centos 7 解除安裝 mariadb 的正確命令
#列出所有被安裝的rpm package 
rpm -qa | grep MariaDB
#解除安裝
rpm -e mariadb-libs-5.5.37-1.el7_0.x86_64
錯誤：依賴檢測失敗：
        libmysqlclient.so.18()(64bit) 被 (已安裝) postfix-2:2.10.1-6.el7.x86_64 需要
        libmysqlclient.so.18(libmysqlclient_18)(64bit) 被 (已安裝) postfix-2:2.10.1-6.el7.x86_64 需要
#強制解除安裝，因為沒有--nodeps
　　rpm -e --nodeps mariadb-libs-5.5.37-1.el7_0.x86_64
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MariaDB 啟動錯誤
Job for mariadb.service failed because the control process exited with error code. See "systemctl status
mariadb.service" and "journalctl -xe" for details
Dec 12 20:56:53 localhost.localdomain systemd[1]: Starting MariaDB 10.3.4 database server...
Dec 12 20:56:53 localhost.localdomain systemd[1]: mariadb.service: control process exited, code=exited status=217
Dec 12 20:56:53 localhost.localdomain systemd[1]: Failed to start MariaDB 10.3.4 database server.
Dec 12 20:56:53 localhost.localdomain systemd[1]: Unit mariadb.service entered failed state.
Dec 12 20:56:53 localhost.localdomain systemd[1]: mariadb.service failed.
解決辦法：
解除安裝，重新安裝：yum -y install mariadb-server  yum -y install mariadb-devel
參考  https://www.cnblogs.com/shanyou/p/3278692.html
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MariaDB 啟動錯誤
 /usr/sbin/mysqld: unknown variable 'default-character-set=utf8mb4'
 Failed to start MariaDB 10.3.4 database server.
參考：https://www.cnblogs.com/felove2013/p/6293710.html
vim /etc/my.cnf.d/server.cnf 
[mysqld] 處 新增
character_set_server=utf8

--------------------C++連結錯誤-----------------------------------------------------
Can't initialize character set utf8mb4 (path: /usr/share/mysql/charsets/)
http://blog.itpub.net/30150152/viewspace-1800526
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Navicat for MySQL連結出現錯誤：
115 - Unknown character set :'utf8'
Navicat for MySQL客戶端：連線屬性--》高階--》編碼--》UTF8

-------------------------------------------------------------------------
mysql：1130 is not allowed to connect to this MariaDB server（沒有遠端登入許可權，注：這裡的MariaDB 是MySQL的延伸版）
解決：use mysql;   update user set Host='%' where Host='localhost'; flush privileges;
-------------------------------------------------------------------------
-----MySQL初始無密碼登入，並修改密碼
vim /etc/my.cnf.d/server.cnf
[mysqld] ##此處新增
skip-grant-tables  ##此處新增
改完密碼載次註解
https://www.cnblogs.com/gumuzi/p/5711495.html

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/usr/bin/ld: cannot find -lmysqlclient_r，原因是/usr/lib64/mysql找不到libmysqlclient_r.so

解決辦法：（參考）

首先你需要找到這個庫的位置 

一般找的話需要將lib 給加上(注意:我這裡是 -lmysqlclient_r 的報錯，於是我找就找 libmysqlclient_r )

find / -name libmysqlclient_r*

/usr/lib64/mysql/libmysqlclient_r.so
/usr/lib64/mysql/libmysqlclient_r.so.16
/usr/lib64/mysql/libmysqlclient_r.so.16.0.0

既然找到了 那應該是路徑的問題 以及庫檔名字的問題，於是做了如下的軟連線

ln -sv /usr/lib64/libmysqlclient_r.so.16.0.0 /usr/lib64/mysql/libmysqlclient_r.so(db_proxy_server/CMakeLists.txt設定的路徑：/usr/lib64/mysql)

名字也改了一下,然後再編譯就沒問題了

一般都是這樣的套路  

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