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.
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.
- Journal Export Format