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#include
#include
#include
#include
#include
#include
#include
#include  
#include  
#include  
//#include
 
#define GETPTY_BUFSIZE 16
#define READ_BUFSIZE 32
char buffer[READ_BUFSIZE]; 
 
int main(int argc,char *argv[])
{
   
      pid_t pid_child;
      pid_t rec_pid;
      pid_t    pid;
     
      int nread;
      sigset_t mask;
      char *name;
      int  signo =0;   
      int  err;
      int  fd;        
      char tty_name[GETPTY_BUFSIZE];
      FILE  *f;
      char  *pidfile = "/var/run/deamon.pid";
      
      sigemptyset(&mask);  
      sigaddset(&mask, SIGUSR1);
      sigprocmask(SIG_SETMASK,&mask,NULL);
      // register PON  happend
      // signal(SIGCHLD, SIG_IGN);     
            
       pid = getpid();
       if ((f = fopen(pidfile, "w")) == NULL)
       {         
         return -1;
       }
       fprintf(f, "%d\n", pid);
       fclose(f);
      
      fd = open("/dev/ptmx", O_RDWR);
        if (fd < 0)
        {
            printf("open pty error\n");
            exit(1);
        }
            grantpt(fd);
          unlockpt(fd);
          name = ptsname(fd);
          if (!name)
          {
                 printf("ptsname error\n");
               exit(1);
          }
          strncpy(tty_name, name, GETPTY_BUFSIZE);
                  
         
           
      while(1)
      {
       
         do{
              err = sigwait(&mask, &signo);
           }while(signo !=SIGUSR1 );
         
           //sleep wait for register
            sleep(3);
         
          if((pid_child = fork())==-1)
          {
              printf("Fork Error\n");
              exit(1);
          }     
          else if(pid_child > 0) //parent
          {
               // printf("pid_child %d \n",pid_child); 
             sleep(6);                  
             write(fd,"exit\n",5);   
             sleep(3); 
             rec_pid = waitpid(pid_child,NULL,WNOHANG);
             if( rec_pid != pid_child )
             {
                   printf("kill  %d \n",pid_child);
                   kill(pid_child,9);
                do{
                    rec_pid = waitpid(pid_child,NULL,WNOHANG);
                  }while( rec_pid != pid_child );
             }
             //clear pty buffer
              do
              {  
                 nread =  read(fd,buffer,READ_BUFSIZE);
                  
              }while(nread > 0);
            
            
          }
          else //child
          {       
                 /* make new session and process group */
                 printf("deamon shell\n");
                 setsid();              
                 fd = open(tty_name, O_RDWR); // becomes our ctty
                 dup2(fd, 0);
                 dup2(fd, 1);
                 dup2(fd, 2);      
                 close(fd);       
                 tcsetpgrp(0, getpid()); // switch this tty's process group to us
                 //shell
                 err = execl("/usr/bin/shell","shell",0);
               printf("execl %d \n",err);
               return 0;
          }          
    } 
   return 0;   
}