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
name=MySQL 5.5 Community Server

# Enable to use MySQL 5.6
name=MySQL 5.6 Community Server

# Enable to use MySQL 5.7
name=MySQL 5.7 Community Server

name=MySQL 8.0 Community Server

name=MySQL Connectors Community

name=MySQL Tools Community

name=MySQL Tools Preview

name=MySQL Cluster 7.5 Community

name=MySQL Cluster 7.6 Community

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
  • Downgrading from 8.0 is not supported. Or at least not easily. – Rick James Jun 14 '19 at 7:35

yum update will only replace an installed package with a newer version unless you tell it otherwise, so it won't downgrade your 8.0 installation even if the repository it came from has been disabled in its config files.

I would suggest uninstalling the current version with yum remove and then installing the version you want. Make sure to protect the data files themselves and/or make copies. Use yum list mysql* or yum list installed | grep mysql to see what you have installed and what versions and then remove anything version 8 related with yum remove packagename.


yum remove mysql-community-client

Make a note of them so you know what to install from 5.6.

The challenge you're having with 8.0 is that going straight there from 5.5 is too big a jump for the updates needed to the data files. Each new version only understands the file formats from a certain range of older versions.

I had problems with 8.0.16 too - I ended up reinitialising the database and then loading a mysqldump from the earlier version as it was the quickest way to get up and running.

  • Thanks for the guidance. Sorry to sound overly simplistic but what would be the exact 'yum remove' command? I am just concerned I will end up removing the wrong package etc. – Craig Jun 14 '19 at 0:13
  • Also, I have downloaded the Database Tables via phpMyAdmin. Is this enough of a backup or is this different to a mysqldump? – Craig Jun 14 '19 at 0:14
  • Updated answer as I couldn't put the asterisk in a comment. Copy all the files in the database folder - these are binaries while mysqldump is a text file containing the SQL statements that will create and populate the database - but you need the database to be running to create it. – Finbarr Jun 14 '19 at 0:30
  • I could be stupid here but I cannot figure which are 'version 8 packages'. I have updated my answer, to reflect what I can see. – Craig Jun 14 '19 at 0:37
  • Ok. That produces a lot more results. I can see an entry mysql-community-client.x86_64 ... 8.0.16-2.el6. Therefore, to remove this, I would simply enter yum remove mysql-community-client.x86_64. Then do the same with all other packages? Once all of these 'version 8' references have been removed, do I then simply go through the installation process again; as per support.plesk.com/hc/en-us/articles/…? – Craig Jun 14 '19 at 0:54

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