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       GetHardwareSerial(in  b interactive,
  62                         out s serial);
  63       Describe(out s json);
  64     properties:
  65       readonly s Hostname = '...';
  66       readonly s StaticHostname = '...';
  67       readonly s PrettyHostname = '...';
  68       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  69       readonly s DefaultHostname = '...';
  70       readonly s HostnameSource = '...';
  71       readonly s IconName = '...';
  72       readonly s Chassis = '...';
  73       readonly s Deployment = '...';
  74       readonly s Location = '...';
  75       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  76       readonly s KernelName = '...';
  77       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  78       readonly s KernelRelease = '...';
  79       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  80       readonly s KernelVersion = '...';
  81       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  82       readonly s OperatingSystemPrettyName = '...';
  83       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  84       readonly s OperatingSystemCPEName = '...';
  85       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  86       readonly s HomeURL = '...';
  87       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  88       readonly s HardwareVendor = '...';
  89       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
  90       readonly s HardwareModel = '...';
  91   };
  92   interface org.freedesktop.DBus.Peer { ... };
  93   interface org.freedesktop.DBus.Introspectable { ... };
  94   interface org.freedesktop.DBus.Properties { ... };
  95 };
  96     </programlisting>
  97
  98     <!--method GetHardwareSerial is not documented!-->
  99
 100     <!--property HardwareVendor is not documented!-->
 101
 102     <!--property HardwareModel is not documented!-->
 103
 104     <!--Autogenerated cross-references for systemd.directives, do not edit-->
 105
 106     <variablelist class="dbus-interface" generated="True" extra-ref="org.freedesktop.hostname1"/>
 107
 108     <variablelist class="dbus-interface" generated="True" extra-ref="org.freedesktop.hostname1"/>
 109
 110     <variablelist class="dbus-method" generated="True" extra-ref="SetHostname()"/>
 111
 112     <variablelist class="dbus-method" generated="True" extra-ref="SetStaticHostname()"/>
 113
 114     <variablelist class="dbus-method" generated="True" extra-ref="SetPrettyHostname()"/>
 115
 116     <variablelist class="dbus-method" generated="True" extra-ref="SetIconName()"/>
 117
 118     <variablelist class="dbus-method" generated="True" extra-ref="SetChassis()"/>
 119
 120     <variablelist class="dbus-method" generated="True" extra-ref="SetDeployment()"/>
 121
 122     <variablelist class="dbus-method" generated="True" extra-ref="SetLocation()"/>
 123
 124     <variablelist class="dbus-method" generated="True" extra-ref="GetProductUUID()"/>
 125
 126     <variablelist class="dbus-method" generated="True" extra-ref="GetHardwareSerial()"/>
 127
 128     <variablelist class="dbus-method" generated="True" extra-ref="Describe()"/>
 129
 130     <variablelist class="dbus-property" generated="True" extra-ref="Hostname"/>
 131
 132     <variablelist class="dbus-property" generated="True" extra-ref="StaticHostname"/>
 133
 134     <variablelist class="dbus-property" generated="True" extra-ref="PrettyHostname"/>
 135
 136     <variablelist class="dbus-property" generated="True" extra-ref="DefaultHostname"/>
 137
 138     <variablelist class="dbus-property" generated="True" extra-ref="HostnameSource"/>
 139
 140     <variablelist class="dbus-property" generated="True" extra-ref="IconName"/>
 141
 142     <variablelist class="dbus-property" generated="True" extra-ref="Chassis"/>
 143
 144     <variablelist class="dbus-property" generated="True" extra-ref="Deployment"/>
 145
 146     <variablelist class="dbus-property" generated="True" extra-ref="Location"/>
 147
 148     <variablelist class="dbus-property" generated="True" extra-ref="KernelName"/>
 149
 150     <variablelist class="dbus-property" generated="True" extra-ref="KernelRelease"/>
 151
 152     <variablelist class="dbus-property" generated="True" extra-ref="KernelVersion"/>
 153
 154     <variablelist class="dbus-property" generated="True" extra-ref="OperatingSystemPrettyName"/>
 155
 156     <variablelist class="dbus-property" generated="True" extra-ref="OperatingSystemCPEName"/>
 157
 158     <variablelist class="dbus-property" generated="True" extra-ref="HomeURL"/>
 159
 160     <variablelist class="dbus-property" generated="True" extra-ref="HardwareVendor"/>
 161
 162     <variablelist class="dbus-property" generated="True" extra-ref="HardwareModel"/>
 163
 164     <!--End of Autogenerated section-->
 165
 166     <para>Whenever the hostname or other metadata is changed via the daemon,
 167     <function>PropertyChanged</function> signals are sent out to subscribed clients. Changing a hostname
 168     using this interface is authenticated via
 169     <ulink url="https://www.freedesktop.org/software/polkit/docs/latest/">polkit</ulink>.</para>
 170   </refsect1>
 171
 172   <refsect1>
 173     <title>Semantics</title>
 174
 175     <para>The <varname>StaticHostname</varname> property exposes the "static" hostname configured in
 176     <filename>/etc/hostname</filename>. It is not always in sync with the current hostname as returned by the
 177     <citerefentry project="man-pages"><refentrytitle>gethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 178     system call. If no static hostname is configured this property will be the empty string.</para>
