I am running a job in R that forks multiple processes. Every once in a while it seems that when the forked processes return and the next job starts, the previously forked processes terminate, but the CPU for those processes moves from 'User' to 'System'. So my activity monitor looks like this:

![enter image description here][1]

How can I debug this? How can I determine what processes are using the 'System' section in the screenshot? They do not show up if I sort by CPU in activity monitor. Only the 'User' processes show up, no matter how I sort it, or which tab (CPU, memory) I use. 

My activity monitor is showing 'all processes', so I do see running processes for the root user. However, all of the 'System' CPU is unaccounted for in activity monitor.

The R use case may not be relevant. Or it may be. But generally, what I'd like to know is how to determine what is using the 'System' portion of the CPU load in OS X Mavericks.



  [1]: https://i.sstatic.net/sP5eE.png