Ubuntu Manpage: systemd-coredump, systemd-coredump.socket, systemd-coredump@.service

Provided by: systemd-coredump_253.5-1ubuntu6.1_amd64

NAME

       systemd-coredump, systemd-coredump.socket, systemd-coredump@.service - Acquire, save and
       process core dumps

SYNOPSIS

       /lib/systemd/systemd-coredump

       /lib/systemd/systemd-coredump --backtrace

       systemd-coredump@.service

       systemd-coredump.socket

DESCRIPTION

systemd-coredump@.service is a system service to process core dumps. It will log a summary
of the event to systemd-journald.service(8), 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. See the "Information about the crashed
process" section below.

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.

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 gdb(1). See coredumpctl(1), in particular
the list and debug verbs.

By default, systemd-coredump 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 /var/lib/systemd/coredump. These core dumps are deleted
after a few days by default; see /usr/lib/tmpfiles.d/systemd.conf 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. Some metadata is attached to core files in
the form of extended attributes, so the core files are useful for some purposes even
without the full metadata available in the journal entry.

For further details see systemd Coredump Handling[1].

Invocation of systemd-coredump
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 and process and save the core file.

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.

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[2] 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.

CONFIGURATION

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 be 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 be installed, see systemd-coredump-python[3].

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. The default is to delete core dumps after a few days;
see the above file for details.

Disabling coredump processing
To disable potentially resource-intensive processing by systemd-coredump, set

Storage=none
ProcessSizeMax=0

in coredump.conf(5).

INFORMATION ABOUT THE CRASHED PROCESS

       coredumpctl(1) can be used to retrieve saved core dumps independently of their location,
       to display information, and to process them e.g. by passing to the GNU debugger (gdb).

       Data stored in the journal can be also viewed with journalctl(1) as usual (or from any
       other process, using the sd-journal(3) API). The relevant messages have
       MESSAGE_ID=fc2e22bc6ee647b6b90729ab34a250b1:

           $ journalctl MESSAGE_ID=fc2e22bc6ee647b6b90729ab34a250b1 -o verbose
           ...
           MESSAGE_ID=fc2e22bc6ee647b6b90729ab34a250b1
           COREDUMP_PID=552351
           COREDUMP_UID=1000
           COREDUMP_GID=1000
           COREDUMP_SIGNAL_NAME=SIGSEGV
           COREDUMP_SIGNAL=11
           COREDUMP_TIMESTAMP=1614342930000000
           COREDUMP_COMM=Web Content
           COREDUMP_EXE=/lib64/firefox/firefox
           COREDUMP_USER_UNIT=app-gnome-firefox-552136.scope
           COREDUMP_CMDLINE=/lib64/firefox/firefox -contentproc -childID 5 -isForBrowser ...
           COREDUMP_CGROUP=/user.slice/user-1000.slice/user@1000.service/app.slice/app-....scope
           COREDUMP_FILENAME=/var/lib/systemd/coredump/core.Web....552351.....zst
           ...

       The following fields are saved (if known) with the journal entry

       COREDUMP_UID=, COREDUMP_PID=, COREDUMP_GID=
           The process number (PID), owner user number (UID), and group number (GID) of the
           crashed process.

           When the crashed process was part of a container (or in a process or user namespace in
           general), those are the values as seen outside, in the namespace where
           systemd-coredump is running.

       COREDUMP_TIMESTAMP=
           The time of the crash as reported by the kernel (in µs since the epoch).

       COREDUMP_RLIMIT=
           The core file size soft resource limit, see getrlimit(2).

       COREDUMP_UNIT=, COREDUMP_SLICE=
           The system unit and slice names.

           When the crashed process was in container, those are the units names outside, in the
           main system manager.

       COREDUMP_CGROUP=
           Control group information in the format used in /proc/self/cgroup. On systems with the
           unified cgroup hierarchy, this is a single path prefixed with "0::", and multiple
           paths prefixed with controller numbers on legacy systems.

           When the crashed process was in a container, this is the full path, as seen outside of
           the container.

       COREDUMP_OWNER_UID=, COREDUMP_USER_UNIT=
           The numerical UID of the user owning the login session or systemd user unit of the
           crashed process, and the user manager unit. Both fields are only present for user
           processes.

           When the crashed process was in container, those are the values outside, in the main
           system.

