Centos系统上安装mysql服务

  最近在CentOS release 6.3上安装了mysql，但是mysqladmin -u root password 123456命令的时候，却出现如下的错误：

/usr/bin/mysqladmin -u root password 123456
/usr/bin/mysqladmin: connect to server at 'localhost' failed
error: 'Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)'
Check that mysqld is running and that the socket: '/var/lib/mysql/mysql.sock' exists!

  发现可能的错误应该是mysqld服务守护进程没运行的原因，然后使用service mysqld status命令查看当前mysqld的服务状态，发现它确实是处于stopped状态，随后便想用service mysqld start命令启动守护进程，却又出现启动服务失败的信息：

service mysqld start
MySQL Daemon failed to start.
Starting mysqld:                                           [FAILED]

  这下就头大了，启动服务竟然失败了。而且又没有任何相关的错误信息，所以只能查看它的错误日志，如下所示：

tail -n 20 /var/log/mysqld.log
120907 13:52:30 [ERROR] Fatal error: Can't open and lock privilege tables: Table 'mysql.host' doesn't exist
120907 13:52:30 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
120907 14:06:24 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
/usr/libexec/mysqld: Table 'mysql.plugin' doesn't exist
120907 14:06:24 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
120907 14:06:24  InnoDB: Initializing buffer pool, size = 8.0M
120907 14:06:24  InnoDB: Completed initialization of buffer pool
InnoDB: Log scan progressed past the checkpoint lsn 0 37356
120907 14:06:24  InnoDB: Database was not shut down normally!
InnoDB: Starting crash recovery.
InnoDB: Reading tablespace information from the .ibd files...
InnoDB: Restoring possible half-written data pages from the doublewrite
InnoDB: buffer...
InnoDB: Doing recovery: scanned up to log sequence number 0 44233
120907 14:06:24  InnoDB: Starting an apply batch of log records to the database...
InnoDB: Progress in percents: 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
InnoDB: Apply batch completed
120907 14:06:24  InnoDB: Started; log sequence number 0 44233
120907 14:06:24 [ERROR] Fatal error: Can't open and lock privilege tables: Table 'mysql.host' doesn't exist
120907 14:06:24 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pi

  从中发现出现一个致命的错误，Can't open and lock privilege tables: Table 'mysql.host' doesn't exist！这样问题也就找到了，table ‘mysql.host’不存在的原因是新安装的mysql服务后，一般需要执行数据库初始化操作 ，从而生成与权限相关的表，执行命令如下：

/usr/bin/mysql_install_db --user=mysql

  以上命令中的mysql_install_db与你安装的mysql服务位置有关，如果不知道在哪，可以使用find / -name mysql_install_db找到其位置，然后执行上面的命令。

  然后在执行数据库服务启动操作，便可以设置你mysql数据库的用户及密码了：

service mysqld start
Starting mysqld:                                           [  OK  ]
[root@host usr]# mysqladmin -u root password 123456
[root@host usr]# mysql -u root -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.1.61 Source distribution

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