What is a Fully Qualified Domain Name (FQDN)?
An FQDN is a domain name that completely and uniquely identifies one and only one host on the Internet. It has this general syntax:
An FQDN can be broken down into four parts:
- Hostname: www, mail, ftp, store, support, etc.
- Domain: apple, microsoft, ibm, facebook, etc.
- Top level domain (TLD): .com, .net, .org, .co.uk, etc.
- Trailing period: the final period in an FQDN indicates the end of the name, implying the previous string is the TLD.
If a domain name is missing any of these parts, then it is not an FQDN but a Partially Qualified Domain Name (PQDN). PQDN can not be used as hostnames.
Additionally, not all FQDNs are equally acceptable to assign as the hostname in a cPanel environment. Here are a few restrictions to always have in mind:
- Do not select a hostname that begins with www or a number
- Do not select a hostname that ends with a hyphen (-)
- Do not choose a hostname that a cPanel account on your server is already using.
- Do not choose a potential service subdomain as a hostname (for example, cpanel.example.com or whm.example.com).
- Do not select a socially-unacceptable hostname. You must always remember that hostnames will appear in mail headers and a lot of other places.
- Only use lowercase, Latin-script letters in hostnames.