Руководство по работе в сети RHEL 7 содержит некоторые сведения об именах хостов :

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There are three classes of hostname: static, pretty, and transient. The “static” host name is the traditional hostname, which can be chosen by the user, and is stored in the /etc/hostname file. The “transient” hostname is a dynamic host name maintained by the kernel. It is initialized to the static host name by default, whose value defaults to “localhost”. It can be changed by DHCP or mDNS at runtime. The “pretty” hostname is a free-form UTF8 host name for presentation to the user.

Note: A host name can be a free-form string up to 64 characters in length. However, Red Hat recommends that both static and transient names match the fully-qualified domain name (FQDN) used for the machine in DNS, such as host.example.com. It is also recommended that the static and transient names consists only of 7 bit ASCII lower-case characters, no spaces or dots, and limits itself to the format allowed for DNS domain name labels, even though this is not a strict requirement. Older specifications do not permit the underscore, and so their use is not recommended. The hostnamectl tool will enforce the following: Static and transient host names to consist of a-z, A-Z, 0-9, “-”, “_” and “.” only, to not begin or end in a dot, and to not have two dots immediately following each other. The size limit of 64 characters is enforced.