# systemd-coredump

## 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"
               ...
    


## 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/
    


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