picnoir
/
Systemd
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

man/hostnamectl,hostaned,hostname1: adjust the docs to match reality 

The semantics were significantly changed in c779a44222
("hostnamed: Fix the way that static and transient host names interact", Feb. 2014),
but when the dbus api documentation was imported much later, it wasn't properly
adjusted to describe those new semantics.

34293dfafd which added systemd.hostname= also
added new behaviour.

Let's ove various bits and pieces around so that they are in more appropriate
places. Drop recommendations to set the hostname for DHCP or mDNS purposes.
Nowadays we expect tools that want to expose some different hostname to the
outside to manage that internally without affecting visible state. Also drop
mentions of DHCP or mDNS directly setting the hostname, since nowadays network
management software is expected to (and does) go through hostnamed.

Also, add a high-level description of semantics. It glosses over the details of
handling of localhost-style names. Later commits will remove this special handling
anyway.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2020-12-04 15:16:24 +01:00
parent a2be8be2cf
commit de31bbc6b1
4 changed files with 122 additions and 85 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

77
man/hostname.xml
View File

@ -1,6 +1,9 @@
<?xml version='1.0'?> <!--*-nxml-*--> <?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
<!ENTITY % entities SYSTEM "custom-entities.ent" >
%entities;
]>
<!-- SPDX-License-Identifier: LGPL-2.1-or-later --> <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="hostname"> <refentry id="hostname">
@ -26,23 +29,65 @@
<refsect1> <refsect1>
<title>Description</title> <title>Description</title>
<para>The <filename>/etc/hostname</filename> file configures the <para>The <filename>/etc/hostname</filename> file configures the name of the local system. Unless
name of the local system that is set during boot using the overridden as described in the next section,
<citerefentry><refentrytitle>sethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry> <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will set this
system call. It should contain a single newline-terminated hostname during boot using the
hostname string. Comments (lines starting with a `#') are ignored. <citerefentry><refentrytitle>sethostname</refentrytitle><manvolnum>2</manvolnum></citerefentry> system
The hostname may be a free-form string up to 64 characters in length; call.</para>
however, it is recommended that it consists only of 7-bit ASCII lower-case
characters and no spaces or dots, and limits itself to the format allowed <para>The file should contain a single newline-terminated hostname string. Comments (lines starting with
for DNS domain name labels, even though this is not a strict a <literal>#</literal>) are ignored. The hostname should be composed of up to 64 7-bit ASCII lower-case
requirement.</para> alphanumeric characters or hyphens forming a valid DNS domain name. It is recommended that this name
contains only a single label, i.e. without any dots. Invalid characters will be filtered out in an
attempt to make the name valid, but obviously it is recommended to use a valid name and not rely on this
filtering.</para>
<para>You may use <para>You may use
<citerefentry><refentrytitle>hostnamectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> <citerefentry><refentrytitle>hostnamectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to change
to change the value of this file during runtime from the command the value of this file during runtime from the command line. Use
line. Use <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry> to
<citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry> initialize it on mounted (but not booted) system images.</para>
to initialize it on mounted (but not booted) system images.</para> </refsect1>
<refsect1>
<title>Hostname semantics</title>
<para><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> and the
associated tools will obtain the hostname in the following ways:</para>
<itemizedlist>
<listitem><para>If the kernel commandline parameter <varname>systemd.hostname=</varname> specifies a
valid hostname,
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will use it
to set the hostname during early boot, see
<citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
</para></listitem>
<listitem><para>Otherwise, the "static" hostname specified by <filename>/etc/hostname</filename> as
described above will be used.</para></listitem>
<listitem><para>Otherwise, a transient hostname may be set during runtime, for example based on
information in a DHCP lease, see
<citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
Both <ulink url="https://developer.gnome.org/NetworkManager/stable/">NetworkManager</ulink> and
<citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
allow this. Note that
<citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
gives higher priority to the static hostname, so the transient hostname will only be used if the static
hostname is not configured.</para></listitem>
<listitem><para>Otherwise, a fallback hostname configured at compilation time will be used
(<literal>&FALLBACK_HOSTNAME;</literal>).</para></listitem>
<!-- what about the "linux" fallback fallback? -->
</itemizedlist>
<para>Effectively, the static hostname has higher priority than a transient hostname, which has higher
priority than the fallback hostname. Transient hostnames are equivalent, so setting a new transient
hostname causes the previous transient hostname to be forgotten. The hostname specified on the kernel
command line is like a transient hostname, with the exception that it has higher priority when the
machine boots. Also note that those are the semantics implemented by systemd tools, but other programs
may also set the hostname.</para>
</refsect1> </refsect1>
<refsect1> <refsect1>