 179
 180     <para>When <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> or
 181     <citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 182     set the hostname, this static hostname <emphasis>has the highest priority</emphasis>.</para>
 183
 184     <para>The <varname>Hostname</varname> property exposes the actual hostname configured in the kernel via
 185     <citerefentry project="man-pages"><refentrytitle>sethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 186     It can be different from the static hostname. This property is never empty.</para>
 187
 188     <para>The <varname>PrettyHostname</varname> property exposes the <emphasis>pretty hostname</emphasis>
 189     which is a free-form UTF-8 hostname for presentation to the user. User interfaces should ensure that the
 190     pretty hostname and the static hostname stay in sync. E.g. when the former is <literal>Lennart’s
 191     Computer</literal> the latter should be <literal>lennarts-computer</literal>. If no pretty hostname is
 192     set this setting will be the empty string. Applications should then find a suitable fallback, such as the
 193     dynamic hostname.</para>
 194
 195     <para>The <varname>DefaultHostname</varname> property exposes the default hostname (configured through
 196     <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>, or a
 197     fallback set at compilation time).</para>
 198
 199     <para>The <varname>HostnameSource</varname> property exposes the origin of the currently configured
 200     hostname. One of <literal>static</literal> (set from <filename>/etc/hostname</filename>),
 201     <literal>transient</literal> (a non-permanent hostname from an external source),
 202     <literal>default</literal> (the value from <filename>os-release</filename> or the compiled-in
 203     fallback).</para>
 204
 205     <para>The <varname>IconName</varname> property exposes the <emphasis>icon name</emphasis> following the
 206     XDG icon naming spec. If not set, information such as the chassis type (see below) is used to find a
 207     suitable fallback icon name (i.e. <literal>computer-laptop</literal>
 208     vs. <literal>computer-desktop</literal> is picked based on the chassis information). If no such data is
 209     available, the empty string is returned. In that case an application should fall back to a replacement
 210     icon, for example <literal>computer</literal>. If this property is set to the empty string, the automatic
 211     fallback name selection is enabled again.</para>
 212
 213     <para>The <varname>Chassis</varname> property exposes a <emphasis>chassis type</emphasis>, one of the
 214     currently defined chassis types: <literal>desktop</literal>, <literal>laptop</literal>,
 215     <literal>server</literal>, <literal>tablet</literal>, <literal>handset</literal>, as well as the special
 216     chassis types <literal>vm</literal> and <literal>container</literal> for virtualized systems. Note that
 217     in most cases the chassis type will be determined automatically from DMI/SMBIOS/ACPI firmware
 218     information. Writing to this setting is hence useful only to override misdetected chassis types, or to
 219     configure the chassis type if it could not be auto-detected. Set this property to the empty string to
 220     reenable the automatic detection of the chassis type from firmware information.</para>
 221
 222     <para>Note that <filename>systemd-hostnamed</filename> starts only on request and terminates after a
 223     short idle period. This effectively means that <function>PropertyChanged</function> messages are not sent
 224     out for changes made directly on the files (as in: administrator edits the files with vi). This is
 225     the intended behavior: manual configuration changes should require manual reloading.</para>
 226
 227     <para>The transient (dynamic) hostname exposed by the <varname>Hostname</varname> property maps directly
 228     to the kernel hostname. This hostname should be assumed to be highly dynamic, and hence should be watched
 229     directly, without depending on <function>PropertyChanged</function> messages from
 230     <filename>systemd-hostnamed</filename>. To accomplish this, open
 231     <filename>/proc/sys/kernel/hostname</filename> and
 232     <citerefentry project="man-pages"><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 233     for <constant>SIGHUP</constant> which is triggered by the kernel every time the hostname changes. Again:
 234     this is special for the transient (dynamic) hostname, and does not apply to the configured (fixed)
 235     hostname.</para>
 236
 237     <para>Applications may read the hostname data directly if hostname change notifications
 238     are not necessary. Use
 239     <citerefentry project="man-pages"><refentrytitle>gethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 240     <filename>/etc/hostname</filename> (possibly with per-distribution fallbacks), and
 241     <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 242     for that. For more information on these files and syscalls see the respective man pages.</para>
 243
 244     <para><varname>KernelName</varname>, <varname>KernelRelease</varname>, and
 245     <varname>KernelVersion</varname> expose the kernel name (e.g. <literal>Linux</literal>), release
 246     (e.g. <literal>5.0.0-11</literal>), and version (i.e. the build number, e.g. <literal>#11</literal>) as
 247     reported by <citerefentry project="man-pages"><refentrytitle>uname</refentrytitle><manvolnum>2</manvolnum></citerefentry>.
