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man: describe coredump fields
We save a wealth of information about the process, but this might not be immediately obvious.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
parent
4f57f77267
commit
9d58abfa25
@ -36,7 +36,8 @@
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log a summary of the event to
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<citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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including information about the process identifier, owner, the signal that killed the process, and the
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stack trace if possible. It may also save the core dump for later processing.</para>
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stack trace if possible. It may also save the core dump for later processing. See the "Information about
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the crashed process" section below.</para>
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<para>The behavior of a specific program upon reception of a signal is governed by a few
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factors which are described in detail in
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@ -141,12 +142,233 @@
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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> as usual.
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<citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> can be
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used to retrieve saved core dumps independent of their location, to display information and to process
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them e.g. by passing to the GNU debugger (gdb).</para>
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<title>Information about the crashed process</title>
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<para><citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> can
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be used to retrieve saved core dumps independently of their location, to display information, and to
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process them e.g. by passing to the GNU debugger (gdb).</para>
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<para>Data stored in the journal can be also viewed with
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<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> as usual
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(or from any other process, using the
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<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry> API).
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The relevant messages have <constant>MESSAGE_ID=fc2e22bc6ee647b6b90729ab34a250b1</constant>:</para>
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<programlisting>$ journalctl MESSAGE_ID=fc2e22bc6ee647b6b90729ab34a250b1 -o verbose
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…
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MESSAGE_ID=fc2e22bc6ee647b6b90729ab34a250b1
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COREDUMP_PID=552351
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COREDUMP_UID=1000
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COREDUMP_GID=1000
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COREDUMP_SIGNAL_NAME=SIGSEGV
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COREDUMP_SIGNAL=11
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COREDUMP_TIMESTAMP=1614342930000000
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COREDUMP_COMM=Web Content
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COREDUMP_EXE=/usr/lib64/firefox/firefox
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COREDUMP_USER_UNIT=app-gnome-firefox-552136.scope
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COREDUMP_CMDLINE=/usr/lib64/firefox/firefox -contentproc -childID 5 -isForBrowser …
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COREDUMP_CGROUP=/user.slice/user-1000.slice/user@1000.service/app.slice/app-….scope
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COREDUMP_FILENAME=/var/lib/systemd/coredump/core.Web….552351.….zst
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…
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</programlisting>
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<para>The following fields are saved (if known) with the journal entry</para>
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<variablelist class='journal-directives'>
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<varlistentry>
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<term><varname>COREDUMP_UID=</varname></term>
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<term><varname>COREDUMP_PID=</varname></term>
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<term><varname>COREDUMP_GID=</varname></term>
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<listitem><para>The process number (PID) and owner (UID and GID) of the crashed process.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_TIMESTAMP=</varname></term>
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<listitem><para>The time of the crash as reported by the kernel (in µs since the epoch).</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_RLIMIT=</varname></term>
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<listitem><para>The core file size soft resource limit, see
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<citerefentry project='man-pages'><refentrytitle>getrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry>.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_UNIT=</varname></term>
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<term><varname>COREDUMP_SLICE=</varname></term>
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<listitem><para>The system unit and slice names.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_CGROUP=</varname></term>
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<listitem><para>Control group information in the format used in
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<filename>/proc/self/cgroup</filename>. On systems with the unified cgroup hierarchy, this is a
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single path prefixed with <literal>0::</literal>, and multiple paths prefixed with controller numbers
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on legacy systems.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_OWNER_UID=</varname></term>
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<term><varname>COREDUMP_USER_UNIT=</varname></term>
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<listitem><para>The numerical UID of the user owning the login session or systemd user unit of the
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crashed process, and the user manager unit. Both fields are only present for user processes.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_SIGNAL_NAME=</varname></term>
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<term><varname>COREDUMP_SIGNAL=</varname></term>
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<listitem><para>The terminating signal name and numerical value. (Both are included because signal
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numbers vary by architecture.)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_CWD=</varname></term>
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<term><varname>COREDUMP_ROOT=</varname></term>
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<listitem><para>The current working directory and root directory of the crashed process.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_OPEN_FDS=</varname></term>
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<listitem><para>Information about open file descriptors, in the following format:</para>
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<programlisting><replaceable>fd</replaceable>:<replaceable>/path/to/file</replaceable>
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pos: ...
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flags: ...
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...
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<replaceable>fd</replaceable>:<replaceable>/path/to/file</replaceable>
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pos: ...
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flags: ...
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...
