無法啟動 Apache HTTP 伺服器 - 單元 apache2.service 失敗

我最近通過安裝了 Apache2，sudo apt install apache2但它似乎無法正常工作。當我嘗試使用sudo /etc/init.d/apache2 restart. 我正在使用 Kubuntu 18.04.1 64 位。

-- Subject: Unit apache2.service has begun start-up
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- Unit apache2.service has begun starting up.
Aug 29 13:31:47 alpaca-desktop apachectl[10871]: AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1. Set the 'ServerName' di
Aug 29 13:31:47 alpaca-desktop apachectl[10871]: (2)No such file or directory: AH02291: Cannot access directory '/var/log/apache2/' for main error log
Aug 29 13:31:47 alpaca-desktop apachectl[10871]: (2)No such file or directory: AH02291: Cannot access directory '/var/log/apache2/' for error log of vhost defined at /etc/apache2
Aug 29 13:31:47 alpaca-desktop apachectl[10871]: AH00014: Configuration check failed
Aug 29 13:31:47 alpaca-desktop apachectl[10871]: Action 'start' failed.
Aug 29 13:31:47 alpaca-desktop apachectl[10871]: The Apache error log may have more information.
Aug 29 13:31:47 alpaca-desktop systemd[1]: apache2.service: Control process exited, code=exited status=1
Aug 29 13:31:47 alpaca-desktop systemd[1]: apache2.service: Failed with result 'exit-code'.
Aug 29 13:31:47 alpaca-desktop systemd[1]: Failed to start The Apache HTTP Server.
-- Subject: Unit apache2.service has failed
-- Defined-By: systemd
-- Support: http://www.ubuntu.com/support
-- 
-- Unit apache2.service has failed.
-- 
-- The result is RESULT.

這是原因：

(2)No such file or directory: AH02291: Cannot access directory '/var/log/apache2/' for main error log

如果該目錄不存在，那麼 Apache 如何啟動？如果是這樣，則為 Apache 指定的使用者無法訪問它，這意味著文件權限不正確。

引用自：https://unix.stackexchange.com/questions/465560