So say you happen to have 2 NICs of the exact same chipset, they will generally show up as the same name, with possibly a different revision in lspci. Normally this is not an issue if you have a server with 4 NICs, generally the eth0 to eth3 appears from left to the right (or right to left on some vendors) so it doesn't take much figuring out.
Generally if you have different chipsets for different NICs, it should be easy to know which one is eth0 or the first NIC in the OS.........
If you are getting this error from systemctl "Loaded: masked (Reason: Unit hostapd.service is masked.)" we need to unmask the service.
Solution
systemctl unmask hostapd
Removed /etc/systemd/system/hostapd.service.
It's fixed
root@routerOS:/var/log# systemctl start hostapd
root@routerOS:/var/log# systemctl status hostapd
● hostapd.service - Access point and authentication server for Wi-Fi and Ethern........
This is not the normal "black screen"issue and I was shocked to eventually find out why. The normal advice of reconfiguring Xorg didn't work. Even booting into "Recovery Mode" did not help.
Here is the short end of the stick that fixed it:
sudo apt-get install mdm mate-desktop-environment
Yes you got it right, mdm and the mate-desktop-environment / gnome were somehow uninstalled. This must be whe........
#if you have nvidia make sure you install the nvidia-cuda-toolkit so hardware acceleration can be used
wget http://ffmpeg.org/releases/ffmpeg-3.3.2.tar.bz2
tar -jxvf ffmpeg-3.3.2.tar.bz2
cd ffmpeg-3.3.2/
./configure --disable-yasm
install prefix /usr/local
source path ........