30
man/hostnamectl.xml
View File

@ -32,33 +32,23 @@
<refsect1> <refsect1>
<title>Description</title> <title>Description</title>
<para><command>hostnamectl</command> may be used to query and <para><command>hostnamectl</command> may be used to query and change the system hostname and related
change the system hostname and related settings.</para> settings.</para>
<para>This tool distinguishes three different hostnames: the <para><citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
high-level "pretty" hostname which might include all kinds of and this tool distinguish three different hostnames: the high-level "pretty" hostname which might include
special characters (e.g. "Lennart's Laptop"), the static hostname all kinds of special characters (e.g. "Lennart's Laptop"), the "static" hostname which is the
which is used to initialize the kernel hostname at boot (e.g. user-configured hostname (e.g. "lennarts-laptop"), and the transient hostname which is a fallback value
"lennarts-laptop"), and the transient hostname which is a fallback received from network configuration (e.g. "node12345678"). If a static hostname is set, and is valid
value received from network configuration. If a static hostname is (something other than localhost), then the transient hostname is not used.</para>
set, and is valid (something other than localhost), then the
transient hostname is not used.</para>
<para>Note that the pretty hostname has little restrictions on the characters and length used, while the static and <para>Note that the pretty hostname has little restrictions on the characters and length used, while the static and
transient hostnames are limited to the usually accepted characters of Internet domain names, and 64 characters at transient hostnames are limited to the usually accepted characters of Internet domain names, and 64 characters at
maximum (the latter being a Linux limitation).</para> maximum (the latter being a Linux limitation).</para>
<para>The static hostname is stored in
<filename>/etc/hostname</filename>, see
<citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for more information. The pretty hostname, chassis type, and icon
name are stored in <filename>/etc/machine-info</filename>, see
<citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
<para>Use <para>Use
<citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry> <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry> to
to initialize the system hostname for mounted (but not booted) initialize the system hostname for mounted (but not booted) system images.</para>
system images.</para>
</refsect1> </refsect1>
<refsect1> <refsect1>

90
man/org.freedesktop.hostname1.xml
View File

@ -144,55 +144,53 @@ node /org/freedesktop/hostname1 {
<refsect1> <refsect1>
<title>Semantics</title> <title>Semantics</title>
<para>The <emphasis>static (configured) hostname</emphasis> is the one configured in <para>The <varname>StaticHostname</varname> property exposes the "static" hostname configured in
<filename>/etc/hostname</filename>. It is chosen by the local user. It is not always in sync with the <filename>/etc/hostname</filename>. It is not always in sync with the current hostname as returned by the
current hostname as returned by the
<citerefentry project="man-pages"><refentrytitle>gethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry> <citerefentry project="man-pages"><refentrytitle>gethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>
system call. If no hostname is configured this property will be the empty string. Setting this property system call. If no static hostname is configured this property will be the empty string.</para>
to the empty string will remove <filename>/etc/hostname</filename>. This property should be an
internet-style hostname, 7-bit lowercase ASCII, no special chars/spaces.</para>
<para>The <emphasis>transient (dynamic) hostname</emphasis> is the one configured via the kernel's <para>When <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> or
<citerefentry><refentrytitle>systemd-hostnamed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
set the hostname, this static hostname <emphasis>has the highest priority</emphasis>.</para>
<para>The <varname>Hostname</varname> property exposes the actual hostname configured in the kernel via
<citerefentry project="man-pages"><refentrytitle>sethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>. <citerefentry project="man-pages"><refentrytitle>sethostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
It can be different from the static hostname if DHCP or mDNS have been configured to change the name It can be different from the static hostname. This property is never empty.</para>
based on network information. <!-- FIXME: it's not DHCP that configures this... -->
This property is never empty. If no hostname is set this will default to
<literal>&FALLBACK_HOSTNAME;</literal> (configurable at compilation time). Setting this property to the
empty string will reset the dynamic hostname to the static hostname. If no static hostname is
configured the dynamic hostname will be reset to <literal>&FALLBACK_HOSTNAME;</literal>. This property
should be an internet-style hostname, 7-bit lowercase ASCII, no special chars/spaces.</para>
<para>The <emphasis>pretty hostname</emphasis> is a free-form UTF-8 hostname for presentation to the <para>The <varname>PrettyHostname</varname> property exposes the <emphasis>pretty hostname</emphasis>
user. User interfaces should ensure that the pretty hostname and the static hostname stay in sync. which is a free-form UTF-8 hostname for presentation to the user. User interfaces should ensure that the
I.e. when the former is <literal>Lennart’s Computer</literal> the latter should be pretty hostname and the static hostname stay in sync. E.g. when the former is <literal>Lennart’s
<literal>lennarts-computer</literal>. If no pretty hostname is set this setting will be the empty Computer</literal> the latter should be <literal>lennarts-computer</literal>. If no pretty hostname is
string. Applications should then find a suitable fallback, such as the dynamic hostname.</para> set this setting will be the empty string. Applications should then find a suitable fallback, such as the
dynamic hostname.</para>
<para>The <emphasis>icon name</emphasis> is a name following the XDG icon naming spec. If not set, <para>The <varname>IconName</varname> property exposes the <emphasis>icon name</emphasis> following the
information such as the chassis type (see below) is used to find a suitable fallback icon name XDG icon naming spec. If not set, information such as the chassis type (see below) is used to find a
(i.e. <literal>computer-laptop</literal> vs. <literal>computer-desktop</literal> is picked based on the suitable fallback icon name (i.e. <literal>computer-laptop</literal>
chassis information). If no such data is available, the empty string is returned. In that case an application vs. <literal>computer-desktop</literal> is picked based on the chassis information). If no such data is
should fall back to a replacement icon, for example <literal>computer</literal>. If this property is set available, the empty string is returned. In that case an application should fall back to a replacement
to the empty string, the automatic fallback name selection is enabled again.</para> icon, for example <literal>computer</literal>. If this property is set to the empty string, the automatic
fallback name selection is enabled again.</para>
<para>The <emphasis>chassis type</emphasis> should be one of the currently defined chassis types: <para>The <varname>Chassis</varname> property exposes a <emphasis>chassis type</emphasis>, one of the
<literal>desktop</literal>, <literal>laptop</literal>, <literal>server</literal>, currently defined chassis types: <literal>desktop</literal>, <literal>laptop</literal>,
<literal>tablet</literal>, <literal>handset</literal>, as well as the special chassis types <literal>server</literal>, <literal>tablet</literal>, <literal>handset</literal>, as well as the special
<literal>vm</literal> and <literal>container</literal> for virtualized systems. Note that in most cases chassis types <literal>vm</literal> and <literal>container</literal> for virtualized systems. Note that
the chassis type will be determined automatically from DMI/SMBIOS/ACPI firmware information. Writing to in most cases the chassis type will be determined automatically from DMI/SMBIOS/ACPI firmware
