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mirror of https://github.com/systemd/systemd-stable.git synced 2024-12-22 13:33:56 +03:00

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 2021-02-27 19:00:51 +01:00
parent 34507fa9e9
commit 4f57f77267
2 changed files with 71 additions and 46 deletions

View File

@ -324,35 +324,47 @@
<title>Examples</title>
<example>
<title>List all the core dumps of a program named foo</title>
<title>List all the core dumps of a program</title>
<programlisting># coredumpctl list foo</programlisting>
<programlisting>$ coredumpctl list /usr/lib64/firefox/firefox
TIME PID UID GID SIG COREFILE EXE SIZE
Tue … 8018 1000 1000 SIGSEGV missing /usr/lib64/firefox/firefox n/a
Wed … 251609 1000 1000 SIGTRAP missing /usr/lib64/firefox/firefox n/a
Fri … 552351 1000 1000 SIGSEGV present /usr/lib64/firefox/firefox 28.7M
</programlisting>
<para>The journal has three entries pertaining to <filename>/usr/lib64/firefox/firefox</filename>, and
only the last entry still has an available core file (in external storage on disk).</para>
<para>Note that <filename>coredumpctl</filename> needs access to the journal files to retrieve the
relevant entries from the journal. Thus, an unprivileged user will normally only see information about
crashing programs of this user.</para>
</example>
<example>
<title>Invoke gdb on the last core dump</title>
<title>Invoke <command>gdb</command> on the last core dump</title>
<programlisting># coredumpctl debug</programlisting>
<programlisting>$ coredumpctl debug</programlisting>
</example>
<example>
<title>Use gdb to display full register info from the last core dump</title>
<title>Use <command>gdb</command> to display full register info from the last core dump</title>
<programlisting># coredumpctl debug --debugger-arguments="-batch -ex 'info all-registers'"</programlisting>
<programlisting>$ coredumpctl debug --debugger-arguments="-batch -ex 'info all-registers'"</programlisting>
</example>
<example>
<title>Show information about a process that dumped core,
matching by its PID 6654</title>
<programlisting># coredumpctl info 6654</programlisting>
<programlisting>$ coredumpctl info 6654</programlisting>
</example>
<example>
<title>Extract the last core dump of /usr/bin/bar to a file named
<filename index="false">bar.coredump</filename></title>
<programlisting># coredumpctl -o bar.coredump dump /usr/bin/bar</programlisting>
<programlisting>$ coredumpctl -o bar.coredump dump /usr/bin/bar</programlisting>
</example>
</refsect1>