 248     <varname>OperatingSystemPrettyName</varname>, <varname>OperatingSystemCPEName</varname>, and
 249     <varname>HomeURL</varname> expose the <varname>PRETTY_NAME=</varname>, <varname>CPE_NAME=</varname> and
 250     <varname>HOME_URL=</varname> fields from
 251     <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>. The
 252     purpose of those properties is to allow remote clients to access this information over D-Bus. Local
 253     clients can access the information directly.</para>
 254
 255     <refsect2>
 256       <title>Methods</title>
 257
 258       <para><function>SetHostname()</function> sets the transient (dynamic) hostname, which is used if no
 259       static hostname is set. This value must be an internet-style hostname, 7-bit lowercase ASCII, no
 260       special chars/spaces. An empty string will unset the transient hostname.</para>
 261
 262       <para><function>SetStaticHostname()</function> sets the static hostname which is exposed by the
 263       <varname>StaticHostname</varname> property. When called with an empty argument, the static
 264       configuration in <filename>/etc/hostname</filename> is removed. Since the static hostname has the
 265       highest priority, calling this function usually affects also the <varname>Hostname</varname> property
 266       and the effective hostname configured in the kernel.</para>
 267
 268       <para><function>SetPrettyHostname()</function> sets the pretty hostname which is exposed by the
 269       <varname>PrettyHostname</varname> property.</para>
 270
 271       <para><function>SetIconName()</function>, <function>SetChassis()</function>,
 272       <function>SetDeployment()</function>, and <function>SetLocation()</function> set the properties
 273       <varname>IconName</varname> (the name of the icon representing for the machine),
 274       <varname>Chassis</varname> (the machine form factor), <varname>Deployment</varname> (the system
 275       deployment environment), and <varname>Location</varname> (physical system location), respectively.
 276       </para>
 277
 278       <para><varname>PrettyHostname</varname>, <varname>IconName</varname>, <varname>Chassis</varname>,
 279       <varname>Deployment</varname>, and <varname>Location</varname> are stored in
 280       <filename>/etc/machine-info</filename>. See
 281       <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 282       the semantics of those settings.</para>
 283
 284       <para><function>GetProductUUID()</function> returns the "product UUID" as exposed by the kernel based
 285       on DMI information in <filename>/sys/class/dmi/id/product_uuid</filename>. Reading the file directly
 286       requires root privileges, and this method allows access to unprivileged clients through the polkit
 287       framework.</para>
 288
 289       <para><function>Describe()</function> returns a JSON representation of all properties in one.</para>
 290     </refsect2>
 291
 292     <refsect2>
 293       <title>Security</title>
 294
 295       <para>The <varname>interactive</varname> boolean parameters can be used to control whether polkit
 296       should interactively ask the user for authentication credentials if required.</para>
 297
 298       <para>The polkit action for <function>SetHostname()</function> is
 299       <interfacename>org.freedesktop.hostname1.set-hostname</interfacename>. For
 300       <function>SetStaticHostname()</function> and <function>SetPrettyHostname()</function> it is
 301       <interfacename>org.freedesktop.hostname1.set-static-hostname</interfacename>. For
 302       <function>SetIconName()</function>, <function>SetChassis()</function>, <function>SetDeployment()</function>
 303       and <function>SetLocation()</function> it is
 304       <interfacename>org.freedesktop.hostname1.set-machine-info</interfacename>.</para>
 305     </refsect2>
 306   </refsect1>
 307
 308   <refsect1>
 309     <title>Recommendations</title>
 310
 311     <para>Here are three examples that show how the pretty hostname and the icon name should be used:
 312     <itemizedlist>
 313       <listitem><para>When registering DNS-SD services: use the pretty hostname in the service name, and pass
 314       the icon name in the TXT data, if there is an icon name. Browsing clients can then show the server icon
 315       on each service. This is especially useful for WebDAV applications or UPnP media sharing.
