發現問題
最近在工作中發現了一個問題，這個問題就是MySQL的磁盤滿了，將數據庫目錄data移動到/data3目錄，/etc/my.cnf里面也修改了相應的datadir目錄，權限也賦予了，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 pages2017-09-15 16:01:01 2420 [Note] InnoDB: The InnoDB memory heap is disabled2017-09-15 16:01:01 2420 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins2017-09-15 16:01:01 2420 [Note] InnoDB: Memory barrier is not used2017-09-15 16:01:01 2420 [Note] InnoDB: Compressed tables use zlib 1.2.82017-09-15 16:01:01 2420 [Note] InnoDB: Using Linux native AIO2017-09-15 16:01:01 2420 [Note] InnoDB: Using CPU crc32 instructions2017-09-15 16:01:01 2420 [Note] InnoDB: Initializing buffer pool, size = 128.0M2017-09-15 16:01:02 2420 [Note] InnoDB: Completed initialization of buffer pool2017-09-15 16:01:02 2420 [ERROR] InnoDB: ./ibdata1 can't be opened in read-write mode2017-09-15 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: InnoDB2017-09-15 16:01:02 2420 [ERROR] Aborting
去先檢查plugin.frm權限，frm是MySQL表結構定義文件，通常frm文件是不會損壞的，但是如果出現特殊情況出現frm文件損壞也不要放棄希望，當修復MyISAM和InnoDB表時，MySQL服務會首先去調用frm文件，所以我們只能通過修復frm文件進行后面的數據恢復。
然后我們發現plugin.frm有權限，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之后發現，原來問題在os這里，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 文件，如果數據目錄不在這里面，則會報錯，
/usr/sbin/mysqld: Can't find file: ‘./mysql/plugin.frm' (errno: 13 - Permission denied)
解決方法
所以解決辦法是在里面加上新的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, #.........這里面寫新的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>}然后重啟mysql實例，ok，問題解決。
總結
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