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This service's job is to talk to a VM associated IMDS service provided by the local Cloud. It tries to abstract the protocol differences various IMDS implementations implement, but does *not* really try to abstract more than a few basic fields of the actual IMDS metadata. IMDS access is wrapped in a Varlink API that local clients can talk to. If possible this makes use of the IMDS endpoint information that has been added to hwdb in the preceeding commit. However, endpoint info can also be provided via kernel command line and credentials. For debugging purposes we also accept them via environment variables and command line arguments. This adds a concept of early-boot networking, just enough to be able to talk to the IMDS service. It is minimally configurable via a kernel cmdline option (and a build-time option): the user may choose between "locked" and "unlocked" mode. In the former mode direct access to IMDS via HTTPS is blocked via a prohibit route (and thus all IMDS communication has to be done via systemd-imdsd@.service). In the latter case no such lockdown takes place, and IMDS may be acquired both via this new service and directly. The latter is typically a good idea for compatibility with current systems, the former is preferable for secure installations. Access to IMDS fields is controlled via PK.
270 lines
13 KiB
XML
270 lines
13 KiB
XML
<?xml version="1.0"?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd-imdsd_.service" conditional='ENABLE_IMDS' xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>systemd-imdsd@.service</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-imdsd@.service</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-imdsd@.service</refname>
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<refname>systemd-imdsd</refname>
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<refname>systemd-imdsd.socket</refname>
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<refname>systemd-imdsd-early-network.service</refname>
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<refpurpose>Cloud IMDS (Instance Metadata Service) client</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>systemd-imdsd@.service</filename></para>
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<para><filename>systemd-imdsd.socket</filename></para>
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<para><filename>systemd-imdsd-early-network.service</filename></para>
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<para><filename>/usr/lib/systemd/systemd-imdsd</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><command>systemd-imdsd@.service</command> is a system service that provides local access to IMDS
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(Instance Metadata Service; or equivalent) functionality, as provided by many public clouds.</para>
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<para>The service provides a Varlink IPC interface via
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<filename>/run/systemd/io.systemd.InstanceMetadata</filename> to query IMDS fields.</para>
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<para><filename>systemd-imdsd-early-network.service</filename> is a system service that generates a
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<citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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compatible
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<citerefentry><refentrytitle>systemd.network</refentrytitle><manvolnum>5</manvolnum></citerefentry> file
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for configuring the early-boot network in order to be able to contact the IMDS endpoint.</para>
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<para>The
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<citerefentry><refentrytitle>systemd-imds</refentrytitle><manvolnum>1</manvolnum></citerefentry> tool may
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be used to query information from this service.</para>
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</refsect1>
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<!-- Note: we do not document the command line switches here for now. The systemd-imdsd binary itself
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should not be called by users, but only as a service, hence the command line options shouldn't be user
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visible, but exist mostly as debugging tools. People should always use the client side tool
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(i.e. systemd-imds; or an equivalent Varlink client) to do actual IMDS operations. -->
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<refsect1>
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<title>Kernel Command Line Options</title>
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<para>The IMDS endpoint is typically determined automatically via
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<citerefentry><refentrytitle>hwdb</refentrytitle><manvolnum>7</manvolnum></citerefentry> records, but can
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also be configured explicitly via the kernel command line, via the following options:</para>
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<variablelist class='kernel-commandline-options'>
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<varlistentry id='kernel-cmdline-imds-network'>
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<term><varname>systemd.imds.network=</varname></term>
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<listitem>
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<para>Takes one of <literal>off</literal>, <literal>locked</literal>,
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<literal>unlocked</literal>. Controls whether and how to set up networking for IMDS endpoint
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access. Unless set to <literal>off</literal> early boot networking is enabled, ensuring that the
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IMDS endpoint can be reached. If set to <literal>locked</literal> (the default) direct access to
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the IMDS endpoint by regular unprivileged processes is disabled via a "prohibit" route, so that any
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access must be done through <filename>systemd-imdsd@.service</filename> or its associated tools. If
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set to <literal>unlocked</literal> this "prohibit" route is not created, and regular unprivileged
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processes can directly contact IMDS.</para>
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<xi:include href="version-info.xml" xpointer="v261"/>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.imds.vendor=</varname></term>
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<listitem>
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<para>A short string identifying the cloud vendor.</para>
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<para>Example: <programlisting>systemd.imds.vendor=foobarcloud</programlisting></para>
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<xi:include href="version-info.xml" xpointer="v261"/>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.imds.token_url=</varname></term>
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<listitem>
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<para>If a bearer token must be acquired to talk to the IMDS service, this is the URL to acquire it
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from.</para>
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<xi:include href="version-info.xml" xpointer="v261"/>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.imds.refresh_header_name=</varname></term>
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<listitem>
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<para>Takes a HTTP header field name (excluding the <literal>:</literal>) that declares the header
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field for passing the TTL value (in seconds) to the HTTP server when acquiring a token. Only
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applies if <varname>systemd.imds.token_url=</varname> is set too.</para>
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<xi:include href="version-info.xml" xpointer="v261"/>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.imds.data_url=</varname></term>
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<listitem>
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<para>Takes the base URL to acquire the IMDS data from (the IMDS "endpoint"). All data fields are
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acquired from below this URL. This URL should typically not end in <literal>/</literal>.</para>
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<para>The data URLs are concatenated from this base URL, the IMDS "key" and the suffix configured
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via <varname>systemd.imds.data_url_suffix=</varname> below. Well-known IMDS "keys" can be
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configured via the <varname>systemd.imds.key=*</varname> options below.</para>
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<para>Example: <programlisting>systemd.imds.data_url=http://169.254.169.254/metadata</programlisting></para>
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<xi:include href="version-info.xml" xpointer="v261"/>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.imds.data_url_suffix=</varname></term>
