libx11-6 software package provides X11 client-side library, you can install in your Ubuntu 14.04 LTS (Trusty Tahr) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install libx11-6
libx11-6 is installed in your system.
Make ensure the libx11-6 package were installed using the commands given below,
$ sudo dpkg-query -l | grep libx11-6 *
You will get with libx11-6 package name, version, architecture and description in a table
| Distro | Ubuntu 14 04 lts trusty tahr |
| Section | Libraries |
| Package | libx11-6 |
| Version | 2:1.6.2-1ubuntu2 |
| Description | X11 client-side library |
| Sub Section | libs |