 316       </para></listitem>
 317
 318       <listitem><para>Set the bluetooth name to the pretty hostname.</para></listitem>
 319
 320       <listitem><para>When your file browser has a "Computer" icon, replace the name with the pretty hostname
 321       if set, and the icon with the icon name, if it is set.</para></listitem>
 322     </itemizedlist></para>
 323
 324     <para>To properly handle name lookups with changing local hostnames without having to edit
 325     <filename>/etc/hosts</filename>, we recommend using <filename>systemd-hostnamed</filename> in combination
 326     with <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 327     </para>
 328
 329     <para>Here are some recommendations to follow when generating a static (internet) hostname from a pretty
 330     name:
 331     <itemizedlist>
 332       <listitem><para>Generate a single DNS label only, not an FQDN. That means no dots allowed. Strip them,
 333       or replace them with <literal>-</literal>.</para></listitem>
 334
 335       <listitem><para>It's probably safer to not use any non-ASCII chars, even if DNS allows this in some way
 336       these days. In fact, restrict your charset to <literal>a-zA-Z0-9</literal> and <literal>-</literal>.
 337       Strip other chars, or try to replace them in some smart way with chars from this set, for example
 338       <literal>ä</literal> → <literal>ae</literal>, and use <literal>-</literal> as the replacement for all
 339       punctuation characters and whitespace.</para></listitem>
 340
 341       <listitem><para>Try to avoid creating repeated <literal>-</literal>, as well as <literal>-</literal> as
 342       the first or last char.</para></listitem>
 343
 344       <listitem><para>Limit the hostname to 63 chars, which is the length of a DNS label.</para></listitem>
 345
 346       <listitem><para>If after stripping special chars the empty string is the result, you can pass this
 347       as-is to <filename>systemd-hostnamed</filename> in which case it will automatically use a suitable
 348       fallback.</para></listitem>
 349
 350       <listitem><para>Uppercase charaacters should be replaced with their lowercase equivalents.
 351       </para></listitem>
 352     </itemizedlist></para>
 353
 354     <para>Note that while <filename>systemd-hostnamed</filename> applies some checks to the hostname you pass
 355     they are much looser than the recommendations above. For example, <filename>systemd-hostnamed</filename>
 356     will also accept <literal>_</literal> in the hostname, but we recommend not using this to avoid clashes
 357     with DNS-SD service types. Also <filename>systemd-hostnamed</filename> allows longer hostnames, but
 358     because of the DNS label limitations, we recommend not making use of this.</para>
 359
 360     <para>Here are a couple of example conversions:
 361     <itemizedlist>
 362       <listitem><para><literal>Lennart's PC</literal> → <literal>lennarts-pc</literal></para></listitem>
 363       <listitem><para><literal>Müllers Computer</literal> → <literal>muellers-computer</literal></para></listitem>
 364       <listitem><para><literal>Voran!</literal> → <literal>voran</literal></para></listitem>
 365       <listitem><para><literal>Es war einmal ein Männlein</literal> → <literal>es-war-einmal-ein-maennlein</literal></para></listitem>
 366       <listitem><para><literal>Jawoll. Ist doch wahr!</literal> → <literal>jawoll-ist-doch-wahr</literal></para></listitem>
 367       <listitem><para><literal>レナート</literal> → <literal>localhost</literal></para></listitem>
 368       <listitem><para><literal>...zack!!! zack!...</literal> → <literal>zack-zack</literal></para></listitem>
 369     </itemizedlist></para>
 370
 371     <para>Of course, an already valid internet hostname label you enter and pass through this
 372     conversion should stay unmodified, so that users have direct control of it, if they want — by simply
 373     ignoring the fact that the pretty hostname is pretty and just edit it as if it was the normal internet
 374     name.</para>
 375   </refsect1>
 376
 377   <refsect1>
 378     <title>Versioning</title>
 379
 380     <para>These D-Bus interfaces follow <ulink url="http://0pointer.de/blog/projects/versioning-dbus.html">
 381     the usual interface versioning guidelines</ulink>.</para>
 382   </refsect1>
 383
 384   <refsect1>
 385     <title>Examples</title>
 386
 387     <example>
 388       <title>Introspect <interfacename>org.freedesktop.hostname1</interfacename> on the bus</title>
 389
 390       <programlisting>$ gdbus introspect --system \
 391   --dest org.freedesktop.hostname1 \
 392   --object-path /org/freedesktop/hostname1
 393       </programlisting>
 394     </example>
 395   </refsect1>
 396
 397   <refsect1>
 398     <title>See also</title>
 399
 400     <para>David Zeuthen's original Fedora
 401     <ulink url="https://fedoraproject.org/wiki/Features/BetterHostname">Feature page about xdg-hostname</ulink></para>
 402   </refsect1>
 403 </refentry>