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@ -32,29 +32,11 @@
<refsect1>
<title>Description</title>
<para><filename>systemd-coredump@.service</filename> is a system service that can acquire core
dumps from the kernel and handle them in various ways. The <command>systemd-coredump</command>
executable does the actual work. It is invoked twice: once as the handler by the kernel, and the
second time in the <filename>systemd-coredump@.service</filename> to actually write the data to
the journal.</para>
<para>When the kernel invokes <command>systemd-coredump</command> to handle a core dump, it runs
in privileged mode, and will connect to the socket created by the
<filename>systemd-coredump.socket</filename> unit, which in turn will spawn an unprivileged
<filename>systemd-coredump@.service</filename> instance to process the core dump. Hence
<filename>systemd-coredump.socket</filename> and <filename>systemd-coredump@.service</filename>
are helper units which do the actual processing of core dumps and are subject to normal service
management.</para>
<para>Core dumps can be written to the journal or saved as a file. Once saved they can be retrieved
for further processing, for example in
<citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
</para>
<para>By default, <command>systemd-coredump</command> will log the core dump including a backtrace
if possible to the journal and store the core dump itself in an external file in
<filename>/var/lib/systemd/coredump</filename>. These core dumps are deleted after a few days by
default; see <filename>/usr/lib/tmpfiles.d/systemd.conf</filename> for details.</para>
<para><filename>systemd-coredump@.service</filename> is a system service to process core dumps. It will
log a summary of the event to
<citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
including information about the process identifier, owner, the signal that killed the process, and the
stack trace if possible. It may also save the core dump for later processing.</para>
<para>The behavior of a specific program upon reception of a signal is governed by a few
factors which are described in detail in
@ -62,14 +44,47 @@
In particular, the core dump will only be processed when the related resource limits are sufficient.
</para>
<para>It is also possible to invoke <command>systemd-coredump</command> with
<option>--backtrace</option> option. In this case, <command>systemd-coredump</command> expects
a journal entry in the journal
<ulink url="https://www.freedesktop.org/wiki/Software/systemd/export">Journal Export Format</ulink>
on standard input. The entry should contain a <varname>MESSAGE=</varname> field and any additional
metadata fields the caller deems reasonable. <command>systemd-coredump</command> will append
additional metadata fields in the same way it does for core dumps received from the kernel. In
this mode, no core dump is stored in the journal.</para>
<para>Core dumps can be written to the journal or saved as a file. In both cases, they can be retrieved
for further processing, for example in
<citerefentry project='man-pages'><refentrytitle>gdb</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
See <citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
in particular the <command>list</command> and <command>debug</command> verbs.</para>
<para>By default, <command>systemd-coredump</command> will log the core dump to the journal, including a
backtrace if possible, and store the core dump (an image of the memory contents of the process) itself in
an external file in <filename>/var/lib/systemd/coredump</filename>. These core dumps are deleted after a
few days by default; see <filename>/usr/lib/tmpfiles.d/systemd.conf</filename> for details. Note that the
removal of core files from the file system and the purging of journal entries are independent, and the
core file may be present without the journal entry, and journal entries may point to since-removed core
files. Metadata is attached to core files in the form of extended attributes, so the core files may be
useful even without the full metadata available in the journal entry.
</para>
<refsect2>
<title>Invocation of <command>systemd-coredump</command></title>
<para>The <command>systemd-coredump</command> executable does the actual work. It is invoked twice:
once as the handler by the kernel, and the second time in the
<filename>systemd-coredump@.service</filename> to actually write the data to the journal and process
and save the core file.</para>
<para>When the kernel invokes <command>systemd-coredump</command> to handle a core dump, it runs in
privileged mode, and will connect to the socket created by the
<filename>systemd-coredump.socket</filename> unit, which in turn will spawn an unprivileged
<filename>systemd-coredump@.service</filename> instance to process the core dump. Hence
<filename>systemd-coredump.socket</filename> and <filename>systemd-coredump@.service</filename> are
helper units which do the actual processing of core dumps and are subject to normal service
management.</para>
<para>It is also possible to invoke <command>systemd-coredump</command> with
<option>--backtrace</option> option. In this case, <command>systemd-coredump</command> expects a
journal entry in the journal
<ulink url="https://www.freedesktop.org/wiki/Software/systemd/export">Journal Export Format</ulink>
on standard input. The entry should contain a <varname>MESSAGE=</varname> field and any additional
metadata fields the caller deems reasonable. <command>systemd-coredump</command> will append additional
metadata fields in the same way it does for core dumps received from the kernel. In this mode, no core
dump is stored in the journal.</para>
</refsect2>
</refsect1>
<refsect1>
@ -118,9 +133,8 @@
<refsect2>
<title>Disabling coredump processing</title>
<para>To disable potentially resource-intensive processing by <command>systemd-coredump</command>,
set <programlisting>Storage=none
ProcessSizeMax=0</programlisting> in
<para>To disable potentially resource-intensive processing by <command>systemd-coredump</command>, set
<programlisting>Storage=none ProcessSizeMax=0</programlisting> in
<citerefentry><refentrytitle>coredump.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para>
</refsect2>
@ -129,10 +143,9 @@ ProcessSizeMax=0</programlisting> in
<refsect1>
<title>Usage</title>
<para>Data stored in the journal can be viewed with
<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
as usual.
<citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
can be used to retrieve saved core dumps independent of their location, to display information and to process
<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> as usual.
<citerefentry><refentrytitle>coredumpctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> can be
used to retrieve saved core dumps independent of their location, to display information and to process
them e.g. by passing to the GNU debugger (gdb).</para>
</refsect1>