apex-nslu2 software package provides APEX Boot Loader for Linksys NSLU2, 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 apex-nslu2
apex-nslu2 is installed in your system.
Make ensure the apex-nslu2 package were installed using the commands given below,
$ sudo dpkg-query -l | grep apex-nslu2 *
You will get with apex-nslu2 package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Administration Utilities |
| Package | apex-nslu2 |
| Version | 1.6.10 |
| Description | APEX Boot Loader for Linksys NSLU2 |
| Sub Section | admin |