MySQL: Can't create/write to file '/tmp/#sql_3c6_0.MYI' (Errcode: 2) - What does it even mean?

Question

For some reason my production DB decided to spew out this message. All application calls fail to the DB with the error:

PreparedStatementCallback; SQL [ /*lo         


        

Answer 1

On debian 7.5 I got the same error. I realized the /tmp folder owner and permissions were off. As another answer suggested I did as follows (must be root):

chown root:root /tmp && chmod 1777 /tmp

I did not even have to restart mysql daemon.