Hello,

This page contains instructions on how to restore a backup:

https://mariadb.com/kb/en/library/full-backup-and-restore-with-mariabackup/#restoring-the-backup 

1. stop MariaDB:

    # systemctl stop mariadb.service

2. datadir must be empty:

    # rm -rf /var/lib/mysql/

3. run mariabackup:

    #mariabackup --copy-back --target-dir=/var/mariadb/backup/

4. fix permissions:

    # chown -R mysql:mysql /var/lib/mysql/

5. start MariaDB:

    # systemctl start mariadb.service

mariabackup said "completed OK!" and I see that datadir contains the restored data.

However, when following these instructions, I can't start MariaDB anymore. I have the following error:

mar 29 07:06:49 myhostname mysqld[11359]: 2019-03-29  7:06:49 0 [ERROR] Plugin 'InnoDB' init function returned error.

mar 29 07:06:49 myhostname mysqld[11359]: 2019-03-29  7:06:49 0 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.

mar 29 07:06:49 myhostname mysqld[11359]: 2019-03-29  7:06:49 0 [Note] Plugin 'FEEDBACK' is disabled.

mar 29 07:06:49 myhostname mysqld[11359]: 2019-03-29  7:06:49 0 [ERROR] Could not open mysql.plugin table. Some plugins may be not loaded

mar 29 07:06:49 myhostname mysqld[11359]: 2019-03-29  7:06:49 0 [ERROR] Unknown/unsupported storage engine: InnoDB

mar 29 07:06:49 myhostname mysqld[11359]: 2019-03-29  7:06:49 0 [ERROR] Aborting

mar 29 07:06:49 myhostname systemd[1]: mariadb.service: main process exited, code=exited, status=1/FAILURE

mar 29 07:06:49 myhostname systemd[1]: Failed to start MariaDB 10.3.13 database server.

mar 29 07:06:49 myhostname systemd[1]: Unit mariadb.service entered failed state.

mar 29 07:06:49 myhostname systemd[1]: mariadb.service failed.