You can’t run all of Munki‘s admin tools on Linux, because some of the things the tools use involve Mac-specific tools, which is why even Munki admins who host their Munki servers on a Linux server will use a Mac for things like munkiimport.

You can, however, run makecatalogs on Linux, though. Here’s just a quick test you can do on a vanilla Ubuntu 18.04 LTS server…

Clone the latest Munki from GitHub

git clone https://github.com/munki/munki

Create a symlink for Python 3

sudo ln -s /usr/bin/python3 /usr/bin/python

Copy the Munki command-line tools to a directory

sudo mkdir -p /usr/local/munki
sudo cp -R munki/code/client/* /usr/local/munki

Run makecatalogs

/usr/local/munki/makecatalogs /path/to/munki_repo

P.S. Your mileage may vary, but I found without making the symlink for Python 3 that I would get a

/usr/bin/env 'python': No such file or directory

error.