创建一个守护进程，有几个关键的步骤，也有几个地方需要注意，
几个关键的步骤有：
1：清除文件创建权限
2：调用fork，然后使父进程退出
3：调用setsid以创建一个新的会话，有三个目的使调用进程 a:成为新会话的首进程，b:成为新进程的组长进程，c:没有控制终端
4：切换工作目录
5：关闭不需要的文件描述符
需要注意的地方
1：因为守护进程没有控制终端，所以不能与标准输入输出出错进行交互，不能使用printf,通常用syslog来解决守护进程的打印信息
参考代码如下：
点击(此处)折叠或打开
#include
#include #include #include #include #include void daemonize(const char *cmd){ int i, fd0, fd1, fd2; pid_t pid; struct rlimit rl; struct sigaction sa; /* * Clear file creation mask. */ umask(0); /* * Get maximum number of file descriptors. */ if (getrlimit(RLIMIT_NOFILE, &rl) < 0) printf("%s: can't get file limit", cmd); /* * Become a session leader to lose controlling TTY. */ if ((pid = fork()) < 0) printf("%s: can't fork", cmd); else if (pid != 0) /* parent */ exit(0); setsid(); /* * Ensure future opens won't allocate controlling TTYs. */ sa.sa_handler = SIG_IGN; sigemptyset(&sa.sa_mask); sa.sa_flags = 0; if (sigaction(SIGHUP, &sa, NULL) < 0) printf("can't ignore SIGHUP"); if ((pid = fork()) < 0) printf("%s: can't fork", cmd); else if (pid != 0) /* parent */ exit(0); /* * Change the current working directory to the root so * we won't prevent file systems from being unmounted. */ if (chdir("/") < 0) printf("can't change directory to /"); /* * Close all open file descriptors. */ if (rl.rlim_max == RLIM_INFINITY) rl.rlim_max = 1024; for (i = 0; i < rl.rlim_max; i++) close(i); /* * Attach file descriptors 0, 1, and 2 to /dev/null. */ fd0 = open("/dev/null", O_RDWR); fd1 = dup(0); fd2 = dup(0); /* * Initialize the log file. */ openlog(cmd, LOG_CONS, LOG_DAEMON); if (fd0 != 0 || fd1 != 1 || fd2 != 2) { syslog(LOG_ERR, "unexpected file descriptors %d %d %d",fd0, fd1, fd2); exit(1); } syslog(LOG_DEBUG, "daem ok ");}int main(){ daemonize("test"); while(1);//守护进程所要干的事情}
收起