Magento after setup for url not loading or frontend not loading solution

Magento_after_setup

First of all, apply proper permissions, enable apache rewrite_module and refresh apache server.
  chmod -R 777 /var/www/html/MAGENTO_2_ROOT_DIRECTORY/ sudo a2enmod rewrite sudo service apache2 restart

For messy frontend, run following command from Magento root:
  php bin/magento setup:static-content:deploy

Now clear var directory except .htaccess file and check admin. If you get 404 page, there may be an issue of Symlink. Fot this, Edit apache config file
sudo gedit /etc/apache2/apache2.conf
and replace this code :
  <Directory /var/www/> 
    Options Indexes FollowSymLinks 
    AllowOverride none 
    Require all granted

with

  <Directory /var/www/> 
    Options Indexes FollowSymLinks 
    AllowOverride All 
    Require all granted
    
Note: changed AllowOverride none to AllowOverride All
Now restart apache sudo service apache2 restart and check admin. This should fix admin 404 issue.

Also make sure, you don't leave /app/etc/ directory writeable

php bin/magento indexers:reindex -> for cron job indexing errors in admin panel

For error: AH01797: client denied by server configuration: /var/www/html/robi_ecommerce/app/etc/config.php
bin/magento module:enable Namespace_Module


for error writing in log file error when adding product:
For Magento 2.0, error folder is not located in Magento/errors but in pub/errors/ So, just like Magento 1, to enable printing errors we need to rename pub/errors/local.xml.sample to pub/errors/local.xml

You can also turn on Magento developer mode by entering this line in Magento CLI
php bin/magento deploy:mode:set developer
Now you can refresh the error page and the error log will be something like this

Reference URL: https://magentoexplorer.com/magento-exception-printing-is-disabled-by-default-for-security-reasons-how-to-fix