涉及好多个错误。一环套一环的。
首先安装问题
首先需要安装mariadb-server
systemctl start mariadb.service
会报错：Failed to start mariadb.service: Unit not found.
yum install mariadb
然后使用命令systemctl start mariadb，提示如下：
Failed to start mariadb.service: Unit mariadb.service failed to load: No such file or directory
意思找不到mariadb这个服务。之所以找不到，是因为mariadb的安装本身就没有完成，执行以下命令，查看mariadb的依赖情况：
执行以下，安装缺少的依赖包：
$ yum install mariadb-embedded mariadb-libs mariadb-bench mariadb mariadb-sever
然后再启动mariadb，正常，如果要设置开机自启动mariadb，使用以下命令：
$ systemctl enable mariadb
但是还是报错了：
Job for mariadb.service failed because the control process exited with error code. See "systemctl status mariadb.service" and "journalctl -xe" for details.
意思是执行
systemctl status mariadb.service
查看报错信息，从这里能够解决问题所在
4月 04 15:41:57 zhujiwu systemd[1]: Starting MariaDB database server...
4月 04 15:41:57 zhujiwu mariadb-prepare-db-dir[19135]: Database MariaDB is probably initialized in /www/server/data already, no... done.
4月 04 15:41:57 zhujiwu mariadb-prepare-db-dir[19135]: If this is not the case, make sure the /www/server/data is empty before ...b-dir.
4月 04 15:41:58 zhujiwu mysqld_safe[19166]: 190404 15:41:58 mysqld_safe Logging to '/www/server/data/zhujiwu.err'.
4月 04 15:41:58 zhujiwu mysqld_safe[19166]: 190404 15:41:58 mysqld_safe A mysqld process already exists
4月 04 15:41:58 zhujiwu systemd[1]: mariadb.service: main process exited, code=exited, status=1/FAILURE
4月 04 15:41:58 zhujiwu systemd[1]: mariadb.service: control process exited, code=exited status=1
4月 04 15:41:58 zhujiwu systemd[1]: Failed to start MariaDB database server.
4月 04 15:41:58 zhujiwu systemd[1]: Unit mariadb.service entered failed state.
4月 04 15:41:58 zhujiwu systemd[1]: mariadb.service failed.
重要的是这一条信息
4月 04 15:41:58 zhujiwu mysqld_safe[19166]: 190404 15:41:58 mysqld_safe A mysqld process already exists
解决方案：
然后执行
restart mariadb.service
status mariadb.service
成功运行
mariadb.service - MariaDB database server
Loaded: loaded (/usr/lib/systemd/system/mariadb.service; disabled; vendor preset: disabled)
Active: active (running) since 四 2019-04-04 15:50:46 CST; 3s ago
Process: 19929 ExecStartPost=/usr/libexec/mariadb-wait-ready $MAINPID (code=exited, status=0/SUCCESS)
Process: 19895 ExecStartPre=/usr/libexec/mariadb-prepare-db-dir %n (code=exited, status=0/SUCCESS)
Main PID: 19926 (mysqld_safe)
CGroup: /system.slice/mariadb.service
├─19926 /bin/sh /usr/bin/mysqld_safe --basedir=/usr
└─20494 /usr/libexec/mysqld --basedir=/usr --datadir=/www/server/data --plugin-dir=/usr/lib64/mysql/plugin --log-error=/www...
4月 04 15:50:44 zhujiwu systemd[1]: Starting MariaDB database server...
4月 04 15:50:44 zhujiwu mariadb-prepare-db-dir[19895]: Database MariaDB is probably initialized in /www/server/data already, no... done.
4月 04 15:50:44 zhujiwu mariadb-prepare-db-dir[19895]: If this is not the case, make sure the /www/server/data is empty before ...b-dir.
4月 04 15:50:44 zhujiwu mysqld_safe[19926]: 190404 15:50:44 mysqld_safe Logging to '/www/server/data/zhujiwu.err'.
4月 04 15:50:45 zhujiwu mysqld_safe[19926]: 190404 15:50:45 mysqld_safe Starting mysqld daemon with databases from /www/server/data
4月 04 15:50:46 zhujiwu systemd[1]: Started MariaDB database server.
Hint: Some lines were ellipsized, use -l to show in full.