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man: make systemd-coredump and coredumpctl descriptions more accessible
Fixes #17910: we didn't clearly explain that coredumps may exist without journal entries, and vice versa. Also, make the examples more concrete, and use '$' instead of '#' to avoid suggesting that running as root is required. The text is extended a bit in various places. In the description of systemd-coredump, the details of executor separation are split out to a separate subsection, since they are rather detailed and not necessary to understand for normal use.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
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34507fa9e9
commit
4f57f77267
@ -324,35 +324,47 @@
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<title>Examples</title>
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<example>
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<title>List all the core dumps of a program named foo</title>
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<title>List all the core dumps of a program</title>
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<programlisting># coredumpctl list foo</programlisting>
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<programlisting>$ coredumpctl list /usr/lib64/firefox/firefox
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TIME PID UID GID SIG COREFILE EXE SIZE
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Tue … 8018 1000 1000 SIGSEGV missing /usr/lib64/firefox/firefox n/a
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Wed … 251609 1000 1000 SIGTRAP missing /usr/lib64/firefox/firefox n/a
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Fri … 552351 1000 1000 SIGSEGV present /usr/lib64/firefox/firefox 28.7M
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</programlisting>
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<para>The journal has three entries pertaining to <filename>/usr/lib64/firefox/firefox</filename>, and
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only the last entry still has an available core file (in external storage on disk).</para>
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<para>Note that <filename>coredumpctl</filename> needs access to the journal files to retrieve the
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relevant entries from the journal. Thus, an unprivileged user will normally only see information about
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crashing programs of this user.</para>
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</example>
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<example>
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<title>Invoke gdb on the last core dump</title>
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<title>Invoke <command>gdb</command> on the last core dump</title>
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<programlisting># coredumpctl debug</programlisting>
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<programlisting>$ coredumpctl debug</programlisting>
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</example>
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<example>
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<title>Use gdb to display full register info from the last core dump</title>
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<title>Use <command>gdb</command> to display full register info from the last core dump</title>
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<programlisting># coredumpctl debug --debugger-arguments="-batch -ex 'info all-registers'"</programlisting>
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<programlisting>$ coredumpctl debug --debugger-arguments="-batch -ex 'info all-registers'"</programlisting>
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</example>
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<example>
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<title>Show information about a process that dumped core,
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matching by its PID 6654</title>
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<programlisting># coredumpctl info 6654</programlisting>
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<programlisting>$ coredumpctl info 6654</programlisting>
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</example>
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<example>
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<title>Extract the last core dump of /usr/bin/bar to a file named
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<filename index="false">bar.coredump</filename></title>
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<programlisting># coredumpctl -o bar.coredump dump /usr/bin/bar</programlisting>
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<programlisting>$ coredumpctl -o bar.coredump dump /usr/bin/bar</programlisting>
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</example>
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</refsect1>
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@ -32,29 +32,11 @@
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<refsect1>
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<title>Description</title>
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<para><filename>systemd-coredump@.service</filename> is a system service that can acquire core
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dumps from the kernel and handle them in various ways. The <command>systemd-coredump</command>
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executable does the actual work. It is invoked twice: once as the handler by the kernel, and the
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second time in the <filename>systemd-coredump@.service</filename> to actually write the data to
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the journal.</para>
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<para>When the kernel invokes <command>systemd-coredump</command> to handle a core dump, it runs
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in privileged mode, and will connect to the socket created by the
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<filename>systemd-coredump.socket</filename> unit, which in turn will spawn an unprivileged
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<filename>systemd-coredump@.service</filename> instance to process the core dump. Hence
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<filename>systemd-coredump.socket</filename> and <filename>systemd-coredump@.service</filename>
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are helper units which do the actual processing of core dumps and are subject to normal service
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management.</para>
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<para>Core dumps can be written to the journal or saved as a file. Once saved they can be retrieved
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for further processing, for example in
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<citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
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</para>
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<para>By default, <command>systemd-coredump</command> will log the core dump including a backtrace
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if possible to the journal and store the core dump itself in an external file in
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<filename>/var/lib/systemd/coredump</filename>. These core dumps are deleted after a few days by
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default; see <filename>/usr/lib/tmpfiles.d/systemd.conf</filename> for details.</para>
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<para><filename>systemd-coredump@.service</filename> is a system service to process core dumps. It will
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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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<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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@ -62,14 +44,47 @@
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In particular, the core dump will only be processed when the related resource limits are sufficient.
