118 lines
5.1 KiB
XML
118 lines
5.1 KiB
XML
<?xml version='1.0'?>
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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/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd-pstore" conditional='ENABLE_PSTORE'
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>systemd-pstore.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-pstore.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-pstore.service</refname>
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<refname>systemd-pstore</refname>
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<refpurpose>A service to archive contents of pstore</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>/usr/lib/systemd/systemd-pstore</filename></para>
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<para><filename>systemd-pstore.service</filename></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-pstore.service</filename> is a system service that archives the
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contents of the Linux persistent storage filesystem, pstore, to other storage,
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thus preserving the existing information contained in the pstore, and clearing
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pstore storage for future error events.</para>
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<para>Linux provides a persistent storage file system, pstore, that can store
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error records when the kernel dies (or reboots or powers-off). These records in
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turn can be referenced to debug kernel problems (currently the kernel stuffs
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the tail of the dmesg, which also contains a stack backtrace, into pstore).</para>
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<para>The pstore file system supports a variety of backends that map onto persistent
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storage, such as the ACPI ERST and UEFI variables. The pstore backends
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typically offer a relatively small amount of persistent storage, e.g. 64KiB,
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which can quickly fill up and thus prevent subsequent kernel crashes from
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recording errors. Thus there is a need to monitor and extract the pstore
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contents so that future kernel problems can also record information in the
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pstore.</para>
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<para>The pstore service is independent of the kdump service. In cloud environments
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specifically, host and guest filesystems are on remote filesystems (eg. iSCSI
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or NFS), thus kdump relies (implicitly and/or explicitly) upon proper operation
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of networking software *and* hardware *and* infrastructure. Thus it may not be
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possible to capture a kernel coredump to a file since writes over the network
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may not be possible.</para>
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<para>The pstore backend, on the other hand, is completely local and provides a path
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to store error records which will survive a reboot and aid in post-mortem
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debugging.</para>
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<para>The <command>systemd-pstore</command> executable does the actual work. Upon starting,
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the <filename>pstore.conf</filename> file is read and the <filename>/sys/fs/pstore</filename>
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directory contents are processed according to the options. Pstore files are written to the
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journal, and optionally saved into <filename>/var/lib/systemd/pstore</filename>.</para>
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</refsect1>
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<refsect1>
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<title>Configuration</title>
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<para>The behavior of <command>systemd-pstore</command> is configured through the configuration file
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<filename>/etc/systemd/pstore.conf</filename> and corresponding snippets
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<filename>/etc/systemd/pstore.conf.d/*.conf</filename>, see
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<citerefentry><refentrytitle>pstore.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
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</para>
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<refsect2>
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<title>Disabling pstore processing</title>
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<para>To disable pstore processing by <command>systemd-pstore</command>,
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set <programlisting>Storage=none</programlisting> in
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<citerefentry><refentrytitle>pstore.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
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</para>
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</refsect2>
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<refsect2>
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<title>Controlling kernel parameters</title>
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<para> The kernel has two parameters,
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<filename>/sys/module/kernel/parameters/crash_kexec_post_notifiers</filename> and
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<filename>/sys/module/printk/parameters/always_kmsg_dump</filename>,
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that control writes into pstore.
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The crash_kexec_post_notifiers parameter enables the kernel to write
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dmesg (including stack trace) into pstore upon a panic or crash, and
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printk.always_kmsg_dump parameter enables the kernel to write dmesg
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upon a normal shutdown (shutdown, reboot, halt). These kernel
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parameters are managed via the
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<citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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mechanism, specifically the file <filename>/usr/lib/tmpfiles/systemd-pstore.conf</filename>.
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</para>
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</refsect2>
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</refsect1>
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<refsect1>
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<title>Usage</title>
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<para>Data stored in the journal can be viewed with
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<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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as usual.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>pstore.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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