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

I'm using mariadb. When I try to put this line at /etc/my.cnf:

[mysqld]
tmpdir=/tmp 

It solved the error generated from website frontend related to /tmp. But, it has backend problem with /tmp. Example, when I try to rebuild mariadb from the backend, it couldn't read the /tmp dir, and then generated the similar error.

mysqldump: Couldn't execute 'show fields from `wp_autoupdate`': Can't create/write to file '/tmp/#sql_1680_0.MAI' (Errcode: 2 "No such file or directory") (1)

So this one work for both front end and back end:

1. mkdir /var/lib/mysql/tmp

2. chown mysql:mysql /var/lib/mysql/tmp

3. Add the following line into the [mysqld] section:

    tmpdir = /var/lib/mysql/tmp

4. Restart mysqld (eg. Centos7: systemctl restart mysqld)