6
Is log file is an actual file or it's a symbolik link? If you efteepee to your site look up command like "ls -al"
if it list something like:
lrwxrwxrwx 1 root 9 Oct 1 19:42 something-> /dev/null
and the first character stands for:
- regular file
d directory
l symbolic link
c character device
b block device
s socket device
You can go to your root and issue a command "pwd" it will tell you full path to your working directory which you enter to mainfile.php.
Good luck and tell me if you have more problems.