PHP FPM refuse to start after upgrading Ubuntu

This weird thing happen after I upgrade my Ubuntu Production server. Suddenly php-fpm refuse to start.

sudo service php5-fpm start

sudo service php5-fpm status

And I always get

* php5-fpm is not running

Checking on the error-log located at sudo tail /var/log/php5-fpm.log show nothing, the last log entry is from previous machine-reboot, so it indicates that php-fpm is not running at all.

So I check wether the standard port 9000 is being used by other service by using

netstat -tap | grep 9000

It give me nothing, so then I try to run php-fpm executable directly from console

php5-fpm

And it show some errors related to configuration file, apparently the upgrade process messing around with my custom config.

Fixing the config and voila! it goes back to work.