發現問題

最近在工作中發現了一個問題，這個問題就是MySQL的磁碟滿了，將資料庫目錄data移動到/data3目錄，/etc/my.cnf裡面也修改了相應的datadir目錄，許可權也賦予了，但是service mysql start;的時候報錯，下面話不多說了，來一起看看詳細的解決方法吧。

error log顯示如下：

2017-09-15 16:01:01 2420 [Warning] Using unique option prefix myisam-recover instead of myisam-recover-options is deprecated and will be removed in a future release. Please use the full name instead.
2017-09-15 16:01:01 2420 [Note] Plugin 'FEDERATED' is disabled.
^G/usr/sbin/mysqld: Can't find file: './mysql/plugin.frm' (errno: 13 - Permission denied)
2017-09-15 16:01:01 2420 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
2017-09-15 16:01:01 2420 [Note] InnoDB: Using atomics to ref count buffer pool pages
2017-09-15 16:01:01 2420 [Note] InnoDB: The InnoDB memory heap is disabled
2017-09-15 16:01:01 2420 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2017-09-15 16:01:01 2420 [Note] InnoDB: Memory barrier is not used
2017-09-15 16:01:01 2420 [Note] InnoDB: Compressed tables use zlib 1.2.8
2017-09-15 16:01:01 2420 [Note] InnoDB: Using Linux native AIO
2017-09-15 16:01:01 2420 [Note] InnoDB: Using CPU crc32 instructions
2017-09-15 16:01:01 2420 [Note] InnoDB: Initializing buffer pool,size = 128.0M
2017-09-15 16:01:02 2420 [Note] InnoDB: Completed initialization of buffer pool
2017-09-15 16:01:02 2420 [ERROR] InnoDB: ./ibdata1 can't be opened in read-write mode
2017-09-15 16:01:02 2420 [ERROR] InnoDB: The system tablespace must be writable!
2017-09-15 16:01:02 2420 [ERROR] Plugin 'InnoDB' init function returned error.
2017-09-15 16:01:02 2420 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
2017-09-15 16:01:02 2420 [ERROR] Unknown/unsupported storage engine: InnoDB
2017-09-15 16:01:02 2420 [ERROR] Aborting

去先檢查plugin.frm許可權，frm是MySQL表結構定義檔案，通常frm檔案是不會損壞的，但是如果出現特殊情況出現frm檔案損壞也不要放棄希望，當修復MyISAM和InnoDB表時，MySQL服務會首先去呼叫frm檔案，所以我們只能通過修復frm檔案進行後面的資料恢復。

然後我們發現plugin.frm有許可權，也是mysql屬主：

root@hutaojie-1-pdd-sh:/data1/mysql/mysql# ll plugin.*
-rwxrwxrwx 1 mysql mysql 8586 Mar 6 2016 plugin.frm*
-rwxrwx--x 1 mysql mysql 116 Mar 6 2016 plugin.MYD*
-rwxrwx--x 1 mysql mysql 2048 Mar 6 2016 plugin.MYI*
root@hutaojie-1-pdd-sh:/data1/mysql/mysql#

google之後發現，原來問題在os這裡，ubatu的mysql通過yum安裝或者rpm安裝的時候，會建一個/etc/apparmor.d/usr.sbin.mysqld 檔案，如果資料目錄不在這裡面，則會報錯，

/usr/sbin/mysqld: Can't find file: ‘./mysql/plugin.frm' (errno: 13 - Permission denied)

解決方法

所以解決辦法是在裡面加上新的datadir目錄。

root@huayuan:/var/lib# vim /etc/apparmor.d/usr.sbin.mysqld 

# vim:syntax=apparmor
# Last Modified: Tue Jun 19 17:37:30 2007
#include <tunables/global>

/usr/sbin/mysqld {
 #include <abstractions/base>
 #include <abstractions/nameservice>
 #include <abstractions/user-tmp>
 #include <abstractions/mysql>
 #include <abstractions/winbind>

 capability dac_override,capability sys_resource,capability setgid,capability setuid,network tcp,/run/mysqld/mysqld.pid rw,/run/mysqld/mysqld.sock w,/sys/devices/system/cpu/ r,#.........這裡面寫新的datadir目錄，寫2行，一行r，一行rwk。
 /data3/mysql/ r,/data3/mysql/** rwk,# Site-specific additions and overrides. See local/README for details.
 #include <local/usr.sbin.mysqld>
}

然後重啟mysql例項，ok，問題解決。

總結

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