CentOS 7上更改MySQL数据库存储目录浅析

 

个人之前总结过两篇文章“MySQL更改数据库数据存储目录”和“Ubuntu上更改MySQL数据库数据存储目录”，都是在工作中遇到相关案例后的一个简单总结。当初的经验不足，认知有限，所以现在来看来，当初的博文确实显得浅析和不够全面，这个也没有办法，当时有些环境或案例没有涉及过，所以文章很难面面俱到，略显单薄和浅显，这个也很正常。博客不是论文，只是个人的笔记和知识点的总结。而且是基于当时的认知的经验总结和知识概括。前阵子将监控工具DPA的数据库切换为MySQL时，又遇到了这个问题，遂总结一下。

系统环境    ：  CentOS Linux release 7.5.1804 (Core)

MySQL版本   ：  8.0.18 MySQL Community Server - GPL

默认情况下，MySQL的数据目录一般位于/var/lib/mysql下

1：首先，弄清楚MySQL的相关配置信息

找到MySQL的数据目录，以及配置文件my.cnf、错误日志的位置。

mysql> show variables like 'datadir%';

+---------------+-----------------+

| Variable_name | Value           |

+---------------+-----------------+

| datadir       | /var/lib/mysql/ |

+---------------+-----------------+

1 row in set (0.03 sec)

mysql> show variables like 'log_error';

+---------------+---------------------+

| Variable_name | Value               |

+---------------+---------------------+

| log_error     | /var/log/mysqld.log |

+---------------+---------------------+

1 row in set (0.01 sec)

mysql> 

[root@KerryDB ~]# whereis my.cnf

my: /etc/my.cnf

2：对数据库做一个冷备份，以备不时之需。当然，你以可以用其它方式备份。

[root@KerryDB ~]# service mysqld stop

Redirecting to /bin/systemctl stop mysqld.service

[root@KerryDB ~]# cp -rp /var/lib/mysql  /tmp/coldbackup

3：移动数据目录到其它目录

这里假设，我需要将数据库的数据目录迁移到/mysql_data/下。

[root@KerryDB ~]# chown -R mysql:mysql /mysql_data/

[root@KerryDB ~]# cd /var/lib

[root@KerryDB lib]# mv mysql  /mysql_data/

注意：这里建议使用mv移动数据库目录，而是不是复制（cp命令），因为执行复制时，SELinux上下文将丢失，并且您稍后必须手动进行设置，如果你使用cp命令复制文件，如果没有使用参数-p，那么要记得修改目录的属主，否则你有可能遇到“MySQL error: 1017 Can’t find file: (errno: 13)”这样的错误。

mv 与cp的区别

4：修改配置文件my.cnf

一般情况下，只需修改datadir和socket等参数，具体根据你实际情况来判断那些参数需要修改。

#datadir=/var/lib/mysql

#socket=/var/lib/mysql/mysql.sock

datadir=/mysql_data/mysql

socket=/mysql_data/mysql/mysql.sock

修改过后，对于CentOS或RHEL操作系统而言，你可能需要修改SELinux的设置，而对于Ubuntu或Debian，你需要修改AppArmor的设置（这篇Ubuntu上更改MySQL数据库数据存储目已经有介绍了，这里就不重复了）。当如，对于CentOS或RHEL，如果你禁用了SELinux的话，那么就可以直接忽略这个设置，因为禁用SELinux的话，就会避免很多杂七杂八的问题，但是我们不是要回避问题，而是要弄清楚问题产生的根本原因。

首先你要检查，是否开启了SELinux。如下所示：

[root@KerryDB ~]# /usr/sbin/sestatus

SELinux status:                 enabled

SELinuxfs mount:                /sys/fs/selinux

SELinux root directory:         /etc/selinux

Loaded policy name:             targeted

Current mode:                   enforcing

Mode from config file:          enforcing

Policy MLS status:              enabled

Policy deny_unknown status:     allowed

Max kernel policy version:      31

[root@KerryDB ~]# getenforce

Enforcing

如果SELinux是开启状态，那么此时如果不做一些配置，那么启动MySQL服务，就会遇到类似下面这样的错误：

[root@KerryDB ~]# systemctl status mysqld.service

● mysqld.service - MySQL Server

   Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)

