The following is a demonstration of the sysbypid.d command, # sysbypid.d Tracing... Hit Ctrl-C to end. ^C EXEC PID SYS VALUE xterm 24030 rawch 1 sched 0 rcvint 1 fsflush 3 pswitch 1 dtrace 19235 inv_swtch 1 xterm 24030 syswrite 2 Xorg 3597 syswrite 2 xterm 24030 inv_swtch 2 dtrace 19235 pswitch 2 dtrace 19235 syswrite 2 soffice.bin 4019 pswitch 3 xterm 24030 pswitch 3 mozilla-bin 3730 inv_swtch 4 xterm 24030 sysread 4 mozilla-bin 3730 readch 9 mozilla-bin 3730 sysread 9 Xorg 3597 pswitch 10 Xorg 3597 sysread 11 mozilla-bin 3730 syswrite 13 java_vm 28209 pswitch 13 sched 0 pswitch 15 mozilla-bin 3730 pswitch 25 setiathome 3929 trap 26 setiathome 3929 pswitch 26 setiathome 3929 inv_swtch 26 dtrace 19235 writech 32 dtrace 19235 outch 34 dtrace 19235 trap 53 Xorg 3597 writech 64 xterm 24030 readch 96 xterm 24030 writech 133 mozilla-bin 3730 writech 905 Xorg 3597 readch 1044 In the above output, the Xorg command with PID 3597 read 1044 bytes, as indicated by readch. mozilla-bin with PID 3730 wrote 905 bytes, as indicated by the writech.