icnsutils software package provides utilities for manipulating Mac OS icns files, 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 icnsutils
icnsutils is installed in your system.
Make ensure the icnsutils package were installed using the commands given below,
$ sudo dpkg-query -l | grep icnsutils *
You will get with icnsutils package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Graphics |
| Package | icnsutils |
| Version | 0.8.1-3 |
| Description | utilities for manipulating Mac OS icns files |
| Sub Section | Graphics |