   Active: failed (Result: exit-code) since Mon 2020-03-09 15:43:06 +08; 2min 54s ago

     Docs: man:mysqld(8)

           http://dev.mysql.com/doc/refman/en/using-systemd.html

  Process: 14903 ExecStart=/usr/sbin/mysqld $MYSQLD_OPTS (code=exited, status=1/FAILURE)

  Process: 14879 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)

 Main PID: 14903 (code=exited, status=1/FAILURE)

   Status: "Server startup in progress"

    Error: 13 (Permission denied)

Mar 09 15:43:06 KerryDB systemd[1]: Starting MySQL Server...

Mar 09 15:43:06 KerryDB systemd[1]: mysqld.service: main process exited, code=exited, status=1/FAILURE

Mar 09 15:43:06 KerryDB systemd[1]: Failed to start MySQL Server.

Mar 09 15:43:06 KerryDB systemd[1]: Unit mysqld.service entered failed state.

Mar 09 15:43:06 KerryDB systemd[1]: mysqld.service failed.

[root@KerryDB ~]# journalctl -xe

Mar 09 15:39:05 KerryDB polkitd[731]: Registered Authentication Agent for unix-process:14836:224127979 (system bus name :1.1355 [/usr/bin/pkttyagent --notify

Mar 09 15:39:05 KerryDB systemd[1]: Stopping MySQL Server...

-- Subject: Unit mysqld.service has begun shutting down

-- Defined-By: systemd

-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel

-- 

-- Unit mysqld.service has begun shutting down.

Mar 09 15:39:07 KerryDB systemd[1]: Stopped MySQL Server.

-- Subject: Unit mysqld.service has finished shutting down

-- Defined-By: systemd

-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel

-- 

-- Unit mysqld.service has finished shutting down.

Mar 09 15:39:07 KerryDB polkitd[731]: Unregistered Authentication Agent for unix-process:14836:224127979 (system bus name :1.1355, object path /org/freedeskt

Mar 09 15:43:06 KerryDB polkitd[731]: Registered Authentication Agent for unix-process:14863:224152052 (system bus name :1.1356 [/usr/bin/pkttyagent --notify

Mar 09 15:43:06 KerryDB systemd[1]: Starting MySQL Server...

-- Subject: Unit mysqld.service has begun start-up

-- Defined-By: systemd

-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel

-- 

-- Unit mysqld.service has begun starting up.

Mar 09 15:43:06 KerryDB systemd[1]: mysqld.service: main process exited, code=exited, status=1/FAILURE

Mar 09 15:43:06 KerryDB systemd[1]: Failed to start MySQL Server.

-- Subject: Unit mysqld.service has failed

-- Defined-By: systemd

-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel

-- 

-- Unit mysqld.service has failed.

-- 

-- The result is failed.

Mar 09 15:43:06 KerryDB systemd[1]: Unit mysqld.service entered failed state.

Mar 09 15:43:06 KerryDB systemd[1]: mysqld.service failed.

Mar 09 15:43:06 KerryDB polkitd[731]: Unregistered Authentication Agent for unix-process:14863:224152052 (system bus name :1.1356, object path /org/freedeskt

lines 4369-4401/4401 (END)

上面日志看不到细节错误信息，此时，应该检查错误日志/var/log/mysqld.log， 如下所示，你会看到“OS errno 13 - Permission denied”和“Can't create test file xxx"类似这样的错误

mysqld: File './binlog.~rec~' not found (OS errno 13 - Permission denied)

2020-03-09T07:43:06.927360Z 0 [Warning] [MY-010091] [Server] Can't create test file /mysql_data/mysql/mysqld_tmp_file_case_insensitive_test.lower-test

2020-03-09T07:43:06.927453Z 0 [System] [MY-010116] [Server] /usr/sbin/mysqld (mysqld 8.0.18) starting as process 14903

2020-03-09T07:43:06.929669Z 0 [Warning] [MY-010091] [Server] Can't create test file /mysql_data/mysql/mysqld_tmp_file_case_insensitive_test.lower-test

2020-03-09T07:43:06.929681Z 0 [Warning] [MY-010159] [Server] Setting lower_case_table_names=2 because file system for /mysql_data/mysql/ is case insensitive

2020-03-09T07:43:06.930542Z 0 [ERROR] [MY-010846] [Server] MYSQL_BIN_LOG::open_purge_index_file failed to open register file.

