后台运行Linux程序的方法

后台运行Linux程序，可以通过crontab设置，这种方法一般用来让一个程序定时运行，也可以通过./test &这样在程序末尾加上一个&使程序在后台运行。

编写代码，下面我将参考httpd写一个程序使其运行不占控制台

#include "detach.h"
void detach(void)
{
        int x;
        int pgrp;

        chdir("/");

        if ((x = fork()) > 0)
            exit(0); //exit parent, so we have the child
        else if (x == -1) {
            perror("fork");
            fprintf(stderr, "unable to fork new process\n");
            exit(1);
        }

        raise(SIGSTOP);
/* setsid - run a program in a new session*/
        if ((pgrp = setsid()) == -1) {
            perror("setsid");
            fprintf(stderr, "setsid failed\n");
            exit(1);
        }

        /* close out the standard file descriptors */
        if (freopen("/dev/null", "r", stdin) == NULL) {
            fprintf(stderr, "unable to replace stdin with /dev/null:\n");
            /* continue anyhow -- note we can't close out descriptor 0 because we
             * have nothing to replace it with, and if we didn't have a descriptor
             * 0 the next file would be created with that value ... leading to
             * havoc.
             */
        }
        if (freopen("/dev/null", "w", stdout) == NULL) {
            fprintf(stderr, "unable to replace stdout with /dev/null: \n");
        }
        /* stderr is a tricky one, we really want it to be the error_log,
         * but we haven't opened that yet.  So leave it alone for now and it'll
         * be reopened moments later.
         */
}