There are multiple instances of MySQL Server running on a single OS that is backed...

There are multiple instances of MySQL Server running on a single OS that is backed up using the mysqlbackup command.

The /etc/my/cnf contains default values, for example, datadir=/var/lib/mysql/, with extra instances having their own separate my.cnf file (for example /etc/mysql/instanceN.cnf) overriding the defaults.

A restore of the second instance is attempted from the mysqlbackup archive using this command:

mysqlbackup --backup-dir=/opt/backup/mysql/instance2 copy-back

Upon starting the second MySQL instance, you notice that the data does not match the expected backup. Which command-line option is required to successfully update the second instance?