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這幾天安裝一個OA軟件，用到linux系統，但是在mysql的時候就出錯，也不曉得哪里問題，有問題就需要排除了，實屬也沒啥好辦法；

(/usr/emp/data/mysqldata/centos-linux-7.pid)

[root@centos74 ~]# service mysqld start
Starting MySQL.. ERROR! The server quit without updating PID file (/usr/emp/data/mysqldata/centos-linux-7.pid).

1、 可能已經存在?mysqld 進程.

[root@centos74 ~]# ps -ef | grep mysqld
[root@centos74 ~]# pkill -9 mysqld
# 查看是否有這個進程，如果有殺死掉

2、數據目錄mysql用戶是否有權限.

[root@centos74 ~]# chown -R mysql.mysql /usr/local/mysql/data

3、機器上面還有上次安裝mysql的殘留.

[root@centos74 ~]# find / -name mysql-binlog*
# 查看mysql的二進制目錄，看是否存在mysqlbinlog.index,有的話刪掉

4、mysql 在啟動的時候會去尋找默認的 配置文件 /etc/my.cnf? 這個目錄下的 datadir 要指定數據目錄.

# 如果沒有，那么在 my.cnf 里面添加 datadir=/usr/local/mysql/data

5、skip-federated字段問題.

# 檢查一下/etc/my.cnf文件中有沒有沒被注釋掉的skip-federated字段，如果有就立即注釋掉.

6、錯誤日志目錄不存在.

# 賦予 mysql 所有者權限 chmod chown .

7、防火墻原因.

# centos 會默認開啟selinux .
[root@centos74 ~]# vim /etc/selinux/config
SELINUX=disabled

8、查看配置文件/usr/local/mysql/my.cnf里有沒有innodb_buffer_pool_size

# innodb_buffer_pool_size：主要作用是緩存innodb表的索引，數據，插入數據時的緩沖.
# 默認值：128M；
# 專用mysql服務器設置此值的大小： 系統內存的70%-80%最佳.
# 如果你的系統內存不大，查看這個參數，把它的值設置小一點.

9、關注 mysql 的報錯日志.

[root@centos74 /]# cd /usr/local/mysql/
[root@centos74 mysql]# cat mysql.err

190718 8:31:56 [Note] Plugin 'FEDERATED' is disabled.
mysqld: Table 'mysql.plugin' doesn't exist
190718 8:31:56 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
190718 8:31:56 InnoDB: The InnoDB memory heap is disabled
190718 8:31:56 InnoDB: Mutexes and rw_locks use GCC atomic builtins
190718 8:31:56 InnoDB: Compressed tables use zlib 1.2.11
190718 8:31:56 InnoDB: Using Linux native AIO
190718 8:31:56 InnoDB: Initializing buffer pool, size = 128.0M
190718 8:31:56 InnoDB: Completed initialization of buffer pool
InnoDB: The first specified data file ./ibdata1 did not exist:
InnoDB: a new database to be created!
190718 8:31:56 InnoDB: Setting file ./ibdata1 size to 10 MB
InnoDB: Database physically writes the file full: wait...
190718 8:31:56 InnoDB: Log file ./ib_logfile0 did not exist: new to be created
InnoDB: Setting log file ./ib_logfile0 size to 5 MB
InnoDB: Database physically writes the file full: wait...
190718 8:31:56 InnoDB: Log file ./ib_logfile1 did not exist: new to be created
InnoDB: Setting log file ./ib_logfile1 size to 5 MB
InnoDB: Database physically writes the file full: wait...
InnoDB: Doublewrite buffer not found: creating new
InnoDB: Doublewrite buffer created
InnoDB: 127 rollback segment(s) active.
InnoDB: Creating foreign key constraint system tables
InnoDB: Foreign key constraint system tables created
190718 8:31:56 InnoDB: Waiting for the background threads to start
190718 8:31:57 InnoDB: 5.5.62 started; log sequence number 0
190718 8:31:57 [ERROR] mysqld: unknown option '--initialize'
190718 8:31:57 [ERROR] Aborting

190718 8:31:57 InnoDB: Starting shutdown...
190718 8:31:58 InnoDB: Shutdown completed; log sequence number 1595675
190718 8:31:58 [Note] mysqld: Shutdown complete

