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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
+<!ENTITY % entities SYSTEM "custom-entities.ent" >
+%entities;
+]>
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="hostname">
+ <refentryinfo>
+ <title>hostname</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>hostname</refentrytitle>
+ <manvolnum>5</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>hostname</refname>
+ <refpurpose>Local hostname configuration file</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <para><filename>/etc/hostname</filename></para>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>The <filename>/etc/hostname</filename> file configures the name of the local system. Unless
+ overridden as described in the next section,
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will set this
+ hostname during boot using the
+ <citerefentry><refentrytitle>sethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry> system
+ call.</para>
+
+ <para>The file should contain a single newline-terminated hostname string. Comments (lines starting with
+ a <literal>#</literal>) 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.</para>
+
+ <para>You may use
+ <citerefentry><refentrytitle>hostnamectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to change
+ the value of this file during runtime from the command line. Use
+ <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry> to
+ initialize it on mounted (but not booted) system images.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Hostname semantics</title>
+
+ <para><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> and the
+ associated tools will obtain the hostname in the following ways:</para>
+ <itemizedlist>
+ <listitem><para>If the kernel command line parameter <varname>systemd.hostname=</varname> specifies a
+ valid hostname,
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will use it
+ to set the hostname during early boot, see
+ <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ </para></listitem>
+
+ <listitem><para>Otherwise, the "static" hostname specified by <filename>/etc/hostname</filename> as
+ described above will be used.</para></listitem>
+
+ <listitem><para>Otherwise, a transient hostname may be set during runtime, for example based on
+ information in a DHCP lease, see
+ <citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
+ Both <ulink url="https://developer.gnome.org/NetworkManager/stable/">NetworkManager</ulink> and
+ <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ allow this. Note that
+ <citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ gives higher priority to the static hostname, so the transient hostname will only be used if the static
+ hostname is not configured.</para></listitem>
+
+ <listitem><para>Otherwise, a fallback hostname configured at compilation time will be used
+ (<literal>&FALLBACK_HOSTNAME;</literal>).</para></listitem>
+
+ <!-- what about the "linux" fallback fallback? -->
+ </itemizedlist>
+
+ <para>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.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>History</title>
+
+ <para>The simple configuration file format of
+ <filename>/etc/hostname</filename> originates from Debian
+ GNU/Linux.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>hostnamectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>