Демоны

volatile sig_atomic_t gGracefulShutdown=0;
volatile sig_atomic_t gCaughtHupSignal=0;
int gLockFileDesc=-1;
int gMasterSocket=-1;
const int gaahzdPort=30333;
const char *const gLockFilePath = "/var/run/aahzd.pid";
int main(int argc,char *argv[])
{ int result; pid_t daemonPID; if (argc > 1) { int fd, len; pid_t pid; char pid_buf[16]; if ((fd = open(gLockFilePath, O_RDONLY)) < 0) { perror("Lock file not found. May be the server is not running?"); exit(fd); } len = read(fd, pid_buf, 16); pid_buf[len] = 0; pid = atoi(pid_buf); if(!strcmp(argv[1], "stop")) { kill(pid, SIGUSR1); exit(EXIT_SUCCESS); } if(!strcmp(argv[1], "restart")) { kill(pid, SIGHUP); exit(EXIT_SUCCESS); } printf ("usage %s [stop|restart]\n", argv[0]); exit (EXIT_FAILURE); } if((result = BecomeDaemonProcess(gLockFilePath, "aahzd", LOG_DEBUG, &gLockFileDesc, &daemonPID))<0) { perror("Failed to become daemon process"); exit(result); } if((result = ConfigureSignalHandlers())<0) { syslog(LOG_LOCAL0|LOG_INFO, "ConfigureSignalHandlers failed, errno=%d", errno); unlink(gLockFilePath); exit(result); } if((result = BindPassiveSocket(INADDR_ANY, gaahzdPort, &gMasterSocket))<0) { syslog(LOG_LOCAL0|LOG_INFO, "BindPassiveSocket failed, errno=%d", errno); unlink(gLockFilePath); exit(result); } do { if(AcceptConnections(gMasterSocket)<0) { syslog(LOG_LOCAL0|LOG_INFO,"AcceptConnections failed, errno=%d",errno); unlink(gLockFilePath); exit(result); } if((gGracefulShutdown==1)&&(gCaughtHupSignal==0)) break; gGracefulShutdown=gCaughtHupSignal=0; } while(1); TidyUp(); return 0;
}

curPID=fork();
switch(curPID) { case 0: /* мы в дочернем процессе */ break; case -1: /* ошибка fork() - случилось что-то страшное */ fprintf(stderr,"Error: initial fork failed: %s\n", strerror(errno)); return -1; break; default: /* мы в родительском процессе, завершаем его */ exit(0); break;
}

void FatalSigHandler(int sig) {
#ifdef _GNU_SOURCE syslog(LOG_LOCAL0|LOG_INFO,"caught signal: %s - exiting",strsignal(sig));
#else syslog(LOG_LOCAL0|LOG_INFO,"caught signal: %d - exiting",sig);
#endif closelog(); TidyUp(); _exit(0);
}

На те три сигнала, которые относятся к категории обрабатываемых, - SIGTERM, SIGUSR1 и SIGHUP, демон реагирует по-разному: 
sigtermSA.sa_handler = TermHandler;
sigemptyset(&sigtermSA.sa_mask);
sigtermSA.sa_flags = 0;
sigaction(SIGTERM, &sigtermSA, NULL);
sigusr1SA.sa_handler = Usr1Handler;
sigemptyset(&sigusr1SA.sa_mask);
sigusr1SA.sa_flags = 0;
sigaction(SIGUSR1, &sigusr1SA, NULL);
sighupSA.sa_handler = HupHandler;
sigemptyset(&sighupSA.sa_mask);
sighupSA.sa_flags = 0;
sigaction(SIGHUP, &sighupSA, NULL);

int BindPassiveSocket(const int portNum, int *const boundSocket)
{ struct sockaddr_in sin; int newsock, optval; size_t optlen; memset(&sin.sin_zero, 0, 8); sin.sin_port = htons(portNum); sin.sin_family = AF_INET; sin.sin_addr.s_addr = htonl(INADDR_ANY); if((newsock= socket(PF_INET, SOCK_STREAM, 0))<0) return -1; optval = 1; optlen = sizeof(int); setsockopt(newsock, SOL_SOCKET, SO_REUSEADDR, &optval, optlen); if(bind(newsock, (struct sockaddr*) &sin, sizeof(struct sockaddr_in))<0) return -1; if(listen(newsock,SOMAXCONN)<0) return -1; *boundSocket = newsock; return 0;
}

int AcceptConnections(const int master)
{ int proceed = 1, slave, retval = 0; struct sockaddr_in client; socklen_t clilen; while((proceed==1)&&(gGracefulShutdown==0)) { clilen = sizeof(client); slave = accept(master,(struct sockaddr *)&client,&clilen); if(slave<0) { /* ошибка accept() */ if(errno == EINTR) continue; syslog(LOG_LOCAL0|LOG_INFO,"accept() failed: %m\n"); proceed = 0; retval = -1; } else { retval = HandleConnection(slave); if(retval) proceed = 0; } close(slave); } return retval;
}

Автор: Андрей Боровский
Источник: www.symmetrica.net