Linux - create a daemon process

Steps to create a daemon

• create child process
• parent process exits
• When the child process is the chairman setsid()
• Switch working directory $HOME
• set mask umask
• Close standard input, or redirect standard output and standard error. To avoid wasting resources
• Execute the core logic
• quit

example

#include <bits/types/FILE.h>
#include <cstdio>
#include <cstdlib>
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>

int main() {
    
    
 
  pid_t pid = fork();
  if (pid > 0) {
    
    
    exit(0);
  }
  //成立一个新会话，丢弃原有控制终端
  pid = setsid();
  if (pid < 0) {
    
    
    perror("setsid is error:");
    exit(0);
  }

  //切换工作目录的意义是保证守护进程能稳定可靠的运行
  //只要工作目录是不可卸载的目录就可以
  chdir("/home/sivin");

  //设置掩码
  umask(0022);
	
  //由于守护进程没有控制终端，不会与用户进行交互，因此可以关闭标准输入
  close(STDIN_FILENO);
  int emptyFd = open("/dev/null", O_RDWR);
  dup2(emptyFd, STDOUT_FILENO);
  dup2(emptyFd, STDERR_FILENO);

  while(1) {
    
    
   //执行守护进程的逻辑
  }

  return 0;
}