daemon.c

来自「unix高级编程源代码.<<unix高级编程>>」· C语言 代码 · 共 48 行

#include	<sys/types.h>
#include	<sys/stat.h>
#include	<errno.h>
#include	<fcntl.h>
#include	"ourhdr.h"

#define	PIDFILE		"daemon.pid"

int
main(void)
{
	int		fd, val;
	char	buf[10];

	if ( (fd = open(PIDFILE, O_WRONLY | O_CREAT, FILE_MODE)) < 0)
		err_sys("open error");

			/* try and set a write lock on the entire file */
	if (write_lock(fd, 0, SEEK_SET, 0) < 0)	{
		if (errno == EACCES || errno == EAGAIN)
			exit(0);	/* gracefully exit, daemon is already running */
		else
			err_sys("write_lock error");
	}

			/* truncate to zero length, now that we have the lock */
	if (ftruncate(fd, 0) < 0)
		err_sys("ftruncate error");

			/* and write our process ID */
	sprintf(buf, "%d\n", getpid());
	if (write(fd, buf, strlen(buf)) != strlen(buf))
		err_sys("write error");

			/* set close-on-exec flag for descriptor */
	if ( (val = fcntl(fd, F_GETFD, 0)) < 0)
		err_sys("fcntl F_GETFD error");
	val |= FD_CLOEXEC;
	if (fcntl(fd, F_SETFD, val) < 0)
		err_sys("fcntl F_SETFD error");

	/* leave file open until we terminate: lock will be held */

	/* do whatever ... */

	exit(0);
}