hostname — Local host name configuration file
/etc/hostname
The /etc/hostname file
configures the name of the local system that is set
during boot, with the
sethostname(2)
system call. It should contain a single
newline-terminated host name string. The
host name may be a free-form string up to 64 characters
in length, however it is recommended that it consists
only of 7bit 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.
Depending on the operating system other configuration files might be checked for configuration of the host name as well, however only as fallback.
You may use hostnamectl(1) to change the value of this file from the command line.