This can be one of two problems -- mysql isn't running, or mysql isn't putting the socket file in /tmp.
If the mysql command line program works, then the database is up, and it's just that php is compiled w/ the wrong location for the socket file. If it were in any other place, you'd get by with just adding a symlink from the place PHP is looking to the correct place, but because /tmp is cleared on reboot, you'll either need to change the my.cnf to write it to /tmp (possibly breaking other things), or you'll need to re-compiled PHP w/ the option for it to look in the right place, or you can add the following to cron:
@reboot ln -s /var/mysql/mysql.sock /tmp/mysql.sock... adjusting /var/mysql/mysql.sock for wherever the correct location is.
If mysql isn't running, the common problems are either that it's not set to launch after reboot, or it's run into some error. Check the error logs for any information, and if there's nothing in there since the last reboot, you'll need to do whatever your flavor's preferred method is to set it to start on reboot.
一、错误现场还原：
下面我们通过三种方式来连接，然后观察提示的错误信息：
- 1、直接使用“mysql”命令，不带主机名参数；
- 2、使用带了主机名“localhost”参数的“mysql -h localhost”命令；
- 3、使用带了主机名“127.0.0.1”参数的“mysql -h 127.0.0.1”命令。
ERROR 2002 (HY000): Can’t connect to local MySQL server through socket ‘/var/lib/mysql/mysql.sock’ (2)
2、[root@lam7 opt]# mysql -h localhostERROR 2002 (HY000): Can’t connect to local MySQL server through socket ‘/var/lib/mysql/mysql.sock’ (2)
[root@lam7 opt]# mysql -h 127.0.0.1 （用此方法是可以进入到MariaDB ，可以进入之后忽略此问题） Welcome to the MariaDB monitor. Commands end with ; or \g. Your MariaDB connection id is 244 Server version: 10.1.19-MariaDB Source distribution
Copyright © 2000, 2013, Oracle, Monty Program Ab and others.
Type ‘help;’ or ‘\h’ for help. Type ‘\c’ to clear the current input statement.
3、[root@lam7 opt]# mysql -h 127.0.0.1 （PS：有些用户也会出现此问题）ERROR 1045 (28000): Access denied for user ‘root’@‘localhost’ (using password: NO)
通过上面实验可以看出，前面两种方式都能产生标题中的错误，而第三种方式连接是不会产生标题中的错误的（第三种方式这里产生的是由于密码问题拒绝访问的错误信息）
二、错误产生原因解析：
这是由于我们连接数据库使用的主机名参数为“localhost”，或者未使用主机名参数、服务器默认使用“localhost”做为主机名。 使用主机名参数为“localhost”连接mysql服务端时，mysql客户端会认为是连接本机，所以会尝试以socket文件方式进行连接(socket文件连接方式，比“ip：端口”方式效率更高)，这时根据配置文件“/etc/mysql.cnf”的路径，未找到相应的socket文件，就会引发此错误。
三、修复故障前准备：
1、看mysql服务是否在运行：
由于“socket”文件是由mysql服务运行时创建的，如果提示“ERROR 2002 (HY000): Can’t connect to local MySQL server through socket ‘***’ (2)”，找不到“socket”文件，我们首先要确认的是mysql服务是否正在运行。
1：端口是否打开[root@lam7 opt]# lsof -i:3306 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME mysqld 57436 mysql 17u IPv6 160456 0t0 TCP *:mysql (LISTEN)
2：mysqld服务是否正在运行（小七这边用的是centos7，所以会提示使用“/bin/systemctl status mysqld.service”）[root@lam7 opt]# service mysqld status Redirecting to /bin/systemctl status mysqld.service mysqld.service Loaded: not-found (Reason: No such file or directory) Active: inactive (dead)
[root@lam7 opt]# service mariadb status Redirecting to /bin/systemctl status mariadb.service mariadb.service - MariaDB database server Loaded: loaded (/usr/lib/systemd/system/mariadb.service; disabled) Active: inactive (dead)
4mysqld服务是否正在运行（此现状是mysql服务正常运行）[root@lam7 opt]# service mariadb status Redirecting to /bin/systemctl status mariadb.service mariadb.service - MariaDB database server Loaded: loaded (/usr/lib/systemd/system/mariadb.service; disabled; vendor preset: disabled) Active: active (running) since 二 2016-11-22 20:09:01 CST; 10min ago
2、确定“socket”文件正确位置：
确定mysql服务正常运行后，产生此错误的原因只剩下“socket”文件路径不正确了，我们可以使用“find”命令或者“lsof”命令来确定socket文件的正确路径：
[root@lam7 opt]# lsof -c mysqld|grep sock$ lsof: WARNING: can’t stat() fuse.gvfsd-fuse file system /run/user/1000/gvfs Output information may be incomplete. mysqld 57436 mysql 18u unix 0xffff88000b55f440 0t0 160457 /opt/lampp/var/mysql/mysql.sock
[root@lam7 opt]# find / -name ‘*.sock’ /storage/db/mysql/mysql.sock
四、故障解决方法：
解决方案一：
修改“/etc/my.cnf”配置文件，在/etc/php.ini文件中"[MySQL]“项下找到"mysql.default_socket”，并设置其值指向正确的mysql服务socket文件即可， 在配置文件中添加“[client]”选项和“[mysql]”选项，并使用这两个选项下的“socket”参数值，与“[mysqld]”选项下的“socket”参数值，指向的socket文件路径完全一致。如下：
[mysqld] datadir=/storage/db/mysql socket=/storage/db/mysql/mysql.sock …省略n行 [client] default-character-set=utf8 socket=/storage/db/mysql/mysql.sock [mysql] default-character-set=utf8 socket=/storage/db/mysql/mysql.sock
修改完后，重启mysqld服务，即可解决此问题。
解决方案二：
使用“ln -s /storage/db/mysql/mysql.sock /var/lib/mysql/mysql.sock”命令，将正确的socket文件位置，软链接到提示错误的socket文件路径位置，即可解决此问题：
[root@lam7 opt]# ls /var/lib/mysql/mysql.sock ls: 无法访问/var/lib/mysql/mysql.sock: 没有那个文件或目录
[root@lam7 opt]# ln -s /storage/db/mysql/mysql.sock /var/lib/mysql/mysql.sock [root@lam7 opt]# ls /var/lib/mysql/mysql.sock /var/lib/mysql/mysql.sock
这边讲述了mysql提供的“mysql”、“mysqldump”、“mysqladmin”等命令提示“ERROR 2002 (HY000): Can’t connect to local MySQL server through socket ‘***’ (2)”的解决方法，如果需要解决“php”、“perl”、“python”等脚本语言提示此错误的问题
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