Can’t create/write to file ‘/tmp/#sql

All of a sudden most of your websites that connect to a database are getting the following error :

Can't create/write to file '/tmp/#sql ........
this means that the root the cache  folder inside your tmp file must have its permission set to 757.
here is what you need to do:
1- login to your root directory via SSH as a root
2- chmod 1757 tmp
3-restart the sql server with this command : service mysql restart
4- reload and check the sites

this is mostly due to permission issue, either the owner " should be root" or should be writable 777

Hope this helps.

Richard F.