守护进程：Linux实现转载

守护（daemon）进程即在后台运行的进程，网上有很多介绍守护进程的文章，这里不再赘述，直接上代码。

[cpp] view
plaincopyprint?

static void _daemon_prep(int stderr_log)

{

/* Avoid keeping any directory in use. */

chdir("/");

/* Reset process session id. */

setsid();

/* If you want to log in console. */

if (stderr_log)

return;

/*

* Close inherited file descriptors to avoid

* keeping unnecessary references.

*/

close(0);

close(1);

close(2);

/*

* Redirect std{in,out,err}, just in case.

*/

open("/dev/null", O_RDWR);

dup(0);

dup(0);

}

static int _daemonize()

{

int pid = fork();

if (pid != 0) {

// parent, exit

if (pid == -1) {

//cerr << "daemonize failed!" << endl;

return -1;

}

exit(0);

} else {

// child, continue

//cout << "daemonnize success!" << endl;

_daemon_prep(0);

return 0;

}

}

在你的 main 函数中调用 _daemonize 方法即可使你的进程变成守护进程。如以下示例：

[cpp] view
plaincopyprint?

int main()

{

_daemonize();

while(1) {

cout << "hello, world" << endl;

sleep(1);

}

exit(0);

}

以上"hello, world"程序会在后台运行，因在_daemon_prep函数中将标准输入输出重定位到了/dev/null，故你在终端看不到任何输出。如你想在终端看到输出，可在调用_daemon_prep时传入参数1。如你想把标准输出、错误输出重定位到文件方便后续查看，可修改代码如下：

[cpp] view
plaincopyprint?

/*

* Redirect std{in,out,err}, just in case.

*/

open("/dev/null", O_RDWR); // stdin

if (open("/var/log/yourapp.log", O_RDWR | O_CREAT | O_TRUNC) < 0 ) {

cerr << "open error!" << endl;

dup(0); // stdout

dup(0); // stderr

} else {

dup(1); // redirect stderr to the file same as stdout

}