gnome-session software package provides GNOME Session Manager - GNOME 3 session, 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 gnome-session
gnome-session is installed in your system.
Make ensure the gnome-session package were installed using the commands given below,
$ sudo dpkg-query -l | grep gnome-session *
You will get with gnome-session package name, version, architecture and description in a table
| Distro | Ubuntu 14 04 lts trusty tahr |
| Section | GNOME |
| Package | gnome-session |
| Version | 3.9.90-0ubuntu12 |
| Description | GNOME Session Manager - GNOME 3 session |
| Sub Section | GNOME |