       COREDUMP_SIGNAL_NAME=, COREDUMP_SIGNAL=
           The terminating signal name (with the "SIG" prefix [4]) and numerical value. (Both are
           included because signal numbers vary by architecture.)

       COREDUMP_CWD=, COREDUMP_ROOT=
           The current working directory and root directory of the crashed process.

           When the crashed process is in a container, those paths are relative to the root of
           the container's mount namespace.

       COREDUMP_OPEN_FDS=
           Information about open file descriptors, in the following format:

               fd:/path/to/file
               pos:     ...
               flags:   ...
               ...

               fd:/path/to/file
               pos:     ...
               flags:   ...
               ...

           The first line contains the file descriptor number fd and the path, while subsequent
           lines show the contents of /proc/pid/fdinfo/fd.

       COREDUMP_EXE=
           The destination of the /proc/pid/exe symlink.

           When the crashed process is in a container, that path is relative to the root of the
           container's mount namespace.

       COREDUMP_COMM=, COREDUMP_PROC_STATUS=, COREDUMP_PROC_MAPS=, COREDUMP_PROC_LIMITS=,
       COREDUMP_PROC_MOUNTINFO=, COREDUMP_ENVIRON=
           Fields that map the per-process entries in the /proc/ filesystem: /proc/pid/comm (the
           command name associated with the process), /proc/pid/exe (the filename of the executed
           command), /proc/pid/status (various metadata about the process), /proc/pid/maps
           (memory regions visible to the process and their access permissions), /proc/pid/limits
           (the soft and hard resource limits), /proc/pid/mountinfo (mount points in the
           process's mount namespace), /proc/pid/environ (the environment block of the crashed
           process).

           See proc(5) for more information.

       COREDUMP_HOSTNAME=
           The system hostname.

           When the crashed process was in container, this is the container hostname.

       COREDUMP_CONTAINER_CMDLINE=
           For processes running in a container, the commandline of the process spawning the
           container (the first parent process with a different mount namespace).

       COREDUMP=
           When the core is stored in the journal, the core image itself.

       COREDUMP_FILENAME=
           When the core is stored externally, the path to the core file.

       COREDUMP_TRUNCATED=
           Set to "1" when the saved coredump was truncated. (A partial core image may still be
           processed by some tools, though obviously not all information is available.)

       COREDUMP_PACKAGE_NAME=, COREDUMP_PACKAGE_VERSION=, COREDUMP_PACKAGE_JSON=
           If the executable contained .package metadata ELF notes, they will be parsed and
           attached. The package and packageVersion of the 'main' ELF module (ie: the executable)
           will be appended individually. The JSON-formatted content of all modules will be
           appended as a single JSON object, each with the module name as the key. For more
           information about this metadata format and content, see the coredump metadata spec[5].

       MESSAGE=
           The message generated by systemd-coredump that includes the backtrace if it was
           successfully generated. When systemd-coredump is invoked with --backtrace, this field
           is provided by the caller.

       Various other fields exist in the journal entry, but pertain to the logging process, i.e.
       systemd-coredump, not the crashed process. See systemd.journal-fields(7).

       The following fields are saved (if known) with the external file listed in
       COREDUMP_FILENAME= as extended attributes:

       user.coredump.pid, user.coredump.uid, user.coredump.gid, user.coredump.signal,
       user.coredump.timestamp, user.coredump.rlimit, user.coredump.hostname, user.coredump.comm,
       user.coredump.exe
           Those are the same as COREDUMP_PID=, COREDUMP_UID=, COREDUMP_GID=, COREDUMP_SIGNAL=,
           COREDUMP_TIMESTAMP=, COREDUMP_RLIMIT=, COREDUMP_HOSTNAME=, COREDUMP_COMM=, and
           COREDUMP_EXE=, described above.

       Those can be viewed using getfattr(1). For the core file described in the journal entry
       shown above:

           $ getfattr --absolute-names -d /var/lib/systemd/coredump/core.Web....552351.....zst
           # file: /var/lib/systemd/coredump/core.Web....552351.....zst
           user.coredump.pid="552351"
           user.coredump.uid="1000"
           user.coredump.gid="1000"
           user.coredump.signal="11"
           user.coredump.timestamp="1614342930000000"
           user.coredump.comm="Web Content"
           user.coredump.exe="/lib64/firefox/firefox"
           ...

NOTES