一个daemon程序的例子

1. 为了便于进行调试，打开syslog。

2. 打开syslog后，可以在/var/log/message中看到保存的log信息。

3. 找到程序的pid后，可以用过kill pid方式杀死daemon，同样可以在log信息中有所显示。

#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <stdio.h>
#include <syslog.h>
#include <signal.h>

int
daemon_init (void)
{
    pid_t pid;
    if ((pid = fork ()) < 0)
        return (-1);
    else if (pid != 0)
        exit (0);    /* parent exit */
    /* child continues */
    setsid ();        /* become session leader */
    chdir ("/");        /* change working directory */
    umask (0);        /* clear file mode creation mask */
    close (0);        /* close stdin */
    close (1);        /* close stdout */
    close (2);        /* close stderr */
    return (0);
}

void
sig_term (int signo)
{
    if (signo == SIGTERM)
    /* catched signal sent by kill(1) command */
    {
        syslog (LOG_INFO, "program terminated.");
        closelog ();
        exit (0);
    }
}

int
main (void)
{
    if (daemon_init () == -1)
    {
        printf ("can't fork self\n");
        exit (0);
    }
    openlog ("daemontest", LOG_PID, LOG_USER);
    syslog (LOG_INFO, "program started.");
    signal (SIGTERM, sig_term);    /* arrange to catch the signal */
    while (1)
    {
        sleep (1);    /* put your main program here */
    }
    return (0);
}