阿里云备份快照后MySQL启动不了解决办法

/etc/init.d/mysqld start
Starting MySQL./usr/local/mysql/bin/mysqld_safe: line 586: /var/lib/mysql/mysqld_safe.pid: No such file or directory
awk: (FILENAME=- FNR=1) warning: error writing standard output (Broken pipe)
2019-01-27T04:16:23.831557Z mysqld_safe error: log-error set to '/var/log/mariadb/mariadb.log', however file don't exists. Create writable for user 'mysql'.
The server quit without updating PID file (/var/lib/mysql/i[FAILED]zg7ppyt15vrbkz.pid).
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阿里云服务器，备份了个快照，备份的时候网站是能用的，然后回滚到这个快照，启动MySQL，报了上面的错，找了网上很多资料都没解决，最后阿里云的工程师解释说，我备份快照的时候就有问题，系统表有问题，mysql.user表不存在,导致数据库无法初始化 。

2019-01-27T10:17:34.838342Z 0 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
2019-01-27T10:17:34.838856Z 0 [Warning] Gtid table is not ready to be used. Table 'mysql.gtid_executed' cannot be opened.
2019-01-27T10:17:34.838945Z 0 [Warning] Failed to set up SSL because of the following SSL library error: SSL context is not usable without certificate and private key
2019-01-27T10:17:34.838956Z 0 [Note] Server hostname (bind-address): '0.0.0.0'; port: 3306
2019-01-27T10:17:34.838984Z 0 [Note]   - '0.0.0.0' resolves to '0.0.0.0';
2019-01-27T10:17:34.839021Z 0 [Note] Server socket created on IP: '0.0.0.0'.
2019-01-27T10:17:34.839302Z 0 [Note] InnoDB: Loading buffer pool(s) from /var/lib/mysql/ib_buffer_pool
2019-01-27T10:17:34.839476Z 0 [Note] InnoDB: Buffer pool(s) load completed at 190127 18:17:34
2019-01-27T10:17:34.841275Z 0 [Warning] Failed to open optimizer cost constant tables
 
2019-01-27T10:17:34.843929Z 0 [ERROR] Fatal error: Can't open and lock privilege tables: Table 'mysql.user' doesn't exist
2019-01-27T10:17:34.843989Z 0 [ERROR] Aborting
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解决办法：暴力的重新安装MySQL，在重新安装之前，记得把数据备份好。

编译安装MySQL

rpm -qa | grep mysql
rpm -qa | grep mariadb
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rpm -e 软件名    #注意：这里的软件名必须包含软件的版本信息，如rpm -e mariadb-libs-5.5.52-1.el7.x86_64。一般使用此命令即可卸载成功。
rpm -e --nodeps 软件名   #卸载不成功时使用此命令强制卸载
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yum install -y libaio-*                         #安装依赖
mkdir -p /usr/local/mysql
cd /usr/local/src
wget http://zy-res.oss-cn-hangzhou.aliyuncs.com/mysql/mysql-5.7.17-linux-glibc2.5-x86_64.tar.gz 
tar -xzvf mysql-5.7.17-linux-glibc2.5-x86_64.tar.gz
mv mysql-5.7.17-linux-glibc2.5-x86_64/* /usr/local/mysql/
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groupadd mysql
useradd -g mysql -s /sbin/nologin mysql
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/usr/local/mysql/bin/mysqld --initialize-insecure --datadir=/usr/local/mysql/data/ --user=mysql
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cd /usr/local/mysql/support-files/
cp mysql.server  /etc/init.d/mysqld
chmod +x /etc/init.d/mysqld             # 添加执行权限
vim /etc/rc.d/rc.local
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/etc/init.d/mysqld start
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mysqladmin -u root password
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提示以下信息：

```
mysqladmin: connect to server at 'localhost' failed
error: 'Access denied for user 'root'@'localhost' (using password: NO)'
```
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service mysqld stop
mysqld_safe --skip-grant-tables &
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mysql -uroot -p #-p和密码之间无空格
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