efivar software package provides Tools to manage UEFI variables, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install efivar
efivar is installed in your system.
Make ensure the efivar package were installed using the commands given below,
$ sudo dpkg-query -l | grep efivar *
You will get with efivar package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Administration Utilities |
| Package | efivar |
| Version | 0.15-3 |
| Description | Tools to manage UEFI variables |
| Sub Section | admin |