Capturing Entire Process Tree with macOS Command Line Tool
If you are looking for a tool to capture the execution of an entire process tree, similar to the tracetree tool for Linux, then you have come to the right place. In this article, we will explore a command line tool for macOS called dtruss that allows you to capture the execution of an entire process tree.
What is dtruss?
dtruss is a command line tool that comes pre-installed with macOS. It is a wrapper around the dtrace command, which is a comprehensive dynamic tracing framework for macOS. dtruss allows you to trace system calls and other events in your application, providing detailed information about the execution of your program.
Using dtruss to Capture a Process Tree
To capture a process tree using dtruss, you can use the following command:
sudo dtruss -f -p [PID]Replace [PID] with the process ID of the parent process that you want to trace. The -f flag tells dtruss to follow child processes, so you will see the entire process tree.
For example, if you want to trace the process tree of the sleep command, you can use the following command:
sudo dtruss -f -p $(pgrep -xn sleep)This command uses the pgrep command to find the process ID of the sleep command and passes it to dtruss.
Interpreting the Output
The output of dtruss can be overwhelming at first, but with a little practice, you can learn to interpret it. Each line of the output represents a system call or other event in your application. The columns in the output provide detailed information about the event, including the process ID, the system call name, the arguments to the system call, and the return value.
Here is an example of the output from dtruss when tracing the sleep command:
SYSCALL(args) = return PID COMM FNAME RET ARGS0x00000100000228f0 open("/dev/dtracehelper\0", 0x0, 0x1b6) = 3 1613 sleep 0x7fff5fbff3c0 0 0x3 0x00x00000100000228f0 close(3) = 0 1613 sleep 0x7fff5fbff3c0 0 0x0 0x00x00000100000228f0 fstat64(0x3, 0x7fff5fbff1b0) = 0 1613 sleep 0x7fff5fbff3c0 0 0x3 0x00x00000100000228f0 mmap(0x0, 0x1000, 0x1, 0x1002, 0x0, 0x0) = 0x100211000 1613 sleep 0x7fff5fbff3c0 0 0x0 0x00x00000100000228f0 mprotect(0x100211000, 0x1000, 0x0) = 0 1613 sleep 0x7fff5fbff3c0 0 0x100211000 0x10000x00000100000228f0 munmap(0x100211000, 0x1000) = 0 1613 sleep 0x7fff5fbff3c0 0 0x100211000 0x10000x00000100000228f0 fstat64(0x0, 0x7fff5fbff1b0) = 0 1613 sleep 0x7fff5fbff3c0 0 0x0 0x00x00000100000228f0 write(0x3, "
", 0x1) = 1 1613 sleep 0x7fff5fbff3c0 0 0x3 0x10x00000100000228f0 exit(0x0) = 0 1613 sleep 0x7fff5fbff3c0 0 0x0 0x0In this example, the first column (SYSCALL) shows the system call name, the second column (args) shows the arguments to the system call, and the last column (RETURN) shows the return value of the system call.
In this article, we have explored the dtruss command line tool for macOS, which allows you to capture the execution of an entire process tree. We have seen how to use dtruss to trace the system calls and other events in your application, and how to interpret the output. With this knowledge, you can gain a deeper understanding of the execution of your program and diagnose issues more effectively.