MySQL中报错：Can’t find file: ‘./mysql/plugin.frm’的解决方法

发现问题

最近在工作中发现了一个问题，这个问题就是mysql的磁盘满了，将数据库目录data移动到/data3目录，/etc/my.cnf里面也修改了相应的datadir目录，权限也赋予了，但是service mysql start;的时候报错，下面话不多说了，来一起看看详细的解决方法吧。

error log显示如下：

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

去先检查plugin.frm权限，frm是mysql表结构定义文件，通常frm文件是不会损坏的，但是如果出现特殊情况出现frm文件损坏也不要放弃希望，当修复myisam和innodb表时，mysql服务会首先去调用frm文件，所以我们只能通过修复frm文件进行后面的数据恢复。

然后我们发现plugin.frm有权限，也是mysql属主：

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之后发现，原来问题在os这里，ubatu的mysql通过yum安装或者rpm安装的时候，会建一个/etc/apparmor.d/usr.sbin.mysqld 文件，如果数据目录不在这里面，则会报错，

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

解决方法

所以解决办法是在里面加上新的datadir目录。

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,
 #.........这里面写新的datadir目录，写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>
}

然后重启mysql实例，ok，问题解决。

总结

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