190718 8:32:07 [Note] Plugin 'FEDERATED' is disabled.
/usr/local/mysql/bin/mysqld: Table 'mysql.plugin' doesn't exist
190718 8:32:07 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
190718 8:32:07 InnoDB: The InnoDB memory heap is disabled
190718 8:32:07 InnoDB: Mutexes and rw_locks use GCC atomic builtins
190718 8:32:07 InnoDB: Compressed tables use zlib 1.2.11
190718 8:32:07 InnoDB: Using Linux native AIO
190718 8:32:07 InnoDB: Initializing buffer pool, size = 128.0M
190718 8:32:07 InnoDB: Completed initialization of buffer pool
190718 8:32:07 InnoDB: highest supported file format is Barracuda.
190718 8:32:07 InnoDB: Waiting for the background threads to start
190718 8:32:08 InnoDB: 5.5.62 started; log sequence number 1595675
190718 8:32:08 [Note] Server hostname (bind-address): '0.0.0.0'; port: 3306
190718 8:32:08 [Note] - '0.0.0.0' resolves to '0.0.0.0';
190718 8:32:08 [Note] Server socket created on IP: '0.0.0.0'.
190718 8:32:08 [ERROR] Fatal error: Can't open and lock privilege tables: Table 'mysql.host' doesn't exist
190718 8:33:17 [Note] Plugin 'FEDERATED' is disabled.
/usr/local/mysql/bin/mysqld: Table 'mysql.plugin' doesn't exist
190718 8:33:17 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
190718 8:33:17 InnoDB: The InnoDB memory heap is disabled
190718 8:33:17 InnoDB: Mutexes and rw_locks use GCC atomic builtins
190718 8:33:17 InnoDB: Compressed tables use zlib 1.2.11
190718 8:33:17 InnoDB: Using Linux native AIO
190718 8:33:17 InnoDB: Initializing buffer pool, size = 128.0M
190718 8:33:17 InnoDB: Completed initialization of buffer pool
190718 8:33:17 InnoDB: highest supported file format is Barracuda.
190718 8:33:17 InnoDB: Waiting for the background threads to start
190718 8:33:18 InnoDB: 5.5.62 started; log sequence number 1595675
190718 8:33:18 [Note] Server hostname (bind-address): '0.0.0.0'; port: 3306
190718 8:33:18 [Note] - '0.0.0.0' resolves to '0.0.0.0';
190718 8:33:18 [Note] Server socket created on IP: '0.0.0.0'.
190718 8:33:18 [ERROR] Fatal error: Can't open and lock privilege tables: Table 'mysql.host' doesn't exist
190718 8:36:58 [Note] Plugin 'FEDERATED' is disabled.
/usr/local/mysql/bin/mysqld: Table 'mysql.plugin' doesn't exist
190718 8:36:58 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
190718 8:36:58 InnoDB: The InnoDB memory heap is disabled
190718 8:36:58 InnoDB: Mutexes and rw_locks use GCC atomic builtins
190718 8:36:58 InnoDB: Compressed tables use zlib 1.2.11
190718 8:36:58 InnoDB: Using Linux native AIO
190718 8:36:58 InnoDB: Initializing buffer pool, size = 128.0M
190718 8:36:58 InnoDB: Completed initialization of buffer pool
190718 8:36:58 InnoDB: highest supported file format is Barracuda.
190718 8:36:58 InnoDB: Waiting for the background threads to start
190718 8:36:59 InnoDB: 5.5.62 started; log sequence number 1595675
190718 8:36:59 [Note] Server hostname (bind-address): '0.0.0.0'; port: 3306
190718 8:36:59 [Note] - '0.0.0.0' resolves to '0.0.0.0';
190718 8:36:59 [Note] Server socket created on IP: '0.0.0.0'.
190718 8:36:59 [ERROR] Fatal error: Can't open and lock privilege tables: Table 'mysql.host' doesn't exist

Linux下徹底卸載mysql詳解

一、使用以下命令查看當前安裝mysql情況，查找以前是否裝有mysql

rpm -qa|grep -i mysql

二、停止mysql服務、刪除之前安裝的mysql

刪除命令：rpm -e --nodeps 包名

三、查找之前老版本mysql的目錄、并且刪除老版本mysql的文件和庫

find / -name mysql

刪除對應的mysql目錄

注意：卸載后/etc/my.cnf不會刪除，需要進行手工刪除

rm -rf /etc/my.cnf

四、再次查找機器是否安裝mysql

rpm -qa|grep -i mysql

無結果，說明已經卸載徹底，接下來直接安裝mysql即可。

初始化 MySQL：

mysqld --initialize

啟動 MySQL：

systemctl start mysqld

查看 MySQL 運行狀態：

systemctl status mysqld

注意：如果我們是第一次啟動 mysql 服務，mysql 服務器首先會進行初始化的配置。

配置服務啟動：

1、查看開機自動啟動的服務使用chkconfig

chkconfig --list

2、確認mysql是否在啟動運行狀態

查詢進程

ps -ef | grep mysqld

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