2020-03-09T07:43:06.930594Z 0 [ERROR] [MY-010817] [Server] MYSQL_BIN_LOG::open_index_file failed to sync the index file.

2020-03-09T07:43:06.930657Z 0 [ERROR] [MY-010119] [Server] Aborting

2020-03-09T07:43:06.930830Z 0 [System] [MY-010910] [Server] /usr/sbin/mysqld: Shutdown complete (mysqld 8.0.18)  MySQL Community Server - GPL.

注意：默认情况下，日志里面的时间是UTC时间，而不是本地时间。除非你设置过。具体参考我的博客“MySQL5.7参数log_timestamps”。

此时如果，你用chcon命令来在新目录中更改SELinux上下文类型，我看有些博客介绍就OK了。但是在我这个环境中，这样处理过后依然报同样的错误

[root@KerryDB ~]# chcon -R -t mysqld_db_t /mysql_data/

[root@KerryDB ~]#

折腾测试后，发现此时需要在file_contexts里面修改mysqld_db_t，如下所示：

[root@KerryDB ~]# cd /etc/selinux/targeted/contexts/files/

[root@KerryDB files]# ls -lrt

修改前：

/var/lib/mysql(-files|-keyring)?(/.*)? system_u:object_r:mysqld_db_t:s0

修改后：

/mysql_data/mysql(-files|-keyring)?(/.*)? system_u:object_r:mysqld_db_t:s0

其实使用chcon修改对象（文件）的安全上下文，相当难掌握，有点难度，除非你是Linux高手，一般用工具semanage对默认目录的安全上下文查询与修改

一般默认可能没有安装policycoreutils-python，需要安装对应组件

#yum -y install policycoreutils-python

如果你要查看MySQL相关文件的设置，那么可以用semanage fcontext -l | grep -i mysql查看。

root@KerryDB ~]# semanage fcontext -l | grep -i mysql

/usr/lib(64)?/nagios/plugins/check_mysql           regular file       system_u:object_r:nagios_services_plugin_exec_t:s0 

/usr/lib(64)?/nagios/plugins/check_mysql_query     regular file       system_u:object_r:nagios_services_plugin_exec_t:s0 

/etc/mysql(/.*)?                                   all files          system_u:object_r:mysqld_etc_t:s0 

/etc/my\.cnf\.d(/.*)?                              all files          system_u:object_r:mysqld_etc_t:s0 

/var/log/mysql.*                                   regular file       system_u:object_r:mysqld_log_t:s0 

/var/lib/mysql(-files|-keyring)?(/.*)?             all files          system_u:object_r:mysqld_db_t:s0 

/var/run/mysqld(/.*)?                              all files          system_u:object_r:mysqld_var_run_t:s0 

/var/log/mariadb(/.*)?                             all files          system_u:object_r:mysqld_log_t:s0 

/var/run/mariadb(/.*)?                             all files          system_u:object_r:mysqld_var_run_t:s0 

/usr/sbin/mysqld(-max)?                            regular file       system_u:object_r:mysqld_exec_t:s0 

/var/run/mysqld/mysqlmanager.*                     regular file       system_u:object_r:mysqlmanagerd_var_run_t:s0 

/usr/lib/systemd/system/mysqld.*                   regular file       system_u:object_r:mysqld_unit_file_t:s0 

/usr/share/munin/plugins/mysql_.*                  regular file       system_u:object_r:services_munin_plugin_exec_t:s0 

/usr/lib/systemd/system/mariadb.*                  regular file       system_u:object_r:mysqld_unit_file_t:s0 

/etc/my\.cnf                                       regular file       system_u:object_r:mysqld_etc_t:s0 

