MariaDB Database cannot start

I’ve been working on a development site with a Trellis workflow for months, and then all of a sudden today I get “Error establishing a database connection”.
I’ve run reload, halt & up on my Vagrant machine.
When running vagrant up --provision i get:

TASK: [mariadb | Start MariaDB MySQL Server] ********************************** 
failed: [default] => {"failed": true}
msg:  * Starting MariaDB database server mysqld
...fail!`

I’ve vagrant ssh'ed and tried database mysql restart but it fails.

service mysql reload and force-reload give the following error:

* Reloading MariaDB database server mysqld                                     
Could not open required defaults file: /etc/mysql/debian.cnf
Fatal error in defaults handling. Program aborted

Any suggestions what else I can try or check?

Did you ever resolve this? Having trouble with this at the moment. Any help appreciated. All of a sudden MySQL stopped working and a reload gives same error as above.

 Could not open required defaults file: /etc/mysql/debian.cnf
Fatal error in defaults handling. Program aborted

Edit: Started working again after second restart of the vagrant box. Strange, maybe related to system resources.