How to stop automatic time update via terminal?

Solution 1:

GNOME Automatic Date & Time doesn't use the ntp service, installable via sudo apt-get install ntp. Therefore stopping or uninstalling the service doesn't help.

Systemd timedatectl is used, therefore one command to switch off

timedatectl set-ntp 0

and one command to switch on

timedatectl set-ntp 1

Example

% timedatectl set-ntp 1

or via timedatectl status

% timedatectl status
      Local time: Do 2015-10-08 18:17:17 CEST
  Universal time: Do 2015-10-08 16:17:17 UTC
        RTC time: Do 2015-10-08 16:17:17
       Time zone: Europe/Berlin (CEST, +0200)
     NTP enabled: no
NTP synchronized: yes
 RTC in local TZ: no
      DST active: yes
 Last DST change: DST began at
                  So 2015-03-29 01:59:59 CET
                  So 2015-03-29 03:00:00 CEST
 Next DST change: DST ends (the clock jumps one hour backwards) at
                  So 2015-10-25 02:59:59 CEST
                  So 2015-10-25 02:00:00 CET

% timedatectl set-ntp 1

% timedatectl status
      Local time: Do 2015-10-08 18:17:35 CEST
  Universal time: Do 2015-10-08 16:17:35 UTC
        RTC time: Do 2015-10-08 16:17:35
       Time zone: Europe/Berlin (CEST, +0200)
     NTP enabled: yes
NTP synchronized: yes
 RTC in local TZ: no
      DST active: yes
 Last DST change: DST began at
                  So 2015-03-29 01:59:59 CET
                  So 2015-03-29 03:00:00 CEST
 Next DST change: DST ends (the clock jumps one hour backwards) at
                  So 2015-10-25 02:59:59 CEST
                  So 2015-10-25 02:00:00 CET

Solution 2:

On a systemd operating system like Ubuntu 15.04 use the timedatectl utility, which makes the same Desktop Bus RPC calls as the GNOME control centre utility does:

timedatectl set-ntp false

Further reading

• timedatectl. Ubuintu 15.04 manual pages. Canonical.
• timedatectl. systemd manual pages. Freedesktop.org.

Solution 3:

What you are looking for is not ntpd which is not installed by default. It's an if-up.d script which run time update whenever a network interface activated.

dconf watch / shows nothing but inotifywait -m -r /etc/ will do.

/etc/network/if-up.d/ MOVED_FROM ntpdate
/etc/network/if-up.d/ MOVED_TO ntpdate.disabled

It belongs to ntpdate package.

$ dpkg -S /etc/network/if-up.d/ntpdate
ntpdate: /etc/network/if-up.d/ntpdate

So to disable time update, rename that file same as the control center does:

sudo mv /etc/network/if-up.d/ntpdate /etc/network/if-up.d/ntpdate.disabled