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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+ -->
+
+<refentry id="org.freedesktop.hostname1" conditional='ENABLE_HOSTNAMED'
+ xmlns:xi="http://www.w3.org/2001/XInclude">
+ <refentryinfo>
+ <title>org.freedesktop.hostname1</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>org.freedesktop.hostname1</refentrytitle>
+ <manvolnum>5</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>org.freedesktop.hostname1</refname>
+ <refpurpose>The D-Bus interface of systemd-hostnamed</refpurpose>
+ </refnamediv>
+
+ <refsect1>
+ <title>Introduction</title>
+
+ <para>
+ <citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ is a system service that can be used to control the host name and related machine meta data from user
+ programs. This page describes the hostname semantics and the D-Bus interface.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>The D-Bus API</title>
+
+ <para>The service exposes the following interfaces on the bus:</para>
+
+ <programlisting>
+$ gdbus introspect --system \
+ --dest org.freedesktop.hostname1 \
+ --object-path /org/freedesktop/hostname1
+
+node /org/freedesktop/hostname1 {
+ interface org.freedesktop.hostname1 {
+ methods:
+ SetHostname(in s name,
+ in b user_interaction);
+ SetStaticHostname(in s name,
+ in b user_interaction);
+ SetPrettyHostname(in s name,
+ in b user_interaction);
+ SetIconName(in s name,
+ in b user_interaction);
+ SetChassis(in s name,
+ in b user_interaction);
+ signals:
+ properties:
+ readonly s Hostname = 'dhcp-192-168-47-11';
+ readonly s StaticHostname = 'lennarts-computer';
+ readonly s PrettyHostname = 'Lennart’s Computer';
+ readonly s IconName = 'computer-laptop';
+ readonly s Chassis = 'laptop';
+ };
+ interface org.freedesktop.DBus.Properties {
+ };
+ interface org.freedesktop.DBus.Introspectable {
+ };
+ interface org.freedesktop.DBus.Peer {
+ };
+};
+ </programlisting>
+
+ <para>Whenever the hostname or other meta data is changed via the daemon,
+ <function>PropertyChanged</function> signals are sent out to subscribed clients. Changing a hostname
+ using this interface is authenticated via PolicyKit.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Semantics</title>
+
+ <para>The <emphasis>static (configured) host name</emphasis> is the one configured in
+ <filename>/etc/hostname</filename>. It is chosen by the local user. It is not always in sync with the
+ current hostname as returned by the
+ <citerefentry project='man-pages'><refentrytitle>gethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ system call. If no host name is configured this property will be the empty string. Setting this property
+ to the empty string will remove <filename>/etc/hostname</filename>. This hostname should be an
+ internet-style hostname, 7-bit lowercase ASCII, no special chars/spaces.</para>
+
+ <para>The <emphasis>transient (dynamic) host name</emphasis> is the one configured via the kernel's
+ <citerefentry project='man-pages'><refentrytitle>sethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
+ It can be different from the static hostname in case DHCP or mDNS have been configured to change the name
+ based on network information. <!-- FIXME: it's not DHCP that configures this... -->
+ This property is never empty. If no hostname is set this will default to
+ <literal>&FALLBACK_HOSTNAME;</literal> (configurable at compilation time). Setting this property to the
+ empty string will reset the dynamic hostname to the static host name. If no static host name is
+ configured the dynamic host name will be reset to <literal>&FALLBACK_HOSTNAME;</literal>. This hostname
+ should be an internet-style hostname, 7-bit lowercase ASCII, no special chars/spaces.</para>
+
+ <para>The <emphasis>pretty host name</emphasis> is a free-form UTF-8 host name for presentation to the
+ user. User interfaces should ensure that the pretty hostname and the static hostname stay in sync.
