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
# 登陸后執行命令出現如下提示：
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.
解決辦法：使用初始密碼登陸后需要修改root密碼才行
alter user 'root'@'localhost' identified by '123liykpntuu9?C';
flush privileges;
然后退出重新登陸操作即可
# mysql5.6是密碼為空直接進入數據庫的，但是mysql5.7就需要初始密碼
cat /var/log/mysqld.log | grep password
# 然后執行 mysql -uroot -p ，輸入上面的到的密碼進入，用該密碼登錄后，必須馬上修改新的密碼，不然會報如下錯誤：
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.
# 如果你想要設置一個簡單的測試密碼的話，比如設置為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有以下取值：
默認是1，即MEDIUM，所以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，只是為了自己測試，不想密碼設置得那么復雜，譬如說，我只想設置root的密碼為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)參數默認為8，我們修改為1
mysql> set global validate_password_length=1;
Query OK, 0 rows affected (0.00 sec)
# 完成之后再次執行修改密碼語句即可成功
mysql> alter user 'root'@'localhost' identified by '123456';
Query OK, 0 rows affected (0.00 sec)
