Kohana's built in log is a bit weak , so I rewrite myself.
1) put log module in MODPATH
2) in bootstrap.php
add log to Kohana::modules Kohana::modules(array( 'auth' => MODPATH.'auth', 'cache' => MODPATH.'cache', //... 'log' => MODPATH.'log', ));
then replace origin with this Kohana::$log->attach(new Log_Writer_File(VARPATH.'log')); // this is just for test Kohana::$log->add(Kohana::INFO, 'someone just click the east egg!');
3) edit MODPATH/log/classes/controller/log.php
replace $log_dir to your own log dir;
4) browser http://localhost/path/to/log/day
first it will show exception, because log file is not exists, then add error to log. refresh , it should show the page.