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</para>
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<para>It is also possible to invoke <command>systemd-coredump</command> with
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<option>--backtrace</option> option. In this case, <command>systemd-coredump</command> expects
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a journal entry in the journal
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<ulink url="https://www.freedesktop.org/wiki/Software/systemd/export">Journal Export Format</ulink>
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on standard input. The entry should contain a <varname>MESSAGE=</varname> field and any additional
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metadata fields the caller deems reasonable. <command>systemd-coredump</command> will append
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additional metadata fields in the same way it does for core dumps received from the kernel. In
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this mode, no core dump is stored in the journal.</para>
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<para>Core dumps can be written to the journal or saved as a file. In both cases, they can be retrieved
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for further processing, for example in
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<citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
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See <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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in particular the <command>list</command> and <command>debug</command> verbs.</para>
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<para>By default, <command>systemd-coredump</command> will log the core dump to the journal, including a
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backtrace if possible, and store the core dump (an image of the memory contents of the process) itself in
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an external file in <filename>/var/lib/systemd/coredump</filename>. These core dumps are deleted after a
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few days by default; see <filename>/usr/lib/tmpfiles.d/systemd.conf</filename> for details. Note that the
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removal of core files from the file system and the purging of journal entries are independent, and the
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core file may be present without the journal entry, and journal entries may point to since-removed core
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files. Metadata is attached to core files in the form of extended attributes, so the core files may be
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useful even without the full metadata available in the journal entry.
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</para>
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<refsect2>
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<title>Invocation of <command>systemd-coredump</command></title>
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<para>The <command>systemd-coredump</command> executable does the actual work. It is invoked twice:
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once as the handler by the kernel, and the second time in the
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<filename>systemd-coredump@.service</filename> to actually write the data to the journal and process
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and save the core file.</para>
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<para>When the kernel invokes <command>systemd-coredump</command> to handle a core dump, it runs in
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privileged mode, and will connect to the socket created by the
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<filename>systemd-coredump.socket</filename> unit, which in turn will spawn an unprivileged
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<filename>systemd-coredump@.service</filename> instance to process the core dump. Hence
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<filename>systemd-coredump.socket</filename> and <filename>systemd-coredump@.service</filename> are
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helper units which do the actual processing of core dumps and are subject to normal service
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management.</para>
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<para>It is also possible to invoke <command>systemd-coredump</command> with
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<option>--backtrace</option> option. In this case, <command>systemd-coredump</command> expects a
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journal entry in the journal
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<ulink url="https://www.freedesktop.org/wiki/Software/systemd/export">Journal Export Format</ulink>
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on standard input. The entry should contain a <varname>MESSAGE=</varname> field and any additional
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metadata fields the caller deems reasonable. <command>systemd-coredump</command> will append additional
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metadata fields in the same way it does for core dumps received from the kernel. In this mode, no core
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dump is stored in the journal.</para>
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</refsect2>
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</refsect1>
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<refsect1>
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@ -118,9 +133,8 @@
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<refsect2>
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<title>Disabling coredump processing</title>
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<para>To disable potentially resource-intensive processing by <command>systemd-coredump</command>,
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set <programlisting>Storage=none
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ProcessSizeMax=0</programlisting> in
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<para>To disable potentially resource-intensive processing by <command>systemd-coredump</command>, set
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<programlisting>Storage=none ProcessSizeMax=0</programlisting> in
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<citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
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</para>
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</refsect2>
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@ -129,10 +143,9 @@ ProcessSizeMax=0</programlisting> in
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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.
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<citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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can be used to retrieve saved core dumps independent of their location, to display information and to process
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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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</refsect1>
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