this setting is hence useful only to override misdetected chassis types, or to configure the chassis type if information. Writing to this setting is hence useful only to override misdetected chassis types, or to
it could not be auto-detected. Set this property to the empty string to reenable the automatic detection of configure the chassis type if it could not be auto-detected. Set this property to the empty string to
the chassis type from firmware information.</para> reenable the automatic detection of the chassis type from firmware information.</para>
<para>Note that <filename>systemd-hostnamed</filename> starts only on request and terminates after a <para>Note that <filename>systemd-hostnamed</filename> starts only on request and terminates after a
short idle period. This effectively means that <function>PropertyChanged</function> messages are not sent short idle period. This effectively means that <function>PropertyChanged</function> messages are not sent
out for changes made directly on the files (as in: administrator edits the files with vi). This is 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.</para> the intended behavior: manual configuration changes should require manual reloading.</para>
<para>The transient (dynamic) hostname maps directly to the kernel hostname. This hostname should be <para>The transient (dynamic) hostname exposed by the <varname>Hostname</varname> property maps directly
assumed to be highly dynamic, and hence should be watched directly, without depending on to the kernel hostname. This hostname should be assumed to be highly dynamic, and hence should be watched
<function>PropertyChanged</function> messages from <filename>systemd-hostnamed</filename>. To accomplish directly, without depending on <function>PropertyChanged</function> messages from
this, open <filename>/proc/sys/kernel/hostname</filename> and <filename>systemd-hostnamed</filename>. To accomplish this, open
<filename>/proc/sys/kernel/hostname</filename> and
<citerefentry project="man-pages"><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry> <citerefentry project="man-pages"><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for <constant>SIGHUP</constant> which is triggered by the kernel every time the hostname changes. Again: for <constant>SIGHUP</constant> 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) this is special for the transient (dynamic) hostname, and does not apply to the configured (fixed)
@ -206,15 +204,17 @@ node /org/freedesktop/hostname1 {
for that. For more information on these files and syscalls see the respective man pages.</para> for that. For more information on these files and syscalls see the respective man pages.</para>
<refsect2> <refsect2>
<title>Methods and Properties</title> <title>Methods</title>
<para><function>SetHostname()</function> sets the transient (dynamic) hostname which is exposed by the <para><function>SetHostname()</function> sets the transient (dynamic) hostname, which is used if no
<varname>Hostname</varname> property. If empty, the transient hostname is set to the static hostname. static hostname is set. This value must be an internet-style hostname, 7-bit lowercase ASCII, no
</para> special chars/spaces. An empty string will unset the transient hostname.</para>
<para><function>SetStaticHostname()</function> sets the static hostname which is exposed by the <para><function>SetStaticHostname()</function> sets the static hostname which is exposed by the
<varname>StaticHostname</varname> property. If empty, the built-in default of <varname>StaticHostname</varname> property. When called with an empty argument, the static
<literal>&FALLBACK_HOSTNAME;</literal> is used.</para> configuration in <filename>/etc/hostname</filename> is removed. Since the static hostname has the
highest priority, calling this function usually affects also the <varname>Hostname</varname> property
and the effective hostname configured in the kernel.</para>
<para><function>SetPrettyHostname()</function> sets the pretty hostname which is exposed by the <para><function>SetPrettyHostname()</function> sets the pretty hostname which is exposed by the
<varname>PrettyHostname</varname> property.</para> <varname>PrettyHostname</varname> property.</para>
@ -287,10 +287,6 @@ node /org/freedesktop/hostname1 {
with <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>. with <citerefentry><refentrytitle>nss-myhostname</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para> </para>
<para>A client that wants to change the local hostname for DHCP/mDNS should invoke
<code>SetHostname("newname", false)</code> as soon as the name is available and afterwards reset it via
<code>SetHostname("")</code>.</para>
<para>Here are some recommendations to follow when generating a static (internet) hostname from a pretty <para>Here are some recommendations to follow when generating a static (internet) hostname from a pretty
name: name:
<itemizedlist> <itemizedlist>

10
man/systemd-hostnamed.service.xml
View File

@ -51,9 +51,15 @@
</listitem> </listitem>
</itemizedlist></para> </itemizedlist></para>
<para>The static hostname is stored in <filename>/etc/hostname</filename>, see
<citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more
information. The pretty hostname, chassis type, and icon name are stored in
<filename>/etc/machine-info</filename>, see
<citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
<para>The tool <para>The tool
<citerefentry><refentrytitle>hostnamectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> <citerefentry><refentrytitle>hostnamectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> is a
is a command line client to this service.</para> command line client to this service.</para>
<para>See <para>See
<citerefentry><refentrytitle>org.freedesktop.hostname1</refentrytitle><manvolnum>5</manvolnum></citerefentry> <citerefentry><refentrytitle>org.freedesktop.hostname1</refentrytitle><manvolnum>5</manvolnum></citerefentry>