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Potentially useful things to know about the Debian NTP packages...
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A list of Public NTP Time Servers is available on the web at
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http://www.eecis.udel.edu/~mills/ntp/servers.htm
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Please make sure to read *and follow* the Rules of Engagement there, please!
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The ntp-simple, ntp-refclock, and ntpdate packages all share a common config
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file for listing servers at /etc/default/ntp-servers. There is debconf
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support in those packages for setting a list of servers. In the case of
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ntpdate, any changes made to that file manually or through the debconf
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interface will take effect the next time /etc/init.d/ntpdate runs.
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If you want to manually set up /etc/default/ntp-servers, it needs to have a
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NTPSERVERS="server_one server_two etc"
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listing one or more space-separated servers. Any other content in the file
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will currently be ignored.
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For the daemon packages, it's more complicated, because the /etc/ntp.conf file
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does not support an include file syntax. There is, therefore, a debconf
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variable to indicate whether the package maintainer scripts should re-create
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/etc/ntp.conf each time the data changes. I'm not really happy about how that
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works right now, and there's at least one bug open against the packages about
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it, so I'm investigating Manoj's ucf package as a potential way of doing a
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better job handling changes in /etc/ntp.conf. Stay tuned.
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Several people have reported that ntpd fails on SMP boxes unless the "Enhanced
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Real-Time Clock" support is enabled in the kernel. This is known to be
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essential on SMP Alpha systems, and is believed to also be necessary on SMP
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By default, ntpd will log via syslog(). Since Debian does not have a LOG_NTP
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facility defined, the daemon will use LOG_DAEMON, leading to ntpd log entries
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going to /var/log/daemon.log. If you define a logfile location in
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/etc/ntp.conf, the daemon will do direct filesystem writes to the specified
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file, avoiding syslog(). Previous Debian packages did this, with the side
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effect that they had to ship a weekly cron job that stopped the daemon,
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rotated the log, then restarted the daemon. This is moderately evil for
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high-stratum NTP servers, where ntpd should be allowed to run more or less
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forever. To handle both modes of logging, the cron.weekly script is still
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provided to rotate /var/log/ntpd if present, but it will not cycle the daemon
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if syslog is in use. By default, new installations of this package will use
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NTP and hwclock issues: hwclock (from the util-linux package) is normally
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called on startup and shutdown. You must ensure that hwclock --adjust is never
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called (make sure it is disabled in /etc/init.d/hwclock.sh) in a host which
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has ntpd active. You should allow hwclock --systohc to be called on shutdown
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unless you are running the NANO kernel patch, because the kernel does not
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fully update the RTC time, and it could be off by a multiple of 30 minutes in
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the next boot if hwclock --systohc is never called by the shutdown sequence.
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See the hwclock README files in the util-linux documentation for more
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If you want to configure a machine to use its own processor clock as a
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reference, so that for example you can get a set of other machines to sync to
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it even if the cluster of machines isn't synced to anything else, then you
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need to make sure to use a less-attractive stratum... just in case the cluster
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someday mingles time with the real world. An example of how to do this is
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to configure the "authoritative" machine's ntp.conf like so:
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fudge 127.127.1.1 stratum 10
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Then, have the other machines peer with each other to some extent, and peer
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(maybe using 'server' instead of 'peer') with the authoritative server, and
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they'll all go to stratum 11 sync'ed to this machine eventually... and if you
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ever get a better source of time, everything will latch onto it instead.
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debian/README.Debian
