Provided by: systemd_249.11-0ubuntu3_amd64 bug

NAME

       hostname - Local hostname configuration file

SYNOPSIS

       /etc/hostname

DESCRIPTION

       The /etc/hostname file configures the name of the local system. Unless overridden as
       described in the next section, systemd(1) will set this hostname during boot using the
       sethostname(2) system call.

       The file should contain a single newline-terminated hostname string. Comments (lines
       starting with a "#") are ignored. The hostname should be composed of up to 64 7-bit ASCII
       lower-case alphanumeric characters or hyphens forming a valid DNS domain name. It is
       recommended that this name contains only a single label, i.e. without any dots. Invalid
       characters will be filtered out in an attempt to make the name valid, but obviously it is
       recommended to use a valid name and not rely on this filtering.

       You may use hostnamectl(1) to change the value of this file during runtime from the
       command line. Use systemd-firstboot(1) to initialize it on mounted (but not booted) system
       images.

HOSTNAME SEMANTICS

       systemd(1) and the associated tools will obtain the hostname in the following ways:

       •   If the kernel commandline parameter systemd.hostname= specifies a valid hostname,
           systemd(1) will use it to set the hostname during early boot, see kernel-command-
           line(7),

       •   Otherwise, the "static" hostname specified by /etc/hostname as described above will be
           used.

       •   Otherwise, a transient hostname may be set during runtime, for example based on
           information in a DHCP lease, see systemd-hostnamed.service(8). Both NetworkManager[1]
           and systemd-networkd.service(8) allow this. Note that systemd-hostnamed.service(8)
           gives higher priority to the static hostname, so the transient hostname will only be
           used if the static hostname is not configured.

       •   Otherwise, a fallback hostname configured at compilation time will be used
           ("localhost").

       Effectively, the static hostname has higher priority than a transient hostname, which has
       higher priority than the fallback hostname. Transient hostnames are equivalent, so setting
       a new transient hostname causes the previous transient hostname to be forgotten. The
       hostname specified on the kernel command line is like a transient hostname, with the
       exception that it has higher priority when the machine boots. Also note that those are the
       semantics implemented by systemd tools, but other programs may also set the hostname.

HISTORY

       The simple configuration file format of /etc/hostname originates from Debian GNU/Linux.

SEE ALSO

       systemd(1), sethostname(2), hostname(1), hostname(7), machine-id(5), machine-info(5),
       hostnamectl(1), systemd-hostnamed.service(8), systemd-firstboot(1)

NOTES

        1. NetworkManager
           https://developer.gnome.org/NetworkManager/stable/