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systemd/man/coredump.conf.xml
Luca Boccassi 587f2a5e56 coredump: check cgroups memory limit if storing on tmpfs
When /var/lib/systemd/coredump/ is backed by a tmpfs, all disk usage
will be accounted under the systemd-coredump process cgroup memory
limit.
If MemoryMax is set, this might cause systemd-coredump to be terminated
by the kernel oom handler when writing large uncompressed core files,
even if the compressed core would fit within the limits.

Detect if a tmpfs is used, and if so check MemoryMax from the process
and slice cgroups, and do not write uncompressed core files that are
greater than half the available memory. If the limit is breached,
stop writing and compress the written chunk immediately, then delete
the uncompressed chunk to free more memory, and resume compressing
directly from STDIN.

Example debug log when this situation happens:

systemd-coredump[737455]: Setting max_size to limit writes to 51344896 bytes.
systemd-coredump[737455]: ZSTD compression finished (51344896 -> 3260 bytes, 0.0%)
systemd-coredump[737455]: ZSTD compression finished (1022786048 -> 47245 bytes, 0.0%)
systemd-coredump[737455]: Process 737445 (a.out) of user 1000 dumped core.
2021-06-08 14:05:56 +01:00

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<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="coredump.conf" conditional="ENABLE_COREDUMP"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>coredump.conf</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>coredump.conf</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>coredump.conf</refname>
<refname>coredump.conf.d</refname>
<refpurpose>Core dump storage configuration files</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>/etc/systemd/coredump.conf</filename></para>
<para><filename>/etc/systemd/coredump.conf.d/*.conf</filename></para>
<para><filename>/run/systemd/coredump.conf.d/*.conf</filename></para>
<para><filename>/usr/lib/systemd/coredump.conf.d/*.conf</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>These files configure the behavior of
<citerefentry><refentrytitle>systemd-coredump</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
a handler for core dumps invoked by the kernel. Whether <command>systemd-coredump</command> is used
is determined by the kernel's
<varname>kernel.core_pattern</varname> <citerefentry project='man-pages'><refentrytitle>sysctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>
setting. See
<citerefentry><refentrytitle>systemd-coredump</refentrytitle><manvolnum>8</manvolnum></citerefentry>
and
<citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry>
pages for the details.</para>
</refsect1>
<xi:include href="standard-conf.xml" xpointer="main-conf" />
<refsect1>
<title>Options</title>
<para>All options are configured in the
[Coredump] section:</para>
<variablelist class='config-directives'>
<varlistentry>
<term><varname>Storage=</varname></term>
<listitem><para>Controls where to store cores. One of <literal>none</literal>,
<literal>external</literal>, and <literal>journal</literal>. When
<literal>none</literal>, the core dumps may be logged (including the backtrace if
possible), but not stored permanently. When <literal>external</literal> (the
default), cores will be stored in <filename>/var/lib/systemd/coredump/</filename>.
When <literal>journal</literal>, cores will be stored in the journal and rotated
following normal journal rotation patterns.</para>
<para>When cores are stored in the journal, they might be
compressed following journal compression settings, see
<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
When cores are stored externally, they will be compressed
by default, see below.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Compress=</varname></term>
<listitem><para>Controls compression for external
storage. Takes a boolean argument, which defaults to
<literal>yes</literal>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>ProcessSizeMax=</varname></term>
<listitem><para>The maximum size in bytes of a core
which will be processed. Core dumps exceeding this size
may be stored, but the backtrace will not be generated.
Like other sizes in this same config file, the usual
suffixes to the base of 1024 are allowed (B, K, M,
G, T, P, and E.)</para>
<para>Setting <varname>Storage=none</varname> and <varname>ProcessSizeMax=0</varname>
disables all coredump handling except for a log entry.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>ExternalSizeMax=</varname></term>
<term><varname>JournalSizeMax=</varname></term>
<listitem><para>The maximum (compressed or uncompressed) size in bytes of a
core to be saved. Unit suffixes are allowed just as in
<option>ProcessSizeMax=</option></para></listitem>.
</varlistentry>
<varlistentry>
<term><varname>MaxUse=</varname></term>
<term><varname>KeepFree=</varname></term>
<listitem><para>Enforce limits on the disk space, specified
in bytes, taken up by externally stored core dumps.
Unit suffixes are allowed just as in <option>ProcessSizeMax=</option>.
<option>MaxUse=</option> makes
sure that old core dumps are removed as soon as the total disk
space taken up by core dumps grows beyond this limit (defaults
to 10% of the total disk size). <option>KeepFree=</option>
controls how much disk space to keep free at least (defaults
to 15% of the total disk size). Note that the disk space used
by core dumps might temporarily exceed these limits while
core dumps are processed. Note that old core dumps are also
removed based on time via
<citerefentry><refentrytitle>systemd-tmpfiles</refentrytitle><manvolnum>8</manvolnum></citerefentry>. Set
either value to 0 to turn off size-based
clean-up.</para></listitem>
</varlistentry>
</variablelist>
<para>The defaults for all values are listed as comments in the
template <filename>/etc/systemd/coredump.conf</filename> file that
is installed by default.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-tmpfiles</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>