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mysql> update mysql.user set password=password("123456") where host="localhost" and user="root";
Query OK, 1 row affected (0.02 sec)
Rows matched: 1 Changed: 1 Warnings: 0

mysql> flush privileges;
Query OK, 0 rows affected (0.01 sec)

mysql>

再次将my.cnf里添加的那一行注释，然后重启mysql

[root@test-huanqiu ~]# vim /etc/my.cnf
........
#skip-grant-tables

[root@test-huanqiu ~]# /etc/init.d/mysqld restart

[root@test-huanqiu ~]# mysql -p123456
mysql>

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发现的一个坑：

mysql之前进行了全量备份，在恢复后，发现用之前的密码登陆不进去了！
使用上面的方法，无密码登陆后再重置密码，但是重置密码后发现仍然登陆不进去。

最后发现是因为mysql.user表内容被清空了！
mysql> select host,user,password from user;
Empty set (0.00 sec)

解决：

插入数据，再重置密码

mysql> insert into user(host,user,password) values("localhost","root","123456");Query OK, 1 row affected, 3 warnings (0.01 sec)mysql> select host,user,password from user;+-----------+------+----------+| host | user | password |+-----------+------+----------+| localhost | root | 123456 |+-----------+------+----------+1 row in set (0.00 sec)mysql> update mysql.user set password=password("123456") where host="localhost" and user="root";Query OK, 1 row affected (0.01 sec)Rows matched: 1 Changed: 1 Warnings: 0mysql> select host,user,password from user;+-----------+------+-------------------------------------------+| host | user | password |+-----------+------+-------------------------------------------+| localhost | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |+-----------+------+-------------------------------------------+1 row in set (0.00 sec)mysql> insert into user(host,user,password) values("127.0.0.1","root","123456");Query OK, 1 row affected, 3 warnings (0.00 sec)mysql> select host,user,password from user;+-----------+------+-------------------------------------------+| host | user | password |+-----------+------+-------------------------------------------+| localhost | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 || 127.0.0.1 | root | 123456 |+-----------+------+-------------------------------------------+2 rows in set (0.00 sec)mysql> update mysql.user set password=password("123456") where user="root";Query OK, 1 row affected (0.00 sec)Rows matched: 2 Changed: 1 Warnings: 0mysql> select host,user,password from user;+-----------+------+-------------------------------------------+| host | user | password |+-----------+------+-------------------------------------------+| localhost | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 || 127.0.0.1 | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |+-----------+------+-------------------------------------------+

然后使用重置后的密码就能正常登陆了！

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mysql登录报错1：

[root@test-huanqiu ~]# mysql -p123456
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (111)

[root@test-huanqiu ~]# ps -ef|grep mysql
root 28279 1 0 12:55 ? 00:00:00 /bin/sh /usr/local/mysql//bin/mysqld_safe --datadir=/data/mysql/data --pid-file=/data/mysql/data/mysql.pid
mysql 29059 28279 0 12:55 ? 00:00:01 /usr/local/mysql/bin/mysqld --basedir=/usr/local/mysql/ --datadir=/data/mysql/data --plugin-dir=/usr/local/mysql//lib/plugin --user=mysql --log-error=/data/mysql/data/mysql-error.log --pid-file=/data/mysql/data/mysql.pid --socket=/usr/local/mysql/var/mysql.sock --port=3306
root 30726 11268 0 12:58 pts/2 00:00:00 grep mysql

可知，当前mysql.sock文件路径是/usr/local/mysql/var/mysql.sock，

解决办法：做软链接

[root@test-huanqiu ~]# ll /usr/local/mysql/var/mysql.sock
rwxrwxrwx. 1 mysql mysql 0 Nov 29 12:55 /usr/local/mysql/var/mysql.sock
[root@test-huanqiu ~]# rm -f /var/lib/mysql/mysql.sock
[root@test-huanqiu ~]# ln -s /usr/local/mysql/var/mysql.sock /var/lib/mysql/mysql.sock

这样就没问题了

[root@test-huanqiu ~]# mysql -p123456
mysql>

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启动mysql的时候报错：

Starting MySQL.... ERROR! The server quit without updating PID file (/data/mysql/data/mysql.pid).

尝试的解决办法：

（1）权限问题

可能是mysql.pid文件没有写的权限，将mysql的安装目录和数据目录的权限都设置成mysql启动用户权限。比如都修改为mysql:mysql权限

（2）可能进程里已经存在mysql进程

ps -ef|grep mysql 查出要是有mysql进程存在，就kill掉，再尝试重启mysql

（3）可能是多次在机器上安装mysql，有残余数据影响了服务的启动。

去mysql的数据目录看看，如果存在mysql-bin.index，就立刻删掉它，它就是罪魁祸首了！