers can be reached via the chrony-dev mailing list. See
-<a href="#question_1.4">question 1.4.</a> for details.
-<hr>
-
-<br clear=all>
-@@ENDPROLOGUE
-S: Administrative issues
-
-Q: Where can I get chrony source code?
-Tarballs are available via the <b>Download</b> link on the Chrony
-Web site. For the current development from the developers' version control
-system see the <b>Git</b> link on the Web site.
-
-Q: Are there any packaged versions of chrony?
-We are aware of packages for Debian, Fedora, Gentoo, Mandriva, Slackware,
-and Ubuntu. We are not involved with how these are built or distributed.
-
-Q: Where is the home page?
-It is currently at <a href="http://chrony.tuxfamily.org/">http://chrony.tuxfamily.org/</a>.
-
-Q: Is there a mailing list?
-Yes, it's currently at chrony-users@chrony.tuxfamily.org. There is a low-volume
-list called chrony-announce which is just for announcements of new releases or
-similar matters of high importance. You can join the lists by sending a
-message with the subject subscribe to <a href="mailto:chrony-users-request@chrony.tuxfamily.org">chrony-users-request@chrony.tuxfamily.org</a> or
-<a href="mailto:chrony-announce-request@chrony.tuxfamily.org">chrony-announce-request@chrony.tuxfamily.org</a> respectively.
-
-For those who want to contribute to the development of chrony, there is a
-developers' mailing list. You can subscribe by sending mail with the
-subject subscribe to
-<a href="mailto:chrony-dev-request@chrony.tuxfamily.org">chrony-dev-request@chrony.tuxfamily.org</a>.
-
-Q: What licence is applied to chrony?
-Starting from version 1.15, chrony is licensed under the GNU General Public
-License, Version 2. Versions prior to 1.15 were licensed under a custom BSD-like
-license.
-
-S: Chrony compared to other programs
-Q: How does chrony compare to xntpd?
-If your computer is permenently connected, or connected for long periods (that
-is, for the several hours it takes xntpd to settle down), or you need to
-support hardware reference clocks to your computer, then xntpd will work fine.
-Apart from not supporting hardware clocks, chrony will work fine too.
-
-If your computer connects to the 'net for 5 minutes once a day (or something
-like that), or you turn your Linux computer off when you're not using
-it, or you want to use NTP on an isolated network with no hardware clocks in
-sight, chrony will work much better for you.
-
-The reason I wrote chrony was that I could not get xntpd to do
-anything sensible on my PC at home, which is connected to the 'net for
-about 5 minutes once or twice a day, mainly to upload/download email
-and news. Nowadays it is also turned off for 22-23 hours a day, when
-not in use. I wanted a program which would :
-
-- slew the time to correct it when I go online and NTP servers become visible
-
-- determine the rate at which the computer gains or loses time and use this
- information to keep it reasonably correct between connects to the 'net. This
- has to be done using a method that does not care about the intermittent
- availability of the references or the fact the computer is turned off between
- groups of measurements..
-
-- maintain the time across reboots, by working out the error and drift rate of
- the computer's real-time clock and using this information to set the system
- clock correctly at boot up. (In the last few months, it became impossible for
- me to leave my computer powered permanently.)
-
-Also, when working with isolated networks with no true time references
-at all, I found xntpd gave me no help with managing the local clock's
-gain/loss rate on the NTP master node (which I set from my watch). I
-added some automated support in chrony to deal with this.
-
-S: Selection of NTP servers
-Q: I have several computers on a LAN. Should I make one the master, or make them all clients of an external server?
-I think the best configuration is to make one computer the master, with the
-others as clients of it. Add a 'local' directive to the master's chrony.conf
-file. This configuration will be better because
-
-* the load on the external connection is less
-* the load on the external NTP server(s) is less
-* if your external connection goes down, the computers on the LAN will maintain
- a common time with each other.
-
-S: My computer is not synchronising.
-This is the most common problem. There are a number of reasons, see the
-following questions.
-
-Q: Behind a firewall?
-If there is a firewall between you and the NTP server you're trying to use,
-the packets may be blocked. Try using a tool like etherfind or tcpdump to see
-if you're getting responses from the server. If you have an external modem,
-see if the receive light blinks straight after the transmit light (when the
-link is quiet apart from the NTP traffic.) Try adding 'log measurements' to
-the chrony.conf file and look in the measurements.log file after chrony has
-been running for a short period. See if any measurements appear.
-
-Most people run chronyd on the firewall itself, to avoid all issues of UDP
-packet forwarding and/or masquerading.
-
-Q: Do you have a non-permanant (i.e. intermittent) Internet connection?
-Check that you're using chronyc's 'online' and 'offline' commands
-appropriately. Again, check in measurements.log to see if you're getting any
-data back from the server.
-
-Q: In measurements.log, do the '7' and '8' flag columns always show zero?
-Do you have a 'local stratum X' directive in the chrony.conf file? If X is
-lower than the stratum of the server you're trying to use, this situation will
-arise. You should always make X quite high (e.g. 10) in this directive.
-
-S: Issues with chronyc
-
-Q: I keep getting the error '506 Cannot talk to daemon'.
-Make sure that the chrony.conf file (on the computer where chronyd is running)
-has a 'cmdallow' entry for the computer you are running chronyc on. This
-isn't necessary for localhost.
