man/org.freedesktop.hostname1.xml

   1 <?xml version="1.0"?>
   2 <!--*-nxml-*-->
   3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   4   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
   5 <!ENTITY % entities SYSTEM "custom-entities.ent" >
   6 %entities;
   7 ]>
   8 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   9
  10 <refentry id="org.freedesktop.hostname1" conditional='ENABLE_HOSTNAMED'
  11     xmlns:xi="http://www.w3.org/2001/XInclude">
  12   <refentryinfo>
  13     <title>org.freedesktop.hostname1</title>
  14     <productname>systemd</productname>
  15   </refentryinfo>
  16
  17   <refmeta>
  18     <refentrytitle>org.freedesktop.hostname1</refentrytitle>
  19     <manvolnum>5</manvolnum>
  20   </refmeta>
  21
  22   <refnamediv>
  23     <refname>org.freedesktop.hostname1</refname>
  24     <refpurpose>The D-Bus interface of systemd-hostnamed</refpurpose>
  25   </refnamediv>
  26
  27   <refsect1>
  28     <title>Introduction</title>
  29
  30     <para>
  31     <citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  32     is a system service that can be used to control the hostname and related machine metadata from user
  33     programs. This page describes the hostname semantics and the D-Bus interface.</para>
  34   </refsect1>
  35
  36   <refsect1>
  37     <title>The D-Bus API</title>
  38
  39     <para>The service exposes the following interfaces on the bus:</para>
  40
  41     <programlisting executable="systemd-hostnamed" node="/org/freedesktop/hostname1" interface="org.freedesktop.hostname1">
  42 node /org/freedesktop/hostname1 {
  43   interface org.freedesktop.hostname1 {
  44     methods:
  45       SetHostname(in  s hostname,
  46                   in  b interactive);
  47       SetStaticHostname(in  s hostname,
  48                         in  b interactive);
  49       SetPrettyHostname(in  s hostname,
  50                         in  b interactive);
  51       SetIconName(in  s icon,
  52                   in  b interactive);
  53       SetChassis(in  s chassis,
  54                  in  b interactive);
  55       SetDeployment(in  s deployment,
  56                     in  b interactive);
  57       SetLocation(in  s location,
  58                   in  b interactive);
  59       GetProductUUID(in  b interactive,
  60                      out ay uuid);
  61     properties:
  62       readonly s Hostname = '...';
  63       readonly s StaticHostname = '...';
  64       readonly s PrettyHostname = '...';
  65       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  66       readonly s FallbackHostname = '...';
  67       readonly s HostnameSource = '...';
  68       readonly s IconName = '...';
  69       readonly s Chassis = '...';
  70       readonly s Deployment = '...';
  71       readonly s Location = '...';
  72       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  73       readonly s KernelName = '...';
  74       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  75       readonly s KernelRelease = '...';
  76       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  77       readonly s KernelVersion = '...';
  78       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  79       readonly s OperatingSystemPrettyName = '...';
  80       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  81       readonly s OperatingSystemCPEName = '...';
  82       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  83       readonly s HomeURL = '...';
  84   };
  85   interface org.freedesktop.DBus.Peer { ... };
  86   interface org.freedesktop.DBus.Introspectable { ... };
  87   interface org.freedesktop.DBus.Properties { ... };
  88 };
  89     </programlisting>
  90
  91     <!--Autogenerated cross-references for systemd.directives, do not edit-->
  92
  93     <variablelist class="dbus-interface" generated="True" extra-ref="org.freedesktop.hostname1"/>
  94
  95     <variablelist class="dbus-interface" generated="True" extra-ref="org.freedesktop.hostname1"/>
  96
  97     <variablelist class="dbus-method" generated="True" extra-ref="SetHostname()"/>
  98
  99     <variablelist class="dbus-method" generated="True" extra-ref="SetStaticHostname()"/>
 100
 101     <variablelist class="dbus-method" generated="True" extra-ref="SetPrettyHostname()"/>
 102
 103     <variablelist class="dbus-method" generated="True" extra-ref="SetIconName()"/>
 104
 105     <variablelist class="dbus-method" generated="True" extra-ref="SetChassis()"/>
 106
 107     <variablelist class="dbus-method" generated="True" extra-ref="SetDeployment()"/>