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</programlisting>
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<para>The first line contains the file descriptor number <replaceable>fd</replaceable> and the path,
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while subsequent lines show the contents of
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<filename>/proc/<replaceable>pid</replaceable>/fdinfo/<replaceable>fd</replaceable></filename>.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_COMM=</varname></term>
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<term><varname>COREDUMP_EXE=</varname></term>
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<term><varname>COREDUMP_PROC_STATUS=</varname></term>
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<term><varname>COREDUMP_PROC_MAPS=</varname></term>
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<term><varname>COREDUMP_PROC_LIMITS=</varname></term>
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<term><varname>COREDUMP_PROC_MOUNTINFO=</varname></term>
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<term><varname>COREDUMP_ENVIRON=</varname></term>
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<listitem><para>Fields that map the per-process entries in the <filename>/proc/</filename>
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filesystem: <filename>/proc/<replaceable>pid</replaceable>/comm</filename> (the command name
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associated with the process), <filename>/proc/<replaceable>pid</replaceable>/exe</filename> (the
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filename of the executed command), <filename>/proc/<replaceable>pid</replaceable>/status</filename>
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(various metadata about the process), <filename>/proc/<replaceable>pid</replaceable>/maps</filename>
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(memory regions visible to the process and their access permissions),
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<filename>/proc/<replaceable>pid</replaceable>/limits</filename> (the soft and hard resource limits),
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<filename>/proc/<replaceable>pid</replaceable>/mountinfo</filename> (mount points in the process's
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mount namespace), <filename>/proc/<replaceable>pid</replaceable>/environ</filename>
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(the environemnt block of the crashed process).</para>
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<para>See
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<citerefentry project='man-pages'><refentrytitle>proc</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for more information.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_HOSTNAME=</varname></term>
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<listitem><para>The system hostname.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_CONTAINER_CMDLINE=</varname></term>
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<listitem><para>For processes running in a container, the commandline of the process spawning the
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container (the first parent process with a different mount namespace).</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP=</varname></term>
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<listitem><para>When the core is stored in the journal, the core image itself.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_FILENAME=</varname></term>
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<listitem><para>When the core is stored externally, the path the the core file.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>COREDUMP_TRUNCATED=</varname></term>
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<listitem><para>Set to <literal>1</literal> when the saved coredump was truncated. (A partial core
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image may still be processed by some tools, though obviously not all information is available.)
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>MESSAGE=</varname></term>
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<listitem><para>The message generated by <command>systemd-coredump</command> that includes the
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backtrace if it was successfully generated. When <command>systemd-coredump</command> is invoked with
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<option>--backtrace</option>, this field is provided by the caller.</para></listitem>
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</varlistentry>
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</variablelist>
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<para>Various other fields exist in the journal entry, but pertain to the logging process,
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i.e. <command>systemd-coredump</command>, not the crashed process. See
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<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
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</para>
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<para>The following fields are saved (if known) with the external file listed in
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<varname>COREDUMP_FILENAME=</varname> as extended attributes:</para>
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<variablelist>
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<varlistentry>
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<term><varname>user.coredump.pid</varname></term>
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<term><varname>user.coredump.uid</varname></term>
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<term><varname>user.coredump.gid</varname></term>
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<term><varname>user.coredump.signal</varname></term>
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<term><varname>user.coredump.timestamp</varname></term>
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<term><varname>user.coredump.rlimit</varname></term>
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<term><varname>user.coredump.hostname</varname></term>
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<term><varname>user.coredump.comm</varname></term>
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<term><varname>user.coredump.exe</varname></term>
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<listitem><para>Those are the same as <varname>COREDUMP_PID=</varname>,
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<varname>COREDUMP_UID=</varname>, <varname>COREDUMP_GID=</varname>,
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<varname>COREDUMP_SIGNAL=</varname>, <varname>COREDUMP_TIMESTAMP=</varname>,
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<varname>COREDUMP_RLIMIT=</varname>, <varname>COREDUMP_HOSTNAME=</varname>,
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<varname>COREDUMP_COMM=</varname>, and <varname>COREDUMP_EXE=</varname>, described above.
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</para></listitem>
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</varlistentry>
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</variablelist>
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<para>Those can be viewed using
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<citerefentry project='man-pages'><refentrytitle>getfattr</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
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For the core file described in the journal entry shown above:
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<programlisting>$ getfattr --absolute-names -d /var/lib/systemd/coredump/core.Web….552351.….zst
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# file: /var/lib/systemd/coredump/core.Web….552351.….zst
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user.coredump.pid="552351"
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user.coredump.uid="1000"
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user.coredump.gid="1000"
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user.coredump.signal="11"
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user.coredump.timestamp="1614342930000000"
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user.coredump.comm="Web Content"
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user.coredump.exe="/usr/lib64/firefox/firefox"
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…
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</programlisting>
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</para>
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</refsect1>
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<refsect1>
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