Ah, yes, that makes sense now. Thanks for decoding this properly! It does look like rt_sigreturn is being used: --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=4909, si_uid=33, si_status=0, si_utime=1, si_stime=2} --- rt_sigreturn() = 0 Rather disconcerting this problem. I'll keep digging... --david