I have created crontab.xml in vendor/module/etc directory

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Cron:etc/crontab.xsd"> <group id="default">     <job name="get_carriers" instance="Vendor\Module\Cron\GetCarriers" method="execute">         <schedule>* * * * *</schedule>     </job> </group> 

And create GetCarriers.php in Vendor/Module/Cron/GetCarriers.php

namespace Vendor\Module\Cron;      class GetCarriers {       protected $  _logger;       public function __construct(\Psr\Log\LoggerInterface $  logger) {            $  this->_logger = $  logger;      }       public function execute() {            $  writer = new \Zend\Log\Writer\Stream(BP . '/var/log/cron.log');            $  logger = new \Zend\Log\Logger();            $  logger->addWriter($  writer);            $  logger->info(__METHOD__);             return $  this;      } } 

Now if i execute php bin/magento cron:run –group=”default” cron run but i want it to execute automatically every week.