I can't start mysqld.service -> status : Data Dictionary upgrade from MySQL 5.7 in progress in centos 7 I've installed mysql 8 on centos 7 

and when i want to start the mysqld service , it says :

Job for mysqld.service failed because the control process exited with error code. See "systemctl status mysqld.service" and "journalctl -xe" for details


and when i run systemctl status mysqld.service it says:

mysqld.service - MySQL Server
Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor 
preset: disabled)
Active: failed (Result: exit-code) since Mon 2020-01-13 06:01:53 EST; 6min ago
Docs: man:mysqld(8)
http://dev.mysql.com/doc/refman/en/using-systemd.html
Process: 5532 ExecStart=/usr/sbin/mysqld $MYSQLD_OPTS (code=exited, status=1/FAILURE)
Process: 5504 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
Main PID: 5532 (code=exited, status=1/FAILURE)
Status: "Data Dictionary upgrade from MySQL 5.7 in progress"

Jan 13 06:01:48 server1.lifeandme.net systemd[1]: Starting MySQL Server...
Jan 13 06:01:53 server1.lifeandme.net systemd[1]: mysqld.service: main process exited, code=exited, status=1/FAILURE
Jan 13 06:01:53 server1.lifeandme.net systemd[1]: Failed to start MySQL Server.
Jan 13 06:01:53 server1.lifeandme.net systemd[1]: Unit mysqld.service entered failed state.
Jan 13 06:01:53 server1.lifeandme.net systemd[1]: mysqld.service failed.


I also tried restart the service and cleaning log files under /var/lib/mysql , but no success

i did the following commands to install lamp on server (history related to lamp installation)

yum install httpd

systemctl start httpd.service

systemctl enable httpd.service

yum install mariadb-server mariadb

systemctl start mariadb

mysql_secure_installation

systemctl enable mariadb.service

yum install php php-mysql

systemctl restart httpd.service

yum remove php php-server

yum clean packages

yum install epel-release

yum install http://rpms.remirepo.net/enterprise/remi-release-7.rpm

yum install yum-utils

yum-config-manager --enable remi-php72

yum install php72

yum remove mariadb mariadb-server

systemctl restart httpd.service

yum localinstall https://dev.mysql.com/get/mysql80-community-release-el7-1.noarch.rpm

yum install mysql-community-server

systemctl enable mysqld

systemctl start mysqld =&gt;  ran to error
This worked for me:

Clear the mysql data directory at /var/lib/mysql assuming that you have backups or you don't really need that data anymore.

Then sudo service mysqld start