Hey there! Totally get why you're cautious here—upgrading MySQL without messing up your data is no joke, especially since 8.0 was still relatively new when you asked. Let’s walk through a safe, in-place upgrade process that skips a full reinstall, so you can unlock all those great 8.0 features without losing a single row of data.

Pre-Upgrade Prep (Critical—Don’t Skip!) #

• Backup everything first: This is non-negotiable. Use mysqldump to create a full backup of all your databases. Run this command (replace root with your admin user if needed):

  mysqldump -u root -p --all-databases --routines --triggers --events > full_mysql_backup.sql
  

  Store this file somewhere safe (not on the same server!). Also, copy your MySQL config files (/etc/my.cnf or /etc/mysql/my.cnf depending on your OS) to a backup location.
• Check for deprecated features: MySQL 8.0 removes or modifies some 5.7 features. Run the built-in upgrade checker to catch issues early:

  mysqlcheck -u root -p --all-databases --check-upgrade
  

  Fix any flags it throws—like old authentication plugins, deprecated SQL syntax, or MyISAM tables (consider converting these to InnoDB if possible, since MyISAM has limited support in 8.0).
• Update system packages: Make sure your OS is fully updated to avoid dependency conflicts during the upgrade.

Step-by-Step Upgrade Process #

1. Stop the MySQL 5.7 service:

   # For systemd systems (Ubuntu 16.04+, CentOS 7+)
   sudo systemctl stop mysql
   # For SysVinit systems
   sudo service mysql stop
   

2. Add the official MySQL 8.0 repository:
   The exact steps depend on your OS:
   • Ubuntu/Debian:

     wget https://dev.mysql.com/get/mysql-apt-config_0.8.22-1_all.deb
     sudo dpkg -i mysql-apt-config_0.8.22-1_all.deb
     # Select MySQL 8.0 from the interactive prompt, then update apt
     sudo apt update
     

   • CentOS/RHEL:

     sudo yum install https://dev.mysql.com/get/mysql80-community-release-el7-3.noarch.rpm
     sudo yum-config-manager --enable mysql80-community
     

3. Upgrade MySQL packages (don’t install fresh!):
   Use your package manager to upgrade existing 5.7 packages to 8.0—this preserves your data directory:

   # Ubuntu/Debian
   sudo apt upgrade mysql-server
   # CentOS/RHEL
   sudo yum upgrade mysql-community-server
   

   Follow any on-screen prompts; this replaces 5.7 binaries with 8.0 ones without wiping your data.
4. Run the system table upgrade script:
   MySQL 8.0 needs to update its system tables to the new schema. Start the service (it might fail initially—this is normal):

   sudo systemctl start mysql
   # Run the upgrade script
   mysql_upgrade -u root -p
   

   This script fixes schema mismatches and ensures system tables work with 8.0.
5. Verify the upgrade:
   Log into MySQL to confirm you’re running 8.0:

   mysql -u root -p
   

   Inside the MySQL shell, run:

   SELECT VERSION();
   

   You should see output like 8.0.x. Double-check that all your databases and tables are present and accessible.
6. Tweak config settings:
   MySQL 8.0 has new default settings. Open your backup my.cnf file and update any deprecated options. For example, default_authentication_plugin defaults to caching_sha2_password—if your apps don’t support this yet, you can temporarily set it back to mysql_native_password until you update your applications.

Post-Upgrade Checks #

• Test all your applications to ensure they connect and function correctly with MySQL 8.0.
• Monitor the MySQL error log (/var/log/mysql/error.log or similar) for warnings or unexpected errors.
• If something goes wrong, roll back using your backup: stop the 8.0 service, restore 5.7 binaries, then import your backup SQL file with mysql -u root -p < full_mysql_backup.sql.

Pro tip: If you’re still nervous, test this entire process on a staging server first! That way you can work out any kinks without risking production data.

内容的提问来源于stack exchange，提问作者Imnotapotato