After installing Magento 2.x, sometimes frontend and admin side js, CSS, and images can not load properly. This problem occurs because of file permission issues.

Though Magento 2 recommends setting ownership of all files & folders to the web server group, sometimes this is not possible due to some reasons. For example on shared hosting, the developer can not change ownership of files & folders.

To overcome this problem, we need to set permission 755 to each directory (Magento recommends 700) and we need to set permission 644 to each file (Magento recommends 600).

In /vendor/magento/framework/Filesystem/DriverInterface.php ,

Change line number 20 from

const WRITEABLE_DIRECTORY_MODE = 0770;

To

const WRITEABLE_DIRECTORY_MODE = 0755;

Also, change the line no 25 from

const WRITEABLE_FILE_MODE = 0660;

To

const WRITEABLE_FILE_MODE = 0644;

After the above change, replace the pub/static folder with a new fresh copy. And now refresh your front page or admin page.