I got the worry message in the midnight, about the web server is down.
When I login, the server shows man directories can not mount as read and write. Directory can not write has happened before, when the disk is full. But can not mount disk as rewrite is not the disk full issue.
出現錯誤訊息 mysql.service: Failed with result ‘exit-code’. Job for mysql.service failed because the control process exited with error code. See “systemctl status mysql.service” and “journalctl -xe” for details.