I always encountered the following issue. and the installation failed. And I check the file is already there.
PHP Warning: include_once(/core/class/conf.class.php): failed to open stream: No such file or directory in /var/www/unilumin-erp/htdocs/install/inc.php on line 282, referer: http://my.domain/install/fileconf.php?selectlang=auto
OS: CentOS 7.0
PHP 7.2
Dolibarr 10.0.2