linux下Mysql的登陆与设置密码(本文基于centos6.4、mysql5.7.3)，mysql安装在/usr/local/mysql目录下：
[root@lnmp ~]# /usr/local/mysql/bin/mysqladmin -uroot password 'admin123' #修改mysql密码为admin123
[root@lnmp ~]# /usr/local/mysql/bin/mysql #如果是空密码可以这样进入mysql
[root@lnmp ~]# /usr/local/mysql/bin/mysql -uroot -p #建议此种方式，后面的不建议/usr/local/mysql/bin/mysql -uroot -p'admin123'
[root@lnmp ~]# /usr/local/mysql/bin/mysqladmin -uroot -p'admin123' password 'admin456'
mysqladmin: [Warning] Using a password on the command line interface can be insecure.
[root@lnmp ~]# /usr/local/mysql/bin/mysql -uroot -p'admin123'
mysql: [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@lnmp ~]# /usr/local/mysql/bin/mysql -uroot -p'admin456'
mysql>
mysql> update mysql.user set password=PASSWORD('admin123') where user='root'; #升级用户表中的密码
Query OK, 4 rows affected (0.03 sec)
Rows matched: 4 Changed: 4 Warnings: 0
mysql> flush privileges; #如果不更新，则新密码不生效
mysql> set password=password('admin123'); #以上方法适用于已知密码或者已经登入到msyql>的情况下！！！
Query OK, 0 rows affected (0.00 sec)
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
忘记mysql的root密码：
[root@lnmp ~]# service mysqld stop #关闭mysql
Shutting down MySQL... SUCCESS!
[root@lnmp ~]# /usr/local/mysql/bin/mysqld_safe --skip-grant-tables & #跳过授权表
[1] 3692
[root@lnmp ~]# 140502 15:40:48 mysqld_safe Logging to '/byrd/server/mysql-5.7.3/data/lnmp.err'.
140502 15:40:48 mysqld_safe Starting mysqld daemon with databases from /byrd/server/mysql-5.7.3/data
[root@lnmp ~]# /etc/init.d/mysqld start #跳过授权表后，重新启动mysql
Starting MySQL SUCCESS!
[root@lnmp ~]# /usr/local/mysql/bin/mysql #直接进入mysql
Welcome to the MySQL monitor. Commands end with ; or g.
mysql> update mysql.user set password=PASSWORD('admin123') where user='root'; #修改需要的mysql的root密码
mysql> flush privileges; #刷新权限，密码修改为admin123
mysql>quit
[root@lnmp ~]# /etc/init.d/mysqld stop
[root@lnmp ~]# /etc/init.d/mysqld start
[root@lnmp ~]# /usr/local/mysql/bin/mysql -uroot -p'admin123' #密码被修改为了admin123
备注：你可以将/usr/local/mysql/bin加入PATH中。这样可以直接输入mysql或者mysqladmin，不用输入全路径