MySQL sock file is missing: server doesn't start

[spacemarc]

hi
MySQL server doesn't start because #2002 the
/var/run/mysqld/mysqld.sock is missing.
The server only start with "sudo mysqld_safe" but without the mysqld.sock file.

I've checked my /etc/mysql/my.cnf file and the paths are correct for
[client] and [mysqld]: /var/run/mysqld/mysqld.sock
I run 5.1.41 on Ubuntu 10.04

How to resolve this issue?

thanks