Discover The Joomla Versions On Your Server
From Joomla! Documentation
When you operate a Dedicated or VPS server as a webhost or reseller with root access you might want to find from time to time outdated Joomla versions which could jeopardize the security of your server. If you have unlimited root access as administrator you will find for each user on your server the exact Joomla version with the following command (root)
find /home/*/public_html/ -type f \( -iwholename '*/libraries/joomla/version.php' -o -iwholename '*/libraries/cms/version.php' -o -iwholename '*/libraries/cms/version/version.php' \) -print -exec perl -e 'while (<>) { $release = $1 if m/RELEASE\s+= .([\d.]+).;/; $dev = $1 if m/DEV_LEVEL\s+= .(\d+).;/; } print qq($release.$dev\n);' {} \; && echo "-"
The output will list all user accounts with their respective Joomla version