$ sudo apt-get update
$ sudo apt-get install root-plugin-gui-sessionviewer 

root-plugin-gui-sessionviewer is installed in your system.

Make ensure the root-plugin-gui-sessionviewer package were installed using the commands given below,

$ sudo dpkg-query -l | grep root-plugin-gui-sessionviewer *

You will get with root-plugin-gui-sessionviewer package name, version, architecture and description in a table

root-plugin-gui-sessionviewer package basic information: