Provided by: systemd_255.4-1ubuntu8.4_amd64 
NAME
org.freedesktop.hostname1 - The D-Bus interface of systemd-hostnamed
INTRODUCTION
systemd-hostnamed.service(8) is a system service that can be used to control the hostname
and related machine metadata from user programs. This page describes the hostname
semantics and the D-Bus interface.
THE D-BUS API
The service exposes the following interfaces on the bus:
node /org/freedesktop/hostname1 {
interface org.freedesktop.hostname1 {
methods:
SetHostname(in s hostname,
in b interactive);
SetStaticHostname(in s hostname,
in b interactive);
SetPrettyHostname(in s hostname,
in b interactive);
SetIconName(in s icon,
in b interactive);
SetChassis(in s chassis,
in b interactive);
SetDeployment(in s deployment,
in b interactive);
SetLocation(in s location,
in b interactive);
GetProductUUID(in b interactive,
out ay uuid);
GetHardwareSerial(out s serial);
Describe(out s json);
properties:
readonly s Hostname = '...';
readonly s StaticHostname = '...';
readonly s PrettyHostname = '...';
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s DefaultHostname = '...';
readonly s HostnameSource = '...';
readonly s IconName = '...';
readonly s Chassis = '...';
readonly s Deployment = '...';
readonly s Location = '...';
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s KernelName = '...';
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s KernelRelease = '...';
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s KernelVersion = '...';
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s OperatingSystemPrettyName = '...';
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s OperatingSystemCPEName = '...';
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly t OperatingSystemSupportEnd = ...;
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s HomeURL = '...';
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s HardwareVendor = '...';
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s HardwareModel = '...';
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s FirmwareVersion = '...';
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s FirmwareVendor = '...';
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly t FirmwareDate = ...;
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly ay MachineID = [...];
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly ay BootID = [...];
};
interface org.freedesktop.DBus.Peer { ... };
interface org.freedesktop.DBus.Introspectable { ... };
interface org.freedesktop.DBus.Properties { ... };
};
Whenever the hostname or other metadata is changed via the daemon, PropertyChanged signals
are sent out to subscribed clients. Changing a hostname using this interface is
authenticated via polkit[1].
SEMANTICS
The StaticHostname property exposes the "static" hostname configured in /etc/hostname. It
is not always in sync with the current hostname as returned by the gethostname(3) system
call. If no static hostname is configured this property will be the empty string.
When systemd(1) or systemd-hostnamed.service(8) set the hostname, this static hostname has
the highest priority.
The Hostname property exposes the actual hostname configured in the kernel via
sethostname(2). It can be different from the static hostname. This property is never
empty.
The PrettyHostname property exposes the pretty hostname which is a free-form UTF-8
hostname for presentation to the user. User interfaces should ensure that the pretty
hostname and the static hostname stay in sync. E.g. when the former is "Lennart’s
Computer" the latter should be "lennarts-computer". If no pretty hostname is set this
setting will be the empty string. Applications should then find a suitable fallback, such
as the dynamic hostname.
The DefaultHostname property exposes the default hostname (configured through os-
release(5), or a fallback set at compilation time).
The HostnameSource property exposes the origin of the currently configured hostname. One
of "static" (set from /etc/hostname), "transient" (a non-permanent hostname from an
external source), "default" (the value from os-release or the compiled-in fallback).
The IconName property exposes the icon name following the XDG icon naming spec. If not
set, information such as the chassis type (see below) is used to find a suitable fallback
icon name (i.e. "computer-laptop" vs. "computer-desktop" is picked based on the chassis
information). If no such data is available, the empty string is returned. In that case an
application should fall back to a replacement icon, for example "computer". If this
property is set to the empty string, the automatic fallback name selection is enabled
again.
The Chassis property exposes a chassis type, one of the currently defined chassis types:
"desktop", "laptop", "server", "tablet", "handset", as well as the special chassis types
"vm" and "container" for virtualized systems. Note that in most cases the chassis type
will be determined automatically from DMI/SMBIOS/ACPI firmware information. Writing to
this setting is hence useful only to override misdetected chassis types, or to configure
the chassis type if it could not be auto-detected. Set this property to the empty string
to reenable the automatic detection of the chassis type from firmware information.
Note that systemd-hostnamed starts only on request and terminates after a short idle
period. This effectively means that PropertyChanged messages are not sent out for changes
made directly on the files (as in: administrator edits the files with vi). This is the
intended behavior: manual configuration changes should require manual reloading.
The transient (dynamic) hostname exposed by the Hostname property maps directly to the
kernel hostname. This hostname should be assumed to be highly dynamic, and hence should be
watched directly, without depending on PropertyChanged messages from systemd-hostnamed. To
accomplish this, open /proc/sys/kernel/hostname and poll(3) for SIGHUP which is triggered
by the kernel every time the hostname changes. Again: this is special for the transient
(dynamic) hostname, and does not apply to the configured (fixed) hostname.
Applications may read the hostname data directly if hostname change notifications are not
necessary. Use gethostname(2), /etc/hostname (possibly with per-distribution fallbacks),
and machine-info(3) for that. For more information on these files and syscalls see the
respective man pages.
