18. Wait example – sshd pid = fork(); if (pid == -1) { fatal(&quot;fork of unprivileged child failed&quot;); } else if (pid != 0) { debug2(&quot;Network child is on pid %ld&quot;, (long)pid); close(pmonitor->m_recvfd); pmonitor->m_pid = pid; monitor_child_preauth(authctxt, pmonitor); close(pmonitor->m_sendfd); /* Sync memory */ monitor_sync(pmonitor); /* Wait for the child's exit status */ while (waitpid(pid, &status, 0) < 0) if (errno != EINTR) break; return (1); } else {

20. Interesting Example - busybox/init.c if (pid > 0) { /* Parent - wait till the child is done */ bb_signals(0 + (1 << SIGINT) + (1 << SIGTSTP) + (1 << SIGQUIT) , SIG_IGN); signal(SIGCHLD, SIG_DFL); waitfor(pid); /* See if stealing the controlling tty back is necessary */ if (tcgetpgrp(0) != getpid()) _exit(EXIT_SUCCESS); /* Use a temporary process to steal the controlling tty. */ pid = fork(); if (pid < 0) { message(L_LOG | L_CONSOLE, &quot;can't fork&quot;); _exit(EXIT_FAILURE); } if (pid == 0) { setsid(); ioctl(0, TIOCSCTTY, 1); _exit(EXIT_SUCCESS); } waitfor(pid); _exit(EXIT_SUCCESS); } /* Child - fall though to actually execute things */

26. Masking Example - ssh/server_loop.c /* block SIGCHLD while we check for dead children */ sigemptyset(&nset); sigaddset(&nset, SIGCHLD); sigprocmask(SIG_BLOCK, &nset, &oset); if (child_terminated) { debug(&quot;Received SIGCHLD.&quot;); while ((pid = waitpid(-1, &status, WNOHANG)) > 0 || (pid < 0 && errno == EINTR)) if (pid > 0) session_close_by_pid(pid, status); child_terminated = 0; } sigprocmask(SIG_SETMASK, &oset, NULL); }

28. Example - inetd memset(&sa, 0, sizeof(sa)); sigaddset(&sa.sa_mask, SIGALRM); sigaddset(&sa.sa_mask, SIGCHLD); sigaddset(&sa.sa_mask, SIGHUP); sa.sa_handler = retry_network_setup; sigaction_set(SIGALRM, &sa); sa.sa_handler = reread_config_file; sigaction_set(SIGHUP, &sa); sa.sa_handler = reap_child; sigaction_set(SIGCHLD, &sa); sa.sa_handler = clean_up_and_exit; sigaction_set(SIGTERM, &sa); sa.sa_handler = clean_up_and_exit; sigaction_set(SIGINT, &sa); sa.sa_handler = SIG_IGN; sigaction(SIGPIPE, &sa, &saved_pipe_handler); static void clean_up_and_exit(int sig UNUSED_PARAM) { servtab_t *sep; /* XXX signal race walking sep list */ for (sep = serv_list; sep; sep = sep->se_next) { if (sep->se_fd == -1) continue; switch (sep->se_family) { case AF_UNIX: unlink(sep->se_service); break; default: /* case AF_INET, AF_INET6 */ #if ENABLE_FEATURE_INETD_RPC if (sep->se_wait == 1 && is_rpc_service(sep)) unregister_rpc(sep); /* XXX signal race */ #endif break; } if (ENABLE_FEATURE_CLEAN_UP) close(sep->se_fd); } remove_pidfile(_PATH_INETDPID); exit(EXIT_SUCCESS); }

34. Time

35. Alarms