From KDE UserBase Wiki

mysqld: unknown variable 'innodb_file_per_table=1'

If the MySQL server log contains the following error, then your MySQL server was built without the InnoDB support which is required by Akonadi or InnoDB needs to be loaded in your mysql.conf file:

[ERROR] /usr/libexec/mysqld: unknown variable 'innodb_file_per_table=1'

[ERROR] Aborting

Try adding:

#sql_mode=strict_trans_tables <- Add underneath this line
plugin_dir=usr/lib/mysql/plugin < - This may be a different path