從ubuntu 14.04 升級ubuntu16.04後，apache2無法啟動，如下報錯：

Starting apache2 (via systemctl): apache2.serviceJob for apache2.service failed because the control process exited with error code. See "systemctl status apache2.service" and "journalctl -xe" for details.
 failed!

解除安裝apache2
再次重灌仍報錯：

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

需要執行以下命令
sudo apt-get purge apache2

sudo apt-get install apache2
啟動ok。

● apache2.service - LSB: Apache2 web server
   Loaded: loaded (/etc/init.d/apache2; bad; vendor preset: enabled)
 

  Drop-In: /lib/systemd/system/apache2.service.d
           └─apache2-systemd.conf
   Active: active (running) since Mon 2016-11-07 20:05:13 CST; 23s ago
     Docs: man:systemd-sysv-generator(8)
   CGroup: /system.slice/apache2.service
           ├─10051 /usr/sbin/apache2 -k start
           ├─10054 /usr/sbin/apache2 -k start
           └─10055
 
 /usr/sbin/apache2 -k start