RFR: 8368551: Core dump warning may be confusing

[David Holmes]

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 core path is unknown, trying core.1552174 (may not exist)
>> #
>> # A fatal error has been detected by the Java Runtime Environment:
>> # [...]
>> # Core dump will be written. Default location: core.1552174 (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 may be processed with "/usr/lib/systemd/systemd-coredump %P %u %g %s %t %e" (or dumping to /home/opc/betterCoreMsg/core.1555400)
>> #
>> # A fatal error has been detected by the Java Runtime Environment:
>> # [...]
>> # Core dump will be written. Default location: "/usr/lib/systemd/systemd-coredump %P %u %g %s %t %e" (or dumping to /home/foo/bar/core.1555400)
> 
> **Scenario 4: the resource limit for core dumps could not be determined**
>> Java HotSpot(TM) 64-Bit Server VM warning: CreateCoredumpOnCrash specified, but couldn't deduce rlim, trying /tmp/cores/core.%e.1560382.%h.%t (may not exist)
>> #
>> # A fatal error has been detected by the Java Runtime Environment:
>> #  [...]
>> # Core dump will be written. Default location: /tmp/cores/core.%e.1560382.%h.%t (may not exist)
> 
> **Scenarios 5, 6, 7: ulimit of 0, 1024, and unlimited**
>> Java HotSpot(TM) 64-Bit Server VM warning: CreateCoredumpOnCrash specified, but core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
>> #
>> # A fatal er...

src/hotspot/os/posix/os_posix.cpp line 132:

> 130:         buf.print("core dumps may be processed with ");
> 131:       }
> 132:       buf.print("%s", core_path);

The only thing I don't like here is this part. I know it looks weird to have "Default location:  Core dumps may be processed with ..." but I think it is less informative to skip pointing out that this case is not actually a location at all.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28174#discussion_r2536569162