Exception printing is disabled by default for security reasons Magento 2

Your store is running Magento 2, when installing new extensions, setting configuration or even server memory is overload. You may get this error Exception printing is disabled by default for security reasons Magento 2 But you still don’t know exactly what kind of problem out there. Follow this guide to show the full message.

ERROR: There has been an error processing your request

There has been an error processing your request
Exception printing is disabled by default for security reasons.
Error log record number: 1234567890

Like this screenshot

Enable Exception printing in Magento 2

It is similar to Magento 1 but it is located in different folder pub/errors
Rename file pub/errors/local.xml.sample to pub/errors/local.xml
See trace result

You can go to var/report and get the list of error report.
There are similar errors:

a:4:{i:0;s:46:"SQLSTATE[HY000] [1049] Unknown database 'ce21'";i:1;s:4514:"#0 \vendor\magento\zendframework1\library\Zend\Db\Adapter\Pdo\Mysql.php(111): Zend_Db_Adapter_Pdo_Abstract->_connect()
#1 \vendor\magento\framework\DB\Adapter\Pdo\Mysql.php(340): Zend_Db_Adapter_Pdo_Mysql->_connect()
#2 \vendor\magento\zendframework1\library\Zend\Db\Adapter\Abstract.php(861): Magento\Framework\DB\Adapter\Pdo\Mysql->_connect()
#3 \vendor\magento\zendframework1\library\Zend\Db\Adapter\Abstract.php(931): Zend_Db_Adapter_Abstract->quote('1', NULL)
#4 \vendor\magento\framework\DB\Adapter\Pdo\Mysql.php(1363): Zend_Db_Adapter_Abstract->quoteInto('`store`.`store_...', '1', NULL, NULL)
#5 \vendor\magento\zendframework1\library\Zend\Db\Select.php(1007): Magento\Framework\DB\Adapter\Pdo\Mysql->quoteInto('`store`.`store_...', '1', NULL)
#6 \vendor\magento\zendframework1\library\Zend\Db\Select.php(477): Zend_Db_Select->_where('`store`.`store_...', '1', NULL, true)
#7 \vendor\magento\framework\DB\Select.php(115): Zend_Db_Select->where('`store`.`store_...', '1', NULL)
#8 \vendor\magento\framework\Model\ResourceModel\Db\AbstractDb.php(367): Magento\Framework\DB\Select->where('`store`.`store_...', '1')
#9 \vendor\magento\module-store\Model\ResourceModel\Store.php(168): Magento\Framework\Model\ResourceModel\Db\AbstractDb->_getLoadSelect('store_id', '1', Object(Magento\Store\Model\Store\Interceptor))
#10 \vendor\magento\framework\Model\ResourceModel\Db\AbstractDb.php(341): Magento\Store\Model\ResourceModel\Store->_getLoadSelect('store_id', '1', Object(Magento\Store\Model\Store\Interceptor))
#11 \var\generation\Magento\Store\Model\ResourceModel\Store\Interceptor.php(89): Magento\Framework\Model\ResourceModel\Db\AbstractDb->load(Object(Magento\Store\Model\Store\Interceptor), '1', NULL)
#12 \vendor\magento\framework\Model\AbstractModel.php(531): Magento\Store\Model\ResourceModel\Store\Interceptor->load(Object(Magento\Store\Model\Store\Interceptor), '1', NULL)
#13 \vendor\magento\module-store\Model\Store.php(488): Magento\Framework\Model\AbstractModel->load('1', NULL)
#14 \var\generation\Magento\Store\Model\Store\Interceptor.php(24): Magento\Store\Model\Store->load('1', NULL)
#15 \vendor\magento\module-store\Model\StoreRepository.php(89): Magento\Store\Model\Store\Interceptor->load('1')
#16 \vendor\magento\module-store\Model\StoreRepository.php(103): Magento\Store\Model\StoreRepository->getById('1')
#17 \vendor\magento\module-store\Model\StoreResolver.php(167): Magento\Store\Model\StoreRepository->getActiveStoreById('1')
#18 \vendor\magento\module-store\Model\StoreResolver.php(105): Magento\Store\Model\StoreResolver->getDefaultStoreById('1')
#19 \vendor\magento\module-store\Model\StoreManager.php(151): Magento\Store\Model\StoreResolver->getCurrentStoreId()
#20 \vendor\magento\module-store\App\Request\PathInfoProcessor.php(39): Magento\Store\Model\StoreManager->getStore('')
#21 \vendor\magento\module-backend\App\Request\PathInfoProcessor.php(47): Magento\Store\App\Request\PathInfoProcessor->process(Object(Magento\Framework\App\Request\Http), '/')
#22 \var\generation\Magento\Backend\App\Request\PathInfoProcessor\Proxy.php(95): Magento\Backend\App\Request\PathInfoProcessor->process(Object(Magento\Framework\App\Request\Http), '/')
#23 \vendor\magento\framework\App\Request\Http.php(165): Magento\Backend\App\Request\PathInfoProcessor\Proxy->process(Object(Magento\Framework\App\Request\Http), '/')
#24 \vendor\magento\framework\HTTP\PhpEnvironment\Request.php(209): Magento\Framework\App\Request\Http->setPathInfo()
#25 \vendor\magento\framework\App\Request\Http.php(208): Magento\Framework\HTTP\PhpEnvironment\Request->getPathInfo()
#26 \vendor\magento\framework\App\Http.php(130): Magento\Framework\App\Request\Http->getFrontName()
#27 \vendor\magento\framework\App\Bootstrap.php(258): Magento\Framework\App\Http->launch()
#28 \index.php(39): Magento\Framework\App\Bootstrap->run(Object(Magento\Framework\App\Http))
#29 {main}";s:3:"url";s:6:"/ce21/";s:11:"script_name";s:15:"/ce21/index.php";}