KernelName, KernelRelease, and KernelVersion expose the kernel name (e.g. "Linux"),
release (e.g. "5.0.0-11"), and version (i.e. the build number, e.g. "#11") as reported
by uname(2). OperatingSystemPrettyName, OperatingSystemCPEName, and HomeURL expose the
PRETTY_NAME=, CPE_NAME= and HOME_URL= fields from os-release(5). The purpose of those
properties is to allow remote clients to access this information over D-Bus. Local clients
can access the information directly.
Methods
SetHostname() sets the transient (dynamic) hostname, which is used if no static hostname
is set. This value must be an internet-style hostname, 7-bit lowercase ASCII, no special
chars/spaces. An empty string will unset the transient hostname.
SetStaticHostname() sets the static hostname which is exposed by the StaticHostname
property. When called with an empty argument, the static configuration in /etc/hostname is
removed. Since the static hostname has the highest priority, calling this function usually
affects also the Hostname property and the effective hostname configured in the kernel.
SetPrettyHostname() sets the pretty hostname which is exposed by the PrettyHostname
property.
SetIconName(), SetChassis(), SetDeployment(), and SetLocation() set the properties
IconName (the name of the icon representing for the machine), Chassis (the machine form
factor), Deployment (the system deployment environment), and Location (physical system
location), respectively.
PrettyHostname, IconName, Chassis, Deployment, and Location are stored in
/etc/machine-info. See machine-info(5) for the semantics of those settings.
GetProductUUID() returns the "product UUID" as exposed by the kernel based on DMI
information in /sys/class/dmi/id/product_uuid. Reading the file directly requires root
privileges, and this method allows access to unprivileged clients through the polkit
framework.
Describe() returns a JSON representation of all properties in one.
Security
The interactive boolean parameters can be used to control whether polkit should
interactively ask the user for authentication credentials if required.
The polkit action for SetHostname() is org.freedesktop.hostname1.set-hostname. For
SetStaticHostname() and SetPrettyHostname() it is
org.freedesktop.hostname1.set-static-hostname. For SetIconName(), SetChassis(),
SetDeployment() and SetLocation() it is org.freedesktop.hostname1.set-machine-info.
RECOMMENDATIONS
Here are three examples that show how the pretty hostname and the icon name should be
used:
• When registering DNS-SD services: use the pretty hostname in the service name, and
pass the icon name in the TXT data, if there is an icon name. Browsing clients can
then show the server icon on each service. This is especially useful for WebDAV
applications or UPnP media sharing.
• Set the bluetooth name to the pretty hostname.
• When your file browser has a "Computer" icon, replace the name with the pretty
hostname if set, and the icon with the icon name, if it is set.
To properly handle name lookups with changing local hostnames without having to edit
/etc/hosts, we recommend using systemd-hostnamed in combination with nss-myhostname(3).
Here are some recommendations to follow when generating a static (internet) hostname from
a pretty name:
• Generate a single DNS label only, not an FQDN. That means no dots allowed. Strip them,
or replace them with "-".
• It's probably safer to not use any non-ASCII chars, even if DNS allows this in some
way these days. In fact, restrict your charset to "a-zA-Z0-9" and "-". Strip other
chars, or try to replace them in some smart way with chars from this set, for example
"ä" → "ae", and use "-" as the replacement for all punctuation characters and
whitespace.
• Try to avoid creating repeated "-", as well as "-" as the first or last char.
• Limit the hostname to 63 chars, which is the length of a DNS label.
• If after stripping special chars the empty string is the result, you can pass this
as-is to systemd-hostnamed in which case it will automatically use a suitable
fallback.
• Uppercase characters should be replaced with their lowercase equivalents.
Note that while systemd-hostnamed applies some checks to the hostname you pass they are
much looser than the recommendations above. For example, systemd-hostnamed will also
accept "_" in the hostname, but we recommend not using this to avoid clashes with DNS-SD
service types. Also systemd-hostnamed allows longer hostnames, but because of the DNS
label limitations, we recommend not making use of this.
Here are a couple of example conversions:
• "Lennart's PC" → "lennarts-pc"
• "Müllers Computer" → "muellers-computer"
• "Voran!" → "voran"
• "Es war einmal ein Männlein" → "es-war-einmal-ein-maennlein"
• "Jawoll. Ist doch wahr!" → "jawoll-ist-doch-wahr"
• "レナート" → "localhost"
• "...zack!!! zack!..." → "zack-zack"
Of course, an already valid internet hostname label you enter and pass through this
conversion should stay unmodified, so that users have direct control of it, if they want —
by simply ignoring the fact that the pretty hostname is pretty and just edit it as if it
was the normal internet name.
VERSIONING
These D-Bus interfaces follow the usual interface versioning guidelines[2].
EXAMPLES
Example 1. Introspect org.freedesktop.hostname1 on the bus
$ gdbus introspect --system \
--dest org.freedesktop.hostname1 \
--object-path /org/freedesktop/hostname1
SEE ALSO
David Zeuthen's original Fedora Feature page about xdg-hostname[3]
HISTORY
The D-Bus API
FirmwareVersion and GetHardwareSerial() were added in version 251.
OperatingSystemSupportEnd, FirmwareVendor, and FirmwareDate were added in version 253.
MachineID, and BootID were added in version 256.
NOTES
1. polkit
https://www.freedesktop.org/software/polkit/docs/latest/
2. the usual interface versioning guidelines
https://0pointer.de/blog/projects/versioning-dbus.html
3. Feature page about xdg-hostname
https://fedoraproject.org/wiki/Features/BetterHostname