Unable to downgrade MySQL from version 8 to 5.6 nor start MySQL (MySQL Error Log Included)

I run a Plesk VPS (**OS:** Centos 6/Linux (Final)), whereby I recently tried to upgrade the MySQL from version 5.5.55 to version 5.6. Being relatively new to this area, I strictly followed this Plesk Article Specifically following the steps within the 'Plesk on CentOS 6' Tab. Unfortunately, I made the mistake of assuming version 8 was disabled as default. As a result, MySQL version 8 was installed and is now causing me major issues. To the point, where I cannot start MySQL. I have tried to downgrade, from version 8 to version 5.6, by opening the file /etc/yum.repos.d/mysql-community.repo Notepad++, where I ensured the below was entered: # Enable to use MySQL 5.5 [mysql55-community] name=MySQL 5.5 Community Server baseurl=http://repo.mysql.com/yum/mysql-5.5-community/el/6/$basearch/ enabled=0 gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql # Enable to use MySQL 5.6 [mysql56-community] name=MySQL 5.6 Community Server baseurl=http://repo.mysql.com/yum/mysql-5.6-community/el/6/$basearch/ enabled=1 gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql # Enable to use MySQL 5.7 [mysql57-community] name=MySQL 5.7 Community Server baseurl=http://repo.mysql.com/yum/mysql-5.7-community/el/6/$basearch/ enabled=0 gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql [mysql80-community] name=MySQL 8.0 Community Server baseurl=http://repo.mysql.com/yum/mysql-8.0-community/el/6/$basearch/ enabled=0 gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql [mysql-connectors-community] name=MySQL Connectors Community baseurl=http://repo.mysql.com/yum/mysql-connectors-community/el/6/$basearch/ enabled=1 gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql [mysql-tools-community] name=MySQL Tools Community baseurl=http://repo.mysql.com/yum/mysql-tools-community/el/6/$basearch/ enabled=1 gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql [mysql-tools-preview] name=MySQL Tools Preview baseurl=http://repo.mysql.com/yum/mysql-tools-preview/el/6/$basearch/ enabled=0 gpgcheck=1 gpgkey=file:/etc/pki/rpm-gpg/RPM-GPG-KEY-mysql [mysql-cluster-7.5-community] name=MySQL Cluster 7.5 Community baseurl=http://repo.mysql.com/yum/mysql-cluster-7.5-community/el/6/$basearch/ enabled=0 gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql [mysql-cluster-7.6-community] name=MySQL Cluster 7.6 Community baseurl=http://repo.mysql.com/yum/mysql-cluster-7.6-community/el/6/$basearch/ enabled=0 gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql Upon entering the command yum update mysql, the following appeared on the screen: Loaded plugins: fastestmirror, security Setting up Update Process Loading mirror speeds from cached hostfile * atomic: www4.atomicorp.com * epel: mirror.freethought-internet.co.uk * remi-safe: mirror.netweaver.uk Package(s) mysql available, but not installed. No Packages marked for Update I then continued with the steps, in the hope that the installation would still miraculously work somehow. I got as far as service mysqld start where I generated the same error as before, which was: MySQL Daemon failed to start. Starting mysqld: [FAILED] I am not just absolutely stumped as to how to downgrade to MySQL version 5.6 and to start back up MySQL. **MySQL Log:** [Warning] [Server] 'Disabling symbolic links using --skip-symbolic-links (or equivalent) is the default. Consider not using this option as it' is deprecated and will be removed in a future release. [System] [Server] /usr/sbin/mysqld (mysqld 8.0.16) starting as process 14057 [System] [Server] Starting upgrade of data directory. [ERROR] [InnoDB] Unsupported redo log format (0). The redo log was created before MySQL 5.7.9 [ERROR] [InnoDB] Plugin initialization aborted with error Generic error. [ERROR] [Server] Failed to initialize DD Storage Engine. [ERROR] [Server] Data Dictionary initialization failed. [ERROR] [Server] Aborting [System] [Server] /usr/sbin/mysqld: Shutdown complete (mysqld 8.0.16) MySQL Community Server - GPL. **Additional Information:** I am not sure if the below helps but after entering the command yum repolist all | grep mysql, the following information appeared: mysql-cluster-7.5-community MySQL Cluster 7.5 Community disabled mysql-cluster-7.6-community MySQL Cluster 7.6 Community disabled mysql-connectors-community MySQL Connectors Community enabled: 94 mysql-tools-community MySQL Tools Community enabled: 78 mysql-tools-preview MySQL Tools Preview disabled mysql55-community MySQL 5.5 Community Server disabled mysql56-community MySQL 5.6 Community Server enabled: 512 mysql57-community MySQL 5.7 Community Server disabled mysql80-community MySQL 8.0 Community Server disabled **Version 8 References** As per the advise in the Comment section, I have performed the command yum list mysql* as to generate the following results as to identify any relevant 'version 8 packages' to be removed. The only problem is, I am not sure which are 'version 8 packages': Loaded plugins: fastestmirror, security Determining fastest mirrors epel/metalink | 30 kB 00:00 * atomic: www4.atomicorp.com * epel: mirror.freethought-internet.co.uk * remi-safe: mirror.netweaver.uk PLESK_17_8_11-extras | 2.9 kB 00:00 PLESK_17_8_11-extras/primary_db | 32 kB 00:00 PLESK_17_PHP56 | 2.9 kB 00:00 PLESK_17_PHP56/primary_db | 14 kB 00:00 PLESK_17_PHP70 | 2.9 kB 00:00 PLESK_17_PHP70/primary_db | 15 kB 00:00 PLESK_17_PHP73 | 2.9 kB 00:00 PLESK_17_PHP73/primary_db | 17 kB 00:00 atomic | 3.4 kB 00:00 atomic/primary_db | 651 kB 00:00 epel | 5.3 kB 00:00 epel/primary_db | 6.1 MB 00:00 mysql-connectors-community | 2.5 kB 00:00 mysql-connectors-community/primary_db | 37 kB 00:00 mysql-tools-community | 2.5 kB 00:00 mysql-tools-community/primary_db | 50 kB 00:00 mysql56-community | 2.5 kB 00:00 mysql56-community/primary_db | 261 kB 00:00 plesk-migrator | 2.9 kB 00:00 plesk-migrator/primary_db | 6.7 kB 00:00 plesk-migrator-tp | 2.9 kB 00:00 plesk-migrator-tp/primary_db | 1.2 kB 00:00 remi-safe | 3.0 kB 00:00 remi-safe/primary_db | 1.2 MB 00:00 Available Packages mysql.i686 5.5.44-30.el6.art atomic mysql.x86_64 5.5.55-1659.el6.art atomic