MySQL not responding?

I’ve managed to set up a running webserver from Ubuntu a couple days ago, but for some reasons it doesnt work since this afternoon ?

MySQL seems to be stuck somehow, here is the status :

root@localhost:~# systemctl status mysql.service ● mysql.service - MySQL Community Server    Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)    Active: failed (Result: exit-code) since Fri 2019-05-31 14:49:29 UTC; 18s ago   Process: 856 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=1/FAILURE)  May 31 14:49:29 localhost systemd[1]: mysql.service: Service hold-off time over, scheduling restart. May 31 14:49:29 localhost systemd[1]: mysql.service: Scheduled restart job, restart counter is at 5. May 31 14:49:29 localhost systemd[1]: Stopped MySQL Community Server. May 31 14:49:29 localhost systemd[1]: mysql.service: Start request repeated too quickly. May 31 14:49:29 localhost systemd[1]: mysql.service: Failed with result 'exit-code'. May 31 14:49:29 localhost systemd[1]: Failed to start MySQL Community Server. 

I tried to reboot the server, but it didn’t change anything.

I’ve no idea why this is happening, since I didn’t make any changes to MySQL in the past hours. Possibly relevant things are: I added Cloudflare to my website, or I also change the owner of all File/Folder of the wordpress installation (so it allows WordPress to updates plugins etc.). Maybe this owner change had an impact on the fact that MySQL cannot connect any longer with root?