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f00c36641a
The systemd pstore service archives the contents of /sys/fs/pstore upon boot so that there is room for a subsequent dump. The issue is that while the service is present, the kernel still needs to be configured to write data into the pstore. The kernel has two parameters, crash_kexec_post_notifiers and printk.always_kmsg_dump, that control writes into pstore. The crash_kexec_post_notifiers parameter enables the kernel to write dmesg (including stack trace) into pstore upon a panic, and printk.always_kmsg_dump parameter enables the kernel to write dmesg upon a shutdown (shutdown, reboot, halt). As it stands today, these parameters are not managed/manipulated by the systemd pstore service, and are solely reliant upon the user [to have the foresight] to set them on the kernel command line at boot, or post boot via sysfs. Furthermore, the user would need to set these parameters in a persistent fashion so that that they are enabled on subsequent reboots. This patch introduces the setting of these two kernel parameters via the systemd tmpfiles technique.
118 lines
5.0 KiB
XML
118 lines
5.0 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+ -->
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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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