原因分析：

1、没有 /var/lib/mysql/mysql.sock 的目录权限

添加权限 chown -R mysql:mysql /var/lib/mysql/

2、没有/var/lib/mysql/mysql.sock文件

通过 find / -name mysql.sock

在 /tmp//mysql.sock

用 ln -s 命令建立连接

或者修改 /etc/my.cnf配置文件，下边有，然后重启

#查看mysql实例的状态
[root@SZDB mysqldata]# netstat -ntlp  | grep 3306
tcp        0      0 :::3306                     :::*                        LISTEN      13001/mysqld
#查看my.cnf关于socket的配置
[root@SZDB mysqldata]# more /etc/my.cnf |grep sock
socket = /tmp/mysql.sock
#由上可知my.cnf中定义的为/tmp目录下，而错误提示为/data/mysqldata/目录下
#也就是说mysqld已经声称了正确的sock文件，但客户端连接还是从初始目录去找sock文件
#下面查看后台日志，有个ERROR，是关于满查询日志的，是由于目录不存在而产生的错误，与当前故障无关
[root@SZDB mysqldata]# more SZDB.err
             ............
2014-10-11 13:17:21 13001 [Note] InnoDB: 5.6.12 started; log sequence number 1625997
/app/soft/mysql/bin/mysqld: File '/log/mysql_logs/slowquery.log' not found (Errcode: 2 - No such file or directory)
2014-10-11 13:17:21 13001 [ERROR] Could not use /log/mysql_logs/slowquery.log for logging (error 2). Turning logging off for the who
le duration of the MySQL server process. To turn it on again: fix the cause, shutdown the MySQL server and restart it.
2014-10-11 13:17:21 13001 [Note] Server hostname (bind-address): '*'; port: 3306
2014-10-11 13:17:21 13001 [Note] IPv6 is available.
2014-10-11 13:17:21 13001 [Note]   - '::' resolves to '::';
2014-10-11 13:17:21 13001 [Note] Server socket created on IP: '::'.
2014-10-11 13:17:21 13001 [Note] Event Scheduler: Loaded 0 events
2014-10-11 13:17:21 13001 [Note] /app/soft/mysql/bin/mysqld: ready for connections.
Version: '5.6.12-log'  socket: '/tmp/mysql.sock'  port: 3306  Source distribution
3、解决故障
通过配置my.cnf mysql选项socket文件位置解决
复制代码 代码如下:
#先停止mysql服务器
[root@SZDB mysqldata]# service mysqld stop
Shutting down MySQL.[  OK  ]
#修改my.cnf，如下
[root@SZDB mysqldata]# vi /etc/my.cnf
[mysql]
no-auto-rehash
socket = /tmp/mysql.sock  #添加该行
[mysql.server]
user=mysql#添加
basedir=/usr/local/mysql#添加
#If there is not currently a section called [client], add one at the bottom of the file and copy the socket= line under the [mysqld] section such as:
[client]#添加
socket=/var/lib/mysql/mysql.sock#添加
#重启mysql服务器
[root@SZDB mysqldata]# service mysqld start
Starting MySQL..[  OK  ]
#再次连接正常
[root@SZDB mysqldata]# mysql -uroot -p
Enter password: 
mysql> show variables like 'version';
+---------------+------------+
| Variable_name | Value      |
+---------------+------------+
| version       | 5.6.12-log |
+---------------+------------+
为socket文件建立链接方式
复制代码 代码如下:
[root@SZDB mysqldata]# ln -s /tmp/mysql.sock /data/mysqldata/mysql.sock 
ln: creating symbolic link `/data/mysqldata/mysql.sock' to `/tmp/mysql.sock': File exists
[root@SZDB mysqldata]# rm mysql.sock    #上面提示文件存在，所以删除之前的mysql.sock文件
[root@SZDB mysqldata]# ln -s /tmp/mysql.sock /data/mysqldata/mysql.sock
[root@SZDB mysqldata]# ls -hltr mysql.sock
lrwxrwxrwx 1 root root 15 Oct 11 14:00 mysql.sock -> /tmp/mysql.sock
[root@SZDB mysqldata]# mysql -uroot -p
Enter password: 
mysql> show variables like 'socket';
+---------------+-----------------+
| Variable_name | Value           |
+---------------+-----------------+
| socket        | /tmp/mysql.sock |
+---------------+-----------------+