+ I.e. when the former is <literal>Lennart’s Computer</literal> the latter should be
+ <literal>lennarts-computer</literal>. If no pretty host name is set this setting will be the empty
+ string. Applications should then find a suitable fallback, such as the dynamic hostname.</para>
+
+ <para>The <emphasis>icon name</emphasis> is a name following the XDG icon naming spec. If not set,
+ information such as the chassis type (see below) is used to find a suitable fallback icon name
+ (i.e. <literal>computer-laptop</literal> vs. <literal>computer-desktop</literal> is picked based on the
+ chassis information). If no such data is available, returns the empty string. In that case an application
+ should fall back to a replacement icon, for example <literal>computer</literal>. If this property is set
+ to the empty string, this automatic fallback name selection is enabled again.</para>
+
+ <para>The <emphasis>chassis type</emphasis> should be one of the following that are currently defined:
+ <literal>desktop</literal>, <literal>laptop</literal>, <literal>server</literal>,
+ <literal>tablet</literal>, <literal>handset</literal>, as well as the special chassis types
+ <literal>vm</literal> and <literal>container</literal> for virtualized systems. Note that in most cases
+ the chassis type will be determined automatically from DMI/SMBIOS/ACPI firmware information. Writing to
+ this setting is hence useful only to override misdetected chassis types, or configure a chassis type if
+ none could be auto-detected. Set this property to the empty string to reenable the automatic detection of
+ the chassis type from firmware information.</para>
+
+ <para>A client which wants to change the local host name for DHCP/mDNS should invoke
+ <code>SetHostname("newname", false)</code> as soon as the name is available and afterwards reset it via
+ <code>SetHostname("")</code>.</para>
+
+ <para>Note that <filename>systemd-hostnamed</filename> starts only on request and terminates after a
+ short idle period. This effectively means that <function>PropertyChanged</function> messages are not sent
+ out for changes made directly on the files (as in: administrator edits the files with vi). This is
+ actually intended behavior: manual configuration changes should require manual reloading of them.</para>
+
+ <para>The transient (dynamic) hostname directly maps to the kernel hostname. This hostname should be
+ assumed to be highly dynamic, and hence should be watched directly, without involving
+ <function>PropertyChanged</function> messages from <filename>systemd-hostnamed</filename>. For that, open
+ <filename>/proc/sys/kernel/hostname</filename> and
+ <citerefentry project='man-pages'><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ for <constant>SIGHUP</constant> which is triggered by the kernel every time the hostname changes. Again:
+ this is special for the transient (dynamic) hostname, and does not apply to the configured (fixed)
+ hostname.</para>
+
+ <para>Applications may bypass the daemon to read the hostname data if notifications of host name changes
+ are not necessary. Use
+ <citerefentry project='man-pages'><refentrytitle>gethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <filename>/etc/hostname</filename> (possibly with per-distribution fallbacks), and
+ <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ for that. For more information on these files and syscalls see the respective man pages.</para>
+
+ <para>The user_interaction boolean parameters can be used to control whether PolicyKit should
+ interactively ask the user for authentication credentials if it needs to.</para>
+
+ <para>The PolicyKit action for <function>SetHostname()</function> is
+ <interfacename>org.freedesktop.hostname1.set-hostname</interfacename>. For
+ <function>SetStaticHostname()</function> and <function>SetPrettyHostname()</function> it is
+ <interfacename>org.freedesktop.hostname1.set-static-hostname</interfacename>. For
+ <function>SetIconName()</function> and <function>SetChassis()</function> it is
+ <interfacename>org.freedesktop.hostname1.set-machine-info</interfacename>.</para>
+
+ <para>Here are three examples how the pretty hostname and the icon name should be used:
+ <itemizedlist>
+ <listitem><para>When registering DNS-SD services: use the pretty host name in the service name, and
+ pass the icon name in the TXT data, if there is an icon name. Browsing clients can then show the server
+ icon on each service. Especially useful for WebDAV stuff. Similar for UPnP media
+ sharing.</para></listitem>
+
+ <listitem><para>Set the bluetooth name to the pretty host name.</para></listitem>
+
+ <listitem><para>When your file browser has a "Computer" icon, replace the name with the pretty hostname if set, and the icon with the icon name, if it is set.</para></listitem>
+ </itemizedlist></para>
+
+ <para>To properly handle name lookups with changing local hostnames without having to edit
+ <filename>/etc/hosts</filename> for them, we recommend using <filename>systemd-hostnamed</filename> in
+ combination with <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
+ </para>
+
+ <para>Here are some recommendations to follow when generating a static (internet) hostname from a pretty
+ name:
+ <itemizedlist>
+ <listitem><para>Generate a single DNS label only, not an FQDN. That means no dots allowed. Strip them,
+ or replace them by <literal>-</literal>.</para></listitem>
+
+ <listitem><para>It's probably safer not to use any non-ASCII chars, even if DNS allows this in some way
+ these days. In fact, restrict your charset to <literal>a-zA-Z0-9</literal> and <literal>-</literal>.
