systemd-coredump, systemd-coredump.socket, systemd-coredump@.service — Acquire, save and process core dumps
/usr/lib/systemd/systemd-coredump
/usr/lib/systemd/systemd-coredump --backtrace
systemd-coredump@.service
systemd-coredump.socket
systemd-coredump@.service is a system service that can acquire core
dumps from the kernel and handle them in various ways. The systemd-coredump
executable does the actual work. It is invoked twice: once as the handler by the kernel, and the
second time in the systemd-coredump@.service to actually write the data to
the journal.
When the kernel invokes systemd-coredump to handle a core dump, it runs
in privileged mode, and will connect to the socket created by the
systemd-coredump.socket unit, which in turn will spawn an unprivileged
systemd-coredump@.service instance to process the core dump. Hence
systemd-coredump.socket and systemd-coredump@.service
are helper units which do the actual processing of core dumps and are subject to normal service
management.
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 gdb(1).
By default, systemd-coredump will log the core dump including a backtrace
if possible to the journal and store the core dump itself in an external file in
/var/lib/systemd/coredump.
The behavior of a specific program upon reception of a signal is governed by a few factors which are described in detail in core(5). In particular, the core dump will only be processed when the related resource limits are sufficient.
It is also possible to invoke systemd-coredump with
--backtrace option. In this case, systemd-coredump expects
a journal entry in the journal
Journal Export Format
on standard input. The entry should contain a MESSAGE= field and any additional
metadata fields the caller deems reasonable. systemd-coredump 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.
For programs started by systemd process resource limits can be set by directive
LimitCore=, see
systemd.exec(5).
In order to be used by the kernel to handle core dumps,
systemd-coredump must be configured in
sysctl(8)
parameter kernel.core_pattern. The syntax of this parameter is explained in
core(5).
systemd installs the file /usr/lib/sysctl.d/50-coredump.conf which configures
kernel.core_pattern accordingly. This file may be masked or overridden to use a different
setting following normal
sysctl.d(5)
rules. If the sysctl configuration is modified, it must be updated in the kernel before it
takes effect, see
sysctl(8)
and
systemd-sysctl(8).
In order to by used in the --backtrace mode, an appropriate backtrace
handler must be installed on the sender side. For example, in case of
python(1), this
means a sys.excepthook must installed, see
systemd-coredump-python.
The behavior of systemd-coredump itself is configured through the configuration file
/etc/systemd/coredump.conf and corresponding snippets
/etc/systemd/coredump.conf.d/*.conf, see
coredump.conf(5). A new
instance of systemd-coredump is invoked upon receiving every core dump. Therefore, changes
in these files will take effect the next time a core dump is received.
Resources used by core dump files are restricted in two ways. Parameters like maximum size of acquired
core dumps and files can be set in files /etc/systemd/coredump.conf and snippets mentioned
above. In addition the storage time of core dump files is restricted by systemd-tmpfiles,
corresponding settings are by default in /usr/lib/tmpfiles.d/systemd.conf.
To disable potentially resource-intensive processing by systemd-coredump, set
Storage=none ProcessSizeMax=0
in coredump.conf(5).
Data stored in the journal can be viewed with journalctl(1) as usual. coredumpctl(1) 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).