How to write a self-replaceable / update binary?

Question

I am trying to write a C program that can search for a URL and display a new version available for updating it.

The method I tried:

• Run a new process to load the new binary. Say BINARY.tmp, the code I use for forkout:

  int
  forkout_cmd(char *cmdstr) {
    pid_t pid;
    char *cmd[4];
  
    cmd[0] = "/bin/bash";
    cmd[1] = "-c";
    cmd[2] = cmdstr;
    cmd[3] = NULL;
  
    pid = vfork();
    if( pid == -1 ) {
      logmsg("Forking for upgradation failed.");
      return -1;
    }else if( pid == 0 ){
      /* we are in child process */
      execvp(cmd[0], cmd);
      logmsg("execl failed while executing upgradation job.");
    }else{
      /* need not to wait for the child to complete. */
      wait(NULL);
    }
      return 0;
  }
  

• The new process is trying to overwrite the original BINARY

  for example, you can consider a routine that can be implemented:

  forkout_cmd("wget -O BINARY.tmp https://someurl.com/BINARY_LATEST; /bin/mv -f BINARY.tmp BINARY");
  

But the rewriting fails because the source binary is still in progress and therefore busy on disk, can anyone give me some suggestions to solve this problem.

Thanks in advance.

Answer 1

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Answer 2

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