 108
 109     <variablelist class="dbus-method" generated="True" extra-ref="SetLocation()"/>
 110
 111     <variablelist class="dbus-method" generated="True" extra-ref="GetProductUUID()"/>
 112
 113     <variablelist class="dbus-property" generated="True" extra-ref="Hostname"/>
 114
 115     <variablelist class="dbus-property" generated="True" extra-ref="StaticHostname"/>
 116
 117     <variablelist class="dbus-property" generated="True" extra-ref="PrettyHostname"/>
 118
 119     <variablelist class="dbus-property" generated="True" extra-ref="FallbackHostname"/>
 120
 121     <variablelist class="dbus-property" generated="True" extra-ref="HostnameSource"/>
 122
 123     <variablelist class="dbus-property" generated="True" extra-ref="IconName"/>
 124
 125     <variablelist class="dbus-property" generated="True" extra-ref="Chassis"/>
 126
 127     <variablelist class="dbus-property" generated="True" extra-ref="Deployment"/>
 128
 129     <variablelist class="dbus-property" generated="True" extra-ref="Location"/>
 130
 131     <variablelist class="dbus-property" generated="True" extra-ref="KernelName"/>
 132
 133     <variablelist class="dbus-property" generated="True" extra-ref="KernelRelease"/>
 134
 135     <variablelist class="dbus-property" generated="True" extra-ref="KernelVersion"/>
 136
 137     <variablelist class="dbus-property" generated="True" extra-ref="OperatingSystemPrettyName"/>
 138
 139     <variablelist class="dbus-property" generated="True" extra-ref="OperatingSystemCPEName"/>
 140
 141     <variablelist class="dbus-property" generated="True" extra-ref="HomeURL"/>
 142
 143     <!--End of Autogenerated section-->
 144
 145     <para>Whenever the hostname or other metadata is changed via the daemon,
 146     <function>PropertyChanged</function> signals are sent out to subscribed clients. Changing a hostname
 147     using this interface is authenticated via
 148     <ulink url="https://www.freedesktop.org/software/polkit/docs/latest/">polkit</ulink>.</para>
 149   </refsect1>
 150
 151   <refsect1>
 152     <title>Semantics</title>
 153
 154     <para>The <varname>StaticHostname</varname> property exposes the "static" hostname configured in
 155     <filename>/etc/hostname</filename>. It is not always in sync with the current hostname as returned by the
 156     <citerefentry project="man-pages"><refentrytitle>gethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 157     system call. If no static hostname is configured this property will be the empty string.</para>
 158
 159     <para>When <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> or
 160     <citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 161     set the hostname, this static hostname <emphasis>has the highest priority</emphasis>.</para>
 162
 163     <para>The <varname>Hostname</varname> property exposes the actual hostname configured in the kernel via
 164     <citerefentry project="man-pages"><refentrytitle>sethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 165     It can be different from the static hostname. This property is never empty.</para>
 166
 167     <para>The <varname>PrettyHostname</varname> property exposes the <emphasis>pretty hostname</emphasis>
 168     which is a free-form UTF-8 hostname for presentation to the user. User interfaces should ensure that the
 169     pretty hostname and the static hostname stay in sync. E.g. when the former is <literal>Lennart’s
 170     Computer</literal> the latter should be <literal>lennarts-computer</literal>. If no pretty hostname is
 171     set this setting will be the empty string. Applications should then find a suitable fallback, such as the
 172     dynamic hostname.</para>
 173
 174     <para>The <varname>FallbackHostname</varname> property exposes the fallback hostname (configured at
 175     compilation time).</para>
 176
 177     <para>The <varname>HostnameSource</varname> property exposes the origin of the currently configured
 178     hostname. One of <literal>static</literal> (set from <filename>/etc/hostname</filename>),
 179     <literal>transient</literal> (a non-permanent hostname from an external source),
 180     <literal>fallback</literal> (the compiled-in fallback value).</para>
 181
 182     <para>The <varname>IconName</varname> property exposes the <emphasis>icon name</emphasis> following the
 183     XDG icon naming spec. If not set, information such as the chassis type (see below) is used to find a
 184     suitable fallback icon name (i.e. <literal>computer-laptop</literal>
