In fact, max memory is not even checked against physical memory on JVM startup even with swap off on OS. 'Don't quote me on this' but VIRT mem is roughly close to or more than Max memory allocated but as long as memory being used is free/available in physical memory, JVM does not throw memory exception. By default it makes a recording per 10 seconds (for the target process, its ancestors and descendants). In the simplest case you point it to the PID of interest and let it record its Procfs metrics including Resident Set Size (RSS). I preferred to go with this method for most of the time. Yes, can achieve exactly this, a bit more with Procpath (author here). This is very simple and straightforward one line script. If you want to get only the current Memory utilization percentage through mail when the system reaches the given threshold, use the following script. Assuming you run a simple class with no mmap or file processing.

You can then guarantee and also do ps to see what parameters were passed and hence being used.įor actual memory usages, you can roughly compare VIRT (allocated and shared) and RES (actual used) compare against the jstat values as well:įor Java 8, see jstat for these values actually mean. It is always a good idea to allocate the heap using -X.m -X.x for all generations. Any approach should give you roughly same number.

Linux command to monitor memory usage