## Support in the Service Manager (PID 1)
The systemd service manager natively provides coredump handling functionality,
-as implemented by the Linux kernel. Specifically, PID 1 provides the following
-functionality:
+as implemented by the Linux kernel.
+Specifically, PID 1 provides the following functionality:
1. During very early boot it will raise the
[`LIMIT_CORE`](https://man7.org/linux/man-pages/man2/getrlimit.2.html)
- resource limit for itself to infinity (and thus implicitly also all its
- children). This removes any limits on the size of generated coredumps, for
- all invoked processes, from earliest boot on. (The Linux kernel sets the
- limit to 0 by default.)
+ resource limit for itself to infinity (and thus implicitly also all its children).
+ This removes any limits on the size of generated coredumps,
+ for all invoked processes, from earliest boot on.
+ (The Linux kernel sets the limit to 0 by default.)
2. At the same time it will turn off coredump handling in the kernel by writing
`|/bin/false` into `/proc/sys/kernel/core_pattern` (also known as the
"`kernel.core_pattern` sysctl"; see
[core(5)](https://man7.org/linux/man-pages/man5/core.5.html) for
- details). This means that coredumps are not actually processed. (The Linux
- kernel sets the pattern to `core` by default, so that coredumps are written
+ details).
+ This means that coredumps are not actually processed.
+ (The Linux kernel sets the pattern to `core` by default, so that coredumps are written
to the current working directory of the crashing process.)
Net effect: after PID1 has started and performed this setup coredumps are
disabled, but by means of the the `kernel.core_pattern` sysctl rather than by
-size limit. This is generally preferable, since the pattern can be updated
-trivially at the right time to enable coredumping once the system is ready,
-taking comprehensive effect on all userspace. (Or to say this differently:
-disabling coredumps via the size limit is problematic, since it cannot easily
-be undone without iterating through all already running processes once the
-system is ready for coredump handling.)
+size limit.
+This is generally preferable, since the pattern can be updated trivially at the right time to enable coredumping once the system is ready, taking comprehensive effect on all userspace.
+(Or to say this differently: disabling coredumps via the size limit is problematic, since it cannot easily
+be undone without iterating through all already running processes once the system is ready for coredump handling.)
Processing of core dumps may be enabled at the appropriate time by updating the
-`kernel.core_pattern` sysctl. Only coredumps that happen later will be
-processed.
+`kernel.core_pattern` sysctl.
+Only coredumps that happen later will be processed.
During the final shutdown phase the `kernel.core_pattern` sysctl is updated
again to `|/bin/false`, disabling coredump support again, should it have been
specified service unit, and thus can take benefit of regular service resource
management and sandboxing.
-The `systemd-coredump` handler will extract a backtrace and [ELF packaging
-metadata](https://systemd.io/ELF_PACKAGE_METADATA) from any coredumps it
-receives and log both. The information about coredumps stored in the journal
-can be enumerated and queried with the
+The `systemd-coredump` handler will extract a backtrace and
+[ELF packaging metadata](https://systemd.io/ELF_PACKAGE_METADATA) from any coredumps it
+receives and log both.
+The information about coredumps stored in the journal can be enumerated and queried with the
[`coredumpctl`](https://www.freedesktop.org/software/systemd/man/coredumpctl.html)
tool, for example for directly invoking a debugger such as `gdb` on a collected
coredump.
-The handler writes coredump files to `/var/lib/systemd/coredump/`. Old files
-are cleaned up periodically by
+The handler writes coredump files to `/var/lib/systemd/coredump/`.
+Old files are cleaned up periodically by
[`systemd-tmpfiles(8)`](https://www.freedesktop.org/software/systemd/man/systemd-tmpfiles.html).
## User Experience
With the above, any coredumps generated on the system are by default collected
and turned into logged events — except during very early boot and late
-shutdown. Individual services, processes or users can opt-out of coredump
-collection, by setting `LIMIT_CORE` to 0 (or alternatively invoke
-[`PR_SET_DUMPABLE`](https://man7.org/linux/man-pages/man2/prctl.2.html)). The
-resource limit can be set freely by daemons/processes/users to arbitrary
-values, which the coredump handler will respect. The `coredumpctl` tool may be
-used to further analyze/debug coredumps.
+shutdown.
+Individual services, processes or users can opt-out of coredump collection,
+by setting `LIMIT_CORE` to 0 (or alternatively invoke
+[`PR_SET_DUMPABLE`](https://man7.org/linux/man-pages/man2/prctl.2.html)).
+The resource limit can be set freely by daemons/processes/users to arbitrary
+values, which the coredump handler will respect.
+The `coredumpctl` tool may be used to further analyze/debug coredumps.
## Alternative Coredump Handlers
While we recommend usage of the `systemd-coredump` handler, it's fully
-supported to use alternative coredump handlers instead. A similar
-implementation pattern is recommended. Specifically:
+supported to use alternative coredump handlers instead.
+A similar implementation pattern is recommended.
+Specifically:
-1. Use a `sysctl.d/` drop-in to register your handler with the kernel. Make
- sure to include the `%c` specifier in the pattern (which reflects the
- crashing process' `RLIMIT_CORE`) and act on it: limit the stored coredump
- file to the specified limit.
+1. Use a `sysctl.d/` drop-in to register your handler with the kernel.
+ Make sure to include the `%c` specifier in the pattern (which reflects the
+ crashing process' `RLIMIT_CORE`) and act on it:
+ limit the stored coredump file to the specified limit.
-2. Do not do heavy processing directly in the coredump handler. Instead,
- quickly pass off the kernel's coredump file descriptor to an
- auxiliary service running as service under the service manager, so that it
- can be done under supervision, sandboxing and resource management.
+2. Do not do heavy processing directly in the coredump handler.
+ Instead, quickly pass off the kernel's coredump file descriptor to an
+ auxiliary service running as service under the service manager,
+ so that it can be done under supervision, sandboxing and resource management.
Note that at any given time only a single handler can be enabled, i.e. the
`kernel.core_pattern` sysctl cannot reference multiple executables.
## Packaging
It might make sense to split `systemd-coredump` into a separate distribution
-package. If doing so, make sure that `/usr/lib/sysctl.d/50-coredump.conf` and
+package.
+If doing so, make sure that `/usr/lib/sysctl.d/50-coredump.conf` and
the associated service and socket units are also added to the split off package.
Note that in a scenario where `systemd-coredump` is split out and not
The default policy of the kernel to write coredumps into the current working
directory of the crashing process is considered highly problematic by many,
-including by the systemd maintainers. Nonetheless, if users locally want to
-return to this behaviour, two changes must be made (followed by a reboot):
+including by the systemd maintainers.
+Nonetheless, if users locally want to return to this behaviour, two changes must be made (followed by a reboot):
```console
$ mkdir -p /etc/sysctl.d
projects / thirdparty / systemd.git / commitdiff
