(1) Install or re-install indicator-datetime:
$ sudo apt-get install indicator-datetime
(2) Re-configure the date/time:
$ sudo dpkg-reconfigure -f noninteractive tzdata
(3) Restart unity service:
sudo killall unity-panel-service
(4) Launch “System Setting” > “Time & Date” > “Clock” Tab.
Check “Show a clock in the menu bar”.
Thanks a lot for your post help me with the same problem in Ubuntu 14.04 cuz after and update suddenly clock desapear but with your instructions now is back
Thanks! It worked.
It is work also Ubuntu =14.10. thanks