-
-Perhaps chronyd is not running. Try using the ps command (e.g. on Linux, 'ps
--auxw') to see if it's running. Or try 'netstat -a' and see if the ports
-123/udp and 323/udp are listening. If chronyd is not running, you may have a
-problem with the way you are trying to start it (e.g. at boot time).
-
-Perhaps you have a firewall set up in a way that blocks packets on port
-323/udp. You need to amend the firewall configuration in this case.
-
-Q: Is the chronyc<->chronyd protocol documented anywhere?
-Only by the source code :-) See cmdmon.c (chronyd side) and client.c (chronyc
-side).
-
-S: Real-time clock issues.
-Q: What is the real-time clock (RTC)?
-This is the clock which keeps the time even when your computer is turned off.
-It works with 1 second resolution. chronyd can monitor the rate at which the
-real-time clock gains or loses time, and compensate for it when you set the
-system time from it at the next reboot. See the documentation for details.
-
-Q: I want to use chronyd's real-time clock support. Must I disable hwclock?
-The hwclock program is often set-up by default in the boot and shutdown scripts
-with many Linux installations. If you want to use chronyd's real-time clock
-support, the important thing is to disable hwclock in the <b>shutdown</b>
-procedure. If you don't, it will over-write the RTC with a new value, unknown
-to chronyd. At the next reboot, chronyd will compensate this (wrong) time with
-its estimate of how far the RTC has drifted whilst the power was off, giving a
-meaningless initial system time.
-
-There is no need to remove hwclock from the boot process, as long as chronyd is
-started after it has run.
-
-Q: I just keep getting the '513 RTC driver not running' message
-For the real time clock support to work, you need the following three things:
-
-* a kernel that is supported (e.g. 2.2 onwards)
-* enhanced RTC support compiled into the kernel
-* an 'rtcfile' directive in your chrony.conf file.
-
-S: Microsoft Windows
-
-Q: Does chrony support Windows?
-No. The chronyc program (the command-line client used for configuring
-chronyd while it is running) has been successfully built and run under Cygwin
-in the past. chronyd is not portable, because part of it is very
-system-dependent. It needs adapting to work with Windows' equivalent of the
-adjtimex() call, and it needs to be made to work as an NT service.
-
-Q: Are there any plans to support Windows?
-We have no plans to do this. Anyone is welcome to pick this work up and
-contribute it back to the project.
-
-Q: What alternative NTP clients are there for Windows?
-Some of the names we've seen mentioned are
- - Automachron
- - NetTime (nettime.sourceforge.net)
-
-S: NTP-specific issues
-Q: Can chrony be driven from broadcast NTP servers?
-No. I remember looking at how they worked when I was first writing chrony.
-Since the 'target market' then was dial-up systems, broadcast packets were not
-relevant so I didn't bother working out how to deal with the complexities of
-doing the delay estimation.
-
-I no longer have root access to a LAN environment to develop and test broadcast
-server support. Neither have I the time to work on this. I would be very
-happy to accept a patch from anyone who can develop, test and debug the
-necessary changes!
-
-Q: Can chronyd transmit broadcast NTP packets (e.g. to synchronise other computers on a private LAN)?
-Yes. Starting from version 1.17, chrony has this capability.
-
-Q: Can chrony keep the system clock a fixed offset away from real time?
-I have not experimented much, but I don't believe this would be possible as
-the program currently stands.
-
-Q: What happens if the network connection is dropped without using chronyc's 'offline' command first?
-In this case chronyd will keep trying to access the server(s) that it thinks
-are online. Eventually it will decide that they are unreachable and no longer
-consider itself synchronised to them. If you have other computers on your LAN
-accessing the computer that is affected this way, they too will become
-'unsynchronised', unless you have the 'local' directive set up on the master
-computer.
-
-The 'auto_offline' option to the 'server' entry in the chrony.conf file may be
-useful to avoid this situation.
-
-S: Development
-
-Q: Can I get the source via git from anywhere?
-Yes. See the Git link at <a
-href="http://chrony.tuxfamily.org/">http://chrony.tuxfamily.org</a> for
-information.
-
-S: Linux-specific issues
-
-Q: Why does the source code include kernel header files?
-The program needs to see the definitions of structures used to interact with
-the real time clock (via /dev/rtc) and with the adjtimex() system call. Sadly
-this has led to a number of compilation problems with newer kernels which have
-been increasingly hard to fix in a way that makes the code compilable on all
-Linux kernel versions. Hopefully
-the situation will not deteriorate further with future kernel versions.
-
-Q: I get "Could not open /dev/rtc, Device or resource busy" in my syslog file.
-Check that you haven't accidentally got two copies of chronyd running (perhaps
-defined in different start-up scripts.)
-
-S: Solaris-specific issues
-Q: On Solaris 2.8, I get an error message about not being able to open kvm to change dosynctodr.
-(The dosynctodr variable controls whether Solaris couples the equivalent of its
-BIOS clock into its system clock at regular intervals). The Solaris port of
-chrony was developed in the Solaris 2.5 era. Some aspect of the Solaris kernel
-has changed which prevents the same technique working. I no longer have root
-access to any Solaris machines to work on this, and am reliant on somebody
-developing the patch and testing it. A good starting point would be to see if
-xntpd has been modified to work for Solaris 2.8.
-
-@@EPILOGUE
-<hr>
-
-Back to
-<a href="mailto:rc@rc0.org.uk?subject=chrony">the author</a>'s
-<a href="http://www.rc0.org.uk/">main page</a>
-</body>
-</html>
-@@ENDEPILOGUE
projects / thirdparty / chrony.git / commitdiff
