YCM is always a pain in the but because it needs vim to be installed with python 3.5+, which is not the default. To do this:
git clone https://github.com/vim/vim.git
cd vim
./configure --with-python3-command=python3 --enable-pythoninterp=yes --enable-python3interp=yes
make -j `nproc`
sudo make install -j `nproc`Then go to the dir where YCM is installed:
git submodule update --init --recursive
./install.py --all