Cannot write to the var/generation directory

Cannot write to the `var/generation` directory

Symptom

After you successfully install Magento, exceptions display when you try to access the storefront or Admin. (You might have to enable developer mode to see the exceptions.)

Sample exceptions follow:

Directory "/var/www/html/magento2/pub/static/_requirejs/adminhtml/Magento/backend/en_US" cannot be created Warning!mkdir(): Permission denied

Error filtering template: Unable to write file into directory /var/www/html/magento2/pub/media/catalog/product/cache/1/small_image/240x300/beff4985b56e3afdbeabfc89641a4582/m/b. Access forbidden.

exception 'Magento\Framework\Exception\LocalizedException' with message 'Can't create directory /var/www/html/magento2/var/generation/Magento/Framework/App/ResourceConnection/.' in /var/www/html/magento2/vendor/magento/framework/Code/Generator.php:103 Stack trace: 
#0 /var/www/html/magento2/vendor/magento/framework/Code/Generator/Autoloader.php(35): Magento\Framework\Code\Generator->generateClass('Magento\\Framewo...') 
#1 [internal function]: Magento\Framework\Code\Generator\Autoloader->load('Magento\\Framewo...') 
#2 [internal function]: spl_autoload_call('Magento\\Framewo...') 
#3 /var/www/html/magento2/vendor/magento/framework/Code/Reader/ClassReader.php(19): ReflectionClass->__construct('Magento\\Framewo...') 
#4 /var/www/html/magento2/vendor/magento/framework/ObjectManager/Definition/Runtime.php(44): Magento\Framework\Code\Reader\ClassReader->getConstructor('Magento\\Framewo...') 
#5 /var/www/html/magento2/vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php(71): Magento\Framework\ObjectManager\Definition\Runtime->getParameters('Magento\\Framewo...') 
#6 /var/www/html/magento2/vendor/magento/framework/ObjectManager/ObjectManager.php(71): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create('Magento\\Framewo...') 
#7 
... more ...

Details

For security reasons, Magento recommends a particular set of file system ownership and permissions rules. These rules require you to give ownership and permissions to two users:

Web server user
A local user on the Magento server

In addition, Magento code creates files with permissions consistent with our recommendations. For details, see:

Suggestion

First, make sure you completed all tasks discussed in the preceding section. In particular, make sure the Magento file system owner and the web server user share groups in one of the ways discussed in Options for shared groups.

If that still does not resolve the issue, try setting the setgid bit (set group-id bit) for problem directories, such as var/generation, as follows:

Identify the directory that does not allow write access.
As a user with root privileges (or with sufficient privileges to set permissions), enter the following command:
```
chmod g+s <directory-path>
```
For example, to set the sticky bit for the /var/www/magento2/var/generation directory, enter:
```
find /var/www/magento2/var/generation -type d -exec chmod g+s {} \;
```

Cannot write to the var/generation directory