/etc/init.d/mysql start won't start why?

Question

MySQL

Good day. Today there is such a problem. I go to the site and it does not open. Writes An unexpected database error occurred. Please try again later. Ok I thought. I try to connect via phpmyadmin and nothing. Okay, I try through the console, it gives an error.
Googling a little came across what to try to start the muscle. launching

/etc/init.d/mysql start

What does it answer me

[FAIL] Starting MySQL database server: mysqld . . . . . . . . . . . . . . failed!

Everywhere it is written that perhaps / var is full. Please tell me in detail. How can I increase the size of this var. And then so I have 120g of free space.

Answer 1

To get started, run forum.ubuntu.ru/index.php?topic=59628.0
Bring the logs and the code of the my.cnf file

Answer 2

df -h |grep var
returns what?

Answer 3

Rule number 1: something does not work - we read the logs.