man/hostname.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
   4 <!ENTITY % entities SYSTEM "custom-entities.ent" >
   5 %entities;
   6 ]>
   7 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   8
   9 <refentry id="hostname">
  10   <refentryinfo>
  11     <title>hostname</title>
  12     <productname>systemd</productname>
  13   </refentryinfo>
  14
  15   <refmeta>
  16     <refentrytitle>hostname</refentrytitle>
  17     <manvolnum>5</manvolnum>
  18   </refmeta>
  19
  20   <refnamediv>
  21     <refname>hostname</refname>
  22     <refpurpose>Local hostname configuration file</refpurpose>
  23   </refnamediv>
  24
  25   <refsynopsisdiv>
  26     <para><filename>/etc/hostname</filename></para>
  27   </refsynopsisdiv>
  28
  29   <refsect1>
  30     <title>Description</title>
  31
  32     <para>The <filename>/etc/hostname</filename> file configures the name of the local system. Unless
  33     overridden as described in the next section,
  34     <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will set this
  35     hostname during boot using the
  36     <citerefentry><refentrytitle>sethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry> system
  37     call.</para>
  38
  39     <para>The file should contain a single newline-terminated hostname string. Comments (lines starting with
  40     a <literal>#</literal>) are ignored. The hostname should be composed of up to 64 7-bit ASCII lower-case
  41     alphanumeric characters or hyphens forming a valid DNS domain name. It is recommended that this name
  42     contains only a single label, i.e. without any dots. Invalid characters will be filtered out in an
  43     attempt to make the name valid, but obviously it is recommended to use a valid name and not rely on this
  44     filtering.</para>
  45
  46     <para>You may use
  47     <citerefentry><refentrytitle>hostnamectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to change
  48     the value of this file during runtime from the command line. Use
  49     <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry> to
  50     initialize it on mounted (but not booted) system images.</para>
  51   </refsect1>
  52
  53   <refsect1>
  54     <title>Hostname semantics</title>
  55
  56     <para><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> and the
  57     associated tools will obtain the hostname in the following ways:</para>
  58     <itemizedlist>
  59       <listitem><para>If the kernel command line parameter <varname>systemd.hostname=</varname> specifies a
  60       valid hostname,
  61       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will use it
  62       to set the hostname during early boot, see
  63       <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
  64       </para></listitem>
  65
  66       <listitem><para>Otherwise, the "static" hostname specified by <filename>/etc/hostname</filename> as
  67       described above will be used.</para></listitem>
  68
  69       <listitem><para>Otherwise, a transient hostname may be set during runtime, for example based on
  70       information in a DHCP lease, see
  71       <citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
  72       Both <ulink url="https://developer.gnome.org/NetworkManager/stable/">NetworkManager</ulink> and
  73       <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  74       allow this. Note that
  75       <citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  76       gives higher priority to the static hostname, so the transient hostname will only be used if the static
  77       hostname is not configured.</para></listitem>
  78
  79       <listitem><para>Otherwise, a fallback hostname configured at compilation time will be used
  80       (<literal>&FALLBACK_HOSTNAME;</literal>).</para></listitem>
  81
  82       <!-- what about the "linux" fallback fallback? -->
  83     </itemizedlist>
  84
  85     <para>Effectively, the static hostname has higher priority than a transient hostname, which has higher
  86     priority than the fallback hostname. Transient hostnames are equivalent, so setting a new transient
  87     hostname causes the previous transient hostname to be forgotten. The hostname specified on the kernel
  88     command line is like a transient hostname, with the exception that it has higher priority when the
  89     machine boots. Also note that those are the semantics implemented by systemd tools, but other programs
  90     may also set the hostname.</para>
  91   </refsect1>
  92
  93   <refsect1>
  94     <title>History</title>
  95
  96     <para>The simple configuration file format of
  97     <filename>/etc/hostname</filename> originates from Debian
  98     GNU/Linux.</para>
  99   </refsect1>
 100
 101   <refsect1>
 102       <title>See Also</title>
 103       <para><simplelist type="inline">
 104         <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 105         <member><citerefentry><refentrytitle>sethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>
 106         <member><citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 107         <member><citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
 108         <member><citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 109         <member><citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 110         <member><citerefentry><refentrytitle>hostnamectl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 111         <member><citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 112         <member><citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 113       </simplelist></para>
 114   </refsect1>
 115
 116 </refentry>