Tron Natthakorn's questions

Today I tried to update ubuntu from 18.04 LTS to 20.04 LTS. with do-release-uprade

After upgrade completed, I tried to start mysql with service mysql start

The result is

Job for mysql.service failed because the control process exited with error code. See "systemctl status mysql.service" and "journalctl -xe" for details.

And then I tried to check with systemctl status mysql.service

The result is

mysql.service - MySQL Community Server
Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Fri 2021-04-09 17:45:14 +07; 1min 52s ago
Process: 13824 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=1/FAILURE)

Apr 09 17:45:14 systemd[1]: Failed to start MySQL Community Server.
Apr 09 17:45:14 systemd[1]: mysql.service: Scheduled restart job, restart counter is at 5.
Apr 09 17:45:14 systemd[1]: Stopped MySQL Community Server.
Apr 09 17:45:14 systemd[1]: mysql.service: Start request repeated too quickly.
Apr 09 17:45:14 systemd[1]: mysql.service: Failed with result 'exit-code'.
Apr 09 17:45:14 systemd[1]: Failed to start MySQL Community Server.

I cannot access to mysql anymore because service cannot start.

I do not want to lost any database. I do not have any backup, too.

Is backup /var/lib/mysql is enough? (Anything else that I should backup?)

I am very confuse. What should I do next?

1. Downgrade to Ubuntu 18.04 Or
2. Find the way to reinstall mysql 5.7 for Ubuntu 20.04 Or
3. Try upgrade mysql to 8. (but I cannot start mysql service this time)

Why ubuntu 20.04 cannot support mysql 5.7.33?

Thanks for any help.