HOSTNAME(5) hostname HOSTNAME(5)
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 strongly recommended that
this name contains only a single DNS label, i.e does not contain any
dots. This recommendation reflects both usual expectations of
applications, and the fact that the Linux kernel limits the length of
the system hostname to 64 (i.e. close to the maximum DNS label length of
63) rather than 255 (the maximum DNS domain name length). When applied,
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 command line 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/
systemd 257.13 HOSTNAME(5)
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