+ Strip other chars, or try to replace them in some smart way with chars from this set, for example
+ <literal>ä</literal> → <literal>ae</literal>, and use <literal>-</literal> as replacement for all kinds
+ of punctuation chars or spaces.</para></listitem>
+
+ <listitem><para>Try to avoid creating repeated <literal>-</literal>, as well as <literal>-</literal> as
+ the first or last char.</para></listitem>
+
+ <listitem><para>Limit the hostname to 63 chars, which is the length of a DNS label.</para></listitem>
+
+ <listitem><para>If after stripping special chars the empty string is the result, you can pass this
+ as-is to <filename>systemd-hostnamed</filename> in which case it will automatically make
+ <literal>&FALLBACK_HOSTNAME;</literal> out of this.</para></listitem>
+
+ <listitem><para>It probably is a good idea to replace uppercase by lowercase chars.</para></listitem>
+ </itemizedlist></para>
+
+ <para>Note that while <filename>systemd-hostnamed</filename> applies some checks to the hostname you pass
+ they are much looser than the recommendations above. For example, <filename>systemd-hostnamed</filename>
+ will also accept <literal>_</literal> in the hostname, but I'd recommend not using this to avoid clashes
+ with DNS-SD service types. Also <filename>systemd-hostnamed</filename> allows longer hostnames, but
+ because of the DNS label limitations, I'd recommend not making use of this.</para>
+
+ <para>Here are a couple of example conversions:
+ <itemizedlist>
+ <listitem><para><literal>Lennart's PC</literal> → <literal>lennarts-pc</literal></para></listitem>
+ <listitem><para><literal>Müllers Computer</literal> → <literal>muellers-computer</literal></para></listitem>
+ <listitem><para><literal>Voran!</literal> → <literal>voran</literal></para></listitem>
+ <listitem><para><literal>Es war einmal ein Männlein</literal> → <literal>es-war-einmal-ein-maennlein</literal></para></listitem>
+ <listitem><para><literal>Jawoll. Ist doch wahr!</literal> → <literal>jawoll-ist-doch-wahr</literal></para></listitem>
+ <listitem><para><literal>レナート</literal> → <literal>localhost</literal></para></listitem>
+ <listitem><para><literal>...zack!!! zack!...</literal> → <literal>zack-zack</literal></para></listitem>
+ </itemizedlist></para>
+
+ <para>Oh, and of course, an already valid internet hostname label you enter and pass through this
+ conversion should stay unmodified, so that users have direct control of it, if they want -- by simply
+ ignoring the fact that the pretty hostname is pretty and just edit it as if it was the normal internet
+ name.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Versioning</title>
+
+ <para>These D-Bus interfaces follow <ulink url="http://0pointer.de/blog/projects/versioning-dbus.html">
+ the usual interface versioning guidelines</ulink>.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>See also</title>
+
+ <para>David Zeuthen's original Fedora
+ <ulink url="https://fedoraproject.org/wiki/Features/BetterHostname">Feature page about xdg-hostname</ulink></para>
+ </refsect1>
+</refentry>
projects / thirdparty / systemd.git / commitdiff
