Embedded Linux application Development detailed------(Create daemon)

Embedded Linux application Development detailed Jie Huaqing Vision This article is just reading the digest.
Steps to create a daemon: 1, create a child process, and then exit the parent process, 2, create a new session in a child process---setsid (), 3, change the current working directory---chdir (), 4, reset the file permission mask---umask (), 5, Close all file descriptors---close (FDX), 6, set the task of the daemon program---This example is mainly reflected in the while loop.

Here is an example program:

  
 

   
  

  
/* daemon
   
  

  
 * how to create a daemon process?
   
  

  
 * --Just follow these steps.
   
  

  
 * 2014-09-28
   
  

  
 * zsl
   
  

  
 */
   
  

  

   
  

  
#include <stdio.h>
   
  

  
#include <stdlib.h>
   
  

  
#include <sys/types.h>
   
  

  
#include <fcntl.h>
   
  

  

   
  

  
#define MAXFILE 65536
   
  

  
int main()
   
  

  
{
   
  

  
 pid_t child_pid, new_pid;
   
  

  
 int fd;
   
  

  
 int i;
   
  

  

   
  

  

   
  

  
 child_pid = fork();
   
  

  
 if ( child_pid < 0 ) // fork failed
   
  

  
 {
   
  

  
 perror("fork");
   
  

  
 exit(1);
   
  

  
 }
   
  

  
 else if (child_pid > 0 ) // parent
   
  

  
 {
   
  

  
 fprintf(stderr, "Parent exit...\n");
   
  

  
 exit(0);
   
  

  
 }
   
  

  
 else // child
   
  

  
 {
   
  

  
 /* Create a new session */
   
  

  
 new_pid = setsid();
   
  

  
 if ( new_pid < 0)
   
  

  
 {
   
  

  
 perror("setsid");
   
  

  
 exit(1);
   
  

  
 }
   
  

  

   
  

  
 /* Change dir */
   
  

  
 if ( chdir("/") != 0 )
   
  

  
 {
   
  

  
 perror("chdir");
   
  

  
 exit(2);
   
  

  
 }
   
  

  

   
  

  
 /* Set umask */
   
  

  
 umask(0000);
   
  

  

   
  

  

   
  

  
 /* Close all file descriptor */
   
  

  
 for (i = 0; i < MAXFILE; i ++)
   
  

  
 {
   
  

  
 close(i);
   
  

  
 }
   
  

  

   
  

  
 
   
  

  
 /* The daemon job */
   
  

  
 while(1)
   
  

  
 {
   
  

  
 if ((fd = open("/tmp/daemon_log.txt", O_CREAT | O_APPEND | O_WRONLY, 0600)) == -1)
   
  

  
 {
   
  

  
 perror("open"); 
   
  

  
 exit(3);
   
  

  
 }
   
  

  

   
  

  
 write(fd, "daemon is working...\n", 21);
   
  

  
 close (fd);
   
  

  
 sleep(10);
   
  

  
 }
   
  

  
 } // end of childe process
   
  

  

   
  

  
 return 0;
   
  

  
}
  
 

From for notes (Wiz)

Embedded Linux application Development detailed------(Create daemon)