解决MySQL忘记root密码

网上有很多关于忘记MySQL root密码的一些文章，里面都有写怎么去解决，但有时觉得写得太恶心，要么一字不漏的抄别人的，要么就说得不清不楚，好了，不吐槽了，以下是解决的整个过程。

首先我们要知道忘记MySQL root密码后，能否重启mysql，能重启的操作是怎么样的？不能重启的操作又会是怎么样的？

情况一：（能重启情况下）

修改my.cnf配置文件，在mysqld栏下添加skip-grant-tables选项，意思是mysqld server启动之后并不使用权限系统（privilege system），也可以理解为跳过授权表。为了安全起见，通常加上skip-networking，mysqld不侦听任何TCP/IP连接请求。

重启mysqld，然后空密码连接：

[root ~]$mysql -uroot -S /data/mysql-5.5/mysql.sock
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is
Server version: 5.5.-log MySQL Community Server (GPL)

Copyright (c) , , Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> 

可以看到已经成功登录了，然后修改root密码：

mysql> update mysql.user set password=password('') where user='root';
Query OK,  rows affected (0.00 sec)
Rows matched:   Changed:   Warnings:
mysql> flush privileges; 
Query OK, 0 rows affected (0.01 sec)

已经成功修改密码了，但还有事情要做，就是把刚刚添加到my.cnf里的skip-grant-tables和skip-networking删除掉或者注释掉。

情况二：(不能重启mysql的情况)

如果不能重启，mysql.user 刚好有权限比较低的用户，如果没有，你请神仙来帮你吧，哈哈

1、为了测试，我自己创建一个用户，可以没什么权限

mysql> create user xuanzhi@'localhost' identified by '';
Query OK,  rows affected (0.00 sec)

2、进到数据目录下：

[root mysql-5.5]$ pwd
/data/mysql-5.5
[root mysql-5.5]$ cp mysql/user.* test/
[root mysql-5.5]$ chown mysql.mysql test/user.*

3、用权限比较小的用户登录：

[root mysql-5.5]$mysql -uxuanzhi -p123456 -S /data/mysql-5.5/mysql.sock
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is
Server version: 5.5.-log MySQL Community Server (GPL)

Copyright (c) , , Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> use test
Database changed
mysql> update user set password=password('') where user='root';
Query OK,  rows affected (0.00 sec)
Rows matched:   Changed:   Warnings: 

4、把修改后的user.MYD和user.MYI复制到mysql目录下，记得备份之前的文件。

[root mysql-5.5]$ pwd
/data/mysql-5.5
[root mysql-5.5]$ mv mysql/user.MYD mysql/user.MYD.bak
[root mysql-5.5]$ mv mysql/user.MYI mysql/user.MYI.bak
[root mysql-5.5]$ cp test/user.MY* mysql/
[root mysql-5.5]$ chown mysql:mysql  mysql/user.*

5.查找mysql进程号，并且发送SIGHUP信号，重新加载权限表。（有时加载一次不行的时候，再加载多一次@。@）

[root mysql]$ pgrep -n mysql

[root mysql]$ kill -SIGHUP
[root mysql]$ /usr/local/mysql-5.5./bin/mysql -uroot -p123123 -S /data/mysql-5.5/mysql.sock
ERROR  (): Access denied for user 'root'@'localhost' (using password: YES)
[root mysql]$ kill -SIGHUP
[root mysql]$ /usr/local/mysql-5.5./bin/mysql -uroot -p123123 -S /data/mysql-5.5/mysql.sock
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is
Server version: 5.5.-log MySQL Community Server (GPL)

Copyright (c) , , Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> 

不重启的第二种方法：

1、创建新的数据目录，并给原来user相应的权限,忘记密码对应的实例它的user是mysql，所以把权限给mysql用户

[root data]$ mkdir -pv /dbdata/datadir/
mkdir: 已创建目录 "/dbdata"
mkdir: 已创建目录 "/dbdata/datadir/"
[root data]$ chown  -R mysql:mysql /dbdata/datadir/

2、执行初始化操作：（报错了）

[root scripts]$ pwd
/usr/local/mysql-5.5./scripts
[root scripts]$ ./mysql_install_db --datadir=/dbdata/datadir/ --user=mysql2

FATAL ERROR: Could not find ./bin/my_print_defaults

If you compiled from source, you need to run 'make install' to
copy the software into the correct location ready for operation.

If you are using a binary release, you must either be at the top
level of the extracted archive, or pass the --basedir option
pointing to that location.

