Ubuntu how to detect if OOM killer have run

It doesn't sound like you are addressing the root cause of the issue by actually debugging why this cron job is using up so much memory.

You can try setting this option

echo 1 > /proc/sys/vm/oom_kill_allocating_task

which will tell the OOM killer to kill the process that triggered the OOM condition, but this is not guaranteed to be your cron job. You can also use "ulimit -m" in your script to set the max amount of resident memory to use. I think your best bet would be to evaluate why the cronjob is using up so much memory and if its perhaps best suited for another host or to be rewritten to consume less memory.

This is a bit of a shot in the dark, but: You're using -Xms12288m -Xmx12288m which will only limit the heap portion of your memory.

Since your process grew to ~ 50 GB memory usage, this could have been caused by a huge stack. So if your application spawns a lot of threads, heavily relies on recursion or stuff like that, this will be your cue.

If that's the case, look into things like GC logging, jmap, jstack, pmap, jvisualvm to analyze the situation and into -Xss, -XX:MaxThreadStackSize JVM parameters and ThreadPool sizes to remedy the problem.

(Not entirely sure about the parameters, Java 5 was the last version I had to do with professionally.)