Magento 2 – Fixing 500 Internal Server Error

8. download magento2 from Magento Commerce website
9. create a folder magento under /var/www/html 10 extract all the files of magento2 under /var/www/html/magento
10. Change the file permissions

sudo chmod -R 777 /var/www/html/magento

12. create a database called magento
13. Visit website url to install magento2
14. after completing installation change the directory permission again

sudo chmod -R 777 /var/www/html/magento

15. set environmental variables in ubuntu

export PATH=$PATH:/var/www/html/magento/bin

16. Setting up cron

crontab -u -e

example

crontab -u harish -e

select nano editor. add the following lines at the end of the file

*/1 * * * * <path-to-binary> -c <ini-file-path> <your Magento install dir>/bin/magento cron:run > 
*/1 * * * * <path-to-binary> -c <ini-file-path> <your Magento install dir>/update/cron.php >
*/1 * * * * <path-to-binary> -c <ini-file-path> <your Magento install dir>/bin/magento setup:cron:run >

where

is the absolute file system path to your PHP binary is the path to a php.ini file to use for the cron job

Example:

*/1 * * * * /usr/bin/php7.0 -c /etc/php/7.0 /var/www/html/magento/bin/magento cron:run > /var/www/html/magento/var/log/magento.cron.log& */1 * * * * /usr/bin/php7.0 -c /etc/php/7.0 /var/www/html/magento/update/cron.php > /var/www/html/magento/var/log/update.cron.log& */1 * * * * /usr/bin/php7.0 -c /etc/php/7.0 /var/www/html/magento/bin/magento setup:cron:run > /var/www/html/magento/var/log/setup.cron.log&

17. Run cron from the command

magento cron: run

I have explained the step by step installation of magento2 on ubuntu 14.04 with php7 in this post. It could help someone at least. Installing Magento2 on ubuntu with php7

The problem is that your constructor does not match the parent class constructor.

To fix that you need to update your constructor:

public function __construct(
    \Magento\Framework\View\Element\Template\Context $context,
    \Magento\Customer\Model\Session $customerSession,  
    \Magento\Framework\ObjectManagerInterface $objectManager,
    array $data = []
 ) {
    parent::__construct($context, $data);
    $this->customerSession = $customerSession;
    $this->_objectManager = $objectManager;
  }

Don't forget to flush the var/cache and var/generation after your changes.