Magento 2 :: 404 Error Page Not Found in Admin

Problem: After upgrading or installing Magento
Solution:
using ssh go to your Magento root folder and run the following commands

php bin/magento cache:clean
sudo rm -rf var/generation/*
sudo rm -rf var/cache/*

Problem: Admin Url not found.

Solution: Please confirm that URL rewrite mode is enabled or not if not enable it and restart apache server.
How to enable rewrite mode:

sudo a2enmod rewrite

apache configuration:

Open configuration file

sudo nane /etc/apache2/apache2.conf

Modify as below:

<Directory /var/www/>
     Options Indexes FollowSymLinks
     AllowOverride None
     Require all granted
</Directory>

Restart apache:

sudo service apache2 restart

And run the following commands:

php bin/magento setup:upg
php bin/magento setup:di:c
php bin/magento setup:static-content:d -f
php bin/magento cache:f
chmod 777 -R var/ pub/ generated/