apache2: Could not reliably determine the server's fully qualified domain name

當設定apache2虛擬主機之後，若出現下列訊息：
 Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName
表示無法參考到本身hostname的設定值。

這時可手動編輯/etc/apache2/apache2.conf這個檔案。

sudo vim /etc/apache2/apache2.conf
將下列這一行加入=>ServerName localhost

重開apache2
sudo service apache2 restart

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AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1. Set the 'ServerName' directive globally to suppress this message