安装mariadb，先搜索一发：
$ sudo yum search mariadb
出现：
$ sudo yum search mariadb
Loaded plugins: langpacks
============================= N/S matched: mariadb =============================
mariadb-bench.x86_64 : MariaDB benchmark scripts and data
mariadb-devel.i686 : Files for development of MariaDB/MySQL applications
mariadb-devel.x86_64 : Files for development of MariaDB/MySQL applications
mariadb-embedded.i686 : MariaDB as an embeddable library
mariadb-embedded.x86_64 : MariaDB as an embeddable library
mariadb-embedded-devel.i686 : Development files for MariaDB as an embeddable : library
mariadb-embedded-devel.x86_64 : Development files for MariaDB as an embeddable : library
mariadb-libs.i686 : The shared libraries required for MariaDB/MySQL clients
mariadb-libs.x86_64 : The shared libraries required for MariaDB/MySQL clients
mariadb-server.x86_64 : The MariaDB server and related files
mariadb.x86_64 : A community developed branch of MySQL
mariadb-test.x86_64 : The test suite distributed with MariaD
嗯，把 mariadb mariadb-bench mariadb-server mariadb-embdedeb mariadb-libs mariadb-server都安装：
$ yum install mariadb-embedded mariadb-libs mariadb-bench mariadb mariadb-sever
启动mariadb，再试试"mysql -u root“发现可以了，好吧，作为一个Archlinuxer表示centos（或者说rpm系列？）的mariadb打包分得真细。
哦，那些个什么service xx start的命令在很多新版本的linux发行版上已经不适用了，正确的打开方式是systemctl [option] [xx],mariadb(mysql)使用:
$ systemctl start mariadb
centos何时用systematl的我不知道，至少centos7用systemctl。开机自启动：
$ systemctl enable mariadb