MySQL: trying to log the queries. File is empty

I'm trying to create a log this way:

sudo 开发者_JS百科mysqld --general_log=1 --general_log_file=/tmp/foo --log-output=FILE

But I find this in foo:

mysqld, Version: 5.1.41-3ubuntu12.9-log ((Ubuntu)). started with:
Tcp port: 3306  Unix socket: /var/run/mysqld/mysqld.sock
Time                 Id Command    Argument

It's for sure that I'm sending queries to the database.

Any idea?

Regards

Javi