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NAME | SYNOPSIS | DESCRIPTION | CONFIGURATION | INFORMATION ABOUT THE CRASHED PROCESS | SEE ALSO | NOTES | COLOPHON |
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SYSTEMD-COREDUMP(8) systemd-coredump SYSTEMD-COREDUMP(8)
systemd-coredump, systemd-coredump.socket, systemd-
[email protected] - Acquire, save and process core dumps
/usr/lib/systemd/systemd-coredump
/usr/lib/systemd/systemd-coredump --backtrace
[email protected]
systemd-coredump.socket
[email protected] 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 [email protected] 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 [email protected] instance to
process the core dump. Hence systemd-coredump.socket and
[email protected] 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.
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).
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/[email protected]/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_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_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 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].
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"
...
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]
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. the coredump metadata spec
https://systemd.io/COREDUMP_PACKAGE_METADATA/
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have
a bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 257~devel SYSTEMD-COREDUMP(8)
Pages that refer to this page: coredumpctl(1), core(5), coredump.conf(5), systemd.directives(7), systemd.index(7), systemd-journald.service(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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