vTiger CRM use Log4PHP to generate the application log.
Sometime you may face issue to read the log file vtigercrm.log it is because log4php only set the file as readonly so nobody can access outside using HTTP.
Here is simple solution to make the file readable. but advice is to revert once your work done.
below file and change the line mentioned.
if (is_readable($fileName)) chmod ($fileName,0222);
comment above line in file LoggerAppenderFile.php
replace it with below line
Happy programming !!!