/app/fuel/app/config/config.php


/**
* Logging Threshold.  Can be set to any of the following:
*
* Fuel::L_NONE
* Fuel::L_ERROR
* Fuel::L_WARNING
* Fuel::L_DEBUG
* Fuel::L_INFO
* Fuel::L_ALL
*/
'log_threshold'    => Fuel::L_WARNING,
'log_path'         => APPPATH.'logs/',
'log_date_format'  => 'Y-m-d H:i:s',

ログの場所

# tail -f /app/fuel/app/logs/2018/03/01.php