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246 lines
13 KiB
XML
246 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-pcrphase.service" conditional='ENABLE_BOOTLOADER HAVE_OPENSSL HAVE_TPM2'
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>systemd-pcrphase.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-pcrphase.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-pcrphase.service</refname>
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<refname>systemd-pcrphase-sysinit.service</refname>
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<refname>systemd-pcrphase-initrd.service</refname>
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<refname>systemd-pcrmachine.service</refname>
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<refname>systemd-pcrfs-root.service</refname>
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<refname>systemd-pcrfs@.service</refname>
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<refname>systemd-pcrextend</refname>
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<refpurpose>Measure boot phase into TPM2 PCR 11, machine ID and file system identity into PCR 15</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>systemd-pcrphase.service</filename></para>
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<para><filename>systemd-pcrphase-sysinit.service</filename></para>
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<para><filename>systemd-pcrphase-initrd.service</filename></para>
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<para><filename>systemd-pcrmachine.service</filename></para>
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<para><filename>systemd-pcrfs-root.service</filename></para>
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<para><filename>systemd-pcrfs@.service</filename></para>
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<para><filename>/usr/lib/systemd/systemd-pcrextend</filename> <optional><replaceable>STRING</replaceable></optional></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>systemd-pcrphase.service</filename>,
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<filename>systemd-pcrphase-sysinit.service</filename>, and
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<filename>systemd-pcrphase-initrd.service</filename> are system services that measure specific strings
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into TPM2 PCR 11 during boot at various milestones of the boot process.</para>
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<para><filename>systemd-pcrmachine.service</filename> is a system service that measures the machine ID
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(see <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>) into
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PCR 15.</para>
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<para><filename>systemd-pcrfs-root.service</filename> and <filename>systemd-pcrfs@.service</filename> are
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services that measure file system identity information (i.e. mount point, file system type, label and
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UUID, partition label and UUID) into PCR 15. <filename>systemd-pcrfs-root.service</filename> does so for
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the root file system, <filename>systemd-pcrfs@.service</filename> is a template unit that measures the
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file system indicated by its instance identifier instead.</para>
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<para>These services require
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<citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> to be
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used in a unified kernel image (UKI). They execute no operation when the stub has not been used to invoke
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the kernel. The stub will measure the invoked kernel and associated vendor resources into PCR 11 before
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handing control to it; once userspace is invoked these services then will extend TPM2 PCR 11 with certain
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literal strings indicating phases of the boot process. During a regular boot process PCR 11 is extended
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with the following strings:</para>
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<orderedlist>
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<listitem><para><literal>enter-initrd</literal> — early when the initrd initializes, before activating
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system extension images for the initrd. It acts as a barrier between the time where the kernel
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initializes and where the initrd starts operating and enables system extension images, i.e. code
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shipped outside of the UKI. (This extension happens when the
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<citerefentry><refentrytitle>systemd-pcrphase-initrd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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service is started.)</para></listitem>
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<listitem><para><literal>leave-initrd</literal> — when the initrd is about to transition into the host
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file system. It acts as barrier between initrd code and host OS code. (This extension happens when the
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<filename>systemd-pcrphase-initrd.service</filename> service is stopped.)</para></listitem>
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<listitem><para><literal>sysinit</literal> — when basic system initialization is complete (which
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includes local file systems having been mounted), and the system begins starting regular system
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services. (This extension happens when the
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<citerefentry><refentrytitle>systemd-pcrphase-sysinit.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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service is started.)</para></listitem>
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<listitem><para><literal>ready</literal> — during later boot-up, after remote file systems have been
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activated (i.e. after <filename>remote-fs.target</filename>), but before users are permitted to log in
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(i.e. before <filename>systemd-user-sessions.service</filename>). It acts as barrier between the time
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where unprivileged regular users are still prohibited to log in and where they are allowed to log in.
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(This extension happens when the <filename>systemd-pcrphase.service</filename> service is started.)
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</para></listitem>
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<listitem><para><literal>shutdown</literal> — when the system shutdown begins. It acts as barrier
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between the time the system is fully up and running and where it is about to shut down. (This extension
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happens when the <filename>systemd-pcrphase.service</filename> service is stopped.)</para></listitem>
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<listitem><para><literal>final</literal> — at the end of system shutdown. It acts as barrier between
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the time the service manager still runs and when it transitions into the final shutdown phase where
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service management is not available anymore. (This extension happens when the
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<citerefentry><refentrytitle>systemd-pcrphase-sysinit.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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service is stopped.)</para></listitem>
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</orderedlist>
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<para>During a regular system lifecycle, PCR 11 is extended with the strings
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<literal>enter-initrd</literal>, <literal>leave-initrd</literal>, <literal>sysinit</literal>,
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<literal>ready</literal>, <literal>shutdown</literal>, and <literal>final</literal>.</para>
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<para>Specific phases of the boot process may be referenced via the series of strings measured, separated
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by colons (the "phase path"). For example, the phase path for the regular system runtime is
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<literal>enter-initrd:leave-initrd:sysinit:ready</literal>, while the one for the initrd is just
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<literal>enter-initrd</literal>. The phase path for the boot phase before the initrd is an empty string;
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because that's hard to pass around a single colon (<literal>:</literal>) may be used instead. Note that
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the aforementioned six strings are just the default strings and individual systems might measure other
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strings at other times, and thus implement different and more fine-grained boot phases to bind policy
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to.</para>
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<para>By binding policy of TPM2 objects to a specific phase path it is possible to restrict access to
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them to specific phases of the boot process, for example making it impossible to access the root file
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system's encryption key after the system transitioned from the initrd into the host root file system.
