Memory overflow issue

I am writing this one to share my experience to you. In the very beginning of my professional career, I have developed an web application for Shylhet Chamber of Commerce using LAMP and delivered it successfully. Almost three months(Couldn't remind exactly) later we have notified from client that they couldn't log into the application. Then i had gone there and investigate the problem. First I was very confused because..

• System not given any types of error message while trying to log-in.
• There is no error message in logger
• There is no problem in code
• Even though, tried to run a sample script in server but I didn't

Think about that, What was the condition that time!!!

Then tried to narrow down the error scope by checking PHP, Apache, Mysql settings and check the application storage and got that "There is no space in document root." which was the culprit for this problem. Even though application couldn't flash a single message because there was no space to show a message.

That's it. So, I think anyone should keep it in mind about storage.