daemonize函数

#include
#include
#include
#include
#include
#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) {
        fprintf(stderr, "%s: can't get file limit: %s\n", cmd,
                    (char *)strerror(errno));
        exit(-1);
    }

    /*
     * Become a session leader to lose controlling TTY.
     */
    if ((pid = fork()) < 0) {
        fprintf(stderr, "%s: can't fork: %s\n", cmd,
                    (char *)strerror(errno));
        exit(-1);
    } 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) {
        fprintf(stderr, "%s: can't ignore SIGHUP: %s\n", cmd,
                    (char *)strerror(errno));
        exit(-1);
    }
    if ((pid = fork()) < 0) {
        fprintf(stderr, "%s: can't fork: %s\n", cmd,
                    (char *)strerror(errno));
        exit(-1);
    } 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) {
        fprintf(stderr, "%s: can't change dir to /: %s\n", cmd,
                    (char *)strerror(errno));
        exit(-1);
    }

    /*
     * 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);
    }
}


参考 <>