首先官網下載mysql5.7的yum源
https://dev.mysql.com/downloads/repo/yum/
安裝yum源
yum localinstall mysql80-community-release-el7-3.noarch.rpm
指定安裝版本-----編輯mysql-community.repo文件
vi /etc/yum.repos.d/mysql-community.repo
打開後設置如下
# Enable to use MySQL 5.6
[mysql56-community]
name=MySQL 5.6 Community Server
baseurl=http://repo.mysql.com/yum/mysql-5.6-community/el/7/$basearch/
enabled=0
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql
# Enable to use MySQL 5.7
[mysql57-community]
name=MySQL 5.7 Community Server
baseurl=http://repo.mysql.com/yum/mysql-5.7-community/el/7/$basearch/
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql
[mysql80-community]
name=MySQL 8.0 Community Server
baseurl=http://repo.mysql.com/yum/mysql-8.0-community/el/7/$basearch/
enabled=0
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-mysql
其中，enabled=0表示不安裝，我們找到mysql5.7然後將enabled設置爲1，其餘設置爲0（以防默認）。
設置好安裝版本後，然後安裝
yum install mysql-community-server
安裝完成後，登錄mysql，因在安裝過程中，沒有設置密碼，第一次登錄用我們直接回車看提示進行試探。
第一次登錄出現如下情況 ：
[root@master yum.repos.d]# mysql -u root -p
Enter password:
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)
解決辦法第一步，查看mysql服務狀態
systemctl status mysqld
[root@master]# systemctl status mysqld
● mysqld.service - MySQL Server
Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
Active: inactive (dead)
Docs: man:mysqld(8)
http://dev.mysql.com/doc/refman/en/using-systemd.html
[root@master]#
可以看出服務沒有激活
解決辦法第二步，開啓mysql服務
[root@master]# systemctl start mysqld
[root@master]# systemctl status mysqld
● mysqld.service - MySQL Server
Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
Active: active (running) since Wed 2019-09-25 22:06:12 CST; 2s ago
Docs: man:mysqld(8)
http://dev.mysql.com/doc/refman/en/using-systemd.html
Process: 1995 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS (code=exited, status=0/SUCCESS)
Process: 1922 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
Main PID: 1998 (mysqld)
CGroup: /system.slice/mysqld.service
└─1998 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid...
Sep 25 22:06:05 master systemd[1]: Starting MySQL Server...
Sep 25 22:06:12 master systemd[1]: Started MySQL Server.
[root@master]#
服務已經開啓，我們再次無密碼登錄
[root@master yum.repos.d]# mysql -u root -p
Enter password:
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)
發現沒有密碼被拒絕，此時應該想到好看日誌，首先查看mysql的錯誤日誌在那個文件
查看mysql錯誤日誌在那個文件夾下
[root@master yum.repos.d]# cat /etc/my.cnf
# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.7/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
#
# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin
#
# 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
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid
[root@master yum.repos.d]# cat /var/log/mysqld.log
從上面看有注意到mysql的錯誤日誌位置（log-error=/var/log/mysqld.log）
查看mysql.log
cat /var/log/mysqld.log
複製密碼再次登錄
[root@master yum.repos.d]# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.27
Copyright (c) 2000, 2019, 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>
登錄成功！查看數據庫試試
mysql> show databases;
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.
mysql>
提示要重置密碼
修改密碼第一步：設置密碼安全檢驗（降低）
mysql> set global validate_password_policy=0;
Query OK, 0 rows affected (0.00 sec)
mysql> set global validate_password_length=1;
Query OK, 0 rows affected (0.00 sec)
修改密碼第二步：修改密碼(xxx爲設置的密碼)
mysql> alter user 'root'@'localhost' identified by 'xxxx';
Query OK, 0 rows affected (0.00 sec)
重新登錄
[root@master yum.repos.d]# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.7.27 MySQL Community Server (GPL)
Copyright (c) 2000, 2019, 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.
查看策略表
可以看出，密碼長度最小設置文4位，設置密碼要求已經最低。到了這個階段，mysql5.7已經安裝好了。
爲了方便遠程連接，現給root用戶授權。
update user set host='%' where user='root';