MediaWiki internal error.

Original exception: [c997cc42d8ac41970a8e46b0] /mw-config/index.php Error: Call to undefined function session_name()
Backtrace:
from /var/www/mediawiki/wiki.swee.codes/includes/Setup.php(499)
#0 /var/www/mediawiki/wiki.swee.codes/includes/WebStart.php(86): require_once()
#1 /var/www/mediawiki/wiki.swee.codes/mw-config/index.php(41): require(string)
#2 {main}

Exception caught inside exception handler: [c997cc42d8ac41970a8e46b0] /mw-config/index.php InvalidArgumentException: Wikimedia\Rdbms\DatabaseFactory::getClass no viable database extension found for type 'mysql'
Backtrace:
from /var/www/mediawiki/wiki.swee.codes/includes/libs/rdbms/database/DatabaseFactory.php(241)
#0 /var/www/mediawiki/wiki.swee.codes/includes/libs/rdbms/database/DatabaseFactory.php(186): Wikimedia\Rdbms\DatabaseFactory->getClass()
#1 /var/www/mediawiki/wiki.swee.codes/includes/libs/rdbms/loadbalancer/LoadBalancer.php(975): Wikimedia\Rdbms\DatabaseFactory->attributesFromType()
#2 /var/www/mediawiki/wiki.swee.codes/includes/libs/rdbms/loadbalancer/LoadBalancer.php(1032): Wikimedia\Rdbms\LoadBalancer->getServerAttributes()
#3 /var/www/mediawiki/wiki.swee.codes/includes/libs/rdbms/loadbalancer/LoadBalancer.php(918): Wikimedia\Rdbms\LoadBalancer->reallyOpenConnection()
#4 /var/www/mediawiki/wiki.swee.codes/includes/libs/rdbms/loadbalancer/LoadBalancer.php(799): Wikimedia\Rdbms\LoadBalancer->reuseOrOpenConnectionForNewRef()
#5 /var/www/mediawiki/wiki.swee.codes/includes/libs/rdbms/loadbalancer/LoadBalancer.php(791): Wikimedia\Rdbms\LoadBalancer->getServerConnection()
#6 /var/www/mediawiki/wiki.swee.codes/includes/libs/rdbms/database/DBConnRef.php(107): Wikimedia\Rdbms\LoadBalancer->getConnectionInternal()
#7 /var/www/mediawiki/wiki.swee.codes/includes/libs/rdbms/database/DBConnRef.php(125): Wikimedia\Rdbms\DBConnRef->ensureConnection()
#8 /var/www/mediawiki/wiki.swee.codes/includes/libs/rdbms/database/DBConnRef.php(338): Wikimedia\Rdbms\DBConnRef->__call()
#9 /var/www/mediawiki/wiki.swee.codes/includes/libs/rdbms/querybuilder/SelectQueryBuilder.php(779): Wikimedia\Rdbms\DBConnRef->selectField()
#10 /var/www/mediawiki/wiki.swee.codes/includes/language/LCStoreDB.php(65): Wikimedia\Rdbms\SelectQueryBuilder->fetchField()
#11 /var/www/mediawiki/wiki.swee.codes/includes/language/LocalisationCache.php(567): LCStoreDB->get()
#12 /var/www/mediawiki/wiki.swee.codes/includes/language/LocalisationCache.php(613): LocalisationCache->isExpired()
#13 /var/www/mediawiki/wiki.swee.codes/includes/language/LocalisationCache.php(524): LocalisationCache->initLanguage()
#14 /var/www/mediawiki/wiki.swee.codes/includes/language/LocalisationCache.php(404): LocalisationCache->loadSubitem()
#15 /var/www/mediawiki/wiki.swee.codes/includes/language/LocalisationCache.php(420): LocalisationCache->getSubitem()
#16 /var/www/mediawiki/wiki.swee.codes/includes/language/MessageCache.php(1206): LocalisationCache->getSubitemWithSource()
#17 /var/www/mediawiki/wiki.swee.codes/includes/language/MessageCache.php(1146): MessageCache->getMessageForLang()
#18 /var/www/mediawiki/wiki.swee.codes/includes/language/MessageCache.php(1041): MessageCache->getMessageFromFallbackChain()
#19 /var/www/mediawiki/wiki.swee.codes/includes/language/Message/Message.php(1545): MessageCache->get()
#20 /var/www/mediawiki/wiki.swee.codes/includes/language/Message/Message.php(1059): MediaWiki\Message\Message->fetchMessage()
#21 /var/www/mediawiki/wiki.swee.codes/includes/language/Message/Message.php(1151): MediaWiki\Message\Message->format()
#22 /var/www/mediawiki/wiki.swee.codes/includes/exception/MWExceptionRenderer.php(262): MediaWiki\Message\Message->text()
#23 /var/www/mediawiki/wiki.swee.codes/includes/exception/MWExceptionRenderer.php(200): MediaWiki\Exception\MWExceptionRenderer::msg()
#24 /var/www/mediawiki/wiki.swee.codes/includes/exception/MWExceptionRenderer.php(116): MediaWiki\Exception\MWExceptionRenderer::reportHTML()
#25 /var/www/mediawiki/wiki.swee.codes/includes/exception/MWExceptionHandler.php(137): MediaWiki\Exception\MWExceptionRenderer::output()
#26 /var/www/mediawiki/wiki.swee.codes/includes/exception/MWExceptionHandler.php(241): MediaWiki\Exception\MWExceptionHandler::report()
#27 /var/www/mediawiki/wiki.swee.codes/includes/exception/MWExceptionHandler.php(209): MediaWiki\Exception\MWExceptionHandler::handleException()
#28 [internal function]: MediaWiki\Exception\MWExceptionHandler::handleUncaughtException()
#29 {main}