Completely remove MariaDB or MySQL from CentOS 7 or RHEL 7
These steps are working on CentOS 6.5 so they should work on CentOS 7 too:
(EDIT - exactly the same steps work for MariaDB 10.3 on CentOS 8)
yum remove mariadb mariadb-server-
rm -rf /var/lib/mysqlIf your datadir in /etc/my.cnf points to a different directory, remove that directory instead of /var/lib/mysql -
rm /etc/my.cnfthe file might have already been deleted at step 1 - Optional step:
rm ~/.my.cnf yum install mariadb mariadb-server
[EDIT] - Update for MariaDB 10.1 on CentOS 7
The steps above worked for CentOS 6.5 and MariaDB 10.
I've just installed MariaDB 10.1 on CentOS 7 and some of the steps are slightly different.
Step 1 would become:
yum remove MariaDB-server MariaDB-client
Step 5 would become:
yum install MariaDB-server MariaDB-client
The other steps remain the same.
To update and answer the question without breaking mail servers. Later versions of CentOS 7 have MariaDB included as the base along with PostFix which relies on MariaDB. Removing using yum will also remove postfix and perl-DBD-MySQL. To get around this and keep postfix in place, first make a copy of /usr/lib64/libmysqlclient.so.18 (which is what postfix depends on) and then use:
rpm -qa | grep mariadb
then remove the mariadb packages using (changing to your versions):
rpm -e --nodeps "mariadb-libs-5.5.56-2.el7.x86_64"
rpm -e --nodeps "mariadb-server-5.5.56-2.el7.x86_64"
rpm -e --nodeps "mariadb-5.5.56-2.el7.x86_64"
Delete left over files and folders (which also removes any databases):
rm -f /var/log/mariadb
rm -f /var/log/mariadb/mariadb.log.rpmsave
rm -rf /var/lib/mysql
rm -rf /usr/lib64/mysql
rm -rf /usr/share/mysql
Put back the copy of /usr/lib64/libmysqlclient.so.18 you made at the start and you can restart postfix.
There is more detail at https://code.trev.id.au/centos-7-remove-mariadb-replace-mysql/ which describes how to replace mariaDB with MySQL