Ubuntu – How to customize the NTP poll rate

ntp

I'm setting up Ubuntu on an embedded machine that runs over a cellular connection, where we pay per byte. The machine also has no RTC battery, so it starts from a random time every boot.

I'd like to ensure that the time gets synced up when the cellular connection comes available so that log messages, etc have real times, but I also don't want to pay an arm and a leg for NTP traffic.

Can I customize the rate at which NTP updates the time? I'm using openntpd currently, but I'm not wedded to it.

The internet is not necessarily up at boot, so ntupdate and related at startup won't work. And scheduling via cron means waiting for the scheduled task to kick in, whereas I want a time daemon to get a time sync ASAP.

Best Answer

Some of these answers could win the obfuscated ntp configuration contest.

Use the ntp reference implementation and use iburst to set the time quickly upon booting. After that the you can use the minpoll directive to limit how often ntpd queries remote time servers. This will allow you to take advantage of ntpd's clock disciplining and keep the bandwidth down.

minpoll minpoll
maxpoll maxpoll
    These options specify the minimum and maximum poll intervals for NTP 
    messages, in seconds as a power of two. The maximum poll interval 
    defaults to 10 (1024 s), but can be increased by the maxpoll option to 
    an upper limit of 17 (36 h). The minimum poll interval defaults to 6 (64 s), 
    but can be decreased by the minpoll option to a lower limit of 3 (8 s).

Chrony is a good alternative to the ntp reference implementation. Openntpd is not.

Related Solutions

Ubuntu – How to force a clock update using ntp

Probably the ntp service is running, that's why ntpdate can't open the socket (port 123 UDP) and connect to ntp server.

Try from command line:

sudo service ntp stop
sudo ntpdate -s time.nist.gov
sudo service ntp start

If you want to put this in /etc/rc.local use the following:

( /etc/init.d/ntp stop
until ping -nq -c3 8.8.8.8; do
   echo "Waiting for network..."
done
ntpdate -s time.nist.gov
/etc/init.d/ntp start )&

Ubuntu – How to change the time server in ubuntu 12.04 LTS without installing the `ntp` package

There are two main ways to set the current time via NTP: ntpdate is a command-line tool that, when run, fetches the current time from an NTP server and sets the system time accordingly. ntpd is the NTP daemon which runs in the background and continuously adjusts the time slightly.

For servers, production environments and such, ntpd is better. However, for normal desktop PCs and end users, ntpdate is perfectly fine. In fact, when you install Ubuntu Desktop, it comes with ntpdate preinstalled, but not ntpd.

When you select "Automatically from the Internet" in your Ubuntu system settings as shown in your screenshot above, what happens is that at each boot Ubuntu will fetch the current time using ntpdate from ntp.ubuntu.com. If you want to change that server, you can edit the value of NTPSERVERS in /etc/default/ntpdate.

The alternative is to install ntpd (in package ntp), and configure that via /etc/ntp.conf. This is explained here in more detail:

https://help.ubuntu.com/lts/serverguide/NTP.html

However, if you do not want to install any additional packages and simply change the default server for ntpdate which comes pre-installed with Ubuntu, simply edit /etc/default/ntpdate.

Best Answer

Related Solutions

Ubuntu – How to force a clock update using ntp

Ubuntu – How to change the time server in ubuntu 12.04 LTS without installing the `ntp` package

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