PHP based website is showing error 500.
If your PHP website is reporting an Error 500 then check the Apache error_log
tail -0f /var/log/apache2/error_log
and then try to load the site to see if there is an error. If there is a lot of output then only show that user by using grep. Let's say the user is George.
tail -0f /var/log/apache2/error_log | grep george
If you're seeing "SoftException in Application" errors this indicates suPHP is being used as the PHP handler and file or directory access has been rejected. After the SoftException part of the output, you will see more information like
File "/home/user/somedomain.com/info.php" is writeable by group
Directory "/home/user/somedomain.com/" is writeable by group
suPHP requires strict permissions on .php extension files.
If the issue is with a directory then the permissions need to be set to 755.
chmod 755 /home/user/somedomain.com/
and a .php extension file needs to be 644
chmod 644 /home/user/somedomain.com/info.php