$ sudo service apache2 restart Job for apache2.service failed because the control process exited with error code. See "systemctl status apache2.service" and "journalctl -xe" for details.

手贱，想解决ssl 无法访问的问题，修改apache2配置，结果出问题了：

$ sudo service apache2 restart
Job for apache2.service failed because the control process exited with error code.
See "systemctl status apache2.service" and "journalctl -xe" for details.

虽然找到了许多网友的解决办法，但是没有一个全套解决办法，只好耐心一个合着试验，
最终解决了。
1、重新安装apache2

$ systemctl restart apache2
$ journal -xe 
$ sudo apt-get purge apache2
$ sudo apt autoremove apache2
$ sudo apt-get purge apache2
$ sudo apt-get purge apache2*
$ sudo apt-get install apache2
$ sudo service apache2 start

2、重点在这里：
重新安装了apache2，网站正常访问了，但是php却无法正常运行，
问题是这个
php7.3没有运行，
所以：sudo  a2enmod php7.3
但是出现如下提示：
Considering dependency mpm_prefork for php7.3:
Considering conflict mpm_event for mpm_prefork:
ERROR: Module mpm_event is enabled - cannot proceed due to conflicts. It needs to be disabled first!
Considering conflict mpm_worker for mpm_prefork:
ERROR: Could not enable dependency mpm_prefork for php7.3, aborting

所以接着：
sudo a2dismod mpm_event
Module mpm_event disabled.
To activate the new configuration, you need to run:
  systemctl restart apache2

OK，解决了