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Exceptions during installation

Symptom: Exceptions display during installation. Users have reported a variety of exceptions, including the following:

Module 'Magento_Indexer':
Running recurring..
[ERROR] exception 'Exception' with message 'Recoverable Error: Argument 1 passed to Magento\Indexer\Model\Config\Data::__construct() must be an instance of Magento\Framework\Indexer\Config\Reader, instance of Magento\Indexer\Model\Config\Reader given, called in /home/magento2_dev/
public_html/var/generation/Magento/Indexer/Model/Config/Data/Interceptor.php on line 14 and defined in /home/magento2_dev/public_html/
app/code/Magento/Indexer/Model/Config/Data.php on line 22' in /home/magento2_dev/public_html/lib/internal/Magento/Framework/App/ErrorHandler.php:67
Stack trace:
#0 /home/magento2_dev/public_html/app/code/Magento/Indexer/Model/Config/Data.php(22): Magento\Framework\App\ErrorHandler->handler(4096, 
'Argument 1 pass...', '/home/magento2...', 22, Array)
#1 /home/magento2_dev/public_html/var/generation/Magento/Indexer/Model/Config/Data/Interceptor.php(14): Magento\Indexer\Model\Config\Data->
__construct(Object(Magento\Indexer\Model\Config\Reader), Object(Magento\Framework\App\Cache\Type\Config), Object(Magento\Indexer\Model\Resource\Indexer\State\Collection), 'indexer_config')
#2 /home/magento2_dev/public_html/lib/internal/Magento/Framework/ObjectManager/Factory/AbstractFactory.php(103): Magento\Indexer\Model\Config\Data\Interceptor->__construct(Object(Magento\Indexer\Model\Config\Reader), Object(Magento\Framework\App\Cache\Type\Config), 
Object(Magento\Indexer\Model\Resource\Indexer\State\Collection), 'indexer_config')

... more ...

Solution

Clear the <your Magento install dir>/var/generation and other directories under var as follows:

rm -rf <your Magento install dir>/var/generation/* <your Magento install dir>/var/di/* <your Magento install dir>/var/cache/* 

After clearing the directories, try the installation again.