root@server [/home/domain.tld/www]# php ./bin/magento module:enable Infortis_Cgen Infortis_Dataporter Infortis_Infortis Infortis_Ultimo Infortis_UltraMegamenu Infor

Check https://getcomposer.org/doc/articles/troubleshooting.md#memory-limit-errors for more info on how to handle out of memory errors.
root@server [/home/domain.tld/www]#

To check the current memory_limit try

root@server [/home/domain.tlm/www]# php -r "echo ini_get('memory_limit').PHP_EOL;"

On WHM

Let’s increase it to 2G, for example.