117 lines
5.7 KiB
XML
117 lines
5.7 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
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<!ENTITY % entities SYSTEM "custom-entities.ent" >
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%entities;
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]>
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="hostname">
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<refentryinfo>
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<title>hostname</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>hostname</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>hostname</refname>
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<refpurpose>Local hostname configuration file</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>/etc/hostname</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>The <filename>/etc/hostname</filename> file configures the name of the local system. Unless
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overridden as described in the next section,
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will set this
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hostname during boot using the
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<citerefentry><refentrytitle>sethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry> system
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call.</para>
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<para>The file should contain a single newline-terminated hostname string. Comments (lines starting with
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a <literal>#</literal>) are ignored. The hostname should be composed of up to 64 7-bit ASCII lower-case
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alphanumeric characters or hyphens forming a valid DNS domain name. It is recommended that this name
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contains only a single label, i.e. without any dots. Invalid characters will be filtered out in an
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attempt to make the name valid, but obviously it is recommended to use a valid name and not rely on this
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filtering.</para>
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<para>You may use
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<citerefentry><refentrytitle>hostnamectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to change
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the value of this file during runtime from the command line. Use
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<citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry> to
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initialize it on mounted (but not booted) system images.</para>
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</refsect1>
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<refsect1>
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<title>Hostname semantics</title>
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<para><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> and the
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associated tools will obtain the hostname in the following ways:</para>
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<itemizedlist>
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<listitem><para>If the kernel commandline parameter <varname>systemd.hostname=</varname> specifies a
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valid hostname,
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will use it
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to set the hostname during early boot, see
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<citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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</para></listitem>
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<listitem><para>Otherwise, the "static" hostname specified by <filename>/etc/hostname</filename> as
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described above will be used.</para></listitem>
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<listitem><para>Otherwise, a transient hostname may be set during runtime, for example based on
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information in a DHCP lease, see
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<citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
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Both <ulink url="https://developer.gnome.org/NetworkManager/stable/">NetworkManager</ulink> and
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<citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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allow this. Note that
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<citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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gives higher priority to the static hostname, so the transient hostname will only be used if the static
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hostname is not configured.</para></listitem>
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<listitem><para>Otherwise, a fallback hostname configured at compilation time will be used
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(<literal>&FALLBACK_HOSTNAME;</literal>).</para></listitem>
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<!-- what about the "linux" fallback fallback? -->
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</itemizedlist>
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<para>Effectively, the static hostname has higher priority than a transient hostname, which has higher
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priority than the fallback hostname. Transient hostnames are equivalent, so setting a new transient
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hostname causes the previous transient hostname to be forgotten. The hostname specified on the kernel
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command line is like a transient hostname, with the exception that it has higher priority when the
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machine boots. Also note that those are the semantics implemented by systemd tools, but other programs
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may also set the hostname.</para>
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</refsect1>
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<refsect1>
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<title>History</title>
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<para>The simple configuration file format of
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<filename>/etc/hostname</filename> originates from Debian
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GNU/Linux.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>hostnamectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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