下載MySQL的rpm包安裝MySQL

cd /usr/local/src

wget https://cdn.mysql.com//Downloads/MySQL-5.7/mysql-community-server-5.7.27-1.el7.x86_64.rpm
wget https://cdn.mysql.com//Downloads/MySQL-5.7/mysql-community-client-5.7.27-1.el7.x86_64.rpm
wget https://cdn.mysql.com//Downloads/MySQL-5.7/mysql-community-libs-5.7.27-1.el7.x86_64.rpm
wget https://cdn.mysql.com//Downloads/MySQL-5.7/mysql-community-common-5.7.27-1.el7.x86_64.rpm

yum remove mariadb-libs
yum install net-tools
yum install *.rpm


systemctl status mysqld.service
systemctl start mysqld.service

# 查看默認密碼
grep 'temporary password' /var/log/mysqld.log
liykpntuu9?C

# 登錄後執行命令出現以下提示：
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.

解決辦法：使用初始密碼登錄後須要修改root密碼才行
alter user 'root'@'localhost' identified by '123liykpntuu9?C';
flush privileges;

而後退出從新登錄操做便可

# mysql5.6是密碼爲空直接進入數據庫的，可是mysql5.7就須要初始密碼
cat /var/log/mysqld.log | grep password

# 而後執行 mysql -uroot -p ，輸入上面的到的密碼進入，用該密碼登陸後，必須立刻修改新的密碼，否則會報以下錯誤：
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.

# 若是你想要設置一個簡單的測試密碼的話，好比設置爲123456，會提示這個錯誤，報錯的意思就是你的密碼不符合要求
mysql> alter user 'root'@'localhost' identified by '123456';
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements

這個其實與validate_password_policy的值有關。

validate_password_policy有如下取值：

默認是1，即MEDIUM，因此剛開始設置的密碼必須符合長度，且必須含有數字，小寫或大寫字母，特殊字符。
有時候，只是爲了本身測試，不想密碼設置得那麼複雜，譬如說，我只想設置root的密碼爲123456。
必須修改兩個全局參數：

首先，修改validate_password_policy參數的值
mysql> set global validate_password_policy=0;
Query OK, 0 rows affected (0.00 sec)

validate_password_length(密碼長度)參數默認爲8，咱們修改成1

mysql> set global validate_password_length=1;
Query OK, 0 rows affected (0.00 sec)

# 完成以後再次執行修改密碼語句便可成功
mysql> alter user 'root'@'localhost' identified by '123456';
Query OK, 0 rows affected (0.00 sec)