iTunes and DTrace

Earlier today, I was using iotop to check the disk activity for the processes on my machine, and immediately started seeing the following error (or variations on this error):

dtrace: error on enabled probe ID 5 (ID 992: io:mach_kernel:buf_strategy:start): invalid user access in action #3 at DIF offset 0

I thought my SSD was dying (it’s something I fear!) – however, after some messing around I discovered¬†iotop doesn’t work when iTunes is running, because Apple have disabled dtrace while iTunes is running. Quitting iTunes sorted the problem for me. There is more about this “quirk” here:¬†