1.备份

（略。）

2.安装8.0软件到新位置

[root@db01 /application]#mv mysql-8.0.16-linux-glibc2.12-x86_64  mysql8

3.停原库

[root@db01 /application]#systemctl stop mysqld

4.修改已有配置

共修改三处配置文件
mysql 改为mysql8

[root@db01 ~]#vim /etc/profile
export PATH=/application/mysql8/bin:$PATH
[root@db01 /application]#source /etc/profile
[root@db01 /application]#mysql -V
mysql  Ver 8.0.16 for linux-glibc2.12 on x86_64 (MySQL Community Server - GPL)

[root@db01 /application]#vim /etc/my.cnf 
[mysqld]
user=mysql
basedir=/application/mysql8
datadir=/data/3306/data
socket=/tmp/mysql.sock
[mysql]
socket=/tmp/mysql.sock

[root@db01 /application]#vim /etc/systemd/system/mysqld.service 
[Unit]
Description=MySQL Server
Documentation=man:mysqld(8)
Documentation=http://dev.mysql.com/doc/refman/en/using-systemd.html
After=network.target
After=syslog.target
[Install]
WantedBy=multi-user.target
[Service]
User=mysql
Group=mysql
ExecStart=/application/mysql8/bin/mysqld --defaults-file=/etc/my.cnf
LimitNOFILE = 5000

  systemctl stop mysqld.service 
  systemctl start  mysqld

5.恢复5.7.26版本

• 把三处配置文件改回去
• 初始化命令：mysqld --initialize-insecure --user=mysql --basedir=/application/mysql --datadir=/data/3306/data

• 重启
  systemctl stop mysqld.service
  systemctl start mysqld

  
  
  成功