If the program named a.out is running and the ps(1) command shows that a.out has a process ID (PID) of 2374, then the following command attaches prex to a.out:
$ prex -p 2374
If you are attaching prex to your already-running program, libtnfprobe must be linked to your program first. If you have not linked with libtnfprobe, prex exits with the error message that libtnfprobe is not linked to your program.