fdclock software package provides freedesktop.org clock, you can install in your Ubuntu 16.04 LTS (Xenial Xerus) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install fdclock
fdclock is installed in your system.
Make ensure the fdclock package were installed using the commands given below,
$ sudo dpkg-query -l | grep fdclock *
You will get with fdclock package name, version, architecture and description in a table
| Distro | Ubuntu 16 04 lts xenial xerus |
| Section | X Window System software |
| Package | fdclock |
| Version | 0.1.0+git.20060122-0ubuntu3 |
| Description | freedesktop.org clock |
| Sub Section | X180 |