[Bitrix\Main\DB\ConnectionException] 
Mysql connect error [localhost]: (2002) Connection refused (400)
/home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php:65
#0: Bitrix\Main\DB\MysqliConnection->connectInternal()
	/home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php:122
#1: Bitrix\Main\DB\MysqliConnection->queryInternal(string, NULL, NULL)
	/home/bitrix/www/bitrix/modules/main/lib/db/connection.php:330
#2: Bitrix\Main\DB\Connection->query(string, NULL, integer, integer)
	/home/bitrix/www/bitrix/modules/main/lib/db/connection.php:358
#3: Bitrix\Main\DB\Connection->queryScalar(string)
	/home/bitrix/www/bitrix/modules/security/lib/session.php:114
#4: Bitrix\Security\SessionTable::lock(string, integer)
	/home/bitrix/www/bitrix/modules/security/classes/general/session_db.php:52
#5: CSecuritySessionDB::read(string)
	
#6: session_start()
	/home/bitrix/www/bitrix/modules/main/include.php:281
#7: require_once(string)
	/home/bitrix/www/bitrix/modules/main/include/prolog_before.php:14
#8: require_once(string)
	/home/bitrix/www/bitrix/modules/main/include/prolog.php:10
#9: require_once(string)
	/home/bitrix/www/bitrix/header.php:1
#10: require(string)
	/home/bitrix/www/courses/index.php:2
#11: include_once(string)
	/home/bitrix/www/bitrix/modules/main/include/urlrewrite.php:159
#12: include_once(string)
	/home/bitrix/www/bitrix/urlrewrite.php:2