RFR: 8368551: Core dump warning may be confusing

[Paul Hübner]

On Thu, 6 Nov 2025 08:51:38 GMT, Paul Hübner <phubner at openjdk.org> wrote:

> Hi all,
> 
> The `os::check_core_dump_prerequisites` function is used to build the strings of 1) warnings if `CreateCoredumpOnCrash` is specified explicitly and some prerequisite is not fulfilled (fully), and 2) the location of the dump when the VM aborts on error.
> 
> This is fine for many cases, but there are some edgecases on POSIX systems where the warning makes little sense. For example, as reported in the issue:
>> OpenJDK 64-Bit Server VM warning: CreateCoredumpOnCrash specified, but /shared/cores/core-%e-585191 (max size 0 k). To ensure a full core dump, try "ulimit -c unlimited" before starting Java again
> 
> This PR refactors overhauls some of these edge cases to ensure that the warning messages and core locations are more clear and user-friendly.
> 
> **Scenario 1: `CreateCoredumpOnCrash` is disabled**
>> #
>> # A fatal error has been detected by the Java Runtime Environment:
>> # [...]
>> # CreateCoredumpOnCrash turned off, no core file dumped
> 
> **Scenario 2: `get_core_path` errors**
> 
>> Java HotSpot(TM) 64-Bit Server VM warning: CreateCoredumpOnCrash specified, but the core path couldn't be determined. It commonly defaults to core.2618391
>> #
>> # A fatal error has been detected by the Java Runtime Environment:
>> # [...]
>> # Core dump will be written. Default location: core.2618391 (may not exist)
> 
> **Scenario 3: the user processes core dump with e.g. `systemd-coredump`**
>> Java HotSpot(TM) 64-Bit Server VM warning: CreateCoredumpOnCrash specified, but core dumps are further processed the following: "/usr/lib/systemd/systemd-coredump %P %u %g %s %t %e" (alternatively, falling back to /home/foo/bar/betterCoreMsg/core.2620900)
>> #
>> # A fatal error has been detected by the Java Runtime Environment:
>> # [...]
>> # Core dump will be written. Default location: Determined by the following: "/usr/lib/systemd/systemd-coredump %P %u %g %s %t %e" (alternatively, falling back to /home/foo/bar/betterCoreMsg/core.2620900)
> 
> **Scenario 4: the resource limit for core dumps could not be determined**
>> Java HotSpot(TM) 64-Bit Server VM warning: CreateCoredumpOnCrash specified, but the rlimit couldn't be determined. If resource limits permit, the core dump will be located at /tmp/cores/core.%e.2623318.%h.%t
>> #
>> # A fatal error has been detected by the Java Runtime Environment:
>> # [...]
>> # Core dump will be written. Default location: /tmp/cores/core.%e.2623318.%h.%t (may not exist)
>> #
> 
> **Scenarios 5, 6, 7: ulimit of 0, 1024, and unlimited**
>> Java HotSpot(TM) 64-Bit Server VM warni...

@dholmes-ora @tstuefe I've taken into account your feedback and refined the messages a bit. I've updated the PR description highlighting all variants. I hope in particular the scenario where the coredump is processed is a bit clearer. I agree on the point that we should probably look into refactoring get_core_path. Perhaps we could do this with three RFEs instead: AIX, BSD and Linux. @tstuefe  if you feel strongly enough about it, feel free to make an RFE (or let me know to make one). I'm happy to take a look, but I don't have knowledge on or hardware for AIX so I'd need support there. 

I'm gonna re-run testing over the weekend; I also merged in the latest mainline changes.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/28174#issuecomment-3563412548