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<listitem>
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<para>If specified, this field is appended to the end of the data URL (after appending the IMDS
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"key" to the data base URL), see above.</para>
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<para>Example: <programlisting>systemd.imds.data_url_suffix=?api-version=2025-04-07&format=text</programlisting></para>
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<xi:include href="version-info.xml" xpointer="v261"/>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.imds.token_header_name=</varname></term>
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<listitem>
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<para>Takes a HTTP header field name (excluding the <literal>:</literal>) that declares the header
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field to pass the bearer token acquired from the token URL (see above) in. Only applies if
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<varname>systemd.imds.token_url=</varname> is set too.</para>
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<xi:include href="version-info.xml" xpointer="v261"/>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.imds.extra_header=</varname></term>
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<listitem>
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<para>Takes a full HTTP header expression (both field name and value, separated by a colon
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<literal>:</literal>) to pass to the HTTP server when requesting data. May be used multiple times
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to set multiple headers.</para>
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<para>Example: <programlisting>systemd.imds.extra_header=Metadata:true</programlisting></para>
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<xi:include href="version-info.xml" xpointer="v261"/>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.imds.address_ipv4=</varname></term>
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<listitem>
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<para>Configures the IPv4 address the IMDS endpoint is contacted on. This should typically be the
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IP address also configured via <varname>systemd.imds.data_url=</varname> (if IPv4 is used) and is
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used to set up IP routing.</para>
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<para>Example: <programlisting>systemd.imds.address_ipv4=169.254.169.254</programlisting></para>
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<xi:include href="version-info.xml" xpointer="v261"/>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.imds.address_ipv6=</varname></term>
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<listitem>
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<para>Configures the IPv6 address the IMDS endpoint is contacted on. This should typically be the
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IP address also configured via <varname>systemd.imds.data_url=</varname> (if IPv6 is used) and is
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used to set up IP routing.</para>
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<xi:include href="version-info.xml" xpointer="v261"/>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>systemd.imds.key.hostname=</varname></term>
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<term><varname>systemd.imds.key.region=</varname></term>
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<term><varname>systemd.imds.key.zone=</varname></term>
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<term><varname>systemd.imds.key.ipv4_public=</varname></term>
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<term><varname>systemd.imds.key.ipv6_public=</varname></term>
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<term><varname>systemd.imds.key.ssh_key=</varname></term>
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<term><varname>systemd.imds.key.userdata=</varname></term>
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<term><varname>systemd.imds.key.userdata_base=</varname></term>
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<term><varname>systemd.imds.key.userdata_base64=</varname></term>
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<listitem>
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<para>Configures strings to concatenate to the data base URL (see above) to acquire data for
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various "well-known" fields. These strings must begin with a <literal>/</literal>. They should
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return the relevant data in plain text.</para>
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<para>A special case are the three "userdata" keys: the option
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<varname>systemd.imds.key.userdata_base=</varname> should be used if the IMDS service knows a
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concept of multiple userdata fields, and a field identifier thus still needs to be appended to the
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userdata base URL. The option <varname>systemd.imds.key.userdata=</varname> should be used if only
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a single userdata field is supported. The option <varname>systemd.imds.key.userdata_base64=</varname>
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should be used in the same case, but only if the userdata field is encoded in Base64.</para>
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<para>Example: <programlisting>systemd.imds.key.hostname=/instance/compute/osProfile/computerName</programlisting></para>
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<xi:include href="version-info.xml" xpointer="v261"/>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Credentials</title>
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<para><filename>systemd-imdsd@.service</filename> supports the service credentials logic as implemented by
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<varname>ImportCredential=</varname>/<varname>LoadCredential=</varname>/<varname>SetCredential=</varname>
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(see <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
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details). The following credentials are used when passed in:</para>
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<variablelist class='system-credentials'>
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<varlistentry>
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<term><varname>imds.vendor</varname></term>
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<term><varname>imds.vendor_token</varname></term>
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<term><varname>imds.refresh_header_name</varname></term>
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<term><varname>imds.data_url</varname></term>
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<term><varname>imds.data_url_suffix</varname></term>
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<term><varname>imds.token_header_name</varname></term>
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<term><varname>imds.extra_header</varname></term>
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<term><varname>imds.extra_header2</varname></term>
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<term><varname>imds.extra_header3</varname></term>
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<term><varname>imds.extra_header…</varname></term>
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<term><varname>imds.address_ipv4</varname></term>
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<term><varname>imds.address_ipv6</varname></term>
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<term><varname>imds.key_hostname</varname></term>
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<term><varname>imds.key_region</varname></term>
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<term><varname>imds.key_zone</varname></term>
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<term><varname>imds.key_ipv4_public</varname></term>
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<term><varname>imds.key_ipv6_public</varname></term>
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<term><varname>imds.key_ssh_key</varname></term>
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<term><varname>imds.key_userdata</varname></term>
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<term><varname>imds.key_userdata_base</varname></term>
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<term><varname>imds.key_userdata_base64</varname></term>
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<listitem><para>The various IMDS endpoint parameters. The semantics are very close to those configurable
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via kernel command line, see above for the matching list.</para>
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<xi:include href="version-info.xml" xpointer="v261"/></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para><simplelist type="inline">
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<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-imds</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-imds-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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