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My system:
Linux Mint 17.2 MATE 32-bit
My settings:
Menu -> Administration -> Time and Date -> Configuration = Manual (that means do not connect to internet time servers)
I do NOT have ntp installed.
But nevertheless, on every boot my computer's clock is being synchronized with true time.
What should I do to disable it?
Given your comment, it can be excluded that your OS re-synchronises with the HW RTC.
I believe that the Mint administration only supports ntpd from the ntp package. But there are other ways to sync your system with network time (and in fact, ntpd is not necessarily the best choice).
You could have chrony or ntpdate installed. They may sync your OS time regardless of the Mint system settings.
Edit
If you want to keep ntpdate, that's also possible. Quoting /usr/share/doc/ntpdate/README.Debian (Linux Mint is derived from Debian):
ntpdate is run whenever a network interface is brought up. To adjust this behavior, the file /etc/network/if-up.d/ntpdate should be edited.
It is easy to adjust /etc/network/if-up.d/ntpdate for your needs. It tests for a variety of conditions before it runs ntpdate (or rather ntpdate-debian. You can even e.g. have it check for the presence of a file somewhere in your home directory to stop the script.
Add something along these lines after the other tests but before the opening round bracket which starts the lock file handling:
if [ -e ~myaccount/settings/dontrun-ntpdate-automatically.txt ]; then
exit 0
fi
ntpdate on my system. But how can I find the place where ntpdate is invoked at boot time?
Oct 5, 2015 at 9:31
ntpdate seems to suggest that it's part of the setup. I would suspect that it is run when a network connection becomes available; running it at boot-time without connectivity would be a poor approach. Why don't you delete the package and use rdate instead, which is intended for manual use only?
ntpdate is executed when the network becomes available, this call will be removed when you uninstall the package. If nothing was configured manually, that is.
As can be seen in the syslog, a connection to ntp.ubuntu.com is made on each connection to a (WiFi) network. To block it, add following to /etc/hosts:
# block clock synchronization by ntpdate
127.0.0.1 ntp.ubuntu.com
The advantage of this over adding exit 0 to /etc/network/if-up.d/ntpdate as suggested in https://superuser.com/a/982325 is that it won't be reverted on next update of the ntpdate package, which that file is part of - see http://packages.ubuntu.com/trusty/i386/ntpdate/filelist.
ntpdate manually as well. Not sure about Ubuntu, but Debian doesn't overwrite modified files on package upgrade without asking you first.
Oct 31, 2015 at 21:26