Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2).

i use mysql and I didn't have a problem.

But today the mysq does not started.
When i try to login it gives an error:

mysql> mysql -u root -p
Enter password: *******
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

I dont understand why.
The mysqld directory and mysqld.sock does not exist.
How can i create the mysqld.sock and what can i write inside?

If someone knows how to resolve this problem please tell me.

Thanks in advance,