Linux 中 FQDN 查詢及設置

FQDN：(Fully Qualified Domain Name)全限定功能變數名稱：同時帶有主機名和功能變數名稱的名稱

其實就是標註一個主機的完整功能變數名稱。比如我的功能變數名稱為 ifrom.top 那麼它的郵件伺服器的主機名為 mail, 所以它的FQDN 為： mail.ifrom.top

Linux 獲取主機名 的命令為：

➜  ~ hostname -f              
➜  ~ hostname --fqdn
➜  ~ hostname --long

三個都返回 fqdn 的值。

我們通過 man hostname 可以發現，其中有對fqdn 有更問詳細的講解：

   THE FQDN
       The FQDN (Fully Qualified Domain Name) of the system is the name that the resolver(3) returns for the host name, such as, ursula.example.com.  It is usually the hostname  followed
       by the DNS domain name (the part after the first dot).  You can check the FQDN using hostname --fqdn or the domain name using dnsdomainname.

       You cannot change the FQDN with hostname or dnsdomainname.

       The  recommended  method  of  setting  the  FQDN  is  to make the hostname be an alias for the fully qualified name using /etc/hosts, DNS, or NIS. For example, if the hostname was
       "ursula", one might have a line in /etc/hosts which reads

              127.0.1.1    ursula.example.com ursula

       Technically: The FQDN is the name getaddrinfo(3) returns for the host name returned by gethostname(2).  The DNS domain name is the part after the first dot.

       Therefore it depends on the configuration of the resolver (usually in /etc/host.conf) how you can change it. Usually the hosts file is parsed before DNS or NIS, so it is most com‐
       mon to change the FQDN in /etc/hosts.

       If  a  machine  has  multiple  network interfaces/addresses or is used in a mobile environment, then it may either have multiple FQDNs/domain names or none at all. Therefore avoid
       using hostname --fqdn, hostname --domain and dnsdomainname.  hostname --ip-address is subject to the same limitations so it should be avoided as well.

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