 185     vs. <literal>computer-desktop</literal> is picked based on the chassis information). If no such data is
 186     available, the empty string is returned. In that case an application should fall back to a replacement
 187     icon, for example <literal>computer</literal>. If this property is set to the empty string, the automatic
 188     fallback name selection is enabled again.</para>
 189
 190     <para>The <varname>Chassis</varname> property exposes a <emphasis>chassis type</emphasis>, one of the
 191     currently defined chassis types: <literal>desktop</literal>, <literal>laptop</literal>,
 192     <literal>server</literal>, <literal>tablet</literal>, <literal>handset</literal>, as well as the special
 193     chassis types <literal>vm</literal> and <literal>container</literal> for virtualized systems. Note that
 194     in most cases the chassis type will be determined automatically from DMI/SMBIOS/ACPI firmware
 195     information. Writing to this setting is hence useful only to override misdetected chassis types, or to
 196     configure the chassis type if it could not be auto-detected. Set this property to the empty string to
 197     reenable the automatic detection of the chassis type from firmware information.</para>
 198
 199     <para>Note that <filename>systemd-hostnamed</filename> starts only on request and terminates after a
 200     short idle period. This effectively means that <function>PropertyChanged</function> messages are not sent
 201     out for changes made directly on the files (as in: administrator edits the files with vi). This is
 202     the intended behavior: manual configuration changes should require manual reloading.</para>
 203
 204     <para>The transient (dynamic) hostname exposed by the <varname>Hostname</varname> property maps directly
 205     to the kernel hostname. This hostname should be assumed to be highly dynamic, and hence should be watched
 206     directly, without depending on <function>PropertyChanged</function> messages from
 207     <filename>systemd-hostnamed</filename>. To accomplish this, open
 208     <filename>/proc/sys/kernel/hostname</filename> and
 209     <citerefentry project="man-pages"><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 210     for <constant>SIGHUP</constant> which is triggered by the kernel every time the hostname changes. Again:
 211     this is special for the transient (dynamic) hostname, and does not apply to the configured (fixed)
 212     hostname.</para>
 213
 214     <para>Applications may read the hostname data directly if hostname change notifications
 215     are not necessary. Use
 216     <citerefentry project="man-pages"><refentrytitle>gethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 217     <filename>/etc/hostname</filename> (possibly with per-distribution fallbacks), and
 218     <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 219     for that. For more information on these files and syscalls see the respective man pages.</para>
 220
 221     <refsect2>
 222       <title>Methods</title>
 223
 224       <para><function>SetHostname()</function> sets the transient (dynamic) hostname, which is used if no
 225       static hostname is set. This value must be an internet-style hostname, 7-bit lowercase ASCII, no
 226       special chars/spaces. An empty string will unset the transient hostname.</para>
 227
 228       <para><function>SetStaticHostname()</function> sets the static hostname which is exposed by the
 229       <varname>StaticHostname</varname> property. When called with an empty argument, the static
 230       configuration in <filename>/etc/hostname</filename> is removed. Since the static hostname has the
 231       highest priority, calling this function usually affects also the <varname>Hostname</varname> property
 232       and the effective hostname configured in the kernel.</para>
 233
 234       <para><function>SetPrettyHostname()</function> sets the pretty hostname which is exposed by the
 235       <varname>PrettyHostname</varname> property.</para>
 236
 237       <para><function>SetIconName()</function>, <function>SetChassis()</function>,
 238       <function>SetDeployment()</function>, and <function>SetLocation()</function> set the properties
 239       <varname>IconName</varname> (the name of the icon representing for the machine),
 240       <varname>Chassis</varname> (the machine form factor), <varname>Deployment</varname> (the system
 241       deployment environment), and <varname>Location</varname> (physical system location), respectively.
