This is a stand alone gateway install hence no replication.
The /var/lib/mysql file system had exhausted disk space and the mysql process was not able to start up.
The ibdata file was 16 Gb in size which is at its max,
What we did to free up some space was move a 'sys' database to /tmp
This then allowed mysql to start up successfully.
We immediately then went into the mysql interface and truncated and optimized the audit tables via the following:
mysql
use ssg;
SET FOREIGN_KEY_CHECKS = 0;
truncate table audit_admin;
optimize table audit_admin;
truncate table audit_detail;
optimize table audit_detail;
truncate table audit_detail_params;
optimize table audit_detail_params;
truncate table audit_main;
optimize table audit_main;
truncate table audit_message;
optimize table audit_message;
truncate table audit_system;
optimize table audit_system;
SET FOREIGN_KEY_CHECKS = 1;
The /var/lib/mysql disk usage then dropped from 100% down to 80%