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</para>
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<para>Use
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<citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry> to
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pre-calculate expected PCR 11 values for specific boot phases (via the <option>--phase=</option> switch).
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</para>
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<para><filename>systemd-pcrfs-root.service</filename> and <filename>systemd-pcrfs@.service</filename> are
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automatically pulled into the initial transaction by
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<citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for the root and <filename>/var/</filename> file
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systems. <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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will do this for all mounts with the <option>x-systemd.pcrfs</option> mount option in
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<filename>/etc/fstab</filename>.</para>
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</refsect1>
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<refsect1>
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<title>Options</title>
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<para>The <filename>/usr/lib/systemd/system-pcrextend</filename> executable may also be invoked from the
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command line, where it expects the word to extend into PCR 11, as well as the following switches:</para>
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<variablelist>
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<varlistentry>
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<term><option>--bank=</option></term>
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<listitem><para>Takes the PCR banks to extend the specified word into. If not specified the tool
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automatically determines all enabled PCR banks and measures the word into all of
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them.</para>
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<xi:include href="version-info.xml" xpointer="v252"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--pcr=</option></term>
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<listitem><para>Takes the index of the PCR to extend. If <option>--machine-id</option> or
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<option>--file-system=</option> are specified defaults to 15, otherwise defaults to 11.</para>
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<xi:include href="version-info.xml" xpointer="v255"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--tpm2-device=<replaceable>PATH</replaceable></option></term>
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<listitem><para>Controls which TPM2 device to use. Expects a device node path referring to the TPM2
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chip (e.g. <filename>/dev/tpmrm0</filename>). Alternatively the special value <literal>auto</literal>
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may be specified, in order to automatically determine the device node of a suitable TPM2 device (of
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which there must be exactly one). The special value <literal>list</literal> may be used to enumerate
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all suitable TPM2 devices currently discovered.</para>
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<xi:include href="version-info.xml" xpointer="v252"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--graceful</option></term>
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<listitem><para>If no TPM2 firmware, kernel subsystem, kernel driver or device support is found, exit
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with exit status 0 (i.e. indicate success). If this is not specified any attempt to measure without a
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TPM2 device will cause the invocation to fail.</para>
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<xi:include href="version-info.xml" xpointer="v253"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--machine-id</option></term>
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<listitem><para>Instead of measuring a word specified on the command line into PCR 11, measure the
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host's machine ID into PCR 15.</para>
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<xi:include href="version-info.xml" xpointer="v253"/></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--file-system=</option></term>
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<listitem><para>Instead of measuring a word specified on the command line into PCR 11, measure
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identity information of the specified file system into PCR 15. The parameter must be the path to the
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established mount point of the file system to measure.</para>
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<xi:include href="version-info.xml" xpointer="v253"/></listitem>
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</varlistentry>
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<xi:include href="standard-options.xml" xpointer="help" />
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<xi:include href="standard-options.xml" xpointer="version" />
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Files</title>
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<variablelist>
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<varlistentry>
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<term><filename>/run/log/systemd/tpm2-measure.log</filename></term>
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<listitem><para>Measurements are logged into an event log file maintained in
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<filename>/run/log/systemd/tpm2-measure.log</filename>, which contains a <ulink
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url="https://www.rfc-editor.org/rfc/rfc7464.html">JSON-SEQ</ulink> series of objects that follow the
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general structure of the <ulink
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url="https://trustedcomputinggroup.org/resource/canonical-event-log-format/">TCG Canonical Event Log
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Format (CEL-JSON)</ulink> event objects (but lack the <literal>recnum</literal>
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field).</para>
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<para>A <constant>LOCK_EX</constant> BSD file lock (<citerefentry
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project='man-pages'><refentrytitle>flock</refentrytitle><manvolnum>2</manvolnum></citerefentry>) on
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the log file is acquired while the measurement is made and the file is updated. Thus, applications
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that intend to acquire a consistent quote from the TPM with the associated snapshot of the event log
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should acquire a <constant>LOCK_SH</constant> lock while doing so.</para>
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<xi:include href="version-info.xml" xpointer="v252"/></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-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
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<member><ulink url="https://systemd.io/TPM2_PCR_MEASUREMENTS">TPM2 PCR Measurements Made by systemd</ulink></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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