 242       </para>
 243
 244       <para><varname>PrettyHostname</varname>, <varname>IconName</varname>, <varname>Chassis</varname>,
 245       <varname>Deployment</varname>, and <varname>Location</varname> are stored in
 246       <filename>/etc/machine-info</filename>. See
 247       <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 248       the semantics of those settings.</para>
 249
 250       <para><function>GetProductUUID()</function> returns the "product uuid" as exposed by the kernel based
 251       on DMI information in <filename>/sys/class/dmi/id/product_uuid</filename>. Reading the file directly
 252       requires root privileges, and this method allows access to unprivileged clients through the polkit
 253       framework.</para>
 254
 255       <para><varname>KernelName</varname>, <varname>KernelRelease</varname>, and
 256       <varname>KernelVersion</varname> expose the kernel name (e.g. <literal>Linux</literal>), release
 257       (e.g. <literal>5.0.0-11</literal>), and version (i.e. the build number, e.g. <literal>#11</literal>) as
 258       reported by
 259       <citerefentry project="man-pages"><refentrytitle>uname</refentrytitle><manvolnum>2</manvolnum></citerefentry>.
 260       <varname>OperatingSystemPrettyName</varname>, <varname>OperatingSystemCPEName</varname>, and
 261       <varname>HomeURL</varname> expose the <varname>PRETTY_NAME=</varname>, <varname>CPE_NAME=</varname> and
 262       <varname>HOME_URL=</varname> fields from
 263       <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>. The
 264       purpose of those properties is to allow remote clients to access this information over D-Bus. Local
 265       clients can access the information directly.</para>
 266     </refsect2>
 267
 268     <refsect2>
 269       <title>Security</title>
 270
 271       <para>The <varname>interactive</varname> boolean parameters can be used to control whether polkit
 272       should interactively ask the user for authentication credentials if required.</para>
 273
 274       <para>The polkit action for <function>SetHostname()</function> is
 275       <interfacename>org.freedesktop.hostname1.set-hostname</interfacename>. For
 276       <function>SetStaticHostname()</function> and <function>SetPrettyHostname()</function> it is
 277       <interfacename>org.freedesktop.hostname1.set-static-hostname</interfacename>. For
 278       <function>SetIconName()</function>, <function>SetChassis()</function>, <function>SetDeployment()</function>
 279       and <function>SetLocation()</function> it is
 280       <interfacename>org.freedesktop.hostname1.set-machine-info</interfacename>.</para>
 281     </refsect2>
 282   </refsect1>
 283
 284   <refsect1>
 285     <title>Recommendations</title>
 286
 287     <para>Here are three examples that show how the pretty hostname and the icon name should be used:
 288     <itemizedlist>
 289       <listitem><para>When registering DNS-SD services: use the pretty hostname in the service name, and pass
 290       the icon name in the TXT data, if there is an icon name. Browsing clients can then show the server icon
 291       on each service. This is especially useful for WebDAV applications or UPnP media sharing.
 292       </para></listitem>
 293
 294       <listitem><para>Set the bluetooth name to the pretty hostname.</para></listitem>
 295
 296       <listitem><para>When your file browser has a "Computer" icon, replace the name with the pretty hostname
 297       if set, and the icon with the icon name, if it is set.</para></listitem>
 298     </itemizedlist></para>
 299
 300     <para>To properly handle name lookups with changing local hostnames without having to edit
 301     <filename>/etc/hosts</filename>, we recommend using <filename>systemd-hostnamed</filename> in combination
 302     with <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 303     </para>
 304
 305     <para>Here are some recommendations to follow when generating a static (internet) hostname from a pretty
 306     name:
 307     <itemizedlist>
 308       <listitem><para>Generate a single DNS label only, not an FQDN. That means no dots allowed. Strip them,
 309       or replace them with <literal>-</literal>.</para></listitem>
 310
 311       <listitem><para>It's probably safer to not use any non-ASCII chars, even if DNS allows this in some way
 312       these days. In fact, restrict your charset to <literal>a-zA-Z0-9</literal> and <literal>-</literal>.