解决方法：

[root scripts]$ /usr/local/mysql-5.6.1/scripts/mysql_install_db --datadir=/dbdata/datadir/ --user=mysql --datadir=/dbdata/datadir/ --basedir=/usr/local/mysql-5.6.1/
Installing MySQL system tables...
 :: [Warning] 'THREAD_CONCURRENCY' is deprecated and will be removed in a future release.
OK
Filling help tables...
 :: [Warning] 'THREAD_CONCURRENCY' is deprecated and will be removed in a future release.
OK

3、启动一个新的进程，这里要注意一下port，sock文件，还有pid文件，这都是新的，user还是忘记密码实例的user，而不是忘记密码对应的那个数据库实例的，这里我们不需要用到InnoDB引擎,设置默认引擎为MyISAM：

[root ~]$  /usr/local/mysql-5.6.10/bin/mysqld_safe --datadir=/dbdata/datadir --plugin-dir=/usr/local/mysql-5.6.10/lib/plugin/  --skip-innodb \
> --default-storage-engine=myisam --socket=/dbdata/datadir/mysql2.sock --user=mysql --port=3305 --log-error=/dbdata/datadir/error2.log --pid-file=/data/mysql-5.6/mysql.pid &
[1] 21204
[root ~]$  :: mysqld_safe Logging to '/dbdata/datadir/error2.log'.
 :: mysqld_safe Starting mysqld daemon with databases from /dbdata/datadir

4、登录新启动的mysql实例，此时密码为空密码：

root datadir]$ /usr/local/mysql-5.6.10/bin/mysql -S /dbdata/datadir/mysql2.sock
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.6.10-log Source distribution

Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> flush tables;
Query OK, 0 rows affected (0.00 sec)

修改root密码：

mysql> select user, host, password from user where user like 'root';
+------+-----------------------+----------+
| user | host                  | password |
+------+-----------------------+----------+
| root | localhost             |          |
| root | localhost.localdomain |          |
| root | 127.0.0.1             |          |
| root | ::1                   |          |
+------+-----------------------+----------+
4 rows in set (0.02 sec)

mysql> update mysql.user set password=password('') where user='root';
Query OK, 4 rows affected (0.03 sec)
Rows matched: 4  Changed: 4  Warnings: 0
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

5、拷备新的user表到忘记密码的实例数据库的mysql目录下

[root mysql]$ pwd
/dbdata/datadir/mysql
[root mysql]$ cp user.* /data/mysql-5.6/mysql/
cp：是否覆盖"/data/mysql-5.6/mysql/user.frm"？ y
cp：是否覆盖"/data/mysql-5.6/mysql/user.MYD"？ y
cp：是否覆盖"/data/mysql-5.6/mysql/user.MYI"？ y
[root mysql]$ chown -R mysql5.:mysql5. /data/mysql-5.6/
[root mysql]$ chmod  /data/mysql-5.6/mysql/user.*

6、我们需要到mysqld发送一个sighup信号，MySQL响应这个信号加载授权表，刷新表，日志，线程缓存。
如果是单个MySQL实例，可以用这样的方法去重新加载

[root ~]$ kill - $(/sbin/pidof mysqld)

如果是多个MySQL实例在一台服务器上的话，就要注意点了，可以通过这样的方法找到pid，我旧实例的端口是3306：

[root mysql-5.6.]$ netstat -nltp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name
tcp               0.0.0.0:                0.0.0.0:*                   LISTEN      /mysqld
tcp               0.0.0.0:                0.0.0.0:*                   LISTEN      /mysqld
tcp               0.0.0.0:                  0.0.0.0:*                   LISTEN      /sshd           

tcp               :::                     :::*                        LISTEN      /mysqld
tcp               :::                       :::*                        LISTEN      /sshd
tcp               :::                     :::*                        LISTEN      /cupsd
tcp               :::                     :::*                        LISTEN      2091/mysqld
[root mysql-5.6.]$ kill - 

有时kill -1一次不行，再执行一次就可以了：

[root mysql-5.6.]$ kill -
[root mysql-5.6.]$ /usr/local/mysql-5.6./bin/mysql -uroot -p654321 -S /data/mysql-5.6/mysql.sock
Warning: Using a password on the command line interface can be insecure.
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
[root mysql-5.6.]$ kill -
[root mysql-5.6.]$ /usr/local/mysql-5.6./bin/mysql -uroot -p654321 -S /data/mysql-5.6/mysql.sock
Warning: Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is
Server version: 5.6.-log MySQL Community Server (GPL)

Copyright (c) , , Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> 

OK，已经成功登录了，如果有更多好的方法，我们可以再一起讨论下

总结：

1）第一种方法简单，但需要重启MySQL,重启会影响线上业务，一般不建议重启

2）第二种方法比较好，不用重启MySQL实例，修改密码，只修改root用户的，而且其它保持不变

3）第三种方法也不需要重启，但是新的user表里，只有root一个用户，如果之前服务器还存在别的用户及权限，这就比较麻烦了

参考资料：http://www.percona.com/blog/2014/12/10/recover-mysql-root-password-without-restarting-mysql-no-downtime/

PS:本人也是参考别人的博客做的，但我没有照搬别人的东西，太恶心了，希望大家有自己的风格。^.^

作者：陆炫志

出处：xuanzhi的博客 http://www.cnblogs.com/xuanzhi201111

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