说明：
编译了2个mysql，mysql5.5的默认不是默认的（/tmp/mysql.sock3307），默认的为/tmp/mysql.sock。导致我mysql5.5 -uroot不指定sock位置，会出现Can’t connect to local MySQL server through socket ‘/tmp/mysql.sock’。有确认mysql5.5的my.cnf加载正确，my.cnf的client也已经指定sock还是也不行。错误如下：
# mysql -uroot ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)
环境：
mysql5.1，配置文件为/etc/my.cnf，sock指向/tmp/mysql.sock
root 7673 1 0 05:14 pts/0 00:00:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --datadir=/usr/local/mysql/var --pid-file=/usr/local/mysql/var/lnmp1.pid mysql 7836 7673 1 05:14 pts/0 00:00:00 /usr/local/mysql/libexec/mysqld --basedir=/usr/local/mysql --datadir=/usr/local/mysql/var --user=mysql --log-error=/usr/local/mysql/var/lnmp1.err --pid-file=/usr/local/mysql/var/lnmp1.pid --socket=/tmp/mysql.sock --port=3306
mysql5.5，配置文件为/data/mysql/3307/my.cnf，scok指向/tmp/mysql3307.sock
# ps -ef|grep mysql root 4603 3438 0 01:29 pts/1 00:00:00 tail -20f /data/mysql/3307/error.log root 6277 1 0 03:46 pts/0 00:00:00 /bin/sh /usr/local/mysql5.5/bin/mysqld_safe --datadir=/data/mysql/3307 --pid-file=/data/mysql/3307/mysql.pid mysql 6603 6277 0 03:46 pts/0 00:00:00 /usr/local/mysql5.5/bin/mysqld --basedir=/usr/local/mysql5.5 --datadir=/data/mysql/3307 --plugin-dir=/usr/local/mysql5.5/lib/plugin --user=mysql --log-error=/data/mysql/3307/error.log --pid-file=/data/mysql/3307/mysql.pid --socket=/tmp/mysql3307.sock --port=3307
排查：
1. 当我把mysql5.1关闭，只留下mysql5.5，mysql登陆里，就会出现以下情况
# mysql -uroot ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)
2. 指定mysql5.5 的sock位置就正常
# mysql -uroot -S /tmp/mysql3307.sock ... mysql>
3. 查看mysql5.5的my.cnf，可以看到client已经有指定sock位置了，但连接还是会出现Can’t connect to local …. ‘/tmp/mysql.sock’。是加载到了mysql5.1的/etc/my.cnf嘛
# cat /data/mysql/3307/my.cnf [client] #password = your_password port = 3307 socket = /tmp/mysql3307.sock
4. 重命名/etc/my.cnf，怕/etc/my.cnf影响到
# mv /etc/my.cnf /etc/my.cnf.bak # /etc/init.d/mysql5.5 restart # mysql -uroot ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2) 连接还是失败。。。。 # mv /etc/my.cnf.bak /etc/my.cnf //改名回去
5. 后面无意中试修改了下/etc/my.cnf，将/etc/my.cnf中的client修改成/tmp/mysql3307.sock，原来是/tmp/mysql.sock
[client] #password = your_password port = 3307 socket = /tmp/mysql3307.sock
mysql5.5不指定sock位置也能正常连接了。。。。
# mysql -uroot ... mysql>
猜测：
mysql -uroot做为客户端，默认会加载/etc/my.cnf配置里的client sock路径。如果/etc/my.cnf不存在，则会按默认编译里指定的sock来连接，亦即/tmp/mysql.sock。
总结：
其实碰到这个，我都是先检查mysql是否有在运行，sock位置是否正确，是否加载了其它的my.cnf，my.cnf里的client配置是否存在