下午把数据库关闭了，准备修改通过skip-granted-tables修改下root的密码，结果关闭之后，重启不成功。
[root@iZ2zehmkcpexiu333gfymtZ ~]# service mysqld start
MySQL Daemon failed to start.
Starting mysqld: [FAILED]
mysql关闭之后无法正常启动，提示启动失败。
查看mysql启动日志：
tail -20 /var/log/mysqld.log
180516 18:33:07 [ERROR] /usr/libexec/mysqld: Can't create/write to file '/var/run/mysqld/mysqld.pid' (Errcode: 13)
180516 18:33:07 [ERROR] Can't start server: can't create PID file: Permission denied
180516 18:33:07 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
180516 18:33:20 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
180516 18:33:20 InnoDB: Initializing buffer pool, size = 8.0M
180516 18:33:20 InnoDB: Completed initialization of buffer pool
180516 18:33:20 InnoDB: Started; log sequence number 0 1455648
180516 18:33:20 [ERROR] /usr/libexec/mysqld: Can't create/write to file '/var/run/mysqld/mysqld.pid' (Errcode: 13)
180516 18:33:20 [ERROR] Can't start server: can't create PID file: Permission denied
180516 18:33:20 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended提示不能启动服务，不能创建PID文件，权限不足
Can't create/write to file '/var/run/mysqld/mysqld.pid' 提示不能创建pid文件，目录为 /var/run/mysqld/ 看了下目录权限为nobody 而mysql使用的是mysql用户运行的，把权限修改 chmod 777 /var/run/mysqld -R
#############################################################################################
重置密码步骤：
1、先查看mysql是否启动，找到mysqld_safe的路径
[root@iZ2zehmkcpexiu333gfymtZ ~]# ps -ef | grep mysqld
root 8702 1 0 18:35 ? 00:00:00 /bin/sh /usr/bin/mysqld_safe --datadir=/var/lib/mysql --socket=/var/lib/mysql/mysql.sock --pid-file=/var/run/mysqld/mysqld.pid --basedir=/usr --user=mysql
mysql 8804 8702 0 18:35 ? 00:00:00 /usr/libexec/mysqld --basedir=/usr --datadir=/var/lib/mysql --user=mysql --log-error=/var/log/mysqld.log --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/lib/mysql/mysql.sock
root 9106 9069 0 18:45 pts/4 00:00:00 grep mysqld 2、关闭mysqld
[root@iZ2zehmkcpexiu333gfymtZ ~]# service mysqld stop
Stopping mysqld: [ OK ]3、 -–skip-grant-tables 跳过授权表启动mysql ， 这个地方重启mysql的时候 需要注意，这个时候mysql只能在 本服务器进行连接不需要用户名密码，直接mysql 就可以进行命令行，可以在这个命令之后在价格 & 表示这个这个进程挂到后台运行
[root@iZ2zehmkcpexiu333gfymtZ ~]# /usr/bin/mysqld_safe --datadir=/var/lib/mysql --socket=/var/lib/mysql/mysql.sock --pid-file=/var/run/mysqld/mysqld.pid --basedir=/usr --user=mysql --skip-grant-tables
180516 18:47:14 mysqld_safe Logging to '/var/log/mysqld.log'.
180516 18:47:14 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql4、进入mysql，直接就可以操作了
[root@iZ2zehmkcpexiu333gfymtZ ~]# mysql
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.1.73 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> 5、查询下user表，其中Host对应的 % 表示允许任意主机访问，如果要限制具体的ip访问，修改为指定的ip就行
mysql> select * from user \G;
*************************** 1. row ***************************
Host: %
User: root
Password: *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9
Select_priv: Y
Insert_priv: Y
Update_priv: Y
Delete_priv: Y
Create_priv: Y
Drop_priv: Y
Reload_priv: Y
Shutdown_priv: Y
Process_priv: Y
File_priv: Y
Grant_priv: Y
References_priv: Y
Index_priv: Y
Alter_priv: Y
Show_db_priv: Y
Super_priv: Y
Create_tmp_table_priv: Y
Lock_tables_priv: Y
Execute_priv: Y
Repl_slave_priv: Y
Repl_client_priv: Y
Create_view_priv: Y
Show_view_priv: Y
Create_routine_priv: Y
Alter_routine_priv: Y
Create_user_priv: Y
Event_priv: Y
Trigger_priv: Y
ssl_type:
ssl_cipher:
x509_issuer:
x509_subject:
max_questions: 0
max_updates: 0
max_connections: 0
max_user_connections: 0
1 row in set (0.00 sec)6、修改root的密码,刷新下权限，MYSQL不同版本修改密码方式不同 （ ps：每次修改完记得刷新下权限 ）
mysql> update user set Password=password('123456');
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1 Changed: 0 Warnings: 0
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
mysql> 7、关闭mysql，重新启动mysql
[root@iZ2zehmkcpexiu333gfymtZ ~]# ps -ef | grep mysql
root 9314 9052 0 18:47 pts/3 00:00:00 /bin/sh /usr/bin/mysqld_safe --datadir=/var/lib/mysql --socket=/var/lib/mysql/mysql.sock --pid-file=/var/run/mysqld/mysqld.pid --basedir=/usr --user=mysql --skip-grant-tables
mysql 9416 9314 0 18:47 pts/3 00:00:00 /usr/libexec/mysqld --basedir=/usr --datadir=/var/lib/mysql --user=mysql --skip-grant-tables --log-error=/var/log/mysqld.log --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/lib/mysql/mysql.sock
root 9798 9069 0 19:02 pts/4 00:00:00 grep mysql
[root@iZ2zehmkcpexiu333gfymtZ ~]# killall mysqld_safe
[root@iZ2zehmkcpexiu333gfymtZ ~]# kill -7 9314
[root@iZ2zehmkcpexiu333gfymtZ ~]# service mysqld start
Starting mysqld: [ OK ]
[root@iZ2zehmkcpexiu333gfymtZ ~]#