linux 守护进程

1.守护进程只能存在一个；

2.由守护进程拉起服务程序，并wait；

3.当服务程序进程退出时，守护进程再次拉起服务程序，如此反复；

代码如下：

#include<sys/types.h> 
#include<sys/wait.h>
#include<unistd.h>
#include<stdio.h>
#include<stdlib.h>

#define RUN_APP_PATH                "./a.out"
#define PARA_0                      "start"
#define PARA_1                      ""

#define SELF_APP_NAME               "pup_daemon"

int getProcessRunningCount(const char * pName)
{
        FILE* fp = 0; 
        int  iCount = -1; 
        char buf[1024] = {0}; 
        char command[1024] = {0};

        if(0 == pName)
                return -1;        

        sprintf(command, "ps -C %s|wc -l", pName ); 

        if((fp = popen(command,"r")) == NULL) 
        {
                printf("[getProcessRunningCount] popen error ......  \r\n");
                return -1;
        }

        if( (fgets(buf, 1024, fp)) != NULL ) 
        {
                iCount = atoi(buf); 
        }

        pclose(fp);

        return iCount;
}

int runDaemon()
{
        int iRunningCount = getProcessRunningCount(SELF_APP_NAME);
        printf("Running count is %d   ...  \r\n", iRunningCount);
        if(0 > iRunningCount)
        {
                printf("[getProcessRunningCount] err ...   \r\n");
                return 0;
        }

        if(2 < iRunningCount)
        {
                printf("App is already running  ...   \r\n");
                return 0;
        }

        pid_t pid = -1;

        while(1)
        {
                pid = fork();

                if (pid < 0)
                {
                        fprintf(stderr, "error!");
                        usleep(1000 * 1000);
                        continue;
                }
                else if( 0 == pid )
                {
                        if( 0 > execl(RUN_APP_PATH, PARA_0, PARA_1, (char*)0) )
                        {
                                printf("execl err \r\n");
                        }

                        printf("This is the child process! \r\n ");

                        return 0;
                }
                else
                {
                        printf("This is the parent process! child process id = %d \r\n", pid);
                }

                wait(0);

                usleep(1000 * 3000);
        }

        return 0;
}

int main(int argc, char ** argv )
{
        for(int i = 0; i < argc; ++i)
        {
                printf("para is %s  \r\n", argv[i]);
        }

        runDaemon();
        return 0;
}