Centos7 上安装mysql遇上的问题：mysql无法正常启动
第一次在Centos上安装mysql遇到的一些问题。
第一步就遇到问题，安装mysql-server报错没有可用包。
【解决方法】
先要安装mysql
# wget http://repo.mysql.com/mysql-community-release-el7-5.noarch.rpm
# rpm -ivh mysql-community-release-el7-5.noarch.rpm之后再安装mysql-server
# yum -y install mysql-server然后systemctl enable mysqld设置mysql自启动 之后systemctl start mysqld这时候出问题了，运行之后一直卡着没有反应，如下
[root@localhost ~]# systemctl start mysqld
Redirecting to /bin/systemctl start mysql.servicesystemctl status mysqld查看mysql服务的状态如下
[root@localhost sbin]# systemctl status mysqld
● mysqld.service - MySQL Community Server
Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
Active: activating (start-post) since 一 2017-05-15 17:04:12 CST; 5min ago
Process: 981 ExecStart=/usr/bin/mysqld_safe --basedir=/usr (code=exited, status=0/SUCCESS)
Process: 938 ExecStartPre=/usr/bin/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
Main PID: 981 (code=exited, status=0/SUCCESS); : 982 (mysql-systemd-s)
CGroup: /system.slice/mysqld.service
└─control
├─ 982 /bin/bash /usr/bin/mysql-systemd-start post
└─2315 sleep 1
5月 15 17:04:12 localhost.localdomain systemd[1]: Starting MySQL Community Server...
5月 15 17:04:15 localhost.localdomain mysqld_safe[981]: 170515 17:04:15 mysqld_safe Logging to '/var/lo...g'.
5月 15 17:04:15 localhost.localdomain mysqld_safe[981]: 170515 17:04:15 mysqld_safe Starting mysqld dae...sql
Hint: Some lines were ellipsized, use -l to show in full.看不出问题，查看mysql的日志终于找到问题vim /var/log/mysqld.log
2017-05-14 16:40:16 0 [Note] Binlog end
170514 16:40:16 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
170515 17:04:15 mysqld_safe Logging to '/var/log/mysqld.log'.
170515 17:04:15 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
2017-05-15 17:04:18 0 [ERROR] /usr/sbin/mysqld: ambiguous option '--character-set=utf8' (character-set-client-handshake, character_sets_dir)
2017-05-15 17:04:18 0 [ERROR] Aborting原来是my.cnf文件中设置默认字符编码我写成character-set=ut8而centos7版本中应该设置为default-character-set=utf8
之后继续启动mysql仍然无法启动，查看日志如下
2017-05-15 17:14:21 1195 [Warning] Buffered warning: Changed limits: table_open_cache: 431 (requested 2000)
2017-05-15 17:14:21 1195 [Note] Plugin 'FEDERATED' is disabled.
/usr/sbin/mysqld: Table 'mysql.plugin' doesn't exist
2017-05-15 17:14:21 1195 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
2017-05-15 17:14:21 1195 [Note] InnoDB: Using atomics to ref count buffer pool pages
2017-05-15 17:14:21 1195 [Note] InnoDB: The InnoDB memory heap is disabled
2017-05-15 17:14:21 1195 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2017-05-15 17:14:21 1195 [Note] InnoDB: Memory barrier is not used
2017-05-15 17:14:21 1195 [Note] InnoDB: Compressed tables use zlib 1.2.3
2017-05-15 17:14:21 1195 [Note] InnoDB: Using Linux native AIO
2017-05-15 17:14:21 1195 [Note] InnoDB: Not using CPU crc32 instructions
2017-05-15 17:14:21 1195 [Note] InnoDB: Initializing buffer pool, size = 128.0M
170515 17:04:18 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended注意ERROR
Can’t open the mysql.plugin table. Please run mysql_upgrade to create it.
【解决方法】
在运行初始化权限表的时候使用增加参数–datadir
mysql_install_db –user=mysql –datadir=/usr/local/mysql/var
百度后
安装完mysql server时，一般要执行这个脚本对数据库初始化。 运行这个脚本，会初始化mysql的data目录，并且创建那些系统表。
同样也会初始化系统表空间并且关联innodb表与数据结构。
更多的相关可以点击这里查看
之后启动服务依然卡住，回看前面执行命令之后的提示
Alternatively you can run:
/usr/bin/mysql_secure_installation即执行MySQL安全配置向导mysql_secure_installation
安装完mysql-server 会提示可以运行mysql_secure_installation。运行mysql_secure_installation会执行几个设置：
a)为root用户设置密码
b)删除匿名账号
c)取消root用户远程登录
d)删除test库和对test库的访问权限
e)刷新授权表使修改生效
执行之后systemctl restart mysqld命令可以正常执行了
可以正常启动登录mysql