Mac Mini Wireless Not Working Correctly After Installing Linux Mint

If you find that your Mac Mini's wireless card is not working correctly after installing Linux Mint (mine was not displaying available wireless networks) try these steps:

first make you you've got the right driver (my Mac Mini needs the Broadcom BCM4321 802.11a/b/g/n driver):

sudo apt update
sudo apt install firmware-b43-installer
sudo reboot

If that doesn't resolve the problem try switching drivers (in my case the wl driver seems to be the problem):

sudo modprobe -r wl
sudo modprobe b43

Check to see if wireless networks are displayed, if so then add the wl driver to the blacklist:

sudo touch /etc/modprobe.d/blacklist.conf
sudo echo "blacklist wl" >> /etc/modprobe.d/blacklist.conf

The b43 should then become the default driver.
You may need to manually edit the blacklist file with elevated privileges
eg: 

# blacklist wl driver as it wont list available wireless networks
#https://www.linuxquestions.org/questions/linux-networking-3/ubuntu-16-04-mac-mini-2009-broadcom-driver-selected-and-wlan-enabled-but-home-network-does-not-show-4175600634/
blacklist wl 

See original article here.

Installing Linux Mint on a Mac Mini

Here's how to go about installing Linux on a Mac:

1. Download your Linux distribution to the Mac. I recommend Linux Mint 18.2 MATE (64-bit) if this is your first Linux install. Save the file to your Downloads folder.
2. Download and install an app called Etcher from Etcher.io. This will be used to copy the Linux install .ISO file to your USB drive.
3. Open Etcher and click the Settings icon in the top-right. Place a tick in Unsafe Mode and click Yes, Continue. Then Click Back.
4. Click Select Image. Choose linuxmint-18.2-mate-64bit.iso (or the image you downloaded in Step 1).
5. Insert your USB Thumb Drive. A reminder that the US Flash drive will be erased during this installation process. Make sure you've got nothing you want on it.
6. Click Change under Select Drive. Look carefully and pick the drive that matches your USB Thumb Drive in size. It should be  /dev/disk1 if you only have a single hard drive in your Mac. Or /dev/disk2, /dev/disk3 and so on (if you have more drives attached). Do not pick /dev/disk0. That's your hard drive. Pick /dev/disk0 and you'll wipe your macOS hard drive You've been warned!
7. Click Flash! Wait for the iso file to be copied to the USB Flash Drive.
8. Remove the USB Flash Drive from your Mac.
9. Shut down the Mac you want to install Linux on and attach the USB stick.
10. Power up the Mac while holding down the Option key.
11. Choose the EFI Boot option from the startup screen and press Return.
12. You will see a black and white screen with options to Try Ubuntu and Install Ubuntu. Don't choose either yet, press "e" to edit the boot entry.
13. Edit the line that begins with Linux and place the word "nomodeset" after "quiet splash". The whole line should read: "linux /casper/vmlinuz.efi            file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash nomodeset --. (See screenshot, below.)
    
    Above: Step 13 (click on image to expand)
14. Press F10.
15. Linux Mint boots into trial mode.
16. Double-click the icon marked "Install Linux Mint".
17. Select English and choose Continue.
18. Select "Install this third-party software" option and click Continue.
19. Click Yes to the /dev/sdb alert.
20. Select "Erase disk and install Linux Mint" and click Continue.
21. Ensure that Select Drive is displaying the main hard drive. Click Install Now. Click Continue in the alert window.
22. Select your location on the map and click Continue.
23. Choosing your keyboard layout and click Continue.
24. Enter the name and password you want to use.
25. Click Continue and Linux Mint will begin installing.
26. When the installation has finished, you can log in using the name and password you chose during installation.

When you install Linux on your Mac, it removes all of the OS X installation including the recovery partition. If you want to reinstall OS X, you'll have to create an OS X recovery disk using the thumb stick.