我的整体升级进行得很顺利，但我留下了一个严重挥之不去的问题，即 mysql-server 无法自行安装，而且我没有尝试任何方法让它工作。
这是我在尝试安装/重新安装时看到的错误：
Setting up mysql-server-5.7 (5.7.11-0ubuntu6) ...
Job for mysql.service failed because the control process exited with error code. See "systemctl status mysql.service" and "journalctl -xe" for details.
invoke-rc.d: initscript mysql, action "start" failed.
dpkg: error processing package mysql-server-5.7 (--configure):
subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of mysql-server:
mysql-server depends on mysql-server-5.7; however:
Package mysql-server-5.7 is not configured yet.
dpkg: error processing package mysql-server (--configure):
dependency problems - leaving unconfigured …