After reinstalling magento2 via the command line, I machinically typed /admin then I discovered a 404...at each install the url is now different. Security level is good, very good move of magento2 even if it's a little bit old for us.
So here's how to get the url of your admin
Go to your magento2 folder at the root and type the following command, it will then give you the result like this :
# php bin/magento info:adminuri
Admin URI: /admin_de3f9z
I hope it will help you,