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