hostname (5) - Linux Man Pages
hostname: Local hostname configuration file
hostname - Local hostname configuration file
The /etc/hostname file configures the name of the local system that is set during boot using the sethostname(2) system call. It should contain a single newline-terminated hostname string. Comments (lines starting with a `#') are ignored. The hostname may be a free-form string up to 64 characters in length; however, it is recommended that it consists only of 7-bit ASCII lower-case characters and no spaces or dots, and limits itself to the format allowed for DNS domain name labels, even though this is not a strict requirement.