SYSTEMD-COREDUMP(8)	       systemd-coredump		   SYSTEMD-COREDUMP(8)

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

SYNOPSIS
       /usr/lib/systemd/systemd-coredump

       /usr/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
       process resource limits (RLIMIT_CORE) 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.

   Core dumps in Containers/Namespaces
       The systemd-coredump@.service service will automatically attempt to
       extract a stacktrace from a process as it crashes. For this stacktrace
       symbols will be resolved based on debug information embedded in the
       crashing ELF image, or equivalent debug information separately
       available on the host OS. For processes that crash inside of local
       containers or other mount namespace-based sandboxes, this auxiliary
       debug information is typically not available on the host (simply
       because containers typically run different software versions than the
       host).  systemd-coredump provides two mechanisms to address this:

	1. For full-OS containers running systemd inside it is a good idea to
	   enable CoredumpReceive= on the unit (see systemd.resource-
	   control(5)), which ensures that coredumps of a container are
	   attempted to be forwarded to systemd-coredump@.service running
	   inside the container, i.e the container gets to process and store
	   its own core dumps. Note that systemd-nspawn(8) defaults to this
	   mode if invoked with the --boot switch. This mode of operation is
	   generally recommended for security reasons: the security-sensitive
	   processing of the core dump is done within the confinements of the
	   container itself, by the container's own code, backed by the
	   container's own storage.

	2. Alternatively, for more restricted containers (that do not run a
	   proper init system as PID 1) it is possible to enable processing of
	   the core dump on the host, with access to the debug information
	   data from the container itself. This mode of operation must be
	   enabled via EnterNamespace= in coredump.conf(5), and defaults to
	   off, for security reasons.

       If both CoredumpReceive= is enabled on the unit of the container the
       core dump belongs to, and EnterNamespace= is enabled in the
       coredump.conf configuration file, the former takes precedence.

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=/usr/lib64/firefox/firefox
	   COREDUMP_USER_UNIT=app-gnome-firefox-552136.scope
	   COREDUMP_CMDLINE=/usr/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.

	   Added in version 248.

       COREDUMP_BY_PIDFD=
	   If the crashed process was analyzed using a PIDFD provided by the
	   kernel (requires kernel v6.16) then this field will be present and
	   set to "1". If this field is not set, then the crashed process was
	   analyzed via a PID, which is known to be subject to race
	   conditions.

	   Added in version 258.

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

	   Added in version 248.

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

	   Added in version 248.

       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.

	   Added in version 248.

       COREDUMP_CGROUP=
	   The primary cgroup of the unit of the crashed process.

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

	   Added in version 248.

       COREDUMP_PROC_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.

	   Added in version 248.

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

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

	   Added in version 248.

       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.)

	   Added in version 248.

       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.

	   Added in version 248.

       COREDUMP_DUMPABLE=
	   The PR_GET_DUMPABLE field as reported by the kernel, see prctl(2).

	   Added in version 258.

       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.

	   Added in version 248.

       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.

	   Added in version 248.

       COREDUMP_CMDLINE=, COREDUMP_COMM=, COREDUMP_ENVIRON=,
       COREDUMP_PROC_AUXV=, COREDUMP_PROC_LIMITS=, COREDUMP_PROC_MAPS=,
       COREDUMP_PROC_MOUNTINFO=, COREDUMP_PROC_STATUS=
	   Fields that map the per-process entries in the /proc/ filesystem:
	   /proc/pid/cmdline (the command line of the crashed process),
	   /proc/pid/comm (the command name associated with the process),
	   /proc/pid/environ (the environment block of the crashed process),
	   /proc/pid/auxv (the auxiliary vector of the crashed process, see
	   getauxval(3)), /proc/pid/limits (the soft and hard resource
	   limits), /proc/pid/maps (memory regions visible to the process and
	   their access permissions), /proc/pid/mountinfo (mount points in the
	   process's mount namespace), /proc/pid/status (various metadata
	   about the process).

	   See proc(5) for more information.

	   Added in version 248.

       COREDUMP_HOSTNAME=
	   The system hostname.

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

	   Added in version 248.

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

	   Added in version 248.

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

	   Added in version 248.

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

	   Added in version 248.

       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.)

	   Added in version 248.

       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 version of the 'main' ELF
	   module (i.e., 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 Package
	   Metadata for Executable Files[5] document.

	   Added in version 249.

       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.

	   Added in version 248.

       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.

	   Added in version 248.

       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="/usr/lib64/firefox/firefox"
	   ...


SEE ALSO
       coredump.conf(5), coredumpctl(1), systemd-journald.service(8), systemd-
       tmpfiles(8), core(5), sysctl.d(5), systemd-sysctl.service(8), systemd
       Coredump Handling[1]

NOTES
	1. systemd Coredump Handling
	   https://systemd.io/COREDUMP

	2. Journal Export Format
	   https://systemd.io/JOURNAL_EXPORT_FORMATS#journal-export-format

	3. systemd-coredump-python
	   https://github.com/systemd/systemd-coredump-python

	4. kill(1) expects signal names without the prefix; kill(2) uses the
	   prefix; all systemd tools accept signal names both with and without
	   the prefix.

	5. Package Metadata for Executable Files
	   https://systemd.io/PACKAGE_METADATA_FOR_EXECUTABLE_FILES/

systemd 258						   SYSTEMD-COREDUMP(8)