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