The following is an example of the readdist.d script, Here the readdist.d script is run for a few seconds, then Ctrl-C is hit, # readdist.d dtrace: description 'sysinfo:::readch ' matched 4 probes ^C [...] gnome-terminal value ------------- Distribution ------------- count 16 | 0 32 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 15 64 |@@@ 1 128 | 0 Xorg value ------------- Distribution ------------- count -1 | 0 0 |@@@@@@@@@@@@@@@@@@@ 26 1 | 0 2 | 0 4 | 0 8 |@@@@ 6 16 |@ 2 32 |@ 2 64 | 0 128 |@@@@@@@@ 11 256 |@@@ 4 512 | 0 This allows us to understand the read behaviour of each process. The Xorg command has executed 26 reads that returned 0 bytes, through to 4 reads that were at least 256 bytes (up to 511).