/root/\.my\.cnf                                    regular file       system_u:object_r:mysqld_home_t:s0 

/usr/sbin/ndbd                                     regular file       system_u:object_r:mysqld_exec_t:s0 

/usr/libexec/mysqld                                regular file       system_u:object_r:mysqld_exec_t:s0 

/usr/bin/mysqld_safe                               regular file       system_u:object_r:mysqld_safe_exec_t:s0 

/usr/bin/mysql_upgrade                             regular file       system_u:object_r:mysqld_exec_t:s0 

/usr/sbin/mysqlmanager                             regular file       system_u:object_r:mysqlmanagerd_exec_t:s0 

/etc/rc\.d/init\.d/mysqld                          regular file       system_u:object_r:mysqld_initrc_exec_t:s0 

/var/lib/mysql/mysql\.sock                         socket             system_u:object_r:mysqld_var_run_t:s0 

/usr/bin/mysqld_safe_helper                        regular file       system_u:object_r:mysqld_exec_t:s0 

/usr/sbin/zabbix_proxy_mysql                       regular file       system_u:object_r:zabbix_exec_t:s0 

/etc/rc\.d/init\.d/mysqlmanager                    regular file       system_u:object_r:mysqlmanagerd_initrc_exec_t:s0 

/usr/sbin/zabbix_server_mysql                      regular file       system_u:object_r:zabbix_exec_t:s0 

/usr/libexec/mysqld_safe-scl-helper                regular file       system_u:object_r:mysqld_safe_exec_t:s0 

/home/[^/]+/\.my\.cnf

[root@KerryDB  ~]# semanage fcontext -a -t mysqld_db_t "/mysql_data/mysql(/.*)?"

[root@KerryDB  ~]# restorecon -Rv /mysql_data/mysql

restorecon reset /mysql_data/mysql context system_u:object_r:default_t:s0->system_u:object_r:mysqld_db_t:s0

此时启动MySQL实例就正常了，关于semanage修改目录或文件安全上下文的更多信息，参考资料有，可以移步那里去学习。

# service mysqld start

Redirecting to /bin/systemctl start mysqld.service

此时，你如果用MySQL客户端工具登录数据库，就会遇到"Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock'"

[root@KerryDB mysql]# mysql -u root -p

Enter password: 

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)

解决下面错误的方法：

1：在连接MySQL时，指定参数--socket的值

[root@KerryDB mysql]# mysql -u root -p   --socket=/mysql_data/mysql/mysql.sock

Enter password: 

Welcome to the MySQL monitor.  Commands end with ; or \g.

Your MySQL connection id is 8

Server version: 8.0.18 MySQL Community Server - GPL

Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its

affiliates. Other names may be trademarks of their respective

owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> 

2：修改配置文件my.cnf，增加客户端参数socket

[client]

socket=/mysql_data/mysql/mysql.sock

注意这个socket参数，跟mysqld下的参数socket是有所区别的。

[client]

socket=/mysql_data/mysql/mysql.sock

[mysqld]

datadir=/mysql_data/mysql

socket=/mysql_data/mysql/mysql.sock

其实这种方法是最简单，最有效的一个方法。

3：可以通过建立mysql.sock文件的软连接

另外，我尝试通过修改Unix-domain Socket 上下文来解决这个问题，但是没有解决，不知是我理解有误，还是其它方面原因。 下面是部分测试内容：

# semanage fcontext -a -t mysqld_var_run_t "/mysql_data/mysql/mysql\.sock"

# restorecon -Rv /mysql_data/mysql/mysql.sock

# mysql -u root -p

Enter password:

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)

依然报错，检查semanage fcontext -l | grep -i mysql 如下所示， 由于对SELinux的知识了解不够深入，暂时还在学习中。临时先记录一下，留待以后解决。

#  semanage fcontext -l | grep -i mysql

参考资料：

https://dev.mysql.com/doc/refman/5.6/en/can-not-connect-to-server.html

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/selinux_users_and_administrators_guide/sect-security-enhanced_linux-working_with_selinux-selinux_contexts_labeling_files