Cache issue

a:5:{i:0;s:71:"Could not determine temp directory, please specify a cache_dir manually";i:1;s:4546:"#0 /home/host/domains/example.com/public_html/lib/Zend/Cache/Backend.php(197): Zend_Cache::throwException('Could not deter...')

Session issue

Warning: SessionHandler::read(): open(/var/lib/php/session/sess_cvevqn06desuj80, O_RDWR) failed: Permission denied (13) in /var/www/vhosts/[site]/httpdocs/vendor/magento/framework/Session/SaveHandler.php on line 74

Registry issue

a:5:{i:0;s:63:"Mage registry key "_singleton/megamenu/observer" already exists";i:1;s:2654:"#0 /home/host/public_html/magento2/app/Mage.php(223): Mage::throwException('Mage registry k...')
#1 /home/host/public_html/magento2/app/Mage.php(477): Mage::register('_singleton/mega...', false)
#2 /home/host/public_html/magento2/app/code/core/Mage/Core/Model/App.php(1335): Mage::getSingleton('megamenu/observ...')
#3 /home/host/public_html/magento2/app/Mage.php(448): Mage_Core_Model_App->dispatchEvent('core_layout_blo...', Array)
#4 /home/host/public_html/magento2/app/code/core/Mage/Core/Model/Layout.php(459): Mage::dispatchEvent('core_layout_blo...', Array)
#5 /home/host/public_html/magento2/app/code/core/Mage/Core/Model/Layout.php(472): Mage_Core_Model_Layout->createBlock('page/html', 'root')
#6 /home/host/public_html/magento2/app/code/core/Mage/Core/Model/Layout.php(239): Mage_Core_Model_Layout->addBlock('page/html', 'root')
#7 /home/host/public_html/magento2/app/code/core/Mage/Core/Model/Layout.php(205): Mage_Core_Model_Layout->_generateBlock(Object(Mage_Core_Model_Layout_Element), Object(Mage_Core_Model_Layout_Element))
#8 /home/host/public_html/magento2/app/code/core/Mage/Core/Controller/Varien/Action.php(344): Mage_Core_Model_Layout->generateBlocks()
#9 /home/host/public_html/magento2/app/code/core/Mage/Cms/Helper/Page.php(113): Mage_Core_Controller_Varien_Action->generateLayoutBlocks()
#10 /home/host/public_html/magento2/app/code/core/Mage/Cms/Helper/Page.php(52): Mage_Cms_Helper_Page->_renderPage(Object(Mage_Cms_IndexController), 'home')
#11 /home/host/public_html/magento2/app/code/core/Mage/Cms/controllers/IndexController.php(45): Mage_Cms_Helper_Page->renderPage(Object(Mage_Cms_IndexController), 'home')
#12 /home/host/public_html/magento2/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Cms_IndexController->indexAction()
#13 /home/host/public_html/magento2/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('index')
#14 /home/host/public_html/magento2/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#15 /home/host/public_html/magento2/app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch()
#16 /home/host/public_html/magento2/app/Mage.php(684): Mage_Core_Model_App->run(Array)
#17 /home/host/public_html/magento2/index.php(84): Mage::run('', 'store')
#18 {main}";s:3:"url";s:19:"/magento2/";s:11:"script_name";s:28:"/magento2/index.php";s:4:"skin";s:7:"default";}

Enable Exception printing in Magento 1

You may rename file errors/local.xml.sample to errors/local.xml
Then Exception printing is enabled, so you can see trace as the following:

Mageplaza One Step Checkout helps reduce the abandonment rate as well as increase the conversion rate dramatically. Mageplaza Layered Navigation brings a list of filters to help your customers search and get the favourite products in the shortest way. Mageplaza Social Login (FREE) supports 11+ types of social networks.

It comes to the end of tutorial: Exception printing is disabled by default for security reasons Magento 2.