Thanks! I did get it to work this way. I just forked, had strace write to a file with the "-o" option, had the parent sleep a second, then send the child a SIGALRM. I then processed the strace output file in a second step. I actually found that using strace isn't the best way to find processes blocking in flock -- but I've been wanting to do other things with strace from Perl, so this will be good for future use.