firejail software package provides sandbox to restrict the application environment, 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 firejail
firejail is installed in your system.
Make ensure the firejail package were installed using the commands given below,
$ sudo dpkg-query -l | grep firejail *
You will get with firejail package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Utilities |
| Package | firejail |
| Version | 0.9.44-1 |
| Description | sandbox to restrict the application environment |
| Sub Section | Utils |