如果使用 MySQL 數據庫忘記了root賬號密碼，可以通過調節配置文件，跳過密碼的方式登數據庫，
在數據庫裏面修改賬號密碼，一般默認的賬號是 root
1、編輯 MySQL 配置文件 my.cnf
注意： 以實際 my.cnf 配置文件路徑爲準
vim /etc/my.cnf
[mysqld]
spik-grant-tables #增加
2、重啓 MySQL 服務
注意：以實際 MySQL 啓動腳本路徑爲準
/etc/init.d/mysqld restart
若報錯，注意觀察my.cnf配置文件中的內容
3、登陸數據庫
/usr/bin/mysql 輸入如下命令：
注意：以實際 MySQL 執行文件路徑爲準
mysql> USE mysql;
mysql> UPDATE user SET Password = password ('新密碼') WHERE User = 'root' ;
mysql> flush privileges ;
mysql> quit
4、刪除或者註釋第一步驟中添加的 spik-grant-tables
5、重啓 MySQL 服務
/etc/init.d/mysqld restart
6、使用新密碼測試
特殊情況：
我這是使用源碼安裝的mysql,默認配置文件my.cnf(/usr/local/mysql/my.cnf)中的內容都沒有配置，都是在啓動文件mysqld(/etc/rc.d/init.d/mysqld)中進行配置的
datadir=/data/mysql
basedir=/usr/local/mysql
若按照上述方法進操作，在my.cnf中添加"spik-grant-tables",則重啓mysql時報錯
正確的解決方法：
根據啓動文件mysqld中的datadir和basedir參數相應的啓用my.cnf中的選項，然後再添加"spik-grant-tables",mysql重啓就不會報錯，也能正常按照下面的步驟進行
未修改前的my.cnf
# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.6/en/server-configuration-defaults.html
[mysqld]
# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M
# spik-grant-tables
# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin
# These are commonly set, remove the # and set as required.
# basedir = .....
# datadir = .....
# port = .....
# server_id = .....
# socket = .....
# Remove leading # to set options mainly useful for reporting servers.
# The server defaults are faster for transactions and fast SELECTs.
# Adjust sizes as needed, experiment to find the optimal values.
# join_buffer_size = 128M
# sort_buffer_size = 2M
# read_rnd_buffer_size = 2M
sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES
修改後的my.cnf
# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.6/en/server-configuration-defaults.html
[mysqld]
# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M
# spik-grant-tables
# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin
# These are commonly set, remove the # and set as required.
basedir = /usr/local/mysql
datadir = /data/mysql
port = 3306
# server_id = .....
# socket = .....
skip-grant-tables
# Remove leading # to set options mainly useful for reporting servers.
# The server defaults are faster for transactions and fast SELECTs.
# Adjust sizes as needed, experiment to find the optimal values.
# join_buffer_size = 128M
# sort_buffer_size = 2M
# read_rnd_buffer_size = 2M
sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES
然後再重啓mysql,進行下面的步驟，重置密碼後，再把my.cnf中的修改的那四項全部註釋掉，再次重啓mysql即可。
來源：http://www.cnblogs.com/sanduzxcvbnm/p/6080380.html