MySQL通过本地socket方式无法正常连接数据库可能出现的原因

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1.在/etc/my.cnf配置文件中，mysqld和mysql标签对应的socket文件路径不对等

#[环境准备]
[root@centos7-db01 ~]# vim /etc/my.cnf
[mysqld]
socket=/tmp/mysql.sock
[mysql]
socket=/tmp/db.sock
#[模拟测试]
[root@centos7-db01 ~]# systemctl restart mysqld
[root@centos7-db01 ~]# mysql -uroot -p
Enter password: 
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/db.sock' (2)

PS：mysql客户端通过db.sock套接字去连接数据库, 但是/tmp/db.sock文件服务启动时未被创建，导致连接失败。

2.有一个或多个配置文件覆盖/etc/my.cnf文件参数

命令：mysqld --help --verbose|grep my.cnf，查看mysqld程序启动过程中，读取配置文件的顺序。

/etc/my.cnf /etc/mysql/my.cnf /usr/local/mysql/etc/my.cnf ~/.my.cnf

#[环境准备]
[root@centos7-db01 ~]# vim /etc/my.cnf
[mysqld]
socket=/tmp/mysql.sock
[mysql]
socket=/tmp/mysql.sock
#添加用户自定义配置
[root@centos7-db01 ~]# vim ~/.my.cnf
[mysqld]
socket=/tmp/db.sock
#[模拟测试]
[root@centos7-db01 ~]# /etc/init.d/mysqld restart
[root@centos7-db01 ~]# ll /tmp/*.sock
srwxrwxrwx. 1 mysql mysql 0 Mar 16 14:21 /tmp/db.sock
[root@centos7-db01 ~]# mysql -uroot -p
Enter password: 
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

PS：参数优先级，mysqld或mysqld_safe命令行方式 > --defaults-file指定配置文件 > 默认配置文件。

3.使用--defaults-file参数强制启用自定义配置

#[环境准备]
#只更新了mysqld服务端的socket参数，未对mysql客户端对应参数进行更新
[root@centos7-db01 ~]# vim db.cnf
[mysqld]
user=mysql
basedir=/application/mysql
datadir=/data/mysql/data
socket=/tmp/db.sock
server-id=6
port=3306
log-error=/data/mysql/data/db3306.err
#[模拟测试]
[root@centos7-db01 ~]# mysqld_safe --defaults-file=~/db.cnf &
[root@centos7-db01 ~]# ll /tmp/*.sock
srwxrwxrwx. 1 mysql mysql 0 Mar 16 14:49 /tmp/db.sock
[root@centos7-db01 data]# mysql -uroot -p
Enter password: 
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

PS: --defaults-file指定配置文件参数，覆盖了默认配置文件对应的参数信息。

4.MySQL服务未启动

[root@centos7-db01 ~]# netstat -lntp|grep mysql
[root@centos7-db01 ~]# mysql -uroot -p
Enter password: 
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

5.误删除socket文件

[root@centos7-db01 tmp]# mv mysql.sock{,.bak}
[root@centos7-db01 tmp]# mysql -uroot -p
Enter password: 
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)