Ensure you have backed up your current website's version files/database
Tested on Joomla 3+ and can be helpful if system files are broken:
Find needed version and download it from https://downloads.joomla.org/latest
cd ~/public_html/ mkdir temp; cd $_ wget https://downloads.joomla.org/cms/joomla3/3-8-11/Joomla_3-8-11-Stable-Full_Package.zip cd - rsync -avz temp/* ./ rm -rf temp installation/ Joomla_3-8-11-Stable-Full_Package.zip