-D option is used to detach strace and tracee processes. E.g.:
# strace -D ./dead_loop
strace: Process 19816 attached
......
Open another terminal to check the process relationship:
# ps -ef | grep dead
root 19816 19684 0 09:28 pts/0 00:00:00 ./dead_loop
root 19820 1 0 09:28 pts/0 00:00:00 strace -D ./dead_loop
You can see now dead_loop is not child process of strace.