How to track child process using strace?

Question

I used strace to attach to a process briefly. The process created 90 threads. When I found the offending thread, I had to tediously search for the parent thread, then the grandparent thread, and so on all the way to the root process.

Is there a trick or tool to quickly figure out which thread created another? Or better yet, print the tree of thread creations like pstree?

Answer 1

strace -f to trace child process that's fork()ed.

Answer 2

There is a perl script called strace-graph. Here is a version from github. It is packaged with crosstool-ng versions of compilers. It works for me even used cross platform.

ARM Linux box.

$ ./strace -f -q -s 100 -o app.trc -p 449
$ tftp -pr app.trc 172.0.0.133

X86_64 Linux box.

$ ./strace-graph /srv/tftp/app.trc 
 (anon)
  +-- touch /tmp/ppp.sleep
  +-- killall -HUP pppd
  +-- amixer set Speaker 70%
  +-- amixer set Speaker 70%
  +-- amixer set Speaker 70%
  +-- amixer set Speaker 70%
  +-- amixer set Speaker 50%
  +-- amixer set Speaker 70%
  `-- amixer set Speaker 50%

The output can be used to help navigate the main trace log.

Answer 3

I can't see an easy way:

You could use the -ff option with -o filename to produce multiple files (one per pid).

eg:

strace -o process_dump -ff ./executable
grep clone process_dump*

that would help you see which parent created what. Maybe that would help you - at least then you could search backwards.