 313       Strip other chars, or try to replace them in some smart way with chars from this set, for example
 314       <literal>ä</literal> → <literal>ae</literal>, and use <literal>-</literal> as the replacement for all
 315       punctuation characters and whitespace.</para></listitem>
 316
 317       <listitem><para>Try to avoid creating repeated <literal>-</literal>, as well as <literal>-</literal> as
 318       the first or last char.</para></listitem>
 319
 320       <listitem><para>Limit the hostname to 63 chars, which is the length of a DNS label.</para></listitem>
 321
 322       <listitem><para>If after stripping special chars the empty string is the result, you can pass this
 323       as-is to <filename>systemd-hostnamed</filename> in which case it will automatically use
 324       <literal>&FALLBACK_HOSTNAME;</literal>.</para></listitem>
 325
 326       <listitem><para>Uppercase charaacters should be replaced with their lowercase equivalents.
 327       </para></listitem>
 328     </itemizedlist></para>
 329
 330     <para>Note that while <filename>systemd-hostnamed</filename> applies some checks to the hostname you pass
 331     they are much looser than the recommendations above. For example, <filename>systemd-hostnamed</filename>
 332     will also accept <literal>_</literal> in the hostname, but we recommend not using this to avoid clashes
 333     with DNS-SD service types. Also <filename>systemd-hostnamed</filename> allows longer hostnames, but
 334     because of the DNS label limitations, we recommend not making use of this.</para>
 335
 336     <para>Here are a couple of example conversions:
 337     <itemizedlist>
 338       <listitem><para><literal>Lennart's PC</literal> → <literal>lennarts-pc</literal></para></listitem>
 339       <listitem><para><literal>Müllers Computer</literal> → <literal>muellers-computer</literal></para></listitem>
 340       <listitem><para><literal>Voran!</literal> → <literal>voran</literal></para></listitem>
 341       <listitem><para><literal>Es war einmal ein Männlein</literal> → <literal>es-war-einmal-ein-maennlein</literal></para></listitem>
 342       <listitem><para><literal>Jawoll. Ist doch wahr!</literal> → <literal>jawoll-ist-doch-wahr</literal></para></listitem>
 343       <listitem><para><literal>レナート</literal> → <literal>localhost</literal></para></listitem>
 344       <listitem><para><literal>...zack!!! zack!...</literal> → <literal>zack-zack</literal></para></listitem>
 345     </itemizedlist></para>
 346
 347     <para>Of course, an already valid internet hostname label you enter and pass through this
 348     conversion should stay unmodified, so that users have direct control of it, if they want — by simply
 349     ignoring the fact that the pretty hostname is pretty and just edit it as if it was the normal internet
 350     name.</para>
 351   </refsect1>
 352
 353   <refsect1>
 354     <title>Versioning</title>
 355
 356     <para>These D-Bus interfaces follow <ulink url="http://0pointer.de/blog/projects/versioning-dbus.html">
 357     the usual interface versioning guidelines</ulink>.</para>
 358   </refsect1>
 359
 360   <refsect1>
 361     <title>Examples</title>
 362
 363     <example>
 364       <title>Introspect <interfacename>org.freedesktop.hostname1</interfacename> on the bus</title>
 365
 366       <programlisting>$ gdbus introspect --system \
 367   --dest org.freedesktop.hostname1 \
 368   --object-path /org/freedesktop/hostname1
 369       </programlisting>
 370     </example>
 371   </refsect1>
 372
 373   <refsect1>
 374     <title>See also</title>
 375
 376     <para>David Zeuthen's original Fedora
 377     <ulink url="https://fedoraproject.org/wiki/Features/BetterHostname">Feature page about xdg-hostname</ulink></para>
 378   </refsect1>
 379 </refentry>